Effects of high fat diets on the activity of palmitoyl-CoA hydrolase in rat liver

Loss of ACOT7 potentiates seizures and metabolic dysfunction

Neurons uniquely antagonize fatty acid utilization by hydrolyzing the activated form of fatty acids, long chain acyl-CoAs, via the enzyme acyl-CoA thioesterase 7, Acot7. The loss of Acot7 results in increased fatty acid utilization in neurons and exaggerated stimulus-evoked behavior such as an increased startle response. To understand the contribution of Acot7 to seizure susceptibility, we generated Acot7 knockout (KO) mice and assayed their response to kainate-induced seizures. Acot7 KO mice exhibited potentiated behavioral and molecular indices of seizure severity following kainic acid administration, suggesting that fatty acid metabolism in neurons can be a critical regulator of neuronal activity. These data are consistent with the presentation of seizures in a human with genomic deletion of ACOT7 demonstrating the conservation of function across species. To further understand the metabolic complications arising from a deletion in Acot7, we subjected Acot7 KO mice to a high-fat diet. While the loss of Acot7 did not result in metabolic complications following a normal chow diet, a high-fat diet induced greater body weight gain, adiposity, and glucose intolerance in Acot7 KO mice. These data demonstrate that Acot7, a fatty acid metabolic enzyme highly enriched in neurons, regulates both brain-specific metabolic processes related to seizure susceptibility and the whole body response to dietary lipid.

Effects of dietary fats (fish, olive and high-oleic-acid sunflower oils) on lipid composition and antioxidant enzymes in rat liver

The effects of two oleic-acid-rich diets (containing olive oil, OO, and high-oleic-acid sunflower oil, HOSO) on plasma and liver lipid composition detoxification enzyme activities, were compared with those of a fish-oil (FO) diet and a control diet. Compared with the control diet, plasma and hepatic total triacylglycerol concentrations were increased in the animals fed on the HOSO and OO diets and decreased in those fed on the FO diet. The animals fed on FO showed the highest level of cholesterol in the liver and had lower plasma cholesterol concentrations when compared with those fed on the two oleic-acid-rich diets. In comparison with the animals fed on the diets enriched in oleic acid, the FO group showed higher hepatic levels of polyunsaturated fatty acids of then-3 series and lower levels of fatty acids of then-6 series. Livers of FO-fed rats, compared with those of OO- and HOSO-fed rats showed: (1) significantly higher activities of catalase (EC1.11.1.6) glutathione peroxidase (EC1.11.1.9) and Cu/Zn superoxide dismutase (EC1.15.1.1); (2) no differences in the NADPH-cytochromecreductase (EC1.6.99.3) activity. The HOSO diet had a similar effect on liver antioxidant enzyme activities as the OO diet. In conclusion, it appears that changes in the liver fatty acid composition due mainly ton-3 lipids may enhance the efficiency of the antioxidant defence system. The two monounsaturated fatty acids oils studied (OO and HOSO), with the same high content of oleic acid but different contents of natural antioxidants, had similar effects on the antioxidant enzyme activities measured.

Modulation of antioxidant defence system by dietary fat in rats intoxicated with o-toluidine

o-Toluidine was administered to rats in the diet for four weeks at levels approximately 40, 80 and 160 mg/kg b.w. per day. Two types of diet have been used, standard (4% fat) and high fat (14% fat). Activity of antioxidant enzymes, level of glutathione and thiobarbituric acid reactive substances were measured in liver. Glutathione peroxidase was significantly increased in all treated groups while glutathione S-transferase and glutathione reductase were elevated in rats fed high-fat diet. o-Toluidine slightly enhanced catalase activity regardless of the kind of diet. Superoxide dismutase was the only enzyme whose activity was lowered in almost all treated groups. Enzymatic and nonenzymatic microsomal lipid peroxidation was enhanced 2- to 3-fold in both diet groups. Reduced glutathione level in liver was 2.3- to 4.0-fold increased in all treated groups. Our findings indicate that free radical processes can be involved in the toxic effects of o-toluidine and dietary fat can modify the response of some antioxidant enzymes to this compound.

The role Acyl-CoA thioesterases play in mediating intracellular lipid metabolism

Acyl-CoA thioesterases are a group of enzymes that catalyze the hydrolysis of acyl-CoAs to the free fatty acid and coenzyme A (CoASH), providing the potential to regulate intracellular levels of acyl-CoAs, free fatty acids and CoASH. These enzymes are localized in almost all cellular compartments such as endoplasmic reticulum, cytosol, mitochondria and peroxisomes. Acyl-CoA thioesterases are highly regulated by peroxisome proliferator-activated receptors (PPARs), and other nutritional factors, which has led to the conclusion that they are involved in lipid metabolism. Although the physiological functions for these enzymes are not yet fully understood, recent cloning and more in-depth characterization of acyl-CoA thioesterases has assisted in discussion of putative functions for specific enzymes. Here we review the acyl-CoA thioesterases characterized to date and also address the diverse putative functions for these enzymes, such as in ligand supply for nuclear receptors, and regulation and termination of fatty acid oxidation in mitochondria and peroxisomes.

Effect of dietary n-3 and n-6 polyunsaturated fatty acids on lipid-metabolizing enzymes in obese rat liver

This study was designed to examine whether n-3 and n-6 polyunsaturated fatty acids at a very low dietary level (about 0.2%) would alter liver activities in respect to fatty acid oxidation. Obese Zucker rats were used because of their low level of fatty acid oxidation, which would make increases easier to detect. Zucker rats were fed diets containing different oil mixtures (5%, w/w) with the same ratio of n-6/n-3 fatty acids supplied either as fish oil or arachidonic acid concentrate. Decreased hepatic triacylglycerol levels were observed only with the diet containing fish oil. In mitochondrial outer membranes, which support carnitine palmitoyltransferase I activity, cholesterol content was similar for all diets, while the percentage of 22:6n-3 and 20:4n-6 in phospholipids was enhanced about by 6 and 3% with the diets containing fish oil and arachidonic acid, respectively. With the fish oil diet, the only difference found in activities related to fatty acid oxidation was the lower sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition. With the diet containing arachidonic acid, peroxisomal fatty acid oxidation and carnitine palmitoyltransferase I activity were markedly depressed. Compared with the control diet, the diets enriched in fish oil and in arachidonic acid gave rise to a higher specific activity of aryl-ester hydrolase in microsomal fractions. We suggest that slight changes in composition of n-3 or n-6 polyunsaturated fatty acids in mitochondrial outer membranes may alter carnitine palmitoyltransferase I activity.

Impact of cytochrome P450 system on lipoprotein metabolism. Effect of abnormal fatty acids (3-thia fatty acids)

Fatty acid omega-hydroxylation, peroxisomal and mitochondrial fatty acid oxidation and related lipid-metabolizing enzymes are constitutive activities of mammalian cells. The past 5 years have witnessed an increased interest in the modulation of these pathways and functions by a new group of abnormal fatty acids (sulfur-substituted fatty acid analogs), due to the metabolic and nutritional aspects related to human health and disease, and possible treatment of certain inherited peroxisomal and mitochondrial disorders. The purpose of this review is to present an overview of current knowledge in the field and to provide an account of recent developments, particularly with respect to the chemical nature of the biologically active factors and their possible mechanism of action.

Evidence for mechanisms of the hypotriglyceridemic effect of n-3 polyunsaturated fatty acids

Ingestion of modest amounts of n-3 polyunsaturated fatty acids (PUFA) (2.8% w/w) decreased plasma triglyceride levels in Syrian hamsters by 49%. This was associated with a 45% increase in hepatic carnitine palmitoyl transferase activity. Significantly, at this low level of n-3 PUFA intake, hepatic peroxisomal oxidation measured as CN- insensitive palmitoyl-CoA dependent NAD reduction was unaffected. Consumption of increasing amounts of dietary n-3 PUFA up to 2% (w/w) in hamster diets containing 15% fat, gradually decreased plasma triglycerides to 56% of the control levels. The diet induced changes in plasma triglyceride levels were highly correlated (r = -0.97, P less than 0.01) with changes in hepatic carnitine palmitoyl transferase activity. A gradual decrease up to 59% in hepatic phosphatidate phosphohydrolase activity with n-3 fatty acid consumption was also observed. The hypotriglyceridemic effects of moderate intakes of n-3 fatty acids are, therefore, associated with changes in key enzymes in hepatic triglyceride synthesis and mitochondrial oxidation, but not peroxisomal oxidation.

Fatty acid metabolism in liver of rats treated with hypolipidemic sulphur-substituted fatty acid analogues

The purpose of this study was to investigate early biochemical changes and possible mechanisms via which alkyl(C12)thioacetic acid (CMTTD, blocked for beta-oxidation), alkyl(C12)thiopropionic acid (CETTD, undergo one cycle of beta-oxidation) and a 3-thiadicarboxylic acid (BCMTD, blocked for both omega- (and beta-oxidation) influence the peroxisomal beta-oxidation in liver of rats. Treatment of rats with CMTTD caused a stimulation of the palmitoyl-CoA synthetase activity accompanied with increased concentration of hepatic acid-insoluble CoA. This effect was already established during 12-24 h of feeding. From 2 days of feeding, the cellular level of acid-insoluble CoA began to decrease, whereas free CoASH content increased. Stimulation of [1-14C]palmitoyl-CoA oxidation in the presence of KCN, palmitoyl-CoA-dependent dehydrogenase (termed peroxisomal beta-oxidation) and palmitoyl-CoA hydrolase activities were revealed after 36-48 h of CMTTD-feeding. Administration of BCMTD affected the enzymatic activities and altered the distribution of CoA between acid-insoluble and free forms comparable to what was observed in CMTTD-treated rats. It is evident that treatment of peroxisome proliferators (BCMTD and CMTTD), the level of acyl-CoA esters and the enzyme activity involved in their formation precede the increase in peroxisomal and palmitoyl-CoA hydrolase activities. In CMTTD-fed animals the activity of cyanide-insensitive fatty acid oxidation remained unchanged when the mitochondrial beta-oxidation and carnitine palmitoyltransferase operated at maximum rates. The sequence and redistribution of CoA and enzyme changes were interpreted as support for the hypothesis that substrate supply is an important factor in the regulation of peroxisomal fatty acid metabolism, i.e., the fatty acyl-CoA species appear to be catabolized by peroxisomes at high rates only when uptake into mitochondria is saturated. Administration of CETTD led to an inhibition of mitochondrial fatty acid oxidation accompanied with a rise in the concentration of acyl-CoA esters in the liver. Consequently, fatty liver developed. The peroxisomal beta-oxidation was marginally affected. Whether inhibition of mitochondrial beta-oxidation may be involved in regulation of peroxisomal fatty acid metabolism and in development of fatty liver should be considered.

Inhibition of palmitoyl co-enzyme A hydrolase in mitochondria and microsomes by pharmaceutical organic anions

Rat microsomes and mitochondria were isolated and incubated with selected pharmaceutical organic anions at concentrations of 0, 0.2, 0.5, 1.0, and 2 mM. Activity of palmitoyl CoA hydrolase (PCAH) was shown to be reduced in a dose-dependent manner in microsomes by ibuprofen, valproate, acetyl salicylate, 2,4-dichlorophenoxyacetate (2,4-D), and 4-pentenoate, but not salicylate. Mitochondrial PCAH activity was inhibited by clofibrate, ibuprofen, valproate, and 2,4-D. Mitochondrial oxidative phosphorylation was impaired or uncoupled by each of the mitochondrial PCAH inhibitors. The inhibition of PCAH by some of these agents may lead to fatty acyl CoA accumulation. Very low concentrations of fatty acyl CoA are known to cause mitochondrial uncoupling and increase permeability. This action may play a role in the mitochondrial injury caused by some of these agents or related disease processes.

Effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate on peroxisomal activities and enzyme activities involved in lipid metabolism in rat liver

The effects of 12-O-tetradecanoylphorbol 13-acetate (TPA) on hepatic lipids and key enzymes involved in esterification, hydrolysis and oxidation of long-chain fatty acids at increasing doses were investigated in rats. TPA administration tended to decrease the mitochondrial activities of palmitoyl-CoA synthetase and carnitine palmitoyltransferase. The microsomal palmitoyl-CoA synthetase activity was increased. TPA administration was also associated with a dose-dependent increase of glycerophosphate acyltransferase activity both in the mitochondrial and microsomal fractions in particular. The data are consistent with a decreased catabolism of long-chain fatty acids at the mitochondrial level, and an increased capacity for esterification of fatty acids in the microsomal fraction. Peroxisomal beta-oxidation was increased about 2-fold in the peroxisome-enriched fraction of TPA-treated rats while the catalase and urate oxidase activities were only marginally affected. TPA administration revealed elevated capacity for hydrolysis of palmitoyl-CoA and palmitoyl-L-carnitine in the microsomal fraction. Neither increased cytosolic palmitoyl-CoA hydrolase activity nor increased hydroxylation of lauric acid nor changes of the hepatic content of cytochrome P-450 isoenzymic forms were observed in the TPA-treated animals. There was no induction of the protein content of the bifunctional enoyl-CoA hydratase. Thus, TPA behaves more like choline-deficient diet and ethionine treatment than well-known peroxisome proliferators. It seems possible that TPA selectively stimulated the peroxisomal activities, i.e., peroxisomal beta-oxidation rather than evoking a peroxisome proliferation capacity.

Rapid stimulation of liver palmitoyl-CoA synthetase, carnitine palmitoyltransferase and glycerophosphate acyltransferase compared to peroxisomal beta-oxidation and palmitoyl-CoA hydrolase in rats fed high-fat diets

Key enzymes involved in oxidation and esterification of long-chain fatty acids were investigated in male rats fed different types and amounts of oil in their diet. A diet with 20% (w/w) fish oil, partially hydrogenated fish oil (PHFO) and partially hydrogenated soybean oil (PHSO) was shown to stimulate the mitochondrial and microsomal palmitoyl-CoA synthetase activity (EC 6.2.1.3) compared to soybean oil-fed animals after 1 week of feeding. Rapeseed oil had no effect. Partially hydrogenated oils in the diet resulted in significantly higher levels of mitochondrial glycerophosphate acyltransferase compared to unhydrogenated oils in the diet. Rats fed 20% (w/w) rapeseed oil had a decreased activity of this mitochondrial enzyme, whereas the microsomal glycerophosphate acyltransferase activity was stimulated to a comparable extent with 20% (w/w) rapeseed oil, fish oil or PHFO in the diet. Increasing the amount of PHFO (from 5 to 25% (w/w)) in the diet for 3 days led to increased mitochondrial and microsomal palmitoyl-CoA synthetase and microsomal glycerophosphate acyltransferase activities with 5% of this oil in the diet. The mitochondrial glycerophosphate acyltransferase was only marginally affected by increasing the oil dose. Administration of 20% (w/w) PHFO increased rapidly the mitochondrial and microsomal palmitoyl-CoA synthetase, carnitine palmitoyltransferase and microsomal glycerophosphate acyltransferase activities almost to their maximum value within 36 h. In contrast, the glycerophosphate acyltransferase and palmitoyl-CoA hydrolase (EC 3.1.2.2) activities of the mitochondrial fraction and the peroxisomal beta-oxidation reached their maximum activities after administration of the dietary oil for 6.5 days. This sequence of enzyme changes (a) is in accordance with the proposal that an increased cellular level of long-chain acyl-CoA species act as metabolic messages for induction of peroxisomal beta-oxidation and palmitoyl-CoA hydrolase, i.e., these enzymes are regulated by a substrate-induced mechanism, and (b) indicates that, with PHFO, a greater part of the activated fatty acids are directed from triacylglycerol esterification and hydrolysis towards oxidation in the mitochondria. It is also conceivable that the mitochondrial beta-oxidation is proceeding before the enhancement of peroxisomal beta-oxidation.

A diet rich in (n-3) fatty acids increases peroxisomal beta-oxidation activity and lowers plasma triacylglycerols without inhibiting glutathione-dependent detoxication activities in the rat liver

By using comparisons with a safflower oil diet (15% w/w) and a control, low-fat diet, the ability of a fish oil diet (15% MaxEPA) rich in the (n-3) fatty acids, eicosapentaenoic acid and docosahexaenoic acid, to alter hepatic activities has been determined in adult, male rats. Compared with the safflower diet, treatment for 2 weeks with the fish oil diet caused significant increases in the ratio of liver weight/body weight and the specific activities in liver homogenates of peroxisomal enzymes fatty acyl-CoA oxidase (263%) and catalase (149%) and caused a significant lowering of plasma triacylglycerol levels. Fish oil diets rich in (n-3) fatty acids should thus be placed in the category of hypotriglyceridemic agents which stimulate peroxisomal beta-oxidation activity. In contrast to the effects seen with the other hypotriglyceridemic, peroxisomal proliferating agents such as clofibrate, hepatic glutathione peroxidase and glutathione S-transferase activities are unchanged or are increased rather than inhibited with the fish oil diet.

Induction of cytosolic clofibroyl-CoA hydrolase activity in liver of rats treated with clofibrate

Among subcellular fractions of liver homogenates of rats, the clofibroyl-CoA hydrolase activity is found mainly in the cytosolic fraction. It is here shown that the subcellular distribution of clofibroyl-CoA hydrolase appears to be different from the distribution of palmitoyl-CoA hydrolase activity. Thus, in contrast to the case with palmitoyl-CoA, no hydrolysis of clofibroyl-CoA was catalysed by the microsomal fraction. Furthermore, the hydrolysis of palmitoyl-CoA and clofibroyl-CoA in the cytosolic fraction seemed to be catalyzed by two different enzymes. Rats treated with clofibrate (0.3%, w/w) showed a significant increased clofibroyl-CoA hydrolase activity where the cytosolic hydrolase was increased 3.5-fold. Clofibrate administration also elevated the specific clofibroyl-CoA hydrolase activity by factors of 1.7 and 1.5 in the mitochondrial and the light-mitochondrial fractions, respectively. Thus, it is possible that clofibroyl-CoA hydrolase has also a multiorganelle localization.

Effect of a high-fat diet with partially hydrogenated fish oil on long-chain fatty acid metabolizing enzymes in subcellular fractions of rat liver

Hepatic metabolism of long-chain fatty acids were studied in young male rats fed a semisynthetic diet containing 20% (w/w) partially hydrogenated fish oil (PHFO)2, with or without 2% (w/w) linoleic acid. The enzymic activities involved in the formation and breakdown of long-chain acyl-CoA were both increased in the animals fed the semisynthetic diet, compared to pellet-fed control animals. Thus, the specific palmitoyl-CoA synthetase activity increased slightly in both the mitochondrial (1.4-fold) and the microsomal (1.6-fold) fractions. In the peroxisome-enriched fraction the activity was increased (about 2.6-fold) only on addition of linoleic acid to the diet. The data are consistent with an increased catabolism of long-chain fatty acids by a peroxisomal and a mitochondrial pathway. Thus, the total carnitine palmitoyltransferase activity increased 2-fold in the mitochondrial fraction, and was partly prevented by added linoleic acid. Peroxisomal beta-oxidation activity was also increased (about 7-fold) in livers of PHFO-fed rats, but did not change when linoleic acid was added. The PHFO-fed rats also revealed elevated capacity for hydrolysis of palmitoyl-CoA in both the mitochondrial (2.4-fold) and the cytosolic (2.0-fold) fractions and the latter was almost completely and selectively prevented by added linoleic acid. The s values of mitochondria and peroxisomes varied with the dietary regime, and some of the observed changes in the specific activities of the fatty acid metabolizing enzymes with multiple subcellular localization can be explained as an effect of changes in the s values of the organelles. Thus, the s value of mitochondria increased 1.8-fold as a result of PHFO feeding, but was fully prevented by linoleic acid in the diet. On the other hand, the s values of peroxisomes decreased by about 50% on feeding a PHFO diet, and by about 25% with added linoleic acid.

The effect of high-fat diets on microsomal lauric acid hydroxylation in rat liver

A diet with 20% (w/w) fish oil or partially hydrogenated fish oil has been shown to stimulate omega-oxidation of lauric acid 2.5-fold with rat liver microsomal preparations after 1 week of feeding. A diet containing either 20% (w/w) soybean oil, partially hydrogenated soybean oil or rapeseed oil had no effect. The omega-oxidation was also stimulated by fasting (3.7-fold) and by clofibrate (13-fold). The stimulation of omega-oxidation with partially hydrogenated fish oil was at its highest level after 3 days of feeding, and was dose dependent in the dietary oil of range 5-25% (w/w). With various high-fat diets, a high correlation was found (r = 0.81) between peroxisomal beta-oxidation of palmitoyl-CoA and microsomal omega-oxidation of lauric acid.

Effect of dietary fat on total and peroxisomal fatty acid oxidation in rat tissues

In this study the effect of dietary trans fatty acids on the peroxisomal and mitochondrial beta-oxidation is compared with that of saturated or cis-monounsaturated fatty acids. Oxidation of [1-14C]- and [16-14C]palmitate was assayed in the absence as well as in the presence of antimycin plus rotenone in homogenates of liver, heart and skeletal muscle of four groups of rats fed diets containing 40 energy% fat of different fatty acid composition. Three groups were given fat blends rich in C16, C18 saturated (cocoa butter), cis-monounsaturated (low-linoleic-acid olive oil) or trans fatty acids (partially hydrogenated soybean oil), respectively. The fourth group received a mixture of these fats with half the amount of trans fatty acids of the third group. Total oxidation rates of [1-14C]- and [16-14C]palmitate in the absence of antimycin were not significantly influenced by the type of dietary fat in the investigated tissues. The antimycin-insensitive [1-14C]palmitate oxidation rate and the proportion of peroxisomal oxidation of the total oxidation were lower in all tissues of those animals fed the mixed dietary fat than in those fed the other diets; both parameters were higher in the liver of cocoa butter-fed rats than in those of the other groups. Comparison of the results with literature data and with previous results obtained with a low-fat diet (Veerkamp and Van Moerkerk (1986) Biochim. Biophys. Acta 875, 301-310) indicates that high-fat diets only induce peroxisomal beta-oxidation activity if they also contain C20, C22 fatty acids. High dietary concentrations of trans C18 fatty acids do not result in a higher peroxisomal activity than that observed for other fatty acids with the same chain length.

Correlation between the cellular level of long-chain acyl-CoA, peroxisomal beta-oxidation, and palmitoyl-CoA hydrolase activity in rat liver. Are the two enzyme systems regulated by a substrate-induced mechanism?

Data obtained in earlier studies with rats fed diets containing high doses of peroxisome proliferators (niadenate, tiadenol, clofibrate, or nitotinic acid) are used to look for a quantitative relationship between peroxisomal beta-oxidation, palmitoyl-CoA hydrolase, palmitoyl-CoA synthetase and carnitine palmitoyltransferase activities, and the cellular concentration of their substrate and reaction products. The order of the hyperlipidemic drugs with regard to their effect on CoA derivatives and enzyme activities was niadenate greater than tiadenol greater than clofibrate greater than nicotinic acid. Linear regression analysis of long-chain acyl-CoA content versus palmitoyl-CoA hydrolase and peroxisomal beta-oxidation activity showed highly significant linear correlations both in the total liver homogenate and in the peroxisome-enriched fractions. A dose-response curve of tiadenol showed that carnitine palmitoyltransferase and palmitoyl-CoA synthetase activities and the ratio of long-chain acyl-CoA to free CoASH in total homogenate rose at low doses before detectable changes occurred in the peroxisomal beta-oxidation and palmitoyl-CoA hydrolase activity. A plot of this ratio parallelled the palmitoyl-CoA synthetase activity. The specific activity of microsomally localized carnitine palmitoyl-transferase was low and unchanged up to a dose where no enhanced peroxisomal beta-oxidation was observed, but over this dose the activity increased considerably so that the specific of the enzyme in the mitochondrial and microsomal fractions became comparable. The mitochondrial palmitoyl-CoA synthetase activity decreased gradually. The correlations may be interpreted as reflecting a common regulation mechanism for palmitoyl-CoA hydrolase and peroxisomal beta-oxidation enzymes, i.e., the cellular level of long-chain acyl-CoA acting as the metabolic message for peroxisomal proliferation resulting in induction of peroxisomal beta-oxidation and palmitoyl-CoA hydrolase activity. The findings are discussed with regard to their possible consequences for mitochondrial fatty acid oxidation and the conversion of long-chain acyl-L-carnitine to acyl-CoA derivatives.