|
|
| THE
MORE YOU KNOW |
Natural Vitamin A (Retinol and Retinaldehyde)
Vitamin A is the generic term for a variety of fat-soluble substances including retinol, retinylaldhyde and retinoic acid. Vitamin A is commonly known as the anti-infective vitamin and has an essential role in cellular differentiation, the latter providing a unique core mechanism helping to explain the influence of vitamin A on epithelial barriers. Vitamin A has an influence on epithelial barrier. Alterations in the epithelial lining of vital organs occur early in deficiency, suggesting a potentially important role for the barrier function (73).
Topical retinoic acid (RA) causes irritation of the skin. To prevent this side effect, natural precursors of retinoic acid have been proposed. The natural retinoids (retinol and retinaldehyde have been found to have a good tolerance profile, in contrast with the irritating potential of retinoic acid (74). However, retinol and retinaldhyde are metabolized by the dermis into retinoic acid. After treatment with retinol and
retinaldhyde, low but significant amounts of retinoic acid could be detected in the epidermis, as well as in the dermis. In comparison, treatments with retinoic acid itself, leads to higher level of retinoic acid in the epidermis and in the dermis. Thus the low proportion of
retinaldehyde, metabolized into a -tran-retenoic acid, explains the low irritancy profile of topical retinaldehyde and supports the concept of controlled delivery of
ligands. Thus the action of retinol or retinaldhyde on the skin is still via a retinoic acid formation through the metabolic function of the dermis (75).
Retinaldehyde (RAL), a natural metabolite of beta-carotene and retinol
(ROL), can be used topically in human skin and exerts biological activity; it may be a convenient way to deliver multipotential vitamin A activity in epidermis. Animal experiments indicated that keratinocytes metabolise topical
retinaldehyde. Keratinocytes differentiating in vitro exhibit greater capacity for retinoic acid synthesis from retinol or retinaldehyde as compared to nondifferentiated cells (76). Experimental study results suggest that increasing cellular concentration of retinoic acids in in-vitro differentiating keratinocytes is achieved by a process of increased activity of the retinoic acid synthesis (77). Thus the concept of using retinaldehyde as a precursor has been confirmed. The keratinocytes predominantly channel retinaldhyde into storage forms should also be considered as a convenient way to load the epidermis with vitamin A.
It has also been found that after experimental topical application of retinol and retinaldhyde that there was a significant amount of 14-hydroxy-4, 14-retro-ROL (14-HRR), a metabolite that could promote the growth of B lymphocytes (humeral antibodies) and activate T-lymphocytes (cellular immunity), suggests distinct potentials of topical retinol and retinaldhyde (78).
Studies showed that topical retinol appears to improve the resistance of the stratum corneum against some chemical and physical (UV) threat. It also limits UV-induced shallow wrinkling (79).
Retinoids was found to inhibit proliferation of melanocytes and melanoma cells and affect disorders of hypo- and
hyperpigmentation. The endogenous concentrations of retinol and its metabolites in melanocytes were found to be five times those in melanoma cells. Dissimilarities in the metabolism and endogenous concentration of retinoids between benign and malignant melanocytes might play a key role in differentiation and growth regulation (80).
(return to
Education Center)
|
|
|
