Reactive oxygen species and L-type calcium channels mediates hypoxia-dependent CCL2 secretion in mast cells

Mast cells (MCs) are well-known cells for their important role in initiating allergic response through of cross-linking of FcɛRI receptor with IgE-Ag complexes. As participants on inflammatory reactions, they are exposed to environmental conditions such as hypoxia, which on MC-dependent cytokine secretion has not been described.

Here, we show that bone marrow derived MCs (BMMCs) exposed to hypoxia, produce important amounts of CCL2 mRNA and protein, that is maximal secreted between 12 and 24 hours. CCL2 production induced by hypoxia was sensitive to the antioxidant trolox and L-type Ca2+ channel blocker nifedipine.

In order to analyze the possible mechanism involved on hypoxia-induced CCL2 production, we found that this conditions caused an increase on reactive oxygen species (ROS) that was maximal after one hour. We also observed an increase on [Ca2+]i two hours after hypoxia, which was sensitive to trolox. With the aim to confirm this mechanism, BMMCs were treated with H2O2 and as expected, H2O2 caused an increase on ROS and [Ca2+]i in BMMCs. Ca2+ increase produced by H2O2 was sensitive to nifedipine. CCL2 mRNA accumulation and CCL2 protein secretion induced by H2O2 was sensitive to trolox and nifedipine too.

When trolox and nifedipine were used in the B16-F1 murine model of melanoma, a close relationship between ROS, Ca2+ rise and CCL2 production was found, since those compounds were able to prevent pimonidazole-positive areas and CCL2 accumulation inside tumors. Our data suggest that conditions prevalent in tumor microenvironment contribute to the generation of ROS and L-type Ca2+ channel-dependent Ca2+ entry in MCs, causing the secretion of the potent immunosuppressor chemokine CCL2.

Mast Cells Localize in Hypoxic Zones of Tumors and Secrete CCL-2 under Hypoxia through Activation of L-Type Calcium Channels

Hypoxia is a condition that together with low pH, high amounts of reactive oxygen species (ROS), and increased adenosine levels characterize tumor microenvironment. Mast cells (MCs) are part of tumor microenvironment, but the effect of hypoxia on the production of MC-derived cytokines has not been fully described. Using the hypoxia marker pimonidazole in vivo, we found that MCs were largely located in the low-oxygen areas within B16-F1 mice melanoma tumors. In vitro, hypoxia promoted ROS production, a ROS-dependent increase of intracellular calcium, and the production of MCP 1 (CCL-2) in murine bone marrow-derived MCs. Hypoxia-induced CCL-2 production was sensitive to the antioxidant trolox and to nifedipine, a blocker of L-type voltage-dependent Ca²⁺ channels (LVDCCs). Simultaneously with CCL-2 production, hypoxia caused the ROS-dependent glutathionylation and membrane translocation of the α1c subunit of Cav1.2 LVDCCs. Relationship between ROS production, calcium rise, and CCL-2 synthesis was also observed when cells were treated with H₂O₂ In vivo, high CCL-2 production was detected on hypoxic zones of melanoma tumors (where tryptase-positive MCs were also found). Pimonidazole and CCL-2 positive staining diminished when B16-F1 cell-inoculated animals were treated with trolox, nifedipine, or the adenosine receptor 2A antagonist KW6002. Our results show that MCs are located preferentially in hypoxic zones of melanoma tumors, hypoxia-induced CCL-2 production in MCs requires calcium rise mediated by glutathionylation and membrane translocation of LVDCCs, and this mechanism of CCL-2 synthesis seems to operate in other cells inside melanoma tumors, with the participation of the adenosine receptor 2A.

Anandamide inhibits FcεRI-dependent degranulation and cytokine synthesis in mast cells through CB2 and GPR55 receptor activation. Possible involvement of CB2-GPR55 heteromers

Activation of high affinity receptor for IgE (FcεRI) by IgE/antigen complexes in mast cells (MCs) leads to the release of preformed pro-inflammatory mediators stored in granules by a Ca²⁺-dependent process known as anaphylactic degranulation. Degranulation inhibition has been proposed as a strategy to control allergies and chronic inflammation conditions. Cannabinoids are important inhibitors of inflammatory reactions but their effects on IgE/Ag-mediated MCs responses are not well described. In this study, we analyzed the effect of the endocannabinoid anandamide (AEA), the selective CB₂ receptor agonist HU308, and the GPR55 receptor agonist lysophosphatidylinositol (LPI) on FcεRI-induced activation in murine bone marrow-derived mast cells (BMMCs). Our results show that AEA, HU380 and LPI inhibited FcεRI-induced degranulation in a concentration-dependent manner. This effect was mediated by CB₂ and GPR55 receptor activation through a mechanism insensitive to pertussis toxin. Degranulation inhibition was prevented by CB₂ and GPR55 antagonism, but not by CB₁ receptor blockage. AEA also inhibited calcium-dependent cytokine mRNA synthesis induced by FcεRI crosslinking, without affecting early phosphorylation events. In addition, AEA, HU308 and LPI inhibited intracellular Ca²⁺ rise in response to IgE/Ag. CB₂ and GPR55 receptor antagonism could not prevent the inhibition produced by AEA and HU308, but partially blocked the one caused by LPI. These results indicate that AEA inhibits IgE/Ag-induced degranulation through a mechanism that includes the participation of CB₂ and GPR55 receptors acting in close crosstalk, and show that CB₂-GPR55 heteromers are important negative regulators of FcεRI-induced responses in MCs.

Jacareubin inhibits FcεRI-induced extracellular calcium entry and production of reactive oxygen species required for anaphylactic degranulation of mast cells

Mast cells (MCs) are important effectors in allergic reactions since they produce a number of pre-formed and de novo synthesized pro-inflammatory compounds in response to the high affinity IgE receptor (FcεRI) crosslinking. IgE/Antigen-dependent degranulation and cytokine synthesis in MCs have been recognized as relevant pharmacological targets for the control of deleterious inflammatory reactions. Despite the relevance of allergic diseases worldwide, efficient pharmacological control of mast cell degranulation has been elusive. In this work, the xanthone jacareubin was isolated from the heartwood of the tropical tree Callophyllum brasilense, and its tridimensional structure was determined for the first time by X-ray diffraction. Also, its effects on the main activation parameters of bone marrow-derived mast cells (BMMCs) were evaluated. Jacareubin inhibited IgE/Ag-induced degranulation in a dose-response manner with an IC₅₀ = 46 nM. It also blocked extracellular calcium influx triggered by IgE/Ag complexes and by the SERCA ATPase inhibitor thapsigargin (Thap). Inhibition of calcium entry correlated with a blockage on the reactive oxygen species (ROS) accumulation. Antioxidant capacity of jacareubin was higher than the showed by α-tocopherol and caffeic acid, but similar to trolox. Jacareubin shown inhibitory actions on xanthine oxidase, but not on NADPH oxidase (NOX) activities. In vivo, jacareubin inhibited passive anaphylactic reactions and TPA-induced edema in mice. Our data demonstrate that jacareubin is a potent natural compound able to inhibit anaphylactic degranualtion in mast cells by blunting FcεRI-induced calcium flux needed for secretion of granule content, and suggest that xanthones could be efficient anti-oxidant, antiallergic, and antiinflammatory molecules.

Xanthone Jacareubin inhibits FcɛRI-dependent degranulation in mast cells by the blockage of extracellular calcium entry

Mast cells are important effectors in allergic reactions since they produce a number of pre-formed and de novo synthesized inflammatory compounds in response to high affinity IgE receptor (FcɛRI) crosslinking. IgE/Antigen-dependent degranulation and cytokine synthesis of this cell type have been recognized as relevant pharmacological targets for the control of deleterious inflammatory reactions. Despite the relevance of allergic diseases worldwide, pharmacological control of mast cell degranulation has not been achieved.

In this work we analyzed the effect of the natural xanthone jacareubin on the main activation parameters of this cell type utilizing bone marrow-derived mast cells (BMMCs).

Jacareubin, the xanthone obtained from the heartwood of the tropical tree Callophyllum brasilense, showed no toxicity when tested on bone marrow-derived mast cells (BMMCs) and did not activate degranulation by itself. However, jacareubin inhibited IgE/Ag-induced degranulation (determined as the secretion of β-hexosaminidase) in a dose-response manner (IC50 = 46 nM). Jacareubin blocked FcɛRI-dependent reactive oxygen species (ROS) formation, intracellular calcium mobilization and calcium-dependent protein kinase C (PKC) phosphorylation.

Detailed analysis suggest that at least one of the molecular actions of jacareubin relies on the inhibition of plasma membrane calcium channels involved in degranulation of mast cells. It is proposed to jacareubin as a natural drug with antioxidant activity and a regulator of calcium channels, with prophylactic potential for the treatment of allergies produced by mast cells.

Mexican Propolis: A Source of Antioxidants and Anti-Inflammatory Compounds, and Isolation of a Novel Chalcone and ε-Caprolactone Derivative

The propolis produced by bees are used in alternative medicine for treating inflammation, and infections, presumably due to its antioxidant properties. In this context, five propolis from México were investigated to determine their inhibitory lipid peroxidation properties. The ethyl acetate extract from a red propolis from Chiapas State (4-EAEP) was the most potent (IC₅₀ = 1.42 ± 0.07 μg/mL) in the TBARS assay, and selected for further studies. This extract afforded two new compounds, epoxypinocembrin chalcone (6), and an ε-caprolactone derivative (10), as well as pinostrobin (1), izalpinin (2), cinnamic acid (3), pinocembrin (4), kaempherol (5), 3,3-dimethylallyl caffeate in mixture with isopent-3-enyl caffeate (7a + 7b), 3,4-dimethoxycinnamic acid (8), rhamnetin (9) and caffeic acid (11). The HPLC profile, anti-mycobacterial, and antioxidant properties of this extract was also determined. Most of the isolated compounds were also tested by inhibition of reactive oxygen species (ROS) in challenged mouse bone marrow-derived mast cells (BMMCs), and DPPH. Their anti-inflammatory activity was evaluated by TPA, and MPO (myeloperoxidase) activity by ear edema test in mice. The most potent compounds were 7a + 7b in the TBARS assay (IC₅₀ = 0.49 ± 0.06 μM), and 2 which restored the ROS baseline (3.5 μM). Our results indicate that 4-EAEP has anti-oxidant, and anti-inflammatory properties due to its active compounds, suggesting it has anti-allergy and anti-asthma potential.