Bradley S. Fleenor

Superoxide signaling in perivascular adipose tissue promotes age-related artery stiffness

We tested the hypothesis that superoxide signaling within aortic perivascular adipose tissue (PVAT) contributes to large elastic artery stiffening in old mice. Young (4–6 months), old (26–28 months), and old treated with 4‐Hydroxy‐2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPOL), a superoxide scavenger (1 mm in drinking water for 3 weeks), male C57BL6/N mice were studied. Compared with young, old had greater large artery stiffness assessed by aortic pulse wave velocity (aPWV, 436 ± 9 vs. 344 ± 5 cm s‐1) and intrinsic mechanical testing (3821 ± 427 vs. 1925 ± 271 kPa) (both P < 0.05). TEMPOL treatment in old reversed both measures of arterial stiffness. Aortic PVAT superoxide production was greater in old (P < 0.05 vs. Y), which was normalized with TEMPOL. Compared with young, old controls had greater pro‐inflammatory proteins in PVAT‐conditioned media (P < 0.05). Young recipient mice transplanted with PVAT from old compared with young donors for 8 weeks had greater aPWV (409 ± 7 vs. 342 ± 8 cm s‐1) and intrinsic mechanical properties (3197 ± 647 vs. 1889 ± 520 kPa) (both P < 0.05), which was abolished with TEMPOL supplementation in old donors. Tissue‐cultured aortic segments from old in the presence of PVAT had greater mechanical stiffening compared with old cultured in the absence of PVAT and old with PVAT and TEMPOL (both, P < 0.05). In addition, PVAT‐derived superoxide was associated with arterial wall hypertrophy and greater adventitial collagen I expression with aging that was attenuated by TEMPOL. Aging or TEMPOL treatment did not affect blood pressure. Our findings provide evidence for greater age‐related superoxide production and pro‐inflammatory proteins in PVAT, and directly link superoxide signaling in PVAT to large elastic artery stiffness.

Aortic perivascular adipose-derived interleukin-6 contributes to arterial stiffness in low-density lipoprotein receptor deficient mice

We tested the hypothesis that aortic perivascular adipose tissue (PVAT) from young low-density lipoprotein receptor-deficient (LDLr(-/-)) mice promotes aortic stiffness and remodeling, which would be mediated by greater PVAT-derived IL-6 secretion. Arterial stiffness was assessed by aortic pulse wave velocity and with ex vivo intrinsic mechanical properties testing in young (4-6 mo old) wild-type (WT) and LDLr(-/-) chow-fed mice. Compared with WT mice, LDLr(-/-) mice had increased aortic pulse wave velocity (407 ± 18 vs. 353 ± 13 cm/s) and intrinsic mechanical stiffness (5,308 ± 623 vs. 3,355 ± 330 kPa) that was associated with greater aortic protein expression of collagen type I and advanced glycation end products (all P < 0.05 vs. WT mice). Aortic segments from LDLr(-/-) compared with WT mice cultured in the presence of PVAT had greater intrinsic mechanical stiffness (6,092 ± 480 vs. 3,710 ± 316 kPa), and this was reversed in LDLr(-/-) mouse arteries cultured without PVAT (3,473 ± 577 kPa, both P < 0.05). Collagen type I and advanced glycation end products were increased in LDLr(-/-) mouse arteries cultured with PVAT (P < 0.05 vs. WT mouse arteries), which was attenuated when arteries were cultured in the absence of PVAT (P < 0.05). PVAT from LDLr(-/-) mice secreted larger amounts of IL-6 (3.4 ± 0.1 vs. 2.3 ± 0.7 ng/ml, P < 0.05), and IL-6 neutralizing antibody decreased intrinsic mechanical stiffness in LDLr(-/-) aortic segments cultured with PVAT (P < 0.05). Collectively, these data provide evidence for a role of PVAT-derived IL-6 in the pathogenesis of aortic stiffness and remodeling in chow-fed LDLr(-/-) mice.

Hesperidin reverses perivascular adipose-mediated aortic stiffness with aging

ABSTRACT We tested the hypothesis that hesperidin would reverse age‐related aortic stiffness, perivascular adipose (PVAT) mediated‐arterial stiffening and PVAT advanced glycation end‐products (AGE) accumulation. Aortic pulse wave velocity (aPWV) and intrinsic mechanical stiffness, two measures of arterial stiffness, were assessed in C57BL/6 mice that were young (6 months), old (27–29 months), or old treated with hesperidin for 4 weeks. Old compared with young mice had increased aPWV (444 ± 10 vs. 358 ± 8 cm/s, P < 0.05) and mechanical stiffness (6506 ± 369 vs. 3664 ± 414 kPa, P < 0.05). In old mice hesperidin reduced both aPWV (331 ± 38 cm/s) and mechanical stiffness (4445 ± 667 kPa) to levels not different from young. Aortic segments from old animals cultured with (+) PVAT had greater mechanical stiffness compared to young (+) PVAT (6454 ± 323 vs. 3575 ± 440 kPa, P < 0.05) that was ameliorated in arteries from old hesperidin treated cultured (+) PVAT (2639 ± 258 kPa). Hesperidin also reversed the aging‐related PVAT AGE accumulation (all, P < 0.05). A 4‐week treatment with the AGE inhibitor aminoguanidine reversed both the age‐related increase in aPWV (390 ± 7 cm/s) and mechanical stiffness (3396 ± 1072 kPa), as well as mechanical stiffness in arteries cultured (+) PVAT (3292 ± 716 kPa) (all, P < 0.05) to values not different from young. In conclusion, hesperidin ameliorates the age‐related increase in aortic stiffness and the PVAT‐mediated effects on arterial stiffening. Hesperidin also reversed PVAT AGE accumulation, where PVAT AGE were shown to promote aortic stiffness with aging. HIGHLIGHTSAging‐related aortic stiffness is reversed with a dietary hesperidin intervention.Aging increases advanced glycation end‐products (AGE) in perivascular adipose.Hesperidin reduces the aging‐induced perivascular adipose AGE accumulation.AGE inhibition reduces perivascular adipose‐related arterial stiffness with aging.

The emerging role of curcumin for improving vascular dysfunction: A review

ABSTRACT Curcumin, when administered in a bioavailable form, has potential to influence vascular health of various populations, leading to decreases in cardiovascular disease risk. Clinical intervention studies with curcumin have demonstrated significant improvements in endothelial function, arterial compliance, arterial stiffness, and other measures of vascular hemodynamics in young, middle-aged, old, post-menopausal, healthy, diabetic, and obese individuals. Mechanistically, curcumin is believed to improve vascular function through its effects on inflammation, oxidative stress, nitric oxide bioavailability, and structural proteins of the artery. Current data give support for curcumin to be administered for improvements in vascular health to individuals that may or may not be at risk for cardiovascular disease. This review briefly summarizes the techniques used for the establishment of vascular health and overviews the literature investigating the role of curcumin in the improvement of vascular health.

Arterial hemodynamics are impaired at rest and following acute exercise in overweight young men

Higher body mass index (BMI) is associated with greater cardiovascular disease (CVD) risk, in part due to aortic stiffening assessed by carotid-femoral pulse wave velocity (cfPWV). Importantly, greater cardiorespiratory fitness (CRF; VO2peak) decreases CVD risk, and is associated with reductions in aortic stiffness. We tested the hypothesis that young adult overweight (OW, n=17) compared with healthy-weight (HW, n=17) men will have greater resting aortic stiffness, reduced CRF and an impaired post-exercise hemodynamic response. Resting cfPWV was greater in OW versus HW individuals (5.81 ± 0.13 vs 4.81 ± 0.12 m/sec, p<0.05). Relative CRF (VO2peak; mL/kg/min) was lower in OW compared with HW individuals (49.4 ± 1.3 vs 57.6 ± 1.0 mL/kg/min, p<0.05), and was inversely related with cfPWV (p<0.05). However, CRF as absolute VO2peak (L/min) was not different between groups and there was no relation between cfPWV and absolute VO2peak (L/min), indicating reduced relative CRF in OW men is due to greater body mass. Following the maximal treadmill exercise test, cfPWV was greater in OW compared with HW subjects from rest to 60 minutes post-exercise (p<0.05). Compared with HW, OW individuals had higher systolic blood pressure (main effect, p<0.05) and diastolic blood pressure was selectively increased for up to 60 minutes following exercise (p<0.05). Overweight individuals had an attenuated post-exercise decrease in mean arterial pressure (p<0.05). Collectively, these results indicate that young, apparently healthy, OW men have greater resting aortic stiffening and an impaired post-exercise hemodynamic response.

Mechanisms of Arterial Stiffness

Current understanding for the mechanisms contributing to arterial stiffness is limited. The field is rapidly growing, however, and the complex process of functional, structural and signaling pathways working together to stiffen arteries is becoming increasingly clear. As such, arterial dilation and constriction, extracellular matrix accumulation and stiffening of individual cells via specific signal transduction pathways inter-connect providing numerous targets for potential therapeutic intervention. Herein we highlight the mechanisms that are largely implicated in arterial stiffness, and those that may be emerging as important targets.

Sex Chromosome Complement Defines Diffuse Versus Focal Angiotensin II–Induced Aortic Pathology

Objective— Aortic pathologies exhibit sexual dimorphism, with aneurysms in both the thoracic and abdominal aorta (ie, abdominal aortic aneurysm [AAA]) exhibiting higher male prevalence. Women have lower prevalence of aneurysms, but when they occur, aneurysms progress rapidly. To define mechanisms for these sex differences, we determined the role of sex chromosome complement and testosterone on the location and progression of angiotensin II (AngII)–induced aortic pathologies. Approach and Results— We used transgenic male mice expressing Sry (sex-determining region Y) on an autosome to create Ldlr (low-density lipoprotein receptor)–deficient male mice with an XY or XX sex chromosome complement. Transcriptional profiling was performed on abdominal aortas from XY or XX males, demonstrating 1746 genes influenced by sex chromosomes or sex hormones. Males (XY or XX) were either sham-operated or orchiectomized before AngII infusions. Diffuse aortic aneurysm pathology developed in XY AngII-infused males, whereas XX males developed focal AAAs. Castration reduced all AngII-induced aortic pathologies in XY and XX males. Thoracic aortas from AngII-infused XY males exhibited adventitial thickening that was not present in XX males. We infused male XY and XX mice with either saline or AngII and quantified mRNA abundance of key genes in both thoracic and abdominal aortas. Regional differences in mRNA abundance existed before AngII infusions, which were differentially influenced by AngII between genotypes. Prolonged AngII infusions resulted in aortic wall thickening of AAAs from XY males, whereas XX males had dilated focal AAAs. Conclusions— An XY sex chromosome complement mediates diffuse aortic pathology, whereas an XX sex chromosome complement contributes to focal AngII-induced AAAs.

Sweet potato (Ipomoea batatas) attenuates diet-induced aortic stiffening independent of changes in body composition

We hypothesized a sweet potato intervention would prevent high-fat (HF) diet-induced aortic stiffness, which would be associated with decreased arterial oxidative stress and increased mitochondrial uncoupling. Young (8-week old) C57BL/6J mice were randomly divided into 4 groups: low fat (LF; 10% fat), HF (60% fat), low-fat sweet potato (LFSP; 10% fat containing 260.3 μg/kcal sweet potato), or high-fat sweet potato diet (HFSP; 60% fat containing 260.3 μg/kcal sweet potato) for 16 weeks. Compared with LF and LFSP, HF- and HFSP-fed mice had increased body mass and percent fat mass with lower percent lean mass (all, P < 0.05). Sweet potato intervention did not influence body composition (all, P > 0.05). Arterial stiffness, assessed by aortic pulse wave velocity and ex vivo mechanical testing of the elastin region elastic modulus (EEM) was greater in HF compared with LF and HFSP animals (all, P < 0.05). Advanced glycation end products and nitrotyrosine abundance were greater in aortic segments from HF mice compared with LF and HFSP animals (all, P < 0.05). Aortic elastin and uncoupling protein 2 expressions, however, were reduced in HF compared with LF and HFSP mice (all, P < 0.05). Aortic segments cultured with 2,4-dinitrophenol (DNP), a mitochondrial uncoupler, for 72 h reduced the EEM of HF arteries compared with nontreated HF segments (P < 0.05). DNP had no effect on the EEM of aortic segments from HFSP mice. In conclusion, sweet potato attenuates diet-induced aortic stiffness independent of body mass and composition, which is associated with a normalization of arterial oxidative stress possibly due to mitochondrial uncoupling.

Implications of Arterial Stiffness

The implications for increased arterial stiffness are just now beginning to be understood. However, there is still much unknown in this emerging field of study. In this chapter we overview several areas of clinical importance that influence arterial stiffness, which include aging, sex, race, body composition, and cardiorespiratory fitness, and the implications of these on cardiovascular health and target organ damage. These discussions merely highlight the complex interactions that occur with aging alone, which become increasingly convoluted with multiple pathologies. Thus, our discussion only begins to elucidate the very complex processes contributing to aortic stiffness and the overall health implications.

Interventions to Destiffen Arteries

Stiffening of arteries is a condition associated with aging and disease that results in a less compliant arterial system. Arterial stiffness is an important CVD risk factor that is associated with premature mortality and heightened morbidity. Intervening to reduce arterial stiffening is a challenge, yet there is mounting evidence supporting the effects of lifestyle and dietary modifications to reduce aortic pulse wave velocity (aPWV), the gold standard measure of aortic stiffness. Plant-based polyphenolic compounds, omega-3 fatty acids, antioxidant vitamins C and E, regular aerobic exercise, sodium reduction and weight loss have all shown to be successful strategies to destiffen arteries. First-line strategies to combat CVD risk factors such as arterial stiffening should include lifestyle modifications.