Cats with progressive renal diseases often exhibit a weakened urinary odor, in contrast to normal cat urine which emits odorants with catty odor, such as 3-mercapto-3-methyl-1-butanol, 3-mercapto-3-methylbutyl formate, 3-methyl-3-methylthio-1-butanol, and 3-methyl-3-(2-methyldisulfanyl)-1-butanol. Felinine, an amino acid, is a precursor of these odorants and metabolized from its precursor, 3-methylbutanol glutathione (MBG), via 3-methylbutanol-cysteinylglycine (MBCG). While previous studies have reported felinine excretion in normal cats, its levels in cats with renal diseases remain unclear. This study investigates the urinary excretion of felinine and its precursors in cats with renal diseases and explores whether changes in these metabolites are linked to reduced volatile felinine derivatives with catty odor. Liquid chromatography/mass spectrometry quantified urinary felinine, MBCG, and MBG in 40 normal cats and 66 cats with renal diseases (classified into mild, moderate, and severe renal diseases), revealing a significant decrease in urinary felinine levels in cats with advanced renal disease, while urinary MBG levels increased. The felinine-to-MBG ratio was significantly lower in cats with severe renal disease compared to normal cats and those with mild renal disease. Gas chromatography/mass spectrometry analysis further showed that the emission of felinine derivatives decreased markedly with renal disease progression. A significant correlation was found between urinary felinine excretion and its major derivative, 3-methyl-3-methylthio-1-butanol. These findings suggest that impaired felinine metabolism, likely due to reduced kidney enzyme activity, contributes to both diminished urinary felinine levels and reduced sulfurous odor in cats with renal diseases.
Keywords: domestic cat; felinine; mass spectrometry; renal diseases; urinary odor.