H2S donors attenuate diabetic nephropathy in rats: Modulation of oxidant status and polyol pathway

Pharmacology of Hydrogen Sulfide and Its Donors in Cardiometabolic Diseases

Cardiometabolic diseases (CMDs) are major contributors to global mortality, emphasizing the critical need for novel therapeutic interventions. Hydrogen sulfide (H2S) has garnered enormous attention as a significant gasotransmitter with various physiological, pathophysiological, and pharmacological impacts within mammalian cardiometabolic systems. In addition to its roles in attenuating oxidative stress and inflammatory response, burgeoning research emphasizes the significance of H2S in regulating proteins via persulfidation, a well known modification intricately associated with the pathogenesis of CMDs. This review seeks to investigate recent updates on the physiological actions of endogenous H2S and the pharmacological roles of various H2S donors in addressing diverse aspects of CMDs across cellular, animal, and clinical studies. Of note, advanced methodologies, including multiomics, intestinal microflora analysis, organoid, and single-cell sequencing techniques, are gaining traction due to their ability to offer comprehensive insights into biomedical research. These emerging approaches hold promise in characterizing the pharmacological roles of H2S in health and diseases. We will critically assess the current literature to clarify the roles of H2S in diseases while also delineating the opportunities and challenges they present in H2S-based pharmacotherapy for CMDs. SIGNIFICANCE STATEMENT: This comprehensive review covers recent developments in H2S biology and pharmacology in cardiometabolic diseases CMDs. Endogenous H2S and its donors show great promise for the management of CMDs by regulating numerous proteins and signaling pathways. The emergence of new technologies will considerably advance the pharmacological research and clinical translation of H2S.

Physiological role of hydrogen sulfide in the kidney and its therapeutic implications for kidney diseases

For over three centuries, hydrogen sulfide (H2S) has been known as a toxic and deadly gas at high concentrations, with a distinctive smell of rotten eggs. However, studies over the past two decades have shown that H2S has risen above its historically notorious label and has now received significant scientific attention as an endogenously produced gaseous signaling molecule that participates in cellular homeostasis and influences a myriad of physiological and pathological processes at low concentrations. Its endogenous production is enzymatically regulated, and when dysregulated, contributes to pathogenesis of renal diseases. In addition, exogenous H2S administration has been reported to exhibit important therapeutic characteristics that target multiple molecular pathways in common renal pathologies in which reduced levels of renal and plasma H2S were observed. This review highlights functional anatomy of the kidney and renal production of H2S. The review also discusses current understanding of H2S in renal physiology and seeks to lay the foundation as a new targeted therapeutic agent for renal pathologies such as hypertensive nephropathy, diabetic kidney disease and water balance disorders.

Hydrogen Sulfide in Diabetic Complications Revisited: The State of the Art, Challenges, and Future Directions

Significance: Diabetes and its related complications are becoming an increasing public health problem that affects hundreds of millions of people globally. Increased disability and mortality rate of diabetic individuals are closely associated with various life-threatening complications, such as atherosclerosis, nephropathy, retinopathy, and cardiomyopathy. Recent Advances: Conventional treatments for diabetes are still limited because of undesirable side effects, including obesity, hypoglycemia, and hepatic and renal toxicity. Studies have shown that hydrogen sulfide (H₂S) plays a critical role in the modulation of glycolipid metabolism, pancreatic β cell functions, and diabetic complications. Critical Issues: Preservation of endogenous H₂S systems and supplementation of H₂S donors are effective in attenuating diabetes-induced complications, thus representing a new avenue to treat diabetes and its associated complications. Future Directions: This review systematically recapitulates and discusses the most recent updates regarding the therapeutic effects of H₂S on diabetes and its various complications, with an emphasis on the molecular mechanisms that underlie H₂S-mediated protection against diabetic complications. Furthermore, current clinical trials of H₂S in diabetic populations are highlighted, and the challenges and solutions to the clinical transformation of H₂S-derived therapies in diabetes are proposed. Finally, future research directions of the pharmacological actions of H₂S in diabetes and its related complications are summarized. Antioxid. Redox Signal. 38, 18-44.

The roles of hydrogen sulfide in renal physiology and disease states

Hydrogen sulfide (H₂S), an endogenous gaseous signaling transmitter, has gained recognition for its physiological effects. In this review, we aim to summarize and discuss existing studies about the roles of H₂S in renal functions and renal disease as well as the underlying mechanisms. H₂S is mainly produced by four pathways, and the kidneys are major H₂S–producing organs. Previous studies have shown that H₂S can impact multiple signaling pathways via sulfhydration. In renal physiology, H₂S promotes kidney excretion, regulates renin release and increases ATP production as a sensor for oxygen. H₂S is also involved in the development of kidney disease. H₂S has been implicated in renal ischemia/reperfusion and cisplatin–and sepsis–induced kidney disease. In chronic kidney diseases, especially diabetic nephropathy, hypertensive nephropathy and obstructive kidney disease, H₂S attenuates disease progression by regulating oxidative stress, inflammation and the renin–angiotensin–aldosterone system. Despite accumulating evidence from experimental studies suggesting the potential roles of H₂S donors in the treatment of kidney disease, these results need further clinical translation. Therefore, expanding the understanding of H₂S can not only promote our further understanding of renal physiology but also lay a foundation for transforming H₂S into a target for specific kidney diseases.

Alpha-lipoic acid treatment improves adverse cardiac remodelling in the diabetic heart - The role of cardiac hydrogen sulfide-synthesizing enzymes

INTRODUCTION

Alpha-lipoic acid (ALA) is a licensed drug for the treatment of diabetic neuropathy. We recently reported that it also improves diabetic cardiomyopathy (DCM) in type 2 diabetes mellitus (T2DM). In this study, we present evidence supporting our hypothesis that the cardioprotective effect of ALA is via upregulation of cardiac hydrogen sulfide (H₂S)-synthesizing enzymes.

METHODS

Following 12 h of overnight fasting, T2DM was induced in 23 out of 30 male Sprague-Dawley rats by intraperitoneal administration of nicotinamide (110 mg/kg) followed by streptozotocin (55 mg/kg) while the rest served as healthy control (HC). T2DM rats then received either oral administration of ALA (60 mg/kg/day; n = 7) or 40 mg/kg/day DL-propargylglycine (PAG, an endogenous H₂S inhibitor; n = 7) intraperitoneally for 6 weeks after which all rats were sacrificed and samples collected for analysis. Untreated T2DM rats served as diabetic control (DCM; n = 9).

RESULTS

T2DM resulted in weight loss, islet destruction, reduced pancreatic β-cell function and hyperglycemia. Histologically, DCM rats showed significant myocardial damage evidenced by myocardial degeneration, cardiomyocyte vacuolation and apoptosis, cardiac fibrosis and inflammation, which positively correlated with elevated levels of cardiac damage markers compared to HC rats (p < 0.001). These pathological alterations worsened significantly in PAG-treated rats (p < 0.05). However, ALA treatment restored normoinsulemia, normoglycemia, prevented DCM, and improved lipid and antioxidant status. Mechanistically, ALA significantly upregulated the expression of cardiac H₂S-synthesizing enzymes and increased plasma H₂S concentration compared to DCM rats (p < 0.001).

CONCLUSION

ALA preserves myocardial integrity in T2DM likely by maintaining the expression of cardiac H₂S-synthezing enzymes and increasing plasma H₂S level.

Activation of renal CSE/H2S pathway by alpha-lipoic acid protects against histological and functional changes in the diabetic kidney

INTRODUCTION

We previously reported that alpha-lipoic acid (ALA) supplementation protects against progression of diabetic kidney disease (DKD). In this study, we aim to investigate whether the mechanism of renal protection by ALA involves renal cystathionine γ-lyase/hydrogen sulfide (CSE/H₂S) system in type 2 diabetes mellitus (T2DM).

METHODS

Thirty-seven male Sprague-Dawley rats underwent 12 h of overnight fasting. To induce T2DM, 30 of these rats received intraperitoneal administration of nicotinamide (110 mg/kg) and streptozotocin (55 mg/kg). T2DM rats then received either oral administration of ALA (60 mg/kg/day) or intraperitoneal administration of 40 mg/kg/day DL-propargylglycine (PAG, a CSE inhibitor) or both for 6 weeks after which rats were sacrificed and samples collected for analysis. Untreated diabetic and non-diabetic rats served as diabetic and healthy controls respectively.

RESULTS

T2DM was characterized by reduced pancreatic β-cell function and hyperglycemia. Histologically, untreated diabetic rats showed significantly damaged pancreatic islets, glomerular and tubular injury, with elevated levels of renal function markers compared to healthy control rats (p < 0.001). These pathological changes worsened significantly following PAG administration (p < 0.05). While some renal protection was observed in ALA+PAG rats, ALA administration in untreated diabetic rats provided superior protection comparable to healthy control rats, with improved antioxidant status, lipid profile and reduced inflammation. Mechanistically, ALA significantly activated renal CSE/H₂S system in diabetic rats, which was markedly suppressed in PAG-treated rats (p < 0.001).

CONCLUSION

Our data suggest that ALA protects against DKD development and progression by activating renal CSE/H₂S pathway. Hence, CSE/H₂S pathway may represent a therapeutic target in the treatment or prevention of DKD in diabetic patients.

Protective effect of H2S on LPS‑induced AKI by promoting autophagy

The present study explored the protective effect of exogenous hydrogen sulfide (H2S) on lipopolysaccharide (LPS)‑induced acute kidney injury (AKI) and the underlying mechanisms. To establish an AKI injury mouse model, LPS (10 mg/kg) was intraperitoneally injected into mice pretreated with 0.8 mg/kg sodium hydrosulfide hydrate (NaHS), an H2S donor. The mouse survival rate and the degree of kidney injury were examined. To construct a cell damage model, HK‑2 cells were pretreated with different concentrations (0.1, 0.3 and 0.5 mM) of NaHS, and then the cells were stimulated with LPS (1 µg/ml). The cell viability, autophagy, apoptosis levels and the release of inflammatory factors were examined in mouse kidney tissue and HK‑2 renal tubular epithelial cells. It was found that pretreatment with NaHS significantly improved the survival rate of septic AKI mice, and reduced the renal damage, release of inflammatory factors and apoptosis. In HK‑2 cells, NaHS protected cells from LPS caused damage via promoting autophagy and inhibiting apoptosis and the release of inflammatory factors. In order to clarify the relationship between autophagy and apoptosis and inflammatory factors, this study used 3‑methyladenine (3‑MA) to inhibit autophagy. The results revealed that 3‑MA eliminated the protective effect of NaHS in HK‑2 cells and AKI mice. Overall, NaHS can protect from LPS‑induced AKI by promoting autophagy and inhibiting apoptosis and the release of inflammatory factors.

Exercise training ameliorates early diabetic kidney injury by regulating the H2 S/SIRT1/p53 pathway

Exercise training exerts protective effects against diabetic nephropathy. This study aimed to investigate whether exercise training could attenuate diabetic renal injury via regulating endogenous hydrogen sulfide (H₂ S) production. First, C57BL/6 mice were allocated into the control, diabetes, exercise, and diabetes + exercise groups. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ). Treadmill exercise continued for four weeks. Second, mice was allocated into the control, diabetes, H₂ S and diabetes + H₂ S groups. H₂ S donor sodium hydrosulfide (NaHS) was intraperitoneally injected once daily for four weeks. STZ-induced diabetic mice exhibited glomerular hypertrophy, tissue fibrosis and increased urine albumin levels, urine protein- and albumin-to-creatinine ratios, which were relieved by exercise training. Diabetic renal injury was associated with apoptotic cell death, as evidenced by the enhanced caspase-3 activity, the increased TdT-mediated dUTP nick-end labeling -positive cells and the reduced expression of anti-apoptotic proteins, all of which were attenuated by exercise training. Exercise training enhanced renal sirtuin 1 (SIRT1) expression in diabetic mice, accompanied by an inhibition of the p53-#ediated pro-apoptotic pathway. Furthermore, exercise training restored the STZ-mediated downregulation of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) and the reduced renal H₂ S production. NaHS treatment restored SIRT1 expression, inhibited the p53-mediated pro-apoptotic pathway and attenuated diabetes-associated apoptosis and renal injury. In high glucose-treated MPC5 podocytes, NaHS treatment inhibited the p53-mediated pro-apoptotic pathway and podocyte apoptosis in a SIRT1-dependent manner. Collectively, exercise training upregulated CBS/CSE expression and enhanced the endogenous H₂ S production in renal tissues, thereby contributing to the modulation of the SIRT1/p53 apoptosis pathway and improvement of diabetic nephropathy.

Effects of Sodium Chloride-Rich Mineral Water on Intestinal Epithelium. Experimental Study

Since knowledge concerning the cellular and tissue substrate that explains the therapeutic action of mineral waters is generally very scarce, we address the different effects that Lanjarón-Capuchina mineral water exerts on the intestinal epithelium in an experimental model as a prototype of the sodium chloride-rich mineral waters used in digestive disorders. In the experimental protocol, two groups of five adult Wistar rats received unrestricted mineral water in their diet or mineral water directly into the gastrointestinal tract through a catheter. A third control group was given a standard diet and water ad libitum. Intestinal samples for scanning electron microscopy were analyzed according to standardized methods. The observations carried out by microscope after the administration of the sodium chloride-rich mineral water clearly indicate that the hypertonic action of this mineral water affects the structure of the intestinal epithelium. It modifies the microvilli absorption in terms of the groups of enterocytes and the secretion of goblet cells, but it particularly affects the epithelial renewal process, accelerating and stimulating cell extrusion. The type of extrusion mechanism observed by microscope allows us to affirm that, although this increased after direct administration, it does not generate an epithelial disruption as it occurs in other circumstances with other extrusion modalities.

Role of Oxidative Stress and Reduced Endogenous Hydrogen Sulfide in Diabetic Nephropathy

Purpose

Persistent hyperglycemia lead towards depletion of hydrogen sulfide (H₂S) resulting in generation of oxidative stress and diabetic nephropathy. The aim of the current study was to explore the antioxidant potential of H₂S and captopril, a -SH containing compound in streptozotocin (STZ)-induced diabetic nephropathy.

Methods

Fifty four Wistar-Kyoto (WKY) rats male (200-250g) were divided into nine groups (n=6) with each group injected once with STZ (60mg/kg i.p) except normal control. After 3 weeks of induction of diabetes, groups were assigned as normal control, diabetic control, diabetic-captopril, diabetic-NaHS, diabetic-captopril-NaHS, diabetic-spironolactone, diabetic-metformin, diabetic-metformin-NaHS and diabetic-vitamin-c. All the animals were served with normal saline (N/S 4mL/kg p.o), captopril (50mg/kg/day p.o), sodium hydrosulfide (NaHS) (56µmol/kg i.p), spironolactone (50mg/kg/day s.c), metformin (500mg/kg/day p.o) and vitamin-c (50mg/kg p.o) on daily basis for next 4 weeks, respectively. Metabolic studies, H₂S levels, renal hemodynamics and oxidative stress markers were analyzed at 0, 14 and 28 days followed by histopathological analysis of renal tissues.

Results

The results showed decreased H₂S levels, body weight, sodium to potassium ratio, glutathione (GSH), superoxide dismutase (SOD), total antioxidant assay (T-AOC) with malondialdehyde (MDA) and blood glucose levels significantly increased among diabetic rats. Treatment with captopril, NaHS, metformin, spironolactone and vitamin C showed significant improvement among renal hemodynamics and oxidative stress markers, respectively. But treatment groups like NaHS in combination with captopril and metformin showed more pronounced effects.

Conclusion

The observations suggest that H₂S mediated protective effects on STZ-induced diabetic nephropathy may be associated with reduced oxidative stress via augmenting the antioxidant effect.

Hydrogen Sulfide and Carnosine: Modulation of Oxidative Stress and Inflammation in Kidney and Brain Axis

Emerging evidence indicates that the dysregulation of cellular redox homeostasis and chronic inflammatory processes are implicated in the pathogenesis of kidney and brain disorders. In this light, endogenous dipeptide carnosine (β-alanyl-L-histidine) and hydrogen sulfide (H₂S) exert cytoprotective actions through the modulation of redox-dependent resilience pathways during oxidative stress and inflammation. Several recent studies have elucidated a functional crosstalk occurring between kidney and the brain. The pathophysiological link of this crosstalk is represented by oxidative stress and inflammatory processes which contribute to the high prevalence of neuropsychiatric disorders, cognitive impairment, and dementia during the natural history of chronic kidney disease. Herein, we provide an overview of the main pathophysiological mechanisms related to high levels of pro-inflammatory cytokines, including interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and neurotoxins, which play a critical role in the kidney–brain crosstalk. The present paper also explores the respective role of H₂S and carnosine in the modulation of oxidative stress and inflammation in the kidney–brain axis. It suggests that these activities are likely mediated, at least in part, via hormetic processes, involving Nrf2 (Nuclear factor-like 2), Hsp 70 (heat shock protein 70), SIRT-1 (Sirtuin-1), Trx (Thioredoxin), and the glutathione system. Metabolic interactions at the kidney and brain axis level operate in controlling and reducing oxidant-induced inflammatory damage and therefore, can be a promising potential therapeutic target to reduce the severity of renal and brain injuries in humans.

Effects of drinking natural hydrogen sulfide (H2S) waters: a systematic review of in vivo animal studies

Natural waters containing originally hydrogen sulfide (H2S) gas with an S2-level at least 1 mg/L are classified as "sulfur waters" or "hydrogen sulfide waters." This systematic review aimed to evaluate in vivo experimental studies investigating the biological effects of natural H2S water drinking in healthy or with disease model laboratory animals. A comprehensive databases search (PubMed, Embase, Web of Science, and Google Scholar) was performed and PICOS criteria were used to assess eligibility. All relevant studies were identified, screened, and examined. The qualitative assessment was performed with the help of the SYRCLE Risk of Bias tool. A total of nine articles were included. The extracted data showed that ad libitum drinking of such waters by rats and mice exert beneficial effects on animal model of diabetes and glucose metabolism plus protective effects on diabetic cardiac, testicular, and nephrological complications as shown biochemically, histopathologically, and bio-molecularly. Additional effects were gastroprotection, antioxidant effects and improvement of intestinal physiology in healthy animals, reduction in general signs of murine model of colitis in mice, improvement in lipid metabolism and lipid-lowering effect, and positive interference with the enterohepatic cycle of the bile acids and biliary functions in hyperlipidemic rats. This systematic review provides preliminary insights into the "biological truth" about natural H2S waters and partly elucidates their potential therapeutic role in balneology and health resort medicine. However, it should be kept in mind that the retrieved preclinical data cannot be directly extrapolated to humans. Additionally, most of the included studies were rated for unclear risk of bias across all categories except random allocation, reflecting very poor reporting of methodological details. These limitations should be addressed when planning similar studies in the future. The question "can traditional hydropinic therapies or drinking cures with H2S waters at natural sulfur water spas/health resorts or natural (even artificial) H2S water consumption at home exert similar effects in humans?" remains to be clarified by clinical trials.

Hydrogen sulfide modulates SIRT1 and suppresses oxidative stress in diabetic nephropathy

DN is recognized as not only a leading cause of end stage renal disease (ESRD) but also an independent risk factor for cardiovascular disease (CVD). Novel therapeutic approaches to diabetic nephropathy (DN) are needed, or else, healthcare resources will be overwhelmed by the expected worldwide increase in associated cases of ESRD and CVD. Reactive oxygen species (ROS) and advanced glycation end product (AGE) are implicated in the development of DN. Hydrogen sulfide (H₂S) is known for its antioxidant and antiapoptotic characteristics. Simultaneously diabetics have lower H₂S levels. Thus, it is worth investigating the use of H₂S in treatment of DN. To investigate the potential therapeutic role of H₂S in DN. Sixty male rats were divided into four groups: control, DN, DN+NaHS30 µmol/kg/day and DN+NaHS100 µmol/kg/day. Fasting blood sugar (FBS), kidney function tests, SIRT1 activity, superoxide dismutase activity (SOD), malondialdehyde (MDA) and expression of caspase3 and p53 in renal tissues were assessed. Kidney was examined histopathologically. DN rats had higher FBS, renal dysfunction, decreased SIRT1 and SOD activity levels, increased caspase3 and p53 relative expression and increased MDA in renal tissues. NaHS increased SIRT1 and reversed biochemical, apoptotic, oxidant and pathologic parameters characteristic of DN, with better results using a dose of 100 µmol/kg/day. H₂S has a protective role against DN through decreasing FBS, ROS, apoptosis and upregulating SIRT1, thus preserving renal cells from further damage caused by DM.

A small-molecule probe for ratiometric photoacoustic imaging of hydrogen sulfide in living mice

A small molecule ratiometric photoacoustic probe was developed for real-time monitoring of hydrogen sulfide in living mice.

Alpha-lipoic acid regulates the autophagy of vascular smooth muscle cells in diabetes by elevating hydrogen sulfide level

Dysfunctional vascular smooth muscle (VSM) plays a vital role in the process of atherosclerosis in patients with type 2 diabetes mellitus (T2DM). Alpha-lipoic acid (ALA) can prevent the altered VSM induced by diabetes. However, the precise mechanism underlying the beneficial effect of ALA is not well understood. This study aimed to determine whether ALA ameliorates VSM function by elevating hydrogen sulfide (H₂S) level in diabetes and whether this effect is associated with regulation of autophagy of VSM cells (VSMCs). We found decreased serum H₂S levels in Chinese patients and rats with type 2 diabetes mellitus (T2DM). ALA treatment could increase H₂S level, which reduced the autophagy-related index and activation of the 5'-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway, thereby protecting vascular function in rats with T2DM. Propargylglycine (PPG), a cystathionine-γ-lyase inhibitor, could weaken the ALA effect. In cultured VSMCs, high glucose level also reduced H₂S level, upregulated the autophagy-related index and activated the AMPK/mTOR pathway, which were reversed by concomitant application of sodium hydrosulfide (NaHS, an H₂S donor) or ALA. The protective effect of NaHS or ALA was attenuated by rapamycin (an autophagy activator), 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide (an AMPK activator) or PPG. In contrast, Compound C (an AMPK inhibitor) enhanced the effect of ALA or NaHS. ALA may have a protective effect on VSMCs in T2DM by elevating H₂S level and downregulating autophagy via the AMPK/mTOR pathway. This study provides a new target for addressing diabetic macroangiopathy.

Balneotherapy, Immune System, and Stress Response: A Hormetic Strategy?

Balneotherapy is a clinically effective complementary approach in the treatment of low-grade inflammation- and stress-related pathologies. The biological mechanisms by which immersion in mineral-medicinal water and the application of mud alleviate symptoms of several pathologies are still not completely understood, but it is known that neuroendocrine and immunological responses—including both humoral and cell-mediated immunity—to balneotherapy are involved in these mechanisms of effectiveness; leading to anti-inflammatory, analgesic, antioxidant, chondroprotective, and anabolic effects together with neuroendocrine-immune regulation in different conditions. Hormesis can play a critical role in all these biological effects and mechanisms of effectiveness. The hormetic effects of balneotherapy can be related to non-specific factors such as heat—which induces the heat shock response, and therefore the synthesis and release of heat shock proteins—and also to specific biochemical components such as hydrogen sulfide (H₂S) in sulfurous water and radon in radioactive water. Results from several investigations suggest that the beneficial effects of balneotherapy and hydrotherapy are consistent with the concept of hormesis, and thus support a role for hormesis in hydrothermal treatments.

Quercetin nanoparticle complex attenuated diabetic nephropathy via regulating the expression level of ICAM-1 on endothelium

The purpose of the study was to reveal the therapeutic effect of quercetin (QUE) nanoparticle complex on diabetic nephropathy (DN) by regulating the expression of intercellular adhesion molecular-1 (ICAM-1) on endothelium as compared to free QUE. QUE 10 mg/kg as a single abdominal subcutaneous injection daily for 8 weeks continuously in diabetic rats and 10 mg/kg QUE nanoparticle complex as a single abdominal subcutaneous injection every 5 days, continuously administered for 8 weeks to diabetic rats. Blood and left kidneys were collected; pathological change of kidney, renal function, oxidative stress level, blood glucose level, serum lipid, urine protein, and albumin/creatinine ratio were measured; and neutrophil adhesion, ICAM-1 expression, and CD11b⁺ cells infiltration were observed. Both QUE and QUE nanoparticle complex preconditioning ameliorated the pathological damage of kidney and improved renal function, alleviated renal oxidative stress injury, restricted inflammatory cells infiltration, and downregulated the ICAM-1 expression as compared to DN group, while QUE nanoparticle complex significantly alleviated this effect.

The smell of renal protection against chronic kidney disease: Hydrogen sulfide offers a potential stinky remedy

Chronic kidney disease (CKD) is a common global health challenge characterized by irreversible pathological processes that reduce kidney function and culminates in development of end-stage renal disease. It is associated with increased morbidity and mortality in addition to increased caregiver burden and higher financial cost. A central player in CKD pathogenesis and progression is renal hypoxia. Renal hypoxia stimulates induction of oxidative and endoplasmic reticulum stress, inflammation and tubulointerstitial fibrosis, which in turn, promote cellular susceptibility and further aggravate hypoxia, thus forming a pathological vicious cycle in CKD progression. Although the importance of CKD is widely appreciated, including improvements in the quality of existing therapies such as dialysis and transplantation, new therapeutic options are limited, as there is still increased morbidity, mortality and poor quality of life among CKD patients. Growing evidence indicates that hydrogen sulfide (H₂S), a small gaseous signaling molecule with an obnoxious smell, accumulates in the renal medulla under hypoxic conditions, and functions as an oxygen sensor that restores oxygen balance and increases medullary flow. Moreover, plasma H₂S level has been recently reported to be markedly reduced in CKD patients and animal models. Also, H₂S has been established to possess potent antioxidant, anti-inflammatory, and anti-fibrotic properties in several experimental models of kidney diseases, suggesting that its supplementation could protect against CKD and retard its progression. The purpose of this review is to discuss current clinical and experimental developments regarding CKD, its pathophysiology, and potential cellular and molecular mechanisms of protection by H₂S in experimental models of CKD.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

Vascular biology of hydrogen sulfide

Hydrogen sulfide (H₂S) is a ubiquitous signaling molecule with important functions in many mammalian organs and systems. Observations in the 1990s ascribed physiological actions to H₂S in the nervous system, proposing that this gasotransmitter acts as a neuromodulator. Soon after that, the vasodilating properties of H₂S were demonstrated. In the past decade, H₂S was shown to exert a multitude of physiological effects in the vessel wall. H₂S is produced by vascular cells and exhibits antioxidant, antiapoptotic, anti-inflammatory, and vasoactive properties. In this concise review, we have focused on the impact of H₂S on vascular structure and function with an emphasis on angiogenesis, vascular tone, vascular permeability and atherosclerosis. H₂S reduces arterial blood pressure, limits atheromatous plaque formation, and promotes vascularization of ischemic tissues. Although the beneficial properties of H₂S are well established, mechanistic insights into the molecular pathways implicated in disease prevention and treatment remain largely unexplored. Unraveling the targets and downstream effectors of H₂S in the vessel wall in the context of disease will aid in translation of preclinical observations. In addition, acute regulation of H₂S production is still poorly understood and additional work delineating the pathways regulating the enzymes that produce H₂S will allow pharmacological manipulation of this pathway. As the field continues to grow, we expect that H₂S-related compounds will find their way into clinical trials for diseases affecting the blood vessels.

H2S as a possible therapeutic alternative for the treatment of hypertensive kidney injury

Hypertension is the most common cause of cardiovascular morbidities and mortalities, and a major risk factor for renal dysfunction. It is considered one of the causes of chronic kidney disease, which progresses into end-stage renal disease and eventually loss of renal function. Yet, the mechanism underlying the pathogenesis of hypertension and its associated kidney injury is still poorly understood. Moreover, despite existing antihypertensive therapies, achievement of blood pressure control and preservation of renal function still remain a worldwide public health challenge in a subset of hypertensive patients. Therefore, novel modes of intervention are in demand. Hydrogen sulfide (H₂S), a gaseous signaling molecule, has been established to possess antihypertensive and renoprotective properties, which may represent an important therapeutic alternative for the treatment of hypertension and kidney injury. This review discusses recent findings about H₂S in hypertension and kidney injury from both experimental and clinical studies. It also addresses future direction regarding therapeutic use of H₂S.

Diabetic nephropathy: A potential savior with 'rotten-egg' smell

Diabetic nephropathy (DN) is currently the leading cause of end-stage renal disease. Despite optimal management, DN is still a major contributor to morbidity and mortality of diabetic patients worldwide. The major pathological alterations in DN include excessive accumulation and deposition of extracellular matrix, leading to expansion of mesangial matrix, thickening of glomerular basement membrane and tubulointerstitial fibrosis. At the molecular level, accumulating evidence suggests that hyperglycemia or high glucose mediates renal injury in DN via multiple molecular mechanisms such as induction of oxidative stress, upregulation of renal transforming growth factor beta-1 expression, production of proinflammatory cytokines, activation of fibroblasts and renin angiotensin system, and depletion of adenosine triphosphate. Also worrying is the fact that existing therapies only retard the disease progression but do not prevent it. Therefore, there is urgent need to identify novel therapies to target additional disease mechanisms. Hydrogen sulfide (H₂S), the third member of the gasotransmitter family, has recently been identified and demonstrated to possess important therapeutic characteristics that prevent the development and progression of DN in experimental animals by targeting several important molecular pathways, and therefore may represent an alternative or additional therapeutic approach for DN. This review discusses recent experimental findings on the molecular mechanisms underlying the therapeutic effects of H₂S against the development and progression of DN and its clinical application in the future.

The Role of Hydrogen Sulfide in Renal System

Hydrogen sulfide has gained recognition as the third gaseous signaling molecule after nitric oxide and carbon monoxide. This review surveys the emerging role of H2S in mammalian renal system, with emphasis on both renal physiology and diseases. H2S is produced redundantly by four pathways in kidney, indicating the abundance of this gaseous molecule in the organ. In physiological conditions, H2S was found to regulate the excretory function of the kidney possibly by the inhibitory effect on sodium transporters on renal tubular cells. Likewise, it also influences the release of renin from juxtaglomerular cells and thereby modulates blood pressure. A possible role of H2S as an oxygen sensor has also been discussed, especially at renal medulla. Alternation of H2S level has been implicated in various pathological conditions such as renal ischemia/reperfusion, obstructive nephropathy, diabetic nephropathy, and hypertensive nephropathy. Moreover, H2S donors exhibit broad beneficial effects in renal diseases although a few conflicts need to be resolved. Further research reveals that multiple mechanisms are underlying the protective effects of H2S, including anti-inflammation, anti-oxidation, and anti-apoptosis. In the review, several research directions are also proposed including the role of mitochondrial H2S in renal diseases, H2S delivery to kidney by targeting D-amino acid oxidase/3-mercaptopyruvate sulfurtransferase (DAO/3-MST) pathway, effect of drug-like H2S donors in kidney diseases and understanding the molecular mechanism of H2S. The completion of the studies in these directions will not only improves our understanding of renal H2S functions but may also be critical to translate H2S to be a new therapy for renal diseases.

The novel mitochondria-targeted hydrogen sulfide (H2S) donors AP123 and AP39 protect against hyperglycemic injury in microvascular endothelial cells in vitro

The development of diabetic vascular complications is initiated, at least in part, by mitochondrial reactive oxygen species (ROS) production in endothelial cells. Hyperglycemia induces superoxide production in the mitochondria and initiates changes in the mitochondrial membrane potential that leads to mitochondrial dysfunction. Hydrogen sulfide (H₂S) supplementation has been shown to reduce the mitochondrial oxidant production and shows efficacy against diabetic vascular damage in vivo. However, the half-life of H₂S is very short and it is not specific for the mitochondria. We have therefore evaluated two novel mitochondria-targeted anethole dithiolethione and hydroxythiobenzamide H₂S donors (AP39 and AP123 respectively) at preventing hyperglycemia-induced oxidative stress and metabolic changes in microvascular endothelial cells in vitro. Hyperglycemia (HG) induced significant increase in the activity of the citric acid cycle and led to elevated mitochondrial membrane potential. Mitochondrial oxidant production was increased and the mitochondrial electron transport decreased in hyperglycemic cells. AP39 and AP123 (30–300 nM) decreased HG-induced hyperpolarisation of the mitochondrial membrane and inhibited the mitochondrial oxidant production. Both H₂S donors (30–300 nM) increased the electron transport at respiratory complex III and improved the cellular metabolism. Targeting H₂S to mitochondria retained the cytoprotective effect of H₂S against glucose-induced damage in endothelial cells suggesting that the molecular target of H₂S action is within the mitochondria. Mitochondrial targeting of H₂S also induced >1000-fold increase in the potency of H₂S against hyperglycemia-induced injury. The high potency and long-lasting effect elicited by these H₂S donors strongly suggests that these compounds could be useful against diabetic vascular complications.

myo-Inositol Oxygenase Overexpression Accentuates Generation of Reactive Oxygen Species and Exacerbates Cellular Injury following High Glucose Ambience: A NEW MECHANISM RELEVANT TO THE PATHOGENESIS OF DIABETIC NEPHROPATHY

Diabetic nephropathy (DN) is characterized by perturbations in metabolic/cellular signaling pathways with generation of reactive oxygen species (ROS). The ROS are regarded as a common denominator of various pathways, and they inflict injury on renal glomerular cells. Recent studies indicate that tubular pathobiology also plays a role in the progression of DN. However, the mechanism(s) for how high (25 mm) glucose (HG) ambience induces tubular damage remains enigmatic. myo-Inositol oxygenase (MIOX) is a tubular enzyme that catabolizes myo-inositol to d-glucuronate via the glucuronate-xylulose (G-X) pathway. In this study, we demonstrated that G-X pathway enzymes are expressed in the kidney, and MIOX expression/bioactivity was up-regulated under HG ambience in LLC-PK1 cells, a tubular cell line. We further investigated whether MIOX overexpression leads to accentuation of tubulo-interstitial injury, as gauged by some of the parameters relevant to the progression of DN. Under HG ambience, MIOX overexpression accentuated redox imbalance, perturbed NAD(+)/NADH ratios, increased ROS generation, depleted reduced glutathione, reduced GSH/GSSG ratio, and enhanced adaptive changes in the profile of the antioxidant defense system. These changes were also accompanied by mitochondrial dysfunctions, DNA damage and induction of apoptosis, accentuated activity of profibrogenic cytokine, and expression of fibronectin, the latter two being the major hallmarks of DN. These perturbations were largely blocked by various ROS inhibitors (Mito Q, diphenyleneiodonium chloride, and N-acetylcysteine) and MIOX/NOX4 siRNA. In conclusion, this study highlights a novel mechanism where MIOX under HG ambience exacerbates renal injury during the progression of diabetic nephropathy following the generation of excessive ROS via an unexplored G-X pathway.