Preliminary chacterization of a small intestinal binding component for retinol and fatty acids in the rat

Genetic Variations Associated with Vitamin A Status and Vitamin A Bioavailability

Blood concentration of vitamin A (VA), which is present as different molecules, i.e., mainly retinol and provitamin A carotenoids, plus retinyl esters in the postprandial period after a VA-containing meal, is affected by numerous factors: dietary VA intake, VA absorption efficiency, efficiency of provitamin A carotenoid conversion to VA, VA tissue uptake, etc. Most of these factors are in turn modulated by genetic variations in genes encoding proteins involved in VA metabolism. Genome-wide association studies (GWAS) and candidate gene association studies have identified single nucleotide polymorphisms (SNPs) associated with blood concentrations of retinol and β-carotene, as well as with β-carotene bioavailability. These genetic variations likely explain, at least in part, interindividual variability in VA status and in VA bioavailability. However, much work remains to be done to identify all of the SNPs involved in VA status and bioavailability and to assess the possible involvement of other kinds of genetic variations, e.g., copy number variants and insertions/deletions, in these phenotypes. Yet, the potential usefulness of this area of research is exciting regarding the proposition of more personalized dietary recommendations in VA, particularly in populations at risk of VA deficiency.

Absorption of Carotenoids and Mechanisms Involved in Their Health-Related Properties

Carotenoids participate in the normal metabolism and function of the human body. They are involved in the prevention of several diseases, especially those related to the inflammation syndrome. Their main mechanisms of action are associated to their potent antioxidant activity and capacity to regulate the expression of specific genes and proteins. Recent findings suggest that carotenoid metabolites may explain several processes where the participation of their parent carotenoids was unclear. The health benefits of carotenoids strongly depend on their absorption and transformation during gastrointestinal digestion. The estimation of the 'bioaccessibility' of carotenoids through in vitro models have made possible the evaluation of the effect of a large number of factors on key stages of carotenoid digestion and intestinal absorption. The bioaccessibility of these compounds allows us to have a clear idea of their potential bioavailability, a term that implicitly involves the biological activity of these compounds.

Differential absorption of vitamin D3 and 1,25-dihydroxyvitamin D3 by intestinal jejunal cells of the rat

An intestinal perfusion technique is reported for the study of the differential absorption of vitamin D3 and its active metabolite, 1,25-dihydroxyvitamin D3, through intact jejunal segments of rats. Samples of introduced and collected perfusates, intestinal homogenates, and portal blood were assayed for [14C]vitamin D3 or [3H]1 alpha,25-dihydroxyvitamin D3 content at specified time intervals in control rats and in rats injected ip with cycloheximide (3 mg/kg body weight). Vitamin D3 uptake from the perfusates in cycloheximide-treated groups did not differ from controls. However, an approximately 2-fold increase of vitamin D3 retention in the perfused intestinal segments was observed after cycloheximide treatment. A 0.25-fold decrease was observed in the uptake of 1,25-dihydroxyvitamin D3 from the perfusates after cycloheximide treatment, and an approximately 2.5-fold increase in its intestinal retention was noted. An increase in the active metabolite concentration was observed in the portal venous system 75 min after initiation of perfusion, with no detectable amounts being recorded prior to the first hour. The results suggest that intracellular binding proteins may be involved in the transport of labeled vitamin D3 and labeled 1,25-dihydroxyvitamin D3 through rat enterocytes. Furthermore, vitamin D3 may have been more readily channeled through an esterification process than 1,25-dihydroxyvitamin D3 prior to their appearance in the portal venous system.

Isolation and characterization of an unsaturated fatty acid-binding protein from developing chick neural retina

An unsaturated fatty acid-binding protein has been isolated from the cytosol fraction of developing chick neural retina. It has a molecular weight of approximately 14,800 and specifically binds not only added radiolabeled arachidonic and oleic acids but has also been found to bind unsaturated fatty acids endogenously. This protein was detected in chick neural retina at all stages examined, from 8 to 16 days of development. It is also present in chick heart, brain, and retinal pigmented epithelium-choroid as well as in adult bovine neural retina. It is distinct from both cellular retinol-binding protein and cellular retinoic acid-binding protein on the bases of binding specificity and isoelectric point.

Carotene-cleavage activity in chick intestinal mucosa cytosol: association with a high-molecular-weight lipid-protein aggregate fraction and partial characterization of the activity

A fluorescent high-molecular weight lipid-protein aggregate was isolated from the cytosol of chick intestinal mucosa or liver by gel filtration on columns of Sepharose 4B or 6B. This aggregate exhibited carotene-cleavage activity. On incubation of this aggregate, dissociation occurred and low-molecular weight fractions containing Cu and Zn and exhibiting carotene-cleavage activity were found. This fraction appeared on sodium dodecyl sulphate polyacrylamide electrophoresis to have a molecular weight of 7000-11000 and resembled the previously described Cu chelatins in amino acid composition. Carotene cleavage may be effected by a copper-zinc metalloprotein of low-molecular weight, associated in intestinal cytosol with a lipid-protein aggregate.

Association of acylglyceride and retinyl palmitate hydrolase activities with zinc and copper metalloproteins in a high molecular weight lipid-protein aggregate fraction from chick liver cytosol

A lipid-protein aggregate fraction of molecular weight approx. 1.8 . 10(6) was isolated by gel filtration from chick liver cytosol. This aggregate fraction had a hydrated density range of 1.06-1.13, was 45% lipid, contained zinc and copper and was associated with triolein, phosphatidylcholine and retinyl palmitate hydrolase activity. Hydrolytic activities were stimulated by albumin and cholate, but not by dihydroxy bile acids, and inhibited by serine esterase and sulphydryl inhibitors. Incubation of the aggregate with fatty acid-labelled acylglycerides resulted in protein-binding fatty acid fractions with molecular weights of 150,000, 60,000, 13,000 and approx. 2000. Incubation of the aggregate with [3H]retinyl palmitate yielded retinol-containing fractions with molecular weights of 150,000, 60,000 and 15,000. The latter peak appears, on the basis of amino acid composition, to be similar to the cellular retinol-binding protein. In addition, on incubation of the aggregate fraction, zinc and copper peaks are found with molecular weights of 150,000, 60,000 and 12,000-8000. The latter were further purified to yield a copper-rich metalloprotein similar to 'copper-chelatin' and a zinc-rich metalloprotein, possibly zinc-metallothionein. Both these metalloprotein fractions had acyl hydrolase activity which was depressed in zinc-depleted animals. This may provide a possible explanation for the documented nutritional interactions between zinc and retinol.