P41 Hydrogen sulfide: Endogenous production and regulatory role in ocular tissues

• Published in: Nitric oxide Vol. 27; p. S30
• Main Authors: Njie-Mbye, Ya Fatou, Chitnis, Madhura, Opere, Catherine, Ohia, Sunny
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15.09.2012
• ISSN: 1089-8603; 1089-8611
• DOI: 10.1016/j.niox.2012.08.042

Hydrogen sulfide (H2S), a colorless gas characterized by its pungent odor, has been portrayed for decades as a toxic pollutant. Evidence of endogenous production of H2S in mammalian tissues, and its potential biological role stimulated our interest in the pharmacological significance of this gaseous molecule in ocular tissues. In the present study, we tested the hypothesis that H2S is endogenously produced in mammalian ocular tissues, and may produce pharmacological effects in retinal pigment epithelial cells. Endogenous levels of H2S were measured in bovine ocular tissues, using a well established colorimetric assay. In addition, basal level of H2S in bovine retina was examined in response to the H2S substrate, l-cysteine as well as the H2S biosynthetic enzymes inhibitors, propargylglycine (PAG) and aminooxyacetic acid (AOA); or activator, S-adenosyl-l-methionine (SAM). Using a H2S-releasing compound, sodium hydrosulfide (NaHS), we also determined the effects of H2S on cyclic AMP (cAMP) production in rat retinal pigment epithelial cells (RPE-J) by Enzyme Immuno Assay. The observed effect of H2S on cAMP was studied in the presence or absence of forskolin, an adenylate cyclase activator; glibenclamide, an ATP-sensitive potassium channel (KATP) antagonist; or flubiprofen and indomethacin, which are cyclooxygenase (COX) inhibitors. H2S is endogenously produced in ocular tissues with highest level detected in cornea (19±2.85nmoles/mg protein) and retina (17±2.1nmoles/mg protein). Interestingly, the inhibitors of cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) (1mM PAG and 1mM AOA, respectively) significantly decreased H2S production in the bovine retina by 56.8 and 42%. On the other hand, activator of CBS (SAM, 100μM), and H2S substrate (l-cysteine, 10–300μM) increased (p<0.05) the endogenous level of H2S in bovine retina. In RPE-J cells, NaHS (1nM–100μM) produced a concentration-dependent increase (p<0.05) in cAMP concentrations over basal level. Surprisingly, the effect of NaHS on cAMP levels was enhanced (p<0.01) in the presence of the COX inhibitors, indomethacin and flurbiprofen. Furthermore, the effects of forskolin (10μM) on cAMP production were potentiated by low concentrations of NaHS and finally, the KATPchannel antagonist, glibenclamide (100μM) inhibited the NaHS-induced increase of cAMP production in RPE-J cells. Our results indicate that H2S is endogenously produced in various tissues in the bovine eye. Endogenous level of H2S is increased in the presence of l-cysteine or SAM, and decreased by PAG or AOA, inhibitors of enzymes that synthesize H2S in neural retina. Moreover, H2S can increase cAMP production in RPE-J cells, and removal of the apparent inhibitory effect of prostaglandins unmasks an excitatory effect of H2S on cAMP production. In addition to the adenylyl cylcase pathway, KATP channels are involved in mediating the observed effects of H2S on cAMP production. The fact that H2S is endogenously produced in ocular tissues and exhibits a regulatory role in cyclic nucleotide production in retina, supports a physiological and/or pharmacological role for this gaseous molecule in the eye.