High gender -specific susceptibility to curare- a neuromuscular blocking agent.

Curare, a selective skeletal muscle relaxant, has been used clinically to reduce shivering and as an anesthetic auxiliary in abdominal surgery. It is also widely used in animal experiments to block neuromuscular junction activity. Effective doses of curare diminish muscle contraction without affecting brain function, but at higher doses it is known to be lethal. However, the exact dose of curare initiating muscle relaxation vs. lethal effect has not been fully characterized in mice. In this study we carefully examined the dose-response for achieving muscle inactivity over lethality in both male and female mice (C57BL6/J). The most striking finding of this study is that female mice were highly susceptible to curare; both the ED50 and LD50 were at least 3-fold lower than male littermates. This study shows that gender-specific differences can be an important factor when administering skeletal muscle relaxants, particularly curare or other analogous agents targeted to the neuromuscular junction.

Novel Insights on MRGPRX2-Mediated Hypersensitivity to Neuromuscular Blocking Agents And Fluoroquinolones.

Neuromuscular blocking agents (NMBAs) like atracurium and rocuronium as well as fluoroquinolones (FQs) cause mast cell-mediated anaphylaxis by activating Mas-related G protein-coupled receptor X2 (MRGPRX2), but many questions remain unanswered. Here, we address three of them, namely whether primary human mast cells show similar activation by these drugs as murine mast cells and mast cell lines, how sugammadex protects from atracurium-induced MRGPRX2-mediated mast cell activation, and why some but not all patients treated with rocuronium develop anaphylaxis. We used peripheral blood-derived cultured mast cells from healthy donors and patients, assessed mast cell activation and degranulation by quantifying intracellular calcium and CD63 expression, respectively, and made use of MRGPRX2-silencing, via electroporation with Dicer-substrate small interfering RNAs, and single cell flow cytometric analyses. Atracurium, ciprofloxacin, and levofloxacin activated and degranulated primary human mast cells, but only MRGPRX2-positive and not MRGPRX2-negative or -silenced mast cells. Sugammadex attenuated the atracurium-induced and MRGPRX2-mediated activation and degranulation of human mast cells by reducing free atracurium levels. The mast cells of patients with IgE-independent anaphylaxis to rocuronium were similar, in their MRGPRX2 expression and function, to those of patients with IgE-mediated anaphylaxis. These findings further improve our understanding of the role and relevance of MRGPRX2-driven mast cell activation in anaphylactic reactions to NMBAs and FQs and may help to improve their prediction, prevention, and treatment.

Synthesis of a bifunctional coordination complex of osmium with curariform activity.

Based on the known curariform action of tris(bipyridyl)iron(II) sulfate and other complex ions, two series of bifunctional ligands designed to hold transition metal ions at approximately the same distance apart as the interquaternary ammonium distance in the potent neuromuscular block agents were synthesized. In the first series two 1,10-phenanthrolines (R1) were joined at the 2 position to form four compounds: R1CO-c-N(CH2CH2)2N-COR1, R1CONH-1,2-C6H10-NHCOR1, R1CONH-1,2-C6H4-NHCOR1, and R1CON(CH3)(CH2)2N(CH3)COR1. In the second series two terpyridines (R1) were joined by different chains to give R2(CH2)2CH=CH(CH2)2R2, R2CH2C(CH3)(OH)(CH2)2C(CH23)(OH)CH2R2, R2CH2C(CH3)(OH)C(CH3)(OH)CH2R2, and R2CH2(OH)-1,4-C6H10-(OH)CH2R2. Three other ligands in which the terpyridines were joined by 5-, 60, and 7-methylene groups were also made. The ligands were converted to nickel(II) complexes and the coordination of each nickel ion was completed by adding terpyridine. These were assayed by the intravenous mouse LD50 method. The most potent ligand, the di-hydroxy compound R2CH2(OH)-1,4-C6H10-(OH)CH2R2 was then converted to the bis(pyridinebipyridine)diosmium-(II) coordinated complex and assayed by the iv mouse LD50 method and by the ED50 isolated guinea-pig diaphragm method. By the iv mouse LD50 method, it was about twice as potent as d-tubocurarine and by the isolated diaphragm method, it was 16 times more potent. The compound has been called dihydroxyosmarine tetrachloride or DHO for short. The term "transarine" ions is proposed for transition metal coordination complexes having curariform action. The position of the transarine ions is discussed in the classification of cholinergic ligands, in structure-action relationships, and in relation to some current ideas on receptor mechanisms.

Lipid peroxidation and changes in cytochrome c oxidase and xanthine oxidase activity in organophosphorus anticholinesterase induced myopathy.

A possible role of radical oxygen species (ROS) initiated lipid peroxidation in diisopropylphosphorofluoridate (DFP)-induced muscle necrosis was investigated by quantifying muscle changes in F2-isoprostanes, novel and extremely accurate markers of lipid peroxidation in vivo. A significant increase in F2-isoprostanes of 56% was found in the diaphragm of rats 60 min after DFP-induced fasciculations. As possible source of ROS initiating lipid peroxidation, the cytocrome-c oxidase (Cyt-ox) and xanthine dehydrogenase-xanthine oxidase (XD-XO) systems were investigated. Within 30 min of onset of fasciculations Cyt-ox activity was reduced by 50% from 0.526 to 0.263 mumol/mg prot/min and XO activity increased from 0.242 to 0.541 mumol/mg prot/min. Total XD-XO activity was unchanged, indicating a conversion from XD into XO. In rats pretreatment with the neuromuscular blocking agent d-tubocurarine, prevented DFP-induced fasciculations, increases in F2-isoprostanes and changes in Cyt-ox or XD-XO. The decrease in Cyt-ox and increase in XO suggest that ROS are produced during DFP induced muscle fasciculations initiating lipid peroxidation and subsequent myopathy.

How do snake curaremimetic toxins discriminate between nicotinic acetylcholine receptor subtypes.

Curaremimetic toxins from snake venoms form a large family of small proteins that adopt a similar fold and which bind to Torpedo nicotinic acetylcholine receptors with high affinity. Notwithstanding its apparent homogeneity, the toxin family is subdivided into short-chain (60-62 residues and four disulfide bonds) and long-chain toxins (66-74 residues and five disulfide bonds). In agreement with this structurally-based distinction we recently showed that only long-chain toxins bind with high affinity to the neuronal nicotinic acetylcholine alpha7 receptor. We suggested that a small loop cyclized by a disulfide bond and uniquely present in long-chain toxins may act as a major discriminative element. To assess the validity of this proposal we prepared various derivatives of a long-chain toxin, using stepwise solid-phase synthesis. We found that replacement of both half cystines of the small loop by a serine caused a 35-fold affinity decrease for the neuronal receptor and only a 6-fold affinity decrease for Torpedo receptor. In addition, insertion of this loop at a homologous position of a short-chain toxin caused a 20-fold affinity increase for the neuronal receptor whereas it did not modify its affinity for the Torpedo receptor. Our findings, therefore, reveal that a small structural deviation from a toxin fold can generate exquisite discriminative recognition for some receptor subtypes.

Tone burst-evoked otoacoustic emissions in cats with acoustic overstimulation and anoxia.

Transient evoked otoacoustic emissions (TEOAE) produced by a 2 kHz tone burst could be detected in 30 out of 37 ears (81% detectability) in 21 cats. The amplitude of tone burst-evoked TEOAE was saturated at a stimulus level between 45 and 50 dB SPL and the latency time of peak amplitude was 6.23 ms on average (5.53-7.28 ms). The effects of pure tone overstimulation and short-term anoxia on the tone burst-evoked TEOAE in cats were evaluated. A permanent detection threshold shift of the TEOAE was confirmed at 24 h and 1 week after the overstimulation at 125 dB SPL. In these cases, damaged first row outer hair cells and inner hair cells were observed over an average length of 3.3 mm (16% of the entire cochlear length) by scanning electron microscopy. These findings suggested that the TEOAE can detect localized cochlear hair cell damage. A temporary detection threshold shift of the TEOAE was observed after the overstimulation at 105 dB SPL, and the threshold shift recovered in 107.5 min on average. In the short-term anoxia trial, the TEOAE amplitude started to decrease 45-90 s after the anoxia and recovered completely when the duration of anoxia was under 1 min. However, the TEOAE amplitude did not recover pre-anoxia values (it remained below 80% of its initial value) after 5 min when the anoxia was over 2 min. These findings demonstrated that the detection threshold and amplitude of the TEOAE were also affected by metabolic changes of the cochlear hair cells. Tone burst-evoked TEOAE are useful for the evaluation of localized histological and functional damage of the cochlear hair cells.

Sterochemical preferences for curarimimetic neuromuscular junction blockade III: enantiomeric bisquaternary amines related to benzoquinonium as probes.

Enantiomeric neuromuscular junction blocking agents, which are of the benzoquinonium type but which have a methyl group introduced adjacent to the quaternary moieties to provide an asymmetric center were synthesized and tested to determine whether the neuromuscular junction exhibits the relatively modest (R) greater than (S) superiority shown toward previously tested bisquaternaries. Testing included a mouse inclined screen assay and an in vivo cat hypoglossal nerve-tongue preparation, as well as standard estimations of anticholinesterase activity since the candidate compounds are known to have such a component in their activity spectrum. The observed 2:1 difference in blocking activity favoring the compound with an (R)-configuration is the same as that for previously tested bisquaternaries, both in direction and magnitude. Furthermore, it cannot be accounted for by preferential inhibition of acetylcholinesterase by the (S)-enantiomer. Absolute configurations of the enantiomers were assigned on the basis of comparison with compounds of known configuration.

Interaction of lipopolysaccharide endotoxin produced from Escherichia coli with D-tubocurarine at the nicotinic2 receptor and adenosine 3':5' cyclic monophosphate during physiological contraction in skeletal muscle.

In this report the murine model of endotoxicosis was used to evaluate hyposensitivity to the neuromuscular relaxant D-tubocurarine (dTC). This hyposensitivity was expressed in terms of a decreased potency to dTC. A rightward shift of the dose-response curve due to endotoxin was observed. Mice were subjected to cumulative intraperitoneal doses of Escherichia coli endotoxin over a 2-wk period. The interaction between endotoxin and dTC was examined during an acute (1 wk) and chronic (2 wk) period of endotoxicosis. Muscle twitch analyses were performed and samples of gastrocnemius muscle were assayed for adenosine 3':5' cyclic monophosphate (cAMP) by [125I]radioimmunoassay. A parallel shift in the dose-response curve occurred in the endotoxin group subjected to doses corresponding to one-third the dose evoking 50% lethality for 2 wk. Both skeletal muscle tension and cAMP levels decreased as cumulative endotoxin doses increased. A relationship between decreasing cAMP levels and increasing dTC and effective dose required to achieve 50% muscle paralysis values was thought to be evoked by the agonistic activity of E. coli endotoxin leading to desensitizing of adenylate cyclase. The perturbations of the classical second messenger cAMP system by endotoxin may be responsible for skeletal muscle dysfunction observed in immunocompromised patients.

[Synthesis and pharmacologic study of 1,5-dialkyl-1,5-benzodiazepine-2,4-dithiones]. / Synthèse et étude pharmacologique des 1,5-dialkyl-1,5-benzodiazépine-2,4-dithiones.

The synthesis and psychotropic activity of 1,5-diakyl-1,5-benzodiazepine-2,4-dithiones (alkyl = methyl, ethyl and benzyl radicals) were studied. Alkylation reactions were performed in catalytic conditions by phase transfer. These reactions allowed us to isolate only one kind of product N-alkyl. Acute toxicity studies were conducted according to European protocols in two species of appropriate mammals in order to discover the lethal doses. The activity of the compounds on the CNS was then studied, using a battery of compartmental tests used in psychopharmacology. No toxicity was demonstrated at therapeutic doses. Each product had a sedative effect more or less pronounced and different from the reference substance clobazam (Urbanyl). They also had myorelaxant and anxiolytic effects, even lengthening the hypnotic effect of thiopental (synergic action).

High gender -specific susceptibility to curare- a neuromuscular blocking agent

Curare, a selective skeletal muscle relaxant, has been used clinically to reduce shivering and as an anesthetic auxiliary in abdominal surgery. It is also widely used in animal experiments to block neuromuscular junction activity. Effective doses of curare diminish muscle contraction without affecting brain function, but at higher doses it is known to be lethal. However, the exact dose of curare initiating muscle relaxation vs. lethal effect has not been fully characterized in mice. In this study we carefully examined the dose-response for achieving muscle inactivity over lethality in both male and female mice (C57BL6/J). The most striking finding of this study is that female mice were highly susceptible to curare; both the EDm and LDm were at least 3-fold lower than male littermates. This study shows that gender-specific differences can be an important factor when administering skeletal muscle relaxants, particularly curare or other analogous agents targeted to the neuromuscular junction.

Doxacurium and mivacurium do not trigger malignant hyperthermia in susceptible swine.

The role of succinylcholine in the precipitation of malignant hyperthermia (MH) necessitates the testing of new neuromuscular relaxants for their ability to trigger MH in MH-susceptible swine before general human use. We tested doxacurium and mivacurium, two new nondepolarizing bis-benzylisoquinolinium neuromuscular relaxants, at ED95 and at four times ED95 doses in swine previously documented to be MH-susceptible. In none of the 16 animals was MH triggered after administration of these relaxants, whereas all animals developed fatal MH after administration of halothane or halothane plus succinylcholine. Muscle biopsy specimens taken before administration of the relaxant confirmed that all animals had increased sensitivity to halothane, caffeine, or both. Thus, we conclude that doxacurium and mivacurium are not triggering agents of malignant hyperthermia in MH-susceptible swine.

[Toxicity of the new antidepolarizing curare-like drug diadonium]. / O toksichnosti novogo antidepoliarizuiushchego kurarepodobnogo sredstva diadoniia.

It has been shown in acute experiments on rats, rabbits and cats that under extracorporeal pulmonary ventilation, the animals could tolerate the 50-100 fold apnoeic doses of diadonium. Chronic experiments have demonstrated that administration of the subapnoeic doses of diadonium to rats, rabbits, and dogs and the apnoeic doses to rats (under extracorporeal respiration) for 10-14 days exerts no significant effect on the peripheral blood, the main biochemical characteristics of blood serum, histological structure of the internal organs, and does not possess local irritant or hemolytic action. The data obtained indicate the safety of diadonium as a myorelaxant.

An investigation of non-depolarizing muscle relaxants on embryonic development in cultured rat embryos.

BACKGROUND AND OBJECTIVE: We have investigated the toxic and teratogenic effects of certain non-depolarizing muscle relaxants on embryonic development in cultured rat embryos. METHODS: Rat embryos of 9.5 days were explanted and cultured in vitro for 48 h in rat serum. Whole rat serum was used as a culture medium for the control group while different concentrations of atracurium, cis-atracurium, rocuronium and mivacurium were added to rat serum for the experimental groups. Dose-dependent effects of these agents on embryonic developmental parameters were compared using morphological and biochemical methods. Each embryo was evaluated for the presence of any malformations. RESULTS: When compared to the control embryos, the muscle relaxants significantly decreased all growth and developmental parameters dose dependently with an increase in overall dismorphology. Among these malformations, maxillary deformity was most frequently observed. These effects were observed in much lower doses with atracurium and cis-atracurium compared to those with rocuronium and mivacurium. CONCLUSIONS: Our results suggest that non-depolarizing muscle relaxants cause dose-dependent toxicity on rat embryos at concentrations much greater than those in clinical practice. Although, these agents seems to have a low potential for causing developmental toxicity during organogenesis, because of the lower toxic effects observed with rocuronium and mivacurium, these agents may be preferred when recurrent administrations are necessary for parturients.