Mass spectrometry evaluation of urine samples in cats with feline interstitial cystitis

In this thesis, the aim was to investigate the urinary metabolites of cats diagnosed with feline interstitial cystitis (FIC) using liquid chromatography–mass spectrometry (LC-MS) to contribute to the understanding of FIC pathophysiology and evaluate the presence of potential biomarkers, thereby supporting updates to treatment protocols. Animal material was selected between June 2024 and March 2025 from among 134 cats presenting with non-specific lower urinary tract disease (LUTD) symptoms and 292 clinically healthy cats brought in for vaccination or routine check-ups at Harran University Faculty of Veterinary Medicine Animal Hospital. Detailed medical history, clinical and laboratory examinations, and LC-MS-based urinary metabolite assessments were conducted for all cats. The data—comprising anamnesis, demographic characteristics, feline environmental modification (MEMO) evaluation, physical and hematobiochemical examinations, ultrasonographic findings (e.g., bladder wall thickness of 0.22 [0.14–0.33 cm]), and radiographic findings—were consistent with previously reported non-obstructive FLUTD characteristics. Based on physical examinations and MEMO evaluations, cats with FIC demonstrated significantly higher respiratory rates (p < 0.001), systolic blood pressure (p < 0.013), body temperature (p < 0.037), bladder wall thickness (p < 0.000), and MEMO scores (p < 0.000) compared to the healthy control group. Urine dipstick and sediment analysis revealed significantly higher urinary red blood cell (RBC) levels in FIC-affected cats than in healthy cats (p < 0.000). Struvite crystals were found in 9 cases, calcium oxalate in 3, and uric acid crystals in 4 cats. Complete blood count (CBC) and serum biochemistry profiles were within reference ranges. LC-MS-based metabolite analysis showed significantly elevated levels (p < 0.05) of malic acid, N-isovalerylglycine, sebacic acid, 2-hydroxybutyric acid, 3-hydroxy-2-methylbutanoic acid, 3-hydroxy-3-methylglutaric acid, and 3-hydroxybutyric acid in FIC cats compared to healthy controls. Considering stress, pain, and hyporexia/anorexia in the development of FIC, along with the MEMO evaluation results, the metabolomic findings suggest a key role of lipolysis, catabolism, ketosis, and reactive oxygen species (ROS) in the pathophysiology of FIC. Specifically, the upregulation of malic acid in urine is indicative of an antioxidant, anti inflammatory, and antidepressant response to prolonged stress; elevated 2-hydroxybutyric acid reflects a compensatory response to bladder hypoperfusion and ischemia; and increased levels of 3-hydroxybutyric acid, 3-hydroxy-2-methylbutanoic acid, and 3-hydroxy-3-methylglutaric acid reflect oxidative stress responses. Furthermore, increases in sebacic acid and N-isovalerylglycine may represent potential antinociceptive and anti-inflammatory responses. In conclusion, useful clinical information in FIC cases can be obtained through ultrasonography and urine sediment analysis. The findings also suggest that stress- and pain-induced disruptions in energy metabolism may lead to ketosis, and ROS may play a significant role in the pathogenesis of FIC, eliciting a repair/protective response from the body. Additionally, employing alternative biomarker identification techniques such as nuclear magnetic resonance (NMR) may provide further insights into the etiopathogenesis of FIC and contribute to the refinement of therapeutic strategies. KEYWORDS: Biomarker, Diagnosis, CAT, Metabolite, Urine