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Abstract: Peroxisomes play an important role in bile acid biosynthesis because the last steps of the synthesis pathway are performed by the β-oxidation system located inside peroxisomes. As a consequence, C27-bile acid intermediates accumulate in several peroxisomal disorders. It has been suggested that C27-bile acids are especially toxic and contribute to the liver disease associated with peroxisomal disorders. For this reason, we investigated the toxicity of C27-bile acids and the underlying mechanisms. We studied the effects of conjugated and unconjugated C27-bile acids on cell viability, mitochondrial respiratory chain function and production of oxygen radicals in the rat hepatoma cell line McA-RH7777. Cell viability decreased progressively after incubation with increasing concentrations of different bile acids with dihydroxycholestanoic acid (DHCA) being clearly the most cytotoxic bile acid. In addition, the different bile acids caused a dose-dependent decrease in ATP synthesis by isolated mitochondria oxidizing malate and glutamate. Finally, there was a dose-dependent stimulation of ROS generation in the presence of C27-bile acids. In conclusion, our studies showed that C27-bile acids are more cytotoxic than mature C24-bile acids. In addition, C27-bile acids are potent inhibitors of oxidative phosphorylation and enhance mitochondrial ROS production by inhibiting the respiratory chain. [Copyright &y& Elsevier]

Abstract: Isoprenoids constitute an important class of biomolecules that participate in many different cellular processes. Most available detection methods allow the identification of only one or two specific nonsterol isoprenoid intermediates following radioactive or fluorescent labeling. We here report a rapid, nonradioactive, and sensitive procedure for the simultaneous detection and quantification of the eight main nonsterol intermediates of the isoprenoid biosynthesis pathway by means of tandem mass spectrometry. Intermediates were analyzed by HPLC–MS/MS in the multiple reaction monitoring mode using a silica-based C18 HPLC column. For quantification, their stable isotope-labeled analogs were used as internal standards. HepG2 cells were used to validate the method. Mevalonate, phosphomevalonate, and the six subsequent isoprenoid pyrophosphates were readily determined with detection limits ranging from 0.03 to 1.0μmol/L. The intra- and interassay variations for HepG2 cell homogenates supplemented with isoprenoid intermediates were 3.6–10.9 and 4.4–11.9%, respectively. Under normal culturing conditions, isoprenoid intermediates in HepG2 cells were below detection limits. However, incubation of the cells with pamidronate, an inhibitor of farnesyl pyrophosphate synthase, resulted in increased levels of mevalonate, isopentenyl pyrophosphate/dimethylallyl pyrophosphate, and geranyl pyrophosphate. This method will be suitable for measuring profiles of isoprenoid intermediates in cells with compromised isoprenoid biosynthesis and for determining the specificity of potential inhibitors of the pathway. [Copyright &y& Elsevier]

Abstract: X-linked adrenoleukodystrophy (X-ALD) is a progressive neurodegenerative disorder characterized by the accumulation of saturated and mono-unsaturated very long-chain fatty acids (VLCFA) and reduced peroxisomal VLCFA β-oxidation activity. In this study, we investigated the role of VLCFA biosynthesis in X-ALD fibroblasts. Our data demonstrate that elongation of both saturated and mono-unsaturated VLCFAs is enhanced in fibroblasts from patients with peroxisomal β-oxidation defects including X-ALD, and peroxisome biogenesis disorders. These data indicate that enhanced VLCFA elongation is a general phenomenon associated with an impairment in peroxisomal β-oxidation, and not specific for X-ALD alone. Analysis of plasma samples from patients with X-ALD and different peroxisomal β-oxidation deficiencies revealed increased concentrations of VLCFAs up to 32 carbons. We infer that enhanced elongation does not result from impaired peroxisomal β-oxidation alone, but is due to the additional effect of unchecked chain elongation. We demonstrate that elongated VLCFAs are incorporated into complex lipids. The role of chain elongation was also studied retrospectively in samples from patients with X-ALD previously treated with “Lorenzo’s oil.” We found that the decrease in plasma C26:0 previously found is offset by the increase of mono-unsaturated VLCFAs, not measured previously during the trial. We conclude that evaluation of treatment protocols for disorders of peroxisomal β-oxidation making use of plasma samples should include the measurement of saturated and unsaturated VLCFAs of chain lengths above 26 carbon atoms. We also conclude that chain elongation offers an interesting target to be studied as a possible mode of treatment for X-ALD and other peroxisomal β-oxidation disorders. [Copyright &y& Elsevier]

Peroxisome biogenesis disorders (PBDs) and D-bifunctional protein (D-BP) deficiency are two types of inherited peroxisomal disorders. Patients with a PBD lack functional peroxisomes and patients with D-BP deficiency lack the enzyme, which is responsible for the second and third step of the peroxisomal β-oxidation. The clinical presentation of these peroxisomal disorders is severe and includes several neurological abnormalities. The pathological mechanisms underlying these disorders are not understood and no therapies are available. Because peroxisomes have been associated with oxidative stress, as oxygen radicals are both produced and scavenged in peroxisomes, we have investigated whether oxidative stress is involved in the pathogenesis of PBDs and D-BP deficiency. We found in D-BP-deficient patients increased levels of thiobarbituric acid-reactive substances (TBARS) and 8-hydroxydeoxyguanosine (8-OHdG), which are markers for lipid peroxidation and oxidative DNA damage, respectively, whereas the levels of the lipophilic antioxidants α-tocopherol and coenzyme Q10 were decreased. In addition, we found in skin fibroblasts from D-BP-deficient patients an imbalance between the activities of the peroxisomal H2O2-generating straight-chain acyl-CoA oxidase (SCOX) and the peroxisomal H2O2-degrading enzyme catalase. In conclusion, we have found clear evidence for the presence of increased oxidative stress in patients with D-BP deficiency, but not in patients with a PBD. [Copyright &y& Elsevier]