It is known in the literature that phenolic compounds in their native form are unstable because of their phenolic functions that can be oxidised by the action of various environmental agents, such as oxygen, light, and certain metal elements.
Under the catalytic effect of sunlight, homolytic cleavage of the OH bond gives rise to oxygen free radicals hydroperoxide (OOH) and alkoxide (RO). These radical species are highly reactive and are involved in various pathologies. Because of their anti-radical properties, phenolic compounds are useful in the preventive or curative treatment of diseases related to radical species such as cancer,1,2 ageing, neurological disorders3 (Alzheimer, Parkinson’s) metabolic disorders4 (diabetes, obesity). Degradation of polyphenols may also occur under the effect of pH. Under basic conditions, the acidic character of phenolic function facilitates the exchange of protons by heterolytic cleavage of the OH bond. It then forms a phenolate anion which is in equilibrium with the quinone form. In the case of proanthocyanidins in an acidic environment, there is a depolymerisation by interflavan bond rupture leading to the formation of coloured derivatives (anthocyanins).5 In a basic environment it may occur, in addition to proton exchange, the opening of the pyran ring. It then forms a phenolate anion in equilibrium with the quinone form, which can undergo a skeletal rearrangement to yield typical structures, such as catechinic acid or epimerisation at carbon C2 (conversion of catechin to epicatechin, for example). This high sensitivity of polyphenols leads to a set of derivatives most often coloured with intensities that change over time and become incompatible with some applications such as cosmetics. Many publications6–11 showed remarkable anti-radical properties of catechic polyphenols that far exceed those of conventional antioxidants such as vitamin E and vitamin C. However, in their native form, these phenols are soluble in water, oxidisable, and to a small degree fat soluble. Thus they are difficult to use in cosmetics by topical application. When these functions are protected as phenolic esters or ethers, the degradation mentioned above is completely inhibited (unable to proton exchange). A judicious choice of an acylating agent enables (in the case of stabilisation by esterification) getting far more lipophilic compounds than hydrophilic compounds.
Phenolic compound stabilisation
It is within this framework that the company Berkem has developed a technique for stabilisation of phenolic compounds to take advantage of their many biological properties. The method used is described and protected by French patent FR2723943 or the American patent US5808119. The technique is to protect the phenol functions as fatty acid esters of long chain hydrocarbons, saturated or unsaturated. The use of fatty acids enables the formulator to obtain a product consistency that is oily-soluble, thus usable in cosmetics. Indeed, oiliness facilitates penetration through phospholipid membranes, an essential factor for good bioavailability. Once in the skin cells, esterified polyphenols are hydrolysed, like lipid compounds by esterases12,13 to release the active polyphenol (antioxidant, antiinflammatory, antimicrobial) and fatty acids that may have interesting properties such as softeners or antimicrobial (undecylenic acid). According to the literature,14–16 the relationship structure and activity of antioxidant phenolic compounds was determined. It appears that the main prerequisite is the presence of free aromatic hydroxyl (OH) (not masked as esters or ethers). Other studies17 show that the astringency of polyphenols and specifically proanthocyanidins derives from their affinity to salivary proteins. Several factors may be mentioned: hydrogen bonds between the phenolic hydroxyl (OH) and nucleophilic sites (nitrogen and sulphur) of proteins are involved. This complexion has a negative effect on the absorption and on the digestibility of macromolecules (e.g. proteins). The esterification of aromatic hydroxyl removes these disadvantages. However, one can logically ask whether the biological properties as antioxidant polyphenols are maintained after esterification.
Antioxidant activity study
To answer this question Berkem conducted a study on the determination of antioxidant activity of various berkemyol (procyanidins stabilised by esterification). The conditions for this study must be close to actual use in humans. The topical application on human skin explants from the abdominoplasty kept alive was chosen as the best model. Free radicals were induced by ultraviolet radiation (UV A + B). It is known that oxygen free radicals cause damage to various cellular components, particularly membrane lipids. These are processed into many derivatives including hydroperoxides malonyldialdehyde (MDA), 4-hydrononenal (4-HNE). The determination of MDA levels in tissues is a good indicator of the production of oxygen free radicals and of the peroxidation of membrane lipids. The comparison of MDA levels between those treated and untreated gives information on the anti-lipoperoxidant action of product used during treatment. The results obtained in this study are illustrated in Figure 1. We note with these results that stabilised polyphenols have a very good anti-lipoperoxidant activity. This action is higher than the antioxidant vitamin E, reference in cosmetology. The radicalscavenging activity is related to the presence of free phenolic hydroxyl (OH) as mentioned previously; this study proves undeniably that the stabilised polyphenols cross the skin barrier and undergo hydrolysis by esterases. The study on human skin explants enables us to consider the stabilisation process used by Berkem and called Phytovector as a means of delivery for the polyphenols and increasing their bioavailability while maintaining the biological properties such as the antilipoperoxidant action (antioxidant). In this way we prove that this technology has significant advantages over other methods which advocate that to maintain the antioxidant activity we must keep some free aromatic hydroxyl (OH) functions. We know the important parts of these free aromatics are hydroxyl in the low stability (easily oxidisable), low lipophilicity, high astringency of phenolic compounds. Skin, to fulfill its primary role of ensuring the protection and the exchanges between the organism with the external environment is composed of three layered tissues: the epidermis (outer), dermis (middle) and hypodermis (inner). The epidermis, or epithelium, is composed predominantly of keratinocytes (80%), melanocytes (melanin synthesis), Langerhans cells (immunity) and Merkel cells (sensory receptor). The main role of the epidermis is the body’s protection against external aggressions. It is a continuously renewing tissue, and is avascular. The transport of substances goes through the epidermis by diffusion. The dermis, connective tissue, plays a supportive role through its dense nutrient vascularisation. It contains fibroblasts and extracellular matrix composed of collagen fibres, elastic fibres, proteoglycans and glycosaminoglycans (hyaluronan, chondroitin sulphate), structural glycoproteins (laminin, fibrillin, fibronectin). The hypodermis consists primarily of adipose tissue. Its main role is to ensure the energy reserve (fat accumulation). In the extracellular matrix, collagen provides the mechanical strength of skin tissue, elastin is responsible for the elasticity of skin tissue, glycosaminoglycans provide hydration, structure glycoproteins ensure the establishment and cohesion of tissues. With ageing, the turnover rate of most macromolecular components of the extracellular matrix is greatly reduced. And the skin loses its firmness and elasticity. We then observe the appearance of unsightly signs such as wrinkles, and dryness of the skin. To enable maintaining of the skin in its normal condition, stimulation of the synthesis of these macromolecules of the extracellular matrix skin is required. Having previously proved that berkemyol could cross the skin barrier and undergo the action of esterases, we investigated their action on some constituents of the extracellular matrix with an ex vivo study on human skin explants maintained in survival. For each test product, three concentrations (0.1%, 0.25% and 0.5%) were prepared in liquid paraffin fluid. The solutions were applied topically on skin explants every day for eight days. After eight days, an immunolabelling and a specific staining of the explants was then performed. The activity was assessed by morphological observation under an optical microscope and image analysis.
Action on collagen I
The potentilla and pine bark active at a concentration of 0.5% induced a respective increase of collagen I in the papillary dermis of 12% and 20% (Fig. 2).
Action on collagen III
The potentilla active at concentration of 0.5% induces an increase of 33% of collagen III in the papillary dermis. The pine bark active at concentrations of 0.5% induces an increase of 30% collagen III in the papillary dermis (Fig. 3).
Action on collagen IV
The green tea active at concentrations of 0.1% and 0.25% respectively induces an increase of 18% and 40% of collagen IV in the dermo-epidermal junction. The potentilla concentration of 0.1% induces an increase of 26% of collagen IV in the dermoepidermal junction (Fig. 4).
Action on fibriline-1
The green tea active at concentrations of 0.25% and 0.5% induces a respective increase of 13% and 21% of the fibriline-1 in the dermo-epidermal junction (Fig. 5).
Action on glycosaminoglycans
The green tea active at a concentration of 0.25% induces an increase in glycosaminoglycans (GAGs) along the dermo-epidermal junction (DEJ). At a concentration of 0.1% potentilla active induced a moderate increase of GAGs along the DEJ and a net increase of GAGs in the papillary dermis. At concentrations of 0.1% and 0.25% the pine bark actives induces a marked increase of GAGs in the papillary dermis (Fig. 6).
Conclusion
The results of this study show that berkemyol, in addition to being powerful antioxidants are involved in active synthesis of macromolecules of the extracellular matrix. As a matter of fact, by stimulating the synthesis of collagen, fibrillin-1, the berkemyol help to maintain the suppleness of the skin, facilitate healing, and help to fight against the visible signs of premature skin ageing. Glycosaminoglycans (GAG), formerly known as “mucopolysaccharide acids” are polysaccharides having a high water retaining capacity. Their main role is to maintain hydration of the skin. By stimulating the synthesis of GAGs berkemyols contribute to the fight against skin dryness one of visible signs of ageing. We can conclude that berkemyol obtained by the phytovector technology generate under the action of esterases the polyphenol enabling the exploitation of the multiple biological properties of polyphenols including antioxidant, anti-glycation, antimicrobial, vascular protective, antiageing properties.
References
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