Restoration of Epithelial Sodium Channel Function by Synthetic Peptides in Pseudohypoaldosteronism Type 1B Mutants.

The synthetically produced cyclic peptides solnatide (a.k.a. TIP or AP301) and its congener AP318, whose molecular structures mimic the lectin-like domain of human tumor necrosis factor (TNF), have been shown to activate the epithelial sodium channel (ENaC) in various cell- and animal-based studies. Loss-of-ENaC-function leads to a rare, life-threatening, salt-wasting syndrome, pseudohypoaldosteronism type 1B (PHA1B), which presents with failure to thrive, dehydration, low blood pressure, anorexia and vomiting; hyperkalemia, hyponatremia and metabolic acidosis suggest hypoaldosteronism, but plasma aldosterone and renin activity are high. The aim of the present study was to investigate whether the ENaC-activating effect of solnatide and AP318 could rescue loss-of-function phenotype of ENaC carrying mutations at conserved amino acid positions observed to cause PHA1B. The macroscopic Na+ current of all investigated mutants was decreased compared to wild type ENaC when measured in whole-cell patch clamp experiments, and a great variation in the membrane abundance of different mutant ENaCs was observed with Western blotting experiments. However, whatever mechanism leads to loss-of-function of the studied ENaC mutations, the synthetic peptides solnatide and AP318 could restore ENaC function up to or even higher than current levels of wild type ENaC. As therapy of PHA1B is only symptomatic so far, the peptides solnatide and AP318, which directly target ENaC, are promising candidates for the treatment of the channelopathy-caused disease PHA1B.

人工合成的环肽索拉肽（又名TIP或AP301）及其同类物AP318，其分子结构模拟人肿瘤坏死因子（TNF）的凝集素样结构域，在多项基于细胞和动物的研究中已被证明可激活上皮钠通道（ENaC）。ENaC功能缺失会导致一种罕见的、危及生命的失盐综合征，即1B型假性醛固酮减少症（PHA1B），其表现为发育不良、脱水、低血压、厌食和呕吐；高钾血症、低钠血症和代谢性酸中毒提示醛固酮减少，但血浆醛固酮和肾素活性较高。本研究的目的是探讨索拉肽和AP318对ENaC的激活作用是否能够挽救在导致PHA1B的保守氨基酸位置发生突变的ENaC的功能缺失表型。在全细胞膜片钳实验中测量时，所有研究的突变体的宏观Na⁺电流与野生型ENaC相比均降低，并且通过蛋白质印迹实验观察到不同突变型ENaC的膜丰度存在很大差异。然而，无论何种机制导致所研究的ENaC突变功能缺失，人工合成的肽索拉肽和AP318都能够将ENaC功能恢复到甚至高于野生型ENaC的当前水平。由于到目前为止PHA1B的治疗仅仅是对症治疗，直接作用于ENaC的索拉肽和AP318是治疗由通道病引起的疾病PHA1B的有希望的候选药物。