An evaluation of Tamm-Horsfall protein glycans in kidney stone formers using novel techniques

Tamm-Horsfall protein (THP) is theorized to play a critical role in preventing kidney stone formation. There is conflicting literature on THP analysis in kidney stone patients; therefore, this study was conducted using sensitive and specific bio-analytical techniques to better understand differences in THP, which play a potential role in nephrolithiasis pathogenesis. THP was isolated from urine samples of 34 male and 19 female kidney stone patients and 30 male and 24 female control subjects using diatomaceous earth. Protein was quantified by Superdex-200 size-exclusion chromatography. Sialic acid was determined by 1,2-diamino-4,5-methylenedioxybenzene high-performance liquid chromatography. Neutral and amino sugars were determined by high pH anion-exchange chromatography (HPAEC) with pulsed amperometric detection. THP N-glycans were derivatized with 2-aminobenzamide (2-AB) and profiled by HPAEC with fluorescence detection. N-glycan structures were confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Results indicate that kidney stone patients had 32% lower protein content compared to controls, while sialic acid content was lower by 29 and 24% in male and female kidney stone patients, respectively, compared to controls. The neutral and amino sugars were also lower by 18 and 20% for male and female kidney stone patients, respectively, compared to controls. All results were statistically significant (p<0.001). These results are supported by 2-AB profiling of THP N-glycans and by MALDI-TOF MS of highly sialylated N-glycans in the range of m/z 3000-6000. This study demonstrates quantitative and qualitative differences in THP, which can be crucial contributing factors for nephrolithiasis.