Effect of a hyperlipidic diet on lipid composition, fluidity, and (Na+-K+)ATPase activity of rat erythrocyte membranes

Antioxidant supplementation improves platelet membrane fluidity in idiopathic retinal periphlebitis (Eales' disease)

PURPOSE

Oxidative damage to cellular membranes plays an important role in the pathobiology of tissue injury. Retinal photoreceptors and platelets are an easy target of oxidants because of high proportion of polyunsaturated fatty acids. A tertiary-care center-based prospective study was undertaken to study the effect of antioxidant supplementation over membrane fluidity in platelets in idiopathic retinal periphlebitis (Eales' disease) for the first time.

METHODS

Assay of thiobarbituric acid reactive substances (TBARS) levels was done following a standard protocol and membrane fluidity in platelets was estimated using a fluorescent probe, 1,6-diphenyl-1,3,5-hexatrience, in 15 cases and 12 healthy controls. Prednisolone (1 mg/kg) in a weekly tapering dose for 6 weeks and a commercially available antioxidant preparation [lutein 3.2 mg (containing zeaxanthin 256 mcg), L-glutathione 5 mg, vitamin E 15 IU, vitamin C 150 mg, zinc 40 mg, copper 2 mg, selenium 40 mcg, and manganese 5 mg] was administered once a day for 3 months to all the cases. Pre- and postantioxidant supplementation platelet TBARS and membrane fluidity levels were assessed in all the cases.

RESULTS

Significant increase was observed in TBARS levels in the cases when compared with controls (P = 0.01). Platelet fluorescence polarization was significantly higher in cases, indicating decreased membrane fluidity, when compared with controls (P = 0.005). Antioxidant supplementation led to marked decrease in TBARS levels (P = 0.01) and improved levels of platelet membrane fluidity (P = 0.001).

CONCLUSION

Antioxidant supplementation leads to significant decrease in oxidative stress and a significant improvement in platelet membrane fluidity, thereby helping to prevent retinal photoreceptor dysfunction.

Decreased platelet membrane fluidity in retinal periphlebitis in Eales' disease

PURPOSE

Oxidative damage to cellular membranes plays an important role in the pathobiology of tissue injury. Free radical-induced peroxidation of membrane lipid and protein is associated with alterations in cellular, morphological, biochemical, and physical dynamics, which are related to the mobility of lipid molecules. Retinal photoreceptors and platelets have been shown to be an easy target of oxidants because of their high proportion of polyunsaturated fatty acids. This study was undertaken, for the first time, to investigate membrane fluidity in the platelets of patients with Eales' disease.

METHODS

Assays of malonaldialdehyde levels and the enzymes superoxide dismutase and catalase and fluorescence polarization, for estimating membrane fluidity, were carried out on platelets from 20 patients with Eales' disease (stage 1 characterized by periphlebitis of small (1a) and large (1b) caliber vessels with superficial retinal hemorrhages) and 15 healthy controls.

RESULTS

A significant increase was observed in the malonaldialdehyde levels. A significant decrease in the activity of superoxide dismutase and catalase was also observed. Platelet fluorescence polarization was significantly higher in the patients, indicating decreased membrane fluidity compared to controls (p<0.01).

CONCLUSION

A decrease in platelet membrane fluidity occurs as a result of oxidative stress in retinal periphlebitis in Eales' disease. The decreased membrane fluidity suggests alterations in the physiological events, which may result in alterations in the functioning of retinal photoreceptors.

The effect of dietary menhaden, olive, and coconut oil fed with three levels of vitamin E on plasma and liver lipids and plasma fatty acid composition in rats

The effect of dietary fats with varying degrees of unsaturation in the presence of different concentrations of vitamin E on tissue lipid levels was studied in rats. Rats were fed either menhaden oil, olive oil or coconut oil at 15% levels with either 0.1, 0.3 or 0.6 mg/g of vitamin E as alpha-tocopherol for four weeks. Rat serum and liver were analyzed for total cholesterol, HDL-cholesterol, triacylglycerol and phospholipids. In addition, fatty acid composition of serum lipids was also analyzed. Serum total cholesterol and triacylglycerol were significantly lower in rats fed menhaden oil than in those fed olive or coconut oil, while the HDL-cholesterol was significantly higher in serum of rats fed menhaden and olive oil than in those fed coconut oil. Levels of vitamin E in the diet had only a significant effect on serum cholesterol and liver phospholipids. The Pearson correlation coefficient showed a significant positive relationship between serum triacylglycerol and total cholesterol, and a negative correlation between triacylglycerol and HDL-cholesterol, and between total and HDL-cholesterol.In the liver, total cholesterol was significantly higher in rats fed coconut oil than in rats fed menhaden oil. Total liver phospholipids were lower in rats fed either coconut oil or olive oil compared to those fed menhaden oil, especially with higher levels of vitamin E intake. Higher levels of vitamin E in the diet appear to increase triacylglycerol and phospholipids in livers of rats fed menhaden oil. In the liver a significant negative correlation was observed between phospholipids and cholesterol. The type and degree of unsaturation (polyunsaturated fatty acids in menhaden oil, monounsaturated fatty acids in olive oil and saturated fatty acids in coconut oil) significantly affected plasma and tissue lipids.

Membrane changes in rat erythrocyte ghosts on ghee feeding

Alterations in membrane lipid composition is known to result in functional and structural changes in the membrane, and dietary lipids play an important role in this change. It was of interest to study the influence of ghee feeding to the rat on membrane structure and function. The activities of membrane bound enzymes Na+ K+ ATPase and Acetylcholinesterase were studied as an index of membrane changes. Male weanling rats were fed 2.5% fresh or thermally oxidized ghee in the diet for a period of 8 weeks. The control rats were fed groundnut oil. A decrease of 28% in the membrane fluidity of erythrocyte ghost membranes was observed in the oxidized ghee fed group at 37 degrees C, by fluorescence polarization measurements using 1,6-Diphenyl-1,3,5-hexatriene as a probe. The activities of Na+ K+ ATPase and Acetylcholinesterase showed an increase of 65 and 200% respectively after feeding oxidized ghee (2.5%). Also changes in Na+, K+ and ATP kinetics were observed in these rats. Increased membrane lipid peroxidation (80%) and C/PL ratio (11%) in the oxidized ghee fed group was observed. Marginal changes in the fatty acid composition were also seen. Further, an increase in the osmotic fragility of erythrocytes was observed in the oxidized ghee fed rats. It is inferred from these experiments that consumption of oxidized ghee with the diet affects the erythrocyte ghost membrane structure and function at 2.5% level, whereas consumption of fresh ghee has no effect on the erythrocyte membrane.

Modifications of erythrocyte membrane fluidity from patients with anorexia nervosa before and after refeeding

Erythrocyte membrane characteristics were compared in 15 normal women and 15 women with anorexia nervosa; the patients were studied at hospital admission and again after 1 month of refeeding. At admission, physical properties of erythrocyte membranes, studied with electron spin resonance spectrometry, significantly differed between the anorexic patients and the normal volunteers. Fluidity from the hydrophobic part of the erythrocyte membrane, estimated by the correlation frequency, was decreased in the patients. After 1 month of refeeding, fluidity increased. One of the possible mechanisms of the variation of membrane fluidity could be the effect of cholesterol on membrane structure. Increased cholesterol levels in anorexic subjects could reduce fluidity. These alterations in membrane fluidity could explain some of the neurobiological abnormalities observed in anorexia nervosa.

Effect of fish oil and vitamin E on ethanol-induced changes in membrane ATPases

We evaluated whether fish oil or vitamin E administration affected ethanol-induced changes in membrane ATPases. Male Wistar rats (225-250 g) were fed, through a gastric tube a liquid diet containing fish oil (25% of calories) and ethanol for one month. Another group of animals was given supplemental vitamin E (300 u/kg). In the pair-fed control animals, ethanol-derived calories were replaced with dextrose. The blood ethanol levels were maintained between 150 and 350 mg/dL. At sacrifice, the red cells were immediately washed with ice-cold saline, membranes were prepared and ATPases measured. These was no difference in the Na+K+ ATPase, Ca2+ ATPase and Mg2+ ATPase activities between the fish oil-dextrose and corn oil-dextrose groups. A decrease in Ca2+ ATPase and an increase in Na+K+ ATPase was seen with ethanol feeding; these change are similar to those seen in corn oil-ethanol fed rats. In contrast, Vitamin E administration prevented the ethanol-induced changes in ATPase. This observation provides support for the role of lipid peroxidation in alcohol-induced changes in cell membrane ATPase activities.

In vitro exposure to mercury and cadmium alters term human placental membrane fluidity

The effect of incubation with mercury (Hg) as HgCl2 and cadmium (Cd) as CdCl2, at levels of 6 or 12 micrograms/ml of medium, on explants of term human placental microvillus membrane fluidity were studied. After incubation for 6 or 24 hr explants for each dose level were pooled and washed with fresh medium to remove any unbound metal. Placental membranes were separated by differential centrifugation and fluidity was studied by steady-state fluorescence polarization, expressed as the fluorescence anisotropy, r, with 1,6-diphenyl-1,3,5-hexatriene as a probe. The results show that membranes derived from explants incubated for 24 hr with either 6 or 12 micrograms/ml medium of either metal showed fluorescence anisotropy values (i.e., decreased fluidity) significantly higher than that of their respective controls. With 6 micrograms/ml of either metal the decrease in fluidity was highly significant for both metals and with 12 micrograms/ml a further decrease in membrane fluidity was observed with either metal. Both metals accumulated in placental membranes in proportion to their level in the medium. Membrane accumulation of Cd was higher than that of Hg. The cholesterol, phospholipid, and cholesterol-to-phospholipid mole ratios in membranes derived from metal-treated explants were unchanged, compared to their respective controls. However, no changes in membrane fluidity were observed in the samples incubated for 6 hr. In conclusion, exposure of placental cells to Hg and Cd caused accumulation of the metals in the membranes and lowered the membrane fluidity, which may affect membrane function and cause damage to the developing fetus.