Hyperglycemia-induced apoptotic cell death in the mouse blastocyst is dependent on expression of p53

Metabolic stages, mitochondria and calcium in hypoxic/ischemic brain damage

Cerebral hypoxia/ischemia leads to mitochondrial dysfunction due to lack of oxygen leaving the glycolytic metabolism as a main pathway for ATP production. Inhibition of mitochondrial respiration thus triggers generation of lactate and hydrogen ions (H+), and furthermore dramatically reduces ATP generation leading to disregulation of cellular ion metabolism with subsequent intracellular calcium accumulation. Upon reperfusion, when mitochondrial dysfunction is (at least partially) reversed by restoring cerebral oxygen supply, bioenergetic metabolism recovers and brain cells are able to re-institute their normal ionic homeostatic mechanisms. However, the initial restoration of normal mitochondrial function may be only transient and followed by a secondary, delayed perturbation of mitochondrial respiratory performance seen as a decrease in cellular ATP levels and known as "secondary energy failure". There have been several mechanisms considered responsible for delayed post-ischemic mitochondrial failure, the mitochondrial permeability transition (MPT) being one that is considered important. Although the amount of calcium available during early reperfusion in vivo is limited, relative to the amount needed to trigger the MPT in vitro; the additional intracellular conditions (of acidosis, high phosphate, and low adenine nucleotideae levels) prevailing during reperfusion, favor MPT pore opening in vivo. Furthermore, the cellular redistribution and/or changes in the intracellular levels of pro-apoptotic proteins can alter mitochondrial function and initiate apoptotic cell death. Thus, mitochondria seem play an important role in orchestrating cell death mechanisms following hypoxia/ischemia. However, it is still not clear which are the key mechanisms that cause mitochondrial dysfunction and lead ultimately to cell death, and which have more secondary nature to brain damage acting as aggravating factors.

Metabolic changes in the glucose-induced apoptotic blastocyst suggest alterations in mitochondrial physiology

Mammalian preimplantation embryos experience a critical switch from an oxidative to a predominantly glycolytic metabolism. In this study, the change in nutrient metabolism between the 2-cell and blastocyst stages was followed by measuring single embryo concentrations of tricarboxylic acid (TCA) cycle and glycolytic metabolites with microfluorometric enzymatic cycling assays. When the normal values were established, further changes that occur as a result of the induction of apoptosis by exposure to high-glucose conditions were examined. From the 2-cell to the blastocyst stage, the embryos experienced an increase in TCA metabolites and a dramatic increase in fructose 1,6-bisphosphate (FBP). The high TCA metabolites may result from accumulation of substrate due to a slowing of TCA cycle metabolism as glycolysis predominates. Embryos exposed to elevated glucose conditions experienced significantly lower FBP, suggesting decreased glycolysis, significantly higher pyruvate, suggesting increased pyruvate uptake by the embryos in response to decreased glycolysis, and increased TCA metabolites, suggesting an inability to oxidize the pyruvate and a slowing of the TCA cycle. We speculate that the glycolytic changes lead to dysfunction of the outer mitochondrial membrane that results in the abnormal TCA metabolite pattern and triggers the apoptotic event.