Lipid peroxidation and the expressional regulation of the heat-shock response during ischemia-reperfusion of rat kidney

Because of the continuing shortage of donor organs, 'marginal kidneys' are increasingly being used. The purpose of our experiments was to characterize the extent of lipid peroxidation after ischemia-reperfusion (IR) injury in rat kidney, to analyze the expressional regulation of the heat-shock respo nse and now to discuss the clinical application of these results. After isc hemia, xanthine oxidase (XO) is thought to be the main oxygen radical-gener ating system and malondialdehyde (MDA) is considered to be a marker of LPO. In young rats (10 weeks) a unilateral warm ischemia of 40 and 60 min durat ion with subsequent reperfusion up to 1 h was conducted. Beside the 'footpr ints' of oxidative stress, the cytosolic antioxidative capacity, expressed as superoxide anion (SOA) scavenging capacity, was investigated. There was only a moderate and transient increase of renal MDA 5 and 10 min after the onset of reoxygenation (133.57/70.67 and 97.84/91.57 vs. 49.47 nmol/g wet w eight (ww) in preischemic controls). ATP breakdown (to 83/65 from 2,947 nmo l/g ww) with consecutive accumulation of hypoxanthine (up to 1,105 nmol/g w w) at the end of the ischemic period and the subsequent rapid decline of hy poxanthine by XO during reperfusion were used for an assessment of the SOA- generating capacity of these kidneys. Only 1/25-1/50 of the kidney cytosol was able to scavenge the whole amount of SOA generated by the total XO acti vity of rat kidney. Thus, it could be analytically and stoichiometrically s hown that after IR there is only a moderate oxidative stress in kidneys of young rats; this is due to their high SOA-scavenging capacity compared to t heir SOA-generating ability. We investigated the time course of HSP70-1 and -2 mRNA expression and its relation to cellular ATP levels in renal cortex after different periods of unilateral warm renal ischemia (10-60 min) and reperfusion (up to 60 min) in 10-week-old male Wistar rats, since IR is kno wn to cause induction of both genes. Immediately after ischemia there was a significant induction of both HSP70i genes. While HSP70-1 expression const antly increased (up to 4-fold) during reperfusion, even to a higher extent with prolongation of ischemia, HSP70-2 mRNA - generally being expressed on a far lower level than HSP70-1 mRNA - was strongly induced (3-fold) during reperfusion only after brief periods (10 min) of ischemia. Cellular AIP lev els rapidly dropped down to 5% with ischemia and the pattern of recovery du ring reperfusion significantly depended on the duration of the ischemic per iod thus showing a good relation to the heat-shock (protein) gene expressio n, We conclude that the HSP70-2 is the more sensitive gene with a lower thr eshold activation by mild injury, while the HSP70-1 gene mediates the big r esponse of HSP induction after severe injury, Thus, the measurement of the cytosolic antioxidative capacity and the differential expression of HSP70-1 and -2 mRNA could be promising clinical tools to assess the donor viabilit y, Copyright (C) 2000 S. Karger AG, Basel.