Pei H. Cui

The ω-3 epoxide of eicosapentaenoic acid inhibits endothelial cell proliferation by p38 MAP kinase activation and cyclin D1/CDK4 down-regulation.

BACKGROUND AND PURPOSE Dietary intake of ω‐3 polyunsaturated fatty acids (ω‐3 PUFAs) like eicosapentaenoic acid (EPA) decreases cancer risk, while arachidonic acid and other ω‐6 PUFAs increase risk, but the underlying mechanisms are unclear. Cytochrome P450 (CYP)‐derived epoxides contribute to enhanced tumourigenesis due to ω‐6 PUFA intake. Thus, ω‐6 arachidonic acid epoxides (EETs) inhibit apoptosis and stimulate proliferation by up‐regulating cyclin D1 expression in cells. The present study evaluated the corresponding ω‐3 PUFA epoxides and assessed their role in the regulation of cell proliferation.

Functional characterization of nonsynonymous single nucleotide polymorphisms in the human organic anion transporter 4 (hOAT4)

Background and purpose:  The human organic anion transporter (hOAT) family of transmembrane carrier proteins mediate the cellular flux of anionic substances, including certain hormones and anti‐cancer drugs. hOAT4 is highly expressed at the apical membrane of the renal tubular cell and facilitates drug re‐absorption in the kidney. In the present study, the impact of 10 nonsynonymous single nucleotide polymorphisms (SNPs) of hOAT4 on transport function in COS‐7 cells was characterized.

Functional analysis of novel polymorphisms in the human SLCO1A2 gene that encodes the transporter OATP1A2.

The solute carrier organic anion transporting polypeptide 1A2 (OATP1A2, SLCO1A2) is implicated in the cellular influx of a number of drugs. We identified five novel single nucleotide polymorphisms (SNPs) in coding exons of the SLCO1A2 gene in a cohort of subjects: G550A, G553A, G673A, A775C, and G862A, that encoded the OATP1A2 variants E184K, D185N, V255I, T259P, and D288N, respectively. The function and expression of these variant transporters were assessed in HEK-293 cells. We found that the novel variants, E184K, D185N, T259P, and D288N, were associated with impaired estrone-3-sulfate, imatinib, and methotrexate transport (∼20–50% of wild-type control); function was retained by OATP1A2-V255I. From biotinylation assays, the decreased function of these variants was due, at least in part, to impaired plasma membrane expression. The four loss-of-function variants were studied further using mutagenesis to produce variants that encode residues with different charges or steric properties. From immunoblotting, the replacement of negatively charged residues at amino acid positions 184 and 185 impaired membrane expression, while either a positive or negative charge at residue 288 supported the correct membrane targeting of OATP1A2. Replacement of T259 with bulky residues disrupted transporter stability. From molecular models, E184, D185, and D288 were located near several charged residues such that intramolecular ionic interactions may stabilize the transporter structure. Individuals who carry these novel SNPs in the SLCO1A2 gene may be at risk from impaired efficacy or enhanced toxicity during treatment with drugs that are substrates for OATP1A2.

Antiproliferative and Antimigratory Actions of Synthetic Long Chain n-3 Monounsaturated Fatty Acids in Breast Cancer Cells That Overexpress Cyclooxygenase-2

Cyclooxygenase-2 (COX-2) is overexpressed in many human cancers and converts the n-6 polyunsaturated fatty acid (PUFA) arachidonic acid to prostaglandin E(2) (PGE(2)), which drives tumorigenesis; in contrast, n-3 PUFA inhibit tumorigenesis. We tested the hypothesis that these antitumor actions of n-3 PUFA may involve the n-3 olefinic bond. n-3 Monounsaturated fatty acids (MUFAs) of chain length C16-C22 were synthesized and evaluated in MDA-MB-468 breast cancer cells that stably overexpressed COX-2 (MDA-COX-2 cells). Longer chain (C19-C22) n-3 MUFAs inhibited proliferation, activated apoptosis, decreased PGE(2) formation, and decreased cell invasion; C16-C18 analogues were less active. Molecular modeling showed that interactions of Arg120, Tyr355, and several hydrophobic amino acid residues in the COX-2 active site with C19-C22 MUFA analogues were favored. Thus, longer-chain n-3 MUFAs may be prototypes of novel anticancer agents that decrease the formation of PGE(2) in tumor cells that contain high levels of COX-2.

Impaired transactivation of the human CYP2J2 arachidonic acid epoxygenase gene in HepG2 cells subjected to nitrative stress

Background and purpose:  Human cytochrome P450 2J2 (CYP2J2) generates epoxyfatty acids that modulate cellular apoptosis and proliferation. CYP2J2 regulation has not been intensively studied but induction of the activator protein‐1 (AP‐1) subunit c‐fos mediates CYP2J2 down‐regulation in hypoxia, a component of ischaemic injury. Decreased CYP2J2 expression may contribute to tissue injury.

Monoepoxy octadecadienoates and monoepoxy octadecatrienoates 2: mass spectral characterization

Methyl esters of C18 polyunsaturated fatty acids, including gamma-linolenic acid, alpha-linolenic acid and stearidonic acid, were epoxidised using m-chloroperbenzoic acid. Nine monoepoxides were obtained by normal-phase HPLC, identified using LC-MS and NMR, and characterized by NMR spectroscopy and mass spectrometry. This study is focused on structural characterization using LC-MS and LC/APCI/MS/MS. The elution profiles of these monoepoxides in RP-HPLC are determined as 12,13->9,10->6,7-epoxy, 9,10->15,16->12,13-epoxy and 15,16->12,13->9,10-epoxy derivatives of gamma-linolenic, alpha-linolenic and stearidonic acid methyl esters, respectively. The major diagnostic fragmentations in MS/MS identified are postulated to be induced by cleavages of the epoxide ring and alpha-bond cleavage to the epoxy group from [M+H]+ and/or [M+H-MeOH]+.

Monoepoxy octadecadienoates and monoepoxy octadecatrienoates

Methyl esters of gamma-linolenic acid, alpha-linolenic acid and stearidonic acid were epoxidised using m-chloroperbenzoic acid to achieve nine cis-monoepoxy-C18 fatty acid methyl esters (FAMEs), including novel methyl cis-monoepoxy derivatives of stearidonic acid and a cis-6,7-epoxy derivative of gamma-linolenic acid. These nine monoepoxy FAMEs were purified by normal-phase HPLC, identified by LC-MS, 1H and 13C NMR, and characterized by mass spectrometry and NMR spectroscopy. This study is focused on structural characterization of these C18 monoepoxy FAMEs using techniques in NMR spectroscopy including 1H, 13C, 1H-1H correlated spectroscopy (COSY) and 1H-13C heteronuclear correlation (HETCOR). The proton and carbon NMR chemical shifts of the epoxide, the double bonds, and the interrupted methylenes are assigned. Also discussed is an interpretation of the 1H and 13C NMR spectra of these monoepoxides including the changes in the 13C resonance of the olefinic carbons on the neighboring double bonds resulting from epoxide formation.

Synthesis and NMR characterization of the methyl esters of eicosapentaenoic acid monoepoxides

The activities of cytochrome P450-derived epoxide metabolites of omega-6 polyunsaturated fatty acids (PUFAs) in cellular homeostasis have generated considerable topical interest, but there is less information on the effects of omega-3 PUFA epoxides. Mass spectroscopic data on the epoxides of the omega-3 PUFA eicosapentaenoic acid (EPA) have been reported but the absence of corresponding NMR data currently hinders their biological assessment. In the present study five monoepoxy derivatives of EPA methyl ester were synthesized by treating EPA methyl ester with m-chloroperbenzoic acid. The individual regioisomers were purified by normal-phase chromatography and characterized by LC-MS/MS and a combination of NMR approaches including (1)H-, (13)C-, (1)H-(1)H-COSY, (1)H-(13)C-HSQC, and (1)H-(13)C-HMBC. The chromatographic properties for these monoepoxides were studied in normal-phase and reversephase-HPLC systems and the MS/MS fragmentation patterns using electrospray ionization were established. This paper also focuses on the NMR characterization of epoxide, olefinic and methylenic moieties and the complete assignments of the isomers.

Roles of Mitogen-Activated Protein Kinases in the Regulation of CYP Genes

Cells undergo phenotypic changes after exposure to a wide range of exogenous stimuli that include growth factors, proinflammatory cytokines and environmental chemicals. Such stimuli may arise as components of disease pathogenesis and cellular injury, or as a result of exposure to environmental chemicals and radiation. These stimuli modulate the proliferation and differentiation of cells by altering the regulation of genes that control homeostasis. A generalized response appears to be a decline in the expression and function of many cytochrome P450 (CYP) genes in liver and other tissues. Thus, individuals who have been exposed to such exogenous stimuli often exhibit a decreased capacity for drug clearance, which has important consequences for concurrent drug therapy. Several signaling pathways transduce exogenous stimuli within cells, with the mitogen-activated protein kinases (MAPKs) being one of the most important. Evidence is increasing that MAPKs may impair the expression of multiple CYP genes by modulating the activity of transcription factors, including nuclear receptors, the aryl hydrocarbon receptor, and the activator protein-1 complex. MAPKs catalyze the phosphorylation of transcription complexes that incorporate these factors, which modulates their capacity to transactivate target genes, including CYPs. An understanding of the mechanisms that account for the regulatory impact of MAPKs on the transcriptional factors that regulate CYP genes will provide critical insight into the consequences from exposure to injurious stresses that impact cellular function.

Activation of the pro-migratory bone morphogenetic protein receptor 1B gene in human MDA-MB-468 triple-negative breast cancer cells that over-express CYP2J2

Secondary metastases are the leading cause of mortality in patients with breast cancer. Cytochrome P450 (CYP) 2J2 (CYP2J2) is upregulated in many human tumors and generates epoxyeicosanoids from arachidonic acid that promote tumorigenesis and metastasis, but at present there is little information on the genes that mediate these actions. In this study MDA-MB-468 breast cancer cells were stably transfected with CYP2J2 (MDA-2J2 cells) and Affymetrix microarray profiling was undertaken. We identified 182 genes that were differentially expressed in MDA-2J2 cells relative to control (MDA-CTL) cells (log[fold of control] ≥2). From gene ontology pathway analysis bone morphogenetic protein (BMP) receptor 1B (BMPR1B) emerged as an important upregulated gene in MDA-2J2 cells. Addition of the BMPR1B ligand BMP2 stimulated the migration of MDA-2J2 cells, but not MDA-CTL cells, from 3D-matrigel droplets. Migration of MDA-2J2 cells was prevented by the BMPR antagonist dorsomorphin. These findings indicate that over-expression of CYP2J2 in MDA-MB-468-derived breast cancer cells activates BMPR1B expression that may contribute to increased migration. Targeting BMPR1B may be a novel approach to inhibit the metastatic activity of breast cancers that contain high levels of CYP2J2.