Kidney Week

Abstract: TH-PO973

A Circadian Pattern in Urine Exosome Excretion Is Not Influenced by Sex or Food-Water Deprivation: Implications for Biomarker Normalization

Session Information

• Pathology and Lab Medicine: Basic
  October 25, 2018 | Location: Exhibit Hall, San Diego Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Pathology and Lab Medicine

• 1501 Pathology and Lab Medicine: Basic

Authors

• Koritzinsky, Erik H., National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland, United States

Erik H. Koritzinsky,

• Street, Jonathan, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland, United States

Jonathan Street,

• Star, Robert A., National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland, United States

Robert A. Star,

• Yuen, Peter S.T., National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland, United States

Peter S.T. Yuen,

Background

Urine exosomes are extracellular vesicles released by all cells along the nephron and represent a promising source of non-invasive biomarkers. Many candidate urine exosomal biomarkers have been described, yet none have reached clinical use, in part because how to normalize them is unknown, as urine flow rate or concentration can vary by over an order of magnitude. We previously showed that urine exosome excretion displays a circadian pattern in male rats (peak at 21:00), but little is known about what factors modulate urine exosome release.

Methods

Timed urine samples from healthy rats (n=6M, 6F) were collected over 24 hr in six 4-hr fractions. A subset of these rats (n=4) underwent a second matched 24 hr collection with 13 hr of food and water deprivation spanning the full dark (active) period. Urine exosomes were isolated by ultracentrifugation and counted by Nanoparticle Tracking Analysis.

Results

24 hr urine exosome excretion varied widely between animals (CV=71%). To study the circadian pattern, variability was reduced by normalizing exosome excretion for each fraction to the peak excretion rate for each animal. Normalized urine exosome excretion displayed a similar circadian pattern in both male and female rats. There was no correlation between urine exosome excretion and urine flow rate (Male: r²=0.004, Female: r²=0.04). Food-water deprivation had no detectable impact on exosome excretion but significantly increased exosome concentration 13-17 hr after removal of food and water (p=0.03), likely due to decreased urine output.

Conclusion

Urine exosome excretion displays a distinct circadian pattern that complicates the measurement of urine exosomal biomarkers. The observed pattern in urine exosome excretion was neither sex specific nor affected by food-water deprivation. Spot urine concentration of exosomal biomarkers can be normalized by exosome concentration. This adjusted measure of biomarker content per exosome appears to be independent of time of collection, sex or food-water intake. Proper exosomal biomarker normalization will be essential in advancing promising candidates to clinical use and can uncover patterns otherwise obscured by natural biological variation, increasing their clinical utility and enabling the reliable use of spot urine measurements instead of timed collections.

Funding

• NIDDK Support