Adiponectin and TNF-Alpha Differentially Mediate the Association Between Cystatin C and Oxidized LDL in Type 2 Diabetes Mellitus Patients

Abstract

In individuals with type 2 diabetes mellitus (T2DM), elevated levels of both plasma and urinary cystatin C (Cys-C) contribute to increased oxidation, which in turn accelerates the oxidation of low-density lipoprotein (LDL). This process may worsen the development of atherosclerosis and cardiovascular disease by promoting endothelial dysfunction and inflammation. Despite its potential significance, the relationship between Cys-C and oxidized LDL (ox-LDL) in T2DM remains poorly understood. This study investigated the relationship between plasma and urinary Cys-C and ox-LDL levels in T2DM patients. The cohort included 57 patients with T2DM (mean age 61.14 ± 9.99 years; HbA1c 8.66 ± 1.60% and BMI 35.15 ± 6.65 kg/m²). Notably, 95% of the patients had hypertension, 82% had dyslipidemia, 59% had an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m², 14% had coronary artery disease (CAD), and 5% had a history of stroke. Plasma and urinary Cys-C and ox-LDL levels were measured using ELISA. Adipokine and cytokine levels were measured using the multiplex^® MAP Human Adipokine Magnetic Bead Panels. Spearman's correlation analysis revealed a significant positive correlation of plasma and urinary Cys-C with ox-LDL (r = 0.569, p = 0.0001 and r = 0.485, p = 0.0001, respectively). Multivariable regression analysis indicated that both plasma and urinary Cys-C were independently associated with ox-LDL, after adjusting for confounding factors (β = 0.057, p = 0.0001 and β = 0.486, p = 0.003, respectively). Stepwise linear regression identified TNFα and adiponectin as the strongest predictors of the relationship between urinary Cys-C and ox-LDL (β = 0.382, p = 0.0001; r² = 0.64), while adiponectin alone was the best predictor of the plasma Cys-C and ox-LDL association (β = 0.051, p = 0.005; r² = 0.46). Furthermore, adiponectin partly mediated the relationship between plasma Cys-C and ox-LDL, explaining 18% of the variance in this association. In contrast, TNFα partly mediated the relationship between urinary Cys-C and ox-LDL, accounting for 28% of the variance. This study emphasizes the complex interaction between Cys-C and ox-LDL in T2DM. It highlights the need for additional research involving larger patient cohorts to improve our understanding of the therapeutic potential of plasma and urinary Cys-C in conjunction with ox-LDL for managing complications associated with T2DM.

Keywords: adipokines; atherosclerosis; cystatin C; cytokines; diabetes; dyslipidemia; endothelial dysfunction; inflammation; insulin resistance; obesity; oxidized LDL; vascular complications.

Figure 1

Plasma Cys-C, urinary Cys-C, and ox-LDL levels were measured using ELISA in patients with T2DM. The plasma Cys-C, urinary Cys-C, and ox-LDL distribution frequencies were calculated for the study cohort (A–C). The correlations between plasma Cys-C, urinary Cys-C, and ox-LDL were assessed using Spearman’s correlation analysis (D–F).

Figure 2

Estimation of the proportion of associations between plasma and urinary Cys-C and ox-LDL mediated by adiponectin (A) or TNF-α (B). Each moderator (adiponectin or TNF-α) was entered individually into the regression model using the PROCESS macro software developed by Andrew F. Hayes (Model 4). The bootstrapping method estimated the confidence interval (CI) of the mediating effect. A p-value of ≤0.05 is considered significant.