P450 isoforms in a murine macrophage cell line, RAW264.7, and changes in the levels of P450 isoforms by treatment of cells with lipopolysaccharide and interferon-gamma

Maternal DHA intake in mice increased DHA metabolites in the pup brain and ameliorated MeHg-induced behavioral disorder

Although pregnant women's fish consumption is beneficial for the brain development of the fetus due to the DHA in fish, seafood also contains methylmercury (MeHg), which adversely affects fetal brain development. Epidemiological studies suggest that high DHA levels in pregnant women's sera may protect the fetal brain from MeHg-induced neurotoxicity, but the underlying mechanism is unknown. Our earlier study revealed that DHA and its metabolite 19,20-dihydroxydocosapentaenoic acid (19,20-DHDP) produced by cytochrome P450s (P450s) and soluble epoxide hydrolase (sEH) can suppress MeHg-induced cytotoxicity in mouse primary neuronal cells. In the present study, DHA supplementation to pregnant mice suppressed MeHg-induced impairments of pups' body weight, grip strength, motor function, and short-term memory. DHA supplementation also suppressed MeHg-induced oxidative stress and the decrease in the number of subplate neurons in the cerebral cortex of the pups. DHA supplementation to dams significantly increased the DHA metabolites 19,20-epoxydocosapentaenoic acid (19,20-EDP) and 19,20-DHDP as well as DHA itself in the fetal and infant brains, although the expression levels of P450s and sEH were low in the fetal brain and liver. DHA metabolites were detected in the mouse breast milk and in human umbilical cord blood, indicating the active transfer of DHA metabolites from dams to pups. These results demonstrate that DHA supplementation increased DHA and its metabolites in the mouse pup brain and alleviated the effects of MeHg on fetal brain development. Pregnant women's intake of fish containing high levels of DHA (or DHA supplementation) may help prevent MeHg-induced neurotoxicity in the fetus.

CYP2C19 Contributes to THP-1-Cell-Derived M2 Macrophage Polarization by Producing 11,12- and 14,15-Epoxyeicosatrienoic Acid, Agonists of the PPARγ Receptor

Although the functional roles of M1 and M2 macrophages in the immune response and drug resistance are important, the expression and role of cytochrome P450s (CYPs) in these cells remain largely unknown. Differential expression of the 12 most common CYPs (CYP1A1, 1A2, 1B1, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 2J2, 3A4, and 3A5) were screened in THP-1-cell-derived M1 and M2 macrophages using reverse transcription PCR. CYP2C19 was highly expressed in THP-1-cell-derived M2 macrophages, but it was negligibly expressed in THP-1-cell-derived M1 macrophages at the mRNA and protein levels as analyzed by reverse transcription quantitative PCR and Western blot, respectively. CYP2C19 enzyme activity was also very high in THP-1-cell-derived M2 compared to M1 macrophages (> 99%, p < 0.01), which was verified using inhibitors of CYP2C19 activity. Endogenous levels of the CYP2C19 metabolites 11,12-epoxyeicosatrienoic acid (11,12-EET) and 14,15-EET were reduced by 40% and 50% in cells treated with the CYP2C19 inhibitor and by 50% and 60% in the culture medium, respectively. Both 11,12-EET and 14,15-EET were identified as PPARγ agonists in an in vitro assay. When THP-1-cell-derived M2 cells were treated with CYP2C19 inhibitors, 11,12- and 14,15-EETs were significantly reduced, and in parallel with the reduction of these CYP2C19 metabolites, the expression of M2 cell marker genes was also significantly decreased (p < 0.01). Therefore, it was suggested that CYP2C19 may contribute to M2 cell polarization by producing PPARγ agonists. Further studies are needed to understand the endogenous role of CYP2C19 in M2 macrophages with respect to immunologic function and cell polarization.

Toxicity to RAW264.7 Macrophages of Silica Nanoparticles and the E551 Food Additive, in Combination with Genotoxic Agents

Synthetic amorphous silica (SAS) is used in a plethora of applications and included in many daily products to which humans are exposed via inhalation, ingestion, or skin contact. This poses the question of their potential toxicity, particularly towards macrophages, which show specific sensitivity to this material. SAS represents an ideal candidate for the adsorption of environmental contaminants due to its large surface area and could consequently modulate their toxicity. In this study, we assessed the toxicity towards macrophages and intestinal epithelial cells of three SAS particles, either isolated SiO₂ nanoparticles (LS30) or SiO₂ particles composed of agglomerated-aggregates of fused primary particles, either food-grade (E551) or non-food-grade (Fumed silica). These particles were applied to cells either alone or in combination with genotoxic co-contaminants, i.e., benzo[a]pyrene (B[a]P) and methane methylsulfonate (MMS). We show that macrophages are much more sensitive to these toxic agents than a non-differenciated co-culture of Caco-2 and HT29-MTX cells, used here as a model of intestinal epithelium. Co-exposure to SiO₂ and MMS causes DNA damage in a synergistic way, which is not explained by the modulation of DNA repair protein mRNA expression. Together, this suggests that SiO₂ particles could adsorb genotoxic agents on their surface and, consequently, increase their DNA damaging potential.

Deactivation of 12(S)-HETE through (ω-1)-hydroxylation and β-oxidation in alternatively activated macrophages

Polarization of macrophages to proinflammatory M1 and to antiinflammatory alternatively activated M2 states has physiological implications in the development of experimental hypertension and other pathological conditions. 12/15-Lipoxygenase (12/15-LO) and its enzymatic products 12(S)- and 15(S)-hydroxyeicosatetraenoic acid (HETE) are essential in the process since disruption of the gene encoding 12/15-LO renders the mice unsusceptible to hypertension. The objective was to test the hypothesis that M2 macrophages catabolize 12(S)-HETE into products that are incapable of promoting vasoconstriction. Cultured M2 macrophages metabolized externally added [14C]12(S)-HETE into more polar metabolites, while M1 macrophages had little effect on the catabolism. The major metabolites were identified by mass spectrometry as (ω-1)-hydroxylation and β-oxidation products. The conversion was inhibited by both peroxisomal β-oxidation inhibitor, thioridazine, and cytochrome P450 inhibitors. Quantitative PCR analysis confirmed that several cytochrome P450 enzymes (CYP2E1 and CYP1B1) and peroxisomal β-oxidation markers were upregulated upon M2 polarization. The identified 12,19-dihydroxy-5,8,10,14-eicosatetraenoic acid and 8-hydroxy-6,10-hexadecadienoic acid metabolites were tested on abdominal aortic rings for biological activity. While 12(S)-HETE enhanced vasoconstrictions to angiotensin II from 15% to 25%, the metabolites did not. These results indicate that M2, but not M1, macrophages degrade 12(S)-HETE into products that no longer enhance the angiotensin II-induced vascular constriction, supporting a possible antihypertensive role of M2 macrophages.

Particulate emissions from modern and old technology wood combustion induce distinct time-dependent patterns of toxicological responses in vitro

Toxicological characterisation of combustion emissions in vitro are often conducted with macrophage cell lines, and the majority of these experiments are based on responses measured at 24h after the exposure. The aim of this study was to investigate how significant role time course plays on toxicological endpoints that are commonly measured in vitro. The RAW264.7 macrophage cell line was exposed to PM₁ samples (150μg/ml) from biomass combustion devices representing old and modern combustion technologies for 2, 4, 8, 12, 24 and 32h. After the exposure, cellular metabolic activity, cell membrane integrity, cellular DNA content, DNA damage and production of inflammatory markers were assessed. The present study revealed major differences in the time courses of the responses, statistical differences between the studied samples mostly limiting to differences between modern and old technology samples. Early stage responses consisted of disturbances in metabolic activity and cell membrane integrity. Middle time points revealed increases in chemokine production, whereas late-phase responses exhibited mostly increased DNA-damage, decreased membrane integrity and apoptotic activity. Altogether, these results implicate that the time point of measurement has to be considered carefully, when the toxicity of emission particles is characterised in in vitro study set-ups.

Isoform-specific expression and induction of udp-glucuronosyltransferase in immunoactivated peritoneal macrophages of the rat

Phase I drug-metabolizing enzymes such as cytochrome P450 in immunocytes are known to play a role in metabolic activation of toxic and immunosuppressive compounds such as polycyclic aromatic hydrocarbon (PAH). UDP-glucuronosyltransferase (UGT), a drug-metabolizing phase II enzyme, accelerates elimination of these compounds; however, there is little information on the expression and function of UGT in immunocytes. In this study, we investigated the expressions of UGT isoforms in rat peritoneal macrophages and the role of UGT in macrophage functions. Expressions of UGT1A1, 1A6, and 1A7 were observed in macrophages by immunohistochemical staining and reverse transcriptase-polymerase chain reaction. When macrophage cells cultured in plates were exposed to 1-naphthol and 3-hydroxybenzo-[a]pyrene (3-OH-B[a]P), these glucuronides increased in the medium, indicating that macrophages glucuronidated the chemicals. The production of the glucuronides of 1-naphthol and 3-OH-B[a]P was induced by lipopolysaccharide (LPS) treatment of the cultured macrophage cells. Northern blot analysis revealed that UGT1A7 mRNA was induced by LPS treatment. This result is the first evidence that a drug-metabolizing enzyme is induced by immunoactivation. The results indicated that macrophages can detoxify various toxic and immunosuppressive compounds with UGT, and that ability is enhanced by immunoactivation. We propose that macrophages contribute to protection against not only macromolecules as immunocytes but also small molecules such as the immunosuppressive agents PAHs in peripheral blood and interstitial tissues.

CHARACTERIZATION OF MOUSE SMALL INTESTINAL CYTOCHROME P450 EXPRESSION

The expression of biotransformation enzymes in mouse small intestine is poorly characterized, which limits the utility of transgenic or knockout mouse models for first-pass drug metabolism studies. In response, we have systematically examined the composition and inducibility of cytochrome P450 (P450) protein and mRNA in mouse small intestinal epithelial cells (enterocytes). RNA-PCR was conducted to confirm the expression and identity of CYP1A1, 1B1, 2B10, 2B19, 2B20, 2C29, 2C38, 2C40, 2E1, 3A11, 3A13, 3A16, 3A25, and 3A44 in the enterocytes of untreated mice, but CYP1A2, 2A4/5, 2A12, 2C37, 2C39, and 2F2 were not detected. The inducibility of CYP2B, 2C, and 3A subfamily forms was determined by real-time quantitative RNA-PCR. All five CYP3A forms were induced, in a range from 1.7- to 4.5-fold, by dexamethasone (DEX). Phenobarbital (PB) induced CYP2B9, CYP2B10, and CYP2B20 mRNAs and suppressed CYP2B19 mRNA levels. PB also induced CYP2C29 and CYP2C40, but not CYP2C38 mRNA. At the protein level, CYP1A1, CYP1B1, CYP2B, CYP2C, CYP2E1, and CYP3A were detected in enterocytes from untreated mice by immunoblot analysis. CYP1A1 was inducible by beta-naphthoflavone (BNF), CYP2B and CYP2C by PB, and CYP3A by DEX. CYP2B, 2C, and 3A proteins were all expressed at high levels proximally, and decreased distally. The inducibility of CYP1A1 followed a similar pattern. Intestinal P450 expression was compared between C57BL/6 (B6) and 129/sv (129) mice, strains commonly used in the preparation of transgenic and knockout mouse models. There was no significant strain difference in constitutive levels or induction patterns for CYP2B, 2C, and 3A protein. However, CYP1A1 was induced to a high level by BNF in B6 mice, but was not induced in the 129 mice.

Characterization and identification of cytochrome P450 metabolites of arachidonic acid released by human peritoneal macrophages obtained from the pouch of Douglas

Cytochrome P450 metabolism of arachidonic acid (AA) was investigated in human peritoneal macrophages which play a central role in chronic pelvic diseases in women (for example in endometriosis). The formation of eicosanoids other than prostaglandins (PGs) by these cells is still unknown. In non-activated macrophages obtained from women in the reproductive age, the main [(3)H]-AA metabolites coeluted with epoxyeicosatrienoic acids, dihydroxyeicosatrienoic acids (DHETs) and hydroxyeicosatetraenoic acids (HETEs) in reverse-phase HPLC. After zymosan activation a shift to PGs pathway was observed. Treatment with low doses of 2,3,7,8-tetrachlorodibenzo- p -dioxin increased the formation of a metabolite coeluting with 5,6-DHET. By gas chromatography/mass spectrometry 5,6-DHET (after beta-naphthoflavone induction), and 14,15-DHET as well as 11,12-DHET (after AA stimulation) were identified as major epoxygenase metabolites, respectively. The enantioselective formation of 12(S)-HETE was demonstrated by chiral-phase HPLC. Our findings demonstrate that non-activated peritoneal macrophages produce substantial amounts of bioactive cytochrome P450 metabolites of AA.