Pancreatic and snake venom presynaptically active phospholipases A2 inhibit nicotinic acetylcholine receptors

Abstract

Phospholipases A2 (PLA2s) are enzymes found throughout the animal kingdom. They hydrolyze phospholipids in the sn-2 position producing lysophospholipids and unsaturated fatty acids, agents that can damage membranes. PLA2s from snake venoms have numerous toxic effects, not all of which can be explained by phospholipid hydrolysis, and each enzyme has a specific effect. We have earlier demonstrated the capability of several snake venom PLA2s with different enzymatic, cytotoxic, anticoagulant and antiproliferative properties, to decrease acetylcholine-induced currents in Lymnaea stagnalis neurons, and to compete with α-bungarotoxin for binding to nicotinic acetylcholine receptors (nAChRs) and acetylcholine binding protein. Since nAChRs are implicated in postsynaptic and presynaptic activities, in this work we probe those PLA2s known to have strong presynaptic effects, namely β-bungarotoxin from Bungarus multicinctus and crotoxin from Crotalus durissus terrificus. We also wished to explore whether mammalian PLA2s interact with nAChRs, and have examined non-toxic PLA2 from porcine pancreas. It was found that porcine pancreatic PLA2 and presynaptic β-bungarotoxin blocked currents mediated by nAChRs in Lymnaea neurons with IC50s of 2.5 and 4.8 μM, respectively. Crotoxin competed with radioactive α-bungarotoxin for binding to Torpedo and human α7 nAChRs and to the acetylcholine binding protein. Pancreatic PLA2 interacted similarly with these targets; moreover, it inhibited radioactive α-bungarotoxin binding to the water-soluble extracellular domain of human α9 nAChR, and blocked acetylcholine induced currents in human α9α10 nAChRs heterologously expressed in Xenopus oocytes. These and our earlier results show that all snake PLA2s, including presynaptically active crotoxin and β-bungarotoxin, as well as mammalian pancreatic PLA2, interact with nAChRs. The data obtained suggest that this interaction may be a general property of all PLA2s, which should be proved by further experiments.

Effect of Traditional Chinese Medicine on Long-Term Outcomes of Snakebite in Taiwan

“…These toxins can be divided into two groups: α-neurotoxins and β-neurotoxins. α-neurotoxins act on postsynaptic terminals, and belong to the family of three-finger toxins that block acetylcholine receptors; β-neurotoxins act on presynaptic terminals, and belong to the family of heterodimeric PLA2s that inhibit the release of acetylcholine from presynaptic terminals [15,38,47]. The combined effects of α-neurotoxins and β-neurotoxins block neuromuscular transmission and result in muscle paralysis.…”

Effects of Mlx-8, a phospholipase A2 from Brazilian coralsnake Micrurus lemniscatus venom, on muscarinic acetylcholine receptors in rat hippocampus

“…OS2 is a single-chain PLA 2 isolated from Oxyuranus scutellatus venom and associates selectively with rat brain membrane proteins termed N-type receptors [52]. Moreover, there is evidence suggesting that the ability to interact with nicotinic acetylcholine receptors may be a general property of several snakes PLA 2 from venoms [53,54]. To check the ability of the PLA 2 isolated from Micrurus lemniscatus (Mlx-8) to interact with mAChRs, the inhibitor of cobra venom phospholipases A 2 activity DEDA, an analogue of arachidonic acid that contains two cis double bonds as well as two methyl groups [55], was used in the present study.…”

Amplification of Snake Venom Toxicity by Endogenous Signaling Pathways

“…This action by β-neurotoxins toxins is more speculative, although it is a mechanism based on many studies of nicotinic receptor regulation in various preparations [111]. It is important to note that there is some evidence that PLA 2 s can act as competitive nAChR antagonists, similar to the better defined α-neurotoxins [112]. The quantitative importance of this α-effect is unresolved.…”