Alternations in lipid membrane fluidity and the physical state of cell-surface sialic acid in zinc-deficient rat erythrocyte ghosts

The Effects of Electromagnetic Fields Generated from 1800 MHz Cell Phones on Erythrocyte Rheological Parameters and Zinc Level in Rats

OBJECTIVE

The aim of this study was to investigate the effects of the electromagnetic field generated from the 1800 MHz radiofrequency radiation (EF) on erythrocyte rheological parameters and erythrocyte zinc levels.

MATERIAL AND METHODS

Twenty-four male Wistar Albino rats were randomly grouped as follows: 1) two control groups and 2) study groups: i) Group A: EF exposed group (2.5 h/day for 30 days, the phone on stand-by), and ii) Group B: EF exposed group (2.5 min/day for 30 days, the phone ringing in silent mode). At the end of the experimental period erythrocyte rheological parameters such as erythrocyte deformability and aggregation were determined by an ectacytometer. Erythrocyte zinc level, which affects hemorheological parameters, was also measured by atomic absorption spectrophotometer.

RESULTS

Erythrocyte deformability was decreased in both study groups but the decrease in group A was not statistically significant. Exposure to EF did not have any significant effect on erythrocyte aggregation. On the other hand, erythrocyte zinc level was significantly reduced in both study groups.

CONCLUSION

Exposure to EF may have decreased tissue oxygenation due to reduced erythrocyte deformability. Decrease in erythrocyte zinc level may have caused the impairment in erythrocyte deformability.

Trace elements in human physiology and pathology: zinc and metallothioneins

Zinc is one of the most abundant nutritionally essential elements in the human body. It is found in all body tissues with 85% of the whole body zinc in muscle and bone, 11% in the skin and the liver and the remaining in all the other tissues. In multicellular organisms, virtually all zinc is intracellular, 30-40% is located in the nucleus, 50% in the cytoplasm, organelles and specialized vesicles (for digestive enzymes or hormone storage) and the remainder in the cell membrane. Zinc intake ranges from 107 to 231 micromol/d depending on the source, and human zinc requirement is estimated at 15 mg/d. Zinc has been shown to be essential to the structure and function of a large number of macromolecules and for over 300 enzymic reactions. It has both catalytic and structural roles in enzymes, while in zinc finger motifs, it provides a scaffold that organizes protein sub-domains for the interaction with either DNA or other proteins. It is critical for the function of a number of metalloproteins, inducing members of oxido-reductase, hydrolase ligase, lyase family and has co-activating functions with copper in superoxide dismutase or phospholipase C. The zinc ion (Zn(++)) does not participate in redox reactions, which makes it a stable ion in a biological medium whose potential is in constant flux. Zinc ions are hydrophilic and do not cross cell membranes by passive diffusion. In general, transport has been described as having both saturable and non-saturable components, depending on the Zn(II) concentrations involved. Zinc ions exist primarily in the form of complexes with proteins and nucleic acids and participate in all aspects of intermediary metabolism, transmission and regulation of the expression of genetic information, storage, synthesis and action of peptide hormones and structural maintenance of chromatin and biomembranes.

Characteristics of zinc binding to human red blood cell membranes

The objective of the present study was to standardize the analysis of zinc binding on human red blood cell (RBC) membranes in 20 normal adults. The displacement studies revealed that at the maximal stable zinc concentration tested (600 microM), 57% (mean) of the bound 65Zn was displaced and to displace half maximal 65Zn, the stable zinc concentration was 300 microM. Scatchard plots revealed two classes of binding sites for zinc on RBC membranes: one with higher affinity, Kd = 1.20 x 10(-5) M (site I), and the other with lower affinity, Kd = 2.77 x 10(-4) M (site II). Binding sites occupancy was 97% means and 58.5% means for sites I and II, respectively. The displacement was affected by temperature, membrane protein concentration, freezing, thawing, and dialysis. Other metal cations, including Co++, Fe++, and Mn++, had very little effect on 65Zn displacement, in contrast copper displaced 65Zn from its binding sites on RBC membranes. Zinc binding to RBC membranes was rapid and readily reversible in a dynamic equilibrium with its binding sites. It is anticipated that this method will be applicable to studies of a wide variety of diseases specifically related to zinc metabolism in humans as well as in animals.

Zinc status before and after zinc supplementation of eating disorder patients

Reduced food consumption is a major manifestation of zinc (Zn) deficiency. Many manifestations of Zn deficiency are complications of anorexia nervosa and bulimia nervosa. We evaluated serum and 24-hour urinary Zn values in 12 healthy volunteers and 33 eating disorder patients before and after hospitalization which included either Zn supplementation (75 mg Zn/day) or placebo. Bulimics had depressed serum Zn concentrations (p < 0.025). Admission urinary Zn was lower in bulimics (258 +/- 44 micrograms/day), and significantly depressed in anorexics (196 +/- 36 micrograms/day, p < 0.005) vs controls (376 +/- 45 micrograms/day). During hospitalization, serum Zn concentrations increased in all supplemented patients vs no change with placebo. Urinary Zn excretion increased in supplemented bulimics (p < 0.001) and placebo (p < 0.05). Urinary Zn excretion markedly increased in supplemented anorexics (179 +/- 65 to 1052 +/- 242 micrograms/day); however, placebo values fell or remained unacceptably low (admission 208 +/- 48 micrograms/day; discharge 160 +/- 17 micrograms/day). By dietary history, controls consumed the Recommended Dietary Allowance (RDA) for Zn (11.95 +/- 1.25 mg/day); anorexics 6.46 +/- 1.14 mg/day; and bulimics 8.93 +/- 1.29 mg/day. We suggest that Zn deficiency may act as a "sustaining" factor for abnormal eating behavior in certain eating disorder patients.

The effect of dietary zinc deficiency on the lipid composition of the rat erythrocyte membrane

The effect of dietary zinc deficiency in the rat on the lipid composition of the erythrocyte membrane was determined. Weanling male Wistar rats were fed an egg white-based diet containing less than 1.0 mg Zn/kg diet ad libitum. Control rats were either pair-fed or ad libitum-fed the basal diet supplemented with 100 mg Zn/kg diet. A zinc refed group was fed the -Zn diet until day 18 and then pair-fed the +Zn diet until day 21. The voluntary feed restriction associated with dietary zinc deficiency resulted in erythrocyte membranes that had depressed phospholipid/protein and elevated cholesterol/phospholipid ratios. Similarly, all feed restricted groups had elevated 22-carbon n-3 polyunsaturated fatty acids (PUFA) and depressed 22-carbon n-6 PUFA concentrations in alkenyl-acyl and diacyl glycerophosphoethanolamine, phosphatidylserine and phosphatidylcholine; they also had depressed 24:2n-6 levels in sphingomyelin. The relative concentrations of phospholipids in the membrane was similar between -Zn and +Zn (ad libitum) groups; however, the -Zn group had significantly less phosphatidyl-serine relative to +Zn (pair-fed) controls.

Persistence of metabolic effects after long-term oral feeding of a structured triglyceride derived from medium-chain triglyceride and fish oil in burned and normal rats

The persistence of metabolic effects following long-term oral feeding of a structured triglyceride rich in omega-3 fatty acids was studied in burned and normal rats, and compared with controls fed safflower oil, a long-chain triglyceride high in omega-6 fatty acid content. Male Sprague-Dawley rats were pair-fed a high fat diet as either structured triglyceride or safflower oil for 42 days. On day 43, a jugular catheter was placed, and rats received either a dorsal surface scald or sham injury. Following a 48-hour fast, body weight, nitrogen loss, energy metabolism, and liver weight were measured, and whole-body and tissue-specific protein kinetics were studied by constant intravenous infusion of [1-14C]leucine. Plasma albumin, free fatty acids, glucose, insulin, and triglyceride fatty acid composition were determined. Urinary nitrogen loss, energy expenditure, and plasma leucine concentration were elevated in burned rats, confirming the presence of an injury response. Rats previously fed structured triglyceride had greater liver weight, total liver protein, and percentage of leucine flux oxidized, and plasma levels of glucose and insulin were increased. Plasma leucine concentration was decreased in rats previously fed structured triglyceride. Plasma triglyceride and phospholipid fatty acid analysis showed a reduction in arachidonic acid and an increase in omega-3 fatty acids in rats previously fed structured triglyceride. Long-term feeding of structured triglyceride induced major systemic metabolic changes related to the dietary fatty acid composition that persist after the diet is discontinued.

The physiological role of zinc as an antioxidant

The purpose of this review is to consider whether an essential biochemical function of zinc (Zn) is to serve as an antioxidant. Zn has been shown to have an antioxidant role(s) in defined chemical systems. Two mechanisms have been elucidated; the protection of sulfhydryl groups against oxidation and the inhibition of the production of reactive oxygens by transition metals. Supraphysiological concentrations of Zn have antioxidant-like effects in organelle-based systems and isolated cell-based systems in vitro. Administration of pharmacological doses of Zn in vivo has a protective effect against general and liver-specific prooxidants. Dietary Zn deficiency causes increased susceptibility to oxidative damage in membrane fractions from some tissues suggesting that increased oxidative stress may be a small but significant component of the pathology observed in dietary Zn deficiency. However, the biochemical basis for Zn deficiency pathology remains unelucidated; critical antioxidant functions for Zn may still be uncovered.

Electron spin resonance investigation of the interaction of the anion and glucose transport inhibitor, p-azidobenzylphlorizin, with the human red cell membrane

The membrane perturbations caused by the interaction of p-azidobenzylphlorizin (p-AzBPhz), a potential photoaffinity labeling agent of the anion and D-glucose transporters in the human erythrocyte, have been studied using electron spin resonance (ESR) spectrometry. Two lipid-specific spin labels have been employed; one of these agents, a hexadecyl-quarternary amine with the nitroxide reporter group covalently attached to the cationic nitrogen, (CAT-16), has been used to monitor changes in the physical state of the membrane's extracellular phospholipid/water interface. The other spin label, 5-doxylstearic acid (5-NS), is designed to examine the order and motion of the lipid bilayer near the cell surface. In separate experiments, intact human red cells labeled with these lipid-specific spin labels were exposed to small amounts of the phlorizin azide. A dose-dependent alteration in CAT-16 motion was observed, but the p-AzBPhz interaction with the membrane had no effect on the spectrum of 5-NS. The half-maximal effect of the phlorizin derivative on the CAT-16 spectrum occurred when about 2 million molecules were bound to each cell. This is also the combined amount of band 3 and band 4.5 present in the red cell membrane and represents the concentration necessary to inhibit both anion and glucose transport. Our results suggest that the first p-AzBPhz molecules binding to the red cell membrane interact with the anion and sugar transporters, and not with the bulk lipid bilayer.