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Combinations of classical and non-classical voltage dependent potassium channel openers suppress nociceptor discharge and reverse chronic pain signs in a rat model of Gulf War illness. Neurotoxicology 2022; 93:186-199. [PMID: 36216193 DOI: 10.1016/j.neuro.2022.10.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 09/27/2022] [Accepted: 10/05/2022] [Indexed: 11/15/2022]
Abstract
In a companion paper we examined whether combinations of Kv7 channel openers (Retigabine and Diclofenac; RET, DIC) could be effective modifiers of deep tissue nociceptor activity; and whether such combinations could then be optimized for use as safe analgesics for pain-like signs that developed in a rat model of GWI (Gulf War Illness) pain. In the present report, we examined the combinations of Retigabine/Meclofenamate (RET/MEC) and Meclofenamate/Diclofenac (MEC/DIC). Voltage clamp experiments were performed on deep tissue nociceptors isolated from rat DRG (dorsal root ganglion). In voltage clamp studies, a stepped voltage protocol was applied (-55 to -40 mV; Vh=-60 mV; 1500 msec) and Kv7 evoked currents were subsequently isolated by Linopirdine subtraction. MEC greatly enhanced voltage dependent conductance and produced exceptional maximum sustained currents of 6.01 ± 0.26 pA/pF (EC50: 62.2 ± 8.99 μM). Combinations of RET/MEC, and MEC/DIC substantially amplified resting currents at low concentrations. MEC/DIC also greatly improved voltage dependent conductance. In current clamp experiments, a cholinergic challenge test (Oxotremorine-M, 10 μM; OXO), associated with our GWI rat model, produced powerful action potential (AP) bursts (85 APs). Optimized combinations of RET/MEC (5 and 0.5 μM) and MEC/DIC (0.5 and 2.5 μM) significantly reduced AP discharges to 3 and 7 Aps, respectively. Treatment of pain-like ambulatory behavior in our rat model with a RET/MEC combination (5 and 0.5 mg/kg) successfully rescued ambulation deficits, but could not be fully separated from the effect of RET alone. Further development of this approach is recommended.
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Development of KVO treatment strategies for chronic pain in a rat model of Gulf War Illness. Toxicol Appl Pharmacol 2022; 434:115821. [PMID: 34896435 DOI: 10.1016/j.taap.2021.115821] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 12/01/2021] [Accepted: 12/04/2021] [Indexed: 12/19/2022]
Abstract
We examined whether combinations of Kv7 channel openers could be effective modifiers of deep tissue nociceptor activity; and whether such combinations could then be optimized for use as safe analgesics for pain-like signs that developed in a rat model of GWI (Gulf War Illness) pain. Voltage clamp experiments were performed on subclassified nociceptors isolated from rat DRG (dorsal root ganglion). A stepped voltage protocol was applied (-55 to -40 mV; Vh = -60 mV; 1500 ms) and Kv7 evoked currents were subsequently isolated by linopirdine subtraction. Directly activated and voltage activated K+ currents were characterized in the presence and absence of Retigabine (5-100 μM) and/or Diclofenac (50-140 μM). Retigabine produced substantial voltage dependent effects and a maximal sustained current of 1.14 pA/pF ± 0.15 (ED50: 62.7 ± 3.18 μM). Diclofenac produced weak voltage dependent effects but a similar maximum sustained current of 1.01 ± 0.26 pA/pF (ED50: 93.2 ± 8.99 μM). Combinations of Retigabine and Diclofenac substantially amplified resting currents but had little effect on voltage dependence. Using a cholinergic challenge test (Oxotremorine, 10 μM) associated with our GWI rat model, combinations of Retigabine (5 uM) and Diclofenac (2.5, 20 and 50 μM) substantially reduced or totally abrogated action potential discharge to the cholinergic challenge. When combinations of Retigabine and Diclofenac were used to relieve pain-signs in our rat model of GWI, only those combinations associated with serious subacute side effects could relieve pain-like behaviors.
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Abstract
Supplemental Digital Content is Available in the Text. Inhibition of K2P potassium channels by pyrethroid insecticides contribute to activate primary sensory neurons to cause paraesthesias and painful sensations. Pyrethroid insecticides are widely used for pest control in agriculture or in human public health commonly as a topical treatment for scabies and head lice. Exposure to pyrethroids such as permethrin or tetramethrin (TM) causes sensory alterations such as transient pain, burning, stinging sensations, and paraesthesias. Despite the well-known effects of pyrethroids on sodium channels, actions on other channels that control sensory neuron excitability are less studied. Given the role of 2-pore domain potassium (K2P) channels in modulating sensory neuron excitability and firing, both in physiological and pathological conditions, we examined the effect of pyrethroids on K2P channels mainly expressed in sensory neurons. Through electrophysiological and calcium imaging experiments, we show that a high percentage of TM-responding neurons were nociceptors, which were also activated by TRPA1 and/or TRPV1 agonists. This pyrethroid also activated and enhanced the excitability of peripheral saphenous nerve fibers. Pyrethroids produced a significant inhibition of native TRESK, TRAAK, TREK-1, and TREK-2 currents. Similar effects were found in transfected HEK293 cells. At the behavioral level, intradermal TM injection in the mouse paw produced nocifensive responses and caused mechanical allodynia, demonstrating that the effects seen on nociceptors in culture lead to pain-associated behaviors in vivo. In TRESK knockout mice, pain-associated behaviors elicited by TM were enhanced, providing further evidence for a role of this channel in preventing excessive neuronal activation. Our results indicate that inhibition of K2P channels facilitates sensory neuron activation and increases their excitability. These effects contribute to the generation of paraesthesias and pain after pyrethroid exposure.
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Behavioral, cellular and molecular maladaptations covary with exposure to pyridostigmine bromide in a rat model of gulf war illness pain. Toxicol Appl Pharmacol 2018; 352:119-131. [PMID: 29803855 DOI: 10.1016/j.taap.2018.05.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 05/16/2018] [Accepted: 05/20/2018] [Indexed: 12/12/2022]
Abstract
Many veterans of Operation Desert Storm (ODS) struggle with the chronic pain of Gulf War Illness (GWI). Exposure to insecticides and pyridostigmine bromide (PB) have been implicated in the etiology of this multisymptom disease. We examined the influence of 3 (DEET (N,N-diethyl-meta-toluamide), permethrin, chlorpyrifos) or 4 GW agents (DEET, permethrin, chlorpyrifos, pyridostigmine bromide (PB)) on the post-exposure ambulatory and resting behaviors of rats. In three independent studies, rats that were exposed to all 4 agents consistently developed both immediate and delayed ambulatory deficits that persisted at least 16 weeks after exposures had ceased. Rats exposed to a 3 agent protocol (PB excluded) did not develop any ambulatory deficits. Cellular and molecular studies on nociceptors harvested from 16WP (weeks post-exposure) rats indicated that vascular nociceptor Nav1.9 mediated currents were chronically potentiated following the 4 agent protocol but not following the 3 agent protocol. Muscarinic linkages to muscle nociceptor TRPA1 were also potentiated in the 4 agent but not the 3 agent, PB excluded, protocol. Although Kv7 activity changes diverged from the behavioral data, a Kv7 opener, retigabine, transiently reversed ambulation deficits. We concluded that PB played a critical role in the development of pain-like signs in a GWI rat model and that shifts in Nav1.9 and TRPA1 activity were critical to the expression of these pain behaviors.
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Flunker LK, Nutter TJ, Johnson RD, Cooper BY. DEET potentiates the development and persistence of anticholinesterase dependent chronic pain signs in a rat model of Gulf War Illness pain. Toxicol Appl Pharmacol 2016; 316:48-62. [PMID: 28025109 DOI: 10.1016/j.taap.2016.12.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 12/16/2016] [Accepted: 12/20/2016] [Indexed: 12/18/2022]
Abstract
Exposure to DEET (N,N-diethyl-meta-toluamide) may have influenced the pattern of symptoms observed in soldiers with GWI (Gulf War Illness; Haley and Kurt, 1997). We examined how the addition of DEET (400mg/kg; 50% topical) to an exposure protocol of permethrin (2.6mg/kg; topical), chlorpyrifos (CP; 120mg/kg), and pyridostigmine bromide (PB;13mg/kg) altered the emergence and pattern of pain signs in an animal model of GWI pain (Nutter et al., 2015). Rats underwent behavioral testing before, during and after a 4week exposure: 1) hindlimb pressure withdrawal threshold; 2) ambulation (movement distance and rate); and 3) resting duration. Additional studies were conducted to assess the influence of acute DEET (10-100μM) on muscle and vascular nociceptor Kv7, KDR, Nav1.8 and Nav1.9. We report that a 50% concentration of DEET enhanced the development and persistence of pain-signs. Rats exposed to all 4 compounds exhibited ambulation deficits that appeared 5-12weeks post-exposure and persisted through weeks 21-24. Rats exposed to only three agents (CP or PB excluded), did not fully develop ambulation deficits. When PB was excluded, rats also developed rest duration pain signs, in addition to ambulation deficits. There was no evidence that physiological doses of DEET acutely modified nociceptor Kv7, KDR, Nav1.8 or Nav1.9 activities. Nevertheless, DEET augmented protocols decreased the conductance of Kv7 expressed in vascular nociceptors harvested from chronically exposed rats. We concluded that DEET enhanced the development and persistence of pain behaviors, but the anticholinesterases CP and PB played a determinant role.
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Affiliation(s)
- L K Flunker
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
| | - T J Nutter
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
| | - R D Johnson
- Dept. of Physiological Sciences, University of Florida College of Veterinary Science, Gainesville, FL 32610, USA.
| | - B Y Cooper
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
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Anziska Y, Rahman A. Pediatric myasthenia gravis exacerbation associated with permethrin cream. Muscle Nerve 2016; 55:E11-E12. [PMID: 27750366 DOI: 10.1002/mus.25434] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/12/2016] [Indexed: 11/12/2022]
Affiliation(s)
- Yaacov Anziska
- SUNY-Downstate Medical Center, Department of Neurology, 450 Clarkson Avenue, Box 1213, Brooklyn, New York, 11203, USA
| | - Afsana Rahman
- SUNY-Downstate Medical Center, Department of Neurology, 450 Clarkson Avenue, Box 1213, Brooklyn, New York, 11203, USA
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Cooper BY, Johnson RD, Nutter TJ. Exposure to Gulf War Illness chemicals induces functional muscarinic receptor maladaptations in muscle nociceptors. Neurotoxicology 2016; 54:99-110. [PMID: 27058124 DOI: 10.1016/j.neuro.2016.04.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 03/31/2016] [Accepted: 04/01/2016] [Indexed: 12/12/2022]
Abstract
Chronic pain is a component of the multisymptom disease known as Gulf War Illness (GWI). There is evidence that pain symptoms could have been a consequence of prolonged and/or excessive exposure to anticholinesterases and other GW chemicals. We previously reported that rats exposed, for 8 weeks, to a mixture of anticholinesterases (pyridostigmine bromide, chlorpyrifos) and a Nav (voltage activated Na(+) channel) deactivation-inhibiting pyrethroid, permethrin, exhibited a behavior pattern that was consistent with a delayed myalgia. This myalgia-like behavior was accompanied by persistent changes to Kv (voltage activated K(+)) channel physiology in muscle nociceptors (Kv7, KDR). In the present study, we examined how exposure to the above agents altered the reactivity of Kv channels to a muscarinic receptor (mAChR) agonist (oxotremorine-M). Comparisons between muscle nociceptors harvested from vehicle and GW chemical-exposed rats revealed that mAChR suppression of Kv7 activity was enhanced in exposed rats. Yet in these same muscle nociceptors, a Stromatoxin-insensitive component of the KDR (voltage activated delayed rectifier K(+) channel) exhibited decreased sensitivity to activation of mAChR. We have previously shown that a unique mAChR-induced depolarization and burst discharge (MDBD) was exaggerated in muscle nociceptors of rats exposed to GW chemicals. We now provide evidence that both muscle and vascular nociceptors of naïve rats exhibit MDBD. Examination of the molecular basis of the MDBD in naïve animals revealed that while the mAChR depolarization was independent of Kv7, the action potential burst was modulated by Kv7 status. mAChR depolarizations were shown to be dependent, in part, on TRPA1. We argue that dysfunction of the MDBD could be a functional convergence point for maladapted ion channels and receptors consequent to exposure to GW chemicals.
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Affiliation(s)
- B Y Cooper
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
| | - R D Johnson
- Dept. of Physiological Sciences, University of Florida College of Veterinary Science, Gainesville, FL 32610, USA.
| | - T J Nutter
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
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Nutter T, Johnson R, Cooper B. A delayed chronic pain like condition with decreased Kv channel activity in a rat model of Gulf War Illness pain syndrome. Neurotoxicology 2015; 51:67-79. [DOI: 10.1016/j.neuro.2015.09.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 09/22/2015] [Accepted: 09/22/2015] [Indexed: 12/26/2022]
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Burgess IF, Brown CM, Nair P. Comparison of phenothrin mousse, phenothrin lotion, and wet-combing for treatment of head louse infestation in the UK: a pragmatic randomised, controlled, assessor blind trial. F1000Res 2014; 3:158. [PMID: 25254106 PMCID: PMC4168840 DOI: 10.12688/f1000research.2026.1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 07/08/2014] [Indexed: 01/08/2023] Open
Abstract
In this investigation of effectiveness of an alternative pediculicide dosage form, we recruited 228 children and 50 adult participants from Bedfordshire, UK, to a randomised, controlled, assessor blind trial comparing two insecticide products with mechanical removal of lice as a control group. Participants using insecticide were treated with either the investigative 0.5% phenothrin mousse, for 30 minutes, or 0.2% phenothrin lotion, for 2 hours as the reference product. Both treatments were applied only once, followed by shampoo washing. Those treated by wet-combing with conditioner were combed 4 times over 12 days. Parents/carers carried out the treatments to mimic normal consumer use. The outcome measure was the absence of lice, 14 days after treatment for the insecticides, and up to 14 days after completion of combing. Intention to treat analysis of the outcomes for 275 participants showed success for phenothrin mousse in 21/105 (20.0%), in 23/107 (21.5%) for phenothrin lotion, and in 12/63 (19.1%) for wet-combing. People receiving mousse were 1.07 (95% CI, 0.63 to 1.81) times more likely to still have lice after treatment compared with those treated with lotion. The group of participants who received the wet combing treatment were 1.13 (95% CI, 0.61 to 2.11) times more likely to still have lice after the treatment. None of the treatments was significantly (p < 0.05) more effective than any other. This study was carried out in an area where moderate resistance to phenothrin was demonstrated after the study by using a bioassay. Analysis of post treatment assessments found that failure of insecticides to kill louse eggs had influenced the outcome.
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Affiliation(s)
- Ian F Burgess
- Medical Entomology Centre, Insect Research & Development Limited, Cambridge, CB25 9AU, UK
| | - Christine M Brown
- Medical Entomology Centre, Insect Research & Development Limited, Cambridge, CB25 9AU, UK
| | - Pat Nair
- Consultant in Communicable Disease Control, Bedfordshire Health Authority and Bedfordshire Family Health Authority, Luton, LU1 3AN, UK
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Persistent modification of Nav1.9 following chronic exposure to insecticides and pyridostigmine bromide. Toxicol Appl Pharmacol 2014; 277:298-309. [DOI: 10.1016/j.taap.2014.04.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Revised: 03/14/2014] [Accepted: 04/03/2014] [Indexed: 12/21/2022]
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Nutter T, Jiang N, Cooper BY. Persistent Na+ and K+ channel dysfunctions after chronic exposure to insecticides and pyridostigmine bromide. Neurotoxicology 2013; 39:72-83. [DOI: 10.1016/j.neuro.2013.08.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 08/07/2013] [Accepted: 08/11/2013] [Indexed: 12/15/2022]
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