HISTOCHEMISTRY OF PEROXISOMES - OVERVIEW

Peroxisomes are present in virtually al eukaryotic cells and known to contain more than fifty enzymes. Their size, number and composition of enzymes vary considerably between different species and between diffe rent cell types within the same species, During the past two decades, there has been an explosion in the amount of information about their b iogenesis, peroxisomal targeting signals, the role of these organelles in lipid metabolism, in the synthesis of cholesterol, bile acids and glycerolipids, and in the degradation of uric acid. The importance of peroxisomes in mammalian metabolism is underscored by the discovery of carcinogenic peroxisomes proliferators and by the occurrence of perox isomal genetic diseases. Of considerable importance is the implication of induction of hepatic peroxisome proliferation and the peroxisomal fatty acid beta-oxidation enzyme system in the development of hepatoce llular carcinomas in rats and mice by structurally diverse peroxisome proliferators. The immunocytochemical and in situ hybridization proced ures are extremely valuable in identifying qualitative and quantitativ e changes of specific enzymes in animals exposed to peroxisome prolife rators. Peroxisome proliferators appear to exert their pleiotropic res ponses by activating a receptor known as peroxisome proliferator-activ ated receptor. An understanding of the ontogeny of this receptor in re lation to the expression of peroxisomal genes is an important consider ation in assessing the implications of peroxisome proliferator-induced toxicity and the role of peroxisomes in genetic diseases.