Effect of secondary hyperparathyroidism serum on endothelial cells and intervention with Klotho

The aim of the present study was to investigate the effect of the serum of patients with secondary hyperparathyroidism (SHPT) on endothelial cells and to examine the protective effect and the possible mechanism of Klotho. A total of three types of mixed serum from 15 patients with SHPT scheduled for parathyroidectomy, 10 chronic kidney disease (CKD) patients at stage 5 without SHPT and 15 healthy volunteers were collected. Initially, human umbilical vein endothelial cells (HUVECs) were incubated in vitro with the three types of serum and levels of proliferation were compared by assessing viable cell numbers with cell counting kit-8 (CCK-8). Subsequently, HUVECs were divided into three groups: Control group (healthy serum medium), SHPT group (SHPT serum) and Klotho treatment group (SHPT serum and Klotho). The proliferative and apoptotic levels of endothelial cells were evaluated by CCK-8 and flow cytometry, respectively. The levels of extracellular signal-regulated kinase (ERK1/2) and phosphorylated forms of ERK1/2 (p-ERK1/2) were detected using western blotting (with or without ERK1/2 inhibitor PD98059). The synthesis of nitric oxide (NO) was measured using the nitrate reduction method. The proliferation of HUVECs was inhibited by the serum from SHPT patients and CKD-5 patients without SHPT and the inhibitory effects of the SHPT serum were the most marked (P<0.05). Inhibition of HUVEC proliferation by SHPT serum occurred in a concentration-dependent manner within a specific range (5-20%; P<0.05) and also in a time-dependent manner within 6-24 h. Proliferation was partly restored and apoptosis was inhibited when 50-100 ng/ml Klotho was added into 10% SHPT serum (P<0.05). At the same time, the expression of p-ERK1/2 was upregulated, which may be inhibited by PD98059. The synthesis of NO was decreased in the SHPT group (P<0.05) and increased following treatment with Klotho (P<0.05). The results of the present study indicated that the proliferation of HUVECs was inhibited by the serum from SHPT patients. Klotho may partly antagonize this effect due to its inhibition of HUVEC apoptosis and upregulation of p-ERK1/2.