Dietary phytol reduces clinical symptoms in experimental autoimmune encephalomyelitis (EAE) at least partially by modulating NOX2 expression.

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system. We investigated the effect of phytol in an animal model of MS, experimental autoimmune encephalomyelitis (EAE), as phytol, a plant-derived diterpene alcohol, exerts anti-inflammatory and redox-protective actions. We observed a significant amelioration of clinical symptoms in EAE C57BL/6N mice fed prophylactically with a phytol-enriched diet. Demyelination, DNA damage, and infiltration of immune cells, specifically TH1 cells, into the central nervous system were reduced in phytol-fed EAE mice. Furthermore, phytol reduced T-cell proliferation ex vivo. Phytanic acid - a metabolite of phytol - also reduced T-cell proliferation, specifically that of TH1 cells. Additionally, phytol-enriched diet increased the mRNA expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX) 2 in white blood cells in the lymph nodes. Accordingly, phytol lost its anti-inflammatory effects in chimeric EAE C57BL/6N mice whose peripheral cells lack NOX2, indicating that phytol mediates its effects in peripheral cells via NOX2. Moreover, the effects of phytol on T-cell proliferation were also NOX2-dependent. In contrast, the T-cell subtype alterations and changes in proliferation induced by phytanic acid, the primary metabolite of phytol, were NOX2-independent. In conclusion, phytol supplementation of the diet leads to amelioration of EAE pathology in both a NOX2-dependent and a NOX2-independent manner via yet unknown mechanisms. KEY MESSAGES: Phytol diet ameliorates EAE pathology. Phytol diet reduces demyelination, immune cell infiltration, and T-cell proliferation. Phytol diet increases NOX2 mRNA expression in white blood cells in the lymph nodes. Phytol mediates its effects in peripheral cells via NOX2. Effects of phytol on T-cell proliferation were NOX2-dependent.

The leukotriene B4 receptors BLT1 and BLT2 form an antagonistic sensitizing system in peripheral sensory neurons.

Sensitization of the heat-activated ion channel transient receptor potential vanilloid 1 (TRPV1) through lipids is a fundamental mechanism during inflammation-induced peripheral sensitization. Leukotriene B4 is a proinflammatory lipid mediator whose role in peripheral nociceptive sensitization is not well understood to date. Two major G-protein-coupled receptors for leukotriene B4 have been identified: the high-affinity receptor BLT1 and the low-affinity receptor BLT2. Transcriptional screening for the expression G-protein-coupled receptors in murine dorsal root ganglia showed that both receptors were among the highest expressed in dorsal root ganglia. Calcium imaging revealed a sensitization of TRPV1-mediated calcium increases in a relative narrow concentration range for leukotriene B4 (100-200 nm). Selective antagonists and neurons from knock-out mice demonstrated a BLT1-dependent sensitization of TRPV1-mediated calcium increases. Accordingly, leukotriene B4-induced thermal hyperalgesia was mediated through BLT1 and TRPV1 as shown using the respective knock-out mice. Importantly, higher leukotriene B4 concentrations (>0.5 µm) and BLT2 agonists abolished sensitization of the TRPV1-mediated calcium increases. Also, BLT2 activation inhibited protein kinase C- and protein kinase A-mediated sensitization processes through the phosphatase calcineurin. Consequently, a selective BLT2-receptor agonist increased thermal and mechanical withdrawal thresholds during zymosan-induced inflammation. In accordance with these data, immunohistochemical analysis showed that both leukotriene B4 receptors were expressed in peripheral sensory neurons. Thus, the data show that the two leukotriene B4 receptors have opposing roles in the sensitization of peripheral sensory neurons forming a self-restricting system.

GPVI and Thromboxane Receptor on Platelets Promote Proinflammatory Macrophage Phenotypes during Cutaneous Inflammation.

Platelets are well known for their role in hemostasis but are also increasingly recognized for their supporting role in innate immune responses. Here, we studied the role of platelets in the development of peripheral inflammation and found that platelets colocalize with macrophages in the inflamed tissue outside of blood vessels in different animal models for cutaneous inflammation. Collagen-treatment of macrophages isolated from paws during zymosan-induced inflammation induced thromboxane synthesis through the platelet-expressed collagen receptor glycoprotein VI. Deletion of glycoprotein VI or its downstream effector thromboxane A2 receptor (TP) reduced zymosan-induced mechanical allodynia without altering macrophage recruitment or formation of macrophage/platelet complexes. Instead, macrophages in inflamed paws of glycoprotein VI- and TP-deficient mice exhibited an increased expression of anti-inflammatory markers and synthesized less proinflammatory mediators (prostaglandin E2 and IL6). TP expression on platelets was necessary to mediate increased prostaglandin E2 and IL6 synthesis, whereas TP expression on macrophages was sufficient to decrease the expression of the anti-inflammatory macrophage marker CD206, showing that TP activation on platelets and macrophages regulates different aspects of macrophage activation.

Alpha-methylacyl-CoA racemase deletion has mutually counteracting effects on T-cell responses, associated with unchanged course of EAE.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. Altering the metabolism of immune cells is an attractive strategy to modify their activity during autoimmunity in MS. We investigated the effect of modulating fatty acid metabolism in an animal model of MS, EAE. Alpha-methylacyl-CoA racemase (AMACR) converts R-configuration branched fatty acids into the S-configuration, thereby preparing them for ß-oxidation. We observed a significant, disease-dependent elevation of AMACR expression in monocytes and T cells from blood, draining lymph nodes and spleen of EAE mice during the preclinical phase. In vitro analysis revealed that the proliferation of T cells was inhibited in AMACR KO mice, but T-cell polarization was switched toward a pathogenic state involving the production of more IFN-γ and IL-17, but less IL-4. These opposing effects appeared to cancel out each other in vivo, because AMACR KO EAE mice showed a marginal increase in the severity of early clinical symptoms. AMACR was not regulated in the white blood cells of MS patients. Our data show that AMACR is regulated in immune cells during EAE, but it is not a suitable target for the treatment of MS due to its opposing effects.

Slack channels expressed in sensory neurons control neuropathic pain in mice.

Slack (Slo2.2) is a sodium-activated potassium channel that regulates neuronal firing activities and patterns. Previous studies identified Slack in sensory neurons, but its contribution to acute and chronic pain in vivo remains elusive. Here we generated global and sensory neuron-specific Slack mutant mice and analyzed their behavior in various animal models of pain. Global ablation of Slack led to increased hypersensitivity in models of neuropathic pain, whereas the behavior in models of inflammatory and acute nociceptive pain was normal. Neuropathic pain behaviors were also exaggerated after ablation of Slack selectively in sensory neurons. Notably, the Slack opener loxapine ameliorated persisting neuropathic pain behaviors. In conclusion, Slack selectively controls the sensory input in neuropathic pain states, suggesting that modulating its activity might represent a novel strategy for management of neuropathic pain.