pubmed.ncbi.nlm.nih.gov

Pharmacological characterization and CNS effects of a novel highly selective alpha2C-adrenoceptor antagonist JP-1302 - PubMed

Pharmacological characterization and CNS effects of a novel highly selective alpha2C-adrenoceptor antagonist JP-1302

J Sallinen et al. Br J Pharmacol. 2007 Feb.

Abstract

Background and purpose: Pharmacological validation of novel functions for the alpha2A-, alpha2B-, and alpha2C-adrenoceptor (AR) subtypes has been hampered by the limited specificity and subtype-selectivity of available ligands. The current study describes a novel highly selective alpha2C-adrenoceptor antagonist, JP-1302 (acridin-9-yl-[4-(4-methylpiperazin-1-yl)-phenyl]amine).

Experimental approach: Standard in vitro binding and antagonism assays were employed to demonstrate the alpha2C-AR specificity of JP-1302. In addition, JP-1302 was tested in the forced swimming test (FST) and the prepulse-inhibition of startle reflex (PPI) model because mice with genetically altered alpha2C-adrenoceptors have previously been shown to exhibit different reactivity in these tests when compared to wild-type controls.

Key results: JP-1302 displayed antagonism potencies (KB values) of 1,500, 2,200 and 16 nM at the human alpha2A-, alpha2B-, and alpha2C-adrenoceptor subtypes, respectively. JP-1302 produced antidepressant and antipsychotic-like effects, i.e. it effectively reduced immobility in the FST and reversed the phencyclidine-induced PPI deficit. Unlike the alpha2-subtype non-selective antagonist atipamezole, JP-1302 was not able to antagonize alpha2-agonist-induced sedation (measured as inhibition of spontaneous locomotor activity), hypothermia, alpha2-agonist-induced mydriasis or inhibition of vas deferens contractions, effects that have been generally attributed to the alpha2A-adrenoceptor subtype. In contrast to JP-1302, atipamezole did not antagonize the PCP-induced prepulse-inhibition deficit.

Conclusions and implications: The results provide further support for the hypothesis that specific antagonism of the alpha2C-adrenoceptor may have therapeutic potential as a novel mechanism for the treatment of neuropsychiatric disorders.

PubMed Disclaimer

Figures

Figure 1
Figure 1

The chemical structure of JP-1302. Molecular weight is 368.47.

Figure 2
Figure 2

Subtype-selective antagonism of JP-1302 on human α2-AR subtypes. [35S]-GTPγS-binding was determined in membranes of CHO cells that were stably transfected with one of the three human α2-subtypes (Pohjanoksa et al., 1997). The α2-ARs in the membranes were stimulated with fixed concentrations of adrenaline that were chosen to represent the 6–7-fold of previously established EC50 values: 5 μ

M

for the α2A (EC50=0,76 μ

M

), 15 μ

M

for the α2B (EC50=2.4 μ

M

) and 5 μ

M

for the α2C (EC50=0.71 μ

M

). In each experiment, every antagonist concentration was run in duplicate and each antagonism experiment was repeated at least three times.

Figure 3
Figure 3

α2-AR antagonism by atipamezole, but not JP-1302, on α2-agonist (dexmedetomidine)-induced inhibition of contractions of vas deferens. The inhibition of electrically evoked contractions by dexmedetomidine was considered to be an indication of agonism at α2-ARs and agonist effects were expressed as percent inhibition of the electrically evoked contractions. No agonism by JP-1302 was observed. Means and s.d. of replicates (n=3 for atipamezole and n=6 for JP-1302) were calculated and used to construct agonist dose–response curves in the absence and presence of antagonists. pA2-values for antagonists were calculated as described in the Methods.

Figure 4
Figure 4

Antagonism of mydriatic effect of α2-agonist as percentage of vehicle control. Dexmedetomidine produced a clear mydriatic effect (i.e. pupil dilatation) that was readily antagonized by atipamezole (P<0.001) but not by JP-1302. After measurement of the baseline pupil diameter, all rats (n=5/group, total of 15) were given the α2-agonist dexmedetomidine 10 μg i.v. The mydriatic effect of dexmedetomidine was measured after 5 min and then cumulative doses of either atipamezole or JP-1302 or equivalent volumes of vehicle were applied intravenously at 5 min intervals.

Figure 5
Figure 5

Antagonism of α2-agonist-induced sedation (a) and hypothermia (b). Atipamezole dose-dependently reversed the immobility and hypothermia produced by dexmedetomidine whereas JP-1302 had no effect. The animals were injected either with JP-1302 or atipamezole 20 min before the injection of dexmedetomidine (50 nmol kg−1 s.c.). Spontaneous locomotor activity was measured 20–30 min after dexmedetomidine injection and the body temperature was recorded at the end of the locomotor test. **P<0.01, ***P<0.001 compared to vehicle+dexmedetomidine group. Data are presented as mean±s.e.m., n=8–12/group.

Figure 6
Figure 6

Effect of JP-1302 and reference antidepressant desipramine (Desipr) in the forced swimming test. Drug treatments were applied during the period between the two sessions, the first 15 min after the pre-test swim and the second dosing at 1 h before the test swim. The effects on immobility are presented as mean±s.e.mean, n=10–16/group. *P<0.05, **P<0.01, **P<0.001 compared to vehicle group.

Figure 7
Figure 7

Effect of JP-1302 and atipamezole (Ati) on startle reactivity (a, c) and PPI as percentage inhibition of the startle reflex to 118dB pulse alone (b, d) in two separate experiments with SD (a, b) and Wistar (c, d) rats. Pulse and prepulse durations were 40 ms, the prepulse level was 15 dB above background noise and the prepulse–pulse interval was 100 ms. Data are expressed as mean±s.e.m., n=8–10. *P<0.05, **P<0.01, ***P<0.001 compared to vehicle+phencyclidine (PCP) group.

Comment in

Similar articles

Cited by

References

    1. Altman JD, Trendelenburg AU, MacMillan L, Bernstein D, Limbird L, Starke K, Kobilka BK, Hein L. Abnormal regulation of the sympathetic nervous system in alpha2A-adrenergic receptor knockout mice. Mol Pharmacol. 1999;56:154–161. - PubMed
    1. Arnsten AF. Adrenergic targets for the treatment of cognitive deficits in schizophrenia. Psychopharmacology (Berlin) 2004;174:25–31. - PubMed
    1. Brede M, Philipp M, Knaus A, Muthig V, Hein L. Alpha2-adrenergic receptor subtypes – novel functions uncovered in gene-targeted mouse models. Biol Cell. 2004;96:343–348. - PubMed
    1. Cervo L, Grignaschi G, Samanin R. Alpha 2-adrenoceptor blockade prevents the effect of desipramine in the forced swimming test. Eur J Pharmacol. 1990;175:301–307. - PubMed
    1. Haapalinna A, Viitamaa T, MacDonald E, Savola J-M, Tuomisto L, Virtanen R, Heinonen E. Evaluation of the effects of a specific α2-adrenoceptor antagonist, atipamezole, on α1- and α2-adrenoceptor subtype binding, brain neurochemistry and behaviour in comparison with yohimbine. Naunyn-Schimiedeberg's Arch Pharmacol. 1997;356:570–582. - PubMed

MeSH terms

Substances