H2S biogenesis by cystathionine beta-synthase: mechanism of inhibition by aminooxyacetic acid and unexpected role of serine

Biochemical and structural impact of two novel missense mutations in cystathionine β-synthase gene associated with homocystinuria

Homocystinuria is a rare disease caused by mutations in the CBS gene that results in a deficiency of cystathionine β-synthase (CBS). CBS is an essential pyridoxal 5'-phosphate (PLP)-dependent enzyme in the transsulfuration pathway, responsible for combining serine with homocysteine to produce cystathionine, whose activity is enhanced by the allosteric regulator S-adenosylmethionine (SAM). CBS also plays a role in generating hydrogen sulfide (H2S), a gaseous signaling molecule with diverse regulatory functions within the vascular, nervous, and immune systems. In this study, we present the clinical and biochemical characterization of two novel CBS missense mutations that do not respond to pyridoxine treatment, namely c.689T > A (L230Q) and 215A > T (K72I), identified in a Chinese patient. We observed that the disease-associated K72I genetic variant had no apparent effects on the spectroscopic and catalytic properties of the full-length enzyme. In contrast, the L230Q variant expressed in Escherichia coli did not fully retain heme and when compared with the wild-type enzyme, it exhibited more significant impairments in both the canonical cystathionine-synthesis and the alternative H2S-producing reactions. This reduced activity is consistent with both in vitro and in silico evidence, which indicates that the L230Q mutation significantly decreases the overall protein's stability, which in turn, may represent the underlying cause of its pathogenicity.

A multifunctional fluorescent probe for sequential detection of hydrogen sulfide and pH in foodstuffs, living cells and mice

BACKGROUND

Cancer as a leading cause of premature death worldwide has become a major threat to human health due to the high incidence and mortality. Monitoring tumor markers are reliable and significantly important for early detection of cancers. In complex biological systems, it is of great urgency but still remains challenging to conceive a fluorescent probe with multiple tumor markers detection property. Hydrogen sulfide (H2S) and pH are two target biomarkers for diagnosis of early cancer. The preparation of a novel probe with H2S and pH dual detection functions is highly anticipated.

RESULTS

Herein, a novel sequential detection probe HTPQ-HS for H2S and pH has been developed. In this system, HPQ (2-(2 -hydroxyphenyl)-4(3H)-quinazolinone) structure combined with triphenylamine is applied as the fluorophore, and 2, 4-dinitrophenylsulfonyl group is used as the recognition group. In the presence of H2S, HTPQ-HS is transformed into product HTPQ-OH which shows fluorescence enhancement (29-fold) at 525 nm in less than 4 min and further displays repeatable acid-base responsive ability. HTPQ-HS is able to sequentially response to H2S and pH in living cells and does not react directly with pH. Owing to the low cytotoxicity, HTPQ-HS is able to detect exogenous and endogenous H2S in colon cancer cells and mice, monitor H2S in inflammation model and in foodstuffs. As the environment changes from acidic to alkaline, the fluorescence intensity ratio (I470/I530) of product HTPQ-OH changes remarkably, illustrating the ratiometric fluorescent responsiveness to pH.

SIGNIFICANCE AND NOVELTY

A multifunctional fluorescent probe HTPQ-HS for sequential detection of H2S and pH is synthesized. Probe HTPQ-OH realizes the monitoring of dynamic changes in intracellular pH and displays prospective application in security printing. We expect that our work could offer an important guidance on the development of multifunctional fluorescent probes for visualizing H2S and pH in biology and environment.

Neurobehavioral dysfunction in a mouse model of Down syndrome: upregulation of cystathionine β-synthase, H2S overproduction, altered protein persulfidation, synaptic dysfunction, endoplasmic reticulum stress, and autophagy

Down syndrome (DS) is a genetic condition where the person is born with an extra chromosome 21. DS is associated with accelerated aging; people with DS are prone to age-related neurological conditions including an early-onset Alzheimer's disease. Using the Dp(17)3Yey/ + mice, which overexpresses a portion of mouse chromosome 17, which encodes for the transsulfuration enzyme cystathionine β-synthase (CBS), we investigated the functional role of the CBS/hydrogen sulfide (H2S) pathway in the pathogenesis of neurobehavioral dysfunction in DS. The data demonstrate that CBS is higher in the brain of the DS mice than in the brain of wild-type mice, with primary localization in astrocytes. DS mice exhibited impaired recognition memory and spatial learning, loss of synaptosomal function, endoplasmic reticulum stress, and autophagy. Treatment of mice with aminooxyacetate, a prototypical CBS inhibitor, improved neurobehavioral function, reduced the degree of reactive gliosis in the DS brain, increased the ability of the synaptosomes to generate ATP, and reduced endoplasmic reticulum stress. H2S levels in the brain of DS mice were higher than in wild-type mice, but, unexpectedly, protein persulfidation was decreased. Many of the above alterations were more pronounced in the female DS mice. There was a significant dysregulation of metabolism in the brain of DS mice, which affected amino acid, carbohydrate, lipid, endocannabinoid, and nucleotide metabolites; some of these alterations were reversed by treatment of the mice with the CBS inhibitor. Thus, the CBS/H2S pathway contributes to the pathogenesis of neurological dysfunction in DS in the current animal model.

VEGF signaling: Role in angiogenesis and beyond

Angiogenesis is a crucial process for tissue development, repair, and tumor survival. Vascular endothelial growth factor (VEGF) is a key driver secreted by cancer cells, promoting neovascularization. While VEGF's role in angiogenesis is well-documented, its influence on the other aspects in tumor microenvironemt is less discussed. This review elaborates on VEGF's impact on intercellular interactions within the tumor microenvironment, including how VEGF affects pericyte proliferation and migration and mediates interactions between tumor-associated macrophages and cancer cells, resulting in PDL-1-mediated immunosuppression and Nrf2-mediated epithelial-mesenchymal transition. The review discusses VEGF's involvement in intra-organelle crosstalk, tumor metabolism, stemness, and epithelial-mesenchymal transition. It also provides insights into current anti-VEGF therapies and their limitations in cancer treatment. Overall, this review aims to provide a thorough overview of the current state of knowledge concerning VEGF signaling and its impact, not only on angiogenesis but also on various other oncogenic processes.

Effects of hydrogen sulfide on relaxation responses in the lower esophageal sphincter in rabbits: the potential role of potassium channels

Hydrogen sulfide (H2S) is a significant physiologic inhibitory neurotransmitter. The main goal of this research was to examine the contribution of diverse potassium (K+) channels and nitric oxide (NO) in mediating the H2S effect on electrical field stimulation (EFS)-induced neurogenic contractile responses in the lower esophageal sphincter (LES). EFS-induced contractile responses of rabbit isolated LES strips were recorded using force transducers in organ baths that contain Krebs-Henseleit solutions (20 ml). Cumulative doses of NaHS, L-cysteine, PAG, and AOAA were evaluated in NO-dependent and NO-independent groups. The experiments were conducted again in the presence of K+ channel blockers. In both NO-dependent and NO-independent groups, NaHS, L-cysteine, PAG, and AOAA significantly reduced EFS-induced contractile responses. In the NO-dependent group, the effect of NaHS and L-cysteine decreased in the presence of 4-AP, and also the effect of NaHS decreased in the NO-dependent and independent group in the presence of TEA. In the NO-independent group, K+ channel blockers didn't change L-cysteine-induced relaxations. K+ channel blockers had no impact on the effects of PAG and AOAA. In addition, NaHS significantly relaxed 80-mM KCl-induced contractions, whereas L-cysteine, PAG, and AOAA did not. In the present study, H2S decreased the amplitudes of EFS-induced contraction responses. These results suggest that Kv channels and NO significantly contribute to exogenous H2S and endogenous H2S precursor L-cysteine inhibitory effect on lower esophageal sphincter smooth muscle.

The Role of Hydrogen Sulfide in the Localization and Expression of p53 and Cell Death in the Nervous Tissue in Traumatic Brain Injury and Axotomy

Traumatic brain injury (TBI) is one of the leading causes of disability and death worldwide. It is characterized by various molecular-cellular events, with the main ones being apoptosis and damage to axons. To date, there are no clinically effective neuroprotective drugs. In this study, we examined the role of hydrogen sulfide (H2S) in the localization and expression of the key pro-apoptotic protein p53, as well as cell death in the nervous tissue in TBI and axotomy. We used a fast donor (sodium sulphide, Na2S) H2S and a classic inhibitor (aminooxyacetic acid, AOAA) of cystathionine β-synthase (CBS), which is a key enzyme in H2S synthesis. These studies were carried out on three models of neurotrauma in vertebrates and invertebrates. As a result, it was found that Na2S exhibits a pronounced neuroprotective effect that reduces the number of TUNEL-positive neurons and glial cells in TBI and apoptotic glia in axotomy. This effect could be realized through the Na2S-dependent decrease in the level of p53 in the cells of the nervous tissue of vertebrates and invertebrates, which we observed in our study. We also observed the opposite effect when using AOAA, which indicates the important role of CBS in the regulation of p53 expression and death of neurons and glial cells in TBI and axotomy.

Hydrogen Sulfide: An Emerging Regulator of Oxidative Stress and Cellular Homeostasis-A Comprehensive One-Year Review

Hydrogen sulfide (H2S), traditionally recognized as a toxic gas, has emerged as a critical regulator in many biological processes, including oxidative stress and cellular homeostasis. This review presents an exhaustive overview of the current understanding of H2S and its multifaceted role in mammalian cellular functioning and oxidative stress management. We delve into the biological sources and function of H2S, mechanisms underlying oxidative stress and cellular homeostasis, and the intricate relationships between these processes. We explore evidence from recent experimental and clinical studies, unraveling the intricate biochemical and molecular mechanisms dictating H2S's roles in modulating oxidative stress responses and maintaining cellular homeostasis. The clinical implications and therapeutic potential of H2S in conditions characterized by oxidative stress dysregulation and disrupted homeostasis are discussed, highlighting the emerging significance of H2S in health and disease. Finally, this review underscores current challenges, controversies, and future directions in the field, emphasizing the need for further research to harness H2S's potential as a therapeutic agent for diseases associated with oxidative stress and homeostatic imbalance. Through this review, we aim to emphasize H2S's pivotal role in cellular function, encouraging further exploration into this burgeoning area of research.

The Role of Hydrogen Sulfide in Regulation of Cell Death following Neurotrauma and Related Neurodegenerative and Psychiatric Diseases

Injuries of the central (CNS) and peripheral nervous system (PNS) are a serious problem of the modern healthcare system. The situation is complicated by the lack of clinically effective neuroprotective drugs that can protect damaged neurons and glial cells from death. In addition, people who have undergone neurotrauma often develop mental disorders and neurodegenerative diseases that worsen the quality of life up to severe disability and death. Hydrogen sulfide (H₂S) is a gaseous signaling molecule that performs various cellular functions in normal and pathological conditions. However, the role of H₂S in neurotrauma and mental disorders remains unexplored and sometimes controversial. In this large-scale review study, we examined the various biological effects of H₂S associated with survival and cell death in trauma to the brain, spinal cord, and PNS, and the signaling mechanisms underlying the pathogenesis of mental illnesses, such as cognitive impairment, encephalopathy, depression and anxiety disorders, epilepsy and chronic pain. We also studied the role of H₂S in the pathogenesis of neurodegenerative diseases: Alzheimer's disease (AD) and Parkinson's disease (PD). In addition, we reviewed the current state of the art study of H₂S donors as neuroprotectors and the possibility of their therapeutic uses in medicine. Our study showed that H₂S has great neuroprotective potential. H₂S reduces oxidative stress, lipid peroxidation, and neuroinflammation; inhibits processes associated with apoptosis, autophagy, ferroptosis and pyroptosis; prevents the destruction of the blood-brain barrier; increases the expression of neurotrophic factors; and models the activity of Ca²⁺ channels in neurotrauma. In addition, H₂S activates neuroprotective signaling pathways in psychiatric and neurodegenerative diseases. However, high levels of H₂S can cause cytotoxic effects. Thus, the development of H₂S-associated neuroprotectors seems to be especially relevant. However, so far, all H₂S modulators are at the stage of preclinical trials. Nevertheless, many of them show a high neuroprotective effect in various animal models of neurotrauma and related disorders. Despite the fact that our review is very extensive and detailed, it is well structured right down to the conclusions, which will allow researchers to quickly find the proper information they are interested in.

Role of Cystathionine β-Synthase and 3-Mercaptopyruvate Sulfurtransferase in the Regulation of Proliferation, Migration, and Bioenergetics of Murine Breast Cancer Cells

Cystathionine β-synthase (CBS), CSE (cystathionine γ-lyase) and 3-mercaptopyruvate sulfurtransferase (3-MST) have emerged as three significant sources of hydrogen sulfide (H2S) in various forms of mammalian cancer. Here, we investigated the functional role of CBS’ and 3-MST’s catalytic activity in the murine breast cancer cell line EO771. The CBS/CSE inhibitor aminooxyacetic acid (AOAA) and the 3-MST inhibitor 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE) were used to assess the role of endogenous H2S in the modulation of breast cancer cell proliferation, migration, bioenergetics and viability in vitro. Methods included measurements of cell viability (MTT and LDH assays), cell proliferation and in vitro wound healing (IncuCyte) and cellular bioenergetics (Seahorse extracellular flux analysis). CBS and 3-MST, as well as expression were detected by Western blotting; H2S production was measured by the fluorescent dye AzMC. The results show that EO771 cells express CBS, CSE and 3-MST protein, as well as several enzymes involved in H2S degradation (SQR, TST, and ETHE1). Pharmacological inhibition of CBS or 3-MST inhibited H2S production, suppressed cellular bioenergetics and attenuated cell proliferation. Cell migration was only inhibited by the 3-MST inhibitor, but not the CBS/CSE inhibitor. Inhibition of CBS/CSE of 3-MST did not significantly affect basal cell viability; inhibition of 3-MST (but not of CBS/CSE) slightly enhanced the cytotoxic effects of oxidative stress (hydrogen peroxide challenge). From these findings, we conclude that endogenous H2S, generated by 3-MST and to a lower degree by CBS/CSE, significantly contributes to the maintenance of bioenergetics, proliferation and migration in murine breast cancer cells and may also exert a minor role as a cytoprotectant.

Recent therapeutic approaches to cystathionine beta-synthase-deficient homocystinuria

Cystathionine beta-synthase (CBS)-deficient homocystinuria (HCU) is the most common inborn error of sulfur amino acid metabolism. The pyridoxine non-responsive form of the disease manifests itself by massively increasing plasma and tissue concentrations of homocysteine, a toxic intermediate of methionine metabolism that is thought to be the major cause of clinical complications including skeletal deformities, connective tissue defects, thromboembolism and cognitive impairment. The current standard of care involves significant dietary interventions that, despite being effective, often adversely affect quality of life of HCU patients, leading to poor adherence to therapy and inadequate biochemical control with clinical complications. In recent years, the unmet need for better therapeutic options has resulted in development of novel enzyme and gene therapies and exploration of pharmacological approaches to rescue CBS folding defects caused by missense pathogenic mutations. Here, we review scientific evidence and current state of affairs in development of recent approaches to treat HCU.

Epigallocatechin gallate is a potent inhibitor of cystathionine beta-synthase: Structure-activity relationship and mechanism of action

Epigallocatechin gallate (EGCG) is the main bioactive component of green tea. Through screening of a small library of natural compounds, we discovered that EGCG inhibits cystathionine β-synthase (CBS), a major H₂S-generating enzyme. Here we characterize EGCG's mechanism of action in the context of CBS-derived H₂S production. In the current project, biochemical, pharmacological and cell biology approaches were used to characterize the effect of EGCG on CBS in cellular models of cancer and Down syndrome (DS). The results show that EGCG binds to CBS and inhibits H₂S-producing CBS activity almost 30-times more efficiently than the canonical cystathionine formation (IC₅₀ 0.12 versus 3.3 μM). Through screening structural analogs and building blocks, we identified that gallate moiety of EGCG represents the pharmacophore responsible for CBS inhibition. EGCG is a mixed-mode, CBS-specific inhibitor with no effect on the other two major enzymatic sources of H₂S, CSE and 3-MST. Unlike the prototypical CBS inhibitor aminooxyacetate, EGCG does not bind the catalytic cofactor of CBS pyridoxal-5'-phosphate. Molecular modeling suggests that EGCG blocks a substrate access channel to pyridoxal-5'-phosphate. EGCG inhibits cellular H₂S production in HCT-116 colon cancer cells and in DS fibroblasts. It also exerts effects that are consistent with the functional role of CBS in these cells: in HCT-116 cells it decreases, while in DS cells it improves viability and proliferation. In conclusion, EGCG is a potent inhibitor of CBS-derived H₂S production. This effect may contribute to its pharmacological effects in various pathophysiological conditions.