Peroxisome proliferator-activated receptor α is required for feedback regulation of highly unsaturated fatty acid synthesis

An association between PPARα-L162V polymorphism and increased plasma LDL cholesterol levels after risperidone treatment

Peroxisome proliferator-activated receptor alpha (PPARα) and antipsychotic medications both influence polyunsaturated fatty acids (PUFA) homeostasis, and thus PPARα polymorphism may be linked to antipsychotic treatment response. Here we investigated whether the functional leucine 162 valine (L162V) polymorphism in PPARα influenced antipsychotic treatment in a group of psychosis patients (N = 186), as well as in a patient subgroup with risperidone, paliperidone, or combination treatment (N = 65). Antipsychotic-naïve first-episode patients and nonadherent chronic individuals were genotyped by polymerase chain reaction analysis. At baseline, and after 8 weeks of treatment with various antipsychotic medications, we assessed the patients' Positive and Negative Syndrome Scale (PANSS) scores; PANSS factors; and metabolic syndrome-related parameters, including fasting plasma lipid and glucose levels, and body mass index. In the total patient group, PPARα polymorphism did not affect PANSS psychopathology or metabolic parameters. However, in the subgroup of patients with risperidone, paliperidone, or combination treatment, PPARα polymorphism influenced changes in plasma LDL cholesterol. Specifically, compared to PPARα-L162L homozygous patients, PPARα-L162V heterozygous individuals exhibited significantly higher increases of LDL cholesterol levels after antipsychotic treatment. The PPARα polymorphism had a strong effect size, but a relatively weak contribution to LDL cholesterol level variations (∼12.8 %).

Diet Regulation of Long-Chain PUFA Synthesis: Role of Macronutrients, Micronutrients, and Polyphenols on Δ-5/Δ-6 Desaturases and Elongases 2/5

Deficiencies in the n-3 (ω-3) long-chain PUFAs (LC-PUFAs) EPA and DHA are associated with increased risk for the development of numerous diseases. Although n-3 LC-PUFAs can be obtained by consuming marine products, they are also synthesized endogenously through a biochemical pathway regulated by the Δ-5/Δ-6 desaturase and elongase 2/5 enzymes. This narrative review collates evidence from the past 40 y demonstrating that mRNA expression and activity of desaturase and elongase enzymes are influenced by numerous dietary components, including macronutrients, micronutrients, and polyphenols. Specifically, we highlight that both the quantity and the composition of dietary fats, carbohydrates, and proteins can differentially regulate desaturase pathway activity. Furthermore, desaturase and elongase mRNA levels and enzyme activities are also influenced by micronutrients (folate, vitamin B-12, vitamin A), trace minerals (iron, zinc), and polyphenols (resveratrol, isoflavones). Understanding how these various dietary components influence LC-PUFA synthesis will help further advance our understanding of how dietary patterns, ranging from caloric excesses to micronutrient deficiencies, influence disease risks.

L-carnitine exerts a nutrigenomic effect via direct modulation of nuclear receptor signaling in adipocytes, hepatocytes and SKMC, demonstrating its nutritional impact

L-carnitine is an indispensable metabolite facilitating the transport of fatty acids into the mitochondrial matrix and has been previously postulated to exert a nutrigenomic effect. However, the underlying molecular mechanisms remain mostly unclear. We hypothesized that L-carnitine interacts with nuclear receptors involved in metabolic regulation, thereby modulating downstream targets of cellular metabolism. Therefore, we investigated the effect of L-carnitine supplementation on protein activity, mRNA expression, and binding affinities of nuclear receptors as well as mRNA expression of downstream targets in skeletal muscle cells, hepatocytes, and differentiated adipocytes. L-carnitine supplementation to hepatocytes increased the protein activity of multiple nuclear receptors (RAR, RXR, VDR, PPAR, HNF4, ER, LXR). Diverging effects on the mRNA expression of PPAR-α, PPAR-δ, PPAR-γ, RAR-β, LXR-α, and RXR-α were observed in adipocytes, hepatocytes, and skeletal muscle cells. mRNA levels of PPAR-α, a key regulator of lipolysis and β-oxidation, were significantly upregulated, emphasizing a role of L-carnitine as a promoter of lipid catabolism. L-carnitine administration to hepatocytes modulated the transcription of key nuclear receptor target genes, including ALDH1A1, a promoter of adipogenesis, and OGT, a contributor to insulin resistance. Electrophoretic mobility shift assays proved L-carnitine to increase binding affinities of nuclear receptors to their promoter target sequences, suggesting a molecular mechanism for the observed transcriptional modulation. Overall, these findings indicate that L-carnitine modulates the activity and expression of nuclear receptors, thereby promoting lipolytic gene expression and decreasing transcription of target genes linked to adipogenesis and insulin resistance.

Fatty acid desaturase 2 is up-regulated by the treatment with statin through geranylgeranyl pyrophosphate-dependent Rho kinase pathway in HepG2 cells

Statins have been reported to increase the plasma concentration of arachidonic acid (AA), an omega-6 long chain polyunsaturated fatty acid (LCPUFA) in several clinical studies indicating that statins affect the endogenous synthesis of LCUFAs. In the present study, we investigated the roles of the intrinsic mevalonate cascade and Rho-dependent pathway in LCPUFA synthesis, especially focusing on fatty acid desaturases (Fads) 2, using the human hepatocellular carcinoma cell line HepG2. Cell number and the activity of caspase-3 and 7 (caspase-3/7) was measured using a commercial kit. Gene expression was analyzed by quantitative real-time PCR. Protein expression was detected by Western blot analysis. Atorvastatin decreased cell viability and increased caspase-3/7 activity in a dose-dependent manner. At lower concentrations, atorvastatin stimulated both mRNA and protein expression of Fads2, and increased mRNA expression of FADS1 and ELVOL5. Both mevalonate and geranylgeranyl-pyrophosphate (GGPP), but not cholesterol, fully reversed atorvastatin-induced upregulation of Fads2, and mevalonate-effected reversal was inhibited by treatment with the Rho-associated protein kinase inhibitor Y-27632. These data clearly demonstrated that in human HepG2 cells, statins affect the endogenous synthesis of LCPUFAs by regulation of not only Fads2, but also Fads1 and Elovl5, through the GGPP-dependent Rho kinase pathway.

Effects of algae supplementation in high-energy dietary on fatty acid composition and the expression of genes involved in lipid metabolism in Hu sheep managed under intensive finishing system

This study aims to investigate the effect of algae supplementation in high-energy diet (HE diet) on lipid metabolism of intensive feeding sheep. The lambs were assigned to two groups and received a standard diet (ST diet, 8.40 MJ/kg) or a HE diet (9.70 MJ/kg) based on corn, wheat bran, soybean meal. Each group was divided into two subgroups: control and algae supplement (3%, DM basis). The body fat, serum cholesterol, and oleic acid in the liver and muscle increased in lambs receiving the HE diet. However, after supplementing the microalgae (Schizochytrium sp.) in the HE diet, these parameters were all reduced. In addition, EPA, DHA and CLA cis-9, trans-11 in muscle and liver increased. Algae supplementation also altered the expression of lipid metabolism-related genes, including up-regulated FADS2, ELOVL2, SCD, CPT1α and SREBF-1, and down-regulated PPARα and PPARγ. In conclusion, algae supplementation in ST and HE diets increased n-3PUFA and improved metabolic disorder caused by the HE diet.

The commonly used nonionic surfactant Span 80 has RXRα transactivation activity, which likely increases the obesogenic potential of oil dispersants and food emulsifiers

Obesity has reached pandemic proportions, and there is mounting evidence that environmental exposures to endocrine disrupting chemicals known as "obesogens" may contribute to obesity and associated medical conditions. The Deepwater Horizon (DWH) oil spill resulted in a massive environmental release of crude oil and remediation efforts applied large quantities of Corexit dispersants to the oil spill. The Corexit-enhanced Water Accommodated Fraction (CWAF) of DWH crude oil contains PPARγ transactivation activity, which is attributed to dioctyl sodium sulfosuccinate (DOSS), a probable obesogen. In addition to its use in oil dispersants, DOSS is commonly used as a stool softener and food additive. Because PPARγ functions as a heterodimer with RXRα to transcriptionally regulate adipogenesis we investigated the potential of CWAF to transactivate RXRα and herein demonstrated that the Corexit component Span 80 has RXRα transactivation activity. Span 80 bound to RXRα in the low micromolar range and promoted adipocyte differentiation of 3T3-L1 preadipocytes. Further, the combination of DOSS and Span 80 increased 3T3-L1 adipocyte differentiation substantially more than treatment with either chemical individually, likely increasing the obesogenic potential of Corexit dispersants. From a public health standpoint, the use of DOSS and Span 80 as food additives heightens concerns regarding their use and mandates further investigations.

An association between the PPARα-L162V polymorphism and nicotine dependency among patients with schizophrenia

OBJECTIVE

Patients with schizophrenia are more likely to be smokers than the general population, which makes them an interesting group with which to study the etiology of nicotine dependency. We studied the prevalence of a gene variant of peroxisome proliferator-activated receptor alpha (PPARα) in schizophrenia, together with nicotine dependency, to investigate whether the PPARα-L162V polymorphism (rs1800206) influences nicotine dependency in schizophrenia. Given evidence suggesting that smoking influences the severity of schizophrenia, together with our recent data linking the PPARα-L162V polymorphism to clinical manifestations of schizophrenia (in the Croatian population), we hypothesized that interactions between the two (smoking and the PPARα-L162V polymorphism) might contribute to disease onset and scores for the Positive and Negative Syndrome Scale. To the best of our knowledge, this is the first study to investigate the possible associations between the PPARα gene and nicotine dependency.

PATIENTS AND METHODS

Genotyping was performed for 267 chronically ill schizophrenia patients (males/females: 140/127) by polymerase chain reaction.

RESULTS

A significant excess of PPARα-L162V genotypes and PPARα-162V alleles were detected among female smokers in comparison to female nonsmokers (18.2% vs. 2.0%, and 9.1% vs. 1.0%, p<0.01, respectively). We also revealed a significant PPARα genotype-smoking interaction that predicted positive symptom severity among male patients (F=4.43, p<0.05). These data indicated that the PPARα-L162V heterozygous genotype, depending on smoking status, might be of relevance as either protective, or a risk factor, for the severity of positive symptoms. No interaction between the PPARα-L162V polymorphism and smoking for the time of onset of schizophrenia was detected (p>0.05, respectively).

CONCLUSION

We demonstrated two significant yet weak effects. The first showed an effect of the PPARα-L162V polymorphism on the risk of nicotine dependency. The second linked the PPARα genotype-smoking interaction to positive symptoms severity among schizophrenia patients; both effects manifested in a gender-specific fashion.

Compensatory induction of Fads1 gene expression in heterozygous Fads2-null mice and by diet with a high n-6/n-3 PUFA ratio

In mammals, because they share a single synthetic pathway, n-6/n-3 ratios of dietary PUFAs impact tissue arachidonic acid (ARA) and DHA content. Likewise, SNPs in the human fatty acid desaturase (FADS) gene cluster impact tissue ARA and DHA. Here we tested the feasibility of using heterozygous Fads2-null-mice (HET) as an animal model of human FADS polymorphisms. WT and HET mice were fed diets with linoleate/α-linolenate ratios of 1:1, 7:1, and 44:1 at 7% of diet. In WT liver, ARA and DHA in phospholipids varied >2× among dietary groups, reflecting precursor ratios. Unexpectedly, ARA content was only <10% lower in HET than in WT livers, when fed the 44:1 diet, likely due to increased Fads1 mRNA in response to reduced Fads2 mRNA in HET. Consistent with the RNA data, C20:3n-6, which is elevated in minor FADS haplotypes in humans, was lower in HET than WT. Diet and genotype had little effect on brain PUFAs even though brain Fads2 mRNA was low in HET. No differences in cytokine mRNA were found among groups under unstimulated conditions. In conclusion, differential PUFA profiles between HET mice and human FADS SNPs suggest low expression of both FADS1 and 2 genes in human minor haplotypes.

Potential role of dietary lipids in the prophylaxis of some clinical conditions

An imbalance of dietary lipids may potentially have a significant role in the pathobiology of some chronic diseases. Public health dietary fat recommendations have emphasized that low saturated fat, high monounsaturated fat, and high polyunsaturated fat with a lower ω-6 to ω-3 fatty acid ratio intake are necessary for normal health. However, such universal recommendations are likely to be hazardous, since the outcome of recommended lipid intake may depend on the consumption of other important dietary constituents that have an important role in the metabolism of lipids. In addition, consumption of fatty acids as per the individually tailored specific requirements in the context of other nutritional factors may have the potential to stabilize hormones, mood and sleep, and minimize adverse events. In support of this proposal, we review various factors that influence fatty acid metabolism, which need to be taken into consideration for appropriate utilization and consequently prevention of various diseases.

PPARα-L162V polymorphism is not associated with schizophrenia risk in a Croatian population

Disturbances of lipid and glucose metabolism have been repeatedly reported in schizophrenia. A functional L162V polymorphism in peroxisome proliferator-activated receptor alpha (PPARα) gene has been extensively investigated in etiology of abnormal lipid and glucose metabolism, yet not in schizophrenia. We determined whether the schizophrenia risk was associated with L162V polymorphism and we examined the impact of L162V variant on age of onset, and data of psychopathology scores. We also hypothesized that plasma glucose and lipid concentrations in patients may be influenced by L162V polymorphism. Genotype and allele frequencies between 203 patients and 191 controls did not differ significantly. Females heterozygous for the PPARα genotype (L162V) manifested significantly lower negative symptom scores, tended toward an earlier onset, and had significantly greater triglyceride levels. The PPARα-L162V polymorphism is not associated with schizophrenia risk in Croatian population, but it impacts clinical expression of the illness and plasma lipid concentrations in female patients.

Sugar-sweetened beverages with moderate amounts of fructose, but not sucrose, induce Fatty Acid synthesis in healthy young men: a randomized crossover study

CONTEXT

The impact of sugar-sweetened beverages (SSB) on lipid metabolism when consumed in moderate amounts by normal weight subjects is debated.

OBJECTIVE

The objective of the study was to investigate the effect of different types of sugars in SSB on fatty acid metabolism (ie, fatty acid synthesis and oxidation) in healthy young men.

DESIGN

Thirty-four normal-weight men were studied in a randomized crossover study. Four isocaloric 3-week interventions with SSB were performed in random order: medium fructose (MF; 40 g/d); high fructose (HF; 80 g/d), high sucrose (HS; 80 g/d), and high glucose (HG; 80g/d). Fasting total plasma fatty acid composition was measured after each intervention. Acylcarnitines were measured in the fasting state and after a euglycemic hyperinsulinemic clamp in nine subjects.

RESULTS

The relative abundance of palmitate (16:0) and the molar fatty acid ratio of palmitate to linoleic acid (16:0 to18:2) as markers of fatty acid synthesis were increased after HF [relative abundance of palmitate: 22.97% ± 5.51% (percentage of total fatty acids by weight ±SD)] and MF (26.1% ± 1.7%) compared with HS (19.40% ± 2.91%, P < .001), HG (19.43% ±3.12 %, P < .001), or baseline (19.40% ± 2.79%, P < .001). After HS and HG, the relative abundance of palmitate was equal to baseline. Fasting palmitoylcarnitine was significantly increased after HF and HS (HF and HS vs. HG: P = .005), decreasing after inhibition of lipolysis by insulin in the clamp.

CONCLUSIONS

When consumed in moderate amounts, fructose but not sucrose or glucose in SSB increases fatty acid synthesis (palmitate), whereas fasting long-chain acylcarnitines are increased after both fructose and sucrose, indicating an impaired β-oxidation flux.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

Postnatal essential fatty acid deficiency in mice affects lipoproteins, hepatic lipids, fatty acids and mRNA expression

We have previously reported that essential fatty acid deficiency (EFAD) during suckling in mice resulted in an adult lean phenotype and a resistance to diet-induced obesity. We now hypothesized that postnatal EFAD would cause long-term effects on lipid metabolism. C57BL/6 mice were fed an EFAD or a control diet from the 16th day of gestation and throughout lactation. The pups were weaned to standard diet (STD) and at 15 weeks of age given either high fat diet (HFD) or STD. Lipoprotein profiles, hepatic lipids, fatty acids and mRNA expression were analyzed in 3-week-old and 25-week-old offspring. At weaning, the EFAD pups had higher cholesterol levels in both plasma and liver and 6-fold higher concentrations of hepatic cholesterol esters than control pups. Adult EFAD offspring had higher levels of hepatic cholesterol and linoleic acid, but lower levels of dihomo-γ-linolenic acid and Pparg mRNA expression in the liver. In addition, HFD fed EFAD offspring had lower plasma total cholesterol, lower hepatic triglycerides and lower liver weight compared to controls fed HFD. In conclusion, early postnatal EFAD resulted in short-term alterations with increased hepatic cholesterol accumulation and long-term protection against diet-induced liver steatosis and hypercholesterolemia.

Altered essential fatty acid metabolism and composition in rat liver, plasma, heart and brain after microalgal DHA addition to the diet

To investigate the effect of docosahexaenoic acid (DHA) without other highly unsaturated fatty acids (HUFA) on n-3 and n-6 essential fatty acid (EFA) metabolism and fatty acid composition in mammals, a stable isotope tracer technique was used in adult rats fed diets with or without 1.3% of algal DHA in a base diet containing 15% of linoleic acid and 3% of alpha-linolenic acid over 8 weeks. The rats were administered orally a mixed oil containing 48 mg/kg body weight of deuterated linoleic and alpha-linolenic acids and euthanized at 4, 8, 24, 96, 168, 240, 360 and 600 h after administration of the isotopes. Fatty acid compositions and the concentrations of deuterated precursors and their respective metabolites were determined in rat liver, plasma, heart and brain as a function of time. DHA, docosapentaenoic acid and eicosapentaenoic acid in the n-3 EFA family were significantly increased in all organs tested in the DHA-fed group, ranging from 5% to 200% greater in comparison with the control group. The accumulation of the metabolites, deuterated-DHA and deuterated-docosapentaenoic acid n-6 was greatly decreased by 1.5- to 2.5-fold in the dietary DHA group. In summary, feeding preformed DHA led to a marked increase in n-3 HUFA content of rat organs at the expense of n-6 HUFA and also prevented the accumulation of newly synthesized deuterated end products. This is the first study which has isolated the effects of DHA on the de novo metabolism on both the n-6 and n-3 EFA pathways.

Omega-3 long chain fatty acid synthesis is regulated more by substrate levels than gene expression

The conversion of linoleic acid (LA) and alpha-linolenic acid (ALA) to long chain polyunsaturated fatty acids (LCPUFA) is known to involve desaturation and elongation steps. Although there is evidence that genes for these steps can be regulated by extremes of dietary PUFA, the degree to which there is meaningful regulation of LCPUFA levels in tissues by diet as a result of changes in expression of desaturase and elongase genes is unclear. In this study, we tested the effect of increasing ALA levels in diets of rats from 0.2% to 2.9% energy (en) against a constant LA level (1%en) on plasma and liver phospholipid LCPUFA content together with the expression of hepatic genes involved in PUFA metabolism, the desaturases FADS1 and FADS2, the elongases ELOV2 and ELOV5, and the transcription factors sterol regulatory element-binding protein-1c (SREBP-1c) and peroxisome proliferator-activated receptor alpha (PPARalpha). The levels of plasma and liver eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA) increased in proportion to dietary ALA whereas docosahexaenoic acid (DHA) increased only up to 1%en ALA. A low PUFA (0.4%en) reference diet stimulated the expression of delta 6 desaturase (FADS2) and elongase 2 (ELOVL2) when compared to higher PUFA diets. There was, however, no difference in the expression of any of the genes in rats, which were fed diets containing between 0.2%en and 2.9%en ALA and mRNA expression was unrelated to tissue/plasma LCPUFA content. These data suggest that the endogenous synthesis of n-3 LCPUFA from the precursor ALA is regulated independently of changes in the expression of the synthetic enzymes or regulatory transcription factor, and provides evidence that n-3 LCPUFA synthesis is regulated more by substrate competition for existing enzymes than by an increase in their mRNA expression.

Alterations in oxidative stress status modulate terminal differentiation in Atlantic salmon adipocytes cultivated in media rich in n-3 fatty acids

Regulation of oxidative stress (OS) in adipocytes is an important mediator of their development and dysfunction. Highly unsaturated fatty acids (HUFAs) play essential roles in marine fish, where they have anti-lipogenic effects, but they are prone to peroxidation. The aim of this study was to investigate how the effects of HUFAs in fish adipocytes are modulated by changes in their intracellular redox status. Adipocytes from Atlantic salmon were cultivated on HUFA-rich media and treated with buthionine sulfoximine (BSO), which is known to deplete stores of the antioxidant glutathione (GSH) thus increasing OS, and alpha-tocopherol (alpha-TOC), which protects from OS. Gene expression was assessed by qPCR. In addition, phospholipid composition, total fatty acid (FA) composition, TBARS, the activities of pro-apoptotic caspase 3 (CASP3) and antioxidant superoxide dismutase (SOD) were determined. BSO treatment decreased the expression of genes encoding GSH-based antioxidant enzymes glutathione peroxidase (GPX) 2 and GPX3. Consequently, depletion of GSH resulted in the highest level of peroxidation products TBARS despite the increased activity of SOD in this group. Significant reduction of TBARS was achieved by alpha-TOC. Further, in comparison to two alpha-TOC supplemented groups, GSH-depleted cells accumulated less fat and their gene expression profile of adipogenic markers was lower. The formation of large intracellular vesicles was prominent in the control and BSO groups while reduction of OS by alpha-TOC coincided with the increased gene expression of the activating transcription factor 6 (ATF6), a transducer of the endoplasmic reticulum (ER)-stress response. CASP3 assay showed no difference between groups; however, depletion of GSH resulted in the increased gene expression of several apoptotic markers. Up-regulation of the apoptosis inducible factor (AIF) implied higher probability of CASP3-independent apoptosis in cells under increased OS. In conclusion, the study provides several lines of evidence in favour of anti-adipogenic effects of OS in a cold blooded vertebrate.

A common FADS2 promoter polymorphism increases promoter activity and facilitates binding of transcription factor ELK1

Fatty acid desaturases (FADS) play an important role in the formation of omega-6 and omega-3 highly unsaturated fatty acids (HUFAs). The composition of HUFAs in the human metabolome is important for membrane fluidity and for the modulation of essential physiological functions such as inflammation processes and brain development. Several recent studies reported significant associations of single nucleotide polymorphisms (SNPs) in the human FADS gene cluster with HUFA levels and composition. The presence of the minor allele correlated with a decrease of desaturase reaction products and an accumulation of substrates. We performed functional studies with two of the associated polymorphisms (rs3834458 and rs968567) and showed an influence of polymorphism rs968567 on FADS2 promoter activity by luciferase reporter gene assays. Electrophoretic mobility shift assays proved allele-dependent DNA-binding ability of at least two protein complexes to the region containing SNP rs968567. One of the proteins binding to this region in an allele-specific manner was shown to be the transcription factor ELK1 (a member of ETS domain transcription factor family). These results indicate that rs968567 influences FADS2 transcription and offer first insights into the modulation of complex regulation mechanisms of FADS2 gene transcription by SNPs.

Activation of PPARalpha and PPARgamma reduces triacylglycerol synthesis in rat hepatoma cells by reduction of nuclear SREBP-1

Fibrates and thiazolidinediones, agonists of PPARalpha and PPARgamma, respectively, reduce triglyceride concentrations in rat liver and plasma. Fatty acid and triacylglycerol synthesis in mammals is regulated by sterol regulatory element-binding protein (SREBP)-1c. Recently, it was shown that insulin-induced gene (Insig)-1, the key regulator of SREBP activity, is up-regulated by both activation of PPARalpha and PPARgamma. In order to elucidate whether inhibition of SREBP-1 activation may contribute to the triacylglycerol lowering effect of PPARalpha and PPARgamma agonists, we incubated rat hepatoma Fao cells with WY 14,643 and troglitazone, strong and selective agonists of PPARalpha and PPARgamma, respectively. Activation of both, PPARalpha and PPARgamma led to increased concentrations of Insig-1 and Insig-2a, with the most prominent effect on Insig-2a after troglitazone incubation. As a result, the amount of nuclear SREBP-1 was reduced in Fao cells by both WY 14,643 and troglitazone treatment. The reduction of nuclear SREBP-1 was associated with decreased mRNA concentrations of its target genes fatty acid synthase and glycerol-3-phosphate acyltransferase, implicated in fatty acid and triacylglycerol synthesis. This was finally reflected in reduced rates of newly synthesized triacylglycerols from de novo-derived fatty acids and decreased intracellular and secreted triacylglycerol concentrations in Fao cells treated with WY 14,643 and troglitazone, respectively. Thus, these data suggest that the triacylglycerol reducing effect of fibrates and thiazolidinediones is partially caused by inhibition of SREBP-1 activation via up-regulation of Insig.

Disruption of FADS2 gene in mice impairs male reproduction and causes dermal and intestinal ulceration

Delta-6 desaturase (D6D) catalyzes the first step in the synthesis of highly unsaturated fatty acids (HUFA) such as arachidonic (AA), docosapentaenoic (DPAn-6), and docosahexaenoic (DHA) acids, as well as the last desaturation of DPAn-6 and DHA. We created D6D-null mice (-/-), which enabled us to study HUFA deficiency without depleting their precursors. In -/-, no in vivo AA synthesis was detected after administration of [U-(13)C]linoleic acid (LA), indicating absence of D6D isozyme. Unexpectedly, all of the -/- developed ulcerative dermatitis when fed a purified diet lacking D6D products but containing ample LA. The -/- also exhibited splenomegaly and ulceration in duodenum and ileocecal junction. Male -/- lacked normal spermatozoa with a severe impairment of spermiogenesis. Tissue HUFAs in -/- declined differentially: liver AA and DHA by 95%, and a smaller decrease in brain and testes. Dietary AA completely prevented dermatitis and intestinal ulcers in -/-. DPAn-6 was absent in -/- brain under AA supplementation, indicating absence of D6D isozyme for DPAn-6 synthesis from AA. This study demonstrated a distinct advantage of the D6D-null mice (-/-) to elucidate (1) AA function without complication of LA deprivation and (2) DHA function in the nervous system without AA depletion or DPAn-6 replacement seen in traditional models.

Differential regulation of peroxisome proliferator-activated receptor (PPAR)-alpha1 and truncated PPARalpha2 as an adaptive response to fasting in the control of hepatic peroxisomal fatty acid beta-oxidation in the hibernating mammal

Seasonal obesity and fasting-associated hibernation are the two major metabolic events governing hepatic lipid metabolism in hibernating mammals. In this process, however, the role of the nuclear receptor known as peroxisome proliferator-activated receptor (PPAR)-alpha has not been elucidated yet. Here we show, as in human, that jerboa (Jaculus orientalis) liver expresses both active wild-type PPARalpha (PPARalpha1wt) and truncated PPARalpha forms and that the PPARalpha1wt to truncated PPARalpha2 ratio, which indicates the availability of active PPARalpha1wt, is differentially regulated during fasting-associated hibernation. Functional activation of hepatic jerboa PPARalpha, during prehibernating and hibernating states, was demonstrated by the induction of its target genes, which encode peroxisomal proteins such as acyl-CoA oxidase 1, peroxisomal membrane protein 70, and catalase, accompanied by a concomitant induction of PPARalpha thermogenic coactivator PPARgamma coactivator-1alpha. Interestingly, sustained activation of PPARalpha by its hypolipidemic ligand, ciprofibrate, abrogates the adaptive fasting response of PPARalpha during prehibernation and overinduces its target genes, disrupting the prehibernation fattening process. In striking contrast, during fasting-associated hibernation, jerboas exhibit preferential up-regulation of hepatic peroxisomal fatty acid oxidation instead of the mitochondrial pathway, which is down-regulated. Taken together, our results strongly suggest that PPARalpha is subject to a hibernation-dependent splicing regulation in response to feeding-fasting conditions, which defines the activity of PPARalpha and the activation of its target genes during hibernation bouts of jerboas.

Unsaturated fatty acid regulation of cytochrome P450 expression via a CAR-dependent pathway

The liver is responsible for key metabolic functions, including control of normal homoeostasis in response to diet and xenobiotic metabolism/detoxification. We have shown previously that inactivation of the hepatic cytochrome P450 system through conditional deletion of POR (P450 oxidoreductase) induces hepatic steatosis, liver growth and P450 expression. We have exploited a new conditional model of POR deletion to investigate the mechanism underlying these changes. We demonstrate that P450 induction, liver growth and hepatic triacylglycerol (triglyceride) homoeostasis are intimately linked and provide evidence that the observed phenotypes result from hepatic accumulation of unsaturated fatty acids, which mediate these phenotypes by activation of the nuclear receptor CAR (constitutive androstane receptor) and, to a lesser degree, PXR (pregnane X receptor). To our knowledge this is the first direct evidence that P450s play a major role in controlling unsaturated fatty acid homoeostasis via CAR. The regulation of P450s involved in xenobiotic metabolism by this mechanism has potentially significant implications for individual responses to drugs and environmental chemicals.

Novel aspects of PPARalpha-mediated regulation of lipid and xenobiotic metabolism revealed through a nutrigenomic study

Peroxisome proliferator-activated receptor-alpha (PPARalpha) is a major transcriptional regulator of lipid metabolism. It is activated by diverse chemicals such as fatty acids (FAs) and regulates the expression of numerous genes in organs displaying high FA catabolic rates, including the liver. The role of this nuclear receptor as a sensor of whole dietary fat intake has been inferred, mostly from high-fat diet studies. To delineate its function under low fat intake conditions (4.8% w/w), we studied the effects of five regimens with contrasted FA compositions on liver lipids and hepatic gene expression in wild-type and PPARalpha-deficient mice. Diets containing polyunsaturated FAs reduced hepatic fat stores in wild-type mice. Only sunflower, linseed, and fish oil diets lowered hepatic lipid stores in PPARalpha-/- mice, a model of progressive hepatic triglyceride accumulation. These beneficial effects were associated, in particular, with dietary regulation of Delta9-desaturase in both genotypes, and with a newly identified PPARalpha-dependent regulation of lipin. Furthermore, hepatic levels of 18-carbon essential FAs (C18:2omega6 and C18:3omega3) were elevated in PPARalpha-/- mice, possibly due to the observed reduction in expression of the Delta6-desaturase and of enoyl-coenzyme A isomerases. Effects of diet and genotype were also observed on the xenobiotic metabolism-related genes Cyp3a11 and CAR.

CONCLUSION

Together, our results suggest that dietary FAs represent--even under low fat intake conditions--a beneficial strategy to reduce hepatic steatosis. Under such conditions, we established the role of PPARalpha as a dietary FA sensor and highlighted its importance in regulating hepatic FA content and composition.

Essential fatty acid deficiency induces fatty acid desaturase expression in rat epididymis, but not in testis

On the molecular level, essential fatty acid deficiency (EFAD) has been associated with induced fatty acid (FA) desaturase expression and activity in several tissues. However, there seem to be exceptions. In the present study, we examine the effects of EFAD in the male rat genital tract, combining FA analysis, gene expression studies, and morphological evaluation of epididymal spermatozoa. When feeding 21-day-old Wistar rats, a fat-free diet for 6 weeks, an increase in 18:1n-9 and 20:3n-9 and a concomitant decrease in the 18:2n-6 and 20:4n-6 species are seen in testis, as well as in liver. However, with regard to desaturase expression the rat testis seems to be unresponsive to EFAD conditions, in contrast to other organs studied. In the sexually mature testis none of the desaturases (SCD1, SCD2, D5D, or D6D) are induced in response to lowered contents of polyunsaturated FAs. This also applies tocaputepididymis, while EFAD sensitivity is regained incaudaepididymis, where the desaturases are upregulated. The FA profile of epididymal spermatozoa is increasingly affected by EFAD during the transport from testis tocaudaepididymis. Furthermore, a significant increase in the number of abnormal spermatozoa is observed incaudaepididymis.

Dietary oxidized fat prevents ethanol-induced triacylglycerol accumulation and increases expression of PPARalpha target genes in rat liver

Alcoholic fatty liver results from an impaired fatty acid catabolism due to blockade of PPARalpha and increased lipogenesis due to activation of sterol regulatory element-binding protein (SREBP)-1c. Because both oxidized fats (OF) and conjugated linoleic acids (CLA) have been demonstrated in rats to activate hepatic PPARalpha, we tested the hypothesis that these fats are able to prevent ethanol-induced triacylglycerol accumulation in the liver by upregulation of PPARalpha-responsive genes. Forty-eight male rats were assigned to 6 groups and fed isocaloric liquid diets containing either sunflower oil (SFO) as a control fat, OF prepared by heating of SFO, or CLA, in the presence and absence of ethanol, for 4 wk. Administration of ethanol lowered mRNA concentrations of PPARalpha and the PPARalpha-responsive genes medium chain acyl-CoA dehydrogenase, long chain acyl-CoA dehydrogenase, acyl-CoA oxidase, carnitine palmitoyl-CoA transferase I, and cytochrome P450 4A1 and increased triacylglycerol concentrations in the liver (P < 0.05). OF increased hepatic mRNA concentrations of PPARalpha-responsive genes and lowered hepatic triacylglycerol concentrations compared with SFO (P < 0.05) whereas CLA did not. Rats fed OF with ethanol had similar mRNA concentrations of PPARalpha-responsive genes and similar triacylglycerol concentrations in the liver as rats fed SFO or CLA without ethanol. In contrast, hepatic mRNA concentrations of SREBP-1c and fatty acid synthase were not altered by OF or CLA compared with SFO. This study shows that OF prevents an alcohol-induced triacylglycerol accumulation in rats possibly by upregulation of hepatic PPARalpha-responsive genes involved in oxidation of fatty acids, whereas CLA does not exert such an effect.

Fibrate therapy in patients with metabolic syndrome and diabetes mellitus

Patients with metabolic syndrome and type 2 diabetes mellitus are usually in moderately high-risk, high-risk, or very high-risk cardiovascular categories and present major therapeutic challenges. The dyslipidemia in such patients is typically a disorder of the triglyceride/high-density lipoprotein axis (TG/HDL axis) characterized by an excess of triglyceride-rich lipoproteins and a reduction of HDL. Very often, lifestyle therapy and statin monotherapy fail to achieve guideline goals, necessitating combination therapies. Fibric acids (or fibrates), are agonists of peroxisome proliferator-activated receptor alpha,which have amassed significant lipid-surrogate and clinical outcome trial data, especially in insulin-resistant patients, typical of those with metabolic syndrome or type 2 diabetes mellitus. Current guidelines advocate fibrate use as an add-on to statin therapy when TG/HDL abnormalities exist in such patients. In this paper, we review pertinent and recent trial data, mechanisms of action, and the safety of fibrate therapy.

A combined 1H-NMR spectroscopy- and mass spectrometry-based metabolomic study of the PPAR-alpha null mutant mouse defines profound systemic changes in metabolism linked to the metabolic syndrome

The mobilization of triacylglycerides from storage in adipocytes to the liver is a vital response to the fasting state in mammalian metabolism. This is accompanied by a rapid translational activation of genes encoding mitochondrial, microsomal, and peroxisomal beta-oxidation in the liver, in part under the regulation of peroxisome proliferator-activated receptor-alpha (PPAR-alpha). A failure to express PPAR-alpha results in profound metabolic perturbations in muscle tissue as well as the liver. These changes represent a number of deficits that accompany diabetes, dyslipidemia, and the metabolic syndrome. In this study, the metabolic role of PPAR-alpha has been investigated in heart, skeletal muscle, liver, and adipose tissue of PPAR-alpha null mice at 1 mo of age using metabolomics. To maximize the coverage of the metabolome in these tissues, (1)H-NMR spectroscopy, magic angle spinning (1)H-NMR spectroscopy, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry were used to examine metabolites in aqueous tissue extracts and intact tissue. The data were analyzed by the multivariate approaches of principal components analysis and partial least squares. Across all tissues, there was a profound decrease in glucose and a number of amino acids, including glutamine and alanine, and an increase in lactate, demonstrating that a failure to express PPAR-alpha results in perturbations in glycolysis, the citric acid cycle, and gluconeogenesis. Furthermore, despite PPAR-alpha being weakly expressed in adipose tissue, a profound metabolic perturbation was detected in this tissue.