Boydens Charlotte, Pauwels Bart, Vanden Daele Laura, Van de Voorde Johan
Department of Pharmacology, Ghent University, Ghent, Belgium.
Department of Pharmacology, Ghent University, Ghent, Belgium.
J Sex Med. 2017 Apr;14(4):502-509. doi: 10.1016/j.jsxm.2017.02.005. Epub 2017 Mar 1.
Intracellular cyclic guanosine monophosphate (cGMP) concentrations are regulated by degradation enzymes (phosphodiesterases) and by active transport across the plasma membrane by multidrug resistance proteins (MRPs) 4 and 5.
To evaluate the functional effect of MRP-4 inhibition and the role of MRP-4-mediated cGMP export in mouse corpora cavernosa.
Isometric tension of mouse corpora cavernosa was measured after cumulative addition of MK-571, an inhibitor of MRP-4, or sildenafil, a phosphodiesterase type 5 inhibitor. In addition, the effect of MRP-4 inhibition on cGMP-independent and cGMP-dependent relaxations was studied. In vivo intracavernosal pressure and mean arterial pressure measurements were performed after intracavernosal injection of MK-571. The effect of MRP-4 inhibition on cGMP content was determined using an enzyme immunoassay kit.
Measurement of the effect of MK-571 on cGMP content, relaxant responses of mouse corpora cavernosa to cGMP-independent and cGMP-dependent vasodilating substances, and determination of the ratio of intracavernosal pressure to mean arterial pressure after intracavernosal injection of MK-571.
MK-571 and sildenafil relaxed the corpora cavernosa concentration dependently, with sildenafil being the more potent relaxing compound. Furthermore, MK-571 enhanced relaxing responses to cGMP-dependent substances, such as sodium nitroprusside, sildenafil, acetylcholine, and electrical field stimulation, with the latter even under in vitro diabetic conditions. In contrast, cGMP-independent relaxations were not altered by MRP-4 inhibition. Intracavernosal administration of MK-571 significantly increased intracavernosal pressure, with minimal effect on mean arterial pressure. The cGMP analysis showed that MRP-4 inhibition was accompanied by increased cGMP levels.
MRP-4, at least when targeted locally in the penis or when combined with a phosphodiesterase type 5 inhibitor, might be a valuable alternative strategy for the treatment of (diabetic) erectile dysfunction.
This study is the first to demonstrate an in vitro direct relaxant and an in vivo pro-erectile effect of the MRP-4 inhibitor, MK-571, on mouse corpora cavernosa. However, the functional effect of MRP-5-mediated export in mouse corpora cavernosa was not explored, which has been suggested to play the predominant role in cGMP export.
Inhibition of MRP-4 increases basal and stimulated levels of cGMP, leading to corpora cavernosa relaxation and penile erection. Therefore, in addition to degradation of cGMP, export of cGMP by MRP-4 could contribute substantially to regulating cGMP levels in mouse corpora cavernosa. Boydens C, Pauwels B, Vanden Daele L, Van de Voorde J. Inhibition of Cyclic GMP Export by Multidrug Resistance Protein 4: A New Strategy to Treat Erectile Dysfunction? J Sex Med 2017;14:502-509.
细胞内环磷酸鸟苷（cGMP）浓度受降解酶（磷酸二酯酶）以及多药耐药蛋白（MRP）4和5介导的跨质膜主动转运调控。
评估MRP-4抑制的功能效应以及MRP-4介导的cGMP外排在小鼠海绵体中的作用。
在累积添加MRP-4抑制剂MK-571或5型磷酸二酯酶抑制剂西地那非后，测量小鼠海绵体的等长张力。此外，研究了MRP-4抑制对非cGMP依赖性和cGMP依赖性舒张的影响。在海绵体内注射MK-571后，进行体内海绵体内压和平均动脉压测量。使用酶免疫分析试剂盒测定MRP-4抑制对cGMP含量的影响。
MK-571和西地那非均浓度依赖性地使海绵体舒张，西地那非是更有效的舒张化合物。此外，MK-571增强了对cGMP依赖性物质（如硝普钠、西地那非、乙酰胆碱和电场刺激）的舒张反应，后者即使在体外糖尿病条件下也是如此。相比之下，MRP-4抑制未改变非cGMP依赖性舒张。海绵体内给予MK-571显著增加海绵体内压，对平均动脉压影响最小。cGMP分析表明，MRP-4抑制伴随着cGMP水平升高。
MRP-4至少在阴茎局部靶向或与5型磷酸二酯酶抑制剂联合使用时，可能是治疗（糖尿病性）勃起功能障碍的一种有价值的替代策略。
本研究首次证明MRP-4抑制剂MK-571对小鼠海绵体具有体外直接舒张和体内促勃起作用。然而，未探讨MRP-5介导的外排在小鼠海绵体中的功能效应，而有人认为其在cGMP外排中起主要作用。
抑制MRP-4可增加cGMP的基础水平和刺激水平，导致海绵体舒张和阴茎勃起。因此，除了cGMP降解外，MRP-4介导的cGMP外排可能在很大程度上有助于调节小鼠海绵体中的cGMP水平。Boydens C, Pauwels B, Vanden Daele L, Van de Voorde J. 多药耐药蛋白4对环磷酸鸟苷外排的抑制作用：治疗勃起功能障碍的新策略？《性医学杂志》2017年；14:502 - 509。
