Pathobiology and Reversibility of Prediabetes in a Biracial Cohort

The Pathobiology and Reversibility of Prediabetes in a Biracial Cohort (PROP-ABC) study is following an extant cohort of 376 initially normoglycemic African American and Caucasian offspring of parents with type 2 diabetes for an additional 5years. The subjects were enrolled between 2006 and 2009 and have been followed up to 2012, during which 10 have developed diabetes and 101 developed prediabetes, without evidence of racial disparities.

The objectives of PROP-ABC are to gain a fuller understanding of the natural history and predictors of early glucose abnormalities, determine the role of race during the second wave of glycemic progression, and to access the time dependency of reversibility of prediabetes. The study tests 4 hypotheses: 1) Among offspring of parents with type 2 diabetes, early progression from normal to impaired glucose regulation (within 5 yr) occurs in the highest-risk subjects independently of race, whereas late progression (5-10 yr) displays racial disparities, and is predicted by physiological, biochemical and behavioral markers; 2) Early microvascular complications, peripheral vascular disease (PVD), and endothelial dysfunction manifest during transition from normal to impaired glucose regulation, display racial disparities, and are predicted by glycemic and nonglycemic factors; 3) The "metabolically healthy" insulin-sensitive obese (ISO) phenotype displays racial disparities in its association with cardiometabolic risk factors and incident dysglycemia among African-Americans and Caucasians offspring of parents with type 2 diabetes; and 4) Duration of the prediabetic state is a major determinant of, and is inversely related to, the efficacy of lifestyle intervention to induce regression of the prediabetic phenotype and restoration of normal glucose regulation. Participants with prediabetes and others who develop prediabetes during PROP-ABC will receive Intensive Lifestyle intervention (ILI).

We define duration of prediabetes as the interval from date of confirmed prediabetes to the date of initiation of ILI, stratified to 3 prediabetes intervals: a) <1 yr, b) 1 to <3 yr, c) 3-6 yr. The primary outcome measure is restoration of normal glucose regulation (fasting plasma glucose <100 mg/dl and 2-hour post-load plasma glucose < 140 mg/dl). Secondary endpoints include normalization of either fasting plasma glucose or 2-hour post-load plasma glucose , occurrence of diabetes, insulin sensitivity and secretion. Data will be analyzed according to the "intention to treat" principle. Based on power calculations, a sample size of 150 subjects (50/prediabetes interval) would allow detection of medium to large effect off ILI with ~85% power. Kaplan-Meier survival curves will be generated for the 3 prediabetes intervals, and log-rank test will be used to analyze the time to occurrence of primary outcome. The prospective PROP-ABC, designed to identify new cases of prediabetes as they occur, is uniquely placed to test the time dependency of reversibility of incident prediabetes.

Inclusion criteria

• As planned these studies will enroll interested persons from among the group of 376 subjects who participated in the Pathobiology of Prediabetes in a Biracial Cohort (POP-ABC) study between 2006 and 2012. That group includes 267 women and 109 men; 217 are African Americans and 159 are Caucasians. At the time of initial enrollment into POP-ABC, these participants were selected for being nondiabetic offspring of parents with type 2 diabetes. Race and ethnicity was by self-report of non-Hispanic white or non-Hispanic black heritage, and their age range was 18-65 years at enrollment. No new subjects will be recruited into this established cohort. To be eligible for inclusion in the renewal study, subjects must be ambulatory, be in good general health, and must not be taking medications known to alter insulin sensitivity, insulin secretion, or body weight.

Exclusion criteria

• Exclusion criteria: Persons not enrolled in POP-ABC study; diagnosis of diabetes or use of any antidiabetic medication; medical conditions that preclude participation in physical activity; history of liposuction, surgical weight reduction; use of glucocorticoids, beta-blockers, thiazide diuretics (> 25 mg/day), or medication known to alter glucose metabolism. Women who are pregnant or become pregnant while participating in this study will have all testing procedures delayed until 12 months after delivery.