Impaired neuromuscular function by conjoint actions of organophosphorus insecticide metabolites omethoate and cyclohexanol with implications for treatment of respiratory failure

Dissanayake, Kosala N.; Chou, Robert Chang-Chih; Thompson, Adrian; Margetiny, Filip; Davie, Charlotte; Mckinnon, S. A.; Patel, Vikas; Sultatos, Lester G.; McArdle, Joseph J.; Clutton, R Eddie; Eddleston, Michael; Ribchester, Richard R.

doi:10.1080/15563650.2021.1916519

Cited by 6 publications

(41 citation statements)

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“…We showed previously that 20 mM cyclohexanol has only a weak effect on AChE activity (Dissanayake et al . 2021) but 5 μM neostigmine was sufficient to completely inhibit AChE activity in FDB muscle homogenates (R. Chou and R. R. Ribchester, unpublished data). Figure 2 and shows EPP responses in a continuous recording from an FDB muscle fibre incubated in 5 μM neostigmine, before and after adding 20 mM cyclohexanol.…”

Section: Resultsmentioning

confidence: 93%

“…Subsequently, we showed that cyclohexanol administered either intravenously in vivo or added to medium bathing isolated murine nerve–muscle preparations mimicked the impairment of neuromuscular function associated with insecticide gavage, in a temperature‐sensitive fashion (Dissanayake et al . 2021). Our aim in the present study was to establish the synaptic mechanisms underlying these myasthenic effects of cyclohexanol.…”

Section: Resultsmentioning

confidence: 99%

“…1– shows muscle force recordings, from the same preparation, after AChE activity was maximally inhibited by adding the carbamate AChE antagonist neostigmine (5 μM), replicating the anticholinesterase effects of the insecticide OP metabolite omethoate (Dissanayake et al . 2021). One hour after adding neostigmine (or omethoate), tetanic stimulation produced powerful muscle responses, notably including a prolonged post‐tetanic ‘aftercontraction’, lasting several seconds (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…2012; Dissanayake et al . 2021). Specifically, muscle force recordings in vivo showed that plasma concentrations of cyclohexanol exceeding 10 mM caused a progressive, temperature‐sensitive decrease in contractile force and ‘fade’ in twitch responses to low frequency train‐of‐four (TOF) stimulation.…”

Section: Introductionmentioning

confidence: 99%

“…These characteristics were replicated, also in temperature sensitive fashion, when cyclohexanol (10–25 mM) was added to medium bathing isolated nerve–muscle preparations from mice (Dissanayake et al . 2021). Neither cyclohexanone nor its metabolite cyclohexanol showed substantial anticholinesterase activity.…”

Section: Introductionmentioning

confidence: 99%

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Antagonistic postsynaptic and presynaptic actions of cyclohexanol on neuromuscular synaptic transmission and function

Dissanayake

Margetiny

Whitmore

et al. 2021

The Journal of Physiology

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Intentional ingestion of agricultural organophosphorus insecticides is a significant public health issue in rural Asia, causing thousands of deaths annually. Some survivors develop a severe, acute or delayed myasthenic syndrome. In animal models, similar myasthenia has been associated with increasing plasma concentration of one insecticide solvent metabolite, cyclohexanol. We investigated possible mechanisms using voltage and current recordings from mouse neuromuscular junctions (NMJs) and transfected human cell lines. Cyclohexanol (10–25 mM) reduced endplate potential (EPP) amplitudes by 10–40% and enhanced depression during repetitive (2–20 Hz) stimulation by up to 60%. EPP decay was prolonged more than twofold. Miniature EPPs were attenuated by more than 50%. Cyclohexanol inhibited whole‐cell currents recorded from CN21 cells expressing human postjunctional acetylcholine receptors (hnAChR) with an IC50 of 3.74 mM. Cyclohexanol (10–20 mM) also caused prolonged episodes of reduced‐current, multi‐channel bursting in outside‐out patch recordings from hnAChRs expressed in transfected HEK293T cells, reducing charge transfer by more than 50%. Molecular modelling indicated cyclohexanol binding (−6 kcal/mol) to a previously identified alcohol binding site on nicotinic AChR α‐subunits. Cyclohexanol also increased quantal content of evoked transmitter release by ∼50%. In perineurial recordings, cyclohexanol selectively inhibited presynaptic K+ currents. Modelling indicated cyclohexanol binding (−3.8 kcal/mol) to voltage‐sensitive K+ channels at the same site as tetraethylammonium (TEA). TEA (10 mM) blocked K+ channels more effectively than cyclohexanol but EPPs were more prolonged in 20 mM cyclohexanol. The results explain the pattern of neuromuscular dysfunction following ingestion of organophosphorus insecticides containing cyclohexanol precursors and suggest that cyclohexanol may facilitate investigation of mechanisms regulating synaptic strength at NMJs. Key points Intentional ingestion of agricultural organophosphorus insecticides is a significant public health issue in rural Asia, causing thousands of deaths annually. Survivors may develop a severe myasthenic syndrome or paralysis, associated with increased plasma levels of cyclohexanol, an insecticide solvent metabolite. Analysis of synaptic transmission at neuromuscular junctions in isolated mouse skeletal muscle, using isometric tension recording and microelectrode recording of endplate voltages and currents, showed that cyclohexanol reduced postsynaptic sensitivity to acetylcholine neurotransmitter (reduced quantal size) while simultaneously enhancing evoked transmitter release (increased quantal content). Patch recording from transfected cell lines, together with molecular modelling, indicated that cyclohexanol causes selective, allosteric antagonism of postsynaptic nicotinic acetylcholine receptors and block of presynaptic K+‐channel function. The data provide insight into the cellular and molecular mechanisms of neuromuscular weakness following int...

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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