^*Division of Endocrinology, Diabetes, and Metabolism, Department of Internal Medicine, The Ohio State University College of Medicine and Public Health, Columbus, Ohio

Correspondence: Kwame Osei, Division of Endocrinology, Diabetes, and Metabolism, Department of Internal Medicine, 491 McCampbell Hall, The Ohio State University College of Medicine and Public Health, Columbus OH 43210. E-mail: osei-1@medctr.osu.edu

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Received 18 November 2003; Accepted 8 November 2004.

Abstract

Objective: 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.

Research Methods and Procedures: 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- 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.

Results: 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 g/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- 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).

Discussion: 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.