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Abstract
Onabotulinum toxin A (onabotox, known as Botox) was approved by the Therapeutic Goods Administration (TGA) initially for the treatment of neurogenic detrusor overactivity (DO), and recently for refractory DO. Onabotox has long been known to block the neuromuscular transmission of acetylcholine (ACh) via cleavage of synaptosomal-associated protein-25 (SNAP-25) at efferent nerves. However, less is known about the effect of onabotox on the release of other transmitters involved in afferent signalling, and on the non-neuronal cells in bladder. The aim of this thesis was to investigate the influence of onabotox on the release of ACh, ATP and substance P (SP) from tissue strips and cultured cells of the porcine bladder. The expression and distribution of SNAP-25 was also examined.
In organ bath experiments, onabotox inhibited electrical field stimulation (EFS)-induced release of ACh, ATP and SP from suburothelial and detrusor strips. Immunofluorescence staining demonstrated that the density of SNAP-25 expression, which was observed on nerve bundles, also on urothelium and myofibroblast-like cells in suburothelium, was reduced significantly by onabotox. We further observed a significant reduction of stretch-induced release of ACh and ATP in onabotox-treated cultured urothelial, suburothelial and detrusor cells, which was correlated with the significantly diminished SNAP-25 expression in onabotox-treated cultured cells. These results provided strong evidence for the direct effects of onabotox on non-neuronal cells in addition to neuronal cells.
Results suggest that firstly, other than the cholinergic system, onabotox influences purinergic and tachykinin pathways in the bladder. Thus, onabotox could affect bladder sensory nerves including pain sensation (i.e. reduction in SP release). Secondly, onabotox targets non-neuronal cells as well as nerves in the bladder. Thirdly, the suburothelial region of the bladder may be a key site for the action of onabotox, apart from detrusor muscle. These findings provide evidence for the action of onabotox on both afferent and efferent signalling pathways in the urinary bladder. Accordingly, this study emphasises that myofibroblasts could be a target for drug design in the treatment of bladder disorders, and that onabotox is not only a suitable drug for DO but also could be used to treat other bladder disorders (e.g. painful bladder syndrome).