Human lens lipids differ markedly from those of commonly used experimental animals

Electrospray ionisation tandem mass spectrometry has allowed the unambiguous identification and

quantification of individual lens phospholipids in human and six animal models. Using this approach ca. 100

unique phospholipids have been characterised. Parallel analysis of the same lens extracts by a novel directinsertion

electron-ionization technique found the cholesterol content of human lenses to be significantly

higher (ca. 6 times) than lenses from the other animals.

The most abundant phospholipids in all the lenses examined were choline-containing phospholipids. In rat,

mouse, sheep, cow, pig and chicken, thesewere present largely as phosphatidylcholines, in contrast 66% of the

total phospholipid in Homo sapienswas sphingomyelin, with the most abundant being dihydrosphingomyelins,

in particular SM(d18:0/16:0) and SM(d18:0/24:1). The abundant glycerophospholipids within human lenses

were found to be predominantly phosphatidylethanolamines and phosphatidylserines with surprisingly high

concentrations of ether-linked alkyl chains identified in both classes. This study is the first to identify the

phospholipid class (head-group) and assign the constituent fatty acid(s) for each lipid molecule and to quantify

individual lens phospholipids using internal standards. These data clearly indicate marked differences in the

membrane lipid composition of the human lens compared to commonly used animal models and thus predict a

significant variation in the membrane properties of human lens fibre cells compared to those of other animals.