Establishing Reference Ranges for C1q/TNF-Related protein3 (CTRP3) Levels in Healthy Adults

C1q/TNF-related protein3 (CTRP3), also known as cartonectin, is a novel adipokine that lowers blood glucose levels, reduces triglyceride synthesis, and is protective against liver steatosis in diet-induced obese mice. In this study, we hypothesized that higher levels of serum CTRP3 expression would be correlated with a more favorable metabolic profile in humans.

Fasting serum samples were obtained from 19 healthy patients. For each patient, serum was analyzed in the core laboratory for the following parameters: A1C, insulin, glucose, AST, ALT and lipid panel. Serum CTRP3 levels were measured by ELISA. Results were analyzed using the Student’s t-test and Pearson correlation testing.   

The cohort included 10 men and 9 women with a mean age of 32 ± 7 years (range 23-52), and mean BMI of 21.9 ± 2 kg/m2 (range 18.7-25.4). All patients were healthy, 17/19 had no past medical history and took no medications.  63% were white, and 37% identified as non-white. Baseline metabolic parameters were normal for all patients, with a mean fasting glucose of 74 ±10 mg/dL (range 56-95), mean AST 19 ± 5 IU/L (range 12-28), mean ALT 15 ± 7 IU/L (range 8-39), mean total cholesterol 167 ± 27 mg/dL (range 123-223), mean TGL 74 ±5 mg/dL (range 34-152), mean HDL 62 ± 15 mg/dL (range 30-88), and mean LDL 90 ±22 mg/dL (range 55-144). Mean CTRP3 was 190 ± 40 ng/mL (range 110-240). We found higher levels of CTRP3 expression in women vs. men (210 ± 30 vs. 160 ± 30 ng/mL, p<0.01), and in non-white vs. white patients (220 ± 30 ng/mL vs. 165 ± 30 ng/mL, p<0.001). Patients with higher blood sugars had lower CTRP3 levels, but this trend was not statistically significant (p=0.056). We did not find any other statistically significant correlations between CTRP3 level and any of the metabolic or demographic parameters.

In conclusion, circulating CTRP3 levels are significantly higher in women, suggesting the possibility of hormonal influence. Though CTRP3 levels in healthy adults are not correlated with metabolic parameters, individuals with higher fasting glucose levels have lower CTRP3, and therefore, glucose metabolism dysregulation may cause further abnormalities in circulating CTRP3 levels. Further studies are needed to investigate the relationship that may exist between CTRP3 and blood sugar levels.