Preclinical Nephrology Research

Preclinical studies aiming to assess kidney function in animal models of kidney disease or in response to a test compound have traditionally included readouts such as serum creatinine and blood urea nitrogen (BUN). However, the use of readouts that are more clinically relevant is highly encouraged, as this can help increase confidence in the test compound’s efficacy profile by improving the translational value of the experimental studies (Figure 1).  

At InnoSer, kidney function in mouse models of kidney disease, such as in the autosomal dominant polycystic kidney disease (ADPKD) model, is assessed using multiple readouts which we have briefly reviewed here. In this blog post, we provide a comprehensive overview of measuring glomerular filtration rate (GFR) transdermally in preclinical mouse models of kidney disease, focusing on its translational value in later stages of preclinical research.  

translational readouts in preclinical kidney mouse models

FIGURE 1. Comparison of the main outcomes measured during preclinical research and in clinical trials (non-exhaustive). The preclinical stage of drug development encompasses various research phases, out of which efficacy studies in animal models of kidney disease form a large part of the time spent investigating the test compound’s characteristics. The use of translational readouts, i.e. readouts that are also typically used in clinical trials, in experimental animal models of kidney disease can increase the translational value of these models to the researchers 

Clinical Significance of Measuring Glomerular Filtration Rate (GFR) 

Physiologically, GFR is the rate at which the glomerulus filters plasma through the glomerular capillary walls to produce an ultrafiltrate per unit of time. Therefore, GFR shows how good kidneys are functioning. Clinically, GFR is the gold standard in kidney function assessment, including the monitoring of disease progression, treatment effectiveness and potential test compound-induced kidney toxicities. In clinical trials, GFR is typically estimated based on serum concentrations of endogenous filtration markers such as creatinine.  

Similarly, as in humans, GFR can be estimated based on serum creatinine levels in preclinical mouse models of kidney disease as well. However, due to their small size and the frequent need for blood and/or urine sampling, this may prove to be difficult. Moreover, the recommendation by the working group in the recently published Kidney international Guideline on Preclinical Nephrology Studies suggests that kidney function needs to be assessed using both serum creatinine levels, as well as other measurements appropriate to the species and the preclinical model of the disease (Nangaku et al. 2023). To avoid repeated blood sampling for measurement of GFR, novel, less-invasive methods are recommended, such as the use of a small device monitoring the GFR via the skin (Scarfe et al. 2018).  

Accordingly, nephrology researchers are nowadays including the measurement of GFR in preclinical research models of kidney diseases more and more by using the transdermal GFR measuring device. Transdermal GFR monitoring is applicable in fundamental kidney disease assessments, efficacy evaluations of new and existing kidney therapeutics or evaluations of nephrotoxicity. A full list of peer-reviewed publications which use transdermal GFR in preclinical research can be found here.  

Commercially available translational readouts that are recognised by both preclinical and clinical scientists are scarce, and therefore, the nephrology team at InnoSer is excited to be able to offer this service to all our clients active in the field of nephrology. 


Transdermal Measurement of GFR in Mouse Models of Kidney Diseases 

GFR can be measured via the skin of a mouse using a miniaturized fluorescence monitor in combination with a fluorescent exogenous GFR tracer (Scarfe et al. 2018). The measurement system consists of a fluorescence detector that is attached to the skin on the back of freely moving mice (Figure 2). The monitor measures the excretion kinetics of the exogenous GFR tracer, which in this case is fluorescein-isothiocyanate (FITC) conjugated sinistrin (inulin analogue), to provide a sensitive measure of GFR.  

Image features transdermal GFR experiment set-up in a mouse model of kidney disease

FIGURE 2. Experimental set-up to measure transdermal GFR in preclinical research mouse models of kidney disease. (A) Preparation of the mice involves anaesthesia, fur removal and careful positioning and attachment of the transdermal monitor. (B) Following secure attachment of the GFR monitor mice are injected with FITC-sinistrin via the tail vein. Following injection, mice are awakened and placed back in the cage for the specified experimental duration of time. (C) GFR measurements are obtained by removing the device and connecting it to a computer via USB cable. Data are processed in line with the software as recommended by the manufacturer of the monitors. 

This relatively simple method allows for a longitudinal measure of kidney function without repeated blood and/or urine sampling as required with traditional methods. This is especially relevant for experimental designs requiring multiple collection timepoints which may not be possible in mice due to their inherently low blood volumes as compared to other rodents. The use of this method also avoids the extensive handling of mice, as they only need to be handled minimally as opposed to multiple venipunctures. Moreover, previous research showed that transdermal GFR correlates with other measures of kidney function such as histological kidney damage, BUN and serum creatinine (Scarfe et al. 2018).  

Transdermal measurement of GFR in the Autosomal Dominant Polycystic Kidney Disease (ADPKD) Model  

To confirm the suitability of this method in preclinical research models, we assessed GFR in our PKD mouse model at different time points. For this experiment, the adult (P18) ADPKD mouse model was used. P18 ADPKD mice have Pkd1 knocked out at postnatal day 18, leading to a relatively slow cyst development and progression which affects all segments of the nephron. This disease model resembles the course of the renal pathophysiology in adult-disease onset ADPKD, ensures that mice are of sufficient size to obtain sensitive GFR measurement results, and allows a chronic course of test item dosing evaluation providing the opportunity to also detect any possible long-term side effects (in life-phase of the study lasts approx. 18 weeks).  

Briefly, following the attachment of the monitor and after administering an IV injection of a tracer, the excretion half-life of the tracer (t1/2) was determined based on the measured signal. In turn, the GFR was calculated based on the excretion half-life of the tracer. As shown in the figure below, the GFR of the healthy control group remains constant over the observed period, confirming the use of this readout in assessing kidney function (Figure 3). In contrast, the GFR of the PKD group decreased throughout the study, which is indicative of renal function loss (Figure 3), confirming the use of this readout in this preclinical mouse model of PKD.  

transdermal GFR in ADPKD mouse model

FIGURE 3. Transdermal GFR assessment shows a decline in kidney function in ADPKD mice. Over time, we observe a significant decrease in the GFR of the PKD group (post-natal day [PND] 81 vs PND115: **P<0.01; PND102 vs PND115: *P<0.05), resulting in a significantly lower GFR in comparison to the healthy control group on PND115 (healthy vs PKD group: ##P<0.01) Data are represented as Mean ± SEM, circles represent data of individual animals. This confirms the loss of renal function in PKD mice and the suitability of this method in preclinical research studies.  

This readout can be added alongside other translational readouts to assess disease progression, such as total kidney volume. The increase in kidney volume is related to a progressive decline in GFR, which together provide highly relevant information about the progression of the renal disease (Figure 4). Altogether, this provides a more complete picture of the obtained data in preclinical study carried out in the ADPKD mouse model.  

FIGURE 4. Assessment of kidney volume by ultrasound allows the determination of disease progression in the mouse model of ADPKD. Compared to healthy control, the kidney volume of PKD mice is significantly increased over time, indicating decline in renal health (**P<0.01, ***P<0.001). Data are represented as Mean ± SEM.  

Choosing the Right Type of Readout to Evaluate Kidney Function in Your Research 

In order to develop safe and efficacious therapeutics for renal indications such as chronic kidney disease (CKD), PKD and other chronic and/or rare conditions, test compounds need to be thoroughly evaluated. The inclusion of translational readouts can help increase confidence in the obtained data during preclinical trials.  

Transdermal GFR measurement can serve as a sensitive and accurate measure of kidney function compared to traditional measures that rely on multiple collection timepoints of urine and/or blood (Scarfe et al. 2018). As such, including transdermal GFR in your study designs can help increase the translational value of your research.  

However, to obtain the full picture of the test compound’s efficacy, it is recommended that other readouts (i.e. biomarkers, histopathology…) combined with pharmacokinetic and pharmacodynamic studies are carried out as well. As such, the most appropriate readout selection ultimately depends on the specific aims of the research question. 

Consulting with our nephrology study experts will allow you to carry out tailored studies while collecting the most study-appropriate data. We also advise you on the most optimal model selection, taking in account your budget and study timelines. Get in contact with our team still today to obtain expert preclinical expertise and industry-competitive study timelines.  

Related Resources

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