A combination of peripherally restricted CB1 and CB2 cannabinoid receptor agonists reduces bladder afferent sensitisation in cystitis

Cannabinoid agonists can potentially ameliorate lower urinary tract symptoms (LUTS), including pain associated with interstitial cystitis/bladder pain syndrome (IC/BPS). This study aims to determine the contributions of the cannabinoid 1 receptors (CB₁Rs) and CB₂Rs in regulating the activity of different functional classes of afferents, comparing normal healthy bladder with bladders from guinea pigs with protamine/zymosan-induced cystitis. The mechanosensitivity of different functional afferent classes was determined by ex vivo single-unit extracellular recordings. Peripherally restricted CB₁R preferential agonists, ACEA and PrNMI and peripherally restricted CB₂R selective agonists, 4Q3C and olorinab all reduced the mechanosensitivity of mucosal bladder afferents. The potency and efficacy of these synthetic cannabinoid agonists were significantly increased in cystitis compared to controls. Combined application of CB₁R agonists, ACEA or PrNMI with the CB₂R agonist, 4Q3C produced additive inhibitory effects. ACEA and PrNMI also inhibited the stretch-induced firing of high-threshold muscular bladder afferents in animals with cystitis. In contrast, low- and high-threshold muscular-mucosal bladder afferents were unaffected by the CB₁R and CB₂R agonists in control and cystitis. Our data indicated that peripherally restricted CB₁R and CB₂R agonists effectively reduce the sensitisation of probable nociceptive afferents in the bladder in cystitis. The findings also suggest a potential benefit of simultaneously targeting both the CB₁Rs and CB₂Rs to ameliorate LUTS in cystitis.