Hypothalamic AMP-Activated Protein Kinase Regulates Biphasic Insulin Secretion from Pancreatic ß Cells during Fasting and in Type 2 Diabetes.

Glucose-stimulated insulin secretion (GSIS) by pancreatic ß cells is biphasic. However, the physiological significance of biphasic GSIS and its relationship to diabetes are not yet fully understood. This study demonstrated that impaired first-phase GSIS follows fasting, leading to increased blood glucose levels and brain glucose distribution in humans. Animal experiments to determine a possible network between the brain and ß cells revealed that fasting-dependent hyperactivation of AMP-activated protein kinase in the hypothalamus inhibited first-phase GSIS by stimulating the ß-adrenergic pancreatic nerve. Furthermore, abnormal excitability of this brain-ß cell neural axis was involved in diabetes-related impairment of first-phase GSIS in diabetic animals. Finally, pancreatic denervation improved first-phase GSIS and glucose tolerance and ameliorated severe diabetes by preventing ß cell loss in diabetic animals. These results indicate that impaired first-phase GSIS is critical for brain distribution of dietary glucose after fasting. Furthermore, ß cells in individuals with diabetes mistakenly sense that they are under conditions that mimic prolonged fasting. The present study provides additional insight into both ß cell physiology and the pathogenesis of ß cell dysfunction in type 2 diabetes.

1-Methylnicotinamide ameliorates lipotoxicity-induced oxidative stress and cell death in kidney proximal tubular cells.

Free fatty acid-bound albumin (FFA-albumin)-related oxidative stress is involved in the pathogenesis of proximal tubular cell (PTC) damage and subsequent renal dysfunction in patients with refractory proteinuria. Nicotinamide adenine dinucleotide (NAD) metabolism has recently been focused on as a novel therapeutic target for several modern diseases, including diabetes. This study was designed to identify a novel molecule in NAD metabolism to protect PTCs from lipotoxicity-related oxidative stress. Among 19 candidate enzymes involved in mammalian NAD metabolism, the mRNA expression level of nicotinamide n-methyltransferase (NNMT) was significantly increased in both the kidneys of FFA-albumin-overloaded mice and cultured PTCs stimulated with palmitate-albumin. Knockdown of NNMT exacerbated palmitate-albumin-induced cell death in cultured PTCs, whereas overexpression of NNMT inhibited it. Intracellular concentration of 1-Methylnicotinamide (1-MNA), a metabolite of NNMT, increased and decreased in cultured NNMT-overexpressing and -knockdown PTCs, respectively. Treatment with 1-MNA inhibited palmitate-albumin-induced mitochondrial reactive oxygen species generation and cell death in cultured PTCs. Furthermore, oral administration of 1-MNA ameliorated oxidative stress, apoptosis, necrosis, inflammation, and fibrosis in the kidneys of FFA-albumin-overloaded mice. In conclusion, NNMT-derived 1-MNA can reduce lipotoxicity-mediated oxidative stress and cell damage in PTCs. Supplementation of 1-MNA may have potential as a new therapy in patients with refractory proteinuria.

Altered unfolded protein response is implicated in the age-related exacerbation of proteinuria-induced proximal tubular cell damage.

Aging is a dominant risk factor for end-stage renal disease. We analyzed the mechanism involved in age-related exacerbation of proteinuria-induced proximal tubular cell (PTC) damage by focusing on endoplasmic reticulum-related unfolded protein response (UPR). After equal-degree induction of proteinuria in 24-month-old (aged) and 3-month-old (young) mice by intraperitoneal free fatty acid-bound albumin overload, tubulointerstitial lesions were more severe in aged than in young mice. In aged PTCs, proteinuria-induced cell-adaptive UPR resulting from induction of the molecular chaperone BiP was significantly suppressed, whereas proapoptotic UPR with CHOP overexpression was enhanced. Treatment with the exogenous molecular chaperone tauroursodeoxycholic acid (TUDCA) ameliorated proteinuria-induced tubulointerstitial lesions and PTC apoptosis in aged mice. Among the three UPR branches, alterations in the inositol-requiring 1α (IRE1α) pathway, but not the activating transcription factor 6 or PERK pathway, were associated with impaired BiP induction in aged kidneys. Moreover, siRNA-mediated suppression of BiP and IRE1α exacerbated free fatty acid-bound albumin-induced apoptosis in cultured PTCs, whereas siRNA-mediated CHOP suppression ameliorated apoptosis. Finally, proteinuria-induced BiP induction in PTCs was diminished in kidney specimens from elderly patients. These results indicate that maladaptive UPRs are involved in proteinuria-induced tubulointerstitial lesions exacerbation in aged kidneys, and that supplementation of chaperones may be used to treat elderly patients with persistent proteinuria. These results should improve understanding of cell vulnerability in aged kidneys.

Angiotensin II type 1 receptor antagonist prevents hepatic carcinoma in rats with nonalcoholic steatohepatitis.

BACKGROUND: Angiotensin II type 1 receptor blockers (ARBs) have been reported to attenuate hepatic fibrosis in non-alcoholic steatohepatitis (NASH). However, it is uncertain whether ARBs prevent hepatocarcinogenesis in NASH even after hepatic fibrosis has developed. METHODS: Male Wistar rats were fed with a choline-deficient, L-amino acid-defined (CDAA) diet for 24 weeks, and then fed with the CDAA diet with telmisartan (2 mg/kg/day), a novel ARB, or vehicle for another 24 weeks. The liver histology and the expression of genes and proteins related to angiogenesis were investigated. RESULTS: The 24-week CDAA diet induced liver cirrhosis. The 48-week CDAA diet exacerbated liver cirrhosis, and developed hepatocellular carcinoma (HCC) in 54.6 % of the rats concurrently with increases of hypoxia-inducible factor-1α (HIF-1α) protein and vascular endothelial growth factor (VEGF) mRNA, which are potent angiogenic factors in the liver. Telmisartan inhibited hepatic fibrosis and preneoplastic lesions and prevented the development of HCC along with inducing decreases in HIF-1α protein and VEGF mRNA. CONCLUSIONS: These data indicated that telmisartan may prevent hepatocarcinogenesis through the inhibition of hepatic angiogenesis even after liver cirrhosis has been established.

Elevated serum levels of interleukin-18 in patients with overt diabetic nephropathy: effects of miglitol.

BACKGROUND: Interleukin-18 (IL-18), a pro-inflammatory cytokine, is a predictor of cardiovascular and renal disease in diabetic patients. Postprandial hyperglycemia is one of the important factors contributing to an increase in the circulating pro-inflammatory cytokine levels. This study investigated the effect of miglitol, an α-glucosidase inhibitor, on postprandial hyperglycemia and IL-18 levels in diabetic patients with nephropathy. METHODS: Fifteen Japanese diabetic patients with persistent proteinuria and preserved renal function were recruited. The patients received 50 mg miglitol thrice daily after the baseline examinations and were followed up for 12 weeks. A meal tolerance test was performed on eight patients at baseline and week 12. The fasting miglitol concentration was measured in seven patients just before the meal tolerance test. RESULTS: There were no changes in the body weight, blood pressure, liver and renal function, and proteinuria from baseline to week 12. However, the levels of glycated hemoglobin and interleukin 18 significantly decreased from baseline to week 12. During the meal tolerance test, plasma glucose was significantly decreased 60 min after treatment with miglitol, whereas the serum concentration of insulin was not changed. Fasting and postprandial levels of IL-18 were significantly decreased from baseline to week 12. Serum miglitol concentrations showed a significantly negative correlation with eGFR (r = -0.82, p = 0.02). However, the serum miglitol concentrations did not changed during the course of this study. CONCLUSION: Miglitol improved postprandial hyperglycemia and reduced serum IL-18 levels in patients with stage 3 diabetic nephropathy. Miglitol may therefore prevent atherosclerotic diseases and diabetic micro-vascular complications through decreasing glucose swings and/or the circulating IL-18 level.