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Determination of the urinary or plasma clearance of exogenous renal markers, such as inulin or iohexol, is considered to be the gold standard for glomerular filtration rate (GFR) measurement. Here, we describe a technique allowing determination of renal function based on transcutaneously measured elimination kinetics of fluorescein isothiocyanate (FITC)-sinistrin, the FITC-labeled active pharmaceutical ingredient of a commercially available marker of GFR. A low cost device transcutaneously excites FITC-sinistrin at 480  nm and detects the emitted light through the skin at 520  nm. A radio-frequency transmission allows remote monitoring and real-time analysis of FITC-sinistrin excretion as a marker of renal function. Due to miniaturization, the whole device fits on the back of freely moving rats, and requires neither blood sampling nor laboratory assays. As proof of principle, comparative measurements of transcutaneous and plasma elimination kinetics of FITC-sinistrin were compared in freely moving healthy rats, rats showing reduced kidney function due to unilateral nephrectomy and PKD/Mhm rats with cystic kidney disease. Results show highly comparable elimination half-lives and GFR values in all animal groups. Bland-Altman analysis of enzymatically compared with transcutaneously measured GFR found a mean difference (bias) of 0.01 and a -0.30 to 0.33 ml/min per 100 g body weight with 95% limit of agreement. Thus, with this device, renal function can be reliably measured in freely moving rats eliminating the need for and influence of anesthesia on renal function.

Background: Inulin/sinistrin (I/S) clearance is a gold standard for an accurate assessment of glomerular filtration rate (GFR). Here we describe and validate an approach for a transcutaneous determination of GFR by using fluorescein-isothiocyanate-labelled sinistrin (FITC-S) in rats., Methods: Using a small animal imager, fluorescence is measured over the depilated ear of a rat after the injection of FITC-S. The decay curve of fluorescence is used for the calculation of half-life and GFR. The thus obtained transcutaneous data were validated by simultaneously performed enzymatic and fluorometric measurements in plasma of both FITC-S and sinistrin., Results: The results of enzymatic sinistrin determination versus transcutaneous half-life of FITC-S or plasma fluorescence correlated well with each other (R(2) > 0.90). Furthermore, Bland-Altman analyses proved a good degree of agreement of the three methods used. The measurements performed in healthy animals as well as different models of renal failure demonstrate its appropriateness in a wide range of renal function., Conclusions: The transcutaneous method described offers a precise assessment of GFR in small animals. As neither blood and/or urine sampling nor time-consuming lab work is required, GFR can be determined immediately after the clearance procedure is finished. This method, therefore, simplifies and fastens GFR determinations in small lab animals compared to conventional bolus clearance techniques based on blood sampling. A low-cost device for the measurement of transcutaneous fluorescence intensity over time is under construction.

Unlabelled: OBJECTIVE Morphologic and dynamic renal imaging is necessary for characterization of kidney function in renal insufficiency. Assessment of renal perfusion and the glomerular filtration rate (GFR) are essential, as the serum creatinine level and urea are not sensitive at an early stage of kidney damage. Currently available GFR estimation methods are time consuming, expensive, and lead to radiation exposure for the patient. Therefore, the aim was to determine the feasibility of morphologic and contrast-enhanced dynamic magnetic resonance imaging for GFR assessment in pcy (polycystic kidneys and fibrosis) mice, using a clinical 3.0 Tesla scanner., Materials and Methods: Fourteen pcy-mice were anesthetized and an internal jugular vein catheter was implanted to which a dedicated extension tube with a 0.28 mm inner diameter was connected, filled with 1:100 microL diluted gadobutrol (Gadovist Bayer Schering Pharma, Berlin, Germany). Imaging of the mice was performed with a dedicated 8-element mouse coil (Rapid Biomedical, Rimpar, Germany) plugged into a clinical 32-channel 3.0 Tesla magnetic resonance-scanner (Magnetom Verio, Siemens Medical Solution, Erlangen, Germany). In this study, different morphologic sequences comprising a T1-w 3D volume-interpolated breathhold examination, T2-w 2D half-Fourier acquired turbo spin echo (HASTE), T2-w 2D BLADE-TSE with fat saturation, and a T2-w 3D SPACE were acquired. The dynamic sequence performed for assessment of GFR, was a 2D SR-Turbo FLASH sequence. Image analysis and data assessment was performed by 2 radiologists who were experienced in assessment of human kidney disease. A 3-point scale for visual assessment of renal cystic changes in the pcy-mice was applied. The appearance of cysts, considering a detailed demarcation of the cyst with an enhancing rim and a hypointense core, were assessed as detailed: (1) faint (2) and not to be differentiated, (3) findings in the morphologic sequences. Quantitative parameters of renal function (cortex plasma flow mL/100 mL/min, cortex plasma volume mL/100 mL, and PT sec) were fitted to a 2-compartment model and compared with blood samples of creatinine and urea. Histologic progression of cysts and fibrosis in the pcy-mice was analyzed., Results: The T2-w 3D SPACE and T1-w 3D volume-interpolated breathhold examination sequence post contrast with thinnest slice thickness of 1 to 1.2 mm were well suited for delineation of the kidneys with detailed demarcation of the cysts (image quality score: 1.14 +/- 0.37 and 1.2 +/- 0.70, respectively). The T2-w 2D BLADE-TSE proved feasible, too (image quality score: 1.28 +/- 0.59). The T2-w 2D HASTE sequence with minimally achievable slice thickness of 2 mm was not suitable for morphologic assessment (image quality score: 2.9 +/- 0.37). The HASTE sequence suffered from blurring artifacts which further decreased the conspicuity of small cystic changes. The 2D SR-Turbo FLASH sequence showed the renal first pass of the contrast agent and enabled assessment of GFR. The data after time resolved 2D SR-Turbo FLASH perfusion analysis was used for GFR evaluation and demonstrated better GFR values in the young pcy-mice (0.558 mL/min) compared with the older pcy-mice (0.066 mL/min)., Conclusion: Application of dedicated coils with a clinical 3.0 Tesla magnetic resonance-scanner have proved feasible for morphologic and dynamic renal imaging with assessment of GFR in pcy-mice.

There is an evident and growing medical need for an accurate determination of kidney function for a broad spectrum of indications. The glomerular filtration rate (GFR) is the most accepted indicator of renal function. Due to difficulties in performing the test, GFR is currently determined rarely in clinical practice. A procedure for such GFR determination has to be safe, accurate and easy to handle. By using the new compound fluorescein isothiocyanate-sinistrin (FS) these requirements are met. The pharmacological profile and tolerability of FS, selected from among various newly synthesized, labelled compounds intended for use as GFR markers, was characterized in male Sprague-Dawley rats following i.v. application. Using the newly described fluorometric method, FS can be determined much more easily in serum and urine than with the established enzymatic method. After i.v. dosing, FS concentrations in serum declined rapidly in various experimental groups to a comparable extent (t (1/2), mean+/-SD: 22.4+/-8.3 to 26.2+/-5.4 min). Its increase after unilateral nephrectomy reflects the loss of filtration capacity. Comparable concentration-time curves of FS in serum measured fluorometrically and enzymatically suggest no relevant alteration of pharmacokinetic behaviour by the labelling. This notion is supported by the high urinary excretion rate and absence of biliary excretion. The higher sensitivity of the fluorometric method suggests a dose of FS of 100 mg in humans compared with 5 g of sinistrin or inulin. FS was well tolerated after single and multiple applications. On the basis of these results, the kinetics of FS are comparable with the gold standard inulin or sinistrin, but FS is superior in handling. Providing the data can be transferred from rat to human, determination of GFR using the new method should result in an improvement of acceptance by both physicians and patients.

There is an obvious and growing medical need for an accurate and easy to handle determination of glomerular filtration rate (GFR) for a broad spectrum of indications. Newly synthesized fluorescein-isothiocyanate (FITC)-sinistrin (FS) with various degrees of labeling was selected by its physicochemical properties and good tolerability out of a number of dye-labeled compounds intended for use as GFR markers for characterization of its pharmacological profile. With respect to solubility FS is more convenient in handling compared to FITC-inulin (FI). Up to 100 mg ml(-1) of FS can be dissolved in aqueous solvents at room temperature, whereas FI can only be solubilized after warming up to 55 degrees C. This reveals a considerable advantage of FS over FI in preparation of galenical formulations for intended i.v. application. A fluorometric method was established to determine FS concentration in blood serum with a comparable accuracy to the established enzymatic method for polyfructosanes. Similar concentration time curves in blood serum of FS measured fluorometrically and enzymatically suggest no relevant change of pharmacokinetic behavior by dye labeling. This notion is supported by the rapid renal and missing of biliary excretion. On the basis of these results, FS is superior in handling to the available GFR markers and makes it highly interesting as a novel diagnostic drug.

There is an obvious and growing medical need for an accurate determination of kidney function in the diagnosis and management of renal diseases. The glomerular filtration rate (GFR) is the accepted gold standard measurement of kidney function. Several approaches to estimate the GFR are available, but most of them are inconvenient and, therefore, of limited acceptance. A new method of quantification with fluorescein-isothiocyanate (FITC) sinistrin (FS), a novel GFR marker, has been evaluated. The method is based on the fluorescence label of FS and can be performed with a standard fluorometer. To control the interference of protein with the fluorescence signal, a calibration function was developed. The accuracy of the fluorometric method established is comparable to the so-called "gold standard" of enzymatic determination of polyfructosan. Moreover, FS is easy to handle and requires low-cost instruments. Our results demonstrate the potential of the direct fluorometric analysis of the new FITC-labelled marker of being a precise, simple, rapid and cost-effective method for diagnosing disturbed kidney function and monitoring its treatment efficacy. The dramatic decrease in analytical effort will result in a significantly higher acceptability of GFR determination.

Background: The aim of this study was the assessment of kidney morphology and glomerular filtration rate (GFR) in rat models of polycystic kidney disease and a healthy control group of Sprague-Dawley rats (SD rats). The performance of two non-invasive GFR estimation methods-3.0 Tesla magnetic resonance imaging (MRI) and optical imaging were investigated. Data of GFR assessment was compared to surrogate markers of kidney function and renal histology. Methods: Optical imaging of GFR was performed transcutaneously in a small animal imaging system with the fluorescent renal marker fluorescein-isothiocyanate-labelled-sinistrin. Morphologic and dynamic renal imaging was done on a clinical 3.0T MR scanner. Renal perfusion analysis was performed with a two-compartment filtration model. Results: The healthy SD rats showed physiological levels of creatinine and urea, indicating normal kidney function. These parameters were elevated in the small animal groups of polycystic kidney disease. For the calculation of perfusion and filtration parameters of kidney function in MRI, a 2D turbo FLASH sequence was performed and allowed to distinguish between normal GFR of healthy rats and reduced GFR of rats with polycystic kidney disease. Also, MRI GFR varied among two different rat strains of polycystic kidney disease, according to their status of renal function impairment. Optical imaging GFR confirmed higher GFR values in healthy rats compared to ill rats but did not show different results among the two rat strains of polycystic kidney disease. For this reason, MRI and optical imaging GFR estimation presented an intra-method bias. Conclusions: Both non-invasive estimation methods of GFR, MRI and optical imaging, can differentiate between healthy rats and animals with limited kidney function. Furthermore, optical imaging, unlike MRI, seems to consider that disease progression with increase of renal polycystic deterioration does not correlate with decrease of GFR in the initial stage of compensatory hyperfiltration. [ABSTRACT FROM AUTHOR]