Demonstration of mRNA for five species of cytochrome P450 in human bone marrow, bone marrow-derived macrophages and human haemopoietic cell lines

Recent Advances in Models of Immune-Mediated Drug-Induced Liver Injury

Hepatic inflammation is a key feature of a variety of liver diseases including drug-induced liver injury (DILI), orchestrated by the innate immune response (Kupffer cells, monocytes, neutrophils, dendritic cells) and the adaptive immune system (T cells and natural killer T cells). In contrast to acute DILI, prediction of immune-mediated DILI (im-DILI) has been more challenging due to complex disease pathogenesis, lack of reliable models and limited knowledge of underlying mechanisms. This review summarizes in vivo and in vitro systems that have been used to model im-DILI. In particular, the review focuses on state-of-the-art in vitro human-based multicellular models which have been developed to supplement the use of in vivo models due to interspecies variation and increasing ethical concerns regarding animal use. Advantages of the co-cultures in maintaining hepatocyte functions and importantly, introducing heterotypic cell-cell interactions to mimic inflammatory hepatic microenvironment are discussed. Challenges regarding cell source and incorporation of different cells with physical cell-cell contact are outlined and potential solutions are proposed. It is likely that better understanding of the interplay of immune cells in liver models will allow for the development of more accurate systems to better predict hepatotoxicity and stratification of drugs that can cause immune-mediated effects.

Human Immunodeficiency Virus Persistence in the Spleen: Opportunities for Pharmacologic Intervention

The persistence of HIV in the spleen, despite combination antiretroviral therapy, is not well understood. Sustained immune dysregulation and delayed immune recovery, in addition to immune cell exhaustion, may contribute to persistence of infection in the spleen. Eliminating HIV from this secondary lymphoid organ will require a thorough understanding of antiretroviral (ARV) pharmacology in the spleen, which has been minimally investigated. Low ARV exposure within the spleen may hinder the achievement of a functional or sterilizing cure if cells are not protected from HIV infection. In this study, we provide an overview of the anatomy and physiology of the spleen, review the evidence of the spleen as a site for persistence of HIV, discuss the consequences of persistence of HIV in the spleen, address challenges to eradicating HIV in the spleen, and examine opportunities for future curative efforts.

Investigation of 1,2-Dimyristoyl-sn-Glycero-3-Phosphoglycerol-Sodium (DMPG-Na) Lipid with Various Metal Cations in Nanocochleate Preformulation: Application for Andrographolide Oral Delivery in Cancer Therapy

This study aimed at carrying out a preformulation investigation of nanocochleates (NCs) and develop andrographolide-loaded nanocochleates. Preformulation study comprised of exploring the effect of trivalent and divalent ions on transition temperature (TT) of lipid (DMPG-Na), on particle size (PS), entrapment efficacy (EE), zeta potential (ZP) of NCs, and effect of NCs on change in lipid solubility post-NC formation. Further, the andrographolide-loaded nanocochleates made with CaCl₂ (ANDNCs) were characterized for ZP, PS, EE, X-ray powder diffraction (PXRD), differential scanning calorimetry (DSC), transition electron microscopy (TEM), in vitro release studies, in vitro anticancer potential on the cell line of human breast cancer (MCF-7), in vivo oral pharmacokinetic studies, and tissue distribution in female Wistar rats. Nanocochleates developed with CaCl₂ had a significant reduction in PS (1.78-fold) and ZP (1.38-fold), and elevation of EE (1.17-fold) as compared to AlCl₃ developed NCs. Trivalent ions demonstrated elevation of TT as compared to divalent ions. Spiral-shaped ANDNCs demonstrated ZP, PS, and EE of - 121.46 ± 15.12 mV, 360 ± 47 nm, and 68.12 ± 3.81% respectively. In vitro release study of ANDNCs showed a strong pH-dependent release profile due to hydrogen bonding between NCs and andrographolide (AND). Formulated ANDNCs demonstrated 26.99-fold decrease in IC50 value as compared to free AND. Additionally, the oral bioavailability of AND from ANDNCs improved by 1.81-fold as compared to free AND. Furthermore, ANDNCs showed minimum accumulation within the vital organs such as liver, kidney, and spleen. Briefly, the preformulation study laid a platform for better understanding the NCs and its components. Further, developed ANDNCs revealed superior physiochemical properties to be used as an alternative for a clinical setting.

Antiretroviral Penetration and Drug Transporter Concentrations in the Spleens of Three Preclinical Animal Models and Humans

Adequate antiretroviral (ARV) concentrations in lymphoid tissues are critical for optimal antiretroviral therapy (ART). While the spleen contains 25% of the body's lymphocytes, there are minimal data on ARV penetration in this organ. This study quantified total and protein-unbound splenic ARV concentrations and determined whether drug transporters, sex, or infection status were modifiers of these concentrations in animal models and humans. Two humanized mice models (hu-HSC-Rag [n = 36; 18 HIV-positive (HIV⁺) and 18 HIV-negative (HIV^-)] and bone marrow-liver-thymus [n = 13; 7 HIV⁺ and 6 HIV^-]) and one nonhuman primate (NHP) model (rhesus macaque [n = 18; 10 SHIV⁺ and 8 SHIV^-]) were dosed to steady state with ARV combinations. HIV⁺ human spleens (n = 14) from the National NeuroAIDS Tissue Consortium were analyzed postmortem (up to 24 h postdose). ARV concentrations were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), drug transporter concentrations were measured with LC-MS proteomics, and protein binding in NHP spleens was determined by rapid equilibrium dialysis. Mice generally had the lowest splenic concentrations of the three species. Protein binding in splenic tissue was 6 to 96%, compared to 76 to 99% in blood plasma. NHPs had quantifiable Mrp4, Bcrp, and Ent1 concentrations, and humans had quantifiable ENT1 concentrations. None significantly correlated with tissue ARV concentrations. There was also no observable influence of infection status or sex. With these dosing strategies, NHP splenic penetration most closely resembled that of humans. These data can inform tissue pharmacokinetic scaling to humans to target HIV reservoirs by identifying important species-related differences.

Cell-type-resolved proteomic analysis of the human liver

BACKGROUND & AIMS

The human liver functions through a complex interplay between parenchymal and non-parenchymal cells. Mass spectrometry-based proteomic analysis of intact tissue has provided an in-depth view of the human liver proteome. However, the predominance of parenchymal cells (hepatocytes) means that the total tissue proteome mainly reflects hepatocyte expression. Here we therefore set out to analyse the proteomes of the major parenchymal and non-parenchymal cell types in the human liver.

METHODS

We applied quantitative label-free proteomic analysis on the major cell types of the human liver: hepatocytes, liver endothelial cells, Kupffer cells and hepatic stellate cells.

RESULTS

We identified 9791 proteins, revealing distinct protein expression profiles across cell types, whose in vivo relevance was shown by the presence of cell-type-specific proteins. Analysis of proteins related to the immune system indicated that mechanisms of immune-mediated liver injury include the involvement of several cell types. Furthermore, in-depth investigation of proteins related to the absorption, distribution, metabolism, excretion and toxicity (ADMET) of xenobiotics showed that ADMET-related tasks are not exclusively confined to hepatocytes, and that non-parenchymal cells may contribute to drug transport and metabolism.

CONCLUSIONS

Overall, the data we provide constitute a unique resource for exploring the proteomes of the major types of human liver cells, which will facilitate an improved understanding of the human liver in health and disease.

Comparison of cytochrome P450 expression in four different human osteoblast models

Cytochromes P450 (CYPs) are important for bone homeostasis, but only limited information is available on their expression in human bone cells. We analyzed the expression levels of eight CYPs in osteoblasts cultured in human bone pieces, in osteoblasts differentiated from human periosteum mesenchymal stem cells, in primary human osteoblasts and in the human osteoblast cell line MG63, respectively. Our results confirm previous reports about the presence of CYP11A1, CYP17A1, CYP24A1 and CYP27B1, while demonstrating expression of CYP2E1, CYP26A1, CYP39A1 and CYP51A1 for the first time. However, expression patterns in the four models were remarkably different from each other.

Expression of CYP4V2 in human THP1 macrophages and its transcriptional regulation by peroxisome proliferator-activated receptor gamma

Because macrophages respond to a variety of pathological and pharmacological reagents, understanding the role of P450s in macrophages is important for therapeutic intervention. There has been a lack of research on CYP4 in macrophages, but fatty acid accumulation and lipid trafficking in macrophages have been suggested to be a main cause of atherosclerosis. All human CYP4 genes (n=12) were screened in THP1 macrophages by gene-specific reverse transcriptase-polymerase chain reaction (RT-PCR). Only CYP4V2 exhibited strong expression of both mRNA and protein. Expression levels of both CYP4V2 mRNA and protein were significantly reduced after treatment with peroxisome proliferator-activated receptor gamma (PPARγ) antagonist GW9662. However, the expression levels of CYP4V2 were not changed by PPARα antagonist (GW6471) and liver X receptor alpha antagonist (22-S hydroxycholesterol). A metabolite of the CYP4V2 enzyme, 12-hydroxydodecanoic acid, was detected in THP1 macrophages, and this metabolite was significantly decreased after treatment with the PPARγ inhibitor GW9662 (>80% decreased, p<0.05). In summary, fatty acid metabolizing protein CYP4V2 was identified in human THP1 macrophages, and its expression was regulated by PPARγ. Further study is required to understand the role of CYP4V2 with regard to fat accumulation in the activated macrophage and atherosclerotic plaque development.

Emerging Role of the Spleen in the Pharmacokinetics of Monoclonal Antibodies, Nanoparticles and Exosomes

After being absorbed, drugs distribute in the body in part to reach target tissues, in part to be disposed in tissues where they do not exert clinically-relevant effects. Therapeutically-relevant effects are usually terminated by drug metabolism and/or elimination. The role that has been traditionally ascribed to the spleen in these fundamental pharmacokinetic processes was definitely marginal. However, due to its high blood flow and to the characteristics of its microcirculation, this organ would be expected to be significantly exposed to large, new generation drugs that can hardly penetrate in other tissues with tight endothelial barriers. In the present review, we examine the involvement of the spleen in the disposition of monoclonal antibodies, nanoparticles and exosomes and the possible implications for their therapeutic efficacy and toxicity. The data that we will review lead to the conclusion that a new role is emerging for the spleen in the pharmacokinetics of new generation drugs, hence suggesting that this small, neglected organ will certainly deserve stronger attention by pharmacologists in the future.

Tobacco smoking effect on HIV-1 pathogenesis: role of cytochrome P450 isozymes

INTRODUCTION

Tobacco smoking is highly prevalent among the HIV-1-infected population. In addition to diminished immune response, smoking has been shown to increase HIV-1 replication and decrease response to antiretroviral therapy, perhaps through drug-drug interaction. However, the mechanism by which tobacco/nicotine increases HIV-1 replication and mediates drug-drug interaction is poorly understood.

AREAS COVERED

In this review, the authors discuss the effects of smoking on HIV-1 pathogenesis. Since they propose a role for the cytochrome P450 (CYP) pathway in smoking-mediated HIV-1 pathogenesis, the authors briefly converse the role of CYP enzymes in tobacco-mediated oxidative stress and toxicity. Finally, the authors focus on the role of CYP enzymes, especially CYP2A6, in tobacco/nicotine metabolism and oxidative stress in HIV-1 model systems monocytes/macrophages, lymphocytes, astrocytes and neurons, which may be responsible for HIV-1 pathogenesis.

EXPERT OPINION

Recent findings suggest that CYP-mediated oxidative stress is a novel pathway that may be involved in smoking-mediated HIV-1 pathogenesis, including HIV-1 replication and drug-drug interaction. Thus, CYP and CYP-associated oxidative stress pathways may be potential targets to develop novel pharmaceuticals for HIV-1-infected smokers. Since HIV-1/TB co-infections are common, future study involving interactions between antiretroviral and antituberculosis drugs that involve CYP pathways would also help treat HIV-1/TB co-infected smokers effectively.

Alcohol dehydrogenase- and rat liver cytosol-dependent bioactivation of 1-chloro-2-hydroxy-3-butene to 1-chloro-3-buten-2-one, a bifunctional alkylating agent

1,3-Butadiene (BD) is an air pollutant whose toxicity and carcinogenicity have been considered primarily mediated by its reactive metabolites, 3,4-epoxy-1-butene and 1,2,3,4-diepoxybutane, formed in liver and extrahepatic tissues by cytochromes P450s. A possible alternative metabolic pathway in bone marrow and immune cells is the conversion of BD to the chlorinated allylic alcohol 1-chloro-2-hydroxy-3-butene (CHB) by myeloperoxidase in the presence of hydrogen peroxide and chloride ion. In the present study, we investigated the in vitro bioactivation of CHB by alcohol dehydrogenases (ADH) under in vitro physiological conditions (pH 7.4, 37 °C). The results provide clear evidence for CHB being converted to 1-chloro-3-buten-2-one (CBO) by purified horse liver ADH and rat liver cytosol. CBO readily reacted with glutathione (GSH) under assay conditions to form three products: two CBO-mono-GSH conjugates [1-chloro-4-(S-glutathionyl)butan-2-one (3) and 1-(S-glutathionyl)-3-buten-2-one (4)] and one CBO-di-GSH conjugate [1,4-bis(S-glutathionyl)butan-2-one (5)]. CHB bioactivation and the ratios of the three GSH conjugates formed were dependent upon incubation time, GSH and CHB concentrations, and the presence of ADH or rat liver cytosol. The ADH enzymatic reaction followed Michaelis-Menten kinetics with a K(m) at 3.5 mM and a k(cat) at 0.033 s(-1). After CBO was incubated with freshly isolated mouse erythrocytes, globin dimers were detected using SDS-PAGE and silver staining, providing evidence that CBO can act as a protein cross-linking agent. Collectively, the results provide clear evidence for CHB bioactivation by ADH and rat liver cytosol to yield CBO. The bifunctional alkylating ability of CBO suggests that it may play a role in BD toxicity and/or carcinogenicity.

Chemical inhibitors of cytochrome P450 isoforms in human liver microsomes: a re-evaluation of P450 isoform selectivity

The majority of marketed small-molecule drugs undergo metabolism by hepatic Cytochrome P450 (CYP) enzymes (Rendic 2002). Since these enzymes metabolize a structurally diverse number of drugs, metabolism-based drug-drug interactions (DDIs) can potentially occur when multiple drugs are coadministered to patients. Thus, a careful in vitro assessment of the contribution of various CYP isoforms to the total metabolism is important for predicting whether such DDIs might take place. One method of CYP phenotyping involves the use of potent and selective chemical inhibitors in human liver microsomal incubations in the presence of a test compound. The selectivity of such inhibitors plays a critical role in deciphering the involvement of specific CYP isoforms. Here, we review published data on the potency and selectivity of chemical inhibitors of the major human hepatic CYP isoforms. The most selective inhibitors available are furafylline (in co-incubation and pre-incubation conditions) for CYP1A2, 2-phenyl-2-(1-piperidinyl)propane (PPP) for CYP2B6, montelukast for CYP2C8, sulfaphenazole for CYP2C9, (-)-N-3-benzyl-phenobarbital for CYP2C19 and quinidine for CYP2D6. As for CYP2A6, tranylcypromine is the most widely used inhibitor, but on the basis of initial studies, either 3-(pyridin-3-yl)-1H-pyrazol-5-yl)methanamine (PPM) and 3-(2-methyl-1H-imidazol-1-yl)pyridine (MIP) can replace tranylcypromine as the most selective CYP2A6 inhibitor. For CYP3A4, ketoconazole is widely used in phenotyping studies, although azamulin is a far more selective CYP3A inhibitor. Most of the phenotyping studies do not include CYP2E1, mostly because of the limited number of new drug candidates that are metabolized by this enzyme. Among the inhibitors for this enzyme, 4-methylpyrazole appears to be selective.

Tertiary-Butanol: a toxicological review

Tert-Butanol is an important intermediate in industrial chemical synthesis, particularly of fuel oxygenates. Human exposure to tert-butanol may occur following fuel oxygenate metabolism or biodegradation. It is poorly absorbed through skin, but is rapidly absorbed upon inhalation or ingestion and distributed to tissues throughout the body. Elimination from blood is slower and the half-life increases with dose. It is largely metabolised by oxidation via 2-methyl-1,2-propanediol to 2-hydroxyisobutyrate, the dominant urinary metabolites. Conjugations also occur and acetone may be found in urine at high doses. The single-dose systemic toxicity of tert-butanol is low, but it is irritant to skin and eyes; high oral doses produce ataxia and hypoactivity and repeated exposure can induce dependence. Tert-Butanol is not definable as a genotoxin and has no effects specific for reproduction or development; developmental delay occurred only with marked maternal toxicity. Target organs for toxicity clearly identified are kidney in male rats and urinary bladder, particularly in males, of both rats and mice. Increased tumour incidences observed were renal tubule cell adenomas in male rats and thyroid follicular cell adenomas in female mice and, non-significantly, at an intermediate dose in male mice. The renal adenomas were associated with alpha(2u)-globulin nephropathy and, to a lesser extent, exacerbation of chronic progressive nephropathy. Neither of these modes of action can function in humans. The thyroid tumour response could be strain-specific. No thyroid toxicity was observed and a study of hepatic gene expression and enzyme induction and thyroid hormone status has suggested a possible mode of action.

Losartan inhibits LPS-induced inflammatory signaling through a PPARgamma-dependent mechanism in human THP-1 macrophages

Macrophages have critical roles in the pathogenesis of atherosclerosis by activating the innate immune system and producing inflammatory cytokines. Accumulating evidence indicates that angiotensin type 1 receptor (AT1R) blockers exert anti-inflammatory effects in inflammatory diseases including atherosclerosis. In this study, we investigated the effect of losartan, an AT1R blocker, on the proinflammatory gene expression induced by bacterial lipopolysaccharide (LPS) in a well-defined in vitro human THP-1 macrophage system. We found that losartan significantly attenuated the LPS-induced expression of proinflammatory genes TNF-alpha, IL-8 and COX-2. However, exogenous angiotensin II (AngII) had no effect on LPS-induced inflammatory signaling despite the expression of AT1R. In addition, losartan did not block LPS-induced IkappaB phosphorylation, which is downstream of Toll-like receptor activation. Peroxisome proliferator-activated receptor-gamma (PPARgamma) antagonists, GW9662 and T0070907, reversed the inhibitory effects of losartan on LPS-induced TNF-alpha and IL-8 expression in THP-1 macrophages. These observations suggest that losartan inhibits LPS-induced proinflammatory gene expression in macrophages by activating the PPARgamma pathway rather than by the competitive inhibition of AT1R binding to AngII.

Expression of the cytochrome P450 epoxygenase CYP2J2 in human monocytic leukocytes

CYP2J2 is one of the cytochrome P450 epoxygenases involved in the metabolism of arachidonic acid. CYP2J2 has been identified in several tissues, especially cardiovascular tissues. CYP2J2 has cardiovascular effects, as epoxyeicosatrienoic acid, one of its metabolites, has anti-inflammatory and vasodilative activities. We investigated the expression of CYP2J2 in human leukocytes using reverse transcription-polymerase chain reaction, immunoblotting and immunostaining. Human monocytic cells, but not human neutrophils, exhibited constitutive expression of CYP2J2. Furthermore, the expression of CYP2J2 mRNA increased when the human monocytic cell line THP-1 cells and human monocytes were stimulated with phorbol 12-myristate 13-acetate and macrophage-colony stimulating factor in combination with granulocyte/macrophage-colony stimulating factor, respectively. These results suggest that expression of CYP2J2 was up-regulated when human monocytes differentiated into macrophages and that human monocytic cells and macrophages have a pathway to metabolize arachidonic acid using CYP epoxygenases.

Sex-dependent expression of CYP2C11 in spleen, thymus and bone marrow regulated by growth hormone

CYP2C11, the most commonly expressed isoform of cytochrome P450 in male rat liver, was measured in spleen, thymus and bone marrow by quantitative real-time PCR and enhanced Western blotting. CYP2C11 concentrations in the lymphoid tissues were a fraction of that observed in liver, but like the liver, were sexually dimorphic (M>F) with mRNA and protein levels in agreement. Although the response to hypophysectomy varied according to tissue and sex, expression levels of CYP2C11 in all measured tissues remained greater in males. Further differences in CYP2C11 expression between liver and lymphoid tissue were observed following restoration of the circulating masculine growth hormone profile in hypophysectomized rats. In contrast to the liver where the renaturalized growth hormone profile elevated CYP2C11 expression in both sexes, the response was opposite in spleen and thymus with isoform concentrations declining in both sexes. Lastly, the divergent response of CYP2C11 between the liver and immune system was examined in cultured splenocytes exposed to different mitogens. In contrast to the dramatic depletion of CYP2C11 reported in proliferating hepatocytes, mitogen-stimulation resulted in a significant elevation in splenocyte CYP2C11 expression. In summary, we report for the first time that thymus, spleen and bone marrow express, albeit nominal, sex-dependent levels of CYP2C11 (M>F) whose regulation appears to be under some hormonal control, but very different from that of the hepatic isoform.

Expression of cytochrome P450 genes in CD34+ hematopoietic stem and progenitor cells

Expression of major cytochrome P450 forms (P450) was followed in preparation of purified hematopoietic CD34+ stem and progenitor cells. Levels of transcripts as well as mature proteins were traced by quantitative real-time polymerase chain reaction and by Northern and Western blotting. P450 1B1 and P450 2E1 proteins and respective mRNAs were found in all cases. On the other hand, no expression of P450 3A4, P450 3A7, and P450 2C9 was found. The results showed that expression of various P450 enzymes starts at different stages of cell differentiation. Both P450 forms found are known to be connected with cancer cells and with activation of procarcinogens (P450 1B1, polycyclic aromatic hydrocarbons; P450 2E1, nitrosamines, and solvents). Hence, cells at the early stage of differentiation already may be influenced by interaction with xenobiotics. This fact should also be taken into consideration when hematopoietic cell transplant therapy is applied.

Atp Binding Cassette Multidrug Transporters Limit the Anti-HIV Activity of Zidovudine and Indinavir in Infected Human Macrophages

Objectives

To investigate whether P-glycoprotein (P-gp) and multidrug resistance proteins (MRPs), which limit the bioavailability of HIV protease inhibitors (PIs) and nucleoside reverse transcriptase inhibitors (NRTIs), modulate the anti-HIV activity of NRTIs, non-NRTIs and PIs in vitro. Design: We used primary cultures of major HIV target cells: human monocyte-derived macrophages (MDMs) and lymphocytes.

Methods

P-gp and MRP expression in response to long-term zidovudine (3′-azido-3′-deoxythymidine; AZT) or indinavir treatment was quantified by RT-PCR. MDM and lymphocytes were infected in vitro with HIV-1/Ba-L and HIV-1-LAI, respectively, and treated with antiretroviral drugs. We evaluated the activity of these drugs in combination with PSC833, a P-gp inhibitor, and/or probenecid, an MRP1 inhibitor. Intracellular AZT triphosphate derivative (AZT-TP) was quantified by HPLC-MSMS. P-gp ATPase activity was measured with inside-out native membrane vesicles enriched in P-gp.

Results

Levels of MDR1, mrp4 and mrp5 mRNA were high following AZT treatment. In infected MDM, PSC833 and probenecid increased the anti-HIV activity of AZT and indinavir. AZT (5 nM) decreased HIV replication by 34% alone and by 72% in combination with P-gp/MRP inhibitors. Indinavir (10 nM) gave 14% inhibition alone and 81% in combination. The increase in anti-HIV activity of AZT was correlated with an increase in intracellular AZT-TP concentration. However, unlike PIs, neither AZT nor its metabolites interacted with P-gp.

Conclusion

AZT increases the expression of multidrug transporters, thereby decreasing its pharmacological activity. The cellular efflux of AZT probably involves MRP4 or MRP5. In contrast, increases in indinavir anti-HIV activity require the inhibition of both P-gp and MRP1.

Characterization of Glutathione Conjugates of the Remoxipride Hydroquinone Metabolite NCQ-344 Formed in Vitro and Detection following Oxidation by Human Neutrophils

Remoxipride is an atypical antipsychotic displaying selective binding to the dopamine D2 receptor. Several cases of aplastic anemia led to the withdrawal of remoxipride from the market in December 1993. The remoxipride metabolite NCQ-344 is a hydroquinone while the structural isomer NCQ-436 is a catechol, both of which have been suggested to be capable of forming a reactive para- and ortho-quinone, respectively. Recently, these two remoxipride metabolites were shown to induce apoptosis in human bone marrow progenitor cells. Furthermore, NCQ-344 also caused necrosis of these cells unlike NCQ-436. Although NCQ-344 has been detected in plasma of humans dosed with remoxipride, to date, no experimental evidence for the formation of the corresponding para-quinone has been obtained. Here, we report the detection of three glutathione (GSH) conjugates of NCQ-344 in vitro that were formed following a chemical reaction and characterized by tandem mass spectrometry and for a cyclized conjugate additionally with derivatization and deuterium exchange. In contrast, NCQ-436 did not form a GSH conjugate. Hypochlorous acid oxidized NCQ-344 to the para-quinone while NCQ-436 was resistant to oxidation. Upon incubation with NCQ-344, stimulated human neutrophils produced from 2- to 5-fold greater amounts of glutathione conjugates than unstimulated neutrophils. Ab initio calculations on these remoxipride metabolites indicated that the reaction leading to the respective quinone was spontaneous for the para-quinone (e.g., from NCQ-344) while ortho-quinone (e.g., from NCQ-436) formation was not. These results demonstrate that NCQ-344 is capable of facile formation of a reactive para-quinone capable of reacting with GSH and may rationalize previous findings regarding the biological effects observed in vitro with these two remoxipride metabolites.

Mechanisms in cutaneous drug hypersensitivity reactions

Up to 3% of all hospital admissions are due to adverse drug reactions (ADRs), and between 10% and 20% of hospital inpatients develop ADRs. Individual susceptibility to becoming 'sensitized' or allergic to a drug is thought to result from altered metabolic handling of the drug. Reactive intermediate compounds form haptens, bind to proteins and induce immune responses. Depending on whether the immune system generates antibodies or sensitized T cells, different clinical patterns of hypersensitivity may result. At present, both in vivo or in vitro tests to identify the culprit drug or to confirm the presence of hypersensitivity are not widely used because they are either not generally robust or not readily accessible. In vitro tests require the true immunogen/antigen to detect antibodies or sensitized T cells. As the metabolic basis underlying susceptibility to adverse drug reactions is elucidated, the resolution of immunological mechanisms and development of reliable tests will ensue. This will also become of great value for prediction of individuals at risk of becoming sensitized by a particular drug.

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.

4-(N,N-dipropylamino)benzaldehyde inhibits the oxidation of all-trans retinal to all-trans retinoic acid by ALDH1A1, but not the differentiation of HL-60 promyelocytic leukemia cells exposed to all-trans retinal

BACKGROUND

The signal transduction pathways mediated by retinoic acid play a critical role in the regulation of cell growth and differentiation during embryogenesis and hematopoiesis as well as in a variety of tumor cell lines in culture. Following the reports that two members of the superfamily of aldehyde dehydrogenase (ALDH) enzymes, ALDH1A1 and ALDH1A2, were capable of catalyzing the oxidation of all-trans retinal to all-trans retinoic acid with submicromolar Km values, we initiated an investigation of the ability of 4-(N,N-dipropylamino)benzaldehyde (DPAB) to inhibit the oxidation of retinal by purified mouse and human ALDH1A1.

RESULTS

Our results show that DPAB potently inhibits retinal oxidation, with IC50 values of 0.11 and 0.13 microM for purified mouse and human ALDH1A1, respectively. Since the HL-60 human myeloid leukemic cell line has been used extensively to study the retinoic acid induced differentiation of HL-60 cells to granulocytes, and ALDH1A1 activity had previously been reported in HL-60 cells, we investigated the ability of DPAB to block differentiation of HL-60 promyelocytic leukemia cells exposed to retinal in culture. In HL-60 cells coincubated with 1 microM retinal and 50 microM DPAB for 144 hours, cell differentiation was inhibited only 30%. Furthermore, the NAD-dependent oxidation of propanal or retinal was less than 0.05 nmoles NADH formed/min-10(7) cells in spectrophotometric assays using HL-60 cell extracts.

CONCLUSION

Although ALDH1A1 may be the major catalytic activity for retinal oxidation in some retinoid-dependent mouse and Xenopus embryonic tissues and in adult human and mouse hematopoietic stem cells, another catalytic activity appears to synthesize the retinoic acid ligand necessary to stimulate the differentiation of HL-60 cells to end stage granulocytes.

Heme oxygenase-1 and NADPH cytochrome P450 reductase expression in experimental allergic encephalomyelitis: an expanded view of the stress response

Oxidative stress is implicated in the pathogenesis of experimental allergic encephalomyelitis (EAE), a model for multiple sclerosis. Heme oxygenase-1 (HO-1) is a heat shock protein induced by oxidative stress. HO-1 metabolizes the pro-oxidant heme to the antioxidant biliverdin and CO. HO-1 requires electrons, donated by NADPH cytochrome P450 reductase (henceforth, reductase), for catalytic activity. EAE was induced with a peptide of proteolipid protein in SJL mice, and the expression of HO-1 and reductase in the hindbrain was analyzed. HO-1 protein levels were significantly increased in EAE animals compared with control mice. HO-1 expression was present in ameboid macrophages, reactive microglia, and astrocytes in white matter tracks. Bergmann glia and ameboid macrophages also were occasionally stained in the molecular layer of the cerebellum. Unlike HO-1, reductase protein levels decreased with disease severity. HO-1 and reductase were associated with each other in endoplasmic reticulum micelles, suggesting that the decrease in reductase does not interfere with its association with HO-1. In cells that express HO-1, the association of reductase with HO-1 should competitively inhibit the interaction of reductase with cytochrome P450 isozymes and thereby limit free radical production as the latter two enzymes act cooperatively to produce superoxide. The increase in HO-1 together with the decrease in reductase may be part of a common defense mechanism attempting to minimize tissue damage in several neurological conditions.