p-Cresol and Cardiovascular Risk in Kidney Transplant Recipients

p-Cresol Sulphate (pCS) is a uremic toxin that originates exclusively from dietary sources and has a high plasma level related to chronic kidney disease (CKD) and cardiovascular disease (CVD). The aim of our study was to evaluate the plasma levels of pCS in kidney transplant recipients (KTRs) related to estimated glomerular filtration rate (eGFR), traditional risk factors, cardiovascular clinical events and endothelial progenitor cells (EPCs), bone marrow-derived cells for the vascular repair system. We considered 51 KTRs and 25 healthy blood donors (HBDs). pCs levels were analyzed using high-performance liquid chromatography (HPLC) coupled with mass spectrometry with an electrospray ionization (ESI) (LC/ESI-MS/MS) on a triple-quadrupole; EPCs were analyzed using flow cytometric analysis. eGFR was 52.61 ± 19.9 mL/min/1.73 m2 in KTRs versus 94 ± 21 mL/min/1.73 m2 in HBDs. We did not find differences in pCS levels between KTRs and HBDs. Levels of pCS were inversely related with eGFR in KTRs and pCS levels were significantly lower in KTRs with eGFR <30 mL/min/1.73 m2 versus eGFR >30 mL/min/1.73 m2. Furthermore, there was a difference in pCS levels between eGFR <30 mL/min/1.73 m2 of KTRs compared with HBDs. Levels of pCS were almost significantly influenced by the presence of a previous vascular event and were inversely related with mature EPCs. These findings suggest that KTRs should not have higher CVD risk than HBDs and their physiological vascular repair system appears to be intact. In KTRs the reduction of eGFR also increased pCS levels and reduced EPCs numbers and angiogenesis capacity. In summary, pCS acts as an emerging marker of a uremic state, helping assess the global vascular competence in KTRs.