A comparison of antioxidant defense mechanisms of a pSV3.neo-transformed cetacean renal epithelial cell line to a continuous artiodactyl renal epithelial cell line

Cetaceans have been shown to bioaccumulate high levels of organochlorine compounds with concomitant adverse health and reproductive effects. Research has shown that the toxic effects are due, in part, to the generation of reactive oxygen species by these organochlorine chemicals. The objectives of this study were to determine basal levels of enzymes, which are known to detoxify reactive oxygen species in terrestrial mammals, in a virus-transformed cetacean renal epithelial cell line (DKN1) and compare them to levels in a continuous artiodactyl renal epithelial cell line (LLC-PK1).; DKN1 cells, previously known as CDK, were originally grown in an enriched medium consisting of several times the normal amount of L-glutamine. This level of L-glutamine was shown to be detrimental to cell growth except in the presence of the antioxidant, glutathione. Both cell lines, when grown in low levels of L-glutamine, exhibited decreased cell growth when exogenous glutathione and its synthetic precursor, N-acetylcysteine were added to culture medium.; Levels of known reactive oxygen scavengers—glutathione and the enzymes glutathione peroxidase, glutathione reductase, and catalase—were determined in DKN1 cells and compared to levels in LLC-PK₁ cells. All were found to be at least two fold lower in DKN1 cells, suggesting a decreased capacity for clearance of reactive oxygen species.; Both cell lines were then challenged with differing concentrations of prototypical oxidants—hydrogen peroxide and tert-butylhydroperoxide—and apoptosis levels were measured. Levels of apoptosis were higher in DKN1 cells treated with 1.0 mM hydrogen peroxide when compared to the LLC-PK₁ cells; however, even though DKN1 cells were shown to have lowered antioxidant defense systems, apoptosis levels in the dolphin cells treated with the organic peroxide tert-butylhydroperoxide were not statistically different from the untreated cells. While the absence of apoptotic markers in the DKN1 cells may be reflecting compensatory mechanisms for neutralizing peroxides, the cells may instead be bypassing the apoptotic pathway and be directly undergoing necrosis.