ROLE OF CANINE SKIN BARRIER ECOSYSTEM IN PROTECTION OF HEALTHY SKIN

April 4, 2023

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ROLE OF CANINE SKIN BARRIER ECOSYSTEM IN PROTECTION OF HEALTHY SKIN

Dogs are like us in that the skin and coat comprise their largest organ, accounting for 10-15% of their total body weight. The skin is composed of three layers, the details of which we’ll leave you to look up if you have a special interest in anatomy. The coat consists of thousands of hairs produced in hair follicles. Because hairs are under constant environmental stress, they are continuously shed and replaced. Seasonal shedding, which replaces the entire coat, is triggered by outdoor climate and duration of daylight.

Selective breeding has produced a variety of coat characteristics in dogs. Some long-haired breeds do not shed seasonally and therefore require regular trips to the groomer for a shampoo and basic cut. Breeds with both an outer coat of guard hairs and an insulating undercoat of fine hairs may require more extensive maintenance. These breeds often go through two heavy seasonal shedding cycles per year, once in late spring and again in late fall, during which much of the undercoat falls out in large clumps. Many short-haired breeds lack a distinctive undercoat and shed at low levels year-round.

The skin has many major roles: protection of outside agressions, temperature regulations, elimination of sebum excess and release of pheromones involved in territorial marking, social and sexual communication. The skin barrier is essential to protect the body from bacteria, yeasts, allergens and all other bad guys out there. It also retains moisture.

To be efficient, the skin barrier protection relies on 3 components which interact:

The mechanical skin barrier: basically cells and skin components acting like a ‘brick and mortar’ wall allowing to keep water in and offenders out.
The immunological skin barrier: cells and molecules that defends the body against offenders. As skin is an interface with the external environment, the immune system is very active.
The microbiological skin barrier: there are many microorganism that live on the skin surface (bacteria, yeasts, etc.). This balanced barrier protect from invasion of pathogen microorganisms.

This balance is fragile and deserves your care and protection. Whatever the colour or the thickness of his fur, all the dogs can be affected by a skin problem. When weakened by agressions, the skin barrier ecosystem is damaged and you can observe signs on your dog’s coat and skin.

A dry skin, a oily or flaky skin, hot spot, itchs, a colonisation of bacteria, overgrowth of yeasts can be symptoms of a defective skin barrier.As the largest organ of your dog’s body, the skin has its work cut out for it.

Working in conjunction with the coat, the skin provides a physical barrier to protect your dog’s internal organs from external threats. The skin also works with your dog’s immune system, helping to protect the body from allergens and infectious agents. It contains nerves that allow your dog to sense pressure, heat, cold and pain. Skin also helps regulate your pet’s body temperature and hydration.

The top layer of the skin, called the epidermis, is crucial to the role of skin as a barrier. Recent studies of humans and dogs with atopic dermatitis, a chronic allergic disease that leads to itching and secondary skin infections, reveal that defects in the epidermal barrier contribute to the disease, and protecting the barrier may be an important part of successful therapy.

The outermost layer of the epidermis is called the stratum corneum, and it’s the skin’s first line of defense, creating a physical barrier against external irritants.Under a special microscope, the stratum corneum looks like a brick wall, with cells representing the bricks and a matrix made of lipids and proteins serving as the mortar. Ceramides are an important part of these lipids because they provide flexibility, enabling this layer to stretch and bend.

A break in the barrier

For years, scientists believed that atopic dermatitis was a result of a genetic defect that caused dogs to have an allergic reaction to environmental allergens such as pollen and dust mites.

Newer studies reveal that genetic defects in skin lipids and proteins, including deficiencies in ceramides,^1,2 may contribute to microscopic breaks in the stratum corneum, even though the skin looks visibly normal. These defects may allow allergens to penetrate the skin and stimulate an immune response that leads to inflammation and itching.³

Why is this important?

Because traditional therapy for skin lesions included a combination of treatments, but the main therapy focused on calming the dog’s immune system. Now, treatments to help maintain the epidermal barrier may help bring dogs relief, too.

New skin therapies

New skin therapies to help support the stratum corneum, and thus the epidermal barrier, include topical formulations that include lipids such as ceramides, which may stimulate the skin to produce more lipids to help heal the barrier. There may also be a benefit to providing dogs with essential fatty acid supplements, especially omega-6, which can be incorporated into ceramides, either as supplements or as part of a balanced diet.

While improving epidermal barrier function shows promise, more research is needed. Dogs with atopic dermatitis will still need a combination of therapies which may include regular bathing, flea control, diet trials, infection control and immune system modulation. If you have questions about your dog’s sensitive skin, your veterinarian is your best source for information on all the new therapies.

Nutrition and Canine Skin Barrier

Importance of Nutrition in Canine Dermatology

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

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

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.

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.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.

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. 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.

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.

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.

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.

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.

How can I keep my dog’s skin and coat healthy?

Diet, diet, diet! A properly balanced diet of fats (including omega-3 fatty acids), digestible proteins, carbohydrates, vitamins, and minerals plays an essential role in maintaining skin and coat health. An ideal diet should be adjusted to suit your dog’s stage of life, state of health, and daily energy requirements.

Recent research has shown that adding omega-3 fatty acids, linoleic acid, and zinc in combination can improve coat gloss and reduce dander.

‍Omega-3 fatty acids

protect the skin and coat and promote a lustrous glow. Eicosapentaenoic acid in particular reduces inflammation. Sources of omega-3 fatty acids include fish oil, algal oil, and flaxseed.

Linoleic acid

is an omega-6 fatty acid found in corn, soy, flaxseed, and many nuts. Dandruff, dry skin, thin or discolored, increased shedding, and poor healing are all associated with low linoleic acid levels in the skin and diet.

Zinc

reduces water loss through the skin. It is especially important because of high cellular turnover rate caused by constant shedding. Pets with a zinc deficiency suffer from hair loss, skin infections, and a dull appearance.

Biotin and B vitamins

play important roles as cofactors in many of the body’s metabolic processes, including fat metabolism. This is important in the skin because biotin and B vitamins are involved in aiding linoleic acid function in the epidermis and dermis.

What role does grooming play in the appearance of my pet’s skin and coat?

All dogs benefit from regular grooming to remove loose hairs and dead skin cells, to keep the coat free of dirt, debris, and parasites, and to distribute natural skin oils along the hair shafts. Dogs with long, silky, or curly coats require daily brushing to keep their hair from becoming tangled or matted, especially around the ears, in the armpits, in the groin, and along the backs of the legs. Dogs with short coats may require less frequent brushing. However, daily brushing of any dog that sheds will cut down dramatically on the amount of loose hair and dander floating around your home.

Regardless of your dog’s coat type, you should inspect their coat regularly to ensure that no matts have developed. Following a romp outdoors, it’s always a good idea to search for burrs, twigs, and other foreign objects that may have become trapped in the coat and could potentially cause a secondary skin infection.

Regularly checking your dog’s coat and skin improves your chances of detecting any unusual lumps or bumps, ectoparasites such as fleas and ticks, or areas of sensitivity.

How often should I bathe my dog?

This depends on your dog’s type of coat, age, lifestyle, and overall health. Aside from puppies not yet house-trained, most dogs require bathing on an occasional basis when the coat becomes dirty or develops that characteristic doggy odor. Non-shedding breeds with no underlying medical condition typically benefit from a bath every four to eight weeks. Dogs with a heavy undercoat should receive a bath in the spring or fall during seasonal shedding. Some dogs with an underlying skin disease may benefit from more frequent bathing or from the use of a medicated shampoo or topical preparation as directed by your veterinarian.

You might also consider using waterless shampoo products or dog-friendly wipes for cleaning between baths. Wipes are good for cleaning paws and bums, and especially good for cleaning between the folds of our wrinkly-faced companions.

Dogs should be bathed only with a shampoo formulated for canine use. Human and canine skin differs not only in obvious respects, but also in terms of physiologic skin pH. Human skin is acidic with a pH below 5, whereas canine skin has a pH close to 7, which is neutral. Shampoos designed for human skin, including baby shampoos, will irritate your dog’s skin. For routine bathing, a moisturizing, hypoallergenic shampoo free from perfumes and fragrances is the best choice. Colloidal oatmeal-based shampoos are another great choice for most healthy pups. For optimal results, a conditioning product may also be applied afterward to restore moisture and minimize the development of dandruff following the bath.

Preserving a healthy skin barrier is crucial to the therapy and long-term maintenance of many of our patients suffering from atopic dermatitis or environmental allergies. There are several other multimodal therapy measures such as skin support diets, weekly medicated baths, application of topical formulations (gosh, do we love mousse preparations), or consideration of allergy testing and desensitization to identify and treat the cause of the allergies. However, allergies open up a whole new can of worms. We will be opening that can of worms in a separate post soon.

How do the skin and coat affect my dog’s overall health?

The skin and coat have several basic functions:

They are barriers protecting your dog from contaminants and environmental stressors.
‍The skin shields the body from pathogens.

A healthy coat serves as an insulating layer and regulates body temperature by moving hair follicles. Hairs can be brought together to conserve heat or separated to permit airflow.