Effects of high-fat diets on hepatic fatty acid oxidation in the rat. Isolation of rat liver peroxisomes by vertical-rotor centrifugation by using a self-generated, iso-osmotic, Percoll gradient.

1. Rat liver peroxisomal fractions were isolated in iso-osmotic Percoll gradients by using vertical-rotor centrifugation. The fractions obtained with rats given various dietary treatments were characterized. 2. The effect on peroxisomal beta-oxidation of feeding 15% by wt. of dietary fat for 3 weeks was investigated. High-fat diets caused induction of peroxisomal beta-oxidation, but diets rich in very-long-chain mono-unsaturated fatty acids produced a more marked induction. 3. Peroxisomal beta-oxidation induced by diets rich in very-long-chain mono-unsaturated fatty acids can oxidize such acids. Trans-isomers of mono-unsaturated fatty acids are oxidized at rates that are faster than, or similar to, those obtained with corresponding cis-isomers. 4. Rates of oxidation of [14-14C]erucic acid by isolated rat hepatocytes isolated from rats fed on high-fat diets increased with the time on those diets in a fashion very similar to that previously reported for peroxisomal beta-oxidation [see Neat, Thomassen & Osmundsen (1980) Biochem, J. 186, 369-371]. 5. Total liver capacities for peroxisomal beta-oxidation (expressed as acetyl groups produced per min) were estimated to range from 10 to 30% of mitochondrial capacities, depending on dietary treatment and fatty acid substrate. A role is proposed for peroxisomal beta-oxidation in relation to the metabolism of fatty acids that are poorly oxidized by mitochondrial beta-oxidation, and, in general, as regards oxidation of fatty acids during periods of sustained high hepatic influx of fatty acids.     

Effect of dietary conjugated linoleic acid (CLA) on lipid composition, metabolism and gene expression in Atlantic salmon (Salmo salar) tissues

Dietary conjugated linoleic acid (CLA) affects fat deposition and lipid metabolism in mammals, including livestock. To determine CLA effects in Atlantic salmon (Salmo salar), a major farmed fish species, fish were fed for 12 weeks on diets containing fish oil or fish oil with 2% and 4% CLA supplementation. Fatty acid composition of the tissues showed deposition of CLA with accumulation being 2 to 3 fold higher in muscle than in liver. CLA had no effect on feed conversion efficiency or growth of the fish but there was a decreased lipid content and increased protein content after 4% CLA feeding. Thus, the protein:lipid ratio in whole fish was increased in fish fed 4% CLA and triacylglycerol in liver was decreased. Liver beta-oxidation was increased whilst both red muscle beta-oxidation capacity and CPT1 activity was decreased by dietary CLA. Liver highly unsaturated fatty acid (HUFA) biosynthetic capacity was increased and the relative proportion of liver HUFA was marginally increased in salmon fed CLA. CLA had no effect on fatty acid Delta6 desaturase mRNA expression, but fatty acid elongase mRNA was increased in liver and intestine. In addition, the relative compositions of unsaturated and monounsaturated fatty acids changed after CLA feeding. CLA had no effect on PPARalpha or PPARgamma expression in liver or intestine, although PPARbeta2A expression was reduced in liver at 4% CLA feeding. CLA did not affect hepatic malic enzyme activity. Thus, overall, the effect of dietary CLA was to increase beta-oxidation in liver, to reduce levels of total body lipid and liver triacylglycerol, and to affect liver fatty acid composition, with increased elongase expression and HUFA biosynthetic capacity.     

A potent PPARalpha agonist stimulates mitochondrial fatty acid beta-oxidation in liver and skeletal muscle

The proposed mechanism for the triglyceride (TG) lowering by fibrate drugs is via activation of the peroxisome proliferator-activated receptor-alpha (PPARalpha). Here we show that a PPARalpha agonist, ureido-fibrate-5 (UF-5), approximately 200-fold more potent than fenofibric acid, exerts TG-lowering effects (37%) in fat-fed hamsters after 3 days at 30 mg/kg. In addition to lowering hepatic apolipoprotein C-III (apoC-III) gene expression by approximately 60%, UF-5 induces hepatic mitochondrial carnitine palmitoyltransferase I (CPT I) expression. A 3-wk rising-dose treatment results in a greater TG-lowering effect (70%) at 15 mg/kg and a 2.3-fold elevation of muscle CPT I mRNA levels, as well as effects on hepatic gene expression. UF-5 also stimulated mitochondrial [3H]palmitate beta-oxidation in vitro in human hepatic and skeletal muscle cells 2.7- and 1.6-fold, respectively, in a dose-related manner. These results suggest that, in addition to previously described effects of fibrates on apoC-III expression and on peroxisomal fatty acid (FA) beta-oxidation, PPARalpha agonists stimulate mitochondrial FA beta-oxidation in vivo in both liver and muscle. These observations suggest an important mechanism for the biological effects of PPARalpha agonists.     

Seasonal variations in the lipid composition of the steelhead trout, Salmo gairdneri Richardson, associated with the parr-smolt transformation

Total lipid and lipid class composition of selected tissues and serum were determined for juvenile steelhead trout Salmo gairdneri , during the smolting period between 25 January and 19 April 1982. The total lipid content of the serum, liver, light muscle and dark muscle was significantly depleted during smolt transformation. Mesenteric fat total lipid concentration fluctuated little over the sampling period. Phospholipids of muscle and mesenteric fat exhibited little seasonality. Cholesterol was significantly depleted from dark muscle and liver. Large stores of triacylglycerol (TGL) in the parrs' mesenteric fat, dark muscle and liver implicate these tissues as lipid depot organs. In those tissues depleted of lipid, TGL concentrations were reduced more than any other lipid class. This supports the hypothesis that increased catabolism is the cause of loss of body fat during salmonid smolt transformation.     

Suppression of peroxisomal lipid beta-oxidation enzymes of TNF-alpha.

TNF-alpha is a potent cytokine which induces marked hyperlipidemia. Because of the important role of peroxisomes in lipid metabolism we investigated the effects of human recombinant TNF-alpha upon rat liver peroxisomal enzymes. Sixteen hours after the administration of a single dose of 25 micrograms of TNF-alpha to male rats the activity of peroxisomal fatty acyl-CoA oxidase was reduced by 50%. This was confirmed also by immunoblotting and by quantitative immunoelectron microscopy which in addition revealed substantial reduction of the trifunctional protein (hydratase-dehydrogenase-isomerase) in peroxisomes. These observations suggest that the suppression of peroxisomal beta-oxidation may contribute to the perturbation of the isomerase) in peroxisomes. These observations suggest that the suppression of peroxisomal beta-oxidation may contribute to the perturbation of the lipid metabolism induced by TNF-alpha.     

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.     

Effect of clofibrate on peroxisomal and mitochondrial beta-oxidation in chicken liver

The effect of a 0.25% clofibrate diet for 2 weeks on peroxisomal and mitochondrial beta-oxidation in chicken liver was studied. The activities of antimycin antimycin A-insensitive palmitoyl-CoA oxidation (peroxisomal beta-oxidation) and carnitine acetyltransferase increased about two-fold. The activities of palmitoyl-CoA-dependent O2 consumption (mitochondrial beta-oxidation) and carnitine palmitoyltransferase were also slightly activated by the administration of clofibrate, but not significant. Thus, clofibrate may be a typical drug which activates the peroxisomal beta-oxidation more than the mitochondrial one in various species. The effect of clofibrate on peroxisomal carnitine acetyltransferase was the same as that on the mitochondrial one in chicken liver. Serum lipids were not lowered, but hepatomegaly was observed in the present experiment with chicken.     

Ubiquinone analyses in fish tissues and in some marine invertebrates.

1. Ubiquinone contents were determined in species of marine invertebrates, and in heart, red and white muscle and liver of three species of fish. 2. Three different methods of determination were compared, based on spectrophotometry, reduction and a reaction with the dimethoxy groups of ubiquinone. 3. Using ubiquinone homologues 6-10 prepared from beef heart and commercially available microorganisms (SCP) as standards, ubiquinone 10 was found in all samples. In addition were found minor amounts of Q-9 in samples of saithe heart and red muscle. 4. Less than 10 mg/kg wet wt of ubiquinone was found in the samples of marine invertebrates and in white muscle and liver of the fish samples, with one exception: 40 mg/kg in a sample of mackerel liver. 5. Higher contents of ubiquinone were found in fish heart and red muscle tissues, ranging from 24 to 116 mg/kg wet wt. The ubiquinone contents were comparable in the two tissues. 6. A test on cellular fragments of red muscle tissue of saithe showed that the ubiquinone was concentrated in the mitochondria fraction.     

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.     

Peroxisomal and mitochondrial beta-oxidation of monocarboxylyl-CoA, omega-hydroxymonocarboxylyl-CoA and dicarboxylyl-CoA esters in tissues from untreated and clofibrate-treated rats

In control rats, long-chain monocarboxylyl-CoA, omega-hydroxymonocarboxylyl-CoA, and dicarboxylyl-CoA esters were substrates for hepatic, renal, and myocardial peroxisomal beta-oxidation. The latter enzyme system could not be detected in skeletal muscle. Clofibrate treatment resulted in an enhancement of peroxisomal beta-oxidizing capacity in various tissues. Intact mitochondria from control rat liver and kidney cortex incubated in the presence of L-carnitine were capable of oxidizing long-chain monocarboxylyl-CoAs and omega-hydroxymonocarboxylyl-CoAs but not dicarboxylyl-CoAs. However, control rat liver mitochondria permeabilized by digitonin oxidized dodecanedioyl-CoA indicating that the liver mitochondrial beta-oxidation system can act on dicarboxylyl-CoA esters even if the overall intact mitochondrial system is inactive on these substrates. Intact liver mitochondria from clofibrate-treated animals rapidly oxidized lauroyl-CoA and 12-hydroxylauroyl-CoA but not dodecanedioyl-CoA. These mitochondria were active on hexadecanedioyl-CoA and this activity amounted to 20-25% of that measured with palmitoyl-CoA and 16-hydroxypalmitoyl-CoA as substrates. No mitochondrial dicarboxylyl-CoA oxidation could be detected in kidney cortex from animals receiving clofibrate in their diet. Heart and skeletal muscle intact mitochondria from untreated and clofibrate-treated rats were capable of oxidizing each type of acyl-CoA as a substrate. Dicarboxylyl-CoA synthetase and carnitine dicarboxylyltransferase activities were detected in various tissues from untreated and clofibrate-treated rats with the exception of carnitine dodecanedioyltransferase reaction in livers from untreated and clofibrate-treated rats. In skeletal muscle, the acyl-CoA synthetase activities could be detected only in the presence of detergents.     

Glucagon and fasting do not activate peroxisomal fatty acid beta-oxidation in rat liver

In a study of the endocrine control of peroxisomes, the effects of acute glucagon treatment and fasting on hepatic peroxisomal beta-oxidation in rats have been investigated. The activity of the rate-limiting peroxisomal beta-oxidation enzyme, fatty acyl-CoA oxidase, was measured to determine whether activation of peroxisomal beta-oxidation could account for the increase in total hepatic fatty acid oxidation following acute glucagon exposure. Catalase, a peroxisomal enzyme not directly involved in beta-oxidation, was also measured as a control for total peroxisomal activity. No changes with acute glucagon treatment of intact animals were observed with either activity as measured in liver homogenates or partially purified peroxisomal fractions. These observations indicate the lack of acute control by glucagon of peroxisomal function at the level of total enzyme activity. Previous work on the effects of fasting on hepatic fatty acid beta-oxidation [H. Ishii, S. Horie, and T. Suga (1980) J. Biochem. 87, 1855-1858] suggested an enhanced role for the peroxisomal beta-oxidation pathway during starvation. It was found that the peroxisomal beta-oxidation system, as measured by fatty acyl-CoA oxidase activity, does increase with duration of fast when expressed on a per gram wet weight liver basis. However, when this activity is expressed as total liver capacity, a decline in activity with increasing duration of fast is observed. Furthermore, this decline in peroxisomal capacity parallels the decline in total liver capacity for citrate synthase, a mitochondrial matrix enzyme, and total liver protein. These data indicate that peroxisomal beta-oxidation activity is neither stimulated nor even preferentially spared from proteolysis during fasting.     

Differential effects of freezing on total hepatic peroxisomal fatty acid oxidation and on the rate-limiting enzyme, acyl-CoA oxidase

Fatty acid oxidation defects can be acutely fatal, leading to the collection of tissues which are frozen for future analysis. Since peroxisomes can also oxidize long-chain fatty acids, differentiation of the contributions from the peroxisome as opposed to the mitochondria is important. We studied the effects of freezing and storage of rat livers on peroxisomal and mitochondrial beta-oxidation as measured by cyanide sensitivity of the oxidation of [1-14C]oleoyl-CoA to 14CO2 and acid-soluble labeled products. In addition, we examined the effects of freezing and storage on the rate-limiting enzyme for peroxisomal beta-oxidation, acyl-CoA oxidase, by the H2O2 generation method. Marked reduction in the oxidation of [1-14C]oleoyl-CoA was found for both peroxisomal and mitochondrial systems upon freezing at -18 or -70 degrees C for 2 days which declined further on storage at these temperatures for 12 weeks. Loss of activity after freezing was greater for the mitochondrial than the peroxisomal beta-oxidation system. By contrast, acyl-CoA oxidase activity was resistant to these changes, maintaining prefrozen activities despite storage for 12 weeks. The contribution of the peroxisomal system to beta-oxidation was 32% of the total rate of oxidation of [1-14C]oleoyl-CoA in the rat liver. These findings indicate that the contributions of the peroxisomal system to total fatty acid oxidation may be considerable, that freezing of the liver results in drastic reduction in enzyme activities of both peroxisomal as well as mitochondrial beta-oxidation, but that the rate-limiting enzyme of the peroxisomal system, acyl-CoA oxidase, retains full activity despite freezing and storage.     

Structure and function of plant acyl-CoA oxidases.

Acyl-CoA oxidases (in peroxisomes) and acyl-CoA dehydrogenases (in mitochondria) catalyse the first step in fatty acid beta-oxidation, the pathway responsible for lipid catabolism and plant hormone biosynthesis. The interplay and differences between peroxisomal and mitochondrial beta-oxidation processes are highlighted by the variation in the enzymes involved. Structure and sequence comparisons are made with a focus on the enzyme's mechanistic means to control electron transfer paths, reactivity towards molecular oxygen, and spatial and architectural requirements for substrate discrimination.     

Postnatal development of peroxisomal and mitochondrial enzymes in rat liver.

Subcellular organellles from livers of rats three days prenatal to 50 weeks postnatal were separated on sucrose gradients. The peroxisomes had a constant density of 1.243 g/ml throughout the life of the animal. The density of the mitochondria changed from about 1.236 g/ml at birth to a constant value of 1.200 g/ml after two weeks. The peroxisomal and mitochondrial fatty acid beta-oxidation and the peroxisomal and supernatant activities of catalase and glycerol-3-phosphate dehydrogenase were measured at each age, as well as the peroxisomal core enzyme, urate oxidase, and the mitochondrial matrix enzyme, glutamate dehydrogenase. All of these activities were very low or undetectable before birth. Mitochondrial glutamate dehydrogenase and peroxisomal urate oxidase reached maximal activities per g of liver at two and five weeks of age, respectively. Fatty acid beta-oxidation in both peroxisomes and mitochondria and peroxisomal glycerol-3-phosphate dehydrogenase exhibited maximum activities per g of liver between one and two weeks of age before weaning and then decreased to steady state levels in the adult. Peroxisomal beta-oxidation accounted for at least 10% of the total beta-oxidation activity in the young rat liver, but became 30% of the total in the liver of the adult female and 20% in the adult male due to a decrease in mitochondrial beta-oxidation after two weeks of age. The greatest change in beta-oxidation was in the mitochondrial fraction rather than in the peroxisomes. At two weeks of age, four times as much beta-oxidation activity was in the mitochondria as in the peroxisomal fraction. Peroxisomal glycerol-3-phosphate dehydrogenase activity accounted for 5% to 7% of the total activity in animals younger than one week, but only 1% to 2% in animals older than one week. Up to three weeks of age, 85% to 90% of the liver catalase was recovered in the peroxisomes. The activity of peroxisomal catalase per g of rat liver remained constant after three weeks of age, but the total activity of catalase further increased 2.5- to 3-fold, and all of the increased activity was in the supernatant fraction.     

Selective inhibition of hepatic peroxisomal fatty acid beta-oxidation by enoximone.

Although beta-oxidation of fatty acids occurs in both peroxisomes and mitochondria, beta-oxidizing enzymes in these organelles have distinct differences in their specifity and sensitivity to inhibitors. In this study, the effects of the phosphodiesterase inhibitor enoximone on hepatic peroxisomal and mitochondrial beta-oxidation were investigated. In liver homogenates from control rats, cyanide-insensitive peroxisomal beta-oxidation of palmitoyl-CoA was inhibited progressively by increasing concentrations of enoximone. Similar results were obtained in liver homogenates from rats pretreated with the known peroxisomal proliferator diethylhexylphthalate. In contrast, mitochondrial beta-oxidation of palmitoyl-CoA was not inhibited by enoximone. These data show that enoximone selectively inhibits basal as well as induced peroxisomal, but not mitochondrial, beta-oxidation of the CoA thioester of long-chain fatty acids. The availability of specific inhibitors of peroxisomal beta-oxidation should prove useful in elucidating regulatory mechanisms operative in this pathway in normal as well as in proliferated peroxisomes.     

Dietary eicosapentaenoic acid supplementation accentuates hepatic triglyceride accumulation in mice with impaired fatty acid oxidation capacity

Reduced mitochondrial fatty acid (FA) β-oxidation can cause accumulation of triglyceride in liver, while intake of eicosapentaenoic acid (EPA) has been recommended as a promising novel therapy to decrease hepatic triglyceride content. However, reduced mitochondrial FA β-oxidation also facilitates accumulation of EPA. To investigate the interplay between EPA administration, mitochondrial activity and hepatic triglyceride accumulation, we investigated the effects of EPA administration to carnitine-deficient mice with impaired mitochondrial FA β-oxidation. C57BL/6J mice received a high-fat diet supplemented or not with 3% EPA in the presence or absence of 500 mg mildronate/kg/day for 10 days. Liver mitochondrial and peroxisomal oxidation, lipid classes and FA composition were determined. Histological staining was performed and mRNA level of genes related to lipid metabolism and inflammation in liver and adipose tissue was determined. Levels of pro-inflammatory eicosanoids and cytokines were measured in plasma. The results showed that mildronate treatment decreased hepatic carnitine concentration and mitochondrial FA β-oxidation and induced severe triglyceride accumulation accompanied by elevated systemic inflammation. Surprisingly, inclusion of EPA in the diet exacerbated the mildronate-induced triglyceride accumulation. This was accompanied by a considerable increase of EPA accumulation while decreased total n-3/n-6 ratio in liver. However, inclusion of EPA in the diet attenuated the mildronate-induced mRNA expression of inflammatory genes in adipose tissue. Taken together, dietary supplementation with EPA exacerbated the triglyceride accumulation induced by impaired mitochondrial FA β-oxidation. Thus, further thorough evaluation of the potential risk of EPA supplementation as a therapy for NAFLD associated with impaired mitochondrial FA oxidation is warranted.     

Effect of dietary alpha-linolenic acid on the activity and gene expression of hepatic fatty acid oxidation enzymes

The activities of hepatic fatty acid oxidation enzymes in rats fed linseed and perilla oils rich in alpha-linolenic acid (alpha-18:3) were compared with those in the animals fed safflower oil rich in linoleic acid (18:2) and saturated fats (coconut or palm oil). Mitochondrial and peroxisomal palmitoyl-CoA (16:0-CoA) oxidation rates in the liver homogenates were significantly higher in rats fed linseed and perilla oils than in those fed saturated fats and safflower oil. The fatty oxidation rates increased as dietary levels of alpha-18:3 increased. Dietary alpha-18:3 also increased the activity of fatty acid oxidation enzymes except for 3-hydroxyacyl-CoA dehydrogenase. Unexpectedly, dietary alpha-18:3 caused great reduction in the activity of 3-hydroxyacyl-CoA dehydrogenase measured with short- and medium-chain substrates but not with long-chain substrate. Dietary alpha-18:3 significantly increased the mRNA levels of hepatic fatty acid oxidation enzymes including carnitine palmitoyltransferase I and II, mitochondrial trifunctional protein, acyl-CoA oxidase, peroxisomal bifunctional protein, mitochondrial and peroxisomal 3-ketoacyl-CoA thiolases, 2, 4-dienoyl-CoA reductase and delta3, delta2-enoyl-CoA isomerase. Fish oil rich in very long-chain n-3 fatty acids caused similar changes in hepatic fatty acid oxidation. Regarding the substrate specificity of beta-oxidation pathway, mitochondrial and peroxisomal beta-oxidation rate of alpha-18:3-CoA, relative to 16:0- and 18:2-CoAs, was higher irrespective of the substrate/albumin ratios in the assay mixture or dietary fat sources. The substrate specificity of carnitine palmitoyltransferase I appeared to be responsible for the differential mitochondrial oxidation rates of these acyl-CoA substrates. Dietary fats rich in alpha-18:3-CoA relative to safflower oil did not affect the hepatic activity of fatty acid synthase and glucose 6-phosphate dehydrogenase. It was suggested that both substrate specificities and alterations in the activities of the enzymes in beta-oxidation pathway play a significant role in the regulation of the serum lipid concentrations in rats fed alpha-18:3.     

Quantitative proteomic comparison of mouse peroxisomes from liver and kidney

The peroxisome plays a central role in the catabolic and anabolic pathways that contribute to the lipid homeostasis. Besides this main function, this organelle has gained functional diversity. Although several approaches have been used for peroxisomal proteome analysis, a quantitative protein expression analysis of peroxisomes from different tissues has not been elucidated yet. Here, we applied a 2-DE-based method on mouse liver and kidney peroxisomal enriched fractions to study the tissue-dependent protein expression. Ninety-one spots were identified from the 2-DE maps from pH 3.0-10.0 and 51 spots from the basic range corresponding to 31 peroxisomal proteins, 10 putative peroxisomal, 6 cytosolic, 17 mitochondrial and 1 protein from endoplasmic reticulum. Based on the identification and on the equivalent quality of both tissue preparations, the differences emerging from the comparison could be quantified. In liver, proteins involved in pathways such as alpha- and beta-oxidation, isoprenoid biosynthesis, amino acid metabolism and purine and pyrimidine metabolism were more abundant whereas in kidney, proteins from the straight-chain fatty acid beta-oxidation were highly expressed. These results indicate that tissue-specific functional classes of peroxisomal proteins could be relevant to study peroxisomal cellular responses or pathologies. Finally, a web-based peroxisomal proteomic database was built.     

Fatty acid composition and lipid peroxidation of soft-shelled turtle, Pelodiscus sinensis, fed different dietary lipid sources

Juvenile soft-shelled turtles (Pelodiscus sinensis) were fed 7 diets containing 8% of lard, soybean oil, olive oil, menhaden fish oil, or mixtures of 1 to 1 ratio of fish oil and lard, soybean oil, olive oil for 10 weeks. Growth and muscle proximate compositions of the turtles were not affected by different dietary treatments (p>0.05). Fatty acid profiles in muscle polar lipids, muscle non-polar lipids, and liver polar lipids reflected the fatty acid composition of dietary lipid source. Turtles fed diets containing fish oil generally contained significantly higher (p<0.05) proportion of highly unsaturated fatty acids (HUFA) in both polar and non-polar lipids of muscle and polar fraction of liver lipids than those fed other oils. Non-polar fraction of liver lipids from all groups of turtles contained less than 1% of HUFA. All turtles contained relatively high proportions of oleic acid in their lipids regardless of the dietary lipid source. Further, lipid peroxidation in both muscle tissue and liver microsomes of turtles fed fish oil as the sole lipid source was greater (p<0.05) than those fed fish oil-free diets. Turtles fed olive oil as the sole lipid source had the lowest lipid peroxidation rate among all dietary groups. The results indicate that dietary n-3 HUFA may not be crucial for optimal growth of soft-shelled turtles although they may be used for metabolic purpose. Further, high level of dietary HUFA not only increases the HUFA content in turtle tissues, but also enhances the susceptibility of these tissues to lipid peroxidation.