Detection of peroxisomal fatty acyl-coenzyme A oxidase activity

Two Argan Oil Phytosterols, Schottenol and Spinasterol, Attenuate Oxidative Stress and Restore LPS-Dysregulated Peroxisomal Functions in Acox1-/- and Wild-Type BV-2 Microglial Cells

Oxidative stress and inflammation are the key players in neuroinflammation, in which microglia dysfunction plays a central role. Previous studies suggest that argan oil attenuates oxidative stress, inflammation, and peroxisome dysfunction in mouse brains. In this study, we explored the effects of two major argan oil (AO) phytosterols, Schottenol (Schot) and Spinasterol (Spina), on oxidative stress, inflammation, and peroxisomal dysfunction in two murine microglial BV-2 cell lines, wild-ype (Wt) and Acyl-CoA oxidase 1 (Acox1)-deficient cells challenged with LPS treatment. Herein, we used an MTT test to reveal no cytotoxicity for both phytosterols with concentrations up to 5 µM. In the LPS-activated microglial cells, cotreatment with each of these phytosterols caused a significant decrease in intracellular ROS production and the NO level released in the culture medium. Additionally, Schot and Spina were able to attenuate the LPS-dependent strong induction of Il-1β and Tnf-α mRNA levels, as well as the iNos gene and protein expression in both Wt and Acox1-/- microglial cells. On the other hand, LPS treatment impacted both the peroxisomal antioxidant capacity and the fatty acid oxidation pathway. However, both Schot and Spina treatments enhanced ACOX1 activity in the Wt BV-2 cells and normalized the catalase activity in both Wt and Acox1-/- microglial cells. These data suggest that Schot and Spina can protect cells from oxidative stress and inflammation and their harmful consequences for peroxisomal functions and the homeostasis of microglial cells. Collectively, our work provides a compelling argument for the protective mechanisms of two major argan oil phytosterols against LPS-induced brain neuroinflammation.

Profiling Transcriptional Response of Dengue-2 Virus Infection in Midgut Tissue of Aedes aegypti

Understanding the mosquito antiviral response could reveal target pathways or genes of interest that could form the basis of new disease control applications. However, there is a paucity of data in the current literature in understanding antiviral response during the replication period. To illuminate the gene expression patterns in the replication stage, we collected gene expression data at 2.5 days after Dengue-2 virus (DENV-2) infection. We sequenced the whole transcriptome of the midgut tissue and compared gene expression levels between the control and virus-infected group. We identified 31 differentially expressed genes. Based on their function, we identified that those genes fell into two major functional categories - (1) nucleic acid/protein process and (2) immunity/oxidative stress response. Our study has identified candidate genes that can be followed up for gene overexpression/inhibition experiments to examine if the perturbed gene interaction may impact the mosquito’s immune response against DENV. This is an important step to understanding how mosquitoes eliminate the virus and provides an important foundation for further research in developing novel dengue control strategies.

Improvement of fatty acid productivity of thraustochytrid, Aurantiochytrium sp. by genome editing

Thraustochytrid strains belonging to the genus Aurantiochytrium accumulate significant amounts of lipids including polyunsaturated fatty acids and carotenoids and, therefore, are expected to be used for industrial production of various valuable materials. Although various efforts such as chemical mutagenesis and homologous gene recombination have been made to improve lipid productivity of Aurantiochytrium species, low specificity and efficiency in the conventional methods hinder the research progress. Here, we attempted to apply a genome editing technology, the CRISPR-Cas9 system as an alternative molecular breeding technique for Aurantiochytrium species to accelerate the metabolic engineering. The efficiency of specific gene knock-in by the homologous recombination increased more than 10-folds by combining the CRISPR-Cas9 system. As a result of disrupting the genes associated with β-oxidation of fatty acids by the improved method, the genome edited strains with higher fatty acid productivity were isolated, demonstrating for the first time that the CRISPR-Cas9 system was effective for molecular breeding of the strains in the genus Aurantiochytrium to improve lipid productivity.

Identification and characterization of two isoforms of acyl-coenzyme A oxidase 1 gene and their expression in fasting-induced grass carp Ctenopharyngodon idella adipocyte lipolysis

Acyl-coenzyme A oxidases 1 (ACOX1) is the first rate-limiting enzyme responsible for peroxisomal β-oxidation. In the present study, two mRNA variants, ACOX1a and ACOX1b, transcribed from a single gene, were for the first time isolated and characterized from grass carp Ctenopharyngodon idella, both encoding putative peptides of 660 amino acids. Analysis of the exon-intron structures clarified that grass carp ACOX1a and ACOX1b comprise 14 coding exons and correspond to 3a and 3b isoforms of exon 3 splicing variants. Both ACOX1a and ACOX1b mRNAs were expressed in a wide range of tissues, but the abundance of each ACOX1 mRNA showed the tissue-dependent expression patterns. Time-course analysis of ACOX1 expressions indicated that the level of ACOX1a mRNA reached an almost maximal level at day 2, while that of ACOX1b mRNA reached an almost maximal level at day 8 during grass carp primary preadipocyte differentiation. In fasting-induced adipocyte lipolysis, only ACOX1a showed a significant increase in adipocyte, indicating that two ACOX1 isoforms may serve somewhat different roles in the peroxisomal β-oxidation. These results suggested that grass carp ACOX1a and ACOX1b were differently modulated by fasting in adipocyte. In addition, we found that mitochondrial β-oxidation might dominate at the early stage of fasting in adipocytes, indicating that mitochondria and peroxisomes might possess different capacities in fasting-induced adipocytes fatty acid oxidation.

Peroxisomes proliferation and pharmacological stimulation of autophagy in rat liver: evidence to support that autophagy may remove the "older" peroxisomes

Like mitochondria, peroxisomes produce reactive oxygen species (ROS), compounds which have been implicated to play an important role in many degenerative diseases and aging itself, and an exaggerated ROS production might occur in altered or older organelles. Growing evidence shows that autophagy, a required function in cell housekeeping during fasting, can remove damaged macromolecules, organelles, and membranes selectively. Proliferation of peroxisomes can be enhanced in liver cells by perfluorooctanoic acid (PFOA), which causes a marked increase of the Acyl-CoA oxidase (ACOX) activity and no significant change in urate oxidase (UOX) activity. The administration of antilipolytic drugs to fasted animals was shown to intensify autophagy. Here we tested the hypothesis that autophagy may distinguish and remove older from younger peroxisomes in rat liver. Male Sprague-Dawley rats were given PFOA (150 mg/kg body weight) or vehicle. Animals were sacrificed at different times following PFOA administration, and 3 h after the induction of autophagy with the antilipolytic agent 3,5-dimethyl pyrazole (DMP, 12 mg/kg body weight). The levels of ACOX and UOX activity were measured in the liver tissue. Results showed that autophagy caused a parallel, significant decrease in both enzymes activity in control rats, and that in PFOA-treated rats the effects were different and changed with PFOA time administration. Changes are compatible with the hypothesis that newly formed ACOX-rich peroxisomes are resistant to pexophagy and that sensitivity to pexophagy increases with increasing peroxisomal "age." In conclusion, there is indirect evidence supporting the hypothesis that autophagy may recognize and degrade older peroxisomes.

Genetic Interactions between PEROXIN12 and Other Peroxisome-Associated Ubiquitination Components

Most eukaryotic cells require peroxisomes, organelles housing fatty acid β-oxidation and other critical metabolic reactions. Peroxisomal matrix proteins carry peroxisome-targeting signals that are recognized by one of two receptors, PEX5 or PEX7, in the cytosol. After delivering the matrix proteins to the organelle, these receptors are removed from the peroxisomal membrane or matrix. Receptor retrotranslocation not only facilitates further rounds of matrix protein import but also prevents deleterious PEX5 retention in the membrane. Three peroxisome-associated ubiquitin-protein ligases in the Really Interesting New Gene (RING) family, PEX2, PEX10, and PEX12, facilitate PEX5 retrotranslocation. However, the detailed mechanism of receptor retrotranslocation remains unclear in plants. We identified an Arabidopsis (Arabidopsis thaliana) pex12 Glu-to-Lys missense allele that conferred severe peroxisomal defects, including impaired β-oxidation, inefficient matrix protein import, and decreased growth. We compared this pex12-1 mutant to other peroxisome-associated ubiquitination-related mutants and found that RING peroxin mutants displayed elevated PEX5 and PEX7 levels, supporting the involvement of RING peroxins in receptor ubiquitination in Arabidopsis. Also, we observed that disruption of any Arabidopsis RING peroxin led to decreased PEX10 levels, as seen in yeast and mammals. Peroxisomal defects were exacerbated in RING peroxin double mutants, suggesting distinct roles of individual RING peroxins. Finally, reducing function of the peroxisome-associated ubiquitin-conjugating enzyme PEX4 restored PEX10 levels and partially ameliorated the other molecular and physiological defects of the pex12-1 mutant. Future biochemical analyses will be needed to determine whether destabilization of the RING peroxin complex observed in pex12-1 stems from PEX4-dependent ubiquitination on the pex12-1 ectopic Lys residue.

Catabolic Functions of Peroxisomes: Modification by Hypoupidemic Drugs

The peroxisome is a subcellular organelle that is widely distributed in nature and which carries out both catabolic and anabolic functions (Ann. NY Acad. Sch 386:1-550, 1982). The catabolic functions include respiration (based on the formation and decomposition of H2O2) and the ß-oxidation of fatty acids. A number of drugs share the attributes of beingi) hypo-lipidemic, (2) inducers of the peroxisomal ß-oxidation enzyme system, (Lazarow, Science 197: 580-581, 1977), 3) peroxisome proliferators, and 4) carcinogens in rodents. Reddy et al. (Nature 283: 397-398, 1980) have hypothesized that peroxisome proliferators as a class may be carcinogenic Data is presented showing that bezafibrate, at a suitable hypolipidemic dose in rats, induces peroxisomal ß-oxidation but does not cause the striking organelle proliferation commonly observed with hypolipidemic drugs. Similar results have been obtained with clofibrate treatment of female rats. Christiansen et al. (Eur.). Cell Biol. 26: 77-20, 7987) have shown that feeding rats a diet rich in partially hydrogenated marine oils produces changes in the peroxisomes similar to those caused by bezafibrate. Aspirin, which is weakly hypolipidemic and a weak peroxisome proliferator, is apparently not carcinogenic in humans. The evidence indicates that the hypolipidemic effects and the peroxisome proliferative effects of these drugs are largely (although incompletely) dissociable. It suggests the need for considerable caution in evaluating the relationship, if any, between hypolipidemic and carcinogenic effects.

Expression of Cyanobacterial Acyl-ACP Reductase Elevates the Triacylglycerol Level in the Red Alga Cyanidioschyzon merolae

Nitrogen starvation is known to induce the accumulation of triacylglycerol (TAG) in many microalgae, and potential use of microalgae as a source of biofuel has been explored. However, nitrogen starvation also stops cellular growth. The expression of cyanobacterial acyl-acyl carrier protein (ACP) reductase in the unicellular red alga Cyanidioschyzon merolae chloroplasts resulted in an accumulation of TAG, which led to an increase in the number and size of lipid droplets while maintaining cellular growth. Transcriptome and metabolome analyses showed that the expression of acyl-ACP reductase altered the activities of several metabolic pathways. The activities of enzymes involved in fatty acid synthesis in chloroplasts, such as acetyl-CoA carboxylase and pyruvate dehydrogenase, were up-regulated, while pyruvate decarboxylation in mitochondria and the subsequent consumption of acetyl-CoA by the tricarboxylic acid (TCA) cycle were down-regulated. Aldehyde dehydrogenase, which oxidizes fatty aldehydes to fatty acids, was also up-regulated in the acyl-ACP reductase expresser. This activation was required for the lipid droplet accumulation and metabolic changes observed in the acyl-ACP reductase expresser. Nitrogen starvation also resulted in lipid droplet accumulation in C. merolae, while cell growth ceased as in the case of other algal species. The metabolic changes that occur upon the expression of acyl-ACP reductase are quite different from those caused by nitrogen starvation. Therefore, there should be a method for further increasing the storage lipid level while still maintaining cell growth that is different from the metabolic response to nitrogen starvation.

Mechanism for prevention of alcohol-induced liver injury by dietary methyl donors

Alcohol-induced liver injury (ALI) has been associated with, among other molecular changes, abnormal hepatic methionine metabolism, resulting in decreased levels of S-adenosylmethionine (SAM). Dietary methyl donor supplements such as SAM and betaine mitigate ALI in animal models; however, the mechanisms of protection remain elusive. It has been suggested that methyl donors may act via attenuation of alcohol-induced oxidative stress. We hypothesized that the protective action of methyl donors is mediated by an effect on the oxidative metabolism of alcohol in the liver. Male C57BL/6J mice were administered a control high-fat diet or diet enriched in methyl donors with or without alcohol for 4 weeks using the enteral alcohol feeding model. As expected, attenuation of ALI and an increase in reduced glutathione:oxidized glutathione ratio were achieved with methyl donor supplementation. Interestingly, methyl donors led to a 35% increase in blood alcohol elimination rate, and while there was no effect on alcohol metabolism in the stomach, a profound effect on liver alcohol metabolism was observed. The catalase-dependent pathway of alcohol metabolism was induced, yet the increase in CYP2E1 activity by alcohol was blunted, which may be mitigating production of oxidants. Additional factors contributing to the protective effects of methyl donors in ALI were increased activity of low- and high-K(m) aldehyde dehydrogenases leading to lower hepatic acetaldehyde, maintenance of the efficient mitochondrial energy metabolism, and promotion of peroxisomal beta-oxidation. Profound changes in alcohol metabolism represent additional important mechanism of the protective effect of methyl donors in ALI.

Mechanisms of resistance of hepatocyte retinoid X receptor alpha-null mice to WY-14,643-induced hepatocyte proliferation and cholestasis

Peroxisome proliferators, such as the lipid-lowering fibrates that function as agonists for peroxisome proliferator-activated receptor alpha (PPARalpha), induce liver tumors in rodents and may produce cholestasis in humans. Considerable attention has focused on peroxisome proliferator-induced hepatocellular carcinoma, a phenomenon not noted in man, whereas limited studies examine fibrates and other therapeutic drugs that induce cholestasis, a common finding in humans. Moreover, the mechanisms by which fibrates induce hepatocyte proliferation and cholestasis are still not fully understood. We have examined the role of hepatocyte retinoid X receptor alpha (RXRalpha), an essential partner of PPARalpha, in modulating WY-14,643-induced hepatocyte proliferation and cholestasis. WY-14,643 treatment induced hepatomegaly in wild type (WT) mice that was also accompanied by induction of the expression of cyclins D1, D3, A2, and B1 and Cdc2 as well as inhibition of Wee 1. Such changes were either absent or greatly reduced in hepatocyte RXRalpha-null mice. Furthermore, neither WY-14,643 treatment nor RXRalpha deficiency affected apoptosis, indicating the importance of PPARalpha/RXRalpha in regulating Wee 1-mediated Cdc2/cyclin B1 expression for cells to enter into mitosis. WY-14,643 treatment also induced cholestasis and liver injury, which is evidenced by induction of alanine aminotransferase, alkaline phosphatase, and hepatic bile acid levels in WT mice. Hepatocyte RXRalpha deficiency protected the mice from WY-14,643-induced liver injury. WY-14,643-mediated induction of the small heterodimer partner, Mrp3, and Cyp3a11 levels was greater in hepatocyte RXRalpha-null than in WT mouse livers suggesting enhanced repression of bile acid synthesis and increased efflux of bile acids into blood for renal excretion as well as hydroxylation of bile acids because of hepatocyte RXRalpha deficiency. These data establish a crucial role of hepatocyte RXRalpha in regulating WY-14,643-mediated cell cycle progression as well as bile acid homeostasis.

Effect of acyl-CoA oxidase activity on the accumulation of γ-decalactone by the yeastYarrowia lipolytica: A factorial approach

beta-Oxidation is a cyclic pathway involved in the degradation of lipids. In yeast, it occurs in peroxisomes and the first step is catalyzed by an acyl-CoA oxidase (Aoxp). The yeast Yarrowia lipolytica possesses several genes (POX) coding for Aoxps. This study is based on the factorial analysis of results obtained with the many POX derivative strains that have been constructed previously. The effect of interactions between Aoxps on the acyl-CoA oxidase (Aox) activity was important even at the second order. We then investigated the effect of Aox activity on growth and lactone production. Aox activity was correlated with acidification of the medium by cells and with cellular growth but not with lactone production, although Aox activity on short chains was inversely correlated with lactone accumulation. Due to the poor correlation between Aox activity and lactone production, the modeling of this parameter gave no satisfactory results but growth depending on Aox activity was modeled.

Different mechanisms of modulation of gap junction communication by non-genotoxic carcinogens in rat liver in vivo

This is a comparative study of the mechanisms by which three different rodent non-genotoxic carcinogens modulate connexin-mediated gap junction intercellular communication in male rat liver in vivo. In the case of the peroxisome proliferating agent Wy-14,643, a non-hepatotoxic dose of 50mg/kg led to a marked loss of inter-hepatocyte dye transfer associated with a loss of both Cx32 and Cx26 protein expression. In contrast, p,p'-dichlorodiphenyltrichloroethane (DDT) at a non-hepatotoxic dose (25mg/kg) was not found to alter Cx32 or Cx26 expression or to produce a measurable Cx32 serine phosphorylation but did give a small, significant reduction of cell communication. Carbon tetrachloride (CCl(4)) did not affect cell communication (despite a small significant reduction of Cx32 content) at a non-hepatotoxic dose. Both loss of communication and Cx32 expression was observed only at a dose that caused hepatocyte toxicity as evidenced by increased serum alanine aminotransferase activity. Overall, the findings emphasise that loss of gap junctional communication in vivo can contribute to carcinogenesis by non-genotoxic carcinogens through different primary mechanism. In contrast to Wy-14,643 and DDT, the results with CCl(4) are consistent with a requirement for hepatotoxicity in its carcinogenic action.

Effect of long-term high-fat feeding on energy balance and liver oxidative activity in rats

The purpose of this work was to study the effect of early long-term high-fat feeding on energy balance and liver oxidative activity. To this end, rats aged about 30 d were fed a high-fat or a low-fat diet for 15, 30 or 60 d. Full energy balance and energy partitioning measurements were carried out. In addition, we measured hepatic mitochondrial and peroxisomal oxidative capacities. Serum levels of free triiodothyronine (T3) and leptin were also determined. Rats fed a high-fat diet showed an increase in metabolizable energy intake as well as in energy expenditure, while lipid gain over the whole period was lower than that expected due to a decrease in metabolic efficiency. An increase in serum free T3 levels was also found in rats fed a high-fat diet after 15 and 30 d. Statistically significant correlations between serum leptin levels and body fat mass were found after 15, 30 and 60 d of high-fat feeding. Finally, no variation in hepatic mitochondrial and peroxisomal fatty acid oxidation capacity was found in rats fed a high-fat diet for 15, 30 or 60 d. In conclusion, the results of the present study show that young Wistar rats fed a high-fat diet for up to 60 d are able to counteract, at least in part, obesity development.

Peroxisomal proliferation protects from beta-amyloid neurodegeneration

Alzheimer disease is a neurodegenerative process that leads to severe cognitive impairment as a consequence of selective death of neuronal populations. The molecular pathogenesis of Alzheimer disease involves the participation of the beta-amyloid peptide (Abeta) and oxidative stress. We report here that peroxisomal proliferation attenuated Abeta-dependent toxicity in hippocampal neurons. Pretreatment with Wy-14.463 (Wy), a peroxisome proliferator, prevent the neuronal cell death and neuritic network loss induced by the Abeta peptide. Moreover, the hippocampal neurons treated with this compound, showed an increase in the number of peroxisomes, with a concomitant increase in catalase activity. Additionally, we evaluate the Wy protective effect on beta-catenin levels, production of intracellular reactive oxygen species, cytoplasmic calcium uptake, and mitochondrial potential in hippocampal neurons exposed to H(2) O(2) and Abeta peptide. Results show that the peroxisomal proliferation prevents beta-catenin degradation, reactive oxygen species production, cytoplasmic calcium increase, and changes in mitochondrial viability. Our data suggest, for the first time, a direct link between peroxisomal proliferation and neuroprotection from Abeta-induced degenerative changes.

Transcription profiling distinguishes dose-dependent effects in the livers of rats treated with clofibrate

Peroxisome proliferators such as the fibrates act via the peroxisome proliferator activated receptor (PPAR)-alpha as hypolipidemic agents. Many peroxisome proliferators are also nongenotoxic hepatic carcinogens and hepatotoxicants in rodents. We performed transcription profiling using cDNA microarrays on livers of rats treated for 5 days with 3 doses of the peroxisome proliferator clofibrate. All 3 doses had hepatic effects as assessed by liver to body weight ratio, alanine aminotransferase (ALT) increases and histopathology examination. Analysis of the transcription profiling data identified changes in the expression of many genes within several mechanistic pathways that support existing hypotheses regarding peroxisome proliferator mediated carcinogenicity. Additionally, the transcription profiling, histopathology, and clinical chemistry results suggested a biphasic response to clofibrate. These findings provide insight into the pathogenesis of toxic and carcinogenic effects of clofibrate in rodents and demonstrate the ability of cDNA microarrays to provide information regarding mechanisms of toxicity identified during the drug development process.

Impaired Ras membrane association and activation in PPARalpha knockout mice after partial hepatectomy

Liver regeneration after partial hepatectomy (PH) involves several signaling mechanisms including activation of the small GTPases Ras and RhoA in response to mitogens leading to DNA synthesis and cell proliferation. Peroxisome proliferator-activated receptor-alpha (PPARalpha) regulates the expression of several key enzymes in isoprenoid synthesis, which are key events for membrane association of Ras and RhoA. Thus the role of PPARalpha in cell proliferation after PH was tested. After PH, an increase in PPARalpha DNA binding was observed in wild-type mice, correlating with an increase in the PPARalpha-regulated enzyme acyl-CoA oxidase. In addition, the PPARalpha-regulated genes farnesyl pyrophosphate synthase and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase were significantly increased in wild-type mice. However, these increases were not observed in PPARalpha knockout (PPARalpha -/-) mice. The peak in DNA synthesis observed 42 h after PH was reduced by approximately 60% in PPARalpha -/- mice, despite increases in TNF-alpha and IL-1. Also, under these conditions, membrane association of Ras was high in wild-type mice after PH but was impaired in PPARalpha -/- mice. Accordingly, Ras was significantly elevated in the cytosol in PPARalpha -/- mice. This observation correlated with lower levels of active GTP-bound Ras after PH in PPARalpha -/- mice compared with wild-type mice. Similar observations were made for RhoA. Moreover, deletion of PPARalpha blunted the activation of cyclin-dependent kinase (cdk)2/cyclin E and cdk4/cyclin D complexes. Collectively, these results support the hypothesis that PPARalpha is necessary for cell cycle progression in regenerating mouse liver via mechanisms involving prenylation of small GTPases Ras and RhoA.

Differential induction of peroxisomal beta-oxidation enzymes by clofibric acid and aspirin in piglet tissues

Peroxisomal beta-oxidation (POX) of fatty acids is important in lipid catabolism and thermogenesis. To investigate the effects of peroxisome proliferators on peroxisomal and mitochondrial beta-oxidation in piglet tissues, newborn pigs (1-2 days old) were allowed ad libitum access to milk replacer supplemented with 0.5% clofibric acid (CA) or 1% aspirin for 14 days. CA increased ratios of liver weight to body weight (P < 0.07), kidney weight to body weight (P < 0.05), and heart weight to body weight (P < 0.001). Aspirin decreased daily food intake and final body weight but increased the ratio of heart weight to body weight (P < 0.01). In liver, activities of POX, fatty acyl-CoA oxidase (FAO), total carnitine palmitoyltransferase (CPT), and catalase were 2.7-, 2.2-, 1.5-fold, and 33% greater, respectively, for pigs given CA than for control pigs. In heart, these variables were 2.2-, 4.1-, 1.9-, and 1.8-fold greater, respectively, for pigs given CA than for control pigs. CA did not change these variables in either kidney or muscle, except that CPT activity was increased approximately 110% (P < 0.01) in kidney. Aspirin increased only hepatic FAO and CPT activities. Northern blot analysis revealed that CA increased the abundance of catalase mRNA in heart by approximately 2.2-fold. We conclude that 1) POX and CPT in newborn pigs can be induced by peroxisomal proliferators with tissue specificity and 2) the relatively smaller induction of POX in piglets (compared with that in young or adult rodents) may be related to either age or species differences.

Phthalates rapidly increase production of reactive oxygen species in vivo: role of Kupffer cells

The role of oxidants in the mechanism of tumor promotion by peroxisome proliferators remains controversial. The idea that induction of acyl-coenzyme A oxidase leads to increased production of H(2)O(2), which damages DNA, seems unlikely; still, free radicals might be important in signaling in specialized cell types such as Kupffer cells, which produce mitogens. Because hard evidence for increased oxidant production in vivo after treatment with peroxisome proliferators is lacking, the spin-trapping technique and electron spin resonance spectroscopy were used. Rats were given di(2-ethylhexyl) phthalate (DEHP) acutely. The spin trapping agent alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone was also given and bile samples were collected for 4 h. Under these conditions, the intensity of the six-line radical adduct signal increased to a maximum value of 2.5-fold 2 h after administration of DEHP, before peroxisomal oxidases were induced. Furthermore, DEHP given with [(13)C(2)]dimethyl sulfoxide produced a 12-line electron spin resonance spectrum, providing evidence that DEHP stimulates (*)OH radical formation in vivo. Furthermore, when rats were pretreated with dietary glycine, which inactivates Kupffer cells, DEHP did not increase radical signals. Moreover, similar treatments were performed in knockout mice deficient in NADPH oxidase (p47(phox) subunit). Importantly, DEHP increased oxidant production in wild-type but not in NADPH oxidase-deficient mice. These data provide evidence for the hypothesis that the molecular source of free radicals induced by peroxisome proliferators is NADPH oxidase in Kupffer cells. On the contrary, radical adduct formation was not affected in peroxisome proliferator-activated receptor alpha knockout mice. These observations represent the first direct, in vivo evidence that phthalates increase free radicals in liver before peroxisomal oxidases are induced.

Fenofibrate prevents and reduces body weight gain and adiposity in diet-induced obese rats

Fibrates are hypolipidemic drugs that activate the peroxisome proliferator-activated receptors. Since fibrates may also increase energy expenditure, we investigated whether fenofibrate (FF) had this effect in diet-induced obese rats. A 2-month administration of a high-fat palatable diet to adult rats increased body weight by 25% and white adipose mass by 163% compared with a standard diet. These effects were prevented by FF, both when administered for the 2 months of high-fat feeding and when given for only the second month. Consequently, FF-treated rats had a final body weight and white adipose tissue mass similar to untreated animals on the standard diet. FF also increased resting metabolic rate, hepatic peroxisomal and mitochondrial palmitoyl-dependent oxygen uptake and mRNA levels of acyl-CoA oxidase and lipoprotein lipase. Finally, FF lowered mRNA levels of uncoupling protein-2 and did not affect mitochondrial respiration in skeletal muscle. Therefore, FF seems to act as a weight-stabilizer mainly through its effect on liver metabolism.

Effect of cold exposure on energy balance and liver respiratory capacity in post-weaning rats fed a high-fat diet

Variations in energy balance, body composition, and nutrient partitioning induced by high-fat feeding, cold exposure or by concomitant high-fat feeding and cold exposure were studied in young Wistar rats. Changes in hepatic metabolism as well as in serum free triiodothyronine and leptin levels were also evaluated. Rats were exposed to either 24 or 4 degrees C and fed either a low- or high-fat diet (10 % or 50 % energy respectively) for 2 weeks. Relative to low-fat feeding at 24 degrees C, both energy intake and expenditure were increased by high-fat feeding or by cold exposure, and these changes were accompanied by increased serum triiodothyronine levels. In response to concomitant high-fat feeding and cold exposure, serum triiodothyronine tended to be further elevated, but no further increases in energy intake or energy expenditure were observed. Independently of diet, the increased energy expenditure in cold-exposed rats was not completely balanced by adaptive hyperphagia, with consequential reductions in protein and fat gain, accompanied by marked decreases in serum leptin. Furthermore, unlike high-fat feeding at 24 degrees C, cold exposure enhanced hepatic mitochondrial oxidative capacity both in the low-fat- and high-fat-fed groups. It is concluded that in this strain of young Wistar rats, despite similarly marked stimulation of energy expenditure by high-fat feeding at 24 degrees C, by cold exposure and by concomitant high-fat feeding and cold exposure, an increased hepatic oxidative capacity occurred only in the presence of the cold stimulus.

Dietary glycine prevents the development of liver tumors caused by the peroxisome proliferator WY-14,643

Previous studies demonstrated that dietary glycine prevents elevated rates of cell proliferation following treatment with the peroxisome proliferator and liver carcinogen WY-14,643. Since increased cell replication is associated with the development of hepatic cancer caused by peroxisome proliferators, glycine may have anti-cancer properties. Therefore, experiments were designed to test the hypothesis that dietary glycine would inhibit the hepatocarcinogenic effect of WY-14,643. Male F344 rats were fed four different NIH 07-based diets: 5% glycine; 5% valine for nitrogen balance (control); 0.1% WY-14,643 + 5% valine (WY-14,643); 0.1% WY-14,643 + 5% glycine (WY-14,643 + glycine). Food consumption did not differ among the groups, but WY-14,643-fed rats weighed 10-25% less than expected based on previous studies. Serum glycine levels were elevated 4-5-fold by glycine-containing diets; however, the 10-fold increase in peroxisomal enzyme activity caused by WY-14,643 was unaffected by the addition of 5% glycine to the diet. After 22 weeks, livers from rats fed WY-14,643 had a similar incidence and multiplicity of proliferative lesions (foci and adenomas) to those fed WY-14,643 + glycine. Moreover, cell proliferation in the surrounding 'normal' parenchyma (labeling index approximately 4%) and foci (labeling index approximately 50%) did not differ between WY-14,643 and WY-14,643 + glycine-fed rats. However, after 51 weeks of dietary exposure to WY-14,643, glycine prevented formation of small (0-5 mm diameter) tumors by 23% and inhibited the development of medium size (5-10 mm) tumors by 64%. Furthermore, glycine prevented the formation of the largest tumors (>10 mm) by nearly 80%. Thus, glycine did not inhibit early foci formation; however, it significantly decreased their ability to progress to tumors. Moreover, the inhibitory effect of glycine was greater with increasing tumor size. These studies demonstrate that dietary glycine prevents the development of hepatic tumors caused by the peroxisome proliferator WY-14,643 consistent with the idea that it may be an effective chemopreventive agent.

Long-chain acyl-CoA oxidases of Arabidopsis

Full-length cDNAs coding for two distinct acyl-CoA oxidases were isolated by screening an Arabidopsis cDNA library. The genes for the two acyl-CoA oxidases have been termed AtACX1 and AtACX2. AtACX1 encodes a peptide of 664 amino acids possessing a molecular mass of 74.3 kDa. AtACX2 encodes a peptide of 691 amino acids in length with a molecular mass of 77.5 kDa. Peroxisomal targeting signals were identified in the primary sequences. AtACX1 has a putative PTS1, whereas AtACX2 has a characteristic PTS2. Expression of AtACX1 and AtACX2 in Escherichia coli gave active enzymes for enzymatic and biochemical analysis. AtACX1 was active with both medium-and long-chain saturated fatty acyl-CoAs and showed maximal activity with C14-CoA. Activity with mono-unsaturated acyl-CoAs was slightly higher than with the corresponding saturated acyl-CoA. AtACX2 was active with long-chain acyl-CoAs and showed maximal activity with C18-CoA. AtACX2 activity with mono-unsaturated acyl-CoAs was approximately twice as high as with the corresponding saturated acyl-CoA. Both enzymes have an apparent Km of approximately 5 microM with the preferred substrate. Northern analysis was conducted to determine the expression patterns of AtACX1 and AtACX2 during germination and in various tissues of a mature plant. The two genes showed generally similar expression profiles and steady-state mRNA levels in seedlings and mature tissues, but subtle differences were observed. Enzymatic analyses of plant extracts revealed that AtACX1 and AtACX2 are members of a family that includes acyl-CoA oxidases specific for shorter-chain acyl-CoAs. Through expression of antisense constructs of the individual genes, we were able to decrease long-chain oxidase activity only in antisense AtACX1 plants. Seedlings with long-chain oxidase activity reduced down to 30% of wild-type levels germinated and established normally; however, reduced root growth appeared to be a general feature of antisense AtACX1 plants.

Evidence for the involvement of the fatty acid and peroxisomal beta-oxidation pathways in the inhibition by dehydroepiandrosterone (DHEA) and induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benz(a)anthracene (BA) of cytochrome P4501B1 (CYP1B1) in mouse embryo fibroblasts (C3H10T1/2 cells)

Treatment of intact C3H10T1/2 cells or microsomes therefrom with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzanthracene (BA) enhanced CYP1B1 activity and CYP1B1 expression as revealed by elevations of CYP1B1-catalyzed DMBA metabolism, CYP1B1 apoprotein level and CYP1B1 gene expression. One hundred microM DHEA caused an 80-90% inhibition of cellular DMBA metabolism without inflicting cell death. Cytosolic glucose-6-phosphate dehydrogenase (G6PDH) was also inhibited in DHEA-treated cells, presumably due to the inhibition of NADP reduction. In contrast, neither DMBA metabolism nor CYP1B1 apoprotein was inhibited by DHEA in the microsomes isolated from these cells. DHEA (100 microM), TCDD (10 nM) and BA (10 microM) stimulated the activities and increased the apoprotein levels of two peroxisomal enzymes, namely, acyl CoA oxidase (ACOX) and acyl CoA hydrolase (ACH2) and also induced the expression of CYP1B1 and ACOX genes. Cytosolic fatty acyl-CoA beta-oxidation was also stimulated by DHEA, TCDD and BA. In corroboratory experiments, it was found that concomitant with the stimulation of the activity of a key enzyme regulator of fatty acid homeostasis, namely, glycerol-3-phosphate dehydrogenase (G3PDH), these agents enhanced arachidonic acid (AA) metabolism as judged by the release of [3H] from AA into the culture medium. Collectively, these data suggest that DHEA mediates the regulation of CYP1B1 and inhibits BA and TCDD-induced CYP1B1-catalyzed carcinogen (DMBA) activation in 10T1/2 cells through metabolic interactions that involve the activation of the peroxisomal and fatty acid beta-oxidation signaling pathways. These results also present evidence for the first time, for the possible peroxisomal effects of TCDD and BA which are similar to those of DHEA in this mouse embryo fibroblast cell line.

Kupffer cell oxidant production is central to the mechanism of peroxisome proliferators

Increased cell proliferation most likely plays a key role in peroxisome proliferator-induced liver cancer. Recently, Kupffer cells were shown to be responsible for Wy-14,643-induced cell proliferation. However, the mechanism by which peroxisome proliferators activate Kupffer cells is unknown. Since gut-derived endotoxin is a known activator of Kupffer cells, the hypothesis that it is involved was evaluated. Increased cell proliferation and peroxisome induction were unaffected by gut sterilization. Moreover, endotoxin was not detectable in portal blood following treatment with Wy-14,643. Therefore, it is concluded that gut-derived endotoxin is not responsible for Kupffer cell activation. To test the hypothesis that Kupffer cells are activated by Wy-14,643 directly, Kupffer cell superoxide production was measured following treatment in vitro. Wy-14,643 increased superoxide production in a dose-dependent manner (0.1 and 50 microM) with half-maximal stimulation at 2.5 microM. Diethylhexylphthalate (DEHP) and ethylhexanol did not increase superoxide production even at doses 50 times higher than Wy-14,643; however, monoethylhexylphthalate (MEHP) activated superoxide production as effectively as Wy-14,643 with half-maximal stimulation at 5 microM. Treatment with Wy-14,643 for 21 days caused a 2-fold increase in Kupffer cell superoxide production while DEHP did not. Pretreatment of Kupffer cells with staurosporine (0.01-10 pM) completely blocked generation of superoxide demonstrating that protein kinase C is required. Moreover, Wy-14,643 increased Kupffer cell protein kinase C activity 3-fold. Pretreatment of Kupffer cells with the amino acid glycine (0.01-3 mM), which blunts calcium signaling, inhibited Wy-14,643-stimulated superoxide production and increased protein kinase C activity completely. These data are consistent with the hypothesis that potent peroxisome proliferators (Wy-14,643 and MEHP) directly activate Kupffer cell production of oxidants via mechanisms involving protein kinase C. Further, peroxisome proliferator treatments that sustain elevated rates of cell proliferation (e.g. Wy-14,643) activate Kupffer cell superoxide production following long-term dietary treatment supporting the hypothesis that Kupffer cell-derived oxidants are involved in peroxisome proliferator-induced neoplasia.

Impairment of peroxisomal structure and function in rat liver allograft rejection: prevention by cyclosporine

BACKGROUND

During allograft rejection, cytokines and lipid mediators contribute to cell injury and organ failure. Peroxisomes play a crucial role in lipid metabolism, including the degradation of lipid mediators by peroxisomal beta-oxidation. Therefore, we investigated the alterations of hepatic peroxisomes after allogeneic rat liver transplantation.

METHODS

MHC-incompatible Dark Agouti (RT1a) donor rats and Lewis (RT1(1)) recipient rats were used for allogeneic transplantation. For immunosuppression, a group of these animals received cyclosporine (CsA) intraperitoneally (1 mg/kg body weight per day). Lewis rats were used for isogeneic transplant combination. Ten days after transplantation, livers were investigated using morphometrical methods for determination of peroxisomal diameter and volume density. The activities of peroxisomal catalase (CAT) and acyl-coenzyme A oxidase (AOX) were determined, and the corresponding proteins were evaluated by quantitative immunocytochemistry and immunoblotting. The expressions of mRNAs encoding CAT and AOX were investigated by Northern blotting.

RESULTS

The volume density and diameter of peroxisomes were significantly decreased in allogeneic transplanted livers but were unchanged in CsA-treated animals. Both the activities of CAT and AOX and their protein levels were significantly reduced in liver allografts. Moreover, the corresponding mRNA levels of CAT and AOX were decreased significantly in liver allografts, whereas CsA treatment led to an increase of those mRNAs. Isogeneic transplanted livers showed only a slight reduction of the corresponding enzyme values.

CONCLUSIONS

Peroxisomes are severely affected both morphologically and functionally after allogeneic liver transplantation. These results suggest that impairment of peroxisomal lipid beta-oxidation could contribute to the pathogenesis of the rejection process by decreased catabolism of lipid mediators involved in the regulation of the inflammatory response. CsA, in addition to its immunosuppressive effects, may contribute to allograft survival by maintenance of those important peroxisomal functions.

Effect of thioridazine or chlorpromazine on increased hepatic NAD+ level in rats fed clofibrate, a hypolipidaemic drug

The effect of the phenothiazines, thioridazine and chlorpromazine, on the increased hepatic NAD+ level of rats fed clofibrate, a hypolipidaemic drug, has been investigated. Short-term (6 days) addition of phenothiazines to the diet negatively affected diet intake and body-weight gain, but increased liver weight and hepatic NAD+ levels, which was synergistic to clofibrate. The phenothiazines were shown to inhibit hepatic peroxisomal fatty acid oxidation in-vivo, as determined by the increased residual catalase activity. In hepatocytes prepared from clofibrate-fed rats, phenothiazines inhibited not only peroxisomal but also mitochondrial fatty acid oxidation to the same extent. In the hepatocytes, NAD+ was maintained at the high level until the phenothiazine concentration was increased to 0.2 mM. The result suggests that the increase of hepatic NAD+ in rats fed clofibrate is not related to peroxisomal fatty acid oxidation.

Dietary glycine prevents increases in hepatocyte proliferation caused by the peroxisome proliferator WY-14,643

Peroxisome proliferators are a group of nongenotoxic carcinogens which include a number of hypolipidemic drugs, solvents, and industrial plasticizers. Although the mechanism by which they cause cancer remains unknown, one likely possibility is that they act as tumor promoters by increasing cell proliferation. Hepatic Kupffer cells represent a rich source of mitogenic cytokines (e.g., tumor necrosis factor alpha, TNF alpha) and are stimulated by peroxisome proliferators. Since glycine prevents activation of Kupffer cells, these experiments were designed to test the hypothesis that a diet containing glycine could block the mitogenic effect of the peroxisome proliferator [[4-chloro-6-(2,3-xylidino)pyrimidinyl]thio]acetic acid (WY-14,643). The effects of a glycine-enriched diet on WY-14,643-induced increases in cell proliferation after a single dose or after feeding WY-14,643 in the diet for 3 weeks were assessed. As expected, 24 h after a single dose of WY-14,643, rates of cell proliferation increased from basal values of 0.7 +/- 0.3% to 5.1 +/- 0.5%. Glycine largely prevented the increase caused by WY-14,643 with proliferation only reaching 1.9 +/- 0.4% (p < 0.05). Acyl CoA oxidase increased from 1.4 +/- 0.1 to 3.5 +/- 0.6 nmol of H2O2 min-1 (mg of protein)-1 (p < 0.05) indicating that peroxisome-specific enzyme activity was induced about 2-fold in livers of WY-14,643-treated rats after 24 h. Unlike cell proliferation, however, acyl CoA oxidase was not affected by dietary glycine, consistent with the hypothesis that cell proliferation and peroxisome proliferation occur via different mechanisms. After 3 weeks, dietary glycine reduced basal rates of cell proliferation by about 50% and completely prevented the sustained 5-fold increase in cell proliferation caused by feeding WY-14,643. Moreover, the 3-fold increase in TNF alpha mRNA caused by WY-14,643 was blocked completely by the glycine-enriched diet. Similarly, immunohistochemical staining for TNF alpha was increased 6-fold by WY-14,643, an increase which was prevented by dietary glycine. However, the 6-fold increase in acyl CoA oxidase activity was unaffected by glycine under similar conditions demonstrating that a diet containing 5% glycine prevents increased hepatocyte proliferation caused by a potent peroxisome proliferator without affecting induction of peroxisomes. These data demonstrate that a glycine-enriched diet prevents stimulated cell proliferation most likely by inhibiting TNF alpha production and raise the possibility that dietary glycine will be effective in preventing cancer caused by nongenotoxic carcinogens such as WY-14,643.

Modulation of fatty acid oxidation alters contact hypersensitivity to urushiols: role of aliphatic chain beta-oxidation in processing and activation of urushiols

Lithraea caustica, or litre, a tree of the Anacardiaceae family that is endemic to the central region of Chile, induces a severe contact dermatitis in susceptible human beings. The allergen was previously isolated and characterized as a 3-(pentadecyl-10-enyl) catechol, a molecule belonging to the urushiol group of allergens isolated from poison ivy and poison oak plants. Because urushiols are pro-electrophilic haptens, it is believed that the reactive species are generated intracellularly by skin keratinocytes and Langerhans cells. The active species are presumed to modify self proteins which, after proteolytic processing, would generate immunogenic peptides carrying the hapten. The presence of a 15-carbon-length hydrophobic chain should impair antigen presentation of self-modified peptides by class I MHC molecules, either by steric hindrance or by limiting their sorting to the ER lumen. We have proposed that the shortening of the aliphatic chain by beta-oxidation within peroxisomes and/or mitochondria should be a requirement for the antigen presentation process. To test this hypothesis we investigated the effect of drugs that modify the fatty acid metabolism on urushiol-induced contact dermatitis in mice. Clofibrate, a peroxisomal proliferator in mice, increased the immune response to the urushiols from litre by 50%. Conversely, tetradecyl glycidic acid, an inhibitor of the uptake of fatty acids by mitochondria, decreased the hypersensitivity to the hapten. An increase in the level in glutathione by treatment of the animals with 2-oxotiazolidin-4-carboxilic acid lowered the response. Those findings strongly support a role for the fatty acid oxidative metabolism in the processing and activation of urushiols in vivo.

Higher-plant medium- and short-chain acyl-CoA oxidases: identification, purification and characterization of two novel enzymes of eukaryotic peroxisomal beta-oxidation

Medium- and short-chain acyl-CoA oxidases were identified in and subsequently purified from dark-grown maize plantlets. The oxidase showing preference for medium-chain fatty acyl-CoAs (C10-C14) was purified to homogeneity. The oxidase showing preference for short-chain fatty acyl-CoAs (C4-C8) was purified over 150-fold. Various catalytic properties confirmed these enzymes to be true acyl-CoA oxidases. They produced trans-2-enoyl-CoA and H2O2 from the saturated acyl-CoA, as verified by various independent assay techniques. They also exhibited FAD-dependent activity; i.e. removal of loosely bound FAD by gel filtration markedly reduced activity, which could be restored upon re-addition of FAD. They showed apparent Km values between 2 and 10 microM for the acyl-CoA substrate giving maximal activity, no activity with the corresponding free fatty acid, high pH optima (8.3-8.6) and a peroxisomal subcellular location. The medium-chain acyl-CoA oxidase was determined to be a monomeric protein with a molecular mass of 62 kDa. The short-chain acyl-CoA oxidase was shown to have a native molecular mass of 60 kDa, but exhibited a labile multimeric structure, as indicated by the elution of multiple peaks of activity during several chromatographic steps, and ultimately by the purification of a subunit of molecular mass 15 kDa. The medium- and short-chain acyl-CoA oxidases were demonstrated to be distinct from the maize equivalent of the cucumber glyoxysomal long-chain acyl-CoA oxidase previously purified and characterized [Kirsch, Loffler and Kindl (1986) J. Biol. Chem. 261, 8570-8575]. The maize long-chain acyl-CoA oxidase was partially purified to permit determination of its substrate specificity; it showed activity with a broad range of acyl-CoAs of chain length greater than C8, and maximal activity with C16. The implications of the existence of multiple acyl-CoA oxidases in the regulation of plant peroxisomal beta-oxidation are discussed.

Higher-plant medium- and short-chain acyl-CoA oxidases: identification, purification and characterization of two novel enzymes of eukaryotic peroxisomal beta-oxidation

Medium- and short-chain acyl-CoA oxidases were identified in and subsequently purified from dark-grown maize plantlets. The oxidase showing preference for medium-chain fatty acyl-CoAs (C10-C14) was purified to homogeneity. The oxidase showing preference for short-chain fatty acyl-CoAs (C4-C8) was purified over 150-fold. Various catalytic properties confirmed these enzymes to be true acyl-CoA oxidases. They produced trans-2-enoyl-CoA and H2O2 from the saturated acyl-CoA, as verified by various independent assay techniques. They also exhibited FAD-dependent activity; i.e. removal of loosely bound FAD by gel filtration markedly reduced activity, which could be restored upon re-addition of FAD. They showed apparent Km values between 2 and 10 microM for the acyl-CoA substrate giving maximal activity, no activity with the corresponding free fatty acid, high pH optima (8.3-8.6) and a peroxisomal subcellular location. The medium-chain acyl-CoA oxidase was determined to be a monomeric protein with a molecular mass of 62 kDa. The short-chain acyl-CoA oxidase was shown to have a native molecular mass of 60 kDa, but exhibited a labile multimeric structure, as indicated by the elution of multiple peaks of activity during several chromatographic steps, and ultimately by the purification of a subunit of molecular mass 15 kDa. The medium- and short-chain acyl-CoA oxidases were demonstrated to be distinct from the maize equivalent of the cucumber glyoxysomal long-chain acyl-CoA oxidase previously purified and characterized [Kirsch, Loffler and Kindl (1986) J. Biol. Chem. 261, 8570-8575]. The maize long-chain acyl-CoA oxidase was partially purified to permit determination of its substrate specificity; it showed activity with a broad range of acyl-CoAs of chain length greater than C8, and maximal activity with C16. The implications of the existence of multiple acyl-CoA oxidases in the regulation of plant peroxisomal beta-oxidation are discussed.

In situ heterogeneity of peroxisomal oxidase activities: an update

Oxidases are a widespread group of enzymes. They are present in numerous organisms and organs and in various tissues, cells, and subcellular compartments, such as mitochondria. An important source of oxidases, which is investigated and discussed in this study, are the (micro)peroxisomes. Oxidases share the ability to reduce molecular oxygen during oxidation of their substrate, yielding an oxidized product and hydrogen peroxide. Besides the hydrogen peroxide-catabolizing enzyme catalase, peroxisomes contain one or more hydrogen peroxide-generating oxidases, which participate in different metabolic pathways. During the last four decades, various methods have been developed and elaborated for the histochemical localization of the activities of these oxidases. These methods are based either on the reduction of soluble electron acceptors by oxidase activity or on the capture of hydrogen peroxide. Both methods yield a coloured and/or electron dense precipitate. The most reliable technique in peroxisomal oxidase histochemistry is the cerium salt capture method. This method is based on the direct capture of hydrogen peroxide by cerium ions to form a fine crystalline, insoluble, electron dense reaction product, cerium perhydroxide, which can be visualized for light microscopy with diaminobenzidine. With the use of this technique, it became clear that oxidase activities not only vary between different organisms, organs, and tissues, but that heterogeneity also exists between different cells and within cells, i.e. between individual peroxisomes. A literature review, and recent studies performed in our laboratory, show that peroxisomes are highly differentiated organelles with respect to the presence of active enzymes. This study gives an overview of the in situ distribution and heterogeneity of peroxisomal enzyme activities as detected by histochemical assays of the activities of catalase, and the peroxisomal oxidases D-amino acid oxidase, L-alpha-hydroxy acid oxidase, polyamine oxidase and uric acid oxidase.

Production of lactones and peroxisomal beta-oxidation in yeasts

Among aroma compounds interesting for the food industry, lactones may be produced by biotechnological means using yeasts. These microorganisms are able to synthesize lactones de novo or by biotransformation of fatty acids with higher yields. Obtained lactone concentrations are compatible with industrial production, although detailed metabolic pathways have not been completely elucidated. The biotransformation of ricinoleic acid into gamma-decalactone is taken here as an example to better understand the uptake of hydroxy fatty acids by yeasts and the different pathways of fatty acid degradation. The localization of ricinoleic acid beta-oxidation in peroxisomes is demonstrated. Then the regulation of the biotransformation is described, particularly the induction of peroxisome proliferation and peroxisomal beta-oxidation and its regulation at the genome level. The nature of the biotransformation product is then discussed (4-hydroxydecanoic acid or gamma-decalactone), because the localization and the mechanisms of the lactonization are still not properly known. Lactone production may also be limited by the degradation of this aroma compound by the yeasts which produced it. Thus, different possible ways of modification and degradation of gamma-decalactone are described.

Expression of the peroxisome proliferator-activated receptor gene is decreased in experimental alcoholic liver disease

Peroxisome proliferator-activated receptor (PPAR) and retinoid x receptor (RXR) play important roles in fatty acid metabolism. The present study examined the regulation of retinoic acid receptor (RAR alpha, beta, and gamma), RXR (alpha, beta, and gamma), PPAR, cytochrome P450 2E1 (CYP2E1), catalase, and beta-actin gene expression in chronic alcoholic liver disease in the rat. The results demonstrated that the expression of genes for RAR and RXR isoforms and catalase were not altered by ethanol in the fatty liver. In contrast, the levels of PPAR and CYP2E1 mRNAs were down- and up-regulated by ethanol in the liver, respectively. The levels of CYP2E1 mRNAs correlated positively with blood alcohol levels (BAL). In addition, ethanol induced expression of beta-actin mRNA was also proportional to the BAL. The level of PPAR mRNA and the content of polyunsaturated fatty acid decreased in ethanol-fed rat livers. Decreased PPAR gene expression in ethanol-fed rats might result from a decrease in the content of polyunsaturated fatty acid in the liver. However, the activities of enzymes involved in hepatic lipid metabolism, including acyl CoA synthetase, acyl CoA oxidase, catalase, and protein kinase C, were not changed by ethanol treatment. The significance of down-regulation of PPAR gene in alcohol liver disease is discussed.

Cetaben is an exceptional type of peroxisome proliferator

1. Cetaben in contrast to fibrates affect differently peroxisomal constituents. 2. Changes in large scale of liver non-peroxisomal parameters were compared after 10 days administration of equal doses (200 mg/kg/day) of cetaben and clofibric acid to male Wistar rats. 3. Clofibric acid treatment increased markedly the activities of FAD-glycerol-3-P dehydrogenase, beta-hydroxyacyl-CoA dehydrogenase, cytochrome-c oxidase, malic enzyme, NAD-glycerol-3-P dehydrogenase, ethoxycoumarin deethylase, p-nitroanisole demethylase and amounts of cytochrome P-450 and b5. 4. However no analogical changes were observed after cetaben treatment in the livers of experimental animals. 5. Both drugs increased the activities of alanine-glyoxylate aminotransferase-1 and acetylcarnitine transferase--enzymes with proven mitochondrial and peroxisomal location. 6. Cetaben contrary to clofibric acid does not increase solubilization of peroxisomal enzymes. 7. Enhanced acetylcarnitine transferase and alanine-glyoxylate aminotransferase-1 activities were distributed in mitochondria as well as in peroxisomes after clofibric acid treatment, however, only peroxisomes were enriched after cetaben administration. 8. The results obtained suggest that cetaben represents an exceptional type of peroxisome proliferator, specifically affecting peroxisomes, without having a negative influence on the processes of peroxisome biogenesis.

The impact of aging on enzyme proteins of rat liver peroxisomes: quantitative analysis by immunoblotting and immunoelectron microscopy

The alterations of hepatic peroxisomes and their enzymes during aging were investigated in male rats. Peroxisomes in the livers of young (2 months) and old (39 months) male Wistar rats were analyzed by morphometry and quantitative immunocytochemistry, as well as by immunoblotting of highly purified peroxisomal fractions. Immunoblots showed that catalase and acyl-CoA oxidase were decreased in peroxisomes of old animals but the trifunctional enzyme, thiolase, and urate oxidase were increased. The morphometrical analysis revealed a heterogeneous distribution of peroxisomes in the liver lobule of the old animals, with a significant elevation of peroxisomal volume density in pericentral over periportal hepatocytes, in contrast to the uniform pattern in the young rats. Furthermore, age-related lobular gradients were also observed by quantitative immunocytochemistry in the peroxisomal concentrations of trifunctional enzyme (central > portal) and, inversely, for catalase (portal > central). Whereas acyl-CoA oxidase was diminished across the liver lobule, the enzyme 3-ketoacyl-CoA thiolase was elevated. These observations show that peroxisomes are significantly altered in aged animals and suggest that these alterations may contribute to the disturbance of lipid metabolism in aged animals. Moreover, the diminution in catalase and the elevation of urate oxidase could contribute to the oxidative stress which is considered to be of fundamental importance in the aging process.

Studies on the effect of fenoprofen on the activation and oxidation of long chain and very long chain fatty acids in hepatocytes and subcellular fractions from rat liver

We studied the effect of fenoprofen on the activation of palmitic acid (C16:0), lignoceric acid (C24:0) and cerotic acid (C26:0) in microsomal and peroxisomal fractions from rat liver. Fenoprofen was found to inhibit the formation of palmitoyl-CoA in both microsomal and peroxisomal fractions whereas the formation of lignoceroyl-CoA and cerotoyl-CoA was not inhibited at all. In freshly isolated rat hepatocytes palmitic acid beta-oxidation was progressively inhibited at increasing concentrations of fenoprofen, most probably due to its inhibitory effect on palmitoyl-CoA synthetase activity. On the other hand, fenoprofen was also found to inhibit the beta-oxidation of lignoceric acid and cerotic acid in rat hepatocytes. It is shown that the acyl-CoA oxidase activity with lignoceroyl-CoA as substrate was inhibited by fenoprofen whereas the palmitoyl-CoA and pristanoyl-CoA oxidase activities were not inhibited by fenoprofen. This finding provides an explanation for the inhibitory effect of fenoprofen on lignocerate and cerotate beta-oxidation in hepatocytes.

Substrate selectivities differ for hepatic mitochondrial and peroxisomal beta-oxidation in an Antarctic fish, Notothenia gibberifrons

Hepatic mitochondrial and peroxisomal beta-oxidation were examined in an Antarctic marine teleost, Notothenia gibberifrons. Enzymic profiles and rates of beta-oxidation by intact organelles were determined by using a range of fatty acyl-CoA substrates to evaluate substrate preferences. Partitioning of beta-oxidation between organelles was estimated. Substrate selectivities are broader for peroxisomal beta-oxidation than for mitochondrial beta-oxidation. Mitochondria show marked preference for the oxidation of a monounsaturated substrate, palmitoleoyl-CoA (C16:1), and two polyunsaturates, eicosapentaenoyl-CoA (C20:5) and docosahexaenoyl-CoA (C22:6). Carnitine palmitoyltransferase activities with palmitoleoyl-CoA (C16:1) are 2.4-fold higher than activities with palmitoyl-CoA (C16:0). Most polyunsaturated acyl-CoA esters measured appear to inhibit by over 40% the oxidation of palmitoyl-CoA by peroxisomes. Our findings suggest that the polyunsaturates, eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6), found in high concentrations in Antarctic fishes [Lund and Sidell (1992) Mar. Biol. 112, 377-382], are utilized as fuels to support aerobic energy metabolism. Metabolic capacities of rate-limiting enzymes and beta-oxidation rates by intact organelles indicate that up to 30% of hepatic beta-oxidation in N. gibberifrons can be initiated by the peroxisomal pathway.

Chronic ethanol treatment induces H2O2 production selectively in pericentral regions of the liver lobule

Chronic treatment with ethanol damages pericentral regions of the liver selectively, and reactive oxygen species such as H2O2 may be involved in the mechanism of hepatotoxicity. To test this idea, the effect of chronic treatment with ethanol on rates of H2O2 production was measured in tissue cylinders isolated from periportal and pericentral regions of livers from ethanol-treated rats. Rates of hydrogen peroxide production, assessed from the oxidation of methanol to formaldehyde by catalase-H2O2, were similar in tissue cylinders isolated from periportal regions in control and ethanol-treated rats. In contrast, rates of H2O2 production were over 4-fold higher in tissue isolated from pericentral regions of livers from ethanol-treated than control animals (1.7 +/- 0.5 vs. 0.4 +/- 0.3 nmol/min/mg protein, respectively). Rates of H2O2-generating acyl CoA oxidase activity were equivalent in tissue cylinders from periportal regions of livers from both groups (approximately 2 nmol/min/mg protein), but were over 2-fold higher in tissue cylinders from pericentral regions of livers from ethanol-treated rats than from controls. In contrast, catalase activity was increased nearly 2-fold in homogenates from both periportal and pericentral regions by ethanol treatment while glutathione peroxidase activity was decreased significantly in both regions. These data demonstrate that ethanol increases H2O2 generation in pericentral regions of the liver lobule in part by elevating rates of peroxisomal beta-oxidation of acyl CoA compounds and are consistent with the hypothesis that local increases in H2O2 production may be involved in the mechanism of ethanol-induced hepatotoxicity.

Intermediates of peroxisomal beta-oxidation of [U-14C]hexadecanedionoate. A study of the acyl-CoA esters which accumulate during peroxisomal beta-oxidation of [U-14C]hexadecanedionate and [U-14C]hexadecanedionoyl-mono-CoA

1. The oxidation of [U-14C]hexadecanedionoyl-mono-CoA was stimulated by CoA, by carnitine in the absence of CoA and by the presence of an NAD(+)-regenerating system. 2. Substrate inhibition was observed with respect to [U-14C]hexadecanedionoyl-mono-CoA at concentrations greater than 35 microM. 3. Acetyl-CoA and the dicarboxyl-CoA esters of chain length C6-16 were detected by HPLC under standard incubation conditions. 4. In the absence of the NAD(+)-regenerating system, 2-enoyl-CoA and 3-hydroxacyl-CoA esters were detected. 5. In general, the peroxisomal beta-oxidation of dicarboxylates is very similar to that of monocarboxylates [Bartlett, K., Hovik, R., Eaton, S., Watmough, N. J. & Osmundsen, H. (1990) Biochem. J. 270, 175-180] except that chain shortening does not proceed beyond C6. 6. We conclude that the peroxisomal beta-oxidation of dicarboxylates is regulated by the redox state of the peroxisomal matrix and CoA availability.

Peroxisomal fatty acid oxidation and inhibitors of the mitochondrial carnitine palmitoyltransferase I in isolated rat hepatocytes

Fatty acid oxidation was studied in the presence of inhibitors of carnitine palmitoyltransferase I (CPT I), in normal and in peroxisome-proliferated rat hepatocytes. The oxidation decreased in mitochondria, as expected, but in peroxisomes it increased. These two effects were seen, in variable proportions, with (+)-decanoylcarnitine, 2-tetradecylglycidic acid (TDGA) and etomoxir. The decrease in mitochondrial oxidation (ketogenesis) affected saturated fatty acids with 12 or more carbon atoms, whereas the increase in peroxisomal oxidation (H2O2 production) affected saturated fatty acids with 8 or more carbon atoms. The peroxisomal increase was sensitive to chlorpromazine, a peroxisomal inhibitor. To study possible mechanisms, palmitoyl-, octanoyl- and acetyl-carnitine acyltransferase activities were measured, in homogenates and in subcellular fractions from control and TDGA-treated cells. The palmitoylcarnitine acyltransferase was inhibited, as expected, but the octanoyltransferase activity also decreased. The CoA derivative of TDGA was synthesized and tentatively identified as being responsible for inhibition of the octanoylcarnitine acyltransferase. These results show that inhibitors of the mitochondrial CPT I may also inhibit the peroxisomal octanoyl transferase; they also support the hypothesis that the octanoyltransferase has the capacity to control or regulate peroxisomal fatty acid oxidation.

Induction of peroxisomes by treatment with perfluorooctanoate does not increase rates of H2O2 production in intact liver

Increases in acyl coenzyme A (CoA) oxidase activity due to peroxisome proliferation are postulated to cause oxidative stress via elevated production of H2O2, leading to DNA damage. These changes are suspected to be responsible for tumor formation caused by non-genotoxic carcinogens which do not bind to DNA but cause proliferation of peroxisomes. However, the activity of the peroxisomal enzyme acyl CoA oxidase assayed in vitro in the presence of excess fatty acyl CoA substrate may not reflect rates of H2O2 generation in intact liver where fatty acid supply is carefully controlled in part by delivery of substrate. The purpose of this work was to determine if rates of hepatic H2O2 generation were altered in perfused liver and in vivo following induction of H2O2-generating acyl CoA oxidase activity. Injection of the potent peroxisome proliferating agent perfluorooctanoate into rats 5 days prior to sacrifice caused an expected 4-fold increase of H2O2-generating acyl CoA oxidase activity measured in hepatic homogenates. In contrast, rates of H2O2 generation in perfused liver measured spectrophotometrically (660-640 nm) through a lobe of the liver were not altered by perfluorooctanoate treatment (7.3 +/- 1.5 vs. 7.8 +/- 0.5 mumol/g/h in livers from untreated control rats). Similar treatment with perfluorooctanoate also increased in vitro acyl CoA oxidase activity 9-fold in livers from deermice; however, rates of elimination of methanol, a selective substrate for catalase in rodents whose oxidation is limited by the supply of H2O2, were not altered significantly in vivo (control, 110 +/- 11 mumol/g/h vs. perfluorooctanoate, 112 +/- 32 mumol/g/h). Taken together, these data demonstrate that elevation of H2O2 formation by acyl CoA oxidase activity measured in vitro is not necessarily associated with increases in rates of H2O2 generation in intact perfused liver or in vivo, most likely due to rate-limitation in intact cells by fatty acid supply. These data do not support the hypothesis that the induction of peroxisomes leads to excessive H2O2 production and oxidative stress. It follows that alternative hypotheses to explain carcinogenesis caused by peroxisome-proliferating agents need to be considered.

Selective inhibition of hepatic peroxisomal fatty acid beta-oxidation by enoximone

Although beta-oxidation of fatty acids occurs in both peroxisomes and mitochondria, beta-oxidizing enzymes in these organelles have distinct differences in their specifity and sensitivity to inhibitors. In this study, the effects of the phosphodiesterase inhibitor enoximone on hepatic peroxisomal and mitochondrial beta-oxidation were investigated. In liver homogenates from control rats, cyanide-insensitive peroxisomal beta-oxidation of palmitoyl-CoA was inhibited progressively by increasing concentrations of enoximone. Similar results were obtained in liver homogenates from rats pretreated with the known peroxisomal proliferator diethylhexylphthalate. In contrast, mitochondrial beta-oxidation of palmitoyl-CoA was not inhibited by enoximone. These data show that enoximone selectively inhibits basal as well as induced peroxisomal, but not mitochondrial, beta-oxidation of the CoA thioester of long-chain fatty acids. The availability of specific inhibitors of peroxisomal beta-oxidation should prove useful in elucidating regulatory mechanisms operative in this pathway in normal as well as in proliferated peroxisomes.