Linolenic acid(abbreviated to LA (18:2)) is a polyunsaturated omega-6 fatty acid with two double bounds in the 9 and 12 carbons. Together with α-linolenic acid (ALA), LA constitutes the essential fatty acids, which the human body cannot synthesize by itself. LA and ALA are needed for the normal growth and development of children.

Linolenic acid is the major fatty acid in sea buckthorn seed oil – up to 42% , being also present in sea buckthorn berry and pulp oil in lower concentration levels (6 to 33%). There are small variations of concentration in seed oil according to the subspecies. In addition, sea buckthorn oil is the only oil that naturally presents a 1:1 ratio of omega-3: omega-6.

Skin condition

Linolenic acid is the most abundant polyunsaturated fatty acid in human skin. Consequently, many studies have focused on the beneficial effects of LA in mucous membrane and skin. The lamellar granules of human skin produce lipids that maintain the protective barrier of the skin in order to avoid the epidermal loss of water. The reproduction of lamellar granules slows down with aging, the skin becoming drier and weaker. Omega-6 might reverse this process by accelerating the production of lipids in lamellar granules, strengthening the lipid barrier of the epidermis, protecting the skin against epidermal loss of water, and normalizing the metabolism of the skin. In addition, people with acne skin present a decrease of LA in sebum, which leads to block pores and formation of comedos and eczema. Also, it is thought that LA might improve sebaceous gland activity, unblocking pores and decreasing the number of comedos.

As mentioned above, a dietary deficiency in LA results in a characteristic scaly skin disorder and an excessive epidermal water loss. The physical structure of the epidermal water barrier is defined as a lipid bilayer, which fills the intracellular spaces of the upper-most layer of the epidermis. This lipid bilayer contains sphingolipids; in turn, those sphingolipids rich in linoleate are called acylglucosylceramide, acylceramide and acylacid.

Although the feeding of LA in fatty acid deficient animals is known to reverse the major coetaneous symptoms, the mechanisms by which this happened remain unknown. A possible mechanism is the transformation of LA into 13-hydroxioctadecadienoic acid (13-HODE). This reaction may be produced by incubated LA with soybean 15-lipoxygenase or 15-lipoxygenase prepared from skin epidermis in vitro. The same study also demonstrated that 13-HODE formed was incorporated into epidermal phosphatidylinsotiol 4, 5-biphosphate, resulting in epidermal phospholipasa C-catalyzed release of 13-HODE into a novel 13-HODE-containing diacylglycerol.

These results were obtained from an in vivo trial in which Guinea pigs were randomized in three groups depending on diet: safflower (control), essential fatty acid deficiency diet, and essential fatty acid diet followed by safflower oil during 2 weeks. The third group showed replenished tissue concentrations of 13-HODE after the introduction of safflower oil, which inversely correlated with the selective down-regulation of protein kinase Cβ. It is possible that this 13-HODE-containing-diacylglycerol could function to decrease the activity of epidermal protein kinase C and epidermal hyperproliferation and differentiation. These results suggest that the epidermal concentration of 13-HODE, which is derived from dietary LA, may play a role in modulating coetaneous hyperporliferation.

Furthermore, LA seems to have an important role in the de novo biosynthesis of the major sebaceous fatty acids. An in vitro study of fatty acids from a biopsy punches from human facial skin rich in sebaceous glands was designed to try and elucidate the metabolisms of sebaceous lipids. Most fatty acids are esterified into triglycerides or polar lipids in sebaceous glands but LA is processed in a different way. It is hypothesized that LA is transformed into hydroxyperoxide by the lipoxygenase enzyme and this intermediate form is highly susceptible to β-oxidation. The results showed a correlation between the function and differentiation of sebaceous cells and the oxidation of LA. The study highlighted that the oxidation of LA is indispensable for the de-novo biosynthesis of the major sebaceous fatty acids, such as palmitic and oleic acids.

Moreover, the positive effect of LA on psoriasis disease has also been considered. a randomized study of 116 patients was carried out. The study was composed in two parts. In the first one the patients were divided in two groups. In one of them (the control group) patients were treated topically with 500 mg of a moderate corticosteroid cream. In the other, patients were treated with a LA-ceramides containing moisturizer in addition to the cream. After this first stage, the patients treated with LA-ceramide were randomized again. During this period, one part of the group maintained the use of moisturizer while the other group discontinued it. The study compared the rates of relapse and rebound between these new groups, being more favorable in the group that maintained the use of moisturizer. Based on the results obtained, the researchers concluded that the topical LA-Ceramide moisturizer could alleviate psoriasis, potentially becoming a valuable tool for its treatment and prevention.

Atherosclerosis

In order to investigate the relation between LA and cholesterol level, a study was carried out, white rabbits with atherosclerosis were divided into two groups according to the diet that they were being administered. The first group was fed with 1 ml of sea buckthorn seed oil, the second group was fed with a high-cholesterol diet, the third group was fed with high-cholesterol diet and after 30 days was administrated 1 ml of sea buckthorn oil, and the fourth was the control group. The results of the study indicated a significant decrease of LDL-cholesterol levels and atherogenic index in group 3 after the administration of the seed oil. The study attributed these effects to LA but other scientists considered that the lowering of serum cholesterol, LDL-cholesterol, triglycerides and other risk factors of cardiovascular disease have been associated not only to intakes of LA but also ALA, PA and sterols of sea-buckthorn oil.