Effects of glucose, Trolox-C, and glutathione disulphide on lipid peroxidation and cell death induced by oxidant stress in rat heart

Effects of fasting and insulin-induced hypoglycemia on brain cell membrane function and energy metabolism during hypoxia-ischemia in newborn piglets

This study was done to determine the effects of 12 h fasting-induced mild hypoglycemia (blood glucose 60 mg/dl) and insulin-induced moderate hypoglycemia (blood glucose 35 mg/dl) on brain cell membrane function and energy metabolism during hypoxia-ischemia in newborn piglets. Sixty-three ventilated piglets were divided into six groups; normoglycemic control (NC, n=8), fasting-induced mildly hypoglycemic control (FC, n=10), insulin-induced moderately hypoglycemic control (IC, n=10), normoglycemic/hypoxic-ischemic (NH, n=11), fasting-induced mildly hypoglycemic/hypoxic-ischemic (FH, n=12) and insulin-induced moderately hypoglycemic/hypoxic-ischemic (IH, n=12) group. Cerebral hypoxia-ischemia was induced by occlusion of bilateral common carotid arteries and simultaneous breathing with 8% oxygen for 30 min. The brain lactate level was elevated in NH group and this change was attenuated in FH and IH groups. The extent of cerebral lactic acidosis during hypoxic-ischemic insult showed significant positive correlation with blood glucose level (r=0.55, p<0.001). Cerebral Na+, K+-ATPase activity and concentrations of high-energy phosphate compounds were reduced in NH group and these changes were not ameliorated in FH or IH group. Cortical levels of conjugated dienes, measured as an index of lipid peroxidation of brain cell membrane, were significantly elevated in NH, FH and IH groups compared with NC, FC and IC groups and these increases were more profound in FH and IH with respect to NH. Blood glucose concentration showed significant inverse correlation with levels of conjugated dienes (r=-0.35, p<0.05). These findings suggest that, unlike in adults, mild or moderate hypoglycemia, regardless of methods of induction such as fasting or insulin-induced, during cerebral hypoxia-ischemia is not beneficial and may even be harmful in neonates.

Oxidative stress-induced perturbations of calcium homeostasis and cell death in cultured myocytes: role of extracellular calcium

The role of extracellular calcium in the process of oxidative stress-induced calcium overload and cell death was investigated in cultured neonatal rat myocytes. Oxidative stress was induced by addition of cumene hydroperoxide (CHPO), a toxic organic hydroperoxide, in combination with varying extracellular calcium concentrations (1. normal calcium buffer: 2.5 mM Ca2+, 2. low calcium buffer: 5 microM Ca2+, 3. zero calcium buffer: 2.5 mM EGTA, no CaC12). Intracellular free calcium ion concentration ([Ca2+]i) was measured with fura-2 using a spectrofluorometer. To study the toxicant-induced changes in [Ca2+]i in more detail, single cell imaging was performed using digital imaging fluorescence microscopy (DIFM). In control experiments (in the absence of CHPO, but under different extracellular Ca2+ conditions) the [Ca2+]i remained at the basal level and cell viability was preserved. Administration of CHPO (50 microM) to the myocyte cultures generated a sustained increase in [Ca2+]i followed by loss of cell viability. A low extracellular calcium concentration (5 microM), in the absence or presence of diltiazem (10 microM), induced a delay in the rise in [Ca2+]i but was not able to prevent the CHPO-induced calcium overload and cell necrosis. Addition of EGTA (2.5 mM) to the low calcium buffer resulted also in CHPO-induced cell death, although no increase in [Ca2+]i was observed. In normal and low calcium buffers, DIFM revealed that CHPO produced a temporally and spatially heterogeneous distribution of [Ca2+]i in a group of myocytes. So, in the presence of normal or low extracellular Ca2+, CHPO intoxication of cultured myocytes leads to an increase of [Ca2+]i prior to the onset of cell death. If extracellular Ca2+ is chelated by EGTA, CHPO also induces cell death which is not preceded by cellular calcium overload. Apparently a disturbance in the calcium homeostasis is not causally related with oxidative stress-induced myocardial cell death.

High concentrations of antioxidants may not improve defense against oxidative stress

It is often assumed that the oxygen radical defense could be further improved by higher concentration of antioxidants. But this has not been demonstrated over a wide range of concentrations. There are different types of oxygen radicals produced in the body and the antioxidant protection against them may not positively related to their concentrations. We report here that by using H(2)O(2) with Cu(2+) as an hydroxyl-radical generator in vitro, ascorbic acid shows no oxygen-radical absorbing capacity. We also found that the net hydroxyl-radical absorbing capacity of a water soluble alpha-tocopherol analogue (Trolox) and uric acid increases with concentration only when the concentration is lower than the normal value found for alpha-tocopherol and uric acid in human serum. At higher concentrations, the hydroxyl-radical absorbing capacity of the alpha-tocopherol analogue and uric acid decreases. The mechanism involved in the decrease of hydroxyl radical absorbance capacity of Trolox and uric acid at high concentration may be related to their reaction with hydroxyl radicals or other oxygen radicals produced in the presence of both H(2)O(2) and Cu(2+). This kind of reaction could lead to the formation of additional many Trolox or uric acid radicals at the same time. These results may be important not only in evaluating antioxidant activities of antioxidants in vitro but also in studying the potential efficiency of antioxidants in vivo in affecting oxidative stress status.