In Diabetic Kidney Disease Urinary Exosomes Better Represent Kidney Specific Protein Alterations Than Whole Urine

Abstract

Background: Predicting or diagnosing underlying kidney disease by analyzing whole urine remains the mainstay of nephrology practice. However, whole urine is a poor compartment to assess many structural changes in the kidney because whole urine contains only a few proteins derived from the kidney itself. Urinary exosomes, on the other hand, which are derived from the kidney, contain proteins secreted by the kidney. We experimentally tested the hypothesis that ‘urinary exosomes more faithfully represent changes in the kidney tissue than whole urine'. A direct comparison between whole urine and urine exosomal levels of two chosen kidney disease markers, gelatinase and ceruloplasmin, was carried out on diabetic kidney disease patients. Methods: Urinary exosomes were separated from whole urine by sequential centrifugation including ultra-centrifugation. Gelatinase activity was measured using fluorosceinated gelatin as the substrate, and ceruloplasmin was measured by sandwich ELISA. A few kidney specimens from patients biopsied for atypical features were histochemically stained for validation of the biochemical results. Results: We found that changes in both, gelatinase (decreased activity) and ceruloplasmin (increased levels), in the urinary exosomes of diabetic kidney patients were in agreement with the alterations of these two proteins in the kidney tissue. In contrast, the levels of these two proteins in whole urine were highly variable and did not correlate with levels in the diabetic kidney tissue. Conclusion: In conclusion, these results confirmed our hypothesis that protein markers in urinary exosomes better reflected the underlying protein changes in the kidney than in whole urine samples.

Matrix Metalloproteinases in Diabetic Kidney Disease

“…A greater understanding of kidney MMPs is still needed to better delineate their pathophysiological role in DKD. Although most of these endopeptidases appear to be increased in human DN and apparently related to tubular atrophy and interstitial fibrosis, it is not certain if the activity and concentrations measured in the urine reflect what is really happening in renal tissue or are the consequence of an increased systemic activity [49]. Moreover, it is not yet established if metalloproteinases upregulation precedes fibrosis or if it is a consequence of this lesion.…”

Urinary Exosomes Contain MicroRNAs Capable of Paracrine Modulation of Tubular Transporters in Kidney

“…The majority of studies concerning urinary exosomes have focused on their potential as biomarkers of disease pathology and progression, including prostate and bladder cancers14151617, but their functional significance is now being addressed. Inter-cellular signalling by exosomes in cultured murine renal epithelial cells was demonstrated for the first time by Street et al 18,.…”

Urinary Extracellular Vesicle

“…[ 13 ] Gudehithlu et al . [ 55 ] found that the measurement of gelatinase in the urinary exosomes was more accurate during the progression of the diabetic nephropathy than the measurement of the whole urine gelatinase. Compared to the whole urine samples, proteins in the urinary exosomes were correlated better with the underlying protein changes in the kidney.…”