LECTIN HISTOCHEMISTRY OF LIPOFUSCIN AND CERTAIN CEROID PIGMENTS

Little is known at present about the saccharide components of lipofusc in (age pigment) and ceroid pigments in situ. The purpose of this stud y was, therefore, to study in detail the lectin reactivities of lipofu scin in neurons and cardiac myocytes of old humans and rats. In additi on, those of diverse ceroid pigments found in human aortic atheromas, in the livers of choline-deficient rats, in the uteri of vitamin E-def icient rats and in the crushed epididymal fat pad of rats, are include d. Cryostat and deparaffinized sections from all these tissues were ei ther extracted with a solvent mixture of chloroform-methanol-water (10 :10:3, v/v) and incubated with 7 different biotinylated lectins or lef t untreated. Delipidation was done in order to study whether it was po ssible to discriminate between the saccharide moieties of glycolipids and glycoproteins of lipofuscin and ceroid pigments in situ. Other sim ilarly treated sections were used to study the autofluorescence, sudan ophilia, acid-fastness and reactivity to PAS. The frequency and intens ity of lectin binding and standard histochemical properties of all the pigments were evaluated semi-quantitatively and blind. The results in dicated that mannose was in general the most consistently detected sug ar residue in lipofuscin granules of humans and rats, and that this pi gment may also contain acetylglucosamine, acetylgalactosamine, sialic acid, galactose and fucose. However, notable differences were found no t only in the lipofuscin saccharide components of different cell types of humans and rats, but also in those in the same type of cells in bo th species. Although mannose was not detected in the hepatic ceroid of choline-deficient rats, this saccharide moiety was almost always pres ent in the other ceroid pigments. Each of the ceroids also contained o ther types of saccharides although the frequency of the latter varied between different ceroid pigments. While lipofuscin and each of the ce roid pigments showed somewhat different lectin binding patterns, the v ariability in the frequency of reactivity to lectins suggests that the se patterns may not be permanent but transient. In this sense, it appe ars that lectin histochemistry may not allow these pigments to be diff erentiated. Furthermore, the extractive procedures used in this study did not enable us to determine whether the saccharides detected in the pigments in situ corresponded to glycolipids or glycoproteins.