Oxidative Modifications as Biomarkers for AMD

Abstract

Purpose:: To develop a blood test for age-related macular degeneration (AMD) that will allow identification of those at risk prior to clinical evidence of the disease.

Methods:: Blood was collected from clinically documented AMD and age-matched normal, healthy donors at the Cole Eye Institute, Cleveland Clinic Foundation and Louis Stokes Cleveland VA Medical Center. Plasma carboxyethylpyrrole (CEP), nitrotyrosine immunoreactivity and CEP autoantibody titer were determined by ELISA. Logistic regression modeling of ELISA data for the c-statistic and odds ratio was performed with SAS/STAT software. Plasma was fractionated on anti-CEP antibody coated magnetic beads then analyzed by high resolution MALDI TOF mass spectrometry to detect peptides. Conventional binomial receiver operating characteristic (ROC) curves were generated to evaluate biomarker specificity and sensitivity.

Results:: ELISA analyses of plasma from AMD (n = 732) and normal control (n = 169) donors has confirmed that AMD donors exhibit overall higher mean levels of CEP immunoreactivity and autoantibody titer relative to age-matched normal donors. Preliminary ELISA results also show that nitrotyrosine immunoreactivity in AMD donors (n = 21) is elevated ~50% compared to age-matched normal donors (n = 22). Mass spectrometric peptide patterns derived from 90 AMD and 80 normal donor plasma has allowed 94% of correct classification of either AMD or normal with 98% sensitivity and 88% specificity.

Conclusions:: Mean CEP immunoreactivity, nitrotyrosine immunoreactivity and CEP autoantibody titer are elevated in AMD plasma and may prove useful for monitoring therapeutic efficacy. Plasma peptidomics may prove useful for early identification of individuals susceptible to developing AMD.

Keywords: age-related macular degeneration • oxidation/oxidative or free radical damage • proteomics