Association of serum C1q/TNF-Related Protein-9 (CTRP9) concentration with visceral adiposity and metabolic syndrome in humans

BACKGROUND: C1q/TNF-Related Protein (CTRP) family members are novel adipokines that have anti-inflammatory, immunomodulatory, glucose-regulating and vascular effects. However, the metabolic effects of CTRP9 remain unclear in humans. OBJECTIVES: The aims of this study were to investigate whether serum CTRP9 concentrations are associated with glucose tolerance, metabolic parameters and abdominal fat accumulation. In addition, the authors investigated whether the aforementioned effects of CTRP9 are independent of serum adiponectin levels. METHODS: A total of 221 subjects (140 men and 81 women), 25-72 years of age (mean age 46.0 years), were randomly selected from two different study populations. The normal glucose tolerance group (n = 120) was selected from one study population and the prediabetes/type 2 diabetes group (n = 101) was selected from the other study population. Serum CTRP9, total adiponectin concentrations and abdominal fat via computed tomography scan were measured in all subjects. RESULTS: Subjects in the lower serum CTRP9 tertile were older, had metabolically unhealthy profiles and had lower serum total adiponectin levels when compared with subjects in the middle or upper serum CTRP9 tertiles. In addition, serum CTRP9 concentration were inversely correlated with age, blood pressure, fasting glucose, homeostasis model assessment for insulin resistance, total cholesterol, triglyceride and low-density lipoprotein cholesterol levels (all P<0.01) and positively correlated with serum total adiponectin levels (P = 0.03). In terms of abdominal fat accumulation, serum CTRP9 concentrations were inversely correlated with visceral fat amount (P<0.01), but no correlation was observed with subcutaneous fat amount. Finally, serum CTRP9 was inversely associated with the presence of metabolic syndrome, independent of age, sex, body mass index, smoking status, total cholesterol, visceral fat and serum total adiponectin concentrations (odds ratio per 1 s.d. 0.47; 95% confidence interval 0.32-0.70; P<0.01). CONCLUSIONS: Serum CTRP9 concentrations were positively associated with favorable glucose or metabolic phenotypes and absence of metabolic syndrome, independent of serum total adiponectin concentrations.