calpain-inhibitor-iii and aloxistatin

Genetic variation in the gene for a cytosolic cysteine protease, calpain-10, increases the susceptibility to type 2 diabetes apparently by altering levels of gene expression. In view of the importance of altered beta-cell function in the pathophysiology of type 2 diabetes, the present study was undertaken to define the effects on insulin secretion of exposing pancreatic islets to calpain inhibitors for 48 hours. Exposure of mouse islets to calpain inhibitors (ALLN, ALLM, E-64-d, MDL 18270, and PD147631) of different structure and mechanism of action for 48 hours reversibly suppresses glucose-induced insulin secretion by 40% to 80%. Exposure of islets to inhibitors of other proteases, ie, cathepsin B and proteasome, did not affect insulin secretion. The 48-hour incubation with calpain inhibitors also attenuates insulin secretory responses to the mitochondrial fuel alpha-ketoisocaproate (KIC). The same incubation also suppresses glucose metabolism and intracellular calcium ([Ca(2+)](i)) responses to glucose or KIC in islets. In summary, long-term inhibition of islet calpain activity attenuates insulin secretion possibly by limiting the rate of glucose metabolism. A reduction of calpain activity in islet could contribute to the development of beta-cell failure in type 2 diabetes thereby providing a link between genetic susceptibility to diabetes and the pathophysiologic manifestations of the disease.

Topics: Animals; Calcium; Calpain; Cell Separation; Cysteine Proteinase Inhibitors; Dipeptides; Energy Metabolism; Glucose; In Vitro Techniques; Insulin; Islets of Langerhans; Leucine; Mice; Mice, Inbred C57BL; Mitochondria; NADP; Oxidation-Reduction

Ca2+ is an important regulator of neurite elongation and growth cone movements but the mechanism(s) mediating these Ca(2+)-dependent effects is unclear. Since cytoskeletal proteins are rapidly degraded by Ca(2+)-dependent proteinases (calpains) in vitro and in vivo, we investigated whether Ca(2+)-induced pruning or regression of neuronal processes is mediated by calpains. Isolated hippocampal pyramidal-like neurons were cultured and the ability of the membrane-permeable calpain inhibitors ethyl(+)-(2S,3S)-3-[(S)-methyl-1-(3-methylbutylcarbamoyl)-butyl carbamoyl]-2 - oxiranecarboxylate (EST) and carbobenzoxyl-valyl-phenylalanyl-H (MDL 28170) to block the Ca2+ ionophore A23187-induced suppression in neurite outgrowth was investigated. Addition of 100 nM A23187 to the culture medium resulted in a retraction of dendrites without altering axonal elongation. The addition of 300 nM A23187 to the culture medium resulted in a significant decrease in the rate of axonal elongation as well as a retraction of dendritic processes. Administration of EST (5 or 20 microM) to the culture medium completely blocked the pruning effect of 100 nM A23187 on dendrites and of 300 nM A23187 on axons, while EST alone did not significantly affect neurite outgrowth rate. MDL 28170 (20 microM) showed the same effect as EST in preventing ionophore-induced pruning of dendrites and axons at 100 and 300 nM concentrations, respectively, of A23187. EST (20 microM) did not block the A23187-induced rise of [Ca2+]i as measured with fura-2. These results suggest that calpains play a role in Ca(2+)-induced pruning of neurites in isolated hippocampal pyramidal neurons.

Topics: Animals; Axons; Calcimycin; Calcium; Calpain; Cells, Cultured; Cysteine Proteinase Inhibitors; Dendrites; Dipeptides; Fetus; Hippocampus; Kinetics; Leucine; Neurites; Pyramidal Cells; Rats; Time Factors