Elsevier

Neuroscience Research

Volume 42, Issue 1, January 2002, Pages 57-63
Neuroscience Research

Structure–activity studies with ring E analogues of methyllycaconitine on bovine adrenal α3β4* nicotinic receptors

https://doi.org/10.1016/S0168-0102(01)00304-2Get rights and content

Abstract

The development of new agents that selectively interact with subtypes of neuronal nicotinic receptors (nAChRs) is of primary importance for the study of physiological processes and pathophysiological conditions involving these receptors. Our laboratory has evidence that simple ring E analogues of methyllycaconitine (MLA) act as antagonists to bovine adrenal α3β4* nAChRs. The following studies were designed to characterize the concentration–response effects of several ring E analogues of MLA in order to assess structural requirements involved with their inhibitory activity on bovine adrenal α3β4* nAChRs. Ring E analogues with various substitutions on the ring E nitrogen were tested for their ability to inhibit nicotinic stimulated adrenal catecholamine release and [3H]epibatidine binding to a bovine adrenal membrane preparation. Several N-alkyl derivatives inhibited secretion with IC50 values in the low micromolar range. The N-phenpropyl analogue was the most potent of the analogues tested (IC50, 11 μM) on adrenal secretion. Competition binding studies suggest a noncompetitive interaction of the analogues with bovine adrenal nAChRs. These studies identify several structural features of ring E analogues of MLA which significantly affect their inhibitory activity on bovine adrenal α3β4* nAChRs.

Introduction

Nicotinic acetylcholine receptors (nAChRs) containing α3 subunits are found on postsynaptic neurons in autonomic ganglia and chromaffin cells of the adrenal medulla. The nAChR subtypes believed to be expressed in these tissues are α3β4*, α3α5β4 and α3α5β2β4 (Lukas et al., 1999). These α3-containing nAChRs play a prominent role in autonomic neurotransmission and adaptive responses to stress. α3-Containing nAChRs have also been found in several brain regions (e.g. substantia nigra, ventral tegmental area, hippocampus, the medial habenula and interpeduncular nucleus) (for reviews, see Jones et al., 1999, Picciotto et al., 2000, Cordero-Erausquin et al., 2000). The precise subunit composition and the physiological role of these nAChRs in the CNS remain to be elucidated, but have been reported to be involved with the control of norepinephrine (Sershen et al., 1997) and dopamine release (Kulak et al., 1997). A diminution of α3 mRNA in regions of the aged brain of humans (Terzano et al., 1998) and rats (Charpantier et al., 1999) has also been reported, suggesting a contribution of neurons expressing α3-containing nAChRs to age associated memory impairment.

Subtypes of neuronal nAChRs can be pharmacologically differentiated by a variety of agents found in nature, including snake venom neurotoxins (Luetje et al., 1990), marine snail conotoxins (McIntosh et al., 1994, Johnson et al., 1995, Cartier et al., 1996), and the plant alkaloid, methyllycaconitine (MLA) (Macallan et al., 1988, Ward et al., 1990). MLA is a potent, nonpeptide, nAChR antagonist showing selectivity for α7 nAChRs. MLA also interacts with other nAChRs subtypes, albeit at lower affinity (Yum et al., 1996, Davies et al., 1999). Recently, our laboratory reported that MLA inhibits nAChR-stimulated adrenal catecholamine secretion (Bergmeier et al., 1999) demonstrating activity of MLA on α3β4* nAChRs. These effects, though, occur at MLA concentrations that are approximately 1000-fold higher than concentrations that affect α7 nAChRs.

Although, the nonpeptide nature of MLA lends itself to structure–activity relationship (SAR) studies, few SAR studies have been reported and are focused on α7 nAChR activity (Davies et al., 1997, Hardick et al., 1996). Our laboratory has recently described simple ring E analogues of MLA containing the succinimidoylanthranilate side chain (Fig. 1). The availability of these analogues allows for the study of structural determinants of MLA which may be important for its activity on bovine α3β4* nAChRs. The demonstration that the ring E analogues inhibit nAChR-stimulated adrenal catecholamine secretion (Bergmeier et al., 1999) suggests that the ring E moiety of MLA containing the succinimidoylanthranilate side chain may be important for the activity of MLA on adrenal nAChRs. The following studies were designed to further characterize the SAR of ring E analogues of MLA to assess structural determinants affecting activity on adrenal nAChRs.

Section snippets

Materials

Ring E analogues (LB-1 to LB-8, IB-1, AB-2) were synthesized as described by Bergmeier et al. (1999). Limited availability of certain analogues due to difficulties in synthesis prevented their use in some studies. (−)Nicotine hydrogen tartrate, α-bungarotoxin (αBGT), polyethyleneimine (PEI) and components of N2+ media were obtained from the Sigma Chemical Company (St. Louis, MO). Dulbecco's Modified Eagle Medium (DMEM) and DMEM/F12 (used in N2+ medium) were obtained from Life Technologies

Results

MLA has been reported to inhibit bovine adrenal catecholamine secretion mediated by both α7 nAChRs (IC50 value, 0.1 μM) (Lopez et al., 1998) and α3β4* nAChRs (low micromolar) (Bergmeier et al., 1999). Our laboratory has previously identified ring E analogues of MLA that also inhibit nicotine–stimulated adrenal catecholamine secretion (Bergmeier et al., 1999), implicating activity of these analogues on α3β4* nAChRs. In the following studies the concentration–response effects of several ring E

Discussion

The principal receptors that mediate adrenal catecholamine secretion are believed to be α3β4* nAChRs (Wenger et al., 1997). Our laboratory has previously identified ring E analogues of MLA that inhibit nicotine–stimulated adrenal catecholamine secretion (Bergmeier et al., 1999), implicating activity of these analogues on α3β4* nAChRs. The N-phenpropyl analogue (LB-8) was the most potent analogue with an IC50 value (11 μM), similar in potency to other inhibitors of adrenal catecholamine release

Acknowledgements

This project was supported by NIH Grants DA12707 (SCB, DBM) and DA10569 (DBM). DLB was supported as a NIDA Underrepresented Minority Supplement Awardee (DA10569). KIA was supported by a fellowship from the Egyptian Cultural and Educational Bureau. RBF was supported by an NIH Training grant (MH19936).

References (27)

Cited by (44)

  • Enantioselective synthesis of BE ring analogues of methyllycaconitine

    2016, Tetrahedron
    Citation Excerpt :

    α]D20 values are given in 10−1 deg cm3 g−1. Ethyl 2-(bromomethyl)acrylate 315 and 2-(3-methyl-2,5-dioxo-2,5-dihydropyrrol-1-yl)benzoic acid 916 were prepared as reported. X-ray crystal structures were obtained using a Bruker SMART platform goniometer with a CCD area detector at 150 K with structural solution and refinement by SHELXTL software package.

  • Nicotine's central cardiovascular actions: Receptor subtypes involved and their possible physiological role in anaesthetized rats

    2011, European Journal of Pharmacology
    Citation Excerpt :

    The failure of the highest dose to have any further effects on renal nerve activity and blood pressure suggests that there is full blockade of this unidentified (renal sympathoinhibitory) neuronal nicotinic receptor. Again, this could be the unidentified sympathoinhibitory β4*-containing neuronal nicotinic receptor and, in this respect, MLA has also been reported to have micromolar affinity for α3β4 neuronal nicotinic receptor (Bryant et al., 2002). The rise in blood pressure evoked by the large doses of MLA is probably due to generalised sympathoexcitation as it parallels the renal sympathoexcitation.

View all citing articles on Scopus
View full text