AGE AND REGIONAL STRUCTURAL CHARACTERIZATION OF LIPID HYDROCARBON CHAINS FROM HUMAN LENSES BY INFRARED, AND NEAR-INFRARED RAMAN SPECTROSCOPIES

Age related changes in the lipid composition of human lens membranes h ave been documented and could be responsible for alterations in the fu nction of lens membranes. To establish age related lipid composition-m embrane structure relationships, we have examined spectroscopically th e hydrocarbon chain structure of lipid membranes from human lens corte x and nucleus 0-95 years of age. Lipid membranes were extracted from h uman lenses using a monophasic methanolic extraction. The lipid compos ition of these membranes was determined by P-31-NMR and has already be en reported. Fourier transform near-infrared Raman and Fourier transfo rm infrared spectroscopies were used to determine human lens lipid str ucture. Lipid compositional differences were related to membrane struc ture. The frequency corresponding to the CH2 symmetric stretching band was found to increase with age in lipid samples from all regions of t he lens. The frequency was used to estimate lipid hydrocarbon order. L ipid order was found to increase with age and was not significantly di fferent for lipids extracted from the cortex compared to those from th e nucleus. These results were confirmed qualitatively by comparing the height of the 2880 cm(-1) band with the height of the 2850 cm(-1) Ram an band. Increased lipid order with age was also confirmed by the anal ysis of the C - C stretching bands. Lipid hydrocarbon chain order incr eased linearly with increasing sphingomyelin content and decreased lin early with increasing phosphatidylcholine content. This trend, similar to that observed in other types of membranes suggests that these two lipids may play a role in modulating lipid order. (C) 1996 John Wiley & Sons, Inc.