Proapoptotic and antiapoptotic effects of hyperglycemia: role of insulin signaling.

Glucose toxicity is an important initiator of cardiovascular disease, contributing to the development of insulin resistance, impaired contractile function, abnormal energy metabolism, cardiomyocyte and endothelial cell death, coronary heart disease, and heart failure. High blood glucose can, however, paradoxically protect the heart against a variety of insults, including ischemia, hypoxia, and calcium overload. To provide information on the underlying basis of these divergent actions of high glucose, the present study examined the hypothesis that the adverse effects of high glucose are linked to impaired insulin signaling, leading to a reduction in the levels of cytoprotective factors, and that the beneficial effects of high glucose occur in the absence of insulin and result in an improvement in Akt signaling.

Mitochondrial DNA damage triggers mitochondrial-superoxide generation and apoptosis.

Recently, it has become apparent that mitochondrial DNA (mtDNA) damage can rapidly initiate apoptosis independent of mutations, although the mechanism involved remains unclear. To elucidate this mechanism, angiotensin II-mediated apoptosis was studied in cells that were transduced with a lentiviral vector to overexpress the DNA repair enzyme 8-oxoguanine glycosylase or were treated with inhibitors known to block angiotensin II-induced mtDNA damage. Cells exhibiting angiotensin II-induced mtDNA damage showed two phases of superoxide generation, the first derived from NAD(P)H oxidase and the second of mitochondrial origin, whereas cells prevented from experiencing mtDNA damage importantly exhibited only the first phase.

Insulin withdrawal induces apoptosis via a free radical-mediated mechanism.

Diabetes is characterized by chronic hyperglycemia as well as insulin deficiency or resistance. However, the majority of research has focused on the consequences of hyperglycemia in development of diabetic complications, whereas the effects of insulin deficiency or resistance, independent of hyperglycemia, have received little attention. Since insulin is a well known cytoprotective factor, we hypothesized that its removal could significantly impact cell survival.

Involvement of the mitochondrial permeability transition pore in angiotensin II-mediated apoptosis.

Background: Angiotensin II plays a central role in the development of congestive heart failure. Among its many actions linked to heart failure is the promotion of ventricular remodelling. Although the growth component of ventricular remodelling may initially be compensatory, the apoptotic component is associated with a decline in contractile function.

Contribution of the PI 3-kinase/Akt survival pathway toward osmotic preconditioning.

Osmolytes are rapidly lost from the ischemic heart, an effect thought to benefit the heart by reducing the osmotic load. However, the observation that chronic lowering of one of the prominent osmolytes, taurine, is more beneficial to the ischemic heart than acute taurine loss suggests that osmotic stress may benefit the ischemic heart through multiple mechanisms. The present study examines the possibility that chronic osmotic stress preconditions the heart in part by stimulating a cardioprotective, osmotic-linked signaling pathway.

Reversal of hyperglycemic preconditioning by angiotensin II: role of calcium transport.

Myocardial cell death is an important contributor to the development of diabetic cardiomyopathy. It has been proposed that diabetes-mediated upregulation of the renin-angiotensin system leads to oxidative stress, the trigger for cardiomyocyte death and contractile dysfunction. However, the adverse effect of ANG II on the diabetic heart may extend beyond the development of the cardiomyopathy.

Possible cause of taurine-deficient cardiomyopathy: potentiation of angiotensin II action.

Taurine, an amino acid that exhibits anti-angiotensin II and osmoregulatory activity, is found in very high concentration in the heart. When the intracellular content of taurine is dramatically reduced, the heart develops contractile defects and undergoes an eccentric form of hypertrophy. The development of myocyte hypertrophy has been largely attributed to angiotensin II, whose growth properties are antagonized by taurine.