ESSENTIAL FATTY ACIDS (EFA) ARE EXACTLY THAT: essential for certain metabolic processes and they are essential dietary elements for normal health, because mammals cannot synthesise them. EFAs are polyunsaturated fatty acids which are divided into two main classes: α linolenic acid (omega 3) known as the n-3 series because the first carbon double bond is between the 3rd and 4th carbon atoms; and linoleic acid (omega 6) known as n-6 series, because the double bond is between the 6th and 7th carbon atoms. γ-linolenic acid (GLA) and arachidonic acid are members of the n-6 series, whereas docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) belong to the n-3 series. EFAs from both series are able to modulate inflammation through the production of anti-inflammatory mediators, by competing for enzymesinvolved in synthesis of arachidonic acid and by helping maintain the epidermal barrier. Generally, the ratios of n-6 to n-3 most beneficial to dogs range from about 5:1. The source of the EFAs varies in the different supplements available in the veterinary market. Borage seed oil contains higher levels (roughly twice) of GLA compared to evening primrose oil and blackcurrant oil. EPA is usually sourced from cold marine fish oil. EFA deficiencies are uncommon to rare, but may be seen in dogs fed on overcooked foods, rancid foods, poorly stored food and food without adequate levels of antioxidants. The clinical signs associated with EFA deficiency are poor growth, scaly skin, poor coat condition and infertility. This paper reviews why EFAs are essential for maintaining good skin and coat conditions and the benefits of EFA supplementation in certain skin conditions.
Why are they essential?
EFAs are essential because they are:
1. Components of cell membranes. Linoleic acid is incorporated within the phospholipids which make up the cell membrane bilayers. They play an important role in fluidity and control the movement of molecules in and out of the cell. They may also play a role in the activity of membrane receptors and enzymes.
2. Necessary to prevent transepidermal water loss (TEWL). Linoleic acid is a major component of the ceramides found in the lamellar bodies of the stratum granulosum and stratum corneum.
The contents of the lamellar granules, containing lipid and hydrolytic enzymes, are extruded into the intercellular spaces where they are re-organised to form the outer layer of the cornified cell envelope and the intercellular lipid lamellae. The cells of the stratum corneum have undergone structural and
biochemical changes to form the cornified envelope, which is formed of two portions: an outer lipid portion and inner proteinaceous portion. The outer lipid portion of the cornified
cell envelope is a continuous layer of hydroxyceramide that is covalently bonded to the inner proteinaceous envelope. Both play an important role in barrier function. The stratum corneum forms a tight barrier, likened to a brick and mortar structure, which
prevents water loss and the loss of other molecules from the body. At the same time it prevents entry into the body of microbes, allergens, etc., through the skin. Increases in TEWL lead to changes in the barrier function, which in turn results in a keratinisation defect making percutaneous passage of allergens,
microbes, etc., easier. EFAs help maintain this barrier, thus reducing percutaneous penetration.
3. Dietary EFAs are precursors of a range of substances such as prostaglandins, leukotrienes, and hydroxyeicosatetranoic acids (HETEs) that can modulate inflammation.
Benefits and clinical uses of EFA supplementation in skin disease
GLA, in the form of borage oil, evening primrose oil and blackcurrant oil and eicosapentaenoic acid, in the form of cold marine fish oil, can modulate inflammation through processes that lead to formation of prostaglandin E1 (PGE1) and 15-hydroxyeicosatetraenoic acid (15-HETrE), both of which are thought to have anti-inflammatory properties. Furthermore, they may inhibit the release of arachidonic acid from cell membrane and production of leukotrienes.
Canine atopic dermatitis (CAD)
The pathogenesis of CAD is multifactorial, involving immunological aspects and the epidermal barrier. The management of CAD requires a multimodal approach, which involves managing pruritus, treating and preventing recurrences of secondary microbial infections and maintaining the epidermal barrier. Studies support the theory that allergens can penetrate the skin and a defective barrier is more likely to allow the percutaneous exposure to environmental allergens and microbes, thus predisposing the individual to microbial infections. As mentioned earlier, EFAs play an important role in maintaining the tight barrier in the stratum corneum and can, therefore, play an important role in the long-term management of atopic dogs. The use of EFAs in the control of allergic skin disease and pruritus through the modulation of inflammation is not entirely understood; however, in a blinded
placebo-controlled study comparing the efficacy of borage seed oil and fish oil to olive oil, it was reported that there was a significant reduction in erythema and self-trauma during supplementation (Harvey, 1999). A later study revealed the steroidsparing effects of borage oil (Savik et al, 2004). Various other studies have reported the beneficial effects of n-6 and n-3 fatty acids in the management of atopic dermatitis and in one beneficial effects when given in conjunction with antihistamines has been reported (Paterson, 1995). In 2010 and 2015 the guidelines for the management of atopic dermatitis (Olivry et al, 2010; Olivry et al, 2015) reported that improving coat hygiene and quality with EFA supplementation
or EFA-enriched diets can help in the long-term management of the
condition, even though as a sole therapy it is not effective in controlling the pruritus. Vitamin E and other co-factors are included in some of the EFA supplements available. A study where
14 atopic dogs received vitamin E (8.1 IU/kg once daily, orally) and 15 received mineral oil as placebo (orally) found lower canine atopic dermatitis extent and severity index (CADESI) scores in the group receiving vitamin E (Plevnik Kapun et al, 2014). It is possible that some EFA supplements on the market which contain vitamin E may be more effective than those with GLA and EPA alone in managing atopic dermatitis.
Cornification disorders include primary idiopathic seborrhoea and conditions such as hypothyroidism, and xerosis that result in excessive scaling. The epidermis has a rapid turnover and requires a constant supply of fatty acids, including linoleic acid, for the maintenance of the superficial water permeability barrier; and arachidonic acid for epidermal proliferation. Dogs suffering from cornification defects may benefit from EFA supplementation (Figures 2a and 2b; Figures 3a and 3b) because these defects arise from a rapid epidermal turnover, often resulting in scaling and in a defective lipid barrier. It is important to also treat the underlying cause of the scaling for optimal results.
Sebaceous adenitis is a scaling disorder whereby the sebaceous glands are destroyed as a result of a cell-mediated process, or as a secondary effect of diseases such as leishmaniosis. This condition results in alopecia, secondary pyoderma and variable degrees of pruritus. The function of the sebaceous gland is to produce sebum, a mixture of lipids that coats the hair shafts and stratum corneum to give the hair structural strength and glossiness. The lack of sebum results in keratinous material surrounding the hair shafts. The lack of lubrication provided by the sebum leads to brittle and broken hairs and scaling of the epidermis. Essential fatty acid supplementation has been used in the management of sebaceous adenitis in some dogs, in conjunction with topical shampoos, as this approach is likely to be safer than using immunomodulating drugs that could have adverse effects.
Symmetric lupoid onychodystrophy
Symmetric lupoid onychodystrophy is an immune-mediated condition which results in the deformation and shedding of multiple claws on multiple feet. In severe cases, aggressive treatment with immunosuppressive drugs may be needed in the early stages. Less aggressive treatment with EFA supplementation is reported to be beneficial (Auxillia et al, 2001; Muller et al, 2003) and it can be used for the long-term management of the condition.
EFA therapy can be very effective in managing scaling, allergic and claw disorders and has a place in veterinary dermatology, especially when long-term management is required. The effects of EFA supplementation can take several weeks to appreciate. To get maximum benefits from EFA supplementation, the underlying causes of pruritus, or scaling (e.g. flea-allergic dermatitis, adverse food reactions and secondary microbial infections), have to be managed successfully. If these underlying disorders are not managed, the benefits of EFA supplementation are greatly reduced. EFAs also have the benefit of having corticosteroid-sparing effects, thereby lowering the risk of adverse effects where long-term steroid therapy is required.
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