title: Sulfa drugs inhibit sepiapterin reduction and chemical redox cycling by sepiapterin reductase.
abstract: 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.
authors.affiliation: 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.).
authors.forename: Shaojun
authors.initials: S
authors.lastname: Yang
authors.affiliation: 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.).
authors.forename: Yi-Hua
authors.initials: YH
authors.lastname: Jan
authors.affiliation: 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.).
authors.forename: Vladimir
authors.initials: V
authors.lastname: Mishin
authors.affiliation: 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.).
authors.forename: Jason R
authors.initials: JR
authors.lastname: Richardson
authors.affiliation: 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.).
authors.forename: Muhammad M
authors.initials: MM
authors.lastname: Hossain
authors.affiliation: 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.).
authors.forename: Ned D
authors.initials: ND
authors.lastname: Heindel
authors.affiliation: 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.).
authors.forename: Diane E
authors.initials: DE
authors.lastname: Heck
authors.affiliation: 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.).
authors.forename: Debra L
authors.initials: DL
authors.lastname: Laskin
authors.affiliation: 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.) jlaskin@eohsi.rutgers.edu.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Laskin
mesh_terms: D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D006801:Humans; D051379:Mice; D010084:Oxidation-Reduction / Q000187:drug effects; D016716:PC12 Cells; D017433:Protein Structure, Secondary; D011622:Pterins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D012460:Sulfasalazine / Q000494:pharmacology*; D000077589:Sulfathiazole; D013432:Sulfathiazoles / Q000494:pharmacology*
chemical_list: D011622:Pterins; D013432:Sulfathiazoles; D012460:Sulfasalazine; C016727:sepiapterin; D000429:Alcohol Oxidoreductases; C022630:sepiapterin reductase; D000077589:Sulfathiazole