The goal of this pilot clinical trial is to learn if injecting hyaluronic acid into the bladder wall is safe and if it works to reduce pain and urinary frequency in people with interstitial cystitis (IC), also called bladder pain syndrome (BPS).

Who can take part? Adults aged 18 and older who have IC/BPS that did not get better after at least two standard treatments (such as diet changes, oral drugs, or bladder instillations) for 6 months or more.

Main questions the study aims to answer:

What side effects (medical problems) do participants have after the injection procedure?

Does the injection lower pain and reduce how often a person needs to urinate, compared to before the treatment?

What will happen in the study? There is no comparison group or placebo (a look-alike substance with no drug). All participants receive the same treatment.

Participants will:

Have a one-time procedure under intravenous anesthesia (medicine that puts them to sleep)

Receive 20 small injections of hyaluronic acid into the bladder wall using a thin tube with a camera (cystoscope)

Have small tissue samples taken from the bladder (biopsy) during the same procedure

Keep a 3-day diary of their urination

Fill out short questionnaires about pain, symptoms, and quality of life

Return for follow-up visits at 1 day, 1 week, 4 weeks, 3 and 6 months after the injection.

At the 4-week visit, participants will have cystoscopy with bladder biopsy and may receive a second injection if the first one helped.

Possible benefits We cannot guarantee that this experimental treatment will help everyone. However, based on years of experience with similar hyaluronic acid injections in other body parts, researchers hope that injecting the substance directly into the bladder wall will give longer-lasting relief than standard bladder instillations.

Risks and side effects

The most common expected side effects are:

Blood in the urine for a few hours or days (usually goes away on its own) Temporary increase in pain or burning when urinating Infection (unlikely; the team will give antibiotics to lower the risk) Serious problems such as bladder wall puncture or allergic reaction are very rare.

Participation is voluntary People can join or leave the study at any time without giving a reason. Refusing or stopping will not affect their regular medical care at the hospital.

Confidentiality All personal information will be kept private. Results will only be shared in combined, anonymous form (no names or identifying details).

Study design in detail This is a prospective, open-label, single-center, pilot phase I-II clinical trial. No randomization or blinding is applied. All enrolled participants receive the same intervention. The study aims to enroll 10-20 evaluable participants with refractory interstitial cystitis/bladder pain syndrome (IC/BPS).

Rationale for submucosal injection of non-cross-linked hyaluronic acid Hyaluronic acid (HA) is a natural component of the extracellular matrix. Intravesical HA instillations are a standard therapy for IC/BPS but require frequent administration (up to 3 times per week for ≥6 months) and provide only temporary relief in many patients. Submucosal injection is hypothesized to achieve a higher and more prolonged local concentration of HA in the lamina propria, enhancing glycosaminoglycan layer repair, reducing inflammation, and stimulating fibroblast activity and neocollagenesis. This technique is technically identical to endoscopic botulinum toxin injection, which has an established safety profile in the bladder.

Extrapolated safety evidence

The safety of submucosal non-cross-linked HA injection is supported by extensive experience in other mucosal sites:

Laryngoplasty (vocal cords): no serious adverse events (SAEs) in published case series; histological evidence of biocompatibility without chronic inflammation or necrosis.

Vulvovaginal atrophy and provoked vestibulodynia: randomized and retrospective studies show only transient edema and pain (10-25%), no SAEs.

Non-surgical rhinoplasty: serious complication rate <0.05% with proper technique.

Endoscopic treatment of vesicoureteral reflux (VUR): >20 years of experience with dextranomer/hyaluronic acid copolymer (Deflux®) in >2500 patients - obstruction requiring intervention occurs in <1% of ureters; long-term follow-up (≥10 years) shows no malignancy or delayed tissue damage.

Intervention details

Device: Flexible or rigid cystoscope.

Injection needle: 23-25 Gauge, length 4 mm (standard endoscopic injection needle).

Product: Non-cross-linked hyaluronic acid (marketing authorization No. РЗН 2024/22715, Russian Federation). Each milliliter contains 10 mg of sodium hyaluronate.

Injection protocol: 20 submucosal injections of 0.5 mL each, evenly distributed over the bladder wall (trigone avoided). Total volume injected = 10 mL.

Anesthesia: Intravenous general anesthesia.

Post-procedure care: No indwelling catheter. Single dose of perioperative antibiotic (cephalosporin) for infection prophylaxis.

Optional repeat procedure Participants who show a positive clinical response (e.g., ≥2-point reduction in VAS pain score at week 4) may be offered a second identical injection at the week-4 visit (V4). This decision is made jointly by the investigator and the participant.

Histological and endoscopic evaluation

At baseline (V1) and at week 4 (V4, before optional repeat injection), punch biopsies are taken from predetermined sites (e.g., posterior wall, lateral wall). Tissue samples are fixed in formalin and stained with hematoxylin and eosin (H&E) and, if feasible, with alcian blue or for mast cell markers (c-kit/tryptase).

Endoscopic images and videos are recorded at V1 and V4 to assess changes in glomerulations, Hunner's lesions, and overall mucosal appearance.

Statistical analysis plan

Primary analysis (safety): Descriptive statistics - frequency and percentage of participants with adverse events (AEs) grade ≥2 according to CTCAE v5.0, and frequency of SAEs.

Secondary analysis (efficacy): Continuous variables (VAS, ICSI, PUF, functional bladder capacity, voiding frequency) are compared between baseline and follow-up time points (week 4, month 3) using paired t-test (if normally distributed) or Wilcoxon signed-rank test (if non-normal). Categorical variables (PGI-I response) are reported as proportions with exact 95% confidence intervals.

Missing data: No imputation for missing values; analysis is per protocol.

Software: SPSS (version 26 or later) or R.

Significance level: α = 0.05 (two-sided), no adjustment for multiple comparisons (pilot, exploratory).

Data monitoring and quality control The study is conducted at a single tertiary care center (Sverdlovsk Regional Clinical Hospital No. 1, Yekaterinburg). An independent data safety monitoring board (DSMB) is not planned because this is a low-risk pilot study. However, all adverse events are reviewed weekly by the principal investigator. Serious adverse events are reported to the local ethics committee within 24 hours. Source data verification will be performed by the sponsor (the institution) according to its standard operating procedures.

Duration of participation Each participant is expected to be in the study for approximately 6 months (screening through month-6 follow-up). The optional repeat injection extends active treatment to 2 injections (day 0 and week 4).

Funding and sponsorship The study is investigator-initiated and funded by the Sverdlovsk Regional Clinical Hospital No. 1. No commercial funding is involved.

Inclusion Criteria:

• Men and women aged ≥ 18 years.
• Confirmed diagnosis of Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) based on cystoscopic findings (glomerulations after hydrodistension or Hunner's lesions).
• Refractory to at least 2 lines of standard therapy (e.g., dietary modifications, oral medications, intravesical hyaluronic acid instillations, hydrodistension) for ≥ 6 months.
• Pain score ≥ 4 on a 0-10 Visual Analog Scale (VAS) at screening.
• Ability and willingness to provide written informed consent and to complete a 3-day voiding diary.

Exclusion Criteria:

• Active urinary tract infection (bacteriuria > 10⁴ CFU/mL).
• History of genital herpes.
• Severe renal failure (eGFR < 30 mL/min/1.73 m²).
• Known allergy to hyaluronic acid or any component of the study product.
• Pregnancy or breastfeeding.
• Psychiatric disorders or substance abuse that would interfere with study participation.
• Participation in another clinical study within 30 days prior to enrollment.

This is a pilot phase I study with a small sample size. The informed consent form does not include provisions for sharing individual participant data with external researchers, and there is no established infrastructure at our institution for de-identifying and transferring such data. Therefore, there is no plan to make IPD available.