Ketamine is a schedule III controlled substance used clinically as an anesthetic and antidepressant. The drug?s hallucinogenic effects have led over the last 20 years to its unregulated consumption by abusers world- wide. At least 2.3 million Americans above age 12 have abused ketamine (NIDA). Ketamine toxicity has been reported in treated patients as well as in ketamine abusers. Indeed, ~30% of ketamine abusers develop ketamine cystitis, a new urological disorder first defined in 2007. Ketamine cystitis is characterized by bladder pain with urinary urgency, frequency, dysuria, and hematuria. Urodynamic and ultrasonic studies indicate a small bladder, and 50% of cases are accompanied by vesicoureteric reflex and hydronephrosis. As the molecular mechanism of ketamine cystitis is unknown, the mainstays of treatment remain abstinence from ketamine and supportive therapies, with cystectomy and bladder reconstruction as a last resort. The overall goals of this application are to define the underlying molecular target of ketamine cystitis and to develop novel effective therapeutic approaches to the disorder. We present compelling evidence that ketamine induces voiding dysfunction by dose-dependent inhibition of bladder smooth muscle (BSM) contraction. We have shown that ketamine inhibits BSM contraction by acting as an inhibitor of the novel ketamine target, the L-type voltage-gated calcium channel, Cav1.2. We have further shown that ketamine inhibits recombinant Cav1.2 activity expressed in Xenopus oocytes. We have also demonstrated that the Cav1.2 agonist Bay k8644 can fully reverse the ketamine-induced voiding abnormality in vivo. In this proposal, we will further examine our hypothesis through the following two aims: (1) we will examine the in-depth mechanism by which ketamine inhibits the Cav1.2 channel as expressed endogenously in bladder smooth muscle cells and as recombinant polypeptides in Xenopus oocytes. (2) We will then examine the hypothesis that Cav1.2 agonists are novel drugs or lead compounds for treatment of ketamine-induced smooth muscle pathology. To achieve our aims, we will use patch clamp techniques to study the mechanism of ketamine inhibition of Cav1.2 channels in both Xenopus oocytes and freshly isolated bladder smooth muscle cells. We will then generate a chronic ketamine cystitis mouse model, and treat these animals with systemic BayK8644 to test the ability of Cav1.2 agonists to reverse or ameliorate ketamine cystitis. The therapeutic effect of BayK8644 will be evaluated by in vivo urodynamic assays (voiding spot assay, cystometrograms), myography, and molecular/cellular approaches. Our findings from this study will characterize Cav1.2 as a novel molecular target for the treatment of ketamine cystitis, and will test candidate preclinical small molecule therapeutics for treatment of ketamine cystitis. We are confident that our preliminary findings and proposed experiments will expedite development of novel Cav1.2 agonists for treatment of ketamine-induced disease of the lower urinary tract, for which available treatments have been largely ineffective.
Ketamine cystitis, a new devastating clinical syndrome with voiding frequency, urgency, and bladder pain, afflicts young ketamine abusers with enormous economic and social burden. This project will determine the molecular target that leads to the development of ketamine cystitis, and develop novel therapeutic strategies to treat this debilitating syndrome.
