#1413 High performance of ACLARA calculator of rat creatinine clearance for the chronic follow up of renal function
Authors: Fuentes-Calvo Isabel , del Valle Mercado Hernández Joana , Pellicer-Valero Óscar , Massaro Giampiero A , Casanova Alfredo G , Sancho María Paniagua , Harvat Mykola , Martín José D , Lopez-Hernandez Francisco J , Salgado Carlos Martinez 
Published: May 2024

Abstract

Background and Aims
A neural network-based calculator to estimate rat creatinine clearance (ClCr), as a measurement of the glomerular filtration rate (GFR), from paired plasma creatinine concentration and body weight data has been recently developed [1]. Like human GFR estimating formulae, ACLARA averts long experimental procedures and reduces animal stress (by obviating the use of individual isolation in metabolic cages). This tool is publicly available for free use among the scientific community (https://idal.uv.es/aclara/). When collated with experimentally measured ClCr, ACLARA performs very well at comparing experiments in the whole, showing almost identical behavior of all experimental groups and conditions. Yet, ACLARA was trained mostly with data from short experiments involving acute changes in renal function, and from young rats. Fewer data from older animals was included in the development of the calculator. Thus, its field performance on longer evolution of renal function in adult rats has not yet been sufficiently validated. Accordingly, the aim of this work was to deepen in the assessment of ACLARA in the long-term evolution of rat ClCr.

Method
The evolution of measured (mClCr) versus ACLARA-estimated ClCr (eClCr) was compared at different time points over a period of 3 months in 20 male Wistar rats with chronic renal damage and 8 age-matched controls. In total, 176 data pairs of mClCr and eClCr were obtained. On the one hand, mClCr was determined by the usual experimental procedure [2]. Briefly, rats were allocated in metabolic cages to obtain 24-hour urine samples and urine flow (UF). Creatinine concentration was measured in the urine (Cru) and plasma (Crp) by a colorimetric assay based on the Jaffe's reaction, and mCrCl was then calculated as Cru x UF / Crp. On the other hand, eClCr was estimated with the ACLARA calculator from the corresponding Crp and body weight data. A Pearson's correlation study between mClCr and eClCr was carried out.

Results
Our results reveal that the information provided by the 90-day evolution of mClCr and eClCr is virtually identical at the whole experiment level (see Fig. 1). Furthermore, ACLARA seems to provide slightly more coherent and homogeneous information, as the considerable experimental error introduced by urine collection is averted in eClCr but present in mClCr. At the individual data level, ACLARA-estimated values are slightly lower than the corresponding measurements. The correlation between mClCr and eClCr was highly significant (r Pearson= 0.83; p &lt; 0.0001).

Conclusion
ACLARA shows high performance at estimating CrCl in rats of growing age. Our results support its use also in chronic studies in which renal function must be evaluated.

Funding
This research was funded by grants from Instituto de Salud Carlos III (ISCIII), Ministerio de Ciencia e Innovación (PI21/01226 and PI21/00548 co-funded by the European Union; and RICORS2040, RD21/0005/0004, co-funded by the European Union – NextGenerationEU, Mecanismo para la Recuperación y la Resiliencia (MRR)) and from Consejería de Educación, Junta de Castilla y León (IES160P20), co-funded by FEDER funds. Joana Mercado-Hernández is recipient of a predoctoral fellowship from the Junta de Castilla y Leon (Spain) and the European Social Fund from the European Commission.