Impaired endothelial function in healthy African-American adolescents compared with Caucasians

Hematologic and biochemical inflammatory markers increase with body mass and positively correlate in adolescents

BACKGROUND

Atherosclerosis is a chronic inflammatory disease that has its origins in childhood. The goal of this study was to explore the relationships of hematologic inflammatory markers to body mass, biochemical inflammatory markers and cardiometabolic risk factors.

METHODS

Healthy, white, non-Hispanic identifying adolescents (n = 75, age 12 to 18 years) were enrolled. Measures studied included body mass index percentile (BMI%), neutrophil and platelet to lymphocyte ratio (NLR, PLR), pan immune inflammation value (PIV), lipids, augmentation index, reactive hyperemia, inflammatory markers (interleukin 6: IL6, c-reactive protein: CRP), complement (C3, C3a, C4, C4a, C5a) insulin secretion and insulin sensitivity (oral glucose tolerance test: Matusda index, and disposition index (DI)).

RESULTS

NLR (rS = 0.31, p < 0.01), PLR (rS = 0.32, p < 0.01), PIV (rS = 0.32, p < 0.01) and CRP (rS = 0.51, p < 0.001) all positively correlated with BMI% but IL-6 did not. NLR, PLR and PIV all positively correlated with each other. NLR correlated with the reactive hyperemia response (rS = 0.29, p < 0.02) but this relationship was lost when BMI% was included. NLR positively correlated with C3a, C4, CRP and IL6 even when BMI% was included.

CONCLUSION

In healthy adolescents hematologic markers of inflammation increase with increasing body mass and neutrocyte to lymphocyte ratio is associated with increased complement and inflammatory markers independent of obesity.

IMPACT STATEMENT

Hematologic and biochemical markers of inflammation increase with increased body mass in healthy adolescents. Hematologic and biochemical markers of inflammation are positively related independent of body mass in healthy adolescents. Hematologic inflammatory markers are not related to markers of cardiometabolic risk in healthy adolescents.

We like to move it, move it: A perspective on performing passive leg movement as a non-invasive assessment of vascular function in pediatric populations

The passive leg movement (PLM) technique is a non-invasive assessment of lower-limb vascular function. PLM is methodologically simple to perform and utilizes Doppler ultrasound to determine leg blood flow (LBF) through the common femoral artery at rest and in response to passive movement of the lower leg. LBF responses to PLM have been reported to be mostly nitric oxide (NO)-mediated when performed in young adults. Moreover, PLM-induced LBF responses, as well as the NO contribution to PLM-induced LBF responses, are reduced with age and in various diseased populations, demonstrating the clinical utility of this non-invasive test. However, no PLM studies to date have included children or adolescents. Since its conception in 2015, our laboratory has performed PLM on hundreds of individuals including a large cohort of children and adolescents. Thus, the purpose of this perspective article is threefold: 1) to uniquely discuss the feasibility of performing PLM in children and adolescents, 2) to report PLM-induced LBF values from our laboratory in 7-17-year-olds, and 3) to discuss considerations for making comparisons among pediatric populations. Based on our experiences performing PLM in children and adolescents (among various other age groups), it is our perspective that PLM can feasibly be performed in this population. Further, data from our laboratory may be used to provide context for typical PLM-induced LBF values that could be observed in children and adolescents, as well as across the lifespan.

Evidence of reduced peripheral microvascular function in young Black women across the menstrual cycle

Black women (BLW) have a higher prevalence of cardiovascular disease (CVD) morbidity and mortality compared with White women (WHW). A racial disparity in CVD risk has been identified early in life as young adult BLW demonstrate attenuated vascular function compared with WHW. Previous studies comparing vascular function between premenopausal WHW and BLW have been limited to the early follicular (EF) phase of the menstrual cycle, which may not reflect their vascular function during other menstrual phases. Therefore, we evaluated peripheral microvascular function in premenopausal WHW and BLW using passive leg movement (PLM) during three menstrual phases: EF, ovulation (OV), and mid-luteal (ML). We hypothesized that microvascular function would be augmented during the OV and ML phases compared with the EF phase in both groups, but would be attenuated in BLW compared with WHW at all three phases. PLM was performed on 26 apparently healthy premenopausal women not using hormonal contraceptives: 15 WHW (23 ± 3 yr), 11 BLW (24 ± 5 yr). There was a main effect of race on the overall change in leg blood flow (ΔLBF) (P = 0.01) and leg blood flow area under the curve (LBF AUC) (P = 0.02), such that LBF was lower in BLW. However, there was no effect of phase on ΔLBF (P = 0.69) or LBF AUC (P = 0.65), nor an interaction between race and phase on ΔLBF (P = 0.37) or LBF AUC (P = 0.75). Despite peripheral microvascular function being unchanged across the menstrual cycle, a racial disparity was apparent as microvascular function was attenuated in BLW compared with WHW across the menstrual cycle.NEW & NOTEWORTHY This is the first study to compare peripheral microvascular function between young, otherwise healthy Black women and White women at multiple phases of the menstrual cycle. Our novel findings demonstrate a significant effect of race on peripheral microvascular function such that Black women exhibit significant attenuations in microvascular function across the menstrual cycle compared with White women.

Oral glucose tolerance response curve predicts disposition index but not other cardiometabolic risk factors in healthy adolescents

OBJECTIVES

In obese adults the shape of the glucose response curve during an oral glucose tolerance test (OGTT) predicts future type 2 diabetes. Patients with an incessant increase or monophasic curves have increased risk compared to those with biphasic curves. Since type 2 diabetes is associated with increased cardiometabolic risk, we studied whether differences in OGTT response curve are associated with differences in cardiometabolic risk factors in healthy adolescents across a wide body mass index (BMI) range.

METHODS

Sixty-nine (33F/36M), white adolescents (age: 15.2 ± 1.7 years; BMI: 21.5 ± 4.7 kg/m²; mean ± SD) were studied. Risk factors measured included percent body fat, blood pressure, lipids, augmentation index, reactive hyperemia, endothelin 1, plasminogen activator 1, inflammatory markers (interleukin 6, c-reactive protein), insulin secretion, insulin sensitivity (Matusda index), and disposition index (DI).

RESULTS

Thirty-two subjects had biphasic responses; 35 subjects had monophasic responses and two females had incessant increases. Sex did not affect the frequency of responses. Glucose area under the curve during OGTT was greater in those with a mono vs. biphasic curves (p=0.01). Disposition index was markedly lower in subjects with a monophasic curve than in those with a biphasic curve (3.6 [2.3-5.0] vs. 5.8 [3.8-7.6], median [25th, 75th%] p=0.003). Triglyceride to high-density lipoprotein cholesterol (HDL) ratio was higher in subjects with a monophasic curve (p=0.046).

CONCLUSIONS

The decreased disposition index indicates that in healthy adolescents a monophasic response to OGTT is due to decreased insulin secretion relative to the degree of insulin resistance present. This was not associated with differences in most other cardiometabolic risk markers.

TRIAL REGISTRATION

Clinical Trials.gov, NCT02821104.

Differential responses of resistance arterioles to elevated intraluminal pressure in blacks and whites

Black Americans have an earlier onset, higher average blood pressure, and higher rates of hypertension-related mortality and morbidity, compared to whites. The racial difference may be related to microvasculature, the major regulatory site of blood pressure. The goal of this study was to compare the response of resistance vessels to high intraluminal pressure between black and white participants. A total of 38 vessels were obtained from human fat samples [21 black, 17 white; mean age 32 ± 12 yr and body mass index (BMI) 26.9 ± 4.9; between-group P ≥ 0.05] and included in this study. Internal diameter was measured in response to the flow induced by various pressure gradients (Δ10, Δ20, Δ40, Δ60, and Δ100 cmH₂O), and flow-induced dilation (FID) was calculated before and after high intraluminal pressure (150 cmH₂O). Before high intraluminal pressure, FID was not different between blacks and whites (P = 0.112). After exposure to high intraluminal pressure, FID was reduced at every pressure gradient in vessels from blacks (P < 0.001), whereas FID did not change in white participants except at Δ100 cmH₂O. When incubated with the hydrogen peroxide (H₂O₂) scavenger polyethylene glycol-catalase (PEG-catalase), the FID response in vessels from black, but not white, individuals was significantly reduced and the magnitude was higher at normal pressure relative to high pressure. Our findings suggest that the vessels from self-identified black individuals are more susceptible to microvascular dysfunction following transient periods of high intraluminal pressure compared to whites and show greater dependence on H₂O₂ as a main contributor to FID at normal pressures.NEW & NOTEWORTHY Microvascular function regulates blood pressure and may contribute to racial differences in the incidence and prevalence of hypertension and other cardiovascular diseases. Here, we show that using an ex vivo model of resistance arterioles isolated from human gluteal fat tissue, flow-induced dilation is not different between black and white participants. However, when exposed to transient increases in intraluminal pressure, the flow-induced dilation in resistance arterioles from black participants demonstrated greater reductions relative to their white counterparts, indicating a higher sensitivity to pressure change in the microvasculature.

Race-specific changes in endothelial inflammation and microRNA in response to an acute inflammatory stimulus

Both aberrant vascular reactivity to acute cardiovascular stress and epigenetic mechanisms such as microRNA (miR) may underlie the increased propensity for African Americans (AA) to develop cardiovascular disease. This study assessed racial differences in acute induced endothelial inflammation and related miRs. Cultured human umbilical vein endothelial cells (HUVECs) derived from AA and Caucasian Americans (CA) were exposed to influenza vaccine to determine changes in inflammatory markers, endothelial nitric oxide synthase (eNOS), and miR expression/release. Endothelial function [flow-mediated dilation (FMD)], circulating IL-6, and circulating miR were also measured in young, healthy AA and CA individuals before and after receiving the influenza vaccine. There were no significant racial differences in any parameters at baseline. The vaccine induced increases in IL-6 release (24%, P = 0.02) and ICAM-1 mRNA (40%, P = 0.03), as well as reduced eNOS mRNA (24%, P = 0.04) in AA HUVECs, but not in CA HUVECs (all P > 0.05). Intracellular levels of anti-inflammatory miR-221-3p and miR-222-3p increased specifically in CA HUVECs (72% and 53%, P = 0.04 and P = 0.06), whereas others did not change in either race. HUVEC secretion of several miRs decreased in both races, whereas the release of anti-inflammatory miR-150-5p was decreased only by AA cells (-30%, P = 0.03). In individuals of both races, circulating IL-6 increased approximately twofold 24 h after vaccination (both P < 0.01) and returned to baseline levels by 48 h, whereas FMD remained unchanged. Although macrovascular function was unaffected by acute inflammation in AA and CA individuals, AA endothelial cells exhibited increased susceptibility to acute inflammation and unique changes in related miR.NEW & NOTEWORTHY Used as an acute inflammatory stimulus, the influenza vaccine induced an inflammatory response and decreased eNOS gene expression in endothelial cells derived from African Americans, but not Caucasian Americans. Race-specific changes in intracellular expression and release of specific microRNAs also occurred and may contribute to an exaggerated inflammatory response in African Americans. In vivo, the vaccine caused similar systemic inflammation but had no effect on endothelial function or circulating microRNAs in individuals of either race.

Examining "race" in physiology

Racial disparities in cardiovascular and cerebrovascular health outcomes are well described, and recent research has shed light on the mechanistic underpinnings of those disparities. However, "race" is a social construct that is poorly defined and continually evolving and is historically based on faulty premises. The continued categorization by race in physiological research suggests that there are inherent differences between races, rather than addressing the specific underlying factors that result in health disparities between groups. The purpose of this Perspectives article is to provide a brief history of the genesis of categorization by race, why such categorization should be reconsidered in physiology research, and offer recommendations to more directly investigate the underlying factors that result in group disparities in cardiovascular and cerebrovascular health.

Assessment of intima-media thickness of the carotid artery and intraluminal diameter of the brachial artery as cardiovascular risk markers in Brazilian adolescents with overweight or obesity

Background The intima-media thickness of the carotid artery (cIMT) and endothelial dysfunction are associated with cardiovascular (CV) disease. Objectives To evaluate the correlation between cIMT, brachial intraluminal diameter and flow-mediated vasodilation on the reactive hyperemia phase in adolescents with obesity with predictors of CV risk. Methods Seventy-three pubertal patients with overweight or obesity were evaluated (45 girls) with a mean (standard deviation [SD]) age of 12.9 (2.5) years. Patients underwent anthropometric measurements and had the lipid profile, oral glucose tolerance test (oGTT) and serum intercellular adhesion molecule-1 (sICAM-1) levels analyzed. The ratios of the waist circumference (WC)/height (WHtR) and triglycerides (TG)/high-density lipoprotein cholesterol (HDL-C), homeostatic model assessment of insulin resistance (HOMA-IR), the Matsuda index and insulin area under the curve (AUC) were calculated. All patients were evaluated for cIMT and arterial blood flow velocity of the brachial artery. Results 75.3% of the patients had high cIMT values. We found a positive correlation between WHtR and cIMT (r = 0.233; p = 0.050). There was a positive correlation between sICAM-1 and insulin AUC (r = 0.323; p = 0.012) and WHtR (r = 0.258; p = 0.047). Patients with abnormal arterial dilation had higher sICAM-1 values (p = 0.02) despite having smaller WHtR (p = 0.046). Conclusions These adolescents with obesity had high cIMT values. Insulin resistance was associated with sICAM-1. Endothelial dysfunction was positively correlated with sICAM-1. There is no consensus about what the best laboratorial approach to evaluate insulin resistance in adolescents is, and the cutoff values of each method are arbitrary. So, as we saw earlier, the association between anthropometric data (WHtR) and ultrasound findings could be useful to evaluate the CV risk of these adolescents with obesity, because of its practical, direct and low-cost value.

Relationships of complement components C3 and C4 and their genetics to cardiometabolic risk in healthy, non-Hispanic white adolescents

BACKGROUND

Complement promotes inflammatory and immune responses and may affect cardiometabolic risk. This study was designed to investigate the effect of complement components C3 and C4 on cardiometabolic risk in healthy non-Hispanic white adolescents.

METHODS

Body mass index (BMI), BMI percentile, waist circumference, and percent body fat were assessed in 75 adolescents. Arterial stiffness was assessed using arterial tomography and endothelial function using reactive hyperemia. Fasting lipids, inflammatory markers, and complement levels were measured and oral glucose tolerance test was performed. A single C3 polymorphism and C4 gene copy number variations were assessed.

RESULTS

C3 plasma levels increased with measures of obesity. Endothelial function worsened with increased C3 and C4 levels. Triglycerides and low-density lipoprotein increased and high-density lipoprotein (HDL) and insulin sensitivity decreased with increasing C3 levels, but the relationships were lost when body habitus was included in the model. C4 negatively related to HDL and positively to inflammatory markers. Subjects with at least one C3F allele had increased BMI and fat mass index. HDL was significantly related to C4L, C4S, C4A, and C4B gene copy number variation.

CONCLUSIONS

C3 levels increase with increasing body mass and increased C4 levels and copy number are associated with increased cardiometabolic risk in healthy adolescents.

Increased body fat and reduced insulin sensitivity are associated with impaired endothelial function and subendocardial viability in healthy, non-Hispanic white adolescents

BACKGROUND

Cardiovascular disease has its origins in adolescents. Endothelial dysfunction, arterial stiffness, and decreased endocardial oxygen supply: demand ratios are early functional markers of cardiovascular risk. The goal of this study was to determine the relationships of these markers to physical, inflammatory, and metabolic markers in healthy non-Hispanic, white adolescents.

METHODS

Thirty-four of the 75 subjects were female. Mean age was 15.0 ± 1.7 years and mean body mass index (BMI) was 22.0 ± 5.8 kg/m² (mean ± SD). Reactive hyperemia was measured using venous occlusion plethysmography. Arterial tonometry was used to measure the augmentation index (AIx₇₅ ) and the Buckberg subendocardial viability ratio. Blood samples were taken to measure inflammatory and lipid markers and oral glucose tolerance test was used to assess insulin sensitivity.

RESULTS

Reactive hyperemia decreased as body mass and fat mass increased. It also decreased with increasing neutrophil count. The Buckberg index was higher in males and was positively related to insulin sensitivity even when accounting for age, sex, and resting heart rate. AIx₇₅ was not related to any of the other variables.

CONCLUSIONS

These results demonstrate that increased fat mass and decreased insulin sensitivity are related to poorer vascular function and cardiac risk in adolescents before the development of actual 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.

Exercise-Derived Microvesicles: A Review of the Literature

Initially suggested as simple cell debris, cell-derived microvesicles (MVs) have now gained acceptance as recognized players in cellular communication and physiology. Shed by most, and perhaps all, human cells, these tiny lipid-membrane vesicles carry bioactive agents, such as proteins, lipids and microRNA from their cell source, and are produced under orchestrated events in response to a myriad of stimuli. Physical exercise introduces systemic physiological challenges capable of acutely disrupting cell homeostasis and stimulating the release of MVs into the circulation. The novel and promising field of exercise-derived MVs is expanding quickly, and the following work provides a review of the influence of exercise on circulating MVs, considering both acute and chronic aspects of exercise and training. Potential effects of the MV response to exercise are highlighted and future directions suggested as exercise and sports sciences extend the realm of extracellular vesicles.

Sex differences in the mechanisms mediating blunted cutaneous microvascular function in young black men and women

The black population exhibits attenuated vasodilatory function across their lifespan, yet little is known regarding the mechanisms of this impairment. Recent evidence suggests a potential role for oxidative stress. Therefore, we tested the hypothesis that NADPH oxidase (NOX) and/or xanthine oxidase (XO) contribute to blunted nitric oxide (NO)-mediated cutaneous microvascular function in young black adults. In 30 white and black subjects (8 men and 7 women in each group), local heating was performed while NOX and XO were inhibited by apocynin and allopurinol, respectively, via intradermal microdialysis. The plateau in cutaneous vascular conductance (red blood cell flux/mean arterial pressure) during 39°C local heating at each site was compared with a control site perfused with lactated Ringer solution. Subsequent inhibition of NO synthase via N^ω-nitro-l-arginine methyl ester allowed for quantification of the NO contribution to vasodilation during heating. Black individuals, relative to white individuals, had a blunted cutaneous vascular conductance plateau at the control site (45 ± 9 vs. 68 ± 13%max, P < 0.001) that was increased by both apocynin (61 ± 15%max, P < 0.001) and allopurinol (58 ± 17%max, P = 0.005). Black men and black women had similar responses to heating at the control site ( P = 0.99), yet apocynin and allopurinol increased this response only in black men (both P < 0.001 vs. control). The NO contribution was also increased via apocynin and allopurinol exclusively in black men. These findings suggest that cutaneous microvascular function is reduced because of NOX and XO activity in black men but not black women, identifying a novel sex difference in the mechanisms that contribute to blunted vascular responses in the black population. NEW & NOTEWORTHY We demonstrate that cutaneous microvascular responses to local heating are consistently reduced in otherwise healthy young black men and women relative to their white counterparts. Inhibition of NADPH oxidase and xanthine oxidase via apocynin and allopurinol, respectively, augments microvascular function in black men but not black women. These data reveal clear sex differences in the mechanisms underlying the racial disparity in cutaneous microvascular function.

Restricted Blood Flow Exercise in Sedentary, Overweight African-American Females May Increase Muscle Strength and Decrease Endothelial Function and Vascular Autoregulation

Objectives:

Exercise with partially restricted blood flow is a low-load, low-intensity resistance training regimen which may have the potential to increase muscle strength in the obese, elderly and frail who are unable to do high-load training. Restricted blood flow exercise has also been shown to affect blood vessel function variably and can, therefore, contribute to blood vessel dysfunction. This pilot study tests the hypothesis that unilateral resistance training of the leg extensors with partially restricted blood flow increases muscle strength and decreases vascular autoregulation.

Methods:

The subjects were nine normotensive, overweight, young adult African-Americans with low cardiorespiratory fitness who underwent unilateral training of the quadriceps’ femoris muscles with partially restricted blood flow at 30% of the 1-repetition maximum (1-RM) load for 3 weeks. The 1-RM load and post-occlusion blood flow to the lower leg (calf) were measured during reactive hyperemia.

Results:

The 1-RM load increased in the trained legs from 77 ± 3 to 84 ± 4 kg (P < 0.05) in the absence of a significant effect on the 1-RM load in the contralateral untrained legs (P > 0.1). Post-occlusion blood flow decreased significantly in the trained legs from 19 ± 2 to 13 ± 2 mL· min^-1· dL^-1 (P < 0.05) and marginally in the contralateral untrained legs from 18 ± 2 to 16 ± 1 mL· min^-1· dL^-1 (P = 0.09). Changes in post-occlusion blood flow to the skin overlying the trained and the contralateral untrained muscles were not significant.

Conclusion:

These results demonstrate that restricted blood flow exercise, which results in significant gains in muscle strength, may produce decrements in endothelial dysfunction and vascular autoregulation. Future studies should determine whether pharmacopuncture plays a role in treatments for such blood vessel dysfunction.

Effect of gender and adiposity on in vivo vascular function in young African Americans

The relationship between obesity and high blood pressure is not as strong among African Americans (AA) as compared to Caucasians. We designed the current study to determine the effect of adiposity on vascular endothelial function (a harbinger of hypertension) among young healthy AA without additional cardiovascular disease risk factors. A total of 108 AA subjects (46 women) between the ages of 18 and 45 years were recruited. All the subjects were normotensive, nonsmokers, and normoglycemic. Anthropometric and cardiovascular disease risk factor measurements (lipid, insulin resistance, and inflammatory markers) were obtained. Vascular endothelial function was measured by brachial artery flow-mediated dilation (FMD). Adiposity distribution was measured by using magnetic resonance imaging scan. There were no gender differences in age and levels of blood pressure, lipids, insulin resistance, and inflammatory markers. Women had higher total body fat percentage and higher peripheral adiposity compared to men. We observed that total and central adiposity did not correlate significantly with brachial artery FMD in women (r = -0.12 and r = 0.23, respectively; P = NS). However, in men, waist circumference was positively associated with FMD (r = 0.3, P ≤ .05). Hyperemic flow was negatively correlated significantly with total and central adiposity in men (r = -0.34 and r = -0.48, respectively; P < .05), but not in women (r = -0.26 and r = 0.03, respectively; P = NS). Our study suggests that increased adiposity may pose greater risk to AA men compared to AA women by adversely affecting resistance vessel function (as measured by hyperemic flow). Larger studies are necessary to validate these findings.

Increased Pre- and Post-Meal Free Fatty Acid Levels in Black, Obese Adolescents

BACKGROUND

Black adolescents are at increased risk of cardiometabolic disease but have lower fasting triglyceride, which is usually associated with decreased risk. No one has studied racial differences in triglycerides or free fatty acids (FFAs) after a high-fat meal.

METHODS

Oral glucose tolerance testing was used to assess insulin secretion, sensitivity, and disposition index (DI). Endothelial function, triglycerides, FFA, c-reactive protein, interleukin 6 (IL6), and adiponectin were measured both pre- and 3 hr postprandially (McDonald's Big Breakfast(®) and 12 ounce Sprite(®)) in obese adolescents (10-13 years, 9 black and 7 white). Endothelial function was assessed using reactive hyperemic changes in forearm vascular resistance (FVR).

RESULTS

Oral glucose tolerance test (OGTT) showed no difference in insulin sensitivity, but blacks tended to have (P = 0.08) higher insulin secretion and had increased DI (P = 0.003). After a high-fat meal, triglycerides increased in both groups (P < 0.001), tended to be lower in blacks compared with whites preprandially (64 ± 33 mg/dL vs 110 ± 80, P = 0.064), and was lower postprandially (112 ± 63 vs 188 ± 112, P = 0.039). Pre- and postprandial FFA (Black: 0.58 ± 0.15 and 0.39 ± 0.18 vs. white: 0.44 ± 0.14 and 0.26 ± 0.06, P = 0.020) and adiponectin (P = 0.002) were increased in blacks. FFA decreased in both groups postprandially (P = 0.002). IL6 increased after the meal (P = 0.022). Endothelial function decreased postprandially (P < 0.02), but this was due to a decrease in preocclusion FVR.

CONCLUSIONS

These results indicate that differences in fat metabolism are present in both black and white obese adolescents. How these differences explain higher rates of cardiometabolic disease in blacks is unclear.

Endothelial dysfunction and negative emotions in adolescent girls

BACKGROUND

Endothelial dysfunction predicts adult cardiovascular disorder and may be associated with negative emotions in adolescents. This study was conducted to determine if hopelessness, hostility, and depressive, anxiety, or conduct disorders were associated with compromised endothelial function and whether those associations were mediated by health risk behaviors.

METHODS

Endothelial function, assessed through brachial artery reactive hyperemia, was measured in a psychopathology enriched sample of 60 15-18-year-old girls. The correlations between hopelessness, hostility, and depressive, anxiety, or conduct disorders and the percent change in forearm vascular resistance (PCFVR) were measured. Possible mediation effects of health risk behaviors were tested.

RESULTS

Hopelessness was negatively associated with PCFVR, controlling for race and body mass index. Conduct disorder without any anxiety disorder was associated with better endothelial function. The other negative emotions were not associated with PCFVR. Risky health behaviors were associated with conduct disorder and hopelessness, but not with PCFVR, so there was no evidence of mediation.

CONCLUSION

The main finding was that hopelessness in adolescent girls was associated with endothelial dysfunction. This may indicate that when present, hopelessness places a girl at risk for later cardiovascular disease, whether she has a psychiatric disorder or not. Possible mechanisms for this finding are examined and the surprising finding that conduct disorder is associated with better endothelial function is also discussed. Suggestions for future research are presented.

Abdominal fat depots associated with insulin resistance and metabolic syndrome risk factors in black African young adults

Background

Individuals of black African ethnicity tend to have less visceral adipose tissue (VAT) but more subcutaneous-abdominal adipose tissue (SCAT) than white Caucasians. However, it is unclear whether such distribution of abdominal fat is beneficial for metabolic disease risk in black individuals. Here we compared the associations between these specific abdominal fat depots, insulin sensitivity and metabolic syndrome risk.

Methods

A cross-sectional analysis of 76 black South African young adults (36 men; 40 women) aged 18–19 years participating in the Birth to Twenty Cohort Study had VAT and SCAT measured by MRI. The metabolic syndrome traits (blood pressure, lipid profile, fasting glucose and insulin) were measured and the values were combined into a metabolic syndrome risk score. Fasting glucose and insulin were used to derive the HOMA-index of insulin resistance (HOMA-IR).

Results

Compared to men, women had greater VAT (mean: 16.6 vs. 12.5 cm²) and SCAT (median 164.0 vs. 59.9 cm²). In men, SCAT (r = 0.50) was more strongly correlated to the metabolic syndrome score (MetS) than was VAT (r = 0.23), and was associated with both MetS (P = 0.001) and HOMA-IR (P = 0.001) after adjustment for VAT and total fat mass. In women, both abdominal fat compartments showed comparable positive correlations with MetS (r = 0.26 to 0.31), although these trends were weaker than in men.

Conclusions

In young black South African adults, SCAT appears to be more relevant than VAT to metabolic syndrome traits.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-015-2147-x) contains supplementary material, which is available to authorized users.

Mineralocorticoid exposure and receptor activity modulate microvascular endothelial function in African Americans with and without hypertension

Prior work suggests blood pressure in African Americans is more sensitive to the effects of aldosterone than in Caucasians. This mechanism may relate to a negative response of the vascular endothelium to aldosterone, including reduced glucose-6-phosphate dehydrogenase (G6PD) activity. Thirty-three African Americans (11 hypertensives, 22 controls) without evidence of diabetes or metabolic syndrome completed the protocol. The protocol included measurement of in vivo microvascular endothelial function by digital pulse arterial tonometry and ex vivo measurement of endothelial function by videomicroscopy of arterioles obtained from these same subjects with and without exposure to aldosterone or spironolactone. Systemic and arteriolar G6PD activities were also measured. In vivo and ex vivo microvascular endothelial function were impaired in African Americans with hypertension. One-hour exposure with aldosterone impaired endothelium-dependent vasodilation in arterioles from normotensive subjects, while 1 hour of spironolactone exposure reversed endothelial dysfunction in arterioles from hypertensive subjects. G6PD activity was impaired in hypertensive arterioles. Aldosterone-related endothelial dysfunction may be responsible for at least a portion of the greater blood pressure sensitivity to aldosterone in African Americans. This may be in part related to vascular suppression of G6PD activity.

Effects of glucose control and variability on endothelial function and repair in adolescents with type 1 diabetes

Background. Endothelial dysfunction and increased inflammation are precursors of cardiovascular disease in type 1 diabetes (T1D) and occur even in adolescents with T1D. The goal of this study was to determine the relationship of endothelial dysfunction to various measures of glycemia. Research Design and Methods. Forearm blood flow (FBF, venous occlusion plethysmography) was measured before and after 5 min of upper arm vascular occlusion in 17 adolescents with uncomplicated type 1 diabetes. Endothelial function was assessed as postocclusion FBF and forearm vascular resistance (FVR, mean arterial pressure/FBF). Fasting glucose, 72 hour mean glucose and standard deviation from continuous glucose monitoring, hemoglobin A1c, and hemoglobin A1c by duration area under the curve were used to assess immediate, short-term, and intermediate- and long-term glycemia. Results. Postocclusion FBF (r = −0.53, P = 0.030) negatively correlated and postocclusion FVR positively correlated (r = 0.52, P = 0.031) with hemoglobin A1c levels. FVR was positively associated with log 3 day mean glucose (r = 0.55, P = 0.027). Postocclusion FBF (2.8 ± 1.1 versus 3.4 ± 0.5 mL/dL/min, mean ± SE, P = 0.084) tended to be lower and FVR (31.4 ± 10.4 versus 23.9 ± 4.4 mmHg dL min/mL, P = 0.015) was significantly higher in subjects with hemoglobin A1c above the median (8.3%) compared to those with lower hemoglobin A1c levels. Conclusions. These results demonstrate that poor intermediate-term glycemic control is associated with impaired endothelial function.

Differential influence of distinct components of increased blood pressure on cardiovascular outcomes: from the atherosclerosis risk in communities study

Elevation in blood pressure (BP) increases risk for all cardiovascular events. Nevertheless, the extent to which different indices of BP elevation may be associated to varying degrees with different cardiovascular outcomes remains unclear. We studied 13340 participants (aged 54 ± 6 years, 56% women and 27% black) of the Atherosclerosis Risk in Communities Study who were free of baseline cardiovascular disease. We used Cox proportional hazards models to compare the relative contributions of systolic BP, diastolic BP, pulse pressure, and mean arterial pressure to risk for coronary heart disease, heart failure, stroke, and all-cause mortality. For each multivariable-adjusted model, the largest area under the receiver-operating curve (AUC) and smallest -2 log-likelihood values were used to identify BP measures with the greatest contribution to risk prediction for each outcome. A total of 2095 coronary heart disease events, 1669 heart failure events, 771 stroke events, and 3016 deaths occurred during 18 ± 5 years of follow-up. In multivariable analyses adjusting for traditional cardiovascular risk factors, the BP measures with the greatest risk contributions were the following: systolic BP for coronary heart disease (AUC=0.74); pulse pressure for heart failure (AUC=0.79); systolic BP for stroke (AUC=0.74); and pulse pressure for all-cause mortality (AUC=0.74). With few exceptions, results were similar in analyses stratified by age, sex, and race. Our data indicate that distinct BP components contribute variably to risk for different cardiovascular outcomes.

Ascorbic acid blocks hyperglycemic impairment of endothelial function in adolescents with type 1 diabetes

OBJECTIVE

To determine whether acute ascorbic acid infusions alter the effect of hyperglycemia on endothelial function in adolescents with type 1 diabetes.

RESEARCH DESIGN AND METHODS

The forearm blood flow (FBF) reactive hyperemic response to 5 min of upper arm occlusion was studied in eight adolescents with type 1 diabetes during euglycemic and hyperglycemic insulin clamp (40 mU/m2/min) with and without ascorbic acid infusion (3 mg/min).

RESULTS

The ratio of post- to preocclusion FBF decreased during hyperglycemia without ascorbic acid (p = 0.013), but did not change during hyperglycemia with ascorbic acid. The changes during hyperglycemia were different between the two studies (p = 0.038). Similar results were found when the percent change in forearm vascular resistance following occlusion was assessed.

CONCLUSIONS

These results indicate that antioxidant treatment with ascorbic acid blocks acute hyperglycemic impairment of endothelial function in adolescents with type 1 diabetes.

Vitamin D and Parathyroid Hormone Relationships with Urinary Nitric Oxide Metabolites and Plasma Isoprostanes in African-Americans

BACKGROUND: Vitamin D deficiency and secondary rises in parathyroid hormone (PTH) are highly prevalent in obese African-Americans. Endothelial dysfunction related to oxidative stress is more common in African-Americans compared to whites. Currently, the association of vitamin D (25-hydroxyvitamin D, 25-OH D) and PTH to nitric oxide metabolites (NOx) - nitrate and nitrite - and oxidative stress in African-Americans is unknown. Objective: A cross-sectional design was utilized to determine the association of 25-OH D and PTH with urinary NOx (UNOx) (n = 101) and plasma isoprostanes (n = 125), an oxidative stress marker, in overweight (body mass index of 25-39.9), normotensive African-Americans aged ≥35 years. Measurements: Multivariable linear regression analysis adjusted for age, sex, body mass index, and season was used to determine the relationship of 25-OH D and PTH to UNOx and isoprostanes. General linear models, adjusted for the same covariates, contrasted UNOx across three mutually exclusive vitamin D/PTH groups: (1) normal 25-OH D (51-249 nmol/l) and normal PTH (≤65 pg/ml); (2) low 25-OH D and normal PTH, and (3) low 25-OH D and high PTH. RESULTS: 25-OH D was directly associated with UNOx before (p = 0.02) and after (p = 0.03) adjustment for PTH levels. A borderline significant association was observed between PTH and isoprostanes (p = 0.08). UNOx was 424, 290, and 270 μmol/8 h, respectively, across vitamin D/PTH groups 1-3 (p = 0.08). CONCLUSION: 25-OH D was directly associated with NO availability and PTH was positively, though borderline, associated with isoprostanes in overweight, normotensive adult African-Americans.

Type 2 diabetes in youth: are there racial differences in β-cell responsiveness relative to insulin sensitivity?

OBJECTIVE

Non-diabetic African American (AA) youth have an upregulated insulin secretion relative to insulin sensitivity (IS) compared with their American White (AW) peers. We investigated if similar racial differences exist in youth with T2DM.

RESEARCH DESIGN AND METHODS

Fourteen AAs and 14 AWs T2DM adolescents underwent evaluation of IS and clearance (hyperinsulinemic-euglycemic clamp), first- and second-phase insulin and C-peptide secretion (hyperglycemic clamp); body composition (DEXA); and abdominal adiposity (CT).

RESULTS

AA and AW T2DM had similar HbA1c, diabetes duration, BMI, and % body fat, with lower visceral fat in AAs (p = 0.013). While insulin-stimulated glucose disposal was similar in AA and AW (7.5 ± 1.0 vs. 7.3 ± 0.9 mg/kg FFM/min), IS tended to be lower (2.5 ± 0.4 vs. 3.8 ± 0.6 mg/kg FFM/min per µU/mL, p = 0.081). First-phase insulin (175.7 ± 52.9 vs. 66.6 ± 10.8 µU/mL, p = 0.01) and second-phase insulin (236.2 ± 40.7 vs. 105.1 ± 17.9 µU/mL, p = 0.008), and first-phase C-peptide (8.2 ± 1.2 vs. 5.0 ± 0.3 ng/mL, p = 0.02) and second-phase C-peptide (10.8 ± 0.9 vs. 7.6 ± 0.6 ng/mL, p = 0.012) were higher in AA. β-Cell function relative to IS was higher in AA vs. AW (259.5 ± 35.3 vs. 168.8 ± 25.1 mg/kg FFM/min, p = 0.043).

CONCLUSIONS

Racial differences in insulin secretion can be demonstrated with the clamp technique in obese adolescents with T2DM. Similar to non-diabetic youth, AA adolescents with T2DM compared with their AW counterparts have an upregulated β-cell function relative to IS, the reasons for which remain to be investigated.

Effect of adolescent obesity on cardiometabolic risk in african-americans and Caucasians

African-Americans have more hypertension, stroke, and type 2 diabetes than do Caucasians. Endothelial dysfunction and insulin resistance are precursors for each. Since these diseases have origins in pediatrics and are associated with obesity, this study was designed to determine if obesity has different effects on endothelial function, insulin sensitivity, and secretion in African-American and Caucasian adolescents. Thirty-three Caucasian and 25 African-Americans (10–18 years old) were subdivided by BMI into lean, overweight, and obesity groups. Endothelial function was measured as forearm vascular resistance (FVR) over 1 min following 5 min of upper arm vascular occlusion. Insulin sensitivity and secretion were measured using intravenous glucose tolerance test and minimal model. Postocclusive FVR was significantly increased in obese African-Americans. Insulin sensitivity was reduced in obese subjects but did not differ by race. Insulin secretion was increased in African-Americans but did not differ by obesity. Subjects were subdivided into risk groups based on 20th percentile for postocclusion FVR response in lean. Seven of nine obese African-Americans were in the high risk group compared to 0 of 5 obese Caucasians. These results demonstrate that obesity significantly impairs endothelial function in African-Americans. Endothelial dysfunction likely predisposes to future cardiometabolic disease in obese African-American adolescents.

Ethnicity, obesity and the metabolic syndrome: implications on assessing risk and targeting intervention

Pediatric obesity threatens the future health of a growing number of children worldwide. An added challenge in identifying the patients at greatest need for intervention due to their elevated risk for future disease is that pediatric obesity and the associated metabolic syndrome manifest differently among different ethnic groups. African-Americans and Hispanics are more likely to exhibit obesity and insulin resistance and are at a higher risk for developing Type 2 diabetes. Nevertheless, using current criteria, African-American adolescents are much less likely to be diagnosed with metabolic syndrome, largely owing to lower rates of dyslipidemia. Further development is needed in ethnicity-inclusive means of risk identification among adolescents to accurately target treatment toward children at highest risk for future disease and to motivate adolescent patients and their families towards lifestyle improvement. Effective targeting and intensive treatment efforts may help in avoiding future sequelae of obesity among all ethnicities.

Population analysis of ethnicity and first-phase insulin release

OBJECTIVE

A mechanistic, physiologically-based pharmacokinetic (PK/PD) model was developed to describe the biphasic insulin release and evaluate the racial effects on the glucose-insulin kinetics in response to intravenous glucose.

METHODS

Fifteen African-American and 18 Caucasian children and adolescents between 8 and 18 years of age were enrolled in the study. Intravenous bolus of glucose (250 mg/kg) was administered and blood samples collected at frequent intervals for three hours following the glucose injection. A nonlinear mixed-effect population kinetic analysis with covariate structure was performed using Monolix.

RESULTS

A significantly higher initial insulin secretion from a readily releasable pool, which is responsible for the first-phase insulin secretion, was detected in African-Americans compared to Caucasians (p<0.05).

CONCLUSIONS

The proposed kinetic model is able to describe the glucose-stimulated insulin response, account for the first-phase insulin release and identify a racially-based pharmacokinetic difference in insulin's biphasic secretion behavior. It is hypothesized that the first-phase insulin component may play an important role in the development of type 2 diabetes. The proposed mechanistic model provides a quantitative analysis of the biphasic insulin release that may be useful in the early detection of diabetes.

Race/ethnic and sex differences in large and small artery elasticity--results of the multi-ethnic study of atherosclerosis (MESA)

OBJECTIVE

Reduction in arterial elasticity marks progression toward cardiovascular morbidity and mortality. Variability in arterial elasticity may help account for race/ethnic and gender differences in cardiovascular risk.

DESIGN

Cross-sectional study.

SETTING

Whites, African Americans, Hispanics and Chinese aged 45-84 years free of clinically recognized cardiovascular disease were recruited in six US communities.

PARTICIPANTS

We examined 3,316 women and 3,020 men according to race/ethnicity and sex.

MAIN OUTCOME MEASURES

Large (LAE) and small artery (SAE) elasticity, derived from radial artery diastolic pulse wave contour registration in all subjects in a supine position using tonometry. LAE and SAE were adjusted for ethnicity, age, clinical site, height, heart rate, blood pressure, antihypertensive medication and body mass index, diabetes, smoking, and circulating lipids.

RESULTS

Much of the sex difference in arterial elasticity was explained by height. After adjustment, LAE did not differ by race/ ethnicity, but mean SAE in African Americans was 4.2 mL/mm Hg x 100 and 4.4 mL/ mm Hg x 100 in Hispanics compared to means of 4.6 mL/mm Hg x 100 in Whites, and 4.8 mL/mm Hg x 100 in Chinese.

CONCLUSIONS

Reduced SAE may indicate earlier vascular disease in African Americans and Hispanics than other groups.

Endothelial dysfunction in African-Americans

The journey of atherosclerosis begins with endothelial dysfunction and culminates into its most fearful destination producing ischemia, myocardial infarction and death. The excess cardiovascular disease morbidity and mortality in African-Americans is one of the major public health problems. In this review, we discuss vascular endothelial dysfunction as a key element for excess cardiovascular disease burden in this target population. It can be logical window of future atherosclerotic outcomes, and further efforts should be made to detect it at the earliest in African American individuals even if they are appearing healthy as the therapeutic interventions if instituted early, might prevent the subsequent cardiac events.

Indices of insulin action calculated from fasting glucose and insulin reflect hepatic, not peripheral, insulin sensitivity in African-American and Caucasian adolescents

Insulin stimulates muscle glucose uptake and inhibits hepatic glucose production. Measures of insulin sensitivity or insulin resistance must take both of these actions into account. Homeostatic model assessment of insulin resistance (HOMA(IR)) and quantitative insulin sensitivity check index (QUICKI) are two simple measures of insulin resistance and insulin sensitivity that are derived from fasting glucose and insulin levels as such it is likely that they reflect primary hepatic insulin action and not muscular effects. To prove this hypothesis, the relationships of HOMA(IR) and QUICKI to peripheral insulin sensitivity (S(I)(*)) and hepatic insulin resistance (HIR) were assessed in 34 adolescents (age 13.5 +/- 2.9 yr, body mass index 23.0 +/- 5.7, mean +/- SD; 16 Caucasian and 14 African-American). S(I)(*) and HIR were determined using the stable-labeled, frequently sampled intravenous glucose tolerance test (250 mg total glucose/kg, 13% [6,6]-D(2)-glucose). The former was calculated using the one-compartment minimal model and stable glucose concentration (S(I)(*)), and the latter was determined over the last hour of the study by multiplying hepatic glucose production (Steele's equation) by mean plasma insulin concentration. As expected, HOMA(IR) and QUICKI were significantly related to HIR (log HOMA(IR) and log HIR, r = 0.73, p < 0.001; QUICKI and log HIR, r = -0.69, p < 0.001) but not S(I)(*). When both S(I)(*) and HIR were included in the equations, only the relationships to log HIR were significant (log HOMA(IR), p < 0.001; QUICKI, p < 0.001). The relationships were similar in African-American and Caucasian subjects. These results demonstrate that in adolescents, HOMA(IR) and QUICKI assess hepatic but not peripheral insulin action.

Racial differences in nitric oxide-dependent vasorelaxation

Along with the growing heterogeneity of the American population, ethnic/racial disparity is becoming a clear health issue in the United States. The awareness of ethnic/racial disparities has been growing because of considerable data gathered from recent clinical and epidemiological studies. These studies have highlighted the importance of addressing these differences in the diagnosis and treatment of various diseases potentially according to race. It is becoming particularly clear that there is a 2- to 3-fold racial difference in certain cardiovascular diseases (eg, preeclampsia) associated with dysfunctional nitric oxide-mediated vasodilation. In this review, the authors summarize the current literature on racial disparities in nitric oxide-mediated vasodilation in relation to cardiovascular health with an emphasis on vascular nitric oxide bioavailability as a balance between production via endothelial nitric oxide synthase and degradation through reactive oxygen species. The major hypotheses postulated on the biological basis of these differences are also highlighted.