Pro-oxidant effects of 6 -aminolevulinic acid (6 -ALA) on Chinese hamster ovary (CHO) cells

6-Aminolevulinic Acid (a-ALA) is a heme precursor accumulated in lead poisoning and acute intermittent porphyria. Although no single mechanism for lead toxicity has yet been defined, recent studies suggest at least some of the lead-induced damage may originate from d-ALA-induced oxidative stress. The present study was designed to test the hypothesis that a-ALA accumulation in Chinese hamster ovary (CHO) cells contributes to the cumulative oxidative challenge of lead poisoning as indicated by the oxidative stress parameters glutathione (GSH), glutathione disulfide (GSSG), malondialdehyde equivalents (MDA), and catalase (CAT). It will also examine the possibility that this oxidative challenge can be reversed by treatment with an antioxidant such as N-acetylcysteine (NAC). First in vitro administration of B-ALA to CHO cells was found to have a concentration-dependent inhibitory effect on colony formation and cell survival. NAC administration was shown to alleviate this inhibition in CHO survival. The oxidative status of CIHO cell cultures exposed to increasing concentrations of B-ALA was then examined. Decreases in GSH levels (P < 0.05) were observed in the a-ALA-treated cultures as compared to the controls, while GSSG and MDA levels were significantly increased in d-ALA-treated cells (P < 0.05). CAT activity was not significantly affected. NAC administration concurrent with B-ALA exposure resulted in GSH and GSSG levels similar to the control levels, while :no significant improvement in MDA was observed. These results indicate a state of oxidative stress and suggest that the a-ALAinduced inhibitory effect on CHO colony formation may be due to its pro-oxidant effect. To assess whether this oxidative challenge would induce antioxidant increases during extended exposure to S-ALA, CHO cells were exposed to 5 mM d-ALA for increasing time periods. The GSH and GSSG levels were measured and a rebound effect was observed after 12 h of B-ALA exposure.