Shoshana Mokady

The interaction between retinol-binding proteins and prealbumins studied by fluorescence polarization

The interaction between retinol-binding proteins and prealbumins of human and chicken was studied by fluorescence polarization techniques. The binding affinity between chicken plasma retinol-binding protein and chicken prealbumin was essentially the same as between the respective human proteins. Human urine retinol-binding protein displayed a similar affinity, though possibly slightly smaller than that of the human plasma protein, toward human prealbumin. Retinol-binding proteins and prealbumins of human and chicken have been found to cross-interact displaying an affinity similar to that displayed by the proteins of the same species. Solution of a binding equation which assumes identical, independent sites, indicated that the number of binding sites on prealbumin for retinol-binding protein is somewhat less than 2 with the human system, and in the neighborhood of 4 with the chicken system. A possible interpretation suggests that prealbumin possesses four identical binding sites for retinol-binding protein, one for each subunit, but that the binding is of a negative cooperative nature. A major share of the negative cooperativity is likely to result from steric hindrance induced by already bound retinol-binding protein molecules, which have a sizable volume compared to the volume of the prealbumin molecule. The cooperativity is likely to be more pronounced with the human system. Rotational relaxation times derived from Perrin plots suggest that 1:1 molecular complexes of retinol-binding proteins with prealbumins have a compact structure.

In vivo antiperoxidative effect of 9-cis β-carotene compared with that of the all-trans isomer

It has been implied that the antiperoxidative activity of beta-carotene is important for its ability to prevent malignant and cardiovascular diseases. In vitro studies have shown that 9-cis beta-carotene is a better antioxidant than the all-trans isomer. In the present study the antiperoxidative biopotency of 9-cis beta-carotene was studied in vivo. For three weeks, weanling female rats were fed diets containing 10% fresh or oxidized soybean oil. The experimental diets were supplemented with beta-carotene at 1 g/kg with the synthetic all-trans isomer or with a carotene extract of Dunaliella bardawil containing 75% 9-cis beta-carotene. Both carotene sources prevented to the same extent hepatic and erythrocyte peroxidation associated with the consumption of oxidized oil. However, this beneficial effect was accompanied, in most of the groups, by a reduction in the hepatic carotene stores. Only in the animals fed Dunaliella extract combined with oxidized oil were the hepatic stores of beta-carotene and vitamin A maintained. The enhanced degradation of 9-cis beta-carotene observed in the livers of these animals might indicate that, like the effect observed under in vitro conditions, this isomer has a greater affinity toward free radicals and therefore might be a more efficient antioxidant than the all-trans form under in vivo conditions. The activity of glutathione peroxidase, glucose-6-phosphate dehydrogenase, and glutathione reductase as affected by the two carotene sources was also studied.

Effect of dietary pectin and algin on blood cholesterol level in growing rats fed a cholesterol-free diet.

The effect of dietary pectin and algin on blood cholesterol level of growing rats fed a cholesterol-free diet was studied. Pectin was found to lower blood cholesterol significantly while the effect of algin was very small. It was shown that the level of endogenic cholesterol in rats was lowered by feeding them a pectin which had a high content of methoxy groups and was highly viscous.

Dietary oxidized oil enhances the activity of (Na+K+) ATPase and acetylcholinesterase and lowers the fluidity of rat erythrocyte membrane

Abstract The effect of dietary oxidized lipids on the fluidity and function of red blood cell (RBC) membranes was studied. Male growing rats were fed diets containing 10% fresh (control) or oxidized (experimental) soybean oil for 8 weeks. Ingestion of the oxidized oil resulted in the accumulation of high levels of fluorescent peroxidation products in the RBC of the experimental animals. Membrane fluidity was studied by fluorescence polarization, using 1,6-diphenyl-1,3,5 hexatriene (DPH) as a probe. The fluidity of RBC membranes isolated from the animals of the experimental group was significantly lower than that of the membranes derived from the control following 3 and 7 weeks of feeding. This lower fluidity was accompanied by a decrease in the content of membrane polyunsaturated fatty acids and an increase in the activity of the membrane-bound enzymes acetylcholinesterase and (Na + K + )ATPase. Despite the excessive oxidative state of the oil used, the changes observed in membrane composition, dynamics, and function emphasize the potential risk of dietary oxidized lipids.

Dietary oxidized oil and the activity of antioxidant enzymes and lipoprotein peroxidation in rats

The relationship between dietary oxidized oil and the activity of some antioxidant enzymes and the peroxidation state of plasma lipoproteins was studied with male growing rats. The animals were fed diets containing 10% fresh or oxidized soybean oil. Ingestion of the oxidized oil resulted in an elevation in the activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase in erythrocytes derived from the experimental rats compared to the controls. In contrast, in animals subjected to the oxidized oil, the hepatic activity of glucose-6-phosphate dehydrogenase was significantly lower, that of glutathione peroxidase and glutathione reductase showed a tendency to decrease, whereas the level of superoxide dismutase activity was unchanged. This could be explained by possible liver damage caused by the oxidized lipids, and indeed, the increased plasma levels of aspartate aminotransferase and alanine aminotransferase activity support this conclusion. Dietary oxidized oil increased the level of lipid peroxidation in various lipoprotein fractions. The study emphasizes the potential risk of dietary oxidized lipids.

Influence of dietary vitamin E and selenium on muscle fatty acid composition in pigs

Abstract A total of 28 female pigs were fed a basal diet containing a low amount of α-tocopherol (10.3 mg/kg; control), and diets supplemented with 0.3 mg selenium/kg (group Se) or with 200 mg α-tocopherol/kg (group V) at the growing-finishing period. Increasing dietary level of vitamin E resulted in higher concentration of α-tocopherol in plasma and muscle immediately after slaughter and 4 h later (P⩽0.05). The fatty acid composition of muscle microsomes and mitochondria was slightly affected by the diet. Corresponding to the minor changes of the membrane fatty acid composition the fluidity was unaffected by the diet. A positive relationship was observed between the resistance to in vitro stimulation of peroxidation and the vitamin E content of the muscle samples. Supplementation with selenium did not reduce the lipid oxidation after stimulation. In conclusion, even though the effect was minor, vitamin E improved the antioxidative status in pork.

The β-carotene-rich alga Dunaliella bardawil as a source of retinol in a rat diet

1. Dunaliella bardawil, a beta-carotene-accumulating alga, has been tested as a source of retinol and beta-carotene in a diet given to rats. The beta-carotene in this alga is composed of about equal amounts of the 9-cis and all-trans isomers. Male weanling rats were fed on a retinol-deficient diet for 60 d. Thereafter, the rats were divided into groups and fed on a diet deficient in retinol or supplemented with retinol, synthetic beta-carotene, dry alga or an algal oil-extract. Following further growth for 7 d, samples were taken for liver analyses of retinol, retinol isomers and beta-carotene. 2. Liver analyses revealed a comparable content of retinol and normal conversion rates in the rats grown on the diets supplemented with synthetic or natural beta-carotene. Rats fed on the alga and the algal-oil-supplemented diets accumulated 9-cis retinol in addition to the all-trans isomer. Rats fed on synthetic beta-carotene, alga and algal oil had a liver retinol: beta-carotene value of about 3:1. 3. These studies demonstrate the possibility of using dried D. bardawil or an oil extract of the alga as a dietary natural beta-carotene supplement which satisfies the total requirement of retinol in rats. 4. Rats fed on alga or on algal oil, accumulated in the liver 9-cis beta-carotene and all-trans beta-carotene in a ratio similar to that present in the alga.

Food restriction and membrane fluidity

The fluidity of the erythrocyte membrane derived from growing rats raised under restricted food intake was found to be higher than the fluidity of the respective membranes from ad libitum fed animals. Considering the apparent relationship between the decrease in membrane fluidity and aging, the results point to the possible beneficial effects of food restriction at a young age.

Age and membrane fluidity

Male rats aged 1, 9 and 19 months were used to study changes in membrane fluidity with age, employing the fluorescence polarization technique with 1,6-diphenyl-1,3,5-hexatriene (DPH) as the fluorescent probe. The intestinal microvillus membranes derived from the 19-month-old rats were found to possess lower fluidity than that observed with the membranes derived from the younger animals. The decrease in fluidity with age was also reflected in a corresponding increase in the gel-to-liquid crystalline transition temperature. Only small insignificant changes with age, were observed in the fluidity of the red blood cell membrane.

Incorporation ofall-trans-or 9-cis-β-carotene into mixed micellesin vitro

Various studies suggest thatall-trans- and 9-cis-β-carotene are absorbed in the intestine to different extents. The present study was undertaken to evaluate the degree ofin vitro incorporation of the two isomers into intestinal mixed micelles, which is an essential early step in the absorption process. The micelles were designed to simulate those present during fat digestion in the lumen of the human small intestine with respect to bile salts, lipids, pH and temperature. Solutions ofall-trans-and 9-cis-β-carotene at various ratios were added to the lipid mixture. A direct correlation was seen between the 9-cis-β-carotene level in the mixture and the degree of total β-carotene incorporation into micelles. An increased level ofall-trans-β-carotene incorporated into the micelles. In contrast, when carotene mixtures enriched with the 9-cis isomer were used, an increase in the level of total carotene in the solution was accompanied by a constant or even enhanced carotene incorporation. The results indicate that the differences in the absorption of β-carotene isomers might be the result of their different ability to be incorporated into the lipid micelles of the intestinal lumen. In addition, the results point toward the possibility that ingestion of 9-cis-β-carotene by humans may increase carotene availability.