Association of novel risk factors with the ankle brachial index in African American and non-Hispanic white populations

Biomarkers and Genetics in Peripheral Artery Disease

BACKGROUND

Peripheral artery disease (PAD) is highly prevalent and there is considerable diversity in the initial clinical manifestation and disease progression among individuals. Currently, there is no ideal biomarker to screen for PAD, to risk stratify patients with PAD, or to monitor therapeutic response to revascularization procedures. Advances in human genetics have markedly enhanced the ability to develop novel diagnostic and therapeutic approaches across a host of human diseases, but such developments in the field of PAD are lagging.

CONTENT

In this article, we will discuss the epidemiology, traditional risk factors for, and clinical presentations of PAD. We will discuss the possible role of genetic factors and gene-environment interactions in the development and/or progression of PAD. We will further explore future avenues through which genetic advances can be used to better our understanding of the pathophysiology of PAD and potentially find newer therapeutic targets. We will discuss the potential role of biomarkers in identifying patients at risk for PAD and for risk stratifying patients with PAD, and novel approaches to identification of reliable biomarkers in PAD.

SUMMARY

The exponential growth of genetic tools and newer technologies provides opportunities to investigate and identify newer pathways in the development and progression of PAD, and thereby in the identification of newer biomarkers and therapies.

Associations of candidate biomarkers of vascular disease with the ankle-brachial index and peripheral arterial disease

BACKGROUND

The use of multiple biomarkers representing various etiologic pathways of atherosclerosis may improve the prediction of interindividual variation in the ankle-brachial index (ABI). To this end, we investigated associations of 47 candidate biomarkers with the ABI and presence of peripheral arterial disease (PAD) in African-Americans (AAs) and non-Hispanic whites (NHWs).

METHODS

Study participants included 1,291 AAs (71.1% women, mean age, 63.4±9.3 years) and 1,152 NHWs (57.5% women, mean age 58.5±10.1 years) belonging to hypertensive sibships. Peripheral arterial disease was defined as an ABI ≤ 0.90. Circulating levels of 47 candidate biomarkers were log-transformed before analysis because of skewed distribution. Multivariate regression analyses were used to identify biomarkers associated with ABI or PAD independently of age, sex, conventional risk factors, and medication use.

RESULTS

After adjustment for covariates, higher levels of nine biomarkers were associated with a lower ABI in AAs (all P ≤ 0.005); these biomarkers were C-reactive protein (CRP), interleukin-6, tumor necrosis factor receptor-II (TNF-R II), lipoprotein(a), N-terminal pro-brain natriuretic peptide (NT-proBNP), pro-atrial natriuretic peptide, C-terminal pro-arginine vasopressin, osteoprotegerin, and fibrinogen. Three biomarkers - myeloperoxidase, NT-proBNP, and D-dimer - were associated with ABI in NHWs (all P ≤ 0.01). C-reactive protein, interleukin-6, TNF-R II, lipoprotein(a), NT-proBNP, pro-atrial natriuretic peptide, D-dimer, and fibrinogen were associated with PAD (all P ≤ 0.005) in AAs after adjustment for covariates. None of the biomarkers were independently associated with PAD in NHWs.

CONCLUSION

A multimarker approach improved the prediction of interindividual variation in the ABI in AAs and NHWs, and improved prediction of the presence of PAD in AAs.

Ethnic differences in ankle brachial index are present in middle-aged individuals without peripheral arterial disease

INTRODUCTION

To better understand the basis for previously reported ethnic differences in ankle brachial index (ABI), we investigated whether these differences were present in individuals without known peripheral arterial disease (PAD).

METHODS

We used data from National Health and Nutrition Examination surveys (NHANES 1999-2004) to determine whether ethnic differences were present in respondents without PAD (1 ≤ ABI ≤ 1.3). We assessed whether ethnicity was an independent predictor of ABI and ankle systolic blood pressure (SBP) in linear regression models that adjusted for conventional and novel cardiovascular risk factors. To minimize effects of atherosclerosis on ABI, we studied adults aged ≤ 60 years, and also repeated our analyses in a subset aged ≤ 50 years that did not have risk factors for PAD.

RESULTS

3348 participants aged ≤ 60 years were included in the study. Mean ABI was 1.11 in non-Hispanic Blacks (NHB) and 1.13 in non-Hispanic Whites (NHW) (P < 0.0001). In multivariable linear regression analysis that adjusted for age, gender, ethnicity, smoking, height, diabetes, brachial SBP, dyslipidemia, diabetes, renal function, concurrent cardiovascular disease, and plasma levels of homocysteine, fibrinogen and C-reactive protein, NHB had lower ABI than NHW (β = -0.03 ± 0.004, P < 0.00001). Although, NHBs had higher ankle SBP than NHWs (by 5.4 mm Hg), NHBs had a lower mean ankle SBP (β = -3.663 mm Hg ± 0.500, P < 0.0001) after adjusting for clinical covariates, including brachial SBP, in multivariable analysis.

CONCLUSION

Ethnic differences in ABI are present in middle-aged adults at low risk for peripheral atherosclerosis.

The role of nutrition and body composition in peripheral arterial disease

Peripheral arterial disease (PAD) has not been as extensively investigated as other cardiovascular diseases. However, the available data suggest that nutrition-based treatment strategies have the potential to reduce the cost-economic burden of PAD substantially. Abdominal obesity is associated with PAD and prospective and cross-sectional studies have shown that a low dietary intake of folate and reduced synthesis of vitamin D are associated with an increased risk of PAD and severe walking impairment in patients who have the disease. However, dietary patterns that are associated with decreased cardiovascular risk might protect against PAD. A small number of clinical trials have provided evidence that increased intakes of niacin and insoluble fiber might be associated with decreased levels of LDL cholesterol and thrombogenic biomarkers, as well as increased serum levels of HDL cholesterol in patients with PAD. However, little evidence that antioxidants, vitamins B(6) and B(12), or essential fatty acid supplements improve clinical outcomes in these patients exists. Overall, data on the effects of nutrition, body composition, and nutritional supplementation on the risk, progression, and prognosis of PAD are scarce. Further research into these areas is required to allow the development of evidence-based nutritional guidelines for the prevention and treatment of the disease.

Hemostatic cardiovascular risk factors, common carotid-intima medial thickness and peripheral arterial disease in South Asians and African Caribbeans: a substudy to the Ethnic-Echocardiographic Heart of England Screening (E-ECHOES) study

OBJECTIVE

To determine whether ethnic differences exist in inflammatory (interleukin-6 and C-reactive protein) and hemostatic biomarkers (soluble P-selectin [sP-sel], von Willebrand factor [VWF], and fibrin D-dimer) between South Asian (people originating from India, Pakistan, and Bangladesh) and African Caribbean (Black Caribbean and Black African) groups, the two largest minority ethnic groups in the UK; and to determine associations between these biomarkers and common carotid intima-media thickness and peripheral artery disease (PAD).

PATIENTS AND METHODS

We recruited 572 subjects (356 South Asian and 216 Black) aged ≥ 45 years as a substudy to a community screening project, the Ethnic-Echocardiographic Heart of England Screening (E-ECHOES) study. All subjects completed an interviewer-led questionnaire, anthropometric measurements were taken, and blood sampling was performed if consent was granted. Ankle brachial pressure index (ABPI) was calculated, and the common carotid intima-media thickness (CCIMT) was measured. PAD was defined as ABPI < 0.9. ELISA was used to quantify inflammatory and hemostatic biomarkers.

RESULTS

The incidence of hypertension (> 70%) and diabetes (> 27%) was high, but non-significantly different between the two ethnic groups. South Asians had higher platelet count and sP-sel levels than African Caribbeans (P < 0.0001 for both), despite there being no significant difference in antiplatelet medication. African Caribbeans had higher D-dimer levels (P = 0.0052). Among South Asians, VWF correlated with ABPI (P = 0.047) and mean (P = 0.002) and maximum CCIMT (P = 0.011) on univariate analysis, and remained an independent predictor of mean and maximum CCIMT on multivariate analysis with traditional cardiovascular risk factors (P = 0.034 and P = 0.046, respectively). In African Caribbeans, D-dimer levels were was higher in PAD than in normal ABPI participants (P = 0.04), and was associated with ABPI in both univariate analysis (P = 0.014) and multivariate analysis (P < 0.0001) with traditional cardiovascular risk factors.

CONCLUSION

Ethnic differences are evident in inflammatory and hemostatic factors, as well as in their associations with CCIMT and PAD. These may reflect differences in cardiovascular risk factors or pathophysiologic processes that characterize each ethnic group.

Socioeconomic and hospital-related predictors of amputation for critical limb ischemia

OBJECTIVE

Disparities in limb salvage procedures may be driven by socioeconomic status (SES) and access to high-volume hospitals. We sought to identify SES factors associated with major amputation in the setting of critical limb ischemia (CLI).

METHODS

The 2003-2007 Nationwide Inpatient Sample was queried for discharges containing lower extremity revascularization (LER) or major amputation and chronic CLI (N = 958,120). The Elixhauser method was used to adjust for comorbidities. Significant predictors in bivariate logistic regression were entered into a multivariate logistic regression for the dependent variable of amputation vs LER.

RESULTS

Overall, 24.2% of CLI patients underwent amputation. Significant differences were seen between both groups in bivariate and multivariate analysis of SES factors, including race, income, and insurance status. Lower-income patients were more likely to be treated at low-LER-volume institutions (odds ratio [OR], 1.74; P < .001). Patients at higher-LER-volume centers (OR, 15.16; P <.001) admitted electively (OR, 2.19; P < .001) and evaluated with diagnostic imaging (OR, 10.63; P < .001) were more likely to receive LER.

CONCLUSIONS

After controlling for comorbidities, minority patients, those with lower SES, and patients with Medicaid were more likely receive amputation for CLI in low-volume hospitals. Addressing SES and hospital factors may reduce amputation rates for CLI.

Determinants of homocysteine levels in Ivorian rural population

In the present study, homocysteine (Hcy) and vitamin B status were determined in healthy subjects living in two opposite regions of the Ivory Coast. Fifty-six subjects from a coastal region (Bodou) having a fish-based diet and 56 subjects from a mountainous area (Glanle) having a vegetarian diet were tested to sample Hcy, folate, vitamin B12, creatinine, and lipid levels, as well as inflammation and nutritional parameters. An increased prevalence of Hcy > or = 15 micromol/L was observed, reaching 60 % of all subjects. The Bodou group exhibited significantly higher Hcy levels than the Glanle group [20.1 (9.7 - 41.4) vs. 13.6 (5.5 - 48.7) micromol/L, p<0.0001], despite higher vitamin B12 levels [593 (163 - 1860) vs. 234 (83 - 585) pg/mL, p<0.0001]. Although folate levels were lower in subjects from Bodou compared to Glanle [3.2 (2.0 - 7.3) vs. 6.0 (1.9 - 18.2) ng/mL, p<0.0001], there was no significant relationship with Hcy levels in any groups. Interestingly, there were significantly higher creatinine levels in subjects from Bodou compared to Glanle and a significant positive relationship with Hcy levels was evident in each group. In conclusion, Hcy levels in an Ivorian population having a fish-based diet appeared significantly higher compared to subjects having a vegetarian diet. However, folate and vitamin B12 status did not emerge as the major determinants of this difference; a stronger relationship was observed with creatinine levels.

Lipoprotein(a), inflammation, and peripheral arterial disease in a community-based sample of older men and women (the InCHIANTI study)

Lipoprotein(a) (Lp[a]) may represent an independent risk factor for peripheral arterial disease of the lower limbs (LL-PAD), but prospective data are scant. We estimated the association between baseline Lp(a) with prevalent and incident LL-PAD in older subjects from the InCHIANTI Study. LL-PAD, defined as an ankle-brachial index <0.90, was assessed at baseline and over a 6-year follow-up in a sample of 1,002 Italian subjects 60 to 96 years of age. Plasma Lp(a) and potential traditional and novel cardiovascular risk factors (including a score based on relevant inflammatory markers) were entered in multivariable models to assess their association with prevalent and incident LL-PAD. At baseline, Lp(a) concentration was directly related to the number of increased inflammatory markers (p <0.05). There were 125 (12.5%) prevalent cases of LL-PAD and 57 (8.3%) incident cases. After adjustment for potential confounders, participants in the highest quartile of the Lp(a) distribution (>/=32.9 mg/dl) were more likely to have LL-PAD compared to those in the lowest quartile (odds ratio [OR] 1.83, 95% confidence interval [CI] 1.01 to 3.33). The association was stronger (OR 3.80, 95% CI 1.50 to 9.61) if LL-PAD was defined by harder criteria, namely an ankle-brachial index <0.70. Compared to subjects in the lowest Lp(a) quartile, those in the highest quartile showed a somewhat increased risk of incident LL-PAD (lowest quartile 7.7%, highest quartile 10.8%), but the association was not statistically significant (OR 1.52, 95% CI 0.71 to 3.22). In conclusion, Lp(a) is an independent LL-PAD correlate in the cross-sectional evaluation, but further prospective studies in larger populations, with longer follow-up and more definite LL-PAD ranking, might be needed to establish a longitudinal association.

Early identification of cardiovascular risk using genomics and proteomics

Coronary heart disease (CHD) will soon become the leading cause of death and morbidity in the world. Early detection and treatment of CHD is thus imperative to improve global health. Atherosclerosis of the coronary arteries is a complex multifactorial disease process involving multiple pathways that can be influenced by both genetic and environmental factors. With the recent advances in genomics and proteomics, many new risk factors with small-to-moderate effects are likely to be identified. Additionally, individualized risk stratification and targeted therapy may become feasible; each individual could potentially be assessed with a panel of tests for genomic and proteomic markers and, on the basis of the individual's composite risk profile, preventive and therapeutic steps could then be undertaken. With a multimarker approach, it may also be possible to identify alterations in pathways involved in atherogenesis, rather than focus on individual risk factors. In this article, we use the specific example of atherosclerosis to discuss the role of genomics and proteomics in cardiovascular risk assessment.

Disparities in vascular surgery: is it biology or environment?

Disparities in health care are well documented for several racial, ethnic, and gender groups. In peripheral arterial disease, differences in prevalence, treatment selection, treatment outcomes, and resulting quality of life have negative effects on some minority groups and women. It may be easy to document disparities, but it is harder to understand their underlying causes. Are there biologic differences between members of racial and ethnic groups that influence disease presentation and outcomes? Or is the socioeconomic environment that surrounds them the true driver of observed differences? This article reviews the evidence for racial and gender disparities in vascular surgery and presents some potential mechanisms that may explain the disparities.

Sex and ethnic differences in 47 candidate proteomic markers of cardiovascular disease: the Mayo Clinic proteomic markers of arteriosclerosis study

BACKGROUND

Cardiovascular disease (CVD) susceptibility differs between men and women and varies with ethnicity. This variability is not entirely explained by conventional CVD risk factors. We examined differences in circulating levels of 47 novel protein markers of CVD in 2561 men and women of African-American (AA) and non-Hispanic White (NHW) ethnicity, enrolled at geographically distinct sites.

METHODOLOGY/PRINCIPAL FINDINGS

Participants (1,324 AAs, mean age 63.5 y, 71% women; 1,237 NHWs, mean age 58.9 y, 57% women) belonged to sibships ascertained on the basis of hypertension. Solid-phase immunoassays and immunoturbidometric, clot-based, chromogenic, and electrophoretic assays were used to measure the 47 protein markers in plasma or serum. Marker levels were log transformed and outliers were adjusted to within 4 SD. To identify markers independently associated with sex or ethnicity, we employed multivariable regression analyses that adjusted for conventional risk factors, prior history of CVD, medication use and lifestyle factors (physical activity, alcohol consumption and education). Generalized estimating equations were used to correct for intrafamilial correlations. After adjustment for the above covariates, female sex was associated with higher levels of 29 markers and lower levels of 6 markers. Female sex was independently associated with higher levels of several inflammatory markers as well as lipoproteins, adipokines, natriuretic peptides, vasoconstrictor peptides and markers of calcification and thrombosis. AA ethnicity was associated with higher levels of 19 markers and lower levels of 6 markers, including higher levels of several inflammatory makers, higher leptin and lower adiponectin levels, lower levels of vasodilator-natriuretic peptides, higher levels of vasoconstrictor-antidiuretic peptides and markers of calcification and thrombosis.

CONCLUSIONS/SIGNIFICANCE

Plasma levels of several novel protein markers of CVD differ significantly in the context of sex and ethnicity. These results have implications for individualized CVD risk assessment.

Novel markers of peripheral arterial disease

Peripheral arterial disease (PAD), a relatively common manifestation of atherosclerotic vascular disease, is associated with significant morbidity and mortality. Although conventional risk factors contribute to the onset and progression of PAD, the role of 'novel' biomarkers in pathways of inflammation, thrombosis, lipoprotein metabolism, and oxidative stress in determining susceptibility to PAD is being increasingly recognized. Validation of novel risk factors for PAD may allow earlier detection, an improved understanding of disease etiology and progression, and the development of new therapies. In this review, we discuss available evidence for associations between novel circulating markers and several aspects of PAD including disease susceptibility, progression, functional limitation, and adverse outcomes.

White blood cell count predicts all-cause mortality in patients with suspected peripheral arterial disease

OBJECTIVE

We investigated whether markers of inflammation-white blood cell (WBC) count, C-reactive protein (CRP), and lipoprotein-associated phospholipase A2-are associated with mortality in patients referred for noninvasive lower-extremity arterial evaluation.

METHODS

Participants (n = 242, mean age 68 years, 54% men) were followed for a median of 71 months. Ankle-brachial index (ABI), WBC count, plasma CRP, and lipoprotein-associated phospholipase A2 were measured at the start of the study. Factors associated with all-cause mortality were identified using Cox proportional hazards.

RESULTS

During the follow-up period, 56 patients (25%) died. Factors associated with higher mortality were greater age, history of coronary artery disease/cerebrovascular disease, lower ABI, higher serum creatinine, and higher WBC count/plasma CRP. In stepwise multivariable regression analysis, ABI, serum creatinine, WBC count, and CRP were associated significantly with mortality. Patients in the top tertile of WBC count and CRP level had a relative risk of mortality of 3.37 (confidence interval [CI], 1.56-7.27) and 2.12 (CI, 0.97-4.62), respectively. However, only the WBC count contributed incrementally to prediction of mortality. Inferences were similar when analyses were limited to patients with peripheral arterial disease (ABI<0.9, n = 114).

CONCLUSION

WBC count, but not plasma CRP level, provides incremental information about the risk of death in patients referred for lower-extremity arterial evaluation and in the subset of these patients with peripheral arterial disease.

Haemostatic markers are associated with measures of vascular disease in adults with hypertension

Haemostatic markers have been implicated in the development and progression of vascular disease. We investigated the associations of several haemostatic markers (fibrinogen, D-dimer, FV, FVII, FVIII, von Willebrand factor (vWF) and antithrombin III) with two quantitative measures of vascular disease in adults with hypertension. Participants included 1051 African Americans (65+/-9 years, 72% women) and 894 non-Hispanic whites (61+/-9 years, 55% women) belonging to hypertensive sibships. Phenotypes of vascular disease included the ankle-brachial index (ABI), a measure of peripheral arterial disease, and urinary albumin/creatinine ratio (UACR), a surrogate of glomerular endothelial function. Generalized estimating equations were used to assess whether plasma levels of haemostatic markers were associated with measures of arteriosclerosis, after adjustment for conventional risk factors and medication (statin, aspirin and oestrogen) use. Higher fibrinogen and D-dimer were significantly associated with lower ABI in African Americans (P<0.001 and 0.004 respectively) and in non-Hispanic whites (P<0.001 and 0.010 respectively). Higher fibrinogen (P<0.001), D-dimer (P=0.003), FVIII (P<0.001) and vWF (P<0.001) were significantly associated with higher UACR in African Americans, whereas, in non-Hispanic whites, higher fibrinogen (P=0.020) and FVII (P=0.006) were significantly associated with higher UACR. Our findings indicate that in adults with essential hypertension, several markers in the haemostatic pathway are independently associated with ABI and UACR, two measures of vascular disease..

Elevated blood pressure, race/ethnicity, and C-reactive protein levels in children and adolescents

OBJECTIVE

Adult hypertension is independently associated with elevated C-reactive protein levels, after controlling for obesity and other cardiovascular risk factors. The objective of this study was to determine, with a nationally representative sample of children, whether the relationship between elevated blood pressure and C-reactive protein levels may be evident before adulthood.

METHODS

Cross-sectional data for children 8 to 17 years of age who participated in the National Health and Nutrition Examination Survey between 1999 and 2004 were analyzed. Bivariate analyses compared children with C-reactive protein levels of >3 mg/L versus <or=3 mg/L with respect to blood pressure and other cardiovascular risk factors. Multivariate linear regression was used to evaluate the relationship between elevated blood pressure and C-reactive protein levels.

RESULTS

Among 6112 children, 3% had systolic blood pressure of >or=95th percentile and 1.3% had diastolic blood pressure of >or=95th percentile. Children with C-reactive protein levels of >3 mg/L had higher systolic blood pressure, compared with children with C-reactive protein levels of <or=3 mg/L (109 vs 105 mm Hg). Obesity, high-density lipoprotein cholesterol levels of <40 mg/dL, and Hispanic ethnicity were independent predictors of elevated C-reactive protein levels. Diastolic blood pressure did not differ between groups. Linear regression analyses showed that systolic blood pressure of >or=95th percentile was independently associated with C-reactive protein levels in boys but not girls. Subset analyses according to race/ethnicity demonstrated that the independent association of elevated systolic blood pressure with C-reactive protein levels was largely limited to black boys.

CONCLUSIONS

These data indicate that there is interplay between race/ethnicity, elevated systolic blood pressure, obesity, and inflammation in children, a finding that has potential implications for disparities in cardiovascular disease later in life.

Measuring subclinical atherosclerosis: is homocysteine relevant?

OBJECTIVES

We systematically reviewed published studies looking at the relationship between total serum homocysteine (tHcy) and subclinical markers of atherosclerosis, such as carotid intimal-medial thickness (C-IMT), coronary artery calcium (CAC) and ankle-brachial index (ABI) in asymptomatic individuals. We analyzed these studies to examine this relationship as well as to guide future avenues of investigation by identifying studies that will help in the inclusion of tHcy levels in current guidelines on atherosclerotic disease management.

BACKGROUND

tHcy has been known to be associated with clinically evident atherosclerotic disease. However, tHcy is not incorporated in current guidelines for diagnosis of subclinical disease in high-risk asymptomatic individuals.

METHODS

We searched online databases (e.g., PUBMED, MEDLINE) for published articles assessing the relationship between tHcy and C-IMT, CAC and ABI. We limited the studies to asymptomatic populations, and excluded any study including symptomatic patients or individuals with a history of coronary, peripheral or cerebrovascular disease.

RESULTS

A systemic review of 19 articles revealed a significant association between elevated levels of tHcy and subclinical markers of atherosclerosis in asymptomatic individuals in most studies. Mean tHcy levels were consistently found to be higher in men compared to women. A total of 12 studies showed a significant association between tHcy and other risk markers of atherosclerosis, even after adjusting for age, sex and conventional risk factors. There were seven studies in unique populations that showed no significant relationship. We also observed that studies lowering baseline tHcy levels did not lead to an improvement in C-IMT, CAC or ABI scores. This might indicate that tHcy has a stronger role as a marker of atherosclerotic disease than as a risk factor for the same.

CONCLUSIONS

Based on our review, we conclude that there is a significant association between the subclinical atherosclerotic process and tHcy, and it shows potential as a cheap marker for risk stratification of asymptomatic patients. However, future studies further elucidating this association and elaborating the exact role of tHcy in the atherosclerotic disease process are required. The results of these studies suggest the incorporation of plasma tHcy levels in future risk reduction protocols for identification of individuals at higher risk of atherosclerotic events, and thus to categorize them for more aggressive treatment with established preventive and therapeutic measures.