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Context Vitamin D regulates glucose homeostasis pathways, but effects of vitamin D supplementation on β-cell function remain unclear. Objective To investigate the effects of vitamin D3 supplementation on insulin sensitivity and β-cell function. Methods This is a prespecified secondary analysis of the Vitamin D and Type 2 Diabetes study. Overweight/obese adults at high risk for type 2 diabetes (prediabetes) were randomly treated with vitamin D3 4000 IU or matching placebo daily for 24 months. Main Outcome Disposition index (DI), as an estimate of β-cell function, was calculated as the product of Homeostasis Model Assessment 2 indices derived from C-peptide values (HOMA2%Scpep) and C-peptide response during the first 30 minutes of a 75-g oral glucose tolerance test (OGTT). Results Mean age was 60.5 ± 9.8 years and body mass index was 31.9 ± 4.4 kg/m2. Mean serum 25(OH)D level increased from 27.9 ± 10.3 ng/mL at baseline to 54.9 ng/mL at 2 years in the vitamin D group and was unchanged (28.5 ± 10.0 ng/mL) in the placebo group. The baseline DI predicted incident diabetes independent of the intervention. In the entire cohort, there were no significant differences in changes in DI, HOMA2%Scpep, or C-peptide response between the 2 groups. Among participants with baseline 25(OH)D level Conclusions Supplementation with vitamin D3 for 24 months did not improve an OGTT-derived index of β-cell function in people with prediabetes not selected based on baseline vitamin D status; however, there was benefit among those with very low baseline vitamin D status.

BACKGROUND AND OBJECTIVES: Low serum 25-hydroxyvitamin D (25[OH]D) concentration has been associated with higher levels of proteinuria and lower levels of eGFR in observational studies. In the Vitamin D and Type 2 Diabetes (D2d) study, we investigated the effect of vitamin D supplementation on kidney outcomes in a population with prediabetes. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Overweight/obese adults with high risk for type 2 diabetes (defined by meeting two of three glycemic criteria for prediabetes) were randomized to vitamin D(3) 4000 IU per day versus placebo. Median duration of treatment was 2.9 years (interquartile range 2.0–3.5 years). Kidney outcomes included (1) worsening in Kidney Disease: Improving Global Outcomes (KDIGO ) risk score (low, moderate, high, very high) on two consecutive follow-up visits after the baseline visit and (2) mean changes in eGFR and urine albumin-to-creatinine ratio (UACR). RESULTS: Among 2166 participants (mean age 60 years, body mass index 32 kg/m(2), serum 25(OH)D 28 ng/ml, eGFR 87 ml/min per 1.73 m(2), UACR 11 mg/g, 79% with hypertension), 10% had moderate, high, or very high KDIGO risk score. Over a median follow-up of 2.9 years, there were 28 cases of KDIGO worsening in the vitamin D group and 30 in the placebo group (hazard ratio, 0.89; 95% confidence interval [95% CI], 0.52 to 1.52]). Mean difference in eGFR from baseline was −1.0 ml/min per 1.73 m(2) (95% CI, −1.3 to −0.7) in the vitamin D group and −0.1 ml/min per 1.73 m(2) (95% CI, −0.4 to 0.2) in the placebo group; between-group difference was −1.0 ml/min per 1.73 m(2) (95% CI, −1.4 to −0.6). Mean difference in UACR was 2.7 mg/g (95% CI, 1.2 to 4.3) in the vitamin D group and 2.0 (95% CI, 0.5 to 3.6) in the placebo group; between-group difference was 0.7 mg/g (95% CI, −1.5 to 2.9). CONCLUSIONS: Among persons with prediabetes, who were not preselected on the basis of serum 25(OH)D concentration, vitamin D supplementation did not affect progression of KDIGO risk scores and did not have a meaningful effect on change in UACR or eGFR.

Context Observational studies suggest that low vitamin D status may be a risk factor for cancer. Objective In a population with prediabetes and overweight/obesity that is at higher risk of cancer than the general population, we sought to determine if vitamin D supplementation lowers the risk of cancer and precancers. Methods The Vitamin D and type 2 diabetes (D2d) cancer outcomes study (D2dCA) is an ancillary study to the D2d study, which was conducted at 22 academic medical centers in the United States. Participants had prediabetes and overweight/obesity and were free of cancer for the previous 5 years. Participants were randomized to receive vitamin D3 4000 IU daily or placebo. At scheduled study visits (4 times/year), cancer and precancer events were identified by questionnaires. Clinical data were collected and adjudicated for all reported events. Cox proportional hazard models compared the hazard ratio (HR) of incident cancers and precancers between groups. Results Over a median follow-up period of 2.9 years, among 2385 participants (mean age 60 years and 25-hydroxyvitamin D 28 ng/mL), there were 89 cases of cancer. The HR of incident cancer for vitamin D vs placebo was 1.07 (95% CI 0.70, 1.62). Of 241 participants with incident precancers, 239 had colorectal adenomatous polyps. The HR for colorectal polyps for vitamin D vs placebo was 0.83 (95% CI 0.64, 1.07). Conclusion In the D2d population of participants with prediabetes and overweight/obesity, not selected for vitamin D insufficiency, vitamin D supplementation did not have a significant effect on risk of incident cancer or colorectal polyps.

Objective Fasting plasma glucose (FPG), 2-hour plasma glucose (2hPG) from a 75-g oral glucose tolerance test (OGTT) and glycated hemoglobin (HbA1c) can lead to different results when diagnosing prediabetes and diabetes. The Hemoglobin Glycation Index (HGI) quantifies the interindividual variation in glycation resulting in discrepancies between FPG and HbA1c. We used data from the Vitamin D and Type 2 Diabetes (D2d) study to calculate HGI, to identify HGI-associated variables, and to determine how HGI affects prediabetes and diabetes diagnosis. Measurements A linear regression equation [HbA1c (%) = 0.0164 × FPG (mg/dL) + 4.2] was derived using the screening cohort (n = 6829) and applied to calculate predicted HbA1c. This was subtracted from the observed HbA1c to determine HGI in the baseline cohort with 2hPG data (n = 3945). Baseline variables plus prediabetes and diabetes diagnosis by FPG, HbA1c, and 2hPG were compared among low, moderate, and high HGI subgroups. Results The proportion of women and Black/African American individuals increased from low to high HGI subgroups. Mean FPG decreased and mean HbA1c increased from low to high HGI subgroups, consistent with the HGI calculation; however, mean 2hPG was not significantly different among HGI subgroups. Conclusions High HGI was associated with Black race and female sex as reported previously. The observation that 2hPG was not different across HGI subgroups suggests that variation in postprandial glucose is not a significant source of population variation in HGI. Exclusive use of HbA1c for diagnosis will classify more Black individuals and women as having prediabetes compared with using FPG or 2hPG.

Aims To assess whether meeting both fasting plasma glucose (FPG) and HbA1c criteria for prediabetes in people at high risk indicates with near certainty the presence of dysglycemia on repeat testing. Methods Observational study using data from Vitamin D and Type 2 Diabetes (D2d) study. HbA1c, FPG were measured at screening visit 1; FPG, HbA1c and 2 h plasma glucose (2hPG) measured at screening visit 2 (a median of 21 days later); participants classified as having normal glucose regulation (all 3 tests in normal range), prediabetes or diabetes (at least 1 of 3 tests in diabetes range). A predictive model was developed to estimate the probability of confirming dysglycemia and for detecting diabetes at screening visit 2 based on values of FPG and HbA1c at screening visit 1. Results Of 1271 participants who met both FPG and HbA1c criteria for prediabetes at screening visit 1, 98.6% exhibited dysglycemia (defined as prediabetes or diabetes) on repeat testing (84.5% were classified as having prediabetes, 14.1% were reclassified as having diabetes). Of those with diabetes, 62.6% were identified by 2hPG alone. Conclusions Combined measurement of FPG and HbA1c is a reliable and reproducible measure to identify presence of dysglycemia among people at high risk. A prediction model is provided to help clinicians decide whether an oral glucose tolerance test will provide value in detecting diabetes based on the 2hPG criterion., Highlights • FPG and HbA1c were tested simultaneously to identify patients with prediabetes. • Median 21 days later, repeat evaluation with FPG, HbA1c and an OGTT to measure the 2hPG criterion was done. • 98.6% of the subjects exhibited dysglycemia (prediabetes (84.5%) or diabetes (14.1%)) on repeat testing. • A prediction model to assess additional value of OGTT in detecting diabetes based on the 2hPG criterion is provided.

OBJECTIVE To describe baseline characteristics of the Vitamin D and Type 2 Diabetes (D2d) study, the first large U.S. diabetes prevention clinical trial to apply current American Diabetes Association (ADA) criteria for prediabetes. RESEARCH DESIGN AND METHODS This is a multicenter (n = 22 sites), randomized, double-blind, placebo-controlled, primary prevention clinical trial testing effects of oral daily 4,000 IU cholecalciferol (D3) compared with placebo on incident diabetes in U.S. adults at risk for diabetes. Eligible participants were at risk for diabetes, defined as not meeting criteria for diabetes but meeting at least two 2010 ADA glycemic criteria for prediabetes: fasting plasma glucose (FPG) 100–125 mg/dL, 2-h postload glucose (2hPG) after a 75-g oral glucose load 140–199 mg/dL, and/or a hemoglobin A1c (HbA1c) 5.7–6.4% (39–46 mmol/mol). RESULTS A total of 2,423 participants (45% of whom were women and 33% nonwhite) were randomized to cholecalciferol or placebo. Mean (SD) age was 60 (9.9) years and BMI 32.1 (4.5) kg/m2. Thirty-five percent met all three prediabetes criteria, 49% met the FPG/HbA1c criteria only, 9.5% met the 2hPG/FPG criteria only, and 6.3% met the 2hPG/HbA1c criteria only. Black participants had the highest mean HbA1c and lowest FPG concentration compared with white, Asian, and other races (P < 0.01); 2hPG concentration did not differ among racial groups. When compared with previous prediabetes cohorts, the D2d cohort had lower mean 2hPG concentration but similar HbA1c and FPG concentrations. CONCLUSIONS D2d will establish whether vitamin D supplementation lowers risk of diabetes and will inform about the natural history of prediabetes per contemporary ADA criteria.

BACKGROUND: Observational studies support an association between a low blood 25-hydroxyvitamin D level and the risk of type 2 diabetes. However, whether vitamin D supplementation lowers the risk of diabetes is unknown. METHODS: We randomly assigned adults who met at least two of three glycemic criteria for prediabetes (fasting plasma glucose level, 100 to 125 mg per deciliter; plasma glucose level 2 hours after a 75-g oral glucose load, 140 to 199 mg per deciliter; and glycated hemoglobin level, 5.7 to 6.4%) and no diagnostic criteria for diabetes to receive 4000 IU per day of vitamin D(3) or placebo, regardless of the baseline serum 25-hydroxyvitamin D level. The primary outcome in this time-to-event analysis was new-onset diabetes, and the trial design was event-driven, with a target number of diabetes events of 508. RESULTS: A total of 2423 participants underwent randomization (1211 to the vitamin D group and 1212 to the placebo group). By month 24, the mean serum 25-hydroxyvitamin D level in the vitamin D group was 54.3 ng per milliliter (from 27.7 ng per milliliter at baseline), as compared with 28.8 ng per milliliter in the placebo group (from 28.2 ng per milliliter at baseline). After a median follow-up of 2.5 years, the primary outcome of diabetes occurred in 293 participants in the vitamin D group and 323 in the placebo group (9.39 and 10.66 events per 100 person-years, respectively). The hazard ratio for vitamin D as compared with placebo was 0.88 (95% confidence interval, 0.75 to 1.04; P = 0.12). The incidence of adverse events did not differ significantly between the two groups. CONCLUSIONS: Among persons at high risk for type 2 diabetes not selected for vitamin D insufficiency, vitamin D(3) supplementation at a dose of 4000 IU per day did not result in a significantly lower risk of diabetes than placebo. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and others; D2d ClinicalTrials.gov number, .)

Aims To establish recruitment approaches that leverage electronic health records in multicenter prediabetes/diabetes clinical trials and compare recruitment outcomes between electronic health record–supported and conventional recruitment methods. Methods Observational analysis of recruitment approaches in the vitamin D and type 2 diabetes (D2d) study, a multicenter trial in participants with prediabetes. Outcomes were adoption of electronic health record–supported recruitment approaches by sites, number of participants screened, recruitment performance (proportion screened who were randomized), and characteristics of participants from electronic health record–supported versus non–electronic health record methods. Results In total, 2423 participants were randomized: 1920 from electronic health record (mean age of 60 years, 41% women, 68% White) and 503 from non–electronic health record sources (mean age of 56.9 years, 58% women, 61% White). Electronic health record–supported recruitment was adopted by 21 of 22 sites. Electronic health record–supported recruitment was associated with more participants screened versus non–electronic health record methods (4969 vs 2166 participants screened), higher performance (38.6% vs 22.7%), and more randomizations (1918 vs 505). Participants recruited via electronic health record were older, included fewer women and minorities, and reported higher use of dietary supplements. Electronic health record–supported recruitment was incorporated in diverse clinical environments, engaging clinicians either at the individual or the healthcare system level. Conclusion Establishing electronic health record–supported recruitment approaches across a multicenter prediabetes/diabetes trial is feasible and can be adopted by diverse clinical environments.

OBJECTIVE: To describe baseline characteristics of the Vitamin D and Type 2 Diabetes (D2d) study, the first large U.S. diabetes prevention clinical trial to apply current American Diabetes Association (ADA) criteria for prediabetes. RESEARCH DESIGN AND METHODS: This is a multicenter (n = 22 sites), randomized, double-blind, placebo-controlled, primary prevention clinical trial testing effects of oral daily 4,000 IU cholecalciferol (D(3)) compared with placebo on incident diabetes in U.S. adults at risk for diabetes. Eligible participants were at risk for diabetes, defined as not meeting criteria for diabetes but meeting at least two 2010 ADA glycemic criteria for prediabetes: fasting plasma glucose (FPG) 100–125 mg/dL, 2-h postload glucose (2hPG) after a 75-g oral glucose load 140–199 mg/dL, and/or a hemoglobin A(1c) (HbA(1c)) 5.7–6.4% (39–46 mmol/mol). RESULTS: A total of 2,423 participants (45% of whom were women and 33% nonwhite) were randomized to cholecalciferol or placebo. Mean (SD) age was 59 (9.9) years and BMI 32 (4.5) kg/m(2). Thirty-five percent met all three prediabetes criteria, 49% met the FPG/HbA(1c) criteria only, 9.5% met the 2hPG/FPG criteria only, and 6.3% met the 2hPG/HbA(1c) criteria only. Black participants had the highest mean HbA(1c) and lowest FPG concentration compared with white, Asian, and other races (P < 0.01); 2hPG concentration did not differ among racial groups. When compared with previous prediabetes cohorts, the D2d cohort had lower mean 2hPG concentration but similar HbA(1c) and FPG concentrations. CONCLUSIONS: D2d will establish whether vitamin D supplementation lowers risk of diabetes and will inform about the natural history of prediabetes per contemporary ADA criteria.

The dietary protein requirements of patients with insulin-dependent diabetes mellitus (IDDM) are unknown. We studied the metabolic adaptation of IDDM patients with early nephropathy to therapeutic, low-protein diets. Six patients were studied at baseline and following 1 and 12 weeks of consuming 0.6 g/kg-1 ideal body weight.day-1 protein. Outcome variables included quadriceps muscle strength, body composition, nitrogen balance, and estimates of whole body protein turnover using an infusion of L-[1-13C]leucine. All subjects experienced decreased muscle strength (6.6% decline in maximal torque, P = 0.05) and increased body fatness (11% increase in fat mass, P = 0.03) with no change in total body weight. This was accompanied by an initial 40% decrease in the rate of whole-body leucine oxidation after 1 week of dietary restriction which returned almost to baseline rates by 12 weeks (P less than 0.001, 1 week vs. 12 weeks). Nitrogen balance remained negative throughout the period of protein restriction. We conclude that IDDM subjects with early nephropathy experience protein undernutrition during the first 3 months of the dietary protein restriction currently recommended for the treatment of nephropathy. This may result, in part, from an inability to conserve essential amino acids from oxidative loss over the time period of the study.

The effects of dietary protein deprivation in insulin-dependent diabetes mellitus (IDDM) have been investigated in a merely rudimentary fashion in human subjects. Moderate dietary protein restriction of 0.6 g/(kg ideal body weight.d) over 3 mo in free-living IDDM patients produces increased adiposity during weight maintenance and decreased muscle strength. These effects might have been predicted from studies of protein deprivation in diabetic subjects, indicating impairment of nitrogen retention. The clinical consequences of dietary protein restriction in IDDM may be more complex than described to date. This is suggested by the overriding paradox that the actions of insulin on protein synthesis are inconsistent among in vitro, animal and human in vivo models. The inconsistency and the observation that insulin deficiency in humans accelerates both proteolysis and protein synthesis imply that knowledge about insulin, diabetes and protein metabolism in humans is inadequate and should be studied in increasing detail. Better understanding of the clinical consequences of dietary protein restriction in diabetes, both beneficial and adverse, is likely to come from future studies incorporating clinically relevant levels of insulin deficiency and protein deprivation into studies of bodily function, clinical outcomes and specific examination of the metabolism of individual proteins.

The purpose of this research was to develop survey instruments to evaluate diabetes knowledge and self-efficacy in a diverse population, and investigate the psychometric properties of data obtained with these instruments using Rasch measurement. Two-hundred and fifty-five urban-dwelling participants with diabetes were recruited to complete surveys through independent interviews. To evaluate the association of health literacy on metabolic control, formal literacy and hemoglobin A1c fingerstick testing were performed. Rasch analysis of the data yielded item and person calibrations for self-efficacy and knowledge, with variable maps created to provide both norm and criterion-referenced interpretations. Knowledge scale person separation reliability was 0.50 and item separation reliability was 0.98; while self-efficacy scale person separation reliability was 0.72 with item separation reliability of 0.92. Statistically significant partial correlations were observed between knowledge and health literacy (r = 0.41, p.001), and self-efficacy and hemoglobin A1c (r = -0.33, p.001). However, there was no correlation between diabetes knowledge and hemoglobin A1c (r = 0.035, p = 0.29), or health literacy and A1c (r = 0.022, p = 0.36). Diabetes knowledge varied, with non-English speaking individuals having lower measures than English speakers (t(252) = -4.86, p.001). Non-English speaking individuals also had lower self-efficacy measures than English speakers (t(251) = -2.68, p = .008). Current knowledge deficits and perceptions of self-management may be estimated visually through variable mapping, which may help in individualizing informational needs for people with diabetes.

Diabetes mellitus is associated with a distinct cardiomyopathy. Whether cardiac myofilament function is altered in human diabetes mellitus is unknown. Myocardial biopsies were obtained from seven diabetic patients and five control, nondiabetic patients undergoing coronary artery bypass surgery. Myofilament function was assessed by determination of the developed force-Ca2+ concentration relation in skinned cardiac cells from flash-frozen human biopsies. Separate control experiments revealed that flash freezing of biopsy specimens did not affect myofilament function. All patients in the diabetes mellitus cohort were classified as Type 2 diabetes mellitus patients, and most showed signs of diastolic dysfunction. Diabetes mellitus was associated with depressed myofilament function, that is, decreased Ca2+ sensitivity (29%, P < 0.05 vs. control) and a trend toward reduction of maximum Ca2+-saturated force (29%, P = 0.08 vs. control). The slope of the force-Ca2+ concentration relation (Hill coefficient) was not affected by diabetes, however. We conclude that human diabetes mellitus is associated with decreased cardiac myofilament function. Depressed cardiac myofilament Ca2+ responsiveness may underlie the decreased ventricular function characteristic of human diabetic cardiomyopathy.

OBJECTIVE—To evaluate a clinic-based multimedia intervention for diabetes education targeting individuals with low health literacy levels in a diverse population.RESEARCH DESIGN AND METHODS—Five public clinics in Chicago, Illinois, participated in the study with computer kiosks installed in waiting room areas. Two hundred forty-four subjects with diabetes were randomized to receive either supplemental computer multimedia use (intervention) or standard of care only (control). The intervention includes audio/video sequences to communicate information, provide psychological support, and promote diabetes self-management skills without extensive text or complex navigation. HbA1c (A1C), BMI, blood pressure, diabetes knowledge, self-efficacy, self-reported medical care, and perceived susceptibility of complications were evaluated at baseline and 1 year. Computer usage patterns and implementation barriers were also examined.RESULTS—Complete 1-year data were available for 183 subjects (75%). Overall, there were no significant differences in change in A1C, weight, blood pressure, knowledge, self-efficacy, or self-reported medical care between intervention and control groups. However, there was an increase in perceived susceptibility to diabetes complications in the intervention group. This effect was greatest among subjects with lower health literacy. Within the intervention group, time spent on the computer was greater for subjects with higher health literacy.CONCLUSIONS—Access to multimedia lessons resulted in an increase in perceived susceptibility to diabetes complications, particularly in subjects with lower health literacy. Despite measures to improve informational access for individuals with lower health literacy, there was relatively less use of the computer among these participants.

Protein undernutrition inhibits adenosine triphosphate (ATP)-dependent muscle protein degradation-a hallmark of the proteasome system. Here we report decreased myofibrillar protein degradation during dietary protein restriction without a concomitant decrease in proteasome gene expression, proteasome protein abundance, or proteasome in vivo fractional synthesis rate. Healthy human subjects consuming the average minimum adult protein requirement (0.71 g x kg(-1) fat-free mass x d(-1)) exhibited substantially lower (68%) excretion of 3-methylhistidine, an indicator of myofibrillar protein breakdown, when compared with subjects consuming an ample, American-style protein intake (1.67 g x kg(-1) fat-free mass x d(-1)). However, they displayed no difference in the expression of mRNA for proteasome subunits C2 or C3, in the content of C2 protein, or in the rate of incorporation of stable isotopically labeled l-[1-(13)C]-leucine into proteasome proteins. The results demonstrate that nutritional inhibition of myofibrillar protein degradation does not involve suppression in vivo of proteasome production in man. This suggests that other elements of the ubiquitin-proteasome system, such as ubiquitination pathways, are more important than proteasome abundance in the nutritional regulation of skeletal muscle mass.

The synthesis of muscle protein is restrained during dietary protein restriction. This is widely understood to vary quantitatively with the degree of nutritional deprivation, but there has been little discussion of qualitative changes in muscle protein deriving from dietary protein restriction. We studied 14 healthy subjects in a 2-sample study. Subjects were randomly assigned to a diet providing an ample, American-style protein intake (1.67 g. kg fat-free mass(-1). d(-1)) or a diet approximating the mean minimum adult protein requirement (0.71 g. kg fat-free mass(-1). d(-1)). We found that consumption of an isoenergetic diet at the mean adult minimum protein requirement for 4 wk produced an 81% lower fractional synthesis rate of myosin heavy chain (MHC) proteins in vastus lateralis muscle than did consumption of an ample protein diet (P = 0.05). Protein deprivation altered the skeletal muscle myosin composition such that the proportion of the total myosin content represented by fast-twitch MHC IIx was 51% lower than with ample intake (P = 0.013). The steady state content of MHC IIx messenger RNA (mRNA) did not differ in subjects consuming the minimum requirement of protein, suggesting that the reduced proportion of MHC IIx arises from posttranscriptional events. A 68% lower rate of 3-methylhistidine excretion with protein restriction (P < 0.01) suggests that myofibrillar protein degradation was lower. We conclude that dietary amino acid scarcity produces a change in myosin isoform distribution via posttranscriptional mechanisms. The relative contribution of inhibited myosin synthesis and inhibited degradation to the altered myosin isoform composition remains unknown. This has implications for the mechanisms by which amino acids govern muscle protein composition in vivo, and further exploration is required.

Background A benefit for eicosapentaenoic acid (EPA) supplementation for protein maintenance in cancer patients exists, although specific mechanisms are unknown. As the ubiquitin-proteasome proteolytic (UPP) pathway has been implicated in protein use in malignancy, we determined mRNA levels for UPP components in the liver and muscles from EPA-treated rats bearing the methylcholanthrene (MCA) fibrosarcoma. Methods Rats implanted with MCA tumor were divided into 3 groups on day 13: EPA (5 g/kg per day plus 10 IU vitamin E/g fat), corn oil (5 g/kg per day plus 10 IU vitamin E/g fat), and saline (5 g/kg per day plus 10 IU E/g saline). On day 29, tumor volume (TV) was determined; liver and quadriceps muscles were also excised to determine gene expression of C2, C3, E2(14k), and E3alpha by reverse transcription-polymerase chain reaction (RT-PCR). Results EPA-treated rats demonstrated a reduced TV of 21% compared with the 28% and 30% TV of corn oil- and saline-treated rats, respectively. Muscle mRNA levels of E2(14k) and E3alpha in EPA-treated animals were decreased compared with corn oil- and saline-treated animals. EPA treatment also decreased hepatic C2, C3, and E2(14k) mRNA levels compared with saline treatment. Conclusion EPA supplement decreased skeletal muscle E2(14k), E3alpha, and hepatic C2 mRNA levels compared with the isocaloric, isonitrogenous corn oil supplement, supporting a treatment-specific effect. The decrease in hepatic C3 and E2(14k) mRNA levels induced by EPA were partly because of caloric benefit and partly attributable to a treatment-specific effect. Additionally, differences in the hepatic and muscle gene expressions of UPP components suggested an organ-specific effect for omega-3 fatty acid activity.

Accumulation of collagen produces organ dysfunction in many pathological conditions. We measured the fractional synthesis rate (FSR) of dermal collagen in five human volunteers from the increment of [13C]proline in detergent-soluble dermal collagen hydroxylated to hydroxyproline during a continuous infusion ofl-[1-13C]proline. In these and eight other volunteers, we measured [13C]proline enrichment in skin aminoacyl-tRNA, skin tissue fluid amino acid, and plasma. The prolyl-[13C]tRNA enrichment was one-half that in tissue fluid proline and more than threefold less than in plasma. The FSR of dermal collagen was 0.076 ± 0.063%/h (mean ± SD), similar to previously reported rates for skeletal muscle contractile proteins and substantially slower than hepatically derived circulating proteins such as albumin or fibrinogen. We conclude that the FSR of human dermal collagen resembles that of other human proteins considered to display slow turnover. The current method for its measurement may be used to determine the regulation of collagen synthesis in other organs and disease states.

Testosterone replacement in hypogonadism has long been known to promote nitrogen retention and increase body density, but the mechanisms of nitrogen retention and body composition changes are poorly defined. We measured body composition and muscle protein synthesis in five hypogonadal men before and 6 months after initiating testosterone replacement. Body composition was examined using dual energy X-ray absorptiometry. Muscle mass was estimated both by excretion of creatinine on a meat-free diet and from appendicular mass measured using dual energy X-ray absorptiometry. Muscle protein synthesis was assessed by measuring the increment of [13C]leucine in mixed muscle protein and myosin heavy chain during a continuous infusion of L-[l-13C]leucine. In all subjects there was an increase in fat-free mass (average, 15%; range, 10-22%; P = 0.02) and a decrease in fat mass (-11%; range, -0.4% to -22.0%; P = 0.03). Muscle mass also increased in everybody (mean, 20%; range, 11-32%; P = 0.04) such that 65% of the increase in fat-free mass could be attributed to accretion of muscle. The accumulation of muscle was associated with a 56% (P = 0.015) increase in the fractional synthesis rate of mixed skeletal muscle proteins and a trend toward a similar increase in the fractional synthesis rate of myosin heavy chain (46%; P = 0.098). We conclude that testosterone replacement in hypogonadal men enhanced skeletal muscle mass by stimulating the muscle protein synthesis rate.

We studied subjects with insulin-dependent diabetes mellitus (IDDM) and controls by administering primed continuous infusions of L-[1-13C,15N)]leucine and L-[2,3-13C2]alanine to measure whole body and forearm metabolism of these amino acids during ample protein intake and again after 4 wk of moderately restricted protein intake. Decreased rates of whole body protein degradation, leucine transamination, leucine oxidation, and increased forearm alanine release produced by dietary protein restriction occurred equivalently in IDDM subjects under short-term tightly managed glycemia and in controls. Dietary protein restriction did not affect whole body alanine appearance or forearm leucine appearance, disposal, or balance in IDDM subjects or controls. IDDM subjects differed from controls only in that normal forearm leucine balance was maintained at higher rates of leucine appearance and disposal. We conclude that IDDM subjects adapt normally to dietary protein restriction. Undernutrition during moderate protein deprivation in these patients likely occurs during episodes of poor glycemic control.

We examined whether the increased rates of protein catabolism (proteolysis and leucine oxidation) associated with moderate insulinopenia in subjects with IDDM would be accentuated by prior bicycle exercise (53% VO2max for 82 min). Insulin infusions maintained plasma glucose concentrations on one study day in “tight” control (TC: 6 mmol/l) and on a separate day in “loose” control (LC: 12 mmol/l). Elevations in serum ketone body, plasma NEFA, and whole-blood branched-chain amino acid concentrations on the loose control day during the basal period persisted throughout the post-exercise recovery period. Amino acid kinetics were estimated during a primed, constant infusion of l-[1-13C]leucine from plasma dilution of α-[1-13C]KIC and expired air 13CO2 enrichments. Loose control was associated with increased rates of whole-body leucine oxidation (LC 25±7 vs TC 21±8 μmol · kg−1 · h−1) and protein degradation (LC 127±12 vs TC 118±18 μmol · kg−1 · h−1) (both p

We studied postexercise amino acid metabolism, in the whole body and across the forearm. Seven volunteers were infused with L-[alpha-15N]lysine and L-[1-13C]-leucine twice [one time during 3 h after cycle exercise (75% VO2max), and one time in the resting state]. Whole body protein breakdown was estimated from dilution of L-[alpha-15N]lysine and L-[1-13C]ketoisocaproic acid (KIC) enrichments in plasma. Leucine oxidation was calculated from 13CO2 enrichments in expired air. Whole body protein breakdown was not increased above resting levels during the recovery period. Leucine oxidation was decreased after exercise (postexercise 13 +/- 2.3 vs. resting 19 +/- 3.2 mumol.kg-1.h-1; P less than 0.02), while nonoxidative leucine disposal was increased (115 +/- 6.1 vs. 103 +/- 5.6 micrograms.kg-1.min-1; P less than 0.02). After exercise, forearm net lysine balance was unchanged (87 +/- 25 vs. 93 +/- 28 nmol.100 ml-1.min-1), but there were decreases in forearm muscle protein degradation (219 +/- 51 vs. 356 +/- 85 nmol.100 ml-1.min-1; P less than 0.05) and synthesis (132 +/- 41 vs. 255 +/- 69 nmol.100 ml-1.min-1; P less than 0.01). In conclusion, after exercise 1) whole body protein degradation is not increased, 2) leucine disposal is directed away from oxidative and toward nonoxidative pathways, 3) forearm protein synthesis is decreased. Postexercise increases in whole body protein synthesis occur in tissues other than nonexercised muscle.

Uncontrolled diabetes in rats is associated with reduced levels of both serum somatomedins and hepatic somatomedins. Hepatic somatomedins are recognized after extraction with 5 mol/L acetic acid, have a higher molecular weight (about 30,000) than serum somatomedins (about 8,000), despite acid conditions that dissociate somatomedins from circulating carrier proteins, and stimulate cartilage when given in vivo. To determine if hepatic somatomedins--as potential prohormones--have insulin-like activity comparable with serum somatomedins, their effects on rat epididymal adipose tissue were examined. Somatomedins were prepared from serum and liver extracts by gel filtration on Sephadex G-75, pH 2.4. In initial studies with fat pad segments, extracted hepatic somatomedins increased glucose oxidation only 64 +/- 11% above buffer (mean +/- SEM), while stimulation of 372 +/- 48% was provided by extracted serum somatomedins of comparable cartilage-stimulating potency (P less than 0.01, liver v serum). Further examination was performed with isolated adipocytes in a system sensitive to insulin at a concentration of 10 microU/mL (stimulation 100% above buffer). In dose-response studies measuring glucose oxidation, hepatic somatomedins had insulin-like activity of 16 microU/mL versus 55 microU/mL for serum somatomedins equipotent on cartilage (P less than 0.05); measuring glucose incorporation into total lipids, hepatic somatomedins had undetectable activity while serum somatomedins had activity of 28 microU/mL. It is concluded that hepatic somatomedins with potent cartilage-stimulating activity have greatly reduced insulin-like activity. The apparent dissociation in biologic activity of hepatic somatomedins suggests that while they may be prohormones, they may also represent a class of growth factors separate from the circulating somatomedins.