The Impact of Methenamine Hippurate Treatment on Urothelial Integrity and Bladder Inflammation in Aged Female Mice and Women with Urinary Tract Infections

Importance Antibiotics are commonly used to treat and prevent urinary tract infection (UTI), but resistance is growing. Nonantibiotic prophylaxis such as methenamine hippurate (MH) shows clinical promise, but its impact on bladder factors influencing recurrent UTIs (rUTIs) is not well described. Objective The aim of the study was to examine the effect of MH on bladder inflammation and barrier function in aged mice and women with rUTI. Study Design This study included urine samples from an experimental study involving aged female mice with and without methenamine treatment as well as women with rUTI who received either no prophylaxis, MH alone, vaginal estrogen therapy and/or d-mannose alone, or MH in addition to vaginal estrogen therapy and/or d-mannose. We performed a comprehensive cytopathological analysis, which included enzyme-linked immunosorbent assay for immunoglobulin A (IgA), interleukin 6 (in human samples), and fluorescein isothiocyanate-conjugated-dextran permeability assay (in mice) to assess for urothelial permeability. Results In the aged mice model, there was a decreased urothelial permeability (as seen by retention of fluorescein isothiocyanate-conjugated-dextran fluorescence in superficial cells) and increased urinary IgA in mice treated with MH compared with controls. There was no significant difference in urothelial shedding (P > 0.05). In human samples, there was significantly increased urinary IgA in those taking MH alone compared with no prophylaxis (830.1 vs 540.1 ng/mL, P = 0.04), but no significant difference in interleukin 6. Conclusions Methenamine hippurate seems to enhance barrier function as evidenced by decreased urothelial permeability and increased urinary IgA levels, without worsening inflammation. This may reflect another beneficial mechanism by which MH helps prevent rUTI.