Non-linear regression and variance ratio analysis of time based NMR data.

Biomedical NMR experiments rely frequently on data obtained sequentially over time. A method is presented for analysis of time based NMR data, which allows modelling of continuous and discontinuous functions to observed intensity changes by non-linear regression and which uses variance ratio analysis to compare these models statistically. The method eliminates many of the usual problems in the parametric analysis of experimental values obtained at discrete time points and of comparison of the coefficients of model functions which require unsubstantiated assumptions about the distribution of parameters and ignore internal correlations which may exist between such parameters. The variance ratio method is illustrated for multiple time courses obtained with 23Na NMR of perfused rat kidney undergoing hypoxic perturbation in the presence of different treatments

Correlation of Breath Biomarkers with Current Gold Standards for Modelling Acute Renal Failure in Rats

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Modelling acute renal failure using blood and breath biomarkers in rats

Invited. Available online 21 August 2010This paper compares three methods for estimating renal function, as tested in rats. Acute renal failure (ARF) was induced via a 60-min bilateral renal artery clamp in 8 Sprague–Dawley rats and renal function was monitored for 1 week post-surgery. A two-compartment model was developed for estimating glomerular filtration via a bolus injection of a radio-labelled inulin tracer, and was compared with an estimated creatinine clearance method, modified using the Cockcroft–Gault equation for rats. These two methods were compared with selected ion flow tube-mass spectrometry (SIFT-MS) monitoring of breath analytes. Determination of renal function via SIFT-MS is desirable since results are available non-invasively and in real time. Relative decreases in renal function show very good correlation between all 3 methods (R2 = 0.84, 0.91 and 0.72 for breath-inulin, inulin-creatinine, and breath-creatinine correlations, respectively), and indicate good promise for fast, non-invasive determination of renal function via breath testing

Hydroxyl radical generation following ischaemia-reperfusion in cell-free perfused rat kidney

The difficulty in direct detection of oxygen-derived free radicals (OFR) in the intact kidney has left uncertain the role of OFR in renal hypoperfusion injury. Salicylate hydroxylation was used as a sensitive method of estimating the extent of production of highly reactive hydroxyl radicals in renal ischaemia-reperfusion injury in the intact rat kidney perfused with recirculating cell-free medium. The reaction products were detected and quantified by HPLC with electrochemical detection. Hydroxyl radicals were detected as 2,5-dihydroxybenzoic acid (2,5-DHBA). Ischaemia for 15 min followed by reperfusion for 15 min caused more than a twofold increase in 2,5-DHBA concentration (to 2279 ± 225 pg/g tissue weight) compared to controls (933 ± 103, P < 0.001). Addition of 15 mM dimethylthiourea (DMTU) before induction of ischaemia prevented this increase. Induction of hypoxia for 15 min with continued perfusion (as a model of low-flow ischaemia) had no significant effect on hydroxyl radical formation. We conclude that significant quantities of hydroxyl radicals form in the absence of circulating leucocytes during reperfusion following ischaemia, but not during hypoxia in the perfused rat kidney

Erratum: Timely Diagnosis of Acute Kidney Injury Using Kinetic eGFR and the Creatinine Excretion to Production Ratio, E/eG - Creatinine Can Be Useful!

Post transplant repeated measurements of urine volume and serum creatinine (sCr) are used to assess kidney function. Under non-steady state conditions, repeated measurement of sCr allows calculation of the kinetic estimated GFR (KeGFR). Additional measurement of urinary creatinine allows the calculation of the creatinine excretion to (estimated) production ratio (E/eG). We hypothesized that post-transplant KeGFR and E/eG would predict delayed graft function (DGF), as early as 4 h and outperform a validated clinical model at 12 h. This was a retrospective analysis of prospectively acquired data in a study of 56 recipients of deceased-donor kidney transplant. We assessed predictive performance with the area under the receiver operator characteristic curve (AUC) and the added value to a clinical model with integrated discrimination improvement analysis. At 4 h, the AUC for E/eG was 0.87 (95% CI 0.77-0.96) and for KeGFR 0.69 (95% CI 0.56-0.83). Both E/eG and KeGFR improved the risk prediction of a clinical model for DGF by 32 and 18%, and for non-DGF by 17 and 10%, respectively. While E/eG had better predictive performance of DGF than KeGFR, KeGFR might also facilitate perioperative management including drug dosing after kidney transplantation. Together these measurements may facilitate the possibility of conducting trials of early intervention to ameliorate the adverse effects of ischaemia-reperfusion injury on long-term DGF

DETECTION OF NITRIC OXIDE REDUCTION DURING ISCHAEMIA-REPERFUSION BY EPR SPECTROSCOPY

Introduction: Acute renal failure is a common consequence of sepisis due to concurrent renal ischaemia. The role of nitric oxide (NO) in endotoxaemia and in ischaemic injury in the kidney is not well defined. Material and Methods: In this study we have used an animal model of sepsis induced by injection of bacterial lipopolysaccharide (LPS) in the rat and measured renal nitric oxide by X-band electron paramagnetic resonance (EPR) spectroscopy using the spin trap Fe2+-N-methyl-D-glucamine dithiocarbamate [Fe(MGD)2] given by intravenous injection 6 minutes before sacrifice. Results: The characteristic EPR spectrum of [Fe(NO)(MGD)2] was observed in kidneys of rats treated with LPS for 5h. Rat kidneys subjected to 20 min ischaemia and 5 min reperfusion had lower concentrations of [Fe(NO)(MGD)2] (1.0 ± 0.6 (M) compared to the contralateral nonischaemic kidneys (1.5 ± 0.9 (M, P<0.05). Conclusion: This study shows reduced levels of NO after renal ischaemia in vivo