PNAS PLUS Key bioactive reaction products of the NO/H2S interaction are S/N-hybrid species, polysulfides, and nitroxyl Miriam M. Cortese-Krotta, Gunter G. C. Kuhnleb,1, Alex Dysonc,1, Bernadette O. Fernandezd,1, Marian Grmane, Jenna F. DuMondf, Mark P. Barrowg, George McLeodh, Hidehiko Nakagawai, Karol Ondriase, Péter Nagyj, S. Bruce Kingf, Joseph E. Saavedrak, Larry K. Keeferl, Mervyn Singerc, Malte Kelma, Anthony R. Butlerm, and Martin Feelischd,2 aCardiovascular Research Laboratory, Department of Cardiology, Pneumology and Angiology, Medical Faculty, Heinrich Heine University of Düsseldorf, 40225 Dusseldorf, Germany; bDepartment of Nutrition, University of Reading, Whiteknights, Reading RG6 6AP, United Kingdom; cBloomsbury Institute of Intensive Care Medicine, University College London, London WC1E 6BT, United Kingdom; dClinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton General Hospital and Institute for Life Sciences, Southampton SO16 6YD, United Kingdom; eCenter for Molecular Medicine, Slovak Academy of Sciences, 83101 Bratislava, Slovak Republic; fDepartment of Chemistry, Wake Forest University, Winston-Salem, NC 27109; gDepartment of Chemistry, Warwick University, Coventry CV4 7AL, United Kingdom; hBruker UK Ltd., Coventry CV4 9GH, United Kingdom; iDepartment of Organic and Medicinal Chemistry, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya-shi, Aichi 467-8603, Japan; jDepartment of Molecular Immunology and Toxicology, National Institute of Oncology, 1122 Budapest, Hungary; kLeidos Biomedical Research, Inc., National Cancer Institute–Frederick, Frederick, MD 21702; lNational Cancer Institute–Frederick, Frederick, MD 21702; and mMedical School, University of St. Andrews, St. Andrews, Fife KY16 9AJ, Scotland Edited by Louis J. Ignarro, University of California, Los Angeles School of Medicine, Beverly Hills, CA, and approved July 2, 2015 (received for review May 12, 2015) Experimental evidence suggests that nitric oxide (NO) and hydro- eukaryotic cells may have originated from the symbiosis of sulfur- gen sulfide (H2S) signaling pathways are intimately intertwined, reducing and -oxidizing lifeforms within a self-contained sulfur with mutual attenuation or potentiation of biological responses in redox metabolome (8), sulfide may have been essential even the cardiovascular system and elsewhere. The chemical basis of earlier by providing the basic building blocks of life. this interaction is elusive. Moreover, polysulfides recently emerged The chemical reactions of sulfur-centered nucleophiles with a CHEMISTRY as potential mediators of H2S/sulfide signaling, but their biosynthesis range of nitrogen-containing species have been studied for dif- and relationship to NO remain enigmatic. We sought to characterize ferent reasons and as independent processes for more than a the nature, chemical biology, and bioactivity of key reaction products century, and early reports indicated complex reaction mecha- formed in the NO/sulfide system. At physiological pH, we find that nisms (9–13). The recent surge of interest in this chemistry in NO and sulfide form a network of cascading chemical reactions that generate radical intermediates as well as anionic and uncharged sol- Significance utes, with accumulation of three major products: nitrosopersulfide (SSNO−), polysulfides, and dinitrososulfite [N-nitrosohydroxylamine- Reactions of sulfur-centered nucleophiles with nitrogenous species N-sulfonate (SULFI/NO)], each with a distinct chemical biology and in PHARMACOLOGY − have been studied independently for more than a century for vitro and in vivo bioactivity. SSNO is resistant to thiols and cyanol- synthetic/industrial purposes; to understand geochemical, atmo- ysis, efficiently donates both sulfane sulfur and NO, and potently spheric, and biological processes; and to explain the origins of life. lowers blood pressure. Polysulfides are both intermediates and prod- − Various products and reaction mechanisms were proposed. We ucts of SSNO synthesis/decomposition, and they also decrease blood here identify a singular process comprising a network of pressure and enhance arterial compliance. SULFI/NO is a weak com- cascading chemical reactions that form three main bioactive bined NO/nitroxyl donor that releases mainly N O on decomposition; 2 products at physiological pH: nitrosopersulfide, polysulfides, although it affects blood pressure only mildly, it markedly increases and dinitrososulfite. These anionic products scavenge, trans- cardiac contractility, and formation of its precursor sulfite likely con- port, and release NO/HNO or sulfide/sulfane sulfur, each dis- tributes to NO scavenging. Our results unveil an unexpectedly rich playing distinct chemistries and bioactivities. Our observations network of coupled chemical reactions between NO and H S/sulfide, 2 provide a chemical foundation for the cross-talk between the suggesting that the bioactivity of either transmitter is governed by NO and H S signaling pathways in biology and suggest that concomitant formation of polysulfides and anionic S/N-hybrid species. 2 the biological actions of these entities can be neither consid- This conceptual framework would seem to offer ample opportunities ered nor studied in isolation. for the modulation of fundamental biological processes governed by redox switching and sulfur trafficking. Author contributions: M.F. conceived, initiated, and coordinated the study; M.M.C.-K., G.G.C.K., A.D., B.O.F., J.F.D., M.P.B., G.M., K.O., P.N., S.B.K., M.S., A.R.B., and M.F. designed sulfide | nitric oxide | nitroxyl | redox | gasotransmitter research; M.M.C.-K., G.G.C.K., A.D., B.O.F., M.G., J.F.D., M.P.B., G.M., and M.F. performed research; M.M.C.-K., G.G.C.K., M.P.B., G.M., H.N., S.B.K., J.E.S., L.K.K., and M.F. contributed new reagents/analytic tools; M.M.C.-K., G.G.C.K., A.D., B.O.F., M.G., J.F.D., M.P.B., G.M., itrogen and sulfur are essential for all known forms of life K.O., P.N., S.B.K., J.E.S., M.S., M.K., A.R.B., and M.F. analyzed data; M.M.C.-K. and M.F. Non Earth. Our planet’s earliest atmosphere is likely to have wrote the paper; and G.G.C.K., A.D., B.O.F., M.G., J.F.D., M.P.B., G.M., H.N., K.O., P.N., S.B.K., L.K.K., M.S., M.K., and A.R.B. contributed to manuscript writing. contained only traces of O2 but rather large amounts of hydrogen The authors declare no conflict of interest. sulfide (H2S) (1). Indeed, sulfide may have supported life long This article is a PNAS Direct Submission. before the emergence of O2 and NO (2, 3).* This notion is Freely available online through the PNAS open access option. consistent with a number of observations: H2S is essential for efficient abiotic amino acid generation as evidenced by the 1G.G.C.K., A.D., and B.O.F. contributed equally to this work. recent reanalysis of samples of Stanley Miller’s original spark 2To whom correspondence should be addressed. Email: [email protected]. discharge experiments (4), sulfide is an efficient reductant in This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. protometabolic reactions forming RNA, protein, and lipid pre- 1073/pnas.1509277112/-/DCSupplemental. *H2S is a weak acid (pKa1 = 7.0, pKa2 = 14.1); at physiological pH, approximately three- cursors (5), and sulfide is both a bacterial and mitochondrial sub- − quarters of the dissolved H2S exist in the form of hydrosulfide (HS ) with negligible strate (6), enabling even multicellular lifeforms to exist and − − − amounts of S2 . The combination of all three forms (H2S, HS , and S2 ) will hereinafter reproduce under conditions of permanent anoxia (7). Thus, although be referred to as sulfide. www.pnas.org/cgi/doi/10.1073/pnas.1509277112 PNAS Early Edition | 1of10 Downloaded by guest on September 26, 2021 the biological community (13–15) was triggered by a growing S1). Inhibition of NO synthase by S-ethylisothiourea prolonged appreciation that NO and sulfide exert similar and often in- the action of sulfide and markedly increased its toxicity (SI Ap- terdependent biological actions within the cardiovascular system pendix,Fig.S1A and B), showing that endogenous NO production “ ” and elsewhere (NO/H2S cross-talk ) (16, 17), resulting in mu- modulates sulfide bioactivity and attesting to the reciprocal nature tual attenuation or potentiation of their responses. This cross- – of interaction of these signaling molecules. In subsequent experi- talk is possibly mediated by chemical interactions (18 20), but ments, NaHS was administered by continuous infusion (2.8 μmol/kg much of the older chemical work seems to have been forgotten. per minute in PBS, pH 7.4) to counter the rapid rate of sulfide Recently, low concentrations of sulfide were shown to quench NO-mediated vascular responses through formation of an unchar- elimination (33), and blood was collected repeatedly for measure- acterized “nitrosothiol” (RSNO) (18–20), assumed to be thionitrous ment of circulating NO biomarkers (Fig. 1 and SI Appendix,Fig.S2 acid (HSNO) (13–15). and Table S2). Consistent with the notion that vascular sulfide levels A recent report of the detection by MS of the highly unstable rise only after inactivation (binding/elimination) pathways become HSNO at physiological pH (21) has attracted considerable at- saturated, no significant hemodynamic changes were observed in the tention from the biological community, because it could be an intermediate in the reaction of sulfide with RSNOs (22) and a + precursor for NO, nitrosonium (NO ) equivalents, and nitroxyl ) 400 (HNO). However, a key aspect of HSNO’s properties that seems AB-1 in to have been overlooked in these discussions is its mobile hy- 10 mmHg 350 20 min drogen, allowing facile 1,3 hydrogen shift and formation of four 5 HR (m 300 isomers with the same chemical equation (13)—a feature de- 0 0 60 120 scribed in the seminal studies by Goehring in the 1950s (23) and -5 by Müller and Nonella later on (24, 25) that distinguishes HSNO -10 from all other RSNOs (26).