Inhibition of rat lipoprotein oxidation after tetradecylthioacetic acid feeding

A mitochondria-targeted fatty acid analogue influences hepatic glucose metabolism and reduces the plasma insulin/glucose ratio in male Wistar rats

A fatty acid analogue, 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA), was previously shown to have hypolipidemic effects in rats by targeting mitochondrial activity predominantly in liver. This study aimed to determine if 1-triple TTA could influence carbohydrate metabolism. Male Wistar rats were treated for three weeks with oral supplementation of 100 mg/kg body weight 1-triple TTA. Blood glucose and insulin levels, and liver carbohydrate metabolism gene expression and enzyme activities were determined. In addition, human myotubes and Huh7 liver cells were treated with 1-triple TTA, and glucose and fatty acid oxidation were determined. The level of plasma insulin was significantly reduced in 1-triple TTA-treated rats, resulting in a 32% reduction in the insulin/glucose ratio. The hepatic glucose and glycogen levels were lowered by 22% and 49%, respectively, compared to control. This was accompanied by lower hepatic gene expression of phosphenolpyruvate carboxykinase, the rate-limiting enzyme in gluconeogenesis, and Hnf4A, a regulator of gluconeogenesis. Gene expression of pyruvate kinase, catalysing the final step of glycolysis, was also reduced by 1-triple TTA. In addition, pyruvate dehydrogenase activity was reduced, accompanied by 10-15-fold increased gene expression of its regulator pyruvate dehydrogenase kinase 4 compared to control, suggesting reduced entry of pyruvate into the TCA cycle. Indeed, the NADPH-generating enzyme malic enzyme 1 (ME1) catalysing production of pyruvate from malate, was increased 13-fold at the gene expression level. Despite the decreased glycogen level, genes involved in glycogen synthesis were not affected in livers of 1-triple TTA treated rats. In contrast, the pentose phosphate pathway seemed to be increased as the hepatic gene expression of glucose-6-phosphate dehydrogenase (G6PD) was higher in 1-triple TTA treated rats compared to controls. In human Huh7 liver cells, but not in myotubes, 1-triple-TTA reduced glucose oxidation and induced fatty acid oxidation, in line with previous observations of increased hepatic mitochondrial palmitoyl-CoA oxidation in rats. Importantly, this work recognizes the liver as an important organ in glucose homeostasis. The mitochondrially targeted fatty acid analogue 1-triple TTA seemed to lower hepatic glucose and glycogen levels by inhibition of gluconeogenesis. This was also linked to a reduction in glucose oxidation accompanied by reduced PHD activity and stimulation of ME1 and G6PD, favouring a shift from glucose- to fatty acid oxidation. The reduced plasma insulin/glucose ratio indicate that 1-triple TTA may improve glucose tolerance in rats.

An immunomodulating fatty acid analogue targeting mitochondria exerts anti-atherosclerotic effect beyond plasma cholesterol-lowering activity in apoe(-/-) mice

Tetradecylthioacetic acid (TTA) is a hypolipidemic antioxidant with immunomodulating properties involving activation of peroxisome proliferator-activated receptors (PPARs) and proliferation of mitochondria. This study aimed to penetrate the effect of TTA on the development of atherosclerotic lesions in apolipoprotein (apo)-E^-/- mice fed a high-fat diet containing 0.3% TTA for 12 weeks. These mice displayed a significantly less atherosclerotic development vs control. Plasma cholesterol was increased by TTA administration and triacylglycerol (TAG) levels in plasma and liver were decreased by TTA supplementation, the latter, probably due to increased mitochondrial fatty acid oxidation and reduced lipogenesis. TTA administration also changed the fatty acid composition in the heart, and the amount of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) was reduced and increased, respectively. The heart mRNA expression of inducible nitric oxidase (NOS)-2 was decreased in TTA-treated mice, whereas the mRNA level of catalase was increased. Finally, reduced plasma levels of inflammatory mediators as IL-1α, IL-6, IL-17, TNF-α and IFN-γ were detected in TTA-treated mice. These data show that TTA reduces atherosclerosis in apoE^-/- mice and modulates risk factors related to atherosclerotic disorders. TTA probably acts at both systemic and vascular levels in a manner independent of changes in plasma cholesterol, and triggers TAG catabolism through improved mitochondrial function.

Tetradecylthioacetic acid attenuates inflammation and has antioxidative potential during experimental colitis in rats

BACKGROUND

The fatty acid analogue tetradecylthioacetic acid (TTA) is a moderate pan-activator of peroxisome proliferator-activated receptors (PPARs), and has in previous studies showed potential as an antioxidant and anti-inflammatory agent, both through PPAR and non-PPAR mediated mechanisms.

AIMS

This study aimed to determine whether TTA could alleviate dextran sulfate sodium (DSS)-induced colitis in rats.

METHODS

Male Wistar rats were fed a control diet (control- and DSS-group) or a diet supplemented with 0.4 % TTA (TTA + DSS-group) for 30 days, and DSS was added to the drinking water the last 7 days. Ultrasound measurements were performed at day 29. At day 30, rats were sacrificed and the distal colon was removed for histological evaluation and measurement of cytokine levels, oxidative damage, and gene expression.

RESULTS

The disease activity index was not improved in the TTA + DSS-group compared to the DSS-group. However, ultrasound measurements showed a significantly reduced colonic wall thickening in the TTA + DSS-group. TNF-α, IL-1β, and IL-6 were reduced at the protein and mRNA level in the TTA + DSS-group. Moreover, TTA-treated rats demonstrated reduced colonic oxidative damage, while inducible nitric oxide synthase 2 mRNA expression was elevated in both the DSS- and TTA + DSS-groups. PPARγ signaling may be involved in the anti-inflammatory response to TTA, as Pparg mRNA expression was significantly upregulated in colon.

CONCLUSIONS

This study demonstrated that the pan-PPAR agonist TTA reduced colonic oxidative damage and cytokine levels in a rat model of colitis, and its potential to ameliorate colitis should be further explored.

Long-term treatment with the pan-PPAR agonist tetradecylthioacetic acid or fish oil is associated with increased cardiac content of n-3 fatty acids in rat

BACKGROUND

Excess peroxisome proliferator-activated receptor (PPAR) stimulation has been associated with detrimental health effects including impaired myocardial function. Recently, supplementation with n-3 polyunsaturated fatty acids (PUFA) has been associated with improved left ventricular function and functional capacity in patients with dilated cardiomyopathy. We investigated the long-term effects of the pan-PPAR agonist tetradecylthioacetic acid (TTA) and/or high-dose fish oil (FO) on cardiac fatty acid (FA) composition and lipid metabolism. Male Wistar rats were given one out of four different 25% (w/v) fat diets: control diet; TTA diet; FO diet; or diet containing both TTA and FO.

RESULTS

After 50 weeks n-3 PUFA levels were increased by TTA and FO in the heart, whereas liver levels were reduced following TTA administration. TTA was associated with a decrease in arachidonic acid, increased activities of carnitine palmitoyltransferase II, fatty acyl-CoA oxidase, glycerol-3-phosphate acyltransferase, and fatty acid synthase in the heart. Furthermore, cardiac Ucp3 and Cact mRNA was upregulated.

CONCLUSIONS

Long-term treatment with the pan-PPAR agonist TTA or high-dose FO induced marked changes in PUFA composition and enzymatic activity involved in FA metabolism in the heart, different from liver. Changes included increased FA oxidation and a selective increase in cardiac n-3 PUFA.

Cardioprotective effect of the PPAR ligand tetradecylthioacetic acid in type 2 diabetic mice

Tetradecylthioacetic acid (TTA) is a novel peroxisome proliferator-activated receptor (PPAR) ligand with marked hypolipidemic and insulin-sensitizing effects in obese models. TTA has recently been shown to attenuate dyslipidemia in patients with type 2 diabetes, corroborating the potential for TTA in antidiabetic therapy. In a recent study on normal mice, we showed that TTA increased myocardial fatty acid (FA) oxidation, which was associated with decreased cardiac efficiency and impaired postischemic functional recovery. The aim of the present study was, therefore, to elucidate the effects of TTA treatment (0.5%, 8 days) on cardiac metabolism and function in a hyperlipidemic type 2 diabetic model. We found that TTA treatment increased myocardial FA oxidation, not only in nondiabetic ( db/+) mice but also in diabetic ( db/db) mice, despite a clear lipid-lowering effect. Although TTA had deleterious effects in hearts from nondiabetic mice (decreased efficiency and impaired mitochondrial respiratory capacity), these effects were not observed in db/db hearts. In db/db hearts, TTA improved ischemic tolerance, an effect that is most likely related to the antioxidant property of TTA. The present study strongly advocates the need for investigation of the cardiac effects of PPAR ligands used in antidiabetic/hypolipidemic therapy, because of their pleiotropic properties.

Different adipose depots: their role in the development of metabolic syndrome and mitochondrial response to hypolipidemic agents

Adipose tissue metabolism is closely linked to insulin resistance, and differential fat distributions are associated with disorders like hypertension, diabetes, and cardiovascular disease. Adipose tissues vary in their impact on metabolic risk due to diverse gene expression profiles, leading to differences in lipolysis and in the production and release of adipokines and cytokines, thereby affecting the function of other tissues. In this paper, the roles of the various adipose tissues in obesity are summarized, with particular focus on mitochondrial function. In addition, we discuss how a functionally mitochondrial-targeted compound, the modified fatty acid tetradecylthioacetic acid (TTA), can influence mitochondrial function and decrease the size of specific fat depots.

A casein diet added isoflavone-enriched soy protein favorably affects biomarkers of steatohepatitis in obese Zucker rats

OBJECTIVE

Dietary supplementation of a soy protein enriched with isoflavones (HDI) has been shown to improve fatty liver in obese rats. The main objective of this study was to investigate whether HDI would influence the inflammatory status in livers of obese rats with fatty liver.

METHODS

Male obese Zucker fa/fa rats were fed casein (controls) or casein supplemented with HDI (containing 4.00 g of genistein and 4.50 g of daidzein per kilogram of diet) for 6 wk.

RESULTS

The HDI-fed rats had a markedly lower hepatic concentration of triacylglycerol when compared with controls. The decreased aspartate transaminase/alanine transaminase ratio in plasma, together with lower circulating levels of alkaline phosphatase and bile acids after HDI feeding, implied an improved hepatitis. This was supported by decreased plasma and hepatic mRNA levels of tumor necrosis factor-alpha, lower plasma levels of interleukin-1beta and monocyte chemoattractant protein-1, and an increased anti-inflammatory fatty acid index in plasma. HDI also seemed to protect the rats from oxidative damage, because the level of lipid peroxides in triacylglycerol-rich lipoproteins after in vitro copper oxidation was lower for HDI-fed rats when compared with controls.

CONCLUSION

These results show that isoflavone-enriched soy protein favorably affects biomarkers of hepatic inflammation in obese Zucker fa/fa rats with fatty liver. Thus, dietary soy proteins enriched in isoflavones may be a promising agent to improve steatohepatitis in patients.

Dietary single cell protein reduces fatty liver in obese Zucker rats

There is growing evidence that dietary proteins may interfere with lipid metabolism. We therefore examined the effects of feeding obese Zucker rats a single cell protein (SCP) with low ratios of methionine:glycine and lysine:arginine for 6 weeks. SCP feeding reduced the hepatic steatosis and lowered the plasma transaminase levels when compared with casein-fed rats (controls). The fatty acid oxidation was increased in liver mitochondria and peroxisomes, whereas the activities of enzymes involved in lipogenesis and TAG biosynthesis were unaffected. SCP feeding affected the fatty acid composition of liver lipids and plasma, and reduced the mRNA levels of the fatty acid desaturases. The decreased gene expression of stearoyl-CoA desaturase suggested that the fatty acids were directed towards oxidation rather than esterification as TAG. The decreased mRNA levels of VLDL-receptor and lipoprotein lipase in the liver after SCP feeding suggested that the uptake of TAG-rich lipoprotein to the liver was decreased. To conclude, the reduced fatty liver by SCP feeding may be caused by the increased capacity for fatty acid β-oxidation in the liver, combined with changed fatty acid composition and possibly a reduced hepatic clearance of circulating VLDL. An increased awareness of the effect of dietary proteins on lipid metabolism could be of relevance in future dietary treatment of non-alcoholic fatty liver disease.

Dose-dependent coronary artery intimal thickening after local delivery of the anti-oxidant tetradecylthioacetic acid from stents

OBJECTIVE

To examine the in vitro uptake and elution of the anti-oxidant tetradecylthioacetic acid (TTA) from phosphorylcholine (PC)-coated stents, and the in vivo uptake, retention, inflammatory response and histomorphometric changes after overstretch injury of the porcine coronary artery.

METHODS

PC-coated stents were loaded in one of three different concentrations of TTA (87, 174 and 347 mmol/L, i.e. 25, 50 and 100 mg/mL) and randomized versus PC-coated stents to the right coronary or left circumflex artery (18 pigs). Uptake of TTA into the coronary wall from the 347 mmol/L concentration was measured after 3 h and 24 h, 7 days, 14 days and 28 days (two pigs at each time point).

RESULTS

In vitro, TTA was successfully loaded onto the stents and elution was nearly complete after 48 h. In vivo, TTA could be demonstrated in the vessel wall for up to 4 weeks. Percent area stenosis was significantly higher in the TTA group, 35.2+/-20.9% versus 27.5+/-17.0% (p=0.03). Dose-related comparison showed increased intimal thickness, 0.66+/-0.53 mm versus 0.29+/-0.26 mm (p=0.008) and intimal area, 2.83+/-1.61 mm2 versus 1.58+/-0.91 mm2 (p=0.004) for the 347 mmol/L TTA versus controls. There was a significantly positive relationship between the TTA-loading dose and both intimal area (B=0.69, p=0.01) and maximal intimal thickness (B=0.17, p=0.02). The pro-inflammatory precursor arachidonic acid increased four-fold in the arterial wall of the TTA group, while the anti-inflammatory fatty acid index, calculated as (docosapentaenoic acid+docosahexaenoic acid+dihomo-linolenic acid)/arachidonic acid, was suppressed to 0.65+/-0.27 compared to 1.13+/-0.23 in control vessels (p<0.001).

CONCLUSION

TTA caused a dose-dependent intimal thickening and reduced anti-inflammatory fatty acid index. Contrary to expectations, TTA seems unsuitable as stent coating.

Dietary soya protein concentrate enriched with isoflavones reduced fatty liver, increased hepatic fatty acid oxidation and decreased the hepatic mRNA level of VLDL receptor in obese Zucker rats

Casein-based diets containing a low (LDI) or high (HDI) dose of soya protein concentrate enriched with isoflavones were fed to obese Zucker rats for 6 weeks. HDI feeding, but not LDI feeding, reduced the fatty liver and decreased the plasma levels of alanine transaminase and aspartate transaminase. This was accompanied by increased activities of mitochondrial and peroxisomal beta-oxidation, acetyl-CoA carboxylase, fatty acid synthase and glycerol-3-phosphate acyltransferase in liver and increased triacylglycerol level in plasma. The decreased fatty liver and the increased plasma triacylglycerol level appeared not to be caused by an increased secretion of VLDL, as HDI decreased the hepatic mRNA levels of apo B and arylacetamide deacetylase. However, the gene expression of VLDL receptor was markedly decreased in liver, but unchanged in epididymal white adipose tissue and skeletal muscle of rats fed HDI, indicating that the liver may be the key organ for the reduced clearance of triacylglycerol-rich lipoproteins from plasma after HDI feeding. The n-3/n-6, 20:4n-6/18:2n-6 and (20:5n-3+22:6n-3)/18:3n-3 ratios were increased in liver triacylglycerol by HDI. The phospholipids in liver of rats fed HDI contained a low level of 20:4n-6 and a high level of 20:5n-3, favouring the production of anti-inflammatory eicosanoids. When obese Zucker rats were fed soya protein, this also resulted in reduced fatty liver, possibly through reduced clearance of VLDL by the liver. We conclude that the isoflavone-enriched soya concentrate as well as soya protein may be promising dietary supplements for treatment of non-alcoholic fatty liver.

Fish protein hydrolysate reduces plasma total cholesterol, increases the proportion of HDL cholesterol, and lowers acyl-CoA:cholesterol acyltransferase activity in liver of Zucker rats

There is growing evidence that soy protein improves the blood lipid profiles of animals and humans. We compared the effects of fish protein hydrolysate (FPH), soy protein, and casein (control) on lipid metabolism in Wistar rats and genetically obese Zucker (fa/fa) rats. In Zucker rats, FPH treatment affected the fatty acid composition in liver, plasma, and triacylglycerol-rich lipoproteins. The mRNA levels of Delta 5 and Delta 6 desaturases were reduced by FPH and soy protein feeding compared with casein feeding. In Zucker rats both FPH and soy protein treatment reduced the plasma cholesterol level. Furthermore, the HDL cholesterol:total cholesterol ratio was greater in these rats and in the Wistar rats fed FPH and soy protein compared with those fed casein. Although fecal total bile acids were greater in soy protein-fed Zucker rats than in casein-fed controls, those fed FPH did not differ from the controls. However, the acyl-CoA:cholesterol acyltransferase activity was reduced in Zucker rats fed FPH and tended to be lower (P = 0.13) in those fed soy protein compared with those fed casein. Low ratios of methionine to glycine and lysine to arginine in the FPH and soy protein diets, compared with the casein diet, may be involved in lowering the plasma cholesterol concentration. Our results indicate that the effects of FPH and soy protein on fatty acid metabolism are similar in many respects, but the hypocholesterolemic effects of FPH and soy protein appear to be due to different mechanisms. FPH may have a role as a cardioprotective nutrient.

Changed energy state and increased mitochondrial beta-oxidation rate in liver of rats associated with lowered proton electrochemical potential and stimulated uncoupling protein 2 (UCP-2) expression: evidence for peroxisome proliferator-activated receptor-alpha independent induction of UCP-2 expression

Lowering of plasma triglyceride levels by hypolipidemic agents is caused by a shift in the liver cellular metabolism, which become poised toward peroxisome proliferator-activated receptor (PPAR) alpha-regulated fatty acid catabolism in mitochondria. After dietary treatment of rats with the hypolipidemic, modified fatty acid, tetradecylthioacetic acid (TTA), the energy state parameters of the liver were altered at the tissue, cell, and mitochondrial levels. Thus, the hepatic phosphate potential, energy charge, and respiratory control coefficients were lowered, whereas rates of oxygen uptake, oxidation of pyridine nucleotide redox pairs, beta-oxidation, and ketogenesis were elevated. Moderate uncoupling of mitochondria from TTA-treated rats was confirmed, as the proton electrochemical potential (Delta(p)) was 15% lower than controls. The change affected the Delta(Psi) component only, leaving the (Delta)pH component unaltered, suggesting that TTA causes induction of electrogenic ion transport rather than electrophoretic fatty acid activity. TTA treatment induced expression of hepatic uncoupling protein 2 (UCP-2) in rats as well as in wild type and PPARalpha-deficient mice, accompanied by a decreased double bond index of the mitochondrial membrane lipids. However, changes of mitochondrial fatty acid composition did not seem to be related to the effects on mitochondrial energy conductance. As TTA activates PPARdelta, we discuss how this subtype might compensate for deficiency of PPARalpha. The overall changes recorded were moderate, making it likely that liver metabolism can maintain its function within the confines of its physiological regulatory framework where challenged by a hypolipemic agent such as TTA, as well as others.

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.