The Antidiabetic Agent Sodium Tungstate Induces Abnormal Glycogen Accumulation in Renal Proximal Tubules from Diabetic IRS2-Knockout Mice.

The kidney is an insulin-sensitive organ involved in glucose homeostasis. One major effect of insulin is to induce glycogen storage in the liver and muscle. However, no significant glycogen stores are detected in normal kidneys, but diabetic subjects present a characteristic renal histopathological feature resulting from extensive glycogen deposition mostly in nonproximal tubules. The mechanism of renal glycogen accumulation is yet poorly understood. Here, we studied in situ glycogen accumulation in the kidney from diabetic IRS2-knockout mice and the effect of the insulin-mimetic agent sodium tungstate (NaW). IRS2-knockout mice displayed hyperglycemia and hyperinsulinemia. NaW only normalized glycemia. There was no evident morphological difference between kidneys from untreated wild-type (WT), NaW-treated WT, and untreated IRS2-knockout mice. However, NaW-treated IRS2-knockout mice showed tubular alterations resembling clear cells in the cortex, but not in the outer medulla, that were correlated with glycogen accumulation. Immunohistochemical detection of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase, mostly expressed by renal proximal tubules, showed that altered tubules were of proximal origin. Our preliminary study suggests that IRS2 differentially regulates glycogen accumulation in renal tubules and that NaW treatment in the context of IRS2 ablation induces abnormal glycogen accumulation in cortical proximal tubules.

Early Effect of Bariatric Surgery on the Circadian Rhythms of Adipokines in Morbidly Obese Women.

BACKGROUND: The circadian pattern of adipokines is blunted in obese subjects, and we tested the hypothesis that bariatric surgery could normalize the 24-hr pattern of adipokines. Therefore, this study was designed to examine the early impact of the newly designed sleeve gastrectomy with transit bipartition (SGTB) surgery on the circadian pattern of leptin, adiponectin, and resistin in morbidly obese subjects. METHODS: The study group included six morbidly obese women [body mass index (BMI) 41.3 ± 1.53 kg/m(2)] who underwent SGTB and four lean women (BMI 18.61 ± 0.92 kg/m(2)). Blood from all subjects was collected before and 3 months after bariatric surgery every 6 hr throughout the 24-hr period. The circadian pattern of leptin, adiponectin, and resistin was measured by enzyme-linked immunosorbent assay or Luminex techniques. RESULTS: Lean women exhibited rise of plasma leptin levels at nighttime, whereas obese women had an increase in the overall plasma leptin levels throughout the 24-hr period, lacking the physiological rise of nocturnal leptin levels compared to controls. Obese women had a decrease in 24-hr adiponectin levels and similar plasma resistin levels compared to controls. Three months after SGTB, obese women lost 16.0% (P < 0.005) of their initial body weight and had a decrease in overall 24-hr leptin levels. However, there was no recovery of the nocturnal rise in leptin levels 3 months after SGTB. The 24-hr adiponectin levels were still decreased after SGTB surgery compared to controls, while resistin levels were decreased only during night time after SGTB. CONCLUSIONS: These results suggested that SGTB is an efficient innovative procedure to rapidly decrease 24-hr leptin levels. However, after 3 months, SGTB was not enough to recover the physiological nocturnal rise of leptin levels present in lean subjects.

Preclinical and Clinical Studies for Sodium Tungstate: Application in Humans.

Diabetes is a complex metabolic disorder triggered by the deficient secretion of insulin by the pancreatic ß-cell or the resistance of peripheral tissues to the action of the hormone. Chronic hyperglycemia is the major consequence of this failure, and also the main cause of diabetic problems. Indeed, several clinical trials have agreed in that tight glycemic control is the best way to stop progression of the disease. Many anti-diabetic drugs for treatment of type 2 diabetes are commercially available, but no ideal normoglycemic agent has been developed yet. Moreover, weight gain is the most common side effect of many oral anti-diabetic agents and insulin, and increased weight has been shown to worsen glycemic control and increase the risk of diabetes progression. In this sense, the inorganic salt sodium tungstate (NaW) has been studied in different animal models of metabolic syndrome and diabetes, proving to have a potent effect on normalizing blood glucose levels and reducing body weight, without any hypoglycemic action. Although the liver has been studied as the main site of NaW action, positive effects have been also addressed in muscle, pancreas, brain, adipose tissue and intestine, explaining the effective anti-diabetic action of this salt. Here, we review NaW research to date in these different target organs. We believe that NaW deserves more attention, since all available anti-diabetic treatments remain suboptimal and new therapeutics are urgently needed.

Melatonin prevents mitochondrial dysfunction and insulin resistance in rat skeletal muscle.

Melatonin has a number of beneficial metabolic actions and reduced levels of melatonin may contribute to type 2 diabetes. The present study investigated the metabolic pathways involved in the effects of melatonin on mitochondrial function and insulin resistance in rat skeletal muscle. The effect of melatonin was tested both in vitro in isolated rats skeletal muscle cells and in vivo using pinealectomized rats (PNX). Insulin resistance was induced in vitro by treating primary rat skeletal muscle cells with palmitic acid for 24 hr. Insulin-stimulated glucose uptake was reduced by palmitic acid followed by decreased phosphorylation of AKT which was prevented my melatonin. Palmitic acid reduced mitochondrial respiration, genes involved in mitochondrial biogenesis and the levels of tricarboxylic acid cycle intermediates whereas melatonin counteracted all these parameters in insulin-resistant cells. Melatonin treatment increases CAMKII and p-CREB but had no effect on p-AMPK. Silencing of CREB protein by siRNA reduced mitochondrial respiration mimicking the effect of palmitic acid and prevented melatonin-induced increase in p-AKT in palmitic acid-treated cells. PNX rats exhibited mild glucose intolerance, decreased energy expenditure and decreased p-AKT, mitochondrial respiration, and p-CREB and PGC-1 alpha levels in skeletal muscle which were restored by melatonin treatment in PNX rats. In summary, we showed that melatonin could prevent mitochondrial dysfunction and insulin resistance via activation of CREB-PGC-1 alpha pathway. Thus, the present work shows that melatonin play an important role in skeletal muscle mitochondrial function which could explain some of the beneficial effects of melatonin in insulin resistance states.