Role of Hydrogen Sulfide in Catalyzing the Formation of No-Ferroheme

Abstract

We recently demonstrated a rapid reaction between labile ferric heme and nitric oxide (NO) in the presence of reduced glutathione (GSH) or other small thiols in a process called thiol-catalyzed reductive nitrosylation yielding a novel signaling molecule, labile nitrosyl ferrous heme (NO-ferroheme), which we and others have shown can regulate vasodilation and platelet homeostasis. Red blood cells (RBCs), abundant in GSH and heme and can generate NO via nitrite reduction and/or RBC endothelial nitric oxide synthase (eNOS), are a key site for this reaction. However, NO-ferroheme may form in other cells and compartments, including in plasma where another small and reactive thiol species, hydrogen sulfide (H2S/HS–), is also present and may catalyze NO-ferroheme formation akin to GSH. Here, we compare the reactivity of GSH and hydrogen sulfide with hemin in physiologically relevant media, including human serum albumin (HSA) and RBC membranes. Strikingly, hydrogen sulfide demonstrated a second-order rate constant over 10 times higher than GSH. We propose that the increased solubility of H2S vs GSH in lipophilic environments – where labile heme is most readily found – and the increased steric hindrance of the bulkier GSH account for the faster reaction kinetics observed with hydrogen sulfide. Our findings suggest that the hydrogen sulfide-catalyzed reductive nitrosylation reaction produces thionitrous acid (HSNO), which readily undergoes further reactions with excess hydrogen sulfide to form nitrosopersulfide (SSNO-) and polysulfides. These results suggest a common theme in thiol-catalyzed reductive nitrosylation of labile ferric heme that could play an important role in NO signaling.

Note:
Funding declaration: This work was supported by NIH grants R01 HL125886 (J.T. and M.T.G.), K99 HL168224 (M.R.D) and R01 HL098032 (M.T.G).

Conflict of Interests: A.W.D., M.T.G., J.T., M.R.D., D.B.K.-S. and L.P. have a patent filed at the University of Pittsburgh related to the creation and use of NO-ferroheme. M.T.G and D.B. K-S. are also co-inventor on patents directed to the use of nitrite salts in cardiovascular diseases, which were previously licensed to United Therapeutics, and licensed to Globin Solutions and Hope Pharmaceuticals M.T.G. and J.T. are co-inventors of patents and patent applications directed to the use of recombinant neuroglobin and heme-based molecules as antidotes for CO poisoning, which have been licensed by Globin Solutions, Inc. M.T.G. is a shareholder, advisor, received research support and is a director in Globin Solutions, Inc. and J.T. is also a shareholder and adviser. MTG is an inventor on an unlicensed patent application directed at the use of nitrite for halogen gas poisoning and smoke inhalation. M.T.G. was a principal investigator in a research collaboration with Bayer Pharmaceuticals to evaluate riociguate as a treatment for patients with SCD, which has concluded. M. T. G. is a textbook author and receives royalties from MedMaster Inc., and is a textbook editor and receives royalties from McGraw-Hill. In the past 36 months, Dr. M.T.G. served as a consultant for Forma Therapeutics and Third Pole Therapeutics, but currently has no active consulting agreements.

Keywords: Sulfide, Nitric oxide, heme, albumin, Thiol