Division of Nephrology, Endocrinology and Metabolism, Tokai University School of Medicine, Isehara, Japan.
Bone. 2013 Oct;56(2):347-54. doi: 10.1016/j.bone.2013.07.002. Epub 2013 Jul 10.
Recent data suggest that several uremic toxins may contribute to the development of bone abnormalities in chronic kidney disease. p-Cresyl sulfate (PCS), the sulfate conjugate of p-cresol, is a protein-bound uremic toxin associated with the progression of chronic kidney disease, cardiovascular risk, and mortality. However, the effects of PCS on bone metabolism remain unclear. In the present study, we evaluated the toxic effects of PCS on primary mouse osteoblasts, compared with an extensively studied uremic toxin indoxyl sulfate (IS). Pre-treatment of osteoblasts with PCS at 0.125 mM and above significantly decreased parathyroid hormone (PTH)-induced cAMP production in a dose-dependent manner. PCS also induced a significant increase in intracellular production of reactive oxygen species (ROS) at 0.25 mM and above, but not at lower concentrations. PCS at 0.125 mM (a concentration that did not induce significant ROS increase) decreased cell viability by augmenting DNA fragmentation and reducing cell proliferation. Inhibition of JNK and p38 mitogen-activated protein kinase (MAPK) abolished the PCS-induced increase in DNA fragmentation and decrease in cAMP production in osteoblastic cells. Compared with PCS, IS induced ROS production at 0.05 mM but did not reduce cAMP production from 0.05 to 0.5 mM. IS induced decrease in cell viability and increase in DNA fragmentation at 0.5mM only. These results suggest that PCS damages osteoblastic cells through not only increasing ROS production but also activating JNK/p38 MAPKs, which is different from the mechanism of injury by IS. These damages of osteoblasts induced by PCS may play a critical role in impairing bone metabolism in patients with chronic kidney disease in whom PCS accumulates.
最近的数据表明，几种尿毒症毒素可能导致慢性肾脏病患者骨骼异常的发生。对甲酚硫酸盐（PCS）是对甲酚的硫酸盐结合物，是一种与慢性肾脏病进展、心血管风险和死亡率相关的蛋白结合尿毒症毒素。然而，PCS 对骨代谢的影响尚不清楚。在本研究中，我们评估了 PCS 对原代小鼠成骨细胞的毒性作用，并与广泛研究的尿毒症毒素吲哚硫酸酯（IS）进行了比较。PCS 在 0.125mM 及以上浓度时，呈剂量依赖性地显著降低甲状旁腺激素（PTH）诱导的 cAMP 产生。PCS 还在 0.25mM 及以上浓度时显著增加细胞内活性氧（ROS）的产生，但在较低浓度时没有增加。0.125mM 的 PCS（不会引起明显 ROS 增加的浓度）通过增加 DNA 片段化和降低细胞增殖来降低细胞活力。抑制 JNK 和 p38 丝裂原活化蛋白激酶（MAPK）可消除 PCS 诱导的成骨细胞中 DNA 片段化增加和 cAMP 产生减少。与 PCS 相比，IS 在 0.05mM 时诱导 ROS 产生，但在 0.05-0.5mM 时不减少 cAMP 产生。IS 仅在 0.5mM 时诱导细胞活力降低和 DNA 片段化增加。这些结果表明，PCS 通过增加 ROS 产生和激活 JNK/p38 MAPK 来损伤成骨细胞，这与 IS 的损伤机制不同。PCS 诱导的成骨细胞损伤可能在慢性肾脏病患者中发挥关键作用，因为这些患者体内 PCS 积累。
