To clinically validate the pathological role of Cer accumulation and evaluate a novel microbiota-targeted intervention, we conducted a comprehensive analysis of bladder mucosal specimens from a well-characterized patient cohort stratified according to the established histopathological criteria for CG severity. Our findings revealed specific accumulation of the sphingolipid species Cer(d18:1/18:0) in high-risk CG tissues, which was absent in both low-risk and control groups. Notably, tissue levels of Cer(d18:1/18:0) demonstrated a strong positive correlation with histopathological grade, highlighting its clinical relevance as a driver of PL-CG progression and supporting its potential utility as a prognostic biomarker.

Given the established association between the urinary microbiota and local metabolite production, and considering that the pathogenic urinary microbiota likely serves as the source of this immunomodulatory Cer, we designed and implemented a randomized controlled trial to assess therapeutic remodeling of the bladder microenvironment through UMT. Following the one-month regimen of weekly intravesical instillations, UMT significantly reduced disease burden in PL-CG patients. At the 12-week follow-up, the UMT group exhibited a substantially lower Interstitial Cystitis Symptom Index (ICSI) compared to controls, with an overall response rate of 58.18%. Significant improvements were also observed in key clinical symptoms, including daytime urinary frequency and voiding-related pain. Notably, clinical improvement occurred without a significant reduction in mucosal colonization levels of B. thetaiotaomicron. This observation suggests that UMT's efficacy does not arise from broad bacterial eradication but rather from functional modulation of the microbiota-host interface. Instead, therapeutic benefit was strongly associated with direct depletion of the pathogenic metabolite. Urinary Cer(d18:1/18:0) levels were markedly reduced following UMT, which coincided with the coordinated down-regulation of key pro-inflammatory cytokines in the bladder mucosa, including IL-6, TNF-α, IL-1β, and CXCL1. This sequential cascade thus establishes a clear mechanistic link between pathogenic metabolite clearance, resolution of inflammation, and symptomatic relief.

Inclusion Criteria:

• Age ≥ 18 years at the time of screening
• Histologically confirmed high-risk chronic cystitis (pathological grade ≥ 3 or presence of dysplasia)
• Elevated urinary ceramide (Cer(d18:1/18:0)) level ≥ 50 ng/mL at baseline
• History of failure with standard-of-care therapy for chronic cystitis
• Ability to provide written informed consent and comply with study procedures and follow-up
• Ability to complete patient-reported outcome questionnaires (e.g., ICSI) independently

Exclusion Criteria:

• Active urinary tract infection (UTI) or untreated genitourinary tract infection at screening
• Severe systemic diseases (e.g., uncontrolled diabetes, malignant tumor, severe cardiovascular/hepatic/renal dysfunction) that may interfere with study evaluation
• History of bladder cancer, intravesical chemotherapy or immunotherapy within the past 6 months
• Pregnancy or breastfeeding, or planned pregnancy during the study period
• Participation in another interventional clinical trial within the past 3 months
• Known allergy or hypersensitivity to any component of the UMT product or placebo (normal saline)
• Severe mental illness or cognitive impairment that prevents completion of study assessments
• Any other condition that, in the investigator's judgment, makes the participant unsuitable for enrollment