Kidney Transplant Recipients with Acute Antibody-Mediated Rejection Show Altered Levels of Matrix Metalloproteinases and Their Inhibitors: Evaluation of Circulating MMP and TIMP Profiles

Abstract

Antibody-mediated rejection (ABMR) remains a major cause of renal graft dysfunction and loss. The histological hallmark of antibody-mediated rejection is progressive tissue damage, in which extracellular matrix turnover plays an important role. This turnover is mainly regulated by matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Recent studies suggest that MMP/TIMP imbalance may favor the progression of renal damage, inflammation, and fibrosis, but the utility of these molecules as a biomarker of antibody-mediated turnover has not been fully explored. We measured plasma MMP and TIMP levels by ELISA in 15 patients with antibody-mediated renal transplant rejection and 12 patients without rejection. There was a significant increase in MMP-1, MMP-2, and MMP-3 concentrations in the plasma of patients with rejection, directly correlating with the severity of different renal lesions. In contrast, TIMP-3 levels were elevated in patients without rejection, showing a negative correlation with the severity of histopathological lesions. The concentrations of these molecules demonstrated good diagnostic capacity for patients with rejection. Our results show that MMP-1, MMP-2, MMP-3, and TIMP-3 could be potential biomarkers of rejection.

Keywords: antibody-mediated rejection; biomarkers; matrix metalloproteases (MMPs); renal graft dysfunction; tissue inhibitors of metalloproteases (TIMPs).

Figure 1

Analysis of plasma levels of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in kidney transplant recipients with and without antibody-mediated rejection (ABMR). (a–c) MMP-1, MMP-2, and MMP-3 levels were significantly increased in ABMR patients compared with NR patients. (g) TIMP-3 levels were significantly higher in NR patients. (d–f) MMP-9, MMP-9/TIMP-1 complex, and TIMP-1 levels did not differ significantly between groups. Data are represented as box plots showing the median and interquartile range. Mann–Whitney U analysis was carried out. Values of p < 0.05 were considered significant. * p < 0.05, ** p < 0.01, ns = not significant.

Figure 2

Analysis of discriminatory capacity of potential biomarkers and their combinations for detecting kidney transplant rejection using ROC curves. (a) ROC curves for individual biomarkers MMP-1, MMP-2, MMP-3, and TIMP-3. (b) ROC curves for combined models MMP-2/TIMP-3 and MMP-1/MMP-2/MMP-3. (c) Combined model including MMP-1 and MMP-3. (d) Combined model including MMP-1, MMP-3, and TIMP-3. The accompanying table presents the odds ratio (OR), positive predictive value (PPV%), sensitivity, specificity, and area under the ROC curve (AUC) with 95% confidence intervals (CI) for each marker and model. Since TIMP-3 levels were decreased in patients with rejection, the test variable was inverted prior to ROC analysis to maintain consistent directionality of the AUC. This transformation only affects the orientation of interpretation and does not alter the discriminative performance of the biomarker.

Figure 3

Spearman’s rank correlation between (a) MMP-9/TIMP-1 complex levels and tubulitis (t), (b) TIMP-3 levels and glomerulitis (g), and (c) MMP-1 levels and peritubular capillaritis (ptc). Each point represents individual sample. Linear regression lines are displayed with corresponding Spearman’s correlation coefficient (Rho) and p-value. Correlations were considered statistically significant at p < 0.05.