Nitrosopersulfide (SSNO-) Is a Unique Cysteine Polysulfidating Agent with Reduction-Resistant Bioactivity

Hydrogen Sulfide (H2S)/Polysulfides (H2Sn) Signalling and TRPA1 Channels Modification on Sulfur Metabolism

Hydrogen sulfide (H2S) and polysulfides (H2Sn, n ≥ 2) produced by enzymes play a role as signalling molecules regulating neurotransmission, vascular tone, cytoprotection, inflammation, oxygen sensing, and energy formation. H2Sn, which have additional sulfur atoms to H2S, and other S-sulfurated molecules such as cysteine persulfide and S-sulfurated cysteine residues of proteins, are produced by enzymes including 3-mercaptopyruvate sulfurtransferase (3MST). H2Sn are also generated by the chemical interaction of H2S with NO, or to a lesser extent with H2O2. S-sulfuration (S-sulfhydration) has been proposed as a mode of action of H2S and H2Sn to regulate the activity of target molecules. Recently, we found that H2S/H2S2 regulate the release of neurotransmitters, such as GABA, glutamate, and D-serine, a co-agonist of N-methyl-D-aspartate (NMDA) receptors. H2S facilitates the induction of hippocampal long-term potentiation, a synaptic model of memory formation, by enhancing the activity of NMDA receptors, while H2S2 achieves this by activating transient receptor potential ankyrin 1 (TRPA1) channels in astrocytes, potentially leading to the activation of nearby neurons. The recent findings show the other aspects of TRPA1 channels-that is, the regulation of the levels of sulfur-containing molecules and their metabolizing enzymes. Disturbance of the signalling by H2S/H2Sn has been demonstrated to be involved in various diseases, including cognitive and psychiatric diseases. The physiological and pathophysiological roles of these molecules will be discussed.

Nitric oxide and thiols: Chemical biology, signalling paradigms and vascular therapeutic potential

Nitric oxide (• NO) interactions with biological thiols play crucial, but incompletely determined, roles in vascular signalling and other biological processes. Here, we highlight two recently proposed signalling paradigms: (1) the formation of a vasodilating labile nitrosyl ferrous haem (NO-ferrohaem) facilitated by thiols via thiyl radical generation and (2) polysulfides/persulfides and their interaction with • NO. We also describe the specific (bio)chemical routes in which • NO and thiols react to form S-nitrosothiols, a broad class of small molecules, and protein post-translational modifications that can influence protein function through catalytic site or allosteric structural changes. S-Nitrosothiol formation depends upon cellular conditions, but critically, an appropriate oxidant for either the thiol (yielding a thiyl radical) or • NO (yielding a nitrosonium [NO+ ]-donating species) is required. We examine the roles of these collective • NO/thiol species in vascular signalling and their cardiovascular therapeutic potential.

Biological Functions of Hydrogen Sulfide in Plants

Hydrogen sulfide (H₂S), which is a gasotransmitter, can be biosynthesized and participates in various physiological and biochemical processes in plants. H₂S also positively affects plants' adaptation to abiotic stresses. Here, we summarize the specific ways in which H₂S is endogenously synthesized and metabolized in plants, along with the agents and methods used for H₂S research, and outline the progress of research on the regulation of H₂S on plant metabolism and morphogenesis, abiotic stress tolerance, and the series of different post-translational modifications (PTMs) in which H₂S is involved, to provide a reference for future research on the mechanism of H₂S action.

Cystathionine β-synthase overexpression drives metastatic dissemination in pancreatic ductal adenocarcinoma via inducing epithelial-to-mesenchymal transformation of cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest of all cancer types with a constant rise in global incidence. Therefore, better understanding of PDAC biology, in order to design more efficient diagnostic and treatment modalities, is a priority. Here we found that the expression levels of cystathionine β-synthase (CBS), a transsulfuration enzyme, is markedly elevated in metastatic PDAC cells compared to cell lines isolated from non-metastatic primary tumors. On human immunohistochemical samples from PDAC patients we also found higher CBS staining in cancerous ductal cells compared to in non-tumor tissue, which was further elevated in the lymph node metastasis of the same patients. In mice, orthotopically injected CBS-silenced T3M4 cells induced fewer liver metastases compared to control cells indicating important roles for CBS in PDAC cancer cell invasion and malignant transformation. Wound healing and colony formation assays in cell culture confirmed that CBS-deficient metastatic T3M4 and non-metastatic BxPC3 primary tumor cells migrate slower and have impaired anchorage-independent growth capacities compared to control T3M4 cells. CBS silencing in T3M4 cells lowered WNT5a and SNAI1 gene expression down to levels that were observed in BxPC3 cells as well as resulted in an increase in E-cadherin and a decrease in Vimentin signals in mouse tumors when injected orthotopically. These observations suggested a primary role for the epithelial to mesenchymal transformation of cancer cells in CBS-mediated tumor aggressiveness. Under normal conditions, STAT3, an upstream regulator of Wnt signaling pathways, was less phosphorylated and more oxidized in shCBS T3M4 and BxPC3 compared to control T3M4 cells, which is consistent with decreased transcriptional activity at lower CBS levels due to less protection against oxidation. Sulfur metabolome analyses suggested that this CBS-mediated protection against oxidative modifications is likely to be related to persulfide/sulfide producing activities of the enzyme rather than its canonical function to produce cystathionine for cysteine synthesis. Taken together, CBS overexpression through regulation of the EMT plays a significant role in PDAC cancer cell invasion and metastasis.

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

Hydropersulfides (RSSH) and Nitric Oxide (NO) Signaling: Possible Effects on S-Nitrosothiols (RS-NO)

S-Nitrosothiol (RS-NO) formation in proteins and peptides have been implicated as factors in the etiology of many diseases and as possible regulators of thiol protein function. They have also been proposed as possible storage forms of nitric oxide (NO). However, despite their proposed functions/roles, there appears to be little consensus regarding the physiological mechanisms of RS-NO formation and degradation. Hydropersulfides (RSSH) have recently been discovered as endogenously generated species with unique reactivity. One important reaction of RSSH is with RS-NO, which leads to the degradation of RS-NO as well as the release of NO. Thus, it can be speculated that RSSH can be a factor in the regulation of steady-state RS-NO levels, and therefore may be important in RS-NO (patho)physiology. Moreover, RSSH-mediated NO release from RS-NO may be a possible mechanism allowing RS-NO to serve as a storage form of NO.

COVID-19: A Redox Disease-What a Stress Pandemic Can Teach Us About Resilience and What We May Learn from the Reactive Species Interactome About Its Treatment

Significance: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing coronavirus disease 2019 (COVID-19), affects every aspect of human life by challenging bodily, socioeconomic, and political systems at unprecedented levels. As vaccines become available, their distribution, safety, and efficacy against emerging variants remain uncertain, and specific treatments are lacking. Recent Advances: Initially affecting the lungs, COVID-19 is a complex multisystems disease that disturbs the whole-body redox balance and can be long-lasting (Long-COVID). Numerous risk factors have been identified, but the reasons for variations in susceptibility to infection, disease severity, and outcome are poorly understood. The reactive species interactome (RSI) was recently introduced as a framework to conceptualize how cells and whole organisms sense, integrate, and accommodate stress. Critical Issues: We here consider COVID-19 as a redox disease, offering a holistic perspective of its effects on the human body, considering the vulnerability of complex interconnected systems with multiorgan/multilevel interdependencies. Host/viral glycan interactions underpin SARS-CoV-2's extraordinary efficiency in gaining cellular access, crossing the epithelial/endothelial barrier to spread along the vascular/lymphatic endothelium, and evading antiviral/antioxidant defences. An inflammation-driven "oxidative storm" alters the redox landscape, eliciting epithelial, endothelial, mitochondrial, metabolic, and immune dysfunction, and coagulopathy. Concomitantly reduced nitric oxide availability renders the sulfur-based redox circuitry vulnerable to oxidation, with eventual catastrophic failure in redox communication/regulation. Host nutrient limitations are crucial determinants of resilience at the individual and population level. Future Directions: While inflicting considerable damage to health and well-being, COVID-19 may provide the ultimate testing ground to improve the diagnosis and treatment of redox-related stress diseases. "Redox phenotyping" of patients to characterize whole-body RSI status as the disease progresses may inform new therapeutic approaches to regain redox balance, reduce mortality in COVID-19 and other redox diseases, and provide opportunities to tackle Long-COVID. Antioxid. Redox Signal. 35, 1226-1268.

Hydrogen Sulfide (H2S) and Polysulfide (H2Sn) Signaling: The First 25 Years

Since the first description of hydrogen sulfide (H₂S) as a toxic gas in 1713 by Bernardino Ramazzini, most studies on H₂S have concentrated on its toxicity. In 1989, Warenycia et al. demonstrated the existence of endogenous H₂S in the brain, suggesting that H₂S may have physiological roles. In 1996, we demonstrated that hydrogen sulfide (H₂S) is a potential signaling molecule, which can be produced by cystathionine β-synthase (CBS) to modify neurotransmission in the brain. Subsequently, we showed that H₂S relaxes vascular smooth muscle in synergy with nitric oxide (NO) and that cystathionine γ-lyase (CSE) is another producing enzyme. This study also opened up a new research area of a crosstalk between H₂S and NO. The cytoprotective effect, anti-inflammatory activity, energy formation, and oxygen sensing by H₂S have been subsequently demonstrated. Two additional pathways for the production of H₂S with 3-mercaptopyruvate sulfurtransferase (3MST) from l- and d-cysteine have been identified. We also discovered that hydrogen polysulfides (H₂S_n, n ≥ 2) are potential signaling molecules produced by 3MST. H₂S_n regulate the activity of ion channels and enzymes, as well as even the growth of tumors. S-Sulfuration (S-sulfhydration) proposed by Snyder is the main mechanism for H₂S/H₂S_n underlying regulation of the activity of target proteins. This mini review focuses on the key findings on H₂S/H₂S_n signaling during the first 25 years.

Comment on "Evidence that the ProPerDP method is inadequate for protein persulfidation detection due to lack of specificity"

The recent report by Fan et al alleged that the ProPerDP method is inadequate for the detection of protein persulfidation. Upon careful evaluation of their work, we conclude that the claim made by Fan et al is not supported by their data, rather founded in methodological shortcomings. It is understood that the ProPerDP method generates a mixture of cysteine-containing and non-cysteine-containing peptides. Instead, Fan et al suggested that the detection of non-cysteine-containing peptides indicates nonspecific alkylation at noncysteine residues. However, if true, then such peptides would not be released by reduction and therefore not appear as products in the reported workflow. Moreover, the authors' biological assessment of ProPerDP using Escherichia coli mutants was based on assumptions that have not been confirmed by other methods. We conclude that Fan et al did not rigorously assess the method and that ProPerDP remains a reliable approach for analyses of protein per/polysulfidation.

Cardiovascular "Patterns" of H2S and SSNO--Mix Evaluated from 35 Rat Hemodynamic Parameters

This work is based on the hypothesis that it is possible to characterize the cardiovascular system just from the detailed shape of the arterial pulse waveform (APW). Since H₂S, NO donor S-nitrosoglutathione (GSNO) and their H₂S/GSNO products (SSNO⁻-mix) have numerous biological actions, we aimed to compare their effects on APW and to find characteristic “patterns” of their actions. The right jugular vein of anesthetized rats was cannulated for i.v. administration of the compounds. The left carotid artery was cannulated to detect APW. From APW, 35 hemodynamic parameters (HPs) were evaluated. H₂S transiently influenced all 35 HPs and from their cross-relationships to systolic blood pressure “patterns” and direct/indirect signaling pathways of the H₂S effect were proposed. The observed “patterns” were mostly different from the published ones for GSNO. Effect of SSNO⁻-mix (≤32 nmol kg⁻¹) on blood pressure in the presence or absence of a nitric oxide synthase inhibitor (L-NAME) was minor in comparison to GSNO, suggesting that the formation of SSNO⁻-mix in blood diminished the hemodynamic effect of NO. The observed time-dependent changes of 35 HPs, their cross-relationships and non-hysteresis/hysteresis profiles may serve as “patterns” for the conditions of a transient decrease/increase of blood pressure caused by H₂S.

Updating NO•/HNO interconversion under physiological conditions: A biological implication overview

Azanone (HNO/NO^-), also called nitroxyl, is a highly reactive compound whose biological role is still a matter of debate. A key issue that remains to be clarified regarding HNO and its biological activity is that of its endogenous formation. Given the overlap of the molecular targets and reactivity of nitric oxide (NO•) and HNO, its chemical biology was perceived to be similar to that of NO• as a biological signaling agent. However, despite their closely related reactivity, NO• and HNO's biochemical pathways are quite different. Moreover, the reduction of nitric oxide to azanone is possible but necessarily coupled to other reactions, which drive the reaction forward, overcoming the unfavorable thermodynamic barrier. The mechanism of this NO•/HNO interplay and its downstream effects in different contexts were studied recently, showing that more than fifteen moderate reducing agents react with NO• producing HNO. Particularly, it is known that the reaction between nitric oxide and hydrogen sulfide (H₂S) produces HNO. However, this rate constant was not reported yet. In this work, firstly the NO•/H₂S effective rate constant was measured as a function of the pH. Then, the implications of these chemical (non-enzymatic), biologically compatible, routes to endogenous HNO formation was discussed. There is no doubt that HNO could be (is?) a new endogenously produced messenger that mediates specific physiological responses, many of which were attributed yet to direct NO• effects.

The Role of Host-Generated H2S in Microbial Pathogenesis: New Perspectives on Tuberculosis

For centuries, hydrogen sulfide (H₂S) was considered primarily as a poisonous gas and environmental hazard. However, with the discovery of prokaryotic and eukaryotic enzymes for H₂S production, breakdown, and utilization, H₂S has emerged as an important signaling molecule in a wide range of physiological and pathological processes. Hence, H₂S is considered a gasotransmitter along with nitric oxide (•NO) and carbon monoxide (CO). Surprisingly, despite having overlapping functions with •NO and CO, the role of host H₂S in microbial pathogenesis is understudied and represents a gap in our knowledge. Given the numerous reports that followed the discovery of •NO and CO and their respective roles in microbial pathogenesis, we anticipate a rapid increase in studies that further define the importance of H₂S in microbial pathogenesis, which may lead to new virulence paradigms. Therefore, this review provides an overview of sulfide chemistry, enzymatic production of H₂S, and the importance of H₂S in metabolism and immunity in response to microbial pathogens. We then describe our current understanding of the role of host-derived H₂S in tuberculosis (TB) disease, including its influences on host immunity and bioenergetics, and on Mycobacterium tuberculosis (Mtb) growth and survival. Finally, this review discusses the utility of H₂S-donor compounds, inhibitors of H₂S-producing enzymes, and their potential clinical significance.