Yang Shaojun, Jan Yi-Hua, Mishin Vladimir, Richardson Jason R, Hossain Muhammad M, Heindel Ned D, Heck Diane E, Laskin Debra L, Laskin Jeffrey D
Department of Environmental and Occupational Medicine, Rutgers Robert Wood Johnson Medical School (S.Y., Y.-H.J., J.R.R., M.H.H., J.D.L.) and Department of Pharmacology and Toxicology, Rutgers University, Piscataway, New Jersey (V.M., D.L.L.); Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania (N.D.H.); and Department of Environmental Health Science, New York Medical College, Valhalla, New York (D.E.H.).
Department of Environmental and Occupational Medicine, Rutgers Robert Wood Johnson Medical School (S.Y., Y.-H.J., J.R.R., M.H.H., J.D.L.) and Department of Pharmacology and Toxicology, Rutgers University, Piscataway, New Jersey (V.M., D.L.L.); Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania (N.D.H.); and Department of Environmental Health Science, New York Medical College, Valhalla, New York (D.E.H.)
J Pharmacol Exp Ther. 2015 Mar;352(3):529-40. doi: 10.1124/jpet.114.221572. Epub 2014 Dec 30.
Sepiapterin reductase (SPR) catalyzes the reduction of sepiapterin to dihydrobiopterin (BH2), the precursor for tetrahydrobiopterin (BH4), a cofactor critical for nitric oxide biosynthesis and alkylglycerol and aromatic amino acid metabolism. SPR also mediates chemical redox cycling, catalyzing one-electron reduction of redox-active chemicals, including quinones and bipyridinium herbicides (e.g., menadione, 9,10-phenanthrenequinone, and diquat); rapid reaction of the reduced radicals with molecular oxygen generates reactive oxygen species (ROS). Using recombinant human SPR, sulfonamide- and sulfonylurea-based sulfa drugs were found to be potent noncompetitive inhibitors of both sepiapterin reduction and redox cycling. The most potent inhibitors of sepiapterin reduction (IC50s = 31-180 nM) were sulfasalazine, sulfathiazole, sulfapyridine, sulfamethoxazole, and chlorpropamide. Higher concentrations of the sulfa drugs (IC50s = 0.37-19.4 μM) were required to inhibit redox cycling, presumably because of distinct mechanisms of sepiapterin reduction and redox cycling. In PC12 cells, which generate catecholamine and monoamine neurotransmitters via BH4-dependent amino acid hydroxylases, sulfa drugs inhibited both BH2/BH4 biosynthesis and redox cycling mediated by SPR. Inhibition of BH2/BH4 resulted in decreased production of dopamine and dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, and 5-hydroxytryptamine. Sulfathiazole (200 μM) markedly suppressed neurotransmitter production, an effect reversed by BH4. These data suggest that SPR and BH4-dependent enzymes, are "off-targets" of sulfa drugs, which may underlie their untoward effects. The ability of the sulfa drugs to inhibit redox cycling may ameliorate ROS-mediated toxicity generated by redox active drugs and chemicals, contributing to their anti-inflammatory activity.
蝶呤还原酶（SPR）催化蝶呤还原为二氢生物蝶呤（BH2），后者是四氢生物蝶呤（BH4）的前体，而四氢生物蝶呤是一氧化氮生物合成以及烷基甘油和芳香族氨基酸代谢所必需的辅因子。SPR还介导化学氧化还原循环，催化包括醌类和联吡啶除草剂（如甲萘醌、9,10-菲醌和敌草快）在内的氧化还原活性化学物质的单电子还原；还原自由基与分子氧的快速反应会产生活性氧（ROS）。使用重组人SPR发现，基于磺胺酰胺和磺酰脲的磺胺类药物是蝶呤还原和氧化还原循环的有效非竞争性抑制剂。蝶呤还原最有效的抑制剂（IC50 = 31 - 180 nM）是柳氮磺胺吡啶、磺胺噻唑、磺胺吡啶、磺胺甲恶唑和氯磺丙脲。抑制氧化还原循环需要更高浓度的磺胺类药物（IC50 = 0.37 - 19.4 μM），这可能是因为蝶呤还原和氧化还原循环的机制不同。在通过BH4依赖性氨基酸羟化酶生成儿茶酚胺和单胺神经递质的PC12细胞中，磺胺类药物抑制了SPR介导的BH2/BH4生物合成和氧化还原循环。BH2/BH4的抑制导致多巴胺及其代谢产物3,4-二羟基苯乙酸和高香草酸以及5-羟色胺的生成减少。磺胺噻唑（200 μM）显著抑制神经递质的生成，这种作用可被BH4逆转。这些数据表明，SPR和BH4依赖性酶是磺胺类药物的“脱靶”对象，这可能是它们产生不良影响的原因。磺胺类药物抑制氧化还原循环的能力可能会减轻氧化还原活性药物和化学物质产生的ROS介导的毒性，这有助于它们的抗炎活性。
