👤 Harvey J Murff

Polyunsaturated fatty acids (PUFAs) including omega-3 and omega-6 are obtained from diet and can be measured objectively in plasma or red blood cells (RBCs) membrane biomarkers, representing different dietary exposure windows. In vivo conversion of omega-3 and omega-6 PUFAs from short- to long-chain counterparts occurs via a shared metabolic pathway involving fatty acid desaturases and elongase. This analysis leveraged genome-wide association study (GWAS) summary statistics for RBC and plasma PUFAs, along with expression quantitative trait loci (eQTL) to estimate tissue-specific genetically predicted gene expression effects for delta-5 desaturase (FADS1), delta-6 desaturase (FADS2), and elongase (ELOVL2) on changes in RBC and plasma biomarkers. Using colocalization, we identified shared variants associated with both increased gene expression and changes in RBC PUFA levels in relevant PUFA metabolism tissues (i.e., adipose, liver, muscle, and whole blood). We observed differences in RBC versus plasma PUFA levels for genetically predicted increase in FADS1 and FADS2 gene expression, primarily for omega-6 PUFAs linoleic acid (LA) and arachidonic acid (AA). The colocalization analysis identified rs102275 to be significantly associated with a 0.69% increase in total RBC membrane-bound LA levels (p = 5.4 × 10 Show less

Polyunsaturated fatty acids (PUFAs) including omega-3 and omega-6 are obtained from diet and can be measured objectively in plasma or red blood cells (RBCs) membrane biomarkers, representing different dietary exposure windows. Show less

n-3 long-chain polyunsaturated fatty acids (LCPUFA) have anti-inflammatory effects and may reduce colorectal cancer risk. The purpose of this study was to evaluate the effects of n-3 LCPUFA supplementation on markers of rectal cell proliferation and apoptosis and examine how genetic variation in desaturase enzymes might modify this effect. We conducted a randomized, double-blind, control six-month trial of 2.5 grams of n-3 LCPUFA per day compared to olive oil. Study participants had a history of colorectal adenomas. Randomization was stratified based on the gene variant rs174535 in the fatty acid desaturase 1 enzyme ( A total of 141 subjects were randomized. We found no difference in apoptosis markers between participants randomized to n-3 LCPUFA compared to olive oil ( Our study did not show evidence of a proliferative or pro-apoptotic effect on n-3 LCPUFA supplementation on rectal mucosa regardless of the Show less

Numerous studies have reported an association between genetic variants in fatty acid desaturases (FADS1 and FADS2) and plasma or erythrocyte long chain polyunsaturated fatty acid (PUFA) levels. Increased levels of n-6 PUFAs have been associated with inflammation and several chronic diseases, including diabetes and cancer. We hypothesized that genetic variants of FADS that more efficiently convert precursor n-6 PUFA to arachidonic acid (AA) may explain the higher burden of chronic diseases observed in African Americans. To test this hypothesis, we measured the level of n-6 and n-3 PUFAs in erythrocyte membrane phospholipids and genotyped the rs174537 FADS variants associated with higher AA conversion among African American and European American populations. We included data from 1,733 individuals who participated in the Tennessee Colorectal Polyp Study, a large colonoscopy-based case-control study. Erythrocyte membrane PUFA percentages were measured using gas chromatography. Generalized linear models were used to estimate association of race and genotype on erythrocyte phospholipid membrane PUFA levels while controlling for self-reported dietary intake. We found that African Americans have higher levels of AA and a higher prevalence of GG allele compared to whites, 81% vs 43%, respectively. Homozygous GG genotype was negatively associated with precursor PUFAs (linoleic [LA], di-homo-γ-linolenic [DGLA]), positively associated with both product PUFA (AA, docosahexaenoic acid [DHA]), product to precursor ratio (AA to DGLA), an indirect measure of FADs efficiency and increased urinary isoprostane F2 (F2-IsoP) and isoprostane F3 (F3-IsoP), markers of oxidative stress. Increased consumption of n-6 PUFA and LA resulting in increased AA and subsequent inflammation may be fueling increased prevalence of chronic diseases especially in African descent. Show less

Fish oil supplementation may represent a potential chemopreventive agent for reducing colorectal cancer risk. The mechanism of action of fish oil is unknown but presumed to be related to eicosanoid modification. The purpose of this study was to evaluate the effects of fish oil supplementation on the levels of urinary and rectal eicosanoids. We conducted a randomized, double-blind, controlled trial of 2.5 g of fish oil per day compared with olive oil supplementation over a 6-month period. Study participants had a history of colorectal adenomas. Randomization was stratified based on the gene variant rs174535 in the fatty acid desaturase 1 enzyme (FADS1), which affects tissue levels of arachidonic acid. A total of 141 participants were randomized. Urinary prostaglandin E2 metabolite (PGE-M) was measured at baseline, 3, and 6 months and rectal prostaglandin E2 (PGE2) at baseline and 6 months. Repeated-measures linear regression was used to determine the effect of the intervention on each outcome measure. Overall, fish oil supplementation was found to reduce urinary PGE-M production compared with olive oil (P=0.03). Fish oil did not reduce rectal PGE2 overall; however, it did significantly reduce PGE2 in the subgroup of participants not using aspirin or NSAIDs (P=0.04). FADS1 genotype did not seem to modify effects of fish oil on PGE2 production. We conclude that fish oil supplementation has a modest but beneficial effect on eicosanoids associated with colorectal carcinogenesis, particularly in those not taking aspirin or NSAIDs. Show less