Differences in the association between type 2 diabetes and impaired microvascular function among Europeans and African Caribbeans

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.

Development and presentation of an objective risk stratification tool for healthcare workers when dealing with the COVID-19 pandemic in the UK: risk modelling based on hospitalisation and mortality statistics compared with epidemiological data

OBJECTIVES

Healthcare workers have greater exposure to SARS-CoV-2 and an estimated 2.5-fold increased risk of contracting COVID-19 than the general population. We wished to explore the predictive role of basic demographics to establish a simple tool that could help risk stratify healthcare workers.

SETTING

We undertook a review of the published literature (including multiple search strategies in MEDLINE with PubMed interface) and critically assessed early reports on preprint servers. We explored the relative risk of mortality from readily available demographics to identify the population at the highest risk.

RESULTS

The published studies specifically assessing the risk of healthcare workers had limited demographics available; therefore, we explored the general population in the literature. Clinician demographics: Mortality increased with increasing age from 50 years onwards. Male sex at birth, and people of black and minority ethnicity groups had higher susceptibility to both hospitalisation and mortality. Comorbid disease. Vascular disease, renal disease, diabetes and chronic pulmonary disease further increased risk. Risk stratification tool: A risk stratification tool was compiled using a white female aged <50 years with no comorbidities as a reference. A point allocated to risk factors was associated with an approximate doubling in risk. This tool provides numerical support for healthcare workers when determining which team members should be allocated to patient facing clinical duties compared with remote supportive roles.

CONCLUSIONS

We generated a tool that provides a framework for objective risk stratification of doctors and healthcare professionals during the COVID-19 pandemic, without requiring disclosure of information that an individual may not wish to share with their direct line manager during the risk assessment process. This tool has been made freely available through the British Medical Association website and is widely used in the National Health Service and other external organisations.

The continuums of impairment in vascular reactivity across the spectrum of cardiometabolic health: A systematic review and network meta-analysis

This study aimed to assess, for the first time, the change in vascular reactivity across the full spectrum of cardiometabolic health. Systematic searches were conducted in MEDLINE and EMBASE databases from their inception to March 13, 2017, including studies that assessed basal vascular reactivity in two or more of the following health groups (aged ≥18 years old): healthy, overweight, obesity, impaired glucose tolerance, metabolic syndrome, or type 2 diabetes with or without complications. Direct and indirect comparisons of vascular reactivity were combined using a network meta-analysis. Comparing data from 193 articles (7226 healthy subjects and 19344 patients), the network meta-analyses revealed a progressive impairment in vascular reactivity (flow-mediated dilation data) from the clinical onset of an overweight status (-0.41%, 95% CI, -0.98 to 0.15) through to the development of vascular complications in those with type 2 diabetes (-4.26%, 95% CI, -4.97 to -3.54). Meta-regressions revealed that for every 1 mmol/l increase in fasting blood glucose concentration, flow-mediated dilation decreased by 0.52%. Acknowledging that the time course of disease may vary between patients, this study demonstrates multiple continuums of vascular dysfunction where the severity of impairment in vascular reactivity progressively increases throughout the pathogenesis of obesity and/or insulin resistance, providing information that is important to enhancing the timing and effectiveness of strategies that aim to improve cardiovascular outcomes.

Diabetes, cardiovascular disease and the microcirculation

Cardiovascular disease (CVD) is the leading cause of mortality in people with type 2 diabetes mellitus (T2DM), yet a significant proportion of the disease burden cannot be accounted for by conventional cardiovascular risk factors. Hypertension occurs in majority of people with T2DM, which is substantially more frequent than would be anticipated based on general population samples. The impact of hypertension is considerably higher in people with diabetes than it is in the general population, suggesting either an increased sensitivity to its effect or a confounding underlying aetiopathogenic mechanism of hypertension associated with CVD within diabetes. In this contribution, we aim to review the changes observed in the vascular tree in people with T2DM compared to the general population, the effects of established anti-diabetes drugs on microvascular outcomes, and explore the hypotheses to account for common causalities of the increased prevalence of CVD and hypertension in people with T2DM.

Flow motion dynamics of microvascular blood flow and oxygenation: Evidence of adaptive changes in obesity and type 2 diabetes mellitus/insulin resistance

An altered spatial heterogeneity and temporal stability of network perfusion can give rise to a limited adaptive ability to meet metabolic demands. Derangement of local flow motion activity is associated with reduced microvascular blood flow and tissue oxygenation, and it has been suggested that changes in flow motion activity may provide an early indicator of declining, endothelial, neurogenic, and myogenic regulatory mechanisms and signal the onset and progression of microvascular pathophysiology. This short conference review article explores some of the evidence for altered flow motion dynamics of blood flux signals acquired using laser Doppler fluximetry in the skin in individuals at risk of developing or with cardiometabolic disease.

Disparities in Cardiovascular Disease and Type 2 Diabetes Risk Factors in Blacks and Whites: Dissecting Racial Paradox of Metabolic Syndrome

Cardiovascular diseases (CVD) remain as the leading cause of mortality in the western world and have become a major health threat for developing countries. There are several risk factors that account for the CVD and the associated mortality. These include genetics, type 2 diabetes (T2DM), obesity, physical inactivity, hypertension, and abnormal lipids and lipoproteins. The constellation of these risk factors has been termed metabolic syndrome (MetS). MetS varies among racial and ethnic populations. Thus, race and ethnicity account for some of the differences in the MetS and the associated CVD and T2DM. Furthermore, the relationships among traditional metabolic parameters and CVD differ, especially when comparing Black and White populations. In this regard, the greater CVD in Blacks than Whites have been partly attributed to other non-traditional CVD risk factors, such as subclinical inflammation (C-reactive protein), homocysteine, increased low-density lipoprotein oxidation, lipoprotein a, adiponectin, and plasminogen activator inhibitor-1, etc. Thus, to understand CVD and T2DM differences in Blacks and Whites with MetS, it is essential to explore the contributions of both traditional and non-traditional CVD and T2DM risk factors in Blacks of African ancestry and Whites of Europoid ancestry. Therefore, in this mini review, we propose that non-traditional risk factors should be integrated in defining MetS as a predictor of CVD and T2DM in Blacks in the African diaspora in future studies.

Attenuated systemic microvascular function in men with coronary artery disease is associated with angina but not explained by atherosclerosis

INTRODUCTION

Refractory angina is the occurrence of clinical symptoms despite maximal therapy. We investigated associations between microvascular function, atherosclerotic burden, and clinical symptoms in subjects with CAD.

METHODS

Skin microvascular response to heating and ischemia was assessed in 167 male volunteers by laser Doppler fluximetry; 82 with CAD on maximal therapy and 85 with no known CAD (noCAD). CAC scores, carotid IMT, and femoral IMT were measured and symptoms were scored using the Rose angina questionnaire.

RESULTS

Patients with CAD had poorer microvascular response to heating (114[95% CI 106-122]au CAD vs. 143[134-153]au no CAD; p < 0.0001) and ischemia (42[38-46]au CAD vs. 53[78-58]au. noCAD; p = 0.001). Thirty-eight percent of the noCAD group had elevated CAC scores. There were no associations between markers of atherosclerosis and microvascular function. Forty-two percent of the CAD group had refractory angina. This was associated with impaired microvascular function compared to those with elevated CAC scores but no symptoms (109 [95-124]au vs. 131[122-140]au; p = 0.008).

CONCLUSIONS

Men with symptomatic CAD have poorer microvascular function compared to individuals without CAD. Microvascular function does not correlate with atherosclerosis, but is impaired in individuals with refractory angina. Microvascular dysfunction may play a role in the symptomatology of angina.

Microvascular autoregulation in children and adolescents with type 1 diabetes mellitus

AIMS/HYPOTHESIS

Deterioration of microvascular function may have an early onset in individuals with type 1 diabetes mellitus. We hypothesised that microvascular autoregulation is impaired in children with type 1 diabetes and can be detected non-invasively by postocclusive reactive hyperaemia (PORH).

METHODS

Microvascular autoregulation was assessed in 58 children with type 1 diabetes and 58 age- and sex-matched healthy controls by PORH using laser Doppler fluxmetry. Baseline perfusion, biological zero (defined as a 'no flow' laser Doppler signal during suprasystolic occlusion), peak perfusion following occlusion, time to peak and recovery time (time until baseline perfusion is resumed) were recorded and compared between the groups.

RESULTS

Peak perfusion was higher in children with type 1 diabetes than in healthy controls (1.7 ± 0.93 AU [arbitrary units] vs 1.29 ± 0.46 AU; p = 0.004), and biological zero was lower in children with type 1 diabetes vs controls (0.14 ± 0.04 AU vs 0.19 ± 0.04 AU; p < 0.0001). No differences were seen between the groups in baseline perfusion, time to peak during PORH and recovery time following PORH.

CONCLUSIONS/INTERPRETATION

PORH reveals impaired microvascular autoregulation in children with type 1 diabetes. The higher peak perfusion might reflect a decline in the vasoconstrictive ability of arteriolar smooth muscle cells upstream of capillary beds in children with type 1 diabetes.

Microcirculation on a large scale: techniques, tactics and relevance of studying the microcirculation in larger population samples

The role of microcirculatory dysfunction is increasingly being recognized in the etiopathogenesis of cardiovascular disease. Whilst the importance of detailed mechanistic studies to determine the exact nature of these disturbances is without question, it was large-scale population-based studies that first identified the associations between deranged microvascular perfusion, autoregulation or structure, and subsequent target organ damage. This is the subject of considerable studies to establish whether there is a causal effect in either direction, or simply represents shared risk factors, although it is most likely to be a complex combination of bidirectional interactions. The techniques for investigating microcirculatory function have evolved almost exponentially over the last 75 years: So too have the strategies for investigation. Current epidemiological studies are focusing on attempting to untangle the inter-relationship between risk factors and pathological mechanisms to attempt to determine whether these represent therapeutic targets or simple markers of unmeasured risk. We plan to review the techniques used for these population-based studies, the advances made, and the clinical implications derived.

Small artery remodelling in diabetes

The aim of this article is to briefly review available data regarding changes in the structure of microvessels observed in patients with diabetes mellitus, and possible correction by effective treatment. The development of structural changes in the systemic vasculature is the end result of established hypertension. In essential hypertension, small arteries of smooth muscle cells are restructured around a smaller lumen and there is no net growth of the vascular wall, although in some secondary forms of hypertension, a hypertrophic remodelling may be detected. Moreover, in non-insulin-dependent diabetes mellitus a hypertrophic remodelling of subcutaneous small arteries is present. Indices of small resistance artery structure, such as the tunica media to internal lumen ratio, may have a strong prognostic significance in hypertensive and diabetic patients, over and above all other known cardiovascular risk factors. Therefore, regression of vascular alterations is an appealing goal of antihypertensive treatment. Different antihypertensive drugs seem to have different effect on vascular structure. In diabetic hypertensive patients, a significant regression of structural alterations of small resistance arteries with drugs blocking the renin–angiotensin system (angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers) was demonstrated. Alterations in the microcirculation represent a common pathological finding, and microangiopathy is one of the most important mechanisms involved in the development of organ damage as well as of clinical events in patients with diabetes mellitus. Renin–angiotensin system blockade seems to be effective in preventing/regressing alterations in microvascular structure.

Associations between cardiac target organ damage and microvascular dysfunction: the role of blood pressure

BACKGROUND

Microvascular dysfunction may be an early precursor of cardiovascular disease (CVD). Increased left ventricular mass (LVM), concentric left ventricular remodelling and increased left atrial size are the factors that could predict future CVD. We investigated whether microvascular dysfunction was associated with these cardiac measures.

METHODS AND RESULTS

Laser Doppler fluximetry of skin vessels was used to study associations with risk factors and echocardiographic measurements of LVM, relative wall thickness (RWT), and left atrial size in 305 people (aged 40-65 years; 117 with type 2 diabetes). Flow in response to a 3-min arterial occlusion was measured. Postischaemic peak flow responses were categorized into three distinct groups: slow rise to peak (normal), nondominant early peak group (mildly abnormal) and a dominant early peak (abnormal). Those with a dominant early peak had higher blood pressure (P = 0.001), weight (P = 0.001), fasting glucose (P = 0.001) and prevalence of diabetes (P = 0.02). LVM (P = 0.01), RWT (P < 0.001) and left atrial size (P < 0.001) were greater with worsening postischaemic peak flow responses. Differences in LVM between postischaemic response groups were accounted for by blood pressure (BP). However, differences in BP and other CVD risk factors did not account for the greater RWT and left atrial size observed in the more adverse peak response groups [geometric mean of RWT [95% confidence interval (CI)] 0.40 (0.38-0.41) vs. 0.41 (0.40-0.42) vs. 0.43 (0.41-0.45), P = 0.007; left atrial size 36.1 (35.4-36.1) vs. 37.4 (36.8-38.0) vs. 38.7 (37.5-40.0), P = 0.002 for normal vs. mildly abnormal vs. abnormal respectively].

CONCLUSION

An abnormal microcirculatory cutaneous peak flow response following ischaemia is associated with adverse cardiac remodelling, independent of CVD risk factors including blood pressure.

Metabolic syndrome in blacks: are the criteria right?

Blacks have a lower prevalence of metabolic syndrome (MetS) that can be partly ascribed to the lower prevalent rates of some major components of MetS, namely the lower serum triglycerides and higher high-density lipoprotein cholesterol levels in blacks when compared with whites. Blacks manifest greater insulin resistance, the pivotal lesion underpinning MetS than whites. However, the relationships among insulin resistance and cardiovascular disease (CVD) risk factors are weaker in blacks than whites. The international bodies have recommended the use of European-based cutoff points for MetS for blacks. However, with the emerging inconsistencies in the association of insulin resistance and CVD risk factors in blacks, the use of these definitions and the cutoff points for MetS have become problematic. Therefore, it is important to review the limitations in the use of the current criteria and cutoff points of MetS in blacks to lessen the CVD risk burden in blacks.

Attenuation of microvascular function in those with cardiovascular disease is similar in patients of Indian Asian and European descent

Background

Indian Asians are at increased risk of cardiovascular death which does not appear to be explained by conventional risk factors. As microvascular disease is also more prevalent in Indian Asians, and as it is thought to play a role in the development of macrovascular disease, we decided to determine whether impaired microcirculation could contribute to this increased cardiovascular risk in Indian Asians.

Methods

Forearm skin laser Doppler fluximetry in response to heating and ischaemia was assessed in 83 Europeans (41 with angiographically confirmed atherosclerotic coronary artery disease (CAD) and 42 from the general population) and 84 Indian Asians (41 with CAD). Explanations for differences in microvascular function were sought using multivariate analysis including conventional cardiovascular risk factors.

Results

Compared to ethnically matched control populations both Europeans and Indian Asians with CAD had poorer microvascular responses to heating than those without (117(95% CI 105-131) vs. 142(130-162) arbitrary units, (au) for Europeans and 111(101-122) vs. 141(131-153)au for Indian Asians) and to ischaemia (44(38-50) vs. 57(49-67)au & 39(34-45) vs. 49(43-56)au respectively). These differences were not accounted for by conventional cardiovascular risk factors. There was no ethnic difference in the attenuation of microvascular function associated with CAD.

Conclusion

Patients of European and Indian Asian descent with symptomatic CAD have poorer microvascular maximal tissue perfusion and reactive hyperaemia in the skin compared to ethnically matched asymptomatic control populations. Despite the increased cardiovascular risk in Indian Asians, the attenuation of microvascular function associated with CAD was equivalent in the ethic groups. This suggests that in Indian Asians microcirculation does not explain the increased susceptibility to CAD.

Small artery remodeling in diabetes mellitus

AIMS

To briefly review available data regarding changes in the structure of microvessels observed in patients with diabetes mellitus, and possible correction by effective treatment.

DATA SYNTHESIS

The development of structural changes in the systemic vasculature is the end result of established hypertension. In essential hypertension, small arteries' smooth muscle cells are restructured around a smaller lumen and there is no net growth of the vascular wall, while in some secondary forms of hypertension, hypertrophic remodeling may be detected. Moreover, in non-insulin-dependent diabetes mellitus hypertrophic remodeling of subcutaneous small arteries is present. Indices of small resistance artery structure, such as the tunica media to internal lumen ratio, may have a strong prognostic significance in hypertensive and diabetic patients, over and above all other known cardiovascular risk factors. Therefore, regression of vascular alterations is an appealing goal of antihypertensive treatment. Different antihypertensive drugs seem to have different effects on vascular structure. In diabetic hypertensive patients, a significant regression of structural alterations to the small resistance arteries with drugs blocking the renin-angiotensin system (ACE inhibitors, angiotensin II receptor blockers) was demonstrated.

CONCLUSION

Alterations in the microcirculation represent a common pathological finding, and microangiopathy is one of the most important mechanisms involved in the development of organ damage as well as of clinical events in patients with diabetes mellitus. Renin-angiotensin system blockade seems to be effective in preventing and/or regressing alterations in the microvascular structure.

Comparison of the retinal microvasculature in European and African-Caribbean people with diabetes

Diabetes aggravates the impact of elevated BP (blood pressure) on the microcirculation, and people of African ancestry with diabetes are more susceptible to microvascular damage than Europeans. In the present study, we investigated possible differences in the retinal microcirculation in people of European and African-Caribbean ethnicity with diabetes that might account for this. A total of 51 subjects with Type 2 diabetes (age 40–65 years; 25 male; 29 African-Caribbean) were studied. Clinic and 24 h ambulatory BP, and fasting glucose, insulin and lipids were measured. Digital retinal images were analysed using custom-written semi-automatic software to determine: LDR (length/diameter ratio) and AVR (arteriolar/venular diameter ratio), branching angles, vessel tortuosity and NT (number of terminal vessel branches). Arterioles were narrower in European people with diabetes than in African-Caribbean people with diabetes [mean (S.D.) arteriolar diameter, 76 (7) compared with 82 (11) μm respectively (P=0.03); arteriolar LDR, 28.1 (8.5) compared with 23.7 (7.0) respectively (P=0.046); and AVR, 0.66 (0.21) compared with 0.90 (0.36) respectively (P=0.028)]. Ethnic differences in arteriolar LDR, arteriolar diameter and AVR were not explained by differences in BP, but were attenuated by adjustment for the duration of diabetes. There was no significant relationship between BP and arteriolar narrowing in the group as a whole, although the relationship between arteriolar LDR and systolic BP was stronger in Europeans than African-Caribbeans [β=0.08 (0.07) compared with β=0.03 (0.06); P=0.03]. In conclusion, in the presence of diabetes, a relationship between BP and retinal arteriolar diameter was not evident and implies impaired small artery remodelling in the presence of diabetes. African-Caribbean people with diabetes have wider retinal arterioles and this could contribute to enhanced microvascular damage in this ethnic group.