Congenital myasthenic syndromes (CMS) are a rare group of heterogeneous disorders, characterised by compromised neuromuscular transmission and symptoms of fatiguable muscle weakness. CMS is caused by mutations in genes that affect the structure and function of the neuromuscular junction (NMJ). In about 20% of CMS cases, patients have mutations in the gene DOK7; the protein product, DOK7, is crucial for maintaining the dense aggregation of acetylcholine receptor (AChR) clusters at the NMJ. DOK7-CMS patients do not respond to treatment with acetylcholinesterase inhibitors which are the first line treatment for most forms of CMS. Instead, a dramatic response to beta-2 adrenergic receptor (ADRB2) agonists, such as salbutamol, is observed. The aim of this project was to investigate the molecular mechanisms that underlie the beneficial effects of ADRB2 agonists. Firstly, NMJ functioning was modelled in vitro by studying AChR clusters formed on cultured C2C12 mouse myotubes in the presence of WT DOK7. Overexpression of mutant DOK7 led to a significant reduction in the number of AChR clusters, explaining the pathogenic effect of the mutation. Importantly, incubation of myotubes with salbutamol increased the number of AChR clusters and their stability. The results provide the first evidence that ADRB2 agonists directly affect proteins located at the NMJ. However, this disease model suffers from limitations. The rest of the thesis focussed on developing alternative cell culture models to explore the AChR clustering pathway. The first model combined optogenetics and fluorescence lifetime microscopy to study the effects of ADRB2 activation on AChR cluster stability in single live cells. The second used CRISPR/Cas9 genome editing tools to directly introduce Dok7 mutations to the genome of C2C12 cells, thereby overcoming some of the drawbacks associated with DOK7 overexpression. Further manipulations of these novel model systems will be used in the future to examine in more detail the molecular events underlying the pathogenic effects of DOK7 mutations and the mechanisms of ADRB2 agonists.

No / A sensitive and rapid high performance liquid chromatography method has been developed and used for the simultaneous determination of formoterol and budesonide in Symbicort Turbuhaler when assessing the aerodynamic characteristics of the emitted dose using Pharmacopoeial methods. This capability results in both time and cost saving. The mobile phase composition was acetonitrile-5 mM sodium dihydrogen orthophosphate, pH 3 (60: 40% v/v), and was passed at 1.5 ml min-1 through a C18 column with a UV detection (wavelength 214 nm). The method was shown to give good analytical performance in terms of linearity, precision (using phenylpropanolamine as an internal standard), sensitivity and solution stability. The intra-day precision for both formoterol and budesonide were 0.75% and 1.11%, respectively (n = 10). The limit of quantitation for formoterol was 10 ¿g L-1 and for budesonide was 120 ¿g L-1, and the limit of detection were 3 and 30 ¿g L-1, for both formoterol and budesonide, respectively. The method has been applied to determine the content of the emitted dose and the fine particle dose of Symbicort Turbuhaler.

No / A novel high-performance liquid chromatography (HPLC) assay for the estimation of formoterol in urine samples was developed and validated. A solid phase extraction (SPE) using Oasis HLB was optimised to isolate formoterol from a urine matrix followed by HPLC with UV detection. This extraction procedure concentrated the final analyte forty times so that UV detection can be used to determine even a low concentration of formoterol in urine samples. The urinary assay was performed in accordance with FDA and ICH regulations for the validation of bioanalytical samples. The samples were injected onto a C18 Spherisorb® (250 mm x 4.6 mm x 5 ¿m) analytical column maintained at 30 °C. The mobile phase consisted of 5 mM of potassium dihydrogen orthophosphate buffer (adjusted to pH 3 with ortho phosphoric acid):acetonitrile (ACN) (70:30, v/v), and the formoterol peak was detected at wavelength 214 nm. The extraction recovery of formoterol from the urine sample was >95%. The calibration curve was linear (r2=0.99) over formoterol concentrations ranging from 1.5 to 25 ng/mL (n=6). The method had an accuracy of >92% and intra and inter-day precision CV% of <3.9% and <2.2%, respectively, at three different concentrations low, medium and high (10, 15, 20 ng/mL). The limit of quantification (LOQ) for formoterol was found to be 1.50 ng/mL. The accuracy and precision at the LOQ level were 95% and %CV <3.7% (n = 10), respectively. The method reported is simple, reliable, precise, and accurate and has the capacity to be used for determination of formoterol in urine samples.