It was shown that in membranes containing raft domains, the macular
xanthophylls lutein and
zeaxanthin are not distributed uniformly, but are excluded from saturated raft domains and about ten times more concentrated in unsaturated bulk
lipids. The selective accumulation of
lutein and
zeaxanthin in direct proximity to unsaturated
lipids, which are especially susceptible to lipid peroxidation, could be very important as far as their
antioxidant activity is concerned. Therefore, the protective role of
lutein against lipid peroxidation was investigated in membranes made of raft-forming mixtures and in models of photoreceptor outer segment membranes and compared with their
antioxidant activity in homogeneous membranes composed of unsaturated
lipids. Lipid peroxidation was induced by photosensitized reactions using
rose Bengal and monitored by an MDA-TBA test, an iodometric assay, and oxygen consumption (using EPR spectroscopy and the mHCTPO
spin label as an
oxygen probe). The results show that
lutein protects unsaturated
lipids more effectively in membranes made of raft-forming mixtures than in homogeneous membranes. This suggests that the selective accumulation of macular
xanthophylls in the most vulnerable regions of photoreceptor membranes may play an important role in enhancing their
antioxidant properties and ability to prevent age-related macular diseases (such as
age-related macular degeneration (AMD)).