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Kidney Week

Abstract: PO0051

Predominance of Mitochondrial Protein Composition in Urinary Sediment Enriched with Muddy Brown Granular Casts During Acute Tubular Necrosis

Session Information

Category: Acute Kidney Injury

  • 102 AKI: Clinical, Outcomes, and Trials

Authors

  • Varghese, Vipin, Ochsner Clinical School - University of Queensland, New Orleans, Louisiana, United States
  • Golbus, Megan, Department of Biology, College of Charleston, Charleston, South Carolina, United States
  • Abbruscato, Frank C., Department of Nephrology, Ochsner Clinic Foundation, New Orleans, Louisiana, United States
  • Janech, Michael G., Department of Biology, College of Charleston, Charleston, South Carolina, United States
  • Velez, Juan Carlos Q., Ochsner Clinical School - University of Queensland, New Orleans, Louisiana, United States

Group or Team Name

  • Ochsner Nephrology
Background

Detection of copious number of “muddy” brown granular casts (MBGCs) during microscopic examination of the urinary sediment (MicrExUrSed) is pathognomonic of acute tubular necrosis (ATN). Because hospital laboratories do not properly report MBGCs, nephrologists are required to independently perform MicrExUrSed, a time-consuming and logistically challenging endeavor that requires expertise. Thus, a diagnostic test to identify MBGCs without the performance of MicrExUrSed could prove useful for busy clinicians. We hypothesized that MBGCs-enriched urinary sediment (MBGC-sedi) contains unique proteins that could serve as surrogate and biomarker of ATN.

Methods

MicrExUrSed was performed in specimens from patients with acute kidney injury (AKI) seen for nephrology consultation with a suspected etiology of ATN. Urine specimens from 3 patients containing numerous (>10 casts per low power field) MBGCs were collected and subjected to low-speed centrifugation (100 g) and stored at -80oC. Thawed pellets and urine were proteolytically digested and analyzed by nano-LC tandem mass spectrometry (Orbitrap Fusion Lumos). Proteins were identified by MASCOT and classified by gene ontology.

Results

We identified 1678 proteins (1% false discovery rate) from supernatant and MBGC-sedi combined. Among them, 711 proteins were unique to MBGC-sedi and 27 were unique to the supernatant. Normalized spectral abundance of 242 MBGC-sedi proteins was greater compared to the supernatant (p<0.05) and had proportionally more mitochondrial proteins (17 ± 1% vs. 6 ± 1%, respectively, p=0.0004). Based on spectral counts, the most abundant and unique mitochondrial proteins in all 3 samples included: ATP synthase alpha and beta-subunit, isocitrate dehydrogenase, 60kDa heat shock protein, and aconitate hydratase. Six out of 7 cytochrome proteins identified were unique to MBGC-sedi.

Conclusion

MBGC-sedi contains unique proteins compared to the supernatant. These proteins can serve as a foundation for the search of an ATN biomarker and surrogate for MBGCs detection by MicrExUrSed in patients with AKI. The predominance of mitochondrial proteins in MBGCs-sedi may explain the characteristic brown pigmentation of MBGCs.