Keratinization vitamin

On a vitamin A-deficient diet, mucus-secreting tissues become keratinized. This condition tends to occur in the trachea, the skin, the saUvary glands, the cornea, and the testes. When this occurs in the cornea, it can be followed by blindness. Vitamin A deficiency is the principal cause of blindness in the very young. This problem is particularly acute in the third world (8). 

Vitamin D3 (VD3) and retinoids synergistically inhibit the growth and progression of squamous cell carcinomas and actinic keratoses in chronically sun exposed skin. One reason for this synergism may be the direct influence of VD3 on the isomerization and the metabolism of RA. Here, VD3 inhibits the isomerization of 13-cis-RA to the more receptor active all-trans and 9-cis-isomers. Moreover, the VD3 derivative secocholestra-trien-l,3,24-triol (tacalcitol), used for the treatment of severe keratinizing disorders inhibits 4-hydroxylation of all-ri ans-RA. 

Especially focal keratinizing metaplasia, as it may occur after a vitamin A deficiency, is sfrengfhening the assumption of an impairmenf of the differentiation on the level of the gene expression. Since vitamin A regulates the expression of different cytokeratins and therefore influences... 

Growth Animals deprived of vitamin A initially lose their appetites, possibly because of keratinization of the taste buds. Bone gcwlh is slow and fails to keep pace with growth of the nervous system, leading to central nervous system damage. 

In vitamin A deficiency the internal epithelial surfaces of lungs and other tissues, which are usually rich in mucous secreting cells and in ciliated cells, develop thick layers of keratinizing squamous cells similar to those on the external surface of the body. 

Abstract The utility of confocal Raman microscopy to study biological events in skin is demonstrated with three examples, (i) monitoring the spatial and structural differences between native and cultured skin, (ii) tracking the permeation and biochemical transformation in skin of a Vitamin E derivative and (iii) tracking the spatial distribution of three major skin proteins (keratin, collagen, and elastin) during wound healing in an explant skin model. 

The intestinal mucosa shows a reduction in the number of goblet cells without keratinization. Alterations in intestinal epithelium and metaplasia of pancreatic ductal epithelium are common. They may be responsible for the diarrhea occasionally seen in vitamin A deficiency. 

Often both taste and smell are impaired in vitamin-A-deficient individuals, undoubtedly a result of a keratinizing effect. Hearing also may be impaired. Vitamin A deficiency can interfere with erythropoiesis, which may be masked by abnormal losses of fluid. Nerve lesions, increased cerebrospinal fluid pressure, and hydrocephalus have been reported. 

Apart from the effects on vision, most of the effects of vitamin A deficiency (Section 2.4) involve derangements of cell proliferation and differentiation (squamous metaplasia and keratinization of epithelia), dedifferentiation, and loss of ciliated epithelia. Retinoic acid has both a general role in growth and a specific morphogenic role in development and tissue differentiation. These functions are the result of genomic actions, modulating gene expression by activation of nuclear receptors. Both deficiency and excess of retinoic acid cause severe developmental abnormalities. 

Vitamin A-deficient experimental animals fail to grow adults are blind and sterile, with testicular degeneration in males and keratinization of the uterine epithelium in females. Although deficient female animals wUl conceive, and the fetuses will implant, formation of the placenta is impaired and the fetuses are resorbed. Epithelia in general are hyperplastic and keratinized, and there is impaired cellular immunity with increased susceptibility to infection. Both retinol and retinoic acid are required for gestation in the rat in deficient animals, retinoic acid alone will not prevent fetal resorption after about day 10 of gestation (WeUik and DeLuca, 1995 WeUik et al., 1997). 

Epidermal keratinization and mucous membrane squamous metaplasia respond to both oral and topical vitamin A therapy. Vitamin A exists in three forms retinol, retinal, and retinoic acid.VitaminA increases the mucous production of goblet cells and perhaps the aqueous and lipid components of the tears as well. Tretinoin is a normal metabolite and the carboxylic form of retinol. Retinol is present in tears and the lacrimal gland appears to be its major provider. Retinoic acid has been shown to be effective in ocular surfece disorders such as squamous metaplasia by reversing the corneal and conjunctival keratinization and improving epithelium wound healing rate. 

An analogue of vitamin A, isotretinoin (Accutane), or 13-cfs-retinoic acid, is used for control of severe recalcitrant cystic acne and other keratinizing dermatoses. Oral administration of 1 to 2 mg/kg body weight daily temporarily suppresses sebaceous gland activity, changes surfece lipid composition of the skin, and inhibits kera-tinization. The therapeutic effect is resolution of lesions and, in most patients, prolonged remission of the disease. 

Urolithiasis In vitamin A deficiency, urino-genital epithelium shows keratinization followed by bacterial invasion and formation of alkaline urine. This factors cause calcium phosphate precipitation, which leads to formation of urinary calculi. 

Vitamin A performs numenius biochemical functions. It promotes the production nf mucus by the basal cells of the epithelium, whereas in its absence keratin can be fonned. Vitamin A performs a function in the biosynthesis of glycogen and some steroids, and increased quantities nf coen/yme Q are found in the livers nf vitamin-deficicnt rats. Significantly. the best-known action of vitamin A is its function in the chemistry of vision. 

The place and importance of these enzymes in the process of normal keratinization and in psoriasis is still obscure however, the fact that vitamin A-acid has been used to treat psoriasis successfully and is a lysosomal labilizer (F21) may indicate that they are of great importance. 

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