Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011860 (type 2 diabetes)
 57,723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In myotubes established from patients with type 2 diabetes (T2D), lipid oxidation and insulin-mediated glucose oxidation are reduced, whereas in myotubes from obese non-diabetic subjects, exposure to palmitate impairs insulin-mediated glucose oxidation. To determine the underlying mechanisms of these metabolic malfunctions, we studied mitochondrial respiration, uncoupled respiration and oxidative enzyme activities (citrate synthase (CS), 3-hydroxy-acyl-CoA-dehydrogenase activity (HAD)) before and after acute exposure to insulin and/or palmitate in myotubes established from healthy lean and obese subjects and T2D patients. Basal CS activity was lower (14%) in diabetic myotubes compared with myotubes from lean controls (P=0.03). Incubation with insulin (1 microM) for 4 h increased the CS activity (26-33%) in myotubes from both lean (P=0.02) and obese controls (P<0.001), but not from diabetic subjects. Co-incubation with palmitate (0.6 mM) for 4 h abolished the stimulatory effect of insulin on CS activity in non-diabetic myotubes. No differences were detected in mitochondrial respiration and HAD activity between myotubes from non-diabetic subjects and T2D patients, and none of these measures responded to high levels of insulin and/or palmitate. These results provide evidence for an intrinsic defect in CS activity, which may play a role in the pathogenesis of T2D. Moreover, the data suggest that insulin resistance at the CS level can be induced by exposure to high free fatty acid levels.
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PMID:Reduced insulin-mediated citrate synthase activity in cultured skeletal muscle cells from patients with type 2 diabetes: evidence for an intrinsic oxidative enzyme defect. 1589 66

AMPK is a key regulator of fat and carbohydrate metabolism. It has been postulated that defects in AMPK signaling could be responsible for some of the metabolic abnormalities of type 2 diabetes. In this study, we examined whether insulin-resistant obese Zucker rats have abnormalities in the AMPK pathway. We compared AMPK and ACC phosphorylation and the protein content of the upstream AMPK kinase LKB1 and the AMPK-regulated transcriptional coactivator PPARgamma coactivator-1 (PGC-1) in gastrocnemius of sedentary obese Zucker rats and sedentary lean Zucker rats. We also examined whether 7 wk of exercise training on a treadmill reversed abnormalities in the AMPK pathway in obese Zucker rats. In the obese rats, AMPK phosphorylation was reduced by 45% compared with lean rats. Protein expression of the AMPK kinase LKB1 was also reduced in the muscle from obese rats by 43%. In obese rats, phosphorylation of ACC and protein expression of PGC-1alpha, two AMPK-regulated proteins, tended to be reduced by 50 (P = 0.07) and 35% (P = 0.1), respectively. There were no differences in AMPKalpha1, -alpha2, -beta1, -beta2, and -gamma3 protein content between lean and obese rats. Training caused a 1.5-fold increase in AMPKalpha1 protein content in the obese rats, although there was no effect of training on AMPK phosphorylation and the other AMPK isoforms. Furthermore, training also significantly increased LKB1 and PGC-1alpha protein content 2.8- and 2.5-fold, respectively, in the obese rats. LKB1 protein strongly correlated with hexokinase II activity (r = 0.75, P = 0.001), citrate synthase activity (r = 0.54, P = 0.02), and PGC-1alpha protein content (r = 0.81, P < 0.001). In summary, obese insulin-resistant rodents have abnormalities in the LKB1-AMPK-PGC-1 pathway in muscle, and these abnormalities can be restored by training.
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PMID:LKB1-AMPK signaling in muscle from obese insulin-resistant Zucker rats and effects of training. 1635 71

Insulin resistance is associated with impaired skeletal muscle oxidation capacity and reduced mitochondrial number and function. Here, we report that adiponectin signaling regulates mitochondrial bioenergetics in skeletal muscle. Individuals with a family history of type 2 diabetes display skeletal muscle insulin resistance and mitochondrial dysfunction; adiponectin levels strongly correlate with mtDNA content. Knockout of the adiponectin gene in mice is associated with insulin resistance and low mitochondrial content and reduced mitochondrial enzyme activity in skeletal muscle. Adiponectin treatment of human myotubes in primary culture induces mitochondrial biogenesis, palmitate oxidation, and citrate synthase activity, and reduces the production of reactive oxygen species. The inhibition of adiponectin receptor expression by siRNA, or of AMPK by a pharmacological agent, blunts adiponectin induction of mitochondrial function. Our findings define a skeletal muscle pathway by which adiponectin increases mitochondrial number and function and exerts antidiabetic effects.
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PMID:Role of adiponectin in human skeletal muscle bioenergetics. 1681 34

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-gamma coactivator 1alpha, 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.
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PMID:Skeletal muscle mitochondrial functions, mitochondrial DNA copy numbers, and gene transcript profiles in type 2 diabetic and nondiabetic subjects at equal levels of low or high insulin and euglycemia. 1713 Apr 74

We tested the hypothesis of a lower respiratory capacity per mitochondrion in skeletal muscle of type 2 diabetic patients compared with obese subjects. Muscle biopsies obtained from 10 obese type 2 diabetic and 8 obese nondiabetic male subjects were used for assessment of 3-hydroxy-Acyl-CoA-dehydrogenase (HAD) and citrate synthase activity, uncoupling protein (UCP)3 content, oxidative stress measured as 4-hydroxy-2-nonenal (HNE), fiber type distribution, and respiration in isolated mitochondria. Respiration was normalized to citrate synthase activity (mitochondrial content) in isolated mitochondria. Maximal ADP-stimulated respiration (state 3) with pyruvate plus malate and respiration through the electron transport chain (ETC) were reduced in type 2 diabetic patients, and the proportion of type 2X fibers were higher in type 2 diabetic patients compared with obese subjects (all P < 0.05). There were no differences in respiration with palmitoyl-l-carnitine plus malate, citrate synthase activity, HAD activity, UCP3 content, or oxidative stress measured as HNE between the groups. In the whole group, state 3 respiration with pyruvate plus malate and respiration through ETC were negatively associated with A1C, and the proportion of type 2X fibers correlated with markers of insulin resistance (P < 0.05). In conclusion, we provide evidence for a functional impairment in mitochondrial respiration and increased amount of type 2X fibers in muscle of type 2 diabetic patients. These alterations may contribute to the development of type 2 diabetes in humans with obesity.
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PMID:Mitochondrial respiration is decreased in skeletal muscle of patients with type 2 diabetes. 1735 Nov 50

The objective of this study was to further establish and confirm the relationship of adipose mitochondrial biogenesis in diabetes/obesity and the effects of rosiglitazone (RSG), a peroxisome proliferator-activated receptor (PPAR) gamma agonist, by systematically analyzing mitochondrial gene expression and function in two mouse models of obesity and type 2 diabetes. Using microarray technology, adipose mitochondrial gene transcription was studied in db/db, high-fat diet-fed C57BL/6 (HFD) and respective control mice with or without RSG treatment. The findings were extended using mitochondrial staining, DNA quantification, and measurements of citrate synthase activity. In db/db and HFD mice, gene transcripts associated with mitochondrial ATP production, energy uncoupling, mitochondrial ribosomal proteins, outer and inner membrane translocases, and mitochondrial heat-shock proteins were decreased in abundance, compared with db/+ and standard-fat diet-fed control mice, respectively. RSG dose-dependently increased these transcripts in both db/db and HFD mice and induced transcription of mitochondrial structural proteins and cellular antioxidant enzymes responsible for removal of reactive oxygen species generated by increased mitochondrial activity. Transcription factors, including PPAR coactivator (PGC)-1beta, PGC-1alpha, estrogen-related receptor alpha, and PPARalpha, were suppressed in both models and induced by RSG. The effects of RSG on adipose mitochondrial genes were confirmed by quantitative RT-PCR and further supported by mitochondrial staining, mitochondrial DNA quantification, and citrate synthase activity. Adipose mitochondrial biogenesis was overwhelmingly suppressed in both mouse models of diabetes/obesity and globally induced by RSG. These findings suggest an important role of adipose mitochondria in diabetes/obesity and the potential for new treatment approaches targeting adipose mitochondria.
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PMID:Adipose mitochondrial biogenesis is suppressed in db/db and high-fat diet-fed mice and improved by rosiglitazone. 1745 54

The objective of this paper is to evaluate adaptations in hepatic mitochondrial protein mass, function and efficiency in a rat model of high-fat diet-induced obesity and insulin resistance that displays several correlates to human obesity. Adult male rats were fed a high-fat diet for 7 weeks. Mitochondrial state 3 and state 4 respiratory capacities were measured in liver homogenate and isolated mitochondria by using nicotinamide adenine dinucleotide, flavin adenine dinucleotide and lipid substrates. Mitochondrial efficiency was evaluated by measuring proton leak kinetics. Mitochondrial mass was assessed by ultrastructural observations and citrate synthase (CS) activity measurements. Mitochondrial oxidative damage and antioxidant defence were also considered by measuring lipid peroxidation, aconitase and superoxide dismutase (SOD) specific activity. Whole body metabolic characteristics were obtained by measuring 24-h oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory quotient (RQ) and nonprotein respiratory quotient (NPRQ), using indirect calorimetry with urinary nitrogen analysis. Whole body glucose homeostasis was assessed by measuring plasma insulin and glucose levels after a glucose load. Adult rats fed a high-fat diet for 7 weeks, exhibit not only obesity, insulin resistance and hepatic steatosis, but also reduced respiratory capacity and increased oxidative stress in liver mitochondria. Our present results indicate that alterations in the mitochondrial compartment induced by a high-fat diet are associated with the development of insulin resistance and ectopic fat storage in the liver. Our results thus fit in with the emerging idea that mitochondrial dysfunction can led to the development of metabolic diseases, such as obesity, type 2 diabetes mellitus and nonalcoholic steatohepatitis.
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PMID:Alterations in hepatic mitochondrial compartment in a model of obesity and insulin resistance. 1827 91

Obesity is a risk factor for type 2 diabetes in cats. The risk of developing diabetes is severalfold greater for male cats than for females, even after having been neutered early in life. The purpose of this study was to investigate the role of different metabolic pathways in the regulation of endogenous glucose production (EGP) during the fasted state considering these risk factors. A triple tracer protocol using (2)H(2)O, [U-(13)C(3)]propionate, and [3,4-(13)C(2)]glucose was applied in overnight-fasted cats (12 lean and 12 obese; equal sex distribution) fed three different diets. Compared with lean cats, obese cats had higher insulin (P < 0.001) but similar blood glucose concentrations. EGP was lower in obese cats (P < 0.001) due to lower glycogenolysis and gluconeogenesis (GNG; P < 0.03). Insulin, body mass index, and girth correlated negatively with EGP (P < 0.003). Female obese cats had approximately 1.5 times higher fluxes through phosphoenolpyruvate carboxykinase (P < 0.02) and citrate synthase (P < 0.05) than male obese cats. However, GNG was not higher because pyruvate cycling was increased 1.5-fold (P < 0.03). These results support the notion that fasted obese cats have lower hepatic EGP compared with lean cats and are still capable of maintaining fasting euglycemia, despite the well-documented existence of peripheral insulin resistance in obese cats. Our data further suggest that sex-related differences exist in the regulation of hepatic glucose metabolism in obese cats, suggesting that pyruvate cycling acts as a controlling mechanism to modulate EGP. Increased pyruvate cycling could therefore be an important factor in modulating the diabetes risk in female cats.
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PMID:The impact of obesity, sex, and diet on hepatic glucose production in cats. 1919 46

Using the hyperphagic, obese, Otsuka Long-Evans Tokushima Fatty (OLETF) rat, we sought to determine if progression to type 2 diabetes alters visceral white adipose tissue (WAT) mitochondrial content and if these changes are modified through prevention of type 2 diabetes with daily exercise. At 4 weeks of age, OLETF rats began voluntary wheel running (OLETF-EX) while additional OLETF rats (OLETF-SED) and Long-Evans Tokushima Otsuka (LETO-SED) rats served as obese and lean sedentary controls, respectively, for 13, 20 and 40 weeks of age (n = 6-8 for each group at each age). OLETF-SED animals displayed insulin resistance at 13 and 20 weeks and type 2 diabetes by 40 weeks. OLETF-SED animals gained significantly (P < 0.001) more weight and omental fat mass compared with OLETF-EX and LETO-SED. Markers of WAT mitochondrial protein content (cytochrome c, COXIV-subunit I, and citrate synthase activity) significantly increased (P < 0.05) from 13 to 40 weeks in the LETO-SED, but were significantly attenuated in the OLETF-SED rats. Daily exercise normalized WAT cytochrome c and COXIV-subunit I protein content in the OLETF-EX to the healthy LETO-SED animals. In conclusion, increases in omental WAT mitochondrial content between 20 and 40 weeks of age in LETO control animals are attenuated in the hyperphagic, obese OLETF rat. These alterations occurred in conjunction with the progression from insulin resistance to type 2 diabetes and were prevented with daily exercise. Reduced ability to increase WAT mitochondrial content does not appear to be a primary cause of insulin resistance, but may play a key role in the worsening of the disease condition.
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PMID:Changes in visceral adipose tissue mitochondrial content with type 2 diabetes and daily voluntary wheel running in OLETF rats. 1949 Dec 43

The temporal changes in skeletal muscle mitochondrial content and lipid metabolism that precede type 2 diabetes are largely unknown. Here we examined skeletal muscle mitochondrial fatty acid oxidation (MitoFAOX) and markers of mitochondrial gene expression and protein content in sedentary 20- and 40-wk-old hyperphagic, obese Otsuka Long-Evans Tokushima fatty (OLETF-SED) rats. Changes in OLETF-SED rats were compared with two groups of rats who maintained insulin sensitivity: age-matched OLETF rats given access to voluntary running wheels (OLETF-EX) and sedentary, nonobese Long-Evans Tokushima Otsuka (LETO-SED) rats. As expected, glucose tolerance tests revealed insulin resistance at 20 wk that progressed to type 2 diabetes at 40 wk in the OLETF-SED, whereas both the OLETF-EX and LETO-SED maintained whole body insulin sensitivity. At 40 wk, complete MitoFAOX (to CO(2)), beta-hydroxyacyl-CoA dehydrogenase activity, and citrate synthase activity did not differ between OLETF-SED and LETO-SED but were significantly (P < 0.05) higher in OLETF-EX compared with OLETF-SED rats. Genes controlling skeletal muscle MitoFAOX (PGC-1alpha, PPARdelta, mtTFA, cytochrome c) were not different between OLETF-SED and LETO-SED at any age. Compared with the OLETF-SED, the OLETF-EX rats had significantly (P < 0.05) higher skeletal muscle PGC-1alpha, cytochrome c, and mtTFA mRNA levels at 20 and 40 wk and PPARdelta at 40 wk; however, protein content for each of these markers did not differ between groups at 40 wk. Limited changes in skeletal muscle mitochondria were observed during the transition from insulin resistance to type 2 diabetes in the hyperphagic OLETF rat. However, diabetes prevention through increased physical activity appears to be mediated in part through maintenance of skeletal muscle mitochondrial function.
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PMID:Changes in skeletal muscle mitochondria in response to the development of type 2 diabetes or prevention by daily wheel running in hyperphagic OLETF rats. 2023 40


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