Nakamura H, Uetrecht J, Cribb A E, Miller M A, Zahid N, Hill J, Josephy P D, Grant D M, Spielberg S P
Department of Pediatrics, University of Toronto, Ontario, Canada.
J Pharmacol Exp Ther. 1995 Sep;274(3):1099-104.
Variation in the formation and disposition of the hydroxylamine of (SMX-HA) is thought to play an important role in the pathogenesis of sulfamethoxazole (SMX)-induced idiosyncratic adverse drug reactions. We hypothesized that, in analogy to carcinogenic arylamines, SMX-HA might be further converted to an electrophilic N-acetoxy metabolite which could play a role in mediating SMX toxicity. Accordingly, we chemically synthesized N-acetoxy-SMX, and examined the characteristics of its formation, metabolism, cytotoxicity and mutagenicity in human and bacterial test systems. The human arylamine N-acetyl-transferases, (NAT)1 and NAT2, were capable of converting SMX-HA to N-acetoxy-SMX. NAT1 and NAT2 possessed similar affinities for SMX-HA (apparent Km values of 650 and 520 microM, respectively), but the apparent maximal velocity of the NAT1-mediated acetylation was higher than that of NAT2. (1332 vs. 37 nmol/min/U of immunoreactive NAT protein). Human peripheral blood mononuclear cells 12,000 x g supernatant fractions converted N-acetoxy-SMX mainly back to SMX-HA, and also to a lesser extent to SMX, at clinically relevant concentrations. Similar pathways were observed in human hepatic cytosolic fractions. In a cytotoxicity assay, N-acetoxy-SMX was significantly more toxic to human peripheral blood mononuclear cells than SMX-HA (16.6 vs. 11.5% dead cells at a concentration of 300 microM). N-acetoxy-SMX was weakly mutagenic to the Salmonella typhimurium TA100 strain in the Ames test. These data suggest that the N-acetoxy metabolites of sulfonamides could potentially play a role in mediating sulfonamide idiosyncratic adverse drug reactions.
（磺胺甲恶唑 - 羟胺，SMX - HA）羟胺的形成和代谢差异被认为在磺胺甲恶唑（SMX）引起的特异质性药物不良反应的发病机制中起重要作用。我们推测，类似于致癌性芳基胺，SMX - HA可能进一步转化为亲电子的N - 乙酰氧基代谢物，其可能在介导SMX毒性中起作用。因此，我们化学合成了N - 乙酰氧基 - SMX，并在人和细菌测试系统中研究了其形成、代谢、细胞毒性和致突变性的特征。人芳基胺N - 乙酰基转移酶（NAT）1和NAT2能够将SMX - HA转化为N - 乙酰氧基 - SMX。NAT1和NAT2对SMX - HA具有相似的亲和力（表观Km值分别为650和520 microM），但NAT1介导的乙酰化的表观最大速度高于NAT2。（免疫反应性NAT蛋白为1332对37 nmol/min/U）。人外周血单核细胞12,000 x g上清液组分在临床相关浓度下将N - 乙酰氧基 - SMX主要转化回SMX - HA，也有较小程度转化为SMX。在人肝细胞溶质组分中观察到类似途径。在细胞毒性试验中，N - 乙酰氧基 - SMX对人外周血单核细胞的毒性明显高于SMX - HA（在300 microM浓度下死细胞分别为16.6%对11.5%）。在Ames试验中，N - 乙酰氧基 - SMX对鼠伤寒沙门氏菌TA100菌株有弱致突变性。这些数据表明，磺胺类药物的N - 乙酰氧基代谢物可能在介导磺胺类药物特异质性不良反应中起作用。
