Establishing a Cut-Off Value for Zinc Alpha-2 Glycoprotein in Serum as a Potential Biomarker in Children and Adolescents with Obesity

Zinc-α2-glycoprotein (ZAG) is a novel adipokine with a plethora of functions meaningful for the regulation of adipose tissue and insulin sensitivity. Despite research, the role of ZAG in the course of childhood obesity is not fully understood. The aim of this study is to investigate whether the levels of ZAG can be used as a predictive or monitoring biomarker of adolescent obesity. Secondly, to determine the cut-off value of ZAG in blood serum in adolescents with obesity. The study included a group of 77 adolescent patients, including 59 obese patients, and 18 without obesity as healthy control subjects. All study participants had their biochemical parameters assessed by a certified medical laboratory. The recommendations of the Polish Society of Hypertensions were used to assess the blood pressure measurements in each group. ELISA enzyme immunoassays (R&D Systems, Minneapolis, MN, USA) were used to detect serum levels of ZAG. Our study showed that obese children and adolescents have significantly higher body mass, cholesterol, LDL-cholesterol, triglycerides (TG), systolic blood pressure (SBP) and diastolic blood pressure (DBP), but lower serum ZAG levels compared to the healthy control subjects. Furthermore, in our study, we found that median ZAG values were comparable between females and males within the same obesity category (median female ZAG level: 2.84, median male ZAG level: 2.89) and healthy control participants (median female ZAG level: 5.20, median male ZAG level: 4.99). Serum ZAG concentrations were significantly lower in obese participants (2.86 ± 0.40 mg/L) than in the control group (5.10 ± 0.74 mg/L; p < 0.001). The multivariable Firth’s logistic regression model, incorporating the selected factors, revealed a significant association between obesity and ZAG. ROC curve analysis indicated strong discriminatory ability of ZAG for identifying obesity, with a proposed cut-off value of 3.62 mg/L. Circulating ZAG level is significantly reduced in children and adolescents with obesity. An important finding of our study is the detection of a cutoff value for serum ZAG levels. Furthermore, the use of the Least Absolute Shrinkage and Selection Operator (LASSO) model can be considered a valuable contribution to defining ZAG as an independent factor associated with obesity.