α-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans

Blood levels of polyunsaturated fatty acids (PUFA) are considered biomarkers of status. Alpha-linolenic acid, ALA, the plant omega-3, is the dietary precursor for the long-chain omega-3 PUFA eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA). Studies in normal healthy adults consuming western diets, which are rich in linoleic acid (LA), show that supplemental ALA raises EPA and DPA status in the blood and in breast milk. However, ALA or EPA dietary supplements have little effect on blood or breast milk DHA levels, whereas consumption of preformed DHA is effective in raising blood DHA levels. Addition of ALA to the diets of formula-fed infants does raise DHA, but no level of ALA tested raises DHA to levels achievable with preformed DHA at intakes similar to typical human milk DHA supply. The DHA status of infants and adults consuming preformed DHA in their diets is, on average, greater than that of people who do not consume DHA. With no other changes in diet, improvement of blood DHA status can be achieved with dietary supplements of preformed DHA, but not with supplementation of ALA, EPA, or other precursors.     

Linkage and association analysis of circulating vitamin D and parathyroid hormone identifies novel loci in Alaska Native Yup’ik people

Background

Vitamin D deficiency is a well-documented public health issue with both genetic and environmental determinants. Populations living at far northern latitudes are vulnerable to vitamin D deficiency and its health sequelae, although consumption of traditional native dietary pattern rich in fish and marine mammals may buffer the effects of reduced sunlight exposure. To date, few studies have investigated the genetics of vitamin D metabolism in circumpolar populations or considered genediet interactions with fish and n-3 fatty acid intake.

Methods

We searched for genomic regions exhibiting linkage and association with circulating levels of vitamin D and parathyroid hormone (PTH) in 982 Yup’ik individuals from the Center for Alaska Native Health Research Study. We also investigated potential interactions between genetic variants and a biomarker of traditional dietary intake, the δ15N value.

Results

We identified several novel regions linked with circulating vitamin D and PTH as well as replicated a previous linkage finding on 2p16.2 for vitamin D. Bioinformatic analysis revealed multiple candidate genes for both PTH and vitamin D, including CUBN, MGAT3, and NFKBIA. Targeted association analysis identified NEBL as a candidate gene for vitamin D and FNDC3B for PTH. We observed significant associations between a variant in MXD1 and vitamin D only when an interaction with the δ15N value was included. Finally, we integrated pathway level information to illustrate the biological validity of the proposed candidate genes.

Conclusion

We provide evidence of linkage between several biologically plausible genomic regions and vitamin D metabolism in a circumpolar population. Additionally, these findings suggest that a traditional dietary pattern may modulate genetic effects on circulating vitamin D.

     

Higher plasma n-3 fatty acid status in the moderately healthy elderly in southern Québec: Higher fish intake or aging-related change in n-3 fatty acid metabolism?

The elderly reportedly have a significantly higher % of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in plasma and red cell lipids. However, these observations are from a few small studies and the health status of the elderly in these studies is for the most part unclear. Since the elderly are susceptible to cardiovascular and neurological illnesses that seem to be related in part to lower intake of n-3 fatty acids it seems paradoxical that their blood levels of EPA and DHA would be higher than in young adults. We report here plasma fatty acid profiles and their response to supplementation with two types of fish oils from several of our recent studies in the moderately healthy elderly. We define the moderately healthy elderly as those who were in good physical condition, had no cognitive decline and, if present, in whom hypothyroidism, hyperlipidemia and/or hypertension were well-controlled. As shown previously, we confirm the higher % EPA and % total n-3 fatty acids (but not DHA) in fasting plasma and extend these findings to include higher plasma concentrations (mg/L) of n-3 fatty acids as well. The EPA-predominant supplement raised DHA only in the young, whereas the DHA-predominant supplement raised EPA more in the young than in the elderly. The moderately healthy elderly clearly have higher plasma n-3 fatty acids but whether this reflects differences in intake versus aging-related changes in n-3 fatty acid metabolism remains to be elucidated.     

Fasting enriches liver triacylglycerol with n-3 polyunsaturated fatty acids: implications for understanding the adipose–liver axis in serum docosahexaenoic acid regulation

We investigated the effect of short-term fasting on coordinate changes in the fatty acid composition of adipose triacylglycerol (TAG), serum non-esterified fatty acids (NEFA), liver TAG, and serum TAG and phospholipids in mice fed ad libitum or fasted for 16 h overnight. In contrast to previous reports under conditions of maximal lipolysis, adipose tissue TAG was not preferentially depleted of n-3 PUFA or any specific fatty acids, nor were there any striking changes in the serum NEFA composition. Short-term fasting did, however, increase the hepatic proportion of n-3 PUFA, and almost all individual species of n-3 PUFA showed relative and absolute increases. The relative proportion of n-6 PUFA in liver TAG also increased but to a lesser extent, resulting in a significant decrease in the n-6:n-3 PUFA ratio (from 14.3 ± 2.54 to 9.6 ± 1.20), while the proportion of MUFA decreased significantly and SFA proportion did not change. Examination of genes involved in PUFA synthesis suggested that hepatic changes in the elongation and desaturation of precursor lipids could not explain this effect. Rather, an increase in the expression of fatty acid transporters specific for 22:6n-3 and other long-chain n-3 and n-6 PUFA likely mediated the observed hepatic enrichment. Analysis of serum phospholipids indicated a specific increase in the concentration of 22:6n-3 and 16:0, suggesting increased specific synthesis of DHA-enriched phospholipid by the liver for recirculation. Given the importance of blood phospholipid in distributing DHA to neural tissue, these findings have implications for understanding the adipose–liver–brain axis in n-3 PUFA metabolism.

Electronic supplementary material

The online version of this article (doi:10.1007/s12263-015-0490-2) contains supplementary material, which is available to authorized users.     

Enhancement in liver SREBP-1c/PPAR-α ratio and steatosis in obese patients: Correlations with insulin resistance and n-3 long-chain polyunsaturated fatty acid depletion

Sterol receptor element-binding protein-1c (SREBP-1c) and peroxisome proliferator-activated receptor-α (PPAR-α) mRNA expression was assessed in liver as signaling mechanisms associated with steatosis in obese patients. Liver SREBP-1c and PPAR-α mRNA (RT-PCR), fatty acid synthase (FAS) and carnitine palmitoyltransferase-1a (CPT-1a) mRNA (real-time RT-PCR), and n-3 long-chain polyunsaturated fatty acid (LCPUFA)(GLC) contents, plasma adiponectin levels (RIA), and insulin resistance (IR) evolution (HOMA) were evaluated in 11 obese patients who underwent subtotal gastrectomy with gastro-jejunal anastomosis in Roux-en-Y and 8 non-obese subjects who underwent laparoscopic cholecystectomy (controls). Liver SREBP-1c and FAS mRNA levels were 33% and 70% higher than control values (P < 0.05), respectively, whereas those of PPAR-α and CPT-1a were 16% and 65% lower (P < 0.05), respectively, with a significant 62% enhancement in the SREBP-1c/PPAR-α ratio. Liver n-3 LCPUFA levels were 53% lower in obese patients who also showed IR and hipoadiponectinemia over controls (P < 0.05). IR negatively correlated with both the hepatic content of n-3 LCPUFA (r = ? 0.55; P < 0.01) and the plasma levels of adiponectin (r = ? 0.62; P < 0.005). Liver SREBP-1c/PPAR-α ratio and n-3 LCPUFA showed a negative correlation (r = ? 0.48; P < 0.02) and positive associations with either HOMA (r = 0.75; P < 0.0001) or serum insulin levels (r = 0.69; P < 0.001). In conclusion, liver up-regulation of SREBP-1c and down-regulation of PPAR-α occur in obese patients, with enhancement in the SREBP-1c/PPAR-α ratio associated with n-3 LCPUFA depletion and IR, a condition that may favor lipogenesis over FA oxidation thereby leading to steatosis.     

The effect of n-3 polyunsaturated fatty acids on leukotriene B₄ and leukotriene B₅ production from stimulated neutrophil granulocytes in patients with chronic kidney disease

The proinflammatory leukotriene B₄ (LTB₄) may be of importance in the progression of chronic kidney disease (CKD). We investigated whether n-3 polyunsaturated fatty acids (PUFA) decrease LTB₄ and increase the formation of the less inflammatory leukotriene B₅ (LTB₅) in patients with CKD.Fifty-six patients with CKD stage 2-5 were randomised to 2.4 g n-3 PUFA or olive oil for 8 weeks. Compared to controls, n-3 PUFA significantly decreased release of LTB₄ (p<0.001) and 5-hydroxyeicosatetraenoic acid (5-HETE) (p<0.01) and significantly increased release of LTB₅ (p<0.001) and 5-hydroxyeicosapentaenoic acid (5-HEPE) (p<0.001) from stimulated neutrophil granulocytes. Kidney function evaluated by creatinine clearance and proteinuria did not improve. In conclusion, n-3 PUFA supplementation for 8 weeks in patients with CKD stage 2-5 significantly decreased LTB₄ and 5-HETE and significantly increased LTB₅ and 5-HEPE. No effect was seen on kidney function.     

Long chain n-3 polyunsaturated fatty acids increase the efficacy of docetaxel in mammary cancer cells by downregulating Akt and PKCε/δ-induced ERK pathways

Taxanes can induce drug resistance by increasing signaling pathways such as PI3K/Akt and ERK, which promote survival and cell growth in human cancer cells. We have previously shown that long chain n-3 polyunsaturated fatty acids, such as docosahexaenoic acid (DHA, 22:6n-3) decrease resistance of experimental mammary tumors to anticancer drugs. Our objective was to determine whether DHA could increase tumor sensitivity to docetaxel by down-regulating these survival pathways. In docetaxel-treated MDA-MB-231 cells, phosphorylated-ERK1/2 levels were increased by 60% in membrane and nuclear compartments, compared to untreated cells. Our data showed that ERK1/2 activation depended on PKC activation since: i) enzastaurin (a pan-PKC inhibitor) blocked docetaxel-induced ERK1/2 phosphorylation ii) docetaxel increased PKC activity by 30% and phosphatidic acid level by 1.6-fold iii) inhibition of PKCε and PKCδ by siRNA resulted in reduced phosphorylated ERK1/2 levels. In DHA-supplemented cells, docetaxel was unable to increase PKCε and δ levels in membrane and nuclear fractions, resulting in diminished ERK1/2 phosphorylation and increased docetaxel efficacy. Reduced membrane level of PKCε and PKCδ was associated with significant incorporation of DHA in all phospholipids, including phosphatidylcholine which is a major source of phosphatidic acid. Additionally, examination of the Akt pathway showed that DHA could repress docetaxel-induced Ser473Akt phosphorylation. In rat mammary tumors, dietary DHA supplementation during docetaxel chemotherapy repressed ERK and Akt survival pathways and in turn strongly improved taxane efficacy. The P-ERK level was negatively correlated with tumor regression. These findings are of potential clinical importance in treating chemotherapy-refractory cancer.     

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. VIII. Temperature effects and a perspective on the curious case of Karenia mikimotoi as a producer of the unusual, ‘green algal’ fatty acid hexadecatetraenoic acid [16:4(n-3)]

Previous studies have shown that dinoflagellates with different plastid ancestries have distinct differences in the fatty acid compositions and regiochemistries of their chloroplast-associated galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), thus reflecting plastid origin as a major factor in plastid membrane composition. Specifically, dinoflagellates with aberrant plastids (e.g. Karenia brevis, Kryptoperidinium foliaceum and Lepidodinium chlorophorum) possess certain MGDG- and DGDG-associated fatty acids which are not found in peridinin-containing dinoflagellates (the largest group of photosynthetic dinoflagellates with a red algal plastid ancestry which is thought to be an evolutionary precursor to aberrant plastids), but which are common to other algal groups. For example, hexadecatetraenoic acid (16:4(n-3)) is common to green algae and is found in the MGDG and DGDG of L. chlorophorum, which agrees with its green algal plastid ancestry, while hexadecatrienoic acid (16:3) and hexadecadienoic acid (16:2) are found in the MGDG and DGDG of K. foliaceum, which agrees with its diatom plastid ancestry. Notably, 16:4 has been found by others in the total fatty acids and galactolipids of Karenia mikimotoi, but in no other examined members of the Kareniaceae (all of which have plastids of haptophyte origin). However, these findings lack information as to the regiochemistry of 16:4. We have utilized positive-ion electrospray ionization/mass spectrometry (ESI/MS) and ESI/MS/MS to demonstrate that 16:4, which aside from L. chlorophorum is not found conclusively in the MGDG and DGDG of any other dinoflagellates examined to date irrespective of plastid ancestry, is found in K. mikimotoi as 18:5/16:4 (sn-1/sn-2 regiochemistry) MGDG and DGDG, and that its presence is not modulated (i.e. does not become more saturated) with an increase in growth temperature. Considering an aberrant pigment composition as described by others, we present a perspective where galactolipid-associated 16:4 in K. mikimotoi indicates a plastid ancestry more convoluted than for other members of the Kareniaceae.