Background
The metabolic syndrome (MetS) is an increasing public health challenge and is the most common condition associated with obesity. While MetS is well defined in the adult population, due to the influence of physical growth on metabolic parameters used for diagnosis, it remains challenging to diagnose MetS in adolescents. In the current study we investigated whether plasma acid phosphatase (AP) activity, a lysosomal hydrolase known to be associated with MetS in adults, could function as a robust biomarker for MetS in adolescents as well as adults.

Methods
Plasma AP activity and other metabolic parameters were assessed in plasma of adolescents (N=128) and adults (N=147) with obesity. Regression analysis was performed to investigate correlations between plasma AP activity and MetS determinants in adolescent and adult cohorts separately and combined. Receiver operating characteristic (ROC) curves were generated to determine the ability of plasma AP activity to predict MetS in adolescents, adults and mixed population.

Results
Plasma AP activity was higher in obese adolescents with MetS compared to adolescents without MetS. Additionally, fasting glucose, TAG and HDL independently correlated with plasma AP activity. Similarly, in obese adults as well as in the combined population of adolescents and adults, plasma AP activity was higher compared to controls and had a strong positive correlation with TAG. Finally, plasma AP activity had an AUC of 0.817 (sensitivity: 1.00, specificity: 0.686) in adolescents, 0.689 (sensitivity: 0.884, specificity: 0.441) in adults and 0.706 (sensitivity: 0.596, specificity: 0.773) in the mixed population for predicting the presence of MetS.

Conclusion
Our data suggests that plasma AP activity is associated with MetS and is a robust parameter that could potentially be used to detect MetS in obese adolescent as well as adult subjects.