Citations

The microbiologic nature of self‐replicating, calcifying entity nanoparticles (NPs) isolated from calcified human tissues, including blood vessels and kidney stones is debated because of the difficulty in discriminating minerals precipitated on microbes from minerals nucleated on macromolecules and cell membranes. To begin to resolve this controversy, calcifying bacteria of aquatic origin ( Caulobacter crescentus ) and NPs cultured from human samples were examined using a Scanning Transmission X‐ray Microscope (STXM). The monochromated soft X‐ray beam (150–2000 eV) produced by synchrotron radiation yields microscopic and spectroscopic information on both organic compounds and minerals at the 25 nm scale. High‐spatial and energy resolution Near‐Edge X‐ray Absorption Fine Structure (NEXAFS) spectra indicative of elemental speciation acquired at the C K‐edge and Ca L 2,3 ‐edge on a single‐cell scale from calcified C. crescentus displayed a unique spectral signature different from non‐biologic hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ). Preliminary NEXAFS measurements of calcium and carbon functional groups of cultured NPs revealed organics associated with hydroxyapatite minerals and in one case, spectroscopic signatures similar to those identified in C. crescentus . Using NEXAFS, it is possible to define a biochemical signature of proteins, polysaccharides, nucleic acids, and hydroxyapatite for cultured calcified bacteria suggesting that NPs isolated from human samples share spectroscopic characteristics with calcifying bacteria.

Introduction The earliest lesion in the kidneys of idiopathic calcium oxalate stone formers is deposition of calcium phosphate in the interstitium, termed a Randall's plaque. Yet the cellular and molecular factors leading to their formation are unknown. Methods The influence of urinary proteins on adhesion of preformed calcium oxalate crystals to rat continuous inner medullary collecting duct (cIMCD) cells was studied in vitro, and cIMCD cells were also exposed to calcifying media containing β-glycerophosphate for up to 28 days. Renal tissue was obtained from a stone-forming and non-stone-forming individual at the time of nephrectomy. These nanoparticles, isolated from renal stones obtained at the time of surgical resection, were analyzed and propagated in standard cell culture medium. Results Urinary proteins influence crystal adhesion to renal epithelial cells, and this activity is abnormal in the urine of stone-forming patients. cIMCD cells assumed an osteoblastic phenotype when exposed to the calcifying medium, expressing two bone matrix proteins (osteopontin and bone sialoprotein) that were also identified in the kidney of the stone-forming patient and associated with crystal deposition. Nanoparticles were propagated from the majority of renal stones. Isolates were susceptible to selected metabolic inhibitors and antibiotics and contained conserved bacterial proteins and deoxyribonucleic acid (DNA). Conclusions These results suggest new paradigms for Randall's plaque formation and idiopathic calcium oxalate stone disease. It seems unlikely that these events are driven solely by physical chemistry; rather, they are critically influenced by specific proteins and cellular responses, and understanding these events will provide clues toward novel therapeutic targets.