Detection and localization of calcium oxalate in kidney using synchrotron deep ultraviolet fluorescence microscopy.

Emmanuel Estève,David Buob,Chantal Jouanneau,Michel Daudon,Slavka Kascakova,Jean-Philippe Haymann,Louise Galmiche,Pierre Ronco,Dominique Bazin,Frédéric Jamme,Matthieu Réfrégiers,Emmanuel Letavernier

doi:10.1107/s1600577521011371

Abstract

Renal oxalosis is a rare cause of renal failure whose diagnosis can be challenging. Synchrotron deep ultraviolet (UV) fluorescence was assayed to improve oxalosis detection on kidney biopsies spatial resolution and sensitivity compared with the Fourier transform infrared microspectroscopy gold standard. The fluorescence spectrum of synthetic mono-, di- and tri-hydrated calcium oxalate was investigated using a microspectrometer coupled to the synchrotron UV beamline DISCO, Synchrotron SOLEIL, France. The obtained spectra were used to detect oxalocalcic crystals in a case control study of 42 human kidney biopsies including 19 renal oxalosis due to primary (PHO, n = 11) and secondary hyperoxaluria (SHO, n = 8), seven samples from PHO patients who received combined kidney and liver transplants, and 16 controls. For all oxalocalcic hydrates samples, a fluorescence signal is detected at 420 nm. These spectra were used to identify standard oxalocalcic crystals in patients with PHO or SHO. They also revealed micrometric crystallites as well as non-aggregated oxalate accumulation in tubular cells. A nine-points histological score was established for the diagnosis of renal oxalosis with 100% specificity (76-100) and a 73% sensitivity (43-90). Oxalate tubular accumulation and higher histological score were correlated to lower estimated glomerular filtration rate and higher urinary oxalate over creatinine ratio.

Highlights

Various conditions may induce high oxalate excretion by the kidneys and subsequent calcium oxalate crystal (CaOxC) deposition in kidney tubules and interstitium, referred to as renal oxalosis (Yuan et al, 1992; Getting et al, 2013)
Synchrotron UV fluorescence emission spectra collected from synthetic samples showed that CaOx had a specific fingerprint centred at 420 nm, separated from aromatic acids autofluorescence [Fig. 1(A)]
After recording a set of UV emission spectra at 275 nm excitation, we found the 420 nm CaOx fluorescence peak identified in synthetic compound [Fig. 1(E)] and the spatial representation of its intensity matched the crystal [Fig. 1(F)]

Summary

Introduction

Various conditions may induce high oxalate excretion by the kidneys and subsequent calcium oxalate crystal (CaOxC) deposition in kidney tubules and interstitium, referred to as renal oxalosis (Yuan et al, 1992; Getting et al, 2013). Renal oxalosis can be due to primary hyperoxaluria (PHO) which is a rare genetic disease that causes recurrent nephrolithiasis, nephrocalcinosis, systemic oxalosis, and endstage renal disease (ESRD) (Cochat & Rumsby, 2013). Clinical course of the disease, oxalate dosage in blood and urine, crystalluria, and genetic findings can lead to accurate diagnosis and treatment (Lieske et al, 2005; Daudon et al, 2008; Zhao et al, 2016). Diagnosis is often missed or delayed by several years and can be challenging in end-stage renal disease patients (Daudon et al, 2008). In 2014, among the 405 patients enrolled in the Rare Kidney Stone Consortium Primary Hyperoxaluria Registry, 112 (27%) patients had reached ESRD at the time or before diagnosis (Zhao et al, 2016). In a previous report of the registry, oxalosis was even diagnosed after recurrence on the transplant in seven out of 95 patients (Lieske et al, 2005)

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Conclusion