South Asians (SA), the fastest growing major ethnic group in the U.S., are also at greater type 2 diabetes (T2DM) and cardiovascular disease (CVD) risk at relatively lower body mass index (BMI) compared to those of European and African ancestry. The mechanism(s) underlying this increased cardiometabolic risk remain undefined. We are submitting this research proposal in response to an NIH program announcement (PA-17-021) requesting proposals addressing health disparities in NIDDK diseases. The increased cardiometabolic risk in SA Americans represent an understudied and disparate risk. Mostly adult, associative studies performed outside the U.S. indicate that SA have higher % body fat, visceral adiposity, and abdominal adiposity for a given BMI than other ethnic groups. These studies have also found increased insulin resistance and dyslipidemia as well as decreased insulin-mediated glucose disposal (inversely proportional to visceral fat) and ?-cell function in SA adults. We propose to study SA adolescents, in order to elucidate early mechanistic changes underlying their increased cardiometabolic risk. Given the unique fat distribution of SA, we propose to define ectopic fat deposition and test for altered fat metabolism and ?-cell insulin secretion in SA adolescents in the U.S. We will use cutting-edge, innovative techniques, including MRI/MRS, mathematical modeling of free fatty acid (FFA) kinetics, and the glucose-potentiated arginine test (GPA) to measure insulin secretory capacity, methods not previously used in SA adolescents. We have assembled a highly experienced, multi-institutional (CNMC, CHOP, NIH), and multi-disciplinary team with a track record of successful collaboration, to perform a cross-sectional study of 12-21 year old adolescents and young adults of SA ancestry (n=50), BMI ? 85%ile, compared to adolescents of European ancestry (White) (n=50) and African American (AA) ancestry (n=50) of comparable age, sex, and BMI %ile. AA individuals are known to also have increased cardiometabolic risk but have decreased visceral adiposity, making them a unique comparison group.
Aims : 1. To examine ancestry-related differences in body fat distribution (by MRI/MRS), FFA flux (by 3-hour oral glucose tolerance test and Minimal Model of fatty acid kinetics), and to compare the relationships between visceral adiposity and FFA flux among ancestral groups. 2. To examine ancestry-related differences in ?-cell insulin secretory capacity (by GPA), and compare the relationship between FFA flux and insulin secretory capacity among groups. 3. To compare CVD and T2DM risk factors and vascular end organ injury (aortic pulse wave velocity) among the three groups, and test for ancestry-related differences in the relationships between FFA flux and cardiometabolic risk profile. Exploratory Aim: to compare adipocyte-derived exosomal microRNAs involved in insulin signaling among the groups, and measure their association with ?-cell insulin secretory capacity, for hypothesis generation. Thus, this proposal will investigate whether associations between ectopic fat, FFA flux, and ?-cell secretion vary by ancestry to impact cardiometabolic risk, with the expectation that this may eventually lead to ancestry-specific treatment options.

Public Health Relevance

South Asians (SA) (those with ancestral roots in India, Pakistan, the Maldives, Bhutan, Nepal, Bangladesh, and Sri Lanka) are the fastest growing major ethnic group in the U.S., nearly doubling in numbers between 2000 and 2013. SA also have increased type 2 diabetes and cardiovascular disease risk at relatively lower body mass index compared to other ethnicities, but the mechanism(s) underlying this increased risk are not known. This study will investigate the possible connections between altered body fat distribution, fatty acid metabolism, and insulin secretion in SA compared to those of African American and European ancestries, to look for differences which in the future, may have implications for ancestry-specific treatments of disease.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Clinical and Integrative Diabetes and Obesity Study Section (CIDO)
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Linder, Barbara
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Johns Hopkins University
Schools of Medicine
United States
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