Early effect of tacrolimus in improving excitation-contraction coupling in myasthenia gravis

Comparison between mono-tacrolimus and mono-glucocorticoid in the treatment of myasthenia gravis

OBJECTIVE

Use of tacrolimus in mild to moderate myasthenia gravis (MG) is generally limited to glucocorticoid-refractory cases; the advantage of mono-tacrolimus over mono-glucocorticoids is unknown.

METHODS

We included mild to moderate MG patients treated with mono-tacrolimus (mono-TAC) or mono-glucocorticoids (mono-GC). The correlation between the immunotherapy options and the treatment efficacy and side effects were examined in 1:1 propensity-score matching. The main outcome was time to minimal manifestations status or better (MMS or better). Secondary outcomes include time to relapse, the mean changes in Myasthenia Gravis-specific Activities of Daily Living (MG-ADL) scores and the rate of adverse events.

RESULTS

Baseline characteristics showed no difference between matched groups (49 matched pairs). There were no differences in median time to MMS or better between the mono-TAC group and mono-GC group (5.1 vs. 2.8 months: unadjusted hazard ratio [HR], 0.73; 95% CI, 0.46-1.16; p = 0.180), as well as in median time to relapse (data unavailable for the mono-TAC group since 44 of 49 [89.8%] participants remained in MMS or better; 39.7 months in mono-GC group: unadjusted HR, 0.67; 95% CI, 0.23-1.97; p = 0.464). Changes in MG-ADL scores between the two groups were similar (mean differences, 0.3; 95% CI, -0.4 to 1.0; p = 0.462). The rate of adverse events was lower in the mono-TAC group compared to the mono-GC group (24.5% vs. 55.1%, p = 0.002).

INTERPRETATION

Mono-tacrolimus performs superior tolerability with non-inferior efficacy compared to mono-glucocorticoids in mild to moderate myasthenia gravis patients who refuse or have a contraindication to glucocorticoids.

Cholinergic System and Its Therapeutic Importance in Inflammation and Autoimmunity

Neurological and immunological signals constitute an extensive regulatory network in our body that maintains physiology and homeostasis. The cholinergic system plays a significant role in neuroimmune communication, transmitting information regarding the peripheral immune status to the central nervous system (CNS) and vice versa. The cholinergic system includes the neurotransmitter\ molecule, acetylcholine (ACh), cholinergic receptors (AChRs), choline acetyltransferase (ChAT) enzyme, and acetylcholinesterase (AChE) enzyme. These molecules are involved in regulating immune response and playing a crucial role in maintaining homeostasis. Most innate and adaptive immune cells respond to neuronal inputs by releasing or expressing these molecules on their surfaces. Dysregulation of this neuroimmune communication may lead to several inflammatory and autoimmune diseases. Several agonists, antagonists, and inhibitors have been developed to target the cholinergic system to control inflammation in different tissues. This review discusses how various molecules of the neuronal and non-neuronal cholinergic system (NNCS) interact with the immune cells. What are the agonists and antagonists that alter the cholinergic system, and how are these molecules modulate inflammation and immunity. Understanding the various functions of pharmacological molecules could help in designing better strategies to control inflammation and autoimmunity.

Clinical Evaluation of the Efficacy and Safety of Co-Administration of Wuzhi Capsule and Tacrolimus in Adult Chinese Patients with Myasthenia Gravis

BACKGROUND

Tacrolimus has been recommended as an effective immunosuppressant for patients with myasthenia gravis (MG), while the high price, variable bioavailability, and narrow therapeutic window restrict its clinical application. Wuzhi capsule (WZC) could improve tacrolimus blood concentration by inhibiting the metabolism of cytochrome P450 3A (CYP3A) and P-glycoprotein (P-gp). There are few studies focused on the coadministration of WZC and tacrolimus in autoimmune diseases. This study was aimed at quantifying the efficacy and safety of coadministration of WZC and tacrolimus in adult Chinese patients with MG.

METHODS

In this retrospective study, 122 patients with MG on tacrolimus were enrolled. The initial tacrolimus dose was 2 mg/d. Patients with standard initial tacrolimus concentration were classified into group A (standard-dose group). Those failed to reach target concentration were divided into group B (high-dose group) and group C (co-administering WZC group), according to treatment adjustment of increasing tacrolimus dose and co-administration of WZC, respectively. A logistic analysis was used to identify factors associated with clinical outcome. Adverse drug reactions (ADRs) were recorded for safety analysis.

RESULTS

The tacrolimus concentration after coadministration of WZC was remarkably increased. It was higher compared with simply increasing the tacrolimus dose (p<0.001). The multivariate logistic analysis indicated that the baseline quantitative MG score was a predictive factor for clinical outcomes (OR=0.189; 95% CI 0.082-0.436; p<0.001). Fourteen patients (11.5%) reported ADRs after tacrolimus therapy. ADRs incidence was not related to WZC coadministration.

CONCLUSION

The coadministration of WZC and tacrolimus can substantially elevate the tacrolimus concentration. It is a safe and economic treatment for adult Chinese patients with MG. Patients with a worse disease condition tend to present a better clinical outcome after tacrolimus therapy.

Measurement of excitation-contraction coupling time in lower extremities

OBJECTIVE

The aim of this study was to apply a novel method to measure excitation-contraction coupling time (ECCT) in normal soleus muscles.

METHODS

We performed simultaneous recordings of soleus compound muscle action potential (CMAP) and foot movement-related potential (MRP), and measured ankle plantar flexion torque in 36 healthy subjects. We calculated ECCT and examined the relations between CMAP, MRP, ECCT and ankle plantar flexion torque.

RESULTS

Statistical analyses established reference ranges (mean ± SE) for CMAP (13.4 ± 0.9 mV), MRP (5.3 ± 0.4 m/s²), ECCT (5.2 ± 0.1 ms), torque (85.9 ± 6.4 Nm) and torque/body weight (1.4 ± 0.1 Nm/kg). The torque showed a positive linear correlation with CMAP (p = 0.041) and a negative linear correlation with ECCT (p = 0.045).

CONCLUSION

Soleus ECCT can be recorded easily, and is useful to assess the impairment of E-C coupling in muscles of the lower extremities.

Impaired post-tetanic potentiation of muscle twitch in myasthenia gravis

OBJECTIVE

The aim of this study was to evaluate post-tetanic potentiation of muscle twitch in myasthenia gravis (MG).

METHODS

Post-tetanic potentiation was evaluated by recording the compound muscle action potential (CMAP) of abductor pollicis brevis and movement-related potential (MRP) of the thumb using an accelerometer after tetanic stimulation of the median nerve at the wrist. After baseline recording, tetanic stimulation was delivered to the median nerve at a frequency of 10 Hz for 10s. The CMAP and MRP were successively recorded at baseline and at 5, 10, 30, 60, 90 and 120 s after tetanic stimulation. The chronological changes of CMAPs and MRPs were recorded bilaterally in 11 patients with MG, 9 patients with myopathies (disease controls), and 25 healthy control subjects.

RESULTS

Maximal acceleration of MRP was significantly elevated during 10s after tetanic stimulation without any CMAP changes in all groups. However, statistical analysis detected a significant decrease in post-tetanic potentiation of maximal acceleration of MRP in MG patients only compared to healthy controls, but not in myopathy patients, which may imply impairment of excitation-contraction coupling in MG.

CONCLUSIONS

Post-tetanic potentiation of muscle twitch is significantly diminished in MG, suggesting impaired excitation-contraction coupling.

SIGNIFICANCE

Measurement of post-tetanic potentiation using an accelerometer is a simple and sensitive method to detect impairment of excitation-contraction coupling in MG.

The emerging role of tacrolimus in myasthenia gravis

OBJECTIVE

To describe and evaluate the available evidence assessing the role of tacrolimus in the management of patients with myasthenia gravis (MG).

DATA SOURCES

A literature search of MEDLINE (1946 to September 2014) and EMBASE (1947 to September 2014) was performed using the terms 'tacrolimus' and 'myasthenia gravis'. Citations of retrieved articles were examined for relevance.

STUDY SELECTION AND DATA EXTRACTION

The search was limited to prospective clinical trials focused on clinical outcomes in patients with generalized MG. Case reports, retrospective evaluations and non-English articles were excluded.

DATA SYNTHESIS

A total of 12 studies met inclusion criteria, of which seven articles evaluated tacrolimus in steroid-dependent patients and two examined the utility of tacrolimus in patients failing corticosteroids and cyclosporine. Other studies evaluated early initiation of tacrolimus after thymectomy, effectiveness of tacrolimus in de novo MG and the effectiveness of tacrolimus post-thymectomy in thymoma patients versus nonthymoma. A total of eight trials showed statistically significant improvements in quantitative MG score (QMGS) and postintervention status criteria - Myasthenia Gravis Foundation of America (PSC-MGFA). Of the trials examining steroid reduction with tacrolimus, two reported high rates of complete withdrawal; however, the most robust trial was unable to detect a difference in mean steroid dose. Long-term effects of tacrolimus (up to 5 years) were assessed in eight trials, which consistently showed positive effects on QMGS or reduction in adjunct therapies.

CONCLUSIONS

There is limited yet promising information to suggest a beneficial role for tacrolimus in reducing QMGS and corticosteroid burden in patients with refractory symptoms or new-onset MG. Long-term use appears to be safe in this population.

Myasthenia gravis: an update for the clinician

This paper provides a thorough overview of the current advances in diagnosis and therapy of myasthenia gravis (MG). Nowadays the term 'myasthenia gravis' includes heterogeneous autoimmune diseases, with a postsynaptic defect of neuromuscular transmission as the common feature. Myasthenia gravis should be classified according to the antibody specificity [acetylcholine, muscle-specific receptor tyrosine kinase (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), seronegative], thymus histology (thymitis, thymoma, atrophy), age at onset (in children; aged less than or more than 50 years) and type of course (ocular or generalized). With optimal treatment, the prognosis is good in terms of daily functions, quality of life and survival. Symptomatic treatment with acetylcholine esterase inhibition is usually combined with immunosuppression. Azathioprine still remains the first choice for long-term immunosuppressive therapy. Alternative immunosuppressive options to azathioprine include cyclosporin, cyclophosphamide, methotrexate, mycophenolate mofetil and tacrolimus. Rituximab is a promising new drug for severe generalized MG. Emerging therapy options include belimumab, eculizumab and the granulocyte- macrophage colony-stimulating factor. One pilot study on etanercept has given disappointing results. For decades, thymectomy has been performed in younger adults to improve non-paraneoplastic MG. However, controlled prospective studies on the suspected benefit of this surgical procedure are still lacking. In acute exacerbations, including myasthenic crisis, intravenous immunoglobulin, plasmapheresis and immunoadsorption are similarly effective.

Unique drug screening approach for prion diseases identifies tacrolimus and astemizole as antiprion agents

Prion diseases such as Creutzfeldt-Jakob disease (CJD) are incurable and rapidly fatal neurodegenerative diseases. Because prion protein (PrP) is necessary for prion replication but dispensable for the host, we developed the PrP-FRET-enabled high throughput assay (PrP-FEHTA) to screen for compounds that decrease PrP expression. We screened a collection of drugs approved for human use and identified astemizole and tacrolimus, which reduced cell-surface PrP and inhibited prion replication in neuroblastoma cells. Tacrolimus reduced total cellular PrP levels by a nontranscriptional mechanism. Astemizole stimulated autophagy, a hitherto unreported mode of action for this pharmacophore. Astemizole, but not tacrolimus, prolonged the survival time of prion-infected mice. Astemizole is used in humans to treat seasonal allergic rhinitis in a chronic setting. Given the absence of any treatment option for CJD patients and the favorable drug characteristics of astemizole, including its ability to cross the blood-brain barrier, it may be considered as therapy for CJD patients and for prophylactic use in familial prion diseases. Importantly, our results validate PrP-FEHTA as a method to identify antiprion compounds and, more generally, FEHTA as a unique drug discovery platform.