BLOOD FLOW SHEAR RATES IN ARTERIOLES OF SPONTANEOUSLY HYPERTENSIVE RATS AT EARLY AND ESTABLISHED STAGES OF HYPERTENSION

Rheological Abnormalities in Human Erythrocytes Subjected to Oxidative Inflammation

Erythrocytes are oxygen carriers and exposed to redox cycle in oxygenation and deoxygenation of hemoglobin. This indicates that circulating erythrocytes are vulnerable to the oxidative injury occurring under the imbalance of redox homeostasis. In this review article, two topics are presented concerning the human erythrocytes exposed to the oxidative inflammation including septic and sterile conditions. First, we demonstrate rheological derangement of erythrocytes subjected to acute oxidative injury caused by exogenous generators of reactive oxygen species (ROS). Erythrocyte filterability as whole-cell deformability has been estimated by the gravity-based nickel mesh filtration technique in our laboratory and was dramatically impaired in a time-dependent manner after starting exposure to the ROS generators, that is associated with concurrent progression of membrane protein degradation, phospholipid peroxidation, erythrocyte swelling, methemoglobin formation, and oxidative hemolysis. Second, we introduce an impairment of erythrocyte filterability confirmed quantitatively in diabetes mellitus and hypertension of animal models and patients under treatment. Among the cell geometry, internal viscosity, and membrane property as the three major determinants of erythrocyte deformability, erythrocyte membrane alteration is supposed to be the primary cause of this impairment in these lifestyle-related diseases associated with persistent oxidative inflammation. Excessive ROS trigger the inflammatory responses and reduce the erythrocyte membrane fluidity. Oxidative inflammation increasing erythrocyte membrane rigidity underlies the impaired systemic microcirculation, which is observed in diabetic and/or hypertensive patients. On the other hand, elevated internal viscosity caused by sickle hemoglobin polymerization is a primary cause of impaired erythrocyte filterability in sickle cell disease (SCD). However, oxidative inflammation is also involved in the pathophysiology of SCD. The physiologic level of ROS acts as signaling molecules for adaptation to oxidative environment, but the pathological level of ROS induces suicidal erythrocyte death (eryptosis). These findings provide further insight into the ROS-related pathophysiology of many clinical conditions.

Proteolytic receptor cleavage in the pathogenesis of blood rheology and co-morbidities in metabolic syndrome. Early forms of autodigestion

Abnormal blood rheological properties seldom occur in isolation and instead are accompanied by other complications, often designated as co-morbidities. In the metabolic syndrome with complications like hypertension, diabetes and lack of normal microvascular blood flow, the underlying molecular mechanisms that simultaneously lead to elevated blood pressure and diabetes as well as abnormal microvascular rheology and other cell dysfunctions have remained largely unknown. In this review, we propose a new hypothesis for the origin of abnormal cell functions as well as multiple co-morbidities. Utilizing experimental models for the metabolic disease with diverse co-morbidities we summarize evidence for the presence of an uncontrolled extracellular proteolytic activity that causes ectodomain receptor cleavage and loss of their associated cell function. We summarize evidence for unchecked degrading proteinase activity, e.g. due to matrix metalloproteases, in patients with hypertension, Type II diabetes and obesity, in addition to evidence for receptor cleavage in the form of receptor fragments and decreased extracellular membrane expression levels. The evidence suggest that a shift in blood rheological properties and other co-morbidities may in fact be derived from a common mechanism that is due to uncontrolled proteolytic activity, i.e. an early form of autodigestion. Identification of the particular proteases involved and the mechanisms of their activation may open the door to treatment that simultaneously targets multiple co-morbidities in the metabolic syndrome.

Vascular structural and functional changes: their association with causality in hypertension: models, remodeling and relevance

Essential hypertension is a complex multifactorial disease process that involves the interaction of multiple genes at various loci throughout the genome, and the influence of environmental factors such as diet and lifestyle, to ultimately determine long-term arterial pressure. These factors converge with physiological signaling pathways to regulate the set-point of long-term blood pressure. In hypertension, structural changes in arteries occur and show differences within and between vascular beds, between species, models and sexes. Such changes can also reflect the development of hypertension, and the levels of circulating humoral and vasoactive compounds. The role of perivascular adipose tissue in the modulation of vascular structure under various disease states such as hypertension, obesity and metabolic syndrome is an emerging area of research, and is likely to contribute to the heterogeneity described in this review. Diversity in structure and related function is the norm, with morphological changes being causative in some beds and states, and in others, a consequence of hypertension. Specific animal models of hypertension have advantages and limitations, each with factors influencing the relevance of the model to the human hypertensive state/s. However, understanding the fundamental properties of artery function and how these relate to signalling mechanisms in real (intact) tissues is key for translating isolated cell and model data to have an impact and relevance in human disease etiology. Indeed, the ultimate aim of developing new treatments to correct vascular dysfunction requires understanding and recognition of the limitations of the methodologies used.

Interleukin-10 released by CD4(+)CD25(+) natural regulatory T cells improves microvascular endothelial function through inhibition of NADPH oxidase activity in hypertensive mice

OBJECTIVE

We previously demonstrated that a reduced number of CD(4+)CD(25+)-regulatory T cells (Tregs) was associated with microvascular dysfunction in hypertension. However, the underlying mechanism by which Tregs regulate vascular endothelial function remains unknown.

METHODS AND RESULTS

Control and interleukin (IL)-10(-/-) knockout mice were infused with angiotensin II (400 ng/kg/min) for 2 weeks (hypertensive [HT] and HT-IL-10(-/-)). Endothelium-dependent relaxation (EDR) in response to acetylcholine was significantly reduced in mesenteric resistance artery (MRA) from HT and HT-IL-10(-/-) compared with control and IL-10(-/-) mice. Importantly, the incubation of MRA from HT mice with the conditioned media of cultured Tregs, isolated from control mice, reduced NADPH oxidase activity and improved EDR, whereas no effect was observed in MRA from control mice incubated with the same media. These effects were reversed when MRAs were preincubated with IL-10 antibody or IL-10 receptor antagonist, whereas incubation with transforming growth factor-β receptor antagonist had no effect. The transfer of cultured Tregs, isolated from control mice, into HT-IL-10(-/-) mice reduced systolic blood pressure (SBP) and NADPH oxidase activity and improved EDR in MRA compared with untreated HT-IL-10(-/-) mice. In vivo treatment of HT mice with IL-10 (1000 ng/mouse) significantly reduced SBP and NADPH oxidase activity and improved EDR in MRA compared with untreated HT mice. The transfer of cultured Tregs, isolated from IL-10(-/-) mice, into HT mice did not reduce SBP or NADPH oxidase activity or improve EDR. The incubation of MRA from HT mice with apocynin improved EDR, whereas NADPH oxidase substrate attenuated EDR in MRA from control mice, which was reversed with exogenous IL-10.

CONCLUSION

These data demonstrate that IL-10 released from Tregs attenuates NADPH oxidase activity, which is a critical process in the improvement of microvascular endothelial function in hypertension, suggesting that Tregs/IL-10 could be a therapeutic target for treatment of vasculopathy in hypertension.

Natural regulatory T cells control coronary arteriolar endothelial dysfunction in hypertensive mice

Coronary artery disease in patients with hypertension is increasing worldwide and leads to severe cardiovascular complications. The cellular and molecular mechanisms that underlie this pathologic condition are not well understood. Experimental and clinical research indicates that immune cells and inflammation play a central role in the pathogenesis of cardiovascular diseases. Recently, it has been reported that CD4(+)CD25(+) regulatory T cells (Tregs) regulate heart fibrosis in hypertension. In this study, we determined the role of Tregs in coronary arteriolar endothelial dysfunction in angiotensin II-dependent hypertensive mice. Mice infused with angiotensin II had significantly increased blood pressure, as determined using telemetry, and apoptotic Treg numbers, as measured using flow cytometry. The mice displayed inflammation, assessed by macrophage activation/infiltration into coronary arterioles and the heart, and increased local tumor necrosis factor-α release, which participates in reduced coronary arteriolar endothelial-dependent relaxation in response to acetylcholine using an arteriograph. Hypertensive mice injected with Tregs isolated from control mice had significantly reduced macrophage activation and infiltration, reduced tumor necrosis factor-α release, and improved coronary arteriolar endothelium-dependent relaxation. Our novel data indicate that Tregs are important in the development of coronary arteriolar endothelial dysfunction in hypertension. These results suggest a new direction in the investigation of vascular disease in hypertension and could lead to a therapeutic strategy that involves immune system modulation using Tregs.

Impaired erythrocyte filterability of spontaneously hypertensive rats: investigation by nickel filtration technique

BACKGROUND

Deformability of erythrocytes plays a key role in the impairment of the microcirculation in hypertension. However, erythrocyte deformability in spontaneously hypertensive rats (SHR) during development of hypertension has not been fully investigated so far.

METHODS AND RESULTS

Erythrocyte filterability (whole cell deformability) was investigated in relation to blood pressure measured by the tail-cuff method in SHR and age-matched Wistar-Kyoto rats (WKY), using a highly sensitive and reproducible nickel mesh filtration technique. Impaired erythrocyte filterability was marked (37.0+/-17.5%) in prehypertensive young SHR (7 weeks of age) and sustained (51.6+/-13.3%) in hypertensive mature SHR (18 weeks of age), when compared with that of age-matched WKY (62.1+/-7.2% in 7 weeks of age, P<0.005, and 71.1+/-3.9% in 18 weeks of age, P<0.005, respectively). This impairment in SHR could not be explained by the mean corpuscular volume or mean corpuscular hemoglobin concentration of erythrocytes, but the erythrocyte count was significantly (P<0.005) greater in SHR than in the age-matched WKY.

CONCLUSIONS

Although the precise mechanisms remain to be elucidated, markedly impaired erythrocyte filterability in SHR is considered to contribute to the development and maintenance of genetic hypertension. (Circ J 2010; 74: 129 - 136).

Flow-induced vascular remodeling in the mesenteric artery of spontaneously hypertensive rats

The effect of an increased blood flow on vascular remodeling was studied in the mesenteric arteries of 11–12-week-old spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar–Kyoto rats (WKY). Increased blood flow was induced by selective ligation of mesenteric arteries. Nearby arteries with normal blood flow were used as controls. 7–10 days after the ligation procedure, mesenteric arteries were fixed in situ at maximal relaxation by perfusion fixation. Morphometric measurement of vascular dimension was carried out with confocal microscopy. Apoptotic cells were detected by the TdT-mediated dUTP nick-end labelling method. Cell growth was quantified by using proliferating cell nuclear antigen (PCNA) in sections of paraffin-embedded vessels. In SHR, elevated blood flow increased the vessel wall dimension and the number of smooth muscle cell (SMC) layers and also increased the wall-to-lumen ratio and the number of PCNA-positive SMC, but did not change lumen size or number of apoptotic SMC. In WKY, on the other hand, increased blood flow resulted in an increase in lumen diameter, a reduction of apoptotic SMC, but no change in wall-to-lumen ratio, number of SMC layers, or number of PCNA-positive SMC. These results showed that mesenteric arteries from hypertensive and normotensive rats respond to an increase in blood flow differently: a lumen enlargement with reduced SMC apoptosis in WKY, but an increased wall-to-lumen ratio with enhanced SMC growth in SHR. Although it remains to be determined whether flow alteration is one of the initiating factors in the development of vascular remodeling in hypertension, we speculate that an increase in cardiac output, and therefore an increase in shear stress that occurs in young SHR, contributes to vascular remodelling in this model of hypertension.

Alterations in hypertensive arteries

Mentoring in academia is often carried out in an informal way depending on individuals and circumstances. I was quite fortunate to make the acquaintance of Professor E.E. Daniel when I was making a transition from my research in entomology to biomedical sciences. Here I recount some of that experience, and describe some of the lessons I have learned from this experience, as my tribute to Dr. Daniel on the occasion of his 80th birthday.

Associations between physical activity, peripheral atherosclerosis and bone status in healthy Japanese women

The aim of this cross-sectional study was to investigate whether physical activity and bone status may affect arterial thickening and stiffening in healthy Japanese women. Healthy women (n = 149; mean age, 54 years) were recruited from those who participated in a local health check program at the Osaka City University Hospital. Physical activity was assessed by physical functioning score of SF-36, and bone status by bone mineral density (BMD) in lumbar spine and calcaneus osteo-sono index (OSI). Arterial wall thickening assessed by intima-media thickness (IMT) in common carotid artery (CA) and femoral artery (FA), and arterial wall stiffening by peak wave velocity (PWV) in heart-carotid (hc) and heart-femoral (hf) as central segment and in heart-brachial (hb) and femoral-ankle (fa) as peripheral segment, respectively. By Spearman Rank correlation, lumbar spine BMD was correlated negatively with CA IMT (rho = -0.225, p < 0.05) and FA IMT (rho = -0.215, p < 0.05), and calcaneus OSI with FA IMT (rho = -0.330, p < 0.0001) but not CA IMT (rho = -0051, p = 0.5335). Both lumbar spine BMD and calcaneus OSI correlated negatively with PWV in all segments (all p < 0.05). Physical functioning score correlated weakly but significantly in a negative manner with all PWV segments (all p < 0.05) but not IMT. Multiple regression analyses revealed a significant association of calcaneus OSI (beta = -0.240, p = 0.0039) but not lumbar spine BMD (beta = -0.067, p = 0.4541) with FA IMT, although neither lumbar spine BMD nor calcaneus OSI was associated with CA IMT. Furthermore, physical functioning score was independently associated with hb and fa PWV but not hc and hf PWV, suggesting the preferential association with peripheral segment including lower extremities. Neither lumbar spine BMD nor calcaneus OSI was associated with any segment of PWV. In conclusion, it was suggested that calcaneus OSI might be associated with arterial wall thickening preferentially in femoral artery, and that physical activity may be associated with arterial wall stiffening in peripheral segment including lower extremity but not in central segment in healthy Japanese women.

Evolution of renal interstitial inflammation and NF-kappaB activation in spontaneously hypertensive rats

Lymphocytes and macrophages infiltrate the kidney of spontaneously hypertensive rats (SHR) and interventions leading to their reduction are associated with improvement of the hypertension. The present studies examined the evolution of the interstitial inflammation in the natural course of the SHR to gain insight on the potential role of interstitial immune cell accumulation in the development of hypertension. We studied SHR and control WKY rats at 3 weeks (SHR-3 wk group, n = 11 and WKY-3 wk group, n = 10), 11 weeks (SHR-11 wk group, n = 5 and WKY-11 wk group, n = 5) and 24 weeks (SHR-24 wk group, n = 10 and WKY-24 wk group, n = 10). The SHR-3 wk group was normotensive and older SHR developed hypertension that was severe in the SHR-24 wk group. Tubulointerstitial accumulation of lymphocytes, macrophages, angiotensin II-positive cells, cells expressing the p65 DNA-binding subunit of NF-kappaB and activation of NF-kappaB in the kidney were all significantly increased (p < 0.01) in the prehypertensive SHR-3 wk group and augmented progressively, with the highest values in the SHR-24 wk group. The SHR-24 wk group showed increased (p < 0.001) helper (CD4) T cell infiltration and a high CD4/CD8 ratio. These findings are consistent with the possibility that activation of NF-kappaB and renal interstitial infiltration of immune cells may be part of the pathophysiologic process that drives hypertension in the SHR.

Increased ability of erythrocytes to aggregate in spontaneously hypertensive rats

The development of hypertension is accompanied by changes in the rheological properties of blood, particularly by increased red blood cell (RBC) aggregation leading to further pathological complications. However, it is not clear whether these changes in aggregation are caused only by increased concentrations of plasma adhesion proteins or if alterations in RBC membranes are also involved. The aim of the present study was to determine if RBC aggregability is altered during hypertension and if these changes correlate with alterations in RBC membrane protein concentrations. Aggregability changes were evaluated by comparing fibrinogen (Fb)-induced aggregation of RBCs from spontaneously hypertensive rats (SHR) with RBCs from age matched normotensive Wistar Kyoto (WKY) rats. ANOVA showed a significant increase in dose-dependent Fb-induced aggregation of RBCs in the SHR group. Analysis of Coomassie-stained gels of RBC membrane proteins using SDS-PAGE showed a significant increase in the amount of a protein at 110 kD in the SHR group. These results show that increased RBC aggregability is accompanied by alterations in RBC membrane protein composition during hypertension development.

Expression and cellular localization of classic NADPH oxidase subunits in the spontaneously hypertensive rat kidney

Phagocytes generate superoxide anion (O(2)(-)) by a classic, 5-component NADPH oxidase. O(2)(-) contributes to hypertension in spontaneously hypertensive rats (SHR). Therefore, we tested the hypothesis that NADPH oxidase expression is enhanced in the SHR kidney. We also analyzed the localization of NADPH oxidase components in SHR kidney. Renal NADPH oxidase was quantified by reverse transcription-polymerase chain reaction and Western blotting and was localized in SHR and Wistar Kyoto rat (WKY) kidney by immunohistochemistry. The mRNA for 5 subunits of phagocyte NADPH oxidase, and also for MOX1 and RENOX (NOX4), was detected in adult rat kidney. Kidneys of adult (10 weeks old) SHR had a significantly (P<0.01) greater mRNA for p47phox (SHR 0.81 +/- 0.05 versus WKY 0.37 +/- 0.01, arbitrary unit), which was confirmed by Western blotting (SHR 0.58 +/- 0.04 versus WKY 0.42 +/- 0.04, arbitrary unit; P<0.05) and by immunohistochemistry. This higher p47phox protein expression was also detected in young prehypertensive SHR (SHR 0.61 +/- 0.05 versus WKY 0.39 +/- 0.04, arbitrary unit; P<0.01). The 10-week-old SHR contained more modest but significantly (P<0.05) greater protein for p67phox (SHR 0.54 +/- 0.02 versus WKY 0.46 +/- 0.02). Immunostaining localized p47phox, p67phox, and p22phox in vasculature, macula densa, distal convoluted tubule, cortical collecting duct, and outer and inner medullary collecting ducts. The kidney of SHR expresses genes for all the main components of phagocyte NADPH oxidase, RENOX, and MOX1. There is a prominent increase in the SHR kidney of the mRNA, and protein expression of p47phox in the vasculature, macula densa, and distal nephron, which precedes development of hypertension.