Biochemical mechanisms of vitamin A action

PNPLA3 genetic variation in alcoholic steatosis and liver disease progression

Alcoholic liver disease (ALD) accounts for the majority of chronic liver diseases in Western countries, and alcoholic cirrhosis is among the premier causes of liver failure, hepatocellular carcinoma (HCC) and liver-related mortality causes. Studies in different genders and ethnic groups, as well as in twins provide strong evidence for a significant contribution of host genetic factors to liver disease development in drinkers. The intense quest for genetic modifiers of alcohol-induced fibrosis progression have identified and repeatedly confirmed a genetic polymorphism in the gene coding for patatin-like phospholipase domain-containing 3 (PNPLA3; adiponutrin; rs738409 C/G, M148I) as a risk factor for alcoholic cirrhosis and its related complication, HCC, in different populations. Although carriership of one or both mutated PNPLA3 alleles does not explain the entire liver phenotypic variability in drinkers, it clearly represents one of the strongest single genetic modulators in a complex trait such as ALD. As more genetic data supporting its important role aggregates, novel insight as to PNPLA3's function and that of its genetic variation in liver injury is unveiled pointing to an important novel pathway in alcohol-mediated hepatic lipid turnover with strong implications on inflammation, extra cellular matrix remodelling, and hepatocarcinogenesis. Future study shall decipher whether the gathered knowledge can be translated into therapeutic benefits of patients.

[The eye and anorexia nervosa. A case report]

INTRODUCTION

Vitamin A deficiency occurs in the poor in developing countries and is one of the main causes of blindness by perforative corneal complications. It is a rare pathology in industrialized countries and it is associated with an absorption syndrome. The authors report the first case of hypovitaminosis A in a patient suffering from chronic and severe anorexia nervosa.

CASE REPORT

The patient suffered from epiphora, photophobia, and hesperanopia. The ophthalmologic findings were keratoconjunctival xerosis with bilateral corneal ulcerations. The visual field showed a concentric bilateral restriction of isopters with tubular central vision, a similar aspect to retinitis pigmentosa. The ERG was modified with a b2 reduction and normal photopic and impaired scotopic responses. The fluorescein angiography was normal. The serum concentration of retinol confirmed the diagnosis of hypovitaminosis A. Corneoconjunctival improvement was obtained with vitamin supplementation, but no campimetric improvement was observed.

DISCUSSION

The corneoconjunctival signs result from direct destruction of goblet cells, whereas the campimetric deficit is explained by a dysfunction of rod cells. Rhodopsin, necessary to the survival of the cell, cannot be renewed if retinol is not present, which causes a permanent bright light stimulation that is lethal for the photoreceptor.

CONCLUSION

Vitamin A deficiency is rarely caused by psychiatric disease. Even if the main clinical finding is xerophthalmia with a high risk of keratomalacia, the visual prognosis can also be engaged by dysfunction of photoreceptors.

Expression of keratinocyte transglutaminase in cornea of vitamin A-deficient rats

PURPOSE

To determine the role played by keratinocyte transglutaminase (TG1, TG(K)) in the abnormal keratinization of the cornea.

METHODS

Vitamin A-deficient rats were produced as a model of severe dry eyes, and the expression of the mRNA and the enzyme activity of TG1 were examined in the corneas. The envelope proteins and keratins of cornified cells were also examined immunohistochemically.

RESULTS

The expression and enzyme activity of TG1 mRNA on the ocular surface were significantly upregulated as the vitamin A deficiency developed. As the TG1 expression was upregulated, involucrin, loricrin, and keratin 10 began to be expressed on the epithelial cells of the cornea.

CONCLUSIONS

Upregulation of TG1 expression followed by the appearance of the envelope proteins and keratin10 in cornified cells indicated that TG1 is involved in the abnormal keratinization of the cornea.

An ideal ocular nutritional supplement?

The role of nutritional supplementation in prevention of onset or progression of ocular disease is of interest to health care professionals and patients. The aim of this review is to identify those antioxidants most appropriate for inclusion in an ideal ocular nutritional supplement, suitable for those with a family history of glaucoma, cataract, or age-related macular disease, or lifestyle factors predisposing onset of these conditions, such as smoking, poor nutritional status, or high levels of sunlight exposure. It would also be suitable for those with early stages of age-related ocular disease. Literature searches were carried out on Web of Science and PubMed for articles relating to the use of nutrients in ocular disease. Those highlighted for possible inclusion were vitamins A, B, C and E, carotenoids beta-carotene, lutein, and zeaxanthin, minerals selenium and zinc, and the herb, Ginkgo biloba. Conflicting evidence is presented for vitamins A and E in prevention of ocular disease; these vitamins have roles in the production of rhodopsin and prevention of lipid peroxidation respectively. B vitamins have been linked with a reduced risk of cataract and studies have provided evidence supporting a protective role of vitamin C in cataract prevention. Beta-carotene is active in the prevention of free radical formation, but has been linked with an increased risk of lung cancer in smokers. Improvements in visual function in patients with age-related macular disease have been noted with lutein and zeaxanthin supplementation. Selenium has been linked with a reduced risk of cataract and activates the antioxidant enzyme glutathione peroxidase, protecting cell membranes from oxidative damage while zinc, although an essential component of antioxidant enzymes, has been highlighted for risk of adverse effects. As well as reducing platelet aggregation and increasing vasodilation, Gingko biloba has been linked with improvements in pre-existing field damage in some patients with normal tension glaucoma. We advocate that vitamins C and E, and lutein/zeaxanthin should be included in our theoretically ideal ocular nutritional supplement.

Molecular aspects of retinal degenerative diseases

Retinal degeneration, either acquired or inherited, is a major cause of visual impairment and blindness in humans. Inherited retinal degeneration comprises a large group of diseases that result in the loss of photoreceptor cells. To date, 131 retinal disease loci have been identified, and 76 of the genes at these loci have been isolated (RetNet Web site). Several of these genes were first considered candidates because of their chromosomal localization or homology to genes involved in retinal degeneration in other organisms. In this review, I will discuss recent advances in the identification of genes that cause retinal degeneration, and I will describe the mechanisms of photoreceptor death and potential treatments for retinal degenerative diseases.

Influence of retinol deficiency and curcumin/turmeric feeding on tissue microsomal membrane lipid peroxidation and fatty acids in rats

The effect of retinol deficiency and curcumin/turmeric on lipid peroxidation and fatty acid profile was studied in liver, kidney, spleen and brain microsomes of rats. Results revealed an increase in lipid peroxidation in retinol deficient liver by 32%, kidney 30%, spleen 24% and brain 43% compared to the controls. Feeding 0.1% curcumin or turmeric for three weeks in diet to retinol deficient rats reduced the lipid peroxidation respectively to 12.5 or 22.6%, in liver, 23.7 or 24.1% in kidney, 14.4 or 18.0% in spleen and 16.0 or 31.4% in brain. Retinol deficiency lead to a reduction in the essential fatty acids. In liver C18:1 showed a reduction by 45.6%, C18:2 by 31.6% and C20:4 by 22.8%. In kidney C18:1 was reduced by 33.6%, 18:2 by 24.6% and 20:4 by 13.7%. In spleen and brain C18:1 showed a reduction by 10.2% and 33.9%, C18:2 by 37.9% and 12.1% and C20:4 by 15.7% and 35.3% respectively. Curcumin and turmeric fed group showed a significant increase in the abnormally reduced fatty acid levels.

Effect of retinol deficiency and curcumin or turmeric feeding on brain Na(+)-K+ adenosine triphosphatase activity

The effect of retinol deficiency and curcumin and turmeric feeding on brain microsomal Na(+)-K(+)ATPase activity was investigated. The brain Na(+)-K(+)ATPase activity registered an increase of 148.5% as compared to the control group. Upon treating retinol deficient rats with curcumin or turmeric, the abnormally elevated activity showed a decrease of 36.9 and 47.1%, respectively, when compared to the retinol deficient group. An increase in Vmax by 67% and Km by 66% for ATP was observed in the retinol deficient group. Curcumin or turmeric fed retinol-deficient groups reduced the Vmax by 25 and 33%, while Km was reduced by 25 and 31%, respectively, compared to the retinol deficient group. Arrhenius plot of Na(+)-K(+) ATPase showed a typical bi-phasic pattern in all the groups. Cholesterol:Phospholipid ratio showed a decrease in the retinol-deficient group by 67.8%, which showed a marked increase in curcumin or turmeric treated groups. Detergents could increase the Na(+)-K(+) ATPase activity more in the control group than in the retinol deficient groups. Curcumin or turmeric improved the detergent action on the enzyme. Subsequent freezing and thawing over a period of 30 min decreased the enzyme activity by 22.8% in the retinol deficient group compared to 15.9% decrease in the control group. Curcumin or turmeric treated groups showed a decrease in the enzyme activity by 22.0 and 19.2%, respectively, when compared to the zero time in each group. In the presence of concanavalin-A (Con-A) there was only 52.4% stimulation in the enzyme activity in retinol deficient groups, compared to 108.0% in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired mucosal antibody response to cholera toxin in vitamin A-deficient rats immunized with oral cholera vaccine

To investigate the importance of vitamin A in the ability to respond to oral antigen administration, rats were fed a vitamin A-free diet. The animals were immunized perorally three times with a mixture of cholera toxin (CT) and a commercial cholera vaccine. The total immunoglobulin A (IgA) concentration as well as the specific IgA anti-CT antibody levels in serum and bile was significantly lower in the vitamin A-deficient animals than in the paired fed controls (animals that were fed a normal commercial diet in an amount equal to the amount the deficient animals consumed), while the levels of total and specific anti-CT IgG were not affected to the same extent by the vitamin A deficiency. The number of IgA anti-CT antibody-producing cells in the mesenteric lymph nodes after immunization was also significantly lower in the vitamin A-deficient rats than in the control rats. Supplementation of the diet with retinyl palmitate restored the ability to mount an IgA antibody response to the antigen, since the level of specific IgA anti-CT antibodies in relation to the total IgA concentration was as high in the vitamin A-supplemented group as in the paired fed control group. Restricted diet intake by itself did not affect the ability to respond adequately to the antigen since there was no difference in IgA anti-CT antibody level between paired fed rats and those being fed ad libitum. Assessment of transforming growth factor beta in cell cultures revealed no difference between vitamin A-deficient and paired fed animals. In summary, vitamin A deficiency resulted in a decreased number of IgA-producing cells, decreased IgA production, and a reduced ability to respond with IgA antibodies to the oral cholera vaccine.

Topical application of all-trans-retinoic acid. A look at the cornea and limbus

A 0.1% all-trans-retinoic acid in petroleum-base ointment was applied daily in eight normal rabbit eyes. Epithelial samples were collected from the cornea and limbus of six rabbits by impression cytology at 3- to 4-day intervals. Cytological changes were followed for 21 days and the eyes subsequently harvested for histochemical, scanning electron microscopic (SEM), and transmission electron microscopic (TEM) analysis of corneal and limbal structures. Two rabbits were treated with 0.1% all-trans-retinoic acid for 24 days without impression cytology until the 21st day. On the 24th day these eyes were harvested for similar studies. Impression cytology studies of the corneal epithelium demonstrated perinuclear halos and vacuolization of the cytoplasm. Additionally, vacuolization of the cytoplasm was observed by TEM, with attendant extrusion of the cytoplasmic contents and a subjective increase in surface microvilli as seen by SEM. Histochemical analysis revealed mucinlike staining of the corneal epithelium.

Topical retinoic acid in dysplastic and metaplastic keratinization of corneoconjunctival epithelium

We report four cases of corneoconjunctival keratinization that were successfully treated with topical retinoic acid ointment. In two cases keratinization was due to squamous metaplasia and in two others it was secondary to intraepithelial corneoconjunctival neoplasia. Treatment reversed severe keratinization in a case of drug-induced pseudopemphigoid and stabilized the disease in one of the two affected eyes without additional treatment. In a case of ocular cicatricial pemphigoid, retinoic acid was useful as an adjuvant therapy to immunosuppression, by reversing keratinization of the conjunctiva. In two cases of corneoconjunctival neoplasia, lesions regressed markedly. Long-term treatment was well tolerated in three patients. Our findings suggest that retinoic acid ointment is effective in treating severe squamous metaplasia in cicatrizing diseases of the conjunctiva. Our findings indicate further that retinoic acid seems to inhibit growth of corneoconjunctival neoplasias and thus might be useful complementary therapy in this situation.

Expression of specific keratin markers by rabbit corneal, conjunctival, and esophageal epithelia during vitamin A deficiency

Using an in vivo rabbit model system, we have studied the morphological and biochemical changes in corneal, conjunctival, and esophageal epithelia during vitamin A deficiency. Light and electron microscopy showed that the three epithelia undergo different degrees of morphological keratinization. Corneal and conjunctival epithelia became heavily keratinized, forming multiple layers of superficial, anucleated cornified cells. In contrast, esophageal epithelium underwent only minor morphological changes. To correlate morphological alterations with the expression of specific keratin molecules, we have analyzed the keratins from these epithelia by the immunoblot technique using the subfamily-specific AE1 and AE3 monoclonal antikeratin antibodies. The results indicate that during vitamin A deficiency, all three epithelia express an AE1-reactive, acidic 56.5-kd keratin and an AE3-reactive, basic 65-67-kd keratin. Furthermore, the expression of these two keratins correlated roughly with the degree of morphological keratinization. AE2 antibody (specific for the 56.5- and 65-67-kd keratins) stained keratinized corneal epithelial sections suprabasally, as in the epidermis, suggesting that these two keratins are expressed mainly during advanced stages of keratinization. These two keratins have previously been suggested to represent markers for epidermal keratinization. Our present data indicate that they can also be expressed by other stratified epithelia during vitamin A deficiency-induced keratinization, and suggest the possibility that they may play a role in the formation of the densely packed tonofilament bundles in cornified cells of keratinized tissues.