Cytotoxic effects of sublethal concentrations of malachite green in isolated hepatocytes from rainbow trout (Oncorhynchus mykiss).

The fish therapeutic dye malachite green (N-[4-[bis]4-(dimethylamino)phenyl[phenyl]-methylene]) was tested for sublethal cytotoxic effects at concentrations of 0, 0.01, 0.1 and 1 mg/litre. Isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) were used to evaluate its cytotoxicity in a subcellular system and compare in vitro effects with those of in vivo experiments. Whereas conventional viability tests [trypan blue exclusion, lactate dehydrogenase (LDH) release]failed to detect any acute toxic effect by malachite green exposure, electron microscopy revealed time- and dose-dependent responses of isolated hepatocytes with first reactions after 1-day exposure to 0.01 mg/litre. Whereas hepatocellular nuclei took a more irregular shape, cytoplasmic changes comprised an increase in heterogeneity of mitochondrial shape, closer association of mitochondria with cisternae of the rough endoplasmic reticulum (RER), fractionation, dilation and vesiculation of RER, formation of cytoplasmic membrane whorls, glycogen bodies and induction of myelinated bodies and cytoplasmic vacuoles. In agreement with conclusions drawn from in vivo experiments, in vitro data provided evidence for nuclei and mitochondria as the major cellular targets of malachite green in both fish and mammals.