A fatty acyl-CoA oxidizing system in rat liver peroxisomes; enhancement by clofibrate, a hypolipidemic drug.

Abstract

Purified rat liver peroxisomes contain a cyanide-insensitive fatty acyl-CoA oxidizing system that uses 02 and NAD as electron acceptors. The system was detected by the ability of added palmitoylCoA to elicit 02 consumption, H202 production, and Ordependent NAD reduction. The activity of this system is increased approximately one order of magnitude in rats treated with clofibrate, a hypolipidemic drug known to cause peroxisomal proliferation. The possibility that rat liver peroxisomes may be involved in lipid metabolism is suggested by the fact that clofibrate*, which decreases serum lipid levels in man (1, 2) and animals (3, 4) and is used clinically for this purpose, also causes a striking increase in hepatic peroxisomes in several species (5, 6). Whether these two effects are related is unknown. Such a possibility was once denied (7), but is supported by the recent observation that two other hypolipidemic drugs, structurally unrelated to clofibrate, also induce proliferation of hepatic peroxisomes (8).Peroxisomes are characterized by their content of H202-producing oxidases and catalase (9). Curiously, although the number of electron microscopic images of peroxisomes increases as much as four to ten times upon clofibrate treatment (5, 6, 10), catalase activity increases only by 30-140% (5, 7, 10), and the known oxidases are either unchanged or decline (5,(10)(11)(12). This raises the intriguing possibility that the increase in protein in peroxisomes during clofibrate treatment might be due, at least in part, to the synthesis of lipid-metabolizing enzymes.Cytoplasmic organelles from castor bean endosperm, glyoxysomes, related to animal peroxisomes by their content of catalase and oxidases, have been shown by Beevers and coworkers (13) to contain enzymes capable of catalyzing fl-oxidation and the glyoxylate cycle reactions, thus playing a central role in the conversion of fat to carbohydrate at germination. The glyoxysomal system of fatty acyl-CoA oxidation resembles that of mitochondria except that the first dehydrogenase transfers its electrons to 02, producing H202 (14).These facts have encouraged us to look for a system of the type pictured in Fig. 1 in rat liver peroxisomes. This paper presents our first results, which establish that fatty acyl-CoA oxidizing activity is present in peroxisomes, and is strikingly increased by treatment of the animals with clofibrate. METHODS Palmitoyl-CoA oxidation was assayed by its ability to elicit the reduction of NAD, or in some cases that of oxygen to H202.NAD reduction was followed spectrophotometrically at 340 nm in a reaction volume of 1.0 ml containing 30 mM potassium phosphate buffer, pH 7.4, 0.2 mM NAD, 0.1 mM CoA, 12 mM dithiothreitol, 0.15 mg/ml of bovine serum albumin, and 0.01% Triton X-100. The temperature was maintained at 37'. Enzyme was added to duplicate cuvettes, and the reaction was started by the addition of palmitoyl-CoA to one of the cuvettes (10 nmol, unless otherwise indicated). The initial reaction rate was measured and expressed in Mmol o...

Fine Structural Changes in the Hepatic Microbodies of Rats Treated With Hypolipidemic Agents, Gemfibrozil and Clofibrate

“…In contrast with this view, Reddy et al (25) reported recently that when clofibrate was administrated to rats with allylisopropylacetamide, which is a inhibitor of catalase synthesis, the increase in the number of microbodies still occurred even though the increase in hepatic catalase activity was negligible, while serum cholesterol and triglyceride were lowered. In fact, Lazarow et al (12) and Goldenberg et al (6), suggested that the peroxisomal fatty acyl-CoA oxidizing system and carnitin acetyltransferase might play more important roles in hypolipidemic action and give the best explanation for a close connection between hypolipidemic effect and microbody proliferation. These results indicate that catalase in hepatic microbodies is not essential for affecting the lipid metabolism, and its increase reflects only the increase in the number of microbodies, as was also pointed out by Goldenberg et al (6).…”

Prehibernation and hibernation effects on the d-3-hydroxybutyrate dehydrogenase of the heavy and light mitochondria from liver jerboa (Jaculus orientalis) and related metabolism

“…Subcellular marker enzymes were assayed according to the following methods: succinate dehydrogenase (King, 1967) for mitochondria; palmitoyl-CoA oxidase (Lazarow and De Duve, 1976) for peroxisomes; NADPH-cytochrome c reductase (Beaufay et al, 1974) for microsomes and glyceraldehyde 3-phosphate dehydrogenase (Serrano et al, 1991) for cytosol.…”

Effects of Ethyl 4-Chloro-2-Methylphenoxyacetate on Bile Composition in Golden Hamsters.

“…Catalase activity in the peroxisomal fraction was measured by the method of Aebi (1974). The activity of peroxisomal cyanide-insensitive fl-oxidation of fatty acids was determined by recording the reduction of NAD to NADH spectrophotometrically in the reaction of the /3-oxidation spiral (Lazarow and de Duve 1976).…”