Plasma phosphate (P_i) levels are tightly controlled, and elevated plasma P_i levels are associated with an increased risk of cardiovascular complications and death. Two renal transport proteins mediate the majority of P_i reabsorption, the Na⁺-phosphate cotransporters Npt2a and Npt2c, with Npt2a accounting for 70-80% of P_i reabsorption. The aim of this study was to determine the in vitro effects of a novel Npt2a inhibitor (Npt2a-I, PF-06869206) in opossum kidney (OK) cells as well as determine its selectivity in vivo in Npt2a knockout (Npt2a^-/-) mice. In OK cells, Npt2a-I caused dose-dependent reductions of Na⁺-dependent P_i uptake (IC₅₀: ~1.4 μmol/L), while the unselective Npt2 inhibitor phosphonoformic acid (PFA) resulted in a ~20% stronger inhibition of P_i uptake. The dose-dependent inhibitory effects were present after 24-hour incubation with both low and high P_i media. Michaelis-Menten kinetics in OK cells identified a ~2.4-fold higher K_m for P_i in response to Npt2a inhibition with no significant change in apparent V_max. Higher PTH concentrations decreased P_i uptake equivalent to the maximal inhibitory effect of Npt2a-I. In vivo, the Npt2a-I induced a dose-dependent increase in urinary P_i excretion in wild-type mice (ED₅₀: ~23 mg/kg), which was completely absent in Npt2a^-/- mice, alongside a lack of decrease in plasma P_i. Of note, the Npt2a-I-induced dose-dependent increase in urinary Na⁺ excretion was still present in Npt2a^-/- mice, a response possibly mediated by an off-target acute inhibitory effect of the Npt2a-I on open probability of the epithelial Na⁺ channel, ENaC, in the cortical collecting duct.

中文翻译：

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PF-06869206 是一种选择性肾磷转运抑制剂：来自体外和体内研究的证据。

血浆磷酸盐 (P _i ) 水平受到严格控制，血浆 P _i水平升高与心血管并发症和死亡风险增加有关。两种肾转运蛋白介导了大部分的 P _i重吸收，即 Na ⁺ -磷酸盐协同转运蛋白 Npt2a 和 Npt2c，其中 Npt2a 占 P _i重吸收的70-80% 。本研究的目的是确定一种新型 Npt2a 抑制剂（Npt2a-I，PF-06869206）在负鼠肾 (OK) 细胞中的体外作用，并确定其在 Npt2a 敲除 (Npt2a ^-/- )中的体内选择性老鼠。在 OK 细胞中，Npt2a-I 引起 Na ⁺依赖性 P _{i 的}剂量依赖性降低摄取 (IC ₅₀ : ~1.4 μmol/L)，而非选择性 Npt2 抑制剂膦甲酸 (PFA) 对 P _i摄取的抑制作用更强~20% 。与低和高 P _i培养基孵育 24 小时后出现剂量依赖性抑制作用。OK 细胞中的 Michaelis-Menten 动力学确定了 P _{i 的}K _m高约 2.4 倍，以响应 Npt2a 抑制，而表观 V _max没有显着变化。较高的 PTH 浓度降低了 P _i摄取，相当于 Npt2a-I 的最大抑制作用。在体内，Npt2a-I 诱导野生型小鼠尿 P _i排泄的剂量依赖性增加（ED ₅₀: ~23 mg/kg)，在 Npt2a ^-/-小鼠中完全不存在，同时血浆 P _i没有减少。值得注意的是，Npt2a-I 诱导的尿 Na ⁺排泄的剂量依赖性增加仍然存在于 Npt2a ^-/-小鼠中，这种反应可能是由 Npt2a-I 对开放概率的脱靶急性抑制作用介导的。皮层集合管中的上皮 Na ⁺通道 ENaC。