Platelet activating factor (PAF) and lyso-PAF in psoriasis

Metabonomics Study on Serum Characteristic Metabolites of Psoriasis Vulgaris Patients With Blood-Stasis Syndrome

Psoriasis is a chronic, refractory, systemic inflammatory skin disease. Traditional Chinese medicine (TCM) shows unique advantage in the treatment of psoriasis based on syndrome differentiation. An untargeted high-throughput metabonomics method based on liquid chromatography coupled to mass spectrometry was applied to study the serum metabolic characteristics in different TCM syndrome types in patients with psoriasis vulgaris (PV), and to discover potential serum biomarkers for its pathogenesis on the endogenous metabolite differentiation basis. The serum metabolic profiles of 45 healthy controls and 124 patients with PV (50 in the blood-stasis group, 30 in the blood-heat group, and 44 in the blood-dryness group) were acquired. The raw spectrometric data were processed using multivariate statistical analysis, and 14 biomarkers related to TCM syndrome differentiation and psoriasis types were screened and identified. The blood-stasis syndrome group showed abnormal lipid metabolism, which was characterized by a low level of phosphatidylcholine (PC) and a high level of lysophosphatidylcholine (LPC). We propose that platelet-activating factor can be applied as a potential biomarker in clinical diagnosis and differentiation of PV with blood-stasis syndrome. The difference in the serum metabolites among PV types with different TCM syndromes and healthy control group illustrated the objective material basis in TCM syndrome differentiation and classification of psoriasis.

p38 MAP-kinase inhibitor protects against platelet-activating factor-induced death in mice

Platelet-activating factor (PAF) is a potent inflammatory agonist. In Swiss albino mice, intraperitoneal injection of PAF causes sudden death with oxidative stress and disseminated intravascular coagulation (DIC), characterized by prolonged prothrombin time, thrombocytopenia, reduced fibrinogen content, and increased levels of fibrinogen degradation products. However, the underlying mechanism(s) is unknown. The PAF-R antagonist WEB-2086 protected mice against PAF-induced death by reducing DIC and oxidative stress. Accordingly, general antioxidants such as ascorbic acid, α-tocopherol, gallic acid, and N-acetylcysteine partially protected mice from PAF-induced death. N-acetylcysteine, a clinically used antioxidant, prevented death in 67% of mice, ameliorated DIC characteristics and histological alterations in the liver, and reduced oxidative stress. WEB-2086 suppressed H₂O₂-mediated oxidative stress in isolated mouse peritoneal macrophages, suggesting that PAF signaling may be a downstream effector of reactive oxygen species generation. PAF stimulated all three (ERK, JNK, and p38) of the MAP-kinases, which were also inhibited by N-acetylcysteine. Furthermore, a JNK inhibitor (SP600125) and ERK inhibitor (SCH772984) partially protected mice against PAF-induced death, whereas a p38 MAP-kinase inhibitor (SB203580) provided complete protection against DIC and death. In human platelets, which have the canonical PAF-R and functional MAP-kinases, JNK and p38 inhibitors abolished PAF-induced platelet aggregation, but the ERK inhibitor was ineffective. Our studies identify p38 MAP-kinase as a critical, but unrecognized component in PAF-induced mortality in mice. These findings suggest an alternative therapeutic strategy to address PAF-mediated pathogenicity, which plays a role in a broad range of inflammatory diseases.

Platelet-activating factor induces Th17 cell differentiation

Th17 cells have been implicated in a number of inflammatory and autoimmune diseases. The phospholipid mediator platelet-activating factor (PAF) is found in increased concentrations in inflammatory lesions and has been shown to induce IL-6 production. We investigated whether PAF could affect the development of Th17 cells. Picomolar concentrations of PAF induced IL-23, IL-6, and IL-1β expression in monocyte-derived Langerhans cells (LCs) and in keratinocytes. Moreover, when LC were pretreated with PAF and then cocultured with anti-CD3- and anti-CD28-activated T cells, the latter developed a Th17 phenotype, with a significant increase in the expression of the transcriptional regulator RORγt and enhanced expression of IL-17, IL-21, and IL-22. PAF-induced Th17 development was prevented by the PAF receptor antagonist WEB2086 and by neutralizing antibodies to IL-23 and IL-6R. This may constitute a previously unknown stimulus for the development and persistence of inflammatory processes that could be amenable to pharmacologic intervention.

Anti-inflammatory activities of LDP-392, a dual PAF receptor antagonist and 5-lipoxygenase inhibitor

Leukotrienes (LTs) and platelet-activating factor (PAF) are important mediators of inflammation and allergy. LDP-392, a novel dual PAF receptor antagonist and 5-lipoxygenase (5-LO) inhibitor, has been identified. LDP-392 is 17.9-fold more potent than zileuton (5-LO inhibitor) in the RBL cytosolic 5-LO assay, and equally potent as MK 287 (PAF receptor antagonist) in the human platelet PAF receptor binding assay. The in vivo dual activities of LDP-392 were confirmed by measuring the inhibition of ex vivo LTB(4)production in rats and PAF-induced hemoconcentration in mice. Intravenous administration of LDP-392 demonstrated greater inhibition than zileuton, BN 50739 or MK 287 on arachidonic acid-induced ear edema and protected mice from LPS-induced lethality. Topical administration of LDP-392, in a dose-dependent manner, inhibited TPA-induced ear edema in mice and UVB-induced erythema in guinea-pigs. These data suggest that LDP-392, as a dual PAF receptor antagonist and 5-LO inhibitor, may be of greater clinical effectiveness.

Platelet-activating factor (PAF) receptor and genetically engineered PAF receptor mutant mice

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active phospholipid mediator. Although PAF was initially recognized for its potential to induce platelet aggregation and secretion, intense investigations have elucidated potent biological actions of PAF in a broad range of cell types and tissues, many of which also produce the molecule. PAF acts by binding to a unique G-protein-coupled seven transmembrane receptor. PAF receptor is linked to intracellular signal transduction pathways, including turnover of phosphatidylinositol, elevation in intracellular calcium concentration, and activation of kinases, resulting in versatile bioactions. On the basis of numerous pharmacological reports, PAF is thought to have many pathophysiological and physiological functions. Recently advanced molecular technics enable us not only to clone PAF receptor cDNAs and genes, but also generate PAF receptor mutant animals, i.e., PAF receptor-overexpressing mouse and PAF receptor-deficient mouse. These mutant mice gave us a novel and specific approach for identifying the pathophysiological and physiological functions of PAF. This review also describes the phenotypes of these mutant mice and discusses them by referring to previously reported pharmacological and genetical data.