Ifosfamide (IF) is an alkylating cytostatic with urotoxic (haemorrhagic cystitis) and nephrotoxic (Fanconi syndrome) side effects. Cyclophosphamide (CP), a structural isomer of IF shows urotoxic but no nephrotoxic side effects. The development of haemorrhagic cystitis during therapy with IF or CP can be prevented by the uroprotective drug sodium-2-mercaptoethanesulphonate (MESNA). However, even in the presence of MESNA, Fanconi syndrome may still develop after therapy with IF. Using the renal tubular cell line LLC-PK1, we investigated whether there is a protective effect of either MESNA or of its major metabolite DIMESNA, in combination with metabolites of IF or CP, on thymidine incorporation, uridine incorporation or total protein. DIMESNA, the dimer of MESNA, is the dominant form of the molecule in the circulation; the proximal tubular cell must convert this back to MESNA at the expense of glutathione, before it can exert its uroprotective action. We did not find a protective effect of DIMESNA under any of the experimental conditions tested. LLC-PK1 cells exposed to 3 mmol/l DIMESNA did not convert DIMESNA to MESNA. The toxic effect of the CP metabolite 4-OOH-CP was more pronounced in the presence of DIMESNA than in its absence. MESNA completely prevented the toxic effects of acrolein and of 4-OOH-CP. The toxic effects of 4-OOH-IF and of chloracetaldehyde, two major metabolites of IF were significantly reduced in the presence of MESNA. However, even at a 30-fold molar excess of MESNA over 4-OOH-IF thymidine incorporation remained reduced by 40% compared with controls, indicating incomplete protection of tubular cells against metabolites of IF. Similarly, the effect of chloracetaldehyde was not completely reversed by MESNA. Our data indicate that DIMESNA is not metabolized sufficiently by LLC-PK1 cells. Moreover, DIMESNA may deprive the cell of glutathione and thus enhance the toxicity of 4-OOH-CP. The finding that MESNA does not protect LLC-PK1 cells completely against the toxic effects of IF metabolites may explain the difference in nephrotoxicity of IF and CP. It also explains the development of tubular damage in the presence of MESNA and in the absence of haemorrhagic cystitis.
