Biochemical markers of the L-arginine-nitric oxide pathway in the aqueous humour in glaucoma patients

Purpose: To study the role of the L-arginine-nitric oxide (NO) pathway in aqueous humour dynamics by measuring nitrate, nitrite and cyclic (cGMP) levels in guanosine 3',5'-monophosphate the aqueous humour of glaucomatous and non-glaucomatous cataract patients. Methods: The study involved 38 glaucoma patients undergoing unilateral cataract surgery in the glaucomatous eye and 38 cataract control patients matched for sex, age, smoking habits and organic nitrate medication. All subjects underwent ophthalmic examination, and blood pressure was measured preoperatively. Nitrite, nitrate and cGMP levels were measured in aqueous humour and serum. Results: The NOx (nitrite + nitrate), nitrite and cGMP concentrations in the aqueous humour were slightly higher in the glaucoma patients than in the control patients, but the differences did not reach statistical significance. The levels of cGMP in serum were higher in the glaucoma patients (P = 0.053). The subgroup of glaucoma patients with pseudoexfoliation had lower NOx and nitrite values in the aqueous humour (P = 0.046 and P = 0.345, respectively) than the matched controls, while cGMP levels were higher (P = 0.043). Levels of NOx and nitrite in the aqueous humour were higher in patients using oral nitroglycerin (P = 0.062 and P = 0.042, respectively) than in patients without this medication. Blood pressure was higher in the glaucoma patients, with a mean of 165/89 mmHg as compared to 153/81 mmHg in the controls (P-values 0.071/0.008). Conclusions: No differences in NO metabolites were found between glaucoma and control patients. However, any real changes may have been disguised by optimal medication of glaucoma. Low NOx and high cGMP levels in the aqueous humour of pseudoexfoliation patients warrant further evaluation in a larger study.