Paraherquamide and 2-Deoxy-paraherquamide Distinguish Cholinergic Receptor Subtypes in Ascaris Muscle

Abstract

Paraherquamide is a novel natural anthelmintic product with a mode of action that is incompletely characterized. Nicotine and cholinergic-anthelmintic agonists of different chemical classes were used to produce contraction in Ascaris muscle strips. Paraherquamide and a semisynthetic derivative, 2-deoxy-paraherquamide, antagonized these responses. Analysis of the actions of the antagonists was made using the simple competitive model and nonlinear regression to estimate the pK B values of the antagonists. The analysis was tested using Clark plots. The pK B values for paraherquamide were: nicotine, 5.86 Ϯ 0.14; levamisole, 6.61 Ϯ 0.19; pyrantel, 6.50 Ϯ 0.11; and bephenium, 6.75 Ϯ 0.15. The pK B of nicotine was significantly different from the pK B values for levamisole, pyrantel, and bephenium, showing that paraherquamide can distinguish a subtype of cholinergic receptors sensitive to nicotine and a subtype of cholinergic receptors sensitive to levamisole, pyrantel, and bephenium. The pK B values for 2-deoxy-paraherquamide were: levamisole, 5.31 Ϯ 0.13; pyrantel, 5.63 Ϯ 0.10; and bephenium, 6.07 Ϯ 0.13. The Clark plots of the antagonism illustrated the degree of fit to the competitive model for 2-deoxy-paraherquamide. 2-Deoxy-paraherquamide selectively antagonized the effects of bephenium; the pK B values of levamisole and pyrantel were significantly different from the pK B of bephenium. Paraherquamide and 2-deoxy-paraherquamide are selective competitive cholinergic antagonists that distinguish subtypes of cholinergic receptor in Ascaris muscle corresponding to nicotine-, levamisole-, and bephenium-sensitive receptors.Nematode parasite infections of humans and animals cause disease with loss of productivity, debility, and occasionally death. Ascariasis and hookworm infections are carried by 1.6 billion people throughout the world and in 2% of cases cause loss of life. The use of therapeutic compounds forms a major component of control, and the development of novel therapeutic agents is required to deal with the increasing levels of resistance to existing drugs.Paraherquamide (Fig. 1) is a novel anthelmintic (Yamazaki et al., 1981) that is an alkaloid fermentation product originally isolated from Penicillium paraherquii. The anthelmintic property of paraherquamide was first identified using jirds infected with Trichostrongylus colubriformis (Ostlind et al., 1990). Paraherquamide produces paralysis of parasitic nematodes in culture, without an effect on ATP, suggesting that it does not act as a metabolic poison (Thompson et al., 1996). Interestingly, one of the toxic effects of paraherquamide in the dog (Shoop et al., 1990) is a prolapsed nictitating membrane, an effect that suggests antagonism of neuronal nicotinic receptors (nAChRs). Recently, it has been reported (E.

The cys-loop ligand-gated ion channel gene family of Brugia malayi and Trichinella spiralis: a comparison with Caenorhabditis elegans

“…The largest selling group of anthelmintic drugs, the macrocyclic lactones, and the nicotinic agonists, such as levamisole and pyrantel, both target members of the cys-loop ligand-gated ion channel (CLGIC) family (Martin et al 2005;Wolstenholme and Rogers 2005), and it is for this reason that this paper concentrates on these receptors. Other anthelmintics also act on this family: piperazine is an agonist at GABA-gated chloride channels (Martin 1982) and paraherquamide is a nicotinic antagonist (Robertson et al 2002). Emodepside, a recent addition to the anti-worm arsenal, also affects the nematode nervous system, via latrophilin-like receptors and potassium channels (Harder et al 2005;Guest et al 2007), but does not interact directly with members of the CLGIC family.…”

Effects of the muscarinic agonist, 5-methylfurmethiodide, on contraction and electrophysiology of Ascaris suum muscle

“…Levamisole belongs to the ionotropic cholinergic agonist group of anthelmintics that includes pyrantel, and that selectively produces muscle cell depolarization and spastic paralysis in parasitic nematodes (Aceves et al, 1970;Aubry et al, 1970). We have shown, using current-clamp, voltage-clamp and patch-clamp, that electrophysiological responses to these anthelmintics can be observed in body muscle cells of the nematode parasites Ascaris suum and Oesophagostomum dentatum (Martin, 1982;Pennington and Martin, 1990;Robertson and Martin, 1993;Robertson et al, 1994Robertson et al, , 2002Dale and Martin, 1995;Evans and Martin, 1996;Martin et al, 2002;Trailovic et al, 2002). These studies have identified nematode nicotinic acetylcholine gated receptor channels (nAChRs) over the nematode muscle cell surface that is selectively and directly gated by these anthelmintics.…”

Comparative Disposition and Metabolism of Paraherquamide in Sheep, Gerbils, and Dogs

“…These adverse effects were only marginally reversible over 7 days, and in subsequent studies in our laboratories, they were also accompanied by occasional deaths (Shoop et al, 1992a). More recent studies have shown that PHQ is an antagonist of nicotinic cholinergic receptors in nematodes and mammals (Robertson et al, 2002;Zinser et al, 2002) and suggest that PHQ exerts its nematodicidal action by inducing nematode paralysis through blockade of cholinergic neuromuscular transmission. The adverse effects observed in dogs may result from the same mechanism.…”