Induction of a novel long-chain acyl-CoA hydrolase in rat liver by administration of peroxisome proliferators

The activity of long-chain acyl-CoA hydrolase in rat liver was increased by the administration of peroxisome proliferators, such as ethyl p-chlorophenoxyisobutyrate, di(2-ethylhexyl)phthalate or acetylsalicylic acid. The induced activity was mainly confined in the soluble fluid after the subcellular fractionation. The enzyme was purified nearly to homogeneity from livers of rats treated with di(2-ethylhexyl)phthalate. The specific activity of the final preparation was 247 mumol palmitoyl-CoA hydrolyzed min-1 mg protein-1. The molecular weight of the native enzyme was estimated to be 150 000 by gel filtration and that of the subunits was 41 000 by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The activity of the enzyme was not increased but inhibited by bovine serum albumin or Triton X-100. The molecular and catalytic properties of the enzyme suggest that the induced enzyme was different from mitochondrial and microsomal long-chain acyl-CoA hydrolyses in liver.     

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

The effects of two peroxisome proliferators, p-chlorophenoxyisobutyric acid (clofibric acid) and 2,2'-(decamethylenedithio)diethanol (tiadenol), on cytosolic long-chain acyl-CoA hydrolase and peroxisomal beta-oxidation were studied in several organs of rat. Among organs of control rats, the brain had the highest activity of long-chain acyl-CoA hydrolase, followed by testis, and a low activity was found in other tissues. Administration of the peroxisome proliferators caused a marked increase in activity of long-chain acyl-CoA hydrolase in both liver and intestinal mucosa and a slight increase in the activity in kidney, but little affected acyl-CoA hydrolase activity in either brain, testis, heart, spleen and skeletal muscle. In accordance with the change in the activity of acyl-CoA hydrolase, the activity of peroxisomal beta-oxidation was markedly increased in liver, intestinal mucosa and kidney, and a slight increase was found in brain and testis, whereas peroxisome proliferators little affected the activity in other organs tested. Gel filtration of cytosol from intestinal mucosa showed that clofibric acid caused an appearance of a new peak in intestinal mucosa. Although cytosol of liver, intestinal mucosa, brain and testis contained two 4-nitrophenyl acetate esterases with different molecular weights (about 105,000 and about 55,000), these esterases are different from cytosolic long-chain acyl-CoA hydrolases of these four organs in respect of molecular weight. The administration of clofibric acid little affected cytosolic 4-nitrophenyl acetate esterases. Comparative studies on cytosolic long-chain acyl-CoA hydrolases from these four organs showed that liver hydrolase I (molecular weight of about 80,000) had properties similar to those of brain and testis enzymes. On the other hand, intestinal mucosa enzyme was different from either hepatic hydrolase I or II (molecular weight of about 40,000). The results from the present study suggest that inductions of peroxisomal beta-oxidation and cytosolic long-chain acyl-CoA hydrolases are essential responses of rats to peroxisome proliferators not only in liver but also in intestinal mucosa and that induced hydrolases are not attributable to non-specific esterases.     

Effects of experimental hypo- and hyperthyroidism on hepatic long-chain fatty acyl-CoA synthetase and hydrolase

The effects of T3 treatment and thyroidectomy on rat liver microsomal long-chain fatty acyl-CoA (LCFA-CoA) synthetase and LCFA-CoA hydrolase activities were determined. Hyperthyroid rats had a 36-42% decrease in LCFA-CoA synthetase with no change in hydrolase activity. This may contribute to the redirection of fatty acids from esterification to oxidation reactions in hyperthyroidism. Thyroidectomized rats had a 40-44% decrease in synthetase and a 27-42% decrease in LCFA-CoA hydrolase activity. The decrease in both LCFA-CoA synthetase and hydrolase activities in hypothyroidism may indicate that the LCFA-CoA turnover in this futile cycle is decreased in the liver.     

Inducible expression of long-chain acyl-CoA hydrolase gene in cell cultures

A long-chain acyl-CoA hydrolase, BACH, is markedly distributed in the brain and localized in neurons. However, the physiological significance of BACH is unclear. To study the gene function, we expressed the mouse BACH gene in C3H 10T1/2 fibroblastic cells using a mifepristone (RU486)-inducible gene expression system. A cell clone, 10T-S6/44, was generated by stable transfection of two plasmids encoding a mifepristone-dependent transactivator and an inducible transgene product, BACH with a C-terminal MYC-tag (BACH-MYC). The transgene expression in the 10T-S6/44 cells was tightly regulated by mifepristone. Induction of BACH-MYC and an increase in palmitoyl-CoA hydrolase activity were observed in the cells treated with 3 × 10^–11 M mifepristone and reached maximal levels at a concentration of 1 × 10^–9 M for 48 h. The growth rate of cells showing the maximal induction of BACH-MYC was reduced, whereas phospholipid synthesis was unchanged. These results suggested that BACH affects specific cellular systems and functions, but not all acyl-CoA-utilizing processes.     

Sex-related difference in the effect of clofibric acid on induction of two novel long-chain acyl-CoA hydrolases in rat liver

The sex differences in the induction of two novel long-chain acyl-CoA hydrolases in hepatic cytosol of rats by clofibric acid (p-chlorophenoxyisobutyric acid)-feeding and the properties of the induced acyl-CoA hydrolases were investigated. Marked sex-related difference was observed in the induction of acyl-Coa hydrolase activity. The sex difference was mainly due to the difference in the induction of acyl-CoA hydrolase with higher molecular weight (hydrolase I), but not to the difference in the induction of acyl-CoA hydrolase with lower molecular weight (hydrolase II). The extent of the induction of the hydrolase I in hepatic cytosol of male rats was 3.5 times over that of female rats. Castration of male rats resulted in the marked depression of the ability to induce hydrolase I. The administration of testosterone to the castrated male rats recovered completely the ability to induce hydrolase I. Unlike hydrolase I, the ability to induce hydrolase II did not respond to the changes in state of androgen. The administration of di-(2-ethylhexyl)phthalate also induced both hydrolase I and II, although the extent of the induction of hydrolase I was less compared to that by clofibric acid treatment. Likewise, marked sex difference was observed in the induction of the hydrolase I on di-(2-ethylhexyl)phthalate administration. These two hydrolases showed different kinetic properties and different substrate specificities to each other. Hydrolase I was inhibited by bovine serum albumin in vitro, but was not affected by Mg2+. Hydrolase II was activated slightly in the presence of lower concentrations of bovine serum albumin, Mg2+ or Ca2+.     

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.     

Purification of long-chain acyl-CoA hydrolase from bovine heart microsomes and regulation of activity by lysophospholipids

Long-chain acyl-CoA hydrolase (EC 3.1.2.2) has been purified 12,000-fold from bovine heart muscle microsomes by extraction with Miranol detergent, followed by column chromatography on Reactive Blue agarose and DEAE-cellulose. The purified enzyme was nearly homogeneous on polyacrylamide gel electrophoresis and had a molecular weight of 41,000 in the presence of dodecyl sulfate. The specificity and kinetic properties of the enzyme were studied using several acyl-CoA derivatives as potential substrates. The enzyme showed a wide degree of specificity with little dependence on either the fatty acyl chain length or the degree of unsaturation of the acyl group. The kinetic properties were in accord with the Michaelis-Menten equation under most conditions, although high concentrations of substrates generally inhibited the enzyme. Arachidonoyl-CoA, which was the most effective substrate, had a K_m value of 0.4 μm and a V_max value of 6.0 μmol min⁻¹ mg⁻¹. The enzyme was strongly and specifically inhibited by lysophosphatidylcholine and lysophosphatidylinositol with kinetic inhibition constants of 16 and 30 nm, respectively. Other lysolipids and detergents such as deoxycholate and Triton X-100 were weak inhibitors. These properties and others distinguish this enzyme from other acyl-CoA hydrolases and support the idea that lysophospholipids may be important in vivo in the regulation of lipid metabolism.     

Purification of long-chain acyl-CoA hydrolase from bovine heart microsomes and regulation of activity by lysophospholipids

Long-chain acyl-CoA hydrolase (EC 3.1.2.2) has been purified 12,000-fold from bovine heart muscle microsomes by extraction with Miranol detergent, followed by column chromatography on Reactive Blue agarose and DEAE-cellulose. The purified enzyme was nearly homogeneous on polyacrylamide gel electrophoresis and had a molecular weight of 41,000 in the presence of dodecyl sulfate. The specificity and kinetic properties of the enzyme were studied using several acyl-CoA derivatives as potential substrates. The enzyme showed a wide degree of specificity with little dependence on either the fatty acyl chain length or the degree of unsaturation of the acyl group. The kinetic properties were in accord with the Michaelis-Menten equation under most conditions, although high concentrations of substrates generally inhibited the enzyme. Arachidonoyl-CoA, which was the most effective substrate, had a Km value of 0.4 microM and a Vmax value of 6.0 mumol min-1 mg-1. The enzyme was strongly and specifically inhibited by constants of 16 and 30 nM, respectively. Other lysolipids and detergents such as deoxycholate and Triton X-100 were weak inhibitors. These properties and others distinguish this enzyme from other acyl-CoA hydrolases and support the idea that lysophospholipids may be important in vivo in the regulation of lipid metabolism.     

Partial purification and properties of long-chain acyl-CoA hydrolase from rat brain cytosol

Long-chain acyl-CoA hydrolase (EC 3.1.2.2.) has been partially purified from the 100,000 × g supernatant fraction of rat brain tissue. The purification procedure included chromatography on gel filtration media, DEAE-cellulose, CM-cellulose, and hydroxyapatite. The partially purified enzyme had a specific activity of 7.1 mol/min-mg, and when analyzed by polyacrylamide gel electrophoresis, revealed one major and three minor bands of protein in the presence of dodecyl sulfate and two major bands of protein in the absence of dodecyl sulfate. The enzyme had a molecular weight of 65,000 and showed no evidence of aggregated or dissociated forms. The highest catalytic activity was exhibited with palmitoyl-CoA and oleoyl-CoA as substrates. Lower activity was found with decanoyl-CoA as the substrate and little or no activity was found with acetyl-CoA, malonyl-CoA, butyryl-CoA, or acetoacetyl-CoA. The enzyme was inhibited by CoA, various metal ions, including Mn²⁺, Mg²⁺ and Ca²⁺, and by bovine serum albumin. Heating the enzyme produced a loss of activity which corresponded to a first-order kinetic process, the rate of which was independent of the choice of substrate used to measure enzyme activity. This finding supports the idea that the purification procedure yields a single species of long-chain acyl-CoA hydrolase.     

Enhancement of long-chain acyl-CoA hydrolase activity in peroxisomes and mitochondria of rat liver by peroxisomal proliferators

The present study has confirmed previous findings of long-chain acyl-CoA hydrolase activities in the mitochondrial and microsomal fractions of the normal rat liver. In addition, experimental evidence is presented in support of a peroxisomal localization of long-chain acyl-CoA hydrolase activity. (a) Analytical differential centrifugation of homogenates from normal rat liver revealed that this activity (using palmitoyl-CoA as the substrate) was also present in a population of particles with an average sedimentation coefficient of 6740 S, characteristic of peroxisomal marker enzymes. (b) The subcellular distribution of the hydrolase activity was greatly affected by administration of the peroxisomal proliferators clofibrate and tiadenol. The specific activity was enhanced in the mitochondrial fraction and in a population of particles with an average sedimentation coefficient of 4400 S, characteristic of peroxisomal marker enzymes. Three populations of particles containing lysosomal marker enzymes were found by analytical differential centrifugation, both in normal and clofibrate-treated rats. Our data do not support the proposal that palmitoyl-CoA hydrolase and acid phosphatase belong to the same subcellular particles. In livers from rats treated with peroxisomal proliferators, the specific activity of palmitoyl-CoA hydrolase was also enhanced in the particle-free supernatant. Evidence is presented that this activity at least in part, is related to the peroxisomal proliferation.     

Purification and characterization of a long-chain acyl-CoA hydrolase from rat liver microsomes.

A long-chain acyl-CoA hydrolase from rat liver microsomes has been purified by solvent extraction and gel chromatography to homogeneity as judged by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate. The enzyme was a monomer of molecular weight 59 000. In a sucrose gradient it sedimented at 4.3 S. The isoelectric point, pI was 6.9, and the Stokes radius was approx. 31 A. The enzyme hydrolyzed long-chain fatty acyl-CoA (C7--C18) with maximum activity for palmitoyl-CoA. Bovine serum albumin activation of the enzyme was related to the ratio acyl-CoA/bovine serum albumin, and at high ratios, acyl-CoA inhibited the enzyme activity. Disregarding the substrate inhibition, an apparent Km of 65 nmol/mg protein or 1-10(-7) M and a V of 750 nmol/mg protein per min were calculated. The enzyme was inhibited by p-hydroxymercuribenzoate and N-ethylmaleimide. Reactivation by means of dithiothreitol was not complete.     

Xenobiotic acyl-CoA formation: evidence of kinetically distinct hepatic microsomal long-chain fatty acid and nafenopin-CoA ligases

Multiplicity of hepatic microsomal coenzyme A ligases catalyzing acyl-CoA thioester formation is an important factor for consideration in relation to the metabolism of xenobiotic carboxylic acids. In this study the kinetic characteristics of rat hepatic microsomal nafenopin-CoA ligase were studied and compared with those of long-chain fatty acid (palmitoyl) CoA ligase. The high affinity component of palmitoyl-CoA formation was inhibited by nafenopin (K_i 53 μM) and ciprofibrate (K_i 1000 μM). Analagous to palmitoyl-CoA, nafenopin-CoA formation was catalyzed by an apparent high affinity low capacity isoform (K_m 6 ± 2.5 μM, (V_max 0.33 ± 0.12 nmol/mg per min) which was inhibited competitively by palmitic acid (mean K_i 1.7 μM, n = 5) and R-ibuprofen (mean K_i 10.8 μM, n = 5) whilst ciprofibrate and clofibric acid were ineffective as inhibitors. The intrinsic metabolic clearance of nafenopin to nafenopin-CoA (V_max/K_m 0.057 ± 0.011 nmol/mg/min ± M) was similar to that reported recently for the formation of ibuprofenyl-CoA by rat liver microsomes. Evidence of both a substantial difference between the K_m and K_i for nafenopin and lack of commonality with regard to xenobiotic inhibitors suggests that the high affinity microsomal nafenopin-CoA and long-chain fatty acid-CoA ligases are kinetically distinct. Thus until the current ‘long-chain like’ xenobiotic-CoA ligases are fully characterised in terms of substrate specificity, inhibitor profile, etc, it will be impossible to rationalize (and possibly predict) the metabolism and hence toxicity of xenobiotic carboxylic acids forming acyl-CoA thioester intermediates.     

Purification, molecular cloning, and genomic organization of human brain long-chain acyl-CoA hydrolase

An acyl-CoA hydrolase, referred to as hBACH, was purified from human brain cytosol. The enzyme had a molecular mass of 100 kDa and 43-kDa subunits, and was highly active with long-chain acyl-CoAs, e.g. a maximal velocity of 295 micromol/min/mg and K(m) of 6.4 microM for palmitoyl-CoA. Acyl-CoAs with carbon chain lengths of C(8-18) were also good substrates. In human brain cytosol, 85% of palmitoyl-CoA hydrolase activity was titrated by an anti-BACH antibody, which accounted for over 75% of the enzyme activity found in the brain tissue. The cDNA isolated for hBACH, when expressed in Escherichia coli, directed the expression of palmitoyl-CoA hydrolase activity and a 44-kDa protein immunoreactive to the anti-BACH antibody, which in turn neutralized the hydrolase activity. The hBACH cDNA encoded a 338-amino acid sequence which was 95% identical to that of a rat homolog. The hBACH gene spanned about 130 kb and comprised 9 exons, and was mapped to 1p36.2 on the cytogenetic ideogram. These findings indicate that the long-chain acyl-CoA hydrolase present in the brain is well conserved between man and the rat, suggesting a conserved role for this enzyme in the mammalian brain, and enabling genetic studies on the functional analysis of acyl-CoA hydrolase.     

Induction of peroxisomal beta-oxidation enzymes in primary cultured rat hepatocytes by clofibric acid

Rat hepatocytes were cultured for 72 h with or without the addition of 0.5 mM clofibric acid. The activities of individual enzymes of the peroxisomal beta-oxidation pathway (acyl-CoA oxidase, enoyl-CoA hydratase-3-hydroxyacyl-CoA dehydrogenase bifunctional protein, and 3-ketoacyl-CoA thiolase) decreased in the control culture, but markedly increased synchronously in the clofibric acid-treated culture. The levels of mRNAs coding for these enzymes and the rates of synthesis of the enzymes were also elevated in the clofibric acid-treated culture, although no proportional relationship was observed between the time-dependent changes of these parameters. The increase in mRNAs was much higher than the increase in the rate of synthesis of the enzymes. The activity of catalase, its mRNA level and the rate of its synthesis were slightly affected. The effects of clofibric acid on the peroxisomal beta-oxidation enzymes and catalase in primary cultured hepatocytes were very similar to those observed in vivo. These results, therefore, suggest that primary culture of hepatocytes should provide a useful means for investigating the mechanism of induction of peroxisomal enzymes and the mechanism of action of peroxisome proliferators.     

Cardiac and hepatic acyl-CoA and acylcarnitine hydrolase activities in clofibrate-fed rabbits

Catalase activity in the heart of male rabbits was 21% of that found in the liver; clofibrate feeding (0.3% w/w for 10 days) resulted in an 80% increase in both cardiac and hepatic catalase activities. Fatty acyl-CoA oxidase activity in control heart was 11% of that found in control liver; this peroxisomal activity did not increase subsequent to clofibrate feeding. Only acyl-CoA hydrolase activity in the cardiac supernatant was elevated by clofibrate feeding. Acylcarnitine hydrolase activity was increased significantly in the homogenate, extract and supernatant of both heart and liver from the clofibrate-fed rabbit. Clofibrate feeding increased CoASH and carnitine tissue levels in heart and liver.     

The long-chain acyl-CoA hydrolase activity in the heart of rat fed on rape-seed oil.

1. Fat feeding (soybean oil or erucic acid-rich rape-seed oil) enhance after 2 to 7 days the palmitoyl-CoA hydrolase activity in the heart of weanling rats in a degree dependent on the content of fat in the diet. 2. The rise in enzyme activity between the 7th and 14th day of feeding, observed only in rats fed on rape-seed oil, coincides with the decrease in lipid infiltration in the heart. 3. The obtained results suggest that palmitoyl-CoA hydrolase may control in the heart the amount of acyl-CoA thioesters in the cell, thus decreasing the lipidosis induced by eurcic acid.     

Differential effects of altered hormonal state on the induction of acyl-CoA hydrolases and peroxisomal beta-oxidation by clofibric acid

Induction of hydrolase I, hydrolase II, peroxisomal beta-oxidation and hepatomegaly caused by clofibric acid (rho-chlorophenoxyisobutyric acid) administration was investigated in relation to alterations in hormonal state of glucocorticoid, thyroid hormone and insulin. (1) In adrenalectomized rats, the ability to induce hydrolase I was depressed effectively and little hepatomegaly was produced. Hydrolase II and peroxisomal beta-oxidation were induced to a similar extent, compared to those of intact rats. (2) In hypothyroid rats, induction of hydrolase I, hydrolase II, peroxisomal beta-oxidation and hepatomegaly was reduced. In hyperthyroid rats, the ability to induce hydrolase I, hydrolase II and peroxisomal beta-oxidation was depressed, although hepatomegaly was produced by the same or a greater extent as in intact rats. (3) In diabetic rats, marked reduction of ability to induce both hydrolase I and II was observed and induction of hepatomegaly was depressed slightly, although peroxisomal beta-oxidation was induced normally. Differences in the response of four parameters (hydrolase I, hydrolase II, peroxisomal beta-oxidation and liver size) to alterations in hormonal state suggest that the four biological responses to clofibric acid may each be mediated through distinct mechanism(s) other and regulated by distinct hormone(s).