Induction of Hepatic Peroxisome Proliferation by Xenobiotics. In: Fahimi HD, Sies H, editors. Peroxisomes in Biology and Medicine. Berlin: Springer Berlin Heidelberg; 1987. pp. 255-62. [DOI: 10.1007/978-3-642-71325-5_25]

Reactive oxygen species, antioxidant systems and nitric oxide in peroxisomes

Peroxisomes are subcellular organelles with an essentially oxidative type of metabolism. Like chloroplasts and mitochondria, plant peroxisomes also produce superoxide radicals (O2*(-)) and there are, at least, two sites of superoxide generation: one in the organelle matrix, the generating system being xanthine oxidase, and another site in the peroxisomal membranes dependent on NAD(P)H. In peroxisomal membranes, three integral polypeptides (PMPs) with molecular masses of 18, 29 and 32 kDa have been shown to generate radicals O2*(-). Besides catalase, several antioxidative systems have been demonstrated in plant peroxisomes, including different superoxide dismutases, the ascorbate-glutathione cycle, and three NADP-dependent dehydrogenases. A CuZn-SOD and two Mn-SODs have been purified and characterized from different types of peroxisomes. The four enzymes of the ascorbate-glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase) as well as the antioxidants glutathione and ascorbate have been found in plant peroxisomes. The recycling of NADPH from NADP(+) can be carried out in peroxisomes by three dehydrogenases: glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and isocitrate dehydrogenase. In the last decade, different experimental evidence has suggested the existence of cellular functions for peroxisomes related to reactive oxygen species (ROS), but the recent demonstration of the presence of nitric oxide synthase (NOS) in plant peroxisomes implies that these organelles could also have a function in plant cells as a source of signal molecules like nitric oxide (NO*), superoxide radicals, hydrogen peroxide, and possibly S-nitrosoglutathione (GSNO).

Elevation of ubiquinone content by peroxisomal inducers in rat liver during aging

The effect of di(2-ethylhexyl)phthalate (DEHP) on the induction of peroxisomes and the content of ubiquinone in the liver was studied in rats between 25 and 496 days of age. During this period, peroxisomal beta-oxidation of fatty acids was greatly decreased but it could be induced many-fold in all ages. The ubiquinone (UQ) content was increased upon induction 6-fold in the first weeks of life, but the extent of this elevation continuously narrowed and no induction could be observed in the oldest animals, even after prolonged treatment with the plasticizer. In contrast, the treatment decreased the amount of liver cholesterol in all age groups. Treatment with this peroxisomal inducer increased the biosynthesis of UQ while the breakdown rate was found to be unaffected, as the half-life of this lipid was 103 and 106 h in control and treated rats, respectively. These results indicate that treatment with peroxisomal inducers increases the liver UQ content by increasing the rate of biosynthesis and that this effect is not apparent in aged rats.

Morphometric analysis of liver and kidney peroxisomes in lactating rats and their pups after treatment with the peroxisomal proliferator di-(2-ethylhexyl)phthalate

Di-(2-ethylexyl)phthalate (DEHP) administered to adult lactating rats from delivery to weaning induces age- and organ-specific modifications of the peroxisomal morphometric parameters (VV, NA and D) in the liver and kidney of both rats and their pups. In both tissues, peroxisomal relative volume and catalase biochemical activity show a similar pattern during the development, as well as under DEHP treatment. Morphometric results suggest that two modalities of peroxisomal proliferation exist, involving: a) increases in both number and mean diameter of the organelles; b) a purely numerical increase of the organelles, accompanied by a remarkable decrement in their mean diameter. A peroxisomal population proliferated through the latter model appears unable to return to normal conditions, following treatment withdrawal. These two proliferation systems, the first implying a swelling and the latter a fragmentation of pre-existing peroxisomal profiles, are supposed to be tissue-specific in the adult animal. In particular, in the liver the 'swelling' model appears more suitable to explain peroxisome proliferation, while the kidney this process would follow the 'fragmentation' model. Immature animals might instead show in both organs intermediate features of peroxisomal proliferation modalities.

The ontogeny of peroxisome-proliferator-activated receptor gene expression in the mouse and rat

The expression of the gene coding for peroxisome-proliferator-activated receptor (PPAR), a novel transacting factor belonging to the steroid superfamily, has been determined in the mouse and rat throughout development using hybridization histochemistry. Messenger RNA is demonstrable in the liver and brown fat from the fetal period onwards and, additionally, in the heart, kidney and gut post-natally. It is proposed that the upregulation of transcription of peroxisomal beta oxidation genes in specific tissues follows binding of the receptor to its natural ligand. Thus PPAR may have an important role in cold adaptation and non-shivering thermogenesis as well as in detoxification.

Estrogen induction of alcohol dehydrogenase in the uropygial gland of mallard ducks

Treatment of mallard ducks with estradiol, or a combination of estradiol and thyroxine, has been shown to result in the proliferation of peroxisomes and production of diesters of 3-hydroxy fatty acids, the female pheromones, in the uropygial gland of male and female mallard ducks. Such a treatment results in the induction of a unique set of proteins. A cDNA library enriched in hormone-induced transcripts was subjected to differential screening. The nucleotide sequence of one of the two unique cDNA clones, DGH1, had high similarity to the Human class I alcohol dehydrogenase (ADH) gamma subunit and represented the carboxy-terminus of the protein from amino acid 190-374. SDS/PAGE and Western blot analysis of the proteins indicated that the level of a 38-kDa protein that cross-reacted with antibodies prepared against the chicken ADH was increased 5-7-fold by hormone treatment. Assays for ADH activity in the uropygial gland extracts of male mallards showed a 5-7-fold induction of the enzyme by hormone treatment. The 1.9-kb ADH mRNA levels were increased 12-14-fold under these conditions. Of all the tissues tested, the uropygial gland had the highest levels of ADH mRNA. Induction of ADH by estradiol treatment occurred only in this tissue. Elevated levels of ADH were also observed in the glands of male mallards in eclipse, the post-nuptial condition when the hormonal balance is shifted to higher estrogen levels, suggesting that this enzyme is regulated by estrogens in this period. Estradiol treatment caused an 80% decrease in the NAD+/NADH ratio in the uropygial gland and a twofold increase in the fatty alcohol oxidation rate catalyzed by the gland extract. These observations could help explain how increased levels of ADH could contribute to the production of the diesters.

Effects of prolonged treatment with phthalate ester on rat liver

Rats were fed a diet containing 2%, 0.2% or 0.02% di(2-ethylhexyl)phthalate (DEHP) for a period of 102 weeks. Only the 2% diet caused a substantial decrease in body weight. Both peroxisomal palmitoyl-CoA dehydrogenase and mitochondrial carnitine acetyltransferase activities were greatly induced by exposure to the highest dose of phthalate ester, reaching maximal plateau values after about 20 weeks of treatment. The diet containing 0.2% DEHP increased both activities slowly, but continuously, and at the end of the two-year period these increases were almost comparable to those obtained with the highest dose. Even the lowest dose gave a slowly increase in these activities. Both microsomal NADPH-cytochrome c reductase activity and the level of cytochrome P-450 were increased initially by exposure to 2% DEHP, but returned almost or completely to the control level after about 30 weeks of exposure. Depending on the dose of DEHP in the diet, peroxisomal catalase activity was elevated above the control level during the first year of treatment but was about the same as in the control animals during the second year. A substantial decrease in peroxisomal urate oxidase activity was observed throughout the entire experimental period. When treatment was ceased after one year, all activities returned to the control values within 2-3 weeks. These results demonstrate the complex nature of the effects caused by prolonged treatment with DEHP with cumulative increases at low doses.

Fatty acid oxidation in hepatic peroxisomes and mitochondria after treatment of rats with di(2-ethylhexyl)phthalate

Rats were fed a diet containing di(2-ethylhexyl)-phthalate, which increases the number of peroxisomes and mitochondria in the liver. This proliferation does not change the ratio of phospholipid to protein in mitochondria or microsomes, but causes certain changes in the fatty acid composition of the phospholipids. The highest rates of peroxisomal and mitochondrial beta-oxidation are obtained with 12:0 and 16:0 fatty acids as substrates, respectively. A 3-4 fold increase in the rate of beta-oxidation by both organelles is caused by DEHP treatment, but there are no qualitative changes in the relative rates of oxidation of individual fatty acids. Short- and medium-chain carnitine acyltransferases in peroxisomes, microsomes and mitochondria, as well as the mitochondrial long-chain carnitine acyltransferase are induced to various extents. These results indicate that the increased beta-oxidation of fatty acids caused by phthalate treatment involves the same peroxisomal and mitochondrial pathways which operate under normal conditions.