Lipofuscin

LIPOFUSCIN (from Greek lipos - fat and Latin fuscus - brown), a granular yellow-brown pigment that does not give the iron reaction; insoluble in acids and alkalis; partially soluble in the same solvents as fats, and partially stains with fat-staining dyes (best of all with Nilblausulfat and Neutralrot). Due to these properties, some authors (Hueck) suggested that lipofuscin is a product of fat breakdown or that fats in one form or another are an essential component of it. At the present time, however, it has been established (Lubarsch, Brahn, Schmidtmann) that lipofuscin is a pigment of protein nature and fats in it are merely an accidental admixture and may be absent altogether, whereupon only some of its microchemical reactions and staining properties change. Thus, lipofuscin in the smooth musculature of the intestine and blood vessels never gives a positive fat reaction. From which protein metabolism products lipofuscin is formed is still not precisely known; it is believed to be derived from nuclear breakdown products. In its qualitative composition (C-50.4%, H-5.9%, N-10.8%, sulfur-3.2%), lipofuscin is extremely close to another protein pigment, melanin (see), and is even identified with it by many authors. The distinction is made only on the plane that melanin is a pigment of ectodermal origin, whereas lipofuscin is also found in derivatives of other germ layers and therefore is probably chemically somewhat different from cutaneous melanin. Lipofuscin is also otherwise called the "wear-and-tear pigment," because it is found chiefly in old age and in pathological states accompanied by general cachexia and atrophy (e.g., cancer, tuberculosis, etc.). However, it is discovered in many organs even in completely healthy people and at a very early age (it is found in the kidneys and the neural lobe of the hypophysis in children in the 1st year of life, in the liver in the 3rd–4th year, in the heart in the 12th year, and in the gonads in the 20th year of life). The usual sites of lipofuscin deposition are nerve ganglia, the myocardium (at both poles of the nucleus), the liver, the kidneys (descending limb of Henle's loop, more rarely the convoluted tubules), the testes, the epithelium of the seminal vesicles, the smooth musculature of the gastrointestinal tract and blood vessels, skeletal musculature, the neural lobe of the hypophysis, the zona pigmentosa of the adrenal glands, and generally the connective tissue stroma of any organ [see separate plate (vol. XV, pp. 575–576), fig. 1]. Apparently belonging to lipofuscin is also the yellow granular pigment of the pineal, thyroid, and parathyroid glands. The accumulation of lipofuscin in tissues causes the respective organs to acquire a brown and even dark brown coloration. The heart and liver stand out particularly sharply in this sense. If organ atrophy is simultaneously present, one speaks of "brown atrophy of the heart, liver." The diffuse brown coloration of the intestine in hemochromatosis (see) and alcoholism also depends on the abundant deposition of lipofuscin (previously it was assumed that this was hemosiderin [see]) in its smooth musculature. In view of the fact that lipofuscin is encountered not only as an age-related change or in debilitating diseases, but also at an early age and in healthy subjects (physiologically), the question arises as to the factors that cause its appearance. They are still unknown. But since lipofuscin is currently identified with melanin, the possibility is not excluded that such factors are ultraviolet rays, the role of which in the formation of melanin has been proven.