Nitric oxide proxies and ocular perfusion pressure in primary open angle glaucoma

Abstract

Background: To investigate the levels of nitric oxide (NO) markers in plasma and aqueous humour of patients with primary open angle glaucoma (POAG) and their relation to ocular perfusion pressure.

Methods: Cyclic guanosine monophosphate (cGMP) and nitrite (NO(2)(-)) were determined in plasma and aqueous humour of 38 patients with POAG and 46 controls. Blood pressure and IOP were measured to calculate ocular perfusion pressure (PP).

Results: cGMP and NO(2)(-) plasma levels were significantly decreased in glaucoma patients compared with controls (p = 0.001 v p = 0.004). In the aqueous humour of subjects with POAG, cGMP and NO(2)(-) concentrations were also lower than in normal eyes (p = 0.0001 v p = 0.001). There was a linear association between cGMP in plasma and aqueous humour in glaucomas and controls (r = 0.514, p = 0.029 and r = 0.558, p = 0.004) and this relation differed in the two groups (p = 0.003). Considering glaucoma patients with controls, a positive correlation was found between cGMP and PP (r = 0.379, p = 0.01) and between NO(2)(-) and PP (r = 0.339, p = 0.040). The cGMP/PP correlation was of borderline statistical significance in controls (p = 0.050), whereas it did not attain statistical significance in POAG, as well as the association between NO(2)(-) and PP when glaucomas and controls were considered separately.

Conclusions: The authors found alterations of NO markers in the plasma and aqueous humour of glaucoma patients. Primary or secondary impaired NO balance could alter ocular perfusion pressure.

Figure 1

cGMP plasma levels in control (2059.68 (697.86) pmoles/mg protein) and glaucoma subjects (1568.62 (625.55) pmoles/mg protein). Values are mean (SD); p = 0.001 by the Student’s t test for unpaired data.

Figure 2

Nitrite (NO₂ ⁻) plasma concentrations in glaucomas (166.68 (38.45) μmol/mg protein) and controls (228.39 (76.22) μmoles/mg protein). Values are mean (SD); p = 0.004 by the Student’s t test for unpaired data.

Figure 3

Amount of cGMP in the aqueous humour of patients with POAG and cataract (1559.32 (619.12) fmol/mg protein) v patients with cataract only (controls) (2931.07 (1387.01) fmol/mg protein). Student’s t test for unpaired data: p = 0.0001.

Figure 4

NO₂ ⁻ levels in the aqueous humour of controls (259.20 (72.62) μmol/mg protein) and patients with glaucoma (156.82 (54.79) μmol/mg protein). Student’s t test for unpaired data: p = 0.001.

Figure 5

Linear regression between cGMP plasma levels and cGMP concentrations in the aqueous humour.

Figure 6

Linear regession between cGMP plasma levels and ocular perfusion pressure (PP).