Hypoxia and reoxygenation-induced injury of renal epithelial cells: effect of free radical scavengers

Contribution of reactive oxygen species to para-aminophenol toxicity in LLC-PK1 cells

para-aminophenol (PAP) causes nephrotoxicity by biochemical mechanisms that have not been fully elucidated. PAP can undergo enzymatic or non-enzymatic oxidation to form reactive intermediates. Using modulators of reactive oxygen species (ROS), the role of ROS in PAP toxicity in LLC-PK(1) cells was investigated. ROS formation was determined using a fluorescein derivative and viability using alamarBlue. Following treatment of cells with PAP, ROS formation occurred prior to loss of cell viability. Several modulators of ROS were used to identify the pathways involved in PAP toxicity. Viability was improved with catalase treatment, while viability was decreased when cells were treated with superoxide dismutase (SOD). Both catalase and SOD exert their effects outside of cells in the incubation medium, since there was no evidence of uptake of these enzymes in LLC-PK(1) cells. In cell-free incubations, hydrogen peroxide (H(2)O(2)) was produced when 0.5 mM PAP was included in the incubation medium. Further, SOD greatly increased and catalase greatly decreased H(2)O(2) production in these cell-free incubations. These data suggest that H(2)O(2) formed in the incubation medium contributes to loss of viability following PAP treatment. When cells were coincubated with 0.5 mM PAP and tiron, pyruvate, bathocuproine, 1, 10-phenanthroline, or dimethylthiourea (DMTU), ROS formation was decreased. However, there was minimal improvement in cell viability. Paradoxically, DMTU exacerbated PAP-induced loss of viability. These data suggest that ROS are generated in cells exposed to PAP but these species are not the predominant cause of cellular injury.

Protection of the kidney by Wen-Pi-Tang against ischemia-reperfusion injury

Electrophoretic and densitometric data revealed induction of apoptosis in the kidney due to experimentally induced ischemia-reperfusion injury. Such apoptosis in the kidney was reduced in rats given 62.5 or 125 mg/kg body wt./day Wen-Pi-Tang orally for 30 days prior to ischemia-reperfusion. An increase in the dose of Wen-Pi-Tang was associated with suppressed fragmentation of DNA, a ladder pattern of low-molecular-weight molecules, resulting in a beneficial effect on renal function.

Ameliorative effect of adenosine on hypoxia-reoxygenation injury in LLC-PK1, a porcine kidney cell line

We studied the effects of adenosine on injury caused by hypoxia and reoxygenation in LLC-PK1 cells. Lactate dehydrogenase and gamma-glutamyltranspeptidase were released from cells exposed to hypoxia for 6 hr and then reoxygenation for 1 hr. The addition of adenosine at 100 microM to the medium before hypoxia began significantly decreased enzyme leakage into medium during both hypoxia and reoxygenation. The adenosine A1-receptor agonist, R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA), at the concentration of 100 microM, did not affect enzyme release, but the adenosine A2-receptor agonist 2-p-[2-car-boxyethyl]phenethyl-amino-5'-N-ethylcarboxamido-adenosi ne hydrochloride (CGS 21680) at the concentration of 100 nM, suppressed the injury caused by hypoxia and reoxygenation. There were decreases in cAMP contents and ATP levels in LLC-PK1 cells injured by hypoxia and reoxygenation. Adenosine (100 microM) restored ATP levels in the cells during reoxygenation. With adenosine, the intracellular cAMP level was increased prominently during reoxygenation. These results suggest that adenosine protects LLC-PK1 cells from injury caused by hypoxia and reoxygenation by increasing the intracellular cAMP level via adenosine A2 receptor.

Effects of ischemia-reperfusion on individual cytochrome P450 isoforms in the rat kidney

Ischemia-reperfusion of organs such as the kidney produces reactive oxygen and free radical species in tissues and leads to injury of intracellular molecules critical to cell homeostasis. Ischemia-reperfusion affects the NADPH-dependent monooxygenase system including P450 system, which is also a source of reactive oxygen species. In this study, the effects of ischemia-reperfusion on monooxygenase activity and levels of individual P450 isoforms including CYP2C23, 4A2, and 4A8 in the rat kidney were investigated. Ischemia of the rat kidney for 30 min had little effect on lauric acid hydroxylation activity and levels of P450 isoforms but ischemia for 60 min significantly decreased lauric acid omega- and (omega-1)-hydroxylation activities and also decreased the levels of CYP2C23, 4A2, and 4A8. Reperfusion for 60 min after 30-min ischemia decreased the levels of CYP2C23 and 4A2 in the rat kidney although 30-min ischemia did not. Reperfusion for 240 min after 30-min or 60-min ischemia recovered the decreased levels of lauric acid hydroxylation activity and the levels of CYP2C23 and 4A2. Changes in the levels of monooxygenase activity and the levels of P450 isoforms in kidneys by ischemia-reperfusion are faster than those in the liver; it takes several hours for ischemia-reperfusion to affect the levels of monooxygenase activity and the levels of P450 in the rat liver. Our findings suggest that damage of P450 isoforms in the kidney by ischemia-reperfusion occurs by a mechanism different from that in the liver and that active oxygen or free radical species directly attack proteins.

Amelioration by cAMP of cephaloridine-induced injury in the porcine kidney cell line LLC-PK1

We investigated the effects of a phosphodiesterase inhibitor and dibutyryl cAMP (dBcAMP) on the cell injury induced by cephaloridine (CER) in an established renal epithelial cell LLC-PK1. CER increased the leakage of lactate dehydrogenase (LDH) from LLC-PK1 cells to the medium and the level of lipid peroxidation in the cells. 3-Isobutyl-1-methylxanthine, a phosphodiesterase inhibitor, increased cAMP content in LLC-PK1 cells and ameliorated the increase in LDH leakage induced by CER, dBcAMP reduced the cell injury induced by CER. Our results suggest that a signalling pathway of cAMP protects against CER-induced renal cell injury, which is probably due to generation of oxygen radicals.