Lysophosphatidic acid (LPA) is a phospholipid known to mediate various physiological functions such as smooth muscle contraction, cell proliferation or afferent nerve activation via G-protein-coupled receptors. At the annual meeting last year, we demonstrated a significant role of type 1 LPA receptors (LPA1) in the regulation of urethral tonus in rats and proliferation of human prostate stromal cells induced by LPA, using ASP6432, a novel antagonist for LPA1 (1).
In cultured human bladder smooth muscle cells, LPA and LPA receptors are suggested to be involved in mechanical stretch-induced activation of mitogen-activated protein kinase presumably through LPA1, whose mRNA is predominantly expressed (2). However, the role of LPA and LPA1 in the regulation of urine storage in the bladder has not been investigated in vivo. To elucidate the role of LPA and LPA1 in bladder storage function, we investigated the effect of LPA and ASP6432 on the micturition reflex in conscious rats. We also evaluated the effect of ASP6432 on the nitric oxide (NO) synthase inhibitor L-NG-Nitroarginine methyl ester (L-NAME)-induced decrease in micturition interval (3) in conscious rats.

Continuous cystometry was performed in conscious rats. After catheterization into the bladder, animals were confined to Ballman’s cages. The bladder catheter was connected to a pressure transducer and a syringe pump via a three-way tap, and a pressure amplifier was connected to the pressure transducer. Saline was continuously infused into the bladder at a rate of 4.2 mL/hr, and the intravesical pressure (IVP) was measured continuously. 
In the first series of experiment, LPA was administered by intravenous (iv) infusion (5 mg/3 mL/kg/hr). After confirming the effect of LPA in at least three micturition cycles for around 30 minutes, vehicle (distilled water containing 0.025 mol/L NaOH; 1 mL/kg) or ASP6432 (0.3, 1, 3 and 10 mg/mL/kg) was administered by iv bolus injection at the end of each micturition cycle.
In the second experiment, animals were treated with L-NAME (10 mg/mL/kg, iv bolus). After confirming the effect of L-NAME in at least two micturition cycles for around 30 minutes, vehicle (saline with 5% N,N-dimethylformamide) or ASP6432 (0.3 and 1 mg/mL/kg) was administered intravenously, and the effect was evaluated for another 30 minutes.

Intravenous infusion of LPA significantly decreased the micturition interval by 47.1%. ASP6432 inhibited the LPA-induced decrease in micturition interval in a dose-dependent manner, with a statistically significant decrease observed at doses of 1 mg/kg and above (Figure 1). LPA and ASP6432 had no significant effect on the maximal IVP during voiding.
Treatment with L-NAME decreased the micturition interval compared to that at baseline. ASP6432 suppressed the L-NAME-induced decrease in micturition frequency.

LPA decreased the micturition interval without affecting the maximum IVP, implicating that LPA may negatively affect bladder storage function by modulating the bladder response after stretching (2) or activating afferent nerve activity. The inhibitory effect of ASP6432 on the LPA-induced decrease in micturition interval suggests that LPA1 mediates the LPA-induced increase in micturition frequency. 
Intravenous L-NAME treatment in conscious rats decreased the micturition interval, which is consistent with a previous finding that L-NAME induces bladder hyperactivity in conscious rats (3). ASP6432 suppressed the L-NAME-induced increase in micturition frequency, suggesting that inhibition of LPA1 activity can ameliorate bladder overactivity caused by impaired NO production.

The present study demonstrates for the first time that LPA can modulate micturition frequency in vivo and that LPA1 is involved in this process. The improved micturition frequency by ASP6432 following L-NAME treatment suggests that LPA1 regulates the micturition reflex via the nitric oxide pathway, and indicates the potential for LPA1 antagonists as novel therapies for the treatment of bladder overactivity associated with benign prostate hyperplasia or overactive bladder.

Sakamoto K, Noguchi Y, Ueshima K, Yamakuni H, Ohtake A, Sato S, Ishizu K, Hosogai N, Kawaminami E, Takeda M, Masuda N. The Effect of ASP6432, a Novel Type 1 Lysophosphatidic Acid Receptor Antagonist, on Urethral Function and Prostate Cell Proliferation. Poster presented at: International Continence Society Annual Meeting; 13 September, 2017; Florence, Italy.
Kawashima Y, Kushida N, Kokubun S, Ogawa S, Shiomi H, Ishibashi K, Aikawa K, Ikegami K, Nomiya M, Yamaguchi O. Possible effect of lysophosphatidic acid on cell proliferation and involvement of lysophosphatidic acid and lysophosphatidic acid receptors in mechanical stretch-induced mitogen-activated protein kinase. Int J Urol. 2015;22(8):778-84.
Persson K, Igawa Y, Mattiasson A, Andersson KE. Effects of inhibition of the L-arginine/nitric oxide pathway in the rat lower urinary tract in vivo and in vitro. Br J Pharmacol. 1992;107(1):178-84.