Serum Cathepsin G Levels and Their Relationship with Glycemic and Inflammatory Markers in Type 2 Diabetes Mellitus

Cathepsin G (CatG), a neutrophil-derived serine protease, contributes to inflammation and vascular remodeling. Dysregulated CatG activity has been implicated in autoimmune and metabolic disorders; however, its role in type 2 diabetes mellitus (T2DM) remains insufficiently characterized. This cross-sectional study investigated serum CatG levels in 76 patients with T2DM and 37 healthy controls. CatG levels were measured using ELISA, and metabolic and inflammatory indices—including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune–inflammation index (SII), and triglyceride-to–high-density lipoprotein cholesterol ratio (TG/HDL)—were assessed. Serum CatG levels were significantly lower in patients with T2DM than in controls (685.6±480.8 vs. 995.4±721.9 pg/mL; p=0.011). In unadjusted analyses, T2DM was negatively associated with CatG levels (B=−309.8; p=0.008); however, this association was no longer statistically significant after adjustment for age, sex, waist circumference, and PLR (p=0.139), indicating attenuation of the crude between-group difference. These findings suggest that baseline demographic and anthropometric imbalances may partly contribute to the observed differences in CatG levels. Serum CatG levels were inversely correlated with HbA1c, fasting plasma glucose, and waist circumference, while no significant associations were observed with inflammatory indices. Despite evidence of low-grade inflammation in T2DM, CatG levels did not parallel NLR, PLR, or SII. Reduced serum CatG levels may therefore be associated with changes in the inflammatory milieu of chronic metabolic disorders rather than with a specific protective or adaptive mechanism. Overall, CatG provides descriptive insight into qualitative aspects of inflammation in long-standing diabetes and warrants further investigation in longitudinal studies.