Mitochondrial 3-hydroxy-3-methylglutaryl coenzyme A synthase and carnitine palmitoyltransferase II as potential control sites for ketogenesis during mitochondrion and peroxisome proliferation

HMGCS2 serves as a potential biomarker for inhibition of renal clear cell carcinoma growth

3-Hydroxymethylglutaryl-CoA synthase 2 (HMGCS2) is the rate-limiting enzyme for ketone body synthesis, and most current studies focus on mitochondrial maturation and metabolic reprogramming. The role of HMGCS2 was evaluated in a pan-cancer multi-database using R language, and HMGCS2 was lowly expressed or not differentially expressed in all tumor tissues compared with normal tissues. Correlation analysis of clinical case characteristics, genomic heterogeneity, tumor stemness, and overall survival revealed that HMGCS2 is closely related to clear cell renal cell carcinoma (KIRC). Single-cell sequencing data from normal human kidneys revealed that HMGCS2 is specifically expressed in proximal tubular cells of normal adults. In addition, HMGCS2 is associated with tumor immune infiltration and microenvironment, and KIRC patients with low expression of HMGCS2 have worse prognosis. Finally, the results of cell counting kit 8 assays, colony formation assays, flow cytometry, and Western blot analysis suggested that upregulation of HMGCS2 increased the expression of key tumor suppressor proteins, inhibited the proliferation of clear cell renal cell carcinoma cells and promoted cell apoptosis. In conclusion, HMGCS2 is abnormally expressed in pan-cancer, may play an important role in anti-tumor immunity, and is expected to be a potential tumor prognostic marker, especially in clear cell renal cell carcinoma.

Mobility Coupled with Motivation Promotes Survival: The Evolution of Cognition as an Adaptive Strategy

Morphine plays a critical regulatory role in both simple and complex plant species. Dopamine is a critical chemical intermediate in the morphine biosynthetic pathway and may have served as a primordial agonist in developing catecholamine signaling pathways. While dopamine remains the preeminent catecholamine in invertebrate neural systems, epinephrine is the major product of catecholamine synthetic pathways in vertebrate species. Given that the enzymatic steps leading to the generation of morphine are similar to those constraining the evolutionary adaptation of the biosynthesis of catecholamines, we hypothesize that the emergence of these more advanced signaling pathways was based on conservation and selective "retrofitting" of pre-existing enzyme activities. This is consistent with observations that support the recruitment of enzymatically synthesized tetrahydrobiopterin (BH4), which is a cofactor for tyrosine hydroxylase, the enzyme responsible for dopamine production. BH4 is also an electron donor involved in the production of nitric oxide (NO). The links that coordinate BH4-mediated NO and catecholaminergic-mediated processes provide these systems with the capacity to regulate numerous downstream signaling pathways. We hypothesize that the evolution of catecholamine signaling pathways in animal species depends on the acquisition of a mobile lifestyle and motivationally driven feeding, sexual, and self-protective responses.

The specific molecular architecture of plant 3-hydroxy-3-methylglutaryl-CoA lyase

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase (HMGL) is involved in branched-chain amino acid catabolism leading to acetyl-CoA production. Here, using bioinformatics analyses and protein sequence alignments, we found that in Arabidopsis thaliana a single gene encodes two HMGL isoforms differing in size (51 kDa, HMGL51 and 46 kDa, HMGL46). Similar to animal HMGLs, both isoforms comprised a C-terminal type 1 peroxisomal retention motif, and HMGL51 contained a mitochondrial leader peptide. We observed that only a shortened HMGL (35 kDa, HMGL35) is conserved across all kingdoms of life. Most notably, all plant HMGLs also contained a specific N-terminal extension (P100) that is located between the N-terminal mitochondrial targeting sequence TP35 and HMGL35 and is absent in bacteria and other eukaryotes. Interestingly, using HMGL enzyme assays, we found that rather than HMGL46, homodimeric recombinant HMGL35 is the active enzyme catalyzing acetyl-CoA and acetoacetate synthesis when incubated with (S)-HMG-CoA. This suggested that the plant-specific P100 peptide may inactivate HMGL according to specific physiological requirements. Therefore, we investigated whether the P100 peptide in HMGL46 alters its activity, possibly by modifying the HMGL46 structure. We found that induced expression of a cytosolic HMGL35 version in A. thaliana delays germination and leads to rapid wilting and chlorosis in mature plants. Our results suggest that in plants, P100-mediated HMGL inactivation outside of peroxisomes or mitochondria is crucial, protecting against potentially cytotoxic effects of HMGL activity while it transits to these organelles.

Associations between fatty acid oxidation, hepatic mitochondrial function, and plasma acylcarnitine levels in mice

Background

The 4-thia fatty acid tetradecylthiopropionic acid (TTP) is known to inhibit mitochondrial β-oxidation, and can be used as chemically induced hepatic steatosis-model in rodents, while 3-thia fatty acid tetradecylthioacetic acid (TTA) stimulates fatty acid oxidation through activation of peroxisome proliferator activated receptor alpha (PPARα). We wished to determine how these two compounds affected in vivo respiration and mitochondrial efficiency, with an additional goal to elucidate whether mitochondrial function is reflected in plasma acylcarnitine levels.

Methods

C57BL/6 mice were divided in 4 groups of 10 mice and fed a control low-fat diet, low-fat diets with 0.4% (w/w) TTP, 0.4% TTA or a combination of these two fatty acids for three weeks (n = 10). At sacrifice, β-oxidation and oxidative phosphorylation (OXPHOS) capacity was analysed in fresh liver samples. Hepatic mitochondria were studied using transmission electron microscopy. Lipid classes were measured in plasma, heart and liver, acylcarnitines were measured in plasma, and gene expression was measured in liver.

Results

The TTP diet resulted in hepatic lipid accumulation, plasma L-carnitine and acetylcarnitine depletion and elevated palmitoylcarnitine and non-esterified fatty acid levels. No significant lipid accumulation was observed in heart. The TTA supplement resulted in enhanced hepatic β-oxidation, accompanied by an increased level of acetylcarnitine and palmitoylcarnitine in plasma. Analysis of mitochondrial respiration showed that TTP reduced oxidative phosphorylation, while TTA increased the maximum respiratory capacity of the electron transport system. Combined treatment with TTP and TTA resulted in a profound stimulation of genes involved in the PPAR-response and L-carnitine metabolism, and partly prevented triacylglycerol accumulation in the liver concomitant with increased peroxisomal β-oxidation and depletion of plasma acetylcarnitines. Despite an increased number of mitochondria in the liver of TTA + TTP fed mice, the OXPHOS capacity was significantly reduced.

Conclusion

This study indicates that fatty acid β-oxidation directly affects mitochondrial respiratory capacity in liver. As plasma acylcarnitines reflected the reduced mitochondrial β-oxidation in TTP-fed mice, they could be useful tools to monitor mitochondrial function. As mitochondrial dysfunction is a major determinant of metabolic disease, this supports their use as plasma markers of cardiovascular risk in humans. Results however indicate that high PPAR activation obscures the interpretation of plasma acylcarnitine levels.

Electronic supplementary material

The online version of this article (10.1186/s12986-018-0241-7) contains supplementary material, which is available to authorized users.

Metabolomic Analysis of Mice Exposed to Gamma Radiation Reveals a Systemic Understanding of Total-Body Exposure

Diagnostic markers are needed for accidental or deliberate radiation exposure that could cause acute and chronic radiation toxicity. Biomarkers of temporal, dose-dependent, aging-attenuated and multiple radiation exposures have been previously described by others. However, the physiological origin and biochemical networks that generate these biomarkers and their association at the molecular level have yet to be explored. Hence, the discovery and identification of total-body-irradiation-induced tissue specific biomarkers remains an enormous challenge within radiation biodosimetry research. To determine the tissue level response of total-body exposure (6 Gy), metabolomics analysis was carried out on radiosensitive tissues bone marrow, ileum, liver, muscle and lung as well as serum and on urine within 12 h postirradiation. Differences in the metabolic signatures between the sham and gamma-irradiated groups were analyzed by hydrophilic interaction liquid chromatography (HILIC)-based ultra-performance liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOFMS). A panel of 67 biomarkers identified in radiosensitive tissues and biofluids (serum and urine) at a 6 Gy dose. Among the identified biomarkers, 3-methylglutarylcarnitine (3-MGC) was found to be a novel metabolite in liver, serum and urine that could potentially be an early radiation response marker. The degree of metabolic changes among different tissues showed perturbations in pathways including DNA methylation, energy, nucleic acid, amino acid, glutathione and bile acid metabolism. These results highlight metabolomics as a potential novel approach to understand functional alterations in the metabolome that could be adapted for use in the rapid assessment of radiation exposure and triage protocols in the case of nuclear incidents.

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.

Proteomics identifies molecular networks affected by tetradecylthioacetic acid and fish oil supplemented diets

Fish oil (FO) and tetradecylthioacetic acid (TTA) - a synthetic modified fatty acid have beneficial effects in regulating lipid metabolism. In order to dissect the mechanisms underlying the molecular action of those two fatty acids we have investigated the changes in mitochondrial protein expression in a long-term study (50weeks) in male Wistar rats fed 5 different diets. The diets were as follows: low fat diet; high fat diet; and three diets that combined high fat diet with fish oil, TTA or combination of those two as food supplements. We used two different proteomics techniques: a protein centric based on 2D gel electrophoresis and mass spectrometry, and LC-MS(E) based peptide centric approach. As a result we provide evidence that fish oil and TTA modulate mitochondrial metabolism in a synergistic manner yet the effects of TTA are much more dramatic. We demonstrate that fatty acid metabolism; lipid oxidation, amino acid metabolism and oxidative phosphorylation pathways are involved in fish oil and TTA action. Evidence for the involvement of PPAR mediated signalling is provided. Additionally we postulate that down regulation of components of complexes I and II contributes to the strong antioxidant properties of TTA.

BIOLOGICAL SIGNIFICANCE

This study for the first time explores the effect of fish oil and TTA - tetradecyl-thioacetic acid and the combination of those two as diet supplements on mitochondria metabolism in a comprehensive and systematic manner. We show that fish oil and TTA modulate mitochondrial metabolism in a synergistic manner yet the effects of TTA are much more dramatic. We demonstrate in a large scale that fatty acid metabolism and lipid oxidation are affected by fish oil and TTA, a phenomenon already known from more directed molecular biology studies. Our approach, however, shows additionally that amino acid metabolism and oxidative phosphorylation pathways are also strongly affected by TTA and also to some extent by fish oil administration. Strong evidence for the involvement of PPAR mediated signalling is provided linking the different metabolic effects. The global and systematic viewpoint of this study compiles many of the known phenomena related to the effects of fish oil and fatty acids giving a solid foundation for further exploratory and more directed studies of the mechanisms behind the beneficial and detrimental effects of fish oil and TTA diet supplementation. This work is already a second article in a series of studies conducted using this model of dietary intervention. In the previous study (Vigerust et al., [21]) the effects of fish oil and TTA on the plasma lipids and cholesterol levels as well as key metabolic enzymes in the liver have been studied. In an ongoing study more work is being done to explore in detail for example the link between the down regulation of the components of the respiratory chain (observed in this study) and the strong antioxidant effects of TTA. The reference diet in this study has been designed to mimic an unhealthy - high fat diet that is thought to contribute to the development of metabolic syndrome - a condition that is strongly associated with diabetes, obesity and heart failure. Fish oil and TTA are known to have beneficial effects for the fatty acid metabolism and have been shown to alleviate some of the symptoms of the metabolic syndrome. To date very little is known about the molecular mechanisms behind these beneficial effects and the potential pitfalls of the consumption of those two compounds. Only studies of each compound separately and using only small scale molecular biology approaches have been carried out. The results of this work provide an excellent starting point for further studies that will help to understand the metabolic effects of fish oil and TTA and will hopefully help to design dietary programs directed towards reduction of the prevalence of metabolic syndrome and associated diseases.

Krill oil versus fish oil in modulation of inflammation and lipid metabolism in mice transgenic for TNF-α

PURPOSE

Biological effects of marine oils, fish oil (FO) and krill oil (KO), are mostly attributed to the high content of n-3 polyunsaturated fatty acids (n-3 PUFAs), predominantly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The study was aimed to investigate the influence of FO and KO on lipid homeostasis and inflammation in an animal model of persistent low-grade exposure to human tumor necrosis factor α (hTNF-α) and to evaluate whether these effects depend on the structural forms of EPA and DHA [triacylglycerols (TAG) vs. phospholipids].

METHODS

Male C57BL/6 hTNF-α mice were fed for 6 weeks a high-fat control diet (24.50 % total fats, w/w) or high-fat diets containing either FO or KO at similar doses of n-3 PUFAs (EPA: 5.23 vs. 5.39 wt%, DHA: 2.82 vs. 2.36 wt% of total fatty acids).

RESULTS

We found that KO, containing bioactive n-3 PUFAs in the form of phospholipids, was capable of modulating lipid metabolism by lowering plasma levels of TAG and cholesterol and stimulating the mitochondrial and peroxisomal fatty acid β-oxidation, as well as improving the overall carnitine turnover. Though the administration of FO was not as effective as KO in the lowering of plasma TAG, FO significantly improved the levels of all cholesterol classes in plasma. Except from the increase in the levels of IL-17 in FO-fed mice and a trend to decrease in MCP-1 levels in KO-fed animals, the levels of pro-inflammatory cytokines were not substantially different between treatment groups.

CONCLUSION

Our findings demonstrate that FO and KO are comparable dietary sources of n-3 PUFAs. However, when quantitatively similar doses of n-3 PUFAs are administered, KO seems to have a greater potential to promote lipid catabolism. The effect of dietary oils on the levels of inflammatory markers in hTNF-α transgenic mice fed a high-fat diet needs further investigations.

Exercise and Omega-3 Polyunsaturated Fatty Acid Supplementation for the Treatment of Hepatic Steatosis in Hyperphagic OLETF Rats

Background and Aims. This study examined if exercise and omega-3 fatty acid (n3PUFA) supplementation is an effective treatment for hepatic steatosis in obese, hyperphagic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Methods. Male OLETF rats were divided into 4 groups (n = 8/group): (1) remained sedentary (SED), (2) access to running wheels; (EX) (3) a diet supplemented with 3% of energy from fish oil (n3PUFA-SED); and (4) n3PUFA supplementation plus EX (n3PUFA+EX). The 8 week treatments began at 13 weeks, when hepatic steatosis is present in OLETF-SED rats. Results. EX alone lowered hepatic triglyceride (TAG) while, in contrast, n3PUFAs failed to lower hepatic TAG and blunted the ability of EX to decrease hepatic TAG levels in n3PUFAs+EX. Insulin sensitivity was improved in EX animals, to a lesser extent in n3PUFA+EX rats, and did not differ between n3PUFA-SED and SED rats. Only the EX group displayed higher complete hepatic fatty acid oxidation (FAO) to CO₂ and carnitine palmitoyl transferase-1 activity. EX also lowered hepatic fatty acid synthase protein while both EX and n3PUFA+EX decreased stearoyl CoA desaturase-1 protein. Conclusions. Exercise lowers hepatic steatosis through increased complete hepatic FAO, insulin sensitivity, and reduced expression of de novo fatty acid synthesis proteins while n3PUFAs had no effect.

Tetradecylthioacetic acid increases hepatic mitochondrial β-oxidation and alters fatty acid composition in a mouse model of chronic inflammation

The administration of tetradecylthioacetic acid (TTA), a hypolipidemic and anti-inflammatory modified bioactive fatty acid, has in several experiments based on high fat diets been shown to improve lipid transport and utilization. It was suggested that increased mitochondrial and peroxisomal fatty acid oxidation in the liver of Wistar rats results in reduced plasma triacylglycerol (TAG) levels. Here we assessed the potential of TTA to prevent tumor necrosis factor (TNF) α-induced lipid modifications in human TNFα (hTNFα) transgenic mice. These mice are characterized by reduced β-oxidation and changed fatty acid composition in the liver. The effect of dietary treatment with TTA on persistent, low-grade hTNFα overexpression in mice showed a beneficial effect through decreasing TAG plasma concentrations and positively affecting saturated and monounsaturated fatty acid proportions in the liver, leading to an increased anti-inflammatory fatty acid index in this group. We also observed an increase of mitochondrial β-oxidation in the livers of TTA treated mice. Concomitantly, there were enhanced plasma levels of carnitine, acetyl carnitine, propionyl carnitine, and octanoyl carnitine, no changed levels in trimethyllysine and palmitoyl carnitine, and a decreased level of the precursor for carnitine, called γ-butyrobetaine. Nevertheless, TTA administration led to increased hepatic TAG levels that warrant further investigations to ascertain that TTA may be a promising candidate for use in the amelioration of inflammatory disorders characterized by changed lipid metabolism due to raised TNFα levels.

Dopamine, morphine, and nitric oxide: an evolutionary signaling triad

Morphine biosynthesis in relatively simple and complex integrated animal systems has been demonstrated. Key enzymes in the biosynthetic pathway have also been identified, that is, CYP2D6 and COMT. Endogenous morphine appears to exert highly selective actions via novel mu opiate receptor subtypes, that is, mu3,-4, which are coupled to constitutive nitric oxide release, exerting general yet specific down regulatory actions in various animal tissues. The pivotal role of dopamine as a chemical intermediate in the morphine biosynthetic pathway in plants establishes a functional basis for its expansion into an essential role as the progenitor catecholamine signaling molecule underlying neural and neuroendocrine transmission across diverse animal phyla. In invertebrate neural systems, dopamine serves as the preeminent catecholamine signaling molecule, with the emergence and limited utilization of norepinephrine in newly defined adaptational chemical circuits required by a rapidly expanding set of physiological demands, that is, motor and motivational networks. In vertebrates epinephrine, emerges as the major end of the catecholamine synthetic pathway consistent with a newly incorporated regulatory modification. Given the striking similarities between the enzymatic steps in the morphine biosynthetic pathway and those driving the evolutionary adaptation of catecholamine chemical species to accommodate an expansion of interactive but distinct signaling systems, it is our overall contention that the evolutionary emergence of catecholamine systems required conservation and selective "retrofit" of specific enzyme activities, that is, COMT, drawn from cellular morphine expression. Our compelling hypothesis promises to initiate the reexamination of clinical studies, adding new information and treatment modalities in biomedicine.

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.

Causes and prevention of tamoxifen-induced accumulation of triacylglycerol in rat liver

Tamoxifen can induce hepatic steatosis in women. In this study, we wanted to elucidate the mechanism behind the tamoxifen-induced accumulation of triacylglycerol in liver in female rats, and we hoped to prevent this development by combination treatment with the modified fatty acid tetradecylthioacetic acid (TTA). The increased hepatic triacylglycerol level after tamoxifen treatment was accompanied by decreased acetyl-coenzyme A carboxylase (ACC) and FAS activities, increased glycerol-3-phosphate acyltransferase (GPAT) activity, and a tendency to increased diacylglycerol acyltransferase (DGAT) activity. The activities and mRNA levels of enzymes involved in beta-oxidation, ketogenesis, and uptake of lipids from liver were unaffected by tamoxifen, whereas the uptake of lipoproteins was unchanged and the uptake of fatty acids was decreased. Combination treatment with tamoxifen and TTA (Tam+TTA) normalized the hepatic triacylglycerol level and increased the activities of ACC, FAS, GPAT, and DGAT compared with tamoxifen-treated rats. The activities and mRNA levels of enzymes involved in beta-oxidation, ketogenesis, and uptake of lipids were increased after Tam+TTA treatment. In conclusion, tamoxifen increased the hepatic triacylglycerol level, probably as a result of increased triacylglycerol biosynthesis combined with unchanged beta-oxidation. The tamoxifen-induced accumulation of triacylglycerol was prevented by cotreatment with TTA, through mechanisms of increased mitochondrial and peroxisomal beta-oxidation.

Sulfur-substituted and alpha-methylated fatty acids as peroxisome proliferator-activated receptor activators

FA with varying chain lengths and an alpha-methyl group and/or a sulfur in the beta-position were tested as peroxisome proliferator-activated receptor (PPAR)alpha, -delta(beta), and -gamma ligands by transient transfection in COS-1 cells using chimeric receptor expression plasmids, containing cDNAs encoding the ligand-binding domain of PPARalpha, -delta, and -gamma. For PPARalpha, an increasing activation was found with increasing chain length of the sulfur-substituted FA up to C14-S acetic acid (tetradecylthioacetic acid = TTA). The derivatives were poor, and nonsignificant, activators of PPARdelta. For PPARgamma, activation increased with increasing chain length up to C16-S acetic acid. A methyl group was introduced in the alpha-position of palmitic acid, TTA, EPA, DHA, cis9,trans11 CLA, and trans10,cis12 CLA. An increased activation of PPARalpha was obtained for the alpha-methyl derivatives compared with the unmethylated FA. This increase also resulted in increased expression of the two PPARalpha target genes acyl-CoA oxidase and liver FA-binding protein for alpha-methyl TTA, alpha-methyl EPA, and alpha-methyl DHA. Decreased or altered metabolism of these derivatives in the cells cannot be excluded. In conclusion, saturated FA with sulfur in the beta-position and increasing carbon chain length from C9-S acetic acid to C14-S acetic acid have increasing effects as activators of PPARalpha and -gamma in transfection assays. Furthermore, alpha-methyl FA derivatives of a saturated natural FA (palmitic acid), a sulfur-substituted FA (TTA), and PUFA (EPA, DHA, c9,t11 CLA, and t10,c12 CLA) are stronger PPARalpha activators than the unmethylated compounds.

Down-regulated expression of PPARalpha target genes, reduced fatty acid oxidation and altered fatty acid composition in the liver of mice transgenic for hTNFalpha

The present study investigated the hepatic regulation of fatty acid metabolism in hTNFalpha transgenic mice. Reduced hepatic mRNA levels and activities of carnitine palmitoyltransferase-II (CPT-II) and mitochondrial HMG-CoA synthase were observed, accompanied by decreased fatty acid oxidation, fatty acyl-CoA oxidase and fatty acid synthase (FAS) activities and down-regulated gene expression of mitochondrial acetyl-CoA carboxylase 2 (ACC2). The mRNA levels of peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARdelta were reduced. The hepatic fatty acid composition was altered, with increased amounts of saturated and polyunsaturated fatty acids. The relative amounts of Delta(9) desaturated fatty acids were decreased, as was Delta(9)desaturase mRNA. The CPT-I mRNA level remained unchanged. The PPARalpha targeted genes CPT-II and HMG-CoA synthase are potential regulators of mitochondrial fatty acid oxidation and ketogenesis in hTNFalpha transgenic mice, and the increased propionyl-CoA level found is a possible inhibitor of these processes. Reduced mitochondrial and peroxisomal fatty acid oxidation may explain the increased hepatic triglyceride level induced by TNFalpha. This is not due to de novo fatty acid synthesis as both FAS activity and gene expression of ACC2 were reduced.

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.

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.

Mitochondrial-targeted fatty acid analog induces apoptosis with selective loss of mitochondrial glutathione in promyelocytic leukemia cells

Some fatty acids and derivatives are known to induce cell death in cancer cells. Mitochondria may have important roles in the death process. Therefore, we investigated the mitochondrial contribution in cell death induced by a modified fatty acid, tetradecylthioacetic acid (TTA), which cannot be beta-oxidized. TTA treatment induced apoptosis in IPC-81 leukemia cells via depolarization of the mitochondrial membrane potential (deltapsi) and early release of cytochrome c, accompanied by depletion of mitochondrial glutathione. Caspase-3 activation and cleavage of poly (ADP-ribose) polymerase (PARP) occurred at a late stage, but the broad-spectra caspase inhibitor zVAD-fmk did not block TTA-induced apoptosis. Overexpression of Bcl-2 partially prevented TTA-induced apoptosis, whereas cAMP-induced cell death was completely blocked. In conclusion, TTA seems to trigger apoptosis through mitochondrial-mediated mechanisms and selective modulation of the mitochondrial redox equilibrium.

Nuclear import of factors involved in signaling is inhibited in C3H/10T1/2 cells treated with tetradecylthioacetic acid

The non-beta-oxidisable tetradecylthioacetic acid (TTA) is incorporated into cellular membranes when C3H/10T1/2 cells are cultured in TTA-containing medium. We here demonstrate that this alteration in cellular membranes affect the nuclear translocation of proteins involved in signal transduction. Analysis of cellular fatty acid composition shows that TTA and TTA:1n-8 constitute approximately 40 mol% of total fatty acids in cellular/nuclear membranes. Activation of c-fos expression is significantly inhibited in TTA-treated cells but the enzymatic activation of mitogen activated protein kinase (ERK) is not affected. Immunofluorescence and confocal microscopy studies demonstrate that in mitogene-stimulated TTA-treated cells, the translocation of phosphorylated ERK1/2, protein kinase C alpha (PKC alpha), and PKC beta(1) from the cytoplasm into the nucleus is considerably decreased and delayed. Concomitant with a decreased nuclear import, ERK1/2 dephosphorylation is decreased in TTA-treated cells. There is no TTA-induced inhibition of nuclear import of proteins with a classical nuclear localization signal (NLS), as seen by in vitro nuclear import experiments of BSA fused to the NLS from SV40 large T, or in vivo studies of hnRNP A1 nuclear import. The expression levels of Importin alpha, Importin beta, Importin 7, and NTF2 are not altered in the TTA-treated cells. Taken together, our data indicate that TTA treatment causes changes in cellular fatty acid composition that negatively affect NLS-independent mechanisms of protein translocation through the nuclear pore complex.

An increase in peroxisomal fatty acid oxidation is not sufficient to prevent tissue lipid accumulation in hHTg rats

We observed earlier that increased skeletal muscle lipid content in the hereditary hypertriglyceridemic (hHTg) rat is accompanied by a decline in plasma leptin. Leptin has recently been shown to enhance peripheral insulin sensitivity by decreasing the tissue triglyceride accumulation, possibly through regulation of fatty acid oxidation and lipogenesis. Thus, to test the hypothesis that insulin resistance and increased skeletal muscle lipid accumulation in hHTg rats are due to a defect in lipid catabolism, we measured mitochondrial and peroxisomal fatty acid oxidation and malonyl-CoA and acetyl-CoA carboxylase-2 content in skeletal muscles of these animals. In addition, we investigated possible molecular mechanisms responsible for the lower leptin levels in hHTg rats by measuring leptin and leptin-receptor (Ob-Ra) mRNA levels. We found the following: (1) in spite of a higher skeletal muscle malonyl-CoA content and an increased sensitivity of carnitine palmitoyltransferase-1 to malonyl-CoA, carnitine palmitoyltransferase-1 activity in muscle of hHTg rats was normal; (2) increased peroxisomal fatty acid oxidation did not seem to be sufficient to prevent the tissue lipid accumulation in these animals; (3) both lower leptin production by white adipose tissue and increased leptin uptake seem to be responsible for lower circulating leptin levels and therefore lower fatty acid catabolism.

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.

Perfluorooctanoate, perflourooctanesulfonate, and N-ethyl perfluorooctanesulfonamido ethanol; peroxisome proliferation and mitochondrial biogenesis

Compounds that cause peroxisome proliferation in rats and mice have been reported to interfere with mitochondrial (mt) bioenergetics and possibly biogenesis. The purpose of this investigation was to establish whether proliferation of peroxisomes and mitochondria are necessarily related. Perfluorooctanesulfonate (PFOS) and N-ethyl perfluorooctanesulfonamido ethanol (N-EtFOSE) were investigated as peroxisome proliferators in comparison to perfluorooctanoic acid (PFOA). Three parameters were chosen to assess peroxisome proliferation, stimulation of lauroyl CoA oxidase activity, reduction of serum cholesterol concentration, and hepatomegaly. mt Biogenesis was assessed through cytochrome oxidase activity, cytochrome content and mitochondrial DNA (mtDNA) copy number. PFOA, PFOS, or N-EtFOSE was administered via a single i.p. injection at 100 mg/kg in male rats, and measurements were made 3 days later. In this model, PFOS and PFOA share similar potencies as peroxisome proliferators, whereas N-EtFOSE showed no activity. mt Endpoints were altered only in the PFOA treatment group, which consisted of a decrease cytochrome oxidase activity in liver tissue and an increase in the mtDNA copy number. None of the perfluorooctanoates significantly altered mt cytochrome content following acute in vivo treatment. These data demonstrate that acute administration of PFOS or PFOA causes hepatic peroxisome proliferation in rats. However, stimulation of mt biogenesis is not a characteristic response of all peroxisome proliferators.

Isoprenoid biosynthesis: the evolution of two ancient and distinct pathways across genomes

Isopentenyl diphosphate (IPP) is the central intermediate in the biosynthesis of isoprenoids, the most ancient and diverse class of natural products. Two distinct routes of IPP biosynthesis occur in nature: the mevalonate pathway and the recently discovered deoxyxylulose 5-phosphate (DXP) pathway. The evolutionary history of the enzymes involved in both routes and the phylogenetic distribution of their genes across genomes suggest that the mevalonate pathway is germane to archaebacteria, that the DXP pathway is germane to eubacteria, and that eukaryotes have inherited their genes for IPP biosynthesis from prokaryotes. The occurrence of genes specific to the DXP pathway is restricted to plastid-bearing eukaryotes, indicating that these genes were acquired from the cyanobacterial ancestor of plastids. However, the individual phylogenies of these genes, with only one exception, do not provide evidence for a specific affinity between the plant genes and their cyanobacterial homologues. The results suggest that lateral gene transfer between eubacteria subsequent to the origin of plastids has played a major role in the evolution of this pathway.