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An approach to understand quantitative traits was recently proposed based on the finding that nonsynonymous (NS) sequence variants in certain genes are preferentially enriched at one extreme of the population distribution. The NS variants, although individually rare, are cumulatively frequent and influence quantitative traits, such as plasma lipoprotein levels. Here, we use the NS variant technique to demonstrate that genetic variation in NPC1L1 contributes to variability in cholesterol absorption and plasma levels of low-density lipoproteins (LDLs). The ratio of plasma campesterol (a plant sterol) to lathosterol (a cholesterol precursor) was used to estimate relative cholesterol absorption in a population-based study. Nonsynonymous sequence variations in NPC1L1 were five times more common in low absorbers (n = 26 of 256) than in high absorbers (n = 5 of 256) (P < 0.001). The rare variants identified in low absorbers were found in 6% of 1,832 African-Americans and were associated with lower plasma levels of LDL cholesterol (LDL-C) (96 +/- 36 mg/dl vs. 105 +/- 36 mg/dl; P = 0.005). These data, together with prior findings, reveal a genetic architecture for LDL-C levels that does not conform to current models for quantitative traits and indicate that a significant fraction of genetic variance in LDL-C is due to multiple alleles with modest effects that are present at low frequencies in the population.

Flavonoids and related polyphenolics with antioxidant and anti-inflammatory activities may play a role in the prevention of cardiovascular disease by decreasing oxidative stress and inflammation. We wished to determine the effects of cocoa extract supplementation on markers of oxidative stress and inflammation. Healthy subjects (n = 25) were studied at baseline, after cocoa supplementation (36.9 g of dark chocolate bar and 30.95 g of cocoa powder drink) for 6 wk and after a 6-wk washout period. Fasting blood and early morning urine were collected at the three time points. Two indices of flavonoid intake, total phenols and oxygen radical absorbance capacity of plasma, were measured after an overnight fast. Neither was affected by supplementation. Measures of oxidative stress included copper-catalyzed LDL oxidation kinetics and urinary F(2) isoprostanes. LDL oxidizability was lower after chocolate supplementation as evidenced by a longer lag time (P < 0.05) of conjugated diene formation (101.0 +/- 20.7 min) compared with baseline (91.3 +/- 18.0 min) and washout (96.4 +/- 7.5 min) phases. There was no effect of chocolate on urinary F(2) isoprostane levels or on markers of inflammation including the whole-blood cytokines, interleukin-1 beta, interleukin-6 and tumor necrosis factor-alpha, high sensitivity C-reactive protein and P-selectin. In conclusion, cocoa products supplementation in humans affects LDL oxidizability, but not urinary F(2) isoprostanes or markers of inflammation.

Atherosclerotic cardiovascular disease is the leading cause of death in patients with end stage renal disease (ESRD) who have undergone dialysis treatment. The oxidation of low density lipoprotein (LDL) appears to be a crucial step in the pathogenesis of atherosclerosis. The increased oxidative stress and attendant increased oxidizability of lipoproteins, such as LDL could contribute to the accelerated atherosclerosis in dialysis patients. Since alpha-tocopherol (AT) is the major antioxidant in LDL, the aim of the present study was to test the effectiveness of RRR-AT supplementation (800 I.U. per day) for 12 weeks on the susceptibility of LDL to oxidation. The study subjects comprised patients with chronic renal failure on hemodialysis (HD), peritoneal dialysis (PD), and age and sex matched controls (C). Plasma fatty acids, lipoproteins and AT levels were measured in these subjects before and after supplementation. Also, LDL AT and oxidizability was studied. LDL was isolated by ultracentrifugation at baseline and after 12 weeks of supplementation, and subjected to a 5-h time course of copper catalyzed oxidation. Oxidation was measured by the formation of conjugated dienes (CD) and lipid peroxides (LP). Supplementation with AT did not alter the plasma lipid or lipoprotein profile of these subjects. Plasma lipid-standardized AT and LDL AT concentrations were not different among the groups at baseline. AT supplementation significantly increased plasma lipid-standardized AT (C=150%, HD=149%, PD=217%, P<0.001) and LDL AT concentrations (C=94%, HD=94%, PD=135%, P<0.003). AT enrichment of LDL resulted in a significant prolongation in conjugated diene lag phase in all groups (C=34%, HD=21%, PD=54%, P<0.02). Lipid peroxide lag phase was also increased significantly in C (27%,) and PD (40%) groups after AT supplementation (P<0.01). There was a significant positive correlation between plasma lipid standardized AT and lag phase (r=0. 54, P=0.0003). Overall, AT decreased the susceptibility of LDL to oxidation in patients with chronic renal failure but the benefit appears to be greater in patients on PD. Therefore, AT supplementation may also provide a measure of protection against CAD in patients with chronic renal failure on dialysis therapy.

Our investigations indicate that most patients with moderate hypertriglyceridemia have marked defects in the metabolism of low-density lipoprotein (LDL) apolipoprotein B. Moreover, these patients have 2 major defects in the metabolism of triglyceride-rich lipoproteins, i.e., an accumulation of remnant lipoproteins (due in part to delayed hepatic clearance) and increased fractional conversion of very-low-density lipoprotein (VLDL) to LDL. Defective triglyceride-rich lipoprotein metabolism has been associated with insulin resistance. Statin therapy in hypertriglyceridemic patients improves the lipoprotein profile by decreasing both LDL cholesterol and remnant lipoproteins. However, statin therapy does not normalize LDL apolipoprotein B metabolism, and high-density lipoprotein (HDL) cholesterol levels remain low. Therefore, consideration may be given to combining a statin with a drug that alters triglyceride metabolism (e.g., fibrate or nicotinic acid) in high-risk patients with hypertriglyceridemia.

Patients with diabetes mellitus have an increased risk of premature atherosclerosis, which may be due in part to increased oxidizability of low-density lipoprotein (LDL). Numerous studies have shown that alpha-tocopherol can reduce the oxidative susceptibility of LDL in normoglycemic subjects; however, there are few studies in persons with diabetes. In addition, alpha-tocopherol may reduce the extent of protein glycation. Therefore, the objective of the present study was to assess the effect of RRR-alpha-tocopheryl acetate supplementation on LDL oxidizability and protein glycation in persons with diabetes without evidence of vascular disease. Twenty-eight persons with insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM) were randomly assigned to receive either placebo or 1632 mg (1200 IU) RRR-alpha-tocopherol/d, as tocopheryl acetate, for 8 wk. Plasma and LDL antioxidant concentrations and LDL oxidizability were assessed at both 0 and 8 wk. Plasma and LDL concentrations of alpha-tocopherol were significantly increased in the supplemented group only. Compared with the placebo group, the alpha-tocopherol-supplemented group had significant reductions in LDL oxidizability at 8 wk, as shown by the time-course curves of conjugated diene and lipid peroxide formation. Also, alpha-tocopherol supplementation produced a significant prolongation in the lag phases of both assays, which was evident in both the NIDDM and IDDM subgroups. However, there were no significant changes in glycated hemoglobin or in glycated plasma proteins after alpha-tocopherol supplementation. Thus, alpha-tocopherol supplementation may be beneficial in reducing LDL oxidizability in patients with diabetes.

One form of hypercholesterolemia is characterized by high levels of LDL cholesterol and normal levels of LDL-apolipoprotein (apo) B. The reason for hypercholesterolemia, therefore, is enrichment of LDL particles with cholesterol. We have reported previously that about one third of patients with primary moderate hypercholesterolemia have this lipoprotein pattern and have no apparent abnormality in LDL-apo B metabolism. The current study was designed to determine whether the combination of the Step I Diet (30% of total calories as fat, <10% saturated fatty acids, and <300 mg per day cholesterol) with or without cholestyramine therapy will correct the hypercholesterolemia in patients of this type. Ten hypercholesterolemic men of this type were identified and recruited into the study. Their LDL cholesterol levels were > or = 160 mg/dL and LDL-apo B levels were <120 mg/dL (LDL cholesterol/apo B ratio >1.60). For patient selection, subjects were challenged with a high fat diet (40% of total calories as fat, 18% saturated fatty acids, and 400 mg per day cholesterol) for 6 weeks to confirm persistence of a high LDL cholesterol/apo B ratio. Thereafter, they were started on a Step I Diet, and lipoprotein analyses were repeated. Finally, cholestyramine (16 g per day) was added to the Step I Diet. The Step I Diet alone significantly reduced the LDL cholesterol/apo B ratios and produced a trend toward lowering LDL cholesterol levels. Cholestyramine therapy further reduced LDL cholesterol levels and maintained a normal LDL cholesterol/apo B ratio. The present investigation thus confirms the existence of a form of moderate hypercholesterolemia that arises from a defect in LDL composition. In addition, it demonstrates that the combination of Step I Diet and cholestyramine therapy corrects this defect and normalizes LDL levels and LDL composition.

The oxidative modification of low density lipoprotein (LDL) may play a role in the pathogenesis of atherosclerosis. Furthermore, evidence of oxidized LDL (ox-LDL) has been found in vivo. Supplementation of some animal models with antioxidants has been shown to retard the formation of aortic atherosclerosis. Ascorbate (vitamin C) is a highly potent aqueous-phase antioxidant in plasma, which has been shown in vitro to retard LDL oxidation. Cigarette smokers have reduced concentrations of ascorbate in their plasma, and their LDL may be more prone to oxidation. Hence, the objective of the present study was to examine the effect of ascorbate depletion and supplementation on the propensity of LDL to oxidize in smokers in a 6-week study. Nineteen healthy smokers followed a low ascorbate diet (< or = 30 mg/day) for 2 weeks, then were randomly assigned to receive placebo or 1000 mg ascorbate per day for 4 weeks. Blood was taken at 0 and 4 weeks of supplementation for study of LDL oxidative susceptibility. LDL was oxidized with 5 mumol/l copper. The ascorbate-supplemented group had significant increases in plasma ascorbate. The placebo group showed no change in the time course of LDL oxidation between 0 and 4 weeks. However, the ascorbate-supplemented group has a significant reduction in LDL oxidative susceptibility as measured by thiobarbituric acid-reactive substances (TBARS) and the formation of conjugated dienes. The ascorbate-supplemented group demonstrated significantly increased lag phase and decreased oxidation rate at 4 weeks compared to 0 weeks. No changes were found in the placebo group. The ascorbate-supplemented group showed no biochemical signs consistent with increased body iron stores. Supplementation of otherwise healthy smokers for 4 weeks with 1000 mg ascorbate per day resulted in increased plasma ascorbate and reduced LDL oxidative susceptibility.

High levels of low-density lipoprotein cholesterol (LDL) (hypercholesterolemia) are commonly present in the nephrotic syndrome. Another pattern of dyslipidemia in nephrotic patients is an elevation of both cholesterol and triglyceride levels (combined hyperlipidemia). It has been postulated that the underlying cause of nephrotic dyslipidemia is an hepatic overproduction of apolipoprotein B (apo B)-containing lipoproteins. To examine this hypothesis, the metabolism of LDL-apo B was compared between nephrotic patients with hypercholesterolemia and with combined hyperlipidemia. Thirteen patients (7 with hypercholesterolemia, and 6 with combined hyperlipidemia) underwent measurements of turnover rates of autologous LDL apo B. The results were compared to normolipidemic controls and to patients with primary combined hyperlipidemia previously studied in our laboratory. Nephrotic patients with hypercholesterolemia generally had: (a) lower fractional catabolic rates of LDL apo B than normolipidemic healthy individuals; (b) LDL particles enriched in cholesterol; but (c) no overproduction of LDL apo B. In contrast, patients with combined hyperlipidemia were found to have: (a) high fractional catabolic rates for LDL apo B compared to normolipidemic controls; (b) cholesterol-poor LDL particles; and (c) markedly elevated production rates for LDL. Also, for the group as a whole, there was a positive correlation between plasma triglyceride levels and fractional catabolic rates. These data indicate that the metabolism of LDL is strikingly different between the two forms of nephrotic dyslipidemia. Although there may be common mechanisms contributing to LDL levels in nephrotic patients, there also appears to be a divergence of mechanisms depending on whether hypertriglyceridemia is associated with hypercholesterolemia.

There is a strong association between increased blood concentrations of low-density lipoprotein (LDL) and severity of coronary atherosclerosis. Multiple mechanisms affect hypercholesterolemia, e.g., diet, aging, hormones, and genetics. LDL receptors apparently are also important--through down-regulation, defects in structure, or decreased numbers--as are changes in LDL binding characteristics caused by alterations in apolipoprotein B content or structure. Current concepts of LDL metabolism are extensively reviewed, including the role of modified or oxidized LDL in atherogenesis.

Background: Data continue to accumulate supporting a proatherogenic role for oxidized low-density lipoprotein (Ox-LDL). Antioxidant micronutrients such as ascorbate, alpha-tocopherol, and beta carotene, levels of which can be favorably manipulated by dietary measures without side effects, could be a safe approach in inhibiting LDL oxidation. In fact, in vitro studies have shown that all three antioxidants can inhibit LDL oxidation. The present study was undertaken to ascertain both the safety and antioxidant effect of combined supplementation with alpha-tocopherol, ascorbate, and beta carotene on LDL oxidation., Methods and Results: The effect of combined supplementation with alpha-tocopherol (800 IU/d) plus ascorbate (1.0 g/d) and beta carotene (30 mg/d) on copper-catalyzed LDL oxidation was tested in a randomized, placebo-controlled study in two groups of 12 male subjects over a 3-month period. Blood samples for the lipoprotein profile, antioxidant levels, and LDL isolation were obtained at baseline and at 3 months. Neither placebo nor combined antioxidant therapy resulted in any side effects or exerted an adverse effect on the plasma lipoprotein profile. Compared with placebo, combined antioxidant therapy resulted in a significant increase in plasma ascorbate and lipid standardized alpha-tocopherol and beta carotene levels (2.6-, 4.1-, and 16.3-fold, respectively). At baseline, there were no significant differences in the time course curves and kinetics of LDL oxidation as evidenced by the thiobarbituric acid reacting substances (TBARS) assay and the formation of conjugated dienes. However, at 3 months, combined supplementation resulted in a twofold prolongation of the lag phase and a 40% decrease in the oxidation rate. The combined antioxidant group was also compared with a group that received 800 IU of alpha-tocopherol only. Although the combined antioxidant group had significantly higher ascorbate and beta carotene levels than the group supplemented with alpha-tocopherol alone, there were no significant differences between the two groups with respect to LDL oxidation kinetics., Conclusions: Combined supplementation with ascorbate, beta carotene, and alpha-tocopherol is not superior to high-dose alpha-tocopherol alone in inhibiting LDL oxidation. Hence, alpha-tocopherol therapy should be favored in future coronary prevention trials involving antioxidants.

According to a new theory, a critical step in atherogenesis is oxidation of low-density lipoprotein (LDL) within the arterial wall. Direct data supporting this theory are limited, but indirect evidence suggests that oxidized LDL plays a role in atherogenesis. An important question is whether the LDL-oxidation hypothesis conforms to what is known about other risk factors for coronary heart disease (CHD), such as hypertension, smoking, low high-density lipoprotein (HDL) levels, and diabetes mellitus. Perhaps a unified theory of atherogenesis could be formulated if these risk factors exert their atherogenic actions in part by promoting, facilitating, or permitting the oxidation of LDL.

The objective of this study was to determine whether normotriglyceridemic patients with low levels of high density lipoprotein (HDL) cholesterol have concomitant defects in the metabolism of low density lipoproteins (LDLs). To address this question, measurements of turnover rates of apolipoprotein A-I (apo A-I) and LDL apolipoprotein B (apo B) were made in 36 middle-aged men with low HDL cholesterol (< 40 mg/dL), normal triglyceride (< 250 mg/dL), and normal total cholesterol (< or = 90th percentile) levels. Similar measurements were made in eight hypertriglyceridemic men having low HDL levels. For control, turnover rates of LDL apo B were measured in 24 healthy, normolipidemic men, and apo A-I kinetics were determined in 20 other healthy men with normal HDL cholesterol levels. In all patients with low HDL levels, fractional catabolic rates (FCRs) for apo A-I were increased compared with control subjects; in contrast, input rates for apo A-I in low-HDL patients were similar to control. Hypertriglyceridemic patients had significantly higher FCRs for LDL (0.463 +/- 0.040 pool/day, [mean +/- SEM]) than control subjects (0.328 +/- 0.008 pool/day, p < 0.001). In normolipidemic patients having low HDL, a bimodal pattern of LDL-apo B kinetics was observed. For 23 low-HDL patients, FCRs for LDL apo B averaged 0.450 +/- 0.017 pool/day and were significantly higher than control values. Additionally, in these patients, levels of very low density lipoprotein plus intermediate density lipoprotein (VLDL+IDL) cholesterol and VLDL+IDL apo B were higher than in control subjects (54 +/- 3 versus 32 +/- 3 mg/dL and 25 +/- 2 versus 18 +/- 1 mg/dL, respectively). The remaining 13 low-HDL patients had lower and essentially normal FCRs for LDL (0.300 +/- 0.009 pool/day); these patients also had relatively low levels of cholesterol and apo B in VLDL+IDL. Thus, two patterns of LDL kinetics were present in normotriglyceridemic patients with low HDL levels. One pattern was indistinguishable from that typically present in patients with hypertriglyceridemia, whereas the other was similar to normal control subjects. These two patterns of LDL-apo B kinetics may reflect different mechanisms for the causation of low HDL cholesterol concentrations.

Recent studies have shown that one cause of primary moderate hypercholesterolaemia is familial defective apolipoprotein B-100 (FDB), a condition in which a mutation in apolipoprotein B-100 (apo B-100) causes low-density lipoproteins (LDL) to bind poorly to LDL receptors. One specific mutation, a glutamine-for-arginine transformation at position 3500 of apo B-100, has been reported to produce FDB. However, other mutations in apo B-100 might also cause FDB. The present study was designed to determine whether some patients with hypercholesterolaemia, who do not have the 3500 defect, may have a slowly cleared subfraction of LDL compatible with other forms of FDB. It was postulated that slowly removed LDL should accumulate excess cholesterol ester and hence be less dense than normal LDL. If so, in patients who are heterozygous for FDB, two forms of LDL might be separable by ultracentrifugation. To test this hypothesis, less-dense (d = 1.030 g ml-1) and more-dense (d = 1.040 g ml-1) subfractions of LDL were isolated from a patient with proven FDB (3500 mutation); the two forms of LDL were labelled with different isotopes of radioiodine and re-injected into the patient. The less-dense form was removed much more slowly (0.285 pools day-1) than more-dense LDL (0.570 pools day-1). This finding appeared to confirm the validity of the approach. The same procedure was then applied to 18 other patients having elevated LDL cholesterol but not the 3500 mutation. In 13 patients, the two forms of LDL were removed at essentially identical rates, suggesting that they did not have an abnormal form of LDL. In the other five, less-dense LDL were removed at a significantly slower rate than more-dense LDL; this finding suggests that a significant portion of patients with moderate hypercholesterolaemia have an abnormal LDL species, which is not the 3500 mutation, but delays clearance of LDL from the circulation.

The effect of 4 months of low-dose probucol treatment (250 mg/day) on LDL oxidation and on plasma-HDL cholesterol was studied in a prospective, double-blind, randomized, placebo-controlled trial involving 26 male volunteers. LDL samples isolated at baseline and at 4 months were subjected to in vitro tests of LDL oxidation, involving copper-catalyzed, time-course experiments. For the placebo group, LDL oxidation did not significantly change over the 4-month period. However, in the probucol group, LDL oxidation was significantly inhibited at 4 months, as evidenced by assays measuring conjugated diene formation, lipid peroxide production and altered electrophoretic mobility of oxidized LDL. In fact, in the probucol group the 'lag-phase' of oxidation was prolonged 2.7-fold. Neither probucol nor placebo had a significant effect on plasma HDL-cholesterol: in the probucol group HDL-cholesterol fell from 37.7 +/- 7.4 mg/dl to 34.2 +/- 8.3 mg/dl (percentage decrease -8.9), while in the placebo group plasma HDL-cholesterol levels were 42.4 +/- 8.3 mg/dl and 40.9 +/- 7.0 mg/dl at baseline and 4 months (percentage decrease -2.7). Therefore, a low dose of probucol (250 mg/day) given daily seems to afford protection against the oxidative modification of LDL, and does not appear to exert any substantial effect on the plasma lipoprotein profile.

Much data has accumulated supporting a proatherogenic role for oxidized low density lipoprotein (Ox-LDL). Micronutrient antioxidants such as alpha-tocopherol, the principal lipid-soluble antioxidant, assume potential significance because levels can be manipulated by dietary measures without resulting in side effects. Co-incubation of LDL in vitro with alpha-tocopherol inhibits its oxidative modification. Hence the effect of dietary supplementation with alpha-tocopherol on the time course of copper-catalyzed oxidation of LDL was tested in a randomized placebo-controlled single-blind study. Two groups of 12 male subjects were given either placebo or alpha-tocopherol (800 IU/day) for a period of 12 weeks. Alpha-tocopherol therapy did not result in any side effects or exert an adverse effect on the plasma lipid and lipoprotein profile. While the lipid standardized alpha-tocopherol levels were similar at baseline, the supplemented group had 3.3-fold and 4.4-fold higher levels compared to placebo at 6 and 12 weeks, respectively. In the 15 subjects in whom both plasma and LDL alpha-tocopherol levels were quantitated, there was a significant correlation (r = 0.79, P less than 0.0001). At baseline there were no significant differences in the time course curves of thiobarbituric acid-reacting substances (TBARS) activity or conjugated diene formation between the alpha-tocopherol and placebo groups. However, at both 6 and 12 weeks the mean levels of TBARS activity and conjugated diene formation were lower in the alpha-tocopherol group; the most significant differences were manifest at the 3-h time point. Also at both 6 and 12 weeks the mean rate of oxidation was lower in the alpha-tocopherol group.2+&#95;

Several lines of evidence indicate that oxidized LDL (Ox-LDL) may promote atherogenesis. Hence, the role of antioxidants in the prevention of LDL oxidation needs to be determined. beta-Carotene, in addition to being an efficient quencher of singlet oxygen, can also function as a radical-trapping antioxidant. Since previous studies have failed to show that beta-carotene inhibits LDL oxidation, we re-examined its effect on the oxidative modification of LDL. For these studies, LDL was oxidized in both a cell-free (2.5 microM Cu2+ in PBS) and a cellular system (human monocyte macrophages in Ham's F-10 medium). beta-Carotene inhibited the oxidative modification of LDL in both systems as evidenced by a decrease in the lipid peroxide content (thiobarbituric-acid-reacting substances activity), the negative charge of LDL (electrophoretic mobility) and the formation of conjugated dienes. By inhibiting LDL oxidation, beta-carotene substantially decreased its degradation by macrophages. beta-Carotene (2 microM) was more potent than alpha-tocopherol (40 microM) in inhibiting LDL oxidation. Thus, beta-carotene, like ascorbate and alpha-tocopherol, inhibits LDL oxidation and might have an important role in the prevention of atherosclerosis.

To determine the mechanisms whereby HMG-CoA reductase inhibitors lower the levels of low density lipoproteins (LDL) in patients with mixed hyperlipidaemia, LDL turnover studies were conducted in 12 such patients during placebo and then during treatment with lovastatin. Drug therapy reduced total cholesterol and triglyceride concentrations by 33% and 32%, respectively. During lovastatin therapy, LDL-cholesterol levels fell by 37%, and LDL-apo B concentrations decreased by an average of 29%. The decrease in LDL-apo B concentrations on lovastatin therapy was largely due to an increase in fractional catabolic rates (FCRs) for LDL apo B. The average increase in FCRs was 34%, whereas transport rates (production rates) for LDL apo B remained unchanged. These results strongly suggest that an increase in LDL-receptor activity is the major mechanism whereby LDL levels are lowered during lovastatin therapy. The data do not indicate that this drug inhibited the input of apo B-containing lipoproteins, which would have been expected to result in a decrease in the rate of production of LDL.

Background: Hypercholesterolemia is a well-established risk factor for coronary heart disease. However, the mechanisms underlying hypercholesterolemia, elevated low density lipoprotein (LDL) in particular, are not well understood. To determine these mechanisms, we studied LDL kinetics in a group of men with primary hypercholesterolemia., Methods and Results: LDL kinetics in 134 middle-aged men with high-risk levels of LDL cholesterol (more than 160 mg/dl) were compared with kinetics in 16 men with borderline high-risk levels of LDL cholesterol (120-159 mg/dl) and 14 men with heterozygous familial hypercholesterolemia (FH). Patients with primary hypercholesterolemia (non-FH) were further divided into moderate hypercholesterolemia (LDL cholesterol, 160-210 mg/dl; n = 108) and severe hypercholesterolemia groups (LDL cholesterol, more than 210 mg/dl; n = 26). Four factors contributed to increasing LDL cholesterol concentrations above the borderline range to moderately elevated levels: 37 patients had no increase in LDL apolipoprotein (apo) B levels but had abnormally high LDL cholesterol-to-apo B ratios; 14 patients had very low fractional catabolic rates (FCRs) for LDL, similar to FH patients; 35 patients had FCRs for LDL in the borderline range but high production rates for LDL; and 22 patients had a high flux of LDL (high production rates and high FCRs). In general, patients with severe hypercholesterolemia resembled those with moderate LDL elevations, except that their LDL particles were enriched with cholesterol., Conclusions: Data from the present study reveal that there are several distinct patterns of LDL metabolism responsible for primary hypercholesterolemia. These patterns can serve as the basis for further investigation to determine the molecular defects responsible for each pattern.

Heterozygous familial hypercholesterolemia (FH) usually presents with severe elevations of low density lipoprotein (LDL) cholesterol. Recently, a family with FH was described in which several members heterozygous for a mutation in the LDL receptor gene had normal LDL cholesterol levels. Kinetic studies of LDL apolipoprotein B (apo B) were conducted to determine the metabolic differences between the normolipidemic and hypercholesterolemic FH heterozygotes in the family. Studies were performed in 14 family members including the proband (who has homozygous FH), four FH heterozygotes with high LDL levels, four FH subjects with normolipidemia, and five healthy relatives without FH. The proband had a very low fractional catabolic rate (FCR) for LDL (0.15 pool/day). All the FH and non-FH subjects studied, excluding the FH homozygote, had higher than expected FCRs for LDL. The average FCRs for LDL of hypercholesterolemic and normocholesterolemic subjects were not significantly different (0.39 +/- 0.06 versus 0.37 +/- 0.02 pool/day), and these values were 70-80% of those in unaffected relatives. Compared with hypercholesterolemic FH heterozygotes, normolipidemic heterozygotes had much lower input rates for LDL (17.1 +/- author query macros2.6 versus 8.7 +/- 0.9 pools/day, respectively). These low input rates, together with the higher than usual FCRs for LDL, are responsible for the normal concentrations of LDL cholesterol in some of the FH heterozygotes. The low input of LDL could be due to either a decreased secretion of apo B-containing lipoproteins or an enhanced clearance of LDL precursor lipoproteins.

The oxidative modification of low density lipoprotein (LDL) may provide a crucial link between plasma LDL and the atherosclerotic lesion. The studies presented herein define time-dependent modifications of LDL constituents caused by CuSO4-catalyzed oxidation. Measurement of the cholesterol content of oxidized LDL by the cholesterol esterase-oxidase assay was found to be inaccurate. The enzymatic assay detected oxysterols as well as cholesterol and thus substantially overestimated the actual cholesterol content. Alteration of electrophoretic mobility and conversion of sterols into oxysterols increased in a parallel, time-dependent manner. Lipid peroxidation, judged by the thiobarbituric acid-reacting substances assay, increased early to maximal values but was not linearly related to either electrophoretic mobility or to oxysterol formation. Neither electrophoretic mobility nor oxysterol formation varied much between repeated oxidative modifications of any given LDL preparation but varied markedly among LDLs from different normolipidemic individuals, suggesting that LDL particles contain some factor conferring susceptibility or resistance to oxidation. Indeed, LDL preparations from different individuals have varying susceptibilities to oxidative modification as evidenced by the three indexes used. The major oxysterol generated was 7-ketocholesterol. Macrophage modification of LDL also resulted in the generation of oxysterols. Thus, measurement of oxysterols may afford an additional index of the oxidative modification of LDL. Since incubation of macrophages with oxidized LDL but not native LDL resulted in the accumulation of oxysterols, this could account for some of the toxic and metabolic effects of oxidized LDL on cells.

Several lines of evidence indicate that the oxidative modification of low density lipoproteins (LDL) may provide an important link between plasma LDL and the genesis of the atherosclerotic lesion. Ascorbate is an important water-soluble, chain-breaking antioxidant in humans. Probucol, a lipid-soluble antioxidant drug has been shown to retard the progression of atherosclerosis. The aim of the present study was to compare the effects of probucol and physiologic levels of ascorbate on the oxidative modification of LDL in both a cell-free (2.5 microM Cu++ in phosphate-buffered saline) and cellular system (human monocyte macrophages in Ham's F-10 medium). Both ascorbate and probucol inhibited the oxidative modification of LDL in both systems to a similar degree as evidenced by the thiobarbituric acid-reacting substance activity, electrophoretic mobility, and degradation by macrophages. However, whereas co-incubation with physiologic levels of ascorbate resulted in a substantial preservation of the alpha-tocopherol, gamma-tocopherol, and beta-carotene of the LDL, probucol in concentrations ranging from 10 to 80 microM failed to protect these antioxidants. Thus, in addition to being as potent as probucol in inhibiting the oxidation of LDL, ascorbate in contrast preserves the endogenous antioxidants in the LDL.

Oxidatively modified low density lipoprotein (LDL) could contribute to the atherosclerotic process by its cytotoxic effect, uptake by the scavenger receptor and influence on monocyte and macrophage motility. The aim of the present study was to examine the effect of physiologic levels of alpha-tocopherol and ascorbate on Cu2(+)-induced oxidative modification of LDL. Whereas alpha-tocopherol had an inhibitory effect on the oxidative modification of LDL only for 5 h, as evidenced by the electrophoretic mobility and lipid peroxide content, ascorbate inhibited the oxidative modification of LDL for both 5 and 24 h. By inhibiting the oxidative modification of LDL, ascorbate prevented the uptake and degradation of oxidatively modified LDL by the scavenger-receptor mechanism of cultured human monocyte derived macrophages. It thus appears that in this cell-free system (2.5 microM Cu2+), ascorbate is a more potent antioxidant than alpha-tocopherol. These findings indicate that ascorbate in physiologic concentrations should inhibit the oxidate modification of LDL in vivo.

A patient is described who has marked palmar xanthomatosis associated with a normal concentration of plasma cholesterol. Analysis of xanthomas revealed them to contain large quantities of cholesterol with both intra- and extracellular lipids. Examination of plasma lipoproteins showed them to be consistent with a pattern of dysbetalipoproteinemia (Type III hyperlipoproteinemia). VLDL had beta-mobility on electrophoresis, a high cholesterol/triglyceride ratio, and increased apoprotein B. However, arginine-rich apoprotein was not increased in VLDL, in contrast to hypercholesterolemic patients with the Type III pattern. Nevertheless, the E3 subfraction of the arginine-rich apoprotein was virtually absent, which is characteristic of dysbetalipoproteinemia. Cholesterol and bile acid synthesis were in the normal range. Thus, of particular interest was the development of severe xanthomatosis without hypercholesterolemia in this patient. Therefore, tissue accumulation of cholesterol was apparently the result of a qualitative abnormality in lipoproteins and not due to an excess of plasma cholesterol.

To evaluate factors regulating the concentrations of plasma low density lipoproteins (LDL), apolipoprotein B metabolism was studied in nine Pima Indians (25 +/- 2 yr, 191 +/- 20% ideal wt) with low LDL cholesterol (77 +/- 7 mg/dl) and apoB (60 +/- 4 mg/dl) and in eight age- and weight-matched Caucasians with similar very low density lipoprotein (VLDL) concentrations, but higher LDL (cholesterol = 104 +/- 18; apoB = 82 +/- 10; P less than 0.05). Subjects received autologous 131I-labeled VLDL and 125I-labeled LDL, and specific activities of VLDL-apoB, intermediate density lipoprotein (IDL)-apoB, and LDL-apoB were analyzed using a multicompartmental model. Synthesis of LDL-apoB was similar (1224 +/- 87 mg/d in Pimas vs 1218 +/- 118 mg/d in Caucasians) but in Pimas the fractional catabolic rate (FCR) for LDL-apoB was higher (0.48 +/- 0.02 vs 0.39 +/- 0.04 d-1, P less than 0.05). In the Pimas, a much higher proportion of VLDL-apoB was catabolized without conversion to LDL (47 +/- 3 vs 30 +/- 5%, P less than 0.01). When all subjects were considered together, LDL-apoB concentrations were negatively correlated with both FCR for LDL-apoB (r = -0.79, P less than 0.0001) and the non-LDL pathway (r = -0.43, P less than 0.05). Also, the direct removal (non-LDL) path was correlated with VLDL-apoB production (r = 0.49, P = 0.03), and the direct removal pathway and FCR for LDL-apoB were correlated (r = 0.49, P = 0.03). In conclusion, plasma LDL appear to be regulated by both the catabolism of LDL and the extent of metabolism of VLDL without conversion to LDL; both of these processes may be mediated by the apoB/E receptor, and appear to increase in response to increasing VLDL production.

Low density lipoprotein (LDL) is probably the most atherogenic of all the lipoproteins. Several abnormalities in LDL metabolism seem to be associated with coronary heart disease (CHD) one of them being an elevation of plasma LDL concentration. Recent findings suggest that disorders in the metabolism of LDL could be associated with accelerated atherosclerosis even without elevated LDL levels such as increased flux of LDL and changes in the LDL composition. Elevation of plasma LDL levels can be caused by two factors, first, a decrease in the clearance of LDL and second, an overproduction of this lipoprotein. Catabolism of LDL is largely determined by the LDL receptors as clearly shown in patients with familial hypercholesterolemia (FH). In this inherited disease the patients do not have normal LDL receptors and their LDL levels are remarkably elevated. LDL production is also increased in these subjects. In the rest of the population LDL levels are regulated by both the LDL clearance and production rate. The latter also seems to be related to the LDL receptor activity. The conversion of the LDL precursor, very low density lipoprotein (VLDL) to LDL is the most important factor regulating LDL synthesis. When the LDL receptor activity is low a large fraction of VLDL apolipoprotein B (apoB), the major structural protein in VLDL, is converted to LDL, and LDL production is high. On the other hand, only a small part of VLDL apoB is converted to LDL resulting in low LDL synthesis rate in conditions with high LDL receptor activity. The relationships between production and clearance of LDL are, however, more complex. There are individuals who produce a large number of VLDL and LDL particles but maintain LDL concentrations at a normal level by clearing their LDL very effectively. These subjects obviously have another abnormality in lipoprotein metabolism namely an overproduction of apoB. This disorder has been observed in several conditions like obesity, adult-onset diabetes mellitus, several patients with familial combined hyperlipidemia and some normolipidemic subjects with premature coronary heart disease. In all these conditions increased transport of LDL can be associated with coronary artery disease even in the absence of hypercholesterolemia. This raises the possibility that increased flux of LDL could itself be atherogenic possibly by overloading reverse cholesterol transport. Finally, there is some evidence that LDL particle composition may be important in the process of atherogenesis. High LDL apoB but normal LDL cholesterol levels, hyperapobetalipoproteinemia, has been associated with premature coronary heart disease.(ABSTRACT TRUNCATED AT 400 WORDS)

This study was carried out to evaluate simplified methods for estimating parameters of kinetics of low density lipoproteins (LDL). Initially, LDL turnover studies were carried out in 78 patients, and fractional catabolic rates (FCRs) for LDL were determined from die-away curves of plasma radioactivity and from urine-to-plasma (U/P) ratios of radioactivity. When U/P ratios were calculated on a daily basis and throughout the study and averaged by a weighting procedure, the weighted U/P ratios were highly correlated with plasma decay FCRs (r = 0.92, P less than 0.001). One simplified method involved calculation of FCR for LDL from the U/P ratio on the seventh day after injection of radioactivity. Seventh-day U/P ratios also were correlated significantly with plasma decay FCRs (P less than 0.001), but the strength of correlation between the two was relatively weak (r = 0.52). Finally, another correlation was found to be significant. This was the plasma decay FCR vs. the fraction of injected dose disappearing from plasma during the first 24 h (r = 0.86). This comparison was extended to 140 turnover studies, and the correlation remained high (r = 0.90, P less than 0.0001). Thus, estimation of FCR for LDL from the fraction of dose disappearing at 24 h appears superior to that determined from the 7th-day U/P ratio.

We have studied a family carrying a variant of the class 2 mutation of familial hypercholesterolemia (FH) in which there is unusual longevity and in which obligate heterozygotes did not express constant or statistically significant hypercholesterolemia. The heterozygotes have the same kinetic defect in the processing of low density lipoprotein (LDL) receptors in their fibroblasts and the reduced fractional catabolic rate for apoLDL that is characteristic of other patients with heterozygous FH. However, their plasma lipid and lipoprotein levels are not as strikingly abnormal because they have normal or near normal rates of apoLDL synthesis.

A method has been described for the measurement of apoB concentration and specific activity in very low density lipoprotein (VLDL) and low density lipoprotein (LDL) during metabolic studies. For measurement of specific activity, apoB was separated from other apolipoproteins and lipids by precipitation in, and subsequent washing with, isopropanol. For determination of apoB concentration, equal volumes of lipoprotein and isopropanol were mixed, and the protein content of the apoB precipitate was measured by the difference between total lipoprotein protein and the protein measured in the supernatant. Evidence that there was no apoB solubilization in isopropanol and that precipitated apoB was virtually free of soluble apolipoproteins was obtained by electrophoresis. Lipid contamination of the apoB precipitate was less than 1%. The methods were applicable to VLDL, intermediate density lipoprotein (IDL), and LDL from normolipemic patients with protein concentrations between 187 micrograms/ml and 1898 micrograms/ml. The data obtained using isopropanol were highly correlated with those using tetramethylurea, and recoveries of apoB were similar. Furthermore, the isopropanol method has been demonstrated to yield consistent data for apoB specific activities in a study of VLDL, IDL, and LDL metabolism.

Cerebrotendinous xanthomatosis (CTX) is a rare disorder characterized by a defect in conversion of cholesterol into bile acids, increased plasma levels of cholestanol, and accumulations of sterols in tendons, brain, and coronary arteries. Despite the presence of tendon xanthomas, patients with CTX frequently have low levels of plasma cholesterol and low density lipoproteins (LDL). The mechanisms for a low LDL are not understood. The present study, therefore, was carried out to examine the metabolism of LDL in a 58-year-old black man with CTX. This particular patient had an LDL-cholesterol in the mid-normal range (149 +/- 6 mg/dL). Nonetheless, his fractional catabolic rate (FCR) for LDL-apolipoprotein (apo-LDL) was 0.45 pools/d, which was increased compared to 15 aged-matched men (FCR, 0.30 +/- 0.01 pools/d). His production rate for apo-LDL (18.5 mg/kg-d) also was increased compared to those of middle-aged men (13.5 +/- 2.5 mg/kg-d). Since the underlying defect in CTX can be reversed by administration of chenodeoxycholic acid (chenodiol), the patient was treated with chenodiol (250 mg 4X daily), and measurements of LDL kinetics were repeated. During chenodiol therapy, his LDL-cholesterol concentration rose significantly to 165 +/- 12 mg/dL; his FCR for apo-LDL fell to 0.29 pools/d; and his production rate of apo-LDL declined to 14.4 mg/kg-d. We postulate that chenodiol suppressed the excessive synthesis of cholesterol and bile acids, which had two effects. It curtailed both the overproduction of LDL and the excessive synthesis of LDL receptors, the latter being responsible for the high FCR of apo-LDL in the untreated state.

Mevinolin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, was used for treatment of 12 patients with moderate hypercholesterolemia, but not classical familial hypercholesterolemia. For most patients, measurements of turnover of low density lipoprotein-apolipoprotein B (LDL-apoB) were made on placebo and during treatment with two doses of mevinolin. LDL turnover was determined after injection of autologous 125I-labeled radioiodinated LDL. Compared to placebo, a low dose of mevinolin (10 mg, twice daily (BID] caused reductions of plasma total cholesterol and LDL-cholesterol averaging 15% and 20%, respectively; corresponding reductions on high doses of mevinolin (20 mg BID) were 22% and 31%, respectively. Triglyceride levels were unchanged by the drug. High density lipoprotein cholesterol levels rose significantly on the high dose, but not on the low dose. Neither dose produced a stastistically significant change in fractional catabolic rate (FCR) for LDL-apoB for the whole group, although several patients had increases in FCR on both doses. In contrast, both doses of mevinolin caused decreases in production rates of LDL-apoB. Thus, the fall in LDL levels in patients with moderate hypercholesterolemia can be explained more by a reduction in the input rate of LDL-apoB than by enhanced fractional removal of LDL from the circulation.

The mechanisms for the hypocholesterolemic actin of neomycin were examined in six patients with various levels of plasma total cholesterol and triglycerides. All patients were studied on a metabolic ward. The first period of 6 weeks was for control. Thereafter, neomycin (1.5 g/day) was started, and the patients were readmitted for another 6-week period after 2 to 3 months of treatment with the drug. Cholesterol balance studies showed that neomycin increased fecal excretion of neutral steroids by an average of 45%; the drug also inhibited absorption of exogenous cholesterol by an average of 44%. During treatment with neomycin, the plasma total cholesterol fell by an average of 20%, low density lipoproteins (LDL) fell by 25%, and high density lipoproteins, by 16%. Neomycin did not change plasma triglyceride levels. Turnover of the apoprotein of LDL (apoLDL) was measured following injection of 125I-apoLDL. Neomycin decreased synthesis of apoLDL by 28%. The decrease in plasma apoLDL level was correlated positively with the decrease in apoLDL synthetic rate. The effect of the drug on clearance of LDL was less constant; four of six patients had an increase in fractional clearance rates of apoLDL, but the change for the whole group was not statistically significant. These data suggest that a decrease in production of LDL is a major factor in the lowering of LDL following inhibition of cholesterol absorption; however, an increase in clearance rates may occur in some patients.

The causes of primary moderate hypercholesterolemia are not understood, but some patients have reduced fractional clearance rates (FCRs) for low density lipoproteins (LDL). This could be due to either decreased activity of LDL receptors or to a defect in structure (or composition) of LDL that reduces its affinity for receptors. To distinguish between these causes, simultaneous turnover rates of autologous and normal homologous LDL were determined in 15 patients with primary moderate hypercholesterolemia. In 10, turnover rates of both types of LDL were indistinguishable, which indicated that autologous LDL was cleared as efficiently as normal homologous LDL. In five others, FCRs for autologous LDL were significantly lower than for homologous LDL. Two of the latter five were treated with mevinolin, and although FCRs for both types of LDL rose during treatment, differences in FCRs between the two types of LDL persisted. In these five patients, autologous LDL appeared to be a poor ligand for LDL receptors.

In subject with heterozygous familial hypercholesterolemia (FH), a 50% deficiency of receptors for plasma low density lipoprotein (LDL) impairs the removal of LDL from plasma and produces hypercholesterolemia. In these patients mevinolin, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, blocks cholesterol synthesis and lowers plasma LDL levels. To determine the mechanism for the LDL-lowering effect, we administered 131I-labeled LDL intravenously to six FH heterozygotes before and during treatment with mevinolin and calculated the apparent fractional catabolic rate (FCR) and synthetic rate for LDL. After mevinolin treatment, the mean plasma LDL-cholesterol level declined from 262 to 191 mg/dl (27% decrease), the mean FCR for 131I-labeled LDL increased from 0.30 to 0.41 pools per day (37% increase), and the mean calculated synthetic rate for LDL-protein did not change significantly. In one of FH heterozygote with an ileal bypass and in another who received colestipol, the addition of mevinolin caused, respectively, a 41% and 60% decrease in plasma LDL levels and a 60% and 100% increase in the FCR for plasma LDL. The contribution of receptor-dependent pathways to the FCR for plasma LDL was estimated in three FH heterozygotes by simultaneous measurements of the FCR for native 131I-labeled LDL and 125I-labeled glucosylated LDL, which does not bind to LDL receptors. Whereas the removal rate for native LDL increased after mevinolin treatment, the removal rate for glucosylated LDL did not change. The current data suggest that mevinolin alone or mevinolin plus bile acid depletion (i.e., ileal bypass or colestipol therapy) decreases plasma LDL levels primarily by raising the number of LDL receptors and, thus, enhancing the removal of LDL from plasma.

To determine whether production or catabolism of low density lipoprotein (LDL) is the major factor controlling LDL concentrations in subjects with plasma cholesterol levels from low-normal to mildly elevated, measurements of apoprotein of LDL (apoLDL) turnover were performed in 16 patients with various plasma cholesterol concentrations. Cholesterol balance studies were done simultaneously in 13 of these patients. Plasma concentrations of apoLDL and LDL-cholesterol were positively correlated with synthetic rates of apoLDL (r = 0.74, P less than 0.001; r = 0.50, P less than 0.05, respectively). No correlation was noted between the fractional catabolic rate for apoLDL and apoLDL levels (or LDL-cholesterol). For further analysis, the patients were divided into three groups with stepwise increases in apoLDL concentrations. When apoLDL levels rose significantly, from 83 +/- 5 SEM to 122 +/- 2 to 149 +/- 5 mg/dl, synthetic rates for apoLDL also increased significantly from 11.6 +/- 12. to 17.0 +/- 0.9 to 23.8 +/- 1.8 mg/d/kg ideal weight. In contrast, the fractional catabolic rate of apoLDL was not different among the three groups (0.32 +/- 0.03 vs. 0.29 +/- 0.02 vs. 0.33 +/- 0.03/d). No relation was noted between synthesis of total body cholesterol (or bile acids) and concentrations, production rates, or removal of apoLDL. Thus, concentrations of apoLDL and LDL-cholesterol in these subjects with plasma cholesterol levels from low-normal to mildly elevated were regulated mainly by synthetic rates of apoLDL and not by LDL catabolism.

To investigate the gene-dosage effect in familial hypercholesterolemia (FH), metabolic studies were conducted in a group of well-characterized patients with either heterozygous (n = 7) or homozygous (n = 7) FH and the results were compared to those obtained in normal subjects (n = 6). The turnover of (125)I-labeled low-density lipoprotein (LDL) was measured in all of the normals, all but one of the FH heterozygotes, and in all of the homozygotes. Chemical cholesterol balance was performed simultaneously with the (125)I-LDL turnover in all seven of the homozygotes. With regard to (125)I-LDL turnover, FH homozygotes, who possess two doses of the mutant FH gene, exhibited a threefold increase in the rate of apoLDL synthesis while the fractional catabolic rate (FCR) for the apoprotein was only about one-third of normal. Heterozygotes, who have only one dose of the mutant FH gene, exhibited intermediate values for both parameters; that is, the FCR was two-thirds of normal and the apoLDL synthetic rate was 1.7-fold greater than normal. THE DATA INDICATE THAT THE SINGLE GENE DEFECT IN FH PRODUCES TWO DISTINCT ABNORMALITIES OF LDL METABOLISM: (a) an increase in the synthetic rate for apoLDL and (b) a decrease in the efficiency of apoLDL catabolism. Both defects are more severe in FH homozygotes than in heterozygotes. The FCR for apoLDL in the homozygotes appeared to be fixed at congruent with 17%/d whereas the plasma LDL level varied about twofold. These findings suggest that the twofold variation in plasma LDL levels observed in these seven patients is caused by variation in the plasma apoLDL synthetic rates. Consistent with this conclusion was the finding that the correlation between the plasma LDL level and the apoLDL synthetic rates in the seven FH homozygotes was 0.943. The rate of total body cholesterol synthesis determined by chemical cholesterol balance did not appear to clearly differ between normals and patients with either one or two mutant FH genes. Two of the youngest FH homozygotes exhibited cholesterol overproduction but the other five did not. No consistent abnormality of bile acid metabolism was observed in these patients. Because the daily plasma flux of cholesterol on LDL is about threefold greater than the amount of cholesterol produced per day, a significant amount of the cholesterol liberated from LDL degradation must be reused.

Certain primary hypertriglyceridemias cause abnormalities in lipoproteins that seemingly predispose patients to coronary heart disease. We examined metabolism of low-density lipoproteins (LDL) in 11 men with both hypertriglyceridemia and coronary heart disease and compared them with that of controls. The LDL turnover was measured during placebo and gemfibrozil therapy. With placebo, LDL-cholesterol level usually was normal, but production and fractional clearance of LDL were high. The LDL composition also was abnormal. Gemfibrozil reduced triglycerides, lowered production and fractional clearance of LDL, and normalized LDL composition. The LDL-cholesterol level usually rose, but generally not to abnormally high levels. Therefore, normalization of LDL metabolism and marked reduction of triglycerides by gemfibrozil suggest benefit to hypertriglyceridemic patients who are at high risk for coronary heart disease. However, when LDL-cholesterol level rises excessively, gemfibrozil may not be sufficient therapy.

Turnover rates of the apolipoprotein of low density lipoproteins (apoLDL) and cholesterol balance were determined in six obese men and six control men. The two groups were of similar age and matched for apoLDL concentrations. Levels of plasma total cholesterol in obese patients (209 +/- 14 SEM mg/dl) were similar to controls (225 +/- 17 mg/dl). LDL-cholesterol was numerically but not statistically lower in obese subjects (111 +/- 18 mg/dl) compared to controls (145 +/- 13 mg/dl). Synthetic rates of apoLDL in contrast were higher in obese patients (1450 mg/day) than in controls (934 mg/day) (p less than 0.002). Three factors could explain the similar concentrations of LDL-cholesterol in obese and control subjects, despite overproduction of apoLDL in the obese. First, LDL was diluted into a larger plasma pool in obese patients; second, fractional catabolic rates of apoLDL were somewhat greater in obese men than in controls; and third, obese patients had higher ratios of protein-to-cholesterol in LDL. The production of apoLDL for all patients was not correlated with total body synthesis of cholesterol. The major finding of this study was that obese patients have increased turnover of apoLDL, not necessarily reflected by high concentrations of LDL-cholesterol. This high turnover rate itself may raise the risk for coronary heart disease in obese patients.

This study examined the effects of dietary saturated and polyunsaturated fat on the chemical composition and metabolism of low density lipoproteins (LDL) in eight normal male subjects. The influence of these diets on fecal sterol excretion was also measured in four of the subjects. When compared with the saturated fat diet, the polyunsaturated diet lowered both plasma cholesterol polyunsaturated diet lowered both plasma cholesterol (23%, P less than 0.001) and triglyceride (14%, P less than 0.001) levels. Sixty-seven percent of the reduction in the former lipid resulted from a fall in LDL cholesterol (23%, P less than 0.001), although very low density (VLDL) and high density lipoprotein (HDL) cholesterol levels also fell (by 27% and 20% of their respective control value). These changes were accompanied by significant alterations in LDL composition. Specifically, during polyunsaturated fat feeding, the relative percentage cholesterol in the LDL fraction fell while that of phospholipid rose. There was no change in the percentage protein or triglyceride. The fatty acid components of LDL triglyceride, cholesteryl esters, and phospholipid were also affected by dietary fat saturation level. Overall, polyunsaturated fat feeding produced an enrichment in linoleate with reciprocal changes in palmitate, stearate, and oleate which affected triglycerides more than cholesteryl esters and phospholipids. The above changes in LDL composition were associated with alterations in the metabolism of LDL apoprotein (apoLDL). The polyunsaturated deit lowered plasma apoLDL by 13% (P less than 0.05). This resulted from an increase in the fractional catabolic rate of LDL (whether determined by plasma decay curve analysis (P less than 0.05) or urine/plasma radioactivity ratios (P less than 0.001) without significant alteration of its corporeal distribution or synthetic rate. The polyunsaturated fat diet did not cause a consistent change in fecal neutral or acidic steroid excretion. We conclude that the hypocholesterolemic action of polyunsaturated fat diets is effected by multiple mechanisms whose expression may vary from patient to patient.

Familial defective apolipoprotein (apo) B-100 is a recently described genetic disorder that appears to result from a mutation in the apoB-100 gene. This disorder is characterized by hypercholesterolemia resulting from elevated plasma concentrations of low density lipoprotein LDL. The disorder was first detected in three members of one family. The LDL from affected subjects binds defectively (approximately 30% of normal) to LDL receptors, retarding the clearance of LDL from plasma. In the present study, two other members of the affected family were found to possess abnormal LDL. In addition, abnormal LDL with a similar binding defect were found in a second, unrelated family. In both families, the defect is transmitted over three generations as an autosomal codominant trait and all affected members are heterozygotes. Since there is only one apoB-100 molecule per LDL particle, the abnormal LDL in heterozygous subjects is made up of two populations of particles: one that has normal binding activity to receptors and one that binds defectively. To localize the mutation in apoB-100, the binding of five apoB-100-specific monoclonal antibodies to abnormal LDL was assessed in a solid-phase RIA. Only antibody MB47, whose epitope is between residues 3350 and 3506, distinguished abnormal LDL from normal LDL isolated from control subjects with normal lipid levels; MB47 bound with a higher affinity (by approximately 60%) to abnormal LDL. In every individual with abnormal LDL, the MB47 antibody bound with a higher affinity. The convenience of this assay will facilitate screening of large populations to determine the frequency of this disorder.

The kinetics of two subfractions of low density lipoproteins (LDL) were examined in nine patients with primary hypertriglyceridemia. LDL was subjected to equilibrium ultracentrifugation, and three patterns of LDL subfractions were noted. The LDL of five patients with moderate hypertriglyceridemia (plasma triglycerides (TG) ranging from 333 to 580 mg/dl) appeared to contain two distinct subfractions. One was less dense and had a high TG content; the other was more dense and had a reduced content of all lipids, particularly cholesterol. Each subfraction was labeled separately and was reinjected into the patient. Of the two subfractions, the more dense LDL usually had a higher fractional catabolic rate (FCR), although the turnover rates of both subfractions for these hypertriglyceridemic patients were higher than normal. Two other patients with mild hypertriglyceridemia had only a single LDL after gradient equilibrium ultracentrifugation. This fraction was divided into less dense and more dense subfractions, and their FCR was determined. In both patients, turnover rates of the two subfractions were similar and both were in the normal range. Finally, two more patients with mildly elevated TG had a very dense LDL, besides having a single, less dense band. For both patients, the FCR for the less dense and very dense subfractions were similar, although the denser LDL had a greater fraction in the extravascular compartment. Thus, patients with primary moderate hypertriglyceridemia often have distinct subfractions that have different turnover rates. For patients with mild hypertriglyceridemia, the LDL is more homogeneous, and its subfractions are kinetically similar.

To quantify more precisely the metabolism of apolipoprotein B (apo B) in human beings, an integrated model was developed for the analysis of the isotope kinetics of apo B in very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), and low density lipoproteins (LDL). The experimental basis for model development was a series of 30 triple-isotope studies in which patients received autologous 131I-VLDL, 125I-IDL, and [3H]glycerol as a precursor of VLDL triglycerides. The currently proposed model contains the following components: (a) a VLDL delipidation cascade that has a variable number of subcompartments, (b) a slowly catabolized pool of VLDL, (c) an IDL compartment consisting of two closely connected subcompartments, one of which is outside the immediate circulation, and (d) a two-compartment subsystem for LDL. Because mass data indicate that not all VLDL were converted to LDL, the model allows for irreversible removal of apo B from VLDL (or IDL) subsystems. It accounts for apparent "direct" input of LDL by postulating an early, rapidly metabolized compartment of VLDL that is converted directly to IDL. The model appears to be consistent with specific activity curves from the current triple-isotope studies and with present concepts of lipoprotein physiology; it also can be used to quantify pathways of lipoprotein apo B transport in normal and abnormal states.

The turnover rates of low density lipoprotein-apolipoprotein (apoLDL) were determined in eight men with coronary heart disease (CHD) and seven men matched for age, weight, and plasma lipid levels who were used for controls. The CHD patients were normocholesterolemic (plasma cholesterol = 204 +/- 8 mg/dl sem) as were the control subjects (227 +/- 15 mg/dl). The concentrations of plasma LDL cholesterol and apoLDL were similar for the two groups. In contrast, the synthetic rates of apoLDL were higher in the CHD patients (20.0 +/- 1.8 mg/kg/day) than in the controls (12.9 +/- 1.1 mg/kg/day) (p less than 0.01). The ratios of protein-to-cholesterol in LDL averaged 19% higher in the CHD patients. These patients with CHD maintained normal LDL levels despite an over-production of apoLDL because of an increased capacity for LDL removal; their fractional catabolic rates of apoLDL averaged 43% higher than those of the controls. These findings indicate that some patients with CHD have abnormalities in the turnover of apoLDL, even with normal concentrations of LDL; these abnormalities may contribute to accelerated atherosclerosis.

Patients with primary hypertriglyceridaemia usually have increased clearance rates for plasma low-density lipoproteins (LDL). To evaluate the mechanisms for this effect, simultaneous turnover rates for autologous and normal homologous LDL were determined in 12 patients with primary hypertriglyceridaemia. On average, the autologous LDL was cleared more rapidly than the normal homologous LDL. Fractional catabolic rates (FCRs) for autologous LDL averaged 0.61 +/- 0.06 (SEM) pools d-1, whereas FCRs for homologous LDL averaged 0.49 +/- 0.04 pools d-1. In eight of the 12 patients the FCRs for 'hypertriglyceridaemic' LDL were found to be significantly higher than for normal LDL; in four others both forms of LDL were cleared at essentially the same rate. In all cases, however, both for the normal and 'hypertriglyceridaemic' LDL, clearance rates were higher than normal. Thus, besides the variability in LDL affinity for removal pathways, hypertriglyceridaemic patients appear to have an increased availability of LDL receptors for removal of circulating LDL.

The turnover rates of low density lipoprotein-apolipoprotein B (LDL-apoB) were determined in 32 men with coronary heart disease (CHD) and 11 control men with normal plasma lipids. Thirty patients with CHD had normal levels of LDL-cholesterol (LDL-C); of these patients, 9 had hypertriglyceridemia and 21 had normal plasma lipids. Mean concentrations of total cholesterol and LDL-C were similar among the control subjects and CHD patients, although the latter had significantly lower HDL-C. In control subjects, transport rates and fractional catabolic rates (FCR) of LDL-B were 10.6 +/- 0.5 (SEM) mg/kg-day and 0.31 +/- 0.01 pools/day, respectively. In 10 hypertriglyceridemic patients with CHD, transport rates were 21.7 +/- 1.7 mg/kg-day, and FCRs averaged 0.56 +/- 0.06 pools/day; both were significantly higher than normal (P less than 0.05). Six normolipidemic patients also had abnormally high transport rates of LDL-apoB (19.4 +/- 2.8 mg/kg-day) and FCRs (0.51 +/- 0.03 pools/day); again both were higher than normal. The remaining 16 normolipidemic patients with CHD had normal transport rates (9.9 +/- 0.6 mg/kg-day) and FCRs (0.28 +/- 0.01 pools/day). Thus, hypertriglyceridemic patients with CHD and a portion of normolipidemic patients with CHD were characterized by increases in both transport and fractional catabolic rate of LDL-apoB; these abnormalities in LDL metabolism may have contributed to their coronary heart disease. However, the majority of normolipidemic patients with CHD did not show a distinct defect in their LDL metabolism.

The current results show that one can exploit the normal regulation of receptor synthesis to stimulate the single normal gene in FH heterozygotes to produce an increased number of LDL receptors. This stimulation can be achieved by drugs that inhibit HMG CoA reductase in the liver and by maneuvers that cause bile acid depletion. These two therapeutic approaches are most effective when they are combined. It seems reasonable to speculate that such a profound lowering of plasma cholesterol levels will minimize the development of atherosclerosis in FH heterozygotes. In a broader sense, the success of this regulatory manipulation raises the possibility that other genetic diseases may be treated through manipulation of regulatory signals that control the rates of synthesis of gene products.