Several artificial urine (AU) formulas have been developed to mimic the normal urine. Most of them are protein-free, particularly when secreted proteins (secretome) is to be analyzed. However, the normal urine actually contains a tiny amount of proteins. We hypothesized that urinary proteins at physiologic level play a role in preservation of renal cell biology and function. This study evaluated the effects from supplementation of 0-10% fetal bovine serum (FBS) into the well-established AU-Siriraj protocol on MDCK renal tubular cells. Time to deformation (T_D) was reduced by both native urine and AU-Siriraj without/with FBS compared with complete culture medium (control). Among the native urine and AU-Siriraj without/with FBS, the cells in AU-Siriraj+2.5% FBS had the longest T_D. Supplementation of FBS increased cell death in a dose-dependent manner (but still <10%). Transepithelial electrical resistance (TER) of the polarized cells in the native urine was comparable to the control, whereas that of the cells in AU-Siriraj+2.5% FBS had the highest TER. These data indicate that supplementation of 2.5% FBS into AU-Siriraj can prolong time to deformation and enhance polarization of renal tubular cells. Therefore, AU-Siriraj+2.5% FBS is highly recommended for in vitro study of cell biology and function (when secretome is not subjected to analysis).

中文翻译：

---

与天然尿液相比，体外细胞研究的人工尿液配方优化

已经开发了几种人工尿液 (AU) 配方来模拟正常尿液。它们中的大多数不含蛋白质，特别是在要分析分泌蛋白质（分泌组）时。然而，正常的尿液实际上含有微量的蛋白质。我们假设生理水平的尿蛋白在肾细胞生物学和功能的保存中发挥作用。本研究评估了在完善的 AU-Siriraj 方案中补充 0-10% 胎牛血清 (FBS) 对 MDCK 肾小管细胞的影响。与完全培养基（对照）相比，不含/含 FBS 的天然尿液和 AU-Siriraj 都减少了变形时间 (T _D )。在天然尿液和无/有 FBS 的 AU-Siriraj 中，AU-Siriraj+2.5% FBS 中的细胞具有最长的 T _D. 补充 FBS 以剂量依赖性方式增加细胞死亡（但仍 <10%）。天然尿液中极化细胞的跨上皮电阻 (TER) 与对照相当，而 AU-Siriraj+2.5% FBS 中的细胞具有最高的 TER。这些数据表明，在 AU-Siriraj 中补充 2.5% FBS 可以延长变形时间并增强肾小管细胞的极化。因此，强烈推荐将 AU-Siriraj+2.5% FBS 用于细胞生物学和功能的体外研究（当分泌组不进行分析时）。