Lipids of human lens fiber cell membranes.

A study of the membranes of human lens fiber cells revealed a very high protein to lipid ratio, which tended to increase with aging and in brunescent cataract. Phospholipids were more abundant than cholesterol, cholesterol esters, and other neutral lipids. With aging and cataract formation, a marked decrease in membranes phospholipid content occurred. Sphingomyelin was present in highest amount. Phosphatidylethanolamine, phosphatidylcholine, lysophosphatidyl-ethanolamine, phosphatidylserine, and phosphatidylglycerol were also present. Cholesterol represented approximately 40% of the total lipids. Saturated and unsaturated fatty acids having 16 to 24 carbons were present. The lipid composition varied according to the portion of the lens examined and the state of the lens. The results do not support a conclusion that lipid peroxidation represents a major mechanism of membrane damage that contributes to cataract formation, since there is no decrease in unsaturated fatty acids with age or in cataractous lenses. We suggest that the aggregation of soluble proteins, and their association with lens membranes, and altered membrane function due to the loss of phospholipids are important processes leading to loss of transparency.