Hypothesis / aims of study
Stress urinary incontinence (SUI) is characterized by involuntary leakage associated with exertion, effort, sneezing, coughing, or lifting. Currently, there is no globally approved pharmacological drug for the treatment of patients with SUI. Peripheral noradrenergic innervation is known to be implicated in maintaining urethral pressure in rats. Therefore, potentiation of the noradrenergic activation at the urethral level through norepinephrine (NE) reuptake inhibition may be expected to be effective for patients with SUI. TAS-303 is a novel selective NE reuptake inhibitor that displays significant NE transporter inhibitory activity toward the serotonin or dopamine transporters (1). At present, clinical trial of TAS-303 in female patients with SUI is being analyzed. The aims of this preclinical study were to investigate the pharmacological properties of TAS-303 and its effects on urethral function, using preclinical in vitro and in vivo studies.
Study design, materials and methods
Measurement of monoamine level in plasma: TAS-303 at 3 mg/kg was orally administered to normal rats for 7 days. After that, monoamine levels in plasma were measured.
Measurement of urethral pressure: In anesthetized female normal rats, the urethra and the bladder were catheterized. Saline was infused into the bladder until the rhythmic contraction were confirmed. Saline was then infused into the urethra (3 mL/h), and urethral pressure was continuously recorded. The urethral pressure was analyzed during 30 minutes at 1, 4, 8, 12, or 24 hour after oral administration of TAS-303 (0.3, 1, or 3 mg/kg) to rats. Duloxetine was intravenously administered just before recording the urethral pressure.
Measurement of leak point pressure (LPP): In vaginal distention (VD) rats, LPP was measured in a blinded manner under urethane anesthesia. TAS-303 (0.3, 1, or 3 mg/kg) was orally administered to rats 60 minutes prior to LPP measurement. Duloxetine was intravenously administered 5 minutes prior to the LPP measurement.
Forced Swimming Test (FST): TAS-303 (10, 30, or 100 mg/kg), or tricyclic antidepressant imipramine at 60 mg/kg was orally administered to rats. One hour after dosing, individual rats were placed in the tank filled with water and the immobility time during 5 minutes was measured in a blinded manner.
Measurement of monoamine level in plasma: Plasma NE levels in 3 mg/kg TAS-303-treated group were significantly higher than those in vehicle-treated group. In contrast, there were no differences in plasma epinephrine, dopamine, or serotonin levels between the 3 mg/kg TAS-303-treated group and the vehicle-treated group.
Measurement of urethral pressure: Intravenous administration of 1 mg/kg duloxetine significantly increased urethral pressure by 15% compared to vehicle-treated group (P<0.05). Oral administration of TAS-303 (0.3, 1, or 3 mg/kg) resulted in a dose-dependent increase in the urethral pressure. At 1 hour after administration, TAS-303 (greater than 1 mg/kg) significantly increased the urethral pressure compared to the vehicle-treated group (P<0.05), and increased by 38% at a dose of 3 mg/kg. After administration of 3 mg/kg TAS-303 the increase in the urethral pressure lasted for at least 12 hours.
Measurement of LPP: LPP of VD rats was 32.5 ± 1.6 cmH2O and was significantly lower than that of sham-operated rats (50.6 ± 2.6 cmH2O, P<0.01). Intravenous administration of 1 mg/kg duloxetine significantly increased LPP by 20% compared to the vehicle-treated group (P<0.01). Oral administration of TAS-303 (0.3, 1, or 3 mg/kg) resulted in a dose-dependent increase in LPP. At greater than 1 mg/kg TAS-303, LPP was significantly increased compared to the vehicle-treated group (P<0.05), and increased by 26% at a dose of 3 mg/kg.
FST: The immobility time in the imipramine-treated group was significantly lower than that in the vehicle-treated group (P<0.01). In contrast, no significant difference between the TAS-303-treated group (at each dose) and the vehicle group was detected.
Interpretation of results
We demonstrated that TAS-303 (0.3, 1, or 3 mg/kg) dose-dependently increased urethral pressure in normal rats and leak point pressure in VD rats, with comparable maximum effect to the clinically effective drug duloxetine. Single dose of 3 mg/kg TAS-303 exhibited a long-lasting increase in the urethral pressure in rats. Moreover, TAS-303 showed no effect on the immobility time of rats in the FST test, indicating that this agent would have a lower risk of central adverse effects.