22 SKIN CARE Retinyl esters, such as retinyl acetate and
palmitate, are commonly used in cosmeceuticals. They are very stable but first they need to be converted to retinol by cleavage of the ester bond, and in the subsequent stage into retinoic acid. It results in decreased effectiveness of anti-wrinkle properties (smaller increase in the epidermal thickness) as compared to retinol and retinoic acid.27 Adapalene is a naphthalenecarboxylic acid
derivative with a retinoid-like activity. As a result of intracellular association with nuclear receptors of retinoic acid, it changes gene expression and mRNA synthesis. It is a strong modulator of keratinisation of hair follicle cells, moreover, it modifies keratinocyte metabolism, increases proliferation, and thus exerts a keratolytic effect.21 Tazarotene, approved by the US Food &
Drug Administration, is a synthetic retinoid (prodrug). It is applied in topical treatment of plaque psoriasis and acne vulgaris (AV). Tazarotene is also used in adjunctive treatment of specific clinical manifestations of chronically photodamaged skin (hyperpigmentation and hypopigmentation, as well as facial fine wrinkling and benign facial lentigines). Topical tazarotene is used in concentration of 0.05% to 0.1%.28 There are numerous publications on
efficacy of various derivatives of vitamin A used in treatment of juvenile acne, AV and other types of acne as well as in treatment of diseases related to keratosis disorders, the so-called ichthyosis and psoriasis.4
There
are reports describing the effects of skin care preparations containing a maximum 0.3% of retinol on the skin condition. The most recent scientific articles on retinol describe the combination of 4% hydroquinone with 1% retinol in a 24-week therapy of the skin with sun damage (photoageing) and melasma28 and combinations of lyophilised retinoic acid and hydroquinone used in treatment of melasma. The lyophilised form of the acid is used to increase penetration efficiency in the case of a sensitive skin.29 Scientists from the Johnson & Johnson
Skin Research Centre reported that a stabilised form of retinol stimulated the synthesis of hyaluronic acid in the skin and influenced the expression of genes stimulating the synthesis of macromolecules. Retinol in the form of retinyl palmitate, retinal and β-carotene is most commonly used in cosmetics.30,31 Recent studies by Kim et al. focus on
the low stability of retinol in cosmetic formulas (due to its sensitivity to light, temperature, etc.). They analysed triple encapsulated emulsions with retinol containing polycaprolactone, lecithin and silica and five biomimetic O/W cosmetic emulsions in order to find solutions against the decomposition of retinol. The results confirmed that retinol stability depends not only on the temperature, but also on the type of substrate used and the method of emulsion preparation.
Wound healing Wound healing is outside the scope of a cosmetic product but I think that it is
PERSONAL CARE October 2021
important to cover an old publication that is referred to in literature. Vitamin A deficiency is associated with impaired immune function and delayed wound healing. The effect of cod liver oil delivered locally and orally on the rate of wound healing was investigated in vitamin A-deficient and normal rats.32
In
the former, wounds treated with cod liver oil healed more quickly than untreated wounds; oral administration also accelerated wound healing in deficient animals, though to a lesser extent than topically applied cod liver oil. In vitamin A-replete rats, cod liver oil had no effect on the rate of wound healing. While it was not specifically determined that the vitamin A in cod liver oil was responsible for the accelerated healing in deficient animals, the authors demonstrated that linseed oil, rich in essential fatty acids, had no effect on the rate of wound healing in either scenario.33
Conclusion Skin is a major retinoid-responsive tissue and vitamin A metabolites have been in use for decades for the treatment of various skin conditions, including AV and photoageing. Topical tretinoin penetrates the skin layers without reaching the systemic circulation. A very common side effect of topical tretinoin is a skin irritation known as ‘retinoid dermatitis’. Treatment with lower tretinoin doses or other retinoid metabolites can achieve similar skin changes with less irritation but require a longer exposure time. Long-term (at least six months), continuous
exposure to topical 0.05% tretinoin results in significant improvement in clinical signs of photoageing, namely fine wrinkling, roughness and hyperpigmentation. With continued
application, clinical improvements are maintained while histological changes in the epidermis and dermis are more variable. In general, it is thought that clinical improvement to photodamaged skin is a consequence of increased dermal collagen synthesis induced by tretinoin. Topical tretinoin is considered a very safe and effective treatment for mild to moderate acne, while oral isotretinoin is used to treat severe cases of acne that are resistant to topical therapies; both therapies require doctor’s oversight. Retinol and its active metabolites, such as
retinal, tretinoin, isotretinoin and alitretinoin, belong to a group of first-generation retinoids. Retinol has the ability to effectively penetrate the stratum corneum, thanks to the lipophilic nature of retinoids. Age, cellular metabolism, cardiovascular function, stratum corneum thickness, the level of hydration and the analysed area of the face are important factors in mature skin therapies. The number of scientific reports on the activity of retinoids was the reason for this review paper.
References 1. Nomenclature of retinoids Recommendations 1981. Eur. J. Biochem. 1982;129:1–5
2. Vivat-Hannah V, Zusi FC. Retinoids as therapeutic agents: today and tomorrow. Mini. Rev. Med. Chem. 2005;5:755–60
3. Antille C., Tran C, Sorg O., et al. Penetration and metabolism of topical retinoids in ex-vivo organ-cultured full-thickness human skin explants. Skin. Pharmacol. Physiol. 2004;17:124–8
4. Khalil S, Bardawil T, Stephan C., et al. Retinoids: a journey from the molecular structures and mechanisms of action to clinical uses in
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