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

Abstract

AIM:

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.

METHODS:

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.

RESULTS:

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.

CONCLUSIONS:

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.

• Authors: Maria G Privitera, Marta Potenza, Claudio Bucolo, Gian M Leggio, Filippo Drago
• Journal: Journal of ocular pharmacology and therapeutics : the official journal of the Association for Ocular Pharmacology and Therapeutics (J Ocul Pharmacol Ther) Vol. 23 Issue 3 Pg. 232-9 (Jun 2007) ISSN: 1080-7683 [Print] United States
• PMID: 17593006 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Protoporphyrins
• zinc protoporphyrin
• Hemin
• betamethasone sodium phosphate
• Betamethasone
• Heme Oxygenase-1
• Chymotrypsin
• alpha-chymotrypsin

Topics

• Analysis of Variance
• Animals
• Betamethasone (analogs & derivatives)
• Chymotrypsin
• Disease Models, Animal
• Dose-Response Relationship, Drug
• Enzyme Induction
• Heme Oxygenase-1 (drug effects, metabolism)
• Hemin (administration & dosage, pharmacology, therapeutic use)
• Injections, Intravenous
• Intraocular Pressure (drug effects)
• Male
• Ocular Hypertension (chemically induced, drug therapy, physiopathology)
• Protoporphyrins
• Rabbits
• Random Allocation