SDS-PAGE-Based Quantitative Assay for Screening of Kidney Stone Disease

Pathogenesis of kidney stone disease involves nucleation, growth, aggregation, and retention of crystals in the kidney. Biochemical tests for urinary electrolytes cannot specifically identify the formation of stone in the kidney. In human, the mechanism against the formation of kidney stone involves macromolecules, i.e., protein and glycosaminoglycan that are polyanionic molecules with substantial amounts of acidic amino acid residues that inhibit crystal aggregation [1]. Tamm Horsfall glycoprotein (THP) is one of the inhibitors to crystalize aggregation in kidney [2,3].Tamm Horsfall glycoprotein is the most abundant urinary protein in healthy individual [4,5]. It is excreted by the thick ascending limb of the loop of Henle [6]. THP is excreted in urine at a rate of ~50 mg/day and can be influenced by many factors including urine volume, diet, and exercise [7]. THP has a molecular weight of ~85 kDa although inclines to form macroaggregates of several million Daltons [8]. THP is heavily glycosylated by N-linked glycans that account for about 30% of its molecular weight [9]. Kidney stone patients excrete THP molecules lacking terminally linked sialic acid that reduces its inhibitory activity against stone formation [10]. Although reduced urinary THP excretion in stone patients had been documented [11-13], quantitative analysis of THP by using electroimmunodiffusion shown no changes in THP excretion levels between stone patients and healthy subjects [14,15]. Other studies by using radioimmunoassay and ELISA shown that THP excretion was inconsistent or reduced in stone patients [17-19] compared to the healthy subjects [16]. In the studies where analysis of THP was carried out by using SDS-PAGE, Yokomizoi et al. [11] showed that THP intensity in stone patients was lower than that of healthy subjects while Pourmand et al. [20] stated there was no significant difference in THP excretion between the two cohorts. In our earlier study, we had reported that THP can be used to