Atherosclerosis is characterized by growing lipid deposits that weaken and narrow blood vessels. Age-related macular degeneration is also characterized by a deposition of lipids in and around the retina in its early stage. One might therefore speculate as to whether age-related problems with the mechanisms responsible for clearing lipids might be at the root of both conditions. Macrophages are the cell responsible for gathering up unwanted lipids, which they then hand off to HDL particles for the journey back to the liver and consequent excretion, a process known as reverse cholesterol transport. This system works well in enough in youth, but falters with age. Macrophages become dysfunctional, with one theory being that this is due to increasing levels of oxidized lipids that cannot easily be broken down, and thus clog up the vital functions of macrophage cells.
A sizable amount of research into reverse cholesterol transport has taken place in the context of atherosclerosis, and this has given rise to a varied set of attempts to increase the flow of cholesterol through macrophages. So far this has resulted in failed clinical trials and limited benefits to patients, but efforts continue on the next generation
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