Importance of Nutrition in Canine Dermatology

1. Food Allergy, Food Hypersensitivity and Nutrition

The terms food allergy and food hypersensitivity should be reserved for those adverse reactions to food that have an immunologic basis.¹ Veterinary dermatologists suggest that adverse food reactions account for 1 to 6% of all dermatoses in general practice and that food allergy constitutes 10 to 49% of allergic responses in dogs and cats.^2-4 Food allergy is one of the most common causes of hypersensitive skin disease in dogs and cats along with arthropod(flea) hypersensitivity and atopic dermatitis triggered by environmental allergens.^2-4 Most of the reported adverse food reactions causing dermatoses have been termed food allergy or food hypersensitivity, although no specific tests were performed to confirm an immunologic basis for the clinical signs.¹

2. Skin, Hair Disorders and Nutrition

Aside from diverse reactions to food, nutritional skin diseases in pets fed nutritionally adequate commercial pet food appear to be very uncommon.⁵ However, the skin and coat can be affected by many nutritional factors such as protein, fat, essential fatty acid (EFA), zinc, copper, vitamin A and vitamin E etc., and many pet owners want to improve the quality and appearance of their pet's coat.⁵ Therefore, veterinary dermatologist and nutritionist emphasize the importance of understanding the nutritional factors that affect normal skin and hair and the nutritional factors that should be investigated in patients with skin disorders.⁵

New Paradigm: Importance of Nutrition in Skin Barrier

1. Homeostatic Fluid (Blood & Body Water) Balance and Skin Barrier

Mammalian skin is a dynamic organ that is constantly adapting to changes in the environment. It performs structural, sensory, immunological and physiological functions and provides an essential barrier against potential environmental insults. Maintenance of homeostatic fluid balance is imperative for many physiological processes in the body and the skin in particular is acutely sensitive to hydration status. From the deeper, highly hydrated layers of the epidermis and dermis, a passive flux of water takes place toward the more superficial, stratum corneum layers, which have a relatively low water content. This is the so-called transepidermal water, which has been measured by some non-invasive, biophysical methods. TEWL is a measure of the rate of water lost through the skin and thus can be used to estimate the skin's ability to retain moisture. It could be also an index of the extent of possible damage to the skin's water barrier function. Because of the importance homeostatic fluid balance in skin barrier function and hydration, dermatologic patients should be considered some problems such as hypovolemia, water imbalance, dehydration, water intake and other diseases that can cause the imbalance of homeostatic fluids.

2. TEWL, Skin Hydration and Skin pH and Skin Barrier

The skin acts as a physiological barrier between an animal and its environment and several biophysical parameters have been measured to assess the barrier functions and biophysical specificities in mammalian skin, an important one of which is control of water loss.^6,7 This can influence not only water loss but also skin hydration and pH, all three of which provide valuable indices of the factors influencing this important complex barrier function. Knowledge of the hydration status, water loss, pH and the factors that influence them is therefore essential, not only for an understanding of the physiological changes in barrier function but also for subsequent interpretation of the influence of water loss in skin diseases. We undertook "Mapping of the dog skin based on biophysical measurements" for the construction of the basis of canine skin barrier for the study of dermatological nutrition in the future.

3. Underlying Diseases and Skin Barrier

TEWL, skin hydration and skin pH do provide a picture of skin health because they can be considerably altered in disease situations.^6,7 These indices reflect not only external ambient conditions but also internal cutaneous changes, such as skin temperature, skin blood flow, local hemodynamics, the degree of corneocyte formation, SC lipid content and various skin conditions and diseases [e.g., atopic dermatitis (AD)]. Various disease and skin diseases altered skin hydration status, TEWL and skin pH, which are thus important for the maintenance of cutaneous barrier integrity and protection from pathogens and environmental injuries.

4. Atopic Dermatitis and Skin Barrier

A well-maintained SC is critical for a functional skin barrier. The architecture of the SC, containing the lipid-depleted corneocytes and highly lipid-enriched extracellular bilayers, enables it to function as a border between the dry environment and the water-enriched organism. Abnormalities in the skin barrier result in an enhanced TEWL in one direction, and increased penetration of harmful substances from the environment into the skin in the other. This triggers the immune system, stimulating a cascade of cytokines and other mediators for repairing the physical barrier as well as influencing the innate and adaptive immune systems, which is one of mechanisms of atopic dermatitis related with skin barrier dysfunction.

5. SC Lipids and Skin Barrier

The major intercellular lipids of the human SC are ceramides, cholesterol, and fatty acids, comprising approximately 50%, 25%, and 10% of the total mass, respectively. Specifically, contents of these lipids are altered in patients with both AD and psoriasis. Likewise, cholesterol, as well as essential and non-essential free fatty acid play separate, critical roles in barrier homeostasis. As all three of the major stratum corneum lipid classes, cholesterol, ceramide, and FFAs derive from their respective precursor lipids, the enzymatic pathways responsible for producing these lipid end-products have garnered much recent attention. It is important to know that these critical enzymatic steps in the generation of epidermal barrier lipids, including details regarding their regulation, as well as their association with cutaneous disease states.

6. Source and Role of SC Hydration and Skin Barrier

The primary function of the skin barrier is to prevent water loss. However, hydration of the corneocyte is essential for SC function. Water acts as a plasticizer on corneocyte proteins giving elastic properties to the cells. If deprived of water dry skin is prone to crack open on mechanical stress. Since atmospheric conditions vary enormously, the corneocytes are hydrated from bodily water lost through the barrier. This imperfect barrier and inbuilt water loss is highly important for tissue functioning and flexibility, and certain metabolic processes. Corneocytes also contain hygroscopic compounds called natural moisturizing factors such as free amino acid, pyrrolidone carboxylic acid, lactate, sugars, urea, chloride, sodium, potassium, ammonia, uric acid, glucosamine, creatine, calcium, magnesium etc. These are essential for maintaining tissue flexibility and, together with the extracellular lipids, tissue hydration. Corneodesmosomes act as intercellular rivets effectively hindering the spatial movement of the corneocytes. In most circumstances these prevent shearing forces from disrupting the intercellular lipid matrix and thereby help to maintain SC barrier function and hydration. The state of SC hydration depends on the rate at which water reaches the SC from the tissue below, the rate at which water leaves the skin surface by evaporation, the ability of the SC to retain water.

7. Hyperammonemia and Skin Disease

Hyperammonemia has been described in dogs with a deficiency of the urea cycle enzyme, argininosuccinate synthetase and with pathologic conditions. Although hyperammonemia has been well known in human medicine as an important causative factor concerned with various pathologic conditions, it has been few reported for the prevalence of hyperammonemia with concurrent skin diseases in dogs. Several reports have been published describing hyperammonemia in dogs and hepatic cutaneous syndrome in hepatic diseased dog. Interestingly, there has been increased patients with hyperammonemia associated with hepatic and/or renal diseases in the past decade in our clinic, especially they likely to have been seen various dermatological signs. The purpose of our study was to describe the prevalence of hyperammonemia in dogs with recurrent dermatitis to evaluate clinical, laboratory, dermatological finding and the correlation between hyperammonemia and recurrent dermatitis in dogs admitted to the Hwang-gum Geriatric Animal Hospital between January 1998 and January 2008. As I am a dermatologist as well as nutritionist who have tried to build novel treatments and nutritional management for dermatologic diseases with geriatric diseases, I expect that the outcome of our study would be helpful to the practitioners who have dealt with recurrent dermatitis with hyperammonemia in small animal practice.

Conclusion

Veterinary dermatology has been focused on food allergy, food hypersensitivity and nutritional deficiency in small animal practice until now. In the future, however, the concept of the skin barrier would be very important to build the basis of nutritional management and treatment for preventive medicine on various skin diseases in small animal practice.

References

1.  Roudebush P, Guilfordd WG, Jackson HA. Adverse reactions to food. In: Hand MS, Novotny BJ, eds. Small Animal Clinical Nutrition 5th ed. Topeka, KS: Mark Morris Institute, 2010:609–635.

2.  MacDonald JM. Food allergy. In: Griffin CE, Kwochka KW, MacDonald JM, eds. Current Veterinary Dermatology. St Louis, MO: Mosby-Year Book Inc, 1993:121–132.

3.  Scott DW, Miller WH, Griffin CE. Small Animal Dermatology, 6th ed. Philadelphia, PA: WB Saunders Co, 2001.

4.  Jackson HA, Murphy KM, Tater KC, et al. The pattern of allergen hypersensitivity (dietary or environmental) of dogs with non-seasonal atopic dermatitis cannot be differentiated on the basis of historical or clinical information: a prospective evaluation 2003–2004 (abstract). Veterinary Dermatology 2004;16:200.

5.  Roudebush P, Schoenherr WD. Skin and hair disorders. In: Hand MS, Novotny BJ, eds. Small Animal Clinical Nutrition 5th ed. Topeka, KS: Mark Morris Institute, 2010:637–665.

6.  Oh WS, Oh TH. Measurement of transepidermal water loss from clipped and unclipped anatomical sites on the dog. Aust Vet J 2009;87(10):409–412.

7.  Oh WS, Oh TH. Mapping of the dog skin based on biophysical measurements. Vet Dermatol 2010;21(4):367–372.