J. Madden

The Impact of Common Gene Variants on the Response of Biomarkers of Cardiovascular Disease (CVD) Risk to Increased Fish Oil Fatty Acids Intakes

The cardioprotective actions of the fish oil (FO)-derived long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated, and dose-response relationships have been defined. However, there is a substantial and well-recognized within-population heterogeneity in response to FO, the etiology of which is poorly understood. Genetic variation may influence responsiveness. Here we review the available literature relating to gene variants shown to influence tissue LC n-3 PUFA status and response to FO intervention. From this review we conclude that the available evidence is relatively limited. A number of individual genotype × LC-n3 PUFA × phenotype associations have been described, but few have been investigated in subsequent cohorts or confirmed in independent studies. In the context of a more stratified approach to the provision of dietary advice, there is a need for further research to refine current dietary EPA and DHA recommendations.

Polymorphisms in the CD36 gene modulate the ability of fish oil supplements to lower fasting plasma triacyl glycerol and raise HDL cholesterol concentrations in healthy middle-aged men

Five SNPs in the CD36 gene, 25444G>A, 27645del>ins, 30294G>C, -31118G>A and -33137A>G in haplotypic combinations, link to fasting plasma NEFA concentrations. Fish oil lowers TAG concentrations. The influence of CD36 SNPs on hypotriglyceridemic effects is unknown. The study examines how four of the SNPs modify the effects of fish oil on fasting plasma TAG, NEFA, glucose LDL and HDL cholesterol concentrations in 111 healthy, middle-aged, Caucasian men. Subjects consumed habitual diets while taking 6g MaxEPA daily for 12 weeks. TAG decreased from 1.48 mol/l to 0.11 mmol/l, and glucose and HDL rose from 5.92 to 0.15 mmol/l and from 1.27 to 0.04 mmol/l, respectively, irrespective of genotype. NEFA was unaffected. Significant falls in TAG only occurred in individuals with the GG variant of the 25444, 30294, -31118 or -33137 SNPs. The TAG-lowering effects may be via stimulation of CD36 activity in extrahepatic tissue in individuals with the GG variants of these SNPs.

Consumption of Fish Oil Providing Amounts of Eicosapentaenoic Acid and Docosahexaenoic Acid That Can Be Obtained from the Diet Reduces Blood Pressure in Adults with Systolic Hypertension: A Retrospective Analysis

BACKGROUND Although many randomized controlled trials (RCTs) have examined the effects of the n-3 (ω-3) fatty acids eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) on blood pressure (BP) and vascular function, the majority have used doses of EPA+DHA of >3 g/d, which are unlikely to be achieved by dietary manipulation. OBJECTIVE The objective was to examine, by using a retrospective analysis from a multicenter RCT, the impact of recommended EPA+DHA intakes achievable through diet on systolic and diastolic BPs and microvascular function in adults in the United Kingdom. METHODS In a double-blind, placebo-controlled RCT, healthy men and women (n = 312) consumed a control oil or fish oil (FO) providing 0.7 or 1.8 g EPA+DHA/d, in random order, each for 8 wk. Fasting BP and microvascular function (using laser Doppler iontophoresis) were assessed and plasma collected for the quantification of markers of vascular function. Participants were retrospectively genotyped for the endothelial nitric oxide synthase (eNOS) rs1799983 variant. RESULTS No effects of n-3 fatty acid treatment or any treatment × eNOS genotype interactions were evident in the group as a whole for any of the clinical or biochemical outcomes. Assessment of response according to hypertension status at baseline indicated a significant (P = 0.046) FO-induced reduction (mean: 5 mm Hg) in systolic BP, specifically in those with isolated systolic hypertension (n = 31). No dose response was observed. CONCLUSIONS These findings indicate that in adults with isolated systolic hypertension, daily doses of EPA+DHA as low as 0.7 g show clinically meaningful BP reductions, which, at a population level, could be associated with lower cardiovascular disease risk. Confirmation of findings in an RCT in which participants are prospectively recruited on the basis of BP status is required to draw definite conclusions.

Plasma hyaluronic acid is increased in peripheral arterial disease and altered by fish oil supplementation

Hyaluroinic acid (HA) is an intra-cellular matrix polymer whose main functions are structural and the maintenance of tissue hydration. The catabolism of the HA polymer to smaller subunits is initiated in membrane lipid rafts and is dependent on CD44. These smaller subunits are released into circulation and are thought to be proinflammatory as plasma levels increase in acute inflammatory conditions such as septicaemia. Plasma HA levels are also a strong indicator of severe liver fibrosis as fibrotic cytokines such as TGF and FGF enhance HA catabolism. We hypothesised that circulating HA levels would be increased in peripheral arterial disease (PAD) as this disease it is known to have both fibrotic and inflammatory components. Furthermore, as fish oil supplementation has been shown to reduce inflammation and monocyte CD44 expression, we investigated the effect of supplementation of 1.7 g EPA+DHA per day for 12 weeks on plasma HA levels in 72 PAD patients. In 83 healthy controls, we found plasma HA levels to be low (mean 1.54 ng/ml 1.35), whereas in 72 PAD patients plasma HA levels were much higher (mean 19.75 ng/ml 3.76) (P<0.001). Following fish oil supplementation in the PAD group plasma HA levels increased (mean 27.03 ng/ml 5.64) (P = 0.02). One possible mechanism for these findings is that fish oil has previously been shown to increase expression of a splice variant form of CD44, CD44v3, on PAD monocytes. CD44v3 can bind fibrotic cytokines such as TGF and FGF, and may increase their potency leading to increased fibrosis and stabilisation of atherosclerotic plaques. Another explanation is that increased circulating HA levels are often seen in high-volume blood loss and thought to act as a intravascular volume expander, so preventing circulatory collapse. In vascular compromised individuals, increased levels of HA may enhance circulatory competence which we have previously demonstrated for fish oil supplementation in PAD.

Influence of CD36 gene polymorphisms on the response of cardiovascular risk factors to fish oil supplementation in middle aged men

In healthy individuals, glucose and fatty acids are substrates for ATP generation in the heart. There is emerging evidence from patients with type 2 diabetes mellitus that preferential use of fatty acid b-oxidation for energy production may be linked to cardiomyopathy (Fink, 2004). PPARa activity is important for regulating fatty acid b-oxidation in the heart and is increased in hearts of rats with experimentally induced diabetes (Fink, 2004). Prenatal undernutrition is related inversely to risk of type 2 diabetes mellitus in man (Poole & Byrne, 2005) and insulin resistance in rats (Bertram & Hanson, 2001). We have shown that maternal dietary protein restriction induces persistent alterations to hepatic and carbohydrate metabolism in the offspring by altering the epigenetic regulation of PPARa and the glucocorticoid receptor (GR) (Lillycrop et al. 2005). Here we have tested the hypothesis that prenatal protein restriction induces hypomethylation of the GR and PPARa promoters in the heart, and that this is prevented by supplementation of the protein-restricted (PR) diet with folic acid.Induction of a modified metabolic phenotype in the offspring by feeding a protein-restricted (PR) diet during pregnancy in the rat involves DNA hypomethylation and altered covalent histone modifications leading to increased expression of specific genes (Lillycrop et al. 2005a,b). Hypomethylation of gene promoters may be achieved by impaired DNA methylation de novo, loss of CpG methylation during mitosis, or active demethylation. Histone modifications which modulate transcription involve binding of methyl CpG binding protein (MeCP)-2 to methylated DNA and recruitment of histone-modifying enzymes (Bird, 2002). We investigated in the offspring the effect of feeding a PR diet during pregnancy on the expression of hepatic DNA methyltransferase (DMNT) 1 which maintains CpG methylation, DNMT 3a and 3b which catalyse DNA methylation de novo and the DNA demethylase MBD2.

Polymorphisms at IL-6-174 and TNF-a-308 and body mass index modulate the effects of fish oil supplementation on cytokine production by monocytes from healthy middle aged men

In healthy individuals, glucose and fatty acids are substrates for ATP generation in the heart. There is emerging evidence from patients with type 2 diabetes mellitus that preferential use of fatty acid b-oxidation for energy production may be linked to cardiomyopathy (Fink, 2004). PPARa activity is important for regulating fatty acid b-oxidation in the heart and is increased in hearts of rats with experimentally induced diabetes (Fink, 2004). Prenatal undernutrition is related inversely to risk of type 2 diabetes mellitus in man (Poole & Byrne, 2005) and insulin resistance in rats (Bertram & Hanson, 2001). We have shown that maternal dietary protein restriction induces persistent alterations to hepatic and carbohydrate metabolism in the offspring by altering the epigenetic regulation of PPARa and the glucocorticoid receptor (GR) (Lillycrop et al. 2005). Here we have tested the hypothesis that prenatal protein restriction induces hypomethylation of the GR and PPARa promoters in the heart, and that this is prevented by supplementation of the protein-restricted (PR) diet with folic acid.Induction of a modified metabolic phenotype in the offspring by feeding a protein-restricted (PR) diet during pregnancy in the rat involves DNA hypomethylation and altered covalent histone modifications leading to increased expression of specific genes (Lillycrop et al. 2005a,b). Hypomethylation of gene promoters may be achieved by impaired DNA methylation de novo, loss of CpG methylation during mitosis, or active demethylation. Histone modifications which modulate transcription involve binding of methyl CpG binding protein (MeCP)-2 to methylated DNA and recruitment of histone-modifying enzymes (Bird, 2002). We investigated in the offspring the effect of feeding a PR diet during pregnancy on the expression of hepatic DNA methyltransferase (DMNT) 1 which maintains CpG methylation, DNMT 3a and 3b which catalyse DNA methylation de novo and the DNA demethylase MBD2.