A possible role for CD26/DPPIV enzyme activity in the regulation of psoriatic pruritus

Pathomechanism of Pruritus in Psoriasis and Atopic Dermatitis: Novel Approaches, Similarities and Differences

Pruritus is defined as an unpleasant sensation that elicits a desire to scratch. Nearly a third of the world's population may suffer from pruritus during their lifetime. This symptom is widely observed in numerous inflammatory skin diseases-e.g., approximately 70-90% of patients with psoriasis and almost every patient with atopic dermatitis suffer from pruritus. Although the pathogenesis of atopic dermatitis and psoriasis is different, the complex intricacies between several biochemical mediators, enzymes, and pathways seem to play a crucial role in both conditions. Despite the high prevalence of pruritus in the general population, the pathogenesis of this symptom in various conditions remains elusive. This review aims to summarize current knowledge about the pathogenesis of pruritus in psoriasis and atopic dermatitis. Each molecule involved in the pruritic pathway would merit a separate chapter or even an entire book, however, in the current review we have concentrated on some reports which we found crucial in the understanding of pruritus. However, the pathomechanism of pruritus is an extremely complex and intricate process. Moreover, many of these signaling pathways are currently undergoing detailed analysis or are still unexplained. As a result, it is currently difficult to take an objective view of how far we have come in elucidating the pathogenesis of pruritus in the described diseases. Nevertheless, considerable progress has been made in recent years.

Peripheral endomorphins drive mechanical alloknesis under the enzymatic control of CD26/DPPIV

BACKGROUND

Mechanical alloknesis (or innocuous mechanical stimuli-evoked itch) often occurs in dry skin-based disorders such as atopic dermatitis and psoriasis. However, the molecular and cellular mechanisms underlying mechanical alloknesis remain unclear. We recently reported the involvement of CD26 in the regulation of psoriatic itch. This molecule exhibits dipeptidyl peptidase IV (DPPIV) enzyme activity and exerts its biologic effects by processing various substances, including neuropeptides.

OBJECTIVE

The aim of the present study was to investigate the peripheral mechanisms of mechanical alloknesis by using CD26/DPPIV knockout (CD26KO) mice.

METHODS

We applied innocuous mechanical stimuli to CD26KO or wild-type mice. The total number of scratching responses was counted as the alloknesis score. Immunohistochemical and behavioral pharmacologic analyses were then performed to examine the physiologic activities of CD26/DPPIV or endomorphins (EMs), endogenous agonists of μ-opioid receptors.

RESULTS

Mechanical alloknesis was more frequent in CD26KO mice than in wild-type mice. The alloknesis score in CD26KO mice was significantly reduced by the intradermal administration of recombinant DPPIV or naloxone methiodide, a peripheral μ-opioid receptor antagonist, but not by that of mutant DPPIV without enzyme activity. EMs (EM-1 and EM-2), selective ligands for μ-opioid receptors, are substrates for DPPIV. Immunohistochemically, EMs were located in keratinocytes, fibroblasts, and peripheral sensory nerves. Behavioral analyses revealed that EMs preferentially provoked mechanical alloknesis over chemical itch. DPPIV-digested forms of EMs did not induce mechanical alloknesis.

CONCLUSION

The present results suggest that EMs induce mechanical alloknesis at the periphery under the enzymatic control of CD26/DPPIV.

The role of Dipeptidyl Peptidase-4 in cutaneous disease

Dipeptidyl peptidase-4 (DPP4) is a multifunctional, transmembrane glycoprotein present on the cell surface of various tissues. It is present in multiple molecular forms including cell surface and soluble. The role of DPP4 and its inhibition in cutaneous dermatoses have been a recent point of investigation. DPP4 exerts a notable influence on T-cell biology, the induction of skin-specific lymphocytes, and the homeostasis between regulatory and effector T cells. Moreover, DPP4 interacts with a broad range of molecules, including adenosine deaminase, caveolin-1, CXCR4 receptor, M6P/insulin-like growth factor II-receptor and fibroblast activation protein-α, triggering downstream effects that modulate the immune response, cell adhesion and chemokine activity. DPP4 expression on melanocytes, keratinocytes and fibroblasts further alters cell function and, thus, has crucial implications in cutaneous pathology. As a result, DPP4 plays a significant role in bullous pemphigoid, T helper type 1-like reactions, cutaneous lymphoma, melanoma, wound healing and fibrotic disorders. This review illustrates the multifactorial role of DPP4 expression, regulation, and inhibition in cutaneous diseases.

Uncovering the mechanism of Jueyin granules in the treatment of psoriasis using network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Our clinical practice demonstrated that Jueyin granules (JYG) benefit patients with mild to moderate psoriasis vulgaris without apparent adverse effects. JYG have been shown to inhibit epidermal proliferation in an imiquimod (IMQ)-induced psoriasis-like mouse model, as well as keratinocyte proliferation. Moreover, JYG causes no acute or chronic toxicity in animal models. However, its related molecular mechanism has still not been elucidated.

AIM OF THE STUDY

To assess the mechanism of JYG against psoriasis.

MATERIALS AND METHODS

This study combined network pharmacology analysis with experiments to investigate the mechanism of JYG against psoriasis. First, the molecular docking technology was used to construct the network of medicinal materials-core active plant ingredients-core targets and identify possible drug targets. Next, high-performance liquid chromatography (HPLC) was used for quality control of JYG. Finally, a mice model of psoriasis was used to further verify the effects of JYG.

RESULTS

(1) Molecular docking analysis of network pharmacology revealed that the therapeutic effects of JYG on psoriasis might be achieved through Vitamin D Receptor (VDR) effects. (2) The concentrations of chlorogenic acid and paeoniflorin were determined using HPLC to establish quality control of JYG. (3) JYG ameliorated pathological characteristics that included in vivo reductions in erythema, scale, and infiltration scores of back and ear lesions in IMQ-induced psoriasis-like mice. Moreover, a reduced number of PCNA-positive and Ki67-positive cells were observed in the epidermis of JYG-treated lesions. JYG also reduced inflammation (interleukin (IL)-17, IL-23) in the peripheral blood of IMQ-induced psoriasis-like mice. As expected, JYG was found to upregulate VDR expression and downregulate p-STAT3 expression in the IMQ group, which may contribute to its mechanism against psoriasis.

CONCLUSION

Overall, this study clarifies the mechanism of JYG against psoriasis and provides evidence to support its clinical use.

Molecular and Cellular Mechanisms of Itch in Psoriasis

Itch (or pruritus) was not previously recognized as a serious symptom of psoriasis. However, approximately 60-90% of psoriatic patients with pruritus have stated that it deteriorates their quality of life. Since conventional antipruritic therapies, such as antihistamines, only exert limited effects, the establishment of a treatment option for itch in psoriasis is urgently needed. Although a definitive drug is not currently available, various itch mediators are known to be involved in pruritus in psoriasis. In this review, we describe the clinical features of pruritus in psoriasis, classify a wide range of itch mediators into categories, such as the nervous, immune, endocrine, and vascular systems, and discuss the mechanisms by which these mediators induce or aggravate itch in the pathophysiology of psoriasis.

Effect of narrowband ultraviolet B therapy on serum levels of CD26/dipeptidyl-peptidase IV and truncated forms of substance P in psoriasis patients with pruritus

Purpose

While pruritus affects approximately 60–90% of psoriasis patients, the pathogenesis of the condition remains unclear. CD26/dipeptidyl-peptidase IV (CD26/DPPIV) and truncated forms of substance P (SP) have been reported to play an important role in the pathogenesis of psoriatic itch. The aim of this study was to determine the serum levels of soluble CD26/DPPIV and truncated forms of SP in response to narrowband ultraviolet B (NBUVB) therapy.

Patients and methods

The peripheral blood of 13 participants with moderate to severe psoriasis (psoriasis area and severity index (PASI) ≥10) who presented with pruritus symptoms and 12 psoriasis-free participants were collected. Seven of the 13 patients agreed to be treated with NBUVB. The PASI was evaluated. Additionally, the clinical assessment of itch was performed with the visual analog scale (VAS) and the itch severity scale (ISS).

Results

The results showed that the levels of truncated SP were significantly higher in participants with psoriasis compared to participants without psoriasis. (302.20±56.87 vs 234.96±78.01 pg/ml, p<0.05). After irradiation, truncated SP significantly decreased from 288.85±66.22 pg/ml to 252.13±49.78 pg/ml, p<0.05. The CD26/DPPIV levels were lower in psoriasis participants compared to the healthy participants (526.34±145.35 vs 593.19±84.92 ng/ml, p>0.05) and increased significantly after NBUVB therapy (518.13±173.0 ng/ml to 592.7±193.9 ng/ml, p<0.05). NBUVB therapy caused alterations to the serum levels of truncated SP and CD26/DPPIV.

Conclusion

The decreased serum levels of truncated SP and increased levels of CD26/DPPIV post-NBUVB treatment observed in this study provides insight into the underlying molecular mechanisms of the treatment; this may be used in the prospective monitoring and development of improved psoriasis-related pruritus therapeutics. Further studies, comprising a larger cohort, are required to confirm these results.