The Zucker Diabetic Fatty Rat as a Model for Vascular Changes in Diabetic Kidney Disease: Characterising Hydronephrosis

Abstract

Background/Objectives: Diabetic kidney disease (DKD) is a significant concern for global healthcare, particularly in individuals with diabetes. The Zucker rat strain is a commonly used model of type 2 diabetes, despite awareness that this animal can develop hydronephrosis. In this study, we present novel imaging data evaluating the accuracy of this animal model in replicating the vascular aspects of human DKD while examining the impact of hydronephrosis on its validity as a disease model. Methods: This study reused data from a population of male Zucker Diabetic Fatty (ZDF; n = 22) rats and Zucker Lean (ZL) rats (n = 22) aged 12 to approximately 40 weeks. Vascular casting was performed to enable visualisation of the renal vasculature. Anatomical regional volumes and vascular density data were obtained from μCT scans using image thresholding and manual analysis. The effects of hydronephrosis were evaluated using renal functional parameters and histological examination. Results: A significantly lower cortical vascular density, as well as lower total renal vascular density, was seen in ZDF rats compared to ZL rats, independent of age. We identified that hydronephrosis affected 92% of ZDF rats and 69% of ZL rats. Hydronephrosis cavity size was significantly correlated with the degree of hyperglycaemia and rate of diuresis but had no other detected impact on renal function, vascularity, or tissue histological architecture. Conclusions: These findings support using the Zucker rat strain as a model for vascular changes in DKD. Despite identifying severe hydronephrosis in this population, it had minimal quantifiable impact on renal function or diabetes modelling.

Keywords: Zucker Diabetic Fatty rat; diabetic kidney disease; hydronephrosis; renal imaging; type 2 diabetes; μCT.

Figure 1

The methodology for generating region of interest (ROI) maps for anatomical analysis. ROI maps (A–C) were created to delineate three anatomical regions for volume and vascular density measurements. (A) ROI A: whole kidney. (B) ROI B: the pelvic cavity. (C) ROI C: renal cortex as delineated by the boundaries of the arcuate arteries and the kidney capsule. The three ROIs are overlaid here in red on the same μCT imaging plane. Three-dimensional regions of interest (ROIs) were manually generated from μCT kidney volumes using ITK-SNAP. ROI outlines were carefully delineated on every 4th to 6th μCT frame and subsequently merged into continuous 3D structures using the ‘Active Contour’ function.

Figure 2

Method for stain deconvolution and colour-based segmentation. This approach was used to separate three categories of interest (B–D) from a single histological slide (A) using colour selection. (A) The ROI before colour selection. (B) ROI with selected areas of fibrosis overlaid in yellow. (C) ROI with selected areas of lumen overlaid in yellow. (D) ROI with selected areas of tubular tissue overlaid in yellow. All images were generated in Image-Pro 9.2 software.

Figure 3

The effect of diabetes on regional vascular density in the investigated ROIs: (A) the total kidney, (B) the renal vascular tissue (pelvic cavity excluded), and (C) the Cortex. The rat strain, D = ZDF or L = ZL, is shown by the x-axis. Data points for individuals are displayed on the plot. Two-way ANOVA results are overlaid on each graph with non-significant interactions shown with “ns”. No significant pairwise comparisons exist in this data, so no significance bars are displayed.

Figure 4

Hydronephrosis prevalence (A) and severity (B) in the ZDF and ZL populations. (A) Stacked boxplot displaying the prevalence of hydronephrosis (defined as a pelvic cavity exceeding 5% of the total renal volume) by rat sub-strain. (B) A box plot displaying the variation in size of the renal pelvic cavity across the population. Two-way ANOVA results are overlaid on the graphs with non-significant interactions shown with “ns”. Significant age-matched t-test results are displayed with significance bars.

Figure 5

The impact of hydronephrosis on the renal vasculature in non-diabetic, ZL rats. (A) Differences in regional vascular density in rats affected or unaffected by hydronephrosis. (B) The linear relationship between relative renal pelvic cavity size and regional vascular density in ZL rats. Data points for individuals are displayed on the plots. Significant results are displayed.

Figure 6

Scatter plot showing the linear relationship between pelvic cavity size and (A) blood glucose and (B) diuresis. Both plots are annotated with separate trend lines for the ZDF and ZL populations, as specified by the key. Correlation statistics for each sub-population are annotated.

Figure 7

A μCT scan displaying a representative example of the anatomical structure of the hydronephrotic cavity in the Zucker Rat. Three matched views, (A) coronal, (B) axial, and (C) sagittal, of a ≈40-week-old ZDF rat kidney. The hydronephrotic cavity is overlaid in red. Images generated using ITK-SNAP (version 4.0.1).