Pancreatic islet overproduction of H2S and suppressed insulin release in Zucker diabetic rats

Chronic methylglyoxal infusion by minipump causes pancreatic beta-cell dysfunction and induces type 2 diabetes in Sprague-Dawley rats

OBJECTIVE

The incidence of high dietary carbohydrate-induced type 2 diabetes is increasing worldwide. Methylglyoxal (MG) is a reactive glucose metabolite and a major precursor of advanced glycation end products (AGEs). MG levels are elevated in diabetic patients. We investigated the effects of chronic administration of MG on glucose tolerance and β-cell insulin secreting mechanism in 12-week-old male Sprague-Dawley rats.

RESEARCH DESIGN AND METHODS

MG (60 mg/kg/day) or 0.9% saline was administered by continuous infusion with a minipump for 28 days. We performed glucose and insulin tolerance tests and measured adipose tissue glucose uptake and insulin secretion from isolated pancreatic islets. We also used cultured INS-1E cells, a pancreatic β-cell line, for molecular studies. Western blotting, quantitative PCR, immunohistochemistry, and transferase-mediated dUTP nick-end labeling (TUNEL) assay were performed.

RESULTS

In rats treated with MG and MG + l-buthionine sulfoximine (BSO), MG levels were significantly elevated in plasma, pancreas, adipose tissue, and skeletal muscle; fasting plasma glucose was elevated, whereas insulin and glutathione were reduced. These two groups also had impaired glucose tolerance, reduced GLUT-4, phosphoinositide-3-kinase activity, and insulin-stimulated glucose uptake in adipose tissue. In the pancreatic β-cells, MG and MG + BSO reduced insulin secretion, pancreatic duodenal homeobox-1, MafA, GLUT-2, and glucokinase expression; increased C/EBPβ, nuclear factor-κB, MG-induced AGE, N(ε)-carboxymeythyllysine, and receptor for AGEs expression; and caused apoptosis. Alagebrium, an MG scavenger and an AGE-breaking compound, attenuated the effects of MG.

CONCLUSIONS

Chronic MG induces biochemical and molecular abnormalities characteristic of type 2 diabetes and is a possible mediator of high carbohydrate-induced type 2 diabetes.

Rescue of mesangial cells from high glucose-induced over-proliferation and extracellular matrix secretion by hydrogen sulfide

BACKGROUND

Hydrogen sulfide (H(2)S) is considered as the third gasotransmitter after nitric oxide and carbon monoxide. This gas molecule participates in the regulation of renal function. Diabetic nephropathy (DN) is one of the major chronic complications of diabetes. The present study aimed to explore the changes in H(2)S metabolism in the early stage of DN and the effects of H(2)S on cultured rat renal glomerular mesangial cells (MCs).

METHODS

Cultured rat MCs and streptozotocin (STZ)-induced diabetic rats were used in this study. Expression levels of cystathionine γ-lyase (CSE), transforming growth factor-β1 (TGF-β1) and collagen IV in rat renal cortex and in cultured MCs were determined by quantitative real-time PCR and western blot. Reactive oxygen species (ROS) released from rat MCs was assessed by fluorescent probe assays. MCs proliferation was analyzed by 5'-bromo-2'-deoxyuridine incorporation assay.

RESULTS

H(2)S levels in the plasma and renal cortex and the levels of CSE messenger RNA (mRNA) and protein in renal cortex were significantly reduced, while the levels of TGF-β1 and collagen IV increased 3 weeks after STZ injection. Administration of NaHS, a H(2)S donor, reversed the increases in TGF-β1 and collagen IV in diabetic rats. By contrast, NaHS did not alter the TGF-β1 and collagen IV levels in non-diabetic rats. But NaHS lowered the CSE mRNA level in renal cortex. Exposure to high glucose promoted ROS generation and cell proliferation, up-regulated the expression of TGF-β1 and collagen IV but decreased the CSE expression in cultured MCs. Treatment of cultured MCs with NaHS reversed the effect of high glucose. NaHS did not change ROS generation, cell proliferation, TGF-β1 and collagen IV expression in the cells cultured with normal glucose. Reduction of endogenous H(2)S generation by DL-propargylglycine, a CSE inhibitor, produced similar cellular effects as high glucose, including increases in cell proliferation, TGF-β1 and collagen IV expressions and ROS generation.

CONCLUSION

Suppressed CSE-catalyzed endogenous H(2)S production in the kidney by hyperglycemia may play an important role in the pathogenesis of DN.

Hydrogen sulphide: novel opportunity for drug discovery

Hydrogen sulphide (H(2)S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H(2)S is biosynthesized in mammalian tissues by cystathionine-β-synthase and cystathionine-γ-lyase. H(2)S exhibits the antioxidant properties of inorganic and organic sulphites, behaving as a scavenger of reactive oxygen species. There is also clear evidence that H(2)S triggers other important effects, mainly mediated by the activation of ATP-sensitive potassium channels (K(ATP)). This mechanism accounts for the vasorelaxing and cardioprotective effects of H(2)S. Furthermore, H(2)S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H(2)S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H(2)S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H(2)S biosynthesis is involved in CV complications associated with diabetes mellitus. There is also evidence of a cross-talk between the H(2)S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H(2 S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H(2)S have led several authors to look at this mediator as "the new NO" that has given attractive opportunities to develop innovative classes of drugs. In this review, the main biological actions of H(2)S are discussed. Moreover, some examples of H(2)S-donors are shown, as well as some hybrids, in which H(2)S-releasing moieties are added to well-known drugs, for improving their pharmacodynamic profile or reducing the potential for adverse effects, are reported.

Development of hydrogen sulfide-based therapeutics for cardiovascular disease

The physiological role of the gaseous signaling molecule hydrogen sulfide (H(2)S) was first realized in the mid-1990s with the work of Abe and Kimura. Since then, it has become evident that this endogenous gas is extremely important in the homeostasis of the cardiovascular system and the pathogenesis of cardiovascular disease. Several biotechnology companies have developed and are developing H(2)S-based therapeutic compounds, and there are ongoing clinical trials investigating the therapeutic potential of H(2)S. Several organic and chemical compounds that are known H(2)S donors have the potential to be developed into effective H(2)S-based therapeutic agents. This review will provide a historical and current perspective on the role(s) of H(2)S in the cardiovascular system and the current state of development and future outlook of H(2)S-based therapies for cardiovascular disease.

Mechanism of inhibition by hydrogen sulfide of native and recombinant BKCa channels

Recent evidence suggests that H(2)S contributes to activation of the carotid body by hypoxia by inhibiting K(+) channels. Here, we determine both the molecular identity of the K(+) channel target within the carotid body and the biophysical characteristics of the H(2)S-evoked inhibition by analyzing native rat and human recombinant BK(Ca) channel activity in voltage-clamped, inside-out membrane patches. Rat glomus cells express the enzymes necessary for the endogenous generation of H(2)S, cystathionine-beta-synthase and cystathionine-gamma-lyase. H(2)S inhibits native carotid body and human recombinant BK(Ca) channels with IC(50) values of around 275 microM. Inhibition by H(2)S is rapid and reversible, works by a mechanism which is distinct from that suggested for CO gas regulation of this channel and does not involve an interaction with either the "Ca bowl" or residues distal to this Ca(2+)-sensing domain. These data show that BK(Ca) is a K(+) channel target of H(2)S, and suggest a mechanism to explain the H(2)S-dependent component of O(2) sensing in the carotid body.

Hydrogen sulfide: the third gasotransmitter in biology and medicine

The last two decades have seen one of the greatest excitements and discoveries in science, gasotransmitters in biology and medicine. Leading the trend by nitric oxide and extending the trudge by carbon monoxide, here comes hydrogen sulfide (H(2)S) who builds up the momentum as the third gasotransmitter. Being produced by different cells and tissues in our body, H(2)S, alone or together with the other two gasotransmitters, regulates an array of physiological processes and plays important roles in the pathogenesis of various diseases from neurodegenerative diseases to diabetes or heart failure, to name a few. As a journal dedicated to serve the emergent and challenging field of H(2)S biology and medicine, Antioxidant and Redox Signaling assembles the most recent discoveries and most provoking ideas from leading scientists in H(2)S fields, which were communicated in the First International Conference of H(2)S in Biology and Medicine, and brings them to our readers in two Forum Issues. Through intellectual exchange and intelligent challenge with an open-mind approach, we can reasonably expect that sooner rather than later the exploration of metabolism and function of H(2)S will provide solutions for many of the biological mysteries of life and pave way for the arrival of many more gasotransmitters.

Interaction of methylglyoxal and hydrogen sulfide in rat vascular smooth muscle cells

Hydrogen sulfide (H(2)S) is a gasotransmitter with multifaceted physiological functions, including the regulation of glucose metabolism. Methylglyoxal (MG) is an intermediate of glucose metabolism and plays an important role in the pathogenesis of insulin resistance syndromes. In the present study, we investigated the effect of MG on H(2)S synthesis and the interaction between these two endogenous substances. In cultured vascular smooth muscle cells (VSMCs), MG (10, 30, and 50 microM) significantly decreased cellular H(2)S levels in a concentration-dependent manner, while H(2)S donor, NaHS (30, 60, and 90 microM), significantly decreased cellular MG levels. The expression level and activity of H(2)S-producing enzyme, cystathionine gamma-lyase (CSE), were significantly decreased by MG treatment. NaHS (30-90 microM) significantly inhibited MG (10 or 30 microM)-induced ROS production. Cellular levels of GSH, cysteine, and homocysteine were also increased by MG or NaHS treatment. Furthermore, direct reaction of H(2)S with MG in both concentration- and time-dependent manners were observed in in vitro incubations. In conclusion, MG regulates H(2)S level in VSMCs by downregulating CSE protein expression and directly reacting with H(2)S molecule. Interaction of MG with H(2)S may be one of future directions for the studies on glucose metabolism and the development of insulin resistance syndromes.

Physiological and pharmacological features of the novel gasotransmitter: hydrogen sulfide

Hydrogen sulfide (H(2)S) has been known for hundreds of years because of its poisoning effect. Once the basal bio-production became evident its pathophysiological role started to be investigated in depth. H(2)S is a gas that can be formed by the action of two enzymes, cystathionine gamma-lyase and cystathionine beta-synthase, both involved in the metabolism of cysteine. It has several features in common with the other two well known "gasotransmitters" (nitric oxide and carbon monoxide) in the biological systems. These three gasses share some biological targets; however, they also have dissimilarities. For instance, the three gases target heme-proteins and open K(ATP) channels; H(2)S as NO is an antioxidant, but in contrast to the latter molecule, H(2)S does not directly form radicals. In the last years H(2)S has been implicated in several physiological and pathophysiological processes such as long term synaptic potentiation, vasorelaxation, pro- and anti-inflammatory conditions, cardiac inotropism regulation, cardioprotection, and several other physiological mechanisms. We will focus on the biological role of H(2)S as a molecule able to trigger cell signaling. Our attention will be particularly devoted on the effects in cardiovascular system and in cardioprotection. We will also provide available information on H(2)S-donating drugs which have so far been tested in order to conjugate the beneficial effect of H(2)S with other pharmaceutical properties.

Is hydrogen sulfide a circulating "gasotransmitter" in vertebrate blood?

Hydrogen sulfide (H(2)S) is gaining acceptance as a signaling molecule and has been shown to elicit a variety of biological effects at concentrations between 10 and 1000 micromol/l. Dissolved H(2)S is a weak acid in equilibrium with HS(-) and S(2-) and under physiological conditions these species, collectively referred to as sulfide, exist in the approximate ratio of 20% H(2)S, 80% HS(-) and 0% S(2-). Numerous analyses over the past 8 years have reported plasma or blood sulfide concentrations also in this range, typically between 30 and 300 micromol/l, thus supporting the biological studies. However, there is some question whether or not these concentrations are physiological. First, many of these values have been obtained from indirect methods using relatively harsh chemical conditions. Second, most studies conducted prior to 2000 failed to find blood sulfide in micromolar concentrations while others showed that radiolabeled (35)S-sulfide is rapidly removed from blood and that mammals have a relatively high capacity to metabolize exogenously administered sulfide. Very recent studies using H(2)S gas-sensing electrodes to directly measure sulfide in plasma or blood, or HPLC analysis of head-space gas, have also indicated that sulfide does not circulate at micromolar levels and is rapidly consumed by blood or tissues. Third, micromolar concentrations of sulfide in blood or exhaled air should be, but are not, malodorous. Fourth, estimates of dietary sulfur necessary to sustain micromolar levels of plasma sulfide greatly exceed the daily intake. Collectively, these studies imply that many of the biological effects of sulfide are only achieved at supra-physiological concentrations and they question whether circulating sulfide is a physiologically relevant signaling molecule. This review examines the blood/plasma sulfide measurements that have been reported over the past 30 years from the perspective of the analytical methods used and the potential sources of error.