High-density lipoprotein subclass distribution in individuals of Asian Indian descent: the National Asian Indian Heart Disease Project

Heightened risks of cardiovascular disease in South Asian populations: causes and consequences

INTRODUCTION

South Asian individuals comprise almost a quarter of the world's population and have an excess risk of atherosclerotic cardiovascular disease (ASCVD) compared to other ethnicities. In part, this can be explained by higher prevalence, earlier onset, and suboptimal control of traditional cardiovascular risk factors, such as insulin resistance, metabolic syndrome, and dyslipidaemia. However, there remains a significant residual excess risk associated with South Asian ethnicity after controlling for traditional risk factors.

AREAS COVERED

In this review, we describe the epidemiology of ASCVD in both native and diaspora South Asian populations. We explore how traditional cardiovascular risk factors, novel cardiovascular risk factors, and social determinants of health may contribute to the excess ASCVD risk seen in South Asian populations.

EXPERT OPINION

There should be increased awareness of the relative importance of South Asian ethnicity and related social determinants of health, as risk factors for ASCVD. Systematic screening processes should be tailored to this population, and modifiable risk factors should be treated aggressively. Further research is required to quantify determinants of the excess ASCVD risk seen in South Asian populations and to develop targeted interventions to address these factors.

South Asian ethnicity: What can we do to make this risk enhancer a risk equivalent?

South Asians account for around 25% of the global population and are the fastest-growing ethnicity in the US. This population has an increasing burden of atherosclerotic cardiovascular disease (ASCVD) which is also seen in the diaspora. Current risk prediction equations underestimate this risk and consider the South Asian ethnicity as a risk-enhancer among those with borderline-intermediate risk. In this review, we discuss why the South Asian population is at a higher risk of ASCVD and strategies to mitigate this increased risk.

Cardiovascular Disease in South Asian Immigrants: a Review of Dysfunctional HDL as a Potential Marker

South Asians (SAs) account for a quarter of the world's population and are one of the fastest-growing immigrant groups in the United States (US). South Asian Immigrants (SAIs) are disproportionately more at risk of developing cardiovascular disease (CVD) than other ethnic/racial groups. Atherosclerosis is a chronic inflammatory disorder and is the major cause of CVD. Traditional CVD risk factors, though important, do not fully explain the elevated risk of CVD in SAIs. High-density lipoproteins (HDLs) are heterogeneous lipoproteins that modify their composition and functionality depending on physiological or pathological conditions. With its cholesterol efflux, anti-inflammatory, and antioxidant functions, HDL is traditionally considered a protective factor for CVD. However, its functions can be compromised under pathological conditions, such as chronic inflammation, making it dysfunctional (Dys-HDL). SAIs have a high prevalence of type 2 diabetes and metabolic syndrome, which may further promote Dys-HDL. This review explores the potential association between Dys-HDL and CVD in SAIs and presents current literature discussing the role of Dys-HDL in CVD.

Dyslipidemia and Cardiovascular Disease Prevention in South Asians: A Review and Discussion of Causes, Challenges and Management Strategies

BACKGROUND

South Asians are at a significantly increased risk of atherosclerotic cardiovascular disease (ASCVD). For a major portion of the South Asian population, the cardiovascular disease events occur at a relatively younger age, are associated with worse outcomes, and have potentially more severe socioeconomic implications compared to their western counterparts.

METHODS

The term "South Asian" typically constitutes individuals from India, Pakistan, Nepal, Bhutan, Bangladesh, Sri Lanka, and Maldives, including expatriates as well as their families from these countries. Based on this, South Asians form approximately 25% of the world's population, with a high ASCVD burden in this group. In this review, we discuss the pathophysiological factors underlying ASCVD in South Asians, the dyslipidemia types and management, and discuss approaches to improve the overall ASCVD prevention efforts in this large subset population of the world. Although the pathophysiological mechanisms underlying the excess risk of cardiovascular disease in South Asians are multifactorial, dyslipidemia is a primary risk factor for the incidence and prevalence of this disease. The traditional "South Asian" dyslipidemia pattern includes levels of low-density lipoprotein cholesterol (LDL-C) in the normal range with a high concentration of LDL particles, elevated triglycerides, low levels of high-density lipoprotein cholesterol (HDL-C) with dysfunctional HDL particles, and high levels of lipoprotein(a).

CONCLUSION

While combined efforts to study the expatriate South Asians in western countries have been able to identify South Asian specific dyslipidemias, causal associations and optimal management remain relatively less explored. Larger scale studies are needed to better quantify the relationship of each lipid parameter with ASCVD risk among South Asians as well as optimal lipid targets and management strategies to reduce morbidity and mortality in this high-risk group.

Pathophysiological Mechanisms Underlying Excess Risk for Diabetes and Cardiovascular Disease in South Asians: The Perfect Storm

BACKGROUND

South Asians are at a significantly increased risk of type 2 diabetes (T2D) and cardiovascular disease (CVD), are diagnosed at relatively younger ages, and exhibit more severe disease phenotypes as compared with other ethnic groups. The pathophysiological mechanisms underlying T2D and CVD risk in South Asians are multifactorial and intricately related.

METHODS

A narrative review of the pathophysiology of excess risk of T2D and CVD in South Asians.

RESULTS

T2D and CVD have shared risk factors that encompass biological factors (early life influences, impaired glucose metabolism, and adverse body composition) as well as behavioral and environmental risk factors (diet, sedentary behavior, tobacco use, and social determinants of health). Genetics and epigenetics also play a role in explaining the increased risk of T2D and CVD among South Asians. Additionally, South Asians harbor several lipid abnormalities including high concentration of small-dense low-density lipoprotein (LDL) particles, elevated triglycerides, low high-density lipoprotein (HDL)- cholesterol levels, dysfunctional HDL particles, and elevated lipoprotein(a) that predispose them to CVD.

CONCLUSION

In this comprehensive review, we have discussed risk factors that provide insights into the pathophysiology of excess risk of T2D and CVD in South Asians.

Lipids in South Asians: Epidemiology and Management

Purpose of Review

This review focuses on lipoprotein abnormalities in South Asians (SA) and addresses risk stratification and management strategies to lower atherosclerotic cardiovascular disease (ASCVD) in this high-risk population.

Recent Findings

South Asians (SAs) are the fastest growing ethnic group in the United States (U.S) and have an increased risk of premature coronary artery disease (CAD). While the etiology may be multifactorial, lipoprotein abnormalities play a key role. SAs have lower low-density lipoprotein cholesterol (LDL-C) compared with Whites and at any given LDL-C level, SA ethnicity poses a higher risk of myocardial infarction (MI) and coronary artery disease (CAD) compared with other non-Asian groups. SAs have lower high-density lipoprotein cholesterol (HDL-C) with smaller particle sizes of HDL-C compared with Whites. SAs also have higher triglycerides than Whites which is strongly related to the high prevalence of metabolic syndrome in SAs. Lipoprotein a (Lp(a)) levels are also higher in SAs compared with many other ethnic groups. This unique lipoprotein profile plays a vital role in the elevated ASCVD risk in SAs. Studies evaluating dietary patterns of SAs in the U.S show high consumption of carbohydrates and saturated fats.

Summary

SAs have a high-risk lipoprotein profile compared with other ethnicities. Lipid abnormalities play a central role in the pathogenesis of CAD in SAs. More studies are needed to understand the true impact of the various lipoproteins and their contribution to increasing ASCVD in SAs. Aggressive lowering of LDL-C in high-risk groups using medications, such as statins, and lifestyle modification including dietary changes is essential in overall CAD risk reduction.

Lipoprotein(a): An underrecognized genetic risk factor for malignant coronary artery disease in young Indians

Malignant coronary artery disease (CAD) refers to a severe and extensive atherosclerotic process involving multiple coronary arteries in young individuals (aged <45 years in men and <50 years in women) with a low or no burden of established risk factors. Indians, in general, develop acute myocardial infarction (AMI) about 10 years earlier; AMI rates are threefold to fivefold higher in young Indians than in other populations. Although established CAD risk factors have a predictive value, they do not fully account for the excessive burden of CAD in young Indians. Lipoprotein(a) (Lp(a)) is increasingly recognized as the strongest known genetic risk factor for premature CAD, with high levels observed in Indians with malignant CAD. High Lp(a) levels confer a twofold to threefold risk of CAD-a risk similar to that of established risk factors, including diabetes. South Asians have the second highest Lp(a) levels and the highest risk of AMI from the elevated levels, more than double the risk observed in people of European descent. Approximately 25% of Indians and other South Asians have elevated Lp(a) levels (≥50 mg/dl), rendering Lp(a) a risk factor of great importance, similar to or surpassing diabetes. Lp(a) measurement is ready for clinical use and should be an essential part of all CAD research in Indians.

Relationship among obesity, blood lipids and insulin resistance in Bangladeshi adults

INTRODUCTION

Insulin resistance (IR) and abnormal lipid profiles are the risk factors for cardiovascular diseases in obesity. To clarify the relationship of the changes in insulin resistance, body weight and lipid profile, the present study was performed on Bangladeshi adults, total of 1500 individuals at the time of their general health examination in the hospital.

METHODS

After exclusion of other endocrine diseases, the remaining 772 patients were classified as IR ≥ 2 and IR < 2 based on the homeostatic model assessment-estimated insulin resistance (HOMA-IR) index. The endocrine disease free subjects were further clustered based on age, gender and obesity. The anthropometric and biochemical profiles were statistically analyzed and correlated with IR ≥ 2 and IR<2 groups as well as other clusters of the subjects. Apart from some disparities, notable differences were observed in all anthropometric data.

RESULTS

Total cholesterol (TC), triglyceride (TG), low density lipoprotein (LDL) and serum insulin levels were significantly higher in IR ≥ 2 group in comparison with IR<2 group. Obesity and dyslipidemia were associated as prevalent components of IR. Generalized linear model revealed that TC: LDL and TG: HDL had significant effect on IR. Age group II (41-60 years old) subjects had significantly higher lipid profile compared to age group I (20-40 years old) and age group III (61-80 years old).

CONCLUSIONS

Results reported herein support the notion that lipoprotein ratios might be the reliable biomarkers to evaluate IR.

South Asian Cardiovascular Disease & Cancer Risk: Genetics & Pathophysiology

South Asians (SAs) are at heightened risk for cardiovascular disease as compared to other ethnic groups, facing premature and more severe coronary artery disease, and decreased insulin sensitivity. This disease burden can only be partially explained by conventional risk factors, suggesting the need for a specific cardiovascular risk profile for SAs. Current research, as explored through a comprehensive literature review, suggests the existence of population specific genetic risk factors such as lipoprotein(a), as well as population specific gene modulating factors. This review catalogues the available research on cardiovascular disease and genetics, anthropometry, and pathophysiology, and cancer genetics among SAs, with a geographical focus on the U.S. A tailored risk profile will hinge upon population customized classification and treatment guidelines, informed by continued research.

Recent trends in epidemiology of dyslipidemias in India

Dyslipidemia is the most important atherosclerotic risk factor. Review of population based studies in India shows increasing mean total cholesterol levels. Recent studies have reported that high cholesterol is present in 25–30% of urban and 15–20% rural subjects. This prevalence is lower than high-income countries. The most common dyslipidemia in India are borderline high LDL cholesterol, low HDL cholesterol and high triglycerides. Studies have reported that over a 20-year period total cholesterol, LDL cholesterol and triglyceride levels have increased among urban populations. Case-control studies have reported that there is significant association of coronary events with raised apolipoproteinB, total cholesterol, LDL cholesterol and non-HDL cholesterol and inverse association with high apolipoproteinA and HDL cholesterol. Prevalence of suspected familial hypercholesterolemia in urban subjects varies from 1:125 to 1:450. Only limited studies exist regarding lipid abnormalities in children. There is low awareness, treatment and control of hypercholesterolemia in India.

HDL functionality in South Asians as compared to white Caucasians

BACKGROUND AND AIMS

South Asians have an exceptionally high risk of developing cardiovascular disease compared to white Caucasians. A contributing factor might be dysfunction of high density lipoprotein (HDL). We aimed to compare HDL function in different age groups of both ethnicities.

METHODS AND RESULTS

HDL functionality with respect to cholesterol efflux, anti-oxidation and anti-inflammation was determined using fasting, apoB-depleted, plasma samples from South Asian and white Caucasian neonates (n = 14 each), adolescent healthy men (n = 12 each, 18-25 y), and adult overweight men (n = 12 each, 40-50 y). Adolescents were subjected to a 5-day high fat high calorie diet (HCD) and adults to an 8-day very low calorie diet (LCD). Additionally, HDL composition was measured in adolescents and adults using (1)H-NMR spectroscopy. Anti-oxidative capacity was lower in South Asian adults before LCD (19.4 ± 2.1 vs. 25.8 ± 1.2%, p = 0.045, 95%-CI = [0.1; 12.7]) and after LCD (16.4 ± 2.4 vs. 27.6 ± 2.7%, p = 0.001, 95%-CI = [4.9; 17.5]). Anti-inflammatory capacity was reduced in South Asian neonates (23.8 ± 1.2 vs. 34.9 ± 1.3%, p = 0.000001, 95%-CI = [-14.6; -7.5]), and was negatively affected by an 8-day LCD only in South Asian adults (-12.2 ± 4.3%, p = 0.005, 95%-CI = [-5.9; -1.2]). Cholesterol efflux capacity was increased in response to HCD in adolescents (South Asians: +6.3 ± 2.9%, p = 0.073, 95%-CI = [-0.02; 0.46], Caucasians: +11.8 ± 3.4%, p = 0.002, 95%-CI = [0.17;0.65]) and decreased after LCD in adults (South Asians: -10.3 ± 2.4%, p < 0.001, 95%-CI = [-0.57; -0.20], Caucasians: -13.7 ± 1.9%, p < 0.00001, 95%-CI = [-0.67; -0.33]). Although subclass analyses of HDL showed no differences between ethnicities, cholesterol efflux correlated best with cholesterol and phospholipid within small HDL compared to other HDL subclasses and constituents.

CONCLUSION

Impaired HDL functionality in South Asians may be a contributing factor to their high CVD risk.

CLINICAL TRIAL REGISTRATION

NTR 2473 (URL: http://www.trialregister.nl/).

Lipoprotein abnormalities in South Asians and its association with cardiovascular disease: Current state and future directions

South Asians have a high prevalence of coronary heart disease (CHD) and suffer from early-onset CHD compared to other ethnic groups. Conventional risk factors may not fully explain this increased CHD risk in this population. Indeed, South Asians have a unique lipid profile which may predispose them to premature CHD. Dyslipidemia in this patient population seems to be an important contributor to the high incidence of coronary atherosclerosis. The dyslipidemia in South Asians is characterized by elevated levels of triglycerides, low levels of high-density lipoprotein (HDL) cholesterol, elevated lipoprotein(a) levels, and a higher atherogenic particle burden despite comparable low-density lipoprotein cholesterol levels compared with other ethnic subgroups. HDL particles also appear to be smaller, dysfunctional, and proatherogenic in South Asians. Despite the rapid expansion of the current literature with better understanding of the specific lipid abnormalities in this patient population, studies with adequate sample sizes are needed to assess the significance and contribution of a given lipid parameter on overall cardiovascular risk in this population. Specific management goals and treatment thresholds do not exist for South Asians because of paucity of data. Current treatment recommendations are mostly extrapolated from Western guidelines. Lastly, large, prospective studies with outcomes data are needed to assess cardiovascular benefit associated with various lipid-lowering therapies (including combination therapy) in this patient population.

Can novel Apo A-I polymorphisms be responsible for low HDL in South Asian immigrants?

Coronary artery disease (CAD) is the leading cause of death in the world. Even though its rates have decreased worldwide over the past 30 years, event rates are still high in South Asians. South Asians are known to have low high-density lipoprotein (HDL) levels. The objective of this study was to identify Apolipoprotein A-I (Apo A-I) polymorphisms, the main protein component of HDL and explore its association with low HDL levels in South Asians. A pilot study on 30 South Asians was conducted and 12-h fasting samples for C-reactive protein, total cholesterol, HDL, low-density lipoprotein (LDL), triglycerides, Lipoprotein (a), Insulin, glucose levels, DNA extraction, and sequencing of Apo A-I gene were done. DNA sequencing revealed six novel Apo A-I single nucleotide polymorphisms (SNPs) in South Asians, one of which (rs 35293760, C938T) was significantly associated with low (<40 mg/dl) HDL levels (P = 0.004). The association was also seen with total cholesterol (P = 0.026) and LDL levels (P = 0.032). This pilot work has highlighted some of the gene-environment associations that could be responsible for low HDL and may be excess CAD in South Asians. Further larger studies are required to explore and uncover these associations that could be responsible for excess CAD risk in South Asians.

The metabolic syndrome: prevalence, associated factors, and impact on survival among older persons in rural Bangladesh

Objectives

To describe the prevalence of the metabolic syndrome (MetS) among older persons in rural Bangladesh, to investigate whether the prevalence varies by age, sex, literacy, marital status, nutritional status and socio-economic status, and to assess the impact of MetS on survival.

Methods

The study consisted of 456 persons who were aged ≥60 years living in a rural area of Bangladesh during July 2003–March 2004. Data were collected through interview, clinical examination, and laboratory tests, and their survival status until 30^th June 2009 was ascertained through the Matlab surveillance system. We defined MetS following the NCEP ATP III criteria, with minor modifications, i.e., presence of any three of the following: hypertension (BP ≥130/85 mm Hg); random blood glucose (RBG) level ≥7.0 mmol/L; hyper-triglyceridemia (≥2.28 mmol/L); low level of HDL-cholesterol (<1.04 mmol/L for men and <1.29 mmol/L for women); and BMI ≥25.0 kg/m². Data were analysed with logistic regressions for the influential factors of MetS, and with Cox models for the association of MetS with the survival status.

Findings

The overall prevalence of MetS was 19.5%, 20.8% in women, and 18.0% in men. Asset-index and nutritional status were independently associated with MetS. During 4.93 years of follow-up, 18.2% died. In the presence of high RBG, MetS has a significant negative effect on survival (69.4% vs 95.2%, log rank p = 0.02).

Conclusion

This study highlights the importance of the metabolic syndrome in rural Bangladesh. Our findings suggest that there is a need for screening programmes involving the metabolic syndrome to prevent diabetes and cardiovascular diseases.

Prevalence of metabolic syndrome in South Asians residing in the United States

AIMS/HYPOTHESIS

The aim of this study was to define the prevalence of the metabolic syndrome and its component risk factors among individuals of South Asian origin living in the United States.

METHODS

We analyzed baseline data from 1,445 participants enrolled in a cohort study investigating risk factors for cardiovascular disease in South Asians. We defined the metabolic syndrome using the International Diabetes Federation criteria for waist circumference (>90 cm for men; >80 cm, women), triglycerides (>150 mg/dL), high-density lipoprotein cholesterol (HDL-C) (<40 mg/dL (men), < mg/dL (women)), blood pressure (>135/80 mmHg), and fasting glucose (>100 mg/dL).

RESULTS

The mean age was 43 +/-10 years, and 30% of participants were women. The prevalence of metabolic syndrome was 27% (31% men vs. 17% women, P < 0.05). Fifty-nine percent of the cohort had high waist circumference (58% men vs. 62% women, P = not significant [N.S.]), 47% had low HDL-C [46% men vs. 48% women (NS)], 19% had elevated triglycerides (23% men vs. 8% women, P < 0.05), 14% had hypertension (16% men vs. 9% women, P < 0.05), and 13% had elevated fasting glucose (18% men vs. 11% women, P < 0.05). The most common metabolic syndrome phenotype is low HDL-C with elevated triglycerides.

CONCLUSIONS

Although the prevalence of the metabolic syndrome is lower than previous reports of South Asians, the prevalence is still unacceptably high despite the presence of protective demographic factors.

The Framingham Heart Study: impact on the prevention and control of cardiovascular diseases in India

India is in the middle of the epidemiological transition, with the burden of disease shifting towards chronic conditions, of which cardiovascular diseases (CVDs) form a major part. Findings from the Framingham Heart Study (FHS) have tremendous potential to circumvent the projected increase in CVD burden in India, as they highlight the importance of measuring risk in individuals and populations, and preventing future onset of disease. The findings of the FHS have stimulated several cross-sectional studies in India documenting a high and increasing burden of CVD risk factors. These have led to policy level changes in the country, in the form of Framework Convention on Tobacco Control ratification, and the National Program on Diabetes, CVD, and Stroke. There is now need for an Indian cohort study on the lines of the FHS, which can more closely evaluate the use of the FHS risk score among Indians and translate FHS findings into the Indian context.

Benefits and difficulties in measuring HDL subfractions and human paraoxonase-1 activity during statin treatment

Dyslipidaemia including decreased high density lipoprotein cholesterol concentration is one of several factors that have been implicated in increased cardiovascular risk. Since their introduction in the 1980s, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have emerged as the one of the best-selling class of medications to date, with numerous trials demonstrating powerful efficacy in preventing cardiovascular diseases. Although statins have been shown to modestly raise or not alter HDL-cholesterol, their effect on HDL subfractions and on HDL-associated enzymes including human paraoxonase-1 (PON1) has not yet been fully explored. This review summarizes the currently available data on the effect of statins on HDL subfractions and on PON1 activity with a particular emphasis on the clinical relevance of these effects. Moreover, methodological problems of HDL subfraction and PON1 activity determinations are also discussed.

The metabolic syndrome and dyslipidemia among Asian Indians: a population with high rates of diabetes and premature coronary artery disease

South Asians have high rates of diabetes and the highest rates of premature coronary artery disease in the world, both occurring about 10 years earlier than in other populations. The metabolic syndrome (MS), which appears to be the antecedent or "common soil" for both of these conditions, is also common among South Asians. Because South Asians develop metabolic abnormalities at a lower body mass index and waist circumference than other groups, conventional criteria underestimate the prevalence of MS by 25% to 50%. The proposed South Asian Modified National Cholesterol Education Program criteria that use abdominal obesity as an optional component and the South Asian-specific waist circumference recommended by the International Diabetes Federation appear to be more appropriate in this population. Furthermore, Asian Indians have at least double the risk of coronary artery disease than that of whites, even when adjusted for the presence of diabetes and MS. This increased risk appears to be due to South Asian dyslipidemia, which is characterized by high serum levels of apolipoprotein B, lipoprotein (a), and triglycerides and low levels of apolipoprotein A1 and high-density lipoprotein (HDL) cholesterol. In addition, the HDL particles are small, dense, and dysfunctional. MS needs to be recognized as a looming danger to South Asians and treated with aggressive lifestyle modifications beginning in childhood and at a lower threshold than in other populations.

Dyslipidemia in South Asian patients

South Asians around the globe have the highest rates of coronary artery disease (CAD). These rates are 50% to 300% higher than other populations, with a higher risk at younger ages. These high rates of CAD are accompanied by low or similar rates of major traditional risk factors. The prevalence of diabetes is three to six times higher among South Asians than Europeans, Americans, and other Asians but does not explain the "South Asian Paradox." A genetic predisposition to CAD, mediated by high levels of lipoprotein(a), markedly magnifies the adverse effects of traditional risk factors related to lifestyle and best explains the South Asian Paradox. Although the major modifiable risk factors do not fully explain the excess burden of CAD, they are doubly important and remain the foundation of preventive and therapeutic strategies in this population. A more aggressive approach to preventive therapy, especially dyslipidemia, at an earlier age and at a lower threshold is clearly warranted.