Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

/pdf/purinergic-signalling-in-the-urinary-tract-in-health-and-1h1ierkd5s.pdf

Purinergic signalling in the urinary tract in health and disease.

Treating pain by inhibiting ATP activation of P2X3-containing receptors heralds an exciting new approach to pain management, and Afferent's program marks the vanguard in a new class of drugs poised to explore this approach to meet the significant unmet needs in pain management. P2X3 receptor subunits are expressed predominately and selectively in so-called C- and Aδ-fiber primary afferent neurons in most tissues and organ systems, including skin, joints, and hollow organs, suggesting a high degree of specificity to the pain sensing system in the human body. P2X3 antagonists block the activation of these fibers by ATP and stand to offer an alternative approach to the management of pain and discomfort. In addition, P2X3 is expressed pre-synaptically at central terminals of C-fiber afferent neurons, where ATP further sensitizes transmission of painful signals. As a result of the selectivity of the expression of P2X3, there is a lower likelihood of adverse effects in the brain, gastrointestinal, or cardiovascular tissues, effects which remain limiting factors for many existing pain therapeutics. In the periphery, ATP (the factor that triggers P2X3 receptor activation) can be released from various cells as a result of tissue inflammation, injury or stress, as well as visceral organ distension, and stimulate these local nociceptors. The P2X3 receptor rationale has aroused a formidable level of investigation producing many reports that clarify the potential role of ATP as a pain mediator, in chronic sensitized states in particular, and has piqued the interest of pharmaceutical companies. P2X receptor-mediated afferent activation has been implicated in inflammatory, visceral, and neuropathic pain states, as well as in airways hyperreactivity, migraine, itch, and cancer pain. It is well appreciated that oftentimes new mechanisms translate poorly from models into clinical efficacy and effectiveness; however, the breadth of activity seen from P2X3 inhibition in models offers a realistic chance that this novel mechanism to inhibit afferent nerve sensitization may find its place in the sun and bring some merciful relief to the torment of persistent discomfort and pain. The development philosophy at Afferent is to conduct proof of concept patient studies and best identify target patient groups that may benefit from this new intervention.

/pdf/in-pursuit-of-p2x3-antagonists-novel-therapeutics-for-3usnsft5gy.pdf

In pursuit of P2X3 antagonists: novel therapeutics for chronic pain and afferent sensitization

Physiology and Pharmacology of the Bladder and Urethra

Background

Botulinum toxin type A (BoNT/A), one of the seven subtypes of Botulinum toxin, is commercially available naked or complexed to other proteins. Onabotulinum toxin type A is the most extensively studied BoNT/A brand. Dose equivalence studies between the different brands have never been carried out. BoNT/A is internalized by nerve fibers after binding synaptic vesicle proteins, and the final target of action is synaptosome-associated protein 25 kDa (SNAP-25), a membrane protein essential for synaptic vesicle fusion with the neuronal membrane.



Methods

The current literature about botulinum toxin mechanisms was reviewed to provide an up to date knowledge about the topic.



Results

Immunoreactivity to cleaved SNAP-25, the end product of BoNT/A activity, has been identified in parasympathetic (pre- and postganglionic), sympathetic, and afferent fibers. A consistent decrease in the release of acetylcholine from parasympathetic, norepinephrine from sympathetic, and glutamate and neuropeptides from sensory neurons follows BoNT/A administration. Immunoreactivity to cleaved SNAP-25 was not identified in the urothelium or in myofibroblasts. Nevertheless, a decreased release of ATP and neurotrophins from the urothelial cells has been consistently observed after BoNT/A. The toxin does not cause apoptosis in the bladder. However, injection in rat and dog prostates was shown to induce apoptosis in acinar and stromal cells.



Conclusion

There is now robust information to support that the mechanism of action of BoNT/A in the bladder involves neurotransmitter release from nerve fibers and urothelial cells. Which neurotransmitter is more relevant is, however, unclear. Likewise, the long duration of effect, the importance of the volume of vehicle injected and the selection of specific injection sites, like the trigone, needs further evaluation. Neurourol. Urodynam. 33:31–38, 2014. © 2013 Wiley Periodicals, Inc.

Targets for botulinum toxin in the lower urinary tract.

Aims
Botulinum neurotoxin serotype A (BoNT/A) has emerged as an effective treatment of urinary bladder overactivity. Intravesical lipotoxin (BoNT/A delivery using liposomes), which may target the urothelium, is effective in blocking acetic acid induced hyperactivity in animals. The objective of this study was to assess the possible site of toxin action within the urothelium.

Effect of botulinum toxin A on urothelial-release of ATP and expression of SNARE targets within the urothelium.

Botulinum toxin type A normalizes alterations in urothelial ATP and NO release induced by chronic spinal cord injury.

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Botulinum toxin type A normalizes alterations in urothelial ATP and NO release induced by chronic spinal cord injury.