Effects of Antihypertensive Drugs on Capillary Rarefaction in Spontaneously Hypertensive Rats: Intravital Microscopy and Histologic Analysis

Microvascular endothelial dysfunction in vascular senescence and disease

Cardiovascular disease (CVD) is the main cause of morbidity and mortality in the adult and the elderly, with increasing prevalence worldwide. A growing body of research has focused on the earliest stage of vascular decline-endothelial dysfunction (ED)-which at the microvascular level can anticipate in decades the diagnosis of CVD. This review aims to provide a prospect of the literature regarding the development of ED as an indissociable feature of the aging of the cardiovascular system, highlighting the role of inflammation in the process. Vascular aging consists of a lifelong continuum, which starts with cell respiration and its inherent production of reactive oxygen species. Molecular imbalance is followed by cellular epigenetic changes, which modulate immune cells, such as macrophage and lymphocyte subtypes. These mechanisms are influenced by lifestyle habits, which affect inflammation hotspots in organism, such as visceral fat and gut microbiota. The process can ultimately lead to an environment committed to the loss of the physiological functions of endothelial cells. In addition, we discuss lifestyle changes targeting the connection between age-related inflammation and vascular dysfunction. Addressing microvascular ED represents a critical endeavor in order to prevent or delay vascular aging and associated diseases.

Vascular Growth Factor Inhibition with Bevacizumab Improves Cardiac Electrical Alterations and Fibrosis in Experimental Acute Chagas Disease

Chagas disease (CD) caused by Trypanosoma cruzi is a neglected illness and a major reason for cardiomyopathy in endemic areas. The existing therapy generally involves trypanocidal agents and therapies that control cardiac alterations. However, there is no treatment for the progressive cardiac remodeling that is characterized by inflammation, microvasculopathy and extensive fibrosis. Thus, the search for new therapeutic strategies aiming to inhibit the progression of cardiac injury and failure is necessary. Vascular Endothelial Growth Factor A (VEGF-A) is the most potent regulator of vasculogenesis and angiogenesis and has been implicated in inducing exacerbated angiogenesis and fibrosis in chronic inflammatory diseases. Since cardiac microvasculopathy in CD is also characterized by exacerbated angiogenesis, we investigated the effect of inhibition of the VEGF signaling pathway using a monoclonal antibody (bevacizumab) on cardiac remodeling and function. Swiss Webster mice were infected with Y strain, and cardiac morphological and molecular analyses were performed. We found that bevacizumab significantly increased survival, reduced inflammation, improved cardiac electrical function, diminished angiogenesis, decreased myofibroblasts in cardiac tissue and restored collagen levels. This work shows that VEGF is involved in cardiac microvasculopathy and fibrosis in CD and the inhibition of this factor could be a potential therapeutic strategy for CD.

Assessments of microvascular function in organ systems

Microvascular disease plays critical roles in the dysfunction of all organ systems, and there are many methods available to assess the microvasculature. These methods can either assess the target organ directly or assess an easily accessible organ such as the skin or retina so that inferences can be extrapolated to the other systems and/or related diseases. Despite the abundance of exploratory research on some of these modalities and their possible applications, there is a general lack of clinical use. This deficiency is likely due to two main reasons: the need for standardization of protocols to establish a role in clinical practice or the lack of therapies targeted toward microvascular dysfunction. Also, there remain some questions to be answered about the coronary microvasculature, as it is complex, heterogeneous, and difficult to visualize in vivo even with advanced imaging technology. This review will discuss novel approaches that are being used to assess microvasculature health in several key organ systems, and evaluate their clinical utility and scope for further development.

Perfusion of Brain Preautonomic Areas in Hypertension: Compensatory Absence of Capillary Rarefaction and Protective Effects of Exercise Training

Remodeling of capillary rarefaction and deleterious arteries are characteristic hallmarks of hypertension that are partially corrected by exercise training. In addition, experimental evidence showed capillary rarefaction within the brain cortex and reduced cerebral blood flow. There is no information on hypertension- and exercise-induced effects on capillary profile and function within preautonomic nuclei. We sought now to evaluate the effects of hypertension and exercise training (T) on the capillary network within hypothalamic paraventricular (PVN) and solitary tract (NTS) nuclei, and on the remodeling of brain arteries. Age-matched spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY), submitted to moderate T or kept sedentary (S) for three months, were chronically cannulated for hemodynamic recordings at rest. Rats were anesthetized for i.v. administration of fluorescein isothiocyanate (FITC)-dextran (capillary volume/density measurements) or 4% paraformaldehyde perfusion (basilar, middle, and posterior arteries' morphometry) followed by brain harvesting and processing. Other groups of conscious rats had carotid blood flow (CBF, ultrasound flowmeter) acquired simultaneously with hemodynamic recordings at rest and exercise. SHR-S exhibited elevated pressure and heart rate, reduced CBF, increased wall/lumen ratio of arteries, but no capillary rarefaction within the PVN and NTS. T improved performance gain and caused resting bradycardia in both groups; reduction of pressure and sympathetic vasomotor activity and normalization of the wall/lumen ratio were only observed in SHR-T. T groups responded with marked PVN and NTS capillary angiogenesis and augmented CBF during exercise; to avoid overperfusion at rest, reduced basal CBF was observed only in WKY-T. Data indicated that the absence of SHR-S capillary rarefaction and the intense SHR-T angiogenesis within autonomic areas associated with correction of deleterious arteries' remodeling are essential adjustments to hypertension and exercise training, respectively. These adaptive responses maintain adequate baseline perfusion in SHR-S and SHR-T preautonomic nuclei, augmenting it in exercised rats when a well-coordinated autonomic control is required.

I1-imidazoline receptor-mediated cardiovascular and metabolic effects in high-fat diet-induced metabolic syndrome in rats

OBJECTIVES

The objective of this study was to investigate the effects of a new I₁-imidazoline receptor-selective pyrroline compound on the hemodynamic, metabolic and microvascular alterations in a high-fat diet (HFD)-induced model of metabolic syndrome in rats.

METHODS

In total, twenty adult male Wistar rats were fed a high-fat diet (HFD, n = 20) for 20 weeks. Thereafter, the rats received a new pyrroline compound selective for I1-imidazoline receptors (LNP599; 10 mg/kg/day) or vehicle (n = 10/group) orally by gavage for 4 weeks. Functional microcirculation was assessed using intravital video microscopy, and structural microcirculation was evaluated using histochemical analysis.

RESULTS

LNP599 induced concomitant reductions in the SBP, HR and plasma catecholamine levels. The animals treated with this new antihypertensive compound also presented an improvement in body weight and the metabolic parameters related to metabolic syndrome, such as the glucose and lipid profiles. These effects were accompanied by a reversal of the functional and structural capillary rarefaction in the skeletal muscle.

CONCLUSIONS

The modulation of the sympathetic nervous system by a selective agonist for I₁-imidazoline receptors improves the hemodynamic and metabolic parameters in an experimental model of metabolic syndrome. LNP599 can also contribute to the restoration of microcirculatory parameters.

Penile microvascular endothelial function in hypertensive patients: effects of acute type 5 phosphodiesterase inhibition

The primary aim of this study was to evaluate penile endothelial microvascular function in patients with primary arterial hypertension and age-matched normotensive subjects using laser speckle contrast imaging (LSCI). Additionally, we analyzed the acute penile microvascular effects induced by oral phosphodiesterase type 5 inhibitor (sildenafil; SIL) administration. Endothelium-dependent microvascular reactivity was evaluated in the penises and forearms of hypertensive patients (aged 58.8±6.6 years, n=34) and age-matched healthy volunteers (n=33) at rest and 60 min following oral SIL (100 mg) administration. LSCI was coupled with cutaneous acetylcholine (ACh) iontophoresis using increasing anodal currents. Basal penile cutaneous vascular conductance (CVC) values were not significantly different between control subjects and hypertensive individuals. Penile CVC values increased significantly after SIL administration in control (P<0.0001) and hypertensive (P<0.0001) subjects. Peak CVC values were not different between the two groups during penile ACh iontophoresis before SIL administration (P=0.2052). Peak CVC values were higher in control subjects than in hypertensive subjects after SIL administration (P=0.0427). Penile endothelium-dependent microvascular function is, to some extent, preserved in patients presenting with primary arterial hypertension under effective anti-hypertensive treatment. LSCI may be a valuable non-invasive tool for the evaluation of penile vascular responses to phosphodiesterase type 5 inhibitor.

Retinal capillary rarefaction in patients with untreated mild-moderate hypertension

Background

Microvascular rarefaction influences peripheral vascular resistance, perfusion and metabolism by affecting blood pressure and flow pattern. In hypertension microvascular rarefaction has been described in experimental animal studies as well as in capillaroscopy of skin and biopsies of muscle tissue in patients. Retinal circulation mirrors cerebral microcirculation and allows non-invasive investigations. We compared capillary rarefaction of retinal vessels in hypertensive versus normotensive subjects.

Methods

In this study retinal capillary rarefaction in 70 patients with long time (more than 67 month of disease duration) and 64 patients with short time hypertension stage 1 or 2 has been compared to 55 healthy control subjects, who participated in clinical trials in our Clinical Research Center (www.clinicaltrials.gov: NCT01318395, NCT00627952, NCT00152698, NCT01319344). Retinal vascular parameters have been measured non-invasively and in vivo in perfusion image by scanning laser Doppler flowmetry (Heidelberg Engineering, Germany). Capillary rarefaction was assessed by capillary area (CapA) (in pixel-number) and intercapillary distance (ICD) (in μm). Additionally retinal capillary flow (RCF) was measured.

Results

ICD was greater in the long time hypertensive group compared to healthy individuals (24.2 ± 6.3 μm vs 20.1 ± 4.2 μm, p = 0.001) and compared to short time hypertensive patients (22.2 ± 5.2 μm, p = 0.020). Long time hypertensive patients showed less CapA compared to healthy people (1462 ± 690 vs 1821 ± 652, p = 0.005). Accordingly, RCF was significantly lower in the long time hypertensive group compared to the healthy control group (282 ± 70 AU vs 314 ± 60 AU, p = 0.032). Our data indicate a lower level of retinal capillary density in hypertensive patients, especially in those with long time hypertension.

Conclusion

Patients with hypertension stage 1 or 2 showed retinal capillary rarefaction in comparison to healthy normotensive subjects. Retinal capillary rarefaction was intensified with duration of disease.

Electronic supplementary material

The online version of this article (10.1186/s12872-017-0732-x) contains supplementary material, which is available to authorized users.

Statins prevent cognitive impairment after sepsis by reverting neuroinflammation, and microcirculatory/endothelial dysfunction

Acute brain dysfunction is a frequent condition in sepsis patients and is associated with increased mortality and long-term neurocognitive consequences. Impaired memory and executive function are common findings in sepsis survivors. Although neuroinflammation and blood-brain barrier dysfunction have been associated with acute brain dysfunction and its consequences, no specific treatments are available that prevent cognitive impairment after sepsis. Experimental sepsis was induced in Swiss Webster mice by intraperitoneal injection of cecal material (5mg/kg, 500μL). Control groups (n=5/group each experiment) received 500μL of saline. Support therapy recover (saline 0.9%, 1mL and imipenem 30mg/kg) were applied (6, 24 and 48h post injection, n=5-10/group, each experiment), together or not with additive orally treatment with statins (atorvastatin/simvastatin 20mg/kg b.w.). Survival rate was monitored at 6, 24 and 48h. In a setting of experiments, animals were euthanized at 6 and 24h after induction for biochemical, immunohistochemistry and intravital analysis. Statins did not prevented mortality in septic mice, however survivors presented lower clinical score. At another setting of experiments, after 15days, mice survivors from fecal supernatant peritoneal sepsis presented cognitive dysfunction for contextual hippocampal and aversive amygdala-dependent memories, which was prevented by atorvastatin/simvastatin treatment. Systemic and brain tissue levels of proinflammatory cytokines/chemokines and activation of microglial were lower in septic mice treated with statins. Brain lipid peroxidation and myeloperoxidase levels were also reduced by statins treatment. Intravital examination of the brain vessels of septic animals revealed decreased functional capillary density and increased rolling and adhesion of leukocytes, and blood flow impairment, which were reversed by treatment with statins. In addition, treatment with statins restored the cholinergic vasodilator response due to sepsis. Taken together, these data demonstrated that statins reverse microvascular dysfunction and reduce neuroinflammation during sepsis, preventing the development of long-term cognitive decline.

Improvement in Retinal Capillary Rarefaction After Valsartan Treatment in Hypertensive Patients

Decreased capillary density influences vascular resistance and perfusion. The authors aimed to investigate the influence of the renin-angiotensin receptor blocker valsartan on retinal capillary rarefaction in hypertensive patients. Retinal vascular parameters were measured noninvasively and in vivo by scanning laser Doppler flowmetry before and after 4 weeks of treatment with valsartan in 95 patients with hypertension stage 1 or 2 and compared with 55 healthy individuals. Retinal capillary rarefaction was determined with the parameters intercapillary distance (ICD) and capillary area (CapA). In hypertensive patients, ICD decreased (23.4±5.5 μm vs 21.5±5.6 μm, P<.001) and CapA increased (1564±621 vs 1776±795, P=.001) after valsartan treatment compared with baseline. Compared with healthy normotensive controls (ICD 20.2±4.2 μm, CapA 1821±652), untreated hypertensive patients showed greater ICD (P<.001) and smaller CapA (P=.019), whereas treated hypertensive patients showed no difference in ICD (P=.126) and CapA (P=.728). Therapy with valsartan for 4 weeks diminished capillary rarefaction in hypertensive patients.

Contribution of the platelet activating factor signaling pathway to cerebral microcirculatory dysfunction during experimental sepsis by ExoU producing Pseudomonas aeruginosa

Intravital microscopy was used to assess the involvement of ExoU, a Pseudomonas aeruginosa cytotoxin with phospholipase A2 activity, in dysfunction of cerebral microcirculation during experimental pneumosepsis. Cortical vessels from mice intratracheally infected with low density of the ExoU-producing PA103 P. aeruginosa strain exhibited increased leukocyte rolling and adhesion to venule endothelium, decreased capillar density and impaired arteriolar response to vasoactive acetylcholine. These phenomena were mediated by the platelet activating factor receptor (PAFR) pathway because they were reversed in mice treated with a PAFR antagonist prior to infection. Brains from PA103-infected animals exhibited a perivascular inflammatory infiltration that was not detected in animals infected with an exoU deficient mutant or in mice treated with the PAFR antagonist and infected with the wild type bacteria. No effect on brain capillary density was detected in mice infected with the PAO1 P. aeruginosa strain, which do not produce ExoU. Finally, after PA103 infection, mice with a targeted deletion of the PAFR gene exhibited higher brain capillary density and lower leukocyte adhesion to venule endothelium, as well as lower increase of systemic inflammatory cytokines, when compared to wild-type mice. Altogether, our results establish a role for PAFR in mediating ExoU-induced cerebral microvascular failure in a murine model of sepsis.

Physical exercise restores microvascular function in obese rats with metabolic syndrome

BACKGROUND

Obesity and metabolic syndrome are related to systemic functional microvascular alterations, including a significant reduction in microvessel density. The aim of this study was to investigate the effects of exercise training on functional capillary density in the skeletal muscle and skin of obese rats with metabolic syndrome.

METHODS

We used male Wistar-Kyoto rats that had been fed a standard commercial diet (CON) or high-fat diet (HFD) for 32 weeks. Animals receiving the HFD were randomly divided into sedentary (HFD+SED) and training groups (HFD+TR) at the 20(th) week. After 12 weeks of aerobic treadmill training, the maximal oxygen uptake (VO2max); hemodynamic, biochemical, and anthropometric parameters; and functional capillary density were assessed. In addition, a maximal exercise test was performed.

RESULTS

Exercise training increased the VO2max (69 ± 3 mL/kg per min) and exercise tolerance (30 ± 1 min) compared with the HFD+SED (41 ± 6 mL/kg per min, P < 0.05 and 16 ± 1 min, P < 0.001) and with the CON (52 ± 7 mL/kg per min and 18 ± 1 min, P < 0.05) groups. The HFD+TR group also showed reduced retroperitoneal fat (0.03 ± 0.00 vs. 0.05 ± 0.00 gram/gram, P < 0.001), epididymal fat (0.01 ± 0.00 vs. 0.02 ± 0.00 gram/gram, P < 0.001), and systolic blood pressure (127 ± 2 vs. 150 ± 2 mmHg, P<0.001). The HFD+TR group also demonstrated improved glucose tolerance, as evaluated by an intraperitoneal glucose tolerance test, fasting plasma glucose levels (5.0 ± 0.1 vs. 6.4 ± 0.2 mmol/L, P<0.001) and fasting plasma insulin levels (26.5 ± 2.3 vs. 38.9 ± 3.7 μIU/mL, P < 0.05). Glucose tolerance did not differ between HFD+TR and CON groups. Exercise training also increased the number of spontaneously perfused capillaries in the skeletal muscle (252 ± 9 vs. 207 ± 9 capillaries/mm(2)) of the training group compared with that in the sedentary animals (260 ± 15 capillaries/mm(2)).

CONCLUSIONS

These results demonstrate that exercise training reverses capillary rarefaction in our experimental model of metabolic syndrome and obesity.

Acute Chagas disease induces cerebral microvasculopathy in mice

Cardiomyopathy is the main clinical form of Chagas disease (CD); however, cerebral manifestations, such as meningoencephalitis, ischemic stroke and cognitive impairment, can also occur. The aim of the present study was to investigate functional microvascular alterations and oxidative stress in the brain of mice in acute CD. Acute CD was induced in Swiss Webster mice (SWM) with the Y strain of Trypanosoma cruzi (T. cruzi). Cerebral functional capillary density (the number of spontaneously perfused capillaries), leukocyte rolling and adhesion and the microvascular endothelial-dependent response were analyzed over a period of fifteen days using intravital video-microscopy. We also evaluated cerebral oxidative stress with the thiobarbituric acid reactive species TBARS method. Compared with the non-infected group, acute CD significantly induced cerebral functional microvascular alterations, including (i) functional capillary rarefaction, (ii) increased leukocyte rolling and adhesion, (iii) the formation of microvascular platelet-leukocyte aggregates, and (iv) alteration of the endothelial response to acetylcholine. Moreover, cerebral oxidative stress increased in infected animals. We concluded that acute CD in mice induced cerebral microvasculopathy, characterized by a reduced incidence of perfused capillaries, a high number of microvascular platelet-leukocyte aggregates, a marked increase in leukocyte-endothelium interactions and brain arteriolar endothelial dysfunction associated with oxidative stress. These results suggest the involvement of cerebral microcirculation alterations in the neurological manifestations of CD.

Chagas disease (CD) is a neglected tropical illness caused by the parasite Trypanosoma cruzi (T. cruzi). It is endemic in Latin America and affects 10 million people worldwide. Meningoencephalitis occurs in children with acute CD and in immunosuppressed patients suffering acute CD reactivation. During the chronic phase, cerebral manifestations, including ischemic stroke and cognitive impairment, can also occur. Although microvascular alterations have been implicated in Chagas cardiomyopathy, the main clinical form of the disease, there is a lack of discussion in some studies regarding alterations of the cerebral microcirculation in CD. In the present study, we evaluated the functionality of the cerebral microcirculation in mice infected by T. cruzi. Utilizing an intravital video-microscope, we observed in the brain of infected mice a reduction in the number of perfused capillaries, an increased interaction between inflammatory cells and venules, the presence of microvascular platelet-leukocyte aggregates and alterations in the dilatation capacity of arterioles. Moreover, cerebral oxidative stress was increased in infected animals. We concluded that acute CD induced cerebral microvasculopathy.

Cardiac microvascular rarefaction in hyperthyroidism-induced left ventricle dysfunction

OBJECTIVE

The pathophysiology underlying hyperthyroidism-induced left ventricle (LV) dysfunction and hypertrophy directly involves the heart and indirectly involves the neuroendocrine systems. The effects of hyperthyroidism on the microcirculation are still controversial in experimental models. We investigated the effects of hyperthyroidism on the cardiac function and microcirculation of an experimental rat model.

METHODS

Male Wistar rats (170-250 g) were divided into two groups: the euthyroid group (n = 10), which was treated with 0.9% saline solution, and the hyperthyroid group (n = 10), which was treated with l-thyroxine (600 μg/kg/day, i.p.) during 14 days. An echocardiographic study was performed to evaluate the alterations in cardiac function, structure and geometry. The structural capillary density and the expression of angiotensin II AT1 receptor in the LV were analyzed using histochemistry and immunohistochemistry, respectively.

RESULTS

Hyperthyroidism was found to induce profound cardiovascular alterations, such as systolic hypertension, tachycardia, LV dysfunction, cardiac hypertrophy, and myocardial fibrosis. This study demonstrates the existence of structural capillary rarefaction and the down-regulation of the cardiac angiotensin II AT1 receptor in the myocardium of hyperthyroid rats in comparison with euthyroid rats.

CONCLUSIONS

Microvascular rarefaction may be involved in the pathophysiology of hyperthyroidism-induced cardiovascular alterations.

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

Cardioankle vascular index evaluations revealed that cotreatment of ARB Antihypertension medication with traditional Chinese medicine improved arterial functionality

Qian Yang He Ji (QYHJ) is a traditional Chinese medicine composed of Digitalis purpurea, Uncaria gambir, Fructus tribuli terrestris, and Ligustrum lucidum. Here, we explored whether combining an antihypertensive angiotensin II receptor blocker (ARB) therapy with QYHJ can improve the arterial functionality of hypertensive patients. One hundred and eight hypertensive patients were randomized into 2 groups; 1 group (n = 53) was treated with ARB and the other group (n = 55) was treated with ARB combined with QYHJ. Each of the 2 groups included 3 subgroups (pure hypertension, hypertension with diabetes, and hypertension with coronary heart disease) and was further divided into patients with and without complications. The cardioankle vascular index and intima-media thickness and pulse pressure were the outcome evaluation parameter. Combined QYHJ and ARB treatment reduced the values of cardioankle vascular index, systolic blood pressure, diastolic blood pressure, and pulse pressure to significantly lower levels than ARB treatment alone did in hypertension patients after 6 months of treatment. ARB improves hypertension, but a combined QYHJ treatment can additionally ameliorate the arterial functionality not only in solely hypertensive patients but also in hypertensive patients with diabetes and coronary heart disease complications. QYHJ coapplication might be a choice to further improve the arterial functionality during an ARB hypertension treatment.

Structural and functional microvascular alterations in a rat model of metabolic syndrome induced by a high-fat diet

OBJECTIVE

To investigate microvascular alterations in an experimental model of metabolic syndrome induced by a high-fat diet (HFD) associated with salt supplementation (0.5% NaCl).

DESIGN AND METHODS

Wistar Kyoto rats were fed standard chow (control group, CONT) or HFD for 20 weeks. The functional capillary density (FCD) was assessed using intravital fluorescence videomicroscopy.

RESULTS

The HFD group presented a higher systolic blood pressure, plasma glucose and insulin levels, total and LDL-cholesterol levels, triglycerides, and visceral and epididymal fat when compared with the CONT group. When compared with the CONT group, the HFD group showed a lower FCD in the skeletal muscle (P < 0.05) but not in the skin (P > 0.05). The HFD group also had a lower capillary-to-fiber ratio in the skeletal muscle (P < 0.01). The capillary volume density-to-fiber volume density ratio in the left ventricle of the HFD was also reduced (P < 0.01). Finally, rats fed with HFD showed ventricular hypertrophy and increased cardiomyocyte diameter (P < 0.01).

CONCLUSIONS

The long-term administration of a HFD associated with salt supplementation to rats generates an experimental model of metabolic syndrome characterized by central body fat deposition, insulin resistance, glucose intolerance, hypertriglyceridemia, hypercholesterolemia, arterial hypertension, cardiac remodeling, and rarefaction of the microcirculation in the heart and skeletal muscle.

Multimodal imaging in rats reveals impaired neurovascular coupling in sustained hypertension

BACKGROUND AND PURPOSE

Arterial hypertension is an important risk factor for cerebrovascular diseases, such as transient ischemic attacks or stroke, and represents a major global health issue. The effects of hypertension on cerebral blood flow, particularly at the microvascular level, remain unknown.

METHODS

Using the spontaneously hypertensive rat (SHR) model, we examined cortical hemodynamic responses on whisker stimulation applying a multimodal imaging approach (multiwavelength spectroscopy, laser speckle imaging, and 2-photon microscopy). We assessed the effects of hypertension in 10-, 20-, and 40-week-old male SHRs and age-matched male Wistar Kyoto rats (CTRL) on hemodynamic responses, histology, and biochemical parameters. In 40-week-old animals, losartan or verapamil was administered for 10 weeks to test the reversibility of hypertension-induced impairments.

RESULTS

Increased arterial blood pressure was associated with a progressive impairment in functional hyperemia in 20- and 40-week-old SHRs; baseline capillary red blood cell velocity was increased in 40-week-old SHRs compared with age-matched CTRLs. Antihypertensive treatment reduced baseline capillary cerebral blood flow almost to CTRL values, whereas functional hyperemic signals did not improve after 10 weeks of drug therapy. Structural analyses of the microvascular network revealed no differences between normo- and hypertensive animals, whereas expression analyses of cerebral lysates showed signs of increased oxidative stress and signs of impaired endothelial homeostasis upon early hypertension.

CONCLUSIONS

Impaired neurovascular coupling in the SHR evolves upon sustained hypertension. Antihypertensive monotherapy using verapamil or losartan is not sufficient to abolish this functional impairment. These deficits in neurovascular coupling in response to sustained hypertension might contribute to accelerate progression of neurodegenerative diseases in chronic hypertension.

Blockade of the renin-angiotensin system improves cerebral microcirculatory perfusion in diabetic hypertensive rats

We examined the functional and structural microcirculatory alterations in the brain, skeletal muscle and myocardium of non-diabetic spontaneously hypertensive rats (SHR) and diabetic SHR (D-SHR), as well as the effects of long-term treatment with the angiotensin AT1-receptor antagonist olmesartan and the angiotensin-converting enzyme inhibitor enalapril. Diabetes was experimentally induced by a combination of a high-fat diet with a single low dose of streptozotocin (35 mg/kg, intraperitoneal injection). D-SHR were orally administered with olmesartan (5 mg/kg/day), enalapril (10 mg/kg/day) or vehicle for 28 days, and compared with vehicle-treated non-diabetic SHR or normotensive non-diabetic Wistar-Kyoto rats. The cerebral and skeletal muscle functional capillary density of pentobarbital-anesthetized rats was assessed using intravital fluorescence videomicroscopy. Chronic treatment with olmesartan or enalapril significantly lowered blood pressure and reversed brain functional capillary rarefaction. Brain oxidative stress was reduced to non-diabetic control levels in animals treated with olmesartan or enalapril. Histochemical analysis of the structural capillary density showed that both olmesartan and enalapril increased the capillary-to-fiber ratio in skeletal muscle and the capillary-to-fiber volume density in the left ventricle. Olmesartan and enalapril also prevented collagen deposition and the increase in cardiomyocyte diameter in the left ventricle. Our results suggest that the association between hypertension and diabetes results in microvascular alterations in the brain, skeletal muscle and myocardium that can be prevented by chronic blockade of the renin-angiotensin system.

Statins decrease neuroinflammation and prevent cognitive impairment after cerebral malaria

Cerebral malaria (CM) is the most severe manifestation of Plasmodium falciparum infection in children and non-immune adults. Previous work has documented a persistent cognitive impairment in children who survive an episode of CM that is mimicked in animal models of the disease. Potential therapeutic interventions for this complication have not been investigated, and are urgently needed. HMG-CoA reductase inhibitors (statins) are widely prescribed for cardiovascular diseases. In addition to their effects on the inhibition of cholesterol synthesis, statins have pleiotropic immunomodulatory activities. Here we tested if statins would prevent cognitive impairment in a murine model of cerebral malaria. Six days after infection with Plasmodium berghei ANKA (PbA) mice displayed clear signs of CM and were treated with chloroquine, or chloroquine and lovastatin. Intravital examination of pial vessels of infected animals demonstrated a decrease in functional capillary density and an increase in rolling and adhesion of leukocytes to inflamed endothelium that were reversed by treatment with lovastatin. In addition, oedema, ICAM-1, and CD11b mRNA levels were reduced in lovastatin-treated PbA-infected mice brains. Moreover, HMOX-1 mRNA levels are enhanced in lovastatin-treated healthy and infected brains. Oxidative stress and key inflammatory chemokines and cytokines were reduced to non-infected control levels in animals treated with lovastatin. Fifteen days post-infection cognitive dysfunction was detected by a battery of cognition tests in animals rescued from CM by chloroquine treatment. In contrast, it was absent in animals treated with lovastatin and chloroquine. The outcome was similar in experimental bacterial sepsis, suggesting that statins have neuroprotective effects in severe infectious syndromes in addition to CM. Statin treatment prevents neuroinflammation and blood brain barrier dysfunction in experimental CM and related conditions that are associated with cognitive sequelae, and may be a valuable adjuvant therapeutic agent for prevention of cognitive impairment in patients surviving an episode of CM.

Cerebral malaria (CM) is the direst consequence of Plasmodium falciparum infection. Cognitive impairment is a common sequela in children surviving CM. Identification of adjunctive therapies that reduce the complications of CM in survivors is a priority. Statins have been suggested for the treatment of neuroinflammatory disorders due to their pleiotropic effects. Here, we examined the effects of lovastatin on neuroinflammation in experimental CM, and its effect on the prevention of cognitive impairment. Lovastatin reduced adhesion and rolling of leukocytes in brain vessels, inhibited blood-brain barrier disruption, and reversed decreases in cerebral capillary density. Lovastatin also inhibited ICAM-1 and CD11b mRNA expression while increasing HMOX-1 mRNA levels. Proinflammatory cytokines and markers of oxidative stress were lower in the brains of infected mice treated with lovastatin. Lovastatin administered together with antimalarial drugs during the acute phase of the disease-protected survivors from impairment in both contextual and aversive memory 15 days after infection. Similar results were observed in a model of bacterial sepsis. Our findings support the possibility that statins may be valuable pharmacologic tools in treatment of patients with neuroinflammation associated with severe systemic inflammatory syndromes. Clinical trials with statins in CM and sepsis should be speedily considered to examine this point.

Does interference with the renin-angiotensin system protect against diabetes? Evidence and mechanisms

Agents interfering with the renin-angiotensin system (RAS) were consistently shown to lower the incidence of type 2 diabetes mellitus (T2DM), as compared to other antihypertensive drugs, in hypertensive high-risk populations. The mechanisms underlying this protective effect of RAS blockade using angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers on glucose metabolism are not fully understood. In this article, we will review the evidence from randomized controlled trials and discuss the proposed mechanisms as to how RAS interference may delay the onset of T2DM. In particular, as T2DM is characterized by β-cell dysfunction and obesity-related insulin resistance, we address the mechanisms that underlie RAS blockade-induced improvement in β-cell function and insulin sensitivity.

PPAR gamma activation protects the brain against microvascular dysfunction in sepsis

Sepsis is a severe disorder characterized by systemic inflammatory responses in the presence of an infection and may progress to multiple organ dysfunction and death. Alterations in cerebral microcirculation fulfill a crucial role in the pathogenesis of severe sepsis, and include a decrease in capillary density and disturbances in leukocyte movement along capillaries. Nevertheless, the mechanisms involved in sepsis-associated cerebral microcirculatory alterations have so far not been defined. We investigated the effect of the peroxisome proliferator-activated receptor gamma (PPARγ) selective agonist rosiglitazone on leukocyte/endothelial cell interaction and functional capillary density in the brain in the cecal ligation and puncture (CLP) model of sepsis. Anti-inflammatory effects of rosiglitazone on the cerebral microcirculation were marked. Functional capillary density increased and leukocyte rolling and adhesion were decreased in animals submitted to CLP and treated with rosiglitazone. Our data provide evidence for involvement of PPARγ activation in leukocyte-endothelium interactions and alterations in capillary density. Improved cerebral perfusion in animals treated with rosiglitazone, suggests that PPARγ activation is protective against cerebral microvascular dysfunction in sepsis.

Angiogenesis in mesenteric microvascular networks from spontaneously hypertensive versus normotensive rats

OBJECTIVE

Elevated blood pressure during hypertension has been associated with microvascular rarefaction, defined as a loss of microvessels. However, whether rarefaction is a result of impaired angiogenesis remains unclear. The objective of this study was to compare angiogenesis across the time course of mesenteric microvascular network remodeling in adult spontaneously hypertensive versus normotensive rats.

METHODS

Angiogenic responses in 15- to 16-week-old SHR and Wistar rats at 0, 3, 5, 10 or 25 days post 20-minute exteriorization of the mesentery were quantified.

RESULTS

Consistent with the phenomenon of rarefaction, vascularized area in unstimulated SHR was decreased compared to Wistar. By 25 days, SHR vascular area had increased to the Wistar level and vascular length density and capillary sprouting were comparable. At 3 and 5 days, SHR and Wistar tissues displayed an increase in the capillary sprouting and vascular density relative to their unstimulated controls. At 10 days, capillary sprouting in the SHR remained elevated. The percent change in vascular density was elevated in the SHR compared to the Wistar group at 3 and 5 days and by 25 days the rate of change was more negative.

CONCLUSIONS

Our results suggest that SHR networks undergo an increased rate of growth followed by an increased rate of pruning.

Valsartan-induced improvement in insulin sensitivity is not paralleled by changes in microvascular function in individuals with impaired glucose metabolism

BACKGROUND

Individuals with impaired glucose metabolism (IGM) are at high risk of developing type 2 diabetes (T2DM). The renin-angiotensin system (RAS) is activated in insulin-resistant states and its inhibition resulted in delayed onset of T2DM. The underlying mechanisms may include improvement in microvascular structure and function, which may increase glucose and insulin delivery to insulin-sensitive tissues. We hypothesized that functional and structural capillary density is impaired in insulin-resistant individuals with IGM and that treatment with the angiotensin-receptor blocker valsartan (VAL) will improve insulin sensitivity and microvascular function.

METHODS

In this randomized controlled trial, individuals with IGM (n = 48) underwent a hyperinsulinaemic-euglycaemic clamp to assess insulin sensitivity (M-value) and capillaroscopy to examine baseline skin capillary density (BCD), capillary density after arterial occlusion (PRH) and capillary density during venous occlusion (VEN) before and after 26 weeks of VAL or placebo (PLB). Sixteen BMI-matched individuals with normal glucose metabolism (NGM) served as controls.

RESULTS

Individuals with IGM were more insulin resistant (P < 0.001) and had impaired microvascular function compared with those with NGM (all P < 0.01). Univariate associations were found for microvascular function (BCD, PRH, VEN) and M-value (all P < 0.005). The relations were independent of age, sex and BMI. VAL improved insulin sensitivity (P = 0.034) and lowered blood pressure as compared with PLB, whereas microvascular function remained unchanged.

CONCLUSION

In insulin-resistant individuals with IGM, impaired functional and structural capillary density was inversely associated with insulin sensitivity. VAL improved insulin sensitivity without affecting the functional and structural capillary density, indicating that other mechanisms may be stronger determinants in the VAL-mediated insulin-sensitizing effect.

The renin-angiotensin system in the pathophysiology of type 2 diabetes

Increased activation of the renin-angiotensin system (RAS) has been related to cardiovascular disease and type 2 diabetes mellitus. Most randomized clinical trials have demonstrated that RAS blockade reduces the incidence of type 2 diabetes, which has been explained by improved insulin secretion and insulin sensitivity. In this review, an overview of the mechanisms that may underlie the association between the RAS and type 2 diabetes will be provided, with focus on skeletal muscle and adipose tissue function. This will include discussion of several human studies performed in our laboratory to investigate the metabolic and hemodynamic effects of the RAS, combining in vivo measurements of whole-body and tissue metabolism with molecular and immunohistochemical approaches. Available data suggest that the detrimental effects of the RAS on insulin secretion are mediated by a reduction in pancreatic blood flow and induction of islet fibrosis, oxidative stress as well as inflammation, whereas both impaired skeletal muscle function and adipose tissue dysfunction may underlie RAS-induced insulin resistance. Thus, although future studies in humans are warranted, current evidence supports that targeting the RAS in intervention studies may improve metabolic and cardiovascular function in conditions of insulin resistance like obesity and type 2 diabetes.

The cardiac (pro)renin receptor is primarily expressed in myocyte transverse tubules and is increased in experimental diabetic cardiomyopathy

BACKGROUND

The pro(renin) receptor is a 350 amino acid transmembrane protein, that on ligand binding, increases the catalytic efficiency of angiotensinogen cleavage by both prorenin and renin, augmenting angiotensin I formation at the cell surface. While implicated in a broad range of diseases, studies to date have focused on the kidney, particularly in the diabetic context. We sought to examine the site-specific expression of the pro(renin) receptor within the heart.

METHODS

Using confocal microscopy, site-specific markers and transmission electron microscopy we assessed the location of the pro(renin) receptor in the heart at both cellular/sub-cellular levels. We assessed pro(renin) receptor expression in the setting of disease and blockade of the renin-angiotensin system, using the TGR[m(Ren2)-27] model of diabetic cardiomyopathy and the direct renin inhibitor, aliskiren.

RESULTS

The pro(renin) receptor was found predominantly at the Z-disc and dyad of cardiac myocytes coinciding closely with the distributions of the vacuolar H⁺-ATPase and ryanodine receptor, known to be located within T-tubules and the sarcoplasmic reticulum's terminal cisternae, respectively. Pro(renin) receptor mRNA/protein abundance were increased ∼3-fold in the hearts of diabetic rats in association with diastolic dysfunction, myocyte hypertrophy and interstitial fibrosis (all P < 0.01). Direct renin inhibition reduced cardiac pro(renin) receptor expression in association with improved cardiac structure/function (all P < 0.05).

CONCLUSION

Together, these findings are consistent with the notion that the pro(renin) receptor is a component of the vacuolar H⁺-ATPase, and that like the latter, is increased in the setting of cardiac stress and lowered by the administration of an ostensibly cardioprotective agent.

Effect of carvedilol on pulse pressure and left ventricular hypertrophy in spontaneously hypertensive rats with adriamycin nephropathy

Recent studies indicated pulse pressure as a risk factor for left ventricular hypertrophy, myocardial infarction, congestive heart failure and stroke as well as chronic renal failure progression. The present study examined the effects of carvedilol and its combination with captopril on blood pressure, left ventricular hypertrophy, kidney vascular changes and kidney function in spontaneously hypertensive rats with adriamycin nephropathy. Four groups of 20 SHR each were involved: (1) control group: SHR; (2) ADR group: SHR treated with ADR (2mg/kg i.v. twice in 20 days); (3) ADR-C group: SHR treated with ADR and carvedilol (30 mg/kg/day) and (4) ADR-CC group: SHR treated with ADR and carvedilol (30 mg/kg/day) and captopril (60 mg/kg/day). Systolic-, diastolic- and mean-pressures and pulse pressure were determined at weeks 6 and 12 after the second ADR injection; and body weight, creatinine clearance and proteinuria at weeks -3, 6 and 12. The rats were sacrificed at week 6 or 12, the weights of the left and right ventricles and kidneys measured and the kidney vascular index was calculated as described by Bader and Mayer. Both carvedilol alone and combined with captopril significantly reduced systemic blood pressure but the effect of the latter was more pronounced and registered from week 4 till the end of the study. Carvedilol and its combination with captopril significantly decreased SBP, DBP and MAP. They also decreased PP, prevented the development of LVH, and renal vascular changes and slowed the progression of chronic renal failure and these effects were stronger in the ADR-CC group than in the ADR-C group. The antihypertensive drugs failed to prevent proteinuria in ADR SHR. Significant positive correlations were found between PP (but not SBP, DBP and MAP) and both proteinuria and Ccr in all groups of rats. In conclusion, carvedilol alone, but more strongly in combination with captopril, significantly reduced blood pressure, PP, LVH, renal blood vessel changes and chronic renal failure progression.