Hypolipidemia in a mutant strain of "acatalasemic" mice

Ultrastructure of the main excretory duct epithelia of the rat parotid and submandibular glands with a review of the literature

The fine structure of the main excretory duct (MED) epithelia of the rat parotid and submandibular glands was investigated by scanning and transmission electron microscopy. The structure of these two MED epithelia was compared. Five principal cell types were observed in the MED epithelium of the parotid gland--cuboidal, basal, light (types I and II), dark, and tuft cells. The cuboidal cells, which were stratified in two or three layers, were the most numerous. Basal cells were situated adjacent to the basal lamina of the epithelium. The type I light cells had well-developed basal plasma membrane infoldings. The type II light cells had poorly developed basal plasma membrane infoldings. The dark and tuft cells resembled those of the MED epithelium of the rat submandibular gland. Four principal cell types were observed in the MED epithelium of the submandibular gland--light cells (types I and II), dark, tuft, and basal cells. The two types of light cells were the most numerous. Dark cells with regular and dense microvilli were relatively narrow in shape and had complicated basal plasma membrane infoldings. There were numerous vesicles or channel-like vesicles in their apical cytoplasm. Tuft cells were characterized by prominent microvilli, many vesicles of various sizes in the apical cytoplasm, and no basal infoldings. Peroxisomes were present in the MED epithelia of the rat parotid and submandibular glands, especially in light and cuboidal cells.

Peroxisome-associated enzymes and serum lipids in tumour-bearing rats treated with peroxisome-proliferating agents

Xenobiotic induction of liver peroxisomes is associated with hypolipidemia. To test the involvement of the peroxisome proliferation with the hypolipidemia, male rats were inoculated in the groin with five different tumors: an aflatoxin-induced hepatoma, a lasiocarpine-induced hepatoma, an actinomycin-D-induced mesothelioma, a lasiocarpine-induced squamous cell carcinoma, and a methylnitrosourea-induced fibrosarcoma. After the tumours reached a suitable size, the rats were fed diets containing the peroxisome-proliferating hypolipidemic agents tibric acid (2-chloro-5-[3,5-dimethylpiperidinosulfonyl] benzoic acid) or Wy-14,643 ([4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid) for 2 weeks. Liver and tumor tissues were then assayed for the peroxisome-associated enzymes, catalase and carnitine acetyltransferase, and correlated with serum levels of triglyceride and cholesterol. The presence of the tumors caused a predictable decrease in liver catalase and a slight elevation of liver carnitine acetyltransferase. Serum cholesterol was elevated slightly, while serum triglyceride levels were elevated, unchanged, or decreased in the tumor-bearing rats maintained on control diet. Inclusion of the xenobiotics in the diet caused increases in liver weight, catalase, and carnitine acetyltransferase. Serum triglycerides were decreased in the three groups which were not already decreased, but a decrease in serum cholesterol was only found in one group after only one of the treatments. The latter finding demonstrates that peroxisomal enzyme induction can be dissociated from the decrease in serum cholesterol. The data were further evaluated by testing for correlations between the changes in these components, comparing changes within groups and between groups. These correlations indicate an inverse biological association between liver catalase and serum cholesterol and between liver carnitine acetyltransferase and serum triglyceride. The latter correlation was inverse only for comparisons between groups, suggesting that carnitine acetyltransferase activity is associated with serum triglycerides only during the perturbational state.

The effects of clofibrate and 3-amino-1,2,4-triazole on liver catalase and lipid metabolism in mice

Clofibrate-treated mice showed a significant decrease in plasma triacylglycerols and a parallel elevation of liver catalase. Repeated administration of aminotriazole to clofibrate-treated mice effectively abolished the elevated catalase activity, but had no significant effect on the reduced plasma triacylglycerol levels. In mice, the hypolipidemic effect of clofibrate may be dissociated from its capacity to elevate liver catalase. Repeated administration of aminotriazole to control mice resulted in significantly lowered carcass fat and plasma triacylglycerol levels even though the liver catalase activity was greatly depressed. The livers of clofibrate-treated mice showed an increase in phospholipid content. Livers of aminotriazole-treated mice showed a decrease in total lipid content, with a profound decrease in free fatty acids and triacylglycerols and a slight increase in phospholipids. The composition of the individual free fatty acids of the liver triacylglycerols showed a shift towards the shorter fatty acids and the nutritionally essential alpha-linolenic acid in clofibrate-treated mice.

Biological autoxidation. II. Cholesterol esters as inert barrier antioxidants. Self-assembly of porous membrane sacs. An hypothesis

The antioxidation defenses recognized thus far appear too weak. Needed are inert barriers to encapsulate foci of activated oxygen (FAOs) and contain their spreading. These capsules must: 1. self-assemble nonenzymatically and spontaneously in face of adversity; 2. resist oxidation and dissolution in water; and 3. be moderately fluid and elastic enough to withstand flexing by tissues. Evidence shows activated oxygen: a. is produced by common cholesterolester (CE)-raising agents; b. boosts accumulation of CEs; and c. splits low-density lipoproteins (LDL), thus releasing CE-rich coalescence-prone lipid micelles. I am proposing that CEs, combined with polar lipids, are uniquely suited to form inert-lipid antioxidation barriers (ILABs). Porous ILAB capsules self-assemble from lipid micelles released by oxidatively degraded LDL. The capsules are thermodynamically unstable but elastic, durable and capable of self-repair through oxidation of ambient LDL. All capsules tend to contract into spheres. Enclosed needle-like "foreign bodies", such as asbestos, puncture the contracting capsules. Hence the odd bulbous architecture of asbestos bodies. ILABs protect from--and their failure initiates and promotes--carcinogenesis and atherosclerosis. ILABs may be mediators of membrane biogenesis. The loss of arterial flexibility in atherosclerosis protects ILAB capsules from breakage.

Hepatic peroxisome proliferation: induction by two novel compounds structurally unrelated to clofibrate

Two hypolipidemic compounds [ 4-chloro-6(2,3-xylidino)-2-pyrimidinyl-thio] acetic acid, and 2-chloro-5(3,5-dimethylpiperidinosufony)benzoic acid (tibric acid) greatly increased the number of peroxisomes (microbodies) in liver cells of rats and mice. This augmented peroxisome population was accompanied by significant elevation of liver catalase activity. These two hypolipidemic peroxisome proliferators are structurally different from ethyl a-p-chlorophenozyisobutyrate (clofibrate) and other hypolipidemic, arylocyisobutyrate derivatives which cause hepatic peroxisome proliferation. Induction of peroxisome proliferation by these structurally unrelated hypolipidemic compounds suggests a possible relation between hepatic peroxisome proliferation and hypolipidemia.

Microbodies (peroxisomes) containing catalase in myocardium: morphological and biochemical evidence

Microbodies characterized by a single limiting membrane and finely granular matrix occur in mouse myocardium and appear in close spatial relation to mitochondria and sarcoplasmic reticulum. The presence of catalase in the microbodies is revealed cytochemically and confirmed biochemically by direct measurement of its activity in myocardial tissue fractions. It is suggested that the microbodies may play an important role in myocardial lipid metabolism.

Peroxisomal and mitochondrial defects in the cerebro-hepato-renal syndrome

The cerebro-hepato-renal syndrome is a rare familial malady with cerebral, renal, and skeletal abnormalities, severe hypotonia, cirrhosis, iron and lipid storage, and death within 6 months. Correlated electron microscopic, histochemical, and biochemical studies demonstrate defects in two oxidative organelles. Peroxisomes cannot be found in hepatocytes and renal proximal tubules. In hepatocytes and cortical astrocytes, mitochondria are distorted in their appearance and glycogen stores are increased. Oxygen consumnption of brain and liver mitochondrial preparations with succinate and with substrates reducing nicotinamide adenine dinucleotide is markedly diminished, but the consumption is normal with ascorbate and tetramethylphenylenediamine, which suggests a defect in electron transport prior to the cytochromes. Histochemical studies of mitochondrial oxidation point to a defect between the succinate dehydrogenase flavoprotein and coenzyme Q, possibly in the region of nonheme iron protein.