Abstract: OBJECTIVE: Adiponutrin is a new transmembrane protein specifically expressed in adipose tissue. In obese subjects, short- or long-term calorie restriction diets were associated with a reduction in adiponutrin gene expression. Adiponut.rin mRNA level was previously shown to be negatively correlated with fasting glucose plasma levels and associated with insulin sensitivity of non-diabetic obese and non-obese subjects. The purpose of the present work was to get more insight into the regulation of adiponutrin gene expression by insulin and/or glucose using clamp studies and to examine its potential dysregulation in subjects with a deterioration of glucose homeostasis. METHODS: Adiponutrin gene expression was quantified by reverse transcriptase-quantitative PCR in s.c. adipose tissue of healthy lean subjects after an euglycemic hyperinsulinemic clamp (EGHI), a hyperglycemic euinsulinemic clamp, and a hyperglycemic hyperinsulinemic (HGHI) clamp. Adiponutrin gene expression was also analyzed in patients with different levels of insulin resistance. RESULTS: During EGHI, insulin infusion induced adiponutrin gene expression 8.4-fold (P = 0.008). Its expression was also induced by glucose infusion, although to a lesser extend (2.2-fold, P = 0.03). Infusion of both insulin and glucose (HGHI) had an additive effect on the adiponutrin expression (tenfold, P = 0.008). In a pathological context, adiponutrin gene was highly expressed in the adipose tissue of type-1 diabetic patients with chronic hyperglycemia compared with healthy subjects. Conversely, adiponutrin gene expression was significantly reduced in type-2 diabetics (P = 0.01), but remained moderately regulated in these patients after the EGHI clamp (2.5-fold increased). CONCLUSION: These results suggest a strong relationship between adiponutrin expression, insulin sensitivity, and glucose metabolism in human adipose tissue.

Abstract: A study was conducted to determine the relationship between ferritin and glycosylated isoforms of ferritin and insulin resistance in 69 HIV-infected men receiving HAART. Ferritin levels were significantly correlated with aspartate aminotransferase, alanine aminotransferase, bilirubin and with insulin resistance. The ferritin isoelectric focusing patterns of five insulin-resistant HIV-infected patients under HAART showed large amounts of hyperglycosylated isoforms, which was not found in 56 control subjects and 46 untreated HIV-1-infected patients.

Abstract: AIMS/HYPOTHESIS: Glucocorticoid treatments are associated with increased whole-body oxygen consumption. We hypothesised that an impairment of muscle energy metabolism can participate in this increased energy expenditure. METHODS: To investigate this possibility, we have studied muscle energetics of dexamethasone-treated rats (1.5 mg kg(-1) day(-1) for 6 days), in vivo by (31)P NMR spectroscopy. Results were compared with control and pair-fed (PF) rats before and after overnight fasting. RESULTS: Dexamethasone treatment resulted in decreased phosphocreatine (PCr) concentration and PCr:ATP ratio, increased ADP concentration and higher PCr to gamma-ATP flux but no change in beta-ATP to beta-ADP flux in gastrocnemius muscle. Neither 4 days of food restriction (PF rats) nor 24 h fasting affected high-energy phosphate metabolism. In dexamethasone-treated rats, there was an increase in plasma insulin and non-esterified fatty acid concentration. CONCLUSIONS/INTERPRETATION: We conclude that dexamethasone treatment altered resting in vivo skeletal muscle energy metabolism, by decreasing oxidative phosphorylation, producing ATP at the expense of PCr.

Abstract: PURPOSE OF REVIEW: It had been thought for a long time that thyroid hormones were the only ones to regulate energy production within mitochondria. Recent findings show that other hormones (steroids, leptin, insulin) regulate the efficiency of mitochondrial adenosine triphosphate production. Furthermore, a mismatch between oxygen consumption and energy intake may not be sufficient to understand body weight regulation. It appears that the efficiency of adenosine triphosphate production may play a role. RECENT FINDINGS: Over the past 2 years a series of results argued that glucocorticoids influence energy balance, the efficiency of adenosine triphosphate production, and are thermogenic. The sites for this effect are discussed, probably both the liver and muscle. Evidence of the genes involved in this regulation is substantial for muscle but remains to be studied in the liver. On the other hand, leptin could be a thermogenic hormone, especially in situations of calorie restriction. Finally, recent data and opinions suggest that mitochondria and adenosine triphosphate production could be central in the pathogenesis of both insulin resistance and beta cell deficiency. SUMMARY: The adaptation of mitochondrial adenosine triphosphate production appears to play a role in both diabetes and weight loss (voluntary and involuntary). Hormonal and nutritional manipulation could be a therapeutic possibility for weight management.

Abstract: The hyperinsulinemic euglycemic glucose clamp method is the gold standard for measuring insulin resistance. However it is complex, and simple indexes have been developed. Some of them are based on formulae that calculate the product or the addition of fasting plasma insulin and glucose values whereas others are based on their ratios. We calculated several simple indexes of insulin resistance and compared them to hyperinsulinemic euglycemic clamp data in 111 subjects with a wide range of insulin resistance. We showed that indexes using insulin and glucose ratios in their formulae are poorly correlated with clamp measurements and give false evaluations, particularly in glucose-intolerant and type 2 diabetic subjects. Thus, whatever the glucose profile of study subjects, we suggest the use of a simple index based on the product or the addition of fasting plasma insulin and glucose values instead of their ratios to obtain insulin resistance evaluations close to the hyperinsulinemic euglycemic clamp technique.

Abstract: Fasting-based index estimates of insulin sensitivity were compared with euglycemic hyperinsulinemic clamp (IS clamp) measurements in 148 subjects: normal controls (n = 46), and obese (n = 12), polycystic ovary syndrome (n = 16), first-degree relatives of type 2 diabetic (n = 17), impaired glucose tolerance (n = 28), and type 2 diabetic (n = 29) patients. The fasting-based indexes tested included log homeostasis model assessment (HOMA), the quantitative insulin sensitivity check index (QUICKI), the revised QUICKI, and a new revised QUICKI using fasting plasma glycerol. In the population studied, at 40 mU/m(2).min (n = 30) revised QUICKI (r = 0.86; P < 0.0001) and QUICKI-glycerol (r = 0.87; P < 0.0001) gave higher correlations with the IS clamp than QUICKI and log HOMA (r = 0.78 and r = -0.78; P < 0.001). For subjects tested at 75 mU/m(2).min (n = 118), comparable correlations were found for all indexes (r > 0.80; P < 0.0001). When studied in subgroups, revised QUICKI and QUICKI-glycerol give significantly higher correlations with the IS clamp than other indexes for lean control subjects studied at 40mU/m(2).min and impaired glucose tolerance subjects. We confirmed, in a large patient population with a wide range of insulin sensitivities, that no single test is superior in all groups of patients. However, QUICKI and revised QUICKI are good indexes that offer correlations similar to or higher than values obtained with log HOMA. Such indexes are simple tools to estimate insulin sensitivity appropriate for epidemiological studies.

Abstract: Polycystic ovary syndrome (PCOS), the main androgen disorder in women, has been suggested to be associated with a high risk of developing cardiovascular disease and type 2 diabetes. In many PCOS patients, overweight or central obesity is generally associated with increases in fasting insulin levels, insulin resistance, and glucose intolerance, and has been identified as a target for new therapeutic strategy, including early change in lifestyle. Early biochemical marker(s) for identifying at-risk patients will be useful for prevention studies. The main goal of the present study was to search for such tool(s). We investigated 16 nonobese PCOS women by performing euglycemic hyperinsulinemic clamp and measuring insulin levels during fasting and oral glucose tolerance test, as well as the serum concentrations of SHBG, leptin, and adiponectin, the newly identified adipose factors. Eight of the 16 patients had a steady-state glucose disposal rate less than 8.5 mg/kg.min, the lowest normal value for nonobese control women. These insulin-resistant patients had significant higher body mass index (BMI) and waist-to-hip ratio (WHR), and lower high-density lipoprotein cholesterol and SHBG levels. As expected, glucose disposal correlated negatively with BMI (P = 0.01), WHR (P = 0.01), and fasting insulin level (P = 0.003). On stepwise regression analysis, however, the glucose-to-insulin ratio (GIR) emerged as the strongest independent parameter to appraise insulin resistance (R(2) = 0.61). SHBG level correlated positively with GIR (P < 0.001) and negatively with BMI (P = 0.003) but did not correlate with either insulin response during the glucose tolerance test or plasma leptin and/or adiponectin levels. In contrast, BMI was the only independent predictive parameter of SHBG (P = 0.003, R(2) = 0.73). Interestingly, plasma adiponectin levels were positively associated with glucose disposal rate (P = 0.043) and negatively with WHR (P = 0.024), waist circumference being the best predictor of adiponectin level (P < 0.01). Leptin level correlated only with BMI (r = 0.62, P = 0.01). This study confirmed that insulin resistance, despite the lack of obesity as such, is clearly present in many PCOS women, and demonstrated that GIR is the best predictor for insulin resistance. It was also shown that adiponectin level is a good indicator of abdominal fat mass and is associated to insulin resistance. Finally, low SHBG levels in PCOS are intimately associated with BMI, suggesting that some signal(s) from the adipose tissue, independent of adiponectin and leptin, may regulate liver production of SHBG.

Abstract: Mitochondrial DNA depletion is a well established cause of severe liver failure in infancy. The autosomal inheritance of this quantitative mitochondrial DNA defect supports the involvement of a nuclear gene in the control of mitochondrial DNA level. We previously described a case of a 28-month-old child presenting with a progressive liver fibrosis due to a mitochondrial DNA depletion (85% at 12 months of age). As this syndrome was clinically liver-restricted, a liver transplant was initially discussed. We report the clinical, biochemical and molecular follow-up of this child, now 6 years old. The patient displayed a spontaneous gradual improvement of his liver function with continuous increment of clotting factor values since 32 months of age. A marked reduction of the previous extensive fibrosis was evidenced on a liver biopsy performed at 46 months of age associated with a dramatic decrease of the mitochondrial DNA depletion (35%). Consequently, an almost complete restoration of respiratory chain activities containing mitochondrial DNA-encoded subunits was observed. This is the first report of a revertant phenotype in liver mitochondrial DNA depletion syndrome.

Abstract: Evidence suggests that increased hydrolysis and/or uptake of triglyceride-rich lipoprotein particles in skeletal muscle can be involved in insulin resistance. We determined the steady state mRNA levels of the low-density lipoprotein-related receptor (LRP) and lipoprotein lipase (LPL) in skeletal muscle of eight healthy lean control subjects, eight type 2 diabetic patients and eight nondiabetic obese individuals. The regulation by insulin of LRP and LPL mRNA expression was also investigated in biopsies taken before and at the end of a 3 h euglycemic hyperinsulinemic clamp (insulinemia of about 1 nM). LRP mRNA was expressed in human skeletal muscle (1.3+/-0.1 amol/microg total RNA in control subjects). Type 2 diabetic patients, but not nondiabetic obese subjects, were characterized by a reduced expression of LRP (0.8+/-0.2 and 1.3+/-0.3 amol/microg total RNA in diabetic and obese patients, respectively; P<0.05 in diabetic vs. control subjects). Insulin infusion decreased LRP mRNA levels in muscle of the control subjects but not in muscle of type 2 diabetic and nondiabetic obese patients. Similar results were found when investigating the regulation of the expression of LPL. Taken together, these results did not support the hypothesis that a higher capacity for clearance or hydrolysis of circulating triglycerides in skeletal muscle is present during obesity- or type 2 diabetes-associated insulin resistance.

Abstract: We have investigated the role of protein kinase B (Akt) in the insulin-stimulated translocation of vesicles containing the insulin-responsive isoform of glucose transporter (GLUT4) to the plasma membrane of adipocytes. Previous reports have suggested that protein kinase B can bind to intracellular GLUT4 vesicles in an insulin-dependent manner, but the functional consequence of this translocation is not known. In this study we have artificially targeted constitutively active and kinase-inactive mutants of protein kinase B to intracellular GLUT4 vesicles by fusing them with the N-terminus of GLUT4 itself. We examined the effect of these mutants on the insulin-dependent translocation of the insulin-responsive amino peptidase IRAP (a bona fide GLUT4-vesicle-resident protein). A kinase-inactive protein kinase B targeted to GLUT4 vesicles was an extremely effective dominant-negative inhibitor of insulin-stimulated IRAP translocation to the plasma membrane. By contrast, a kinase-inactive protein kinase B expressed in the cytoplasm did not have an effect. The results suggest that protein kinase B has an important functional role at, or in the vicinity of, GLUT4 vesicles in the insulin-dependent translocation of those vesicles to the plasma membrane of adipocytes.