Preliminary study of the role of nanobacteria in the formation of renal stones in experimental rats and its mechanism
Authors: Yang Heng , Cheng Xiaofeng , Chen Yujun , Zeng Zhenhao , Wang Gongxian 
Published: February 2024

Introduction

The aim of the study was to study the role of nanobacteria in the formation of renal calculi and the underlying mechanism.

Material and methods

A total of 90 clean Wistar male rats were randomly divided into a negative control group, an experimental group, and an interference group. From the end of the first week of modelling, 10 consecutive times once a week, 3 rats in each group were randomly selected to measure the biochemical blood markers and urine metabolism. After sacrifice, the formation of kidney stones was assessed by observing the ultrastructure of the kidney by electron microscopy and pathohistology. Finally, the expression of calcium-sensitive receptor (CaSR) and claudin-14 protein in the kidney tissue was examined by western blotting.

Results

Compared with the control group, the gross structure of the kidney was changed in the model group. At the fourth week of modelling, the rats in the nanobacteria group had significantly enlarged kidneys and increased kidney-to-body ratio, and the difference had statistical significance (p < 0.05). The colour of the kidney profile was dark, the structure of the skin pulp was less clear, and the accumulation of yellowish particles was observed at the junction of the cortical pulp. The creatinine, uric acid, urea nitrogen, and urinary calcium of the rats in the nanobacteria group began to increase at the third week, and the difference between the third and eighth week had statistical significance (p < 0.05). However, the difference between the 3 groups had no statistical significance after the eighth week. At the fourth week, we observed the formation of calculi, which were mainly distributed in the renal tubules and surrounding tissues. The kidney stone formation rate was 52.4% in the nanobacteria group and 27.8% in the interference group, and the difference had statistical significance (p < 0.05). Ultrastructure observations revealed that from the fourth week, the renal tissues in the nanobacteria group showed expanded renal tubules, swollen renal tubular epithelium, granular degeneration, shedding and lymphocyte infiltration of renal tubular epithelial cells, and a small amount of calcium salt crystals in renal tubules. At the third week, the expression of CaSR and Claudin-14 protein in the nanobacteria group increased, and the difference had statistical significance (p < 0.05). The expression of CaSR and Claudin-14 was positively correlated with urinary calcium (p < 0.05).

Conclusions

The formation of renal calculi began in the fourth week after the model was established, and the crystals were mostly located in the renal tubules. During the formation of renal calculi, the renal tubular epithelial cells were damaged, showing granular degeneration and small amounts of calcium salt crystals, accompanied by a few renal tubules beginning to expand and epithelial swelling, granular degeneration, necrosis and shedding of renal tubular epithelial cells, lymphocyte infiltration in the renal interstitium, and small amounts of calcium salt crystals in the renal tubules, which aggravated with time. The serum creatinine, serum uric acid, urea nitrogen, and urinary calcium levels increased with time from the third week and returned to normal after the eighth week. The expression of CaSR and Claudin-14 protein was upregulated and positively correlated with the 24-h urinary calcium excretion value.