A selective estrogen receptor modulator, tamoxifen, and membrane fluidity of erythrocytes in normotensive and hypertensive postmenopausal women: an electron paramagnetic resonance investigation

BACKGROUND: Recent studies have shown that tamoxifen, which belongs to a group called selective estrogen receptor modulators (SERM), may exert protective effects against cardiovascular diseases and stroke in postmenopausal women. On the other hand, abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. The present study was performed to investigate the effects of tamoxifen on cell membrane fluidity (a reciprocal value of membrane microviscosity) in normotensive and hypertensive postmenopausal women. METHODS AND RESULTS: We used an electron paramagnetic resonance (EPR) and spin-labeling method. Tamoxifen significantly 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 normotensive postmenopausal women (mean +/- SEM, order parameter value; control 0.719 +/- 0.002, n = 41; tamoxifen 1 x 10(-7) mol/L 0.704 +/- 0.002, n = 41, P < .0001; tamoxifen 1 x 10(-6) mol/L 0.696 +/- 0.002, n = 41, P < .0001; tamoxifen 1 x 10(-5) mol/L 0.692 +/- 0.002, n = 41, P < .0001). The finding indicated that tamoxifen increased the membrane fluidity and improved the membrane microviscosity of erythrocytes. The membrane action of tamoxifen was antagonized by the estrogen receptor antagonist ICI 182,780. The effect of tamoxifen was significantly potentiated by the nitric oxide (NO) donors, l-arginine and S-nitroso-N-acetylpenicillamine, and a cGMP analog 8-bromo-cGMP. In contrast, the change evoked by tamoxifen was counteracted by the NO synthase inhibitors 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 in normotensive postmenopausal women. The effect of tamoxifen on the membrane fluidity was more pronounced in hypertensive postmenopausal women than in normotensive postmenopausal women. CONCLUSIONS: These results showed that tamoxifen increased the membrane fluidity of erythrocytes and improved the rigidity of cell membranes in postmenopausal women, to some extent, through the NO- and cGMP-dependent mechanisms. Furthermore, the greater effect of tamoxifen in hypertensive postmenopausal women suggests that tamoxifen could have a beneficial effect in regulating the blood rheologic behavior and in the improvement of the microcirculation in hypertension.     

Regulation of glucose transport by ROCK1 differs from that of ROCK2 and is controlled by actin polymerization

A role of Rho-associated coiled-coil-containing protein kinase (ROCK)1 in regulating whole-body glucose homeostasis has been reported. However, cell-autonomous effects of ROCK1 on insulin-dependent glucose transport in adipocytes and muscle cells have not been elucidated. To determine the specific role of ROCK1 in glucose transport directly, ROCK1 expression in 3T3-L1 adipocytes and L6 myoblasts was biologically modulated. Here, we show that small interfering RNA-mediated ROCK1 depletion decreased insulin-induced glucose transport in adipocytes and myoblasts, whereas adenovirus-mediated ROCK1 expression increased this in a dose-dependent manner, indicating that ROCK1 is permissive for glucose transport. Inhibition of ROCK1 also impaired glucose transporter 4 translocation in 3T3-L1 adipocytes. Importantly, the ED?? of insulin for adipocyte glucose transport was reduced when ROCK1 was expressed, leading to hypersensitivity to insulin. These effects are dependent on actin cytoskeleton remodeling, because inhibitors of actin polymerization significantly decreased ROCK1's effect to promote insulin-stimulated glucose transport. Unlike ROCK2, ROCK1 binding to insulin receptor substrate (IRS)-1 was not detected by immunoprecipitation, although cell fractionation demonstrated both ROCK isoforms localize with IRS-1 in low-density microsomes. Moreover, insulin's ability to increase IRS-1 tyrosine 612 and serine 632/635 phosphorylation was attenuated by ROCK1 suppression. Replacing IRS-1 serine 632/635 with alanine reduced insulin-stimulated phosphatidylinositol 3-kinase activation and glucose transport in 3T3-L1 adipocytes, indicating that phosphorylation of these serine residues of IRS-1, which are substrates of the ROCK2 isoform in vitro, are crucial for maximal stimulation of glucose transport by insulin. Our studies identify ROCK1 as an important positive regulator of insulin action on glucose transport in adipocytes and muscle cells.     

The serum vaspin levels are reduced in Japanese chronic hemodialysis patients

Background

Visceral adipose tissue-derived serine proteinase inhibitor (vaspin) is an adipokine identified in genetically obese rats that correlates with insulin resistance and obesity in humans. Recently, we found that 7% of the Japanese population with the minor allele sequence (A) of rs77060950 exhibit higher levels of serum vaspin. We therefore evaluated the serum vaspin levels in Japanese chronic hemodialysis patients.

Methods

Healthy Japanese control volunteers (control; n?=?95, 49.9±6.91?years) and Japanese patients undergoing hemodialysis therapy (HD; n?=?138, 51.4±10.5?years) were enrolled in this study, and serum samples were subjected to the human vaspin RIA system.

Results

The measurement of the serum vaspin levels demonstrated that a fraction of control subjects (n?=?5) and HD patients (n?=?11) exhibited much higher levels (> 10?ng/ml; Vaspin_High group), while the rest of the population exhibited lower levels (< 3?ng/ml; Vaspin_Low group). By comparing the patients in the Vaspin_Low group, the serum vaspin levels were found to be significantly higher in the control subjects (0.87±0.24?ng/ml) than in the HD patients (0.32±0.15?ng/ml) (p?<?0.0001). In the stepwise regression analyses, the serum creatinine and triglyceride levels were found to be independently and significantly associated with the vaspin concentrations in all subjects.

Conclusions

The creatinine levels are negatively correlated with the serum vaspin levels and were significantly reduced in the Japanese HD patients in the Vaspin_Low group.

     

Alpha2-macroglobulin as a promising biomarker for cerebral small vessel disease in acute ischemic stroke patients

Alpha2-macroglobulin is a protease inhibitor that enhances procoagulant properties via the neutralization of plasmin, plasminogen activators and metalloproteinases. Additionally, alpha2-macroglobulin is thought to be involved in inflammatory reactions as a carrier protein for interleukin-6 (IL-6). The objective of this study was to evaluate the usefulness of alpha2-macroglobulin as a biomarker for cerebrovascular diseases. Patients with acute ischemic stroke (n = 159; 93 male and 66 female, 71.6 ± 10.3 years) and patients with no previous history of stroke (n = 77; 38 male and 39 female, 70.7 ± 9.5 years) were consecutively enrolled in this study. White matter lesions were assessed via the fluid-attenuated inversion recovery image of magnetic resonance images using the Fazekas classification. The serum alpha2-macroglobulin levels were measured by nephelometry. The serum alpha2-macroglobulin levels at admission in patients with acute ischemic stroke were higher than those in the control patients (230.2 ± 73.7 vs. 205.0 ± 55.8 mg/dl, p = 0.009). The serum alpha2-macroglobulin levels were positively correlated with age and the severity of the white matter lesions (R ² = 0.048, p < 0.001 and R ² = 0.058, p < 0.001, respectively), although there was no significant association between serum alpha2-macroglobulin levels and IL-6 levels. In addition, multivariate analysis showed that increased serum alpha2-macroglobulin levels were independently associated with the severity of white matter lesions [standardized partial regression coefficient (β) 0.102, p = 0.026]. Increased serum alpha2-macroglobulin levels might be involved in the pathophysiology of acute ischemic stroke. Furthermore, serum alpha2-macroglobulin levels, which were associated with high-grade white matter lesions, may reflect the chronic pathophysiological condition of cerebral small vessel disease.