Neurogenic inflammation has been suggested as an etiopathogenic factor of psoriasis. Previous reports revealed an increased concentration of nerve fibers as well as a high level of neuropeptides of cutaneous sensory nerve origin, primarily Substance P and calcitonin gene-related peptide (CGRP).
Some investigators reported improvement of psoriatic plaques after injuries that compromised peripheral nerves. Hence, it was postulated that cutaneous sensory afferent neurons are involved in the etiopathogenesis of psoriasis and may serve as a potential therapeutic target.
Substance P (SP) is a neuropeptide of sensory nerve origin that can influence the immune cell functions and the inflammatory responses in psoriasis. By binding to NK1R on T cells, SP can stimulate Th17 cell differentiation and production of interleukin-17A cytokine (IL-17A). IL-17A is a key effector cytokine in psoriasis, by releasing several pro-inflammatory cytokines, such as TNF alpha, stimulating abnormal keratinocytes' proliferation and promoting angiogenesis.
Topical drug therapy is the cornerstone of the treatment of mild to moderate psoriasis. It offers a direct skin targeting and avoids systemic adverse events. Several topical therapies are currently available for the treatment of psoriasis such as topical steroids, topical vitamin D3 analogues e.g. Calcipotriol, tar, anthraline, topical calcineurin inhibitors and tazarotene.
Tacrolimus, formerly known as FK506, is a macrolide antibiotic possessing immunosuppressive properties. Tacrolimus disrupts the intracellular activation of T-lymphocytes and inhibits the ability of calcineurin to regulate gene transcription. Thus, tacrolimus intervenes at an early stage of T-cell activation, leads to several secondary consequences providing effective and therapeutically efficient results to overcome problems associated with psoriatic skin disease.
Botulinum Toxin-A (BoNT-A) is an injectable neuromodulator produced by Clostridium Botulinum, a Gram-positive bacillus that causes Botulism. The clinical utility of BoNT-A originates from the ability to block muscular contractions by inhibiting neurotransmission between peripheral nerve cells and muscle fibers. Currently, BoNT-A is widely used for multiple aesthetic concerns that can be alleviated by local muscle relaxation, such as upper facial dynamic rhytides .
Botulinum Toxin-A can inhibit the release of neurotransmitters e.g. SP from the sensory motor neurons. SP is an important neuropeptide in the pathophysiological process of cutaneous neurogenic inflammation. Thus, it was hypothesized that BoNT-A can potentially be used for treating several inflammatory skin diseases, including psoriasis.
