Biomarkers of cardiovascular disease are possible risk factors for AMD

Certain biomarkers of cardiovascular disease may be risk factors for age-related macular degeneration (AMD), according to Andrew K. Vine, MD, FRCSC, who presented the results of a case-control study during the American Academy of Ophthalmology annual meeting.

Dr. Vine and colleagues examined the levels of two markers for cardiovascular diseases-C-reactive protein (CRP) and homocysteine-in individuals affected by AMD and a control group without the disease. High-sensitivity CRP is a marker of systemic inflammation and a predictor of cardiovascular disease.

Homocysteine, an amino acid formed from methionine, is an independent risk factor for heart disease, he said.

Patients from the AMD Genetic Study Group participated in the case-control study, providing data and blood samples for DNA analysis. Seventy-nine patients with AMD and 77 controls without AMD were evaluated for CRP and homocysteine. A complete cardiovascular and drug history was taken.

CRP, homocysteine levels The results showed the CRP and homocysteine levels were elevated in the group with AMD when compared with the unaffected controls. The mean CRP level was 3.42 mg/l in the AMD group and 2.30 mg/l in the controls (p = 0.03). The mean homocysteine level was 11.72 µmole/l in the AMD patients and 8.88 µmole/l in the unaffected patients (p < 0.0001).

"Our study supports the role of low-grade chronic inflammation in AMD. Low-grade chronic inflammation plays a pivotal role in atherosclerosis," Dr. Vine explained.

"Elevated homocysteine in individuals with AMD supports the cardiovascular role in the pathogenesis of AMD. It remains unclear whether homocysteine is causative of atherosclerosis, or a marker of existing vascular disease," Dr. Vine said.

There were some limitations to the study, he explained. Patients in each group were not individually matched. Homocysteine levels are usually higher in men than women and will increase as one ages. Also, homocysteine should be measured in the fasting state, but was measured after individuals had a small non-protein breakfast, he said.

So Dr. Vine posed the question: "Will reducing CRP and homocysteine levels reduce the incidence of AMD?" He noted that studies have tried to answer that question by evaluation of statin therapy on AMD. While statin therapy is able to reduce the CRP levels in AMD patients, previous study results are conflicting.

Dr. Vine also said that larger studies are being conducted to evaluate the role of homocysteine reduction with cardiovascular endpoints.

"Further studies are needed to differentiate which common disease mechanisms of chronic inflammation and atherosclerosis contribute to the pathogenesis of AMD," he concluded.