Effect of hydrogen sulfide on cyclic AMP production in isolated bovine and porcine neural retinae

Neuroprotective Actions of Hydrogen Sulfide-Releasing Compounds in Isolated Bovine Retinae

Background: We have evidence that hydrogen sulfide (H2S)-releasing compounds can reduce intraocular pressure in normotensive and glaucomatous rabbits by increasing the aqueous humor (AH) outflow through the trabecular meshwork. Since H2S has been reported to possess neuroprotective actions, the prevention of retinal ganglion cell loss is an important strategy in the pharmacotherapy of glaucoma. Consequently, the present study aimed to investigate the neuroprotective actions of H2S-releasing compounds against hydrogen peroxide (H2O2)-induced oxidative stress in an isolated bovine retina. Materials and Methods: The isolated neural retinae were pretreated with a substrate for H2S biosynthesis called L-cysteine, with the fast H2S-releasing compound sodium hydrosulfide, and with a mitochondrial-targeting H2S-releasing compound, AP123, for thirty minutes before a 30-min oxidative insult with H2O2 (100 µM). Lipid peroxidation was assessed via an enzyme immunoassay by measuring the stable oxidative stress marker, 8-epi PGF2α (8-isoprostane), levels in the retinal tissues. To determine the role of endogenous H2S, studies were performed using the following biosynthesis enzyme inhibitors: aminooxyacetic acid (AOAA, 30 µM); a cystathione-β-synthase/cystathionine-γ-lyase (CBS/CSE) inhibitor, α-ketobutyric acid (KBA, 1 mM); and a 3-mercaptopyruvate-s-sulfurtransferase (3-MST) inhibitor, in the absence and presence of H2S-releasing compounds. Results: Exposure of the isolated retinas to H2O2 produced a time-dependent (10-40 min) and concentration-dependent (30-300 µM) increase in the 8-isoprostane levels when compared to the untreated tissues. L-cysteine (10 nM-1 µM) and NaHS (30 -100 µM) significantly (p < 0.001; n = 12) prevented H2O2-induced oxidative damage in a concentration-dependent manner. Furthermore, AP123 (100 nM-1 µM) attenuated oxidative H2O2 damage resulted in an approximated 60% reduction in 8-isoprostane levels compared to the tissues treated with H2O2 alone. While AOAA (30 µM) and KBA (1 mM) did not affect the L-cysteine evoked attenuation of H2O2-induced oxidative stress, KBA reversed the antioxidant responses caused by AP123. Conclusions: In conclusion, various forms of H2S-releasing compounds and the substrate, L-cysteine, can prevent H2O2-induced lipid peroxidation in an isolated bovine retina.

Unmet needs in glaucoma therapy: The potential role of hydrogen sulfide and its delivery strategies

Glaucoma is an optic neuropathy disorder marked by progressive degeneration of the retinal ganglion cells (RGC). It is a leading cause of blindness worldwide, prevailing in around 2.2% of the global population. The hallmark of glaucoma, intraocular pressure (IOP), is governed by the aqueous humor dynamics which plays a crucial role in the pathophysiology of the diesease. Glaucomatous eye has an IOP of more than 22 mmHg as compared to normotensive pressure of 10-21 mmHg. Currently used treatments focus on reducing the elevated IOP through use of classes of drugs that either increase aqueous humor outflow and/or decrease its production. However, effective treatments should not only reduce IOP, but also offer neuroprotection and regeneration of RGCs. Hydrogen Sulfide (H₂S), a gasotransmitter with several endogenous functions in mammalian tissues, is being investigated for its potential application in glaucoma. In addition to decreasing IOP by increasing aqueous humor outflow, it scavenges reactive oxygen species, upregulates the cellular antioxidant glutathione and protects RGCs from excitotoxicity. Despite the potential of H₂S in glaucoma, its delivery to anterior and posterior regions of the eye is a challenge due to its unique physicochemical properties. Firstly, development of any delivery system should not require an aqueous environment since many H₂S donors are susceptible to burst release of the gas in contact with water, causing potential toxicity and adverse effects owing to its inherent toxicity at higher concentrations. Secondly, the release of the gas from the donor needs to be sustained for a prolonged period of time to reduce dosing frequency as per the requirements of regulatory bodies. Lastly, the delivery system should provide adequate bioavailability throughout its period of application. Hence, an ideal delivery system should aim to tackle all the above challenges related to barriers of ocular delivery and physicochemical properties of H₂S itself. This review discusses the therapeutic potential of H₂S, its delivery challenges and strategies to overcome the associated chalenges.

Altered transsulfuration pathway enzymes and redox homeostasis in inherited retinal degenerative diseases

Retinal degenerative diseases result from apoptotic photoreceptor cell death. As endogenously produced gaseous molecules such as hydrogen sulfide (H2S) and nitric oxide (NO) play a key role in apoptosis, we compared the expression levels of genes and proteins involved in the production of these molecules in the retina of normal dogs and three canine models (rcd1, crd2, and xlpra2) of human inherited retinal degeneration (IRD). Using qRT-PCR, Western blot, and immunohistochemistry (IHC), we showed that mRNA and protein levels of cystathionine β-synthase (CBS), an enzyme that produces H2S in neurons, are increased in retinal degeneration, but those of cystathionine γ-lyase (CSE), an enzyme involved in the production of glutathione (GSH), an antioxidant, are not. Such findings suggest that increased levels of H2S that are not counterbalanced by increased antioxidant potential may contribute to disease in affected retinas. We also studied the expression of neuronal and inducible nitric oxide synthase (nNOS and iNOS), the enzymes responsible for NO production. Western blot and IHC results revealed increased levels of nNOS and iNOS, resulting in increased NO levels in mutant retinas. Finally, photoreceptors are rich in polyunsaturated fatty acids (PUFAs) that can make these cells vulnerable to oxidative damage through reactive oxygen species (ROS). Our results showed increased levels of acrolein and hydroxynonenal (4HNE), two main toxic products of PUFAs, surrounding the membranes of photoreceptors in affected canines. Increased levels of these toxic products, together with increased NO and ROS, likely render these cells susceptible to an intrinsic apoptotic pathway involving mitochondrial membranes. To assess this possibility, we measured the levels of BCL2, an anti-apoptotic protein in the mitochondrial membrane. Western blot results showed decreased levels of BCL2 protein in affected retinas. Overall, the results of this study identify alterations in the expression of enzymes directly involved in maintaining the normal redox status of the retina during retinal degeneration, thereby supporting future studies to investigate the role of H2S and NO in retinal degeneration and apoptosis.

Comparative Effects of Hydrogen Sulfide-Releasing Compounds on [3H]D-Aspartate Release from Bovine Isolated Retinae

We investigated the pharmacological actions of a slow-releasing H₂S donor, GYY 4137; a substrate for the biosynthesis of H₂S, L-cysteine and its precursor, N-acetylcysteine on potassium (K⁺; 50 mM)-evoked [³H]D-aspartate release from bovine isolated retinae using the Superfusion Method. GYY 4137 (10 nM-10 µM), L-cysteine (100 nM-10 µM) and N-acetylcysteine (10 µM-1 mM) elicited a concentration-dependent decrease in K⁺-evoked [³H]D-aspartate release from isolated bovine retinae without affecting basal tritium efflux. At equimolar concentration of 10 µM, the rank order of activity was as follows: L-cysteine > GYY 4137 > N-acetylcysteine. A dual inhibitor of the biosynthetic enzymes for H₂S, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), amino-oxyacetic acid (AOA; 3 mM) reversed the inhibitory responses caused by GYY 4137, L-cysteine and N-acetylcysteine on K⁺-evoked [³H]D-aspartate release. Glibenclamide (300 µM), an inhibitor of K_ATP channels blocked the inhibitory action of GYY 4137 and L-cysteine but not that elicited by N-acetylcysteine on K⁺-induced [³H]D-aspartate release. The inhibitory effect of GYY 4137 and L-cysteine on K⁺-evoked [³H]D-aspartate release was reversed by the non-specific inhibitor of nitric oxide synthase (NOS), L-NAME (300 µM). Furthermore, a specific inhibitor of inducible NOS (iNOS), aminoguanidine (10 µM) blocked the inhibitory action of L-cysteine on K⁺-evoked [³H]D-aspartate release. We conclude that both donors and substrates for H₂S production can inhibit amino acid neurotransmission in bovine isolated retinae, an effect that is dependent, at least in part, upon the intramural biosynthesis of this gas, and on the activity of K_ATP channels and NO synthase.

Regulation of Aqueous Humor Dynamics by Hydrogen Sulfide: Potential Role in Glaucoma Pharmacotherapy

Hydrogen sulfide (H₂S) is a gaseous transmitter with well-known biological actions in a wide variety of tissues and organs. The potential involvement of this gas in physiological and pathological processes in the eye has led to several in vitro, ex vivo, and in vivo studies to understand its pharmacological role in some mammalian species. Evidence from literature demonstrates that 4 enzymes responsible for the biosynthesis of this gas (cystathionine β-synthase, CBS; cystathionine γ-lyase, CSE; 3-mercaptopyruvate sulfurtransferase, 3MST; and d-amino acid oxidase) are present in the cornea, iris, ciliary body, lens, and retina. Studies of the pharmacological actions of H₂S (using several compounds as fast- and slow-releasing gas donors) on anterior uveal tissues reveal an effect on sympathetic neurotransmission and the ability of the gas to relax precontracted iris and ocular vascular smooth muscles, responses that were blocked by inhibitors of CSE, CBS, and K_ATP channels. In the retina, there is evidence that H₂S can inhibit excitatory amino acid neurotransmission and can also protect this tissue from a wide variety of insults. Furthermore, exogenous application of H₂S-releasing compounds was reported to increase aqueous humor outflow facility in an ex vivo model of the porcine ocular anterior segment and lowered intraocular pressure (IOP) in both normotensive and glaucomatous rabbits. Taken together, the finding that H₂S-releasing compounds can lower IOP and can serve a neuroprotective role in the retina suggests that H₂S prodrugs could be used as tools or therapeutic agents in diseases such as glaucoma.

Role of Hydrogen Sulfide in Retinal Diseases

As the third gasotransmitter, hydrogen sulfide (H₂S) plays a crucial role in the physiology and pathophysiology of many systems in the body, such as the nervous, cardiovascular, respiratory, and gastrointestinal systems. The mechanisms for its effects, including inhibiting ischemic injury, reducing oxidative stress damage, regulating apoptosis, and reducing the inflammation reaction in different systems, have not been fully understood. Recently, H₂S and its endogenous synthesis pathway were found in the mammalian retina. This review describes the production and the metabolism of H₂S and the evidence of a role of H₂S in the retina physiology and in the different retinal diseases, including retinal degenerative diseases and vascular diseases. In the retina, H₂S is generated in the presence of cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase from L-cysteine. The role of endogenous H₂S and its physiologic effect in the retina are still elusive. However, strong evidence shows that retina-derived H₂S might play protective or deleterious role in the pathogenesis of retinal diseases. For example, by regulating Ca²⁺ influx, H₂S can protect retinal neurons against light-induced degeneration. H₂S preconditioning can mediate the anti-apoptotic effect of retinal ganglion cells in retinal ischemia/reperfusion injury. Treatment with H₂S in rats relieves diabetic retinopathy by suppressing oxidative stress and reducing inflammation. Further studies would greatly improve our understanding of the pathophysiologic mechanisms responsible for retinal diseases and the potential for the H₂S-related therapy of the retinal diseases as well.

Effects of Hydrogen Sulfide-Releasing Compounds on Aqueous Humor Outflow Facility in Porcine Ocular Anterior Segments, Ex Vivo

PURPOSE

To investigate the pharmacological actions of hydrogen sulfide (H₂S)-releasing compounds l-cysteine and sodium hydrosulfide (NaHS) on aqueous humor (AH) outflow facility in porcine ocular anterior segment.

METHODS

Porcine ocular anterior segments were perfused with Dulbecco's modified Eagle's medium at a constant pressure of 7.35 mmHg. After stable outflow baseline, explants were exposed to NaHS or l-cysteine. The increase in outflow generated by the H₂S-releasing compounds was measured in the absence and presence of inhibitor of H₂S biosynthesis (aminooxyacetic acid; AOAA), blocker of K_ATP channels (glibenclamide), and inhibitor of adenylyl cyclase (SQ 22536). Hematoxylin and eosin (H&E) staining was used to assess trabecular meshwork (TM) morphology.

RESULTS

l-cysteine elicited a concentration-dependent increase in AH outflow facility, reaching maximal effect at 100 nM (150.6% ± 17.2% of basal level). This increase in outflow induced by l-cysteine was significantly (P < 0.001) antagonized by AOAA (30 μM) and glibenclamide (100 μM). AOAA and glibenclamide had no significant action on baseline outflow, whereas SQ 22536 (100 μM) increased outflow for only an hour. In addition, NaHS produced a concentration-dependent increase in AH outflow, with a maximal effect at 10 μM (151.4% ± 22.9% of basal level). Likewise, the increase in outflow caused by NaHS was significantly (P < 0.04) blocked by glibenclamide and SQ 22536. H&E staining revealed that l-cysteine or NaHS did not alter TM conformation.

CONCLUSION

H₂S-releasing compounds can increase outflow facility in porcine ocular anterior segment. The stimulatory action of these compounds on outflow is mediated, in part by endogenously produced H₂S, K_ATP channels, and adenylyl cyclase.

Effect of Hydrogen Sulfide Donors on Intraocular Pressure in Rabbits

PURPOSE

In this study, we investigated the effect of a slow-releasing hydrogen sulfide (H2S) donor, GYY 4137, on intraocular pressure (IOP) in normotensive rabbits. Furthermore, we compared the IOP-lowering action of GYY 4137 with those elicited by other H2S-producing compounds, l-cysteine and ACS67 (a hybrid compound of latanoprost with an H2S-releasing moiety).

METHODS

IOP was measured in New Zealand normotensive male albino rabbits using a pneumatonometer (model 30 classic; Reichert Ophthalmic Instruments, Depew, NY). At 0 h, 50 μL of test compounds were applied topically to 1 eye of each animal, while the contralateral eye received the same quantity of vehicle (saline). IOP was measured hourly until baseline IOP readings were attained and animal eyes monitored for potential side effects (i.e., tearing, hyperemia).

RESULTS

GYY 4137 (0.1%-2%) produced a dose-dependent decrease in IOP reaching a maximum of 27.8% ± 3.14% (n = 5) after 6 h. Interestingly, a significant contralateral effect was observed in vehicle-treated controls eyes at all doses tested. l-cysteine (5%) and ACS67 (0.005%) also elicited a significant (P < 0.01) decrease in IOP that achieved a maximum of 28.84% ± 1.53% (n = 5) and 23.27% ± 0.51% (n = 5), respectively, after 3 h. All 3 H2S-producing compounds also caused a significant contralateral effect in vehicle-treated control eyes.

CONCLUSION

We conclude that GYY 4137 and other H2S-producing donors can reduce IOP in normotensive rabbits. However, the profile of IOP-lowering action of GYY 4137 was different from the other H2S donors affirming its ability to act as a slow-releasing gas donor.

H2S induces vasoconstriction of rat cerebral arteries via cAMP/adenylyl cyclase pathway

Hydrogen sulfide (H2S), traditionally known for its toxic effects, is now involved in regulating vascular tone. Here we investigated the vasoconstrictive effect of H2S on cerebral artery and the underlying mechanism. Sodium hydrosulfide (NaHS), a donor of H2S, concentration-dependently induced vasoconstriction on basilar artery, which was enhanced in the presence of isoprenaline, a β-adrenoceptor agonist or forskolin, an adenylyl cyclase activator. Administration of NaHS attenuated the vasorelaxant effects of isoprenaline or forskolin. Meanwhile, the NaHS-induced vasoconstriction was diminished in the presence of 8B-cAMP, an analog of cAMP, but was not affected by Bay K-8644, a selective L-type Ca(2+) channel agonist. These results could be explained by the revised effects of NaHS on isoprenaline-induced cAMP elevation and forskolin-stimulated adenylyl cyclase activity. Additionally, NaHS-induced vasoconstriction was enhanced by removing the endothelium or in the presence of L-NAME, an inhibitor of nitric oxide synthase. L-NAME only partially attenuated the effect of NaHS which was given together with forskolin on the pre-contracted artery. In conclusion, H2S induces vasoconstriction of cerebral artery via, at least in part, cAMP/adenylyl cyclase pathway.

Mechanisms of hydrogen sulfide (H2S) action on synaptic transmission at the mouse neuromuscular junction

Hydrogen sulfide (H2S) is a widespread gasotransmitter also known as a powerful neuroprotective agent in the central nervous system. However, the action of H2S in peripheral synapses is much less studied. In the current project we studied the modulatory effects of the H2S donor sodium hydrosulfide (NaHS) on synaptic transmission in the mouse neuromuscular junction using microelectrode technique. Using focal recordings of presynaptic response and evoked transmitter release we have shown that NaHS (300 μM) increased evoked end-plate currents (EPCs) without changes of presynaptic waveforms which indicated the absence of NaHS effects on sodium and potassium currents of motor nerve endings. Using intracellular recordings it was shown that NaHS increased the frequency of miniature end-plate potentials (MEPPs) without changing their amplitudes indicating a pure presynaptic effect. Furthermore, NaHS increased the amplitude of end-plate potentials (EPPs) without influencing the resting membrane potential of muscle fibers. L-cysteine, a substrate of H2S synthesis induced, similar to NaHS, an increase of EPC amplitudes whereas inhibitors of H2S synthesis (β-cyano-L-alanine and aminooxyacetic acid) had the opposite effect. Inhibition of adenylate cyclase using MDL 12,330A hydrochloride (MDL 12,330A) or elevation of cAMP level with 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (pCPT-cAMP) completely prevented the facilitatory action of NaHS indicating involvement of the cAMP signaling cascade. The facilitatory effect of NaHS was significantly diminished when intracellular calcium (Ca(2+)) was buffered by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester (BAPTA-AM) and ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid acetoxymethyl ester (EGTA-AM). Activation of ryanodine receptors by caffeine or ryanodine increased acetylcholine release and prevented further action of NaHS on transmitter release, likely due to an occlusion effect. Inhibition of ryanodine receptors by ryanodine or dantrolene also reduced the action of NaHS on EPC amplitudes. Our results indicate that in mammalian neuromuscular synapses endogenously produced H2S increases spontaneously and evoked quantal transmitter release from motor nerve endings without changing the response of nerve endings. The presynaptic effect of H2S appears mediated by intracellular Ca(2+) and cAMP signaling and involves presynaptic ryanodine receptors.

Hydrogen sulphide induces vasoconstriction of rat coronary artery via activation of Ca(2+) influx

AIM

Hydrogen sulphide (H2S) exhibits a dual modulation of isolated artery tension. This study investigated the vasoconstrictive effect of sulphur sodium hydride (NaHS), a donor of gaseous H2S, on rat coronary artery.

METHODS

The contractile response of isolated arteries was recorded using a wire myograph. Fluo-3/AM was used to load vascular smooth muscle, and intracellular calcium was determined using confocal laser microscopy. The protein expression of Rho kinase was examined using Western blot.

RESULTS

NaHS induced concentration-dependent contractions of rat coronary artery, and the contraction reached approx. 65% of 60 mm KCl-induced contraction. The NaHS-induced contraction was elevated following the removal of endothelium or the use of the nitric oxide synthase inhibitor L-NAME. The cyclooxygenase inhibitor indomethacin reduced NaHS-induced contraction. The Rho kinase inhibitor Y-27632 significantly attenuated NaHS-induced vasoconstriction. Furthermore, NaHS elevated the protein expression of Rho kinase. NaHS-induced contraction was completely abolished in a Ca(2+)-free solution and suppressed by the Ca(2+) influx blocker nifedipine (100 nm). NaHS also significantly increased the change rate of Ca(2+) fluorescence intensity. However, treatment with a Cl(-)/HCO(3-) exchanger blocker, K(+) channel blockers, the mitogen-activated protein kinase inhibitor U-0126 or cyclic adenosine monophosphate did not affect contraction. Species-dependent differences in NaHS-induced vasoconstriction were observed because these effects were only modest in dog coronary artery and absent in rabbit coronary artery.

CONCLUSIONS

NaHS induces the contraction of rat coronary artery, which is dependent on the activation of Ca(2+) influx. Rho kinase likely participates in the vasoconstriction.

Inhibitory action of novel hydrogen sulfide donors on bovine isolated posterior ciliary arteries

In the present study, we investigate the inhibitory effect of novel H2S donors, AP67 and AP72 on isolated bovine posterior ciliary arteries (PCAs) under conditions of tone induced by an adrenoceptor agonist. Furthermore, we examined the possible mechanisms underlying the AP67- and AP72-induced relaxations. Isolated bovine PCA were set up for measurement of isometric tension in organ baths containing oxygenated Krebs solution. The relaxant action of H2S donors was studied on phenylephrine-induced tone in the absence or presence of enzyme inhibitors for the following pathways: cyclooxygenase (COX); H2S; nitric oxide and the ATP-sensitive K(+) (KATP) channel. The H2S donors, NaSH (1 nM - 10 μM), AP67 (1 nM - 10 μM) and AP72 (10 nM - 1 μM) elicited a concentration-dependent relaxation of phenylephrine-induced tone in isolated bovine PCA. While the COX inhibitor, flurbiprofen (3 μM) blocked significantly (p < 0.05) the inhibitory response elicited by AP67, it had no effect on relaxations induced by NaSH and AP72. Both aminooxyacetic acid (30 μM) and propargylglycine (1 mM), enzyme inhibitors of H2S biosynthesis caused significant (p < 0.05) rightward shifts in the concentration-response curve to AP67 and AP72. Furthermore, the KATP channel antagonist, glibenclamide (300 μM) and the NO synthase inhibitor, l-NAME (100 μM) significantly attenuated (p < 0.05) the relaxation effect induced by AP67 and AP72 on PCA. We conclude that H2S donors can relax pre-contracted isolated bovine PCA, an effect dependent on endogenous production of H2S. The inhibitory action of only AP67 on pre-contracted PCA may involve the production of inhibitory endogenous prostanoids. Furthermore, the observed inhibitory action of H2S donors on PCA may depend on the endogenous biosynthesis of NO and by an action of KATP channels.

NaHS induces relaxation response in prostaglandin F(2α) precontracted bovine retinal arteries partially via K(v) and K(ir) channels

Hydrogen sulphide (H2S) is known to be produced endogenously in ocular tissues with the highest levels in the retina and cornea. However, it is yet unclear whether it can modulate retinal arterial tone. Herein, we aimed to investigate the effectiveness and the mechanism of the action of H2S in the isolated bovine retinal arteries. For this purpose, the probable vasorelaxant and inhibitory effects of H2S on vascular reactivity were tested comparatively in the retinal arteries by using the donor, sodium hydrosulphide (NaHS). Thereafter, in relation to the mechanism of action of H2S, the role of nitric oxide (NO) and endothelial vasodilators of cyclooxygenase pathway as well as ATP-sensitive potassium channel (KATP), voltage-dependent potassium channel (Kv), calcium-activated potassium channel (KCa(++)), inwardly rectifying potassium channel (Kir), L-type voltage-dependent calcium channel and adenylate cyclase pathway were evaluated. NaHS (1μM-3mM) displayed prominent relaxations over the concentrations of 300 μM in both PGF2α and K(+) precontracted retinal arteries. Comparatively, in the presence of NaHS (3 mM) pretreatment, the maximum contractile responses and pEC50 values to PGF2α and K(+) were significantly reduced as well. Neither the presence of the known inhibitors of NO synthase, guanylate cyclase, cyclooxygenase, adenylate cyclase, KATP and KCa(++) type K(+) channels, and L-type voltage-dependent calcium channels nor the removal of endothelium, modified the relaxation response to NaHS in retinal arteries. However, a remarkable decrease was observed in the presence of the inhibitors of Kv or Kir type K(+) channels. In addition, administration of l-cysteine (1μM-3mM), the precursor of H2S, induced a modest relaxation response in PGF2α precontracted retinal arteries, which was significantly decreased in the presence of cystathionine-β-synthase (CBS) inhibitor, aminooxyacetic acid, but was unmodified in the presence of the cystathionine-γ-lyase (CSE) inhibitor, dl-propargylglycine or the deendothelization of retinal arteries. Our findings suggested that H2S might play a substantial role in the regulation of retinal arterial tone possibly by acting on Kv and Kir channels.

In vitro-controlled release delivery system for hydrogen sulfide donor

Hydrogen sulfide (H2S) is having many potential pharmacological and physiological actions which reported that therapeutically useful concentration is low (100-160 μM) and a higher concentration could be toxic. Most of its donors produce it on coming into contact with water. All of these problems could be solved by a controlled-release delivery system which does not utilize water in any of its development steps. Therefore, 12 sustained release formulations were prepared by dissolving sodium hydrogen sulfide (NaHS)-a model H2S donor-in polymer solutions, prepared by dissolving polymers (consisted of either polylactide (PLA) or polylactide co-glycolide (PLGA), containing free carboxylic acid or capped allyl ester end group) in a mixture of benzyl benzoate (BB) and benzyl alcohol (BA). The formulation was injected in simulated tear fluid (STF) from which samples were withdrawn at specified times and assayed for NaHS content. We found decrease in burst and overall release with increase in polymer concentration from 10 to 20% w/v. The formulations containing free end group showed significant (p < 0.05) reduction of burst release (11% vs 21%). However, the overall release or the average amount released per hour was found to be significantly (p < 0.05) increased for formulations containing polymers with free end group than those with capped end group. A sustained level of H2S was found to be maintained for 72 h which should be further increased to a month to make it a viable H2S donor delivery system in addition to investigating toxicity profile specifically for the purpose of subconjunctival ocular delivery.

The role of endogenous hydrogen sulfide in pathogenesis of chronotropic dysfunction in rats with cirrhosis

Endogenous hydrogen sulfide is produced by cystathionine-γ-lyase and cystathionine-β-synthase in a variety of tissues and has recently been implicated in the regulation of cardiac functions. Acceleration of the heart rate in response to catecholamines is impaired in patients with cirrhosis. The present study was aimed to examine the role of endogenous hydrogen sulfide in the pathogenesis of chronotropic dysfunction in rats with cirrhosis. Cirrhosis was induced by surgical ligation of bile duct in rats. There was no significant difference in atrial cystathionine-γ-lyase and cystathionine-β-synthase mRNA levels in control and cirrhotic rats as assessed by quantitative RT-PCR. Four weeks after bile duct ligation or sham surgery the atria were isolated and chronotropic responsiveness to adrenergic stimulation was assessed using standard organ bath. Incubation of the atria with propargylglycine (PAG, a cystathionine-γ-lyase inhibitor) and amino-oxyacetic acid (AOAA, a cystathionine-β-synthase inhibitor) was associated with a significant desensitization of chronotropic response to adrenergic stimulation in controls rats. This indicates that endogenous hydrogen sulfide might be involved in modulation of adrenergic signaling in the atrium. Bile duct ligation was associated with impaired chronotropic responsiveness to adrenergic stimulation in comparison with sham-operated rats. In contrast to control group, incubation of the atria with PAG and AOAA was able to partially improve the chronotropic responsiveness to adrenergic stimulation in cirrhotic rats. Our data shows that local inhibition of endogenous hydrogen sulfide in atria has opposite effect in cirrhotic versus control rats and may play a role in physiological modulation of adrenergic signaling in the atrium.

Hydrogen sulfide: role in ion channel and transporter modulation in the eye

Hydrogen sulfide (H₂S), a colorless gas with a characteristic smell of rotten eggs, has been portrayed for decades as a toxic environmental pollutant. Since evidence of its basal production in mammalian tissues a decade ago, H₂S has attracted substantial interest as a potential inorganic gaseous mediator with biological importance in cellular functions. Current research suggests that, next to its counterparts nitric oxide and carbon monoxide, H₂S is an important multifunctional signaling molecule with pivotal regulatory roles in various physiological and pathophysiological processes as diverse as learning and memory, modulation of synaptic activities, cell survival, inflammation, and maintenance of vascular tone in the central nervous and cardiovascular systems. In contrast, there are few reports of a regulatory role of H₂S in the eye. Accumulating reports on the pharmacological role of H₂S in ocular tissues indicate the existence of a functional trans-sulfuration pathway and a potential physiological role for H₂S as a gaseous neuromodulator in the eye. Thus, understanding the role of H₂S in vision-related processes is imperative to our expanding knowledge of this molecule as a gaseous mediator in ocular tissues. This review aims to provide a comprehensive and current understanding of the potential role of H₂S as a signaling molecule in the eye. This objective is achieved by discussing the involvement of H₂S in the regulation of (1) ion channels such as calcium (L-type, T-type, and intracellular stores), potassium (K_ATP and small conductance channels) and chloride channels, (2) glutamate transporters such as EAAT1/GLAST and the L-cystine/glutamate antiporter. The role of H₂S as an important mediator in cellular functions and physiological processes that are triggered by its interaction with ion channels/transporters in the eye will also be discussed.

Mechanism of action of hydrogen sulfide on cyclic AMP formation in rat retinal pigment epithelial cells

Hydrogen sulfide (H(2)S), a colorless gas with the pungent odor of rotten eggs has been reported to produce pharmacological actions in ocular and non-ocular tissues. We have evidence that H(2)S, using sodium hydrosulfide (NaHS) and sodium sulfide (Na(2)S) as donors can increase cyclic AMP (cAMP) production in neural retina. In the present study, we investigated the mechanism of action of H(2)S on cyclic nucleotide production in rat retinal pigment epithelial cells (RPE-J). Cultured RPE-J cells were incubated for 30 min in culture medium containing the cyclic nucleotide phosphodiesterase (PDE) inhibitor, IBMX (2 mM). Cells were exposed to varying concentrations of NaHS, the H(2)S substrate (L-cysteine), cyclooxygenase (COX) inhibitors or the diterpene activator of adenylate cyclase, forskolin in the presence or absence of H(2)S biosynthetic enzymes or the ATP-sensitive potassium (K(ATP)) channel antagonist, glibenclamide. Following drug-treatment at different time intervals, cell homogenates were prepared for cAMP assay using a well established methodology. In RPE-J cells, NaHS (10 nM-1 μM) produced a time-dependent increase in cAMP concentrations over basal levels which reached a maximum at 20 min. At this time point, both NaHS (1 nM-100 μM) and L-cysteine (1 nM-10 μM) produced a concentration-dependent significant (p<0.05) increase in cAMP concentrations over basal level. The effects of NaHS on cAMP levels in RPE-J cells was enhanced significantly (p<0.01) in the presence of the COX inhibitors, indomethacin and flurbiprofen. In RPE-J cells, the effects caused by forskolin (10 μM) on cAMP production were potentiated by addition of low concentrations of NaHS. Both the inhibitor of cystathionine β-synthase (CBS), aminooxyacetic acid (AOA, 1 mM) and the inhibitor of cystathionine γ-lyase (CSE), proparglyglycine (PAG, 1mM) significantly attenuated the increased effect of L-cysteine on cAMP production. The K(ATP) channel antagonist, glibenclamide (100 μM) caused inhibition of NaHS induced-increase of cAMP formation in RPE-J cells. We conclude that, H(2)S (using H(2)S donor and substrate) can increase cAMP production in RPE-J cells, and removal of the apparent inhibitory effect of prostaglandins unmasks an excitatory activity of H(2)S on cAMP. Effects elicited by the H(2)S substrate on cAMP formation are dependent on biosynthesis of H(2)S catalyzed by the biosynthetic enzymes, CBS and CSE. In addition to the adenylyl cylcase pathway, K(ATP) channels are involved in mediating the observed effects of the H(2)S on cAMP production.

Endogenous production of hydrogen sulfide in isolated bovine eye

Hydrogen sulfide (H(2)S) is a novel gasotransmitter with physiological and pathological functions in vascular homeostasis, cardiovascular system and central nervous system. In the present study, we determined the endogenous levels of H(2)S in various tissues of the bovine eye. We also examined the basal levels of H(2)S in response to donors (sodium hydrosulfide, NaHS and sodium sulfide, Na(2)S), substrate (L: -cysteine), inhibitors (propargylglycine, PAG and aminooxyacetic acid, AOA) and activator (S-adenosyl-L: -methionine, SAM) of this gas in the bovine retina. H(2)S was measured using a well established spectrophotometric method. The highest concentration of endogenous H(2)S was detected in cornea (19 ± 2.85 nmoles/mg protein, n = 6) and retina (17 ± 2.1 nmoles/mg protein, n = 6). Interestingly, H(2)S was not present in vitreous humor. The inhibitors of CSE and CBS; PAG (1 mM) and AOA (1 mM), significantly attenuated the production of H(2)S in the bovine retina by 56.8 and 42%, respectively. On the other hand the activator of CBS; SAM (100 μM), H(2)S donors; NaHS (1 μM) and Na(2)S (100 μM), significantly increased endogenous levels of H(2)S in bovine retina. L: -cysteine (10-300 μM) produced a significant (P < 0.05) concentration-dependent increase in H(2)S levels reaching a maximal at 300 μM. We conclude that H(2)S is endogenously produced in various tissues of the isolated bovine eye. Moreover, endogenous levels of H(2)S are enhanced in the presence of substrate (L: -cysteine), an activator of CBS (SAM) and H(2)S donors but are blocked by inhibitors of enzymes that synthesize this gas in neural retina.