The in vitro preparation and histochemical properties of substances resembling ceroid.

Substances possessing the same histochemical properties as the ceroid in cirrhotic livers of rats fed choline-deficient diets have been prepared from various unsaturated fats, fatty acids and their esters by autoxidation but could not be obtained from hydrocarbons or saturated fats or fatty acids. The formation of ceroid-like substances occurred first on surfaces or at interfaces in the reaction mixtures. It was inhibited by antioxidants and was accelerated by the addition of tissues, blood cells, erythrocytic stroma, or hemoglobin, by emulsification, by increasing the surface exposed to the air, and by increasing the temperature. Histochemical studies provided much evidence that the following properties of ceroid might be attributed to the products of the autoxidation of unsaturated lipids: insolubility in organic solvents, sudanophilia, yellowing by concentrated nitric acid, positive periodic acid-Schiff's reaction, basophilia, acid fastness, positive hernofuscin reaction, and reduction of diammine silver carbonate and alkaline potassium permanganate. The normal reactivity of cells or tissues embedded in ceroid was effectively masked by the pigment, apparently, initially at least, by preventing the reagents' gaining access to them. It is suggested that the iron sometimes demonstrated in ceroid may be that of blood cells or tissue fragments incompletely masked by the ceroid. It is concluded that whenever conditions are such that unsaturated fats accumulate in tissues to such an extent that a relative lack of biological anti-oxidants results, autoxidation of the fats and their conversion to ceroid pigment are favored, and that ceroid and the lipofuscin pigment of vitamin E deficiency may be fundamentally similar.