Urinary macromolecules and renal tubular cell protection from oxalate injury: Comparison of normal subjects and recurrent stone formers

Aim: To determine whether urinary macromolecules (UMM), which are the high molecular weight substances in urine, can provide protection against the oxalate‐associated injury to the renal tubular cells. Methods: UMM were extracted from 24‐h urine of 12 healthy adult male volunteers and 13 recurrent‐stone‐former male patients. Urine parameters in relation to urolithiasis were measured, including the level of glycosaminoglycans (GAG) in the UMM. Madin‐Darby canine kidney (MDCK) cells were used to evaluate the protective activity of UMM from oxalate‐induced cytotoxicity by LDH release measurement and methyl‐thiazolyl tertrazolium (MTT) assay. Results: Considering urinary parameters, citrate was significantly higher in urine from normal subjects than stone‐former subjects; the other parameters show no differences between the groups. Total UMM and the level of GAG in the UMM were also significantly higher in the normal subject group. Compared with normal subject and stone‐former subject UMM, after cells were treated with the UMM and then exposed to oxalate solution, LDH release was significantly higher in stone‐former group. In the MTT assay, we found that more viable cells were observed after treatment with UMM compared to control in both groups. Moreover, UMM from the normal subjects showed higher protective activity against oxalate‐related cytotoxicity than UMM from the stone‐former subjects. Conclusion: UMM protected renal epithelial cells from oxalate‐related injury. This protective activity was found to be higher in normal subject UMM than stone‐former UMM. Among other factors, a higher concentration of GAG and citrate in normal subject UMM might affect some parts in this finding.