Univ. Lyon, CarMeN lab, INSERM U1060, INRA U1397, INSA-Lyon, Université Claude Bernard Lyon 1, Villeurbanne, France.
Hospices Civils de Lyon, Department of Nephrology, Centre Hospitalier Lyon-Sud, Pierre-Bénite, France.
Nephrol Dial Transplant. 2017 Dec 1;32(12):2000-2009. doi: 10.1093/ndt/gfx089.
The role of uraemic toxins in insulin resistance associated with chronic kidney disease (CKD) is gaining interest. p-Cresol has been defined as the intestinally generated precursor of the prototype protein-bound uraemic toxins p-cresyl sulphate (p-CS) as the main metabolite and, at a markedly lower concentration in humans, p-cresyl glucuronide (p-CG). The objective of the present study was to evaluate the metabolism of p-cresol in mice and to decipher the potential role of both conjugates of p-cresol on glucose metabolism.
p-CS and p-CG were measured by high performance liquid chromatography-fluorescence in serum from control, 5/6 nephrectomized mice and mice injected intraperitoneously with either p-cresol or p-CG. The insulin sensitivity in vivo was estimated by insulin tolerance test. The insulin pathway in the presence of p-cresol, p-CG and/or p-CS was further evaluated in vitro on C2C12 muscle cells by measuring insulin-stimulated glucose uptake and the insulin signalling pathway (protein kinase B, PKB/Akt) by western blot.
In contrast to in humans, where p-CS is the main metabolite of p-cresol, in CKD mice both conjugates accumulated, and after chronic p-cresol administration with equivalent concentrations but a substantial difference in protein binding (96% for p-CS and <6% for p-CG). p-CG exhibited no effect on insulin sensitivity in vivo or in vitro and no synergistic inhibiting effect in combination with p-CS.
The relative proportion of the two p-cresol conjugates, i.e. p-CS and p-CG, is similar in mouse, in contrast to humans, pinpointing major inter-species differences in endogenous metabolism. Biologically, the sulpho- (i.e. p-CS) but not the glucuro- (i.e. p-CG) conjugate promotes insulin resistance in CKD.
尿毒症毒素在慢性肾脏病（CKD）相关胰岛素抵抗中的作用越来越受到关注。对甲酚已被定义为原型蛋白结合尿毒症毒素对甲酚硫酸盐（p-CS）的肠内生成前体，作为主要代谢物，而在人类中浓度明显较低的对甲酚葡萄糖醛酸（p-CG）。本研究的目的是评估对甲酚在小鼠体内的代谢，并解析这两种对甲酚结合物对葡萄糖代谢的潜在作用。
通过高效液相色谱-荧光法在对照、5/6 肾切除小鼠和腹腔内注射对甲酚或对甲酚葡萄糖醛酸的小鼠血清中测量 p-CS 和 p-CG。通过胰岛素耐量试验评估体内胰岛素敏感性。在存在对甲酚、p-CG 和/或 p-CS 的情况下，通过测量胰岛素刺激的葡萄糖摄取和胰岛素信号通路（蛋白激酶 B，PKB/Akt）的 Western blot，进一步在 C2C12 肌肉细胞上评估体外胰岛素通路。
与人类不同，在人类中 p-CS 是对甲酚的主要代谢物，而在 CKD 小鼠中，两种结合物均有蓄积，并且在给予慢性对甲酚后，两者的浓度相等，但蛋白结合差异很大（对 p-CS 为 96%，对 p-CG 则<6%）。p-CG 对体内或体外胰岛素敏感性均无影响，与 p-CS 联合使用也无协同抑制作用。
与人类相比，两种对甲酚结合物，即 p-CS 和 p-CG，在小鼠中的相对比例相似，这表明内源性代谢存在重大种间差异。从生物学角度来看，只有硫酸盐（即 p-CS）而不是葡萄糖醛酸（即 p-CG）结合物在 CKD 中促进胰岛素抵抗。
