Metabolic pathways in mammalian peroxisomes

Loss of pex5 sensitizes zebrafish to fasting due to deregulated mitochondria, mTOR, and autophagy

Animal models have been utilized to understand the pathogenesis of Zellweger spectrum disorders (ZSDs); however, the link between clinical manifestations and molecular pathways has not yet been clearly established. We generated peroxin 5 homozygous mutant zebrafish (pex5^-/-) to gain insight into the molecular pathogenesis of peroxisome dysfunction. pex5^-/- display hallmarks of ZSD in humans and die within one month after birth. Fasting rapidly depletes lipids and glycogen in pex5^-/- livers and expedites their mortality. Mechanistically, deregulated mitochondria and mechanistic target of rapamycin (mTOR) signaling act together to induce metabolic alterations that deplete hepatic nutrients and accumulate damaged mitochondria. Accordingly, chemical interventions blocking either the mitochondrial function or mTOR complex 1 (mTORC1) or a combination of both improve the metabolic imbalance shown in the fasted pex5^-/- livers and extend the survival of animals. In addition, the suppression of oxidative stress by N-acetyl L-cysteine (NAC) treatment rescued the apoptotic cell death and early mortality observed in pex5^-/-. Furthermore, an autophagy activator effectively ameliorated the early mortality of fasted pex5^-/-. These results suggest that fasting may be detrimental to patients with peroxisome dysfunction, and that modulating the mitochondria, mTORC1, autophagy activities, or oxidative stress may provide a therapeutic option to alleviate the symptoms of peroxisomal diseases associated with metabolic dysfunction.

The pleiotropic peroxisome proliferator activated receptors: Regulation and therapeutics

The Peroxisome proliferator-activated receptors (PPARs) are key regulators of metabolic events in our body. Owing to their implication in maintenance of homeostasis, both PPAR agonists and antagonists assume therapeutic significance. Understanding the molecular mechanisms of each of the PPAR isotypes in the healthy body and during disease is crucial to exploiting their full therapeutic potential. This article is an attempt to present a rational analysis of the multifaceted therapeutic effects and underlying mechanisms of isotype-specific PPAR agonists, dual PPAR agonists, pan PPAR agonists as well as PPAR antagonists. A holistic understanding of the mechanistic dimensions of these key metabolic regulators will guide future efforts to identify novel molecules in the realm of metabolic, inflammatory and immunotherapeutic diseases.

Peroxisomes in the mouse parotid glands: An in-depth morphological and molecular analysis

BACKGROUND

The parotid gland is a major salivary gland that has important roles in the digestive and immune system. Peroxisomes are ubiquitous, single-membrane-bound organelles that are present in all eukaryotic cells. Peroxisomes help mediate lipid and reactive oxygen species metabolism, as well as polyunsaturated fatty acid, cholesterol and plasmalogen synthesis. Much of the knowledge on peroxisomes has derived from metabolic organs, however no detailed knowledge is available on peroxisomes in the parotid glands. We thus aimed to comprehensively delineate the localization and characterization of peroxisomal proteins in the murine parotid gland.

METHODS

We characterized peroxisomes in the acinar and striated duct cells of the murine parotid gland by fluorescence and electron microscopy, as well as protein and mRNA expression analyses for important peroxisomal genes and proteins.

RESULTS

We found that peroxisomes are present in all cell types of the mouse parotid gland, however, exhibit notable cell-specific differences in their abundance and enzyme content. We also observed that mouse parotid glands contain high levels of peroxisomal β-oxidation enzymes (including Acox1, Mfp2 and Acaa1), catalase and other peroxisomal anti-oxidative enzymes.

CONCLUSIONS

This data suggests that peroxisomes are highly abundant in the murine parotid gland and might help to protect against oxidative stress. This comprehensive description of peroxisomes in the parotid gland lays the groundwork for further research concerning their role in the pathogenesis of parotid gland diseases and tumors.

Herpes simplex virus 1 infection dampens the immediate early antiviral innate immunity signaling from peroxisomes by tegument protein VP16

Background

Herpes simplex virus 1 (HSV-1) is an archetypal member of the alphaherpesvirus subfamily with a large genome encoding over 80 proteins, many of which play a critical role in virus-host interactions and immune modulation. Upon viral infections, the host cells activate innate immune responses to restrict their replications. Peroxisomes, which have long been defined to regulate metabolic activities, are reported to be important signaling platforms for antiviral innate immunity. It has been verified that signaling from peroxisomal MAVS (MAVS-Pex) triggers a rapid interferon (IFN) independent IFN-stimulated genes (ISGs) production against invading pathogens. However, little is known about the interaction between DNA viruses such as HSV-1 and the MAVS-Pex mediated signaling.

Results

HSV-1 could activate the MAVS-Pex signaling pathway at a low multiplicity of infection (MOI), while infection at a high MOI dampens MAVS-Pex induced immediately early ISGs production. A high-throughput screen assay reveals that HSV-1 tegument protein VP16 inhibits the immediate early ISGs expression downstream of MAVS-Pex signaling. Moreover, the expression of ISGs was recovered when VP16 was knockdown with its specific short hairpin RNA.

Conclusion

HSV-1 blocks MAVS-Pex mediated early ISGs production through VP16 to dampen the immediate early antiviral innate immunity signaling from peroxisomes.

Disrupting Dimerization Translocates Soluble Epoxide Hydrolase to Peroxisomes

The epoxyeicosatrienoic acid (EET) neutralizing enzyme soluble epoxide hydrolase (sEH) is a neuronal enzyme, which has been localized in both the cytosol and peroxisomes. The molecular basis for its dual localization remains unclear as sEH contains a functional peroxisomal targeting sequence (PTS). Recently, a missense polymorphism was identified in human sEH (R287Q) that enhances its peroxisomal localization. This same polymorphism has also been shown to generate weaker sEH homo-dimers. Taken together, these observations suggest that dimerization may mask the sEH PTS and prevent peroxisome translocation. In the current study, we test the hypothesis that dimerization is a key regulator of sEH subcellular localization. Specifically, we altered the dimerization state of sEH by introducing substitutions in amino acids responsible for the dimer-stabilizing salt-bridge. Green Fluorescent Protein (GFP) fusions of each of mutants were co-transfected into mouse primary cultured cortical neurons together with a PTS-linked red fluorescent protein to constitutively label peroxisomes. Labeled neurons were analyzed using confocal microscopy and co-localization of sEH with peroxisomes was quantified using Pearson's correlation coefficient. We find that dimer-competent sEH constructs preferentially localize to the cytosol, whereas constructs with weakened or disrupted dimerization were preferentially targeted to peroxisomes. We conclude that the sEH dimerization status is a key regulator of its peroxisomal localization.

PPAR- γ impairment alters peroxisome functionality in primary astrocyte cell cultures

Peroxisomes provide glial cells with protective functions against the harmful effects of H2O2 on neurons and peroxisome impairment results in nervous lesions. Agonists of the γ -subtype of the Peroxisome-Proliferator-Activated-Receptors (PPAR) have been proposed as neuroprotective agents in neurodegenerative disorders. Nevertheless, the role of PPAR- γ alterations in pathophysiological mechanisms and the relevance of peroxisome functions in the PPAR- γ effects are not yet clear. In a primary cell culture of rat astrocytes, the irreversible PPAR- γ antagonist GW9662 concentration-dependently decreased the activity of catalase, the most important antioxidant defense enzyme in peroxisomes. Catalase functionality recovered in a few days and the PPAR- γ agonist rosiglitazone promoted reversal of enzymatic damage. The reversible antagonist G3335 reduced both the activity and expression of catalase in a rosiglitazone-prevented manner. G3335 reduced also the glutathione reductase expression, indicating that enzyme involved in glutathione regeneration was compromised. Neither the PPAR- α target gene Acyl-Coenzyme-A-oxidase-1 nor the mitochondrial detoxifying enzyme NADH:ubiquinone-oxidoreductase (NDFUS3) was altered by PPAR- γ inhibition. In conclusion, PPAR- γ inhibition induced impairment of catalase in astrocytes. A general decrease of the antioxidant defenses of the cell suggests that a PPAR- γ hypofunction could participate in neurodegenerative mechanisms through peroxisomal damage. This series of experiments could be a useful model for studying compounds able to restore peroxisome functionality.

Xenobiotic metabolism of plant secondary compounds in the English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae)

Plant secondary compounds have been documented to be deleterious to insects and other herbivores in diverse ways. In this study, the effect of catechol (phenolics), gramine (alkaloid) and L-ornithine-HCI (non-protein amino acid) on the activities of xenobiotic metabolizing enzymes in English grain aphid, Sitobion avenae, was evaluated. Phase I enzymes investigated in this study included carboxylesterase (CarE), and oxidoreductase, whereas Phase II enzymes were represented by glutathione S-transferase (GST). In general, CarE and GST activities in S. avenae were positively correlated with the concentration of plant secondary compounds in artificial diets. Oxidoreductase activity, however, displayed a different profile. Specifically, peroxidase (POD) and polyphenol oxidase (PPO) activities in S. avenae were positively correlated with concentrations of dietary catechol and gramine, respectively, whereas catalase (CAT) activity was significantly suppressed by the higher concentration of catechol, gramine and L-ornithine-HCl. These combined results suggest that CarE and GST in S. avenae are key enzymes to breakdown a broad spectrum of plant secondary compounds, whereas oxidoreductase, including PPO and POD, degrades specific groups of plant secondary compounds.

Pathways for repairing and tolerating the spectrum of oxidative DNA lesions

Reactive oxygen species (ROS) arise from both endogenous and exogenous sources. These reactive molecules possess the ability to damage both the DNA nucleobases and the sugar phosphate backbone, leading to a wide spectrum of lesions, including non-bulky (8-oxoguanine and formamidopyrimidine) and bulky (cyclopurine and etheno adducts) base modifications, abasic sites, non-conventional single-strand breaks, protein-DNA adducts, and intra/interstrand DNA crosslinks. Unrepaired oxidative DNA damage can result in bypass mutagenesis during genome copying or gene expression, or blockage of the essential cellular processes of DNA replication or transcription. Such outcomes underlie numerous pathologies, including, but not limited to, carcinogenesis and neurodegeneration, as well as the aging process. Cells have adapted and evolved defense systems against the deleterious effects of ROS, and specifically devote a number of cellular DNA repair and tolerance pathways to combat oxidative DNA damage. Defects in these protective pathways trigger hereditary human diseases that exhibit increased cancer incidence, developmental defects, neurological abnormalities, and/or premature aging. We review herein classic and atypical oxidative DNA lesions, outcomes of encountering these damages during DNA replication and transcription, and the consequences of losing the ability to repair the different forms of oxidative DNA damage. We particularly focus on the hereditary human diseases Xeroderma Pigmentosum, Cockayne Syndrome and Fanconi Anemia, which may involve defects in the efficient repair of oxidative modifications to chromosomal DNA.

Screening and confirmatory analysis of glyoxylate: a biomarker of plants resistance against herbicides

The evidence that glyoxylate is a biomarker of tolerance or susceptibility to the action of herbicides belonging to the glycine family makes necessary to develop simple methods for the determination of this metabolite. Glyoxylate level allows both to know the presence/absence of members of the glycine family in plants and plant response to these herbicides. With this aim, a colorimetric-screening method has been developed for determination of glyoxylate based on formation of a phenylhydrazone, then oxidised to red coloured 1,5-diphenylformazan. Simultaneous optimization of ultrasound-assisted extraction of glyoxylate from plants and derivatization by a multivariate design has allowed the determination of the target analyte in fresh plants without interferences from pheophytines and compounds with carbonyl groups. Limits of detection and quantification are 0.05 μg ml(-1) and 0.17 μg ml(-1), respectively, with precision, expressed as relative standard deviation, of 3.3% for repeatability and 5.6% for the within-day laboratory reproducibility. Only 50mg of plant is necessary for determination of glyoxylate within 32 min. Confirmatory analysis by capillary electrophoresis-diode array detection in samples of Lolium spp. subjected to treatment with glyphosate shows that the relative error of the proposed method is always lower than 7%.

Medium-chain fatty acids ameliorate insulin resistance caused by high-fat diets in rats

BACKGROUND

High dietary intake of saturated fat impairs insulin sensitivity and lipid metabolism. The influence of fatty acid chain length, however, is not yet fully understood, but evidence exists for different effects of saturated long-chain (LC) versus saturated medium-chain (MC) fatty acids (FA).

METHODS

To investigate the effects of the FA chain length, male Wistar rats were fed high-fat diets containing triacylglycerols composed of either MC- or LCFA for 4 weeks; rats fed maintenance diet served as a control. The animals underwent euglycemic hyperinsulinemic clamping or oral metabolic tolerance testing respectively; enzyme activities of mitochondrial (EC2.3.1.21 carnitine palmitoyl transferase) and peroxisomal (EC1.3.3.6 acyl-CoA oxidase) FA oxidation were measured in liver and muscle.

RESULTS

LCFA consumption resulted in higher fasted serum insulin and glucose concentrations compared to controls, while MCFA-fed animals did not differ from controls. Insulin sensitivity was reduced by 30% in the LCFA group while the MCFA group did not differ from controls. Feeding MCFA resulted in the controls' lowered fasted and post-prandial triacylglycerol concentration compared to LCFA, while triacylglycerol concentrations in muscle were higher in both high-fat groups compared to controls. No diet-induced changes were found in acyl-CoA oxidase (ACO) activity (liver and muscle), while LCFA feeding significantly raised carnitine palmitoyltransferase activity.

CONCLUSIONS

The chain length of saturated fatty acids in isocaloric diets affects insulin sensitivity, lipid metabolism and mitochondrial fatty acid oxidation without influencing body weight. While dietary LCFA clearly impair insulin sensitivity and lipid metabolism, MCFA seem to protect from lipotoxicity and subsequent insulin resistance without caloric restriction.

Peroxisomes in mouse and human lung: their involvement in pulmonary lipid metabolism

Only sparse information is available from the literature on the peroxisomal compartment and its enzyme composition in mouse and human lungs. Therefore, in the present investigation we have characterized peroxisomes in different cell types of adult mouse (C57BL/6J) and human lungs in a comprehensive study using a variety of light-, fluorescence- and electron microscopic as well as biochemical techniques and by the use of various peroxisomal marker proteins (Pex13p, Pex14p, ABCD3, beta-oxidation enzymes and catalase). In contrast to previous reports, we have found that peroxisomes are present in all cell types in human and mouse lungs. However, they differ significantly and in a cell-type-specific manner in their structure, numerical abundance and enzyme composition. Whereas catalase showed significant differences between distinct cell types, Pex14p proved to be the marker of choice for labeling all lung peroxisomes. In alveolar type II cells and alveolar macrophages peroxisomes contained significant amounts of the lipid transporter ABCD3 and beta-oxidation enzymes, suggesting their involvement in the modification and recycling of surfactant lipids and in the control of lipid mediators and ligands for nuclear receptors of the PPAR family. Possible connections between ROS and lipid metabolism of lung peroxisomes are discussed.

Free flow isoelectric focusing : a method for the separation of both hydrophilic and hydrophobic proteins of rat liver peroxisomes

Peroxisomes take part in various metabolic pathways related to the regulation of lipid homeostasis. Although detailed information on the enzymes involved in the peroxisomal lipid metabolism was acquired in the past, the mechanisms of metabolic exchange between peroxisomes and the cytosol or other organelles still remain an enigma. Therefore, a detailed analysis of the peroxisomal membrane proteome could help identify potential metabolite transporters. However, because of their highly hydrophobic character, membrane proteins tend to precipitate in aqueous media, making their fractionation still a challenging task. To overcome these obstacles, we have elaborated a protocol for the separation of both hydrophilic as well as hydrophobic proteins using free flow isoelectric focusing (FF-IEF). Similar to traditional gel-based isoelectric focusing, a denaturing electrophoresis buffer containing a mixture of urea, thiourea and detergents is applied to keep highly hydrophobic proteins in solution. Electrophoresis is conducted on a BD Free Flow Electrophoresis System with a linear pH gradient from 3 to 10 and sampled into 96 fractions. As a second dimension, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) is used to further separate and visualize the protein pattern of the peroxisomal subfractions of matrix, peripheral and integral membrane proteins. The identification of the known peroxisomal membrane proteins PMP22, PMP70 as well as mGST in the subsequent matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) analysis of the 100 most prominent protein bands has documented the suitability of this new technique for the analysis of hydrophobic proteins.

The use of biomarkers in biomonitoring: a 2-tier approach assessing the level of pollutant-induced stress syndrome in sentinel organisms

The paper outlines a 2-tier approach for wide-scale biomonitoring programmes. To obtain a high level of standardization, we suggest the use of caged organisms (mussels or fish). An "early warning", highly sensitive, low-cost biomarker is employed in tier 1 (i.e. lysosomal membrane stability (LMS) and survival rate, a marker for highly polluted sites). Tier 2 is used only for animals sampled at sites in which LMS changes are evident and there is no mortality, with a complete battery of biomarkers assessing the levels of pollutant-induced stress syndrome. Possible approaches for integrating biomarker data in a synthetic index are discussed, along with our proposal to use a recently developed Expert System. The latter system allows a correct selection of biomarkers at different levels of biological organisation (molecular/cellular/tissue/organism) taking into account trends in pollutant-induced biomarker changes (increasing, decreasing, bell-shape). A selection of biomarkers of stress, genotoxicity and exposure usually employed in biomonitoring programmes is presented, together with a brief overview of new biomolecular approaches.

On the presence of C2-ceramide in mammalian tissues: possible relationship to etherphospholipids and phosphorylation by ceramide kinase

C(2)-ceramide (N-acetyl-sphingenine) is often used as an analog to study ceramide-mediated cellular processes. According to Lee et al. [J. Biol. Chem. 271 (1996), 209-217], C(2)-ceramide is formed by an acetyl transfer from platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) to sphingenine. To substantiate these unconfirmed findings, we (i) developed a method to quantify C(2)-ceramide and (ii) analyzed C(2)-ceramide levels in Pex5(-/-) mice, a model for Zellweger syndrome, in which the synthesis of ether lipids such as PAF is impaired. The presence of C(2)-ceramide could be established in brain (+/-10 pmol/g) and liver (+/-25 pmol/g) from control mice, and was approximately 5000-fold less than the main long-chain ceramide species. In Pex5(-/-) mice, C(2)-ceramide levels did not differ significantly compared to control tissues. Given the presence of a ceramide kinase in mammals, phosphorylation of C(2)-ceramide by human ceramide kinase (HsCERK) was tested. C(2)-ceramide appears to be a good substrate when albumin is used as carrier. In CHO cells overexpressing HsCERK, phosphorylation of exogenously added C(2)-ceramide could also be demonstrated. Our data indicate that C(2)-ceramide is present in mammalian tissues and can be converted to C(2)-ceramide-1-phosphate, in addition to other documented metabolic alterations, but does not seem to be linked to ether lipid metabolism.

Flow cytometric assessment of peroxisome proliferation from frozen liver of fibrate-treated monkeys

Multiple methods currently exist for the assessment of peroxisome proliferation, including gene expression, enzyme activity, immunolabeling coupled with image analysis, and electron microscopy. This study describes a novel flow cytometric method to efficiently quantify peroxisome proliferation in cells from frozen livers. Frozen livers from cynomolgus monkeys treated with ciprofibrate at doses of 0, 3, 30, 150, and 400 mg/kg/day for 15 days were mechanically disaggregated using an automated dispersion method. The resulting cell suspensions were labeled using an allophycocyanin (APC)-conjugated antibody directed against peroxisomal membrane protein 70 (PMP70). Statistically significant increases in mean fluorescence intensity were observed from animals dosed at 30, 150, and 400 mg/kg/day compared to control. Parallel comparisons using electron microscopy and immunofluorescence microscopy suggest that flow cytometry may be an alternative to electron microscopy in determinations of peroxisome proliferation. Flow cytometric analysis of freshly isolated hepatocytes and frozen liver from rats treated with fenofibrate at 200 mg/kg/day for 10 days showed the flow cytometric method could detect peroxisome proliferation in both species. The research described here demonstrates the feasibility of applying flow cytometry for the detection of peroxisome proliferation.

Insights into the membrane proteome of rat liver peroxisomes: microsomal glutathione-S-transferase is shared by both subcellular compartments

Peroxisomes are ubiquitous "multipurpose" organelles of eukaryotic cells. Their matrix enzymes catalyze mainly catabolic and anabolic reactions of lipid metabolism, thus contributing to the regulation of lipid homeostasis. Since most metabolites must be actively transported across the peroxisomal membrane and since individual proteins and protein complexes play functional roles in such transport processes, we analyzed the peroxisomal membrane proteome. Benzyldimethyl-n-hexadecylammoniumchloride (16-BAC)/SDS-2-D-PAGE and mass spectrometry were used to characterize the proteomes of highly purified "light" and "heavy" peroxisomes of rat liver obtained by density gradient centrifugation. In both populations, the major integral membrane proteins could be detected in high concentrations, verifying 16-BAC/SDS-2-D-PAGE as a suitable tool for the preparation of membrane proteomes destined for mass spectrometric analysis. Both reliable and reproducible detection of a distinct set of microsomal (ER) membrane proteins, including microsomal glutathione-S-transferase (mGST), in light and heavy peroxisomal fractions was also possible. Compared with the abundance of most microsomal membrane proteins, we found mGST to be specifically enriched in peroxisomal membrane fractions. Furthermore, C terminus epitope-tagged mGST versions were localized at least in part to peroxisomes in different mammalian cell lines. Taken together, these data suggest that the peroxisomal GST is not a mere ER-contaminant, but a bona fide protein comprising the membrane proteome of both intracellular compartments. In addition, we could detect several mitochondrial proteins in light peroxisome fractions. This finding may likely indicate a physical association of light peroxisomes with mitochondria, since the organelles could be partly separated by mechanical stress. Whether this association is of functional importance awaits further investigation.

Proteomic analysis of mouse kidney peroxisomes: identification of RP2p as a peroxisomal nudix hydrolase with acyl-CoA diphosphatase activity

Proteomic analysis of mouse kidney peroxisomes resulted in the identification of a novel nudix hydrolase designated RP2p, which is encoded by the D7RP2e gene. RP2p consists of 357 amino acids and contains two conserved domains: a nudix hydrolase domain and a CoA-binding domain. In addition, a PTS (peroxisomal targeting signal) type 1 (Ala-His-Leu) was found at the C-terminus. Analysis of the enzyme characteristics revealed that RP2p is a CoA diphosphatase with activity towards CoA, oxidized CoA and a wide range of CoA esters, including choloyl-CoA and branched-chain fatty-acyl-CoA esters. The enzymatic properties of RP2p indicate that at low substrate concentrations medium and long-chain fatty-acyl-CoA esters are the primary substrates. Enzyme activity was optimal at pH 9 or above, and required the presence of Mg2+ or Mn2+ ions. Subcellular fractionation studies revealed that all CoA diphosphatase activity in mouse kidney is restricted to peroxisomes.

Carnitine prevents cyclic GMP-induced inhibition of peroxisomal enzyme activities

Peroxisomes, also termed as microbodies, are now known to carry out several specialized metabolic activities that are vital to cellular function. A defect in peroxisomal function leads to development of a fatal human disease, and a number of peroxisomal disorders are now linked to inherited peroxisomal enzyme abnormalities. Peroxisomal enzyme activities are also altered during pathophysiological conditions through various endogenously produced bio-molecules such as nitric oxide (NO). NO produced by cytokines or NO-donors is known to modulate peroxisomal functions, and these effects of NO are mediated through cGMP. We are reporting for the first time that L-carnitine (1-5 mm) prevents cGMP-mediated impairment of peroxisomal enzyme activities. Cyclic GMP (250-1000 muM) significantly inhibited (p < 0.01) the specific activities of catalase, acyl CoA oxidase and dihydroxyacetone-phosphate acyltransferase (DHAPATase) in human dermal fibroblasts, and treatment of cells with 1-5 mM of carnitine significantly (p < 0.001) reduced the inhibitory effects of cGMP on peroxisomal enzyme activities. These findings suggest that carnitine, previously thought to participate only in fatty acid oxidation, may in fact be regulating other cellular events including oxidative stress, and could possibly be used to correct cytokine-impaired peroxisomal functions.

Reduction of palmitate-induced cardiac apoptosis by fenofibrate

The objective of this study was to test the hypothesis that a strategy based on alteration of lipid metabolism would moderate the cellular toxicity of the C16:0 saturated fatty acid-palmitate. Cardiomyocytes from neonatal mice and embryonic chicks were treated with palmitate and both oncotic and apoptotic death were observed. Fenofibrate pretreatment, 1 microM, 24 h prior to palmitate, significantly (p < 0.05) reduced palmitate-induced apoptosis. In contrast, fenofibrate had no significant effect on palmitate-induced apoptosis when fenofibrate treatment was concomitant with palmitate. The protective effect of fenofibrate was restricted to the apoptotic population. The more potent and specific PPARalpha agonist WY 14643, 1 microM, also reduced palmitate-induced apoptosis but to a smaller extent than fenofibrate. The long pretreatment time, 24 h, was necessary to show fenofibrate's effect on apoptosis, suggesting an increase in gene transcription and protein expression. Indeed, fenofibrate increased PPARalpha expression that was mainly demonstrated in the nucleus. These data suggest a novel approach to the reduction of cardiac apoptosis by the chronic treatment with the PPARalpha agonist fenofibrate.

Changes of peroxisomal fatty acid metabolism during cold acclimatization in hibernating jerboa (Jaculus orientalis)

Jerboa (Jaculus orientalis) is a deep hibernator originating from sub-desert highlands and represents an excellent model to help to understand the incidence of seasonal variations of food intake and of body as well as environmental temperatures on lipid metabolism. In jerboa, hibernation processes are characterized by changes in the size of mitochondria, the number of peroxisomes in liver and in the expression of enzymes linked to fatty acid metabolism. In liver and kidney, cold acclimatization shows an opposite effect on the activities of the mitochondrial acyl-CoA dehydrogenase (-50%) and the peroxisomal acyl-CoA oxidase (AOX) (+50%), while in brown and white adipose tissues, both activities are decreased down to 85%. These enzymes activities are subject to a strong induction in brown and in white adipose tissue (3.4- to 7.5-fold, respectively) during the hibernation period which is characterized by a low body temperature (around 10 degrees C) and by starvation. Expression level of AOX mRNA and protein are increased during both pre-hibernation and hibernation periods. Unexpectedly, treatment with ciprofibrate, a hypolipemic agent, deeply affects lipolysis in brown adipose tissue by increasing acyl-CoA dehydrogenase activity (3.4-fold), both AOX activity and mRNA levels (2.8- and 3.8-fold, respectively) during pre-hibernation. Therefore, during pre-hibernation acclimatization, there is a negative regulation of fatty acid degradation allowing to accumulate a lipid stock which is later degraded during the hibernation period (starvation) due to a positive regulation of enzymes providing the required energy for animal survival.

Antioxidant enzymes and peroxisome proliferation in relation to contaminant body burdens of PAHs and PCBs in bivalve molluscs, crabs and fish from the Urdaibai and Plentzia estuaries (Bay of Biscay)

With the aim of studying levels of antioxidant and peroxisomal enzymes and the structure of peroxisomes in relation to body burdens of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), mussels Mytilus galloprovincialis, oysters Crassostrea sp., crabs Carcinus maenas and mullets Mugil cephalus were sampled in two Basque estuaries (Bay of Biscay): Urdaibai (Laida, Txatxarramendi, Arteaga, and downstream a sewage treatment plant-STP) and Plentzia. In general, animals showed higher concentrations of contaminants in winter than in summer and no relevant differences were detected among locations. Conversely, antioxidant enzyme activities were higher in summer. Enzyme expression was studied in mullets using immunochemical methods. By immunoblotting season-dependent differences were detected for Mn-superoxide dismutase (Mn-SOD). As for the immunohistochemical staining, mullets sampled in summer in Plentzia showed significantly higher optical densities for acyl-CoA oxidase and lower for both Cu,Zn-SOD and Mn-SOD than those collected downstream a STP as well as higher catalase immunostaining than those collected in winter. Peroxisomal volume density (V(vp)) of mussels sampled in Laida and Txatxarramendi did not show seasonal variations, while for oysters collected in Laida and Arteaga V(vp) was higher in summer. Crab and mullet V(vp) were also higher in summer. In conclusion, the estuaries of Urdaibai and Plentzia can be considered as low to moderately polluted areas and levels of PAHs and PCBs do not show marked variations apart from seasonal variations. Animals can be adapted to low pollution conditions and, under these circumstances, seasonal factors might affect biomarker responses to a greater extent than pollution variations.

Cell biology of peroxisomes and their characteristics in aquatic organisms

The general characteristics of peroxisomes in different organisms, including aquatic organisms such as fish, crustaceans, and mollusks, are reviewed, with special emphasis on different aspects of the organelle biogenesis and mechanistic aspects of peroxisome proliferation. Peroxisome proliferation and peroxisomal enzyme inductions elicited by xenobiotics or physiological conditions have become useful tools to study the mechanisms of peroxisome biogenesis. During peroxisome proliferation, the induction of peroxisomal proteins is heterogeneous, enzymes that show increased activity being involved in different aspects of lipid homeostasis. The process of peroxisome biogenesis is coordinately triggered by a whole array of structurally dissimilar compounds known as peroxisome proliferators, and investigating the effect of some of these compounds that commonly appear as pollutants in the environment on the peroxisomes of aquatic animals inhabiting marine and estuarine habitats seems interesting. It is also important to determine whether peroxisome proliferation in these animals is a phenomenon that might occur under normal physiological or season-related conditions and plays a metabolic or functional role. This would help set the basis for understanding the process of peroxisome biogenesis in aquatic animals.

Cultured granule cells and astrocytes from cerebellum differ in metabolizing sphingosine

Sphingosine metabolism was studied in primary cultures of differentiated cerebellar granule cells and astrocytes. After a 2-h pulse with [C3-(3)H]sphingosine at different doses (0.1-200 nmol/mg of cell protein), both cell types efficiently incorporated the long chain base; the percentage of cellular [(3)H]sphingosine over total label incorporation was extremely low at sphingosine doses of <10 nmol/mg of cell protein and increased at higher doses. Most of the [(3)H]sphingosine taken up underwent metabolic processing by N-acylation, 1-phosphorylation, and degradation (assessed as (3)H(2)O released in the medium). The metabolic processing of exogenous sphingosine was extremely efficient in both cells, granule cells and astrocytes being able to metabolize, respectively, an amount of sphingosine up to 80- and 300-fold the cellular content of this long chain base in 2 h. At the different doses, the prevailing metabolic route of sphingosine was different. At lower doses and in a wide dose range, the major metabolic fate of sphingosine was N-acylation. With increasing doses, there was first increased sphingosine degradation and then increased levels of sphingosine-1-phosphate. The data demonstrate that, in neurons and astrocytes, the metabolic machinery devoted to sphingosine processing is different, astrocytes possessing an overall higher capacity to synthesize the bioactive compounds ceramide and sphingosine-1-phosphate.

Presence and inducibility of peroxisomes in a human glioblastoma cell line

We investigated the effect of the peroxisomal proliferator (PP) perfluorodecanoic acid (PFDA), alone or in combination with 9-cis-retinoic acid (RX) on the human glioblastoma cell line Lipari (LI). Cell proliferation, apoptotic rate, peroxisome morphology and morphometry, peroxisomal enzyme activities and the presence of peroxisome proliferator-activated receptors (PPARs) were examined. We show that PFDA alone produces pleiotropic effects on LI cells and that RX enhances some of these effects. Peroxisomal number and relative volume, as well as palmitoyl-CoA oxidase activity and protein, are increased by PFDA treatment, with a synergistic effect by RX. The latter, alone or in association with PFDA, induces catalase activity and protein, increases apoptosis and decreases cell proliferation. PPAR isotypes alpha and gamma were detected in LI cells. While the former is apparently unaffected by either treatment, the latter increases in response to PFDA, independent of the presence of RX. The results of this study are discussed in terms of PPARalpha activation and PPARgamma induction by PFDA, by either a direct or an indirect mechanism.

Cloning and characterization of AOEB166, a novel mammalian antioxidant enzyme of the peroxiredoxin family

Using two-dimensional electrophoresis, we have recently identified in human bronchoalveolar lavage fluid a novel protein, termed B166, with a molecular mass of 17 kDa. Here, we report the cloning of human and rat cDNAs encoding B166, which has been renamed AOEB166 for antioxidant enzyme B166. Indeed, the deduced amino acid sequence reveals that AOEB166 represents a new mammalian subfamily of AhpC/TSA peroxiredoxin antioxidant enzymes. Human AOEB166 shares 63% similarity with Escherichia coli AhpC22 alkyl hydroperoxide reductase and 66% similarity with a recently identified Saccharomyces cerevisiae alkyl hydroperoxide reductase/thioredoxin peroxidase. Moreover, recombinant AOEB166 expressed in E. coli exhibits a peroxidase activity, and an antioxidant activity comparable with that of catalase was demonstrated with the glutamine synthetase protection assay against dithiothreitol/Fe3+/O(2) oxidation. The analysis of AOEB166 mRNA distribution in 30 different human tissues and in 10 cell lines shows that the gene is widely expressed in the body. Of interest, the analysis of N- and C-terminal domains of both human and rat AOEB166 reveals amino acid sequences presenting features of mitochondrial and peroxisomal targeting sequences. Furthermore, human AOEB166 expressed as a fusion protein with GFP in HepG2 cell line is sorted to these organelles. Finally, acute inflammation induced in rat lung by lipopolysaccharide is associated with an increase of AOEB166 mRNA levels in lung, suggesting a protective role for AOEB166 in oxidative and inflammatory processes.

The glyoxylate cycle: does it function in the dormant or active bear?

The presence of or induction of an active glyoxylate cycle (GC) in the dormant black bear whose sole source of energy is body fat is an attractive concept which would allow lipid (acetate) to be directed from oxidation via the tricarboxylic acid cycle to many biosynthetic pathways. However, in spite of earlier claims, the present report establishes that isocitrate lyase and malate synthetase, GC marker enzymes, could not be detected in liver or kidney of active or dormant bears; liver peroxisome numbers were similar. The absence of brown fat (by light microscopy) and of the GC enzymes in the dormant bear raises questions about the prior report.

Metabolism of n-butyl benzyl phthalate in the female Wistar rat. Identification of new metabolites

n-Butyl benzyl phthalate (BBP), a plasticizer used in polyvinylchloride (PVC) and other polymers, has been orally administered to female Wistar rats with four doses (150, 475, 780 and 1500 mg/kg body weight/day) for 3 consecutive days. Metabolites recovered in urines were analysed by gas chromatography-mass spectrometry (GC-MS) after 24, 48 and 72 hours. Six metabolites were identified. Mono-n-butyl phthalate (MBuP) and mono-n-benzyl phthalate (MBeP) represented respectively 29-34% and 7-12% of the total recovered metabolites. Hippuric acid, the main metabolite of benzoic acid, represented the second major metabolite (51-56%). Phthalic acid, benzoic acid and an omega-oxidized metabolite of MBuP were also recovered in urine but in small quantities. BBP was never identified in urines. Total urinary metabolites recovery represented 56% of the dose administered in the first 24 hours. However, total recovery decreased when the dose increases (43% at 780 mg/kg body weight/day, only 30% at 1500 mg/kg body weight/day). Whatever the time was, BBP metabolites recovered in urines were all present and in the same proportions for the two lowest doses. Discrepancy in metabolites quantities expressed as percentages of the dose observed in urine of rat treated with the highest BBP dose disappeared with time as MBuP, MBeP and hippuric acid recovery has significantly increased at day 3. Metabolic profile of BBP in female rats has been established. The aim of the present study is to identify further the active(s) agent(s) involved in the BBP malformations and teratogenic effects.

Overexpression of human catalase gene decreases oxidized lipid-induced cytotoxicity in vascular smooth muscle cells

Reactive oxygen metabolites such as hydrogen peroxide (H(2)O(2)) and oxidized fatty acids are proinflammatory and are involved in the pathophysiology of various diseases including atherosclerosis. The effects of these oxidants could be inhibited by the external addition of an antioxidant, suggesting the promotion or propagation of further oxidation. In this study, we describe the stable overexpression of human catalase in smooth muscle cells and the resistance of these cells to cytotoxicity induced not only by the addition of H(2)O(2) but also by the addition of 13-hydroperoxyoctadecadienoic acid (13-HPODE). The results pose an intriguing possibility of the generation of H(2)O(2) from a peroxidized fatty acid. Accordingly, incubation of cells with both 13-HPODE and 13-hydroxyoctadecadienoic acid resulted in the generation of intracellular H(2)O(2). To explain the observed results by which catalase could overcome the effects of 13-HPODE, we propose that oxidized fatty acids are degraded in the cellular peroxisomes, resulting in the generation of H(2)O(2). In other words, the cellular effects of peroxidized fatty acids could be attributed to the generation of H(2)O(2).

The role of the carnitine system in peroxisomal fatty acid oxidation

Peroxisomes are small, subcellular organelles that play a major role in lipid metabolism. Inherited disorders of peroxisomal structure and metabolism can result from defective assembly, missing protein import transporters, or individual enzyme deficiencies. Molecular studies helped by the range of disorders have now elucidated many of the pathways, including the paths of alpha-oxidation for phytanic acid and beta-oxidation for very-long-chain and branched-chain fatty acids and for bile acid synthesis. The mechanism of the transfer of substrates, intermediates, and products across the membrane is poorly understood. The carnitine system, known to transport activated acyl groups between localized coenzyme A pools, is presented. The evidence for the involvement of carnitine in the transfer of activated acyl groups to and from the peroxisomes is reviewed.

Purification, localisation and characterisation of glucose-6-phosphate dehydrogenase of Trypanosoma brucei

Cell-fractionation and digitonin titration of procyclic trypomastigotes of Trypanosoma brucei, revealed that almost half of the total NADP+ -dependent glucose-6-phosphate dehydrogenase (G6PDH) activity, the first enzyme of the pentose phosphate pathway (PPP), is associated with glycosomes. The specific activity of G6PDH in the purified organelles was increased 4-fold relative to a total cell extract and showed latency. Moreover, in the absence of detergents this activity was totally resistant to the action of trypsin. The cytosolic counterpart was neither latent, nor was it resistant to trypsin. Both cytosolic and glycosomal G6PDH activities behaved identically on phenyl-, CM-, heparin-, and Affigel-blue-Sepharose columns. Both isoenzymes had a subunit Mr of 62 000 and an isoelectric point of 6.85, while kinetic studies carried out on the partially purified G6PDH from both cell compartments did not reveal any differences. The purified enzyme had an apparent Km of 138 and 5.3 microM for glucose 6-phosphate (G6P), and for NADP+, respectively, and had a specific activity of 14 micromol. (min mg of protein)(-1). We conclude that while in procyclic stages of T. brucei G6PDH activity is present in two different cell compartments, i.e. the cytosol and the glycosomes, these two activities most likely represent one and the same isoenzyme.

Responses of GlutathioneS-transferase and Glutathione Peroxidases to Feeding Rate of a Wolf SpiderPardosa prativaga

Groups of large juvenile wolf spiders ( Pardosa prativaga) were kept on constant Drosophila melanogaster rations of 0 (starvation), 1, 2, 3.5, 7, 14 or 28 flies per week, or ad libitum feeding. After 3–4 weeks, they were sacrificed and the activities of three biomarker enzyme systems — glutathione S-transferase (GST) with chlorodinitrobenzene as substrate, glutathione peroxidase with H2O2as substrate (GSH-Px[H2O2]), or glutathione peroxidase with t-butyl-hydroperoxide as substrate (GSH-Px[TBH]) — were assayed. Two systems (GST and GSH-Px[H2O2]) showed decreasing enzyme activity with increasing feeding rate, whereas the variation in GSH-Px(TBH) was independent of feeding rate. Sex and body weight had no influence on enzyme activity.

Synaptic immunolocalization of glyoxylate-complex molecules in the striate areas of the rat cerebral cortex: light and electron microscopic studies

The location of glyoxylate-complex molecules has been investigated in several areas of the rat cerebral cortex using the immunohistochemical peroxidase-antiperoxidase (PAP) method. Antibodies against glyoxylate-complex molecules have been developed in the rabbit after immunization with a glyoxylate-bovine serum albumin conjugate. Observations carried out with the light microscope demonstrated positive immunostaining at the membrane level of scattered neurons located in all cortical areas, mainly in cortical layer IV. The striate areas (17, 18, 18a) had both the greatest number of immunopositive neurons and the most intense ones. At the electron microscopic level, it was observed that in the striate areas an immunopositive reaction was located mainly in the periphery of synaptic vesicles of some nerve endings, and in both pre- and postsynaptic membranes of these synaptic structures. The presence of glyoxylic acid and glyoxylate-complex molecules in such areas leads us to suggest that these substances could play an important role in selected synaptic contacts in which some pyramidal and non-pyramidal neurons are involved.

Mitochondrial, but not peroxisomal, beta-oxidation of fatty acids is conserved in coenzyme A-deficient rat liver

Hepatic coenzyme A (CoA) plays an important role in cellular lipid metabolism. Because mitochondria and peroxisomes represent the two major subcellular sites of lipid metabolism, the present study was designed to investigate the specific impact of hepatic CoA deficiency on peroxisomal as well as mitochondrial beta-oxidation of fatty acids. CoA deficiency (47% decrease in free CoA and 23% decrease in total CoA) was produced by maintaining weanling male Sprague-Dawley rats on a semipurified diet deficient in pantothenic acid (the precursor of CoA) for 5 weeks. Hepatic mitochondrial fatty acid oxidation of short-chain and long-chain fatty acids were not significantly different between control and CoA-deficient rats. Conversely, peroxisomal beta-oxidation was significantly diminished (38% inhibition) in livers of CoA-deficient rats compared to control animals. Peroxisomal beta-oxidation was restored to normal levels when hepatic CoA was replenished. It is postulated that since the role of hepatic mitochondrial beta-oxidation is energy production while peroxisomal beta-oxidation acts mainly as a detoxification system, the mitochondrial pathway of beta-oxidation is spared at the expense of the peroxisomal pathway when liver CoA plummets. The present study may offer an animal model to investigate mechanisms involved in peroxisomal diseases.

The dihydroxyacetonephosphate pathway for biosynthesis of ether lipids in Leishmania mexicana promastigotes

Biosynthetic studies using both [14C]- and [32P]-labelled substrates and a cell-free system to synthesise 1-O-alkyl moieties in glycerolipids, have shown that the three initial steps in ether-lipid biosynthesis in Leishmania mexicana promastigotes resemble those described for mammals and are associated with glycosomes. Purified glycosomes were able to sequentially synthesise the first intermediates of the ether-lipid biosynthetic pathway [acyl-dihydroxyacetonephosphate (DHAP), alkyl-DHAP and acyl/alkyl-glycerol-3-phosphate (G3P)] when incubated in the presence of radiolabelled DHAP, palmitoyl-CoA, hexadecanol and NADPH. However, when glycosomes were incubated under the same conditions in the presence of radiolabelled G3P, a rapid synthesis of acyl-G3P and phosphatidic acid was observed without any formation of alkyl-G3P, suggesting that the enzyme alkyl-synthase recognises only acyl-DHAP as substrate. Both the DHAP acyltransferase (DHAP-AT) and alkyl-DHAP synthase activities were located inside glycosomes whereas the alkyl/acyl-DHAP oxidoreductase activity was associated with the cytoplasmic face of the glycosomal membrane. The G3P acyltransferase (G3P-AT) and lyso-phosphatidic acid acyltransferase activities were not found inside glycosomes. The results suggest that the DHAP-AT and G3P-AT activities are catalysed by two distinct enzymes associated with different sub-cellular compartments.

Regulation of the biosynthesis of 4,7,10,13,16-docosapentaenoic acid

It is now established that fatty acid 7,10,13,16-22:4 is metabolized into 4,7,10,13,16-22:5 as follows: 7,10,13,16-22:4-->9,12,15, 18-24:4-->6,9,12,15,18-24:5-->4,7,10,13,16-22:5. Neither C24 fatty acid was esterified to 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC) by microsomes, whereas the rates of esterification of 4, 7,10,13,16-22:5, 7,10,13,16-22:4 and 5,8,11,14-20:4 were respectively 135, 18 and 160 nmol/min per mg of microsomal protein. About four times as much acid-soluble radioactivity was produced when peroxisomes were incubated with [3-14C]9,12,15,18-24:4 compared with 6,9,12,15,18-24:5. Only [1-14C]7,10,13,16-22:4 accumulated when [3-14C]9,12,15,18-24:4 was the substrate, but both 4,7,10,13,16-22:5 and 2-trans-4,7,10,13,16-22:6 were produced from [3-14C]6,9,12,15, 18-24:5. When the two C24 fatty acids were incubated with peroxisomes, microsomes and 1-acyl-GPC there was a decrease in the production of acid-soluble radioactivity from [3-14C]6,9,12,15, 18-24:5, but not from [3-14C]9,12,15,18-24:4. The preferential fate of [1-14C]4,7,10,13,16-22:5, when it was produced, was to move out of peroxisomes for esterification into the acceptor, whereas only small amounts of 7,10,13,16-22:4 were esterified. By using 2H-labelled 9,12,15,18-24:4 it was shown that, when 7,10,13,16-22:4 was produced, its primary metabolic fate was degradation to yield esterified arachidonate. Collectively, the results show that an inverse relationship exists between rates of peroxisomal beta-oxidation and of esterification into 1-acyl-GPC by microsomes. Most importantly, when a fatty acid is produced with its first double bond at position 4, it preferentially moves out of peroxisomes for esterification to 1-acyl-GPC by microsomes, rather than being degraded further via a cycle of beta-oxidation that requires NADPH-dependent 2,4-dienoyl-CoA reductase.

Evidence that multifunctional protein 2, and not multifunctional protein 1, is involved in the peroxisomal beta-oxidation of pristanic acid

The second (enoyl-CoA hydratase) and third (3-hydroxyacyl-CoA dehydrogenase) steps of peroxisomal beta-oxidation are catalysed by two separate multifunctional proteins (MFPs), MFP-1 being involved in the degradation of straight-chain fatty acids and MFP-2 in the beta-oxidation of the side chain of cholesterol (bile acid synthesis). In the present study we determined which of the two MFPs is involved in the peroxisomal degradation of pristanic acid by using the synthetic analogue 2-methylpalmitic acid. The four stereoisomers of 3-hydroxy-2-methylpalmitoyl-CoA were separated by gas chromatography after hydrolysis, methylation and derivatization of the hydroxy group with (S)-2-phenylpropionic acid, and the stereoisomers were designated I-IV according to their order of elution from the column. Purified MFP-1 dehydrated stereoisomer IV but dehydrogenated stereoisomer III, so by itself MFP-1 is not capable of converting a branched enoyl-CoA into a 3-ketoacyl-CoA. In contrast, MFP-2 dehydrated and dehydrogenated the same stereoisomer (II), so it is highly probable that MFP-2 is involved in the peroxisomal degradation of branched fatty acids and that stereoisomer II is the physiological intermediate in branched fatty acid oxidation. By analogy with the results obtained with the four stereoisomers of the bile acid intermediate varanoyl-CoA, stereoisomer II can be assigned the 3R-hydroxy, 2R-methyl configuration.

Metabolism of dolichol, dolichoic acid and nordolichoic acid in cultured cells

The uptake and metabolism of [1-(14)C]-labelled dolichol, dolichoic acid and nordolichoic acid were investigated in MDCK and HepG2 cells. Each of the three isoprenoids, bound to human serum albumin, was taken up effectively. None of the compounds was broken down in HepG2 cells, although these converted dolichol into fatty acid esters. In MDCK cells dolichoic acid gave rise to the formation of [14C]CO2 and radiolabelled formic acid, indicating that dolichoic acid can be broken down by alpha-oxidation. Dolichoic acid was also converted to a mixture of polar compounds, possibly polyols. MDCK cells generated radiolabelled CO2 from nordolichoic acid, presumably through beta-oxidation, although we could not find any labelled propionic acid. No oxidative breakdown of dolichol was found, apparently due to the lack of or very low conversion to dolichoic acid.

2-methylacyl racemase: a coupled assay based on the use of pristanoyl-CoA oxidase/peroxidase and reinvestigation of its subcellular distribution in rat and human liver

Because of the 2S-methyl-stereospecificity of the acyl-CoA oxidases acting on the CoA esters of 2-methyl-branched fatty carboxylates such as pristanic acid and the side chain of trihydroxycoprostanic acid (Van Veldhoven P.P., Croes K., Asselberghs S., Herdewijn P. and Mannaerts G.P. (1996) FEBS Lett. 388, 80-84), naturally occurring 2R-pristanic acid and 25R- (corresponding to 2R in the side chain) trihydroxycoprostanic acid, after activation to their CoA-esters, need to be racemized to the S-isomers before they can be degraded by peroxisomal beta-oxidation. A coupled assay to measure 2-methyl-acyl racemases was developed by using purified rat pristanoyl-CoA oxidase. Upon incubation of rat and human liver homogenates with 2R-methyl-pentadecanoyl-CoA, the formed 2S-methyl isomer was desaturated by an excess of added oxidase and the concomitant production of hydrogen peroxide was monitored by means of peroxidase in the presence of a suitable hydrogen donor. Application of this assay to subcellular fractions of rat liver revealed the presence of racemase activity not only in mitochondria, as described by Schmitz W., Albers C., Fingerhut R. and Conzelmann E. (Eur. J. Biochem. (1995) 231, 815-822), but also in peroxisomes and cytosol. A similar distribution was seen in human liver. In rat the highest activities were found in liver, followed by Harderian gland, kidney and intestinal mucosa.

The human peroxisomal multifunctional protein involved in bile acid synthesis: activity measurement, deficiency in Zellweger syndrome and chromosome mapping

The dehydrogenation of 24R,25R-varanoyl-CoA, the physiological intermediate formed during the peroxisomal breakdown of the bile acid intermediate trihydroxycoprostanic acid, was studied in human liver. The reaction appeared to be catalyzed by two different enzymes. A first one, present in the cytosol, did not discriminate between the four possible varanoyl-CoA isomers and did not require the CoA moiety. The second enzymic activity was associated with peroxisomes and acted only on the 24R,25R-isomer, in which the 24-hydroxy group possesses the D-configuration. The D-specific dehydrogenase is part of a 79 kDa protein which represents the human counterpart of a recently discovered second multifunctional protein in rat liver peroxisomes, named multifunctional protein 2 (MFP-2). Human MFP-2, like its rat counterpart, is also responsible for the formation (by hydratation) of 24R,25R-varanoyl-CoA. A deficiency of MFP-2 in Zellweger liver could be demonstrated immunologically by using antibodies against the rat enzyme and enzymically -- after removal of the cytosol -- by using 24R,25R-varanoyl-CoA. The gene coding for MFP-2 was mapped to chromosome 5q2.3.

A fibroblast cell line defective in alkyl-dihydroxyacetone phosphate synthase: a novel defect in plasmalogen biosynthesis

Using fluorescence-activated cytotoxicity selection, followed by colony autoradiographic screening of the surviving population, we have isolated a unique plasmalogen-deficient Chinese hamster ovary (CHO) cell line. The mutant, NZel-1, showed a dramatic (90%) reduction in the rate of biosynthesis and levels of plasmalogens, as determined using short- and long-term labeling with 32Pi. Enzymatic assays and lipid supplementation studies showed that NZel-1 was defective in a single step in the biosynthetic pathway for plasmalogens. This step, catalyzed by the peroxisomal enzyme, alkyl-dihydroxyacetone phosphate (DHAP) synthase, is responsible for the introduction of the ether bond found in plasmalogens. The activity of alkyl-DHAP synthase was reduced in whole-cell homogenates from NZel-1 to 18% of wild-type values. Unlike previously described plasmalogen-deficient mutants, NZel-1 contained peroxisomes, as confirmed by immunofluorescence microscopy and catalase release by digitonin. Peroxisomal functions, including the breakdown of very long-chain (>20 carbons) fatty acids, phytanic acid oxidation, and the acylation of DHAP, were normal. Cell fusion studies revealed that the mutation is recessive and belongs to a new complementation group. To our knowledge this is the first report describing the isolation and characterization of a mutant CHO cell line defective in plasmalogen biosynthesis which contains intact, functional peroxisomes. These cells will allow us to examine the role of ether lipids in cellular functions without complications associated with peroxisome deficiency.

Biosynthesis of docosahexaenoic acid in trout hepatocytes proceeds via 24-carbon intermediates

The role of 24:5n-3 and 24:6n-3 as intermediate in the formation of 22:6n-3 in trout liver was examined. Microsomes prepared from trout liver converted [1-14C]-eicosapentaenoic acid (20:5n-3) to 24: 5n-3 and 24:6n-3 but not docosahexaenoic acid (22:6n-3). The radiolabeled 24:5n-3 and 24:6n-3 were isolated from the microsomal incubations by argentation chromatography and used as substrates in incubations with hepatocytes isolated from trout liver. Both 14C-labelled 24:6n-3 and 22:6n-3-were produced by hepatocytes incubated with radiolabelled 24:5n-3. When hepatocytes were incubated with radiolabelled 24:6n-3, the amount of radioactivity recovered in 22:6n-3 over 6 hr increased in direct relation to the decrease observed in the amount of radioactivity recovered in 24:6n-3. The results suggest that the formation of 22:6n-3 in trout liver does not involve delta 4 desaturation of 22:5n-3 but rather proceeds via the delta 6 desaturation of 24:5n-3 with the subsequent chain shortening of the 24:6n-3 produced.