Synergic stimulation of serotonin 5-HT1A receptor and α2-adrenoceptors for neuropathic pain relief: Preclinical effects of 2-substituted imidazoline derivatives
摘要:
Neuropathic pain affects millions of people causing disability and impairing quality of life. Commonly used analgesics are generally characterized by limited therapeutic outcomes. The serotonin 5-HT1A receptor and the alpha(2) adrenergic receptors are involved in central nociceptive mechanisms with a pivotal role in the inhibitory descending pain pathway. Since their stimulation may modulate the nervous signaling altered by neuropathies, the purpose of the present research is the study of the combined activation of 5-HT1A and alpha(2) receptors by rationally designed imidazoline ligands ((S)-(-)-1 and 2-5) in a rat model of neuropathic pain (chronic constriction injury - CCI). On day 14 after nerve damage, the acute administration per os (p.o.) of low doses of (S)-(-)-1 (0.1-1 mg/kg) was able to significantly increase the pain threshold to mechanical noxious stimuli for more than 1 h. (S)-(-)-1 efficacy was confirmed by the decrease of spontaneous pain evaluated as hind limb weight bearing alterations. The clinically-used compound gabapentin (100 mg/kg p.o.) induced a pain relieving effect similar to (S)-(-)-1 administered at 100 fold lower dose. In the same model, the selected analogues, compounds 2-5 (1 mg/kg p.o.) were effective 30 min after administration. In particular, 5 fully reverted the CCI-induced hypersensitivity. The pain relieving activity of 5 was significantly prevented by the selective 5-HTSA receptor antagonist WAY 100635 (1 mg/kg intraperitoneally, i,p.) and, at a lesser extent, by the alpha(2) antagonist yohimbine (3 mg/kg i.p.). A novel pharmacodynamic approach to the treatment of neuropathic pain is presented.
α2-Adrenoreceptors Profile Modulation. 4. From Antagonist to Agonist Behavior
摘要:
The goal of the present study was to modulate the receptor interaction properties of known alpha(2)-adrenoreceptor (AR) antagonists to obtain novel alpha(2)-AR agonists with desirable subtype selectivity. Therefore, a phenyl group or one of its bioisosteres or aliphatic moieties with similar steric hindrance were introduced into the aromatic ring of the antagonist lead basic structure. The functional properties of the novel compounds allowed our previous observations to be confirmed. The high efficacy of 7, 12, and 13 as alpha(2)-AR agonists and the significant alpha(2C)-AR subtype selective activation displayed by 11 and 15 demonstrated that favorable interactions to induce alpha(2)-AR activation were formed between the pendant groups of the ligands and the aromatic cluster present in transmembrane domain 6 of the binding site cavity of the receptors.