Erythrocyte membrane abnormalities in hypertension: a comparison between two animal models

Ultra-Small Superparamagnetic Iron-Oxide Nanoparticles Exert Different Effects on Erythrocytes in Normotensive and Hypertensive Rats

We determined erythrocyte physiological and biochemical properties after the single and repeated administration of ultra-small superparamagnetic iron-oxide nanoparticles (USPIONs) in normotensive Wistar–Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Polyethylene glycol-coated USPIONs (transmission electron microscope detected a mean size of ~30 nm and hydrodynamic size ~51 nm) were intravenously administered to rats either in one infusion at nominal dose 1 mg Fe/kg or in two infusions (administered with a difference of 24 h) at nominal dose 2 mg Fe/kg. Results showed that USPIONs did not deteriorate erythrocyte deformability, nitric oxide production, and osmotic resistance in both experimental settings. Both the single and repeated USPION administration elevated erythrocyte deformability in WKY. However, this effect was not present in SHR; deformability in USPION-treated SHR was significantly lower than in USPION-treated WKY. Nitric oxide production by erythrocytes was increased after a single USPION treatment in WKY, so it can be associated with improvement in erythrocyte deformability. Using biomagnetometry, we revealed significantly lower amounts of USPION-originated iron in erythrocytes in SHR compared with WKY. We found a much faster elimination of USPIONs from erythrocytes in hypertensive rats compared with the normotensive ones, which might be relevant for clinical practice in hypertensive patients undergoing clinical examination with the use of iron-oxide nanoparticles.

Disorders of erythrocyte structure and function in hypertensive patients

Background

The prevalence of hypertension is growing at an alarming rate. Increasing attention is being focussed on the oxidative stress accompanying this disease. In this study we examined the impact of this disease on some parameters of erythrocytes and human blood plasma.

Material/Methods

We examined the impact of hypertension on some parameters of erythrocytes and human plasma. The study involved 13 patients with hypertension and 19 healthy subjects. We determined lipid peroxidation, SH groups concentration, antioxidants enzymes activity, ATPase activity, total antioxidant capacity, total cholesterol level and erythrocyte membrane fluidity.

Results

We found an increased level of lipid peroxidation and the concentration of SH groups in membrane proteins in patients with hypertension, and a decrease in the activity of catalase and superoxide dysmutase. No changes were observed in glutathione peroxidase and ATPase activity, level of total antioxidant capacity, total cholesterol level and fluidity of erythrocyte membranes.

Conclusions

These results suggest the existence of an impaired oxidative balance in hypertensive human erythrocytes.

Abnormality of calmodulin activity in hypertension. Evidence of the presence of an activator

An apparent increase of calmodulin (CaM) activity was previously observed in the heart and kidney but not in the liver of spontaneously-hypertensive rats (SHR) and mice compared with their corresponding normotensive controls. As this change was due to an elevated recovery of CaM in the organs of the hypertensive animals, the present study was designed to evaluate its activity in hypertension. A CaM activator, detected in heart and kidney supernatants from hypertensive animals, was found to be responsible for this enhanced recovery. Similar results were obtained with passaged, cultured aortic smooth muscle cells from SHR, indicating that the anomaly was not a mere consequence of elevated blood pressure but rather a genetic expression of cells of hypertensive origin. The activator was heat stable, nondialyzable, and recovered in the fraction precipitated with 30-50% ammonium sulfate. Preliminary extraction studies suggest that the activator is contained in a glycolipid fraction. The stimulation of phosphodiesterase by this activator was calcium and CaM dependent. The activator appears to affect the affinity of the phosphodiesterase for CaM rather than the maximal stimulation. The activator was also present at a low concentration in the heart and kidney of normotensive animals. These findings indicate that at least some of the calcium abnormalities implicated in the pathogenesis of hypertension could be the result of interactions between CaM, calcium, and this activator.

Decreased calcium pump adenosine triphosphatase in red blood cells of hypertensive subjects

Several operationally defined adenosine triphosphatase (ATPase) activities were determined in vitro in red blood cell lysates of normotensive or hypertensive humans: Mg2+-ATPase, Na+,K+-ATPase, and Ca2+ pump ATPase, the latter in the calmodulin-activated and basal states. Basal Ca2+ pump ATPase was defined as the Ca2+-activated ATPase resistant to 10(-4) M trifluoperazine. Subjects were part of a double-blind study in which treatment was divided into several phases: baseline (4 weeks), placebo or calcium (1 g elemental calcium/day, 8 weeks), placebo washout (4 weeks), placebo or calcium (1 g elemental calcium/day, 8 weeks). Irrespective of the phase of treatment, the basal Ca2+ pump ATPase activity in red blood cell lysates of 36 hypertensive subjects was significantly less than that in lysates from 18 normotensive subjects. Other ATPase activities did not differ significantly, although all ATPases tended to be decreased in hypertension. The data are consistent with previous reports of altered membrane Ca2+ binding and transport in hypertension, but the precise changes are not elucidated.

Erythrocyte membrane properties of the chronic alcoholic rat

There is growing evidence for essential or genetic hypertension to be associated with certain membrane abnormalities. We have published previous results on biochemical studies performed on erythrocyte membranes of the Okamoto-Aoki spontaneously hypertensive rat (SHR) and its normotensive control the WKY, reporting evidence of structural and functional alterations in the membranes. These changes could lead to increased calcium permeability and possibly compensatory increase in calcium pump activity that we observed concurrently. Chronic ethanol consumption resulted in mild hypertension in the rats used in the present study. The elevation in blood pressure is not associated with gross membrane changes in the erythrocyte. We noticed, however, that there is a slight elevation in the high affinity Ca2+/Mg2+-ATPase activities together with a trend towards higher osmotic fragility in the red cells of the ethanol-treated rats when compared with controls. These changes could be the result of concurrent reduction in plasma and membrane cholesterol contents also observed in the ethanol-treated animals.