Elevated Aqueous Humour Level of The Collagen Cross-Linking Protein Lysyl-Oxidase-Like-1 (LOXL1) in Primary Open Angle Glaucoma

Abstract

Purpose: Lysyl-oxidase-like-1 (LOXL1) plays a significant role in pseudoexfoliative glaucoma (PXFG), however its association with primary open angle glaucoma (POAG) is unclear. LOXL1 is a collagen-elastin crosslinking protein which alters the biomechanical properties of the extracellular matrix (ECM) in the trabecular meshwork (TM). Abnormal cross-linking results in TM stiffness, thereby increasing aqueous outflow resistance. In this study, we measured the levels of LOXL1 in the aqueous and serum samples of normal patients and patients with glaucoma (POAG, PXFG and normal tension glaucoma [NTG]).

Methods: Aqueous humour samples were collected from 66 non-glaucoma patients and 31 POAG, 6 PXFG and 11 NTG patients. Serum samples were collected from 28 non-glaucoma patients and 11 POAG, 3 PXFG and 4 NTG patients. We measured the LOXL1 protein concentrations using enzyme-linked immune-sorbent assay (ELISA).

Results: There was significantly higher level of aqueous LOXL1 (ng/mL) in POAG (Median = 22.3, p = 0.007) and PXFG (Median = 23.3, p = 0.02) compared with non-glaucoma controls (Median = 12.2). Serum LOXL1 (ng/mL) was elevated in PXFG (Median = 79.3, p = 0.004) compared with non-glaucoma controls (Median 15.9). There was no difference (p > 0.05) in either aqueous or serum LOXL1 in NTG compared with non-glaucoma controls.

Conclusion: We describe an increased aqueous humour (but not serum) level of LOXL1 in POAG.

Keywords: Glaucoma; LOXL1; Cross-linking Proteins