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The activity and levels of SIRT1, which promotes cell survival in several models, are linked to glucose concentrations and cellular energy metabolism. The present study aimed to determine whether impaired Sirt1 activity is involved in the induction of apoptosis by the nutrientsensing hexosamine biosynthesis pathway (HBP). Pancreatic Nit-1, Rin-m5F, and Min6 b-cells were acutely treated at different doses and times with glucosamine, which enters and stimulates the HBP. Sirt1 levels were genetically modulated by retroviral infection. Expression levels, cellular localization, and activity of apoptosis-related markers were determined by qPCR, immunoblotting, and co-immunoprecipitation. Glucosamine treatment dose-and time dependently induced cell apoptosis in all cell lines studied. HBP stimulation time dependently modified SIRT1 protein levels, notably in the cytoplasm. This was concomitant with increased E2F1 binding to the c-myc promoter. In both NIT-1 and min6 b-cells, genetic knockdown of Sirt1 expression resulted in higher susceptibility to HBPstimulated apoptosis, whereas overexpression of Sirt1 had the opposite impact. These findings indicate that reduction of SIRT1 levels by hexosamines contributes to b-cell apoptosis. Methods to increase SIRT1 levels or activity could thus prevent the decrease in b-cell mass, notably that observed in type 2 diabetes.

SUMMARYThe administration of ammonium salts to free ventilated dogs causes an increase in the anaerobic consumption of glucose.Prior and simultaneous administration of the drug ornithine alpha ketoglutarate not only attenuates the rise in blood ammonia but also favourably affects these changes in brain metabolism.In patients with severe hepatic encephalopathy there is a fall in cerebral blood flow and in cerebral oxygen consumption (Fazekas, Ticktin, Ehrmantraut, and Alman, 1956;Posner and Plum, 1960). There is in addition an abnormality in the handling of glucose by the brain which probably precedes the reduction in oxygen utilization (Bianchi Porro, Maiolo, and Della Porta, 1969; James, Nashat, Sampson, Williams, and Gerassini, 1969 The drug ornithine alpha ketoglutarate has been widely used on the continent for a number of years for reducing blood ammonia levels in patients with encephalopathy.Ornithine is a base and alpha ketoglutarate is a diacid. When combined in the proportions 2:1 aneutral salt is obtained.The mechanism of this drug in lowering blood ammonia has recently been outlined by Michel, Oge, and Bertrand (1971). In the liver a molecule of ammonia combines with carbonic anhydride and ATP, carbamyl-phosphate being formed. This then combines with ornithine to form citrulline, which is transformed into arginine on receiving a second NH4+ group. Subsequently under the influence of arginase, urea and ornithine are formed. A total of two molecules of NH4+ have thus been transformed into urea.In the peripheral tissues, alpha ketoglutarate fixes an NH4+ molecule and transforms it into glutamic acid which by collecting a second NH4+ molecule produces glutamine.The fact that ornithine alpha ketoglutarate can lower blood ammonia concentrations in patients with liver disease has already been demonstrated by Michel et al (1971).The purpose of the present experiment was to determine in dogs the way in which ornithine alpha ketoglutarate1 could affect the response of cerebral metabolism to an infusion of an ammonium salt.Three parts of the experiment were planned. First, ammonium bicarbonate was given to dogs in a Ledsome, and Norman (1965) and glucose