Age-related aqueous humor (AH) and lens epithelial cell/capsule protein carbonylation and AH protein concentration in cataract patients who have pseudoexfoliative diseases

Abstract

Purpose: The aim of this study is to investigate the age-correlation of oxidative stress (OS, assessed by the accumulative OS damage marker protein carbonyls) in aqueous humour (AH; together with protein concentration) and lens epithelial cells plus capsule (LECs/capsule) in patients with cataract (CAT), and also suffering from pseudoexfoliation syndrome (PEX), primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXG).

Methods: AH samples from 78 male/female patients (21, 20, 19 and 18 with CAT, PEX, PXG, and POAG, respectively), and LECs/capsule samples from 104 male/female patients (34, 32, 18, and 20 with CAT, PEX, PXG and POAG, respectively) were collected during phacoemulsification CAT surgery. Average protein carbonyl concentrations were measured in patients grouped in 5-year age intervals (ranging from 56-60 to 86-90). The non-overlapping age ranges and numbers of the tested subjects did not allow comparative follow up studies for the tested diseases.

Results: There is an age-dependent increase of protein carbonyls in AH (nmol mg^-1 protein and ml^-1), and in the order CAT<PXG=~POAG<PEX and CAT<PEX=~POAG<PXG respectively. Moreover, protein concentration in AH accumulates in the order CAT<PEX<POAG<PXG but is not age-related. An age-dependent increase of protein carbonyls (nmol mg^-1 protein) is also observed in LECs/capsule, and in the order CAT<PEX=~POAG<PXG.

Conclusions: The present study shows for the first time an age-increased OS-induced protein damage (protein carbonyl formation) in the AH and LECs/capsule of CAT patients with PEX, POAG or PXG. The slow rate of change of protein carbonyls strongly suggests a long-term implication of OS in ocular disease pathogenesis. Additionally, protein concentration levels in the AH of CAT patients increase independently of age, and in same as with protein carbonyls increasing order levels for CAT<POAG<PXG in AH and LECs/capsule. This may suggest a protein cross-diffusion taking place between AH and LECs/capsule, most likely originating from PEX deposition and/or necrotic/apoptotic LECs/capsule. Moreover, the findings of the present study establish the use of protein carbonyls (together with a methodology for their more accurate quantification, which overcomes serious unreliability problems of past methods) as an age accumulative marker of OS damage, for future studies that investigate long-term OS involvement in pseudoexfoliative ocular disorders.

Figure 1

Age-related association of protein carbonyls in aqueous humor (AH). The association is expressed as a linear function of the change (rate) in the protein carbonyl concentration (nmoles ml⁻¹ and mg⁻¹ in A and B, respectively) versus the patient’s 5-year age intervals. Data are presented as mean ± standard error of the mean (SEM).

Figure 2

Age-related association of protein carbonyls in lens epithelial cells plus the capsule (LECs/capsule). The association is expressed as a linear function of the change (rate) in the protein carbonyl concentration (nmoles mg⁻¹) versus the patient’s 5-year age intervals. Data are presented as mean ± standard error of the mean (SEM).

Figure 3

Age-related association of protein concentration in AH. The association is expressed as the protein concentration (mg ml⁻¹) versus the patient’s 5-year age intervals. Note that the straight lines are nearly horizontal, and the corresponding slopes are near zero, showing no age correlation. Data are presented as mean ± standard error of the mean (SEM).