dolichols and Vitamin-A-Deficiency

Fetal alcohol spectrum disorder (FASD) is an umbrella term used to describe the craniofacial dysmorphic features, malformations, and disturbances in growth, neurodevelopment and behavior occurring in individuals prenatally exposed to alcohol. Fetal alcohol syndrome (FAS) represents the severe end of this spectrum. Many pathophysiological mechanisms have hitherto been proposed to account for the disrupted growth and morphogenesis seen in FAS. These include impaired cholesterol-modification of the Sonic hedgehog morphogen, retinoic acid deficiency, lipoperoxidative damage due to alcohol-induced reactive oxygen species combined with reduced antioxidant defences, and malfunctioning cell adhesion molecules. In this report, we propose a completely novel concept regarding the pathogenesis of FAS. Based on our observation that transferrin isoelectric focusing (TIEF) - the most widely used screening tool for congenital disorders of glycosylation (CDG) - was transiently abnormal in a newborn with FAS and a confirmed maternal history of gestational alcohol abuse, we came to believe that FAS exemplifies a congenital disorder of glycosylation secondary to alcohol-inflicted disruption of (N-linked) protein glycosylation. Various pieces of evidence were found in the literature to substantiate this hypothesis. This observation implies, among others, that one might need to consider the possibility of maternal alcohol consumption in newborns with transient glycosylation abnormalities. We also present an integrated pathophysiological model of FAS, which incorporates all existing theories mentioned above as well as our novel concept. This model highlights the pivotal role of disrupted isoprenoid metabolism in the origination of FAS.

Topics: Alcohol Drinking; Alcoholism; Antioxidants; Cholesterol; Dolichols; False Positive Reactions; Female; Fetal Alcohol Spectrum Disorders; Glycosylation; Hedgehog Proteins; Humans; Infant; Infant, Newborn; Isoelectric Focusing; Male; Models, Theoretical; Pregnancy; Reactive Oxygen Species; Transferrin; Tretinoin; Vitamin A Deficiency

The molecular mechanism of reduced incorporation of radioactively labeled mannose into hamster liver glycoconjugates during the progression of vitamin A deficiency was investigated. In particular the in vivo incorporation of [2-3H]mannose into GDP-mannose, dolichyl phosphate mannose (Dol-P-Man), lipid-linked oligosaccharides, and glycopeptides of hamster liver was examined. Hamsters maintained on a vitamin A-free diet showed a reduction in the incorporation of mannose into GDP-mannose about 10 days before clinical signs of vitamin A deficiency could be observed. The decrease in [2-3H]mannose incorporated into GDP-mannose was accompanied by a reduction in label incorporated into Dol-P-Man, lipid linked oligosaccharides and glycopeptides, which became more severe with the progression of vitamin A deficiency. By the time they reached a plateau stage of growth, hamsters fed the vitamin A-free diet showed a 50% reduction in the amount of [2-3H]mannose converted to GDP-mannose, and the radioactivity associated with Dol-P-Man and glycopeptides was reduced by approximately 60% as compared to retinoic acid-supplemented controls. These results strongly indicate that the reduced incorporation of mannose into lipidic intermediates and glycoproteins observed during vitamin A deficiency is due to impaired GDP-mannose synthesis.

Topics: Animals; Cricetinae; Dolichols; Fasting; Glycosylation; Guanosine Diphosphate Mannose; Liver; Male; Mannose; Mesocricetus; Nucleoside Diphosphate Sugars; Vitamin A Deficiency

Epithelial cells from hamster small intestine, in short term culture, incorporated [carbinol-14C]retinol into a compound that is identical to synthetic retinyl phosphate, as judged by chromatography on DEAE-cellulose, silicic acid, and thin layers of silica gel. The biological compound displays the same absorption spectrum as does synthetic retinyl phosphate with a maximum at 325 nm. Hydrolysis with mild alkali yields anhydroretinol, as it does for synthetic retinyl phosphate, with absorption maxima at 388, 368, and 346 nm. Enzymic hydrolysis by alkaline phosphatase releases 9% of the radioactivity as [14C]retinol. Under the same conditions, 9% of synthetic retinyl phosphate is hydrolyzed to retinol. The biological compound was tested for biological activity. At a concentration of 5.5 x 10-8 M it was as active as retinol and retinyl phosphate in reversing keratinization induced in hamster tracheal epithelium by vitamin A deficiency. It is concluded that hamster intestinal cells synthesize retinyl phosphate.

Topics: Alkaline Phosphatase; Animals; Cricetinae; Diterpenes; Dolichols; Epithelial Cells; Epithelium; Intestine, Small; Keratins; Male; Metaplasia; Organ Culture Techniques; Organophosphorus Compounds; Phosphates; Tracheal Diseases; Vitamin A; Vitamin A Deficiency