Asymmetric dimethylarginine and reduced nitric oxide bioavailability in young Black African men

Endothelin A receptor inhibition increases nitric oxide-dependent vasodilation independent of superoxide in non-Hispanic Black young adults

Young non-Hispanic Black adults have reduced microvascular endothelial function compared with non-Hispanic White counterparts, but the mechanisms are not fully elucidated. The purpose of this study was to investigate the effect of endothelin-1 A receptor (ET_AR) and superoxide on cutaneous microvascular function in young non-Hispanic Black (n = 10) and White (n = 10) adults. Participants were instrumented with four intradermal microdialysis fibers: 1) lactated Ringer's (control), 2) 500 nM BQ-123 (ET_AR antagonist), 3) 10 μM tempol (superoxide dismutase mimetic), and 4) BQ-123 + tempol. Skin blood flow was assessed via laser-Doppler flowmetry (LDF), and each site underwent rapid local heating from 33°C to 39°C. At the plateau of local heating, 20 mM l-NAME [nitric oxide (NO) synthase inhibitor] was infused to quantify NO-dependent vasodilation. Data are means ± standard deviation. NO-dependent vasodilation was decreased in non-Hispanic Black compared with non-Hispanic White young adults (P < 0.01). NO-dependent vasodilation was increased at BQ-123 sites (73 ± 10% NO) and at BQ-123 + tempol sites (71 ± 10%NO) in non-Hispanic Black young adults compared with control (53 ± 13%NO, P = 0.01). Tempol alone had no effect on NO-dependent vasodilation in non-Hispanic Black young adults (63 ± 14%NO, P = 0.18). NO-dependent vasodilation at BQ-123 sites was not statistically different between non-Hispanic Black and White (80 ± 7%NO) young adults (P = 0.15). ET_AR contributes to reduced NO-dependent vasodilation in non-Hispanic Black young adults independent of superoxide, suggesting a greater effect on NO synthesis rather than NO scavenging via superoxide.NEW & NOTEWORTHY Endothelin-1 A receptors (ET_ARs) have been shown to reduce endothelial function independently and through increased production of superoxide. We show that independent ET_AR inhibition increases microvascular endothelial function in non-Hispanic Black young adults. However, administration of a superoxide dismutase mimetic alone and in combination with ET_AR inhibition had no effect on microvascular endothelial function suggesting that, in the cutaneous microvasculature, the negative effects of ET_AR in non-Hispanic Black young adults are independent of superoxide production.

The Correlation of Interleukin-6, Malnutrition Inflammation Score and Asymmetric Dimethylarginine in Chronic Kidney Disease Patients Undergoing Routine Hemodialysis

Introduction: Chronic kidney disease (CKD) patients undergoing routine hemodialysis (HD) have a high prevalence of protein-energy malnutrition (PEM) and inflammation. The combination of inflammation and PEM is associated with cardiovascular disease and poor outcomes. Interleukin-6 (IL-6) is an inflammatory factor that runs parallel to endothelial damage and is closely related to the nutritional status of CKD HD patients. The tool to assess nutrition status is Malnutrition Inflammation Score (MIS) and to assess endothelial damage is Asymmetric Dimethylarginine (ADMA). It is currently unclear whether there is a correlation between inflammation, malnutrition, and endothelial dysfunction. Therefore the aim of this study is to determine the correlation between IL-6, MIS and ADMA in CKD HD patients.  Methods: A cross-sectional design with analytic observational study was conducted on end stage renal disease patient who undergo routine hemodialysis for at least 2 years with the duration of hemodialysis is 4-5 hours and at least twice per week. IL-6 was examined by kit (ELISA) and ADMA using LC-MS/MS at a certified laboratory in Manado city. History taking and physical examination were used to calculate MIS. Data analysis was done using SPSS version 22. Results: There were 30 participants consisting of 22 men (72%) and 8 women (28%). The median age of the subjects was 56.50 years. There was a statistically significant positive correlation between IL-6 and ADMA (r = 0.440, p = 0.015), MIS and ADMA (r = 0.378, p = 0.039), and IL-6 and MIS (r = 0.682, p = 0.0001). Conclusion: There was a significant correlation between IL-6, MIS and ADMA.

Contributions of endothelin-1 and l-arginine to blunted cutaneous microvascular function in young, black women

Non-Hispanic black (BL) individuals have the greatest prevalence of cardiovascular disease (CVD), relative to other racial/ethnic groups (e.g., non-Hispanic white population; WH), which may be secondary to blunted vascular function. Although women typically present with reduced CVD relative to men of the same racial/ethnic group, the prevalence is similar between BL women and men though the mechanisms differ. This study hypothesized that reduced microvascular function in young, BL women is associated with endothelin-1 (ET-1) overactivity or insufficient l-arginine bioavailability. Nine BL and nine WH women participated (age: 20 ± 2 vs. 22 ± 2 yr). Cutaneous microvascular function was assessed during 39°C local heating, whereas lactated Ringer's (control), BQ-123 (ET-1 receptor type A antagonist), BQ-788 (ET-1 receptor type B antagonist), or l-arginine were infused via intradermal microdialysis to modify cutaneous vascular conductance (CVC). Subsequent infusion of N^ω-nitro-l-arginine methyl ester allowed for quantification of the nitric oxide (NO) contribution to vasodilation, whereas combined sodium nitroprusside and 43°C heating allowed for normalization to maximal CVC (%CVC_max). BL women had blunted %CVC_max and NO contribution to dilation during the 39°C plateau (P < 0.027 for both). BQ-123 improved this response through augmented NO-mediated dilation (P < 0.048 for both). BQ-788 and l-arginine did not alter the CVC responses (P > 0.835 for both) or the NO contribution (P > 0.371 for both). Cutaneous microvascular function is reduced in BL women, and ET-1 receptor type A may contribute to this reduced function. Further research is needed to better characterize these mechanisms in young, BL women.NEW & NOTEWORTHY Cardiovascular disease remains a burden in the United States non-Hispanic black (BL) population, although its manifestation through blunted vasodilation in this population is different between men and women. Accordingly, this study determined that reduced microvascular function in young, BL women may be partially controlled by endothelin-1 (ET-1) type A receptors, although neither type B receptors nor insufficient l-arginine bioavailability seems to contribute to this response. Accordingly, further research is needed to better characterize these ET-1 related mechanisms and illuminate other pathways that may contribute to this disparate vascular function in young, BL women.

Diversity in modern heart failure trials: Where are we, and where are we going

Over the last three decades, increased attention has been given to the representation of historically underrepresented groups within the landscape of pivotal clinical trials. However, recent events (i.e., coronavirus pandemic) have laid bare the potential continuation of historic inequities in available clinical trials and studies aimed at the care of broad patient populations. Anecdotally, cardiovascular disease (CVD) has not been immune to these disparities. Within this review, we examine and discuss recent landmark CVD trials, with a specific focus on the representation of Blacks within several critically foundational heart failure clinical trials tied to contemporary treatment strategies and drug approvals. We also discuss solutions for inequities within the landscape of cardiovascular trials. Building a more diverse clinical trial workforce coupled with intentional efforts to increase clinical trial diversity will advance equity in cardiovascular care.

l-Arginine and COVID-19: An Update

l-Arginine is involved in many different biological processes and recent reports indicate that it could also play a crucial role in the coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein, we present an updated systematic overview of the current evidence on the functional contribution of L-Arginine in COVID-19, describing its actions on endothelial cells and the immune system and discussing its potential as a therapeutic tool, emerged from recent clinical experimentations.

Central systolic blood pressure relates inversely to nitric oxide synthesis in young black adults: the African-PREDICT study

Lower nitric oxide (NO) bioavailabilty associates with hypertension in patients and elderly populations. With hypertension known to develop earlier in black populations, we compared both plasma and urinary NO-related markers and their associations with central systolic blood pressure (cSBP) and arterial stiffness in healthy young black and white adults. We included healthy black and white men and women (n = 1110; 20-30 years) and measured cSBP and pulse wave velocity (PWV), along with both plasma and urinary arginine, homoarginine, asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), as well as urinary ornithine/citrulline, nitrite and nitrate. In addition, the urinary nitrate-to-nitrite ratio (U_NOxR) was calculated. The black men and women had higher cSBP and higher plasma arginine and ADMA, but lower urinary nitrate and U_NOxR (all p ≤ 0.003) than their white counterparts. In single and forward stepwise multiple regression analyses, we found an inverse association of cSBP (adj. R² = 0.124; β = -0.134; p = 0.006) and plasma homoarginine in black men. Central SBP associated inversely with U_NOxR in black women only (adj. R² = 0.171; β = -0.130; p = 0.029). In the white women, cSBP associated positively with urinary ADMA (adj. R² = 0.372; β = 0.162; p = 0.015). PWV associated inversely with plasma ADMA (adj. R² = 0.253; β = -0.163; p = 0.024) in the white women only. The lower NO synthesis and the higher cSBP in our black cohort support the notion of a potential increased risk for future large artery stiffness and hypertension development in later life.

Knockout of Macula Densa Neuronal Nitric Oxide Synthase Increases Blood Pressure in db/db Mice

[Figure: see text].

Role of endothelial function determined by asymmetric dimethylarginine in the prediction of resistant hypertension: A subanalysis of ReHOT trial

The authors conducted a subanalysis of the ReHOT (Resistant Hypertension Optimal Treatment) study to evaluate the association between endothelial dysfunction and resistant hypertension in a population of patients treated in a staged fashion for hypertension. One hundred and three hypertensive patients were followed for 6 months and participated in seven visits (V0-V6) 28 days apart. There was a first phase (V0-V3) of antihypertensive adjustment with three drugs and determination of resistant hypertension and a second randomized phase (V3-V6) of treatment with a fourth drug (clonidine or spironolactone) in the hypertensive patients characterized as resistant. Of the 103 patients included, 86 (83.5%) underwent the randomization visit (V3), 71 were characterized as non-resistant hypertensives (82.5%), and 15 as resistant hypertensives (17.5%). Serum asymmetric dimethylarginine (ADMA) was shown to be an independent predictor of resistant hypertension after adjustment for multiple variables (OR: 11.42, 95% CI: 1.02-127.71, P = .048), and in addition, there was a reduction in blood pressure levels and ADMA values during follow-up with a positive correlation in both groups and a greater reduction in the group of resistant hypertensives. We demonstrated that ADMA was an independent predictor of resistant hypertension, and we observed that the improvement in blood pressure levels obtained with the treatment was proportional to the reduction in ADMA values, suggesting a complementary role of ADMA not only as a stratification tool for the occurrence of resistant hypertension, but also as a possible therapeutic target in this population.

Influence of sex on heightened vasoconstrictor mechanisms in the non-Hispanic black population

Cardiovascular disease (CVD) affects individuals of all races and ethnicities; however, its prevalence is highest in non-Hispanic black individuals (BL) relative to other populations. While previous research has provided valuable insight into elevated CVD risk in the BL population, this work has been almost exclusively conducted in men. This is alarming given that BL women suffer from CVD at an equivalent rate to BL men and each has a greater prevalence when compared to all other ethnicities, regardless of sex. The importance of investigating sex differences in mechanisms of cardiovascular function is highlighted by the National Institute of Health requiring sex to be considered as a biological variable in research studies to better our "understanding of key sex influences on health processes and outcomes." The mechanism(s) responsible for the elevated CVD risk in BL women remains unclear and is likely multifactorial. Limited studies in BL women suggest that, while impaired vasodilator capacity is involved, heightened vasoconstrictor tone and/or responsiveness may also contribute. Within this mini-review, we will discuss potential mechanisms of elevated rates of hypertension and other CVDs in BL individuals with a particular focus on young, otherwise healthy, college-aged women. To stimulate academic thought and future research, we will also discuss potential mechanisms for impaired vascular function in BL women, as well as possible divergent mechanisms between BL men and women based on either preliminary data or plausible speculation extending from findings in the existing literature. Last, we will conclude with potential future research directions aimed at better understanding the elevated risk for hypertension and CVD in BL women.

Characterization of the blood pressure response during cycle ergometer cardiopulmonary exercise testing in black and white men : Data from the Fitness Registry and Importance of Exercise: A National Database (FRIEND)

It has been established that blacks have higher overall incidence and prevalence of hypertension compared to their white counterparts. However, the maximum blood pressure (BP) response of blacks to exercise has not been characterized. A total of 5996 apparently healthy men from the Fitness Registry and Importance of Exercise: A National Database (FRIEND) who underwent maximum cardiopulmonary exercise tests on a cycle ergometer were included in this analysis. Of these participants, 1245 (21%) self-identified as black while the remaining 4751 (79%) identified as white. All subjects had a respiratory exchange ratio (RER) of ≥1.0 and had no reports of cardiovascular or pulmonary disease. Systolic BP (BP) response to exercise was indexed according to increase in workload (SBP/MET-slope). Both racial groups were subdivided into age groups by decade. Black men had higher peak SBP and higher SBP/MET-slopes compared to white men across all age groups (p < 0.001). Resting SBP was not different between blacks and whites except within the 18-29-year age group. The differences in peak SBP and SBP/MET-slope between age and race groups indicate that black men have an exaggerated BP response to exercise irrespective of resting BP values. Further investigation is warranted to determine the underlying mechanisms responsible and clinical implications for this exaggerated BP response to exercise.

Increased Serum Levels of Asymmetric Dimethylarginine and Symmetric Dimethylarginine and Decreased Levels of Arginine in Sudanese Patients with Essential Hypertension

INTRODUCTION

Essential hypertension (EH) is a disease caused by various environmental and genetic factors. Nitric oxide (NO) is important for the functional integrity of the endothelium. It is produced in endothelial cells by endothelial NO synthase (eNOS) that mediates the conversion of the amino acid arginine into NO and citrulline. Asymmetric dimethylarginine (ADMA) acts as an inhibitor of eNOS. In contrast, symmetric dimethylarginine (SDMA) has no direct effect on eNOS but plays an important role competing with arginine for transport across the amino acid transporter. ADMA and SDMA have been found to play a central role in the development of cardiovascular diseases. Serum ADMA levels may serve as a future diagnostic marker and a target of therapy in hypertensive patients in the Sudanese population. This study aimed to investigate the relation between serum arginine, ADMA, and SDMA levels with EH in the Sudanese population.

METHODS

Patients (n = 260) with established hypertension and controls (n = 144) with normal blood pressure were included in this case-control study. Serum blood samples were analyzed for arginine, ADMA, and SDMA, using high-performance liquid chromatography-tandem mass spectrometry. Other laboratory data were measured using routine methods. Mann-Whitney's U test and χ2 tests were used for continuous and categorical data, respectively. A multivariate logistic regression analysis was conducted to investigate the independent effect of multiple variables on the development of hypertension.

RESULTS

Serum arginine levels were significantly lower in the patient group than in the control group (p < 0.001). ADMA and SDMA levels were significantly higher in the patient group than the control group (p < 0.001, p = 0.001, respectively). Multivariate logistic regression analysis showed that only older age, being a male, and arginine levels are independent factors controlling the development of hypertension (p < 0.001, p < 0.001, and p = 0.046, respectively). ADMA and SDMA levels were not independent factors for the development of hypertension.

CONCLUSIONS

This study demonstrated increased serum levels of ADMA and SDMA and decreased arginine levels in Sudanese patients with EH. Lowering serum ADMA levels or increasing the arginine levels might be a novel therapeutic target in these individuals.

Urinary albumin-to-creatinine ratio is inversely related to nitric oxide synthesis in young black adults: the African-PREDICT study

Hypertension is common in black populations and is known to be associated with low nitric oxide (NO) bioavailability. We compared plasma and urinary NO-related markers and plasma creatine kinase (CK) levels between young healthy black and white adults along with the associations of these markers with the urinary albumin-to-creatinine ratio (uACR), which is a surrogate marker of endothelial and kidney function. We included 1105 participants (20-30 years). We measured the uACR, plasma CK, plasma and urinary arginine, homoarginine, asymmetric (ADMA) and symmetric dimethylarginine (SDMA), urinary ornithine/citrulline, nitrate and nitrite, and malondialdehyde (MDA). In addition, the urinary nitrate-to-nitrite ratio (U_NOxR) was calculated and used as a measure of circulating NO bioavailability. The uACR was comparable between the groups, yet the black group had lower urinary nitrate (by -15%) and U_NOxR values (by -18%) (both p ≤ 0.001), higher plasma (by +9.6%) and urinary (by +5.9%) arginine (both p ≤ 0.004), higher plasma (by +13%) and urinary (by +3.7%) ADMA (both p ≤ 0.033), and higher CK (by +9.5%) and MDA (by +19%) (both p < 0.001) compared with white adults. Plasma and urinary homoarginine were similar between the groups. In the multiple regression analysis, we confirmed the inverse associations of the uACR with both plasma (adj. R² = 0.066; β = -0.209; p = 0.005) and urinary (adj. R² = 0.066; β = -0.149; p = 0.010) homoarginine and with the U_NOxR (adj. R² = 0.060; β = -0.122; p = 0.031) in the black group only. The overall less favorable NO profile and higher CK and MDA levels in the black cohort along with the adverse associations with the uACR may reflect the vulnerability of this cohort to the early development of hypertension.

Role of the eNOS Uncoupling and the Nitric Oxide Metabolic Pathway in the Pathogenesis of Autoimmune Rheumatic Diseases

Atherosclerosis and its clinical complications constitute the major healthcare problems of the world population. Due to the central role of endothelium throughout the atherosclerotic disease process, endothelial dysfunction is regarded as a common mechanism for various cardiovascular (CV) disorders. It is well established that patients with rheumatic autoimmune diseases are characterized by significantly increased prevalence of cardiovascular morbidity and mortality compared with the general population. The current European guidelines on cardiovascular disease (CVD) prevention in clinical practice recommend to use a 1,5-factor multiplier for CV risk in rheumatoid arthritis as well as in other autoimmune inflammatory diseases. However, mechanisms of accelerated atherosclerosis in these diseases, especially in the absence of traditional risk factors, still remain unclear. Oxidative stress plays the major role in the endothelial dysfunction and recently is strongly attributed to endothelial NO synthase dysfunction (eNOS uncoupling). Converted to a superoxide-producing enzyme, uncoupled eNOS not only leads to reduction of the nitric oxide (NO) generation but also potentiates the preexisting oxidative stress, which contributes significantly to atherogenesis. However, to date, there are no systemic analyses on the role of eNOS uncoupling in the excess CV mortality linked with autoimmune rheumatic diseases. The current review paper addresses this issue.

An Ethnic Comparison of Arginine Dimethylation and Cardiometabolic Factors in Healthy Black and White Youth: The ASOS and African-PREDICT Studies

Proteinic arginine dimethylation (PADiMe) is a major post-translational modification. Proteolysis of asymmetric and symmetric PADiMe products releases asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), respectively, two endogenous atherogenic substances. SDMA, ADMA, and its major metabolite dimethylamine (DMA) are eliminated by the kidney. The urinary concentrations of DMA+ADMA, SDMA, and DMA+ADMA+SDMA are useful measures of the whole-body asymmetric and symmetric PADiMe, respectively. Urinary (DMA+ADMA)/SDMA is an index of the asymmetric to symmetric PADiMe balance. In two bi-ethnic studies, the ASOS (39 black boys, 41 white boys) and the African-PREDICT (292 black young men, 281 white young men) studies, we investigated whether ethnicity is a major determinant of PADiMe, and whether PADiMe is associated with blood pressure and ethnicity-dependent growth and inflammatory factors, including HDL. DMA, ADMA, and SDMA were measured in spot urine samples by gas chromatography-mass spectrometry, and their excretion was corrected for creatinine excretion. In black boys, creatinine-corrected DMA, DMA+ADMA, and DMA+ADMA+SDMA concentrations were lower by 11.7%, 9.5%, and 7.6% (all p < 0.05), respectively, compared to the white boys, and 3.4%, 2.0%, and 1.8% lower (all p < 0.05), respectively, in black compared to white men. (DMA+ADMA)/SDMA did not differ between black boys and black men, but was higher in white boys compared to white men. ADMA did not differ between black and white boys, or between black and white men. Creatinine-corrected SDMA excretion was lower in black boys compared to white boys (by 8%) and to white men (by 3.1%). None of the PADiMe indices were associated with blood pressure in either study. IGF-binding protein 3 correlated inversely with all PADiMe indices in the black men only. Our study showed that asymmetric proteinic arginine dimethylation is higher in white boys than in black boys, and that this difference disappears in adulthood. ADMA metabolism and SDMA excretion were lower in the black subjects compared to the white subjects, suggesting ethnicity-dependent hepatic and renal elimination of ADMA and SDMA in the childhood. The results of our study may have clinical relevance beyond atherosclerosis, such as in growth and inflammation, which have not been sufficiently addressed thus far.

Acute consumption of flavanol-rich cocoa beverage improves attenuated cutaneous microvascular function in healthy young African Americans

Flavanols have beneficial effects on vascular health and we have recently demonstrated that cerebral vasodilatory capacity in healthy young African Americans (AA) is improved with acute flavanol intake relative to aged-matched Caucasian Americans (CA). However, whether the positive benefits of acute flavanol consumption would also be present in the cutaneous microvascular circulation of AA remains unknown. Thus, we hypothesized that acute consumption of flavanol-rich cocoa (FC) would improve the previously reported reduced cutaneous microvascular responses to local heating in young AA. Seven AA and seven CA participated in this double-blind crossover study. Data were collected on two different days, separated by a minimum of one week. Two intradermal microdialysis membranes were inserted in the forearm and each site was randomly assigned to receive lactated Ringer's solution or NO synthase (NOS) inhibitor. Participants were randomly assigned to consume either a non-flavanol containing (NF) beverage or FC beverage. Cutaneous vascular conductance (CVC) was calculated as cutaneous blood flux/mean arterial pressure and normalized as % maximal CVC (%CVCmax). The difference in %CVCmax between the Ringer's site and NOS inhibited site was calculated to assess NO contribution (Δ %CVCmax). In the Ringer's site, acute consumption of FC beverage improved %CVCmax during 39 °C heating when compared to NF beverage in AA (NF: 36 ± 6 vs. FC: 47 ± 5%CVCmax; P < .01) while there was similar %CVCmax during 39 °C heating between beverages in CA (NF: 55 ± 4 vs. FC: 59 ± 5%CVCmax; P = .40). During 39 °C heating, NO contribution was significantly higher with FC beverage than NF beverage in AA (NF: 27 ± 5 vs. FC: 35 ± 4 Δ %CVCmax; P = .03) while there was similar NO contribution between beverages in CA (NF: 42 ± 4 vs. FC: 45 ± 4 Δ %CVCmax; P = .36). This data suggests that acute consumption of FC could be a therapeutic solution to improve an attenuated microvascular function in young AA.

Contribution of prostaglandins to exercise hyperaemia: workload, ethnicity and sex matter!

The contribution of prostaglandins (PGs) to exercise hyperaemia is controversial. In this review, we argue this is partly explained by differences in exercise intensity between studies. The effects of cyclooxygenase (COX) inhibition and PG assays indicate that PGs contribute more at moderate to heavy than at light workloads and are mainly released by low tissue O₂ . But, the release and actions of PGs also depend on other O₂ -dependent dilators including ATP, adenosine and NO. K⁺ may inhibit the action of PGs and other mediators by causing hyperpolarization, but contributes to the hyperaemia. Thus, at lighter loads, the influence of PGs may be blunted by K⁺ , while COX inhibition leads to compensatory increases in other O₂ -dependent dilators. In addition, we show that other sources of variability are sex and ethnicity. Our findings indicate that exercise hyperaemia following rhythmic contractions at 60% maximum voluntary contraction, is smaller in young black African (BA) men and women than in their white European (WE) counterparts, but larger in men than in women of both ethnicities. We propose the larger absolute force in men causes greater vascular occlusion and accumulation of dilators, while blunted hyperaemia in BAs may reflect lower oxidative capacity and O₂ requirement. Nevertheless, COX inhibition attenuated peak hyperaemia by ∼30% in WE, BA men and WE women, indicating PGs make a substantial contribution in all three groups. There was no effect in BA women. Lack of PG involvement may provide early evidence of endothelial dysfunction, consistent in BA women with their greater risk of cardiovascular disease.

Racial disparities in cardiovascular disease risk: mechanisms of vascular dysfunction

Cardiovascular disease (CVD) accounts for a third of all deaths in the United States making it the leading cause of morbidity and mortality. Although CVD affects individuals of all races/ethnicities, the prevalence of CVD is highest in non-Hispanic black (BL) individuals relative to other populations. The mechanism(s) responsible for elevated CVD risk in the BL population remains incompletely understood. However, impaired vascular vasodilator capacity and exaggerated vascular vasoconstrictor responsiveness are likely contributing factors, both of which are present even in young, otherwise healthy BL individuals. Within this review, we highlight some historical and recent data, collected from our laboratories, of impaired vascular function, in terms of reduced vasodilator capacity and heightened vasoconstrictor responsiveness, in the peripheral and cerebral circulations in BL individuals. We provide data that such impairments may be related to elevated oxidative stress and subsequent reduction in nitric oxide bioavailability. In addition, divergent mechanisms of impaired vasodilatory capacity between BL men and women are discussed. Finally, we propose several directions where future research is needed to fill in knowledge gaps, which will allow for better understanding of the mechanisms contributing to impaired vascular function in this population. Ultimately, this information will allow for better lifestyle and therapeutic approaches to be implemented in an effort to minimize the increased CVD burden in the BL population.

Optimal management of HIV- positive adults at risk for kidney disease in Nigeria (Renal Risk Reduction "R3" Trial): protocol and study design

Background

Individuals with two copies of the apolipoprotein-1 (APOL1) gene risk variants are at high risk (HR) for non-diabetic kidney disease. The presence of these risk variants is highest in West Africa, specifically in Nigeria. However, there is limited availability of dialysis and kidney transplantation in Nigeria, and most individuals will die soon after developing end-stage renal disease. Blocking the renin angiotensin aldosterone system with angiotensin-converting enzyme inhibitors (ACEi) is a well-recognized strategy to slow renal disease progression in patients with diabetes mellitus with chronic kidney disease (CKD) and in patients with HIV-associated nephropathy. We propose to determine whether presence of the APOL1 HR genotype alters or predicts responsiveness to conventional therapy to treat or prevent CKD and if addition of an ACEi to standard combination antiretroviral therapy (ART) reduces the risk of kidney complications among non-diabetic Nigerian adults.

Methods/design

We will screen 2600 HIV-positive adults who have received ART to (1) determine the prevalence of APOL1 risk variants and assess whether APOL1 HR status correlates with prevalent albuminuria, estimated glomerular filtration rate (eGFR), and/or prevalent CKD; (2) assess, via a randomized, placebo-controlled trial (RCT) in a subset of these participants with microalbuminura (n = 280) whether addition of the ACEi, lisinopril, compared to standard of care, significantly reduces the incidence or progression of albuminuria; and (3) determine whether the APOL1 HR genotype is associated with worse kidney outcomes (i.e. eGFR slope or regression of albuminuria) among participants in the RCT.

Conclusions

This study will examine the increasing prevalence of kidney diseases in HIV-positive adults in a West African population, and the relationship between these diseases and the APOL1 high-risk genotype. By evaluating the addition of an ACEi to the care of individuals with HIV infection who have albuminuria, our trial will provide definitive evidence to guide strategies for management and clinical care in this population, with the goal of reducing HIV-related kidney complications.

Trial registration

ClinicalTrials.gov, NCT03201939. Registered on 26 August 2016.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3436-y) contains supplementary material, which is available to authorized users.

Decline of popliteal artery flow-mediated dilation with aging and possible involvement of asymmetric dimethylarginine in healthy men

Purpose

We examined the influences of age and gender on flow-mediated endothelial function and the involvement of the competitive inhibition of l-arginine in endothelial function.

Methods

We measured brachial and popliteal flow-mediated vasodilation (FMD) responses, nitrate/nitrite (NOx) concentrations, and plasma levels of asymmetric dimethylarginine (ADMA) in four healthy, nonsmoking groups: young men (mean 26 ± 2 years, n = 17), middle-aged men (mean 50 ± 3 years, n = 19), young women (mean 27 ± 2 years, n = 16), and middle-aged women (mean 51 ± 2 years, n = 18).

Results

In young men, we found no significant differences between brachial and popliteal artery FMDs (10.6 ± 1.5 vs 8.7 ± 1.6%, p = 0.06). However, the popliteal artery FMD was significantly lower than the brachial artery FMD in middle-aged men (11.4 ± 1.5 vs 6.4 ± 1.0%, p < 0.001). In women, we found no significant differences between brachial and popliteal artery FMDs in young and middle-aged individuals (young, p = 0.17; middle-aged, p = 0.08). Popliteal artery FMD correlated with plasma NOx and ADMA levels as well as with the NOx/ADMA ratio in men but not in women (r = 0.485, − 0.544, and 0.672, respectively).

Conclusion

We concluded that a decrease in flow-mediated endothelial function in arteries of the lower extremities was evident in healthy middle-aged men, but not in middle-aged women. The competitive inhibition of l-arginine may contribute to this decrease in men.

Attenuated cutaneous microvascular function in healthy young African Americans: Role of intradermal l-arginine supplementation

It has been established that endothelial function in conduit vessels is reduced in young African Americans (AA) relative to Caucasian Americans (CA). However, less is known regarding endothelial function in microvasculature of young AA. We hypothesized that microvascular function in response to local heating of skin is attenuated in young AA relative to age-matched CA due largely to the lack of NO bioavailability, which is in turn improved by intradermal l-arginine supplementation and/or inhibition of arginase. Nine AA and nine CA adults participated in this study. Participants were instrumented with four microdialysis membranes in the cutaneous vasculature of one forearm and were randomly assigned to receive 1) lactated Ringer's solution as a control site; 2) 20 mM NG-nitro-l-arginine (l-NAME) to inhibit NO synthase activity; 3) 10 mM l-arginine to local supplement l-arginine; or 4) a combination of 5.0 mM (S)-(2‑boronoethyl)-l-cysteine-HCL (BEC) and 5.0 mM Nω-hydroxy-nor-l-arginine (nor-NOHA) at a rate of 2.0 μl/min to locally inhibit arginase activity. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux divided by mean arterial pressure. All CVC data were presented as a percentage of maximal CVC (%CVCmax) that was determined by maximal cutaneous vasodilation induced by 44 °C heating plus sodium nitroprusside administration. The response during the 42 °C local heating plateau was blunted in the AA at the control site (CA: 84 ± 12 vs. AA: 62 ± 6 vs. %CVCmax; P < 0.001). This response was improved in AA at the l-arginine site (Control: 62 ± 6 vs. l-arginine: 70 ± 18%CVCmax; P < 0.05) but not in the arginase inhibited site (Control: 62 ± 6 vs. Arginase inhibited: 62 ± 13%CVCmax; P = 0.91). In addition, the AA group had an attenuated NO contribution to the plateau phase during 42 °C local heating relative to the CA group (CA: 56 ± 14 vs. AA: 44 ± 6 Δ %CVCmax; P < 0.001). These findings suggest that 1) cutaneous microvascular function in response to local heating is blunted in young AA when compared to age-matched young CA; 2) this attenuated response is partly related to decrease in NO bioavailability in young AA; and 3) a local infusion of l-arginine, but not arginase inhibition, improves cutaneous microvascular responses to local heating in young AA relative to CA.

Tempol augments the blunted cutaneous microvascular thermal reactivity in healthy young African Americans

NEW FINDINGS

What is the central question of this study? The purpose was to determine whether there is a difference between African Americans and Caucasians in cutaneous microvascular function and whether this difference is attributable to elevated oxidative stress. What is the main finding and its importance? The main finding is that African Americans have an attenuated cutaneous vasodilatation during local heating relative to Caucasians that is restored with local infusion of the superoxide dismutase mimetic, tempol. This suggests that superoxide mediates microvascular dysfunction and might contribute to the greater prevalence of cardiovascular disease in this population.

ABSTRACT

African Americans (AA) have elevated risk for cardiovascular disease relative to other populations. We hypothesized that the cutaneous hyperaemic response to local heating is reduced in young AA relative to Caucasian Americans (CA) and that this is attributable to elevated oxidative stress. As such, ascorbic acid (a global antioxidant) and tempol (a superoxide dismutase mimetic) would improve this response in AA. Microdialysis fibres received lactated Ringer solution (control), 10 mm ascorbic acid or 10 μm 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol) at a rate of 2.0 μl min^-1 . Cutaneous vascular conductance (CVC) was calculated as the red blood cell flux divided by mean arterial pressure. Data were presented as a percentage of maximal CVC (%CVC_max ) induced by 44°C heating plus sodium nitroprusside. Twenty-four (12 AA, 12 CA) young (23 ± 4 years old) subjects participated. During 39°C heating, the %CVC_max was lower in AA at the control (CA, 65 ± 20% versus AA, 47 ± 15%; P < 0.05) and ascorbic acid sites (CA, 73 ± 14% versus AA: 49 ± 17%; P < 0.01). At the tempol site, there were no differences between groups. This was followed by infusion of 10 mm l-NAME at all sites to assess the contribution of nitric oxide to vasodilatation during local heating. The contribution of nitric oxide was lower in AA relative to CA at 39°C; however, this was restored with tempol. These data suggest that: (i) cutaneous vasodilatation in response to local heating is blunted in AA relative to CA; and (ii) elevated superoxide generation attenuates nitric oxide-mediated cutaneous vasodilatation in AA.

Pulse pressure amplification and its relationship with age in young, apparently healthy black and white adults: The African-PREDICT study

BACKGROUND

Pulse pressure amplification (PPA), i.e. the amplification from central arteries to the periphery, is inversely related to arterial stiffness, organ damage and mortality. It is known that arterial stiffness is higher in black than white populations, but it is unclear if this is due to early vascular aging. We therefore investigated whether PPA declines earlier in young normotensive black South Africans, when compared to their white counterparts.

METHODS

We included 875 black and white men and women from the African-PREDICT study (55% black, 41% men), aged 20-30years, with no prior diagnosis of chronic disease, screened for normotensive clinic blood pressure (BP). We determined supine central PP (cPP), and supine brachial systolic- and diastolic BP, from which brachial PP (bPP) was calculated. PPA was defined as the ratio of the amplitude of the PP between these distal and proximal locations (bPP/cPP).

RESULTS

We found the mean PPA to be lower in black compared to white participants (1.43 vs. 1.46; P=0.013). In black adults PPA declined earlier with increasing age (P-trend<0.001), with a weak trend in whites (P=0.069) after adjustment for sex, socio-economic status, height, heart rate and mean arterial pressure. In multivariable-adjusted regression, we found an independent inverse association between PPA and age only in the black group (β=-0.18, P=0.002).

CONCLUSION

PPA declines earlier with age in normotensive black adults younger than 30years, exemplifying early vascular aging which may predispose black individuals to future cardiovascular outcomes.

Effects of Sugar-Sweetened Beverage Consumption on Microvascular and Macrovascular Function in a Healthy Population

Objective—

To assess vascular function during acute hyperglycemia induced by commercial sugar-sweetened beverage (SSB) consumption and its effect on underlying mechanisms of the nitric oxide pathway.

Approach and Results—

In a randomized, single-blind, crossover trial, 12 healthy male participants consumed 600 mL (20 oz.) of water or a commercial SSB across 2 visits. Endothelial and vascular smooth muscle functions were assessed in the microcirculation using laser speckle contrast imaging coupled with iontophoresis and in the macrocirculation using brachial artery ultrasound with flow- and nitrate-mediated dilation. Compared with water, SSB consumption impaired microvascular and macrovascular endothelial function as indicated by a decrease in the vascular response to acetylcholine iontophoresis (208.3±24.3 versus 144.2±15.7%, P <0.01) and reduced flow-mediated dilation (0.019±0.002 versus 0.014±0.002%/s, P <0.01), respectively. Systemic vascular smooth muscle remained preserved. Similar decreases in endothelial function were observed during acute hyperglycemia in an in vivo rat model. However, function was fully restored by treatment with the antioxidants, N -acetylcysteine and apocynin. In addition, ex vivo experiments revealed that although the production of reactive oxygen species was increased during acute hyperglycemia, the bioavailability of nitric oxide in the endothelium was decreased, despite no change in the activation state of endothelial nitric oxide synthase.

Conclusions—

To our knowledge, this is the first study to assess the vascular effects of acute hyperglycemia induced by commercial SSB consumption alone. These findings suggest that SSB-mediated endothelial dysfunction is partly due to increased oxidative stress that decreases nitric oxide bioavailability.

Clinical Trial Registration—

URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=366442&isReview=true . Australian New Zealand Clinical Trials Registry Number: ACTRN12614000614695.

The relationship of nitric oxide synthesis capacity, oxidative stress, and albumin-to-creatinine ratio in black and white men: the SABPA study

Inadequate substrate availability and increased nitric oxide synthase inhibitor levels attenuate nitric oxide (NO) synthesis, whereas increased vascular oxidative stress may lead to inactivation of NO. We compared markers of NO synthesis capacity and oxidative stress in a bi-ethnic male population. Inter-relationships of ambulatory blood pressure and urinary albumin-to-creatinine ratio with NO synthesis capacity and oxidative stress markers were investigated. NO synthesis capacity markers (L-arginine, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA)) and oxidative stress markers (serum peroxides, total glutathione, glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), and catalase) were measured. Black men displayed higher blood pressure and albumin-to-creatinine ratio (all p < 0.001), while NO synthesis capacity was more favorable (higher L-arginine and lower ADMA (p ≤ 0.003)). Antioxidant enzyme activities were similar except for the redox status markers (GR activity and GR/GPx ratio), which were upregulated in black men (p < 0.001). In black men, ADMA was inversely related to GPx activity (R (2) = 0.15; β = -0.20; p = 0.050) and GPx/SOD ratio (R (2) = 0.24; β = -0.37; p < 0.001), but none of these markers related to blood pressure or albumin-to-creatinine ratio. In white men, albumin-to-creatinine ratio was positively associated with ADMA (R (2) = 0.18; β = 0.39; p < 0.001) while ADMA was inversely related to GR activity (R (2) = 0.26; β = -0.29; p = 0.002) and GR/GPx ratio (R (2) = 0.25; β = -0.28; p = 0.003). Black men with elevated blood pressure and albumin-to-creatinine ratio displayed a favorable NO synthesis capacity. This may be counteracted by increased inactivation of NO, although it was not linked to vascular or renal phenotypes. In white men, reduced NO synthesis capacity may lower NO bio-availability, thereby influencing the albumin-to-creatinine ratio.

Nitric oxide synthesis capacity, ambulatory blood pressure and end organ damage in a black and white population: the SABPA study

Nitric oxide (NO) synthesis capacity is determined by the availability of substrate(s) such as L-arginine and the influence of nitric oxide synthase (NOS) inhibitors, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). These factors may be important in black South Africans with a very high prevalence of hypertension. We compared ambulatory blood pressure (BP), markers of end organ damage and NO synthesis capacity markers [L-arginine, L-homoarginine, L-citrulline, L-arginine:ADMA, ADMA, SDMA and dimethylarginine (DMA)], between black and white teachers (n = 390). Associations of nighttime BP and markers of end organ damage with NO synthesis capacity markers were also investigated. Although black men and women had higher BP and albumin-to-creatinine ratio (ACR) (all p < 0.001), they also had higher L-arginine, L-homoarginine, L-arginine:ADMA and lower SDMA and DMA levels (all p < 0.05). Only in white men ADMA concentrations associated positively with nighttime systolic blood pressure (R (2) = 0.20, β = 0.26, p = 0.009), nighttime diastolic blood pressure (R (2) = 0.23, β = 0.27, p = 0.007), carotid intima media thickness (cIMT) (R (2) = 0.36, β = 0.22, p = 0.008) and ACR (R (2) = 0.14, β = 0.32, p = 0.001). Our findings suggest that despite an adverse cardiovascular profile in blacks, their NO synthesis capacity profile seems favourable, and that other factors, such as NO inactivation, may prove to be more important.

Vascular responses of the extremities to transdermal application of vasoactive agents in Caucasian and African descent individuals

PURPOSE

Individuals of African descent (AFD) are more susceptible to non-freezing cold injury than Caucasians (CAU) which may be due, in part, to differences in the control of skin blood flow. We investigated the skin blood flow responses to transdermal application of vasoactive agents.

METHODS

Twenty-four young males (12 CAU and 12 AFD) undertook three tests in which iontophoresis was used to apply acetylcholine (ACh 1 w/v %), sodium nitroprusside (SNP 0.01 w/v %) and noradrenaline (NA 0.5 mM) to the skin. The skin sites tested were: volar forearm, non-glabrous finger and toe, and glabrous finger (pad) and toe (pad).

RESULTS

In response to SNP on the forearm, AFD had less vasodilatation for a given current application than CAU (P = 0.027-0.004). ACh evoked less vasodilatation in AFD for a given application current in the non-glabrous finger and toe compared with CAU (P = 0.043-0.014) with a lower maximum vasodilatation in the non-glabrous finger (median [interquartile], AFD n = 11, 41[234] %, CAU n = 12, 351[451] %, P = 0.011) and non-glabrous toe (median [interquartile], AFD n = 9, 116[318] %, CAU n = 12, 484[720] %, P = 0.018). ACh and SNP did not elicit vasodilatation in the glabrous skin sites of either group. There were no ethnic differences in response to NA.

CONCLUSION

AFD have an attenuated endothelium-dependent vasodilatation in non-glabrous sites of the fingers and toes compared with CAU. This may contribute to lower skin temperature following cold exposure and the increased risk of cold injuries experienced by AFD.

Attenuated cerebral vasodilatory capacity in response to hypercapnia in college-aged African Americans

African Americans (AAs) have increased risk for cardiovascular, cerebral vascular and metabolic disease, including hypertension, stroke, coronary artery disease, metabolic syndrome and type II diabetes, relative to Caucasian Americans (CAs). While it is accepted that endothelial function is impaired in AAs, less is known regarding their cerebral vasodilatory capacity in response to hypercapnia. We hypothesized that AAs have a reduction in the total range of change in cerebral blood flow velocity (CBFV) measured in the middle cerebral artery and an index of cerebral vascular conductance (CVCI) in response to changes in the partial pressure of end-tidal carbon dioxide () during rebreathing-induced hypercapnia when compared with CAs. Twenty-one healthy, college-aged AA (10 male) and 21 age- and sex-matched CA (10 male) subjects participated in this study. A four-parameter logistic regression was used for curve fitting the responses of CBFV and CVCI relative to changes in . The total ranges of change in CBFV (101 ± 18 versus 69 ± 23%; P < 0.001) and CVCI (83 ± 21 versus 58 ± 21%; P < 0.001) as well as the maximal increase in CBFV (205 ± 24 versus 169 ± 24%; P < 0.001) and CVCI (188 ± 30 versus 154 ± 19%; P < 0.001) were reduced during hypercapnia in AAs relative to CAs despite a similar increase in (change, 15 ± 3 versus 15 ± 3 mmHg; P = 0.65). In conclusion, these data indicate that AAs have attenuated cerebral vascular capacity to respond to hypercapnia when compared with CAs.

Asymmetric dimethylarginine, race, and mortality in hemodialysis patients

BACKGROUND AND OBJECTIVES

Levels of asymmetric dimethylarginine, an inhibitor of nitric oxide synthase, are elevated in kidney disease and associated with mortality in white European hemodialysis populations. Nitric oxide production and degradation are partially genetically determined and differ by racial background. No studies have measured asymmetric dimethylarginine in African Americans on dialysis and assessed whether differences exist in its association with mortality by race.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Asymmetric dimethylarginine was measured in 259 patients on maintenance hemodialysis assembled from 2004 to 2012 in Boston area outpatient centers. Cox proportional hazards models were used to determine the association between asymmetric dimethylarginine and all-cause mortality, and an interaction with race was tested.

RESULTS

Mean (SD) age was 63 (17) years, 46% were women, and 22% were African American. Mean asymmetric dimethylarginine in non-African Americans was 0.79 µmol/L (0.16) versus 0.70 µmol/L (0.11) in African Americans (P<0.001); 130 patients died over a median follow-up of 2.3 years. African Americans had lower mortality risk than non-African Americans (hazard ratio, 0.27; 95% confidence interval, 0.15 to 0.50) that was robust to adjustment for age, comorbidity, and asymmetric dimethylarginine (hazard ratio, 0.35; 95% confidence interval, 0.17 to 0.69). An interaction was noted between race and asymmetric dimethylarginine (P=0.03), such that asymmetric dimethylarginine was associated with higher mortality in non-African Americans (adjusted hazard ratio, 1.29; 95% confidence interval, 1.06 to 1.57 per 1 SD higher asymmetric dimethylarginine) but not in African Americans (adjusted hazard ratio, 0.57; 95% confidence interval, 0.28 to 1.18). Additional adjustment for fibroblast growth factor 23 partially attenuated the association for non-African Americans (adjusted hazard ratio, 1.22; 95% confidence interval, 0.98 to 1.50).

CONCLUSIONS

African Americans have lower asymmetric dimethylarginine levels and lower hazard for mortality compared with non-African Americans. Levels of asymmetric dimethylarginine did not explain lower hazard for mortality in non-African American patients. High asymmetric dimethylarginine was a risk factor for mortality exclusively in non-African Americans. Mechanisms explaining these relationships need to be evaluated.

Differences in vascular nitric oxide and endothelium-derived hyperpolarizing factor bioavailability in blacks and whites

OBJECTIVE

Abnormalities in nitric oxide (NO) bioavailability have been reported in blacks. Whether there are differences in endothelium-derived hyperpolarizing factor (EDHF) in addition to NO between blacks and whites and how these affect physiological vasodilation remain unknown. We hypothesized that the bioavailability of vascular NO and EDHF, at rest and with pharmacological and physiological vasodilation, varies between whites and blacks.

APPROACH AND RESULTS

In 74 white and 86 black subjects without known cardiovascular disease risk factors, forearm blood flow was measured using plethysmography at rest and during inhibition of NO with N(G)-monomethyl-L-arginine and of K(+) Ca channels (EDHF) with tetraethylammonium. The reduction in resting forearm blood flow was greater with N(G)-monomethyl-L-arginine (P=0.019) and similar with tetraethylammonium in whites compared with blacks. Vasodilation with bradykinin, acetylcholine, and sodium nitroprusside was lower in blacks compared with whites (all P<0.0001). Inhibition with N(G)-monomethyl-L-arginine was greater in whites compared with blacks with bradykinin, acetylcholine, and exercise. Inhibition with tetraethylammonium was lower in blacks with bradykinin, but greater during exercise and with acetylcholine.

CONCLUSIONS

The contribution to both resting and stimulus-mediated vasodilator tone of NO is greater in whites compared with blacks. EDHF partly compensates for the reduced NO release in exercise and acetylcholine-mediated vasodilation in blacks. Preserved EDHF but reduced NO bioavailability and sensitivity characterizes the vasculature in healthy blacks.

CLINICAL TRIAL REGISTRATION URL

http://clinicaltrials.gov/. Unique identifier: NCT00166166.

Leptin is associated with vascular endothelial function in overweight patients with type 2 diabetes

BACKGROUND

The adipocyte-derived hormone leptin plays a key role in the regulation of appetite and body weight. Recent studies have suggested that leptin is also involved in the pathogenesis of obesity-related atherosclerosis and cardiovascular disease. In this study, we investigated the association of plasma leptin levels with vascular endothelial function in lean and overweight patients with type 2 diabetes.

METHODS

One hundred seventy-one type 2 diabetic patients, of which 85 were overweight (body mass index (BMI) ≥ 25 kg/m2), were enrolled in this cross-sectional study. Plasma leptin concentrations were measured by enzyme-linked immunosorbent assay. Flow-mediated dilatation (FMD) of the brachial artery was measured to evaluate vascular endothelial function using ultrasound.

RESULTS

No significant difference in FMD was found between the lean and overweight groups (7.0 ± 3.8% and 6.5 ± 3.6%, respectively; p = 0.354). FMD was negatively correlated with age (r = -0.371, p < 0.001) and serum creatinine levels (r = -0.236, p = 0.030), but positively correlated with BMI (r = 0.330, p = 0.002) and plasma leptin levels (r = 0.290, p = 0.007) in the overweight group. FMD was not associated with any parameters in the lean group. Multiple regression analysis including possible atherosclerotic risk factors revealed that the plasma leptin level (β = 0.427, p = 0.013) was independently associated with FMD in the overweight group (R2 = 0.310, p = 0.025), but not the lean group.

CONCLUSION

Plasma leptin levels are associated with vascular endothelial function in overweight patients with type 2 diabetes.

Predictors of improvement in endothelial function after exercise training in a diverse sample of postmenopausal women

BACKGROUND

Endothelial dysfunction measured via flow-mediated dilation (FMD) is associated with greater risk of future hypertension and cardiovascular events in postmenopausal women. Aerobic exercise training has been shown to improve endothelial function in Caucasian populations, but has not been evaluated specifically in African Americans. This has clinical importance due to the increased prevalence of cardiovascular disease in African Americans.

METHODS

In the present pilot study, 8 African American (age: 55.8±1.7 years, peak oxygen uptake [VO2 peak]: 21.0±3.9 mL/kg/minute, body mass index [BMI]: 30.1± 6.3 kg/m(2)) and 16 Caucasian (age: 57.2±5.9 years, VO2 peak: 21.8±3.7 mL/kg/minute, BMI: 29.3±5.2 kg/m(2)) sedentary postmenopausal women underwent brachial artery FMD measurements before and after 12 weeks of aerobic exercise training. FMD was quantified by comparing B-mode ultrasound images of the brachial artery at rest and following reactive hyperemia after 5 minutes of forearm occlusion. Participants performed aerobic exercise training 4 days per week for 12 weeks.

RESULTS

Despite improvements in fitness in both groups, aerobic exercise training did not significantly improve FMD in African American (5.8% to 5.7%, p=0.950) or Caucasian postmenopausal women (5.7% to 6.6%, p=0.267). In women with the greatest impairment in endothelial function at baseline (FMD<4.5%), a significant improvement in FMD was observed, independent of race, following exercise training (2.2% to 6.2%, p=0.007).

CONCLUSION

The benefits of aerobic exercise training on endothelial function in postmenopausal women are most pronounced in women with endothelial dysfunction prior to training and do not appear to be affected by race.

Effects of acute and chronic stress on the L-arginine nitric oxide pathway in black and white South Africans: the sympathetic activity and ambulatory blood pressure in Africans study

OBJECTIVE

This study investigated the impact of stress on effectors of the L-arginine/nitric oxide (NO) system including the endogenous inhibitor asymmetric dimethylarginine (ADMA).

METHODS

Black (n = 168) and white (n = 206) South African teachers were exposed to a mental and a physical stressor for 1 minute, respectively. Serum samples for determination of l-arginine, NO metabolites, ADMA, and symmetric dimethylarginine (SDMA) were obtained at rest and during stress exposure. Perception of task stressfulness was assessed on a 7-point Likert scale, and psychological distress was estimated by the General Health Questionnaire.

RESULTS

Black South Africans exhibited higher resting levels of NO metabolites (adjusted mean [standard error of the mean] = 11.3 [1.3] versus 3.9 [1.1] μmol/l, p < .001) but lower circulating ADMA (0.62 [0.02] versus 0.70 [0.02] μmol/l, p = .004) and SDMA (0.41 [0.01] versus 0.53 [0.01] μmol/l, p < .001) than did white South Africans. Ethnicity-by-psychological distress interaction was observed for resting levels of ADMA (p = .002), SDMA (p = .038), and L-arginine (p = .048). Ethnic differences in responses to experimental stress were evident for NO metabolites (blacks versus whites: 5.94 [1.55] versus -0.74 [1.25] μmol/l, p = .004) and SDMA (blacks versus whites: -0.02 [0.01] versus 0.02 [0.01] μmol/l, p = .004). Ethnicity-by-psychological distress interaction for stress responses was found for l-arginine/ADMA ratio (p = .027).

CONCLUSIONS

The l-arginine/NO system is affected by psychosocial distress with higher susceptibility in black South Africans. This interaction may contribute to the higher cardiovascular disease risk in black South Africans.

Salt sensitivity: a review with a focus on non-Hispanic blacks and Hispanics

The purpose of this review is to summarize the available information regarding salt sensitivity particularly as it relates to non-Hispanic blacks and Hispanics and to clarify possible etiologies, especially those that might shed light on potential treatment options. In non-Hispanic blacks, there is evidence that endothelial dysfunction, reduced potassium intake, decreased urinary kallikrein excretion, upregulation of sodium channel activity, dysfunction in atrial natriuretic peptide (ANP) production, and APOL1 gene nephropathy risk variants may cause or contribute to salt sensitivity. Supported treatment avenues include diets high in potassium and soybean protein, the components of which stimulate nitric oxide production. Racial heterogeneity complicates the study of salt sensitivity in Hispanic populations. Caribbean Hispanics, who have a higher proportion of African ancestry, may respond to commonly prescribed anti-hypertensive agents in a way that is characteristic of non-Hispanic black hypertensives. The low-renin hypertensive phenotype commonly seen in non-Hispanic blacks has been linked to salt sensitivity and may indicate an increased risk for salt sensitivity in a portion of the Hispanic population. In conclusion, increased morbidity and mortality associated with salt sensitivity mandates further studies evaluating the efficacy of tailored dietary and pharmacologic treatment in non-Hispanic blacks and determining the prevalence of low renin hypertension and salt sensitivity within the various subgroups of Hispanic Americans.

Postprandial endothelial function does not differ in women by race: an insulin resistance paradox?

Insulin resistance is associated with endothelial dysfunction. Because African-American women are more insulin-resistant than white women, it is assumed that African-American women have impaired endothelial function. However, racial differences in postprandial endothelial function have not been examined. In this study, we test the hypothesis that African-American women have impaired postprandial endothelial function compared with white women. Postprandial endothelial function following a breakfast (20% protein, 40% fat, and 40% carbohydrate) was evaluated in 36 (18 African-American women, 18 white women) age- and body mass index (BMI)-matched (age: 37 ± 11 yr; BMI: 30 ± 6 kg/m(2)) women. Endothelial function, defined by percent change in brachial artery flow-mediated dilation (FMD), was measured at 0, 2, 4, and 6 h following a meal. There were no significant differences between the groups in baseline FMD, total body fat, abdominal visceral fat, and fasting levels of glucose, insulin, total cholesterol, low-density lipoprotein cholesterol, or serum estradiol. Although African-American women were less insulin-sensitive [insulin sensitivity index (mean ± SD): 3.6 ± 1.5 vs. 5.2 ± 2.6, P = 0.02], both fasting triglyceride (TG: 56 ± 37 vs. 97 ± 49 mg/dl, P = 0.007) and incremental TG area under the curve (AUC(0-6hr): 279 ± 190 vs. 492 ± 255 mg·dl(-1)·min(-1)·10(-2), P = 0.008) were lower in African-American than white women. Breakfast was associated with a significant increase in FMD in whites and African-Americans, and there was no significant difference in postprandial FMD between the groups (P > 0.1 for group × time interactions). Despite being insulin-resistant, postprandial endothelial function in African-American women was comparable to white women. These results imply that insulin sensitivity may not be an important determinant of racial differences in endothelial function.

Cardiovascular Risk in Women With PCOS

Polycystic ovary syndrome (PCOS), or Stein-Leventhal syndrome, is a common endocrine disorder defined by two of the three following features: i) oligoovulation or anovulation, ii) clinical and/or biochemical signs of hyperandrogenism, or iii) polycystic ovaries, once the related endocrinological and gynaecological disorders have been excluded. PCOS does not exclusively involve the reproductive apparatus , it has a complex number of systemic relevancy symptoms. It leads to Metabolic Syndrome, with severe consequences on the cardiovascular apparatus. Many clinical studies have underlined the connection between PCOS and the cardiovascular risk profile of such female patients, due to a lipid/glucose altered metabolism, hypertension, systemic inflammatory condition (assessable by markers such as VES, TNF-alfa, citokines and C-reactive protein (hsPCR) levels), and vascular injuries. Considering the early onset of the disease, PCOS could be considered as a real cardiovascular risk factor which affects the quality of life seriously. The current review aimed to point out the main connections between PCOS and cardiovascular risk factors according to the latest findings coming from literature data analysis, and try to depict the great influences that such a common disease can have on the patients' health integrity.

The Role of Asymmetric Dimethylarginine (ADMA) in Endothelial Dysfunction and Cardiovascular Disease

Endothelium plays a crucial role in the maintenance of vascular tone and structure. Endothelial dysfunction is known to precede overt coronary artery disease. A number of cardiovascular risk factors, as well as metabolic diseases and systemic or local inflammation cause endothelial dysfunction. Nitric oxide (NO) is one of the major endothelium derived vaso-active substances whose role is of prime importance in maintaining endothelial homeostasis. Low levels of NO are associated with impaired endothelial function. Asymmetric dimethylarginine (ADMA), an analogue of L-arginine, is a naturally occurring product of metabolism found in human circulation. Elevated levels of ADMA inhibit NO synthesis and therefore impair endothelial function and thus promote atherosclerosis. ADMA levels are increased in people with hypercholesterolemia, atherosclerosis, hypertension, chronic heart failure, diabetes mellitus and chronic renal failure. A number of studies have reported ADMA as a novel risk marker of cardiovascular disease. Increased levels of ADMA have been shown to be the strongest risk predictor, beyond traditional risk factors, of cardiovascular events and all-cause and cardiovascular mortality in people with coronary artery disease. Interventions such as treatment with L-arginine have been shown to improve endothelium-mediated vasodilatation in people with high ADMA levels. However the clinical utility of modifying circulating ADMA levels remains uncertain.

Vascular endothelial function assessed by a noninvasive ultrasound method and serum asymmetric dimethylarginine concentrations in mild-to-moderate plaque-type psoriatic patients

OBJECTIVES

Our aim was to evaluate vascular endothelial function assessed by serum asymmetric dimethylarginine (ADMA) concentrations and noninvasive ultrasonographic parameters such as flow-mediated dilatation (FMD) and nitroglycerin-induced dilatation (NID) in mild-to-moderate plaque-type psoriatic patients, as rated by the Psoriasis Area and Severity Index.

DESIGN AND METHODS

Plaque-type psoriatic patients (n = 29) diagnosed with clinical and/or histopathological findings and control subjects (n = 25) without skin and systemic metabolic diseases were included in the study.

RESULTS

There was no statistically significant difference between patients and control subjects in respect to FMD (p = 0.441), NID (p = 0.557), or serum ADMA concentrations (p = 0.225). Also, among the acute-phase reactants, serum C-reactive protein and plasma fibrinogen levels were moderately higher in patients when compared to control subjects (p = 0.008 and p = 0.011, respectively).

CONCLUSIONS

Mild-to-moderate plaque-type psoriatic patients with low-to-medium grade systemic inflammation did not have evidence of vascular endothelial function.

Role of asymmetrical dimethylarginine in inflammation-induced endothelial dysfunction in human atherosclerosis

We explored the role of asymmetrical dimethylarginine (ADMA) as a cause of endothelial dysfunction induced by systemic inflammation. In vitro data suggest that ADMA bioavailability is regulated by proinflammatory stimuli, but it is unclear whether ADMA is a link between inflammation and endothelial dysfunction in humans. In study 1 we recruited 351 patients with coronary artery disease (CAD) and 87 healthy controls. In study 2 we recruited 69 CAD, 69 healthy, and 10 patients with rheumatoid arthritis, whereas in study 3, 22 healthy and 70 CAD subjects were randomly assigned to Salmonella typhii vaccination (n=11 healthy and n=60 CAD) or placebo (n=11 healthy and n=10 CAD). Circulating interleukin 6/ADMA and flow-mediated dilation (FMD) were measured at 0 and 8 hours. In study 1, ADMA was inversely correlated with FMD in healthy individuals and CAD patients (P<0.0001 for both). However, interleukin 6 was inversely correlated with FMD (P<0.0001) in healthy subjects but not in CAD patients. The positive correlation between ADMA and interleukin 6 was stronger in healthy (r=0.515; P<0.0001) compared with CAD (r=0.289; P=0.0001) subjects. In study 2, both patients with rheumatoid arthritis and CAD had higher interleukin 6 (P<0.0001) and ADMA (P=0.004) but lower FMD (P=0.001) versus healthy subjects. In study 3, vaccination increased interleukin 6 in healthy (P<0.001) and CAD (P<0.001) subjects. FMD was reduced in healthy subjects (P<0.05), but its reduction in CAD was borderline. Vaccination increased ADMA only in healthy subjects (P<0.001). Systemic, low-grade inflammation leads to increased ADMA that may induce endothelial dysfunction. This study demonstrated that ADMA may be a link between inflammation and endothelial dysfunction in humans.

Cardiovascular disease markers in women with polycystic ovary syndrome with emphasis on asymmetric dimethylarginine and homocysteine

BACKGROUND AND OBJECTIVES

Polycystic ovary syndrome (PCOS) is a disorder characterized by hyperandrogenism, ovulatory dysfunction, and polycystic ovaries. Little is known about cardiovascular risk factors in patients with PCOS. We investigated plasma markers of cardiovascular disease in Saudi women with PCOS, with an emphasis on asymmetric dimethylarginine (ADMA) and total homocysteine (tHcy).

PATIENTS AND METHODS

Fifty Saudi women with PCOS diagnosed by the Rotterdam criteria (mean age [SD] 30.2 [3.0] years) and 40 controls without PCOS (mean age 29.3 [2.5] years) had measyrements taken of clinical, metabolic, and hormonal parameters, including plasma ADMA, tHcy, lipoprotein (a) ([Lp(a)], and serum high sensitivity C-reactive protein (hs-CRP), nitric oxid, and fibrinogen. Insulin resistance was calculated by the homeostasis model assessment (HOMA-IR).

RESULTS

Women with PCOS had significantly higher fasting insulin, HOMA-IR, and luteinizing hormone (LH) levels than healthy controls (P P P CONCLUSION: Our study revealed that Saudi women with PCOS had a significantly different levels of plasma markers of cardiovascular disease compared with normal controls. Therefore, clinicians who manage women with PCOS should follow up on these markers to reduce the risk of cardiovascular disease.

Interethnic differences in ADMA concentrations and negative association with nitric oxide formation in preeclampsia

BACKGROUND

Recent studies have suggested that impaired nitric oxide (NO) formation in preeclampsia may result from increased concentrations of an endogenous NO synthase inhibitor, the asymmetric dimethylarginine (ADMA). However, no previous study has examined whether a negative association exists between ADMA and nitrite concentrations in preeclampsia. Moreover, no previous study has compared ADMA and nitrite levels in black and white preeclamptic pregnant women.

METHODS

We measured plasma nitrite concentrations using an ozone-based chemiluminescence assay, and plasma ADMA levels using enzyme immunoassays in 94 pregnant (47 healthy pregnant: 16 blacks and 31 whites; and 47 preeclamptic: 14 blacks and 33 whites).

RESULTS

We found higher ADMA (2.199 + or -0.016 micromol/l vs. 2.112 + or - 0.012 micromol/l; P<0.0001) and lower plasma nitrite levels (102 + or - 7.1 nmol/l vs. 214.8 + or - 26.1 nmol/l; P<0.0001) in preeclamptic compared with healthy pregnant women. Black pregnant had higher ADMA levels than white pregnant women (P<0.05), both in preeclamptic (2.239 + or - 0.020 micromol/l vs. 2.144 + or - 0.019 micromol/l) and in healthy pregnant (2.172 + or - 0.025 micromol/l vs. 2.077 + or - 0.018 micromol/l). Conversely, we found no significant effects of ethnicity on the plasma nitrite levels, both in healthy pregnant and in preeclamptic women (P>0.05). We found a significant negative correlation (P<0.05) between these markers (r=-0.28; P<0.05).

CONCLUSIONS

Our findings show higher ADMA and lower nitrite levels in preeclamptic compared with healthy pregnant, and the concentrations of these biomarkers are inversely associated. While ethnicity affected ADMA concentrations, no such effect was found with respect to nitrite levels. These results may have important implications for studies on NO biology and therapeutic approaches of preeclampsia.

A significant decline in IGF-I may predispose young Africans to subsequent cardiometabolic vulnerability

OBJECTIVES

Low serum IGF-I is an independent risk factor for diabetes and cardiovascular disease. These noncommunicable diseases are extremely common in urban black South Africans, but their IGF-I concentration is unknown. We aimed to compare serum IGF-I concentrations of African and Caucasian people, investigate their age-related IGF-I decline, and determine whether IGF-I could account, at least in part, for the high prevalence of noncommunicable diseases in black Africans.

RESEARCH DESIGN AND METHODS

This cross-sectional study involved 211 African and 316 Caucasian men and women (aged 20-70 yr). Fasting glucose, insulin, lipids, albumin, creatinine, liver enzymes, cotinine, high-sensitivity C-reactive protein, reactive oxygen species, IGF-I, blood pressure (BP), and pulse wave velocity were determined.

RESULTS

IGF-I was lower in Africans (P < 0.001) and in both ethnicities declined significantly by age quartiles (P < 0.001). In African men and women, IGF-I declined significantly from age quartile 1 to 2 (r = -0.65, P < 0.001), not seen in young Caucasian men and women (r = -0.08, P = 0.45; r = -0.10, P = 0.34). This was confirmed after adjustment for BP, insulin resistance, high-sensitivity C-reactive protein, cotinine, gamma-glutamyl transferase, and reactive oxygen species. Only young Africans showed significant negative correlations of IGF-I with BP, pulse wave velocity, and high-density lipoprotein cholesterol.

CONCLUSIONS

Africans presented lower IGF-I levels than Caucasians due to an accelerated decline in serum IGF-I concentration prior to 40 yr of age. Strong associations of low serum IGF-I with blood pressure and arterial stiffness in young Africans suggest that the loss of cardiometabolic protection by IGF-I could predispose them to earlier disease onset.

The biochemistry, measurement and current clinical significance of asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide synthase and an important cause of endothelial dysfunction. Its increased plasma concentration is associated with a variety of traditional cardiovascular risk factors, and may mediate their effects on the vascular endothelium. ADMA is also an independent predictor of cardiovascular events and mortality, and predicts outcomes in critically ill patients in the intensive care unit. This work has provided insights into the role of ADMA as an endogenous regulator of nitric oxide synthesis. At present there is no specific therapy to modify ADMA concentration, but increasing interest and work on protein arginine methyltransferases and dimethylarginine dimethylaminohydrolase, which synthesize and metabolize ADMA, respectively, might provide novel therapeutic targets.

Cardiovascular disease, diabetes and established risk factors among populations of sub-Saharan African descent in Europe: a literature review

Background

Most European countries are ethnically and culturally diverse. Globally, cardiovascular disease (CVD) is the leading cause of death. The major risk factors for CVD have been well established. This picture holds true for all regions of the world and in different ethnic groups. However, the prevalence of CVD and related risk factors vary among ethnic groups.

Methods

This article provides a review of current understanding of the epidemiology of vascular disease, principally coronary heart disease (CHD), stroke and related risk factors among populations of Sub-Sahara African descent (henceforth, African descent) in comparison with the European populations in Europe.

Results

Compared with European populations, populations of African descent have an increased risk of stroke, whereas CHD is less common. They also have higher rates of hypertension and diabetes than European populations. Obesity is highly prevalent, but smoking rate is lower among African descent women. Older people of African descent have more favourable lipid profile and dietary habits than their European counterparts. Alcohol consumption is less common among populations of African descent. The rate of physical activity differs between European countries. Dutch African-Suriname men and women are less physically active than the White-Dutch whereas British African women are more physically active than women in the general population. Literature on psychosocial stress shows inconsistent results.

Conclusion

Hypertension and diabetes are highly prevalent among African populations, which may explain their high rate of stroke in Europe. The relatively low rate of CHD may be explained by the low rates of other risk factors including a more favourable lipid profile and the low prevalence of smoking. The risk factors are changing, and on the whole, getting worse especially among African women. Cohort studies and clinical trials are therefore needed among these groups to determine the relative contribution of vascular risk factors, and to help guide the prevention efforts. There is a clear need for intervention studies among these populations in Europe.