Structure-activity relationship of quaternary acetylcholinesterase inhibitors - outlook for early myasthenia gravis treatment.

Myasthenia gravis is a rare autoimmune neuromuscular junction disorder mainly caused by antibodies being targeted against the muscle acetylcholine receptors (AChRs). The loss of AChRs leads to a defect in neuromuscular transmission resulting in muscle weakness and fatigue. Although once an often fatal illness, Myasthenia gravis can now be well managed with relatively safe and effective treatments. However, the severe myasthenic cases associated with thymus tumors remain often fatal exception in the management of the disease. The early treatment includes the use of acetylcholinesterase inhibitors (AChEI) which enhance neuromuscular transmission. To ensure a peripheral effect, charged molecules are used, particularly quaternary ammonium salts. The structure of AChEIs has been continuously modified to obtain the optimal ratio between AChE inhibition and potential side-effects. This review summarizes progress in the use of quaternary compounds as AChE inhibitors in vitro with respect to their structure and inhibitory ability. Namely, carbamic acid esters, piperidinium and pyridinium salts, bisquaternary pyridinium salts and heterogeneous quaternary inhibitors are all discussed. Among data found in the literature, many compounds have shown promising inhibition of AChE when compared to commercial standards (pyridostigmine, neostigmine). Besides a promising inhibitory ability, selectivity for AChE versus butyrylcholinesterase (BChE) for the most potent compounds (sub-nanomolar IC(50)) was also identified.

Myasthenia gravis: An embryologic and phylogenetic perspective.

Myasthenia gravis is a rare disease with unique clinical features. These include (1) progressive fatigue on exertion, most evident clinically in the muscles of the head and neck (2) a definite relationship of the disease to the thyroid, parathyroid and thymus glands. A hypothesis is advanced with correlates these facts on the basis of a common embryologic origin of these glands and the branchial arch muscles. A corollary is that the muscles of the head and neck differ from the somatic musculature in some as-yet-unidentified manner, for example, pharmacologically. A plea is made for comparative studies between the two.