lycoctonine and methyllycaconitine

The purpose of this study was to determine whether larkspur toxins conjugated to protein carriers would promote active immunity in mice. Mice were injected with several larkspur toxin-protein conjugates or adjuvant alone to determine whether the resulting immunological response altered animal susceptibility to methyllycaconitine, the major toxic larkspur alkaloid. Although vaccinations increased the calculated lethal dose 50% (LD50) for intravenous methyllycaconitine toxicity, overlapping confidence intervals did not provide evidence of differences between the vaccinated and control groups. In the lycoctonine conjugate (LYC)-vaccinated group, mouse survival was related (P = 0.001) to serum titers for methyllycaconitine doses up to 4.5 mg/kg of body weight. When mice withlow antibody titers were removed from the vaccinated groups in which titer was related to survival, the recalculated LD50 estimates were 20% greater than the LD50 of the control group. However, the 95% confidence intervals of the recalculated LD50 groups overlapped with the control groups. Overall, these results suggest that vaccination altered methyllycaconitine toxicity in mice and that vaccination may be useful in decreasing the effects of larkspur toxins in animals. Additional studies are warranted to continue development of potential larkspur vaccines for livestock.

Topics: Aconitine; Animals; Animals, Domestic; Binding, Competitive; Biological Assay; Delphinium; Dose-Response Relationship, Drug; Immunity, Active; Lethal Dose 50; Mice; Plant Extracts; Plant Poisoning; Random Allocation; Survival Analysis; Vaccination

A series of bicyclic analogues incorporating the homocholine motif of methyllycaconitine has been prepared to test the hypothesis that this is the essential pharmacophore of this potent, selective nicotinic receptor antagonist. A double Mannich reaction has been employed to construct the 3-azabicyclo[3.3.1]-nonane ring system, containing an N-ethylpiperidine moiety. The neopentyl-like alcohol was then esterified, using isatoic anhydride under basic conditions, to afford the corresponding anthranilate.

Topics: Aconitine; Insecticides; Molecular Structure

Methyllycaconitine (MLA) is a competitive antagonist of nicotinic acetylcholine receptors, with a remarkable preference for neuronal [125I]alpha Bgt binding sites. We have begun to investigate the structural basis of its potency and subtype selectivity. MLA is a substituted norditerpenoid alkaloid linked to a 2-(methylsuccinimido)benzoyl moiety. Hydrolysis of the ester bond in MLA to produce lycoctonine diminished affinity for rat brain [125I]alpha Bgt binding sites 2500-fold and abolished affinity for [3H]nicotine and muscle [125I]alpha Bgt binding sites. The voltage-gated Na+ channel activator aconitine, also a norditerpenoid alkaloid, but with significant structural differences from lycoctonine, displayed comparable weak or absent nicotinic activity. Addition of a 2-(methylsuccinimido)benzoyl sidechain to O-demethylated aconitine, to mimic MLA, abolished Na+ channel activation and conferred nanomolar affinity for brain [125I]alpha Bgt binding sites, comparable to that of MLA. We propose that the ester-linked 2-(methylsuccinimido)benzoyl group is necessary for nicotinic potency, but alpha 7 selectivity resides in the norditerpenoid core of the molecule.

Topics: Aconitine; Animals; Binding Sites; Binding, Competitive; Brain; Bungarotoxins; Dopamine; Dose-Response Relationship, Drug; Ligands; Membranes; Rats; Receptors, Nicotinic; Sodium Channel Blockers; Structure-Activity Relationship; Tetrodotoxin; Veratridine