Early evaluation of renal reperfusion injury after prolonged cold storage using proton nuclear magnetic resonance spectroscopy

BACKGROUND: Proton nuclear magnetic resonance (NMR) spectroscopy can be used as a non-invasive tool to measure renal damage. In the present investigation, proton NMR spectroscopy of urine was assessed in order to detect cellular damage after different periods of cold ischaemia in two standard preservation solutions. METHODS: The isolated perfused pig kidney was used to assess initial renal function after in situ cold flush and cold storage (CS) for 24 or 48 h in two standard preservation solutions: EuroCollins (EC) and University of Wisconsin (UW) solutions. Kidneys flushed with cold heparinized saline and immediately perfused were used as a control group. Kidneys were perfused for 2 h at 37.5 degrees C for functional evaluation. During reperfusion, renal perfusion flow rate was measured. Glomerular filtration rate (GFR), tubular reabsorption of sodium ions, and lactate dehydrogenase (LDH) and N-acetyl-beta-D-glucosaminidase (NAG) excretion were determined. Impairment caused by ischaemia and reperfusion was also determined by histological techniques and proton NMR spectroscopy. RESULTS: The perfusion flow rate, GFR and tubular reabsorption of sodium were significantly decreased in experimental groups compared with the control group. There was no significant difference between experimental groups after 24 h of CS. The perfusion flow rate was significantly decreased in the EC group after 48 h of cold ischaemia compared with that in the UW group. After 48 h of CS, GFR and tubular reabsorption of sodium were significantly reduced in the EC group compared with those in the UW group. The release of LDH into the effluent and the urinary excretion of NAG were not significantly different after 24 h of CS. After more than 45 and 60 min of reperfusion respectively, LDH and NAG excretion was no different in the 48-h CS groups. The most relevant resonances determined by proton NMR spectroscopy were of citrate, trimethylamine-N-oxide, lactate, acetate and amino acids. Excretion of these markers was significantly more accurate and efficient to assess renal ischaemia-reperfusion injury than that of biochemical markers. A resonance (P) detected particularly in the EC group after 48 h of CS was identified and correlated well with renal dysfunction. After CS for 48 h and 2 h of reperfusion, renal injury was histologically more pronounced in EC groups than in UW groups. However, the difference was not significant after CS for 24 h. CONCLUSION: NMR spectroscopy, which is a non-invasive and non-destructive technique, is more accurate and efficient when assessing kidney damage after cold ischaemia and reperfusion when compared to conventional histological and biochemical analysis.