Phosphodiesterase IV inhibitors synergistically potentiate relaxation induced by forskolin in guinea-pig trachea

New phosphodiesterase-4 inhibitors present airways relaxant activity in a guinea pig acute asthma model

Asthma is a disease characterized by chronic inflammation and hyper responsiveness of airways. We aimed to assess the relaxant potential of phosphodiesterase-4 (PDE4) inhibitors N-sulfonilhidrazonic derivatives on non-asthmatic and asthmatic guinea pig trachea. Firstly, guinea pigs were sensitized and challenged with ovalbumin, and then morphological, and contractile changes were evaluated resulting from asthma, followed by evaluation of relaxant effect of derivatives on guinea pig trachea and the cAMP levels measurement by ELISA. It has been evidenced hypertrophy of airway smooth muscle, inflammatory infiltrate, and vascular abnormalities. Moreover, only sensitized tracheal rings were responsive to OVA. Contractile response to histamine, but not to carbachol, was greater in sensitized animals, however the relaxant response to aminophylline and isoprenaline were the same in non-asthmatics and asthmatics. N-sulfonilhidrazonic derivatives presented equipotent relaxant action independent of epithelium, with exception of LASSBio-1850 that presented a low efficacy (< 50%) and LASSBio-1847 with a 4-fold higher potency on asthmatics. LASSBio-1847 relaxant curve was impaired in the presence of propranolol and potentiated by isoprenaline in both groups. Furthermore, relaxation was potentiated 54- and 4-fold by forskolin in non-asthmatics and asthmatics, respectively. Likewise, LASSBio-1847 potentiated relaxant curve of aminophylline 147- and 4-fold in both groups. The PKA inhibitor H-89 impaired the relaxant potency of the derivative. Finally, LASSBio-1847 increased tracheal intracellular cAMP levels similarly to rolipram, selective PDE4 inhibitor, in both animals. LASSBio-1847 showed to be promising to relax guinea pig trachea from non-sensitized and sensitized guinea pigs by activation of β2-adrenergic receptors/AC/cAMP pathway.

Synthesis of intramolecular cross-coupling analogues of forskolin

A ring distortion strategy was applied to the synthesis of a series of intramolecular cross-coupled analogues of forskolin 1. Treatment with palladium acetate, forskolin underwent an intramolecular cross-coupling reaction to generate a novel cycloalkene ether 2 in 85% yield. Under the same conditions, a series of forskolin ester analogues 4a-4d were prepared from 1-OH ester derivatives of forskolin 3a-3d in 85-93% yields. Treating cycloalkene ether 2 with aryl iodides in the presence of a palladium catalyst afforded Z-isomers arylation products 5a-5e in a stereoselective manner in 70-85% yields.

In vitro and in silico studies of 8(17),12E,14-labdatrien-18-oic acid in airways smooth muscle relaxation: new molecular insights about its mechanism of action

In the field of experimental pharmacology, researchers continuously investigate new relaxant agents of the airway smooth muscle cells (ASMCs), since the pathophysiology of respiratory illnesses, such as asthma, involves hyperresponsiveness and changes in ASMC homeostasis. In this scenario, labdane-type diterpenes, like forskolin (FSK), are a class of compounds known for their relaxing action on smooth muscle cells (SMCs), being this phenomenon related to the direct activation of AC-cAMP-PKA pathway. Considering the continuous effort of our group to study the mechanism of action and prospecting for compounds isolated from natural sources, in this paper, we presented how the diterpene 8(17),12E,14-labdatrien-18-oic acid (LBD) promotes relaxant effect on ASMC, performing in vitro experiments using isolated guinea pig trachea and in silico molecular docking/dynamics simulations. In vitro experiments showed that in the presence of aminophylline, FSK and LBD had their relaxant effect potentiated (EC₅₀ from 1.4 ± 0.2 × 10^-5 M to 1.5 ± 0.3 × 10^-6 M for LBD and from 2.0 ± 0.2 × 10^-7 M to 6.4 ± 0.4 × 10^-8 M for FSK) while in the presence of Rp-cAMPS this effect was attenuated (EC₅₀ from 1.4 ± 0.2 × 10^-5 M to 3 × 10^-4 M for LBD and from 2.0 ± 0.2 × 10^-7 to 3.1 ± 1.0 × 10^-6 M for FSK). Additionally, in silico simulations evidenced that the lipophilic character of LBD is probably responsible for its stability on AC binding site. LBD presented two preferential orientations, where the double bonds of the isoprene moiety as well as the unique polar group (carboxylic acid) in this compound form important anchoring points. In this sense, we consider that the LBD can interact stabilizing the catalytic dimmer of AC as the FSK, although less efficiently.

The Therapeutic Potential of the Labdane Diterpenoid Forskolin

Forskolin is mainly found in the root of a plant called Coleus forskohlii (Willd.) Briq., which has been used in the traditional medicine of Indian Ayurvedic and Southeast Asia since ancient times. Forskolin is responsible for the pharmacological activity of this species. Forskolin is a labdane diterpenoid with a wide biological effect. Several studies suggested a positive role of forskolin on heart complications, respiratory disorders, high blood pressure, obesity, and asthma. There are numerous clinical and pre-clinical studies representing the effect of forskolin on the above-mentioned disorders but more clinical studies need to be performed to support its efficacy.

Forskolin compared with beclomethasone for prevention of asthma attacks: a single-blind clinical trial

This single-blind study compared the efficacy of oral forskolin versus inhaled beclomethasone for mild or moderately persistent adult asthma. Patients were randomly assigned to receive forskolin (one 10-mg capsule orally per day; n = 30) or beclomethasone (two 50 microg inhalations every 12 h; n = 30) for 2 months. No statistically significant improvement occurred in any lung function parameter in the forskolin-treated patients. Subjects in the beclomethasone-treated group presented a slight but statistically significant improvement in percentage forced expiratory volume in 1 s (FEV(1)), percentage forced expiratory flow in the middle (25 - 75%) expiratory phase (FEF(25 - 75%)) and percentage forced vital capacity (FVC) after 2 months of treatment, though the improvement in absolute values for FEV(1), FEF(25 - 75%), FVC and FEV(1):FVC did not reach statistical significance. There was no statistically significant difference between the forskolin and beclomethasone treatment groups for any lung function parameter at baseline or after treatment. None of the beclomethasone-treated patients had an asthma attack and one forskolin-treated patient had a mild asthma attack during the 2-month study period. More studies are needed in adult asthma patients to confirm whether forskolin may be a useful preventive treatment for mild or moderately persistent adult asthma.

Forskolin versus sodium cromoglycate for prevention of asthma attacks: a single-blinded clinical trial

To determine the efficacy of forskolin in preventing asthma attacks, we performed a single-blinded clinical study in children and adult out-patients at a public hospital in Mexico. Forty patients of either sex with mild persistent or moderate persistent asthma were assigned randomly to 6 months of treatment with forskolin at 10 mg/day orally (capsules) or with two inhalations of sodium cromoglycate every 8 h, i.e. three times a day. The number of patients who had asthma attacks during the treatment period was significantly lower among those receiving forskolin (8/20, 40%) than among those receiving sodium cromoglycate (17/20, 85%). Values of forced expiratory volume in 1 s and forced expiratory flow, mid-phase, A similar in the two groups during the treatment period. We conclude that forskolin is more effective than sod cromoglycate in preventing asthma attacks in patients with mild persistent or moderate persistent asthma.

Antiasthmatic activity of the methanol extract of leaves of Passiflora incarnata

The methanol extract of the leaves of P. incarnata was evaluated for its antiasthmatic effects against acetylcholine chloride (Ach)-induced-bronchospasm in guinea-pigs at doses of 50, 100 and 200 mg/kg. Using a 7-day treatment regimen, significant prevention of dyspnoea-related-convulsions was noted in the animals treated with a 100 mg/kg dose of this extract. No preventive effect was exhibited by the 50 mg/kg dose and at a higher dose, i.e. 200 mg/kg, the preventive effects against Ach-chloride-induced-dyspnoea were also reduced. This may be due to defective alpha-adrenoceptor function reported after excessive or continuous administration of an alpha-receptor agonist.

Different effects of beta-adrenoceptor desensitization on inhibitory actions in guinea-pig trachealis

1. To determine the inhibitory effects of agents that pass through and bypass beta-adrenoceptors under conditions of tolerance to beta-adrenoceptor agonists, we examined the inhibition by the beta-adrenoceptor agonists forskolin and theophylline against contraction induced by methacholine (MCh) after exposure to higher concentrations of a beta-adrenoceptor agonist for a long time in guinea-pig tracheal smooth muscle, using isometric tension records. 2. After exposure to procaterol (0.0003-3 micromol/L) for 45 min, the inhibitory effect of 0.03 micromol/L procaterol on 1 micromol/L MCh-induced contraction was attenuated in a concentration-dependent manner, whereas after exposure to isoprenaline (0.0003-3 micromol/L) for an equivalent time, the inhibitory effect of isoprenaline was markedly attenuated at each concentration. However, after exposure to 3 micromol/L procaterol for 45 min, the inhibitory actions of forskolin and theophylline were, conversely, augmented. 3. These phenomena were observed under conditions whereby the response to MCh returned to control levels 6 h after removal of 3 micromol/L procaterol. The percentage inhibition produced by 0.1 micromol/L forskolin against 1 micromol/L MCh after exposure to normal bathing solution or 3 micromol/L procaterol for 45 min was 9.8 +/- 5.5 and 82.8 +/- 6.5%, respectively (P < 0.001). These values for 100 micromol/L (18 microg/mL) theophylline on MCh resposnes were 9.9 +/- 8.5 and 88.0 +/- 4.4% (n = 6 for both), respectively (P < 0.001). 4. The inhibitory action of agents that bypass beta-adrenoceptors was markedly augmented under conditions of beta-adrenoceptor desensitization in airway smooth muscle. 5. In conclusion, procaterol is less potent in causing desensitization of beta-adrenoceptors than isoprenaline. The activity of adenylyl cyclase may be enhanced after exposure to a high concentration of beta-adrenoceptor agonists.

Prevention by theophylline of beta-2-receptor down regulation in healthy subjects

Adrenergic down-regulation can occur rapidly in many tissues. Therefore beta 2-agonists might have a rapidly decreasing effect in time, which is a potential problem for the treatment of bronchial asthma. This in vivo study tested the hypothesis that theophyline can prevent adrenergic down-regulation. A randomised, double blind, placebo-controlled cross-over study was performed in eight healthy subjects. Terbutaline concentration-effect relationships were studied before and after one week of dosing of terbutaline, with or without theophylline. Slow-release terbutaline 5 mg daily was administered for 7 days in combination with either placebo or slow-release theophylline. Concentration-effect relationships of terbutaline after a single subcutaneous injection were studied before and after the 7 day terbutaline treatment. Eosinopenia and hypokalemia were the systemic effect parameters. Terbutaline concentration-time courses were described with a two-compartment model and those of theophylline with a polynomial equation. A hypothetical effect compartment model was applied to link terbutaline plasma concentration via an Emax model to the studied effects. The interaction of theophylline and terbutaline was described with a non-competitive pharmacodynamic model. After one week of oral terbutaline, the mean EC50 (ng/L) of terbutaline increased for the eosinopenia from 1.87 +/- 1.66 to 3.78 +/- 2.18 (+102%) (p = 0.012) with placebo, and to 2.73 +/- 1.99 (+46%) (p = 0.025) with theophylline; for the hypokalemia the EC50 increased from 4.70 +/- 2.91 to 8.52 +/- 7.26 (+81%) (p = 0.012) with placebo, and to 5.64 + 2.59 (+20%) (p = 0.16) with theophylline. The results indicate that the non-specific phosphodiesterase inhibitor theophylline can prevent terbutaline-induced adrenergic down-regulation to a substantial degree.