Safety and Efficacy of HU-014 in the Treatment of Post-Stroke Upper Limb Spasticity: A Phase I Pilot Study.

Botulinum toxin type A (BTX-A) is widely used for treating post-stroke upper limb spasticity. We evaluated the safety and efficacy of HU-014 in treating post-stroke upper limb spasticity. Thirteen patients were administered with HU-014. The primary outcome was safety, including adverse events, vital signs, physical examination, laboratory tests, and antibody formation test. The secondary outcomes were changes in the Modified Ashworth Scale (MAS) score for wrist, elbow, and finger flexor; Disability Assessment Scale (DAS); Investigator's Global Assessment (IGA) and Subject's Global Assessment (SGA); Caregiver Burden Scale (CBS); and Columbia Suicide Severity Rating Scale (C-SSRS) at weeks 4, 8, and 12 from baseline. No notable safety-related issues were reported. MAS and DAS scores were significantly decreased from those at baseline at 4, 8, and 12 weeks (p < 0.05). At weeks 4, 8, and 12, the IGA and SGA scores were 5.85 ± 0.55, 5.69 ± 0.48, and 5.62 ± 0.65 and 5.46 ± 1.20, 5.85 ± 0.38, and 5.77 ± 0.73, respectively. CBS scores decreased at all timepoints and those for cutting fingernails significantly decreased at 8 and 12 weeks compared with baseline (p < 0.05). C-SSRS scores showed that suicidal ideation in all patients was "low" at all timepoints. HU-014 is a safe treatment that can improve post-stroke upper limb spasticity.

An Observational Cross-Sectional Study of Gender and Disability as Determinants of Person-Centered Medicine in Botulinum Neurotoxin Treatment of Upper Motoneuron Syndrome.

The motor behaviour of patients with Upper Motor Neuron Syndrome (UMNS) is characterised by spasticity. The first-line treatment for this clinical condition is Botulinum neurotoxin A (BoNTA), but the number and key locations of muscles which need to be treated is not much discussed in the literature. Cross-sectional analysis of outpatient cohort with UMNS spasticity, who were potential candidates for BoNTA treatment, was performed. Between November 2020 and November 2021, all consecutive adult patients eligible for BoNTA treatment were enrolled. The inclusion criteria encompass UMNS spasticity (onset being ≥6 months), with disabling muscles hypertonia. Patients underwent a clinical evaluation, a comprehensive assessment with the Modified Ashworth Scale, with the Modified Rankin Scale, and a patients' perception-centred questionnaire. In total, 68 participants were enrolled in the study, among them 40 (58.8%) were male; mean age 57.9 ± 15.1. In women, BoNTA was more frequently required for adductor group muscles, independently from potential confounders (OR = 7.03, 95%CI: 1.90-25.97). According to the pattern of disability, patients with hemiparesis more frequently need to be treated in the upper limb, whereas the diplegia/double-hemiparesis group needed to be treated more frequently at the adductor and crux muscles compared to their counterparts. UMNS spasticity in women could require more attention to be paid to the treatment of adductor muscle spasticity, potentially because the dysfunction of those muscles could influence sphincteric management, required for perineal hygiene and/or sexual life.

OnabotulinumtoxinA Displays Greater Biological Activity Compared to IncobotulinumtoxinA, Demonstrating Non-Interchangeability in Both In Vitro and In Vivo Assays.

Differences in botulinum neurotoxin manufacturing, formulation, and potency evaluation can impact dose and biological activity, which ultimately affect duration of action. The potency of different labeled vials of incobotulinumtoxinA (Xeomin®; 50 U, 100 U, or 200 U vials; incobotA) versus onabotulinumtoxinA (BOTOX®; 100 U vial; onabotA) were compared on a unit-to-unit basis to assess biological activity using in vitro (light-chain activity high-performance liquid chromatography (LCA-HPLC) and cell-based potency assay (CBPA)) and in vivo (rat compound muscle action potential (cMAP) and mouse digit abduction score (DAS)) assays. Using LCA-HPLC, incobotA units displayed approximately 54% of the protease activity of label-stated equivalent onabotA units. Lower potency, reflected by higher EC50, ID50, and ED50 values (pooled mean ± SEM), was displayed by incobotA compared to onabotA in the CBPA (EC50: incobotA 7.6 ± 0.7 U/mL; onabotA 5.9 ± 0.5 U/mL), cMAP (ID50: incobotA 0.078 ± 0.005 U/rat; onabotA 0.053 ± 0.004 U/rat), and DAS (ED50: incobotA 14.2 ± 0.5 U/kg; onabotA 8.7 ± 0.3 U/kg) assays. Lastly, in the DAS assay, onabotA had a longer duration of action compared to incobotA when dosed at label-stated equivalent units. In summary, onabotA consistently displayed greater biological activity than incobotA in two in vitro and two in vivo assays. Differences in the assay results do not support dose interchangeability between the two products.

Comparison of efficacy and toxicity between botulinum toxin subtypes A1 and A2 in cynomolgus macaques.

Botulinum toxin type A (subtype A1) is used as therapeutic agent for some neurological disorders causing spasticity. The toxin products have an upper dosage limit, and their adverse events, such as side effects of diffusion following high-dose administration, have become serious issues. Therefore, a preparation with greater therapeutic efficacy at lower dosages and less diffusion in the body is desired. We have attempted to produce neurotoxin derived from subtype A2 (A2NTX), which has a different amino acid sequence from that of neurotoxin derived from subtype A1. In this study, to investigate whether A2NTX is applicable for treatment, we compared the muscle relaxation effects and the toxicity between A1LL and A2NTX in adult cynomolgus macaques. In the isometric muscle contraction test elicited by 30 Hz tetanus stimulation, the contractions observed in the 0.4 U/site A1LL-treated group were similar in value to those in the 0.13 U/site A2NTX-treated group. In the toxicity test, the 12 and 24 U/kg A1LL- and A2NTX-treated groups all exhibited similar signs of toxicity regarding symptoms, rate of weight loss, and decrease in the length of the right lower leg perimeter. Thus, A2NTX demonstrated approximately 3.0-times higher muscle relaxation activity than A1LL, and their toxicity was equivalent. This study suggested that A2NTX products are more suitable for the treatment of neurological disorders.

Botulinum toxin type A affects the transcriptome of cell cultures derived from muscle biopsies of controls and spastic patients.

Botulin toxin (BTX) is widely used for treating skeletal muscle spasticity. Experimental reports on BTX treatment were mainly focused on the neuromuscular junction, while relatively little is known about toxin effects on the muscle cell itself. We investigated possible impact of BTX type A on skeletal muscle cell transcriptome by microarray analysis in muscle-derived cell cultures (fibroblasts, myoblasts and myotubes) from controls and spastic patients, and results were then validated at transcript and protein level. BTX-A treatment of control cells induced major changes in the myogenic component of the transcriptome, whereas the same treatment had a negligible effect in the fibrogenic component. BTX-A treatment of cell cultures from spastic patients induced an increased number of genes differentially expressed both in the fibrogenic and myogenic components. Specifically, BTX-A had a major effect on cell cycle-related genes in myoblasts, on muscle contraction-related genes in myotubes, and on extracellular matrix-related genes in fibroblasts from spastic patients. Our findings show that in vitro BTX-A treatment differentially affects transcript expression in muscle cells from spastic patients compared to those from controls suggesting a direct effect of BTX-A on muscle-specific functional pathways.

Pregnancy outcomes after maternal use of thiocolchicoside: A case series.

OBJECTIVE: The 2014 report by European Medicines Agency (EMA) restricted the use of thiocolchicoside for all reproductive-age women. In this study, we aim to expand the systematically-collected human data and discuss it within the frame provided by this report. METHODS: We identified and evaluated the outcomes of 48 prospectively recorded pregnancies referred to Terafar (Teratology Information Service, Izmir, Turkey). RESULTS: Of 42 pregnancies with first-trimester exposure and known outcomes, 31 resulted in live births, four in miscarriage and seven ended with elective terminations. There were 26 normal outcomes, two major and three minor congenital malformations among the live births. CONCLUSIONS: Despite a number of limitations, our results and previous case series collectively strengthen the view that thiocolchicoside is unlikely to be a major teratogen. EMA's 2014 report should be revised to reflect this finding, while current restrictions on use should continue until more detailed safety information is available.

Loading of the Condylar Cartilage Can Rescue the Effects of Botox on TMJ.

The purpose of this study is to evaluate whether the effects of botulinum neurotoxin (botox) injection into the masseter in the mandibular condylar cartilage (MCC) and subchondral bone could be rescued by compressive loading of the temporomandibular joint (TMJ). Twenty-four 6-week-old female mice (C57BL/6J) were used. Mice were divided in three groups: (1) Botox (n = 8); (2) Botox plus loading (n = 8); (3) Pure control (n = 8). Bone labels (3 and 1 day before sacrifice) and the proliferation marker EdU (2 and 1 day before sacrifice) were intraperitoneally injected into all groups of mice. Condyles were dissected and examined by micro-CT and histology. Sagittal sections of condyles were stained for TRAP, alkaline phosphatase, EdU, TUNEL, and toluidine blue. In addition, immunostaining for pSmad, VEGF, and Runx2 was performed. Bone volume fraction, tissue density, and trabecular thickness were significantly decreased on the subchondral bone of botox-injected side when compared to control side and control mice, 4 weeks after injection. Furthermore, histological analysis revealed decrease in mineralization, matrix deposition, TRAP activity, EdU, and TUNEL-positive cells in the MCC of the botox-injected side, 4 weeks after injection. However, compressive loading reversed the reduced bone volume and density and the cellular changes in the MCC caused by Botox injection. TMJ compressive loading rescues the negative effects of botox injection into the masseter in the MCC and subchondral bone.

Muscle paralysis induces bone marrow inflammation and predisposition to formation of giant osteoclasts.

Transient muscle paralysis engendered by a single injection of botulinum toxin A (BTxA) rapidly induces profound focal bone resorption within the medullary cavity of adjacent bones. While initially conceived as a model of mechanical disuse, osteoclastic resorption in this model is disproportionately severe compared with the modest gait defect that is created. Preliminary studies of bone marrow following muscle paralysis suggested acute upregulation of inflammatory cytokines, including TNF-α and IL-1. We therefore hypothesized that BTxA-induced muscle paralysis would rapidly alter the inflammatory microenvironment and the osteoclastic potential of bone marrow. We tested this hypothesis by defining the time course of inflammatory cell infiltration, osteoinflammatory cytokine expression, and alteration in osteoclastogenic potential in the tibia bone marrow following transient muscle paralysis of the calf muscles. Our findings identified inflammatory cell infiltration within 24 h of muscle paralysis. By 72 h, osteoclast fusion and pro-osteoclastic inflammatory gene expression were upregulated in tibia bone marrow. These alterations coincided with bone marrow becoming permissive to the formation of osteoclasts of greater size and greater nuclei numbers. Taken together, our data are consistent with the thesis that transient calf muscle paralysis induces acute inflammation within the marrow of the adjacent tibia and that these alterations are temporally consistent with a role in mediating muscle paralysis-induced bone resorption.

Neutralising ability of Terminalia fagifolia extract (Combretaceae) against the in vitro neuromuscular effects of Bothrops jararacussu venom.

The ability of Terminalia fagifolia hydroalcoholic extract (Tf-HE) to neutralise the paralysis and myotoxicity induced by Bothrops jararacussu venom was assayed using mouse phrenic nerve-diaphragm (PND) preparation and two varieties of chick biventer cervicis (BC) preparations. Tf-HE 100 µg/mL and 500 µg/mL were tested against 40 and 200 µg of venom/mL in PND and BC preparations, respectively, using pre- and post-venom incubation treatments. The effects of Tf-HE against the myotoxicity caused by venom were evaluated via histological analysis (PND) and creatine kinase (CK) release (BC). Tf-HE was able to reverse the venom paralysis in both preparation types. The contractures to exogenous ACh in BC preparations showed that Tf-HE may act on extrinsic, preserving those intrinsic postsynaptic receptors. There was a positive correlation between CK and morphological changes. The high non-hemolytic saponin content can explain the Tf-HE efficacy against the toxic effects of B. jararacussu venom in vertebrate neuromuscular preparations.

Alterations in gene expression precede sarcopenia and osteopenia in botulinum toxin immobilized mice.

OBJECTIVES: To investigate alteration of bone and muscle gene expression at different time points during 3 weeks of botulinum toxin (BTX) induced immobilization and how this correlate with conventional analysis of bone and muscle. METHODS: Thirty-five 16-week-old female C57BL/6-mice were investigated; 15 were injected with BTX, 15 served as age-matched controls, and 5 as baseline. 5 BTX-injected and 5 control mice were euthanized after 1, 2, and 3 weeks. Analysis included RT-qPCR, dynamic bone histomorphometry, DEXA, µCT, mechanical testing, and muscle cell cross-sectional-area (CSA). RESULTS: Genes related to osteoblasts were expressed at a lower level after 1 week, but not after 2 and 3 weeks of disuse. Moreover, genes related to osteoclasts were expressed at a higher level after 1 and 2 weeks of disuse, whereafter they approached the level of the controls. Genes related to muscle atrophy were upregulated 1 and 2 weeks after the BTX-injection, but not after 3 weeks. In contrast, deterioration of bone microstructure and strength, and reduction in muscle cell CSA were most evident after 3 weeks of disuse. CONCLUSIONS: Gene expression should be investigated during the first two weeks of immobilization, whereas changes in bone microstructure and muscle cell CSA are most prominent after 3 weeks of immobilization.

Botulinum toxin injection causes hyper-reflexia and increased muscle stiffness of the triceps surae muscle in the rat.

Botulinum toxin is used with the intention of diminishing spasticity and reducing the risk of development of contractures. Here, we investigated changes in muscle stiffness caused by reflex activity or elastic muscle properties following botulinum toxin injection in the triceps surae muscle in rats. Forty-four rats received injection of botulinum toxin in the left triceps surae muscle. Control measurements were performed on the noninjected contralateral side in all rats. Acute experiments were performed, 1, 2, 4, and 8 wk following injection. The triceps surae muscle was dissected free, and the Achilles tendon was cut and attached to a muscle puller. The resistance of the muscle to stretches of different amplitudes and velocities was systematically investigated. Reflex-mediated torque was normalized to the maximal muscle force evoked by supramaximal stimulation of the tibial nerve. Botulinum toxin injection caused severe atrophy of the triceps surae muscle at all time points. The force generated by stretch reflex activity was also strongly diminished but not to the same extent as the maximal muscle force at 2 and 4 wk, signifying a relative reflex hyperexcitability. Passive muscle stiffness was unaltered at 1 wk but increased at 2, 4, and 8 wk (P < 0.01). These data demonstrate that botulinum toxin causes a relative increase in reflex stiffness, which is likely caused by compensatory neuroplastic changes. The stiffness of elastic elements in the muscles also increased. The data are not consistent with the ideas that botulinum toxin is an efficient antispastic medication or that it may prevent development of contractures.

Pre-Clinical Study of a Novel Recombinant Botulinum Neurotoxin Derivative Engineered for Improved Safety.

Cyto-012 is a recombinant derivative of Botulinum neurotoxin Type A (BoNT/A). It primarily differs from wild type (wt) BoNT/A1 in that it incorporates two amino acid substitutions in the catalytic domain of the light chain (LC) metalloprotease (E224 > A and Y366 > A), designed to provide a safer clinical profile. Cyto-012 is specifically internalized into rat cortical and hippocampal neurons, and cleaves Synaptosomal-Associated Protein 25 (SNAP-25), the substrate of wt BoNT/A, but exhibits slower cleavage kinetics and therefore requires a higher absolute dose to exhibit pharmacologic activity. The pharmacodynamics of Cyto-012 and wt BoNT/A have similar onset and duration of action using the Digital Abduction Assay (DAS). Intramuscular LD50 values for Cyto-012 and wt BoNT/A respectively, were 0.63 ug (95% CI = 0.61, 0.66) and 6.22 pg (95% CI = 5.42, 7.02). ED50 values for Cyto-012 and wt BoNT/A were respectively, 0.030 ug (95% CI = 0.026, 0.034) and 0.592 pg (95% CI = 0.488, 0.696). The safety margin (intramuscular LD50/ED50 ratio) for Cyto-012 was found to be improved 2-fold relative to wt BoNT/A (p < 0.001). The DAS response to Cyto-012 was diminished when a second injection was administered 32 days after the first. These data suggest that the safety margin of BoNT/A can be improved by modulating their activity towards SNAP-25.

Evaluation of skeletal muscle relaxant activity of aqueous extract of Nerium oleander flowers in Albino rats.

OBJECTIVES: Nerium oleander is traditionally used in various diseases because of its medicinal properties. One of its uses is in musculoskeletal disorder. The aim of the study was to evaluate the skeletal muscle relaxant activity of the aqueous extract of Nerium oleander flowers (AENOF) in albino rats in comparison with diazepam. MATERIALS AND METHODS: A total of 20 Swiss albino rats aged 6-7 weeks, of either sex, weighing about 100-150 g, were taken, and after acute toxicity studies two different doses were selected. The animals were divided into four different groups. The first group was kept as the control (normal saline), second as the standard (diazepam) and the remaining two groups as Test I and Test II, and given different doses of the AENOF. Skeletal muscle relaxant activity (motor coordination) on Rotarod and locomotor activity on photoactometer was performed. Statistical analysis was carried out by using analysis of variance, followed by Dunnett's multiple comparison tests. RESULTS: The result from the Actophotometer test and Rotarod test showed that the extract of AENOF significantly reduced (P < 0.05) the motor coordination of the tested animals. CONCLUSIONS: Our data indicates that AENOF possesses skeletal muscle relaxant activities.

Vertical Trabeculae are Thinned More Than Horizontal Trabeculae in Skeletal-Unloaded Rats.

Skeletal unloading results in a rapid thinning of the trabecular bone network, but it is unknown whether vertical and horizontal trabeculae are equally affected. Therefore, the purpose of the present study was to investigate whether horizontal and vertical trabeculae were thinned similarly during skeletal unloading in rats. Fifty-seven 16-week-old female Wistar rats were randomized into six groups: baseline; control 4 weeks; botulinum toxin A (BTX) 4 weeks; control 8 weeks; BTX 8 weeks; and two BTX injections 8 weeks (BTX + BTX8). The BTX animals were injected in the right hind limb with 4 IU BTX at the start of the study, while the BTX + BTX8 were also injected with 2 IU BTX after 4 weeks. The animals were killed after 0, 4, or 8 weeks. The distal femoral metaphyses were µCT scanned, and the strengths of the femoral necks, mid-diaphyses, and distal femoral metaphyses were ascertained. Disuse resulted in a significant loss of BV/TV, thinning of the trabeculae, and decrease in the degree of anisotropy, and in a significant reduced bone strength after both 4 and 8 weeks. The ratio of horizontal to vertical trabecular thickness (Tb.Th.horz/Tb.Th.vert) and the ratio of horizontal to vertical bone volume (BV.horz/BV.vert) were significantly higher in BTX animals than in control animals. In addition, the horizontal and vertical trabecular thickness probability density functions were more similar in BTX animals than in control animals. In conclusion, skeletal unloading decreased BV/TV, Tb.Th, the degree of anisotropy, and mechanical strength, while BV.horz/BV.vert and Tb.Th.horz/Tb.Th.vert were increased. This indicates that the more loaded vertical trabeculae are pronouncedly more thinned than the less loaded supporting horizontal trabeculae during unloading.

Comparison between quantitative X-ray imaging, dual energy X-ray absorptiometry and microCT in the assessment of bone mineral density in disuse-induced bone loss.

OBJECTIVES: We recently introduced a new methodology called quantitative X-ray imaging (qXRI) to investigate bone mineral density in isolated rodent bones. The aims of the present study were to compare DXA and microCT with qXRI in a rat model of disuse osteoporosis. METHODS: Fourteen Copenhagen rats were injected with a single dose of botulinum toxin (BTX - 2 UI) in the right Mus quadriceps femoris. The left hindlimb serves as control. Areal BMD and vBMD were determined with a Hologic Discovery-W device and a Skyscan 1172 microcomputed tomograph (microCT). Absorbing material density (AMD) was determined on digitized X-ray images obtained with a Faxitron M020 device. RESULTS: All three methods highlighted significant lower values for aBMD, vBMD and AMD in trabecular and cortical bone in the BTX-injected side. In trabecular bone, aBMD, vBMD and AMD were significantly correlated with BV/TV. In cortical bone, only aBMD and vBMD were significantly correlated with cortical bone mass On the other hand, only AMD was significantly correlated with the mechanical parameters bending strength and bending modulus. CONCLUSIONS: qXRI is a rapid and cheap method to assess trabecular bone mass in isolated rodent bones and can be used as a surrogate for the densitometry of small animals.

Neuromuscular effects of venoms and crotoxin-like proteins from Crotalus durissus ruruima and Crotalus durissus cumanensis.

A myographic study was performed to compare the neuromuscular effects of venoms and crotoxin-like proteins from Crotalus durissus ruruima and Crotalus durissus cumanensis in mice phrenic-diaphragm preparation. It was concluded that both venoms present neurotoxic activity as a consequence of their crotoxin content. Furthermore, crotoxin from C.d. cumanensis is more potent than that from C.d. ruruima venom. At the concentration range in which both venoms express neurotoxic activity, only C.d. cumanensis venom also manifest a direct myotoxic effect that probably involves the synergic participation of other components than crotoxin.

Interaction between gastrocnemius muscle weakness and moderate exercise deteriorates joint integrity in rat knee.

The aim of this study was to determine the effect on the knee joint of the interaction between ankle muscle weakness and moderate exercise. Gastrocnemius muscle weakness was induced by intramuscular injection of botulinum toxin type A (BTX) in rats. Low-speed treadmill running (12 m/min for 60 min) was applied for 6 weeks in rats with and without BTX. Untreated animals were used as controls. After BTX injection, the gastrocnemius muscle weakness was confirmed by 3-D motion analysis in kinematic features of the hindlimb during locomotion as an increased maximal dorsiflexion angle during the stance phase. Serum biomarker analysis by enzyme-linked immunosorbent assay revealed that low-speed running decreased the catabolic effect on type II collagen. However, the inhibition of catabolism induced by running exercise was significantly counteracted by BTX injection. In addition, thinning of the cartilage layer and a reduction in the chondrocyte density was also found in the tibial plateau of the knee in the BTX-injected rats after running for 6 weeks. These data suggest that moderate exercise have a positive effect on joint homeostasis. However, ankle muscle weakness may alter the mechanical environment of the knee and impair the integrity of joint cartilage with moderate exercise.

Growth hormone mitigates loss of periosteal bone formation and muscle mass in disuse osteopenic rats.

Growth hormone (GH) is a potent anabolic agent capable of increasing both bone and muscle mass. The aim was to investigate whether GH could counteract disuse-induced loss of bone and muscle mass in a rat model. Paralysis was induced by injecting 4 IU Botox (BTX) into the muscles of the right hind limb. Sixty female Wistar rats, 14 weeks old, were divided into the following groups: baseline, controls, BTX, BTX+GH, and GH. GH was given at a dosage of 5 mg/kg/d for 4 weeks. Compared with controls, BTX resulted in lower periosteal bone formation rate (BFR/BS,-79%, P<0.001), bone mineral density (aBMD, -13%, P<0.001), trabecular bone volume (BV/TV, -26%, P<0.05), and mid-femoral bone strength (-12%, P<0.05). In addition, BTX reduced rectus femoris muscle mass (-69%, P<0.001) and muscle cell cross sectional area (CSA) (-73%, P<0.001) compared with controls. GH counteracted disuse-induced losses of periosteal BFR/BS (2-fold increase vs. BTX, P<0.001), whereas no effect on aBMD, trabecular BV/TV, or bone strength was found. In addition, GH partly prevented loss of muscle mass (+29% vs. BTX, P<0.001), and tended to prevent loss of muscle CSA (+11%, P=0.064). In conclusion, GH mitigates disuse-induced loss of periosteal BFR/BS at the mid-femur and rectus femoris muscle mass.

Acute and chronic effects of botulinum neurotoxin a on the mammalian neuromuscular junction.

INTRODUCTION: Botulinum neurotoxin A (BoNT/A) cleaves SNAP-25 and inhibits acetylcholine (ACh) release at the neuromuscular junctions (NMJ) to cause neuroparalysis. Previous reports indicate a dyssynchrony between the inhibitory effect of BoNT/A on ACh release and SNAP-25 cleavage. METHODS: We tested the in vitro (acute; 90 min) and in vivo (chronic; 12 h) effects of BoNT/A on stimulus-evoked ACh release (SEAR), twitch tension, and SNAP-25 cleavage in isolated extensor digitorum longus (EDL) nerve-muscle preparations (NMP). RESULTS: In vitro or in vivo BoNT/A poisoning inhibited SEAR and twitch tension. Conversely, SNAP-25 cleavage and inhibition of spontaneous release frequency were observed only in NMP poisoned with BoNT/A in vivo. Moreover, chronic treatment of BoNT/A inhibited ionomycin stimulated Ca(2+) signals in Neuro 2a cells. CONCLUSIONS: These results demonstrate that the inhibition of SEAR precedes SNAP-25 cleavage and suggest involvement of a more complex mechanism for the inhibitory effect of BoNT/A at the NMJ.

Analysis of the action of gymnodimine-A and 13-desmethyl spirolide C on the mouse neuromuscular system in vivo.

Gymnodimine-A and 13-desmethyl spirolide C are marine toxins belonging to the cyclic imine group produced by Karenia selliformis and Alexandrium ostenfeldii/peruvianum dinoflagellates, respectively. The aim of this work was to analyze the pharmacological properties of both toxins (at sub-lethal doses) on neuromuscular excitability, when injected locally to isoflurane-anesthetized mice, using a multimodal minimally-invasive in vivo electrophysiological approach. The main effect of both toxins was a marked reversible time- and dose-dependent decrease of the compound muscle action potential recorded from the tail muscle in response to caudal motor nerve stimulation. The dose-response curves of gymnodimine-A and 13-desmethyl spirolide C effect on the maximal amplitude of compound muscle action potential revealed 50% inhibitory doses of 51 ng/mouse (i.e. 1.6 µg/kg or 3.3 nmol/kg mouse) and 0.18 ng/mouse (i.e. 6 ng/kg or 0.01 nmol/kg mouse), respectively. The blocking effect occurred without significant modification of motor nerve excitability parameters. It is concluded that the inhibition of the mouse compound muscle action potential, induced by gymnodimine-A and 13-desmethyl spirolide C, results from an action of these toxins at the level of the skeletal neuromuscular junction, since both cyclic imine toxins are known to interact and block muscle-type nicotinic acetylcholine receptors. In the present in vivo study, 13-desmethyl spirolide C was about 300 fold more active than gymnodimine-A on equimolar basis. The present in vivo approach, associated to recent progress in chemical synthesis of cyclic imine toxins, paves the way for more detailed structure-activity studies to obtain new and more potent synthetic analogs.