Polyunsaturated fatty acid biosynthesis is involved in phenylephrine-mediated calcium release in vascular smooth muscle cells

α-linolenic acid interconversion is sufficient as a source of longer chain ω-3 polyunsaturated fatty acids in humans: An opinion

α-linolenic acid (αLNA) conversion into the functionally important ω-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), has been regarded as inadequate for meeting nutritional requirements for these PUFA. This view is based on findings of small αLNA supplementation trials and stable isotope tracer studies that have been interpreted as indicating human capacity for EPA and, in particular, DHA synthesis is limited. The purpose of this review is to re-evaluate this interpretation. Markedly differing study designs, inconsistent findings and lack of trial replication preclude robust consensus regarding the nutritional adequacy of αLNA as a source of EPC and DHA. The conclusion that αLNA conversion in humans is constrained is inaccurate because it presupposes the existence of an unspecified, higher level of metabolic activity. Since capacity for EPA and DHA synthesis is the product of evolution it may be argued that the levels of EPA and DHA it maintains are nutritionally appropriate. Dietary and supra-dietary EPA plus DHA intakes confer health benefits. Paradoxically, such health benefits are also found amongst vegetarians who do not consume EPA and DHA, and for whom αLNA conversion is the primary source of ω-3 PUFA. Since there are no reported adverse effects on health or cognitive development of diets that exclude EPA and DHA, their synthesis from αLNA appears to be nutritionally adequate. This is consistent with the dietary essentiality of αLNA and has implications for developing sustainable nutritional recommendations for ω-3 PUFA.

Effects of dietary palmitoleic acid on vascular function in aorta of diabetic mice

BACKGROUND

Chronic hyperglycemia in diabetes causes atherosclerosis and progresses to diabetic macroangiopathy, and can lead to coronary heart disease, myocardial infarction and cerebrovascular disease. Palmitoleic acid (POA) is a product of endogenous lipogenesis and is present in fish and vegetable oil. In human and animal studies, POA is reported as a beneficial fatty acid related to insulin sensitivity and glucose tolerance. However, few studies have reported its effects on aortic function in diabetes. Here, we investigated the effects of POA administration on vascular function in KKAy mice, a model of type 2 diabetes.

METHODS

Male C57BL/6 J (control) and KKAy (experimental) mice at the age of 14 weeks were used in the present study. For each mouse strain, one group was fed with reference diet and a second group was fed POA-containing diet for 2 weeks. The vascular reactivities of prepared aortic rings were then measured in an organ bath to determine if POA administration changed vascular function in these mice.

RESULTS

KKAy mice treated with POA exhibited decreased plasma glucose levels compared with mice treated with reference diet. However, endothelium-dependent vasorelaxant responses to acetylcholine and protease-activated receptor 2 activating protein, which are attenuated in the aorta of KKAy mice compared to C57BL/6 J mice under a reference diet, were not affected by a 2-week POA treatment. In addition, assessment of vasoconstriction revealed that the phenylephrine-induced vasoconstrictive response was enhanced in KKAy mice compared to C57BL/6 J mice under a reference diet, but no effect was observed in KKAy mice fed a POA-containing diet. In contrast, there was an increase in vasoconstriction in C57BL/6 J mice fed the POA-containing diet compared to mice fed a reference diet. Furthermore, the vasoconstriction in aorta in both C57BL/6 J and KKAy mice fed a POA-containing diet were further enhanced under hyperglycemic conditions compared to normal glucose conditions in vitro. In the hyperinsulinemic, and hyperinsulinemic combined with hyperglycemic conditions, vasoconstriction was increased in KKAy mice fed with POA.

CONCLUSION

These results suggest that POA intake enhances vasoconstriction under hyperglycemic and hyperinsulinemic conditions, which are characteristics of type 2 diabetes, and may contribute to increased vascular complications in diabetes.

Is essential fatty acid interconversion an important source of PUFA in humans?

Humans can obtain pre-formed long-chain PUFA from the diet and are also able to convert essential fatty acids (EFA) to longer-chain PUFA. The metabolic pathway responsible for EFA interconversion involves alternating desaturation and carbon chain elongation reactions, and carbon chain shortening by peroxisomal β-oxidation. Studies using stable isotope tracers or diets supplemented with EFA show that capacity for PUFA synthesis is limited in humans, such that DHA (22 : 6n-3) synthesis in men is negligible. PUFA synthesis is higher in women of reproductive age compared with men. However, the magnitude of the contribution of hepatic PUFA synthesis to whole-body PUFA status remains unclear. A number of extra-hepatic tissues have been shown to synthesise PUFA or to express genes for enzymes involved in this pathway. The precise function of extra-hepatic PUFA synthesis is largely unknown, although in T lymphocytes PUFA synthesis is involved in the regulation of cell activation and proliferation. Local PUFA synthesis may also be important for spermatogenesis and fertility. One possible role of extra-hepatic PUFA synthesis is that it may provide PUFA in a timely manner to facilitate specific cell functions. If so, this may suggest novel insights into the effect of dietary PUFA and/or polymorphisms in genes involved in PUFA synthesis on health and tissue function.

Polyunsaturated Fatty Acid Biosynthesis Involving Δ8 Desaturation and Differential DNA Methylation of FADS2 Regulates Proliferation of Human Peripheral Blood Mononuclear Cells

Polyunsaturated fatty acids (PUFAs) are important for immune function. Limited evidence indicates that immune cell activation involves endogenous PUFA synthesis, but this has not been characterised. To address this, we measured metabolism of 18:3n-3 in quiescent and activated peripheral blood mononuclear cells (PBMCs), and in Jurkat T cell leukaemia. PBMCs from men and women (n = 34) were incubated with [1-¹³C]18:3n-3 with or without Concanavalin A (Con. A). 18:3n-3 conversion was undetectable in unstimulated PBMCs, but up-regulated when stimulated. The main products were 20:3n-3 and 20:4n-3, while 18:4n-3 was undetectable, suggesting initial elongation and Δ8 desaturation. PUFA synthesis was 17.4-fold greater in Jurkat cells than PBMCs. The major products of 18:3n-3 conversion in Jurkat cells were 20:4n-3, 20:5n-3, and 22:5n-3. ¹³C Enrichment of 18:4n-3 and 20:3n-3 suggests parallel initial elongation and Δ6 desaturation. The FADS2 inhibitor SC26196 reduced PBMC, but not Jurkat cell, proliferation suggesting PUFA synthesis is involved in regulating mitosis in PBMCs. Con. A stimulation increased FADS2, FADS1, ELOVL5 and ELOVL4 mRNA expression in PBMCs. A single transcript corresponding to the major isoform of FADS2, FADS20001, was detected in PBMCs and Jurkat cells. PBMC activation induced hypermethylation of a 470bp region in the FADS2 5'-regulatory sequence. This region was hypomethylated in Jurkat cells compared to quiescent PBMCs. These findings show that PUFA synthesis involving initial elongation and Δ8 desaturation is involved in regulating PBMC proliferation and is regulated via transcription possibly by altered DNA methylation. These processes were dysregulated in Jurkat cells. This has implications for understanding the regulation of mitosis in normal and transformed lymphocytes.