Impaired Activation of Glucose Oxidation and NADPH Supply in Human Endothelial Cells Exposed to H2O2 in High-Glucose Medium

Abstract

The effects of glucose concentration on D-glucose oxidation and reduced nicotinamide adenine dinucleotide phosphate (NADPH) supply were studied during exposure of cultured human umbilical vein endothelial cells to hydrogen peroxide (H2O2). The activation of glucose oxidation via the pentose phosphate pathway (PPP), induced by exposure of cells to 200 mumol/l H2O2 for 1 h, was reduced by 50% (P < 0.01) in cells cultured for 5-7 days in 33 mmol/l D-glucose (HG) versus those cultured in 5.5 mmol/l D-glucose without (NG) or with (HR) 27.5 mmol/l D-raffinose. The intracellular NADPH content in HG cells, but not in NG or HR cells, was decreased by 42% (P < 0.01) by exposing cells to 200 mumol/l H2O2. The decrease in NADPH was dependent on D-glucose concentration in the medium and was prevented in glutathione (GSH)-depleted cells. The latter observation suggests that the decrease in NADPH is associated with activation of the GSH redox cycle. In the presence of 200 mumol/l H2O2, lactate release into the medium, NADH/NAD ratio, and phosphofructokinase activity in HG cells were 56, 53, and 68% greater, respectively, than in the NG group, which indicates that inhibition of glycolysis by H2O2 is less marked in the HG group compared with NG group. These results indicate that activation of the PPP was impaired in endothelial cells cultured under conditions of high-glucose and oxidative stress, resulting in a decreased supply of NADPH to various NADPH-dependent pathways, including the GSH redox cycle.

Antidyslipidemic and antioxidant activities of different fractions ofTerminalia arjuna stem bark

“…Hyperlipidemia may also induce abnormalities with oxidation of fatty acids leading to the formation of ketone bodies as well as making liver and muscle resistance to insulin which initiate and progress diabetes in patients (26). Furthermore, due to hyperglycaemia, increase in non enzymic glycosylation occurs, accompanied with glucose oxidation and these reactions are catalysed by Cu *z and Fe .2, resulting in formation of 02 and OH-radicals which further accelerates the risk of cardiac diseases in dyslipidemia (27).…”

Nitric oxide and vascular responses in Type I diabetes

“…Aldose reductase has been shown to be present in the vascular endothelial cells [111] and is the rate-limiting enzyme in the initial conversion of glucose to sorbitol. This process is dependent on nicotinamide-adenine dinucleotide phosphate (NADPH) and therefore results in an increase in its use [109,112]. Because NADPH is also an essential cofactor for NOS for the synthesis of NO, its depletion as a result of chronic hyperglycaemia could lead to a reduction in NO production.…”

The pathogenesis of transaldolase deficiency

“…Age-related immune dysfunctions including lymphocyte proliferation and macrophage phagocytosis correlate with impaired glucose metabolism via PPP (4). The PPP is important in host defense mechanisms in all tissues against oxidative stress (5), in embryogenesis/morphogenesis (6), neurulation (7), myelination (8), inflammation (9), lymphocyte activation (10,11), phagocytosis (4,12), radiation resistance of malignant tumors (13), and toxicity of high glucose concentrations in diabetes mellitus (14). Many of these processes are associated with apoptosis, a fundamental form of programmed cell death (PCD) (15).…”