A Novel Treatment of Contact Dermatitis by Topical Application of Phospholipase A2 Inhibitor: A Double-Blind Placebo-Controlled Pilot Study

CD1-Restricted T Cells in Inflammatory Skin Diseases

Autoimmunity results from the breaking of immune tolerance, leading to inflammation and pathology. Although well studied in the conventional T-cell field, the role of nonconventional T cells in autoimmunity is less understood. CD1-restricted T cells recognize lipid antigens rather than peptide antigens and have been implicated in various autoimmune skin conditions, including psoriasis and atopic dermatitis. In this review, we will discuss the self-lipids that CD1-restricted T cells recognize and how these T cells become aberrantly regulated in pathogenic skin conditions.

Local inflammatory mediators alterations induced by Daboia siamensis venom

The ability of Russell's viper (Daboia siamensis) venom (total RVV) and phospholipase A₂ (purified PLA₂) to induce the local pathological effects were investigated by the local inflammatory events and the release of inflammatory mediators. Both 0.5 μg of total RVV/mouse and 0.15 μg of purified PLA₂/mouse were administered via intra-peritoneal injection. After 30 min, 1 h, 2 h, and 4 h incubation time, the peritoneal cavity was flooded with normal saline and the total leukocytes were collected. The eicosanoids (lipid mediators) and the leukocyte expression of cyclooxygenase (COX-1 and COX-2) were investigated by ELISA assay and western blotting, respectively. The amounts of total leukocytes were increased from 30 min to 2 h, then decreased at 4 h, by both total RVV and purified PLA₂. Both treatments also induced the expression of COX-2 which was increased at 2 h and then decreased at 4 h, whereas only purified PLA₂ induced the expression level of a COX-1 protein which was increased at 30 min, then constantly expressed until 4 h. In addition, total RVV and purified PLA₂ caused the release of the eicosanoids; PGE₂, TXB₂, and LTB₄, which reached the peak after 2 h. The findings of this study indicate that purified PLA₂ has the potential effects to induce the local inflammation relating the amounts of leukocytes cells, lipid mediators and COX-2 more than the total RVV.

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Purified phospholipase A₂ or the venom could induce eicosanoids and cyclooxygenase-2 expression relating to leukocytes cells.

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Thromboxane B₂ could be the important mediator induced by Russell's viper venom and purified phospholipase A₂.

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Russell's viper venom and purified phospholipase A₂ involved the cyclooxygenase-2 expression, but not cyclooxygenase-1.

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The purified phospholipase A₂ showed more predominant inflammatory response at site than total Russell's viper venom.

Phospholipase A2-dependent Release of Inflammatory Cytokines by Superantigen-Stimulated Nasal Polyps of Patients with Chronic Rhinosinusitis

Background

Chronic rhinosinusitis (CRS) is an inflammatory/allergic disease with unclear pathophysiology, but it has been linked to an imbalance in the production of eicosanoids, which are metabolites of arachidonic acid, and results from phospholipids hydrolysis by phospholipase A2 (PLA2). As of yet, the role of PLA2 in CRS has hardly been studied, except for a report that group II PLA2 expression is elevated in interleukin (IL) 1β or tumor necrosis factor α-stimulated CRS nasal tissues with and without polyps. The PLA2 families include extracellular (secretory) and intracellular isoforms, which are involved in the regulation of inflammatory processes in different ways. Here we comprehensively investigated the expression of PLA2s, particularly those reported to be involved in respiratory disorders, in superantigen (SAE)-stimulated nasal polyps from patients with CRS with polyps, and determined their role in inflammatory cytokine production by inhibition of PLA2 expression.

Methods

The release of IL-5, IL-13, IL-17, and interferon γ by nasal polyps dispersed cells (NPDC) was determined concomitantly with PLA2 messenger RNA expression, under SAE stimulation, with or without dexamethasone, as a regulator of PLA2 expression.

Results

Stimulation of NPDCs by SAE-induced cytokine secretion with enhanced expression of several secretory PLA2 and Ca2+-independent PLA2, while suppressing cytosolic PLA2 expression. All these were reverted to the level of unstimulated NPDCs on treatment with dexamethasone.

Conclusion

This study further supports the key role of secretory PLA2 in the pathophysiology of respiratory disorders and presents secretory PLA2 inhibition as a therapeutic strategy for the treatment of CRS and airway pathologies in general.

Serum metabolomics study and eicosanoid analysis of childhood atopic dermatitis based on liquid chromatography-mass spectrometry

Atopic dermatitis (AD) is the most common inflammatory skin disease in children. In the study, ultra high performance liquid chromatography-mass spectrometry was used to investigate serum metabolic abnormalities of AD children. Two batch fasting sera were collected from AD children and healthy control; one of them was for nontargeted metabolomics analysis, the other for targeted eicosanoids analysis. AD children were divided into high immunoglobulin E (IgE) group and normal IgE group. On the basis of the two analysis approaches, it was found that the differential metabolites of AD, leukotriene B4, prostaglandins, conjugated bile acids, etc., were associated with inflammatory response and bile acids metabolism. Carnitines, free fatty acids, lactic acid, etc., increased in the AD group with high IgE, which revealed energy metabolism disorder. Amino acid metabolic abnormalities and increased levels of Cytochrome P450 epoxygenase metabolites were found in the AD group with normal IgE. The results provided a new perspective to understand the mechanism and find potential biomarkers of AD and may provide a new reference for personalized treatment.

Phospholipase A2 in experimental allergic bronchitis: a lesson from mouse and rat models

Background

Phospholipases A₂ (PLA₂) hydrolyzes phospholipids, initiating the production of inflammatory lipid mediators. We have previously shown that in rats, sPLA₂ and cPLA₂ play opposing roles in the pathophysiology of ovalbumin (OVA)-induced experimental allergic bronchitis (OVA-EAB), an asthma model: Upon disease induction sPLA₂ expression and production of the broncho-constricting CysLTs are elevated, whereas cPLA₂ expression and the broncho-dilating PGE₂ production are suppressed. These were reversed upon disease amelioration by treatment with an sPLA₂ inhibitor. However, studies in mice reported the involvement of both sPLA₂ and cPLA₂ in EAB induction.

Objectives

To examine the relevance of mouse and rat models to understanding asthma pathophysiology.

Methods

OVA-EAB was induced in mice using the same methodology applied in rats. Disease and biochemical markers in mice were compared with those in rats.

Results

As in rats, EAB in mice was associated with increased mRNA of sPLA₂, specifically sPLA₂gX, in the lungs, and production of the broncho-constricting eicosanoids CysLTs, PGD₂ and TBX₂ in bronchoalveolar lavage (BAL). In contrast, EAB in mice was associated also with elevated cPLA₂ mRNA and PGE₂ production. Yet, treatment with an sPLA₂ inhibitor ameliorated the EAB concomitantly with reverting the expression of both cPLA₂ and sPLA₂, and eicosanoid production.

Conclusions

In both mice and rats sPLA₂ is pivotal in OVA-induced EAB. Yet, amelioration of asthma markers in mouse models, and human tissues, was observed also upon cPLA₂ inhibition. It is plausible that airway conditions, involving multiple cell types and organs, require the combined action of more than one, essential, PLA₂s.

Bioactive lipid mediators in skin inflammation and immunity

The skin is the primary barrier from the outside environment, protecting the host from injury, infectious pathogens, water loss and solar ultraviolet radiation. In this role, it is supported by a highly organized system comprising elements of innate and adaptive immunity, responsive to inflammatory stimuli. The cutaneous immune system is regulated by mediators such as cytokines and bioactive lipids that can initiate rapid immune responses with controlled inflammation, followed by efficient resolution. However, when immune responses are inadequate or mounted against non-infectious agents, these mediators contribute to skin pathologies involving unresolved or chronic inflammation. Skin is characterized by active lipid metabolism and fatty acids play crucial roles both in terms of structural integrity and functionality, in particular when transformed to bioactive mediators. Eicosanoids, endocannabinoids and sphingolipids are such key bioactive lipids, intimately involved in skin biology, inflammation and immunity. We discuss their origins, role and influence over various cells of the epidermis, dermis and cutaneous immune system and examine their function in examples of inflammatory skin conditions. We focus on psoriasis, atopic and contact dermatitis, acne vulgaris, wound healing and photodermatology that demonstrate dysregulation of bioactive lipid metabolism and examine ways of using this insight to inform novel therapeutics.

Impact of Porcine Orexin a on Glucagon Plasma Concentrations in Pigs

In 1998, Orexin A was added to the long list of orexigenic neuropeptides of the brain's physiology. Orexin A is involved in the central control of appetite and in energy homeostasis, as well as in the regulation of many other physiological functions. It is produced by a small cluster of the brain's neurons, located mainly in and around the lateral hypothalamic area. This site is known to be involved in regulating feeding in mammals. An intracerebroventricular injection of Orexin A into the rat's brain causes an impressive increase in the consumption of food, while an intravenous injection induces changes on glucagon plasma concentrations in rats. In addition, there are signs of changes on glucagon plasma concentrations when Orexin A acts on individual pancreatic islets of rats. In this study, we investigated the potential effects of the central administration of porcine Orexin A on glucagon plasma concentrations in pigs, and examined whether these changes are associated with the possible effect of the neuropeptide on the enteroinsular axis.

Involvement of cPLA2 Inhibition in Dexamethasone-Induced Thymocyte Apoptosis

Various molecular mechanisms have been suggested to be involved in dexamethasone induced thymocyte apoptosis. In this study we show that pharmacological inhibition of cytoplasmic PLA2 in mouse thymocytes for 18 h with arachidonyl trifluoromethyl ketone (AACOCF3) (10 μM) and palmitoyl trifluoromethyl ketone (PACOCF3) (10 μM) induced a drastic increase of thymocyte apoptosis comparable to that observed following Dex (10−7 M) treatment, while inhibition of secretory PLA2 with p-bromophenacyl bromide (pBPB) (20 μM) did not. AACOCF3-induced thymocyte apoptosis, similarly to Dex-induced thymocyte apoptosis, was eliminated by cell pre-treatment with the PI-PLCβ inhibitor, U73122, but not by the PC-PLC inhibitor D609. These observations were corroborated by the ability of AACOCF3, like Dex, to induce a rapid and transient increase in DAG generation. In addition, AACOCF3-induced apoptosis involved the activation of the acidic sphingomyelinase (aSMase) but not of the neutral sphingomyelinase (nSMase), as evaluated by measurements of enzyme activity in cell extracts following thymocyte exposure to AACOCF3 and by the ability of monensin to inhibit AACOCF3-induced thymocyte apoptosis. In addition, the AACOCF3 apoptotic effect resulted in an early increase of ceramide levels. AACOCF3-induced thymocyte apoptosis involved the activation of caspase 3, and cell pre-treatment with a caspase 3 inhibitor prevented AACOCF3-induced apoptosis. These observations suggest that cPLA2 inhibition may have a role in Dex-induced thymocyte apoptosis and highlight the importance of cPLA2 activity in thymocyte survival.