Calcium oxalate kidney stones, where is the organic matter?: A synchrotron based infrared microspectroscopy study

Abstract

Kidney stones are collections of microcrystals formed inside the kidneys, which affect 6% to 12% of the population worldwide, with an increasing recurrence (50%-72%) after the first episode. The most abundant type is calcium oxalate (66%), described as monohydrated (COM) and dihydrated (COD). An issue in their chemistry is the transformation process of the metastable specie (COD) into the stable one, which is chemically, and in appearance, monohydrated. Since the origin of these species is different, it is important to differentiate between the transformation stage (and what stabilize COD) to understand the physiopathology and prevent the patients' recurrence. This work focuses on the organic matter distribution along these nephroliths by synchrotron radiation-based infrared microspectroscopy. Differences in the asymmetric stretching of the aliphatic hydrocarbons suggest that lipids may participate in the stabilization of COD and as inhibitors of COM formation/development; however, the presence of proteins in the nucleus could indicate a promoting role.

Kidney stone growth through the lens of Raman mapping

“…Chemical mapping using Raman microscopy has long been used to better understand the growth and function of biomineral systems including bones 1 , 2 , teeth 3 , 4 , and, more recently, kidney stones (urinary calculi) 5 – 8 . Compositional and/or structural maps of urinary calculi have been produced using micro computed tomography (µCT) 6 – 15 , fluorescence microscopies 6 – 8 , electron microscopies 6 , 7 , 16 , 17 , optical microscopies 6 – 8 , 18 , multi-photon spectroscopy 19 , infrared microscopy 20 – 22 , and Raman microscopy 5 – 8 . Micro computed tomography allows complete volume imaging of intact stones but has limited voxel resolution of 2–5 µm depending on stone size 14 .…”

“…Multiphoton spectroscopy provides mineral phase identification but requires specialized laser systems 19 . Reflectance-mode infrared microscopy offers similar vibrational information as Raman spectroscopy but spatial resolution is limited to > 5 µm by the diffraction limit of infrared light 22 or the size of attenuated total reflectance probes 23 . In contrast, commercially available Raman microscopes can map with spatial resolution < 1 µm while providing direct identification of minerals through their vibrational signatures.…”