Lipofuscin

Lipofuscin is the name given to finely granular yellow-brown pigment granules composed of lipid-containing residues of lysosomal digestion. It is considered to be one of the aging or "wear-and-tear" pigments, found in the liver, kidney, heart muscle, retina, adrenals, nerve cells, and ganglion cells. It is specifically arranged around the nucleus, and is a type of lipochrome.

It appears to be the product of the oxidation of unsaturated fatty acids and may be symptomatic of membrane damage, or damage to and lysosomes. Aside from a large lipid content, lipofuscin is known to contain sugars and metals, including mercury, aluminum, iron, copper and zinc.

The accumulation of lipofuscin-like material may be the result of an imbalance between formation and disposal mechanisms: Such accumulation can be induced in rats by administering a protease inhibitor (leupeptin); after a period of three months, the levels of the lipofuscin-like material return to normal, indicating the action of a significant disposal mechanism. However, this result is controversial, as it is questionable if the leupeptin-induced material is true lipofuscin. There exists evidence that "true lipofuscin" is not degradable in vitro; whether this holds in vivo over longer time periods is not clear.

Lipofuscin accumulation is a major risk factor implicated in macular degeneration, a degenerative disease of the eye, as well as Stargardt disease, an inherited juvenile form of macular degeneration.

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