Role of ATP-gated P2X7 purinergic receptor in urinary bladder cystitis

Abstract

Bladder cystitis is a chronic lower urinary tract condition characterised by pain perceived to be associated with the bladder filling. The effectiveness of the currently available therapies is low, and new and effective therapeutic options should be developed. There is strong evidence of inflammation in the bladder of cystitis patients and for a role of purinergic P2X7 receptor in the process of inflammation. Therefore, the question arises: could P2X7 antagonism be a possible treatment for bladder cystitis. In this study I will determine whether blockade of purinergic P2X7 receptor prevents urothelial damage induced by either chemical or bacterial stimuli. In this study, an ex-vivo model of bladder cystitis has been established, by perfusing acrolein into the whole porcine bladder. The effect of acrolein and a uropathogenic E. coli strain, UTI89, on the integrity of urothelial cells has also been explored using an in-vitro model of urothelial barrier integrity. A selective P2X7 receptor antagonist, A804598, has been used to determine whether inhibition of P2X7 receptor can protect against cystitis-induced damage to the urothelium in the above mentioned models. As a result, acrolein showed significant damage to urothelial histology, tight junction expression and contractile responses. Acrolein also induced cell apoptosis in the mucosa layer in the ex-vivo model and extreme damage to the urothelial barrier integrity in the in-vitro model. An important finding of this study was the revelation of the role of P2X7 receptor in acrolein-induced urothelial inflammation and that the blockade of the P2X7 receptor by its antagonist remarkably protected the urothelium from this damage. UTI89 has also shown a very strong damaging effect on urothelial integrity, but P2X7 receptor blockade did not show any protective action against this damage. However, UTI89-induced damage was significantly diminished in cells treated with the non-selective P2 receptor antagonist, PPADS. This thesis has provided strong evidence that the P2X7 receptor is involved in acrolein-induced bladder cystitis and indicates the possible therapeutic role for P2X7 receptor antagonists in this type of bladder cystitis. The broad spectrum P2 receptor antagonist PPADS showed partial protection against the effects of bacteria, but it was independent of the P2X7 receptor, suggesting that other purinergic P2 receptors may be involved in this protective action.