Complement Factor 3 is associated with insulin resistance and with incident type 2 diabetes mellitus over a 7-year follow-up period: the CODAM study

OBJECTIVE - Immune dysregulation can affect insulin resistance (IR) and b-cell function and hence contribute to development of type 2 diabetes mellitus (T2DM). The complement system, as a regulator of immune and inflammatory homeostasis, may be a relevant contributor therein. However, longitudinal studies focusing on complement as a determinant of T2DMand IR are scarce. Therefore, we prospectively investigated the association of plasma complement factor 3 (C3) with (estimates of) IR in muscle, liver, and adipocytes, as well as with glucose tolerance, including incident T2DM. RESEARCH DESIGN AND METHODS - Fasting C3, nonesterified fatty acids, glucose, and insulin (the latter two during oral glucose tolerance tests) weremeasured at baseline (n = 545) and after 7 years of follow-up (n = 394) in a prospective cohort study. RESULTS - Over the 7-year period, C3 levels (per 0.1 g/L) were longitudinally associated with higher homeostasis model assessment of IR (HOMA2-IR; b = 15.2% [95% CI 12.9–17.6]), hepatic IR (b = 6.1%[95% CI 4.7–7.4]), adipocyte IR (b = 16.0% [95%CI 13.0–19.1]), fasting glucose (b = 1.8% [95% CI 1.2–2.4]), 2-h glucose (b = 5.2% [95% CI 3.7–6.7]), and area under the curve for glucose (b = 3.6% [95% CI 2.7–4.6]). In addition, greater changes in C3 (per 0.1 g/L) were associated with greater changes in HOMA2-IR (b = 0.08 [95% CI 0.02–0.15]) and greater changes in hepatic IR (b = 0.87 [95% CI 0.12–1.61]) over 7 years, but not glucose tolerance. Moreover, baseline C3 was associated with the 7-year incidence of T2DM (odds ratio 1.5 [95% CI 1.1–2.0]). CONCLUSIONS - Changes in C3 were associated with changes in several measures of IR and may reflect progression of metabolic dysregulation, which eventually leads to abnormalities in glucose tolerance and T2DM.