The cloning and characterization of a novel cytochrome P450 family, CYP26, with specificity toward retinoic acid

Dietary vitamin A supplementation ameliorates the effects of poly-aromatic hydrocarbons in Atlantic salmon (Salmo salar)

Several studies have reported on the interaction between vitamin A (VA) and aryl hydrocarbon receptor (AhR)-binding toxicants, including poly-aromatic hydrocarbons (PAHs). In aquaculture, the use of plant oils in novel aquafeeds can increase PAH levels while simultaneously lowering natural VA background levels, causing the need to supplement plant oil-based feeds with synthetic VA. To study dietary VA-PAH interactions, Atlantic salmon (initial weight 195±0.15g) were fed four identical plant-based diets that were supplemented with PAHs (100 and 10mgkg(-1) benzo[a]pyrene (BaP) and phenanthrene (Phe), respectively) or VA (retinyl acetate 8721IUkg(-1)) separately or combined for 2.5 months in a 2×2 factorial design, with triplicate net-pens per diet. Dietary PAH significantly reduced hepatic VA storage, and VA-enriched diets restored hepatic VA. There was a significant PAH-VA interaction effect on hepatic BaP, but not Phe, accumulation, with reduced hepatic BaP concentrations in fish fed VA+PAH compared to fish fed PAH alone. Concurrently, PAH and VA significantly interacted in their effects on CYP1A phase I biotransformation as observed from increased ethoxyresorufin-O-deethylase (EROD) activity, increased CYP1A protein concentration, and elevated transcription (cyp1a1 gene expression) in fish fed PAH+VA compared to PAH alone. Dietary VA supplementation alone had no significant effect on CYP1A phase I biotransformation. Metabolomic assessment showed that dietary VA caused a restoration of metabolic intermediates involved in energy metabolism that were affected by dietary PAH. Moreover, a PAH-induced growth inhibition was partially ameliorated by dietary VA supplementation. In conclusion, dietary VA interacted with PAH toxicity on the level of CYP1A-mediated detoxification, hepatic PAH accumulation, energy allocation, and growth.

Host and microbial factors in regulation of T cells in the intestine

The intestine is divided into specialized tissue areas that provide distinct microenvironments for T cells. Regulation of T-cell responses in the gut has been a major focus of recent research activities in the field. T cells in the intestine are regulated by the interplay between host and microbial factors. In the small intestine, retinoic acid (RA) is a major tissue factor that plays important roles in regulation of immune responses. In the large intestine, the influence of RA diminishes, but that of commensal bacterial products increases. RA, gut microbiota, and inflammatory mediators co-regulate differentiation, distribution, and/or effector functions of T cells. Coordinated regulation of immune responses by these factors promotes well-balanced immunity and immune tolerance. Dysregulation of this process can increase infection and inflammatory diseases.

Enhanced fatty acid flux triggered by adiponectin overexpression

Adiponectin overexpression in mice increases insulin sensitivity independent of adiposity. Here, we combined stable isotope infusion and in vivo measurements of lipid flux with transcriptomic analysis to characterize fatty acid metabolism in transgenic mice that overexpress adiponectin via the aP2-promoter (ADNTg). Compared with controls, fasted ADNTg mice demonstrated a 31% reduction in plasma free fatty acid concentrations (P = 0.008), a doubling of ketones (P = 0.028), and a 68% increase in free fatty acid turnover in plasma (15.1 ± 1.5 vs. 25.3 ± 6.8 mg/kg · min, P = 0.011). ADNTg mice had 2-fold more brown adipose tissue mass, and triglyceride synthesis and turnover were 5-fold greater in this organ (P = 0.046). Epididymal white adipose tissue was slightly reduced, possibly due to the approximately 1.5-fold increase in the expression of genes involved in oxidation (peroxisome proliferator-activated receptor α, peroxisome proliferator-activated receptor-γ coactivator 1α, and uncoupling protein 3). In ADNTg liver, lipogenic gene expression was reduced, but there was an unexpected increase in the expression of retinoid pathway genes (hepatic retinol binding protein 1 and retinoic acid receptor beta and adipose Cyp26A1) and liver retinyl ester content (64% higher, P < 0.02). Combined, these data support a physiological link between adiponectin signaling and increased efficiency of triglyceride synthesis and hydrolysis, a process that can be controlled by retinoids. Interactions between adiponectin and retinoids may underlie adiponectin's effects on intermediary metabolism.

Chronic High Doses of Thioacetamide Followed by Vitamin A Modify Dolichol, Dolichol Isoprenoids, and Retinol Content in Rat Liver Cells

Our line of researches follows the hypothesis that dolichol and retinol metabolism might be interrelated and involved in liver fibrosis. To this end, in this study rats were subjected to chronic treatment with thioacetamide (TAA) (300 mg/L liquid diet) for 1 and 2 months and, after liver damage had occurred, supplemented with vitamin A before sacrifice. Dolichol, dolichol isoprene units, and retinol content were determined in isolated parenchymal and sinusoidal liver cells (hepatic stellate cells; Kupffer cells; sinusoidal endothelial cells). Dolichol increased in hepatocytes after TAA treatment, with or without vitamin A. Dolichol decreased in the other cells. Retinol in general decreased. In hepatocytes, retinol decreased only on normal nutrition, while the vitamin A load was taken up normally. The percentages of dolichol isoprene units (Dol-16 to Dol-20, in rats) confirm that Dol-18, which was not modified in percentage by TAA on normal nutrition, did not increase after vitamin A, as it did in control cells (7-12%). The behavior of Dol-18 was similar in all the cells studied. Vitamin A might reveal a latent damage produced by TAA on dolichol homologues. These data support previous hypotheses that the action of TAA depends on the administration modality, the dosage, and the diet, and that Dol-18 might have different functions and compartmentalization in the cells. Furthermore, the results support the hypothesis that dolichol chain length might be interrelated with retinol metabolism, perhaps through their metabolites.

Some 1,2-Diphenylethane Derivatives as Inhibitors of Retinoic Acid—Metabolising Enzymes

In a search for novel inhibitors of RA-metabolising enzyme inhibitors as potential anti-cancer agents some 1,2-ethandiones, 2-hydroxyethanones and 1-ethylenedioxyethanones based on aryl-substituted 1,2-diphenylethane have been examined. Several of the compounds were weak inhibitors of the non-specific rat liver microsomal P450 enzymes and moderate inhibitors of the RA-induced enzymes in cultured human genital fibroblasts, where the RA-specific enzyme CYP26 is probably expressed. The 2-hydroxyethanone (13) with a 1-(4-dimethylaminophenyl) substituent was overall the most potent compound for rat liver microsomal enzyme (IC50 = 52.1 microM; ketoconazole, 2.8 microM) and the RA-induced enzyme (100 microM, 65.9% inhibition; ketoconazole, 20 microM, 75.0%). Modification of the dimethylamino group in (13) with more hydrophobic dialkylamino functions or separate modification of the 2-(2,4-dichlorophenyl) function did not improve potency.

Retinoic acid pathway genes show significantly altered expression in uterine fibroids when compared with normal myometrium

Fibroids are benign neoplasms of myometrial smooth muscle cells (SMC). Despite being the most common tumor in humans, their etiology is poorly understood. Recent microarray studies have demonstrated that multiple members of the retinoid pathway are differentially expressed between myometrium and fibroids. The aim of this present study was to investigate gene expression of members of the retinoid pathway in matched myometrium and fibroids. We have demonstrated differential gene expression of two binding proteins [cellular retinol-binding proteins (CRBP) 1 and 2], three enzymes [alcohol dehydrogenase 1 (ADH1), aldehyde dehydrogenase (ALDH1) and retinol dehydrogenase (RODH)] and two receptors [retinoid X receptors (RXR) alpha and gamma] involved in the retinoid pathway by real-time PCR. There were no differences in gene expression for retinoid receptors RARalpha, beta, gamma and RXRbeta, and for the metabolizing enzyme cytochrome P450, family 26 subfamily A. We confirmed results for ADH1, ALDH1, CRBP1 and CRABP2 at the protein level by western blot. Using immunohistochemistry these proteins were mostly localized to myometrial and fibroid SMC. An exception to this was ALDH1 protein, which displayed strong staining localized to cells of the connective tissue, presumably fibroblasts, with a striking differential expression pattern between myometrium and fibroids. These results demonstrate that the retinoid pathway is altered in fibroids when compared with normal myometrium and specifically identify ALDH1 in fibroid fibroblasts. These alterations can lead to aberrant retinoic acid (RA) production and signaling, and alter the expression of RA target genes, which may be an important step in fibroid development.

Retinoic acid metabolism blocking agents (RAMBAs) for treatment of cancer and dermatological diseases

The naturally occurring retinoids and their synthetic analogs play a key role in differentiation, proliferation, and apoptosis, and their use/potential in oncology, dermatology and a variety of diseases are well documented. This review focuses on the role of all-trans-retinoic acid (ATRA), the principal endogenous metabolite of vitamin A (retinol) and its metabolism in oncology and dermatology. ATRA has been used successfully in differentiated therapy of acute promyelocytic leukemia, skin cancer, Kaposi's sarcoma, and cutaneous T-cell lymphoma, and also in the treatment of acne and psoriasis. However, its usefulness is limited by the rapid emergence of acquired ATRA resistance involving multifactoral mechanisms. A key mechanism of resistance involves ATRA-induced catabolism of ATRA. Thus, a novel strategy to overcome the limitation associated with exogenous ATRA therapy has been to modulate and/or increase the levels of endogenous ATRA by inhibiting the cytochrome P450-dependent ATRA-4-hydroxylase enzymes (particularly CYP26s) responsible for ATRA metabolism. These inhibitors are also referred to as retinoic acid metabolism blocking agents (RAMBAs). This review highlights development in the design, synthesis, and evaluation of RAMBAs. Major emphasis is given to liarozole, the most studied and only RAMBA in clinical use and also the new RAMBAs in development and with clinical potential.

Cytochrome p450: a target for drug development for skin diseases

Enzymes of the cytochrome P450 (P450 or CYP) super family are the most versatile and important class of drug-metabolizing enzymes that are induced in mammalian skin in response to xenobiotic exposure. At the same time, CYP have numerous important roles in endogenous and exogenous substrate metabolism in the skin. For example, they participate in the metabolism of therapeutic drugs, fatty acids, eicosonoids, sterols, steroids, vitamin A, and vitamin D, to name a few. In addition, in some skin diseases, for example in psoriasis, many CYP are elevated. CYP are the target of special interest in the development of drugs for skin diseases because most, if not all, drugs available in the armamentarium of the dermatologists are either substrate, inducer, or inhibitor of this enzyme family. The functional significance of drug metabolism in skin and the implication of CYP in skin pathology and therapy is an area for future investigation. A detailed insight into the mechanism of action of various cutaneous CYP, being capable of modulating the drug bioavailability, will be helpful in the development of better strategies for novel therapy against constantly increasing skin disorders. This brief review discusses some of these perspectives and suggests additional work in this research area with regard to the expression and modulation of CYP in mammalian skin as well as their implication in dermatological disorders and the therapy of skin diseases.

Retinoids suppress epidermal growth factor-associated cell proliferation by inhibiting epidermal growth factor receptor-dependent ERK1/2 activation

Human papillomavirus (HPV) is an important etiological agent in the genesis of cervical cancer. HPV-positive cervical tumors and human papillomavirus-positive cell lines display increased epidermal growth factor receptor (EGFR) expression, which is associated with increased cell proliferation. ECE16-1 cells are an HPV-immortalized human ectocervical epithelial cell line that is a model of HPV-associated cervical neoplasia and displays elevated EGFR levels. In the present study, we evaluated the effects of receptor-selective retinoid ligands on EGFR-associated signal transduction. We show that retinoic acid receptor (RAR)-selective ligands reduce EGFR level and the magnitude and duration of EGFR activation in EGF-stimulated cells. These effects are reversed by cotreatment with an RAR antagonist. To identify the mechanism, we examined the effects of retinoid treatments on EGF-dependent signaling. Stimulation with EGF causes a biphasic activation of the ERK1/2 MAPK. The first peak of activation is present at 20 min, and the second is present at 36 h. This activation subsequently leads to an increase in the cyclin D1 level and increased cell proliferation. Simultaneous treatment with EGF and a RAR-selective retinoid inhibits both phases of ERK1/2 activation, completely eliminates the cyclin D1 induction, and suppresses EGF-dependent cell proliferation. This effect is specific as retinoid treatment does not alter the level or activity of other EGFR-regulated kinases, including AKT and the MAPKs p38 and JNK. Retinoid X receptor-selective ligands, in contrast, did not regulate these responses. These results suggest that RAR ligand-associated down-regulation of EGFR activity reduces cell proliferation by reducing the magnitude and duration of EGF-dependent ERK1/2 activation.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

The effect of retinol on hepatic and renal drug-metabolising enzymes

Retinol pretreatment (75 mg/kg/day, 4 days) potentiated paracetamol-induced hepatotoxicity in BALB/c mice (alanine aminotransferase (ALT) activity; 2510+/-602 vs 1155+/-282 IU/l; retinol+paracetamol vs corn oil+paracetamol, respectively, P<0.05); however, this potentiation did not occur in the kidney, indicating an organ-specific response. Retinol treatment alone was not toxic in either organ, as indicated by ALT activity, blood urea nitrogen and creatinine. The potentiation effect could be mediated by retinol's induction of CYP450 isoforms relevant to paracetamol metabolism or through depletion of glutathione. Therefore, these parameters were investigated in both organs. Following retinol treatment, renal CYP2E1 and hepatic CYP1A2 and CYP2E1 catalytic activities and polypeptide levels were unchanged. However, retinol significantly decreased both the catalytic activity (0.23+/-0.03 vs 0.53+/-0.06 nmol/mg/min; retinol vs untreated, respectively, P<0.05) and polypeptide levels (58+/-0.6% of control) of hepatic CYP3A. Inhibition of renal CYP3A did not occur as catalytic activity and polypeptide levels were unchanged from control. Following retinol treatment, total reduced glutathione levels, in both organs, were not significantly different from control. Therefore, the potentiation of paracetamol-induced hepatotoxicity is independent of CYP450 and glutathione.

HIV-1 protease inhibitors decrease proliferation and induce differentiation of human myelocytic leukemia cells

Inhibitors of the protease of human immunodeficiency virus type 1 (HIV-1) may inhibit cytoplasmic retinoic acid-binding proteins, cytochrome P450 isoforms, as well as P-glycoproteins. These features of the protease inhibitors might enhance the activity of retinoids. To explore this hypothesis, myeloid leukemia cells were cultured with all-trans retinoic acid (ATRA) either alone or in combination with the HIV-1 protease inhibitors indinavir, ritonavir, and saquinavir. Consistent with the hypothesis, the HIV-1 protease inhibitors enhanced the ability of ATRA to inhibit growth and induce differentiation of HL-60 and NB4 myeloid leukemia cells, as measured by expression of CD11b and CD66b cell surface antigens, as well as reduction of nitroblue tetrazolium. Growth of ATRA-resistant UF-1 cells was also inhibited when cultured with the combination of ATRA and indinavir. Moreover, indinavir enhanced the ability of ATRA to induce expression of the myeloid differentiation-related transcription factor C/EBPε messenger RNA in NB4 cells by 9.5-fold. Taken together, the results show that HIV-1 protease inhibitors enhance the antiproliferative and differentiating effects of ATRA on myeloid leukemia cells. An HIV-1 protease inhibitor might be a useful adjuvant with ATRA for patients with acute promyelocytic leukemia and possibly retinoid-resistant cancers.

HIV-1 protease inhibitors decrease proliferation and induce differentiation of human myelocytic leukemia cells

Inhibitors of the protease of human immunodeficiency virus type 1 (HIV-1) may inhibit cytoplasmic retinoic acid-binding proteins, cytochrome P450 isoforms, as well as P-glycoproteins. These features of the protease inhibitors might enhance the activity of retinoids. To explore this hypothesis, myeloid leukemia cells were cultured with all-trans retinoic acid (ATRA) either alone or in combination with the HIV-1 protease inhibitors indinavir, ritonavir, and saquinavir. Consistent with the hypothesis, the HIV-1 protease inhibitors enhanced the ability of ATRA to inhibit growth and induce differentiation of HL-60 and NB4 myeloid leukemia cells, as measured by expression of CD11b and CD66b cell surface antigens, as well as reduction of nitroblue tetrazolium. Growth of ATRA-resistant UF-1 cells was also inhibited when cultured with the combination of ATRA and indinavir. Moreover, indinavir enhanced the ability of ATRA to induce expression of the myeloid differentiation-related transcription factor C/EBPε messenger RNA in NB4 cells by 9.5-fold. Taken together, the results show that HIV-1 protease inhibitors enhance the antiproliferative and differentiating effects of ATRA on myeloid leukemia cells. An HIV-1 protease inhibitor might be a useful adjuvant with ATRA for patients with acute promyelocytic leukemia and possibly retinoid-resistant cancers.