A 30% incidence of renal cysts with varying sizes and densities in biomedical research swine is not associated with renal dysfunction

Abstract

Background: Renal cystic disease arising from various etiologies results in fluid-filled cavities within the kidneys. Moreover, preexisting renal dysfunction has been shown to exacerbate multiple pathologies. While swine bred for biomedical research are often clinically inspected for illness/parasites, more advanced diagnostics may aid in uncovering underlying renal abnormalities.

Methods: Computed tomography was performed in 54 female prepubertal Yorkshire swine to characterize renal cysts; urine and blood chemistry, and histology of cysts were also performed.

Results: Digital reconstruction of right and left kidneys demonstrated that roughly one-third of the animals (17/54; 31%) had one or more renal cyst. Circulating biomarkers of renal function were not different between animals that had cysts and those that did not. Alternatively, urinary glucose (P = .03) was higher and sodium (P = .07) tended to be lower in animals with cysts compared to animals without, with no differences in protein (P = .14) or potassium (P = .20). Aspiration of cystic fluid was feasible in two animals, which revealed that the cystic fluid urea nitrogen (97.6 ± 28.7 vs 911.3 ± 468.2 mg/dL), potassium (29.8 ± 14.4 vs 148.2 ± 24.85 mmol/L), uric acid (2.55 ± 1.35 vs 11.4 ± 5.65 mg/dL), and creatinine (60.34 ± 17.26 vs 268.99 ± 95.79 mg/dL) were much lower than in the urine. Histology demonstrated a cyst that markedly compresses the adjacent cortex and is lined by a single layer of flattened epithelium, bounded by fibrous connective tissue which extends into the parenchyma. There is tubular atrophy and loss in these areas.

Conclusion: This study provides valuable insight for future studies focusing on kidney function in swine bred for biomedical research.

Keywords: computed tomography; cyst; kidney; renal dysfunction; swine.

FIGURE 1

Axial (A) and coronal (B) CT scans in an animal without cysts in the kidney. (C) 3D reconstruction of bone, vasculature, and kidneys in the same animal. (D‐F) Axial, coronal, and 3D scans views in animal #1 showing five of the six total cysts. (G‐I) Animal #2, axial, coronal and 3D scans showing all four cysts

FIGURE 2

A and B, Kidneys are irregular in shape, wherein the superior end of individual animals’ right kidney showed an abnormal lack of elongation and blunting. C and D, Coronal scans of demonstrating location of cysts within kidney that are not visible at a macroscopic level

FIGURE 3

(A) Excised kidneys of animal with no visual abnormalities, but coronal CT (B) and dissection (C) indicate presence of a cyst. (D) Cyst wall is visible on right kidney, and (E) coronal scan aligns with location of cyst. (F) Dissection of the right kidney to expose cyst wall

FIGURE 4

A, Female Yorkshire pig renal cyst H&E stain at low magnification shows that the cyst markedly compresses the adjacent cortex (c). Note the atrophic tubules (red arrow) in the cortex. Cyst lumen (l). B, H&E and (C) Masson's Trichome shows an epithelial lined cyst bounded by fibrous connective tissue (black arrow) which extends into the parenchyma. Note the atrophic tubules (red arrows) and lymphoplasmacytic inflammation (blue arrow)

FIGURE 5

TUNEL and DAPI staining was performed to identify apoptotic cells in the renal cyst of a female Yorkshire pig. A 400x image of adjacent renal tubules not associated with the cyst has been provided as an internal negative control (A‐C). (D) DAPI, (E) TUNEL, and (F) merge of an epithelial layer containing apoptotic cells. Higher magnification images of this epithelium is shown in (G‐I). (l) indicates the lumen