Comparison of the effects of griseofulvin and dihydropyridines on ferrochelatase activity and porphyrin accumulation in primary cultures of mouse and rat hepatocytes

Abstract

The ability of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), 3,5-diethoxycarbonyl-4-ethyl-1,4-dihydro-2,6-dimethyl pyridine (EDDC) and griseofulvin to induce porphyria in primary cultures of mouse and rat hepatocytes was determined. Exposure of mouse hepatocytes to DDC, EDDC or griseofulvin (5–100 μ m) for 4 days resulted in a marked inhibition of ferrochelatase activity (up to 95%). However, whereas exposure of rat hepatocytes to DDC or EDDC (5–100 μ m) for 4 days also resulted in marked inhibition of ferrochelatase activity (up to 96%), exposure to griseofulvin (5–100 μ m) had no effect. DDC, EDDC and griseofulvin induced porphyrin accumulation in both mouse and rat hepatocyte cultures. In mouse hepatocyte cultures exposed to each xenobiotic the porphyrin that accumulated was predominantly protoporphyrin. In rat hepatocyte cultures exposed to DDC or EDDC the porphyrin that accumulated was also predominantly protoporphyrin, whereas following exposure to griseofulvin it was coproporphyrin. Time course studies confirmed that in rat hepatocyte cultures exposed to griseofulvin (25 or 100 μ m) over a 4-day exposure period, ferrochelatase activity was not inhibited and coproporphyrin was always the predominant porphyrin accumulating (45–72% of total). Addition of 5-aminolaevulinic acid to mouse or rat hepatocyte cultures (10–1000 μ m) also resulted in marked accumulation of porphyrin but whereas uroporphyrin accumulated in mouse hepatocyte cultures, coproporphyrin accumulated in rat hepatocyte cultures. These studies demonstrated that the hepatic porphyrias produced by the dihydropyridines and griseofulvin can be modelled in vitro in primary cultures of hepatocytes. Furthermore, the species differences in sensitivity of mouse and rat hepatocyte cultures in vitro to inhibition of ferrochelatase activity by griseofulvin mirrors, and therefore probably explains, the species differences in porphyria observed in vivo.