Abstract

Introduction Kidney fibrogenesis, which is a common final pathway of all renal injuries, leads to progressive loss of kidney graft function, hampers graft survival and remains a major challenge to improve long-term outcomes of kidney transplant recipients (KTR). Biomarkers of extracellular matrix (ECM) turnover may allow timely and non-invasive detection of pathological changes prior to its clinical detection. In the current study, we aimed to investigate cross-sectional and longitudinal associations between PRO-C6, which detects the C-terminal fragment of collagen VI released during deposition in the ECM, and biopsy proven histological changes in KTR of the MECANO Trial. Methods Six-months and 24-months post-transplant, plasma PRO-C6 was measured in adult KTR of the MECANO Trial, which is a 24-month prospective, multicenter, open-label randomized controlled trial aimed to minimize exposure to calcineurin inhibitors. At 6-months, immunosuppression was tapered to either prednisolone (P)/cyclosporine A (CsA), P/mycophenolate sodium (MPS), or P/everolimus (EVL). The P/MPS arm was prematurely halted. The trial continued with the P/CsA (n=89) and P/EVL (n=96) arms. Primary outcomes were kidney fibrosis and inflammation as assessed at 6- and 24-months post-transplant, by biopsy proven collagen staining (picro-sirius red; PSR), Banff interstitial fibrosis/tubular atrophy (IF/TA) score, and tubule-interstitial inflammation (ti-score). Multivariable-adjusted linear regression analyses were performed to study the association of PRO-C6 with PSR, IF/TA score, and ti-score at both 6- and 24- months post-transplant, and delta (difference between both visits; D6-24) PSR, D6-24 IF/TA score, and D6-24 ti-score. Results Mean (standard deviation) plasma PRO-C6 at 6- and 24-months was 9.5 (3.4) and 9.4 (4.3) ng/mL, respectively, without significant differences between both arms. While PSR, IF/TA score, and ti-score at 24-months post-transplant were significantly higher in the P/CsA arm than in the P/EVL arm (P=0.001, 0.03 and 0.01, respectively), plasma PRO-C6 at 24-months post-transplant did not associate with histological changes in neither of both arms. On the other hand, age and sex-adjusted plasma PRO-C6 at 6-months post-transplant, was associated with 6-months post-transplant PSR and IF/TA score (Std. b=0.37 and 0.46, respectively; both P<0.05), and with 24-months ti-score and D6- 24 ti-score (Std. b=0.34 and 0.33, respectively; both P<0.05), among patients of the P/CsA arm, but not among patients of the P/EVL arm. Conclusions Interstitial fibrosis and inflammation were significantly higher in the P/CsA arm. In the P/CsA arm, measurement of plasma levels of the biomarker for collagen type VI formation PRO-C6 —early post-transplant— were positively associated with cross-sectional and longitudinal biopsy proven histological analyses indicative of progressive local inflammation and ECM turnover reflecting pro-fibrotic events, while plasma PRO-C6 measurement at 24-months post-transplant did not relate to contemporaneous histological analyses. This is a promising first step towards non-invasive detection of pro-fibrotic ECM turnover in KTR, early after transplantation.