Protection against nitrofurantoin-induced oxidative stress by coelenterazine analogues and their oxidation products in rat hepatocytes

Coelenterazine (3,7-dihydro-2-(p-hydroxybenzyl)-6-(p -hydroxyphenyl)-8-benz ylimidazolo [1,2-a]pyrazin-3-one) is a substrate for the bioluminescence re action in many marine animals, Recent work showed that CLZn, its synthetic analogue CLZm, and their common oxidation product coelenteramine (CLM) have strong antioxidative properties in acellular lipid peroxidation systems as well as in rat hepatocytes subjected to tert-butyl hydroperoxide (t-BHP). Here, we analyzed the ability of CLZm and several imidazolopyrazinone (IMPZ s) analogues to protect primary cultures of rat hepatocytes against a nitro furantoin (NF)-induced oxidative stress. Comparison of protection capabilit ies with reference antioxidants yielded the following ranking: CLZm >>> BHT > Trolox C (R) > prohucol > alpha -tocopherol. The comparison of CLZm with analogues lacking the phenol group in R-1 revealed no differences although the presence of this phenol conferred superior protection against t-BHP. C LM, as well as its methoxylated analogue mCLM which lacks chain-breaking pr operties, were equally potent in preventing cellular damage caused by NF. m CLM and alpha -naphthoflavone, an inhibitor of cytochrome P450 (CYP450) IAI , similarly protected cells against NF-induced mortality and also equally i nhibited EROD activity in methylcholanthrene-induced hepatocytes. The inhib ition of EROD by CLZm and CLM was less pronounced. We suggest that the exte nt of protection conferred by IMPZs against NF-toxicity reflects both the o ccurrence of antioxidative properties detoxifying ROS produced within cells and inhibitory actions on CYP450 isoforms involved in the bioreduction of NF.