Hypertension study in anaesthetized rabbits: protocol proposal for AT1 antagonists screening.

INTRODUCTION: The aim of this study was to establish an optimized fast and safe protocol for the pharmacological screening of AT(1) antagonists. MATERIALS AND METHODS: The pharmaceutical prototype AT(1) antagonist losartan, its active metabolite EXP3174 and the synthetic compound MMK1 were analysed in order to validate the protocol. Ang II was continuously infused while the animals received the drugs in two procedures. RESULTS: In the post-treatment procedure drugs were administered either in a single bolus dose or in a sequential manner. When losartan was administered in a single bolus dose, efficacy was evident until the 7th min (p=0.012) whilst EXP3174 infusion extended the efficiency up to the end of the study (p=0.006). In addition, the sequential injections of losartan prolonged the inhibitory time interval until the end of the study (p=0.045). In the pre-treatment procedure, results suggested a dose-dependent inhibitory effect for both antagonists. The pressor response to Ang II was unchanged after MMK1 administration either in the post- or in the pre-treatment mode. CONCLUSIONS: The proposed protocol appears to be safe, simple and fast for the pharmacological screening of AT(1) antagonists and enables the evaluation of new antagonists using lower doses than any other reported in the literature.

A computational study on cannabinoid receptors and potent bioactive cannabinoid ligands: homology modeling, docking, de novo drug design and molecular dynamics analysis.

When X-ray structure of a ligand-bound receptor is not available, homology models of the protein of interest can be used to obtain the ligand-binding cavities. The steroelectronic properties of these cavities are directly related to the performed molecular model coordinates. Thus, the use of different template structures for homology may result in variation of ligand-binding modes. We have recently reported the MD simulations of a potent CB ligand at bovine rhodopsin-based CB1 and CB2 receptors (Durdagi et al., Bioorg Med Chem 16:7377-7387, 2008). In this present study, a homology modeling study based on the beta2-adrenergic receptor for both CB1 and CB2 receptors was performed, and the results were compared with rhodopsin-based models. In addition, the role of membrane bilayers to the adopted conformations of potent AMG3 CB ligand has been analyzed for receptor-free and membrane-associated receptor systems. The performed MD trajectory analysis results have shown that gauche conformations at the terminal segment of the alkyl side chain of AMG3 are not favored in solution. Different adopting dihedral angles defined between aromatic and dithiolane rings at the active sites of the CB1 and CB2 receptors, which are adapted lead to different alkyl side chain orientations and thus, may give clues to the medicinal chemists to synthesize more selective CB ligands. The binding sites of receptors derived by rhodopsin-based models have been regenerated using the beta2-adrenergic based template receptors. The re-obtained models confirmed the ligand-binding pockets that were derived based on rhodopsin.