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

Abstract

Hydrogen sulfide (H2S), 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 H2S, using sodium hydrosulfide (NaHS) and sodium sulfide (Na2S) as donors can increase cyclic AMP (cAMP) production in neural retina. In the present study, we investigated the mechanism of action of H2S on cyclic nucleotide production in rat retinal pigment epithelial cells (RPE-J). Cultured RPE-J cells were incubated for 30min in culture medium containing the cyclic nucleotide phosphodiesterase (PDE) inhibitor, IBMX (2mM). Cells were exposed to varying concentrations of NaHS, the H2S substrate (l-cysteine), cyclooxygenase (COX) inhibitors or the diterpene activator of adenylate cyclase, forskolin in the presence or absence of H2S biosynthetic enzymes or the ATP-sensitive potassium (KATP) 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 (10nM–1μM) produced a time-dependent increase in cAMP concentrations over basal levels which reached a maximum at 20min. At this time point, both NaHS (1nM–100μM) and l-cysteine (1nM–10μM) 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 (10μM) on cAMP production were potentiated by addition of low concentrations of NaHS. Both the inhibitor of cystathionine β-synthase (CBS), aminooxyacetic acid (AOA, 1mM) and the inhibitor of cystathionine γ-lyase (CSE), proparglyglycine (PAG, 1mM) significantly attenuated the increased effect of l-cysteine on cAMP production. The KATP channel antagonist, glibenclamide (100μM) caused inhibition of NaHS induced-increase of cAMP formation in RPE-J cells. We conclude that, H2S (using H2S 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 H2S on cAMP. Effects elicited by the H2S substrate on cAMP formation are dependent on biosynthesis of H2S catalyzed by the biosynthetic enzymes, CBS and CSE. In addition to the adenylyl cylcase pathway, KATP channels are involved in mediating the observed effects of the H2S on cAMP production.