Oxidant-induced alterations in glucose and phosphate transport in LLC-PK1 cells: mechanisms of injury

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

Oxidative Stress and DNA Damage Induced by Chromium in Liver and Kidney of Goldfish, Carassius auratus

Chromium (Cr) is an abundant element in the Earth’s crust. It exhibits various oxidation states, from divalent to hexavalent forms. Cr has diverse applications in various industrial processes and inadequate treatment of the industrial effluents leads to the contamination of the surrounding water resources. Hexavalent chromium (Cr (VI)) is the most toxic form, and its toxicity has been associated with oxidative stress. The present study was designed to investigate the toxic potential of Cr (VI) in fish. In this research, we investigated the role of oxidative stress in chromium-induced genotoxicity in the liver and kidney cells of goldfish, Carassius auratus. Goldfish were acclimatized to the laboratory conditions and exposed them to 5% and 10% of 96 hr-LC₅₀ (85.7 mg/L) of aqueous Cr (VI) in a continuous flow through system. Fish were sampled every 7 days for a period of 28 days to analyze the lipid hydroperoxides (LHP) levels and genotoxic potentials in the liver and kidney. LHP levels were analyzed by spectrophotometry while genotoxicity was assessed by single cell gel electrophoresis (comet) assay. LHP levels in the liver increased significantly at week 1, followed by a decrease. LHP levels in the kidney increased significantly at weeks 1, 2, and 3, and decreased at week 4 compared to the control. The percentage of DNA damage increased in both liver and kidney at both test concentrations. The results clearly indicate that Cr (VI) induces significant levels of DNA damage in liver and kidney cells of goldfish. The induced LHP levels in both organs were concentration-dependent and were directly correlated with the levels of DNA damage. The two tested Cr (VI) concentrations induced significant levels of oxidative stress in both organs, however the kidney appears to be more vulnerable and sensitive to Cr-induced toxicity than the liver.

Toxicity of ifosfamide and its metabolite chloroacetaldehyde in cultured renal tubule cells

Renal injury is a common side effect of the chemotherapeutic agent ifosfamide. Current evidence suggests that the ifosfamide metabolite chloroacetaldehyde may contribute to this nephrotoxicity. The present study examined the effects of ifosfamide and chloroacetaldehyde on rabbit proximal renal tubule cells in primary culture. The ability of the uroprotectant medication sodium 2-mercaptoethanesulfonate (mesna) to prevent chloroacetaldehyde-induced renal cell injury was also assessed. Chloroacetaldehyde (12.5-150 microM) produced dose-dependent declines in neutral red dye uptake, ATP levels, glutathione content, and cell growth. Coadministration of mesna prevented chloroacetaldehyde toxicity while pretreatment of cells with the glutathione-depleting agent buthionine sulfoximine enhanced the toxicity of chloroacetaldehyde. Ifosfamide (1000-10,000 microM) toxicity was detected only at concentrations of 4000 microM or greater. Analysis of media collected from ifosfamide-treated cell cultures revealed the presence of several ifosfamide metabolites, demonstrating that renal proximal tubule cells are capable of biotransforming this chemotherapeutic agent. This primary renal cell culture system should prove useful in studying the cause and prevention of ifosfamide nephrotoxicity.

Na/K-ATPase under oxidative stress: molecular mechanisms of injury

1. The authors compare oxidative injury to brain and kidney Na/K-ATPase using in vitro and in vivo approaches. The substrate dependence of dog kidney Na/K-ATPase was examined both before and after partial hydrogen peroxide modification. A computer simulation model was used for calculating kinetic parameters. 2. The substrate dependence curve for the unmodified endogenous enzyme displayed a typical curve with an intermediate plateau, adequately described by the sum of hyperbolic and sigmoidal components. 3. The modified enzyme demonstrated a dependent curve that closely approximates normal hyperbola. The estimated ATP K(m) value for the endogenous enzyme was about 85 microM; the Kh was equal to 800 microM. The maximal number of protomers interacting was 8. Following oxidative modification, the enzyme substrate dependence curve did not show a significant change in the maximal protomer rate Vm, while the K(m) was increased slightly and interprotomer interaction was abolished. 4. Na/K-ATPase from an ischemic gerbil brain showed a 22% decrease in specific activity. The maximal rate of ATP hydrolysis by an enzyme protomer changed slightly. but the sigmoidal component, characterizing the enzyme's ability to form oligomers was abolished completely. The K(m) value was almost unchanged, but the Hill coefficient fell to 1. These data show that Na/K-ATPase molecules isolated from the ischemic brain have lost the ability to interact with one another. 5. We suggest that the most important consequence of oxidative modification is Na/K-ATPase oligomeric structure formation and subsequent hydrolysis rate suppression.

Oxidative resistance of Na/K-ATPase

1. Oxidative modification of Na/K-ATPase from brain and kidney has been studied. Brain enzyme has been found to be more sensitive than kidney enzyme to inhibition by both H2O2 and NaOCl. 2. The inhibition of Na/K-ATPase correlates well with the decrease in a number of SH groups, suggesting that the latter belong mainly to ATPase protein and are essential for the enzyme activity. We suggest that the differences in the number, location, and accessibility of SH groups in Na/K-ATPase isozymes predict their oxidative stability. 3. The hydrophilic natural antioxidant carnosine, the hydrophobic natural antioxidant alpha-tocopherol, and the synthetic antioxidant ionol as well as the ferrous ion chelating agent deferoxamine were found to protect Na/K-ATPase from oxidation by different concentrations of H2O2. The data suggest that these antioxidants are effective due to their ability to neutralize or to prevent formation of hydroxyl radicals.

Epidermal growth factor accelerates recovery of LLC-PK1 cells following oxidant injury

In renal tubular epithelial cells, oxidant injury results in several metabolic alterations including ATP depletion, decreased Na+K+ATPase activity, and altered intracellular sodium and potassium content. To investigate the recovery of LLC-PK1 cells following oxidant injury and to determine if recovery can be accelerated, we induced oxidant stress in LLC-PK1 cells with 500 microM hydrogen peroxide for 60 min. Identical cohorts of oxidant-stressed cells were incubated in recovery medium without epidermal growth factor (EGF) or recovery medium containing 25 ng EGF per ml. ATP levels, Na+K+ATPase activity in whole cells, Na+K+ATPase activity in disrupted cells, and intracellular sodium and potassium ion content were determined at 0, 5, 24, 48, and 72 h following oxidant injury in each cohort of cells. In oxidant-stressed cells recovering in medium without EGF, ATP levels, Na+K+ATPase activity, and intracellular ion content improved but continued to remain substantially lower than control values at all time points following oxidant stress. In cells recovering in medium with EGF, ATP levels, Na+K+ATPase activity, and the intracellular potassium-to-sodium ratio were significantly higher at nearly all time points than values in cells recovering in medium alone. In cells recovering with added EGF, Na+K+ATPase activity had improved to control levels, whereas ATP levels and intracellular ion content approached control values by 72 h following oxidant stress. We conclude that oxidant-mediated ATP depletion, altered Na+K+ATPase activity, and intracellular ion content remain depressed for several d following oxidant stress and that EGF accelerated recovery of LLC-PK1 cells from oxidant injury.

Inorganic phosphate enhances phosphonucleotide concentrations in cultured fetal rat cortical neurons

Our laboratory has recently characterized saturable Na(+)-dependent P(i) import into cultured fetal rat cortical neurons and shown that a substantial fraction of the P(i) so accumulated is incorporated into ATP. We now report that the ATP, NADPH and intracellular free P(i) ([P(i)]i) concentrations of cultured fetal rat cortical neurons are dependent on the extracellular P(i) concentration ([P(i)]e). [ATP], [NADPH] and [P(i)]i display a hyperbolic dependence upon [P(i)]e, being significantly increased after incubation with [P(i)]e of > or = 10 microM, and maximal at > or = 500 microM. Increases in both [ATP] and [NADPH] are abolished in the absence of glucose. In the absence of extracellular P(i), both [ATP] and [P(i)]i decline over time. Our data suggest that in cultured fetal rat cortical neurons [P(i)]e has a direct effect on glucose utilization, stimulating both ATP and NADPH synthesis via glycolysis and the pentose phosphate pathway.