Advances and Opportunities in H2S Measurement in Chemical Biology.

Hydrogen sulfide (H2S) is an important biological mediator across all kingdoms of life and plays intertwined roles in various disciplines, ranging from geochemical cycles to industrial processes. A common need across these broad disciplines is the ability to detect and measure H2S in complex sample environments. This Perspective focuses on key advances and opportunities for H2S detection and quantification that are relevant to chemical biology. Specifically, we focus on methods for H2S detection and quantification most commonly used in biological samples, including activity-based H2S probes, the methylene blue assay, the monobromobimane assay, and H2S-sensitive electrode measurements. Our goal is to help simplify what at first may seem to be an overwhelming array of detection and measurement choices, to articulate the strengths and limitations of individual techniques, and to highlight key unmet needs and opportunities in the field.

Thiol-Activated 1,2,4-Thiadiazolidin-3,5-diones Release Hydrogen Sulfide through a Carbonyl-Sulfide-Dependent Pathway.

Recent efforts have expanded the development of small molecule donors that release the important biological signaling molecule hydrogen sulfide (H2S). Previous work on 1,2,4-thiadiazolidin-3,5-diones (TDZNs) reported that these compounds release H2S directly, albeit inefficiently. However, TDZNs showed promising efficacy in H2S-mediated relaxation in ex vivo aortic ring relaxation models. Here, we show that TDZNs release carbonyl sulfide (COS) efficiently, which can be converted to H2S by the enzyme carbonic anhydrase (CA) rather than releasing H2S directly as previously reported.

Influence of Ring Modifications on Nucleolar Stress Caused by Oxaliplatin-Like Compounds.

Oxaliplatin, a platinum compound in broad clinical use, can induce cell death through a nucleolar stress pathway rather than the canonical DNA damage response studied for other Pt(II) compounds. Previous work has found that the oxaliplatin 1,2-diaminocyclohexane (DACH) ring but not the oxalate leaving group is important to the ability to induce nucleolar stress. Here we study the influence of DACH ring substituents at the 4-position on the ability of DACH-Pt(II) compounds to cause nucleolar stress. We determine that DACH-Pt(II) compounds with 4-position methyl, ethyl, or propyl substituents induce nucleolar stress, but DACH-Pt(II) compounds with 4-isopropyl substituents do not induce nucleolar stress. This effect is independent of whether the substituent is in the axial or equatorial position relative to the trans diamines of the ligand. These results suggest that spatially sensitive interactions could be involved in the ability of platinum compounds to cause nucleolar stress.

Misregulation of cell adhesion molecules in the Ciona neural tube closure mutant bugeye.

Neural tube closure (NTC) is a complex multi-step morphogenetic process that transforms the flat neural plate found on the surface of the post-gastrulation embryo into the hollow and subsurface central nervous system (CNS). Errors in this process underlie some of the most prevalent human birth defects, and occur in about 1 out of every 1000 births. Previously, we discovered a mutant in the basal chordate Ciona savignyi (named bugeye) that revealed a novel role for a T-Type Calcium Channel (Cav3) in this process. Moreover, the requirement for CAV3s in Xenopus NTC suggests a conserved function among the chordates. Loss of CAV3 leads to defects restricted to anterior NTC, with the brain apparently fully developed, but protruding from the head. Here we report first on a new Cav3 mutant in the related species C. robusta. RNAseq analysis of both C. robusta and C. savignyi bugeye mutants reveals misregulation of a number of transcripts including ones that are involved in cell-cell recognition and adhesion. Two in particular, Selectin and Fibronectin leucine-rich repeat transmembrane, which are aberrantly upregulated in the mutant, are expressed in the closing neural tube, and when disrupted by CRISPR gene editing lead to the open brain phenotype displayed in bugeye mutants. We speculate that these molecules play a transient role in tissue separation and adhesion during NTC and failure to downregulate them leads to an open neural tube.

N-Methylation of Self-Immolative Thiocarbamates Provides Insights into the Mechanism of Carbonyl Sulfide Release.

Hydrogen sulfide (H2S) is an important biomolecule, and self-immolative thiocarbamates have shown great promise as triggerable H2S donors with suitable analogous control compounds; however, thiocarbamates with electron-deficient payloads are less efficient H2S donors. We report here the synthesis and study of a series of N-methylated esterase-triggered thiocarbamates that block the postulated unproductive deprotonation-based pathway for these compounds. The relative reaction profiles for H2S release across a series of electron-rich and electron-poor N-Me aniline payloads are examined experimentally and computationally. We show that thiocarbamate N-methylation does block some side reactivity and increases the H2S release profiles for electron-poor donors. Additionally, we show that isothiocyanate release is not a competitive pathway, and rather that the reduced efficiency of electron-poor donors is likely due to other side reactions.