Cnr1-/- has minimal impact on chlorpyrifos-mediated effects in the mouse endocannabinoid system, but it does alter lipopolysaccharide-induced cytokine levels in splenocytes

Chlorpyrifos (CPF) is an organophosphate pesticide that can inhibit endocannabinoid (eCB) metabolizing enzymes in animal models at levels that do not significantly alter acetylcholinesterase (AChE) in the central nervous system (CNS). Previous studies indicated that repeated low-level CPF exposure in developing rats increased the levels of eCBs in the brain. Because eCBs play a role in immune homeostasis through their engagement with cannabinoid receptors, we investigated the role of cannabinoid receptor 1 (CB1, encoded by the Cnr1 gene) on the CPF-mediated effects in the spleen and lung of neonatal and adult female mice. We treated neonatal and adult female Cnr1^-/- mice with 2.5 mg/kg oral CPF or vehicle for 7 days. Tissues were harvested 4 h after the last CPF dose to evaluate eCB metabolic enzyme activity, levels of eCBs, and tissue immunophenotype. There were a small number of genotype-dependent alterations noted in the endpoints following CPF treatment that were specific to age and tissue type, and differences in eCB metabolism caused by CPF treatment did not correlate to changes in eCB levels. To explore the role of CB1 in CPF-mediated effects on immune endpoints, in vitro experiments were performed with WT murine splenocytes exposed to chlorpyrifos oxon (CPO; oxon metabolite of CPF) and challenged with lipopolysaccharide (LPS). While CPO did not alter LPS-induced pro-inflammatory cytokine levels, inactivation of CB1 by the antagonist SR141716A augmented LPS-induced IFN-γ levels. Additional experiments with WT and Cnr1^-/- murine splenocytes confirmed a role for CB1 in altering the production of LPS-induced pro-inflammatory cytokine levels. We conclude that CPF-mediated effects on the eCB system are not strongly dependent on CB1, although abrogation of CB1 does alter LPS-induced cytokine levels in splenocytes.

Effects of Chlorpyrifos on Serine Hydrolase Activities, Lipid Mediators, and Immune Responses in Lungs of Neonatal and Adult Mice

Chlorpyrifos (CPF) is an organophosphate (OP) pesticide that causes acute toxicity by inhibiting acetylcholinesterase (AChE) in the nervous system. However, endocannabinoid (eCB) metabolizing enzymes in brain of neonatal rats are more sensitive than AChE to inhibition by CPF, leading to increased levels of eCBs. Because eCBs are immunomodulatory molecules, we investigated the association between eCB metabolism, lipid mediators, and immune function in adult and neonatal mice exposed to CPF. We focused on lung effects because epidemiologic studies have linked pesticide exposures to respiratory diseases. CPF was hypothesized to disrupt lung eCB metabolism and alter lung immune responses to lipopolysaccharide (LPS), and these effects would be more pronounced in neonatal mice due to an immature immune system. We first assessed the biochemical effects of CPF in adult mice (≥8 weeks old) and neonatal mice after administering CPF (2.5 mg/kg, oral) or vehicle for 7 days. Tissues were harvested 4 h after the last CPF treatment and lung microsomes from both age groups demonstrated CPF-dependent inhibition of carboxylesterases (Ces), a family of xenobiotic and lipid metabolizing enzymes, whereas AChE activity was inhibited in adult lungs only. Activity-based protein profiling (ABPP)-mass spectrometry of lung microsomes identified 31 and 32 individual serine hydrolases in neonatal lung and adult lung, respectively. Of these, Ces1c/Ces1d/Ces1b isoforms were partially inactivated by CPF in neonatal lung, whereas Ces1c/Ces1b and Ces1c/BChE were partially inactivated in adult female and male lungs, respectively, suggesting age- and sex-related differences in their sensitivity to CPF. Monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) activities in lung were unaffected by CPF. When LPS (1.25 mg/kg, i.p.) was administered following the 7-day CPF dosing period, little to no differences in lung immune responses (cytokines and immunophenotyping) were noted between the CPF and vehicle groups. However, a CPF-dependent increase in the amounts of dendritic cells and certain lipid mediators in female lung following LPS challenge was observed. Experiments in neonatal and adult Ces1d^-/- mice yielded similar results as wild type mice (WT) following CPF treatment, except that CPF augmented LPS-induced Tnfa mRNA in adult Ces1d^-/- mouse lungs. This effect was associated with decreased expression of Ces1c mRNA in Ces1d^-/- mice versus WT mice in the setting of LPS exposure. We conclude that CPF exposure inactivates several Ces isoforms in mouse lung and, during an inflammatory response, increases certain lipid mediators in a female-dependent manner. However, it did not cause widespread altered lung immune effects in response to an LPS challenge.

Inactivation of CES1 Blocks Prostaglandin D2 Glyceryl Ester Catabolism in Monocytes/Macrophages and Enhances Its Anti-inflammatory Effects, Whereas the Pro-inflammatory Effects of Prostaglandin E2 Glyceryl Ester Are Attenuated

Human monocytic cells in blood have important roles in host defense and express the enzyme carboxylesterase 1 (CES1). This metabolic serine hydrolase plays a critical role in the metabolism of many molecules, including lipid mediators called prostaglandin glyceryl esters (PG-Gs), which are formed during cyclooxygenase-mediated oxygenation of the endocannabinoid 2-arachidonoylglycerol. Some PG-Gs have been shown to exhibit anti-inflammatory effects; however, they are unstable compounds, and their hydrolytic breakdown generates pro-inflammatory prostaglandins. We hypothesized that by blocking the ability of CES1 to hydrolyze PG-Gs in monocytes/macrophages, the beneficial effects of anti-inflammatory prostaglandin D₂-glyceryl ester (PGD₂-G) could be augmented. The goals of this study were to determine whether PGD₂-G is catabolized by CES1, evaluate the degree to which this metabolism is blocked by small-molecule inhibitors, and assess the immunomodulatory effects of PGD₂-G in macrophages. A human monocytic cell line (THP-1 cells) was pretreated with increasing concentrations of known small-molecule inhibitors that block CES1 activity [chlorpyrifos oxon (CPO), WWL229, or WWL113], followed by incubation with PGD₂-G (10 μM). Organic solvent extracts of the treated cells were analyzed by liquid chromatography with tandem mass spectrometry to assess levels of the hydrolysis product PGD₂. Further, THP-1 monocytes with normal CES1 expression (control cells) and "knocked-down" CES1 expression (CES1KD cells) were employed to confirm CES1's role in PGD₂-G catabolism. We found that CES1 has a prominent role in PGD₂-G hydrolysis in this cell line, accounting for about 50% of its hydrolytic metabolism, and that PGD₂-G could be stabilized by the inclusion of CES1 inhibitors. The inhibitor potency followed the rank order: CPO > WWL113 > WWL229. THP-1 macrophages co-treated with WWL113 and PGD₂-G prior to stimulation with lipopolysaccharide exhibited a more pronounced attenuation of pro-inflammatory cytokine levels (interleukin-6 and TNFα) than by PGD₂-G treatment alone. In contrast, prostaglandin E₂-glyceryl ester (PGE₂-G) had opposite effects compared to those of PGD₂-G, which appeared to be dependent on the hydrolysis of PGE₂-G to PGE₂. These results suggest that the anti-inflammatory effects induced by PGD₂-G can be further augmented by inactivating CES1 activity with specific small-molecule inhibitors, while pro-inflammatory effects of PGE₂-G are attenuated. Furthermore, PGD₂-G (and/or its downstream metabolites) was shown to activate the lipid-sensing receptor PPARγ, resulting in altered "alternative macrophage activation" response to the Th2 cytokine interleukin-4. These findings suggest that inhibition of CES1 and other enzymes that regulate the levels of pro-resolving mediators such as PGD₂-G in specific cellular niches might be a novel anti-inflammatory approach.

Electronic-Cigarette Vehicles and Flavoring Affect Lung Function and Immune Responses in a Murine Model

The use of electronic nicotine delivery systems (ENDS), also known as electronic-cigarettes (e-cigs), has raised serious public health concerns, especially in light of the 2019 outbreak of e-cig or vaping product use-associated acute lung injury (EVALI). While these cases have mostly been linked to ENDS that contain vitamin E acetate, there is limited research that has focused on the chronic pulmonary effects of the delivery vehicles (i.e., without nicotine and flavoring). Thus, we investigated lung function and immune responses in a mouse model following exposure to the nearly ubiquitous e-cig delivery vehicles, vegetable glycerin (VG) and propylene glycol (PG), used with a specific 70%/30% ratio, with or without vanilla flavoring. We hypothesized that mice exposed sub-acutely to these e-cig aerosols would exhibit lung inflammation and altered lung function. Adult female C57BL/6 mice (n = 11–12 per group) were exposed to filtered air, 70%/30% VG/PG, or 70%/30% VG/PG with a French vanilla flavoring for 2 h a day for 6 weeks. Prior to sacrifice, lung function was assessed. At sacrifice, broncho-alveolar lavage fluid and lung tissue were collected for lipid mediator analysis, flow cytometry, histopathology, and gene expression analyses. Exposures to VG/PG + vanilla e-cig aerosol increased lung tidal and minute volumes and tissue damping. Immunophenotyping of lung immune cells revealed an increased number of dendritic cells, CD4+ T cells, and CD19+ B cells in the VG/PG-exposed group compared to air, irrespective of the presence of vanilla flavoring. Quantification of bioactive lung lipids demonstrated a >3-fold increase of 2-arachidonoylglycerol (2-AG), an anti-inflammatory mediator, and a 2-fold increase of 12-hydroxyeicosatetraenoic acid (12-HETE), another inflammatory mediator, following VG/PG exposure, with or without vanilla flavoring. This suggests that e-cig aerosol vehicles may affect immunoregulatory molecules. We also found that the two e-cig aerosols dysregulated the expression of lung genes. Ingenuity Pathway Analysis revealed that the gene networks that are dysregulated by the VG/PG e-cig aerosol are associated with metabolism of cellular proteins and lipids. Overall, our findings demonstrate that VG and PG, the main constituents of e-liquid formulations, when aerosolized through an e-cig device, are not harmless to the lungs, since they disrupt immune homeostasis.

Characterization of Endocannabinoid-Metabolizing Enzymes in Human Peripheral Blood Mononuclear Cells under Inflammatory Conditions

Endocannabinoid-metabolizing enzymes are downregulated in response to lipopolysaccharide (LPS)-induced inflammation in mice, which may serve as a negative feedback mechanism to increase endocannabinoid levels and reduce inflammation. Increased plasma levels of the pro-inflammatory cytokine interleukin-6 (IL-6) and decreased fatty acid amide hydrolase (FAAH) activity in peripheral lymphocytes from individuals diagnosed with Huntington’s disease (HD) suggests that a similar negative feedback system between inflammation and the endocannabinoid system operates in humans. We investigated whether CpG- (unmethylated bacterial DNA) and LPS-induced IL-6 levels in peripheral blood mononuclear cells (PBMCs) from non-HD and HD individuals modulated the activities of endocannabinoid hydrolases monoacylglycerol lipase (MAGL) and carboxylesterase (CES). Baseline plasma IL-6 levels and 2-arachidonoylglycerol (2-AG) hydrolytic activity in PBMC lysates were not different in HD and non-HD individuals. Inhibition of MAGL and CES1 activity in PBMCs using the inhibitors JZL184 and WWL113, respectively, demonstrated that MAGL was the dominant 2-AG hydrolytic enzyme in PBMCs, regardless of disease state. Correlative analyses of 2-AG hydrolytic activity versus enzyme abundance confirmed this conclusion. Flow cytometric analysis of PBMCs showed that MAGL and CES1 were primarily expressed in monocytes and to a lesser extent in lymphocytes. In conclusion, these data suggest that IL-6 did not influence 2-AG hydrolytic activity in human PBMCs; however, monocytic MAGL was shown to be the predominant 2-AG hydrolytic enzyme.