Metabolism of furazolidone: alternative pathways and modes of toxicity in different cell lines

1. The metabolism and cytotoxicity of the antimicrobial nitrofuran drug fur azolidone have been studied in Caco-2, HEp-2 and V79 cell lines. Free radic al production, metabolite pattern, formation of bound residues, inhibition of cellular replication and protection by the antioxidant glutathione were compared for the three cell lines. 2. All three cell lines produced the same nitro-anion radical with similar kinetics. Little further metabolic breakdown was observed in V79 cells, whe reas Caco-2 and HEp-2 cells showed extensive degradation of furazolidone, b ut with different end patterns. 3. Under hypoxic conditions, the colony-forming ability was extensively imp aired in HEp-2 cells whereas the other two cell lines were less affected, s uggesting that irreversible damage to DNA occurred prevalently in HEp-2 cel ls. In V79 cells the absence of oxygen caused a 25-fold increase in the for mation of protein-bound residues. 4. Brief exposure to furazolidone caused a 50% loss of endogenous glutathio ne in Caco-2 cells, but no loss could be detected in V79 and HEp-2 cells. C onsistently, when glutathione was depleted by buthionine-[S,R]-sulphoximine (BSO) and diethylmaleate (DEM) treatment, the viability of V79 and HEp-2 c ells was minimally affected by furazolidone, whereas that of Caco-2 cells w as substantially reduced. 5. It is concluded that the cytotoxicity of furazolidone in these cell line s can be exerted by a number of different mechanisms, possibly related to d ifferent metabolic pathways. The cytotoxicity of nitrofuran drugs, therefor e, cannot be ascribed to a single toxic intermediate, but in Caco-2 cells f urazolidone is extensively metabolized and detoxified by GSH, in V79 is onl y partially activated and then bound to proteins, whereas in HEp-2, once ac tivated, may react with DNA.