We studied plasma adiponectin, insulin sensitivity, and insulin secretion before and after oral glucose challenge in normal glucose tolerant, impaired glucose tolerant, and type 2 diabetic first degree relatives of African-American patients with type 2 diabetes.
We studied 19 subjects with normal glucose tolerance (NGT), 8 with impaired glucose tolerance (IGT), and 14 with type 2 diabetes. Serum glucose, insulin, C-peptide, and plasma adiponectin levels were measured before and 2 hours after oral glucose tolerance test. Homeostasis model assessment-insulin resistance index (HOMA-IR) and HOMA-beta cell function were calculated in each subject using HOMA. We empirically defined insulin sensitivity as HOMA-IR<2.68 and insulin resistance as HOMA-IR>2.68.
Subjects with IGT and type 2 diabetes were more insulin resistant (as assessed by HOMA-IR) when compared with NGT subjects. Mean plasma fasting adiponectin levels were significantly lower in the type 2 diabetes group when compared with NGT and IGT groups. Plasma adiponectin levels were 2-fold greater (11.09+/-4.98 vs. 6.42+/-3.3811 microg/mL) in insulin-sensitive (HOMA-IR, 1.74+/-0.65) than in insulin-resistant (HOMA-IR, 5.12+/-2.14) NGT subjects. Mean plasma adiponectin levels were significantly lower in the glucose tolerant, insulin-resistant subjects than in the insulin sensitive NGT subjects and were comparable with those of the patients with newly diagnosed type 2 diabetes. We found significant inverse relationships of adiponectin with HOMA-IR (r=-0.502, p=0.046) and with HOMA-beta cell function (r=-0.498, p=0.042) but not with the percentage body fat (r=-0.368, p=0.063), serum glucose, BMI, age, and glycosylated hemoglobin A1C (%A1C).
In summary, we found that plasma adiponectin levels were significantly lower in insulin-resistant, non-diabetic first degree relatives of African-American patients with type 2 diabetes and in those with newly diagnosed type 2 diabetes. We conclude that a decreased plasma adiponectin and insulin resistance coexist in a genetically prone subset of first degree African-American relatives before development of IGT and type 2 diabetes.