Amino Acids and the Natural Moisturizing Factor

Filaggrin, an essential protein in skin barrier function, is gaining attention as a vital component of healthy skin. It serves a key role in the process of forming a protective layer in the stratum corneum, and helps keep water in and foreign organisms out. As aging cells move toward the stratum corneum, the cells clump proteins into granules, which are then filled with filaggrin. Afterward, a complex of keratin proteins and filaggrin is produced to protect the filaggrin from proteolytic breakdown. As old cells move toward the stratum corneum, enzymes break down this complex, causing the filaggrin to reside outside of corneocytes, and the keratin inside the corneocytes, Marino explained, noting, "When the moisture content of the skin is decreased, specific proteolytic enzymes in the stratum corneum are triggered to further break down filaggrin into free amino acids."

exCel Cosmeuticals, manufacturer of the patented AFA™ formulation based on the body’s natural acid amino acids, added, "Filaggrin is metabolized in the epidermis into several acidic amino acids and these amino acids are the primary agents responsible for the skin’s ability to retain moisture."

Research suggests a lack of filaggrin can result in conditions such as dry skin (ichthyosis vulgaris) and atopic eczema, a chronic inflammatory skin disease characterized by a defective skin barrier function that affects 10 to 20 percent of children and 1 to 3 percent of adults in industrialized countries.¹ University of Dundee, Scotland researchers, led by Irwin Mclean, found a defect in the filaggrin gene can cause dry skin, eczema, eczema-associated asthma and other allergies.² Additionally, researchers from the National Jewish Medical and Research Center, Denver, investigated whether reduced filaggrin expression already existed in patients with atopic dermatitis (AD), or if the filaggrin was modulated as a response to atopic inflammation. They concluded after evaluating 69 subjects that patients with AD have an acquired defect in filaggrin expression that can be modulated by the atopic inflammatory response.³

Current topical solutions for these conditions consist of emollients and ointments used to keep the skin moist, as well as anti-inflammatories to treat inflammation. New cosmeceutical ingredients also hold promise in helping ease the symptoms or lower the risk of eczema. For example, a study published in the Journal of Allergy and Clinical Immunology found mothers taking probiotic supplementation during pregnancy and providing young infants with Lactobacillus reuteri after birth could reduce the incidence of eczema.⁴ Another study suggested supplementation with the omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) may offer bioactive benefits for atopic eczema sufferers.⁵

THE NATURAL MOISTURIZING FACTOR

In the course of the last few decades, a group of compounds, consisting of free amino acids (some of which are broken down filaggrins), lactic acid, urea and salts, have been identified as key nutrients in attracting and retaining water, which are responsible for maintaining a healthy balance for moist and pliable skin. These components, as well as ingredients that mimic their actions, are often referred to as the natural moisturizing factor (NMF). "The natural moisturizing factor is an integral component of the horny layer of the skin," said Bruce Gesslein, technical manager, Ajinomoto USA Inc., Specialty Chemicals Division. "The horny layer is comprised of about 30 percent NMF, 10 percent lipids and 60 percent PCA [pyrrolidone carboxylic acid, an amino acid-derived component]. The NMF is responsible for maintaining moisture and suppleness of the skin. It has been shown that in unhealthy and damaged skin, the NMF is depleted to an extent."

NMF components absorb water from outside elements and combine the liquid with its own water content, keeping the outer layer of the stratum corneum hydrated. Interestingly, because these compounds are water soluble, overhydration can make the skin drier. In a study published in the Journal of Investigative Dermatology, researchers investigated the specific influences of NMF components other than amino acids and found seasonal changes in the physical properties of the stratum corneum from summer to winter were accompanied by significant decreases in the levels of lactate, potassium, sodium and chloride.⁶ Lactate and potassium were the two components found to correlate significantly with the state of hydration, stiffness and pH level. Moreover, potassium lactate restored the stratum corneum hydration state decreased by extraction of NMF, suggesting lactate and potassium may play roles in maintaining the physical properties of the stratum corneum.

When the NMF content is reduced, a variety of complications can occur, ranging from tough skin and flaking to wrinkles. A prolonged stratum corneum malfunction can weaken the skin’s intercellular matrix.^7,8 A variety of constituents such as amino acids, proteins, ceramides, hyaluronic acid, fatty acids, linoleic acid are just a few elements that work in keeping the skin moisturized.

WATER RETENTION

Amino acids are fundamental constituents of the 100,000 different proteins found in the human body. The sequence of amino acids determines the unique properties of each protein. If one essential amino acid is missing, the protein cannot be formed. Each protein is composed of different quantities of amino acids, which include alanine, arginine, asparagine, aspartic acid, cysteine, cystine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine. Some of these amino acids, called non-essential, can be synthesized by the body; essential amino acids must be obtained from the diet. According to Ajinomoto, about half of the NMF in the skin is made up of amino acids and PCA derived from glutamate, another amino acid. "Skeletal muscles, organs, skin and hair are comprised of these proteins," Gesslein added. "They also occur in the free state in the skin where they act as moisturizers, enter into metabolic cycles and are essential for health and life."

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