Application of quantitative structure-toxicity relationships for acute NSAID cytotoxicity in rat hepatocytes

Non-steroidal anti-inflammatory agents (NSAIDs) are widely used for pain relief. However, they have been associated with harmful and sometimes fatal side effects. Usually, the target organs are the GI tract and liver. In this study, we have investigated the physicochemical requirements of 21 NSAIDs for glucuronidation and cytotoxicity by quantitative structure-toxicity relationships (QSTRs) in isolated rat hepatocytes. Furthermore, we have investigated the contrast in physicochemical variables that correlated with NSAID-induced hepatocyte cytotoxicity when glucuronidation was inhibited with borneol. The competitive inhibition of hepatocyte p-nitrophenol glucuronidation by NSAIDs was determined by HPLC. Glucuronidation-inhibited hepatocytes were more susceptible to NSAID-induced cytotoxicity. Also, we found a parabolic correlation between lipophilicity and the inhibition of glucuronidation for a subset of NSAIDs. For NSAIDs with a benzoic acid moiety, cytotoxicity also correlated parabolically with lipophilicity, but correlated linearly with the HOMO-LUMO gap, and the first-order valence connectivity index. The cytotoxicity of NSAIDs with a phenylacetic acid (or propionic acid) substructure also correlated with lipophilicity, but not with the HOMO-LUMO gap. Our findings indicated that the inhibition of glucuronidation resulted in increased NSAID cytotoxicity, suggesting that acyl-glucuronide metabolites were acutely less cytotoxic. Also, comparative QSTRs revealed that benzoic acid NSAIDs may form cytotoxic radical metabolites (parameterized by the HOMO-LUMO gap) or alter mitochondrial respiration (parameterized by the connectivity index), whereas phenylacetic acid derived NSAIDs may form different cytotoxic metabolites, since they did not correlate with these parameters. In summary, we have used QSTRs as a tool to distinguish the cytotoxic mechanism of two groups of NSAIDs, which, if analyzed together as one group, did not reveal such mechanism-based differences.