German biochemists Karl Meyer and John Palmer isolated a glycosaminoglycan (GAG) for the first time from a bovine eye and claimed it as “hyaluronic acid” in 1934. The term hyaluronan, frequently used to describe hyaluronic acid, was introduced in 1986 to align with polysaccharide nomenclature identifying the various presentations of HA.1 Other names used to describe HA products include: glycosaminoglycan, hyaluronique, glycoaminoglycane, hyaluran, sodium hyaluronate and hylan.
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German biochemists Karl Meyer and John Palmer isolated a glycosaminoglycan (GAG) for the first time from a bovine eye and claimed it as “hyaluronic acid” in 1934. The term hyaluronan, frequently used to describe hyaluronic acid, was introduced in 1986 to align with polysaccharide nomenclature identifying the various presentations of HA.1 Other names used to describe HA products include: glycosaminoglycan, hyaluronique, glycoaminoglycane, hyaluran, sodium hyaluronate and hylan.
HA Function
Biologically, the most natural form of hyaluronic acid occurs in the human body and is found throughout tissues and fluids including the eyes, cartilage, synovial fluid and joint junctures. The average person has roughly 15g of native HA in the body, one-third of which is degraded and re-synthesized every day. Hyaluronic acid is a major structural component of the extracellular matrix and involved in water retention, maintenance of the extracellular spaces, storage, diffusion of cell growth factors and nutrients. It is also involved in the structure and organization as a key macromolecule of the extracellular matrix and appears in concentration during the activation of rapid tissue proliferation, regeneration and repair. HA is also important in ion solute transport and integral to the spacing of collagen fibrils. More than 50% of the HA of the body is present in skin.2
Skin Hydration and HA
The nature of native HA is to instinctively perform hydration tasks, as the large volume of water associated with HA is said to be a mechanism supporting the process for maintaining the normal hydration of the skin. With regard to skin physiology, the function of the skin barrier is in part due to the organelle lamellar bodies in the epidermis that play a crucial role in the permeability and the storage of lipids, lipid metabolizing enzymes, enzyme inhibitors and antimicrobial peptides. The lamellar bodies also contain enzymes that fuse with membranes of mature keratinocytes and modify various lipids. It is important to note that diffusion of aqueous materials through the epidermis is obstructed by lipids that are synthesized by keratinocytes in the stratum granulosum. The area below the stratum granulosum may receive water from the moisture rich dermis; however, the water contained in this area cannot penetrate below the lipid rich stratum granulosum.
The hydration level of the skin relies on the HA bound water in the dermis and in the vital area of the epidermis, while the maintenance of skin hydration depends on the stratum granulosum. The HA content of the dermis is said to be significantly higher than of the epidermis, and the papillary dermis has greater levels of HA than the reticular dermis. Native HA may be found in the stratum corneum as a high molecular weight polysaccharide and is changed into a low molecular weight in the presence of inflammation or tissue injury. Low molecular weight HA fragments are biologically active by their ability to trigger built-in immune defense mechanisms and promote cytokine production. The moist environment provided by low molecular weight HA’s hydrophilic nature allows for effects on cellular behavior. High molecular weight HA permits tissue hydration contributing to the osmotic balance (the fluid balance of electrolytes and salts in body fluids) and stabilizes the extra cellular matrix structure. HA interacts with different receptor binding proteins, and its molecular weight can influence the receptor potential or its uptake by the cells. The general hydration effect of the skin may also optimize dermal absorption of active ingredients and can assist their retention within the moisturized epidermal layers.
HA Size and Penetration
The barrier function of the skin is principally attributed to the stratum corneum. Only small molecules, usually less than 500 Da and lipophilic compounds can penetrate the skin barrier. Hyaluronic acid is a non-sulfated glycosaminoglycan with a molecular weight of over 1,000 kDa.
HA applied topically does not permeate through the skin because it is a water-soluble macromolecule and remains on the skin surface and functions as a moisture agent. With a low molecular weight of 20-300 kDa, it passes through the stratum corneum in contrast of the impermeability of high molecular weight HA (1000-1400 kDa).3
The permeation of any HA formulation is subject to specific binding interactions including local environment, temperature, humidity, ionic strength, the presence of proteins and lipids, product composition and delivery system. Likewise, the efficacy and performance of a hyaluronic formula is also subject to the composition and quality of companion ingredients. Commercial HA products are selected by molecular weight for various applications, which is an important quality parameter in manufacturing. The fermentation of a HA product is a mixture of HAs with different molecular weights. It should be noted that creating a uniform molecular weight control in HA is a definitive chemical challenge.
Forms of HA
Native HA has a low resistance towards enzymatic digestion and has a high rate of turnover, which limits the efficacy of the native HA to be used topically. Most forms of pure hyaluronic acid molecules are too large to penetrate deeply into the skin to be utilized. Therefore, sodium hyaluronate, hydrolyzed hyaluronic acid or sodium acetylated hyaluronate are typically featured in HA skin care formulas.4 These are usually synthetically derived, as it is easier to control the concentration and size of the molecule for a greater uniformity and predictability. This is the reasoning why chemical modifications have a stronger and necessary binding capacity to the skin as non-modified HA.
Newer progressive strategies of these modifications suggest that the formulas should be biocompatible and biodegradable, as well as placing an emphasis on hydrating and moisturizing properties. Many formulas now cross-link materials for this purpose rather than using the native HA as often presumed. Sodium hyaluronate is frequently derived from wheat fermentation with specific bacteria, then purified
and precipitated.
HA Molecular Weight
HA molecular weight influences its penetration into the skin and its biological activity. When in contact with water, HA has the capacity to augment its volume, offering the potential effect of lessening the appearance of wrinkles by filling the cellular spaces forming a viscid gel matrix.
A high molecular weight of HA does not permit it to penetrate the deeper layers of the skin, restricting its benefits to topical effects.
Low molecular weight HA (LMW-HA) has the ability to enhance the level of moisture of the skin and expedite regeneration. High molecular weight HA (HMW-HA) forms a viscoelastic film when applied onto the skin and has a moisturizing effect. The main action of the HMW-HA polymer is film forming and it reduces evaporation of water from the skin, thus possessing an occlusive effect. Additionally, HMW-HA, medium molecular weight HA (MMW-HA) and LMW-HA have hygroscopic properties that justify the ability to maintain skin hydration.5
High-molecular HA has an average molar mass (molecular weight) of 2,000,000 Dalton. For comparison, water has a molar mass of 18. Low-molecular HA has an average molar mass (molecular weight) of about 20,000 up to 50,000 Dalton.
In terms of the HA molecular weight, the MW counts are only significant if their particle size distribution also is known. This is due to the fact that the average values of substances by their very nature, are composed of smaller and larger molecules. This means that the MW will vary greatly within a formula even though the HA may be a particular count. The particle size distribution will vary depending on what other ingredients that are contained in the formula.6
A potentially challenging consideration of topically applied HA preparations has been that of its molecules. They are 3,000 nm in diameter, whereas the intercellular space is only 15 to 50 nm. This makes it impossible for conventionally produced HA to penetrate into deep layers of the dermis.7 Hyaluronic acid biosynthesis sources include: microbial formulations such as Escherichia coli and Bacillus subtilis, bacteria formulations including Streptococcus genus (uberis, equisimilis, zooepidermicus, pyogenes, equi), Pasteurella multocid, Corynebacterium glutamicum, from the green algae chlorella purposely infected by the Chlorovirus saccharomycetes (Cryptococcus neoformans) and from Molluscan shellfish, bivalve mollusc Mytilus galloprovincialis.8
Alternative and Botanical Humectant Agents
Anti-aging research has long supported the use of natural botanical products derived from plants sources after much scientific validation. Constituents such as phytomolecules, ginsenoside, curcumin, epicatechin, gallic acid, hydroxycinnamic acids, hydroxybenzoic acids, etc. act as free radical scavengers, prevent transepidermal water loss and contribute to help hydrate, soothe and protect the skin. Although the methodology of treating aging skin continues to advance technologically, herbal products including botanicals are quite relevant, especially in novel hybrid formulas combining them with molecular techniques. The hydrators, humectants and film-forming substances discussed here have been used in hybrid technologies for their similarity to hyaluronic acid to hydrate, sooth and protect the skin.
1. Aloe Vera
Aloe barbadensis miller belongs to Asphodelaceae (Liliaceae) species and contains 75 potentially active constituents including vitamins, enzymes, minerals, sugars, lignin, saponins, salicylic acids and amino acids. Aloe barbadensis is rich in mucopolysaccharides that help in binding moisture into the skin and decreases the appearance of wrinkles and erythema. Aloe barbadensis precipitate of high quality offers a cohesive effect on the superficial flaking of epidermal cells, smoothing and softening the skin. Aloe barbadensis stimulates the fibroblast encouraging collagen and elastin fibers and its profound moisturizing effects have also been studied in the treatment of dry skin associated with occupational exposure.
One study showed that aloe formulations with higher concentrations increased the water content of the stratum corneum after a single application.9 When various formulations were applied twice daily for a period of two weeks, all the formulations had the same effect. However, the transepidermal water loss was not changed by inclusion of the Aloe barbadensis in the formulations compared to the vehicle used in the formulations. It was proposed that the Aloe barbadensis containing products improved skin hydration possibly by means of a humectant mechanism.
Aloe barbadensis contains the substance glucomannan (polysaccharide) and gibberellin (growth hormone) that interact with growth factor receptors on the fibroblast and significantly increases collagen synthesis after the use of both topical and oral aloe vera. In wound healing, Aloe barbadensis not only increased collagen content of the wound, but also changed collagen composition and increased the degree of collagen cross-linking. An increased synthesis of hyaluronic acid and dermatan sulfate in the granulation tissue occurs in the healing of a wound.10,11 Another study showed that aloe sterols stimulated collagen and HA production by human dermal fibroblasts and that aloe sterols reduced facial wrinkles in women.12
2. Astragalus Membranaceus (Chinese Huangdi)
Astragalus membranaceus (Huangdi) is a major herb that has been commonly used in many formulations in the practice of traditional Chinese medicine (TCM) to treat a wide variety of diseases and disorders in China for more than 2,000 years. The major components of Astragalus membranaceus are polysaccharides, flavonoids and saponins. Pharmacological research indicates that the extract component of Astragalus membranaceus can increase telomerase activity, and it is an antioxidant and anti-inflammatory. Astragalus membranaceus is comprised of saponin astragaloside IV (AST), which has been shown to decrease MMP-1 activity caused by UV damage. Astragalus membranaceus has been found to increase the content of hyaluronic acid by increasing hyaluronan synthase-3 and hyaluronan synthase-2, the enzymes responsible for hyaluronic acid synthesis in the skin. Therefore, Astragalus membranaceus may have the ability to promote natural HA synthesis within the body leading to fuller more hydrated skin through the aging process.13,14
3. Beta-glucan
Beta-glucan is a glucose polysaccharide that can be found in the cell wall of baker’s yeast, plant cellulose, bran, oats, fungi, barley and mushrooms. The most biologically active are isolated from cell membranes of baker’s yeast (Saccharomyces cerevisiae). Long-term use of glucan shows reduction of wrinkle depth, height and overall roughness, likely caused by stimulation of fibroblasts and increased production of collagen. One study details that despite its large molecular size, beta-glucan can deeply permeate into the epidermis and dermis. A clinical study of 27 subjects was performed to evaluate the effects of beta-glucan on facial fine-lines and wrinkles. After eight weeks of treatment, digital image analysis of silicone replicas indicated a significant reduction of wrinkle depth and height, and overall roughness.15,16
4. Blue Agave
Agave produces a particular class of secondary metabolites called saponins. The saponin from the blue agave leaves work by stimulating the natural internal synthesis of hyaluronic acid. Saponins have been proven as one of the most effective substances for stimulating natural hyaluronic acid production in the skin. It stimulates fibroblasts that are responsible for dermal hyaluronic acid production to boost the synthesis of new HA. According to a study regarding blue agave, the ingredient increased expression of hyaluronan synthase (HAS2) synthesis enzyme, which further activates the natural mechanism of hyaluronic acid production. In vitro studies showed a 237% increase in hyaluronic acid synthesis.17
5. Cassia Angustifolia (Senna)
Cassia angustifolia—known as senna, Cassia senna or Alexandrian senna—is a native plant from India that has been used in Ayurveda for over 2,000 years. In cosmetic manufacture, it is primarily used as a skin conditioning agent because of its high content of polysaccharides. Research has shown that isolations of senna include a beta glycan fraction and galactomannan from the seeds of the senna plant, which is laden with polysaccharides. Galactomannan has been shown to mimic hyaluronic acid. Studies have demonstrated cassia to effectively repair dryness, provide long lasting moisture, exhibit film-forming capacities and provide humectant properties.18
6. Chitosan Ascorbate
Chitosan ascorbic acid is a salt of chitosan, a polysaccharide derived from the outer skeleton of crustaceans. Chitosan ascorbate functions as an antioxidant, skin conditioner and film-forming agent. Chitosan can act as a carrier of other active ingredients due to its technological properties. It is soluble in acid aqueous solutions and can easily produce different conformations such as micro, nano and milli particles, and films that benefit the skin. As a stabilized form of vitamin C, it offers the antioxidant and anti-aging properties of ascorbic acid. The chemical structure of one of its main components, chitin, closely resembles that of mucopolysaccharides (i.e. hyaluronic acid) substances found within human skin tissue. Chitosan ascorbate hydrates by supplying water to the skin, avoiding dehydration through water retention, and providing a protective film on the epidermis. Its protective film-forming capabilities help fix other active ingredients contained in a cosmetic solution to the skin, heightening their effectiveness. Studies have also shown chitosan ascorbate to create a protective film, encourage wound healing and expedite tissue regeneration.19,20
7. Edelweiss
Leontopodium alpinum (edelweiss) is from the family Asteraceae, which is a wildflower that grows in rocky limestone places that are familiar and native to the Swiss Alps. Leontopodium alpinum (edelweiss) callus culture extract (LACCE) showed strong antioxidant activity in response to UVB treatment, suppressing inflammation and wrinkling, as well as increasing moisturizing activity. A study showing consistent application of LACCE on the face and skin tissues improved anti-periorbital wrinkles, skin elasticity, dermal density and skin thickness. Sequencing results showed at least 16.56% of human genes were expressed in keratinocyte cells.21
8. Glycerin
Glycerin is a humectant and emollient that has been used for decades in skin care. Plant glycerin differs from sodium hyaluronate regarding its ability to attract and retain water to a much lesser degree. Respectively, sodium hyaluronate offers thousands of potential water capacity vs. glycerin at 170 times water capacity. Glycerin has a naturally lower molecular weight, giving it a greater potential to provide deeper hydration. In contrast to the LMW HA, glycerin offers this hydration without the potential for the activation of inflammation (unless an allergy potential exists). In vitro studies in a study have shown glycerin to prevent crystallization of a stratum corneum model lipid mixture at low room humidity. The study questioned whether this may affect the skin’s barrier function during repeated application of glycerin in a cream base to normal skin. Considered was the influence of a cream containing 20%, glycerin compared to a placebo cream in a bilateral, double-blind study on 17 volunteers. The effect was evaluated as influence on hydration with a corneometer and on skin barrier function. Skin barrier function was assessed as permeability to water (TEWL) with an evaporimeter and as sensitivity to an irritating surfactant by measuring the biological response (measured as TEWL and skin blood flow). Ten days of treatment to normal skin with 20% glycerin significantly increased skin corneometer values, indicating an increased hydration.22
9. Polyglumatic Acid
The scientific name for polyglumatic acid (PGA) is natto gum and it is classified as a film-forming agent. The fermented soybean mucilage consists of a mixture of PGA and fructan produced by Bacillus natto. When applied topically, gamma polyglutamic acid is a remarkably potent hydrating compound that is said to be 10 times more hydrating than hyaluronic acid, and far more elastic than collagen. It is 100% natural, biodegradable and non-toxic. Qualities of PGA include the ability to form a smooth, elastic, self-moisturizing and soft film on the skin, resulting in improved sensory perception and protection of the outer layer of skin. It is an excellent hydrophilic humectant and can increase the production of such natural moisturizing factors as pyrrolidone carboxylic acid (PCA), lactic acid and urocanic acid, as compared to hyaluronic acid and soluble collagen. Products containing PGA reinforce the skin’s support structure to energize cells, stimulating the production of lipids and renewal of the epidermis. It has been shown to replenish and nourish the skin, leaving it smoother and plumper. It also is non-toxic to humans, natural and environmentally friendly.23,24
10. Snow Mushroom
The hydration capacity of Tremella fuciformis (snow mushroom) is due to the nature of the polysaccharides it contains, as well as high amounts of carbohydrates, proteins, and vitamins and a variety of amino acids. In addition, the T. fuciformis polysaccharide, when coated on the skin, can form a transparent film that is able to improve its water retention rate. This results in an anti-wrinkle and natural moisturizing material, which can be used as a natural moisturizer to relieve skin dehydration, repair the skin barrier and maintain skin health. Tremella extract holds a molecular weight of 1M Da and contains sugar constituents mannose, xylose, and glucuronic acid, which is a major component of hyaluronic acid.
Tremella polysaccharides are cost effective compared to traditional humectant hyaluronic acid. The moisturizing effect of products with 0.05% tremella polysaccharides is faired better than products with 0.02% hyaluronic acid, but the cost is only 14% of hyaluronic acid.25,26
11. Sodium PCA
Sodium PCA is a naturally occurring hygroscopic, hydrating agent and humectant derived from naturally occurring ingredients such as plants, fruits and oils. Sodium PCA is the sodium salt form of pyroglutamic acid, which is also known as the amino acid proline. PCA is found in all living cells and can be extracted from ingredients such as coconut oil and seaweeds. While most of sodium PCA used is synthetically formulated (salt of pyrrolidone carbonic acid), it can also be extracted from these plant-based sources and fermented to create a plant-derived form of the ingredient. PCA is also created through the breakdown of the protein filaggrin within corneocytes. Sodium PCA forms about 12% of the skin’s natural moisturizing factor (NMF). Sodium PCA aims to improve the appearance of dehydrated, aged or disrupted skin, similarly as hyaluronic acid with the exception that PCA can hold water up to 250 times its weight, and 1.5 times better than glycerin.27,28
12. Xylitol
Xylitol is found naturally in various berries, corn husks, oats and mushrooms. Xylitol is used in cosmetics and personal care products as a humectant. It is thought to help the skin retain its natural moisture and boost levels of hyaluronic acid, a natural lubricant that assists in collagen production. Xylitol is also thought to improve the skin’s barrier function and increase ceramide synthesis. A study regarding glycerol (glycerin) and xylitol used together to hydrate the skin, showed an improved barrier function over a short period. The study intended to illustrate the effects of glycerol and xylitol on the physiological properties and morphology of the skin after longer-term application. The product was applied twice daily with a formulation containing glycerol (5%) and xylitol (5%) for 14 days to 12 volunteers with dry skin. TEWL, hydration and biomechanical properties of the skin were monitored. Histology and immunohistochemistry for filaggrin and matrix metalloproteinase-1 (MMP-1) were evaluated. The data showed an increase of skin hydration and protein quantity of filaggrin, decrease of TEWL and improved biomechanical properties of the skin, but no change to the protein expression of MMP-1. 29,30
The Quest Continues
The global hyaluronic acid market size is expected to reach an astounding USD 16.6 billion by 2027.31 The global increase in population also gives rise to an encouraging demand for anti-aging cosmetic and aesthetic treatments with variations of hyaluronic acid products and of course anti-aging cosmeceuticals. As this market expands, the exciting potential for new and innovative hyaluronic acid product development will continue to span our industry with ingenuity, and the integrative technologies ever expanding the quest for the ultimate skin quench.
Erin Madigan-Fleck, N.M.D., LEI, LMC, is a licensed esthetic instructor and esthetician with over 30 years of experience in the esthetic and wellness industries. She is a nationally certified natural health professional and holds a doctorate degree in naturopathic medicine. Madigan-Fleck can be reached at [email protected].
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