Dr. Grossman’s Blog

Homocysteine, an amino acid believed to contribute to heart attack, stroke and dementia, may also play a role in retinal damage and vision loss.  Homocysteine levels rise when folic acid levels drop, a common problem for Americans whose diets are often poor in folate-rich fruits, tomatoes, vegetables and grains.

Dr. Sylvia Smith, cell biologist at Medical College of Georgia (MCG), and Dr. Vadivel Ganapathy, chair of the MCG Department of Biochemistry and Molecular Biology are studying the consequence of slightly elevated homocysteine on the retina under a $1.8 million grant from the National Institutes of Health.  They want to learn the impact of elevated homocysteine levels on the extensive blood vessel and neuronal network of the retina; their preliminary evidence suggests that it isn’t good.

“You don’t have to be a cell biologist to see that there is a problem in this retina. It’s terribly disrupted,” Dr. Smith says, looking at images of a fragmented 10-layer retina exposed to high levels of homocysteine.  A healthy retina is “beautifully” organized, horizontally and vertically, she says.

Folate and vitamin B12 convert homocysteine to methionine, an amino acid essential to protein synthesis.  Dr. Ganapathy notes that people need only about 1 microgram per day of vitamin B12, which comes from microorganisms common in animals’ gastrointestinal tract. Strict vegetarians are typically the only Americans who have problems with B12 deficiency, he says. People need about 400 micrograms of folate daily. Pregnant women as well as those trying to become pregnant need at least double that.

Researchers are studying a mouse model with a slightly elevated homocysteine level that simulates a low-folate diet in humans; a version of the mouse that also has diabetes, which goes along with cardiovascular disease and retinopathy; and a second model of the rare genetic defect that results in extraordinarily high homocysteine levels.  These mice will be put on diets that elevate and lower folate levels, so that resultant homocysteine levels and the impact on the retina can be studied.

Researchers hypothesize that sustained elevation will compromise retinal function and degrade the once well-stratified tissue; in pilot studies, the researchers have shown that diabetes exacerbates this problem.

SOURCE:  Medical College of Georgia, “Impact of elevated homocysteine levels on vision under study,” Oct. 15, 2007.