Vitamin A: probe of immune complement reactions

Children's consumption of dark green, leafy vegetables with added fat enhances serum retinol

A randomized, double-blind, controlled study was conducted to determine whether the consumption of leafy vegetables by preschool children would enhance their serum vitamin A concentration to acceptable levels. Preschool children (n = 519; 2.5-6 y) in Saboba, northern Ghana, were randomly assigned to five feeding groups, differing essentially in the amount of fat and beta-carotene, fed once per d, 7 d per wk, for 3 mo. Serum retinol levels, anthropometric measurements, hemoglobin, rapid turnover proteins (pre-albumin and retinol-binding protein), worm infestation (stool examinations) and level of acute and chronic infection (serum C-reactive protein and acid glycoprotein) were determined before and after study. Relative to the baseline serum retinol values, consumption of dark green, leafy vegetables (Manihot sp. and Ceiba sp.) with fat (10 g/100 g) significantly (P < 0.05) enhanced serum retinol; consequently, the percentage of children with adequate retinol status increased from 28.2-48.2% after feeding (P < 0.05). There were no significant differences among groups, ages or pre- versus post-anthropometric measurements, hemoglobin concentration, or levels of worm infestation. The importance of these findings in alleviating and/or controlling vitamin A deficiency in developing countries is discussed.

Vitamin A in liposomes. Inhibition of complement binding and alteration of membrane structure

Incorporation of vitamin A aldehyde (retinal) into liposomes had an inhibitory effect on the amount of human complement protein bound in the presence of specific antiserum. The total membrane-bound protein was directly measured on liposomes which were washed after incubation in antiserum and fresh human serum (complement). At every concentration of complement, decreased protein binding was found with liposomes which contained retinal. Binding of the third component of complement (C3) was also measured directly on washed liposomes and was found to be decreased in the presence of retinal. The diminution in protein binding due to retinal was not caused by differences in the amount of antibody bound and this was shown by two experiments. First, specific antibody protein binding to liposomes was directly measured and was essentially unaffected by retinal. Second, liposomes were prepared from lipid extracts of sheep erythrocytes. These liposomes were used as as immunoadsorbants to remove antisheep erythrocyte antibodies. The immunoadsorbant capacity was the same in both the presence and the absence of retinal. A further conclusion from these experiments was that retinal did not change the number of liposomal glycolipid antigen molecules available for antibody binding and thus presumably did not change the total number of lipid molecules present on the outer surface of the liposomes. Retinal did have an effect on the geometric structure of the liposomes. Size distribution measurements were performed in the diameter range of 1-6.35 mum by using an electronic particle size analyzer (Coulter Counter). Liposomes containing retinal were shifted toward smaller sizes and had less total surface area and volume. It was suggested that retinal-containing liposomes may have had a tighter packing of the molecules in the phospholipid bilayer. This effect of retinal on liposomal structure may have been responsible for the observed decreased binding of C3 and total complement protein.