In Vitro Nimesulide Studies toward Understanding Idiosyncratic Hepatotoxicity: Diiminoquinone Formation and Conjugation

Abstract

Nimesulide is a nonsteroidal anti-inflammatory drug (NSAID) marketed in more than 50 countries. This drug has caused rare and idiosyncratic but severe hepatotoxicity. The mechanisms associated with and factors responsible for this toxicity remain unknown. One of the nimesulide metabolites identified in human urine is 4-amino-2-phenoxy-methanesulfonanilide (M1). In the current study, we demonstrate that M1 is a stable metabolite that is highly susceptible to facile oxidation by cytochrome P450 enzymes (P450s) to form a reactive diiminoquinone intermediate (M2). Direct detection of M2 was difficult by LC-MS. However, its formation was confirmed indirectly by identification of N-acetyl-cysteine (NAC) adducts of M2. The formation of diiminoquinone M2 was P450 mediated with 2C19 and 1A2 as the two principal P450 enzymes catalyzing M1 oxidation. M1 metabolism irreversibly inhibited 2C19 but activated 1A2 in a time-dependent manner. P450 2C19 exclusively mediated further metabolism of M1 to the amino hydroxynimesulide M3 and its diiminoquinone M4. Similar to M2, M4 is also reactive and can be observed indirectly as its NAC adduct. Nucleophilic addition to diiminoquinone M2 occurs with low regioselectivity, yielding three adducts (the peak area ratio 1:0.08:12). The three regioisomers have the same m/z for [M + H](+), presumably due to nucleophilic addition at the three possible electrophilic sites (C-3, -5, and -6 positions of the sulfonaniline ring). The primary adduct, R, was derived from the attack of the nucleophile at the C-5 position of the sulfonaniline ring and was determined by MS/MS and (1)H and (13)C NMR analyses. The structural assignments were confirmed by chemical synthesis of the adduct R. M2 demonstrated its electrophilic reactivity by selectively alkylating human serum albumin (HSA) at the only free thiol, Cys-34. This suggests the possibility that other proteins may undergo a similar conjugation to form irreversible adducts. Under oxidizing conditions in the presence of cumene hydroperoxide (CHP), the formation of M2 was enhanced, indicating that oxidative stress may accelerate the production of reactive diiminoquinone species (M2 and M4).

Hyaluronic acid–nimesulide conjugates as anticancer drugs against CD44-overexpressing HT-29 colorectal cancer in vitro and in vivo

“…67 In addition, NiNH 2 can completely suppress the uncoupling and NAD(P)H oxidant effects on mitochondria. 68,69 In this study, the nitro group of nimesulide was reduced to amine first and then grafted onto HA, suggesting that HA-nimesulide might reduce the liver toxicity effects of free nimesulide.…”

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Apparent Solubility and Dissolution Profile at Non-Sink Conditions as Quality Improvement Tools

“…The EMA has concluded that the benefits of these medicines outweigh their risks, but that there is a need to limit the duration of use to ensure that the risk of patients developing liver problems is kept to a minimum. Therefore the EMA has limited the use of systemic formulations (tablets, solutions, suppositories) of NIM-containing medicinal products to 15 days because of reports of severe hepatic adverse reactions (EMA, 2007;Li et al, 2009). …”