Erectile Dysfunction Articles 3 – PDE5

© 2010

Discovery of potent inhibitors for phosphodiesterase 5 by virtual screening and pharmacophore analysis

            (Chen, Chang et al. 2009) Download

AIM: To explore the potent inhibitor from one of the Traditional Chinese medicine (TCM), Epimedium sagittatum. METHODS: We predicted the potent compound, ES03b, de novo evolution from the four Epimedium sagittatum components were verified by molecular docking, pharmacophore analysis, and analysis of quantitative structure-activity relationship (QSAR) model, which was constructed by multiple linear regression. RESULTS: ES03b was chosen to undergo drug modification via de novo evolution. By analyzing the pharmacophore features, we found that the hydrophobic core in the binding site and the hydrogen bond generated at Asn663 played key roles in designing PDE5 inhibitors. ES03b generated 49 diversities (Evo01-49). Evo48 had high activity in prediction. Although the value of prediction was overestimated, Evo48 was suggested as the potent lead. CONCLUSION: In this study, we showed that the hydrophobic core in the binding site and hydrogen bond production on Asn663 played key roles to design PDE5 inhibitors. From several require validation analysis, Evo48 was suggested to be a potent inhibitor.

The use of Butea superba (Roxb.) compared to sildenafil for treating erectile dysfunction

            (Cortes-Gonzalez, Arratia-Maqueo et al. 2010) Download

OBJECTIVE: To evaluate the effect of an extract of Butea superba (Roxb.) (BS) compared to sildenafil for treating erectile dysfunction (ED). PATIENTS AND METHODS: An open label study was carried out among 32 men with organic ED to evaluate the response on the International Index of Erectile Function 5 (IIEF-5) to BS, a 'natural health' product (100 mg), compared to 50 mg of sildenafil (a phosphodiesterase-5 inhibitor). After a 1-week wash-out, responders to BS received either 100 mg starch or 100 mg of another batch of BS (double-blind). RESULTS: Of the patients in the BS group, 27 (84%) responded positively, compared with 26 (81%) in the sildenafil group. When assessing the score alone, 12 (38%) had a better score after taking BS, compared to seven (22%) after sildenafil, and eight (25%) had the same score. The results were surprising and could not be repeated in the double-blind part of the study, where no effect of BS was recorded. CONCLUSIONS: A 'natural' health product containing BS was more effective than sildenafil in the first part of the study, but in the second, using another batch of BS, the positive result could not be repeated and no effect was recorded. The conclusion is that the first preparation of BS was most likely blended with a phosphodiesterase-5 inhibitor, later confirmed by the supplier of BS (a natural health products company) after their own analysis.

Inhibition of cGMP-phosphodiesterase-5 by biflavones of Ginkgo biloba

            (Dell'Agli, Galli et al. 2006) Download

Ginkgo biloba dimeric flavonoids (GBDF) were shown to inhibit cAMP phosphodiesterase activity and to promote vasorelaxation. In particular, amentoflavone exhibited endothelium-dependent relaxation of rat aorta rings via enhanced generation and/or increased biological activity of nitric oxide, leading to elevated cGMP levels. The aim of this study was to investigate whether GBDF were able to inhibit cGMP-specific phosphodiesterase-5 (PDE5) as well. Human recombinant PDE5A1 was prepared by expression of the full-length cDNA of PDE5A1 in COS-7 cells. The PDE activity was determined in the presence of biflavones at 0.1-100 microM. All biflavones inhibited PDE5A1 in a concentration-dependent fashion, ginkgetin being the most potent (IC50 = 0.59 microM). The ability to inhibit the enzyme followed this order: ginkgetin > bilobetin > sciadopitysin > amentoflavone > sequoiaflavone. These data suggest that GBDF could exert a vasodilating effect through a mechanism independent of NO release.

Potent inhibition of human phosphodiesterase-5 by icariin derivatives

            (Dell'Agli, Galli et al. 2008) Download

Plant extracts traditionally used for male impotence (Tribulus terrestris, Ferula hermonis, Epimedium brevicornum, Cinnamomum cassia), and the individual compounds cinnamaldehyde, ferutinin, and icariin, were screened against phosphodiesterase-5A1 (PDE5A1) activity. Human recombinant PDE5A1 was used as the enzyme source. Only E. brevicornum extract (80% inhibition at 50 microg/mL) and its active principle icariin (1) (IC50 5.9 microM) were active. To improve its inhibitory activity, 1 was subjected to various structural modifications. Thus, 3,7-bis(2-hydroxyethyl)icaritin (5), where both sugars in 1 were replaced with hydroxyethyl residues, potently inhibited PDE5A1 with an IC50 very close to that of sildenafil (IC50 75 vs 74 nM). Thus, 5 was 80 times more potent than 1, and its selectivity versus phosphodiesterase-6 (PDE6) and cyclic adenosine monophosphate-phosphodiesterase (cAMP-PDE) was much higher in comparison with sildenafil. The improved pharmacodynamic profile and lack of cytotoxicity on human fibroblasts make compound 5 a promising candidate for further development.


Evidence for contamination of herbal erectile dysfunction products with phosphodiesterase type 5 inhibitors

            (Fleshner, Harvey et al. 2005) Download

PURPOSE: We determined if pharmacological dosages of phosphodiesterase type 5 inhibitors (PDE5) inhibitors were present within a group of natural products marketed for the treatment of erectile dysfunction. MATERIALS AND METHODS: Seven herbal products marketed for the treatment of erectile dysfunction were purchased via the Internet or at local health food stores. Specimens were batched, relabeled and blindly analyzed for contamination with PDE5 inhibitors. High performance liquid chromatography and mass spectrometry were used to detect evidence of contamination with sildenafil, tadalafil or vardenafil. RESULTS: Of the 7 tested products 2 contained pharmacological dosages of sildenafil and tadalafil. Contamination with vardenafil was not identified. Mean dosages of sildenafil and tadalafil were 30.2 and 19.7 mg, respectively. CONCLUSIONS: A significant proportion of natural products marketed for erectile dysfunction contains PDE5 inhibitors. Although marketed as natural products devoid of adverse effects, these agents are known to have potentially fatal drug interactions with nitrates. Better regulation of the natural health products industry is urged.

Relaxation of isolated guinea pig trachea by genistein via inhibition of phosphodiesterase

            (Lin, Chen et al. 2007) Download

We investigated the mechanisms of the relaxant action of genistein, an isoflavone, phytoestrogen and non-specific protein tyrosine kinase inhibitor. Changes in tension of guinea pig tracheal segments were isometrically recorded on a polygraph. Genistein concentration-dependently relaxed histamine (30 microM)-, carbachol (0.2 microM)-, KCl (30 mM)- and leukotriene D4 (10 nM)-induced precontractions and inhibited cumulative histamine- and carbachol-induced contractions in a non-competitive manner. Genistein also concentration-dependently and non-competitively inhibited the cumulative, Ca2+-induced contractions in the depolarized (K+, 60 mM) trachealis. The remaining nifedipine (10 microM)-induced tension of the histamine (30 microM)-induced precontraction was further relaxed by genistein, suggesting that regardless of whether voltage-dependent calcium channels are blocked genistein may have other mechanisms of relaxant action. These other mechanisms of the relaxant effect of genistein appeared to be epithelium-independent and were not affected by the presence of propranolol (1 microM), 2',5'-dideoxyadenosine (10 microM), methylene blue (25 microM), glibenclamide (10 microM), Nomega-nitro-L-arginine (20 microM) or alpha-chymotrypsin (1 U/mL), suggesting that the mechanisms are unrelated to activation of the beta-adrenoceptor, of adenylate cyclase, of guanylate cyclase, of adenosine triphosphate-sensitive potassium channel opening, of nitric oxide formation or of neuropeptide release, respectively. However, genistein (17.5-35 microM) produced parallel, leftward shifts in the concentration-response curves of forskolin and nitroprusside and significantly increased the pD2 values of these two agonists. Both genistein and 3-isobutyl-1-methylxanthine at various concentrations (10-300 microM) concentration-dependently and significantly inhibited cAMP- and cGMP-phosphodiesterase (PDE) activities of the trachealis. The -log IC50 values of genistein were estimated to be 4.28 and 4.17, respectively. The above results reveal that the mechanisms of the relaxant action of genistein may be due to its non-selective inhibition of both PDE activities. IBMX:3-ixobutyl-1-methylxanthine VDCCs:voltage-dependent calcium channels cAMP:adenosine 3',5'-cyclic monophosphate cGMP:guanosine 3',5'-cyclic monophosphate ATP:adenosine triphosphate PDE:phosphodiesterase LTD4:leukotriene D4L-NNA:Nomega-nitro-L-arginine DMSO:dimethyl sulfoxide EGTA: N,N,N',N'-tetraacetic acid ANOVA:analysis of variance.

Effects of icariin on phosphodiesterase-5 activity in vitro and cyclic guanosine monophosphate level in cavernous smooth muscle cells

            (Ning, Xin et al. 2006) Download

OBJECTIVES: 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.

A review of the herbal phosphodiesterase inhibitors; future perspective of new drugs

            (Rahimi, Ghiasi et al. 2010) Download

Phosphodiesterase inhibitors (PDEIs) are a class of drugs that are widely used because of their various pharmacological properties including cardiotonic, vasodilator, smooth muscle relaxant, antidepressant, antithrombotic, bronchodilator, antiinflammatory and enhancer of cognitive function. In the recent years, interest in drugs of plant origin has been progressively increased. Some pharmacologically active substances that come from plants demonstrate PDEI activity. They mainly belong to alkaloids, flavonoids, and saponins. In this review, studies on herbal PDEI were reviewed and their possible therapeutic applications were discussed. Screening plants for PDE inhibitory activity may help to develop standardized phytotherapeutic products or find new sources for new lead structures with PDEI pharmacological activity. The studies discussed in this paper are mainly in vitro and for more reasonable and conclusive results, it is required to conduct in vivo and finally human and clinical tests.

Inhibition of cAMP-phosphodiesterase by biflavones of Ginkgo biloba in rat adipose tissue

            (Saponara and Bosisio 1998) Download

This work compares the inhibition of cAMP-phosphodiesterase in rat adipose tissue by a mixture of Ginkgo biloba biflavones with the effect of individual dimeric flavonoids. The degree of enzyme inhibition by G. biloba biflavones was amentoflavone > bilobetin > sequoiaflavone > ginkgetin = isoginkgetin. Sciadopitysin was almost inactive.

The identification of a nitrosated prodrug of the PDE-5 inhibitor aildenafil in a dietary supplement: a Viagra with a pop

            (Venhuis, Zomer et al. 2011) Download

A new unapproved analogue of sildenafil was detected in capsules of a herbal dietary supplement promoted as a libido enhancing product. Using LC-DAD-MS, MS-MS, HRMS, IR and NMR the analogue was shown to be a derivative of the PDE-5 inhibitor aildenafil with a nitrosamine moiety. A hydrolysis experiment showed that the new analogue was a prodrug of aildenafil and was therefore named nitroso-prodenafil. A capsule contained 108 mg of nitroso-prodenafil which is equivalent to 84 mg of aildenafil and 5.1 mg of nitrogen monoxide (NO). Although it is unknown how much NO can be usefully generated there is 3-fold more NO present than in a 10 mg isorbide nitrate tablet. Both PDE-5 inhibitors and nitrosamines cause vasodilatation by increasing levels of NO. To their coincidental use is warned against because it may cause a fatal drop in blood pressure. In addition, nitrosamines are known carcinogens. This is the first time a PDE-5 inhibitor and a potential NO donor were identified in one molecule. The findings indicate the dangerous level of advancement in medicinal chemistry by producers of unapproved drugs.


References

Chen, C. Y., Y. H. Chang, et al. (2009). "Discovery of potent inhibitors for phosphodiesterase 5 by virtual screening and pharmacophore analysis." Acta Pharmacol Sin 30(8): 1186-94.

Cortes-Gonzalez, J. R., J. A. Arratia-Maqueo, et al. (2010). "The use of Butea superba (Roxb.) compared to sildenafil for treating erectile dysfunction." BJU Int 105(2): 225-8.

Dell'Agli, M., G. V. Galli, et al. (2006). "Inhibition of cGMP-phosphodiesterase-5 by biflavones of Ginkgo biloba." Planta Med 72(5): 468-70.

Dell'Agli, M., G. V. Galli, et al. (2008). "Potent inhibition of human phosphodiesterase-5 by icariin derivatives." J Nat Prod 71(9): 1513-7.

Fleshner, N., M. Harvey, et al. (2005). "Evidence for contamination of herbal erectile dysfunction products with phosphodiesterase type 5 inhibitors." J Urol 174(2): 636-41; discussion 641; quiz 801.

Lin, C. C., J. L. Chen, et al. (2007). "Relaxation of isolated guinea pig trachea by genistein via inhibition of phosphodiesterase." Planta Med 73(4): 323-9.

Ning, H., Z. C. Xin, et al. (2006). "Effects of icariin on phosphodiesterase-5 activity in vitro and cyclic guanosine monophosphate level in cavernous smooth muscle cells." Urology 68(6): 1350-4.

Rahimi, R., S. Ghiasi, et al. (2010). "A review of the herbal phosphodiesterase inhibitors; future perspective of new drugs." Cytokine 49(2): 123-9.

Saponara, R. and E. Bosisio (1998). "Inhibition of cAMP-phosphodiesterase by biflavones of Ginkgo biloba in rat adipose tissue." J Nat Prod 61(11): 1386-7.

Venhuis, B. J., G. Zomer, et al. (2011). "The identification of a nitrosated prodrug of the PDE-5 inhibitor aildenafil in a dietary supplement: a Viagra with a pop." J Pharm Biomed Anal 54(4): 735-41.