5-nitroxide Stearate Research Articles

PS-C05-12: OMENTIN-1 PREDICTS MEMBRANE FLUIDITY OF RED BLOOD CELLS AND MICROCIRCULATORY FUNCTION IN HYPERTENSIVE SUBJECTS BY THE NITRIC OXIDE-DEPENDENT MECHANISM

Objective: It has been shown that abnormalities in physical properties of the cell membranes may strongly be linked to hypertension. Recent evidence indicates that omentin-1, an adipokine with anti-inflammatory properties, may actively participate in the pathophysiology of hypertension, atherosclerosis and other cardiovascular diseases. However, few studies have evaluated the association between omentin-1 and membrane function in hypertension. The present study was performed to investigate possible relationships among omentin-1, endothelial function and membrane fluidity (a reciprocal value of membrane microviscosity) of red blood cells (RBCs) in patients with essential hypertension and normotensive subjects. Design and method: We measured the membrane fluidity of RBCs with an electron spin resonance (ESR) and spin labeling method. In each ESR spectrum, we calculated the order parameter (S) for the spin-label agent (5-nitroxide stearate). The greater the value of the order parameter (S) was, the lower the membrane fluidity of RBC was. Results: (1) The order parameter (S) obtained from the ESR spectra of RBC membranes was significantly greater in hypertensive subjects (0.727 ± 0.001, n = 64) than in normotensive subjects (0.719 ± 0.001, n = 49, P < 0.0001), indicating that membrane fluidity of RBCs might be reduced in hypertensive subjects compared with normotensive subjects. (2) Plasma omentin-1 levels were lower in hypertensive subjects than in normotensive subjects (HT 0.486 ± 0.014 ng/mL, n = 64, NT 0.537 ± 0.019 ng/mL, n = 49, P < 0.05). Plamsa omentin-1 significantly correlated with plasma nitric oxide (NO)-metabolite levels (an index of endothelial function) (r = 0.392, n = 113, P < 0.0001). (3) Furthermore, the order parameter (S) of RBCs inversely correlated with both plasma omentin-1 (r = -0.347, n = 113, P < 0.001) and plasma NO-metabolites, suggesting that reduced membrane fluidity of RBCs might be associated with decreased levels of plasma omentin-1 and endothelial dysfunction. (4) Multivariate regression analysis showed that, after adjusting for confounding factors, plasma omentin-1 might be an independent predictor of membrane fluidity of RBCs. Conclusions: The ESR study demonstrated that lower plasma omentin-1 levels might have a close correlation with reduced membrane fluidity of RBCs and impaired hemorheologic behavior in hypertensive subjects by the NO-dependent mechanism. It is strongly suggested that plasma omentin-1 could be a putative biomarker for the microcirculatory function in hypertension.

Association of resistin with impaired membrane fluidity of red blood cells in hypertensive and normotensive men: an electron paramagnetic resonance study.

Abnormalities in physical properties of the cell membranes may strongly be linked to hypertension. Recent evidence indicates that resistin may actively participate in the pathophysiology of insulin resistance, diabetes mellitus, hypertension and other circulatory disorders. The present study was undertaken to investigate the possible relationships among plasma resistin, oxidative stress and membrane fluidity (a reciprocal value of membrane microviscosity) in hypertension. We measured the membrane fluidity of red blood cells (RBCs) in hypertensive and normotensive men using an electron paramagnetic resonance (EPR) and spin-labeling method. The order parameter (S) for the spin-label agents (5-nitroxide stearate) in EPR spectra of red blood cell (RBC) membranes was significantly higher in hypertensive men than in normotensive men, indicating that membrane fluidity was decreased in hypertension. Plasma resistin levels were correlated with systolic blood pressure and 8-iso-prostaglandin F2α levels (an index of oxidative stress). Furthermore, the order parameter (S) of RBCs significantly correlated with plasma resistin and plasma 8-isoPG F2α, suggesting that reduced membrane fluidity of RBCs might be associated with hyperresistinemia and increased oxidative stress. Multivariate regression analysis showed that, after adjustment for confounding factors, plasma resistin might be an independent determinant of membrane fluidity of RBCs. The EPR study suggests that resistin might have a close correlation with impaired rheologic behavior of RBCs and microcirculatory dysfunction in hypertension, at least in part, via an oxidative stress-dependent mechanism.

Chronic Kidney Disease Predicts Impaired Membrane Microviscosity of Red Blood Cells in Hypertensive and Normotensive Subjects

Current evidence indicates that abnormalities in physical properties of the cell membranes may be strongly linked to hypertension and other circulatory disorders. Recent studies have shown that chronic kidney disease (CKD) might be a risk factor for cardiovascular and cerebrovascular outcomes. The purpose of the present study was to examine the possible relationship between kidney function and membrane fluidity (a reciprocal value of membrane microviscosity) of red blood cells (RBCs) in hypertensive and normotensive subjects using an electron spin resonance (ESR) and spin-labeling method. The order parameter (S) for the ESR spin-label agent (5-nitroxide stearate) in RBC membranes was significantly higher in hypertensive subjects than in normotensive subjects, indicating that membrane fluidity was decreased in hypertension. The order parameter (S) of RBCs was inversely correlated with estimated glomerular filtration rate (eGFR), suggesting that a decreased eGFR value might be associated with reduced membrane fluidity of RBCs. Multivariate regression analysis also demonstrated that, after adjustment for general risk factors, eGFR might be a significant predictor of membrane fluidity of RBCs. The reduced levels of both membrane fluidity of RBCs and eGFR were associated with increased plasma 8-iso-prostaglandin F2α (an index of oxidative stress) and decreased plasma nitric oxide (NO)-metabolites, suggesting that kidney function could be a determinant of membrane microviscosity of RBCs, at least in part, via oxidative stress- and NO-dependent mechanisms. The ESR study suggests that CKD might have a close correlation with impaired rheologic behavior of RBCs and microcirculatory disorders in hypertensive subjects.

Associations of oxidative stress and inflammation and their role in the regulation of membrane fluidity of red blood cells in hypertensive and normotensive men: An electron spin resonance investigation

There is evidence showing that increased levels of oxidative stress and C-reactive protein (CRP) might be associated with obesity, hypertension, atherosclerosis and other cardiovascular diseases. This study was undertaken to investigate possible relationships among plasma 8-iso-prostaglandin F2α (8-iso-PG F2α: an index of oxidative stress), high-sensitivity (hs)-CRP and membrane fluidity (a reciprocal value of microviscosity) in hypertensive and normotensive men using an electron spin resonance (ESR)-method. The order parameter (S) for the spin-label agents (5-nitroxide stearate) of red blood cell (RBC) membranes in the ESR spectra was significantly higher in hypertensive men than in normotensive men, indicating that membrane fluidity was decreased in hypertensive men. Both plasma 8-iso-PG F2α and hs-CRP levels were significantly increased in hypertensive men compared with normotensive men. In addition, plasma plasma 8-iso-PG F2α levels were correlated with plasma hs-CRP levels. In contrast, plasma nitric oxide (NO)-metabolites were lower in hypertensive men than in normotensive men, and inversely correlated with plasma 8-iso-PG F2α and hs-CRP. The order parameter(S) of RBCs was correlated with plasma 8-iso-PG F2α and plasma hs-CRP, and inversely correlated with plasma NO-metabolites, suggesting that reduced membrane fluidity of RBCs might be associated with increased oxidative stress, inflammation and endothelial dysfunction. Multivariate regression analysis also showed that, after adjusting for general risk factors, both plasma 8-iso-PG F2α and hs-CRP were significant determinants of membrane fluidity of RBCs. The ESR suggests that associations of oxidative stress and inflammation might have a close correlation with impaired rheologic behavior of RBCs and microcirculatory dysfunction in hypertensive men.

Roles of Adiponectin and Oxidative Stress in the Regulation of Membrane Microviscosity of Red Blood Cells in Hypertensive Men—An Electron Spin Resonance Study

This study was undertaken to investigate possible relationships among plasma adiponectin, 8-iso-prostaglandin F2α (8-iso-PG F2α: an index of oxidative stress), and membrane fluidity (a reciprocal value of microviscosity) in hypertensive and normotensive men using an electron spin resonance-method. The order parameter (S) for the spin-label agent (5-nitroxide stearate) in red blood cell (RBC) membranes was higher in hypertensive men than in normotensive men, indicating that membrane fluidity was decreased in hypertension. Plasma adiponectin and NO metabolites levels were lower in hypertensive men than in normotensive men. In contrast, plasma 8-iso-PG F2α levels were increased in hypertensive men compared with normotensive men. Plasma adiponectin concentration was correlated with plasma NO-metabolites, and inversely correlated with plasma 8-iso-PG F2α. The order parameter (S) of RBCs was inversely correlated with plasma adiponectin and plasma NO metabolite levels, and positively correlated with plasma 8-iso-PG F2α, suggesting that the reduced membrane fluidity of RBCs might be associated with hypoadiponectinemia, endothelial dysfunction, and increased oxidative stress. In a multivariate regression analysis, adiponectin and 8-iso-PG F2α were significant determinants of membrane fluidity of RBCs after adjustment for general risk factors. These results suggest that adiponectin and oxidative stress might have a close correlation with rheologic behavior and microcirculation in hypertension.

Electron paramagnetic resonance investigation on modulatory effect of benidipine on membrane fluidity of erythrocytes in essential hypertension

It has been shown that benidipine, a long-lasting calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate whether orally administered benidipine might influence the membrane function in patients with essential hypertension. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. In the preliminary study using erythrocytes obtained from healthy volunteers, benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS in the EPR spectra in vitro. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. In addition, it was demonstrated that the effect of benidipine on membrane fluidity of erythrocytes was significantly potentiated by the NO-substrate, L-arginine. In the separate series of the study, we observed that orally administered benidipine for 4 weeks significantly increased the membrane fluidity of erythrocytes with a concomitant increase in plasma NO metabolite levels in hypertensive subjects. The results of the present study demonstrated that benidipine might increase the membrane fluidity and improve the microviscosity of erythrocytes both in vitro and in vivo, to some extent, by the NO-dependent mechanism. Furthermore, it is strongly suggested that orally administered benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in hypertensive subjects.

Adiponectin and Membrane Fluidity of Erythrocytes in Normotensive and Hypertensive Men

Abnormalities in physicochemical properties of the cell membranes may underlie the defects that are strongly linked to hypertension. Recent evidence indicates that adiponectin may have protective effects against cardiovascular diseases. The purpose of the present study was to assess the possible link between plasma adiponectin and membrane fluidity in normotensive (NT) and hypertensive (HT) men. We measured the membrane fluidity (a reciprocal value of membrane microviscosity) of erythrocytes in NT and HT men by using an electron paramagnetic resonance and spin-labeling method. The order parameter (S) for the spin label agent (5-nitroxide stearate) and the peak height ratio (h0/h(-1)) for 16-nitroxide stearate in the electron paramagnetic resonance spectra of erythrocytes were significantly higher in HT men than in NT men, indicating that membrane fluidity of erythrocytes was decreased in HT men compared with NT men. Both of plasma adiponectin and nitric oxide (NO) metabolite levels were significantly lower in HT men than in NT men. The plasma adiponectin levels were correlated with plasma NO metabolites. The S and the h0/h(-1) of erythrocytes were inversely correlated with the plasma adiponectin and NO metabolite levels, indicating that the decreased membrane fluidity of erythrocytes was associated with hypoadiponectinemia and reduced plasma NO metabolites. The results of the present study demonstrated that plasma adiponectin levels were lower in HT men than in NT men and that hypoadiponectinemia was associated with decreased membrane fluidity of erythrocytes. The finding suggests that adiponectin may be linked to the rheologic behavior of the erythrocytes and the microcirculation in men, at least in part, by the NO-dependent mechanism.

An Association Between Plasma Asymmetric Dimethylarginine and Membrane Fluidity of Erythrocytes in Hypertensive and Normotensive Men: An Electron Paramagnetic Resonance Investigation

Evidence indicates that increased levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, are associated with increased risk of vascular dysfunction. The present study was performed to assess the possible relationship between plasma ADMA levels and membrane fluidity in hypertensive and normotensive men. Membrane fluidity (a reciprocal value of membrane microviscosity) of erythrocytes in hypertensive (n = 38) and normotensive (n = 35) men were measured using an electron paramagnetic resonance (EPR) and spin-labeling method. The order parameter (S) for the spin-label agent (5-nitroxide stearate) in the EPR spectra of erythrocyte membranes was significantly higher in hypertensive men than in normotensive men (mean +/- SEM: hypertensive subjects, 0.725 +/- 0.001,n = 38; normotensive subjects, 0.713 +/- 0.001, n = 35, P < .001), indicating that membrane fluidity of erythrocytes was decreased in hypertensive men compared with normotensive men. Plasma NO metabolite (nitrite and nitrate) concentration was lower in hypertensive than in normotensive men. In contrast, plasma ADMA levels were higher in hypertensive than in normotensive men. In the overall analysis of hypertensive and normotensive men, the order parameter (S) of erythrocytes was inversely correlated with plasma NO metabolites (r = -0.36, n = 73, P < .01) and positively correlated with plasma ADMA levels (r = 0.44, n = 73, P < .001), indicating that the reduced membrane fluidity of erythrocytes was associated with decreased NO and increased ADMA levels in plasma. When correlation analysis was performed separately for hypertensive and normotensive men, there was a positive correlation between plasma ADMA levels and the order parameter (S) of erythrocytes in both groups. The results of the present study showed that the plasma ADMA levels were elevated in hypertensive men and associated with lower membrane fluidity of erythrocytes, suggesting that ADMA might have a close correlation with the rheologic behavior of erythrocytes and the microcirculation in hypertension.

A calcium channel blocker, benidipine, improves cell membrane fluidity in human subjects via a nitric oxide—dependent mechanism: An electron paramagnetic resonance investigation

Recent studies have revealed that benidipine, a long-acting dihydropyridine-type of calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate the effects of benidipine and NO on the membrane function in human subjects. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. Benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(o)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in normotensive volunteers. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of benidipine was significantly potentiated by the NO donor, S-nitroso-n-acetylpenicillamine, and by the cyclic guanosine 3', 5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by benidipine was counteracted by the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester and asymmetric dimethyl-L-arginine. These results demonstrated that benidipine increased the membrane fluidity of erythrocytes, at least in part, via the NO- and cGMP-dependent mechanism. Furthermore, the data strongly suggest that benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in humans.

Hormone replacement therapy improves membrane fluidity of erythrocytes in postmenopausal women: an electron paramagnetic resonance investigation

Background Many studies have shown that hormone replacement therapy (HRT) might provide protection against the development of hypertension and arteriosclerosis in postmenopausal women. However, the precise mechanism underlying its benefits is unclear. This question was addressed in an electron spin resonance (EPR) study of membrane function of erythrocytes in postmenopausal women. The purpose of this study was to investigate the effects of HRT on membrane fluidity of erythrocytes in postmenopausal women by means of the EPR and spin-labeling method. Methods The healthy postmenopausal women were randomly divided into the HRT group ( n = 14) receiving the conjugated estrogen with medroxyprogesterone for 3 months and the non-HRT control group ( n = 14). We measured membrane fluidity of erythrocytes in postmenopausal women before and after the trial period. Results The HRT group showed a significant decrease in blood pressure (BP) after treatment (systolic BP 145.7 ± 5.5 v 123.3 ± 5.1 mm Hg, n = 14, mean ± SEM, P < .05). The order parameter (S) for 5-nitroxide stearate in the EPR spectra of erythrocyte membranes decreased significantly in the HRT group (S: 0.718 ± 0.002 v 0.695 ± 0.002, n = 14, P < .01). The finding indicated that HRT increased the membrane fluidity of erythrocytes and improved the microviscosity of the cell membranes in postmenopausal women. Conclusions These results are consistent with the hypothesis that HRT might have a beneficial effect on the membrane rheologic behavior of erythrocytes and the microcirculation in postmenopausal women.

Nitric oxide is a determinant of membrane fluidity of erythrocytes in postmenopausal women: an electron paramagnetic resonance investigation

In the present study, to determine a possible role of nitric oxide (NO) in the regulation of membrane functions, we examined the relationship between plasma NO level and membrane fluidity of erythrocytes in postmenopausal women. We evaluated the membrane fluidity of erythrocytes obtained from hypertensive and normotensive postmenopausal women by means of an electron paramagnetic resonance (EPR) and spin labeling method. The EPR study revealed that the order parameter (S) for 5-nitroxide stearate in erythrocyte membranes was significantly greater in hypertensive postmenopausal women than in normotensive postmenopausal women. The finding indicated that the membrane fluidity of erythrocytes was decreased in hypertensive postmenopausal women compared with normotensive postmenopausal women. The plasma level of the NO metabolites (nitrite and nitrate) while fasting was significantly lower in hypertensive postmenopausal women than in normotensive postmenopausal women. In addition, the order parameter (S) in the EPR spectra of erythrocyte membranes was inversely correlated with the plasma NO metabolite level, which indicated that the lower membrane fluidity of erythrocytes was associated with the lower plasma NO level in postmenopausal women. These results are consistent with the hypothesis that NO may have a crucial role in the regulation of membrane fluidity of erythrocytes in postmenopausal women.

Effect of oestrone on membrane fluidity of erythrocytes is mediated by a nitric oxide-dependent pathway: An electron paramagnetic resonance study.

1. It has been recognized that hormone replacement therapy (HRT) may have a beneficial effect on protection against cardiovascular diseases. Oestrone is the major component of conjugated equiline oestrogens, which are commonly used in HRT. The present study was performed in order to investigate the effects of oestrone on the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labelling method. 2. In an in vitro study, oestrone significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-nitroxide stearate (16-NS) obtained from EPR spectra of erythrocyte membranes. This finding indicated that oestrone may increase the membrane fluidity and improve the membrane microviscosity of erythrocytes. 3. The effect of oestrone was significantly potentiated by the nitric oxide (NO) donor s-nitroso-N-acetylpenicillamine and the cGMP analogue 8-bromo-cGMP. 4. In contrast, the change in membrane fluidity induced by oestrone was antagonized by the NO synthase inhibitors NG-nitro-l-arginine methyl ester and asymmetric dimethyl-l-arginine. 5. The results of the present study show that oestrone significantly increases membrane fluidity and improves the rigidity of cell membranes, which is partially mediated by a NO- and cGMP-dependent pathway. Furthermore, the data may be consistent with the hypothesis that oestrone could have a beneficial effect on the rheological behaviour of erythrocytes and have a crucial role in the regulation of the microcirculation.

Leptin improves membrane fluidity of erythrocytes in humans via a nitric oxide-dependent mechanism—an electron paramagnetic resonance investigation

Abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. Recently, there has been an indication that leptin, the product of the human obesity gene, actively participates not only in the metabolic regulations but also in the control of cardiovascular functions. In the present study, to assess the role of leptin in the regulation of membrane properties, the effects of leptin on membrane fluidity of erythrocytes in humans are examined. The membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method is determined. In an in vitro study, leptin decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in healthy volunteers. The finding indicated that leptin increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of leptin on the membrane fluidity was significantly potentiated by the nitric oxide (NO) donors, l-arginine and S-nitroso- N-acetylpenicillamine (SNAP), and a cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by leptin was significantly attenuated in the presence of the NO synthase inhibitors, N G-nitro- l-arginine-methyl-ester ( l-NAME) and asymmetric dimethyl- l-arginine (ADMA). The results of the present study showed that leptin increased the membrane fluidity and improved the rigidity of cell membranes to some extent via an NO- and cGMP-dependent mechanism. Furthermore, the data also suggest that leptin might have a crucial role in the regulation of rheological behavior of erythrocytes and microcirculation in humans.

Synergistic role of progesterone and nitric oxide in the regulation of membrane fluidity of erythrocytes in humans: an electron paramagnetic resonance investigation

Background It has been shown that progesterone may actively participate in the regulation of blood pressure and other cardiovascular regulations. However, the precise mechanism underlying its effects is unclear. Methods In the present study, we examined the effects of progesterone on membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method. Results In an in vitro study, progesterone significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. The finding indicates that progesterone might increase the membrane fluidity and improve the membrane microviscosity of erythrocytes. The effect of progesterone was significantly potentiated by the nitric oxide (NO) donor, S-nitroso- N-acetylpenicillamine (SNAP) and a cyclic guanosine monophosphate (cGMP) analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by progesterone was attenuated in the presence of the NO synthase inhibitors, N G-nitro- l-arginine-methyl-ester (L-NAME) and asymmetric dimethyl- l-arginine (ADMA). Conclusions The results of the present study showed that progesterone increased the membrane fluidity of erythrocytes and ameliorated the rigidity of cell membranes, at least in part, by an NO-dependent mechanism. Furthermore, the data strongly suggest that progesterone might be involved in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in humans.

Electron paramagnetic resonance investigation on modulatory effect of 17beta-estradiol on membrane fluidity of erythrocytes in postmenopausal women.

Many studies have shown that estrogen may exert cardioprotective effects and reduce the risk of hypertension and coronary events. On the other hand, it has been proposed that cell membrane abnormalities play a role in the pathophysiology of hypertension, although it is not clear whether estrogen would influence membrane function in essential hypertension. The present study was performed to investigate the effects of 17beta-estradiol (E(2)) on membrane fluidity of erythrocytes in normotensive and hypertensive postmenopausal women. We determined the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance and spin-labeling method. In an in vitro study, E(2) significantly decreased the order parameter for 5-nitroxide stearate and the peak height ratio for 16-nitroxide stearate obtained from electron paramagnetic resonance spectra of erythrocyte membranes in normotensive postmenopausal women. The finding indicates that E(2) might increase the membrane fluidity of erythrocytes. The effect of E(2) was significantly potentiated by the NO donor, S-nitroso-N-acetylpenicillamine, and a cGMP analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by E(2) was attenuated in the presence of the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester, and asymmetric dimethyl-L-arginine. In hypertensive postmenopausal women, the membrane fluidity of erythrocytes was significantly lower than that in normotensive postmenopausal women. The effect of E(2) on membrane fluidity was significantly more pronounced in the erythrocytes of hypertensive postmenopausal women than in the erythrocytes of normotensive postmenopausal women. The results of the present study showed that E(2) significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the greater action of E(2) in hypertension might be consistent with the hypothesis that E(2) could have a beneficial effect in regulating rheological behavior of erythrocytes and could have a crucial role in the improvement of the microcirculation in hypertension.

Hyperinsulinemia and membrane fluidity: Hyperinsulinemia is a determinant of membrane fluidity of erythrocytes in essential hypertension

In the present study, to determine a possible role of insulin in the regulation of membrane functions, we have examined the relationship between plasma insulin level and membrane fluidity of erythrocytes in patients with essential hypertension and normotensive subjects. Membrane fluidity of erythrocytes obtained from hypertensive and normotensive subjects were evaluated by means of an electron paramagnetic resonance and spin-labeling method. The order parameter (S for 5-nitroxide stearate) and the peak height ratio (ho/h-1 for 16-nitroxide stearate) obtained from electron paramagnetic resonance spectra of erythrocyte membranes were significantly higher in patients with essential hypertension than in normotensive subjects. The finding indicated that the erythrocyte membrane fluidity was lower in essential hypertension than in normotensive controls. The plasma concentration of insulin while fasting was also significantly greater in hypertensive patients than in normotensive subjects. In addition, the plasma insulin level was significantly correlated with the values of the order parameter (S) and the peak height ratio (ho/h-1), which showed that the higher plasma insulin was associated with the lower membrane fluidity of erythrocytes. These results support the hypothesis that insulin may actively participate in the regulation of membrane fluidity of erythrocytes in essential hypertension.

5-Aminosalicylic acid protection against oxidative damage to synaptosomal membranes by alkoxyl radicals in vitro.

The antioxidant properties of 5-aminosalicylic acid in vitro were evaluated in a synaptosomal membrane system prepared from gerbil cortical synaptosomes using EPR spin labeling and spectroscopic techniques. MAL-6 (2,2,6,6-tetramethyl-4-maleimidopiperidin-1-oxyl) and 5-NS (5-nitroxide stearate) spin labels were used to assess changes in protein oxidation and membrane lipid fluidity, respectively. Synaptosomal membranes were subjected to oxidative stress by incubation with 1 mM azo-bis(isobutyronitrile) (AIBN) or 1 mM 2,2'-azobis(amidino propane) dihydrochloride (AAPH) at 37 degrees C for 30 minutes. The EPR analyses of the samples showed significant oxidation of synaptosomal proteins and a decrease in membrane fluidity. 5-Aminosalicylic acid also was evaluated by means of FRAP (the ferric reducing ability of plasma) test as a potential antioxidant. 5-Aminosalicylic acid also showed protection against the oxidation in gerbil cortical synaptosomes system caused by AIBN and AAPH. These results are consistent with the notion of antioxidant protection against free radical induced oxidative stress in synaptosomal membrane system by this agent.

Estriol improves membrane fluidity of erythrocytes by the nitric oxide-dependent mechanism: an electron paramagnetic resonance study.

The present in vitro study was performed to investigate the effects of estriol (E3) on membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labeling method. E3 was shown to significantly decrease the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. This finding indicated that E3 might increase the membrane fluidity of erythrocytes. The effect of E3 was significantly potentiated by the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine 3',5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change in the membrane fluidity induced by E3 was antagonized by the NO synthase inhibitor, L-NG-nitroarginine-methyl-ester (L-NAME), and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that E3 significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the data might be consistent with the hypothesis that E3 could have a beneficial effect on the rheological behavior of erythrocytes and may play a crucial role in the regulation of microcirculation.

Nitric Oxide Improves Membrane Fluidity of Erythrocytes in Essential Hypertension: An Electron Paramagnetic Resonance Investigation

It has been shown that rheological abnormality might be an etiological factor in hypertension. Recent studies have revealed that human erythrocytes possess a nitric oxide (NO) synthase and that this activation might be involved in the regulation of rheological properties of erythrocytes. The present study was undertaken to investigate the role of NO in the regulation of membrane functions of erythrocytes in patients with essential hypertension by means of an electron paramagnetic resonance (EPR) and spin-labeling method. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h0/h−1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner. The finding indicated that the NO donor increased the membrane fluidity of erythrocytes. In addition, the effect of SNAP was significantly potentiated by 8-bromo-cyclic guanosine monophosphate. By contrast, the change of the fluidity induced by SNAP was reversed in the presence of l-NG-nitroarginine methyl ester and asymmetric dimethyl l-arginine. In patients with essential hypertension, the membrane fluidity of erythrocytes was significantly lower than in the normotensive subjects. The effect of SNAP was more pronounced in essential hypertension than in normotensive subjects. These results showed that NO increased the membrane fluidity and decreased the rigidity of cell membranes. Furthermore, the greater effect of NO on the fluidity in essential hypertension suggests that NO might actively participate in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in hypertension.

Role of insulin in the regulation of membrane fluidity of erythrocytes in essential hypertension: an electron paramagnetic resonance investigation

In the present study, to determine a possible role of insulin in the regulation of membrane functions, we have examined the effects of insulin on the membrane fluidity of erythrocytes in patients with essential hypertension and normotensive subjects. Membrane fluidity of erythrocytes obtained from hypertensive and normotensive subjects were evaluated by means of an electron paramagnetic resonance (EPR) and a spin-labeling method. In an in vitro study, insulin increased the order parameter (S for 5-nitroxide stearate) and the peak height ratio (ho/h-1 for 16 nitroxide stearate) in the EPR spectra of erythrocyte membranes, which indicated that insulin decreased the membrane fluidity of erythrocytes. The effects of insulin on the membrane fluidity were potentiated in the presence of extracellular Ca 2 + , and in contrast, were antagonized by the Ca 2 + channel blocker diltiazem. Furthermore, the effects of insulin alone and in combination with Ca 2 + on the membrane fluidity were reduced in the erythrocytes from hypertensive subjects compared with the erythrocytes from normotensive controls. The high concentrations of glucose alone produced no significant effects on the membrane fluidity of erythrocytes. These results demonstrated that insulin might actively participate in the regulation of membrane fluidity of erythrocytes, which might be mediated by the intracellular Ca 2 + kinetics.