Lipofuscin

Micrograph showing lipofuscin, in brown/yellow, in a liver biopsy with ground glass hepatocytes; H&E stain

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.

Formation and turnover

It appears to be the product of the oxidation of unsaturated fatty acids and may be symptomatic of membrane damage, or damage to mitochondria 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.

Relation to diseases

Micrograph of heart muscle showing lipofucin pigment, H&E stain

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.

Abnormal accumulation of lipofuscin is associated with a group of diseases of neurodegenerative disorder type called lipofuscinoses, e.g., neuronal ceroid lipofuscinosis, also known as Batten disease, as well as some other names.

Pathological accumulation of lipofuscin is implicated in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, certain lysosomal diseases, acromegaly, denervation atrophy, lipid myopathy, chronic obstructive pulmonary disease, and centronuclear myopathy. Accumulation of lipofuscin in the colon is the cause of the condition melanosis coli.

Possible therapies

Calorie restriction, vitamin E, and increased glutathione appear to reduce or halt the production of lipofuscin.

The nootropic drug piracetam appears to significantly reduce accumulation of lipofuscin in the brain tissue of rats.

Other possible treatments:

• Centrophenoxine
• Acetyl-L-Carnitine
• Ginkgo Biloba
• DMAE [1]

Wet macular degeneration can be treated using Selective Photothermolysis where a pulsed unfocused laser predominantly heats and kills pigment- (i.e.: lipofuscin-) rich cells, leaving untouched healthy cells to multiply and fill in the gaps. The technique is also used as a skin treatment to remove tattoos, liverspots, and in general make skin appear younger. This ability to selectively target lipofuscin has opened up research opportunities in the field of Anti-aging medicine.

Recently it was discovered that a new drug can remove lipofuscin from retinal pigment epithelial cells. This opens up a new therapy option for the treatment of dry age-related macular degeneration and Stargardt disease, for which there is currently no treatment. The drug has now been granted orphan drug designation for the treatment of Stargardt disease by the European Medicines Agency.

Other uses

Lipofuscin quantification is used for age determination in various crustaceans such as lobsters and spiny lobsters. Since these animals lack bony parts, they cannot be aged in the same way as bony fish, in which annual increments in the ear-bones or otoliths are commonly used. Age determination of fish and shellfish is a fundamental step in generating basic biological data such as growth curves, and is needed for many stock assessment methods. Several studies have indicated that quantifying the amount of lipofuscin present in the eye-stalks of various crustaceans can give an index of their age. This method has not yet been widely applied in fisheries management mainly due to problems in relating lipofuscin levels in wild-caught animals with accumulation curves derived from aquarium-reared animals.

See also

• Residual body

External links for general reviews

• Histology at neuro.wustl.edu
• Histology image: 20301loa – Histology Learning System at Boston University
• Destroying Lipofuscin and Destroying Cancer, FightAging.org
• Unfocused Pulsed Lasers Selectively Destroy Lipofuscin, AcceleratingFuture.com