Abstract
Abstract: :
Purpose: The human lens is the only cellular system known in which dihydrosphingomyelin (DHS) is the most abundant class of phospholipid. The molecular species composition of DHS in cataractous lenses has never been reported. Methods: Phospholipids (PL) extracted from young, old and cataractous lenses were analyzed using high performance liquid chromatography with detection by both electrospray ionization mass spectrometry (MS) and atmospheric pressure chemical ionization (APCI) MS, simultaneously. The areas under peaks in APCI-MS mass chromatograms were used to perform quantitative analysis of the compositions of molecular species of DHS, sphingomyelin (SPM) and phosphatidylcholine (PC). Results: Sphingolipids from young human lens extracts contained 82.2% DHS and 17.8% SPM, giving a DHS/SPM ratio of 4.6:1. Old human lens extracts contained 80.5% and 19.5% of DHS and SPM, respectively, for a DHS/SPM ratio of 4.1:1. Cataractous lens extracts contained 81.1% DHS and 18.9% SPM, for a DHS/SPM ratio of 4.3:1. In all samples, the most abundant sphingolipids were the 16:0 and 24:1 molecular species, accounting for 83% of all DHS species and 68 to 69% of all SPM species. The percentages of 16:0 DHS and SPM decreased with increasing age, while in cataractous lenses the percentage of 16:0 increased, and was higher than the amount of that species in either old or young lenses. Conversely, the amounts of 24:1 DHS and SPM increased with age, but the percentage in cataractous lenses was lower than in either old or young lenses. The ratio of 24:1/24:0 DHS was ~ 5:1 in young, old and cataractous lenses, while the ratio of 24:1/24:0 SPM was only ~1.5:1. This difference between DHS and SPM indicated a clear preference for mono-unsaturated molecular species in all ages and in cataractous lenses (SPM already containing one site of unsaturation in the ceramide backbone). PC molecular species were similar in both young and old lenses, but in cataractous lenses, the levels of PC were so low as to be unobservable in this sample. Conclusions: Small changes were observed in the compositions of DHS and SPM molecular species. The composition of PC species changed dramatically with the onset of cataracts.
Keywords: lipids • cataract