Search

Beta-hydroxy-beta-methyl butyrate (HMB) is a unique product of leucine catabolism with positive effects on protein balance. We have examined the effects of HMB (200 mg/kg/day via osmotic pump for 7 days) on rats with diabetes induced by streptozotocin (STZ, 100 mg/kg intraperitoneally). STZ induced severe diabetes associated with muscle wasting, decreased ATP in the liver, and increased α-ketoglutarate in muscles. In plasma, liver, and muscles increased branched-chain amino acids (BCAAs; valine, isoleucine, and leucine) and decreased serine. The decreases in mass and protein content of muscles and increases in BCAA concentration were more pronounced in extensor digitorum longus (fast-twitch muscle) than in soleus muscle (slow-twitch muscle). HMB infusion to STZ-treated animals increased glycemia and serine in the liver, decreased BCAAs in plasma and muscles, and decreased ATP in the liver and muscles. The effects of HMB on the weight and protein content of tissues were nonsignificant. We concluded that fast-twitch muscles are more sensitive to STZ than slow-twitch muscles and that HMB administration to STZ-treated rats has dual effects. Adjustments of BCAA concentrations in plasma and muscles and serine in the liver can be considered beneficial, whereas the increased glycemia and decreased ATP concentrations in the liver and muscles are detrimental.

The purpose of this experiment was to determine if supplying butyrate to the postruminal gastrointestinal tract of growing lambs alters blood flow and nutrient flux across the portal-drained viscera (PDV) and hepatic tissues. Polled Dorset wether lambs ( = 10; initial BW = 55 ± 3.3 kg) had catheters surgically implanted into the portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta. A cannula was placed in the abomasum to deliver the treatment. Lambs were fed a pelleted ration once daily consisting of 69.7% dehydrated alfalfa, 30.0% ground corn, and 0.3% salt at 1.3 × NE requirement. The experimental design was a crossover balanced in time, so that each lamb received both treatments. Treatments consisted of either a pulse dose infusion of butyrate (buffered solution) to supply butyrate (10 mg/kg BW) or a buffered saline solution (1 mL/kg BW) once daily at the time of feeding. On d 14 of the treatment period, nutrient fluxes were measured using para-aminohippuric acid as a blood flow marker. Blood samples were collected from the aorta, portal vein, and hepatic vein every hour for 9 h beginning at 30 min prior to treatment/feeding. There was a tendency for a treatment × time interaction ( = 0.05) for portal vein blood flow, indicating that blood flow began to decrease earlier postprandial in lambs receiving butyrate. The butyrate treatment tended to increase the uptake of O ( = 0.07) and increased the uptake of glucose ( = 0.002), glutamate ( = 0.04), and glutamine ( = 0.02) by the PDV. There was a treatment × time interaction ( < 0.01) for flux of acetate, propionate, butyrate, isobutyrate, and valerate across the PDV. The interaction was mainly due to an earlier postprandial peak and associated decrease in the flux rate of the VFA. The alteration in timing of the postprandial peak of VFA flux was also observed in hepatic fluxes of VFA. It appears that supplying butyrate to the postruminal tissues through an abomasal cannula increases glucose, glutamate, and glutamine metabolism by the PDV.

A multicatheter sow model was established to study the effects of dietary β-hydroxy β-methyl butyrate (HMB) supplementation on net portal flux (NPF) and net hepatic flux (NHF) of HMB, glucose, and the AA Ala, Gly, Ile, Leu, Phe, Tyr, and Val. Eight second parity sows were fitted with permanent indwelling catheters in an artery and in the portal, hepatic, and mesenteric veins. Eight hourly sets of blood samples were taken starting 30 min before the morning meal on day -3 and day 3 relative to parturition. Four control (CON) sows were fed a standard lactation diet from day -15 and throughout the experiment, and 4 HMB sows were fed the control diet supplemented with 15 mg Ca(HMB)(2)/kg BW mixed in one third of the morning meal from day -10 until parturition. Net portal flux of HMB was affected by treatment (Trt; P < 0.01) and peaked in the HMB sows at 6.9 mmol/h 30 min after the morning meal and then decreased towards preprandial level (0.0 mmol/h) 3.5 h after the meal, revealing that dietary HMB was rapidly absorbed from the intestine. The NHF of HMB tended to be affected by Trt (P = 0.06) showing a small hepatic uptake of HMB (1.1 mmol/h) in HMB sows. Net portal flux of glucose and all measured AA, except for Gly and Tyr, were affected the Trt × time interaction (P < 0.01). The NPF was positive for all nutrients, indicating absorption from the intestine to the portal blood. Absorption rates appeared to be more stable for HMB than for CON sows. Net hepatic flux of glucose was not affected by Trt. It was negative from 1.5 to 2.5 h after the meal, indicating hepatic uptake, but positive before and after, indicating net hepatic release of glucose. Net hepatic fluxes of AA were negative and were not affected by Trt (P > 0.10), except for Phe (P < 0.05). In conclusion, HMB reduced the variation in net portal flux of glucose and AA during 8 h of blood sampling and suggest that the improved sow productivity observed by others may be due to a more uniform nutrient absorption pattern into portal blood.

Purpose: The purpose of this investigation was to examine the effects of differing amounts of beta-hydroxy-beta-methylbutyrate (HMB), 0, 36, and 76 mg x kg(-1) x d(-1), on hematology, hepatic and renal function during 8 wk of resistance training., Methods: Thirty-seven, untrained collegiate males and were randomly assigned to one of the three groups, 0, 38, or 76 mg x kg(-1) x d(-1). Resistance training consisted of 10 exercises, performed 3 d x wk(-1) for 8 wk at 80% of their 1-repetition maximum. Blood and urine was obtained before training, 48 h after the initial session, 1 wk, 2 wk, 4 wk, and at 8 wk of resistance training. Blood was analyzed for glucose, blood urea nitrogen, hemoglobin, hepatic enzymes, lipid profile, total leukocytes, and individual leukocytes. Urine was analyzed for pH, glucose, and protein excretion., Results: The 38 mg x kg(-1) x d(-1) group had a greater increase in basophils compared with 0 or 76 mg x kg(-1) x d(-1) groups (P < 0.05). No difference occurred in any other blood and urine measurements., Conclusion: These data indicate that 8 wk of HMB supplementation (< or = 76 mg x kg(-1) x d(-1)) during resistance training had no adverse affects on hepatic enzyme function, lipid profile, renal function, or the immune system.

The etiology of T-cell-mediated liver injury involves the migration of immune cells, notably CD4+ T lymphocytes, into liver tissues. This process is mediated primarily by integrin-recognition of the sub-endothelium basement membranes and the extracellular matrix. The Arg-Gly-Asp-containing peptide, a major cell-adhesive ligand of extracellular matrix, is present in various plasma- and matrix-glycoproteins, such as fibronectin. Recently, we have described the design and usage of nonpeptide mimetics of Arg-Gly-Asp which bind specifically to integrins, and thereby, inhibit T cell immunity in vivo. We examined the efficacy of Arg-Gly-Asp-mimetics as potential therapeutic compounds for the treatment of experimental T-cell-mediated liver injury induced in mice by injection of Concanavalin-A. We now report that the Arg-Gly-Asp-mimetics specifically inhibited the binding of murine T cells to fibronectin, but did not affect the proliferative response of these cells in vitro. Intraperitoneal or oral administration of the Arg-Gly-Asp-mimetics but not the Arg-Gly-Asp-containing peptide, inhibited liver damage in mice if given before their inoculation with Con-A, as manifested by a lesser elevation in their serum levels of hepatic enzymes. The inhibitory effect of the Arg-Gly-Asp-mimetics was dose-dependent, the ED50 of the tested molecules being in the range of 100 micrograms per mouse and reaching maximal effect, e.g. approximately 95% inhibition, at 500 micrograms per mice. Thus, the Arg-Gly-Asp-mimetics described here may be used therapeutically to prevent immune-cell-mediated acute or chronic pathological reactions in the liver.

Three-week oral administration of 4-(decahydro-6-methyl-3-oxo-cyclopenta(f)quinoline-7-yl)valeric acid (32-1328) in the diet supplemented at concentrations of 0.1% or 0.3% was associated with hepatomegaly and hypotriglyceridemia in male F344 rats. Electron microscopic examination of the liver revealed a remarkable increase of peroxisomes in hepatocytes both in number and size. Biochemically, there were increased activities of peroxisomal marker enzymes including the heat-labile enoyl-CoA hydratase and catalase while the mitochondrial enoyl-CoA hydratase activity was unchanged after feeding of 32-1328. These findings indicate that 32-1328 can exert peroxisome-proliferating activity to rat liver in a manner similar to typical peroxisome proliferators such as clofibrate or di(2-ethylhexyl)phthalate.

We have shown that a microbial cholic acid catabolite (4R)-4-(2,3,4,6,6a beta,7,8,9,9a alpha,9b beta-decahydro-6a beta-methyl-3-oxo- 1H-cyclopenta[f]quinolin-7 beta-yl)valeric acid (DCQVA), is a potent peroxisome proliferator. In this paper a possible key stage in DCQVA metabolism, the activation of DCQVA to its CoA ester, has been investigated in rat liver microsomes and particulate fractions. The microsomal reaction was dependent on CoA, ATP, DCQVA (0.2-1 mM) and protein content. The reaction was decreased by storage at 4 degrees C, preincubation of microsomes at 37 degrees C for 5 min, or inclusion of Triton X-100 in the reaction mixture. Such treatments also enhanced generation of long-chain fatty acyl-CoAs, as determined by h.p.l.c. analysis. The same effect was caused by exposing the microsomes to phospholipase A2, suggesting that endogenous fatty acids may compete with DCQVA for esterification with CoA. Subcellular fractionation of rat liver demonstrated that the activity of DCQVA-CoA synthesis was localized predominantly in the microsomal fraction, in contrast to long-chain fatty acyl-CoA synthetase, which was distributed among all particulate fractions. Administration of clofibrate of rats did not affect the distribution of DCQVA-CoA synthesis activity. In contrast to a 2-fold induction of long-chain fatty acyl-CoA synthetase by clofibrate treatment, the activity of DCQVA-CoA synthesis in the microsomal fraction decreased by 80%. These results suggest that DCQVA is activated by an enzyme distinct from long-chain fatty acyl-CoA synthetase. The resulting perturbation of fatty acid metabolism may be involved in the mechanism whereby DCQVA causes peroxisome proliferation.

The capability of (4R)-4-(2,3,4,6,6a beta,7,8,9,9a alpha,9b beta-decahydro-6a beta-methyl-3-oxo-1H-cyclopental[f]quinolin-7 beta-yl)valeric acid (DCQVA), a catabolite of cholic acid produced by enterobacteria, to induce peroxisome proliferation in vivo and in vitro was studied. Rats given 0.3% DCQVA in the diet for 2 weeks showed marked increases in peroxisomal beta-oxidation, mitochondrial 2,4-dienoyl-CoA reductase and microsomal laurate omega-oxidation activities in the liver compared with control rats given the diet without DCQVA. Cultured rat hepatocytes treated with DCQVA for 72 h also exhibited greatly enhanced beta-oxidation activity. The increased activity was concentration-dependent and the effective concentrations were comparable with those of clofibric acid that produced the same degree of induction in the assay. The results demonstrate that DCQVA is a potent peroxisome proliferator that occurs naturally in rat intestine.

Class III alcohol dehydrogenase (chi chi-ADH) from human liver binds both ethanol and acetaldehyde so poorly that their Km values cannot be determined, even at ethanol concentrations up to 3 M. However, long-chain carboxylates, e.g., pentanoate, octanoate, deoxycholate, and other anions, substantially enhance the binding of ethanol and other substrates and hence the activity of class III ADH up to 30-fold. Thus, in the presence of 1 mM octanoate, ethanol displays Michaelis-Menten kinetics. The degree of activation depends on the size both of the substrate and of the activator; generally, longer, negatively charged activators result in greater activation. At pH 10, the activator binds to the E-NAD+ form of the enzyme to potentiate substrate binding. Pentanoate activates methylcrotyl alcohol oxidation and methylcrotyl aldehyde reduction 14- and 30-fold, respectively. Such enhancements of both oxidation and reduction are specific for class III ADH; neither class I nor class II shows this effect. The implications as to the nature of the physiological substrate(s) of class III ADH are discussed in light of the recent finding that this ADH and glutathione-dependent formaldehyde dehydrogenase are identical. A new rapid purification procedure for chi chi-ADH is presented.

The effect of 4-pentenoate on rat liver ornithine transcarbamylase was studied. No effect was found. It is concluded that the effect of 4-pentenoic acid on ornithine transcarbamylase reported by others was probably due to technical errors. Available evidence indicates that 4-pentenoate inhibits ureagenesis by interfering with mitochondrial energy metabolism, which in turn impairs mitochondrial ornithine transport or depletes mitochondrial ATP, impairing carbamyl phosphate synthesis, or both.

Pent-4-enoate at 0.1 to 1.0 mM strongly inhibited urea synthesis in isolated rat hepatocytes. Pent-4-enoate at the same concentrations markedly decreased concentrations of N-acetyl-L-glutamate, an essential activator of carbamoyl-phosphate synthase-I (EC 2.7.2.5), and the decrease was well in parallel with the inhibition of urea synthesis by pent-4-enoate. This compound also lowered cellular concentrations of acetyl-CoA, a substrate of acetylglutamate synthase (EC 2.3.1.1). Pent-4-enoate in a dose of 1 mM did not significantly affect cellular concentrations of ATP, and had no direct effect on acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by pent-4-enoate is due to decrease in N-acetyl-L-glutamate concentration and that the decrease is probably brought about by decreased rate of its synthesis due to the lowered concentration of cellular acetyl-CoA.

1. The effect of long-term administration, including recovery, of allylisopropylacetylurea to rats was investigated. 2. In the liver, cytochromes P-450, b5, catalase and 5-aminolaevulinic acid synthetase were measured. Serum glutamate-pyruvate, transaminase, glutamate-oxalacetate transaminase and alkaline phophatase were determined to assess cell damage, while urinary coproporphyrin and uroporphyrin were measured to assess the degree of porphyia. 3. In the liver the lowering of cytochrome P-450 and catalase was paralleled by an increase in 5-aminolaevulinate synthetase. Cytochrome b5 was only marginally affected. 4. Rats recover well from long-term treatment with high doses of allylisopropylacetylurea and revert to normal values for parameters measured. 5. A mechanism for the intracellular action of allylisopropylacetylurea on cytochrome P-450 and other haem-containing compounds is presented.

Previous reports have demonstrated that butyrate inhibits metabolism of propionate by liver cells isolated from sheep and goats. Our objectives were to examine some possible mechanisms for this inhibition and to test for this inhibition in the bovine animal. Incorporation of label from 2.5 mM [2-(14)C]propionate into glucose (nmol propionate/mg cell DM/h) in the presence of 0, 1.25, and 2.5 mM butyrate was 107, 66, and 62 by goat hepatocytes and 79, 25, and 29 by calf hepatocytes; therefore, butyrate inhibited propionate metabolism at least as effectively in calves as in goats. In goat hepatocytes 1.25 mM butyrate reduced 1.25 mM propionate uptake to 46% of control, and 1.25 mM [2-(14)C] propionate incorporation into glucose to 44% of control. Propionate had no effect on butyrate uptake. Isovalerate and valerate tended to be cleared from the media to a greater extent than butyrate but had no effect on propionate uptake. Therefore, inhibition of propionate conversion to glucose by butyrate is specific and is not due to a general competition among VFA for metabolism. Butyrate inhibits hepatic propionate utilization generally, not specifically propionate conversion to glucose. Butyrate also inhibited propionate utilization by goat liver homogenates, indicating that butyrate inhibits propionate metabolism at a step subsequent to propionate transport across the hepatocyte plasma membrane.

Rats were injected twice intraperitoneally with 20 mg of allylisopropylacetylcarbamide (Sedormid) per 100 g of body weight at an interval of 12 hr. The level of catalase [EC 1.11.1.6] in various liver cell fractions was determined both enzymatically and immunochemically 12 hr after the second injection. 1. The decrease in catalase protein assayed by the immunochemical method directly confirmed the inhibition of biosynthesis of the enzyme by this porphyrinogenic drug. 2. The occurrence of a considerable amount of catalase protein with no enzymatic activity was demonstrated both in the peroxisomes and in the supernatant fraction. 3. The amount of catalase-synthesizing polysomes in hepatic cell was reduced in Sedormid-treated rats by the extent comparable to the decrease in the concentration of liver catalase.

Isolated caprine hepatocytes were incubated with fatty acids of various chain lengths. Short-chain fatty acids effects on rates of gluconeogenesis and oxidation from [2-14C]propionate were determined. Additions of glucose (2.5 mM) had no effect on hepatic [2-14C]propionate metabolism in the presence and absence of amino acids. A complete mixture of amino acids increased label incorporation from [2-14C]propionate into [14C]glucose by 22%. Butyrate inhibited [2-14C]propionate metabolism and increased the apparent Michaelis constant for [2-14C]propionate incorporation into [14C]glucose from 2.4 +/- 1.5 to 5.6 +/- .9 mM. Butyrate's effects on propionate were similar in the presence and absence of L-carnitine (1 mM). Isobutyrate, 2-methylbutyrate, and valerate (1.25 mM) had no effect on [14C]glucose production but decreased 14CO2 production to 57, 61, and 54% of the control [2-14C]propionate (1.25 mM). This inhibition on 14CO2 production was not competitive. Isovalerate had no effect on either [2-14C]propionate incorporation into glucose or CO2. An increase in ratio of [14C]glucose to 14CO2 from [2-14C]propionate demonstrated that short-chain fatty acids other than butyrate do not inhibit gluconeogenesis from propionate. In addition, fatty acids that generate a net synthesis of intracellular oxaloacetate may partition propionate carbons toward gluconeogenic rather than oxidative pathways in goat hepatocytes.

Urea cycle function was evaluated in liver obtained from six patients with Reye's syndrome and from five control subjects. Reye's syndrome patients demonstrated normal activities for the extramitochondrial portion of the urea cycle, but showed marked abnormalities of the mitochondrial enzymes, i.e., carbamyl phosphate synthetase (CPS) and ornithine transcarbamylase (OTC) (Tables 2,3). CPS activity was reduced to less than 15% of control values in all four patients from whom tissues was obtained during the first 72 hr after the onset of encephalopathy. Two patents from whom tissue was not obtained until after 9 days of symptoms showed no reduction in CPS activity. The OTC activity was also reduced (3-67% of control values) in the four patients from whom tissue was obtained early in the illness. In addition, greater than 60% reduction in Vmax and Km for carbamyl phosphate was noted in all four patients in whom sample size permitted kinetic analysis, including both patients in whom CPS and OTC activity were not markedly reduced. The same kinetic abnormality as well as decreased CPS activity were experimentally produced in normal rate liver incubated in the presence of 1.0 mM 4-pentenoic acid, a short chain fatty acid and known hepatic mitochondrial toxin (Table 4).

Double-labeling of liver catalase [EC 1.11.1.6] with [14-c]leucine and delta-[3H]aminolevulinic acid was carried out both in vivo and in vitro using rats treated with allylisopropylacetylcarbamide (Sedormid). These radioactive precursors were incorporated into catalase at a lower rate than in normal rats. In particular, the incorporation of 3H was remarkably inhibited. The results suggest that the administration of Sedormid can inhibit synthesis of the protein moiety of catalase, and possibly interfere with the binding of heme to the catalase protein.

1 and 10 mmol/l isovalerate strongly inhibited urea synthesis in isolated rat hepatocytes incubated with 10 mmol/l alanine and 3 mmol/l ornithine. Isovalerate also markedly decreased N-acetylglutamate levels, and the decrease correlated with the inhibition of urea synthesis by isovalerate. This compound also lowered cellular levels of acetyl-CoA, a substrate of N-acetylglutamate synthase (EC 2.3.1.1). Isovalerate did not significantly affect the cellular levels of ATP and had no direct effect on N-acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by isovalerate is due to decrease in N-acetylglutamate levels.