Age-related macular degeneration (AMD) is a burden to the elderly population, and its consequences are increasing because treatment options are limited. Prevention remains the best approach for decreasing the impact of this leading cause of blindness.
According to lead author Johanna M. Seddon, director of the Epidemiology Unit at the Massachusetts Eye and Ear Infirmary and associate professor of ophthalmology at Harvard Medical School, the investigation of inflammatory biomarkers in AMD followed from the observation that many factors associated with AMD are also related to cardiovascular disease. One of these factors is C-reactive protein (CRP), a marker of systemic inflammation that has been shown to be an independent indicator of risk for cardiovascular disease and peripheral arterial disease. Furthermore, inflammation is associated with angiogenesis (excess blood vessel growth), and proliferation of blood vesels can occur in inflammatory eye diseases, similar to the most advanced form of AMD.
“It is possible that AMD represents another chronic, age-related inflammatory disease that is manifested in the eye and other organs such as the heart and brain,” Seddon said. “Therefore, we examined the relationship between CRP levels and AMD in an ancillary study of 930 individuals from the multicenter Age-Related Eye Disease Study (AREDS).” AREDS is a prospective study designed to assess the incidence, clinical course, prognosis, and risk factors for AMD and cataract.
“After adjustment for age, sex, and other variables, including smoking and body mass index, CRP levels were significantly higher among individuals with intermediate and advanced stages of AMD as compared with controls,” Seddon said. A twofold increased risk of AMD was associated with highest levels of CRP for both smokers and nonsmokers. “These results may shed light on the mechanisms and pathogenesis of AMD development and prognosis. Moreover, CRP levels may add clinically relevant predictive information about risk of AMD, in addition to known risk factors. Anti-inflammatory agents might have a role in preventing AMD, and inflammatory biomarkers such as CRP may provide a method of identifying individuals for whom these agents and other therapies would be more or less effective.”
Their findings have important implications and suggest that inflammation is associated with the pathogenesis of AMD. Other than smoking, several mechanisms could potentially lead to inflammatory responses, including oxidative stresses, insufficient antioxidants in the diet, dietary fat, and obesity, which Seddon and colleagues have previously shown to be associated with AMD, as well as other independent factors. Co-authors are Gary Gensler and Roy Milton from the EMMES Corporation, Rockville, Md.; Michael Klein, from Casey Eye Institute, Portland, Ore.; and Nader Rifai, from Harvard Medical School.