There are many situations in which the urinary bladder becomes inflamed or infected. Some of these relate to the constant or frequent use of catheters for voiding urine. Bladder pain syndrome (BPS)/Interstitial cystitis (IC) refers to "spontaneous" conditions that are currently unknown as specific pathogenesis and have varied aetiologies for bladder pain and both urgency and discomfort with urination in the absence of infection. It is characterized by bladder wall inflammation, defective atrophic bladder urothelium, and significantly high levels of the pro-inflammatory cytokine TNF-α in the bladder tissue. TNF-α induces pro-inflammatory cytokine release by the urothelial cells, further aggravating the inflammatory condition. Several clinical treatments are currently available to repair the urothelium barrier damage by against interacting urinary salutes with underlying urothelial cell compartments. Medihoney® (MH) is a medical-grade Manuka honey with strong pro-healing and anti-microbial properties. Our recent results highlighted its anti-inflammatory effects through inhibition of mast cell degranulation. In addition, it was very well tolerated by the rat urothelial cells and was even cytoprotective against chemical injuries.

This is the first study we investigated the efficacy of Manuka honey on human urothelial cell damage in an inflammatory in vitro of the BPS/IC model.

MTT assay (Roche, Germany) was used to evaluate cell viability of primary human bladder urothelial cells (ScienCell, USA) following incubation with serial concentrations of MH at 0.5, 1, 1.5, 2, 24, 48, and 72 hours. In addition, ELISA assays (R&D Systems, USA) were used to assess the production of the pro-inflammatory cytokines (IL-8 and IL-6) by the human urothelial cells after 24-hour incubation with TNF-α (10 ng/ml) with or without pre-treatment with various MH concentrations.

Pre-treatment of primary human urothelial cell with low concentrations of Manuka honey (2%w/v and 4%w/v) showed significantly protect human urothelial cell death compared to 6% and 8% at all exposure times (Figure 1), and 4% w/v Manuka honey showed significantly decrease induced cytokine expression (IL-6 & IL-8) in an inflammatory status induced by TNF-α (Figure 2).

MH at 2 and 4% concentrations (w/v) were well tolerated by the HUCs at 0.5, 1, 1.5, 2, and 24 hour- incubation, whereas 6 and 8% concentrations showed a significant cytotoxic effect at all exposure durations. In addition, 24-hour incubation with TNF-α induced a significant release of the pro-inflammatory cytokines IL-6 and IL-8 by primary human urothelial cells while there was completely blocked by 4% MH pre-incubation.

This functional experiment suggested that pre-treatment with 4% w/v Manuka honey improves the recovery of the human urothelial cell after damage in vitro model of BPS/IC. Therefore, our results showed that Manuka honey had a positive cytoprotective effect and could be explored as an alternative natural agent in treating IC/BPS to alleviate the chronic bladder wall inflammation and restore healthy impermeable lining urothelium in the bladders of BPS/IC patients.