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 µg/mL) and its active principle icariin (1) (IC 50 5.9 µM) 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 IC 50 very close to that of sildenafil (IC 50 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.The inability to achieve or maintain an erection sufficient for satisfactory sexual function is an increasing problem with a considerable impact on interpersonal relationships and quality of life for men.1 During erection, nitric oxide is released from the axon terminals of the parasympathetic nerves and diffuses into smooth muscle cells of the arterial walls of the corpus cavernosum. The consequent activation of guanyl cyclase, converting guanosine triphosphate (GTP) into cyclic guanosine monophosphate (cGMP), causes smooth muscle relaxation, leading to dilation and increased influx of blood into the penile tissue. The trapping of blood in the penis results in an erection.2 Selective inhibitors of cGMPphosphodiesterase-5 (PDE5) such as sildenafil (Viagra), tadalafil, and vardenafil are currently used for erectile dysfunction (ED). However, several adverse effects have been recorded in clinical trials, including priapism and visual disturbances.3 Furthermore, therapy with PDE5 inhibitors is cost-effective. Thus, the search for new compounds of this type for drug development could be worthwhile. A variety of natural plant products, including berberine, forskolin, papaverine, and yohimbine, are claimed to be useful for improving sexual performance. Extracts from Lepidium meyenii Walp. (maca), Panax ginseng C.A. Meyer, Ginkgo biloba L., Ferula hermonis Boiss., and many other herbal remedies, alone or in combination, have been promoted for the treatment of sexual problems. 4,5 With the aim of looking for new leads for selective PDE5 inhibitors, plant extracts and their putative active principles were selected for screening against human PDE5 activity in vitro. Our attention focused on Tribulus terrestris L., Ferula hermonis, Epimedium breVicornum Maxim., and Cinnamomum cassia L., since these extracts are claimed traditionally to improve sexual performance. T. terrestris caused vasodilating and antihypertensive effects in rats 6 and a pro-erectile eff...

The aim of the present study was to confirm that olive oil phenols reduce human platelet aggregability and to verify the hypothesis that cAMP-and cGMP-phosphodiesterases (PDE) could be one of the targets of the biological effect. Four extracts from oils characterized by a high phenol content (HPE), and low phenol levels (LPE) were prepared and analyzed quali-and quantitatively by HPLC-UV and electrospray ionization -MS/MS. Human washed platelets stimulated with thrombin were used for the aggregation assay. Human platelet cAMP-PDE and recombinant PDE5A1 were used as enzyme source. Platelet aggregation and enzyme activity were assayed in the presence of HPE, LPE and individual phenols. The phenol content of HPE ranged between 250 and 500 mg/kg, whereas the LPE content was 46 mg/kg. The compounds identified were hydroxytyrosol (HT), tyrosol (TY), oleuropein aglycone (OleA) and the flavonoids quercetin (QU), luteolin (LU) and apigenin (AP). OleA was the most abundant phenol (range 23·3 to 37·7 %) and LU was the most abundant flavonoid in the extracts. Oil extracts inhibited platelet aggregation with an 50% inhibitory concentration interval of 1·23 -11·2 mg/ml. The inhibitory effect of individual compounds (10 mM) including homovanillyl alcohol (HVA) followed this order: OleA . LU . HT ¼ TY ¼ QU ¼ HVA, while AP was inactive. All the extracts inhibited cAMP-PDE, while no significant inhibition of PDE5A1 (50mg/ml) was observed. All the flavonoids and OleA inhibited cAMP-PDE, whereas HT, TY, HVA (100 mM) were inactive. Olive oil extracts and part of its phenolic constituents inhibit platelet aggregation; cAMP-PDE inhibition is one mechanism through which olive oil phenols inhibit platelet aggregation.

Mechanisms underlying the spasmolytic activity of chamomile still remain unclear. Inhibition of cAMP- and cGMP-phosphodiesterases (PDE) is one of the mechanisms operated by spasmolytic drugs. In this study, the effect of chamomile on PDE was investigated. Human platelet cAMP-PDE and recombinant PDE5A1 were assayed in the presence of infusions prepared from sifted flowers and capitula. LC-ESI-MS/MS analysis showed different compositions in infusions made with sifted flowers and capitula. Chamomile inhibited cAMP-PDE activity (IC50 = 17.9-40.5 microg/mL), while cGMP-PDE5 was less affected (-15% at 50 microg/mL). Among the individual compounds tested, only flavonoids showed an inhibitory effect (IC50 = 1.3-14.9 microM), contributing to around 39% of the infusion inhibition; other compounds responsible for cAMP-PDE inhibition still remain unknown. Although experimental evidence supporting the use of chamomile for gastrointestinal minor spasms dates back to the fifties, cAMP-PDE inhibition as a likely mechanism underlying the spasmolytic activity is reported for the first time.

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