Long-term effect of tetradecylthioacetic acid: a study on plasma lipid profile and fatty acid composition and oxidation in different rat organs

Genome wide response to dietary tetradecylthioacetic acid supplementation in the heart of Atlantic Salmon (Salmo salar L)

Background

Under-dimensioned hearts causing functional problems are associated with higher mortality rates in intensive Atlantic salmon aquaculture. Previous studies have indicated that tetradecylthioacetic acid (TTA) induces cardiac growth and also stimulates transcription of peroxisome proliferator activated receptors (PPAR) αand βin the Atlantic salmon heart. Since cardiac and transcriptional responses to feed are of high interest in aquaculture, the objective of this study was to characterize the transcriptional mechanisms induced by TTA in the heart of Atlantic salmon.

Results

Atlantic salmon were kept at sea for 17 weeks. During the first 8 weeks the fish received a TTA supplemented diet. Using microarrays, profound transcriptional effects were observed in the heart at the end of the experiment, 9 weeks after the feeding of TTA stopped. Approximately 90% of the significant genes were expressed higher in the TTA group. Hypergeometric testing revealed the over-representation of 35 gene ontology terms in the TTA fed group. The GO terms were generally categorized into cardiac performance, lipid catabolism, glycolysis and TCA cycle.

Conclusions

Our results indicate that TTA has profound effects on cardiac performance based on results from microarray and qRT-PCR analysis. The gene expression profile favors a scenario of ”physiological”lright hypertrophy recognized by increased oxidative fatty acid metabolism, glycolysis and TCA cycle activity as well as cardiac growth and contractility in the heart ventricle. Increased cardiac efficiency may offer significant benefits in the demanding Aquaculture situations.

Dietary supplementation of tetradecylthioacetic acid increases feed intake but reduces body weight gain and adipose depot sizes in rats fed on high-fat diets

AIM

The pan-peroxisome proliferator-activated receptor (PPAR) ligand and fatty acid analogue tetradecylthioacetic acid (TTA) may reduce plasma lipids and enhance hepatic lipid metabolism, as well as reduce adipose tissue sizes in rats fed on high-fat diets. This study further explores the effects of TTA on weight gain, feed intake and adipose tissue functions in rats that are fed a high-fat diet for 7 weeks.

METHODS

The effects on feed intake and body weight during 7 weeks' dietary supplement with TTA ( approximately 200 mg/kg bw) were studied in male Wistar rats fed on a lard-based diet containing approximately 40% energy from fat. Adipose tissue mass, body composition and expression of relevant genes in fat depots and liver were measured at the end of the feeding.

RESULTS

Despite higher feed intake during the final 2 weeks of the study, rats fed on TTA gained less body weight than lard-fed rats and had markedly decreased subcutaneous, epididymal, perirenal and mesenteric adipose depots. The effects of TTA feeding with reduced body weight gain and energy efficiency (weight gain/feed intake) started between day 10 and 13. Body contents of fat, protein and water were reduced after feeding lard plus TTA, with a stronger decrease in fat relative to protein. Plasma lipids, including Non-Esterified Fatty Acids (NEFA), were significantly reduced, whereas fatty acid beta-oxidation in liver and heart was enhanced in lard plus TTA-fed rats. Hepatic UCP3 was expressed ectopically both at protein and mRNA level (>1900-fold), whereas Ucp1 mRNA was increased approximately 30-fold in epididymal and approximately 90-fold in mesenteric fat after lard plus TTA feeding.

CONCLUSION

Our data support the hypothesis that TTA feeding may increase hepatic fatty acid beta-oxidation, and thereby reduce the size of adipose tissues. The functional importance of ectopic hepatic UCP3 is unknown, but might be associated with enhanced energy expenditure and thus the reduced feed efficiency.

Cardiac peroxisome proliferator-activated receptor-alpha activation causes increased fatty acid oxidation, reducing efficiency and post-ischaemic functional loss

AIMS

Myocardial fatty acid (FA) oxidation is regulated acutely by the FA supply and chronically at the transcriptional level owing to FA activation of peroxisome proliferator-activated receptor-alpha (PPARalpha). However, in vivo administration of PPARalpha ligands has not been shown to increase cardiac FA oxidation. In this study we have examined the cardiac response to in vivo administration of tetradecylthioacetic acid (TTA, 0.5% w/w added to the diet for 8 days), a PPAR agonist with primarily PPARalpha activity.

METHODS AND RESULTS

Despite the fact that TTA treatment decreased plasma concentrations of lipids [FA and triacylglycerols (TG)], hearts from TTA-treated mice showed increased mRNA expression of PPARalpha target genes. Cardiac substrate utilization, ventricular function, cardiac efficiency, and susceptibility to ischaemia-reperfusion were examined in isolated perfused hearts. In accordance with the mRNA changes, myocardial FA oxidation was increased 2.5-fold with a concomitant reduction in glucose oxidation. This increase in FA oxidation was abolished in PPARalpha-null mice. Thus, it appears that the metabolic effects of TTA on the heart must be owing to a direct stimulatory effect on cardiac PPARalpha. Hearts from TTA-treated mice also showed a marked reduction in cardiac efficiency (because of a two-fold increase in unloaded myocardial oxygen consumption) and decreased recovery of ventricular contractile function following low-flow ischaemia.

CONCLUSION

This study for the first time observed that in vivo administration of a synthetic PPARalpha ligand elevated FA oxidation, an effect that was also associated with decreased cardiac efficiency and reduced post-ischaemic functional recovery.

Thia fatty acids with the sulfur atom in even or odd positions have opposite effects on fatty acid catabolism

As tools for mechanistic studies on lipid metabolism, with the long-term goal of developing a drug for the treatment of lipid disorders, thia FA with the sulfur atom inserted at positions 3-9 from the carboxyl group were fed to male Wistar rats for 1 wk to determine their impact on key parameters in lipid metabolism and hepatic levels of thia FA metabolites. Thia FA with the sulfur atom in even positions decreased hepatic and cardiac mitochondrial beta-oxidation and profoundly increased hepatic and cardiac TAG levels. The plasma TAG level was unchanged and the hepatic acyl-CoA oxidase activity increased. In contrast, thia FA with the sulfur atom in odd positions, especially 3-thia FA, tended to increase hepatic and cardiac FA oxidation and acyl-CoA oxidase and carnitine palmitoyltransferase-II activities, and decreased the plasma TAG levels. The effects seem to be related to differences in the catabolic rate of the thia FA. Differences between the two groups of acids were also observed with respect to the regulation of genes involved in FA transport and catabolism. Feeding experiments with 3- and 4-thia FA in combination indicated that the 4-thia FA partly attenuated the effects of the 3-thia FA on mitochondrial FA oxidation and the hepatic TAG level. In summary, the position of the sulfur atom in the alkyl chain, especially whether it is placed in the even or odd position, is crucial for the biological effect of the thia FA.

Effects of dietary thia fatty acids on lipid composition, morphology and macrophage function of Atlantic salmon (Salmo salar L.) kidney

High lipid levels are being used in modern salmonid diets to promote rapid growth; however there is a limiting supply of the traditional fish oils as the fish farming industry expands. One way to utilize the lipid sources better, could be to find ways to stimulate fatty acid (FA) oxidation so that Atlantic salmon use more energy for muscle growth and less for storage in perivisceral adipose tissue. We have previously shown that dietary inclusion of the thia FA tetradecylthioacetic acid (TTA) promoted hepatic beta-oxidation and reduced total body lipid levels. However, dietary TTA also had some negative effects, leading to accumulation of sulfone and sulfoxide metabolites of TTA in the kidney and increasing mortality rates, particularly at low water temperatures. Therefore we also wish to investigate the effects of TTA on kidney function at high and low temperatures, including some immune system parameters. The production of leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) immunoreactive material from exogenously added arachidonic acid in isolated head kidney macrophages was affected by both diet and temperature. The phagocytic activity in these cells was reduced by DTA in the 12 degrees C group and there was significantly higher protein degradation in head kidney macrophages at 12 degrees C compared to 5 degrees C in all dietary groups. Interestingly, the incorporation of thia FAs in the kidney was higher at 5 degrees C (0.3% TTA and 0.6% DTA) than at 12 degrees C (0.1% TTA and 0.5% DTA). Additionally, there were lower levels of saturated FAs, while higher levels of polyunsaturated FAs (PUFAs) in the kidney of TTA fed fish at 5 degrees C. We also observed temperature-independent tubular dilatation and a reduction in the density of melanomacrophages of the kidney in salmon fed TTA. Nevertheless, the mRNA expression of some immune-relevant genes in head kidney tissue was not affected by TTA-inclusion in salmon diets. In conclusion, it is clear that 0.6% TTA-inclusion in the feed leads to changes in the kidney function particularly at low water temperatures.

Prevention of Hypertension and Organ Damage in 2-Kidney, 1-Clip Rats by Tetradecylthioacetic Acid

Dietary lipids are reported to affect the blood pressure in both humans and experimental animal models with hypertension. In the present study, 2-kidney, 1-clip (2K1C) hypertensive rats were treated with the modified fatty acid tetradecylthioacetic acid (TTA) from the time of clipping or after hypertension was established. TTA treatment attenuated the development of hypertension and reduced established 2K1C hypertension. The mRNA level of renin in the clipped kidney and the plasma renin activity were markedly reduced, and the plasma angiotensin II level tended to decrease after TTA treatment. In addition, TTA reduced the mRNA level of angiotensinogen in white adipose tissue. Prevention of organ damage was demonstrated by normal urinary excretion of protein, maintained serum albumin, lower heart weight, and clearly reduced vascular, glomerular, and tubulointerstitial damage in the nonclipped kidney. Renal function was not affected as estimated by unchanged plasma creatinine. Furthermore, the serum levels of triacylglycerol and cholesterol were reduced by TTA. The serum fatty acid composition was changed, resulting in a favorable increase of oleic acid. However, the levels of all of the omega-3 fatty acids and of linoleic acid were reduced, and no change was seen in the level of arachidonic acid, but the urinary excretion of 8-iso-prostaglandin F2α was declined. In conclusion, TTA attenuated the development of hypertension, reduced established hypertension, and prevented the development of organ damage in 2K1C rats, possibly by reducing the amounts of the vasoconstrictors angiotensin II and 8-iso-prostaglandin F2α and by inducing a favorable increase of oleic acid in serum.

Effects of 3-thia fatty acids on expression of some lipid related genes in Atlantic salmon (Salmo salar L.)

In this study, the effects of in vivo administration of 3-thia fatty acids (FAs) on lipid metabolism in muscle and liver of Atlantic salmon were investigated. Prior to analysis, the fish were kept in tanks supplied with 5 degrees C seawater for 20 weeks. The fish were fed fish meal and fish oil (FO)-based diets supplemented with either nothing (FO), or 0.3% and 0.6% of the 3-thia FAs dodecylthioacetic acid (DTA) and tetradecylthioacetic acid (TTA) respectively. The fish grew from an initial weight of 110 g to 220 g in the FO group and to approximately 160 g in the 3-thia FA groups. There was a significant higher mortality (66%) in fish fed 0.6% TTA than in fish fed the 0.3% DTA (15%) and FO diets (15%). None of the 3-thia FA diets affected the lipid content of the salmon muscle. The liver index, however, was significantly higher and the total liver fat content lower in the TTA group than in the FO group. Both DTA and TTA were incorporated into the lipid fraction of muscle and liver (0.4% to 0.9%). There were no major differences in the total FA composition of liver and muscle between the dietary groups; except for a small increase of n-3 polyunsaturated FAs (PUFAs) in liver of the DTA group. The mRNA expression of peroxisome proliferator-activated receptor (PPAR) alpha, apolipoprotein AI (ApoAI), apolipoprotein CII (ApoCII) and low-density lipoprotein receptor (LDL-R) was down-regulated in liver of the salmon fed 0.3% DTA. PPARalpha and ApoAI transcripts were also reduced in liver of salmon fed 0.6% TTA. Additionally, the hepatic lipoprotein lipase (LPL) mRNA level was 3.8 fold increased in TTA fish relative to the FO group. In muscle there were no significant changes in gene expression pattern of any of the genes investigated. This is the first report on the effects of 3-thia FAs on gene expression in Atlantic salmon.

Phospholipid molecular species, beta-oxidation, desaturation and elongation of fatty acids in Atlantic salmon hepatocytes: effects of temperature and 3-thia fatty acids

We have investigated the effects of a 3-thia fatty acid (TTA) and of temperature on the fatty acid (FA) metabolism of Atlantic salmon (Salmo salar). One experiment investigated the activity of the peroxisomal beta-oxidation enzyme, acyl-CoA oxidase (ACO), and the incorporation of TTA into phospholipid (PL) molecular species. Salmon hepatocytes in culture were incubated either without TTA (control(spades)) or with 0.8 mM TTA (TTA(spades)) in a short term (48 h) temperature study at 5 degrees C and at 12 degrees C. TTA was incorporated into the four PL classes studied: phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidylserine (PS). TTA was preferentially esterified with 18:1, 16:1, 20:4 and 22:6 in the PLs. Hepatocytes incubated with TTA had higher ACO activity at 5 degrees C than at 12 degrees C. In a second experiment salmon were fed a diet based on fish meal-fish oil without any TTA added (control) or a fish meal-fish oil diet supplemented with 0.6% TTA for 8 weeks at 12 degrees C and 20 weeks at 5 degrees C. At the end of the feeding trial, hepatocytes from fish acclimated to high or low temperatures were isolated from both dietary groups and incubated with either [1-(14)C]18:1 n-9 or [1-(14)C]20:4 n-3 at 5 degrees C or 12 degrees C. Radiolabelled 18:1 n-9 was mainly esterified into neutral lipids (NL), whereas [1-(14)C]20:4 n-3 was mainly esterified into PL at both temperatures. The rate of elongation of [1-(14)C]18:1 n-9 to 20:1 n-9 was twice as high in hepatocytes from fish fed the control diet than it was in hepatocytes from fish fed the TTA diet, at both temperatures. The amount of [1-(14)C]20:4 n-3 converted to 22:6 n-3 was approximately the same in hepatocytes from the two dietary groups, but there was a tendency to higher production of 22:6 n-3 at the lower temperature. Oxidation of [1-(14)C]18:1 n-9 to acid soluble products (ASP) and CO(2) was approximately 10-fold greater in hepatocytes kept at 5 degrees C than in those kept at 12 degrees C and the main oxidation products formed were acetate, oxaloacetate and malate.

Effects of 3-thia fatty acids on feed intake, growth, tissue fatty acid composition, beta-oxidation and Na+,K+-ATPase activity in Atlantic salmon

Atlantic salmon (Salmo salar) with an initial mass of 86 g were reared in 12 degrees C seawater for 8 weeks to a final average mass of 250 g. The fish were fed fish meal and fish oil-based diet supplemented with either 0%, 0.3% or 0.6% of tetradecylthioacetic acid (TTA), a 3-thia fatty acid. The specific growth rate (SGR) decreased with increasing dietary dose of TTA. The SGR of the group fed 0% of TTA (Control) was 1.8; that of the group fed 0.3% of TTA (TTA-L) was 1.7, and that of the group fed 0.6% of TTA (TTA-H) was 1.5. The mortality increased with increased dietary dose of TTA. The mitochondrial beta-oxidation capacity in the liver of fish fed the TTA diets was 1.5 to 2 times higher than that of the Control fish. TTA supplementation caused substantial changes in the fatty acid compositions of the phospholipids (PL), triacylglycerols (TAG) and free fatty acids (FFA) of gills, heart and liver. The percentages of n-3 fatty acids, particularly 22:6 n-3, increased in fish fed diets containing TTA, while the percentage of the saturated FAs 14:0 and 16:0 in the PL fractions of the gills and heart decreased. The sum of monounsaturated FAs in the PL and TAG fractions from liver was significantly higher in fish fed diets containing TTA. TTA itself was primarily incorporated into PL. Two catabolic products of TTA (sulphoxides of TTA) were identified, and these products were particularly abundant in the kidney. TTA supplementation had no significant effect on the activity of the membrane-bound enzyme Na(+),K(+)-ATPase.

The metabolic syndrome and the hepatic fatty acid drainage hypothesis

Much data indicates that lowering of plasma triglyceride levels by hypolipidemic agents is caused by a shift in the liver metabolism towards activation of peroxisome proliferator activated receptor (PPAR)alpha-regulated fatty acid catabolism in mitochondria. Feeding rats with lipid lowering agents leads to hypolipidemia, possibly by increased channeling of fatty acids to mitochondrial fatty acid oxidation at the expense of triglyceride synthesis. Our hypothesis is that increased hepatic fatty acid oxidation and ketogenesis drain fatty acids from blood and extrahepatic tissues and that this contributes significantly to the beneficial effects on fat mass accumulation and improved peripheral insulin sensitivity. To investigate this theory we employ modified fatty acids that change the plasma profile from atherogenic to cardioprotective. One of these novel agents, tetradecylthioacetic acid (TTA), is of particular interest due to its beneficial effects on lipid transport and utilization. These hypolipidemic effects are associated with increased fatty acid oxidation and altered energy state parameters of the liver. Experiments in PPAR alpha-null mice have demonstrated that the effects hypolipidemic of TTA cannot be explained by altered PPAR alpha regulation alone. TTA also activates the other PPARs (e.g., PPAR delta) and this might compensate for deficiency of PPAR alpha. Altogether, TTA-mediated clearance of blood triglycerides may result from a lowered level of apo C-III, with a subsequently induction of hepatic lipoprotein lipase activity and (re)uptake of fatty acids from very low density lipoprotein (VLDL). This is associated with an increased hepatic capacity for fatty acid oxidation, causing drainage of fatty acids from the blood stream. This can ultimately be linked to hypolipidemia, anti-adiposity, and improved insulin sensitivity.

Metabolic effects of thia fatty acids

Thia substituted fatty acids are saturated fatty acids which are modified by insertion of a sulfur atom at specific positions in the carbon backbone. During the last few years pleiotropic effects of the 3-thia fatty acid tetradecylthioacetic acid have been revealed. The biological responses to tetradecylthioacetic acid include mitochondrial proliferation, increased catabolism of fatty acids, antiadiposity, improvement in insulin sensitivity, antioxidant properties, reduced proliferation and induction of apoptosis in rapidly proliferating cells, cell differentiation and antiinflammatory action. These biological responses indicate that tetradecylthioacetic acid changes the plasma profile from atherogenic to cardioprotective. As a pan-peroxisome proliferator-activated receptor ligand, tetradecylthioacetic acid regulates the adipose tissue mass and the expression of lipid metabolizing enzymes, particularly those involved in catabolic pathways. In contrast, circumstantial evidences suggest that peroxisome proliferator-activated receptor-independent metabolic pathways may be of importance for the antioxidant, antiproliferative and antiinflammatory action of tetradecylthioacetic acid.

Inhibition of rat lipoprotein oxidation after tetradecylthioacetic acid feeding

We have previously shown that tetradecylthioacetic acid (TTA), a sulfur containing saturated fatty acid analogue, inhibits the oxidative modification of human low-density lipoprotein (LDL) in vitro. The oxidative modification of LDL is believed to be a crucial step in the progression of atherosclerosis. In the present study, we investigated the effect of TTA oral administration on the susceptibility of rat lipoprotein to undergo oxidative modification ex vivo. Lipoprotein resistance to copper-induced oxidation was highly improved after TTA administration to rats. Conjugated dienes produced after 150 min of lipoprotein oxidation were dramatically lowered in the TTA treated rats compared to controls. Malondialdehyde and lipid peroxides production by oxidation was highly limited. These effects were independent of any Vitamin E effects. More than 50% relative reduction in polyunsaturated fatty acids of the n-3 family, and more than 30% relative increase in 18:1n-9 fatty acid in the triacylglycerol (TAG)-rich lipoprotein were observed. TAG-rich lipoprotein lipids of TTA fed rats were decreased with more than 50% reduction in TAG. The data reported in this paper indicate a potent in vivo antioxidant capability of TTA that beside its hypolipidemic effect might be of importance in relation to the development of atherosclerosis.

Increase in hepatic expression of SREBP-2 by gemfibrozil administration to rats

It is well known that gemfibrozil increases the biliary output of cholesterol and phospholipids, but we have little knowledge about the impact these changes have on liver cholesterol and phospholipid biosynthetic pathways. In the present study, no changes were detected in liver lipids and CTP:phosphocholine cytidylyltransferase after gemfibrozil administration to rats. On the contrary, 3-hydroxy-3-methylglutaryl-CoA reductase mRNA (9.9-fold) and Rd activity (16.7-fold) and phosphatidate phosphohydrolase activity (1.7-fold) increased, while plasma apo B-cholesterol (40%) and triglyceride (43%) levels decreased. As a part of a compensatory homeostatic response, we report for the first time that gemfibrozil administration to rats increased the hepatic sterol regulatory element binding protein-2 (SREBP-2) mRNA (2.9-fold) and mature protein (2.2-fold) levels. An early increase in the transcriptional activity of SREBP-2 elicited by gemfibrozil administration might be responsible for the observed changes in HMG-CoA reductase, phosphatidate phosphohydrolase, and SREBP-2 expression.

The biochemistry of hypo- and hyperlipidemic fatty acid derivatives: metabolism and metabolic effects

A selection of amphipatic hyper- and hypolipidemic fatty acid derivatives (fibrates, thia- and branched chain fatty acids) are reviewed. They are probably all ligands for the peroxisome proliferation activation receptor (PPARalpha) which has a low selectivity for its ligands. These compounds give hyper- or hypolipidemic responses depending on their ability to inhibit or stimulate mitochondrial fatty acid oxidation in the liver. The hypolipidemic response is explained by the following metabolic effects: Lipoprotein lipase is induced in liver where it is normally not expressed. Apolipoprotein CIII is downregulated. These two effects in liver lead to a facilitated (re)uptake of chylomicrons and VLDL, thus creating a direct transport of fatty acids from the gut to the liver. Fatty acid metabolizing enzymes in the liver (CPT-I and II, peroxisomal and mitochondrial beta-oxidation enzymes, enzymes of ketogenesis, and omega-oxidation enzymes) are induced and create an increased capacity for fatty acid oxidation. The increased oxidation of fatty acids "drains" fatty acids from the body, reduces VLDL formation, and ultimately explains the antiadiposity and improved insulin sensitivity observed after administration of peroxisome proliferators.

Methylated eicosapentaenoic acid and tetradecylthioacetic acid: effects on fatty acid metabolism

We introduced methyl or ethyl groups to the 2- or 3-position of the eicosapentaenoic acid (EPA) molecule to investigate whether the branching of EPA could influence its hypolipidemic effect in rats. The most effective branching involved two methyl groups in the 2-position and one methyl group in the 3-position. These EPA derivatives increased hepatic mitochondrial and peroxisomal beta-oxidation and decreased plasma lipids concomitant with suppressed acetyl-coenzyme A (CoA) carboxylase (EC 6.4.1.2) and fatty acid synthase (EC 2.3.1.85) activities. This was followed by elevated activities of camitine O-palmitoyltransferase (EC 2.3.1.21) and possibly 2,4-dienoyl-CoA reductase (EC 1.3.1.34), as well as induced mRNA levels of these enzymes and fatty acyl-CoA oxidase. The fatty acid composition in liver changed, with an increased 18:1 n-9 content, whereas the expression of delta9-desaturase remained unchanged. We investigated the flux of fatty acids in cultured hepatocytes, and found that oxidation of [1-14C]-labeled palmitic acid increased but the secretion of palmitic acid-labeled triglycerides decreased after addition of 2-methyl-EPA. The fatty acyl-CoA oxidase (EC 1.3.3.6) activity in these cells remained unchanged. A significant negative correlation was obtained between palmitic acid oxidation and palmitic acid-labeled synthesized triglycerides. To investigate whether the hypolipidemic effect occurred independently of induced peroxisomal beta-oxidation, we fed rats 2-methyl-tetradecylthioacetic acid. This compound increased the peroxisomal but not the mitochondrial beta-oxidation, and the plasma lipid levels were unchanged. In conclusion, EPA methylated in the 2- or 3-position renders it more potent as a hypolipidemic agent. Furthermore, this study supports the hypothesis that the mitochondrion is the primary site for the hypolipidemic effect.

Early modulation of genes encoding peroxisomal and mitochondrial beta-oxidation enzymes by 3-thia fatty acids

The aim of the present study was to elucidate the effects of a single dose of 3-thia fatty acids (tetradecylthioacetic acid and 3-thiadicarboxylic acid) over a 24-hr study period on the expression of genes related to peroxisomal and mitochondrial beta-oxidation in liver of rats. The plasma triglyceride level decreased at 2-4 hr, 4-8 hr, and 8-24 hr, respectively, after a single dose of 150, 300, or 500 mg of 3-thia fatty acids/kg body weight. Four to eight hours after administration of 3-thia fatty acids, a several-fold-induced gene expression of peroxisomal multifunctional protein, fatty acyl-CoA oxidase (EC 1.3.3.6), fatty acid binding protein, and 2,4-dienoyl-CoA reductase (EC 1.3.1.43) resulted, concomitant with increased activity of 2,4-dienoyl-CoA reductase and fatty acyl-CoA oxidase. The expression of carnitine palmitoyltransferase-I and carnitine palmitoyltransferase-II increased at 2 and 4 hr, respectively, although at a smaller scale. In cultured hepatocytes, 3-thia fatty acids stimulated fatty acid oxidation after 4 hr, and this was both L-carnitine- and L-aminocarnitine-sensitive. The hepatic content of eicosapentaenoic acid and docosahexaenoic acid decreased throughout the study period. In contrast, the hepatic content of oleic acid tended to increase after 24 hr and was significantly increased after repeated administration of 3-thia fatty acids. Similarly, the expression of delta9-desaturase was unchanged during the 24-hr study, but increased after feeding for 5 days. To conclude, carnitine palmitoyltransferase-I expression seemed to be induced earlier than 2,4-dienoyl-CoA reductase and fatty acid binding protein, and not later than the peroxisomal fatty acyl-CoA oxidase. The expression of delta9-desaturase showed a more delayed response.

Carnitine palmitoyltransferase I, carnitine palmitoyltransferase II, and acyl-CoA oxidase activities in Atlantic salmon (Salmo salar)

Salmon farmers are currently using high-energy feeds containing up to 35% fat; the fish's capability of fully utilizing these high-energy feeds has received little attention. Carnitine is an essential component in the process of mitochondrial fatty acid oxidation and, with the cooperation of two carnitine palmitoyltransferases (CPT-I and CPT-II) and a carnitine acylcarnitine transporter across the inner mitochondrial membrane, acts as a carrier for acyl groups into the mitochondrial matrix where beta-oxidation occurs. However, no reports are available differentiating between CPT-I and CPT-II activities in fish. In order to investigate the potential for fatty acid catabolism, the activities of key enzymes involved in fatty acid oxidation were determined in different tissues from farmed Atlantic salmon (Salmo salar), i.e., acyl-CoA oxidase (ACO) and CPT-I and CPT-II. Malonyl-CoA was a potent inhibitor of CPT-I activity not only in red muscle but also in liver, white muscle, and heart. By expressing the enzyme activities per wet tissue, the CPT-I activity of white muscle equaled that of the red muscle, both being >> liver. CPT-II dominated in red muscle whereas the liver and white muscle activities were comparable. ACO activity was high in the liver regardless of how the data were calculated. Based on the CPT-II activity and total palmitoyl-L-carnitine oxidation in white muscle, the white muscle might have a profound role in the overall fatty acid oxidation capacity in fish.

Tetradecylthioacetic acid inhibits the oxidative modification of low density lipoprotein and 8-hydroxydeoxyguanosine formation in vitro

Oxidative modification of low-density lipoprotein (LDL) is thought to play a key role in the formation of foam cells and in initiation and progression of atherosclerotic plaque. The hypolipidemic 3-thia fatty acids contain a sulfur atom and might therefore possess reducing (antioxidant) properties. Consequently, the effects of 3-thia fatty acids on the susceptibility of LDL particles to undergo oxidative modification in vitro were studied. Tetradecylthioacetic acid (TTA), incorporated into the LDL particle and increased the lag time of copper ion induced LDL oxidation in a dose-dependent manner, 80 mumol/L TTA reduced the generation of lipid peroxides during copper ion induced LDL oxidation (for 2 hours) by 100%, 2,2'-azobis-(2,4-dimethylvaleronitrile) induced LDL oxidation by 64%, and 2,2'-azobis-(2-amidinopropane hydrochloride) induced LDL oxidation (for 6 hours) by 21%. The electrophoretic mobility of the oxidized LDL was reduced by TTA in both copper ion and azo-compounds initiated oxidation. This fatty acid analogue was effectively able to reduce in a dose dependent manner the formation of 8-hydroxydeoxyguanosine from 2-deoxyguanosine with ascorbic acid as the radical producer. TTA bound copper(II) ions and did not reduce copper(II) to copper(I). It failed to scavenge the 1,1-diphenyl-2-picrylhydrazyl radicals. The results suggest that the modification of LDL in the lipid and protein moieties can be significantly reduced by TTA. This acid may exert its antioxidant effect partially through metal ion binding and through free radical scavenging.

Thia fatty acids, metabolism and metabolic effects

(1) The chemical properties of thia fatty acids are similar to normal fatty acids, but their metabolism (see below: points 2-6) and metabolic effects (see below: points 7-15) differ greatly from these and are dependent upon the position of the sulfur atom. (2) Long-chain thia fatty acids and alkylthioacrylic acids are activated to their CoA esters in endoplasmatic reticulum. (3) 3-Thia fatty acids cannot be beta-oxidized. They are metabolized by extramitochondrial omega-oxidation and sulfur oxidation in the endoplasmatic reticulum followed by peroxisomal beta-oxidation to short sulfoxy dicarboxylic acids. (4) 4-Thia fatty acids are beta-oxidized mainly in mitochondria to alkylthioacryloyl-CoA esters which accumulate and are slowly converted to 2-hydroxy-4-thia acyl-CoA which splits spontaneously to an alkylthiol and malonic acid semialdehyde-CoA ester. The latter presumably is hydrolyzed and metabolized to acetyl-CoA and CO2. (5) Both 3- and 4-thiastearic acid are desaturated to the corresponding thia oleic acids. (6) Long-chain 3- and 4-thia fatty acids are incorporated into phospholipids in vivo, particularly in heart, and in hepatocytes and other cells in culture. (7) Long-chain 3-thia fatty acids change the fatty acid composition of the phospholipids: in heart, the content of n-3 fatty acids increases and n-6 fatty acids decreases. (8) 3-Thia fatty acids increase fatty acid oxidation in liver through inhibition of malonyl-CoA synthesis, activation of CPT I, and induction of CPT-II and enzymes of peroxisomal beta-oxidation. Activation of fatty acid oxidation is the key to the hypolipidemic effect of 3-thia fatty acids. Also other lipid metabolizing enzymes are induced. (9) Fatty acid- and cholesterol synthesis is inhibited in hepatocytes. (10) The nuclear receptors PPAR alpha and RXR alpha are induced by 3-thia fatty acids. (11) The induction of enzymes and of PPAR alpha and RXR alpha are increased by dexamethasone and counteracted by insulin. (12) 4-Thia fatty acids inhibit fatty acid oxidation and induce fatty liver in vivo. The inhibition presumably is explained by accumulation of alkylthioacryloyl-CoA in the mitochondria. This metabolite is a strong inhibitor of CPT-II. (13) Alkylthioacrylic acids inhibits both fatty acid oxidation and esterification. Inhibition of esterification presumably follows accumulation of extramitochondrial alkylthioacryloyl-CoA, an inhibitor of microsomal glycerophosphate acyltransferase. (14) 9-Thia stearate is a strong inhibitor of the delta 9-desaturase in liver and 10-thia stearate of dihydrosterculic acid synthesis in trypanosomes. (15) Some attempts to develop thia fatty acids as drugs are also reviewed.