Hemin, an inducer of heme oxygenase-1, lowers intraocular pressure in rabbits

• Published in: Journal of ocular pharmacology and therapeutics Vol. 23; no. 3; p. 232
• Main Authors: Privitera, Maria G, Potenza, Marta, Bucolo, Claudio, Leggio, Gian M, Drago, Filippo
• Format: Journal Article
• Language: English
• Published: United States 01-06-2007
• Subjects: Analysis of Variance; Animals; Betamethasone - analogs & derivatives; Chymotrypsin; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Induction; Heme Oxygenase-1 - drug effects; Heme Oxygenase-1 - metabolism; Hemin - administration & dosage; Hemin - pharmacology; Hemin - therapeutic use; Injections, Intravenous; Intraocular Pressure - drug effects; Male; Ocular Hypertension - chemically induced; Ocular Hypertension - drug therapy; Ocular Hypertension - physiopathology; Protoporphyrins; Rabbits; Random Allocation
• ISSN: 1080-7683
• DOI: 10.1089/jop.2006.101

Carbon monoxide (CO) generated from heme may induce vasodilation and exert cyto-protective properties in the eye. This study was undertaken to investigate the effects of hemin, a potent inducer of heme oxygenase-1 (HO-1), on models of ocular hypertension in rabbits.
Ocular hypertension was induced by injecting alpha-chymotrypsin in both eyes under local anesthesia. Only rabbits with an intraocular pressure (IOP) of 25 mmHg or more were used. The dose-response study of the hemin effect on IOP was made by an intravenous injection of the drug (50, 75, and 100 mg/kg) and subsequent IOP monitoring every 6 h. A separate set of animals was pretreated with the HO-1 inhibitor, zinc protoporphyrin-IX (ZnPP-IX, 0.1 mg/kg) 6 h before the vehicle or a 100-mg/kg hemin injection. Ocular hypertension was also obtained by the subconjunctival injection of betamethasone 21-phosphate disodium (4 mg/mL) in both eyes every week for 4 weeks. Only animals with an IOP of 30 mmHg or more were included in the experimental session. A group of these animals was pretreated with ZnPP-IX (0.1 mg/kg) 6 h before the vehicle or a 100-mg/kg hemin injection, and IOP was assessed every 6 hours.
Hemin caused a significant dose-related reduction of IOP in rabbits with alpha-chymotrypsin-induced ocular hypertension. No significant effect was observed in the normotensive eyes of the control animals or on pupil diameter. Pretreatment with the HO-1 inhibitor, ZnPP-IX, abolished the decrease of IOP that was induced by the maximum dose of hemin (100 mg/kg). A similar reduction in IOP was observed in those rabbits with betamethasone-induced ocular hypertension who were treated with 100 mg/kg of hemin. Furthermore, pretreatment with ZnPP-IX prevented the hemin effect on IOP.
The induction of HO-1 by hemin leads to a reduction of IOP in the alpha-chymotrypsin and betamethasone models of ocular hypertension. These results suggest an involvement of CO in the regulation of ocular pressure in rabbits.