Impact of arterial stiffness on cerebrovascular function: a review of evidence from humans and preclincal models.

With advancing age, the cerebral vasculature becomes dysfunctional, and this dysfunction is associated with cognitive decline. However, the initiating cause of these age-related cerebrovascular impairments remains incompletely understood. A characteristic feature of the aging vasculature is the increase in stiffness of the large elastic arteries. This increase in arterial stiffness is associated with elevated pulse pressure and blood flow pulsatility in the cerebral vasculature. Evidence from both humans and rodents supports that increases in large elastic artery stiffness are associated with cerebrovascular impairments. These impacts on cerebrovascular function are wide-ranging and include reductions in global and regional cerebral blood flow, cerebral small vessel disease, endothelial cell dysfunction, and impaired perivascular clearance. Furthermore, recent findings suggest that the relationship between arterial stiffness and cerebrovascular function may be influenced by genetics, specifically APOE and NOTCH genotypes. Given the strength of the evidence that age-related increases in arterial stiffness have deleterious impacts on the brain, interventions that target arterial stiffness are needed. The purpose of this review is to summarize the evidence from human and rodent studies, supporting the role of increased arterial stiffness in age-related cerebrovascular impairments.

Effects of dietary soy content on cerebral artery function and behavior in ovariectomized female mice.

As females age, they transition through menopause, experiencing a decrease in estrogen and an increase in cardiovascular and neurodegenerative disease risk. Most standard rodent chows contain phytoestrogen-rich soybean meal, which can mimic the effects of estrogen. Understanding the impact of this soybean meal on vascular outcomes is crucial to proper experimental design. Thus, this study aimed to compare the effects of standard and soy-free chows on cerebral artery endothelial function and cognitive function in ovariectomized mice. Young female C57Bl/6J mice (n = 43; ∼6 mo) were randomly assigned to three groups: sham, ovariectomy (OVX), or ovariectomy on a diet containing soy (OVX + Soy). In posterior cerebral arteries, the OVX mice had a 27% lower maximal response to insulin compared with the sham mice. The OVX + Soy mice had a 27% greater maximal vasodilation to insulin compared with the OVX mice and there were no differences in vasodilation between the OVX + Soy and sham groups. The group differences in vasodilation were mediated by differences in nitric oxide bioavailability. The OVX + Soy mice also had greater insulin receptor gene expression in cerebral arteries compared with the OVX mice. However, no differences in aortic or cerebral artery stiffness were observed between groups. Interestingly, the OVX + Soy group scored better on nesting behavior compared with both sham and OVX groups. In summary, we found that ovariectomy impairs insulin-mediated vasodilation in cerebral arteries, but a diet containing soy mitigates these effects. These findings highlight the importance of considering dietary soy when performing vascular and behavioral tests in mice, particularly in females.NEW & NOTEWORTHY To properly design experiments, we must consider how variables like diet impact our outcomes, particularly the effects of soy on females. We found that cerebral artery vasodilation in response to insulin was impaired in ovariectomized female mice compared with intact shams. However, ovariectomized mice fed a soy diet had a preserved cerebral artery insulin-mediated vasodilation. These results highlight that the effects of diet on vascular function may explain inconsistencies found between studies.

In vivo arterial stiffness, but not isolated artery endothelial function, varies with the mouse estrous cycle.

With the increasing appreciation for sex as a biological variable and the inclusion of female mice in research, it is important to understand the influence of the estrous cycle on physiological function. Sex hormones are known to modulate vascular function, but the effects of the mouse estrous cycle phase on arterial stiffness, endothelial function, and arterial estrogen receptor expression remain unknown. In 23 female C57BL/6 mice (6 mo of age), we determined the estrous cycle stage via vaginal cytology and plasma hormone concentrations. Aortic stiffness, assessed by pulse wave velocity, was lower during the estrus phase compared with diestrus. In ex vivo assessment of isolated pressurized mesenteric and posterior cerebral arteries, the responses to acetylcholine, insulin, and sodium nitroprusside, as well as nitric oxide-mediated dilation, were not different between estrous cycle phases. In the aorta, expression of phosphorylated estrogen receptor-α was higher for mice in estrus compared with mice in proestrus. In the cerebral arteries, gene expression for estrogen receptor-ß (Esr2) was lowest for mice in estrus compared with diestrus and proestrus. These results demonstrate that the estrus phase is associated with lower in vivo large artery stiffness in mice. In contrast, ex vivo resistance artery endothelial function is not different between estrous cycle phases. Estrogen receptor expression is modulated by the estrus cycle in an artery-dependent manner. These results suggest that the estrous cycle phase should be considered when measuring in vivo arterial stiffness in young female mice.NEW & NOTEWORTHY To design rigorous vascular research studies using young female rodents, the influence of the estrous cycle on vascular function must be known. We found that in vivo aortic stiffness was lower during estrus compared with the diestrus phase in female mice. In contrast, ex vivo mesenteric and cerebral artery endothelial function did not differ between estrous cycle stages. These results suggest that the estrous cycle stage should be accounted for when measuring in vivo arterial stiffness.

Large artery stiffness and brain health: insights from animal models.

There are no effective treatments available to halt or reverse the progression of age-related cognitive decline and Alzheimer's disease. Thus, there is an urgent need to understand the underlying mechanisms of disease etiology and progression to identify novel therapeutic targets. Age-related changes to the vasculature, particularly increases in stiffness of the large elastic arteries, are now recognized as important contributors to brain aging. There is a growing body of evidence for an association between greater large artery stiffness and cognitive impairment among both healthy older adults and patients with Alzheimer's disease. However, studies in humans are limited to only correlative evidence, whereas animal models allow researchers to explore the causative mechanisms linking arterial stiffness to neurocognitive dysfunction and disease. Recently, several rodent models of direct modulation of large artery stiffness and the consequent effects on the brain have been reported. Common outcomes among these models have emerged, including evidence that greater large artery stiffness causes cerebrovascular dysfunction associated with increased oxidative stress and inflammatory signaling. The purpose of this mini-review is to highlight the recent findings associating large artery stiffness with deleterious brain outcomes, with a specific focus on causative evidence obtained from animal models. We will also discuss the gaps in knowledge that remain in our understanding of how large artery stiffness affects brain function and disease outcomes.

Transforming Psychiatry from the Classroom to the Clinic: Lessons from the National Neuroscience Curriculum Initiative.

OBJECTIVE: Individual residency programs often struggle to keep pace with scientific advances and new training requirements. Integrating a modern neuroscience perspective into the clinical practice of psychiatry is particularly emblematic of these challenges. The National Neuroscience Curriculum Initiative (NNCI) was established in 2013 to develop a comprehensive set of shared, open-access resources for teaching neuroscience in psychiatry. METHODS: The NNCI developed a collaborative, team-based approach with a peer-review process for generating and reviewing content. Teaching resources have included interactive sessions for the classroom paired with a comprehensive facilitator's guide. Brief accessible reviews and short videos have been developed for self-study and teaching in clinical settings. Dissemination efforts have included hands-on training for educators through national workshops. All resources are freely available on the NNCI website. Outcome measures have included the number of educational resources developed, feedback from workshop attendees, the number of US psychiatry residency programs who have adopted NNCI resources, as well as analytics from the NNCI website. RESULTS: To date, the NNCI has developed over 150 teaching sessions, reflecting the work of 129 authors from 49 institutions. The NNCI has run over 50 faculty development workshops in collaboration with numerous national and international organizations. Between March 2015 and June 2019, the website (www.NNCIonline.org) has hosted 48,640 unique users from 161 countries with 500,953 page views. More than 200 psychiatry training programs have reported implementing NNCI teaching materials. CONCLUSIONS: This multisite collaborative provides a model for integrating cutting-edge science into medical education and the practice of medicine more broadly.

Induced Trf2 deletion leads to aging vascular phenotype in mice associated with arterial telomere uncapping, senescence signaling, and oxidative stress.

Age-related vascular dysfunction in large elastic and resistance arteries is associated with reductions in microvascular perfusion and elevations in blood pressure. Recent evidence indicates that telomere uncapping-induced senescence in vascular cells may be an important source of oxidative stress and vascular dysfunction in aging, but the causal relationship between these processes has yet to be elucidated. To test this important unexplored hypothesis, we measured arterial senescence signaling and oxidative stress, carotid and mesenteric artery endothelium-dependent vasodilatory capacity, markers of mesenteric microvascular perfusion and endothelial glycocalyx deterioration, and blood pressure in a novel mouse model of Cre-inducible whole body Trf2 deletion and telomere uncapping. Trf2 deletion led to a 320% increase in arterial senescence signaling (P < .05). There was a concurrent 29% and 22% reduction in peak endothelium-dependent vasodilation in carotid and mesenteric arteries, respectively, as well as a 63% reduction in mesenteric microvascular endothelial glycocalyx thickness (all P ≤ .01). Mesenteric microvascular perfusion was reduced by 8% and systolic blood pressure was increased by 9% following Trf2 deletion (both P < .05). Trf2 deletion also led to a pro-oxidative arterial phenotype characterized by increased in NADPH oxidase gene expression; a 210% increase in superoxide levels that was partly dependent on NADPH oxidase activity; and an oxidative stress mediated reduction in carotid artery vasodilation (all P ≤ .05). Collectively, our findings demonstrate that induced Trf2 deletion leads to telomere uncapping, increased senescence signaling, and oxidative stress mediated functional impairments in the vasculature similar to those seen in human aging.

Deletion of Robo4 prevents high-fat diet-induced adipose artery and systemic metabolic dysfunction.

OBJECTIVE: Accumulating evidence suggests the vascular endothelium plays a fundamental role in the pathophysiology of obesity by regulating the functional status of white adipose and systemic metabolism. Robo4 is expressed specifically in endothelial cells and increases vascular stability and inhibits angiogenesis. We sought to determine the role of Robo4 in modulating cardiometabolic function in response to high-fat feeding. METHODS: We examined exercise capacity, glucose tolerance, and white adipose tissue artery gene expression, endothelium-dependent dilation (EDD), and angiogenesis in wild type and Robo4 knockout (KO) mice fed normal chow (NC) or a high-fat diet (HFD). RESULTS: We found Robo4 deletion enhances exercise capacity in NC-fed mice and HFD markedly increased the expression of the Robo4 ligand, Slit2, in white adipose tissue. Deletion of Robo4 increased angiogenesis in white adipose tissue and protected against HFD-induced impairments in white adipose artery vasodilation and glucose intolerance. CONCLUSIONS: We demonstrate a novel functional role for Robo4 in endothelial cell function and metabolic homeostasis in white adipose tissue, with Robo4 deletion protecting against endothelial and metabolic dysfunction associated with a HFD. Our findings suggest that Robo4-dependent signaling pathways may be a novel target in anti-obesity therapy.

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.

Telomere uncapping and vascular aging.

Although most telomere biology research continues to focus on telomere shortening, there is increasing evidence that telomere deprotection, or "uncapping," is more biologically and possibly clinically important. Telomeres form t-loops to prevent the chromosome ends from appearing as a double-stranded DNA break and initiating a DNA damage response. Breakdown of the t-loop structure, referred to as uncapping, can lead to cellular senescence, increased oxidative stress, and inflammation in tissues. In this review, we describe how telomere uncapping potentially leads to age-related vascular dysfunction and increased cellular senescence, oxidative stress, and inflammation. Importantly, we present evidence to argue that telomere uncapping is more biologically relevant than telomere shortening and a better marker of vascular aging and target for antiaging interventions.

Strategy for identifying repurposed drugs for the treatment of cerebral cavernous malformation.

BACKGROUND: Cerebral cavernous malformation (CCM) is a hemorrhagic stroke disease affecting up to 0.5% of North Americans that has no approved nonsurgical treatment. A subset of patients have a hereditary form of the disease due primarily to loss-of-function mutations in KRIT1, CCM2, or PDCD10. We sought to identify known drugs that could be repurposed to treat CCM. METHODS AND RESULTS: We developed an unbiased screening platform based on both cellular and animal models of loss of function of CCM2. Our discovery strategy consisted of 4 steps: an automated immunofluorescence and machine-learning-based primary screen of structural phenotypes in human endothelial cells deficient in CCM2, a secondary screen of functional changes in endothelial stability in these same cells, a rapid in vivo tertiary screen of dermal microvascular leak in mice lacking endothelial Ccm2, and finally a quaternary screen of CCM lesion burden in these same mice. We screened 2100 known drugs and bioactive compounds and identified 2 candidates, cholecalciferol (vitamin D3) and tempol (a scavenger of superoxide), for further study. Each drug decreased lesion burden in a mouse model of CCM vascular disease by ≈50%. CONCLUSIONS: By identifying known drugs as potential therapeutics for CCM, we have decreased the time, cost, and risk of bringing treatments to patients. Each drug also prompts additional exploration of biomarkers of CCM disease. We further suggest that the structure-function screening platform presented here may be adapted and scaled to facilitate drug discovery for diverse loss-of-function genetic vascular disease.

Cellular and molecular biology of aging endothelial cells.

Cardiovascular disease (CVD) is the leading cause of death in the United States and aging is a major risk factor for CVD development. One of the major age-related arterial phenotypes thought to be responsible for the development of CVD in older adults is endothelial dysfunction. Endothelial function is modulated by traditional CVD risk factors in young adults, but advancing age is independently associated with the development of vascular endothelial dysfunction. This endothelial dysfunction results from a reduction in nitric oxide bioavailability downstream of endothelial oxidative stress and inflammation that can be further modulated by traditional CVD risk factors in older adults. Greater endothelial oxidative stress with aging is a result of augmented production from the intracellular enzymes NADPH oxidase and uncoupled eNOS, as well as from mitochondrial respiration in the absence of appropriate increases in antioxidant defenses as regulated by relevant transcription factors, such as FOXO. Interestingly, it appears that NFkB, a critical inflammatory transcription factor, is sensitive to this age-related endothelial redox change and its activation induces transcription of pro-inflammatory cytokines that can further suppress endothelial function, thus creating a vicious feed-forward cycle. This review will discuss the two macro-mechanistic processes, oxidative stress and inflammation, that contribute to endothelial dysfunction with advancing age as well as the cellular and molecular events that lead to the vicious cycle of inflammation and oxidative stress in the aged endothelium. Other potential mediators of this pro-inflammatory endothelial phenotype are increases in immune or senescent cells in the vasculature. Of note, genomic instability, telomere dysfunction or DNA damage has been shown to trigger cell senescence via the p53/p21 pathway and result in increased inflammatory signaling in arteries from older adults. This review will discuss the current state of knowledge regarding the emerging concepts of senescence and genomic instability as mechanisms underlying oxidative stress and inflammation in the aged endothelium. Lastly, energy sensitive/stress resistance pathways (SIRT-1, AMPK, mTOR) are altered in endothelial cells and/or arteries with aging and these pathways may modulate endothelial function via key oxidative stress and inflammation-related transcription factors. This review will also discuss what is known about the role of "energy sensing" longevity pathways in modulating endothelial function with advancing age. With the growing population of older adults, elucidating the cellular and molecular mechanisms of endothelial dysfunction with age is critical to establishing appropriate and measured strategies to utilize pharmacological and lifestyle interventions aimed at alleviating CVD risk. This article is part of a Special Issue entitled "SI: CV Aging".

Greater impairments in cerebral artery compared with skeletal muscle feed artery endothelial function in a mouse model of increased large artery stiffness.

KEY POINTS: Increased large artery stiffness is a hallmark of arterial dysfunction with advancing age and is also present in other disease conditions such as diabetes. Increased large artery stiffness is correlated with resistance artery dysfunction in humans. Using a mouse model of altered arterial elastin content, this is the first study to examine the cause-and-effect relationship between large artery stiffness and peripheral resistance artery function. Our results indicate that mice with genetically greater large artery stiffness have impaired cerebral artery endothelial function, but generally preserved skeletal muscle feed artery endothelial function. The mechanisms for impaired cerebral artery endothelial function are reduced nitric oxide bioavailability and increased oxidative stress. These findings suggest that interventions that target large artery stiffness may be important to reduce disease risk associated with cerebral artery dysfunction in conditions such as advancing age. ABSTRACT: Advancing age as well as diseases such as diabetes are characterized by both increased large artery stiffness and impaired peripheral artery function. It has been hypothesized that greater large artery stiffness causes peripheral artery dysfunction; however, a cause-and-effect relationship has not previously been established. We used elastin heterozygote mice (Eln(+/-) ) as a model of increased large artery stiffness without co-morbidities unrelated to the large artery properties. Aortic stiffness, measured by pulse wave velocity, was ∼35% greater in Eln(+/-) mice than in wild-type (Eln(+/+) ) mice (P = 0.04). Endothelium-dependent dilatation (EDD), assessed by the maximal dilatation to acetylcholine, was ∼40% lower in Eln(+/-) than Eln(+/+) mice in the middle cerebral artery (MCA, P < 0.001), but was similar between groups in the gastrocnemius feed arteries (GFA, P = 0.79). In the MCA, EDD did not differ between groups after incubation with the nitric oxide (NO) synthase inhibitor N(ω) -nitro-l-arginine methyl ester (P > 0.05), indicating that lower NO bioavailability contributed to the impaired EDD in Eln(+/-) mice. Superoxide production and content of the oxidative stress marker nitrotyrosine was higher in MCAs from Eln(+/-) compared with Eln(+/+) mice (P < 0.05). In the MCA, after incubation with the superoxide scavenger TEMPOL, maximal EDD improved by ∼65% in Eln(+/-) (P = 0.002), but was unchanged in Eln(+/+) mice (P = 0.17). These results indicate that greater large artery stiffness has a more profound effect on endothelial function in cerebral arteries compared with skeletal muscle feed arteries. Greater large artery stiffness can cause cerebral artery endothelial dysfunction by reducing NO bioavailability and increasing oxidative stress.

The impact of ageing on adipose structure, function and vasculature in the B6D2F1 mouse: evidence of significant multisystem dysfunction.

The critical influence of the white adipose tissue (WAT) on metabolism is well-appreciated in obesity, but adipose tissue dysfunction as a mechanism underlying age-associated metabolic dysfunction requires elucidation. To explore this possibility, we assessed metabolism and measures of epididymal (e)WAT mitochondria and artery function in young (6.1 ± 0.4 months) and old (29.6 ± 0.2 months) B6D2F1 mice. There were no group differences in average daily oxygen consumption, fasted blood glucose or plasma free fatty acids, but fasted plasma insulin and the homeostatic model assessment of insulin resistance (HOMA-IR%) were higher in the old (∼50-85%, P < 0.05). Tissue mass (P < 0.05) and adipocyte area were lower (∼60%) (P < 0.01) and fibrosis was greater (sevenfold, P < 0.01) in eWAT with older age. The old also exhibited greater liver triglycerides (∼60%, P < 0.05). The mitochondrial respiratory oxygen flux after the addition of glutamate and malate (GM), adenosine diphosphate (d), succinate (S) and octanoyl carnitine (O) were one- to twofold higher in eWAT of old mice (P < 0.05). Despite no change in the respiratory control ratio, substrate control ratios of GMOd/GMd and GMOSd/GMd were ∼30-40% lower in old mice (P < 0.05) and were concomitant with increased nitrotyrosine (P < 0.05) and reduced expression of brown adipose markers (P < 0.05). Ageing reduced vascularity (∼50%, P < 0.01), angiogenic capacity (twofold, P < 0.05) and expression of vascular endothelial growth factor (∼50%, P < 0.05) in eWAT. Finally, endothelium-dependent dilation was lower (P < 0.01) in isolated arteries from eWAT arteries of the old mice. Thus, metabolic dysfunction with advancing age occurs in concert with dysfunction in the adipose tissue characterized by both mitochondrial and arterial dysfunction.

Prevention of age-related endothelial dysfunction by habitual aerobic exercise in healthy humans: possible role of nuclear factor κB.

Habitual aerobic exercise prevents age-related impairments in endothelium-dependent dilation (EDD). We have hypothesized that the pro-inflammatory transcription factor nuclear factor κB (NF-κB) impairs EDD with sedentary aging, and habitual aerobic exercise prevents this age-related suppression of EDD by NF-κB. To test this hypothesis, we have inhibited NF-κB signalling via oral salsalate administration in healthy older aerobic exercise-trained adults (OT, n=14, 58 ± 2 years), older non-exercising adults (ON, n=16, 61 ± 1 years) and young non-exercising controls (YN, n=8, 23 ± 1 years). Salsalate reduced endothelial cell expression of NF-κB p65 by ~25% in ON (P<0.05) but did not significantly change expression in OT or YN (P>0.05). EDD, assessed by brachial artery flow-mediated dilation (FMD), was improved by salsalate in ON (4.0 ± 0.7% compared with 6.8 ± 0.7%, placebo compared with salsalate, P<0.001) but did not change with salsalate in OT or YN (OT: 7.2 ± 0.7% compared with 7.7 ± 0.6%; YN: 7.6 ± 0.9% compared with 8.1 ± 0.8%; placebo compared with salsalate, P>0.05). Endothelium-independent dilation was not affected by salsalate in any group (P>0.05). In ON, vitamin C infusion improved FMD by ~30% during placebo (P<0.001) but had no affect during salsalate (P>0.05). In OT and YN, vitamin C infusion did not affect FMD during either placebo or salsalate (P>0.05). Salsalate reduced endothelial cell nitrotyrosine content by ~25% and NADPH oxidase p47phox expression by ~30% in ON (P<0.05) but had no effect in OT or YN (P>0.05). Our results suggest that endothelial NF-κB signalling is associated with oxidative stress-related impairment of EDD in healthy non-exercising but not aerobically exercising older adults. This may be a key mechanism by which regular aerobic exercise preserves endothelial function and reduces cardiovascular risk with aging.

Regular aerobic exercise protects against impaired fasting plasma glucose-associated vascular endothelial dysfunction with aging.

In the present study, we tested the hypothesis that age-associated vascular endothelial dysfunction is exacerbated by IFG (impaired fasting plasma glucose) and that regular aerobic exercise prevents this effect. Data were analysed from a cohort of 131 non-smoking men and women without overt clinical disease. Compared with young adult controls (age=24±1 years, n=29; values are means±S.E.M.), brachial artery FMD (flow-mediated dilation), a measure of conduit artery EDD (endothelium-dependent dilation), was 33% lower [7.93±0.33 against 5.27±0.37%Δ (% change), P<0.05] in MA/O (middle-aged/older) adults with NFG (normal fasting plasma glucose) (≤99 mg/dl, 62±1 years, n=35). In MA/O adults with IFG (100-125 mg/dl, 64±1 years, n=28), FMD was 30% lower (3.37±0.35%Δ) than in their peers with NFG and 58% lower than young controls (P<0.05). Brachial artery FMD was greater (6.38±0.35%Δ) in MA/O adults with NFG who regularly performed aerobic exercise (>45 min/day for ≥5 days/week, 62±1 years, n=23) compared with their non-exercising peers and only slightly less than young controls (P<0.05). Most importantly, FMD was completely preserved in MA/O adults with IFG who regularly performed aerobic exercise (6.99±0.69%Δ, 65±1 years, n=16). In the pooled sample, fasting plasma glucose was inversely related to FMD (r=-0.42, P<0.01) and was the strongest independent predictor of FMD (R(2)=0.32). Group differences in FMD were not affected by other subject characteristics or brachial artery properties, including brachial artery dilation to sublingual NTG (nitroglycerine, i.e. endothelium-independent dilation). IFG exacerbates age-associated vascular endothelial dysfunction and this adverse effect is completely prevented in MA/O adults who regularly perform aerobic exercise.

INFLUENCE OF OBESITY ON VASCULAR DYSFUNCTION AFTER TRAUMATIC HEMORRHAGE.

ABSTRACT: Background: Obesity increases the risk for morbidity and mortality after trauma. These complications are associated with profound vascular damage. Traumatic hemorrhage acutely attenuates vascular responsiveness, but the impact of obesity on this dysfunction is not known. The local inflammatory response in vascular cells is also unknown. We hypothesized that obesity potentiates trauma-induced vascular inflammation and dysfunction. Methods: Male Sprague-Dawley rats (~250 g) were fed normal chow (NC; 13.5% kcal fat, n = 20) or high-fat (HF; 60% kcal fat, n = 20) diets for 6 to 8 weeks. Under anesthesia, hemorrhage was induced by a mesenteric artery laceration, a Grade V splenic injury, and hypotension (MAP = 30-40 mm Hg) for 30 minutes. Vascular responsiveness was assessed ex vivo in isolated mesenteric arteries prehemorrhage and posthemorrhage. Gene expression for IL-1ß, and IL-6, prooxidant nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2), and α-adrenergic receptor were assessed in carotid artery endothelial cells (ECs) and non-ECs (media + adventitia). Results: In NC rats, hemorrhage attenuated norepinephrine-induced vasoconstriction and endothelium-dependent vasodilation to acetylcholine. In HF rats, baseline norepinephrine-induced vasoconstriction was attenuated compared with NC, but vasoconstriction and endothelium-dependent vasodilation did not change prehemorrhage to posthemorrhage. Hemorrhage led to elevated IL-1ß gene expression in ECs and elevated IL1ß, IL-6, NOX2, and α-adrenergic receptor gene expression in the media + adventitia compared with sham. HF rats had greater EC IL-1 ß and NOX2 gene expression compared with NC rats. The hemorrhage-induced elevation of IL-1ß in the media + adventitia was greatest in HF rats. Conclusion: Traumatic hemorrhage attenuates vascular responsiveness and induces vascular inflammation. The attenuated vascular responsiveness after hemorrhage is absent in obese rats, while the elevated vascular inflammation persists. A HF diet amplifies the arterial inflammation after hemorrhage. Altered vascular responsiveness and vascular inflammation may contribute to worse outcomes in obese trauma patients.

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.

Advancing age increases the size and severity of spontaneous atheromas in mouse models of atherosclerosis.

Using multiple mouse models, we explored the impact of aging on the size and severity of atherosclerotic lesions. In young, middle-aged and old apolipoprotein E knockout mice (ApoE-/-) fed an atherogenic diet (AD) for 3-8 weeks, plaque/atheroma formation in the descending aorta and aortic root, and atheroma development in the carotid in response to partial carotid ligation (PCL) were assessed. Total and LDL cholesterol, and triglycerides were higher in old compared to both other age groups, regardless of AD duration. Aortic plaque burden increased with AD duration in all ages. The size and plaque morphology grade of aortic root atheromas was higher with age; however, there was no effect of age on the size or severity of carotid atheromas after PCL. We additionally induced hyperlipidemia in young and old C57BL/6 mice by adeno-associated virus mediated upregulation of LDL receptor regulator, Pcsk9, and 5 weeks of AD. Despite lower cholesterol in old compared to young Pcsk9 mice, there was a greater size and severity of aortic root atheromas in old mice. However, like the ApoE-/- mice, there was no effect of age on size or severity of PCL-induced carotid artery atheromas in Pcsk9 mice. Together, these results suggest that aging increases the size and severity of spontaneous aortic atheromas.

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.

Heterozygosity for ADP-ribosylation factor 6 suppresses the burden and severity of atherosclerosis.

Atherosclerosis is the root cause of major cardiovascular diseases (CVD) such as myocardial infarction and stroke. ADP-ribosylation factor 6 (Arf6) is a ubiquitously expressed GTPase known to be involved in inflammation, vascular permeability and is sensitive to changes in shear stress. Here, using atheroprone, ApoE-/- mice, with a single allele deletion of Arf6 (HET) or wildtype Arf6 (WT), we demonstrate that reduction in Arf6 attenuates atherosclerotic plaque burden and severity. We found that plaque burden in the descending aorta was lower in HET compared to WT mice (p˂0.001) after the consumption of an atherogenic Paigen diet for 5 weeks. Likewise, luminal occlusion, necrotic core size, plaque grade, elastic lamina breaks, and matrix deposition were lower in the aortic root atheromas of HET compared to WT mice (all p≤0.05). We also induced advanced human-like complex atherosclerotic plaque in the left carotid artery using partial carotid ligation surgery and found that atheroma area, plaque grade, intimal necrosis, intraplaque hemorrhage, thrombosis, and calcification were lower in HET compared to WT mice (all p≤0.04). Our findings suggest that the atheroprotection afforded by Arf6 heterozygosity may result from reduced immune cell migration (all p≤0.005) as well as endothelial and vascular smooth muscle cell proliferation (both p≤0.001) but independent of changes in circulating lipids (all p≥0.40). These findings demonstrate a critical role for Arf6 in the development and severity of atherosclerosis and suggest that Arf6 inhibition can be explored as a novel therapeutic strategy for the treatment of atherosclerotic CVD.