Cisplatin nephrotoxicity in vivo and in vitro and the use of the immediate early genes c-Fos and c-Jun as early markers of toxicity
The aim of this thesis is to investigate the mechanism of cisplatin nephrotoxicity and to examine the responses of rat and human proximal tubular cell cultures to platinum analogues for potential early markers of toxicity. Nephrotoxicity was induced in male Sprague Dawley rats (N = 4 +/- standard deviation) and male C57BL/6 mice (N = 6 +/- standard deviation) with doses of 6 milligrams per kilogram and 10 milligrams per kilogram cisplatin administered by intraperitoneal injection respectively. These doses increased blood urea nitrogen and serum creatinine significantly. Male Spraque Dawley rats and C57BL/6 mice had control blood urea nitrogen day 5 and day 4 values of 8 +/- 1 micromoles per millilitre and 7 +/- 0.7 micromoles per millilitre respectively compared with values post cisplatin treatment of 36 +/- 4 micromoles per millilitre and 31 +/- 11.6 micromoles per millilitre. Histological analysis revealed significant damage to the proximal tubules, including loss of brush border membrane, cellular vacuolation and loss of cell-cell adhesion. The inhibition of aminopeptidase N and renal dipeptidase in vivo in male Sprague Dawley rats (N = 4 +/- standard deviation) or in rat and human proximal tubule cell cultures did not alter the toxicity of cisplatin (N = 5 +/- standard deviation). These data show that the dipeptidase enzymes are not implicated in the nephrotoxicity of cisplatin and contradict the publications of Hanigan and Townsend (2002) and Townsend et al (2003b), which hypothesise that dipeptidase activity is an integral part of a cisplatin biotransformation, pathway that is responsible for cisplatin nephrotoxicity. The inhibition of cysteine S-conjugate b-lyase activity in male Sprague Dawley rats (N = 4 +/- standard deviation) and C57BL/6 mice (N = 6 +/- standard deviation) did not affect the level of cisplatin toxicity. The inhibition of cysteine S-conjugate b-lyase in vitro significantly increased cisplatin toxicity in rat and human proximal tubule cell cultures at 24 hours (N = 5 +/- standard deviation). These data contradict the published data of Hanigan and Townsend (2002) and Townsend et al (2003b) in which cysteine S-conjugate b-lyase inhibition prevented cisplatin nepthrotoxicity in C57BL/6 mice and reduced toxicity in LLC-PK1 cell cultures.