Mammary tumour development is dose-dependently inhibited by n-3 polyunsaturated fatty acids in the MMTV-neu(ndl)-YD5 transgenic mouse model.

BACKGROUND: Breast cancer is attributable to modifiable risk factors including the intake of dietary n-3 polyunsaturated fatty acids (PUFA). A key piece of evidence, yet to be addressed, that would demonstrate a causal relationship between n-3 PUFA and breast cancer, is a dose-dependent effect of n-3 PUFA on tumour outcomes. Thus, the objective of the present study was to determine whether n-3 PUFA reduces mammary gland tumor outcomes in a dose-dependent manner in female MMTV-neu(ndl)-YD5 transgenic mice, an aggressive model of human breast cancer. METHODS: Harems were provided one of three experimental diets comprised of 0, 3 or 9% (w/w) menhaden fish oil containing n-3 PUFA. Female offspring were weaned onto the same parental diet and maintained on their respective diet for 20 weeks. Tumour onset, size and multiplicity were measured throughout the study. Fatty acid composition of mammary gland and tumours were determined by gas-liquid chromatography. RESULTS: Tumour size was significantly (p < 0.05) reduced in a dose-dependent manner. n-3 PUFA were also incorporated in a dose-dependent manner; differential incorporation was observed for eicosapentaenoic and docosapentaenoic acids into mammary gland tissue, while docosahexaenoic acid was preferentially incorporated into tumours. CONCLUSION: Overall, the present study provides fundamental knowledge about the dose-dependent effect of n-3 PUFA on tumour outcomes in a pre-clinical model and also sheds light on the differential role of individual n-3 PUFA on tumour outcomes.

Dietary and plasma retinoids are not associated with fatty acid desaturase indices in healthy young adults.

Past research in rodents suggests that fatty acid (FA) desaturase expression and activity may be modified by vitamin A; however, this has not been investigated in humans. The primary objective of this study was to examine associations between dietary retinoid intakes, plasma retinoid concentrations, and FA desaturase indices in young adults. As a secondary objective, biological sex and estrogen-containing contraceptive (EC) use were investigated due to prior evidence demonstrating that both can influence plasma retinol concentration and FA desaturase indices. Dietary retinoid intake (food frequency questionnaire), plasma retinoid concentrations (high-performance liquid chromatography-tandem mass spectrometry), plasma FA (gas chromatography), and FA desaturase indices (product-to-precursor ratios) from 945 adults recruited for the cross-sectional Toronto Nutrigenomics and Health study were analyzed. Participants were stratified into quartiles based on plasma retinol concentration and data analyzed by one-way analysis of covariance. Dietary retinoid intakes were not associated with the overall n-3 pathway, overall n-6 pathway, delta-5 desaturase, delta-6 desaturase, or delta-9 desaturase indices (all r < 0.10, p > 0.05). The overall n-6 pathway index was significantly higher (p = 0.0004) and the delta-5 desaturase index was significantly lower (p = 0.0003) in individuals with higher plasma retinol levels; however, these differences were lost when participants were grouped by biological sex and EC use. Although weak relationships were observed between plasma retinol and some FA desaturase indices in the total population, these associations appear to be driven by biological sex and EC usage rather than retinoids. We therefore find little evidence of a relationship between retinoids and FA desaturase indices in young, healthy adults.

CAT-1-mediated arginine uptake and regulation of nitric oxide synthases for the survival of human breast cancer cell lines.

Growth of the human MCF-7 breast cancer cell line is highly dependent on L-arginine. We have reported that L-arginine, released from extracellular substrates by prolactin (PRL)- and 17ß-estradiol (E2)-induced carboxypeptidase-D in the cell membrane, promotes nitric oxide (NO) production for MCF-7 cell survival. Arginine uptake is mediated by members of the cationic amino acid transporter (CAT) family and may coincide with induction of nitric oxide synthase (NOS) for the production of NO. The present study investigated the CAT isoforms and PRL/E2 regulation of CAT and NOS in breast cancer cell lines. Using RT-PCR analysis, CAT-1, CAT-2A, and CAT-2B transcripts were detected in MCF-7, T47D, and MDA-MB-231 cells. The CAT-4 transcript was detected in MDA-MB-231 only. CAT-3 was not detected in any of these cells. PRL and E2 did not significantly alter levels of CAT-1 mRNA and protein, nor CAT-2A and CAT-2B mRNAs in MCF-7 and T47D cells. PRL and E2 also had no effect on the overall uptake of L-[2,3,4,5-H(3)] arginine into these cells. However, confocal immunofluorescent microscopy showed that PRL and E2 upregulated eNOS and iNOS proteins, which distributed in the cytoplasm and/or nucleus of MCF-7 cells. Knockdown of CAT-1 gene expression using small interfering RNA significantly decreased L-[2,3,4,5-H(3)]-arginine uptake, decreased viability and increased apoptosis of MCF-7 and T47D cells. In summary, several CAT isoforms are expressed in breast cancer cells. The CAT-1 isoform plays a role in arginine uptake and, together with PRL/E2-induced NOS, contribute to NO production for the survival of MCF-7 and T47D cells.

Soy Consumption, but Not Dairy Consumption, Is Inversely Associated with Fatty Acid Desaturase Activity in Young Adults.

Past research using hepatic rat microsomes showed that soy protein suppressed delta-6 desaturase activity (D6D) compared to casein (a dairy protein). The effects of soy and dairy on desaturase pathway activity in humans remain poorly investigated. The objective of this analysis was to investigate the association between soy and dairy consumption with plasma fatty acids and estimate the desaturase pathway activity in a multiethnic Canadian population of young adults. We analyzed data from men (n = 319) and women (n = 764) previously collected for the Toronto Nutrigenomics and Health Study. Food frequency questionnaires and plasma fatty acids were assessed. Relationships between soy and dairy beverages and food consumption with estimated desaturase activities were assessed by regression models and by grouping participants according to beverage and food intake data. Weak inverse associations (p ≤ 0.05) were found between soy consumption and the overall desaturation pathway activity, specifically D6D activity. When participants were grouped based on soy and dairy consumption habits, omega-6 LC-PUFAs, as well as various estimates of the desaturase pathway activity, were significantly lower in individuals consuming soy (with or without dairy) compared to individuals consuming only fluid milk and dairy products. In conclusion, soy consumption, not dairy consumption, appears to suppress desaturase pathway activity.

The Association between Plasma Omega-6/Omega-3 Ratio and Anthropometric Traits Differs by Racial/Ethnic Groups and NFKB1 Genotypes in Healthy Young Adults.

Evidence for a relationship between omega-6/omega-3 (n-6/n-3) polyunsaturated fatty acid (PUFA) ratio and obesity in humans is inconsistent, perhaps due to differences in dietary intake or metabolism of PUFAs between different subsets of the population. Since chronic inflammation is central to obesity and inflammatory pathways are regulated by PUFAs, the objective of this study was to examine whether variants in the NFKB1 gene, an upstream regulator of the inflammatory response, modify the association between the n-6/n-3 ratio (from diet and plasma) and anthropometric traits in a multiethnic/multiracial population of young adults. Participants' (n = 898) dietary PUFA intake was assessed using a food frequency questionnaire and plasma PUFA concentrations by gas chromatography. Nine tag single nucleotide polymorphisms (SNP) in NFKB1 were genotyped. Significant interactions were found between racial/ethnic groups and plasma n-6/n-3 ratio for body mass index (BMI) (p = 0.02) and waist circumference (WC) (p = 0.007). Significant interactions were also observed between racial/ethnic groups and three NFKB1 genotypes (rs11722146, rs1609798, and rs230511) for BMI and WC (all p ≤ 0.04). Significant interactions were found between two NFKB1 genotypes and plasma n-6/n-3 ratio for BMI and WC (rs4648090 p = 0.02 and 0.03; rs4648022 p = 0.06 and 0.04, respectively). Our findings suggest that anthropometric traits may be influenced by a unique combination of n-6/n-3 ratio, racial/ethnic background, and NFKB1 genotypes.

Prolactin and estrogen up-regulate carboxypeptidase-d to promote nitric oxide production and survival of mcf-7 breast cancer cells.

Carboxypeptidase-D (CPD) and carboxypeptidase-M (CPM) release C-terminal arginine (Arg) from polypeptides, and both are present in the plasma membrane. Cell-surface CPD increases intracellular Arg, which is converted to nitric oxide (NO). We have reported that prolactin (PRL) regulated CPD mRNA levels in MCF-7 breast cancer cells. This study examined PRL/17beta-estradiol (E2) regulation of CPD/CPM expression, and the role of CPD in NO production for survival of MCF-7 cells. We showed that PRL or E2 up-regulated CPD mRNA and protein expression. PRL/E2 increased CPD mRNA levels by 3- to 5-fold but had no effect on CPM. In Arg-free DMEM, exogenous L-Arg or substrate furylacryloyl-Ala-Arg (Fa-Ala-Arg) increased NO levels and cell survival, measured using 4,5-diaminofluorescein diacetate and the MTS assay, respectively. In the presence of Fa-Ala-Arg, NO production was enhanced by PRL and/or E2 but inhibited by CPD/CPM-specific inhibitor, 2-mercaptomethyl-3-guanidinoethylthio-propanoic acid (MGTA). MGTA also decreased MCF-7 cell survival. In Arg-free medium, annexin-V staining showed that apoptotic MCF-7 cells (approximately 60%) were rescued by Fa-Ala-Arg (25%) or diethylamine/NO (10%). Finally, CPD or CPM gene expression was knocked down with small interfering (si) CPD or siCPM, respectively, with nontargeting siNT as controls. In Arg-free DMEM, the stimulatory effect of Fa-Ala-Arg on NO production was inhibited by siCPD only, showing that CPD depletion inhibited Fa-Ala-Arg cleavage. Furthermore, more than 60% of siCPD-transfectants were apoptotic, and L-Arg, not Fa-Ala-Arg, significantly decreased apoptosis to 32% (P

Marine fish oil is more potent than plant-based n-3 polyunsaturated fatty acids in the prevention of mammary tumors.

Marine-derived n-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been shown to inhibit mammary carcinogenesis. However, evidence regarding plant-based α-linolenic acid (ALA), the major n-3 PUFA in the Western diet, remains equivocal. The objective of this study was to examine the effect of lifelong exposure to plant- or marine-derived n-3 PUFAs on pubertal mammary gland and tumor development in MMTV-neu(ndl)-YD5 mice. It is hypothesized that lifelong exposure to n-3 PUFA reduces terminal end buds during puberty leading to delayed tumor onset, volume and multiplicity. It is further hypothesized that plant-derived n-3 PUFAs will exert dose-dependent effects. Harems of MMTV-FVB males were bred with wild-type females and fed either a (1) 10% safflower (10% SF, n-6 PUFA, control), (2) 10% flaxseed (10% FS), (3) 7% safflower plus 3% flaxseed (3% FS) or (4) 7% safflower plus 3% menhaden (3% FO) diet. Female offspring were maintained on parental diets. Compared to SF, 10% FS and 3% FO reduced (P<.05) terminal end buds at 6 weeks and tumor volume and multiplicity at 20 weeks. A dose-dependent reduction of tumor volume and multiplicity was observed in mice fed 3% and 10% FS. Antitumorigenic effects were associated with altered HER2, pHER-2, pAkt and Ki-67 protein expression. Compared to 10% SF, 3% FO significantly down-regulated expression of genes involved in eicosanoid synthesis and inflammation. From this, it can be estimated that ALA was 1/8 as potent as EPA+DHA. Thus, marine-derived n-3 PUFAs have greater potency versus plant-based n-3 PUFAs.

Circulating concentrations and relative percent composition of trans fatty acids in healthy Canadian young adults between 2004 and 2010: a cross-sectional study.

BACKGROUND: Trans fatty acids (TFAs) produced from industrial partial hydrogenation of vegetable oils have been the subject of much research regarding their negative effect on the development of chronic diseases, and recommendations to label foods with partially hydrogenated vegetable oils and limit their levels were introduced in Canada in 2003 and 2007, respectively. Our aim was to determine temporal changes in circulating plasma TFAs in a population of young healthy Canadian adults after the introduction of the guidelines. METHODS: In this study, circulating plasma concentrations and relative percent composition of individual TFAs over time (2004-2010) were determined in a cross-sectional cohort of young healthy Canadian adults as part of the Toronto Nutrigenomics study. RESULTS: A total of 1294 participants were included in the cohort. Relative to 2004, total TFA levels were significantly lower in 2005-2009 (p < 0.05), but not in 2010. Although levels of 16:1t9 and 18:1t11 declined after 2004, levels of 18:1t9 and 18:1t10 were significantly lower in 2005-2009 (p < 0.05), but not in 2010. INTERPRETATION: Trans fatty acids were lower in 2009 relative to 2004, but not different in 2010, suggesting that young Canadians may remain vulnerable to partially hydrogenated vegetable oil exposure and that there is a need for further monitoring of specific food categories and vulnerable populations.

Characterization of a novel, cytokine-inducible carboxypeptidase D isoform in haematopoietic tumour cells.

CPD-N is a cytokine-inducible CPD (carboxypeptidase-D) isoform identified in rat Nb2 T-lymphoma cells. The prototypic CPD (180 kDa) has three CP domains, whereas CPD-N (160 kDa) has an incomplete N-terminal domain I but intact domains II and III. CPD processes polypeptides in the TGN (trans-Golgi network) but the Nb2 CPD-N is nuclear. The present study identified a cryptic exon 1', downstream of exon 1 of the rat CPD gene, as an alternative transcription start site that encodes the N-terminus of CPD-N. Western-blot analysis showed exclusive synthesis of the 160 kDa CPD-N in rat Nb2 and Nb2-Sp lymphoma cells. Several haematopoietic cell lines including human K562 myeloma, Jurkat T-lymphoma and murine CTLL-2 cytotoxic T-cells express a 160 kDa CPD-immunoreactive protein, whereas mEL4 T-lymphoma cells express the 180 kDa CPD. The CPD-immunoreactive protein in hK562 cells is also nuclear and cytokine-inducible. In contrast, MCF-7 breast cancer cells express only the 180 kDa CPD, which is mainly in the TGN. CPD/CPD-N assays using substrate dansyl-L-alanyl-L-arginine show approx. 98% of CPD-N activity in the Nb2 nucleus, whereas MCF-7 CPD activity is enriched in the post-nuclear 10000 g pellet. The K(m) for CPD-N and CPD are 132+/-30 and 63+/-9 microM respectively. Specific activity/K(m) ratios show that dansyl-L-alanyl-L-arginine is a better substrate for CPD-N than for CPD. CPD-N has an optimal pH of 5.6 (due to domain II), whereas CPD has activity peaks at pH 5.6 (domain II) and pH 6.5-7.0 (domain I). CPD and CPD-N are inhibited non-competitively by zinc chelator 1,10-phenanthroline and competitively by peptidomimetic inhibitor DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid. The Nb2 CPD-N co-immunoprecipitated with phosphatase PP2A (protein phosphatase 2A) and alpha4 phosphoprotein. In summary, a cytokine-inducible CPD-N is selectively expressed in several haematopoietic tumour cells. Nuclear CPD-N is enzymatically active and interacts with known partners of CPD.

Role of n-3 Polyunsaturated Fatty Acids and Exercise in Breast Cancer Prevention: Identifying Common Targets.

Diet and exercise are recognized as important lifestyle factors that significantly influence breast cancer risk. In particular, dietary n-3 polyunsaturated fatty acids (PUFAs) have been shown to play an important role in breast cancer prevention. Growing evidence also demonstrates a role for exercise in cancer and chronic disease prevention. However, the potential synergistic effect of n-3 PUFA intake and exercise is yet to be determined. This review explores targets for breast cancer prevention that are common between n-3 PUFA intake and exercise and that may be important study outcomes for future research investigating the combined effect of n-3 PUFA intake and exercise. These lines of evidence highlight potential new avenues for research and strategies for breast cancer prevention.

The delta 6 desaturase knock out mouse reveals that immunomodulatory effects of essential n-6 and n-3 polyunsaturated fatty acids are both independent of and dependent upon conversion.

Typically fatty acids (FA) exert differential immunomodulatory effects with n-3 [α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] and n-6 [linoleic acid (LA) and arachidonic acid (AA)] exerting anti- and pro-inflammatory effects, respectively. This over-simplified interpretation is confounded by a failure to account for conversion of the parent FA (LA and ALA) to longer-chain bioactive products (AA and EPA/DHA, respectively), thereby precluding discernment of the immunomodulatory potential of specific FA. Therefore, we utilized the Δ6-desaturase model, wherein knockout mice (D6KO) lack the Fads2 gene encoding for the rate-limiting enzyme that initiates FA metabolism, thereby providing a model to determine specific FA immunomodulatory effects. Wild-type (WT) and D6KO mice were fed one of four isocaloric diets differing in FA source (9weeks): corn oil (LA-enriched), arachidonic acid single cell oil (AA-enriched), flaxseed oil (ALA-enriched) or menhaden fish oil (EPA/DHA-enriched). Splenic mononuclear cell cytokine production in response to lipopolysaccharide (LPS), T-cell receptor (TCR) and anti-CD40 stimulation was determined. Following LPS stimulation, AA was more bioactive compared to LA, by increasing inflammatory cytokine production of IL-6 (1.2-fold) and TNFα (1.3-fold). Further, LPS-stimulated IFNγ production in LA-fed D6KO mice was reduced 5-fold compared to LA-fed WT mice, indicating that conversion of LA to AA was necessary for cytokine production. Conversely, ALA exerted an independent immunomodulatory effect from EPA/DHA and all n-3 FA increased LPS-stimulated IL-10 production versus LA and AA. These data definitively identify specific immunomodulatory effects of individual FA and challenge the simplified view of the immunomodulatory effects of n-3 and n-6 FA.

Comprehensive profiling of plasma fatty acid concentrations in young healthy Canadian adults.

Circulating fatty acids (FA) are associated with a multitude of chronic diseases. However, a major gap in establishing such relationships is the lack of accepted fatty acid reference ranges representing healthy individuals. Data on validated FA reference ranges would provide a better understanding of study baseline measures and aid in the evaluation and interpretation of pharmaceutical or dietary interventions. Reference ranges for plasma FA levels have been reported in a few small studies and on a limited number of FA. Therefore, we determined the average and percentiles of a broad set of 61 FA (C14 - C24:1) from plasma total lipids from an ethnically diverse population of healthy young Canadian males and females (Total n = 826). Plasma concentrations of some of the major FA ranged from 0.3 to 4.1 mmol/L for palmitic acid, 0.1 to 1.0 mmol/L for stearic acid, 0.03 to 3.2 mmol/L for oleic acid, 0.2 to 5.0 mmol/L for linoleic acid (LA), 12.0 to 186.9 µmol/L for α-linolenic acid, and 7.2 to 237.5 µmol/L for docosahexaenoic acid (DHA). Males had significantly higher plasma concentrations of γ-linolenic acid (GLA) and n-3 docosapentaenoic acid and lower concentrations of palmitoleic acid, LA and DHA than females. Comparison of FA concentrations between Caucasians, East Asians and South Asians revealed that South Asians had significantly lower levels of palmitoleic acid (p < 0.01) and oleic acid (p = 0.01) while East Asians had lower levels of GLA (p = 0.02) and dihomo-γ-linolenic acid (p = 0.03). Overall, these data provide a comprehensive set of quantitative values that profiles a small cohort of Canadians which highlights the utility of establishing validated FA reference ranges that may be used to understand how deficient, suboptimal, or excess amounts of a given FA may be associated with chronic disease.

Ethnicity, sex, FADS genetic variation, and hormonal contraceptive use influence delta-5- and delta-6-desaturase indices and plasma docosahexaenoic acid concentration in young Canadian adults: a cross-sectional study.

BACKGROUND: There is great interest in the relationship between polyunsaturated fatty acids and health. Yet, the combinatory effect of factors such as sex, ethnicity, genetic polymorphisms and hormonal contraceptives (HC) on the concentrations of these fatty acids is unknown. Therefore, we sought to determine the effects of FADS polymorphisms, and HC use in females, on aggregate desaturase indices (ADI), and plasma docosahexaenoic acid (DHA) concentrations in Caucasian and East Asian males and females. METHODS: Fasting plasma samples were collected from subjects (Caucasian males: 113 and females: 298; East Asian males: 98 and females: 277) from the Toronto Nutrigenomics and Health Study. Fatty acid concentrations were measured by gas chromatography. ADI were estimated by dividing concentrations of arachidonic acid by linoleic acid (n-6 ADI) and eicosapentaenoic acid (EPA) by α-linolenic acid (n-3 ADI). [DHA/EPA] desaturase index was used to determine effects of FADS2 polymorphisms and HC use on EPA conversion to DHA. RESULTS: In Caucasians, associations between n-6 ADI and multiple SNP (FADS1 rs174547, FADS2 rs174576, and rs174611 in males; FADS1 rs174547, FADS2 rs174570, rs174576, rs174679, rs174611, rs174593, rs174626, rs2072114, rs2845573, and rs2851682 in females) withstood multiple testing. In East Asian females, 5 SNP-n-6 ADI associations (FADS2 rs174602, rs174626, rs2072114, rs2845573, and rs2851682) withstood multiple testing. One FADS2 SNP was associated with altered [DHA/EPA] desaturase index in Caucasian females only (rs174576, p < 0.0001). HC use had a significant effect on DHA concentrations in Caucasian females only (P < 0.0001). CONCLUSIONS: We demonstrate ethnic- and sex-specific effects of FADS polymorphisms on desaturase indices, and ethnic-specific effect of HC use on plasma DHA concentrations.

Plasma levels of 14:0, 16:0, 16:1n-7, and 20:3n-6 are positively associated, but 18:0 and 18:2n-6 are inversely associated with markers of inflammation in young healthy adults.

Inflammation is a recognized risk factor for the development of chronic diseases, such as type 2 diabetes and atherosclerosis. Evidence suggests that individual fatty acids (FA) may have distinct influences on inflammatory processes. The goal of this study was to conduct a cross-sectional analysis to examine the associations between circulating FA and markers of inflammation in a population of young healthy Canadian adults. FA, high-sensitivity C-reactive protein (hsCRP), and cytokines were measured in fasted plasma samples from 965 young adults (22.6 ± 0.1 years). Gas chromatography was used to measure FA. The following cytokines were analyzed with a multiplex assay: regulated upon activation normal T cell expressed and secreted (RANTES/CCL5), interleukin 1-receptor antagonist (IL-1Ra), interferon-γ (IFN-γ), interferon-γ inducible protein 10 (IP-10), and platelet-derived growth factor ß (PDGF-ßß). Numerous statistically significant associations (p < 0.05, corrected for multiple testing) were identified between individual FA and markers of inflammation using linear regression. Myristic (14:0), palmitic (16:0), palmitoleic (16:1n-7), and dihomo-γ-linolenic (20:3n-6) acids were positively associated with all markers of inflammation. In contrast, stearic acid (18:0) was inversely associated with hsCRP and RANTES, and linoleic acid (18:2n-6) was inversely associated with hsCRP, RANTES and PDGF-ßß. In conclusion, our results indicate that specific FA are distinctly correlated with various markers of inflammation. Moreover, the findings of this study suggest that FA profiles in young adults may serve as an early indicator for the development of future complications comprising an inflammatory component.

Plasma concentration of cis9trans11 CLA in males and females is influenced by SCD1 genetic variations and hormonal contraceptives: a cross-sectional study.

BACKGROUND: The conjugated linoleic acid isomer cis9trans11 CLA can be endogenously synthesized from trans vaccenic acid (C18:1 t11) via desaturation at the delta 9 position catalyzed by the stearoyl-CoA desaturase 1 (SCD1), also known as delta-9 desaturase (D9D). Diet, hormonal regulation of gene expression and single nucleotide polymorphisms (SNPs) have been implicated in altering circulating levels of fatty acids. Hormonal contraceptives (HC) have also been shown to influence levels of some fatty acids. SNPs in SCD1 have been associated with altered levels of palmitoleic and oleic acids; however, associations between SCD1 SNPs and D9D desaturation index have not been previously examined in relation to CLA. Herein, we investigated the effects of sex and HC use on circulating concentrations of c9t11 CLA and D9D desaturation index. Furthermore, we determined the effects of ten SCD1 SNPs on D9D desaturation indices estimated by product to precursor ratio of c9t11 CLA to C18:1 t11. METHODS: PLASMA SAMPLES WERE COLLECTED FROM SUBJECTS (CAUCASIAN MALES: n = 113; Caucasian females: n = 298; Asian males: n = 98; Asian females: n = 277) from the Toronto Nutrigenomics and Health Study. Circulating fatty acids levels were measured by gas chromatography. RESULTS: Results show that circulating c9t11 CLA concentrations are significantly higher in females than males and they are further elevated in females using HC. In addition, a significant sex- and ethnic-specific association was found between SCD1 SNP rs10883463 (p = 0.0014) and altered D9D activity in Caucasian males. CONCLUSION: Findings from the present study identify SCD1 SNPs and hormonal contraceptives as factors altering endogenous c9t11 CLA levels in a sex- and ethnic-specific manner.