Search

Population studies have shown that the α-Aminoadipic Acid (AAA) , a lysine metabolite, predicts future type 2 diabetes and AAA concentrations decrease following administration of insulin sensitizers. To determine whether women with PCOS and insulin resistance have altered lysine and AAA kinetics we compared age-matched 18 women with PCOS to 12 women without PCOS using stable isotopes labeled [α-15N1]-lysine and [13C1]-AAA to measure lysine and AAA kinetics. Baseline levels of AAA flux and lysine concentrations were higher in PCOS compared to women without PCOS. Insulin decreased the concentrations and flux values of lysine and AAA. The conversion of lysine to AAA and AAA-metabolic clearance rates were increased on insulin infusion in both groups (Table) . Insulin sensitivity was negatively correlated with lysine concentration (r = - 0.547, p < 0.05) and AAA flux (r= - 0.587, p < 0.05) . In conclusion, our results indicate that insulin sensitivity is a determinant of AAA metabolism and insulin administration modulate the kinetics thus reducing AAA concentration indicating that altered AAA and lysine metabolism may result from insulin resistance. Disclosure A.Y.Chang: None. A.K.Asokan: None. D.Sakrikar: Employee; The Binding Site. A.Lalia: None. M.Petterson: None. K.Nair: None. Funding National Institutes of Health (RAG62859)

Muscle glucose metabolism is improved by either aerobic or resistance exercise (RE) training, but the mechanisms leading to improved metabolism for each of these exercise modes are not identical. Much work has been done onimproved oxidative metabolism by aerobic exercise, but far less is known about how RE impacts fuel metabolism. Here, TCA and amino acid metabolites are measured in skeletal muscle after a single bout of RE. Twenty one healthy subjects performed a session of one-legged knee extension RE that consisted of 3 sets of 10 reps at 70% of their 1 rep max. Two muscle biopsies were obtained from the vastus lateralis of each leg. From the RE leg, biopsies were obtained ≤10min post-RE (0hr PEX) and approximately 1hr post-RE (1hr PEX), respectively. From the non-RE leg, biopsies were obtained before and 1hr PEX, respectively. Muscle samples were frozen and stored until mass spectrometry analysis of metabolites was performed. A 2-fold increase in plasma lactate (P Disclosure M. W. Pataky: None. A. Prabha kumar: None. K. Klaus: None. K. Nair: None. Funding National Institutes of Health (R01AG062859)

Insulin resistance has been linked to cognitive dysfunction and increased risk for Alzheimer’s disease and other dementias. It is unclear if cognitive decline during insulin resistance is due to systemic or brain-specific insulin resistance. Previous studies demonstrated that brain mitochondrial function is reduced concurrent to diminished insulin signaling in high fat-fed mice. However, it remains to be determined whether insulin signaling in the brain directly impacts brain mitochondrial function and cognition. Therefore, we developed a tamoxifen inducible brain-specific insulin receptor knockout (BIRKO) mouse by breeding C57/BL6J mice with a floxed insulin receptor gene with mice that express a tamoxifen-inducible Nestin-Cre. These BIRKO mice were used to identify if brain insulin signaling is required for maintenance of brain mitochondrial function and cognition. Four weeks after tamoxifen administration, we confirmed using western blotting that the insulin receptor was completely absent in all regions of the brain, but not the muscle, heart, liver, kidney, or adipose from the BIRKO mice. Spatial learning was reduced (P Disclosure M.W. Pataky: None. G. Ruegsegger: None. K. Klaus: None. P. Starski: None. K. Nair: None. Funding National Institutes of Health (T32DK07352)

Insulin deficiency and uncontrolled diabetes lead to a catabolic state with decreased muscle strength, contributing to disease-related morbidity. FoxO transcription factors are suppressed by insulin and thus are key mediators of insulin action. To study their role in diabetic muscle wasting, we created mice with muscle-specific triple knockout of FoxO1/3/4 and induced diabetes in these M-FoxO-TKO mice with streptozotocin (STZ). Muscle mass and myofiber area were decreased 20–30% in STZ-Diabetes mice due to increased ubiquitin-proteasome degradation and autophagy alterations, characterized by increased LC3-containing vesicles, and elevated levels of phosphorylated ULK1 and LC3-II. Both the muscle loss and markers of increased degradation/autophagy were completely prevented in STZ FoxO-TKO mice. Transcriptomic analyses revealed FoxO-dependent increases in ubiquitin-mediated proteolysis pathways in STZ-Diabetes, including regulation of Fbxo32 (Atrogin1), Trim63 (MuRF1), Bnip3L, and Gabarapl. These same genes were increased 1.4- to 3.3-fold in muscle from humans with type 1 diabetes after short-term insulin deprivation. Thus, FoxO-regulated genes play a rate-limiting role in increased protein degradation and muscle atrophy in insulin-deficient diabetes.

Introduction: Diabetes is associated with impaired cognition but the effect of the transient insulin deprivation on cognition and its underlying mechanisms remain unclear. Objective: We determined whether transient insulin deprivation in type 1 diabetic adults (T1D) and adolescents alters brain structure, functions and blood flow compared to nondiabetics (ND). Methods: We performed structural MRI, phosphorous31 NMR spectroscopy, and neuropsychiatric testing at baseline and following 6 hours of insulin deprivation in 14 adolescent (14-17 years) and adult (18-44 years) T1D and age- sex- and BMI-matched ND controls. Results: There were no significant changes on baseline structural MRI between the groups. After insulin deprivation, T1D had a significantly greater blood glucose (272 vs. 85 mg/dL), greater beta hydroxybutyrate (1.45 vs. 0.3 mmol/L), and decreased bicarbonate level (25.5 vs. 21.5 mmol/L) at six hours compared to ND. Following insulin deprivation, there was a significant difference in T1D left cortical volume compared to ND. On diffusion tensor imaging at baseline and after insulin deprivation, T1D had a higher fractional anisotropy compared to ND. T1D also had a significant decline in phosphocreatine/ATP after insulin deprivation compared to ND. Lastly after insulin deprivation, T1D failed to have learned improvement on repeat neuropsychiatric testing, with ND having significantly greater improvements in executive function, attention and working memory compared to T1D. Conclusion: Transient hyperglycemia and insulin deprivation caused a significant decline in some important aspects of cognition and brain energy metabolism, indicating that even transient insulin deprivation affects brain function and morphology. This may have important clinical implications as many diabetic patients inadvertently have occasional periods of transient insulin deprivation. Disclosure A. Creo: Consultant; Self; Ultragenyx. T.M. Cortes: None. A.R. Huebner: None. A. Lteif: None. J. Port: None. K. Nair: None.

Insulin resistance increases the risk for Alzheimer’s disease and other dementias; however, the underpinning mechanisms for this increased risk remain to be fully defined. Insulin resistance impairs mitochondrial oxidative metabolism and increases reactive oxygen species (ROS) in skeletal muscle, both of which are counteracted by aerobic exercise (AE). Therefore, we considered whether similar events occur in the brain, specifically in regions such as cerebrum and hippocampus which are rich in insulin receptors and mitochondria. We determined whether AE would counteract mitochondrial deficits in hippocampal and cerebral mitochondrial function in high fat diet (HFD) induced insulin resistance. Four weeks of HFD in mice induced hippocampal insulin resistance which was corrected by AE. HFD decreased ATP production and increased ROS emission in isolated cerebral mitochondria, which were rescued with AE. Impairments in mitochondrial function with HFD were paralleled by reductions in mtDNA copy number, mRNA expression of mitochondrial genes, and oxidative enzyme activities (e.g., citrate synthase, COX) in the hippocampus, which were corrected by AE. We also observed excessive mitochondrial fission in the hippocampus following HFD, which was prevented by AE. Proteomic analysis of the hippocampus showed that HFD led to oxidative post-translational modifications (PTMs) of mitochondrial proteins; however, this increase in oxidative PTMs to mitochondrial proteins with HFD was almost completely reversed by AE. Further, intranasal administration of the insulin receptor antagonist S961 prevented AE-induced improvements in ATP production and ROS emission in isolated cerebral mitochondrial during HFD, demonstrating that AE enhances cerebral mitochondrial function during HFD by resensitizing brain insulin signaling. Disclosure G. Ruegsegger: None. P.M. Vanderboom: None. S. Dasari: Consultant; Self; The Binding Site. K. Klaus: None. K. Nair: None.

Diet-induced insulin resistance (IR) adversely affects human health and life span. We show that muscle-specific overexpression of human mitochondrial transcription factor A (TFAM) attenuates high-fat diet (HFD)-induced fat gain and IR in mice in conjunction with increased energy expenditure and reduced oxidative stress. These TFAM effects on muscle are shown to be exerted by molecular changes that are beyond its direct effect on mitochondrial DNA replication and transcription. TFAM augmented the muscle tricarboxylic acid cycle and citrate synthase facilitating energy expenditure. TFAM enhanced muscle glucose uptake despite increased fatty acid (FA) oxidation in concert with higher β-oxidation capacity to reduce the accumulation of IR-related carnitines and ceramides. TFAM also increased pAMPK expression, explaining enhanced PGC1α and PPARβ, and reversing HFD-induced GLUT4 and pAKT reductions. TFAM-induced mild uncoupling is shown to protect mitochondrial membrane potential against FA-induced uncontrolled depolarization. These coordinated changes conferred protection to TFAM mice against HFD-induced obesity and IR while reducing oxidative stress with potential translational opportunities.

Accumulating evidence indicates a strong association between diabetic status and degenerative brain disease, including cognitive impairment. Here we hypothesized that although insulin is not necessary for glucose metabolism in brain, like in skeletal muscle insulin is critical for mitochondrial function in brain. We measured oxygen consumption rate (OCR), maximal ATP production rate (MAPR), and reactive oxygen species (ROS) production in isolated brain mitochondria of streptozotocin (STZ) diabetic mice. STZ mice deprived of insulin treatment for 96 hours (D-I), in comparison to nondiabetic mice (ND) showed a significant reduction in State 3 MAPR [1.77±0.14 vs. 2.35±0.27 (pmol/s/ug)], phosphorylation efficiency [0.42±0.04 vs. 0.54±0.07 (mol ATP produced/mol of oxygen consumed)] and respiratory control ratio [2.95±0.16 vs. 3.12±0.18] indicating reduced mitochondrial coupling efficiency during insulin deprivation. Citrate synthase and cytochrome c oxidase activities were significantly decreased in the hypothalamus of D-I compared ND. Surprisingly, no significant differences in ROS emission were detected between ND and D-I suggesting additional factors, potentially elevated ketone bodies, may protect against increased oxidative stress in the D-I brain. Proteomics analysis of the cerebrum found post-translational modification involving oxidative damage of several mitochondrial proteins that potentially cause tau phosphorylation and neurofibrillary degeneration in D-I vs. ND. In STZ mice with continued insulin treatment (D+I), state 3 OCR, MAPR, and phosphorylation efficiency were comparable to ND, demonstrating the restorative effects of insulin and euglycemia on brain mitochondrial function. We conclude that insulin deprivation and hyperglycemia significantly alter brain mitochondrial function. Insulin treatment and control of glycemia could have salutary effects on these parameters. Disclosure G. Ruegsegger: None. M. Shankarappa: None. P. Summer: None. S. Gopala: None. P. Zabielski: None. K. Klaus: None. S. Dasari: None. I.R. Lanza: None. K. Nair: None.

Objective: Statins are well known to cause myalgia and in very rare cases rhabdomyolysis. It remains to be determined whether statin treatment causes any adverse effects on muscle precluding benefits of exercise. We investigated the impact of statin therapy on exercise capacity, muscle strength, mitochondrial respiration, and gene expression in older adults before and after a 12 week exercise program consisting of either aerobic interval (HIIT), resistance (RT), or combined aerobic and resistance (CT) training. Design: Participants aged 65 and older reported in a prior exercise study were analyzed to determine the impact of statin use. Anthropometric measurements, muscle strength, exercise tolerance and a muscle biopsy for determination of mitochondrial respiration and gene transcripts (RNA sequence) were obtained at baseline and then repeated after 12 weeks of exercise training. Results: Among participants, 7 were in CT (2 on statins, 5 not on statins), 8 were in HIIT (4 on statins, 4 not on statins), and 8 were in RT (2 on statins, 6 not on statins) groups. Statin and non-statin users at baseline had no observed significant difference in BMI (p=0.936), VO2 (p=0.812), leg press strength (p=0.916), state 2 respiration (p=0.266), state 3 respiration complex I and II (p=0.345), stage 4 respiration (p=0.231) or gene transcripts of 15232 genes examined. Following 12 week exercise program, no significant differences were noted between statin and non-statin users in their BMI (9=0.149), VO2 (p=0.681), leg press strength (p=0.925), state 2 respiration (p=0.078), state 3 respiration complex 1 and II (p=0.142), or state 4 respiration (p=0.945). Significant differences were noted in gene transcripts in statin and non-statin users in CT+RT group (6 genes) and HIIT group (33 genes). Conclusion: Although there is a slight difference in gene expression in statin and non-statin users, this difference does not have a significant effect on exercise tolerance, muscle strength or mitochondrial respiration after a 12 week exercise program. Disclosure T.M. Cortes: None. S. Dasari: None. M.M. Robinson: None. K. Nair: None.

Background: Familial Partial Lipodystrophy, Dunnigan variety (FPLD) is characterized by post-natal fat loss leading to severe insulin resistance. Affected individuals also display striking skeletal muscle hypertrophy, but there is limited information on muscle function and energy metabolism. We therefore systematically investigated muscle and mitochondrial function in 6 individuals with FPLD and 6 matched controls. Methods: Body composition and intramyocellular lipid content (IMCL) were assessed by DEXA and magnetic resonance spectroscopy, respectively. Maximal voluntary strength and fatigue were assessed for both recumbent leg press and seated chest press. Vastus lateralis muscle biopsies were obtained prior to and following a high fat (40%) mixed-meal. Oxygen consumption in isolated mitochondria was measured using substrates supporting carbohydrate or lipid-based respiration. Insulin Sensitivity Index (SI) was calculated by minimal modelling. Results: Individuals with FPLD had significantly lower SI, lower body fat content, and higher lean mass. Peak leg press and chest press force were not different, but FPLD individuals had earlier fatigue during chest press (number of repetitions: 15 ± 0.6 vs. 20 ± 0.3, p = 0.01). They also had a 50-60% decrease in state 3 respiration measured using substrates supporting lipid-based respiration (p = 0.04). Further, mitochondrial oxidative capacity showed a strong correlation with muscle fatigue (r = 0.76, p = 0.003), and inversely correlated with fasting and post-prandial lipemia and measures of insulin resistance. Conclusion: Individuals with FPLD have higher lean body mass and lower insulin sensitivity. Despite preserved peak muscle strength, they demonstrated earlier muscle fatigue. Decreased mitochondrial fatty acid oxidative capacity, likely related to elevated IMCL, may contribute to muscular and metabolic abnormalities. Disclosure V. Simha: None. I.R. Lanza: None. N. LeBrasseur: None. K. Klaus: None. J. Port: None. M.C. Laurenti: Other Relationship; Self; GlySens Incorporated. C. Cobelli: Research Support; Self; Sanofi-Aventis. Advisory Panel; Self; Novo Nordisk Inc.. K. Nair: None.

Insulin plays pivotal role in cellular fuel metabolism in skeletal muscle. Despite being the primary site of energy metabolism, the underlying mechanism on how insulin deficiency deranges skeletal muscle mitochondrial physiology remains to be fully understood. Here we report an important link between altered skeletal muscle proteome homeostasis and mitochondrial physiology during insulin deficiency. Deprivation of insulin in streptozotocin-induced diabetic mice decreased mitochondrial ATP production, reduced coupling and phosphorylation efficiency, and increased oxidant emission in skeletal muscle. Proteomic survey revealed that the mitochondrial derangements during insulin deficiency were related to increased mitochondrial protein degradation and decreased protein synthesis, resulting in reduced abundance of proteins involved in mitochondrial respiration and β-oxidation. However, a paradoxical upregulation of proteins involved in cellular uptake of fatty acids triggered an accumulation of incomplete fatty acid oxidation products in skeletal muscle. These data implicate a mismatch of β-oxidation and fatty acid uptake as a mechanism leading to increased oxidative stress in diabetes. This notion was supported by elevated oxidative stress in cultured myotubes exposed to palmitate in the presence of a β-oxidation inhibitor. Together, these results indicate that insulin deficiency alters the balance of proteins involved in fatty acid transport and oxidation in skeletal muscle, leading to impaired mitochondrial function and increased oxidative stress.

A recent editorial in the Journal of Clinical Investigation by Nathan et al. (1) dwelt on the decision to cease direct National Institutes of Health (NIH) funding of Clinical Research Centers (CRCs). As the authors rightly point out, the lack of extramural support for the CRC infrastructure will doom this valuable resource for human research at academic institutions without the wherewithal to support clinical research. CRCs as they currently exist might no longer require NIH support if we already knew the entirety of human physiology as it relates to disease or if entities such as industry would fund the studies needed to understand the primary mechanisms of complex human disease. We are certain the former is untrue and highly doubtful the latter will occur. The subsequent demise of the CRCs and our diminished ability to perform complex, mechanistic studies in humans will have both immediate and long-term adverse effects on biomedical research. Support obtained by the NIH Research Project Grant (R01) mechanism will be insufficient to maintain the necessary research infrastructure. Consequently, investigators will abandon comprehensive, mechanistic studies in humans because of the costs involved. The eventual fall in the number of investigators capable of designing, conducting, and interpreting such studies threatens to make the U.S. a second-tier biomedical research environment. This is especially important for the field of diabetes and metabolism where related human studies account for a significant proportion of CRC use. Certainly, rigorous metabolic research requires meticulous control of diet and activity prior to study. Moreover, ensuring participant safety with intensive monitoring often requires extended inpatient stays. The elimination of the NIH-supported CRC system will also substantially constrain the infrastructure necessary for intensive human studies, such as those requiring tissue biopsy, vascular catheterization, and frequent sampling of the …

Insulin regulates many cellular processes, but the full impact of insulin deficiency on cellular functions remains to be defined. Applying a mass spectrometry–based nontargeted metabolomics approach, we report here alterations of 330 plasma metabolites representing 33 metabolic pathways during an 8-h insulin deprivation in type 1 diabetic individuals. These pathways included those known to be affected by insulin such as glucose, amino acid and lipid metabolism, Krebs cycle, and immune responses and those hitherto unknown to be altered including prostaglandin, arachidonic acid, leukotrienes, neurotransmitters, nucleotides, and anti-inflammatory responses. A significant concordance of metabolome and skeletal muscle transcriptome–based pathways supports an assumption that plasma metabolites are chemical fingerprints of cellular events. Although insulin treatment normalized plasma glucose and many other metabolites, there were 71 metabolites and 24 pathways that differed between nondiabetes and insulin-treated type 1 diabetes. Confirmation of many known pathways altered by insulin using a single blood test offers confidence in the current approach. Future research needs to be focused on newly discovered pathways affected by insulin deficiency and systemic insulin treatment to determine whether they contribute to the high morbidity and mortality in T1D despite insulin treatment.

OBJECTIVE Reductions in insulin sensitivity in conjunction with muscle mitochondrial dysfunction have been reported to occur in many conditions including aging. The objective was to determine whether insulin resistance and mitochondrial dysfunction are directly related to chronological age or are related to age-related changes in body composition. RESEARCH DESIGN AND METHODS Twelve young lean, 12 young obese, 12 elderly lean, and 12 elderly obese sedentary adults were studied. Insulin sensitivity was measured by a hyperinsulinemic-euglycemic clamp, and skeletal muscle mitochondrial ATP production rates (MAPRs) were measured in freshly isolated mitochondria obtained from vastus lateralis biopsy samples using the luciferase reaction. RESULTS Obese participants, independent of age, had reduced insulin sensitivity based on lower rates of glucose infusion during a hyperinsulinemic-euglycemic clamp. In contrast, age had no independent effect on insulin sensitivity. However, the elderly participants had lower muscle MAPRs than the young participants, independent of obesity. Elderly participants also had higher levels inflammatory cytokines and total adiponectin. In addition, higher muscle MAPRs were also noted in men than in women, whereas glucose infusion rates were higher in women. CONCLUSIONS The results demonstrate that age-related reductions in insulin sensitivity are likely due to an age-related increase in adiposity rather than a consequence of advanced chronological age. The results also indicate that an age-related decrease in muscle mitochondrial function is neither related to adiposity nor insulin sensitivity. Of interest, a higher mitochondrial ATP production capacity was noted in the men, whereas the women were more insulin sensitive, demonstrating further dissociation between insulin sensitivity and muscle mitochondrial function.

OBJECTIVE Transgenic expression of diacylglycerol acyltransferase-1 (DGAT1) in skeletal muscle leads to protection against fat-induced insulin resistance despite accumulation of intramuscular triglyceride, a phenomenon similar to what is known as the “athlete paradox.” The primary objective of this study is to determine how DGAT1 affects muscle fatty acid oxidation in relation to whole-body energy metabolism and insulin sensitivity. RESEARCH DESIGN AND METHODS We first quantified insulin sensitivity and the relative tissue contributions to the improved whole-body insulin sensitivity in muscle creatine kisase (MCK)-DGAT1 transgenic mice by hyperinsulinemic-euglycemic clamps. Metabolic consequences of DGAT1 overexpression in skeletal muscles were determined by quantifying triglyceride synthesis/storage (anabolic) and fatty acid oxidation (catabolic), in conjunction with gene expression levels of representative marker genes in fatty acid metabolism. Whole-body energy metabolism including food consumption, body weights, oxygen consumption, locomotor activity, and respiration exchange ratios were determined at steady states. RESULTS MCK-DGAT1 mice were protected against muscle lipoptoxicity, although they remain susceptible to hepatic lipotoxicity. While augmenting triglyceride synthesis, DGAT1 overexpression also led to increased muscle mitochondrial fatty acid oxidation efficiency, as compared with wild-type muscles. On a high-fat diet, MCK-DGAT1 mice displayed higher basal metabolic rates and 5–10% lower body weights compared with wild-type littermates, whereas food consumption was not different. CONCLUSIONS DGAT1 overexpression in skeletal muscle led to parallel increases in triglyceride synthesis and fatty acid oxidation. Seemingly paradoxical, this phenomenon is characteristic of insulin-sensitive myofibers and suggests that DGAT1 plays an active role in metabolic “remodeling” of skeletal muscle coupled with insulin sensitization.

OBJECTIVE— We determined whether reduced insulin sensitivity, mitochondrial dysfunction, and other age-related dysfunctions are inevitable consequences of aging or secondary to physical inactivity. RESEARCH DESIGN AND METHODS— Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp and ATP production in mitochondria isolated from vastus lateralis biopsies of 42 healthy sedentary and endurance-trained young (18–30 years old) and older (59–76 years old) subjects. Expression of proteins involved in fuel metabolism was measured by mass spectrometry. Citrate synthase activity, mitochondrial DNA (mtDNA) abundance, and expression of nuclear-encoded transcription factors for mitochondrial biogenesis were measured. SIRT3, a mitochondrial sirtuin linked to lifespan-enhancing effects of caloric restriction, was measured by immunoblot. RESULTS— Insulin-induced glucose disposal and suppression of endogenous glucose production were higher in the trained young and older subjects, but no age effect was noted. Age-related decline in mitochondrial oxidative capacity was absent in endurance-trained individuals. Although endurance-trained individuals exhibited higher expression of mitochondrial proteins, mtDNA, and mitochondrial transcription factors, there were persisting effects of age. SIRT3 expression was lower with age in sedentary but equally elevated regardless of age in endurance-trained individuals. CONCLUSIONS— The results demonstrate that reduced insulin sensitivity is likely related to changes in adiposity and to physical inactivity rather than being an inevitable consequence of aging. The results also show that regular endurance exercise partly normalizes age-related mitochondrial dysfunction, although there are persisting effects of age on mtDNA abundance and expression of nuclear transcription factors and mitochondrial protein. Furthermore, exercise may promote longevity through pathways common to effects of caloric restriction.

Caloric restriction (CR) improves insulin sensitivity and reduces the incidence of diabetes in obese individuals. The underlying mechanisms whereby CR improves insulin sensitivity are not clear. We evaluated the effect of 16 weeks of CR on whole-body insulin sensitivity by pancreatic clamp before and after CR in 11 obese participants (BMI = 35 kg/m2) compared with 9 matched control subjects (BMI = 34 kg/m2). Compared with the control subjects, CR increased the glucose infusion rate needed to maintain euglycemia during hyperinsulinemia, indicating enhancement of peripheral insulin sensitivity. This improvement in insulin sensitivity was not accompanied by changes in skeletal muscle mitochondrial oxidative capacity or oxidant emissions, nor were there changes in skeletal muscle ceramide, diacylglycerol, or amino acid metabolite levels. However, CR lowered insulin-stimulated thioredoxin-interacting protein (TXNIP) levels and enhanced nonoxidative glucose disposal. These results support a role for TXNIP in mediating the improvement in peripheral insulin sensitivity after CR.

DHEA (dehydroepiandrosterone) replacement is not part of the current standard of care in hypoadrenal subjects. Animal studies have shown that DHEA administration prevents diabetes. To determine the physiological effect of DHEA replacement on insulin sensitivity in adrenal-deficient women, we performed a single-center, randomized, double-blind, placebo-controlled, crossover study in 28 hypoadrenal women (mean age 50.2 ± 2.87 years) who received a single 50-mg dose of DHEA daily or placebo. After 12 weeks, insulin sensitivity was assessed using a hyperinsulinemic-euglycemic clamp. DHEA replacement significantly increased DHEA-S (sulfated ester of DHEA), bioavailable testosterone, and androstenedione and reduced sex hormone−binding globulin levels. Fasting plasma insulin and glucagon were lower with DHEA (42 ± 4.94 vs. 53 ± 6.58 pmol/l [P = 0.005] and 178 ± 11.32 vs. 195.04 ± 15 pmol/l [P = 0.02], respectively). The average amount of glucose needed to maintain similar blood glucose levels while infusing the same insulin dosages was higher during DHEA administration (358 ± 24.7 vs. 320 ± 24.6 mg/min; P < 0.05), whereas endogenous glucose production was similar. DHEA also reduced total cholesterol (P < 0.005), triglycerides (P < 0.011), LDL cholesterol (P < 0.05), and HDL cholesterol (P < 0.005). In conclusion, replacement therapy with 50 mg of DHEA for 12 weeks significantly increased insulin sensitivity in hypoadrenal women, thereby suggesting that DHEA replacement could have a potential impact in preventing type 2 diabetes.

Time has come again for the “changing of the guard,” which has occurred every 3–5 years since the journal’s inception in 1952. The new, and 13th, editorial team began overseeing new submissions to Diabetes on 1 July 2016 and now officially takes the helm with this issue. As I profoundly thank my editorial colleagues for their remarkable contributions and collegiality, I also wish the best to the new editorial team led by Dr. Martin G. Myers Jr. (University of Michigan). The transition has been a smooth one, thanks to the American Diabetes Association’s (ADA’s) editorial office staff in Indianapolis, IN, and the ADA’s production team in Alexandria, VA. One of the most important pillars of scientific advancement is the integrity of the peer-review system. As journal editors, we strive to ensure that we are selecting the best science from among numerous submissions being considered for publication. We are only able to accomplish this by relying on a vast number of investigators representing multiple areas of diabetes research who regularly offer their valuable time …

Insulin resistance increases and muscle oxidative capacity decreases during aging, but lifestyle changes—especially physical activity—may reverse these trends. Here we report the effect of a 16-week aerobic exercise program (n = 65) or control activity (n = 37) performed by men and women aged 21–87 years on insulin sensitivity and muscle mitochondria. Insulin sensitivity, measured by intravenous glucose tolerance test, decreased with age (r = −0.32) and was related to abdominal fat content (r = −0.65). Exercise increased peak oxygen uptake (Vo2peak; 10%), activity of muscle mitochondrial enzymes (citrate synthase and cytochrome c oxidase, 45–76%) and mRNA levels of mitochondrial genes (COX4, ND4, both 66%) and genes involved in mitochondrial biogenesis (PGC-1α, 55%; NRF-1, 15%; TFAM, 85%). Exercise also increased muscle GLUT4 mRNA and protein (30–52%) and reduced abdominal fat (5%) and plasma triglycerides (25%). None of these changes were affected by age. In contrast, insulin sensitivity improved in younger people but not in middle-aged or older groups. Thus, the muscle mitochondrial response to 4 months of aerobic exercise training was similar in all age-groups, although the older people did not have an improvement in insulin sensitivity.

To determine the in vivo effect of amino acids (AAs) alone or in combination with insulin on splanchnic and muscle protein dynamics, we infused stable isotope tracers of AAs in 36 healthy subjects and sampled from femoral artery and vein and hepatic vein. The subjects were randomized into six groups and were studied at baseline and during infusions of saline (group 1), insulin (0.5 mU · kg−1 · min−1) (group 2), insulin plus replacement of AAs (group 3) insulin plus high-dose AAs (group 4), or somatostatin and baseline replacement doses of insulin, glucagon and GH plus high dose of AAs (group 5) or saline (group 6). Insulin reduced muscle release of AAs mainly by inhibition of protein breakdown. Insulin also enhanced AA-induced muscle protein synthesis (PS) and reduced leucine transamination. The main effect of AAs on muscle was the enhancement of PS. Insulin had no effect on protein dynamics or leucine transamination in splanchnic bed. However, AAs reduced protein breakdown and increased synthesis in splanchnic bed in a dose-dependent manner. AAs also enhanced leucine transamination in both splanchnic and muscle beds. Thus insulin’s anabolic effect was mostly on muscle, whereas AAs acted on muscle as well as on splanchnic bed. Insulin achieved anabolic effect in muscle by inhibition of protein breakdown, enhancing AA-induced PS, and reducing leucine transamination. AAs largely determined protein anabolism in splanchnic bed by stimulating PS and decreasing protein breakdown.

The present study sought to determine whether elevated plasma free fatty acids (FFAs) alter the splanchnic and muscle glucose metabolism in women. To do so, FFAs were increased in seven women by an 8-h Intralipid/heparin (IL/hep) infusion, and the results were compared with those observed in nine women who were infused with glycerol alone. Glucose was clamped at approximately 8.3 mmol/l and insulin was increased to approximately 300 pmol/l to stimulate both muscle and hepatic glucose uptake. Insulin secretion was inhibited with somatostatin. Leg and splanchnic glucose metabolism were assessed using a combined catheter and tracer dilution approach. The glucose infusion rates required to maintain target plasma glucose concentrations were lower (P < 0.01) during IL/hep than glycerol infusion (30.8 +/- 2.6 vs. 65.0 +/- 7.9 micro mol. kg(-1). min(-1)). Whole-body glucose disappearance (37.0 +/- 2.2 vs. 70.9 +/- 8.7 micro mol. kg(-1). min(-1); P < 0.001) and leg glucose uptake (24.3 +/- 4.2 vs. 59.6 +/- 10.0 micro mol. kg fat-free mass of the leg(-1). min(-1); P < 0.02) were also lower, whereas splanchnic glucose production (8.2 +/- 0.8 vs. 4.3 +/- 0.7 micro mol. kg(-1). min(-1); P < 0.01) was higher during IL/hep than glycerol infusion. We conclude that in the presence of combined hyperinsulinemia and hyperglycemia, elevated FFAs impair glucose metabolism in women by inhibiting whole- body glucose disposal, muscle glucose uptake, and suppression of splanchnic glucose production.

The present study sought to determine whether elevated plasma free fatty acids (FFAs) alter the ability of insulin and glucose to regulate splanchnic as well as muscle glucose metabolism. To do so, FFAs were increased in 10 subjects to approximately 1 mmol/l by an 8-h Intralipid/heparin (IL/Hep) infusion, whereas they fell to levels near the detection limit of the assay (

Starting with the January 2012 issue, a new team takes the reins of Diabetes . A question that many people have asked is whether the new leadership will change Diabetes . My answer would be, of course, that change is necessary to respond to new challenges arising from the continual transformation of technology and science. Such changes have been continuously transforming Diabetes since its inception in 1952 under the editorship of Dr. Frank N. Allan (of Boston, Massachusetts) and the 11 editors that have succeeded him. This evolution will continue under our stewardship, though the core principles and mission of the journal will remain unchanged. The overriding mission of Diabetes is to publish the most original and important scientific works of relevance to diabetes and related disorders. The majority of the early editions of Diabetes published articles relevant to clinical problems. Gradually the journal began expanding toward more laboratory-based mechanistic studies. Diabetes will continue to publish both human and animal studies that advance our understanding about the pathophysiology of diabetes and its complications. Our ultimate goal—to prevent and cure diabetes—lies ahead. Continuing toward this goal, our aim is to serve the immediate need of reporting research that contributes to improving the quality of the lives of people suffering from diabetes. Most of the mechanistic experiments published in Diabetes are performed in animals or in vitro models. These are the cornerstones of medical discovery. Before applications in humans can occur, basic experimentation lights the way, as exemplified by Dr. Frederick Banting and Charles Best, who performed their landmark experiments in dogs before applying their findings to treat type 1 diabetic individuals with insulin. Although there are many obvious limitations in performing human studies, we also believe that novel observations in humans are critically important to stimulating basic science research in animals …

We have previously reported that splanchnic glucose uptake, hepatic glycogen synthesis, and hepatic glucokinase activity are decreased in people with type 2 diabetes during intravenous glucose infusion. To determine whether these defects are also present during more physiological enteral glucose administration, we studied 11 diabetic and 14 nondiabetic volunteers using a combined organ catheterization-tracer infusion technique. Glucose was infused into the duodenum at a rate of 22 micromol. kg(-1). min(-1) while supplemental glucose was given intravenously to clamp glucose at approximately 10 mmol/l in both groups. Endogenous hormone secretion was inhibited with somatostatin, and insulin was infused to maintain plasma concentrations at approximately 300 pmol/l (i.e., twofold higher than our previous experiments). Total body glucose disappearance, splanchnic, and leg glucose extractions were markedly lower (P < 0.01) in the diabetic subjects than in the nondiabetic subjects. UDP-glucose flux, a measure of glycogen synthesis, was approximately 35% lower (P < 0.02) in the diabetic subjects than in the nondiabetic subjects. This was entirely accounted for by a decrease (P < 0.01) in the contribution of extracellular glucose because the contribution of the indirect pathway to hepatic glycogen synthesis was similar between groups. Neither endogenous and splanchnic glucose productions nor rates of appearance of the intraduodenally infused glucose in the portal vein differed between groups. In summary, both muscle and splanchnic glucose uptake are impaired in type 2 diabetes during enteral glucose administration. The defect in splanchnic glucose uptake appears to be due to decreased uptake of extracellular glucose, implying decreased glucokinase activity. Thus, abnormal hepatic and muscle (but not gut) glucose metabolism are likely to contribute to postprandial hyperglycemia in people with type 2 diabetes.

Insulin’s effect on the synthesis of liver proteins remains to be fully defined. Previous studies using various surrogate measures of amino acyl–tRNA have reported variable results of insulin’s effect on liver protein synthesis. We determined the effect of insulin with or without amino acid supplementation on the synthesis rates of liver proteins (tissue, albumin, and fibrinogen) using l-[1-13C]Leu as a tracer in 24 male miniature swine. In addition, we compared the isotopic enrichment of different precursors of liver proteins with that of amino acyl−tRNA using l-[1-13C]Leu and l-[15N]Phe as tracers. Although liver tissue fluid enrichment of [13C]Leu and [15N]Phe and that of plasma [13C]ketoisocaproatic acid (KIC) were very similar to that of tRNA, plasma isotopic enrichment of both Leu and Phe were substantially higher (P < 0.01) and VLDL apolipoprotein-B100 enrichment was lower (P < 0.01) than the respective amino acyl−tRNA enrichment. Plasma KIC enrichment most accurately predicted leucyl-tRNA enrichment, whereas plasma Leu enrichment was best correlated with that of tRNA. Neither insulin alone nor insulin plus amino acid infusion had an effect on liver tissue protein synthesis. In contrast, insulin alone decreased the albumin synthesis rate, and insulin with amino acids maintained the albumin synthesis rate. Insulin with or without amino acids inhibited the fibrinogen synthesis rate. These results, based on synthetic rates using amino acyl–tRNA, were consistent with those obtained using KIC or tissue fluid Leu or Phe as precursor pools. These studies demonstrated that plasma KIC enrichment is a convenient and reliable surrogate measure of leucyl-tRNA in liver. We also concluded that insulin has differential effects on the synthesis rates of liver proteins. Whereas insulin with or without amino acid supplement has no acute effect on the synthesis of liver tissue protein, insulin has a substantial inhibitory effect on fibrinogen synthesis. In contrast, insulin administration along with amino supplement is necessary to maintain albumin synthesis rate.

Although insulin's anticatabolic effect on protein metabolism in type 1 diabetes has been clearly shown to be related to the inhibition of protein breakdown, insulin's effect on muscle protein synthesis remains controversial. Cross-limb studies and measurements of synthesis rates of mixed muscle protein have yielded conflicting results. These measurements represent the mean synthesis of several muscle proteins and may miss changes in the synthesis rates of individual muscle proteins. We measured the fractional synthesis rates of myosin heavy chain (MHC), the principal muscle contractile protein, and mixed muscle protein (MMP) in six type 1 diabetic patients during insulin deprivation and insulin treatment. Comparisons were made with six healthy control subjects. Muscle biopsies were taken at 2 h and 8 h during a primed continuous infusion of l-[1- 13C]leucine. MHC was purified by a preparative continuous elution gel electrophoresis, and fractional synthesis rates were calculated. We found that in type 1 diabetic subjects, the fractional synthesis rates of MHC and MMP during insulin treatment are similar to those of control subjects. Acute insulin deprivation did not affect either the synthesis rate or the ratio of MHC to MMP in type 1 diabetic subjects. In the postabsorptive state, acute insulin deprivation has no effect on MHC or MMP synthesis in type 1 diabetic patients.

It has been 2 years since the current editorial board accepted stewardship of the premier journal of the American Diabetes Association (ADA), Diabetes . We believe this is an appropriate time to reflect upon our past experiences and to share our vision for the coming 3 years with our readership. The concept of a journal for the ADA was originally proposed by the first president of the ADA, Dr. Cecil Striker, in his Presidential lecture in 1941. Dr. Striker stated with reference to the publication of a journal, “We appreciate the fact that a plethora of scientific journals already exists, and I reluctantly present this question to our Association” (1). The journal finally came to fruition in 1952, replacing precedent publications of Proceedings of the American Diabetes Association (1941) and Diabetes Abstracts (1942). In his “Salute to Diabetes ” in the first issue of Diabetes , Dr. Elliott P. Joslin, honorary president of the ADA wrote that the association was “hitching its wagon to a very important star with its new Journal Diabetes ” (2). He further stated “Diabetes is a universal disease. It knows no political boundaries. What happens anywhere in the world to improve the condition of the diabetic is important to diabetics everywhere else” (3). One of the main reasons for …

OBJECTIVE—Muscle mitochondrial dysfunction occurs in many insulin-resistant states, such as type 2 diabetes, prompting a hypothesis that mitochondrial dysfunction may cause insulin resistance. We determined the impact of insulin deficiency on muscle mitochondrial ATP production by temporarily depriving type 1 diabetic patients of insulin treatment. RESEARCH DESIGN AND METHODS—We withdrew insulin for 8.6 ± 0.6 h in nine C-peptide–negative type 1 diabetic subjects and measured muscle mitochondrial ATP production and gene transcript levels (gene array and real-time quantitative PCR) and compared with insulin-treated state. We also measured oxygen consumption (indirect calorimetry); plasma levels of glucagon, bicarbonate, and other substrates; and urinary nitrogen. RESULTS—Withdrawal of insulin resulted in increased plasma glucose, branched chain amino acids, nonesterified fatty acids, β-hydroxybutyrate, and urinary nitrogen but no change in bicarbonate. Insulin deprivation decreased muscle mitochondrial ATP production rate (MAPR) despite an increase in whole-body oxygen consumption and altered expression of many muscle mitochondrial gene transcripts. Transcript levels of genes involved in oxidative phosphorylation were decreased, whereas those involved in vascular endothelial growth factor (VEGF) signaling, inflammation, cytoskeleton signaling, and integrin signaling pathways were increased. CONCLUSIONS—Insulin deficiency and associated metabolic changes reduce muscle MAPR and expression of oxidative phosphorylation genes in type 1 diabetes despite an increase in whole-body oxygen consumption. Increase in transcript levels of genes involved in VEGF, inflammation, cytoskeleton, and integrin signaling pathways suggest that vascular factors and cell proliferation that may interact with mitochondrial changes occurred.

We investigated whether previously reported muscle mitochondrial dysfunction and altered gene transcript levels in type 2 diabetes might be secondary to abnormal blood glucose and insulin levels rather than an intrinsic defect of type 2 diabetes. A total of 13 type 2 diabetic and 17 nondiabetic subjects were studied on two separate occasions while maintaining similar insulin and glucose levels in both groups by 7-h infusions of somatostatin, low- or high-dose insulin (0.25 and 1.5 mU/kg of fat-free mass per min, respectively), and glucose. Muscle mitochondrial DNA abundance was not different between type 2 diabetic and nondiabetic subjects at both insulin levels, but the majority of transcripts in muscle that are involved mitochondrial functions were expressed at lower levels in type 2 diabetes at low levels of insulin. However, several gene transcripts that are specifically involved in the electron transport chain were expressed at higher levels in type 2 diabetic patients. After the low-dose insulin infusion, which achieved postabsorptive insulin levels, the muscle mitochondrial ATP production rate (MAPR) was not different between type 2 diabetic and nondiabetic subjects. However, increasing insulin to postprandial levels increased the MAPR in nondiabetic subjects but not in type 2 diabetic patients. The lack of MAPR increment in response to high-dose insulin in type 2 diabetic patients occurred in association with reduced glucose disposal and expression of peroxisome proliferator–activated receptor-γ coactivator 1α, citrate synthase, and cytochrome c oxidase I. In conclusion, the current data supports that muscle mitochondrial dysfunction in type 2 diabetes is not an intrinsic defect, but instead a functional defect related to impaired response to insulin.

The present study sought to determine whether elevated plasma free fatty acids (FFAs) alter the splanchnic and muscle glucose metabolism in women. To do so, FFAs were increased in seven women by an 8-h Intralipid/heparin (IL/hep) infusion, and the results were compared with those observed in nine women who were infused with glycerol alone. Glucose was clamped at approximately 8.3 mmol/l and insulin was increased to approximately 300 pmol/l to stimulate both muscle and hepatic glucose uptake. Insulin secretion was inhibited with somatostatin. Leg and splanchnic glucose metabolism were assessed using a combined catheter and tracer dilution approach. The glucose infusion rates required to maintain target plasma glucose concentrations were lower (P0.01) during IL/hep than glycerol infusion (30.8 +/- 2.6 vs. 65.0 +/- 7.9 micro mol. kg(-1). min(-1)). Whole-body glucose disappearance (37.0 +/- 2.2 vs. 70.9 +/- 8.7 micro mol. kg(-1). min(-1); P0.001) and leg glucose uptake (24.3 +/- 4.2 vs. 59.6 +/- 10.0 micro mol. kg fat-free mass of the leg(-1). min(-1); P0.02) were also lower, whereas splanchnic glucose production (8.2 +/- 0.8 vs. 4.3 +/- 0.7 micro mol. kg(-1). min(-1); P0.01) was higher during IL/hep than glycerol infusion. We conclude that in the presence of combined hyperinsulinemia and hyperglycemia, elevated FFAs impair glucose metabolism in women by inhibiting whole- body glucose disposal, muscle glucose uptake, and suppression of splanchnic glucose production.

Improvement of glycemic status by insulin is associated with profound changes in amino acid metabolism in type 1 diabetes. In contrast, a dissociation of insulin effect on glucose and amino acid metabolism has been reported in type 2 diabetes. Type 2 diabetic patients are reported to have reduced muscle oxidative enzymes and Vo2max. We investigated the effect of 11 days of intensive insulin treatment (T2D+) on whole-body amino acid kinetics, muscle protein synthesis rates, and muscle functions in eight type 2 diabetic subjects after withdrawing all treatments for 2 weeks (T2D−) and compared the results with those of weight-matched lean control subjects using stable isotopes of the amino acids. Whole-body leucine, phenylalanine and tyrosine fluxes, leucine oxidation, and plasma amino acid levels were similar in all groups, although plasma glucose levels were significantly higher in T2D−. Insulin treatment reduced leucine nitrogen flux and transamination rates in subjects with type 2 diabetes. Synthesis rates of muscle mitochondrial, sarcoplasmic, and mixed muscle proteins were not affected by glycemic status or insulin treatment in subjects with type 2 diabetes. Muscle strength was also unaffected by diabetes or glycemic status. In contrast, the diabetic patients showed increased tendency for muscle fatigability. Insulin treatment also failed to stimulate muscle cytochrome C oxidase activity in the diabetic patients, although it modestly elevated citrate synthase. In conclusion, improvement of glycemic status by insulin treatment did not alter whole-body amino acid turnover in type 2 diabetic subjects, but leucine nitrogen flux, transamination rates, and plasma ketoisocaproate level were decreased. Insulin treatments in subjects with type 2 diabetes had no effect on muscle mitochondrial protein synthesis and cytochrome C oxidase, a key enzyme for ATP production.

Type 2 diabetes is characterized by muscle insulin resistance. Nondiabetic first-degree relatives of type 2 diabetic patients have also been reported to have insulin resistance. A polygenic basis for pathogenesis of type 2 diabetes has been proposed. A gene expression profile was evaluated in the skeletal muscle of patients with type 2 diabetes while not on treatment for 2 weeks and after 10 days of intensive insulin treatment. Comparison of gene expression pattern with age-, sex-, and BMI-matched people with no family history of diabetes was performed using a microarray technique (Hu6800 arrays; Affymetrix, Santa Clara, CA). Only those gene transcripts showing ≥1.9-fold changes and an average difference in fluorescence intensity of ≥1,000 in all subjects are reported. Insulin sensitivity (SI) was measured using an intravenous glucose tolerance test. Of 6,451 genes surveyed, transcriptional patterns of 85 genes showed alterations in the diabetic patients after withdrawal of treatment, when compared with patterns in the nondiabetic control subjects. Insulin treatment reduced the difference in patterns between diabetic and nondiabetic control subjects (improved) in all but 11 gene transcripts, which included genes involved in structural and contractile functions, growth and tissue development, stress response, and energy metabolism. These improved transcripts included genes involved in insulin signaling, transcription factors, and mitochondrial maintenance. However, insulin treatment altered the transcription of 29 additional genes involved in signal transduction; structural and contractile functions; growth and tissue development; and protein, fat, and energy metabolism. Type 2 diabetic patients had elevated circulating insulin during the insulin-treated phase, although their blood glucose levels (98.8 ± 6.4 vs. 90.0 ± 2.9 mg/dl for diabetic vs. control) were similar to those of the control subjects. In contrast, after withdrawal of treatment, the diabetic patients had reduced SI and elevated blood glucose (224.0 ± 26.2 mg/dl), although their insulin levels were similar to those of the nondiabetic control subjects. This study identified several candidate genes for muscle insulin resistance, complications associated with poor glycemic control, and effects of insulin treatment in people with type 2 diabetes.

Cystic fibrosis (CF) patients are reported to experience chronic protein catabolism. Since diabetes or impaired glucose tolerance (IGT) is common in CF, we hypothesized that their protein catabolic state is related to reduced insulin secretion or reduced insulin action. A total of 12 clinically stable adult CF patients with abnormal glucose tolerance and 12 age-, sex-, and lean body mass-matched healthy control subjects underwent protein turnover studies using L-[1-(13)C]leucine, L-[(15)N]phenylalanine, and L-[(2)H(4)]tyrosine, with and without exogenous insulin infusion. In the baseline fasting state, protein metabolism was entirely normal in CF patients, with no evidence of increased protein catabolism. In contrast, striking abnormalities were seen in CF patients when insulin was infused, since they did not experience normal suppression of the appearance rates of leucine, phenylalanine, or tyrosine (indexes of protein breakdown). At an insulin concentration of 45 +/- 2 microU/ml, normal control subjects suppressed the leucine appearance rate by 19 +/- 5% (P0.01), ketoisocaproate appearance rate by 10 +/- 3% (P = 0.03), tyrosine appearance rate by 11 +/- 2% (P = 0.03), and phenylalanine appearance rate by 6 +/- 3% (P = 0.07). Phenylalanine conversion to tyrosine decreased by 22 +/- 7% (P = 0.03). At a similar insulin concentration of 44 +/- 3 microU/ml, normal suppression of amino acid appearance did not occur in CF. The leucine appearance rate decreased by 4 +/- 2% (P = 0.65), ketoisocaproate appearance rate by 1 +/- 2% (P = 0.94), tyrosine appearance rate by 0 +/- 6% (P = 0.56), phenylalanine appearance rate by 5 +/- 6% (P = 0.34), and phenylalanine conversion to tyrosine by 5 +/- 6% (P = 0.95). Poor suppression of the amino acid appearance rate in CF was not related to previously documented glucose tolerance status (IGT or CF-related diabetes without fasting hyperglycemia), fasting insulin levels, the acute insulin response, insulin sensitivity, cytokine or counterregulatory hormone levels, resting energy expenditure, caloric intake, pulmonary function, or clinical status. Protein synthesis was not significantly affected by insulin infusion in either normal control subjects or CF patients. In conclusion, clinically stable adult CF patients have normal indexes of protein breakdown and synthesis in the fasting state. In contrast, elevation of plasma insulin to physiological postprandial levels fails to normally suppress indexes of protein breakdown. It is therefore likely that inability to spare protein during the postprandial state is the cause of protein catabolism in these patients.

The contribution of the kidneys to postabsorptive endogenous glucose production is a matter of controversy. To assess whether this could relate to the use of various isotopical methods with different analytical performance capabilities, we measured glucose kinetics in 12 healthy subjects. Blood samples were taken from the femoral artery and the renal vein after 4 h of [6,6-2H2]glucose infusion (for gas chromatography [GC]/mass spectrometry [MS] analysis), and renal plasma flow was determined with paraaminohippurate. In addition, six subjects received uniformly labeled [13C]glucose (for GC/combustion/isotope ratio MS [IRMS]) and [3-3H]glucose (for counting of radioactive disintegrations). Arterial glucose concentrations (means +/- SD) were 4.2+/-0.1 mmol/l, and endogenous glucose production rates using [2H2]glucose were 2.2+/-0.1 mg x kg(-1) x min(-1) or 818+/-50 micromol/min. Dilution of [2H2]glucose across the kidney was 0.79+/-1.32%, and renal glucose production (RGP) rates were 27+/-72 micromol/min. In the six subjects receiving additional tracers, dilutions across the kidney were 2.83+/-0.72 and 0.54+/-1.20 (for [U-13C]glucose and [3-3H]glucose, respectively, the dilution with [U-13C] being higher than that with [2H2] (P = 0.007). Corresponding RGP values were 144+/-39 and 43+/-76 micromol/min for [U-13C] and [3-3H], respectively. In conclusion, we found that the highly sensitive [U-13C] GC/Combustion/IRMS technique showed consistent dilution of label across the kidney, whereas the less sensitive techniques gave some negative values and smaller RGP rates. Thus, depending on which technique is being used, a fivefold difference in calculated RGP values may be encountered. The methodological variability of our data suggests that extrapolation from regional renal measurements to the whole-body level should be perfumed with caution.

The celebrated Greek physician Aretaeus the Cappadocian some 1900 years ago described diabetes as a condition with “a melting down of the flesh and limbs into urine.” Remarkably, his observations are amazingly durable and accurate even by the standards of today with reference to type 1 diabetes. For example, insulin deprivation in type 1 diabetic patients causes a profound increase in catabolism, especially in skeletal muscle (1–4). Moreover, this net muscle protein catabolism is due to a net increase in protein breakdown rather than a decline in protein synthesis (1–4). In contrast, despite substantial alterations in glucose and lipid metabolism, the effect of type 2 diabetes on changes in protein metabolism is at best subtle, and results are inconsistent (5–8). A key difference is that in type 1 diabetic patients on insulin deprivation, muscle mass withers away (as demonstrated by profound cachexia in type 1 diabetic patients during the preinsulin era), whereas no such dramatic changes occur in type 2 diabetic patients with poor glycemic control. Withdrawal of treatment for 10 days in type 2 diabetic patients had little effect on amino acid levels or protein metabolism (8), although glucose metabolism is substantially altered; this may relate to differences in portal …