55 The two key regulatory enzymes that PCI-32765 datasheet catalyze glycogenesis and glycogenolysis are glycogen synthase and glycogen phosphorylase. Glycogen synthase is the rate-limiting

enzyme in glycogen metabolism which catalyzes the transfer of glucose from UDP-glucose to glycogen in animal cells. Because of its central role in glucose homeostasis, glycogen synthase is responsive to endocrine factors, including insulin, glucagon, and catecholamine, as well as to metabolic status, such as the concentration of the allosteric activator glucose-6-phosphate (G6P). Further, the decreased glycogen content in diabetic disorder is due to the increased activity of glycogen phosphorylase and decreased activity of glycogen synthase.56 Glycogen phosphorylase, a rate-limiting enzyme of glycogenolysis, cleaves α (1, 4) linkage to remove glucose molecules from the glycogen. During diabetic conditions, the glycogen levels, glycogen synthase activity and selleck sensitivity to insulin signaling are lessened and glycogen phosphorylase activity is significantly amplified.57 Oral administration of fruit extract to diabetic rats regulated the activity of glycogen metabolizing enzymes thereby alleviated the altered glycogen content. The activities of citric acid cycle enzymes such as isocitrate dehydrogenase,

α-ketoglutarate dehydrogenase, succinate dehydrogenase and malate dehydrogenase in the liver and kidney of control and experimental groups of rats were significantly (p < 0.001) low in the liver and during kidney of STZ induced diabetic rats when compared with those in control rats. The activities of these enzymes were found to be significantly increased to near normalcy in MFE as well as gliclazide treated diabetic rats. The normal β cell, highly dependent on mitochondrial energy is the only cell, which increases its function (energy production) during hyperglycemia.

During diabetic condition, the activity of the enzyme glucokinase is found to be lessened due to defective insulin release. This in turn affects phosphorylation, the first step in glycolysis which is glucokinase dependent. 58 Thus, glucokinase mutations can directly impair glucose sensing, while mitochondrial DNA mutations can indirectly impair glucose sensing by reducing intracellular concentrations of ATP, oxidation of glucose derived acetyl residues increases in a time related and concentrations dependent manner when islet or purified β-cells are exposed to a rise in hexose concentration.59 It was proposed that the increased oxidations of glucose derived acetyl residues is attributed to Ca2+dependent activation of NAD-isocitrate dehydrogenase and α-ketoglutarate dehydrogenase. In pancreatic β cell, redox imbalance is reported to potentiate apoptosis.60 Apoptosis or programmed cell death has also been implicated in diabetic retinopathy and neuropathy due to abnormalities in mitochondrial function.