Effects of icariin on phosphodiesterase-5 activity in vitro and cyclic guanosine monophosphate level in cavernous smooth muscle cells.
OBJECTIVE
To investigate the effect of icariin on the cyclic guanosine monophosphate (cGMP)-hydrolytic activity of phosphodiesterase-5 (PDE5) isoforms and the cGMP levels in cavernous smooth muscle cells treated with sodium nitroprusside (SNP).


METHODS
PDE5 isoforms (PDE5A1, A2, and A3) were isolated from sf9 insect cells infected with baculoviruses carrying PDE5 isoform cDNA. Icariin was isolated from Epimedii herba. Varying amounts (10(-6) to 10(-11) M) of icariin or zaprinast were added to reaction mixtures containing PDE5 isoforms and cGMP. The inhibitory effects of icariin and zaprinast were analyzed by GraphPad Software and are expressed as concentration that inhibits 50% (IC50) values. Cavernous smooth muscle cells were isolated from 3-month-old rats, treated with icariin (100 and 200 microM) or zaprinast (200 microM) for 15 minutes, and then with 10 microM SNP for 30, 60, 120, 240, and 360 minutes. The cells were then analyzed for the cGMP concentration using an enzyme immunoassay system.


RESULTS
Icariin inhibited PDE5A1, A2, and A3 with an IC50 value of 1.0, 0.75, and 1.1 microM, respectively. The corresponding IC50 values for zaprinast were 0.33, 0.23, and 0.32 microM. Icariin consistently outperformed the control (SNP-only treatment) in maintaining greater cGMP levels, particularly at the greater concentration of 200 microM. In contrast, zaprinast at 200 microM did better than the control only at 60 and 360 minutes.


CONCLUSIONS
Icariin was inhibitory to all three PDE5 isoforms with similar IC50 values, which were approximately three times greater than those for zaprinast. Icariin was able to enhance cGMP levels in SNP-treated cavernous smooth muscle cells.
Ning
Hongxiu
H
Knuppe Molecular Urology Laboratory, Department of Urology, University of California, San Francisco, School of Medicine, San Francisco, California 94115, USA.
Xin
Zhong-Cheng
ZC
Lin
Guiting
G
Banie
Lia
L
Lue
Tom F
TF
Lin
Ching-Shwun
CS
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D006152:Cyclic GMP / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D004365:Drugs, Chinese Herbal / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010413:Penis / Q000166:cytology / Q000378:metabolism*; D051381:Rats
D004365:Drugs, Chinese Herbal; D005419:Flavonoids; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517384:Pde5a protein, rat; D006152:Cyclic GMP; C056599:icariin