Nicotinic acetylcholine receptor gene expression is altered in burn patients

In vitro permeation of nicotine and tobacco specific nitrosamines from smokeless tobacco product extracts in a 3D buccal tissue model

Tobacco product use is a risk factor in the development of oral cancer, although epidemiology studies show this risk is far less with smokeless tobacco product use than cigarette smoking. While smokeless tobacco contains harmful and potentially harmful constituents (HPHCs), the oral permeation of HPHCs in oral tobacco products is not completely understood. To improve the understanding, three different extract concentrations of the CORESTA reference products (CRP) for snus (CRP1.1) and moist snuff (CRP2.1) were applied to cellular tissue derived from two donors of EpiOral™ model, a 3D human buccal model, and permeation of nicotine and tobacco-specific nitrosamines (TSNAs) were measured over two hours. Permeation of 0.15% caffeine in complete artificial saliva and cell viability were also measured. Results showed that a consistent and concentration dependent cumulative permeation of nicotine and TSNAs was observed with high percent recovery in all conditions. A high degree of sensitivity was seen for all analytes, with minimal cytotoxicity for both CRPs. The data presented here show the EpiOral™ model is fit-for-purpose to evaluate the permeation of nicotine and TSNAs in nicotine-containing snus and moist snuff oral tobacco.

Chronic exposure to dexamethasone may not affect sugammadex reversal of rocuronium-induced neuromuscular blockade: an in vivo study on rats

BACKGROUND

Chronic glucocorticoid exposure is associated with resistance to nondepolarizing neuromuscular blocking agents. Therefore, we hypothesized that sugammadex-induced recovery would occur more rapidly in subjects exposed to chronic dexamethasone compared to those who were not exposed. This study evaluated the sugammadex-induced recovery profile after neuromuscular blockade (NMB) in rats exposed to chronic dexamethasone.

METHODS

Sprague-Dawley rats were allocated to three groups (dexamethasone, control, and pair-fed group) for the in vivo study. The mice received daily intraperitoneal dexamethasone injections (500 μg/kg) or 0.9% saline for 15 days. To achieve complete NMB, 3.5 mg/kg rocuronium was administered on the sixteenth day. The recovery time to a train-of-four ratio ≥ 0.9 was measured to evaluate the complete recovery following the sugammadex injection.

RESULTS

Among the groups, no significant differences were observed in the recovery time to a train-of-four ratio ≥ 0.9 following sugammadex administration (P = 0.531). The time to the second twitch of the train-of-four recovery following rocuronium administration indicated that the duration of NMB was significantly shorter in Group D than that in Groups C and P (P = 0.001).

CONCLUSIONS

Chronic exposure to dexamethasone did not shorten the recovery time of sugammadex-induced NMB reversal. However, the findings of this study indicated that no adjustments to sugammadex dosage or route of administration is required, even in patients undergoing long-term steroid treatment.

Molecular mechanisms of muscular and non-muscular actions of neuromuscular blocking agents in critical illness: a narrative review

Despite frequent use of neuromuscular blocking agents in critical illness, changes in neuromuscular transmission with critical illness are not well appreciated. Recent studies have provided greater insights into the molecular mechanisms for beneficial muscular effects and non-muscular anti-inflammatory properties of neuromuscular blocking agents. This narrative review summarises the normal structure and function of the neuromuscular junction and its transformation to a 'denervation-like' state in critical illness, the underlying cause of aberrant neuromuscular blocking agent pharmacology. We also address the important favourable and adverse consequences and molecular bases for these consequences during neuromuscular blocking agent use in critical illness. This review, therefore, provides an enhanced understanding of clinical therapeutic effects and novel pathways for the salutary and aberrant effects of neuromuscular blocking agents when used during acquired pathologic states of critical illness.

Suxamethonium-Induced Hyperkalemia: A Short Review of Causes and Recommendations for Clinical Applications

After the introduction of suxamethonium in 1953, cases of cardiac arrest during induction of anesthesia were recorded. In the following years, hyperkalemia was identified as the cause, and the connection to acetylcholine receptor modulation as the underlying molecular mechanism was made. Activation of the acetylcholine receptor with suxamethonium, acetylcholine, or choline causes an efflux of potassium to the extracellular space. However, certain pathological conditions cause acetylcholine receptor proliferation and the emergence of immature receptors capable of a larger potassium efflux to the bloodstream. These pathologic conditions include upper and lower neuron injuries, major burns, trauma, immobility, muscle tumors, muscular dystrophy, and prolonged critical illness. The latter is more important and relevant than ever due to the increasing number of COVID-19 patients requiring prolonged respiratory support and consequent immobilization. Suxamethonium can be used safely in the vast majority of patients. Still, reports of lethal hyperkalemic responses to suxamethonium continue to emerge. This review serves as a reminder of the pathophysiology behind extensive potassium release. Proficiency in the use of suxamethonium includes identification of patients at risk, and selection of an alternative neuromuscular blocking agent is imperative.

Enhancing Autophagy Protects Against Sepsis-Induced Neuromuscular Dysfunction Associated with Qualitative Changes to Acetylcholine Receptors

Sepsis-induced myopathy is a heavy burden for patients during respiratory failure as well as after discharge, which could be characterized with qualitative changes to nAChR in a rat model of sepsis, regulated by NRG-1. Autophagy is an innate immune defense mechanism against microbial challenges. We found neuromuscular dysfunction in anterior tibial muscle of male Sprague-Dawley rats 24 h after cecal ligation and puncture (CLP). CLP resulted in increased systemic and local inflammation in anterior tibial muscle tissue. The start-up phase of autophagy, as measured by LC3II, was activated immediately after CLP and continued until 24 h; the degradation phase was suppressed until 24 h, after a brief increase at 4 h (revealed by p62). NRG-1 first increased, and then decreased to a level lower than that in the sham group. Meanwhile, expression of γ- and α7- acetylcholine receptors was detected at 8 and 16 h after CLP; levels increased continuously until 24 h. Subsequently, we investigated the significance of autophagy in CLP-induced neuromuscular dysfunction by treatment with rapamycin or 3-methyladenine, which were classical pharmaceuticals for enhancing or suppressing autophagy. Rapamycin activated autophagy, limited the CLP-induced systemic pro-inflammatory response and blood bacterial load without affecting local inflammatory response, upregulated NRG-1, downregulated γ- and α7-acetylcholine receptors, and improved 7-day neuromuscular function and survival rate. In contrast, 3-methyladenine enhanced local inflammatory response, suppressed autophagy, worsened 7-day neuromuscular function. We conclude that impaired autophagy may contribute to sepsis-induced neuromuscular dysfunction in young male rats. Enhancing autophagy with rapamycin alleviated qualitative changes to acetylcholine receptors without triggering local anti-inflammatory response and improved anterior tibial muscle function in septic early phase (24 h) as well as in septic chronic phase (7d). Enhancing autophagy soon after sepsis is a potential strategy for treatment of sepsis-induced myopathy.

Challenges in anaesthesia and pain management for burn injuries

Burn-injured patients provide unique challenges to those providing anaesthesia and pain management. This review aims to update both the regular burn anaesthetist and the anaesthetist only occasionally involved with burn patients in emergency settings. It addresses some aspects of care that are perhaps contentious in terms of airway management, fluid resuscitation, transfusion practices and pharmacology. Recognition of pain management failures and the lack of mechanism-specific analgesics are discussed along with the opioid crisis as it relates to burns and nonpharmacological methods in the management of distressed patients.

Nicotinic acetylcholine receptor subunit expression in the gastrocnemius and in the orbicularis oris before and after facial nerve injury in rats

Objectives: To observe the expression of nicotinic acetylcholine receptor (AChR) subunits in normal orbicularis oris and gastrocnemius muscles and to explore the relationships between the expression of AChR subunits and the severity of facial nerve injury. Methods: Gene and protein expression of AChR subunits in the orbicularis oris and gastrocnemius muscles of male Sprague-Dawley rats was measured by reverse transcription polymerase chain reaction and western blotting, respectively, 1-90 days after graded facial nerve injury. Results: Expression of ε-AChR in the normal orbicularis oris was significantly higher than that in the gastrocnemius, whereas no γ subunit expression was observed. Expression of α, β, δ, ε, and γ subunits was upregulated in the orbicularis oris and was positively correlated with the degree of facial nerve injury. Discussion: We demonstrated the higher expression of the AChR subunits in the orbicularis oris, compared to gastrocnemius muscles. The differences in expression of these subunits between muscles innervated by the facial nerve and somatic nerves and the correlation of AChR subunit expression with the degree of facial nerve injury yield insights into the sensitivity to muscle relaxants during intraoperative facial nerve monitoring.

GTS-21 attenuates loss of body mass, muscle mass, and function in rats having systemic inflammation with and without disuse atrophy

Muscle changes of critical illness are attributed to systemic inflammatory responses and disuse atrophy. GTS-21 (3-(2,4-dimethoxy-benzylidene)anabaseine), also known as DMBX-A) is a synthetic derivative of the natural product anabaseine that acts as an agonist at α7-acetylcholine receptors (α7nAChRs). Hypothesis tested was that modulation of inflammation by agonist GTS-21 (10 mg/kg b.i.d. intraperitoneally) will attenuate body weight (BW) and muscle changes. Systemic sham inflammation was produced in 125 rats by Cornyebacterium parvum (C.p.) or saline injection on days 0/4/8. Seventy-four rats had one immobilized-limb producing disuse atrophy. GTS-21 effects on BW, tibialis muscle mass (TMM), and function were assessed on day 12. Systemically, methemoglobin levels increased 26-fold with C.p. (p < 0.001) and decreased significantly (p < 0.033) with GTS-21. Control BW increased (+ 30 ± 9 g, mean ± SD) at day 12, but decreased with C.p. and superimposed disuse (p = 0.005). GTS-21 attenuated BW loss in C.p. (p = 0.005). Compared to controls, TMM decreased with C.p. (0.43 ± 0.06 g to 0.26 ± 0.03 g) and with superimposed disuse (0.18 ± 0.04 g); GTS-21 ameliorated TMM loss to 0.32 ± 0.04 (no disuse, p = 0.028) and to 0.22 ± 0.03 (with disuse, p = 0.004). Tetanic tensions decreased with C.p. or disuse and GTS-21 attenuated tension decrease in animals with disuse (p = 0.006) and in animals with C.p. and disuse (p = 0.029). C.p.-induced 11-fold increased muscle α7nAChR expression was decreased by > 60% with GTS-21 treatment. In conclusion, GTS-21 modulates systemic inflammation, evidenced by both decreased methemoglobin levels and decrease of α7nAChR expression, and mitigates inflammation-mediated loss of BW, TMM, fiber size, and function.

Differences in pharmacodynamic responses to rocuronium in normal or injured orbicularis oris are associated with expression of acetylcholine receptor subunits

Previous research has indicated that differences in sensitivities to muscle relaxants exist between facial nerve- and somatic nerve-innervated muscles. Here, we report that the 50% inhibitory concentration (IC50) values for rocuronium were significantly larger in the normal orbicularis oris than those in the gastrocnemius. Increased IC50 values and reduced twitch tension were observed after facial nerve injury. The normal orbicularis oris had a smaller muscle fiber cross-sectional area (CSA) and a larger ratio of endplate surface area (ESA) to muscle fiber CSA (ESA/CSA), but no difference was found in the density of nicotinic acetylcholine receptor (nAChR) subunits on endplates between normal orbicularis oris and gastrocnemius. Expression of the nAChR α1, β1, δ, ε, and γ subunits increased significantly on the postsynaptic membranes of endplates and extra-junctional muscle membranes after facial nerve injury. Our results suggest that facial nerve-innervated muscle was less sensitive than somatic nerve-innervated muscle, and the mechanisms underlying this result may be related to muscle fiber CSA and the ESA/CSA ratio, but not to the density of nAChR subunits on endplates. Facial nerve injury caused the resistance to neuromuscular blockers and reduced twitch tension, which was related to qualitative, quantitative, and locational changes in nAChR subunits.

The Protective Effect of Alpha 7 Nicotinic Acetylcholine Receptor Activation on Critical Illness and Its Mechanism

Critical illnesses and injuries are recognized as major threats to human health, and they are usually accompanied by uncontrolled inflammation and dysfunction of immune response. The alpha 7 nicotinic acetylcholine receptor (α7nAchR), which is a primary receptor of cholinergic anti-inflammatory pathway (CAP), exhibits great benefits for critical ill conditions. It is composed of 5 identical α7 subunits that form a central pore with high permeability for calcium. This putative structure is closely associated with its functional states. Activated α7nAChR exhibits extensive anti-inflammatory and immune modulatory reactions, including lowered pro-inflammatory cytokines levels, decreased expressions of chemokines as well as adhesion molecules, and altered differentiation and activation of immune cells, which are important in maintaining immune homeostasis. Well understanding of the effects and mechanisms of α7nAChR will be of great value in exploring effective targets for treating critical diseases.

The effect of nicotine on the expressions of the α7 nicotinic receptor gene and Bax and Bcl-2 proteins in the mammary gland epithelial-7 breast cancer cell line and its relationship to drug resistance

The binding of nicotine with nicotinic acetylcholine receptors (nAChRs) stimulates cell division and increases drug resistance in cancer. Experiments with specific inhibitors such as RNAi, hexamethonium, and α-bungarotoxin showed that α7 nicotinic receptor plays a key role in the pro-proliferation activity of nicotine. However, the mechanism of nicotine in the progress of breast cancer, the commonest malignancy in women, remains unknown. This study focuses on the effect of nicotine on the expressions of the α7 nicotinic receptor gene and Bax and Bcl-2 proteins in mammary gland epithelial-7 (MCF-7) breast cancer cells and its relationship to drug resistance. To evaluate the effect on drug resistance, human mammary gland epithelial adenocarcinomas from the MCF-7 line were exposed to 100 μl of nicotine at a concentration of 9.2 mg/ml for varying periods of time. Then, the cells were treated with 1, 2, 3 or 5 μl/ml of doxorubicin, either with or without the continued presence of nicotine. Cell viability was determined using the MTT assay. The biochemical parameters of apoptosis, including the expressions of Bax, Bcl-2 and α7 nicotinic receptor proteins were determined via western blotting, and the α7 nicotinic receptor gene expression level was assessed via real-time qPCR using the 2(-ΔΔCt) method. Differences in the target gene expression levels were evaluated with ANOVA with p ≤ 0.05 considered significant. We found a novel and effective signaling pathway of nicotine in the MCF-7 breast cancer cell line. The levels of α7 nicotinic receptor and Bcl-2 protein increased but the Bax protein levels decreased, while the α7 nicotinic receptor gene expression level was not significantly different compared with the control.

Sepsis induced denervation-like changes at the neuromuscular junction

BACKGROUND

The aim of this study was to determine the functional and biochemical changes at the neuromuscular junction (NMJ) induced by sepsis.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into three groups as follows: control, denervation, and sepsis. The rats were subjected to cecal ligation and puncture (CLP) or tibias nerve transection. NMJ function and the area of end plates were assessed, and the protein level of acetylcholine receptors and axonal neuregulin-1 was evaluated on postoperative days 1, 7, and 14.

RESULTS

In the control group, the amplitude of compound muscle action potential (CMAP) was 16.51 ± 2.53 mV. In the sepsis group, the amplitude of CMAP decreased, and duration was prolonged on postoperative days 7 and 14 (P < 0.01). Meanwhile, motor conduction velocity decreased significantly (P < 0.01). CMAP was lost in the denervation group. The twitch tension magnitude gradually declined (P < 0.05) in the sepsis group, although it could not be recorded after lesion. Sepsis and denervation upregulated the expression of γ-nicotinic acetylcholine receptor (nAChR) and α7-nAChR in muscle membrane, compared with those in normal NMJ (261.4 ± 26.5 μm(2)). The NMJ area decreased from 254.6 ± 23.8 μm(2) (1 d after CLP) to 275.4 ± 22.6 μm(2) (7 d after CLP) to 322.7 ± 34.4 μm(2) (14 d after CLP). The postsynaptic NMJ had more discrete fragments (3.84 ± 0.6) compared with the control group (2.13 ± 0.4; P < 0.01). After denervation, NMJ underwent fragmentation and the number of discrete fragments increased (5.57 ± 1.2; P < 0.01). NMJ area increased from 254.6 ± 23.8 μm(2) (1 d after CLP) to 275.4 ± 22.6 μm(2) (7 d after CLP) to 322.7 ± 34.4 μm(2) (14 d after CLP). Sepsis induced neuregulin-1 to decrease from 1 d up to 2 wk compared with the control group (P < 0.05).

CONCLUSIONS

Chronic sepsis has a denervation-like effect on the NMJ, which was indicated by upregulation of heterogeneous nAChRs, the increased area of end plates, and demyelination of the motoneuron axon.

Receptor analysis of differential sensitivity change to succinylcholine induced by nerve injury in rat gastrocnemius

BACKGROUND

Urgent tracheal intubation is common in intensive care units and the emergency room, and succinylcholine is a first-line neuromuscular blocker used in these situations. Paraplegic or critically ill patients may be at a high risk of receiving succinylcholine because the denervation stage changes nicotinic receptors, which affect the efficacy and safety of succinylcholine. The objective of this study was to determine the receptor subtypes associated with changes in the pharmacodynamics of succinylcholine and its time-line trend.

METHODS

Denervated gastrocnemius was collected from tibial nerve transected rats. To determine the 50% effective dose of succinylcholine and rocuronium at 0 (control), 1, 3, 7, 14, and 28 d after denervation, action potential amplitude was monitored by an intracellular recording method. Subunits α1, α7, ε, and γ of the acetylcholine receptor (AChR) were quantified by real-time polymerase chain reaction. Receptor amount and pharmacodynamic changes were analyzed by correlation and regression analysis.

RESULTS

The pharmacodynamic change in succinylcholine was a dynamic process, and at the same time α7, ε, and γ-nicotinic AChR genes in denervated muscle were significantly changed but only α7 was closely correlated with the action of succinylcholine. Subunit γ and α7 were related to pharmacodynamic change in the nondepolarizing neuromuscular agent, rocuronium.

CONCLUSIONS

Nerve injury may alter nicotinic AChR subtypes in skeletal muscle at different stages, which probably affected the pharmacodynamics of neuromuscular blockers in different ways. Denervation time and stage and the type of neuromuscular blocker and dosage should be taken into consideration when using these drugs in patients with nerve injury.

Pharmacodynamic changes with vecuronium in sepsis are associated with expression of α7- and γ-nicotinic acetylcholine receptor in an experimental rat model of neuromyopathy

BACKGROUND

Resistance to non-depolarizing neuromuscular blocking agents induced by sepsis is associated with the qualitative change in the nicotinic acetylcholine receptor (nAChR). This study aims to investigate the effects of sepsis on the neuromuscular block properties of vecuronium in relation to the expression of fetal and neuronal α7 type nAChR.

METHODS

Male Sprague-Dawley rats were randomly divided into sham and sepsis groups. Sepsis was induced by caecal ligation and puncture (CLP). The rats were injected i.v. with ulinastatin or normal saline on Day 10. Neuromuscular block properties of vecuronium were evaluated and neuromuscular function was assessed by electromyography on Days 1, 3, 7, and 14 after CLP. Expression of fetal and neuronal type α7-nAChR on the tibialis anterior muscle was assessed using immunohistochemistry and western blot. The mRNA encoding for γ- and α7 subunits was evaluated by real-time polymerase chain reaction.

RESULTS

The half maximal inhibitory response of vecuronium in the sepsis group significantly increased, peaked on Day 7, and then declined on Day 14 (P<0.05). The neuromuscular function decreased with increasing postoperation time in the sepsis group (P<0.05). Sepsis significantly increased the expression of γ- and α7-nAchR along with expression of γ- and α7 subunits mRNA, peaked on Day 7, and declined on Day 14 (P<0.05). Ulinastatin suppressed the expression of receptor protein and mRNA encoding for γ- and α7 subunits (P<0.05).

CONCLUSIONS

Pharmacodynamic changes with vecuronium seem to be associated with the expression of γ- and α7-nAChR in the skeletal muscle. Ulinastatin can improve this effect by inhibiting the expression of these receptors.

Pediatric burn injuries

Pediatric burns comprise a major mechanism of injury, affecting millions of children worldwide, with causes including scald injury, fire injury, and child abuse. Burn injuries tend to be classified based on the total body surface area involved and the depth of injury. Large burn injuries have multisystemic manifestations, including injuries to all major organ systems, requiring close supportive and therapeutic measures. Management of burn injuries requires intensive medical therapy for multi-organ dysfunction/failure, and aggressive surgical therapy to prevent sepsis and secondary complications. In addition, pain management throughout this period is vital. Specialized burn centers, which care for these patients with multidisciplinary teams, may be the best places to treat children with major thermal injuries. This review highlights the major components of burn care, stressing the pathophysiologic consequences of burn injury, circulatory and respiratory care, surgical management, and pain management of these often critically ill patients.