SAT-133 A novel, phosphorescence-based technique to assess urinary oxygen tension

Abstract

Renal hypoxia aggravates acute kidney injury and accelerates chronic kidney disease. Recently, the importance of urinary bladder oxygen tension, employed as a window of renal oxygen tension, has been shown in patients under cardiac surgery in the point that low urinary oxygen tension predicts postoperative acute kidney injury (Zhu MZL et al. Nephrol Dial Transplant 2018). However, measurement technique of urinary oxygen tension in murine is not established. Phosphorescence is a light which has unique character whose lifetime is inversely correlated to oxygen concentration, and we established oxygen tension measurement method at renal surface using phosphorescence (Hirakawa Y et al Sci Rep 2016, Hirakawa Y et al. Kidney Int 2018). This time we applied phosphorescence to urinary bladder oxygen tension measurement. The aim of this study is to establish a novel method to measure urinary oxygen tension, and to examine factors influencing urinary oxygen tension Balb/c mice were used in this research. A water-soluble small-molecule phosphorescent dye, BTP-PEG24, was administered via tail vein injection. Phosphorescence lifetime was measured by quantaurus-tau by Hamamatsu Photonics with two-branched optical fiber. Results of phosphorescence lifetime measurement were shown as mean ± standard deviation. Both of fluorescence stereoscopy and phosphorescence lifetime imaging microscopy revealed that this phosphorescent dye was rapidly excreted into urine and accumulated in the urinary bladder. Phosphorescence lifetime measurement was done after median incision in lower abdomen and placement of two-branched optical fiber near the urinary bladder. After BTP-PEG24 administration, phosphorescence lifetime was measured in normoxia, general hypoxia by 10% oxygen inhalation, and reoxygenation by return to room air inhalation, and phosphorescence lifetime changed from 2.18±0.15μs to 2.51±0.22μs (hypoxia) and 2.08±0.12μs (reoxygenation). The phosphorescence lifetime measurement could be done after the ligation of both ureters, and the value changed from 1.92±0.08μs to 2.11±0.17 (hypoxia) and 1.88±0.11μs (reoxygenation). Considering that shorter phosphorescence lifetime means higher oxygen tension, ligation of both ureters raised oxygen tension of bladder urine, which meant oxygen tension in pelvic urine was indeed affected by renal oxygenation. However, at least in part, the oxygen tension in pelvic urine was indicated to reflect the oxygen tension of bladder epithelia, since the phosphorescence lifetime changes according to oxygen concentration of inspired air. The results of phosphorescence lifetime measurement in urinary bladder with BTP-PEG24 were shown. Each “21%”, “10%”, and “Re21%” indicates normoxia, hypoxia, and reoxygenation, respectively. The dots with same color were obtained from the same mouse. N = 4 for sham group and N = 5 for ligation group. Each mouse underwent three phosphorescence lifetime measurements. We established novel technique to assess pelvic urine oxygen tension. Pelvic urine oxygen tension was shown to be influenced by both of oxygen tension in kidney and in bladder epithelia. Therefore, fresh urine, which might remain unaffected by bladder epithelia oxygenation, must be used as the window of renal oxygenation.