Effects of clofibric acid and tiadenol on cytosolic long-chain acyl-CoA hydrolase and peroxisomal β-oxidation in liver and extrahepatic tissues of rats

Inducing effect of clofibric acid on stearoyl-CoA desaturase in intestinal mucosa of rats

Fibrates have been reported to elevate the hepatic proportion of oleic acid (18:1n-9) through inducing stearoyl-CoA desaturase (SCD). Despite abundant studies on the regulation of SCD in the liver, little is known about this issue in the small intestine. The present study aimed to investigate the effect of clofibric acid on the fatty acid profile, particularly monounsaturated fatty acids (MUFA), and the SCD expression in intestinal mucosa. Treatment of rats with a diet containing 0.5% (w/w) clofibric acid for 7 days changed the MUFA profile of total lipids in intestinal mucosa; the proportion of 18:1n-9 was significantly increased, whereas those of palmitoleic (16:1n-7) and cis-vaccenic (18:1n-7) acids were not changed. Upon the treatment with clofibric acid, SCD was induced and the gene expression of SCD1, SCD2, and fatty acid elongase (Elovl) 6 was up-regulated, but that of Elovl5 was unaffected. Fat-free diet feeding for 28 days increased the proportions of 16:1n-7 and 18:1n-7, but did not effectively change that of 18:1n-9, in intestinal mucosa. Fat-free diet feeding up-regulated the gene expression of SCD1, but not that of SCD2, Elovl6, or Elovl5. These results indicate that intestinal mucosa significantly changes its MUFA profile in response to challenges by clofibric acid and a fat-free diet and suggest that up-regulation of the gene expression of SCD along with Elovl6 is indispensable to elevate the proportion of 18:1n-9 in intestinal mucosa.

Sterol Regulatory Element-Binding Protein-2 modulates human brain acyl-CoA hydrolase gene transcription

The brain shows high catalyzing activity during hydrolysis of long-chain acyl-CoAs into fatty acids and CoA-SH. Brain acyl-CoA hydrolase (BACH) is responsible for most of the long-chain acyl-CoA hydrolyzing activity in the brain and is localized exclusively in neurons. We analyzed the human BACH gene promoter, focusing on transcriptional regulation by Sterol Regulatory Element-Binding Protein-2 (SREBP-2), which is a transcription factor that activates genes involved in cholesterol biosynthesis and uptake. When the nuclear form of SREBP-2 gene was transfected into human neuroblastoma cells, transcription of a BACH gene promoter-luciferase reporter gene was activated through a sterol regulatory element (SRE) motif. Moreover, a gel shift assay demonstrated that SREBP-2 specifically bound to the SRE motif. These results suggest that transcription of the BACH gene is activated by SREBP-2. This study also provides insights into BACH function in the interaction between the metabolism of acyl-CoAs and cholesterol in neurons.

Localization of a long-chain acyl-CoA hydrolase in spermatogenic cells in mice

Brain acyl-CoA hydrolase (BACH) hydrolyzes long-chain acyl-CoAs to free fatty acids and CoA-SH. BACH is highly distributed in brain and is localized in neurons, but not glial cells. This suggests that BACH plays a specific role in neurons. BACH is also detected in testis, although the expression profile of BACH is unknown in testis. In this study, developmental changes and cellular distribution of BACH were examined in mouse testis. Before postnatal day (P) 10, BACH was detected at very low levels by Western blotting. Then, BACH content rapidly increased from P14 and reached maximum levels at P21, remaining high until at least P70. The increase in BACH content corresponded to the appearance of pachytene spermatocytes, which was confirmed by immunohistochemistry. BACH was also detectable in spermatids, but not in spermatogonia, mature spermatozoa. These results suggest that BACH is expressed in a cell-specific manner and plays a role in spermatogenesis.

Characterization of mouse homolog of brain acyl-CoA hydrolase: molecular cloning and neuronal localization

Acyl-CoA hydrolase could provide a mechanism via its potency to modulate cellular concentrations of acyl-CoAs for the regulation of various cellular events including fatty acid metabolism and gene expression. However, only limited evidence of this is available. To better understand the physiological role of this enzyme, we characterized a mouse brain acyl-CoA hydrolase, mBACH. The cloned cDNA for mBACH encoded a 338-amino-acid polypeptide with >95% identity to the human and rat homologs, indicating that the BACH gene is highly conserved among species. This was supported by the similarity in genomic organization of the BACH gene between humans and mice. Bacterially expressed mBACH was highly active against long-chain acyl-CoAs with a relatively broad specificity for chain length. While palmitoyl-CoA hydrolase activity was widely distributed in mouse tissues, it was marked in the brain, consistent with mBACH being almost exclusively distributed in this tissue, where >80% of the enzyme activity was explained by mBACH present in the cytosol. Immunohistochemistry demonstrated a neuronal localization of mBACH in both the central and peripheral nervous systems. In neurons, mBACH was distributed throughout the cell body and neurites. Although four isoforms except mBACH itself, that may be generated by the alternative use of exons of a single mBACH gene, were cloned, their mRNA levels in the brain were estimated to be negligible. However, a 50-kDa polypeptide besides the major one of 43-kDa seemed to be translated from the mBACH mRNA with differential in-frame ATG triplets used as the initiation codon. These findings will contribute to the functional analysis of the BACH gene using mice including genetic studies.

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.

Cloning and regulation of peroxisome proliferator-induced acyl-CoA thioesterases from mouse liver

1.1. Acyl-CoA thioesterases hydrolyze acyl-CoAs to the corresponding free fatty acid plus CoASH. The activity is strongly induced in rat and mouse liver after feeding the animals peroxisome proliferators. To elucidate the role of these enzymes in lipid metabolism, we have cloned the cDNAs corresponding to the inducible cytosolic and mitochondrial type I enzymes (CTE-I and MTE-I) and studied tissue expression and nutritional regulation of expression of the mRNAs in mice. The constitutive expression of both mRNAs was low in liver, with CTE-I being expressed mainly in kidney and brown adipose tissue and MTE-I expressed in brown adipose tissue and heart. As expected, the expression in liver of both the CTE-I and MTE-I mRNAs was strongly induced (> 50-fold) by treatment with clofibrate. A similar level of induction was observed by fasting and a time-course study showed that both mRNAs were increased already at 6 hours after removal of the diet. Refeeding normal chow diet to mice fasted for 24 hours normalized the mRNA levels with a T1/2 of about 3-4 hours. Feeding mice a fat-free diet further decreased the expression, possibly indicating repression of expression. The strong expression of MTE-I and CTE-I in the heart was increased about 10-fold by fasting. To further characterize these highly regulated enzymes, we have cloned the corresponding genes and promoter regions. The structures of the two genes were found to be very similar, consisting of three exons and two introns. Exon-intron borders conform to general consensus sequences and especially the first exon appears to be highly conserved. The promoter regions of both the CTE-I and MTE-I genes contain putative peroxisome proliferator response elements (PPREs), suggesting an involvement of peroxisome proliferator-activated receptors in the regulation of these genes.

Trans-vaccenic acid is desaturated to conjugated linoleic acid in mice

Mice were fed pure trans11 octadecenoic acid (trans-vaccenic acid; TVA) to determine whether it is desaturated to cis9, trans11 octadecadienoic acid, a predominant isomer of conjugated linoleic acid (CLA). In a preliminary trial, 12% of the TVA consumed during a 2-wk feeding period was recovered in the carcass as CLA. As a proportion of TVA in the tissues available for bioconversion, 48.8% was desaturated. We tested whether desaturation could be modified by supplementing no modifier, 0.5% clofibric acid to stimulate desaturation, or increasing the polyunsaturated fatty acids (PUFA) (10% corn oil vs. 4% corn oil) to inhibit desaturation in diets with or without 1% TVA. These diets were fed to six groups of mice in a 3x2 factorial arrangement of treatments. Feeding 1% TVA with 10% corn oil decreased feed intake (2.70 vs. 3.73 g/d, SEM 0.23; P<0.05). Bioconversion of dietary TVA was 12.0, 7.5 and 5.1% for mice fed no modifier of desaturation, clofibrate and increased PUFA, respectively. Conversion based on TVA available for desaturation was 52.6, 55.5 and 37.0%, respectively. Thus, clofibrate did not increase bioconversion, but increasing PUFA decreased conversion by 30%. To test whether TVA decreases food intake directly or after conversion to CLA, four groups of mice were fed diets containing 1% stearic, TVA, elaidic or conjugated linoleic acid. Dietary CLA decreased food intake and body fat, but did not change body protein. CLA was found in the carcass only when TVA or CLA was fed. CLA was found in both triacylglycerol and phospholipids when CLA was fed, but only in triacylglycerol when TVA was fed, suggesting that bioconversion occurred in the adipose tissue. In three trials, conversion of dietary TVA to CLA was 11.4+/-1.25%; conversion of stored TVA was 50.8+/-1.91%. Similar bioconversion of TVA in humans would increase current estimates of CLA available for the general population by 6- to 10-fold.

Hepatocarcinogenic potential of di(2-ethylhexyl)phthalate in rodents and its implications on human risk

The plasticizer di(2-ethylhexyl) phthalate (DEHP), to which humans are extensively exposed, was found to be hepatocarcinogenic in rats and mice. DEHP is potentially set free from objects made of synthetic materials (e.g., those used in medicine). Chronically, the greatest amounts are transferred to persons undergoing hemodialysis (up to 3.1 mg/kg b.w. per day) who would thus be considered the individuals most endangered by tumorigenesis. Although toxicokinetics seem to play a certain unclear role in the course of DEHP-related toxicity, toxicodynamic factors appear more decisive. DEHP is a representative of "peroxisome proliferators" (PP), a distinct group of substances that, in rodents, do not only induce peroxisomes but also specific enzymes in other organelles, organ growth, and DNA synthesis. The cluster of the characteristic effects of PP is generally, although perhaps not quite appropriately summarized as "peroxisome proliferation," and is strongest in the liver. The lowest observed effect level (LOEL) and the no observed effect level (NOEL) of peroxisome proliferation in the rat, as determined by the induction of specific enzymes (peroxisomal beta-oxidation, carnitine-acetyl-transferase, cytochrome P-452), DNA synthesis, and hepatomegaly, may be assumed as 50 and 25 mg/kg b.w. per day, respectively. DEHP and other carcinogenic PP are neither genotoxic nor tumor initiators, but they appear to be tumor promoters, also implicating a threshold level for the carcinogenic effect. Although a causal relationship between a particular effect of peroxisome proliferation and hepatocarcinogenesis is as yet unknown, peroxisome proliferation as a whole phenomenon appears to be associated with the potential of tumor induction, as shown by comparison of the relative strength of individual PP and by comparison of species and organ specificities. Likewise, LOEL and NOEL of rodent carcinogenesis, that is, 300 and 50 to 100 mg/kg b.w. per day, respectively, are above but not too far from the corresponding values for the investigated parameters of peroxisome proliferation. Thus, with respect to dose alone, worst-case exposure in hemodialysis patients is at least 16-fold below the LOEL of any characterized PP-specific effect of DEHP and approximately 100-fold below that of DEHP-related tumorigenesis. Also, primates are less responsive to PP than rats with respect to the investigated biochemical and morphological parameters. If this lower primate responsiveness is extrapolated to estimate carcinogenicity in humans, we might thus arrive at an even larger safety margin than when based on exposure alone. Doses of PP hypolipidemics that had clearly induced several indicators of peroxisome proliferation in rats did not cause any clear-cut enhancements in the peroxisomes of patients, even though most of these hypolipidemics were considerably stronger PP than DEHP. Thus, an actual threat to humans by DEHP seems rather unlikely. Accordingly, hepatocarcinogenesis was neither enhanced in workers exposed to DEHP nor in patients treated with hypolipidemics.

Molecular cloning and expression of cDNA encoding rat brain cytosolic acyl-coenzyme A thioester hydrolase

The cDNA encoding rat brain cytosolic acyl-CoA thioester hydrolase (ACT) has been cloned and sequenced, and the primary structure of the enzyme has been deduced. A partial amino acid sequence (38 amino acids) of the enzyme was determined using the peptides generated after CNBr digestion of the purified enzyme. Primers synthesized on the basis of this information were used to isolate two cDNA clones, each encoding the full length of the enzyme. The nucleotide sequences of these clones contained an open reading frame encoding a 358-amino acid polypeptide with a calculated molecular mass of 39.7 kDa, similar to that determined for the purified enzyme (40.9 kDa). The deduced ACT sequence showed no homology to the known sequences of any other thioesterases nor to any other known protein sequence. However, there was a strong homology to a number of expressed sequence tag human brain cDNA clones. The identity of the ACT cDNA was confirmed by the expression of ACT activity in Escherichia coli. There was a 10-15-fold increase in ACT-specific activity in the bacterial extracts after induction with isopropyl thiogalactoside, and the properties of the expressed enzyme (fusion protein) were the same as those of the purified rat brain ACT. Northern blot analysis showed that a 1.65-kilobase ACT transcript was present in rat brain and testis but not in any other rat tissues examined. However, the ACT mRNA was induced in the liver of rats that were fed Wy-14,643, a peroxisome proliferator and inducer of rodent liver cytosolic acyl-CoA thioesterase. These results indicate that the induced rat liver ACT is homologous to the constitutive rat brain ACT.

The effects of probucol and clofibrate alone and in combination on hepatic cholesterol metabolism in the male rat

Male rats were fed for 10 days on a diet supplemented with either probucol or clofibrate, alone or in combination, and the effects of the drugs on hepatic cholesterol metabolism studied. Plasma triacylglycerols were significantly lowered (15.6%, P < 0.05) by the drugs in combination but not individually whereas plasma cholesterol levels were reduced by probucol alone (22.4%, P < 0.05) and the combined treatment effected a further decrease leading to a total reduction of 50.6% (P < 0.001). Probucol reduced hepatic cellular triacylglycerols (20.0%, P < 0.05) and cholesterol (15.3%, P < 0.05) but cholesteryl esters were unaffected. In combination with clofibrate, probucol accentuated the reductions in both cellular cholesterol and cholesteryl esters produced by clofibrate alone and lowered their levels by 22.8%, P < 0.01 and 38.5%, P < 0.001, respectively. Although probucol, on its own, did not affect the activity of acyl-coenzyme A:cholesterol acyltransferase (ACAT), its combination with clofibrate caused less inhibition (43.5%, P < 0.01) of this enzyme activity than clofibrate alone (65.7%, P < 0.001). Probucol had a similarly moderating effect on the clofibrate-induced reductions in microsomal cholesterol and cholesteryl esters. Neither the microsomal nor the cytosolic neutral cholesteryl ester hydrolase was affected by probucol alone although both enzymes were dramatically increased (between 350% and 550%) by clofibrate and the combined treatment. The activity of the hepatic cytosolic inhibitor of cholesteryl ester hydrolase was unaffected by clofibrate or probucol individually but the two drugs in combination increased the total activity of the inhibitor by 52.1%, P < 0.01. When allowance was made for this increased inhibitor activity, it was clear that probucol accentuated the stimulatory effect of clofibrate on the cytosolic nCEH.

Relationship between plasma lipids and palmitoyl-CoA hydrolase and synthetase activities with peroxisomal proliferation in rats treated with fibrates

1. The time-course of the effect of clofibrate (CFB), bezafibrate (BFB) and gemfibrozil (GFB) on lipid plasma levels and palmitoyl-CoA hydrolase and synthetase activities, as well as the correlations with the peroxisomal proliferation phenomenon have been studied in male Sprague-Dawley rats. 2. The administration of the three drugs caused a significant reduction in body weight gain, accompanied with a paradoxical increase in food intake in groups treated with BFB and GFB. 3. Drug treatment produced gross hepatomegaly and increase in peroxisomal beta-oxidation, and these parameters were strongly correlated. The order of potency was BFB > CFB > or = GFB. 4. Both plasma cholesterol (BFB approximately CFB > GFB) and triglyceride (BFB approximately GFB > CFB) levels were reduced in treated animals. There was an inverse correlation between these parameters and peroxisomal beta-oxidation, although the peroxisomal proliferation seemed to explain only a small part of the hypolipidemic effect observed. 5. Cytosolic and microsomal (but not mitochondrial) palmitoyl-CoA hydrolase activities were increased by the three drugs (BFB > CFB > GFB), probably by inducing the hydrolase I isoform, which is insensitive to inhibition by fibrates in vitro. The increased hydrolase activities were directly and strongly correlated with peroxisomal beta-oxidation. 6. Palmitoyl-CoA synthetase activity was also increased by the treatment with fibrates (BFB > CFB > GFB), probably as a consequence of the enhancement of hydrolase activities. 7. Some of the effects of fibrate treatment can be explained, at least in part, in terms of peroxisomal induction and caution should be exercised in the extrapolation of these results to species, such as man,that are insensitive to peroxisomal proliferation.

Differential inhibition of long-chain acyl-CoA hydrolases by hypolipidemic drugs in vitro

The effect of in vitro addition of three hypolipidemic drugs (clofibric acid, bezafibrate and gemfibrozil) on rat palmitoyl-CoA hydrolases has been studied, by using a spectrophotometric method (Berge RK, Biochim Biophys Acta 574: 321-333, 1979) optimized for valoration of crude enzyme preparations. Mitochondrial and microsomal hepatic palmitoyl-CoA hydrolase activities were inhibited by the three drugs in a concentration-dependent fashion. The order of inhibitory potency was gemfibrozil greater than bezafibrate greater than clofibric acid, irrespective of the enzyme activity tested. Cytosolic rat brain palmitoyl-CoA hydrolase activity was not affected. Kinetic studies with gemfibrozil on the solubilized microsomal palmitoyl-CoA hydrolase activity point to a mixed non-competitive type of inhibition.

Induction by perfluorooctanoic acid of microsomal 1-acylglycerophosphocholine acyltransferase in rat kidney. Sex-related difference

Response of rat kidney to the challenges by perfluorooctanoic acid (PFOA) was studied using microsomal 1-acyglycerophosphocholine (1-acyl-GPC) acyltransferase as a parameter. Marked induction of the enzyme was brought about in kidney of male rats, whereas the induction in kidney of female rats was far less pronounced. The sex-related difference in the response of kidney to PFOA was much more marked than those seen with p-chlorophenoxyisobutyric acid (clofibric acid) or 2,2'-(decamethy-lenedithio)diethanol (tiadenol). Hormonal manipulations revealed that the sex-related difference in the response of kidney to PFOA was strongly dependent on the state of gonadal hormones of rats. Even after a prolonged administration of PFOA for up to 26 weeks, this sex-related difference was still evident. Induction of peroxisomal beta-oxidation was brought about concurrently with microsomal 1-acyl-GPC acyltransferase and a high correlation was confirmed between the inductions of these two parameters.

Enzymes that metabolize acyl-coenzyme A in the monkey--their distribution, properties and roles in an alternative pathway for the excretion of nitrogen

1. In various tissues from the monkey (Macaca fuscata), acyl-coenzyme A (CoA) hydrolase activities were found to be widely distributed within a 2-10 times range and present in liver cytosol having mol. wt of ca 60,000. 2. Acyl-CoA: amino acid N-acyltransferase activity were 4-250 times higher in liver and kidney than in other tissues, even no activity in heart, lung, and plasma. 3. The transferases abounded in liver mitochondria, being distributed evenly between the intracristate space, the inner membrane, and the matrix. 4. The partially purified transferases with benzoyl-CoA or phenylacetyl-CoA as substrates were shown to have mol. wt of ca 30,000 and reacted only with glycine or L-glutamine, respectively. 5. No amino acid tested had any effects on the enzyme as either inhibitors or activators. 6. These results suggest that the enzymes that metabolize acyl-CoA constitute an alternative pathway for the excretion of nitrogen.

The effect of di(ethylhexyl)phthalate on fatty acid oxidation and carnitine palmitoyltransferase in various rat tissues

Male rats were fed a diet with or without 2% di(2-ethylhexyl)phthalate (DEHP) for 12 days. Total and peroxisomal oxidation rates of palmitic and arachidonic acid were increased in homogenates of liver and kidney after DEHP administration. The relative peroxisomal contribution to the total oxidation was only higher in liver. The activities of acyl-CoA oxidase and carnitine palmitoyltransferase were also higher in both tissues. Immunoblots showed that the increase of fatty acid oxidation was associated with a higher concentration of enzymes of peroxisomal and mitochondrial beta-oxidation. DEHP did not change total and peroxisomal fatty acid oxidation and activity of carnitine palmitoyltransferase of homogenates of heart and skeletal muscle. The cause for the tissue-specific response is discussed.

Induction of peroxisomal enzymes in cultured porcine endothelial cells by the hypolipidemic drug ciprofibrate

The purpose of this study was to determine if the hypolipidemic peroxisome proliferator ciprofibrate, which induces peroxisomes in the liver, can induce peroxisomes in cultured porcine pulmonary endothelial cells. Ciprofibrate was added at three concentrations to cell cultures for a 6-day period. The induction of peroxisomes in the cells was detected by determining total peroxisomal beta-oxidation and peroxisomal catalase activity. The addition of ciprofibrate was found to increase peroxisomal enzyme activities in a dose-dependent manner, with the highest activity being reached at 1000 microM ciprofibrate. Ciprofibrate also caused an increased transfer of albumin across endothelial cells cultured on micropore filters. This study shows that peroxisomal enzyme activities can be induced by ciprofibrate in endothelial cells, which may have implications in diseases mediated by vascular injury.

Proliferation of peroxisomes and induction of cytosolic and microsomal epoxide hydrolases in different strains of mice and rats after dietary treatment with clofibrate

1. The effects of dietary clofibrate (0.5%, w/w, for 10 days) on seven inbred strains of mice--C57BL/6, C57BL/B10A(5R), ATL/OLA, C3H/HE/OLA, BALB/C, CBA/CA and A/J/OLA--and three strains of rats--Sprague-Dawley, Wistar and LOU/OLA--have been investigated. Liver weight, peroxisome proliferation, catalase activity, cytosolic, microsomal and mitochondrial epoxide hydrolase activities, cytochrome oxidase activity, microsomal cytochrome P-450 content and cytosolic glutathione transferase activity in liver were determined, together with cytosolic and microsomal epoxide hydrolase and cytosolic glutathione transferase activities in the kidneys. 2. In all cases peroxisome proliferation and induction of cytosolic epoxide hydrolase were observed in livers of rodents exposed to clofibrate. Thus, no non-responsive strains were found and further evidence for a coupling between these two phenomena was provided. In many cases significant increases in the liver microsomal cytochrome P-450 content and decreases in the hepatic cytosolic glutathione transferase activity were also seen. 3. High levels of cytosolic epoxide hydrolase were found in the rat kidney. In several strains of mice and rats renal cytosolic epoxide hydrolase activity was increased by clofibrate. 4. There were often considerable strain differences. However, in general mice had higher cytosolic epoxide hydrolase and glutathione transferase activities, whereas rats had higher microsomal epoxide hydrolase activities.