Clofibrate elevates enzyme activities of the tricarboxylic acid cycle in rat liver

Effects of clofibrate and KH176 on life span and motor function in mitochondrial complex I-deficient mice

Mitochondrial complex I (CI), the first multiprotein enzyme complex of the OXPHOS system, executes a major role in cellular ATP generation. Consequently, dysfunction of this complex has been linked to inherited metabolic disorders, including Leigh disease (LD), an often fatal disease in early life. Development of clinical effective treatments for LD remains challenging due to the complex pathophysiological nature. Treatment with the peroxisome proliferation-activated receptor (PPAR) agonist bezafibrate improved disease phenotype in several mitochondrial disease mouse models mediated via enhanced mitochondrial biogenesis and fatty acid β-oxidation. However, the therapeutic potential of this mixed PPAR (α, δ/β, γ) agonist is severely hampered by hepatotoxicity, which is possibly caused by activation of PPARγ. Here, we aimed to investigate the effects of the PPARα-specific fibrate clofibrate in mitochondrial CI-deficient (Ndufs4^-/-) mice. Clofibrate increased lifespan and motor function of Ndufs4^-/- mice, while only marginal hepatotoxic effects were observed. Due to the complex clinical and cellular phenotype of CI-deficiency, we also aimed to investigate the therapeutic potential of clofibrate combined with the redox modulator KH176. As described previously, single treatment with KH176 was beneficial, however, combining clofibrate with KH176 did not result in an additive effect on disease phenotype in Ndufs4^-/- mice. Overall, both drugs have promising, but independent and nonadditive, properties for the pharmacological treatment of CI-deficiency-related mitochondrial diseases.

Role of hypolipidemic drug clofibrate in altering iron regulatory proteins IRP1 and IRP2 activities and hepatic iron metabolism in rats fed a low-iron diet

In addition to reducing the expression of transferrin and ceruloplasmin genes, hypolipidemic peroxisome proliferators may alter iron homeostasis in the liver. Therefore, this study investigates the effects of clofibrate on proteins related to liver iron metabolism in a rat model using a 2 x 2 experimental design: two dose levels of clofibrate in diet (0 and 0.5%) and two dietary iron levels (35 ppm as normal level and 15 ppm as low-iron diet). Twenty-four Wistar rats were assigned to the four diets and fed for 6 weeks. Subsequent measurements of iron parameters in the blood and the liver indicated that, in addition to mild anemia and the reduction in serum iron and total iron-binding capacity, clofibrate treatment altered IRP1 and IRP2 activities differentially and increased mitochondrial aconitase both at activity and protein levels. At both normal and low-iron intakes, clofibrate caused a 50% reduction in serum iron and TIBC with a corresponding reduction in transferrin mRNA. The RNA-binding activities of IRP1 were selectively activated by clofibrate treatment even though liver iron concentration was not depleted. The RNA-binding activity of IRP2 was selectively activated by the low iron intake and correlated with an increase of transferrin receptor mRNA, while clofibrate treatment offset the effects of the low iron intake.

Peroxisome proliferators differentially regulate long-chain acyl-CoA thioesterases in rat liver

We have investigated the effects of peroxisome proliferators on rat liver long-chain acyl-CoA thioesterase activities. Subcellular fractionations of liver homogenates from control, clofibrate- and di(2-ethylhexyl)phthalate-treated rats confirmed earlier studies which demonstrated that peroxisome-proliferating drugs induce long-chain acyl-CoA thioesterase activity mainly in the mitochondrial and cytosolic fractions. The aim of the present study was to investigate whether the induced activities were due to increases in normally expressed enzymes, or due to induction of novel enzymes. To investigate whether structurally different peroxisome proliferators differentially induced thioesterase activities, we tested the effects of di(2-ethylhexyl)phthalate (a plastisizer) and the hypolipidemic drug clofibrate. For this purpose, we established an analytical size exclusion chromatography method. Chromatography of solubilised mitochondrial matrix proteins showed that the activity in control mitochondria was mainly due to enzymes with molecular masses of about 50 kDa and 35 kDa. The activity in samples prepared from clofibrate- and di(2-ethylhexyl)phthalate-treated rats eluted as proteins of about 40 kDa and 110 kDa. Highly purified peroxisomes contained two peaks of activity, which were not induced, that corresponded to molecular masses of 40 kDa and 80 kDa. The 80-kDa peak was shown to be due to dimerization by addition of glycerol. Chromatography of cytosolic fractions from control rat livers indicated the presence of long-chain acyl-CoA thioesterases with molecular masses of approximately 35 kDa and 125 kDa and a broad peak corresponding to a high-molecular-mass protein. The activity in cytosolic fractions from peroxisome-proliferator-treated rats eluted mainly as peaks corresponding to 40, 110 and 150 kDa. In addition, in the 110-kDa peak, a different degree of induction and different chain-length specificities were caused by clofibrate and di(2-ethylhexyl)phthalate, suggesting that these peroxisome proliferators differentially regulate the cytosolic acyl-CoA thioesterase activities. Western blot analysis showed that enzymes in the 40-kDa peak of the peroxisomal and cytosolic fractions were structurally related, but not identical, to a 40-kDa mitochondrial very-long-chain acyl-CoA thioesterase. Our data show that the increased acyl-CoA thioesterase activities in mitochondria and cytosol were mainly due to induction of acyl-CoA thioesterases which are not, or only weakly, expressed under normal conditions.

Effects of hypolipidaemics cetaben and clofibrate on mitochondrial and peroxisomal enzymes of rat liver

Clofibrate or cetaben was administered to male rats for 10 days. Peroxisomal and mitochondrial enzymes were assayed in liver subcellular fractions. Clofibrate affected the specific activities of both mitochondrial enzymes (glycerol-3-phosphate dehydrogenase and nicotinamide-linked isocitrate dehydrogenase) and peroxisomal enzymes (fatty acyl-CoA oxidase, glycerone phosphate acyltransferase, urate oxidase, and D-amino-acid oxidase). In contrast, cetaben raised only the peroxisomal enzymes, acyl-CoA oxidase, glycerone-phosphate acyltransferase, D-amino-acid oxidase, catalase, and urate oxidase. Thus, the hypolipidaemic activity of these drugs may be exclusively related to stimulated peroxisomal functioning, while mitochondria play only a minor role.