Response to micronized fenofibrate treatment is associated with the peroxisome-proliferator-activated receptors alpha G/C intron7 polymorphism in subjects with type 2 diabetes

Associations of the PPARα and Lipoprotein Lipase Enzyme Gene Polymorphisms with Dyslipidemia in Obese and Non-obese Males

Background

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear transcription factor responsible for gene expression, particularly those associated with lipid metabolism. The lipoprotein lipase enzyme (LPL) is considered a key enzyme in lipid metabolism and transport. The link between dyslipidemia and obesity is well understood. Dyslipidemia is also an established risk feature for cardiovascular disease. Thus, it becomes progressively essential to identify the role of genetic factors as risk markers for the development of dyslipidemia among obese males.

Methods

A case-control study was performed including 469 males. Anthropometric characteristics and serum lipid profiles such as triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) were evaluated. Genomic DNA extraction and purification were performed using whole blood samples. Restriction enzyme fragment length polymorphism was used to genotype PPARα and LPL single nucleotide polymorphisms. The associations between these polymorphisms and dyslipidemia were examined.

Results

The CC and CG genotypes of PPARα gene polymorphisms were significantly associated with higher TC and LDL-C levels (P<0.05). The TT genotype of the LPL gene polymorphism was significantly associated with higher TG levels and lower HDL-C levels (P<0.05). In contrast, the GG genotype may have a protective action against dyslipidemia.

Conclusion

The study reaches the interesting conclusion that there was a significant association between PPARα as well as LPL gene polymorphisms and dyslipidemia among obese and non-obese males.

Pharmacogenomics of Cardiovascular Drugs for Atherothrombotic, Thromboembolic and Atherosclerotic Risk

PURPOSE OF REVIEW

Advances in pharmacogenomics have paved the way for personalized medicine. Cardiovascular diseases still represent the leading cause of mortality in the world. The aim of this review is to summarize the background, rationale, and evidence of pharmacogenomics in cardiovascular medicine, in particular, the use of antiplatelet drugs, anticoagulants, and drugs used for the treatment of dyslipidemia.

RECENT FINDINGS

Randomized clinical trials have supported the role of a genotype-guided approach for antiplatelet therapy in patients with coronary heart disease undergoing percutaneous coronary interventions. Numerous studies demonstrate how the risk of ineffectiveness of new oral anticoagulants and vitamin K anticoagulants is linked to various genetic polymorphisms. Furthermore, there is growing evidence to support the association of some genetic variants and poor adherence to statin therapy, for example, due to the appearance of muscular symptoms. There is evidence for resistance to some drugs for the treatment of dyslipidemia, such as anti-PCSK9.

SUMMARY

Pharmacogenomics has the potential to improve patient care by providing the right drug to the right patient and could guide the identification of new drug therapies for cardiovascular disease. This is very important in cardiovascular diseases, which have high morbidity and mortality. The improvement in therapy could be reflected in the reduction of healthcare costs and patient mortality.

Pharmacogenomics of lipid-lowering agents: the impact on efficacy and safety

Hyperlipidemia is a significant risk factor for cardiovascular disease morbidity and mortality. The lipid-lowering drugs are considered the cornerstone of primary and secondary prevention of atherosclerotic cardiovascular disease. Unfortunately, the lack of efficacy and associated adverse effects, ranging from mild-to-moderate to potentially life-threatening, lead to therapy discontinuation. Numerous reports support the role of gene polymorphisms in drugs' pharmacokinetic parameters and their associated adverse reactions. Therefore, this study aims to understand the pharmacogenomics of lipid-lowering drugs and the impact of genetic variants of key genes on the drugs' efficacy and toxicity. Indeed, genetically guided lipid-lowering therapy enhances overall safety, improves drug adherence and achieves long-term therapy.

Fibrate pharmacogenomics: expanding past the genome

Fibrates are a medication class prescribed for decades as 'broad-spectrum' lipid-modifying agents used to lower blood triglyceride levels and raise high-density lipoprotein cholesterol levels. Such lipid changes are associated with a decrease in cardiovascular disease, and fibrates are commonly used to reduce risk of dangerous cardiovascular outcomes. As with most drugs, it is well established that response to fibrate treatment is variable, and this variation is heritable. This has motivated the investigation of pharmacogenomic determinants of response, and multiple studies have discovered a number of genes associated with fibrate response. Similar to other complex traits, the interrogation of single nucleotide polymorphisms using candidate gene or genome-wide approaches has not revealed a substantial portion of response variation. However, recent innovations in technological platforms and advances in statistical methodologies are revolutionizing the use and integration of other 'omes' in pharmacogenomics studies. Here, we detail successes, challenges, and recent advances in fibrate pharmacogenomics.

Impact of PPAR-Alpha Polymorphisms-The Case of Metabolic Disorders and Atherosclerosis

Peroxisome proliferator activated receptor α (PPARα) has the most relevant biological functions among PPARs. Activation by drugs and dietary components lead to major metabolic changes, from reduced triglyceridemia to improvement in the metabolic syndrome. Polymorphisms of PPARα are of interest in order to improve our understanding of metabolic disorders associated with a raised or reduced risk of diseases. PPARα polymorphisms are mainly characterized by two sequence changes, L162V and V227A, with the latter occurring only in Eastern nations, and by numerous SNPs (Single nucleotide polymorphisms) with a less clear biological role. The minor allele of L162V associates with raised total cholesterol, LDL-C (low-density lipoprotein cholesterol), and triglycerides, reduced HDL-C (high-density lipoprotein metabolism), and elevated lipoprotein (a). An increased cardiovascular risk is not clear, whereas a raised risk of diabetes or of liver steatosis are not well supported. The minor allele of the V227A polymorphism is instead linked to a reduction of steatosis and raised γ-glutamyltranspeptidase levels in non-drinking Orientals, the latter being reduced in drinkers. Lastly, the minor allele of rs4353747 is associated with a raised high-altitude appetite loss. These and other associations indicate the predictive potential of PPARα polymorphisms for an improved understanding of human disease, which also explain variability in the clinical response to specific drug treatments or dietary approaches.

The Polymorphisms of the Peroxisome-Proliferator Activated Receptors' Alfa Gene Modify the Aerobic Training Induced Changes of Cholesterol and Glucose

Background: PPARα is a transcriptional factor that controls the expression of genes involved in fatty acid metabolism, including fatty acid transport, uptake by the cells, intracellular binding, and activation, as well as catabolism (particularly mitochondrial fatty acid oxidation) or storage. PPARA gene polymorphisms may be crucial for maintaining lipid homeostasis and in this way, being responsible for developing specific training-induced physiological reactions. Therefore, we have decided to check if post-training changes of body mass measurements as well as chosen biochemical parameters are modulation by the PPARA genotypes. Methods: We have examined the genotype and alleles’ frequencies (described in PPARA rs1800206 and rs4253778 polymorphic sites) in 168 female participants engaged in a 12-week training program. Body composition and biochemical parameters were measured before and after the completion of a whole training program. Results: Statistical analyses revealed that PPARA intron 7 rs4253778 CC genotype modulate training response by increasing low-density lipoproteins (LDL) and glucose concentration, while PPARA Leu162Val rs1800206 CG genotype polymorphism interacts in a decrease in high-density lipoproteins (HDL) concentration. Conclusions: Carriers of PPARA intron 7 rs4253778 CC genotype and Leu162Val rs1800206 CG genotype might have potential negative training-induced cholesterol and glucose changes after aerobic exercise.

Pharmacogenomics of blood lipid regulation

Blood lipids are important modifiable risk factors for coronary heart disease and various drugs have been developed to target lipid fractions. Considerable efforts have been made to identify genetic variants that modulate responses to drugs in the hope of optimizing their use. Pharmacogenomics and new biotechnologies now allow for meaningful integration of human genetic findings and therapeutic development for increased efficiency and precision of lipid-lowering drugs. Polygenic predictors of disease risk are also changing how patient populations can be stratified, enabling targeted therapeutic interventions to patients more likely to derive the highest benefit, marking a shift from single variant to genomic approaches in pharmacogenomics.

Association of polymorphisms of peroxisome proliferator activated receptors in early and late onset of type 2 diabetes mellitus

OBJECTIVE

Genetic variation of disease susceptible genes is different in different ethnic groups and there is an evidence of association of polymorphisms of Peroxisome Proliferator Activated Receptors (PPARs) in Type 2 Diabetes Mellitus (T2DM). This research analyses the association of PPARs in early and late onset of T2DM in North Indian Population (NIP).

METHODS

Total of 703 subjects were recruited from north of India and subjects were further divided into subjects of early onset (less than 25 years of onset, 26 T2DM and 26 controls) and late onset (more than 25 years of onset, 326 T2DM and 325 controls).

RESULT

The onset of T2DM begins from 15 years and continues further to maximum T2DM subjects to the age of 50 (76% of T2DM). High BMI and WHR, high blood pressure leading to early onset of hypertension, early mortality due to T2DM (7% of T2DM is above 75 years and 3% of T2DM has 20 years duration of onset) and high hyperglycemic NIP were the few outcomes of this research.

CONCLUSION

There is a strong association of PPAR γ, PPAR α and PPAR δ genes on the susceptibility of T2DM in late onset but not with the early onset of T2DM subjects in North Indian Population: Dual association of PPAR γ was observed with its genotype G/G (Ala/Ala) favoring protection against T2DM and genotype C/C (Pro/Pro) favoring susceptibility to T2DM. Association of intron7 polymorphism of PPAR α and +T294C polymorphism of PPAR δ on the susceptibility to T2DM requires further analysis.

PPARα gene variants as predicted performance-enhancing polymorphisms in professional Italian soccer players

Background

The PPARα gene encodes the peroxisome proliferator-activator receptor alpha, a central regulator of expression of other genes involved in fatty acid metabolism. The purpose of this study was to determine the prevalence of G allele of the PPARα intron 7 G/C polymorphism (rs4253778) in professional Italian soccer players.

Methods

Sixty professional soccer players and 30 sedentary volunteers were enrolled in the study. Samples of venous blood were obtained at rest, in the morning, by conventional clinical procedures; blood serum was collected and total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides were measured. An aliquot of anticoagulant-treated blood was used to prepare genomic DNA from whole blood. The G/C polymorphic site in PPARα intron 7 was scanned by using the PCR-RFLP (polymerase chain reaction restriction fragment length polymorphism) protocol with TaqI enzyme.

Results

We found variations in genotype distribution of PPARα polymorphism between professional soccer players and sedentary volunteers. Particularly, G alleles and the GG genotype were significantly more frequent in soccer players compared with healthy controls (64% versus 48%). No significant correlations were found between lipid profile and genotype background.

Conclusion

Previous results demonstrated an association of intron 7 G allele as well as the GG genotype in endurance athletes. Our result suggests that this is the case also in professional soccer players.

Genetic risk scores associated with baseline lipoprotein subfraction concentrations do not associate with their responses to fenofibrate

Lipoprotein subclass concentrations are modifiable markers of cardiovascular disease risk. Fenofibrate is known to show beneficial effects on lipoprotein subclasses, but little is known about the role of genetics in mediating the responses of lipoprotein subclasses to fenofibrate. A recent genomewide association study (GWAS) associated several single nucleotide polymorphisms (SNPs) with lipoprotein measures, and validated these associations in two independent populations. We used this information to construct genetic risk scores (GRSs) for fasting lipoprotein measures at baseline (pre-fenofibrate), and aimed to examine whether these GRSs also associated with the responses of lipoproteins to fenofibrate. Fourteen lipoprotein subclass measures were assayed in 817 men and women before and after a three week fenofibrate trial. We set significance at a Bonferroni corrected alpha <0.05 (p < 0.004). Twelve subclass measures changed with fenofibrate administration (each p = 0.003 to <0.0001). Mixed linear models which controlled for age, sex, body mass index (BMI), smoking status, pedigree and study-center, revealed that GRSs were associated with eight baseline lipoprotein measures (p < 0.004), however no GRS was associated with fenofibrate response. These results suggest that the mechanisms for changes in lipoprotein subclass concentrations with fenofibrate treatment are not mediated by the genetic risk for fasting levels.

Paradoxical reduction in HDL-C with fenofibrate and thiazolidinedione therapy in type 2 diabetes: the ACCORD Lipid Trial

OBJECTIVE

To determine the occurrence of extremely low HDL cholesterol (HDL-C) among participants in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) Lipid Trial and to examine the relationship of this finding with treatment with fenofibrate and thiazolidinedione (TZD).

RESEARCH DESIGN AND METHODS

The ACCORD Lipid Trial was a randomized, double-blind, placebo-controlled study conducted in patients with type 2 diabetes at 77 clinical centers across the U.S. and Canada in a 5,518-patient subset of the larger 10,251 ACCORD Glycemia Trial. Patients were enrolled from 11 January 2001 to 29 October 2005 and followed until the end of study visits between 1 March and 30 June 2009. Follow-up in the ACCORD Lipid Trial was 4-8 years (mean 4.7 years). Patients were treated with blinded fenofibrate or placebo on a background of simvastatin therapy. The main outcome measures for these descriptive, post hoc analyses was the occurrence of extremely low HDL-C (defined as <25 mg/dL [0.647 mmol/L]) during the trial.

RESULTS

Among ACCORD Lipid Trial participants, the occurrence of extremely low HDL-C ever during study follow-up was 106% higher among those randomized to fenofibrate (10.1% fenofibrate vs. 4.9% placebo, P < 0.001). The occurrence of low HDL-C was associated with concurrent treatment with fenofibrate and TZD (7.0% for both vs. 2.2% for neither at 48 months postrandomization).

CONCLUSIONS

Idiosyncratic and marked reduction in HDL-C can occur in some patients treated with both fenofibrate and TZD. Practitioners should recognize this important potential idiosyncratic reaction and take appropriate corrective action.

PPAR-α as a key nutritional and environmental sensor for metabolic adaptation

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that belong to the superfamily of nuclear hormone receptors and regulate the expression of several genes involved in metabolic processes that are potentially linked to the development of some diseases such as hyperlipidemia, diabetes, and obesity. One type of PPAR, PPAR-α, is a transcription factor that regulates the metabolism of lipids, carbohydrates, and amino acids and is activated by ligands such as polyunsaturated fatty acids and drugs used to treat dyslipidemias. There is evidence that genetic variants within the PPARα gene have been associated with a risk of the development of dyslipidemia and cardiovascular disease by influencing fasting and postprandial lipid concentrations; the gene variants have also been associated with an acceleration of the progression of type 2 diabetes. The interactions between genetic PPARα variants and the response to dietary factors will help to identify individuals or populations who can benefit from specific dietary recommendations. Interestingly, certain nutritional conditions, such as the prolonged consumption of a protein-restricted diet, can produce long-lasting effects on PPARα gene expression through modifications in the methylation of a specific locus surrounding the PPARα gene. Thus, this review underlines our current knowledge about the important role of PPAR-α as a mediator of the metabolic response to nutritional and environmental factors.

Pharmacogenomics of lipid-lowering therapies

Statins are the most widely used group of lipid-lowering drugs and they have been shown to be effective in the prevention of cardiovascular disease, primarily by reducing plasma low-density lipoprotein cholesterol concentrations and possibly through other pleiotropic effects. However, there are large variations in lipid responses to statins and some patients have intolerable muscle adverse drug reactions, which may in part be related to genetic factors. In the last decade, pharmacogenetic studies on statins ranging from the candidate gene approach to the more recent genome-wide association studies have provided evidence that genetic variations play an important role in determining statin responses. This review summarizes the current understanding on the pharmacogenomics of statins and other lipid-lowering drugs in current use.

Variants identified in a GWAS meta-analysis for blood lipids are associated with the lipid response to fenofibrate

A recent large-scale meta-analysis of genome-wide studies has identified 95 loci, 59 of them novel, as statistically significant predictors of blood lipid traits; we tested whether the same loci explain the observed heterogeneity in response to lipid-lowering therapy with fenofibrate. Using data from the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN, n = 861) we fit linear mixed models with the genetic markers as predictors and high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, total cholesterol, and triglyceride concentrations as outcomes. For all four traits, we analyzed both baseline levels and changes in response to treatment with fenofibrate. For the markers that were significantly associated with fenofibrate response, we fit additional models evaluating potential epistatic interactions. All models were adjusted for age, sex, and study center as fixed effects, and pedigree as a random effect. Statistically significant associations were observed between the rs964184 polymorphism near APOA1 (P-value≤0.0001) and fenofibrate response for HDL and triglycerides. The association was replicated in the Pharmacogenetics of Hypertriglyceridemia in Hispanics study (HyperTG, n = 267). Suggestive associations with fenofibrate response were observed for markers in or near PDE3A, MOSC1, FLJ36070, CETP, the APOE-APOC1-APOC4-APOC2, and CILP2. Finally, we present strong evidence for epistasis (P-value for interaction =  0.0006 in GOLDN, 0.05 in HyperTG) between rs10401969 near CILP2 and rs4420638 in the APOE-APOC1-APOC4-APOC2 cluster with total cholesterol response to fenofibrate. In conclusion, we present evidence linking several novel and biologically relevant genetic polymorphisms to lipid lowering drug response, as well as suggesting novel gene-gene interactions in fenofibrate pharmacogenetics.

Fenofibrate-associated changes in renal function and relationship to clinical outcomes among individuals with type 2 diabetes: the Action to Control Cardiovascular Risk in Diabetes (ACCORD) experience

AIMS/HYPOTHESIS

Fenofibrate has been noted to cause an elevation in serum creatinine in some individuals. Participants in the Action to Control Cardiovascular Risk in Diabetes Lipid Study were studied to better characterise who is at risk of an increase in creatinine level and to determine whether those with creatinine elevation have a differential risk of adverse renal or cardiovascular outcomes.

METHODS

A fenofibrate-associated creatinine increase (FACI) was defined as an increase in serum creatinine of at least 20% from baseline to month 4 in participants assigned to fenofibrate. Baseline patient characteristics, and baseline and 4-month drug, clinical, laboratory characteristics and study outcomes were examined by FACI status.

RESULTS

Of the sample, 48% of those randomised to receive fenofibrate had at least a 20% increase in serum creatinine within 4 months. In multivariable analysis, participants who were older, male, used an ACE inhibitor at baseline, used a thiazolidinedione (TZD) at 4 months post-randomisation, had baseline CVD, and had lower baseline serum creatinine and LDL-cholesterol levels were all more likely to meet the criteria for FACI. Participants in the FACI group were also more likely to have a decrease in their serum triacylglycerol level from baseline to 4 months. No differences in study outcomes were seen by FACI criteria.

CONCLUSIONS/INTERPRETATION

Several characteristics predict a rapid rise in serum creatinine upon starting fenofibrate. Participants who met the criteria for FACI also had a greater change in triacylglycerol levels. In the setting of careful renal function surveillance and reduction of fenofibrate dose as indicated, no increase in renal disease or cardiovascular outcome was seen in those individuals demonstrating FACI.

TRIAL REGISTRATION

ClincalTrials.gov: NCT00000620.

FUNDING

The ACCORD Trial was supported by grants (N01-HC-95178, N01-HC-95179, N01-HC-95180, N01-HC-95181, N01-HC-95182, N01-HC-95183, N01-HC-95184, IAA-Y1-HC-9035 and IAA-Y1-HC-1010) from the National Heart, Lung, and Blood Institute; by the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Aging, and the National Eye Institute; by the Centers for Disease Control and Prevention; by General Clinical Research Centers and by the Clinical and Translational Science Awards. Abbott Laboratories, Amylin Pharmaceutical, AstraZeneca Pharmaceuticals LP, Bayer HealthCare LLC, Closer Healthcare, GlaxoSmithKline Pharmaceuticals, King Pharmaceuticals, Merck, Novartis Pharmaceuticals, Novo Nordisk, Omron Healthcare, sanofi-aventis US and Takeda Pharmaceuticals provided study medications, equipment or supplies.

The PPAR alpha gene is associated with triglyceride, low-density cholesterol and inflammation marker response to fenofibrate intervention: the GOLDN study

As a peroxisome proliferator-activated receptor alpha (PPARα) agonist, fenofibrate favorably modulates dyslipidemia and inflammation markers, which are associated with cardiovascular risk. To determine whether variation in the PPARα receptor gene was associated with lipid and inflammatory marker response, we conducted a three week trial of fenofibrate in 861 men and women. Mixed linear models which controlled for age and sex, as well as family pedigree and study-center, were constructed using SNPs in the PPARα gene as predictors and changes in fasting triglycerides (TGs), cholesterol and inflammatory markers as outcomes. Significant associations with low-density cholesterol (LDL-C) and interleukin-2 (IL-2; P<.001) responses to fenofibrate were found. Although there were suggestive associations with tumour necrosis factor-alpha (TNF-α) and TG responses (P<.05), these did not survive the correction for multiple testing. We conclude that variants in the PPARα gene may contribute to future pharmacogenomic paradigms seeking to predict fenofibrate responders from both an anti-dyslipidemic and anti-inflammatory perspective.

Is PPARα intron 7 G/C polymorphism associated with muscle strength characteristics in nonathletic young men?

Peroxisome proliferator-activated receptor alpha (PPARα), a ligand-dependent transcription factor, regulates fatty acid metabolism in heart and skeletal muscle. The intron 7 G/C polymorphism (rs4253778) has been associated with athletic performance. The rare C-allele was predominant in power athletes, whereas the G-allele was more frequent in endurance athletes. In the present study, we investigated the association between this polymorphism and strength characteristics in nonathletic, healthy young adults (n = 500; age 24.2 ± 4.4 years). Knee torque was measured during concentric knee flexion and extension movements at 60°/s, 120°/s, and 240°/s during 3, 25, and 5 repetitions, respectively. Also, resistance to muscle fatigue (i.e. work last 20% repetitions/work first 20% repetitions *100) was calculated. Differences in knee strength phenotypes between GG homozygous individuals and C-allele carriers were analyzed. The polymorphism did not influence the ability to produce isometric or dynamic knee flexor or extensor peak torque during static or dynamic conditions in this population (0.23 < P < 0.95). Similar results were found for the endurance ratio, a measure for resistance to muscle fatigue. In conclusion, the PPARα intron 7 G/C polymorphism does not seem to influence strength characteristics in a nonathletic population.

PPAR Genomics and Pharmacogenomics: Implications for Cardiovascular Disease

The peroxisome proliferator-activated receptors (PPARs) consist of three related transcription factors that serve to regulate a number of cellular processes that are central to cardiovascular health and disease. Numerous pharmacologic studies have assessed the effects of specific PPAR agonists in clinical trials and have provided insight into the clinical effects of these genes while genetic studies have demonstrated clinical associations between PPAR polymorphisms and abnormal cardiovascular phenotypes. With the abundance of data available from these studies as a background, PPAR pharmacogenetics has become a promising and rapidly advancing field. This review focuses on summarizing the current state of understanding of PPAR genetics and pharmacogenetics and the important implications for the individualization of therapy for patients with cardiovascular diseases.

Association of PPARα Intron 7 Polymorphism with Coronary Artery Disease: A Cross-Sectional Study

The allelic variants of peroxisome proliferator-activated receptor alpha (PPARα) can influence the risk of coronary artery disease (CAD) by virtue of its effect on lipid metabolism. However, the role of PPARα intronic polymorphism with CAD has received little attention. The association of allelic variants G/C at intron 7 of the PPAR-alpha gene with CAD was examined in a hospital-based Indian population. PPAR genotyping was performed in 110 male patients with CAD and 120 age and ethnically matched healthy males by PCR amplification of the gene followed by restriction digestion. Presence of C allele showed a positive association with CAD (OR = 2.9; 95% CI [1.65–4.145]; P = .009) and also with dyslipidaemia (OR = 2.95, 95% CI (1.5–4.39); P < .05). Impaired lipid metabolism in carriers of the PPARα Intron 7C allele is possibly responsible for the predilection to CAD.

Association of gene variants with lipid levels in response to fenofibrate is influenced by metabolic syndrome status

OBJECTIVE

Fenofibrate therapy reduces serum triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C) and thus addresses the atherogenic dyslipidemia associated with metabolic syndrome (MetS). Our hypothesis is that genetic factors contribute to the variability of lipid response to fenofibrate differently in subjects with MetS and without MetS.

METHODS

We investigated the association in 25 candidate genes with lipid responses to a 3-weeks trial on fenofibrate in subjects with and without MetS. We employed growth curve mixed models to generate the response phenotypes to fenofibrate in TG, HDL-C, and low-density lipoprotein-cholesterol (LDL-C) and examined the genetic associations accounting for family dependencies.

RESULTS

After correcting for multiple testing (p<0.05) and accounting for significant differences in the association effect sizes between subjects with and without MetS (p<0.05), variants of APOA5 (rs662799) and APOE (rs429358) were associated with HDL-C and LDL-C responses in MetS subjects, while APOA4 (rs675) was associated with TG response in non-MetS subjects. There was also suggestive evidence that MetS may interact with APOA4 (p=0.017), APOA5 (p=0.06), and APOE (p=0.09) to the variation to lipid responses.

CONCLUSIONS

Genetic effects that contributed to the variability of lipid responses to fenofibrate may differ in subjects with and without MetS. This research may provide guidance for more personalized and effective therapies.

Apolipoprotein E polymorphisms and postprandial triglyceridemia before and after fenofibrate treatment in the Genetics of Lipid Lowering and Diet Network (GOLDN) Study

BACKGROUND

Although much is known about the effect of Apolipoprotein E (APOE) alleles on fasting lipid concentrations, less is known about the effect of APOE alleles on postprandial triglyceridemia or the triglyceride response to fenofibrate.

METHODS AND RESULTS

We evaluated the effects of the APOE locus on fasting and postprandial triglyceride concentrations as part of the Genetics of Lipid Lowering and Diet Network (GOLDN) study. Participants were evaluated after a high-fat meal challenge before (n=1072) and after 3 weeks of daily treatment with 160 mg of fenofibrate (n=738). Mixed models adjusted for sex, age, waist circumference, and family relationship were used to examine the association of the ε4 carrier and ε2 carrier status versus ε3 homozygotes with fasting triglycerides and the area under the curve (AUC) for triglycerides during the high-fat meal challenge. Compared with the ε3/ε3 genotype, ε2 carriers had on average higher fasting triglyceride concentrations (130.5 mg/dL versus 109.3 mg/dL, P<0.001). After fenofibrate treatment, the APOE genotype differences persisted in the fasting state (ε2 carriers: 85.1 mg/dL versus ε3/ε3: 75.9 mg/dL, P<0.05). Carriers of the ε4 allele had significantly higher fasting triglyceride concentrations only prefenofibrate (120.9 mg/dL versus 109.3 mg/dL, P=0.008). APOE alleles did not have an effect on response to fenofibrate. Postprandial triglycerides were significantly higher for ε2 carriers versus ε3 homozygotes (but not ε4 carriers) both before and after fenofibrate treatment (P=0.01 and P=0.005, respectively).

CONCLUSIONS

APOE polymorphisms are important determinants of triglyceride concentrations, especially in the fasting state.

A reexamination of the PPAR-alpha activation mode of action as a basis for assessing human cancer risks of environmental contaminants

BACKGROUND

Diverse environmental contaminants, including the plasticizer di(2-ethylhexyl)phthalate (DEHP), are hepatocarcinogenic peroxisome proliferators in rodents. Peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activation and its sequelae have been proposed to constitute a mode of action (MOA) for hepatocarcinogenesis by such agents as a sole causative factor. Further, based on a hypothesized lower sensitivity of humans to this MOA, prior reviews have concluded that rodent hepatocarcinogenesis by PPAR-alpha agonists is irrelevant to human carcinogenic risk.

DATA SYNTHESIS

Herein, we review recent studies that experimentally challenge the PPAR-alpha activation MOA hypothesis, providing evidence that DEHP is hepatocarcinogenic in PPAR-alpha-null mice and that the MOA but not hepatocarcinogenesis is evoked by PPAR-alpha activation in a transgenic mouse model. We further examine whether relative potency for PPAR-alpha activation or other steps in the MOA correlates with tumorigenic potency. In addition, for most PPAR-alpha agonists of environmental concern, available data are insufficient to characterize relative human sensitivity to this rodent MOA or to induction of hepatocarcinogenesis.

CONCLUSIONS

Our review and analyses raise questions about the hypothesized PPAR-alpha activation MOA as a sole explanation for rodent hepatocarcinogenesis by PPAR-alpha agonists and therefore its utility as a primary basis for assessing human carcinogenic risk from the diverse compounds that activate PPAR-alpha. These findings have broad implications for how MOA hypotheses are developed, tested, and applied in human health risk assessment. We discuss alternatives to the current approaches to these key aspects of mechanistic data evaluation.

Retinoid X receptor heterodimer variants and cardiovascular risk factors

Nuclear receptors are transcription factors that can be activated by specific ligands. Recent progress has shown that retinoid X receptor (RXR) and its heterodimerization partners, including peroxisome proliferator-activated receptors, regulate many important genes involved in energy homeostasis and atherosclerosis, and should be promising therapeutic targets of metabolic syndrome. RXR heterodimers regulate a number of complex cellular processes, and genetic studies of RXR heterodimers have provided important clinical information in addition to knowledge gained from basic research. Genetic variants of RXR heterodimers were screened and investigated, and some variants were shown to have a considerable impact on metabolic disorders, including phenotypic components of familial combined hyperlipidemia. The combined efforts of basic and clinical science regarding nuclear receptors have achieved significant progress in unraveling the inextricably linked control system of energy expenditure, lipid and glucose homeostasis, inflammation, and atherosclerosis.This review summarizes the current understanding regarding RXR heterodimers based on their human genetic variants, which will provide new clues to uncover the background of multifactorial disease, such as metabolic syndrome or familial combined hyperlipidemia.

Association between the FABP2 Ala54Thr, PPARα Leu162/Val, and PPARα intron7 polymorphisms and blood lipids ApoB and ApoCIII in hypertriglyceridemic subjects in Tehran

BACKGROUND

The alanine to threonine substitution at codon 54 in the FABP2 gene and PPARα Val162 allele have been associated with hypertriglyceridemia.

OBJECTIVE

We sought to determine the prevalence of the Ala54Thr polymorphism of fatty acid binding protein (FABP) 2 gene and the Leu162/Val in exon 5 and G/C in intron7 polymorphism of peroxisome proliferator-activated receptor alpha (PPARα) gene in hypertriglyceridemic patients and their associations with blood lipid concentrations.

METHODS

A total of 170 hypertriglyceridemic subjects were enrolled and genotyped for Ala54Thr, Leu162Val, and intron 7 polymorphism by the use of a polymerase chain reaction-restriction fragment length polymorphism method. Fasting blood triglyceride, total cholesterol (TC), low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apolipoprotein (Apo)B, and ApoCIII also were determined.

RESULTS

We found frequency of 81.2% for the Thr54 polymorphism among hypertriglyceridemic subjects. Positive associations were observed between this polymorphism and greater blood triglyceride, very low-density lipoprotein, and ApoCIII levels and lower blood high-density lipoprotein cholesterol concentration both in men and women. However, no association was found between the Thr54 polymorphism and TC, low-density lipoprotein cholesterol, ApoB, and body mass index. Frequency of the Leu162Val polymorphism was 21.8%. The Leu162Val polymorphism was not associated with lipid and lipoprotein concentrations in hypertriglyceridemic subjects (both in men and women). The frequency of intron7 polymorphism was 55.3% in subjects studied and, except for body mass index and TC, no association was found between the intron7 allele and blood lipids ApoB, and ApoCIII.

CONCLUSION

Frequency of the Thr54 polymorphism is high in hypertriglyceridemic subjects, and the presence of this allele may increase some blood lipid and lipoprotein concentrations. In addition, the frequency of intron7 polymorphism may be greater than Leu162Val in hypertriglyceridemic patients.

Common sequence variant in lipoprotein lipase gene conferring triglyceride response to fibrate treatment

Aims: Little is known about whether the variations in the lipoprotein lipase (LPL) and apolipoprotein gene cluster (APOA1/C3/A5) confer appreciable triglyceride lowering after fibrate treatment among patients with hypertriglyceridemia. Materials & methods: We investigated whether variations in these genes confer a triglyceride lowering response after fibrate treatment among 145 patients with hypertriglyceridemia receiving 6 months of fibrate treatment. Results: Overall triglycerides decreased from 746.2 mg/dl to 465.9 mg/dl and the mean percentage of triglyceride lowering was 50.7 ± 38.6%. A total of two polymorphisms, LPL IVS8 +483T>G and APOA1 +2169G>C, were associated with a significant percentage of triglyceride lowering. Common haplotype effects of LPL on the triglyceride lowering percentage were significant (p = 0.002) and the percentage of variance explained by the LPL haplotype was 7.5%. One common LPL haplotype encompassing three polymorphisms was associated with a -45.40% change (p < 0.001) and risk of a 5.9-fold risk for developing a poor response (95% confidence interval: 1.11–31, p = 0.037), compared with the most frequent LPL haplotype. Conclusion: Our results indicate that the LPL gene variant may cause triglyceride lowering after fibrate treatment among patients with hypertriglyceridemia.

Enhanced detection of genetic association of hypertensive heart disease by analysis of latent phenotypes

Hypertension and hypertensive heart disease (HHD) are inter-related phenotypes frequently observed with other comorbidities such as diabetes, obesity, and dyslipidemia, which probably reflect the complex gene-gene and/or gene-environment interactions resulting in HHD. The complexity of HHD led us to examine intermediate phenotypes (e.g., echocardiographically-derived measures) for simpler clues to the genetic underpinnings of the disease. We applied the method of independent component analysis to a prospective study of the metabolic predictors of left ventricular hypertrophy and extracted latent traits of HHD from panels of multi-dimensional anthropomorphic, hemodynamic echocardiographic and metabolic data. Based on the latent trait values, classification of subjects into different risk groups for HHD captured meaningful subtypes of the disease as reflected in the distributions of primary clinical indicators. Furthermore, we detected genetic associations of the latent HHD traits with single nucleotide polymorphisms in three candidate genes in the peroxisome proliferator-activated receptors complex, for which no significant association was found with the original clinical indicators of HHD. Consensus analysis of the results from repeated independent component analysis runs showed satisfactory robustness and estimated about 3-4 separate unseen sources for the observed HHD-related outcomes.

Common variation in the CETP gene and the implications for cardiovascular disease and its treatment: an updated analysis

Human plasma contains cholesteryl ester transfer protein (CETP) which, besides other functions, enables the transfer of cholesteryl esters in plasma from high-density lipoproteins (HDL) towards triglyceride-rich lipoproteins, thereby contributing to lower HDL cholesterol. Variations in the CETP gene, including the intronic TaqIB polymorphism (rs708272), are common in the population. Although HDL cholesterol is approximately 10% higher in TaqIB B2B2 than in B1B1 carriers, the association of this polymorphism with cardiovascular disease has not been unequivocally established. We present an updated pooled analysis concerning the association of cardiovascular disease with the TaqIB polymorphism, including only studies that predominantly comprise Caucasian subjects. The distribution of this CETP genotype was observed to be different in population-based studies (n = 10,526) compared with studies in populations selected by high cardiovascular risk (n = 10,947), with B2B2 carriers being less frequent among cases from high-risk populations compared with cases from population-based studies (p = 0.0009 for the difference in genotype distribution). In population-based studies, the odds ratio (OR) for cardiovascular disease was found to be 1.45 (95% CI: 1.07–1.95) in B2B2 compared with B1B1 carriers, contrasting the lower OR of 0.84 (95% CI: 0.74–0.96) in B2B2 versus B1B1 carriers from high-risk populations. Thus, it is possible that in the general population, the B2 allele is associated with higher cardiovascular risk, despite higher HDL cholesterol. Our analysis agrees with the contention that selection towards a lower frequency of B2B2 homozygotes may have occurred in selected populations, which would result in a apparently protective effect of the B2 allele when determined in high-risk populations. We also evaluated whether the TaqIB polymorphism would predict efficacy of lipid-lowering treatment with respect to plasma lipids and cardiovascular outcome, but the results of published studies were contradictory. Likewise, no definite conclusion can be made at present concerning the effect of this CETP polymorphism on the lipid response to diet intervention.

Single gene contributions: genetic variants of peroxisome proliferator-activated receptor (isoforms alpha, beta/delta and gamma) and mechanisms of dyslipidemias

PURPOSE OF REVIEW

Polymorphisms in peroxisome proliferator-activated receptor isoforms may be among the most important single-gene contributors to dyslipidemias, insulin resistance, and maturity-onset diabetes.

RECENT FINDINGS

Familial partial lipodystrophy is a rare but characteristic phenotype associated with carriers of peroxisome proliferator-activated receptor-gamma missense mutations. Mutant receptors are transcriptionally defective, exhibit aberrant affinity for co-regulator molecules, and can exert dominant-negative or haplo-insufficiency effects on normal peroxisome proliferator-activated receptor-gamma function. The P12A variant of isoform gamma is estimated to reduce diabetes risk by 19% in many populations, and has a large attributable risk because of high prevalence of the normal allele. Variants L162V and V227A of isoform alpha (common in white and Oriental populations, respectively) are associated with sexually dimorphic perturbations of lipid metabolism and cardiovascular risk. Polymorphisms in isoforms alpha and beta/delta are reported to influence lipid and glucose utilization. Apart from lipodystrophic syndromes, metabolic and cardiovascular risk in peroxisome proliferator-activated receptor variants is apparently modulated by dietary and exercise interventions, and interactions with polymorphisms in other genetic loci.

SUMMARY

Polymorphisms in peroxisome proliferator-activated receptors are critical susceptibility risk factors for dyslipidemias and diabetes. They provide attractive targets for gene-environment interventions to reduce the burden of metabolic disease.

Pharmacogenetics of the PPAR genes and cardiovascular disease

The goal of pharmacogenetics is to define the genetic determinants of individual drug responsiveness, and thereby provide personalized treatment to each individual. The peroxisome proliferator-activated receptors (PPARs) are polypeptide products of a set of related genes functioning to regulate several cellular processes that are central to cardiovascular health and disease. Given their pleiotropic roles in lipid and glucose homeostasis, cardiac energy balance and regulation of adipocyte release of circulating inflammatory factors, it is not surprising that PPARs represent an attractive target for clinical investigation and intervention in disease states, such as diabetes, obesity, atherosclerosis, cardiomyopathy, cardiac hypertrophy and heart failure. Research into the manipulation of PPAR function by pharmacologic agents has already resulted in important advances in the treatment of diabetes mellitus and cardiovascular disease. It follows that PPAR pharmacogenetics promises important advances in the personalized treatment of cardiovascular disease.

Peroxisome proliferator-activated receptors as molecular targets in relation to obesity and Type 2 diabetes

The three isotypes of peroxisome proliferator-activated receptors (PPARs) are currently perceived as major regulatory nodes (or hubs) of metabolic pathway networks, linking most prevalent diseases including Type 2 diabetes, obesity, dyslipidemia and atherosclerosis. The integrative functions of PPARs are also reflected in their ecogenetic profile, when the variants underlying pharmacogenetic interactions were also shown to modulate the effect of lifestyle factors. Despite their extensive clinical use, there are many outstanding issues, especially concerning their safety. Critical pharmacogenomic assessment is warranted for the new potent ligands of multiple PPAR isoforms as many have displayed serious side-effects in a limited number of treated subjects. Nevertheless, the advent of genomic, transcriptomic and system biology-level approaches, integrating knowledge from model systems and human biology, should greatly facilitate the transition to individualized PPAR-based therapies.

APOC3 promoter polymorphisms C-482T and T-455C are associated with the metabolic syndrome

BACKGROUND

Despite the growing epidemic of the metabolic syndrome (MetS), few studies have evaluated genetic polymorphisms associated with the MetS phenotype. One candidate, APOC3, modulates lipid and lipoprotein metabolism and the promoter polymorphisms C-482T/T-455C are associated with loss of insulin downregulation.

METHODS

One hundred twenty two consecutive MetS cases were matched by age, sex and race in a 1:1 case-control design to evaluate the prevalence of common polymorphisms in the following candidate genes: APOC3, APOE, B3AR, FABP2, GNB3, LPL, and PPARalpha and PPARgamma.

RESULTS

Compared to controls, MetS subjects exhibited a greater prevalence of APOC3 promoter polymorphisms. Specifically, the frequency of the variant C-482T and T-455C alleles was 70.5 and 81.9% of cases compared to 43.4 and 54.1% in controls, respectively (p <0.0001). Overall, APOC3 promoter variants were associated with a greater likelihood of MetS compared to wild type [C-482T (OR: 4.3; 95% CI: 2.2, 8.6 [p <0.0001]), T-455C (OR: 3.6; 95% CI: 2.0, 6.7 [p <0.0001])]. No material differences were identified between the other genetic variants tested and prevalence of MetS.

CONCLUSIONS

These data, therefore, suggest that the APOC3 promoter polymorphisms C-482T and T-455C are associated with the MetS.

The PPAR genes, cardiovascular disease and the emergence of PPAR pharmacogenetics

The peroxisome proliferator-activated receptors (PPARs) comprise a group of related transcription factors that serve to regulate a number of cellular processes that are central to cardiovascular health and disease. Two large bodies of work strongly implicate the PPARs as key factors in normal cardiovascular physiology and in cardiovascular pathophysiology: i) studies demonstrating associations between PPAR and abnormal cardiovascular phenotypes; and ii) pharmacological studies assessing the effects of specific PPAR agonists in clinical trials. With the abundance of data available from these studies as a background, PPAR pharmacogenetics has become a promising and rapidly-advancing field. This review summarises the current state of understanding of PPAR pharmacogenetics and its profound implications for the individualisation of therapy for patients with a diverse group of cardiovascular diseases.

PPARalpha gene variation and physical performance in Russian athletes

Peroxisome proliferator-activated receptor alpha (PPARalpha) regulates genes responsible for skeletal and heart muscle fatty acid oxidation. Previous studies have shown that the PPARalpha intron 7 G/C polymorphism was associated with left ventricular growth in response to exercise. We speculated that GG homozygotes should be more prevalent within a group of endurance-oriented athletes, have normal fatty acid metabolism, and increased percentages of slow-twitch fibers. We have tested this hypothesis in the study of a mixed cohort of 786 Russian athletes in 13 different sporting disciplines prospectively stratified by performance (endurance-oriented athletes, power-oriented athletes and athletes with mixed endurance/power activity). PPARalpha intron 7 genotype and allele frequencies were compared to 1,242 controls. We found an increasing linear trend of C allele with increasing anaerobic component of physical performance (P=0.029). GG genotype frequencies in endurance-oriented and power-oriented athletes were 80.3 and 50.6%, respectively, and were significantly (P<0.0001) different compared to controls (70.0%). To examine the association between PPARalpha gene variant and fiber type composition, muscle biopsies from m. vastus lateralis were obtained and analyzed in 40 young men. GG homozygotes (n=25) had significantly (P=0.003) higher percentages of slow-twitch fibers (55.5+/-2.0 vs 38.5+/-2.3%) than CC homozygotes (n=4). In conclusion, PPARalpha intron 7 G/C polymorphism was associated with physical performance in Russian athletes, and this may be explained, in part, by the association between PPARalpha genotype and muscle fiber type composition.

Association of common variation in the PPARA gene with incident myocardial infarction in individuals with type 2 diabetes: a Go-DARTS study

BACKGROUND

Common variants of the PPARA gene have been found to associate with ischaemic heart disease in non diabetic men. The L162V variant was found to be protective while the C2528G variant increased risk. L162V has also been associated with altered lipid measures. We therefore sought to determine the effect of PPARA gene variation on susceptibility to myocardial infarction in patients with type 2 diabetes. 1810 subjects with type 2 diabetes from the prospective Go-DARTS study were genotyped for the L162V and C2528G variants in the PPARA gene and the association of the variants with incident non-fatal myocardial infarction was examined. Cox's proportional hazards was used to interrogate time to event from recruitment, and linear regression for analysing association of genotype with quantitative clinical traits.

RESULTS

The V162 allele was associated with decreased risk of non-fatal myocardial infarction (HR = 0.31, 95%CI 0.10-0.93 p = 0.037) whereas the C2528 allele was associated with increased risk (HR = 2.77 95%CI 1.34-5.75 p = 0.006). Similarly V162 was associated with a later mean age of diagnosis with type 2 diabetes and C2582 an earlier age of diagnosis. C2528 was also associated with increased total cholesterol and LDL cholesterol, which did not account for the observed increased risk. Haplotype analysis demonstrated that when both rare variants occurred on the same haplotype the effect of each was abrogated.

CONCLUSION

Genetic variation at the PPARA locus is important in determining cardiovascular risk in both male and female patients with diabetes. This genotype associated risk appears to be independent of the effect of these genotypes on lipid profiles and age of diagnosis with diabetes.

Peroxisome proliferator-activated receptor alpha gene variation influences age of onset and progression of type 2 diabetes

Dysregulation of fatty acid metabolism is important in the pathogenesis of type 2 diabetes. Peroxisome proliferator-activated receptor (PPAR)alpha is a master regulator of fatty acid catabolism, and PPARalpha activators delay the onset of type 2 diabetes. We examined association between three PPARalpha gene polymorphisms (an A-->C variant in intron 1, the L162V variant, and the intron 7 G-->C variant) and age at diagnosis of type 2 diabetes in 912 Caucasian type 2 diabetic subjects. Individually, PPARalpha gene variants did not influence age at diagnosis, but in combination, the rare alleles of both the intron 1 A-->C (P < 0.001) and intron 7 G-->C (P = 0.025) variants synergistically lowered age at diagnosis (interaction P < 0.001). Overall, the PPARalpha haplotype signficantly influenced age at diagnosis (P = 0.027), with the C-L-C and C-V-C haplotypes (intron 1-L162V-intron 7) accelerating onset of diabetes by 5.9 (P = 0.02) and 10 (P = 0.03) years, respectively, as compared with the common A-L-G haplotype, and was associated with an odds ratio for early-onset diabetes (age at diagnosis </=45 years) of 3.75 (95% CI 1.65-8.56, P = 0.002). Intron 1 C-allele carriers also progressed more rapidly to insulin monotherapy (AA 9.4 +/- 1.5 and AC + CC 5.3 +/- 1.1 years, P = 0.002). These data indicate that PPARalpha gene variation influences the onset and progression of type 2 diabetes.