Capsaicin and substance P

Effects of pulsed dye laser treatment in psoriasis: A nerve-wrecking process?

Pulsed dye laser (PDL) therapy can be effective in treating psoriasis, with a long duration of remission. Although PDL therapy, albeit on a modest scale, is being used for decades now, the underlying mechanisms responsible for the long-term remission of psoriasis remain poorly understood. The selective and rapid absorption of energy by the blood causes heating of the vascular wall and surrounding structures, like perivascular nerves. Several studies indicate the importance of nerves in psoriatic inflammation. Interestingly, denervation leads to a spontaneous remission of the psoriatic lesion. Among all dermal nerves, the perivascular nerves are the most likely to be affected during PDL treatment, possibly impairing the neuro-inflammatory processes that promote T-cell activation, expression of adhesion molecules, leukocyte infiltration and cytokine production. Repeated PDL therapy could cause a prolonged loss of innervation through nerve damage, or result in a 'reset' of neurogenic inflammation after temporary denervation. The current hypothesis provides strong arguments that PDL treatment affects nerve fibres in the skin and thereby abrogates the persistent and exaggerated inflammatory process underlying psoriasis, causing a long-term remission of psoriasis.

Effects of Neuropeptides on Dendritic Cells in the Pathogenesis of Psoriasis

Psoriasis is an autoimmune disease that is characterized by discolored, scaled patches of skin. Clinically, it is found that psychological factors often induce or aggravate the disease. Current research suggests that the pathogenesis of psoriasis involves the nervous and immune systems. This article reviews how neuropeptides secreted by nerve fibers affect dendritic cells in psoriasis. In this review, we describe that the neuropeptides calcitonin gene-related peptide, substance P, and vasoactive intestinal peptide can act on dendritic cells and participate in the pathogenesis of psoriasis. These neuropeptides can affect the secretion of interleukin (IL)-12 and IL-23 by dendritic cells, which stimulate T helper (Th)1, Th17, and Th22 cells to produce immune responses and cause the manifestation of psoriasis. The application of neuropeptide inhibitors can improve the skin lesions of psoriasis, which has been confirmed in clinical trials. Therefore, neuroimmune response may be a new direction to develop new drug treatments and perspectives in the development of psoriasis.

TRPV channel expression in human skin and possible role in thermally induced cell death

Cell death via necrosis and apoptosis is a hallmark of deep dermal to full-thickness cutaneous burn injuries. Keratinocytes might act as thermosensory cells that transmit information regarding ambient temperature via heat-gated transient receptor potential vanilloid (TRPV) ion channels. The aim of this study was to investigate the distribution of TRPV1, 2, 3, and 4 in uninjured and thermally burned skin. The authors investigated warmth-evoked currents in keratinocytes and cell kinetics of thermally injured keratinocytes in culture with agonists and antagonists of TRPV channels. Specimens of uninjured normal skin and discarded tissue of thermally injured skin were stained for TRPV1, 2, 3, and 4. Cultured primary human keratinocytes were heated for 5 minutes at the following temperatures: 37°C (control), 42°C, and 60°C and thereafter cultured for 24 or 48 hours at 37°C. Thermally stressed cells were treated with TRPV antagonists capsazepine or ruthenium red, and cell viability capacity was determined. TRPV1, TRPV2, TRPV3, and TRPV4 immunoreactivity was differentially identified on basal and suprabasal keratinocytes of healthy human skin. Patch clamp analysis showed a functional response of human keratinocytes at temperatures >40°C. Cell death of keratinocytes after heating at 42°C was reduced by 15 and 5% with ruthenium red and by 20 and 30% by capsazepine at 24 and 48 hours, respectively. Cell death after treatment at 60°C was significantly reduced at 24 hours with capsazepine (22%) or ruthenium red (18%) but only minimally affected after 48 hours postinjury. Interaction with TRPV channels on keratinocytes may offer a new strategy to counteract cell death after thermal injury.

The reinnervation pattern of wounds and scars may explain their sensory symptoms

Anaesthesia, pruritus and pain are common in cutaneous scars. The reinnervation pattern of healing wounds and scars might help to explain these symptoms, as sensory neurotransmitters are known to be mediators of inflammation and healing. We quantified the regeneration patterns of blood vessels and nerves in excisional skin wounds as they matured into scars. Mice underwent 1cm(2) full thickness skin excisions. Wounds were harvested between five and 84 days. Sections underwent immunohistochemical staining for protein gene product 9.5 (PGP9.5) a pan-neuronal marker, and the sensory neuropeptides calcitonin gene related peptide (CGRP) and substance P (SP). The endothelial marker von Willebrand factor (VWF) was used to allow co-localisation and quantification of blood vessels. Nerve fibre density was quantified at multiple sites within wounds. There was no difference in the reinnervation/revascularisation pattern between peripheral and central sites. The density of PGP9.5, CGRP, SP and VWF peaked between 14 and 42 days, and levels of PGP9.5, CGRP and VWF all decreased to approximately those found in unwounded skin by 84 days (mature scar). SP levels, however, remained elevated at approximately twice the density found in unwounded skin. Increased densities of SP and CGRP in healing wounds could explain the unpleasant sensory symptoms of healing wounds.

Alternative therapy in pruritus

Because of its multitude of origins, the symptom complex of pruritus has a plethora of purported remedies and few therapeutic indications. Very few topical and systemic FDA approved medications have the indication of pruritus. Specific therapy still awaits a better definition of the exact physiologic events in chronic pruritus. Hence most medications actually focus on the central nervous system--the peripheral receptors--and the lack of specific physiologic targets has inhibited pharmacologic development. The resulting gap has opened the door to a variety of alternative therapies.

Review of the effectiveness of capsaicin for painful cutaneous disorders and neural dysfunction

BACKGROUND

Topical capsaicin is known to be a safe and effective pain management adjunct for rheumatoid arthritis, osteoarthritis, neuralgias, and diabetic neuropathy. However, studies and case reports in the literature have indicated that other conditions may also benefit from capsaicin: painful or itching cutaneous disorders from operations, injuries, or tumors; neural dysfunction; or inflammation of the airways and urinary tract.

METHODS

To determine the effectiveness of capsaicin for painful cutaneous disorders and neural dysfunction, the authors analyzed data from 33 reports (MEDLINE search of 1966-96) on the efficacy of capsaicin. Outcome measures consisted of the response rate and degree of pain relief. Results from placebo-controlled trials were pooled when possible; effect of treatment was estimated by the method of DerSimonian and Laird.

RESULTS

Pain relief for postmastectomy syndrome and cluster headache was greater with capsaicin than with placebo; also, psoriasis and pruritus responded better to capsaicin. Uncontrolled studies and case reports have indicated that pain or dysfunction was less at the end of capsaicin therapy for neck pain, loin pain/hematuria syndrome, oral mucositis, rhinopathy, reflex sympathetic dystrophy syndrome, detrusor hyperreflexia, and cutaneous pain due to tumor of the skin.

CONCLUSIONS

Capsaicin is effective for psoriasis, pruritus, and cluster headache; it is often helpful for the itching and pain of postmastectomy pain syndrome, oral mucositis, cutaneous allergy, loin pain/hematuria syndrome, neck pain, amputation stump pain, and skin tumor; and it may be beneficial for neural dysfunction (detrusor hyperreflexia, reflex sympathetic dystrophy, and rhinopathy). A universal problem for many of the studies analyzed was the absence of a "burning placebo" such as camphor.

Cutaneous vascular response to calcitonin gene-related peptide in psoriasis and normal subjects

To determine whether cutaneous blood vessels in subjects with psoriasis possess a generalized inherently abnormal response to neuropeptides, the effect of three doses of intradermally injected calcitonin gene-related peptide (CGRP) on skin blood flow in normal subjects (n = 10), and on clinically normal skin (greater than 5 cm from psoriatic lesions) in subjects with psoriasis (n = 9) was measured using a laser Doppler technique. Calcitonin gene-related peptide caused a dose-dependent increase in local blood flow in both psoriatic and normal subjects, which was not statistically different between the two groups. This study has shown that the cutaneous vasculature at sites distant from lesions of psoriasis (> 5 cm) is not inherently different from normal skin in its response to CGRP.

Contact dermatitis associated with capsaicin: Hunan hand syndrome

"Hunan hand" is a contact dermatitis resulting from the direct handling of chili peppers containing capsaicin. Capsaicin also is found in an over-the-counter topical agent for treatment of postherpetic neuralgia, diabetic neuropathy, and arthritis. We present the case of a patient with capsaicin-induced dermatitis and discuss the pathophysiology, therapy, and current uses of capsaicin.