High pulse pressure impairs cerebral artery endothelial function in young, but not old, mice.

One of the hallmarks of vascular aging is increased pulse pressure. This elevated pulse pressure is associated with deleterious effects on cerebral vascular function; however, it is unknown if age modulates the susceptibility to high pulse pressure. To examine the effects of age on the cerebral artery response to pulse pressure, we studied isolated cerebral arteries collected from young (6.1 ± 0.2 mo) and old (26.7 ± 0.5 mo) male C57BL/6 mice. Isolated cerebral arteries were exposed ex vivo to static pressure, low pulse pressure (25 mmHg), and high pulse pressure (50 mmHg). In cerebral arteries from young mice, endothelium-dependent dilation was similar between the static and low pulse pressure conditions. Exposure to high pulse pressure impaired endothelium-dependent dilation in cerebral arteries from young mice, mediated by less nitric oxide bioavailability and greater oxidative stress. Cerebral arteries from old mice had impaired cerebral artery endothelium-dependent dilation at static pressure compared with young cerebral arteries. However, exposure to low or high pulse pressure did not cause any further impairments to endothelium-dependent dilation in old cerebral arteries compared with static pressure. The old cerebral arteries had less distension during exposure to high pulse pressure and greater stiffness compared with young cerebral arteries. These results indicate that acute exposure to high pulse pressure impairs endothelium-dependent dilation in young, but not old, cerebral arteries. The greater stiffness of cerebral arteries from old mice potentially protects against the negative consequences of high pulse pressure.

Pyridoxamine treatment ameliorates large artery stiffening and cerebral artery endothelial dysfunction in old mice.

Age-related increases in large artery stiffness are associated with cerebrovascular dysfunction and cognitive impairment. Pyridoxamine treatment prevents large artery stiffening with advancing age, but the effects of pyridoxamine treatment on the cerebral vasculature or cognition is unknown. The purpose of this study was to investigate the effects of pyridoxamine on blood pressure, large artery stiffness, cerebral artery function, and cognitive function in old mice. Old male C57BL/6 mice consumed either pyridoxamine (2 g/L) or vehicle control in drinking water for ∼7.5 months and were compared with young male C57BL/6 mice. From pre- to post-treatment, systolic blood pressure increased in old control mice, but was maintained in pyridoxamine treated mice. Large artery stiffness decreased in pyridoxamine-treated mice but was unaffected in control mice. Pyridoxamine-treated mice had greater cerebral artery endothelium-dependent dilation compared with old control mice, and not different from young mice. Old control mice had impaired cognitive function; however, pyridoxamine only partially preserved cognitive function in old mice. In summary, pyridoxamine treatment in old mice prevented age-related increases in blood pressure, reduced large artery stiffness, preserved cerebral artery endothelial function, and partially preserved cognitive function. Taken together, these results suggest that pyridoxamine treatment may limit vascular aging.

Elastin Insufficiency Confers Proximal and Distal Pulmonary Vasculopathy in Mice, Partially Remedied by the KATP Channel Opener Minoxidil: Considerations and Cautions for the Treatment of People With Williams-Beuren Syndrome.

Background: Williams Beuren syndrome (WBS) is a recurrent microdeletion disorder that removes one copy of elastin (ELN), resulting in large artery vasculopathy. Early stenosis of the pulmonary vascular tree is common, but few data are available on longer-term implications of the condition. Methods: Computed tomography (CT) angiogram (n = 11) and echocardiogram (n = 20) were performed in children with WBS aged 3.4-17.8 years. Controls (n = 11, aged 4.4-16.8 years) also underwent echocardiogram. Eln +/- mice were analyzed by invasive catheter, echocardiogram, micro-CT (µCT), histology, and pressure myography. We subsequently tested whether minoxidil resulted in improved pulmonary vascular endpoints. Results: WBS participants with a history of main or branch pulmonary artery (PA) stenosis requiring intervention continued to exhibit increased right ventricular systolic pressure (RVSP, echocardiogram) relative to their peers without intervention (p < 0.01), with no clear difference in PA size. Untreated Eln +/- mice also show elevated RVSP by invasive catheterization (p < 0.0001), increased normalized right heart mass (p < 0.01) and reduced caliber branch PAs by pressure myography (p < 0.0001). Eln +/- main PA medias are thickened histologically relative to Eln +/+ (p < 0.0001). Most Eln +/- phenotypes are shared by both sexes, but PA medial thickness is substantially greater in Eln +/- males (p < 0.001). Eln +/- mice showed more acute proximal branching angles (p < 0.0001) and longer vascular segment lengths (p < 0.0001) (µCT), with genotype differences emerging by P7. Diminished PA acceleration time (p < 0.001) and systolic notching (p < 0.0001) were also observed in Eln +/- echocardiography. Vascular casting plus µCT revealed longer generation-specific PA arcade length (p < 0.0001), with increased PA branching detectable by P90 (p < 0.0001). Post-weaning minoxidil decreased RVSP (p < 0.01) and normalized PA caliber (p < 0.0001) but not early-onset proximal branching angle or segment length, nor later-developing peripheral branch number. Conclusions: Vascular deficiencies beyond arterial caliber persist in individuals with WBS who have undergone PA stenosis intervention. Evaluation of Eln +/- mice reveals complex vascular changes that affect the proximal and distal vasculatures. Minoxidil, given post-weaning, decreases RVSP and improves lumen diameter, but does not alter other earlier-onset vascular patterns. Our data suggest additional therapies including minoxidil could be a useful adjunct to surgical therapy, and future trials should be considered.

Airflow Obstruction in Adults with Williams Syndrome and Mice with Elastin Insufficiency.

Williams−Beuren syndrome (WS) results from the deletion of 25−27 coding genes, including elastin (ELN), on human chromosome 7q11.23. Elastin provides recoil to tissues; emphysema and chronic obstructive pulmonary disease have been linked to its destruction. Consequently, we hypothesized that elastin insufficiency would predispose to obstructive features. Twenty-two adults with WS (aged 18−55) and controls underwent pulmonary function testing, 6 min walk, and chest computed tomography (CT). Lung and airspace dimensions were assessed in Eln+/− and control mice via microCT and histology. The forced expiratory volume in 1 s (FEV1) and the ratio of FEV1 to forced vital capacity (FVC) were lower in adults with WS (p < 0.0001 and p < 0.05, respectively). The FEV1/FVC ratio was more frequently below the lower limit of normal in cases (p < 0.01). The ratio of residual volume to total lung capacity (RV/TLC, percent predicted) was higher in cases (p < 0.01), suggesting air trapping. People with WS showed reduced exercise capacity (p < 0.0001). In Eln+/− mice, ex vivo lung volumes were increased (p < 0.0001), with larger airspaces (p < 0.001). Together these data show that elastin insufficiency impacts lung physiology in the form of increased air trapping and obstruction, suggesting a role for lung function monitoring in adults with WS.

Inhibition of NOX1 Mitigates Blood Pressure Increases in Elastin Insufficiency.

Elastin (ELN) insufficiency leads to the cardiovascular hallmarks of the contiguous gene deletion disorder, Williams-Beuren syndrome, including hypertension and vascular stiffness. Previous studies showed that Williams-Beuren syndrome deletions, which extended to include the NCF1 gene, were associated with lower blood pressure (BP) and reduced vascular stiffness. NCF1 encodes for p47phox, the regulatory component of the NOX1 NADPH oxidase complex that generates reactive oxygen species (ROS) in the vascular wall. Dihydroethidium and 8-hydroxyguanosine staining of mouse aortas confirmed that Eln heterozygotes (Eln+/- ) had greater ROS levels than the wild-types (Eln+/+ ), a finding that was negated in vessels cultured without hemodynamic stressors. To analyze the Nox effect on ELN insufficiency, we used both genetic and chemical manipulations. Both Ncf1 haploinsufficiency (Ncf1+/- ) and Nox1 insufficiency (Nox1-/y ) decreased oxidative stress and systolic BP in Eln+/- without modifying vascular structure. Chronic treatment with apocynin, a p47phox inhibitor, lowered systolic BP in Eln+/- , but had no impact on Eln+/+ controls. In vivo dosing with phenylephrine (PE) produced an augmented BP response in Eln+/- relative to Eln+/+ , and genetic modifications or drug-based interventions that lower Nox1 expression reduced the hypercontractile response to PE in Eln+/- mice to Eln+/+ levels. These results indicate that the mechanical and structural differences caused by ELN insufficiency leading to oscillatory flow can perpetuate oxidative stress conditions, which are linked to hypertension, and that by lowering the Nox1-mediated capacity for vascular ROS production, BP differences can be normalized.

Vascular Casting of Adult and Early Postnatal Mouse Lungs for Micro-CT Imaging.

Blood vessels form intricate networks in 3-dimensional space. Consequently, it is difficult to visually appreciate how vascular networks interact and behave by observing the surface of a tissue. This method provides a means to visualize the complex 3-dimensional vascular architecture of the lung. To accomplish this, a catheter is inserted into the pulmonary artery and the vasculature is simultaneously flushed of blood and chemically dilated to limit resistance. Lungs are then inflated through the trachea at a standard pressure and the polymer compound is infused into the vascular bed at a standard flow rate. Once the entire arterial network is filled and allowed to cure, the lung vasculature may be visualized directly or imaged on a micro-CT (µCT) scanner. When performed successfully, one can appreciate the pulmonary arterial network in mice ranging from early postnatal ages to adults. Additionally, while demonstrated in the pulmonary arterial bed, this method can be applied to any vascular bed with optimized catheter placement and endpoints.

Cerebral and skeletal muscle feed artery vasoconstrictor responses in a mouse model with greater large elastic artery stiffness.

NEW FINDINGS: What is the central question of this study? Greater large artery stiffness is associated with dysfunctional resistance artery vasodilatory responses, impaired memory and greater risk of Alzheimer's disease. However, it is unknown whether stiffer large arteries affect cerebral and skeletal muscle feed artery responses to vasoconstrictors. What is the main finding and its importance? In a mouse model with greater large artery stiffness (Eln+/- ), we find an exacerbated vasoconstrictor response to angiotensin II in cerebral arteries, but not skeletal muscle feed arteries, thus implicating altered cerebral artery angiotensin II responsiveness in the poor brain outcomes associated with greater large artery stiffness. ABSTRACT: Greater stiffness of the large elastic arteries is associated with end-organ damage and dysfunction. At the same time, resistance artery vasoconstrictor responsiveness influences vascular tone and organ blood flow. However, it is unknown whether large elastic artery stiffness modulates the responsiveness to vasoconstrictors in resistance arteries of the cerebral or skeletal muscle circulations. We previously described the elastin haploinsufficient (Eln+/- ) mouse as a model with greater aortic stiffness, but with similar cerebral and skeletal muscle feed artery stiffness to wild-type (Eln+/+ ) mice. Here, we used this model to examine the relationship between large elastic artery stiffness and resistance artery vasoconstrictor responses. In middle cerebral arteries (MCAs), vasoconstriction in response to angiotensin II (Ang II) was ∼40% greater in Eln+/- compared with Eln+/+ mice (P = 0.02), and this group difference was ameliorated by losartan, indicating a role for Ang II type 1 receptors (AT1Rs). In gastrocnemius feed arteries, Eln+/- and Eln+/+ mice did not differ in the response to Ang II. In addition, the vasoconstrictor responses to noradrenaline, endothelin-1 and potassium chloride were not different between Eln+/- and Eln+/+ mice for either MCAs or gastrocnemius feed arteries. The MCA AT1R gene expression did not differ between groups, whereas Ang II type 2 receptor gene expression was ∼50% lower in MCAs from Eln+/- versus Eln+/+ mice (P = 0.01). In conclusion, greater large elastic artery stiffness is associated with an exacerbated vasoconstriction response to Ang II in cerebral arteries, but is not associated with the responses to other vasoconstrictors in either cerebral or skeletal muscle feed arteries.