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from LA, may be 50 times lower than this (100 mg). As a percentage of fatty acids, GLA constitutes 0.04% of free fatty acids, 0.48% of triglycerides, 0.13% of phospholipids, and 1.07% of cholesterol esters. These are significantly lower than the LA concentrations reported above. Therefore, in these studies the authors are providing very little LA over the background diet (600 mg vs 8 mg) but much greater quantities of GLA (300 mg vs 100 mg, estimated). In a study by Brosche and Platt (11) using borage oil
supplementation in analysis of the red blood cell (RBC) percentage weight fatty acids, the levels of GLA and DGLA contents increased significantly (0.04% and 1.37% to 0.07% and 1.69%, respectively, at 8 weeks; p< 0.05). The authors explained that simple incorporation of GLA into skin lipids is unlikely to be the cause of the TEWL changes in these subjects, but it is more likely to be an effect of the GLA on regulatory mechanisms controlling cutaneous barrier function. Despite the borage oil containing twice as much LA as that of GLA, no changes in RBC membrane LA contents was observed. As previously discussed, the lack of increase in RBC LA levels is anticipated because the dose of LA eaten is lower than that of the probable background diet. However, the levels of GLA are increased during the intervention as there is very little present in blood circulating lipids, and therefore little in the diet. It is clear from this study that low doses of dietary‑derived GLA in borage oil can influence skin functioning.
Support for GLA Further support for the effects of GLA and especially borage oil–derived GLA on skin barrier function comes from animal studies (26). Borage oil–derived GLA, where it is supplied in the sn‑2
position of the triglyceride oil, is more effective than evening primrose oil–derived GLA, which is present in the sn‑3 position of the triglyceride, in reversing epidermal hyper‑proliferation and increasing ceramide synthesis in guinea pigs induced into an EFAD state using a hydrogenated coconut diet (HCO) for 8 weeks. In this study, guinea pigs were fed HCO (14 g kg−1
) to induce
the deficiency state. To reverse the EFAD, the animals were fed for 10 weeks with 60 g kg−1
oils of primrose
oil (PO), borage oil (BO), or equal quantities of BO + PO (BP). The latter was designed to provide a similar level of GLA as PO, but in a different position on the triglyceride backbone. All three GLA‑containing diets suppressed the epidermal thickening induced by the HCO diet with the BO diets being the most effective. Equally, on examination of thymidine incorporation into epidermal DNA, the GLA diets were effective but the BO diet was the best. GLA was not detected in epidermal lipid fractions, but DGLA was. DGLA showed a greater incorporation into epidermal phospholipids and ceramides in the order BO > BP > PO. The borage oil diets also showed a greater incorporation of linoleic acid into epidermal ceramides.
prime-journal.com | May 2011 in a study by
brosche and Platt using borage oil
supplementation in analysis of the red blood cell
percentage weight fatty acids, the
levels of GLaand DGLa contents increased
significantly. These results suggest that the absolute level of GLA in
oils determines the accumulation of DGLA in epidermal phospholipids and ceramides and that the presence of GLA in the sn‑2 position of the triglyceride oil mediates this, whereas the presence of LA in the sn‑1 position of the triglyceride facilitates the accumulation of linoleic acid in epidermal ceramides. The content of other anti‑inflammatory and antiproliferative metabolites of these lipids (13-HODE and HETrE) reflects their incorporation into the epidermal lipid fractions. Stimulation of epidermal ceramide synthesis was
greater for the borage oil diet alone, but was in the order BO > BP > PO (26). In these studies a sunflower oil (SO) diet alone was included, which overall was inferior to the PO diet and was significantly inferior to the BO diet. On the SO diet, only 0.7 g of DGLA/100 g of total epidermal fatty acids was found in the skin. In comparison, the PO diet delivered 2.9 g, the BS diet delivered 11.7 g, and the BO diet delivered 15.2 g. These gave DGLA/LA ratios of 0.9%, 5%, 17.4%, and 27.5%. Therefore, owing to its more efficient bioavailability,
borage oil is more effective than evening primrose oil in these studies. More importantly, however, as skin cannot make GLA from LA because it lacks the necessary desaturase enzyme to perform this metabolic step, it is therefore highly dependent on the blood for its supply of GLA and its further metabolites as a result. Although the precise mechanism of action of GLA has not been determined in these studies, it is believed to be a direct effect of GLA itself on the keratinocyte differentiation process, or due to the effects of its downstream metabolites (DGLA or 15-HETrE). Nevertheless, its effects are probably due to improving the epidermal differentiation process
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