|
|
Interaction of food additives with xenobiotic metabolising enzymes
Jandová, Eliška ; Hodek, Petr (advisor) ; Koblihová, Jitka (referee)
Recently the use of various food supplements as a part of a healthy lifestyle has been very popular. Although most of them are natural products, their excessive consumption may not always be beneficial for health. Dietary supplements are usually of a flavonoid character. Flavonoid compounds are found in plants and they have beneficial effects on human health. For their antioxidant, anti-allergy and chemopreventive effects they are extensively studied. However, in recent years the negative impacts of flavonoids have been described, often caused by their excessive consumption. It has been shown that they interact with cytochrome P450, which play an important role in the biotransformation of xenobiotics. The change in the metabolism of xenobiotics (whether drugs or carcinogens) can cause serious health problems, including a tumor growth. Beside cytochrome P450, there is another possible points of intervention, cytochrome b5 (or NADH:cytochrome b5 reductase), which effects the catalytic cycle of cytochrome P450. Another point of potential danger is the elimination of xenobiotics out of the organism. There is a complex system of transporters, in which P-glycoprotein plays a very significant role. P-glycoprotein is involved in transmembrane efflux of xenobiotics, preventing the aggregation of these...
|
|
|
Mechanism of cancerogenic effect of nitroaromates pollutants in present environment
Čechová, Tereza ; Stiborová, Marie (advisor) ; Svobodová, Martina (referee)
Nitroaromatic compounds are mutagenic and carcinogenic substances present in all environmental compartments. Polycyclic aromatic hydrocarbons react with nitrogen oxides to form nitroaromatics under the conditions that might be expected in polluted air and in combustion processes (fossil fuel combustion, waste heat recovery, metal processing, etc.). Most of nitroaromatic compounds are potent mutagens in bacterial and mammalian systems. They are also carcinogens causing cancer, primarily in the liver, lungs and mammary glands. Nitrobenzanthrones (NBA) are nitroaromatic compounds which were recently found in environmental compartments, especially in the air. 3-Nitrobenzanthrone (3-NBA, 3-nitro-7H-benz [de] anthracene-7-one) is one of the polycyclic aromatic nitro compounds with high toxic effects. 3-NBA is present in environmental pollution, in diesel exhaust and was also detected in soil and in rain water. Bachelor's thesis describes the metabolism of this substance and it also studies its mutagenic and carcinogenic effects. This work also compares the mutagenic and carcinogenic effects of 3-NBA and its derivative, isomer 2-nitrobenzanthrone (2-NBA, 2-nitro-7H-benz [de] anthracene-7-one), which also occurs as a pollutant in air. (In Czech)
|
|
|
Heterologous expression and isolation of human cytochromes P450 1A1/2
Milichovský, Jan ; Martínek, Václav (advisor) ; Hodek, Petr (referee)
Cytochromes P450 form a large family of hemoproteins. Some of them are responsible for the metabolism of endogenous substrates, but their major role is in detoxification of exogenous substrates (xenobiotics), some of them are activated to reactive species forming covalent adducts with DNA and increasing intracellular oxidative stress. Cytochrome P450 are considered by very promiscuous in terms of their substrate specificity, thus one enzyme can typically oxidize many substrates. Cytochrome P450 1A1 prefers a planar aromatic compounds (e.g. polycyclic aromatic hydrocarbons, azo dyes, etc.). Cytochrome P450 1A2 elicits similar substrate specificity, but prefers slightly basic aromatic derivatives, for example caffeine. This work focuses on (i) the preparation of expression vectors containing genes encoding human cytochromes P450 1A1 and 1A2, (ii) their consequent expression in heterologous system followed by (iii) isolation of corresponding proteins. The genes coding both proteins were modified and transferred from older vectors to the more efficient to expression plasmids pET-22b. However, the new constructs did not produce stable native proteins. The modified genes were therefore transferred to the original expression plasmids pCW. The problem with the incorporation of native human form of...
|
|
|
Modulation of activities and expression of enzymes metabolizing ellipticine by histone deacetylase inhibitor trichostatin A
Kopejtková, Barbora ; Stiborová, Marie (advisor) ; Kubíčková, Božena (referee)
Histone deacetylase inhibitor trichostatin A (TSA) increases cytotoxicity of antineoplastic agent ellipticine to human neuroblastoma cells. Its mechanism of action has not yet been explained. One of the possible mode of action is conformational change in chromatin, which leads to changes in DNA that is more accessible to covalent modification and intercalation. The aim of this work is to study another mode of action, which can explain this phenomenon. The question is, if TSA can increase cytotoxicity of ellipticine to human neuroblastoma cells by modulation of activities and expression of cytochromes P450 and peroxidases. These enzymes are responsible for cytotoxicity of ellipticine to human neuroblastoma cells. TSA has no effect on oxidation of ellipticine mediated by cytochromes P450 leading to metabolites responsible for formation of ellipticine-DNA adducts and detoxication metabolites. TSA increases formation of ellipticine dimer, which is a detoxication metabolite, forming during its oxidation by peroxidases. TSA has no effect on activities of CYP1A1, CYP1A2, CYP3A, which significantly participate in oxidation of ellipticine. TSA modulates expression of enzymes oxidizing ellipticin in human neuroblastoma cells. TSA in the presence of ellipticine increases expression of CYP1A1 a CYP3A4 in...
|
|
|
Construction of vectors for heterologous expression of human cytochrome P450 1B1
Sojka, Pavel ; Martínek, Václav (advisor) ; Moserová, Michaela (referee)
The thesis was worked out in Laboratory of Molecular Carcinogenesis and Drug Development, which is focus on study of drug metabolizing enzymes including cytochromes P450. Cytochromes P450 are participating at initial phase of biotransformation of xenobiotics and endogenous substances and metabolism of several endogenous compounds, i.e. steroids. This work is focused on construction of expression vectors, based on the plasmid pET- 22b, suitable for heterologous expression of the human cytochrome P450 1B1. This enzyme is predominantly present in the endoplasmic reticulum of extra-hepatic tissues and its expression is induced by dioxins and polycyclic aromatic hydrocarbons. The human gene for cytochrome P450 1B1 was modified using PCR. The cleavage sites for restriction endonucleases were added to both ends of the gene. Another construct also contained N-terminal histidine tag to facilitate easier purification of the enzyme. Both insert and digested plasmids were verified using the agarose electrophoresis and used for ligation and transformation into competent cells (E. coli DH5. Final steps in construction was, however, not successful, probably due to low yields of DNA fragment extraction from agarose gels. Key words: cytochrome P450 1B1, carcinogenesis, plasmid, heterologous expression [In Czech]
|
|
|
Molecular mechanism of carcinogenicity of aristolochic acid
Levová, Kateřina ; Stiborová, Marie (advisor) ; Ryšlavá, Helena (referee) ; Souček, Pavel (referee)
Aristolochic acids (AA) are carcinogenic and nephrotoxic alkaloids from Aristolochia species. Aristolochic acid I (AAI), the major component of AA, causes the development of Aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN). These two diseases cause total renal failure and urothelial malignancies. The fact that these diseases have not been developed in all persons, who have been exposed to their action, might be causd by different activities and protein levels of the enzymes metabolizing AAI. Thus, the identification of enzymes involved in the metabolism, and detailed knowledge of their expression and catalytic specifities is a major importance. Aristolochic acid I (AAI) can be metabolized by several types of reactions. Like most nitroaromatics, the main activation pathway of AAI is reduction of its nitro group to form a cyclic acylnitrenium ion, which can bind to the purine bases, thereby forming AAI-DNA adducts. The detoxication pathway of AAI is its oxidative demethylation by cytochromes P450 forming detoxication metabolite 8-hydroxyaristolochic acid Ia (AAIa). In the present thesis, using rat and human enzymes and as well as several mice models, the metabolism of AAI in vitro and in vivo was investigated. The first model has deleted gene for NADPH:cytochrome P450...
|
|
|
The comparison of properties of cell lines resistant to ellipticine, doxorubicin, and cisplatin
Černá, Tereza ; Poljaková, Jitka (advisor) ; Eckschlager, Tomáš (referee)
7 Abstract Neuroblastoma is the most common extracranial solid tumor of childhood. Despite advances in cancer diagnosis and therapy, the treatment of some forms of neuroblastoma is still complicated. One of the major complications of the chemotherapy is a developed drug resistance. This master thesis deals with the effect of cytostatics on protein and gene expression of selected proteins, which may contribute to chemoresistance of the human neuroblastoma cell line UKF-NB-4. The sensitive line UKF-NB-4 and the resistant line UKF-NB-4CDDP , UKF-NB-4DOXO and UKF-NB-4ELLI were exposed to cisplatin, doxorubicin, ellipticine for 24, 48 and 72 hours. The Western blot analysis showed that cytostatic agents cisplatin, doxorubicin or ellipticine added to the sensitive neuroblastoma cell line UKF-NB-4 in amounts which are added to resistant neuroblastoma cell lines in order to maintain resistance induced expression of p53 and reduced expression of retinoblastoma protein pRb after 72 hours of cultivation. Differences in the expression of RAS protein, cytochrome P450 1A1, 3A4 and cytochrome b5 has not been shown. Changes in the expression of the studied proteins in resistant lines UKF-NB-4CDDP , UKF-NB-4DOXO and UKF-NB-4ELLI cultured with and without cytostatic agents were not detected by the Western blot analysis....
|
|
|
Activation of carcinogens in gastrointestinal tract
Zawadová, Dorota ; Hodek, Petr (advisor) ; Koblihová, Jitka (referee)
HAA are compounds which are showing numerous carcinogenic impacts on studied animals even human cells. These carcinogenes arise during the heat processing of meat or during (cigarette) smoking. Activation of these compounds is required to their carcinogenic effect. Most of all HAA are first activated by cytochrome P450 (CYP) especially subfamily 1A1 and 1A2. As a consequence of activation with these enzymes are created N-hydroxylamines, which weakly reacting with DNA. For better formation of DNA aducts one more activation is essential. More reactive acetate and sulphate esters arise by second activation from N- hydroxylamines. The esters are produced by sulphotranspherase (SULT) even N- acetotranspherase (NAT). When we affect these enzymes we could positive control the formation of carcinoma. Caffeic acid is considered as a strong inhibitor of one SULT subfamily (phenolic sulfotranspherase P - PST). On the other side as a good inhibitor of NAT is considered (known) quercetin. (in czech) Key words: Heterocyclic amine, biotransformation, cytochrome P450, sulfotransferase, N-acetyltransferase
|
|
|
Optimalization of expression of photoactivatable cytochrome P450 as a nano-probe for the membrane topology studies of enzymes metabolizing drugs and carcinogens
Smolová, Jana ; Hodek, Petr (advisor) ; Černá, Věra (referee)
The cytochromes P450 are among the most important enzymes involved in the biotransformation of xenobiotics in the body. They are part of the moooxygenase system that interact with other enzymes - NADPH:cytochrome P450 reductase and cytochrome b5. Mutual interaction of enzymes in mooxygenase system are not completely solved. Covalent crosslinking technique could contribute to clarify the possible protein-protein interactions and their consequences. One of the possible realization of this plan is to use photoactivatable cytochrome P450, which after exposure to UV radiation created covalent complex with components of monooxygenase system, with which it is in contact. Therefore, this paper focuses on developing optimal conditions for the production of recombinant cytochrome P450 2B4 in order to gain knowledge for the production of photoactivatable cytochrome P450 with incorporated amino acids L-photomethionine and L-photoleucine. In experiments was cytochrome P450 2B4 expressed in two strains of Escherichia coli, C41 (DE3) and BL21 (DE3) Gold, and two culture flasks, glass Erlenmeyer flask and plastic Fernbach flask. During expression optical density of the bacterial suspension (absorbation at 600 nm) and concentration of cytochrome P450 were measured. Methodology of measuring the concentration of...
|
|
|
Study of inhibition activity of new antitumor drugs against chosen isoforms of cytochromes P450
Kroulíková, Pavla ; Červený, Lukáš (referee)
Charles University Faculty of Pharmacy in Hradec Králové Department of Pharmacology and Toxicology Student: Mgr. Pavla Kroulíková Supervisor: RNDr. Jakub Hofman, Ph.D. Title of Thesis: Study of inhibitory activity of new anticancer drugs toward selected isoforms of cytochromes P450 Cytochromes P450 are important biotransformation enzymes that affect pharmacokinetic behavior of many clinically used drugs and are the cause of many major drug interactions. They may have a role in overcoming multidrug resistance of cancer cells because many cytostatic drugs are deactivated by them. Aim of this thesis was in vitro study of inhibition of selected isoforms (CYP3A4, CYP3A5, CYP1A2, CYP2C8, CYP2D6, CYP2C9, CYP2C19 and CYP2B6) by substances from the group of tyrosine kinase inhibitors - alectinib, brivanib, osimertinib and selumetinib. We used commercially available Vividâ CYP Screening kits for the study. In these kits, human cytochromes P450 are recombinantly inserted into insect microsomes. The advantage of this method is that during the experiment no other reaction catalyzed by a different enzyme occurs simultaneously. The principle of this method is conversion of fluorogenic substrate into fluorescent product by CYP450. We determined the inhibition by measuring fluorescence in the 15th minute from start...
|
guest ::
