Intracellular complement - the complosome - in immune cell regulation.
BACKGROUND Complement-C1q/TNF-related protein 13 (CTRP13) is a novel adipokine involved in the regulation of energy metabolism. Here, we sought to evaluate serum levels of CTRP13 and adiponectin in patients with type 2 diabetes (T2D) (n = 40) and healthy subjects (n = 40) and also to study the association of CTRP13 levels with diabetes-related indices. METHODS Circulating levels of CTRP13 and adiponectin were measured by enzyme-linked immunosorbent assay (ELISA) in T2D patients (n = 40) and in an age and gender-matched control group (n = 40). The anthropometric assessment and biochemical evaluation were done in all subjects. RESULTS Circulating levels of CTRP13 and adiponectin were significantly lower in T2D patients in comparison with controls ( = 0.025 and p < 0.001, respectively). CTRP13 was inversely correlated with fasting blood sugar (Spearman's = -0.420, p < 0.001), HbA1C (Spearman's = -0.554, p < 0.001), and HOMA-IR (Spearman's = -0.403, p < 0.001). ROC curve analysis showed that CTRP13 might be used as a biomarker for differentiating T2D patients from healthy individuals (area under the curve with 95% confidence intervals = 0.841, 0.752 - 0.929). A CTRP13 level equal to or lower than 0.885 ng/mL was found to be the optimal cutoff (sensitivity = 92.5%, specificity = 70%, Youden Index = 0.625) for differentiating T2D patients from healthy individuals. CONCLUSIONS It appears that CTRP13 is a novel adipokine associated with T2D in humans as its serum level was significantly lower in T2D patients and also was inversely correlated with insulin resistance and FBS in humans.