Uranium XAFS analysis of kidney from rats exposed to uranium

Abstract

The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structure (mXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U L III -edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. mXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate.

Phosphorus Localization and Its Involvement in the Formation of Concentrated Uranium in the Renal Proximal Tubules of Rats Exposed to Uranyl Acetate

“…Our previous XAFS study of uranium showed that the XANES spectrum of uranium absorbed into cellulose phosphate under biological conditions (pH 7.4) was similar to that of UA, uranium (VI) [16], indicating that interactions between uranyl ions (VI) and phosphorus could explain the uranium colocalization in the S3 segments. Most of the uranium that accumulated in the kidneys was uranium (VI), but some had an edge that slightly shifted towards lower energy, meaning that uranium was reduced after administration [16].…”

“…Our previous XAFS study of uranium showed that the XANES spectrum of uranium absorbed into cellulose phosphate under biological conditions (pH 7.4) was similar to that of UA, uranium (VI) [16], indicating that interactions between uranyl ions (VI) and phosphorus could explain the uranium colocalization in the S3 segments. Most of the uranium that accumulated in the kidneys was uranium (VI), but some had an edge that slightly shifted towards lower energy, meaning that uranium was reduced after administration [16]. The reduction of uranium (VI) to (V) or (IV) results in a slight shift of the edge jump at 1–2 eV and a slight narrower peak [17,18], indicating that the proximal tubules without concentrated phosphorus could contain chemical forms of uranium that varied between (VI) and a reduced form.…”

“…Analyzed areas were selected based on the findings on these elemental images. U L III -edge μXAFS measurements of concentrated uranium in microregions in the S3 of the proximal tubule were carried out at the BL37XU, SPring-8 [16]. In brief, further uranium imaging was obtained using the X-ray intensity data of the U Lα by scanning the specimens with 17.250 keV X-ray beam.…”

A novel calibration strategy based on internal standard–spiked gelatine for quantitative bio-imaging by LA-ICP-MS: application to renal localization and quantification of uranium

“…The precise location and accurate quantification of uranium in rodents' kidneys would facilitate trustworthy information for reconstructing a more realistic dosimetry model for a better estimation of health risk that could be related to renal dysfunction or cancer occurrence in workers exposed to uranium. To date, few quantitative studies have been carried out employing high-energy synchrotron radiation X-ray fluorescence (SR-XRF) analysis and X-ray absorption fine structure (XAFS) [16,17]. Unfortunately, the limited access to these analytical techniques limits considerably its daily use for routine analysis [18].…”

Single-Cell Imaging for Studies of Renal Uranium Transport and Intracellular Behavior

“…The uranium-concentrated areas were still detected during recovery [17]. Uranium in these areas was partially reduced [18]. In addition, phosphorus and potassium were colocalized in some of these areas [19].…”