# Neutrophil Extracellular Traps Promote Urolithiasis Formation in Dogs: A Preliminary Study

## TL;DR

This study shows that immune system structures called neutrophil extracellular traps may help form and grow urinary stones in dogs, suggesting new ways to prevent and treat the condition.

## Contribution

The study is the first to link neutrophil extracellular traps to urolithiasis in dogs, revealing a novel inflammatory mechanism.

## Key findings

- Neutrophil extracellular traps (NETs) were found within urinary stones and their surrounding environment in dogs.
- Common urinary tract bacteria triggered NET formation, which promoted mineral crystal growth in lab experiments.
- Enzymatic breakdown of NETs reduced stone growth in vitro, suggesting a potential treatment strategy.

## Abstract

Urinary stones are common in dogs and often return after treatment. The most common types are struvite and calcium oxalate stones. Stone formation has traditionally been explained by changes in urine acidity, high mineral concentrations, and urinary tract infections. However, these factors cannot fully explain why stones continue to grow and recur in many dogs. In this study, we explored whether the dog’s immune system may also play a role in this process. Certain immune cells can release web-like structures made of deoxyribonucleic acid and antimicrobial proteins to trap invading microorganisms. We found that these structures were present within urinary stones and in the surrounding environment. In laboratory experiments, common bacteria from canine urinary tract infections triggered the formation of these structures, which then promoted the formation and growth of mineral crystals. When these structures were broken down using a specific enzyme, stone growth was reduced. These findings suggest that urinary stone formation in dogs may be linked not only to chemical changes in urine but also to inflammation-related processes. Understanding this mechanism could help to explain why stones recur and may support the development of new prevention and treatment strategies.

Canine urolithiasis is a common and highly recurrent urinary tract disease, with struvite and calcium oxalate being the predominant stone types. Stone formation has traditionally been attributed to urinary physicochemical factors, including urine pH, mineral supersaturation, and urinary tract infection. However, these factors alone cannot fully explain the persistent growth and rapid progression of stones in affected dogs. In this study, we provide evidence that innate immune mechanisms, particularly neutrophil extracellular traps (NETs), are associated with canine urolith formation. We found that neutrophils, key cells of the innate immune system, release neutrophil extracellular traps composed of DNA and antimicrobial proteins, which are consistently present within urinary stones and their surrounding microenvironments. Common canine urinary pathogens were shown to trigger this response, and these immune-derived structures promoted crystal nucleation, aggregation, and stone growth in experimental systems. Importantly, enzymatic degradation of NETs by DNase I attenuated NET-associated stone growth under in vitro conditions. These findings suggest that canine urinary stones develop not only as a consequence of physicochemical factors, but also in association with inflammation-driven biomineralization processes involving NETs. Recognizing the contribution of innate immunity provides new insight into stone recurrence and may inform future preventive and therapeutic strategies.