• BMB Reports
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• 제36권1호
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• pp.20-27
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• 2003

Dihaloalkanes constitute an important group of chemicals because of their widespread use in industry and agriculture and their potential for causing toxicity and cancer. Chronic toxic effects are considered to depend upon bioactivation, either by oxidation or thiol conjugation. Considerable evidence links genotoxicity and cancer with glutathione conjugations reactions, and some aspects of the mechanisms have been clarified with 1,2-dihaloalkanes and dihalomethanes. Recently the DNA repair protein $O^6$-alkylguanine transferase has been shown to produce cytotoxicity and genotoxicity by mans of a thiol-dependent process with similarities to the glutathione reactions.

• Asian Pacific Journal of Cancer Prevention
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• 제16권7호
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• pp.2679-2683
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• 2015

Background: Phenethyl isothiocyanate (PEITC), the most comprehensively studied aromatic isothiocyanate, has been shown to act as an anti-cancer agent mainly through modulation of biotransformation enzymes responsible for metabolizing carcinogens in the human body. Humans are often exposed to carcinogenic factors, some of which through the diet, such as polycyclic aromatic hydrocarbon benzo[a]pyrene via the consumption of over-cooked meats. Inhibition of the enzymes responsible for the bioactivation of this carcinogen, for example CYP1A1, the major enzyme required for polycyclic aromatic hydrocarbons (PAHs) bioactivation, is recognized as a chemoprevention strategy. Objective: To evaluate the inhibitory effects of PEITC against benzo[a]pyrene-induced rise in rat liver CYP1A1 mRNA and apoprotein levels. Materials and Methods: Precision cut rat liver slices were treated with benzo[a]pyrene at 1 and $5{\mu}M$ in the presence of PEITC ($1-25{\mu}M$) for 24 hours, followed by determination of CYP1A1 mRNA and apoprotein levels using quantitative polymerase chain reaction and immunoblotting. Results: Findings revealed that PEITC inhibited benzo[a]pyrene-induced rise in rat liver CYP1A1 mRNA in a dose-dependent manner as well as the apoprotein levels of CYP1A. Conclusions: It was demonstrated that PEITC can directly inhibit the bioactivation of benzo[a]pyrene, indicating chemopreventive potential.

• 농약과학회지
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• 제2권2호
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• pp.10-15
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• 1998

Carbofuran 및 N-dimethoxyphosphinothioyl carbofuran (PSC)의 AChE에 대한 이분자 저해 속도상수(bimolecular inhibition rate constant, $k_{i}$)를 관찰하였다. Carbofuran은 $7.7{\times}10^{5}\;M^{-1}{\cdot}min^{-1}$으로 높은 저해효과를 보이고 있는 반면, PSC는 $1.2{\times}10^{3}\;M^{-1}{\cdot}min^{-1}$으로 carbofuran에 비하여 AChE에 대한 저해력이 600배 정도 낮은 저해력을 갖고 있는 것으로 관찰되어 독성발현을 위하여 활성화 과정이 필요한 것으로 확인되었다. AChE/mixed function oxidase(mfo) coupling system을 이용한 microsomal oxidative activation 실험에서 PSC의 AChE에 대한 저해력이 control에 비하여 NADPH가 첨가된 oxidase 처리구에서 800배 더 강하게 나타났으며, cytochrome $P_{450}$의 저해제를 첨가한 oxidase+PBO 처리구에서는 control의 저해 경향과 유사하였다. 또한 생쥐 뇌 AChE에 대한 PSC의 $I_{50}$은 28 mg/kg인 반면 PBO를 전처리하였을 경우 $I_{50}$은 57 mg/kg으로 나타나 cytochrome $P_{450}$ 저해제로 인하여 PSC의 저해력이 2배정도 감소된 것을 관찰할 수 있었고, PSC는 독성발현을 위하여 활성화 과정을 거쳐야 하며, 이 과정에서 cytochrome $P_{450}$ 이 작용함을 확인할 수 있었다. PSC와 MCPBA를 반응시켜 산화 과정을 통하여 생성된 독성대사물을 분석한 결과 반응산물의 약 55%가 carbofuran임을 확인할 수 있었다. 본 연구를 통하여 PSC의 활성화 과정을 통한 독성발현에 cytochrome $P_{450}$이 중요한 역할을 하는 효소임을 확인할 수 있었고, PSC의 산화적 활성화 과정을 통한 주된 독성대사물이 carbofuran임을 확인할 수 있었다.

• 농약과학회지
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• 제7권1호
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• pp.45-50
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• 2003

Procarbamate계 살충제인 benfuracarb의 산화효소계에 의한 활성화 과정과 이 과정을 통하여 생성되는 독성 대사물의 전환 정도를 확인하고자 수행되었다. Acetylcholinesterase(AChE) 에 대한 henfuracarb의 이 분자속도저해상수$(k_i)$가 $1.1\times10^3\;M^{-1}\;min^{-1}$로 매우 낮은 저해력을 보인 바, 이 약제가 체내에서 독성을 발현하기 위해서는 활성화 과정이 필수적임을 가정할 수 있었다. Benfuracarb의 활성화 과정에 관여하는 cytochrome $P_{450}$의 역할을 in vitro 에서 관찰하기 위하여 AChE/MFO coupling system을 사용하였다. AChE/MFO coupling system에서 AChE에 대한 저해력은 NADPH가 처리된 oxidase system이 NADPH 가 결핍된 대조구에 비하여 약 10배정도 증가하였으며, oxidase+PBO system 에서는 약간의 저해력 감소 경향이 관찰되었다. 생쥐에 henfuracarb을 처리한 후 brain AChE 활성을 조사해 본 결과 henfuracarb만 처리한 benfuracarb 처리구에서의 $I_{50}$은 22.7mg $kg^{-1}$이었으며, PBO를 전처리 한 후 henfuracarb을 처리한 benfuracarb+PBO 처리구에서는 $I_{50}$이 >100mg $kg^{-1}$으로 저해정도가 급격히 경감되어 benfuracarb의 활성화 과정에 cytochrome $P_{450}$이 관련되어 있음을 확인할 수 있었다. Microsomal oxidase system 을 이용하여 henfuracarb이 독성 대사물인 carbofuran으로 전환되는 정도를 관찰하였다. Oxidase system 에서는 처리된 benfuracarb의 58.0%가 carbofuran으로 전환되었지만, oxidase+PBO system에서 1.7%만 생성되어 benfuracarb의 활성화과정에 산화효소인 cytochrome $P_{450}$의 역할이 중요함을 확인할 수 있었다. 본 연구를 통하여 benfuracarb의 독성 발현에 관여하는 주된 독성 대사물은 carbofuran이며, 이 활성화 과정 에 cytochrome $P_{450}$이 중요한 역할을 하는 것으로 확인되었다.

• Applied Biological Chemistry
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• 제38권2호
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• pp.174-178
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• 1995

유기인계 살충제인 phosalone의 활성화과정을 통한 독성발현기작에서 cytochrome $P_{450}$의 역할을 조사하기 위하여 시험관 내와 생체 내 system을 이용하였다. Phosalone의 AChE와 BuChE에 대한 이분자 저해 속도상수$(k_i)$는 약 1$10^2\;M^{-1}{\cdot}min^{-1}$으로 측정되어 그 자체로는 저해력이 상당히 낮은 약제임이 관찰되었다. AChE 또는 BuChE/MFO coupling system에서는 $I_{50}$값이 control에서 각각 $3.7{\times}10^{-6}$, $2.5{\times}10^{-7}M$로 관찰되었고, cytochrome $P_{450}$의 조효소인 NADPH를 첨가한 oxidase에서는 $1.2{\times}10^{-8}$과 $6.0{\times}10^{-9}M$로 나타나 약 $40{\sim}300$배 정도의 활성화 효과가 관찰되었다. Cytochrome $P_{450}$의 특이적 저해제인 PB를 처리하였을때 저해곡선이 control쪽으로 이동하여 phosalone의 활성화과정에 cytochrome $P_{450}$이 관여하고 있슴이 확인되었다. 그러나 생체 내 실험에서 생쥐의 뇌 AChE 활성저해는 phosalone만을 투여한 경우 $I_{50}$이 170 mg/kg, PB를 전처리 하였을 경우에서 42.5 mg/kg으로 나타나 PB 처리에 의하여 오히려 약 4배의 상승효과가 관찰되었으며, 쥐 혈액에서의 AChE와 BuChE활성저해 결과는 PB 전처리가 phosalone의 저해 경향에 큰 영향을 주지 않는 것으로 나타나 시험관 내 실험에서의 결과와는 상이하게 나타났다.

• Toxicological Research
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• 제7권2호
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• pp.231-238
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• 1991

The pesticide and carcinogen ethylene dibromide(EDB) is metabolized both by cytosolic GSH S-transferase and by microsomal mixed function oxygenase. Cytochrome P-450 IIE1 appears to be major enzyme to metabolize EDB.EDB is activated to a mutagen by enzymatic conjugation with glutathione (GSH). Such activation is an exception to the general mode of detoxification via GSH S-transferase action. The primary DNA adduct (>95) is S-[2-(N7-guanyl)ethyl] GSH and a minor adduct is S-[2-(N7-guanyl)ethyl]cysteine, which is excreted in the urine and may serve as a biomarker of damage.

• Toxicological Research
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• 제26권3호
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• pp.171-175
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• 2010

The human genome contains approximately 13 orphan cytochrome P450 (P450, CYP) genes, of which the apparent function or substrate has not been identified. However, they seem to possess their own biological relevance in some tissues or developmental stages. Here, we characterized the heterologously expressed CYP2W1, an orphan P450 enzyme. The recombinant CYP2W1 protein containing a $6{\times}$(His)-tag at Nterminus has been expressed in Escherichia coli and purified. Expression level of CYP2W1 holoenzyme was around 500 nmol P450 holoenzyme per liter culture medium. The reduced CO difference spectrum of CYP2W1 showed a maximum absorption at 449 nm. CYP2W1 indicated the significant induction to bioactivate Trp-P-1, MeIQ, and IQ in E. coli DJ701 tester strain. However, the bioactivation of B[$\alpha$]P, and NNK by CYP2W1 was relatively low. The model structure of CYP2W1 suggested the characteristic P450 folds with the lengths and orientations of the individual secondary elements. The F-G loop is situated on the distal side of heme to accommodate the flexibility of active site of CYP2W1. These studies can provide useful information for the finding of its biological roles and structure-function relationships of an orphan CYP2W1 enzyme.

• Toxicological Research
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• 제32권2호
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• pp.89-93
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• 2016

Human cytochrome P450 enzymes (P450s, CYPs) are major oxidative catalysts that metabolize various xenobiotic and endogenous compounds. Many carcinogens induce cancer only after metabolic activation and P450 enzymes play an important role in this phenomenon. P450 1B1 mediates bioactivation of many procarcinogenic chemicals and carcinogenic estrogen. It catalyzes the oxidation reaction of polycyclic aromatic carbons, heterocyclic and aromatic amines, and the 4-hydroxylation reaction of $17{\beta}$-estradiol. Enhanced expression of P450 1B1 promotes cancer cell proliferation and metastasis. There are at least 25 polymorphic variants of P450 1B1 and some of these have been reported to be associated with eye diseases. In addition, P450 1B1 polymorphisms can greatly affect the metabolic activation of many procarcinogenic compounds. It is necessary to understand the relationship between metabolic activation of such substances and P450 1B1 polymorphisms in order to develop rational strategies for the prevention of its toxic effect on human health.

• Archives of Pharmacal Research
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• 제14권2호
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• pp.130-136
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• 1991

Nicotine (100 .mu. M) was incubated with microsomes (1 mg/ml) prepared from New Zealand White rabbits. On the basis of microsomal weight, the rate of nicotine oxidation were calculated on the basis of cytochrome P-450 concentration, the specific activity of the metabolic oxidation catalyzed by lung was approximately 4 times greater than liver (6.4 vs 1, 65 nmoles nicotine oxidized. nmole cytochrome $P-450^{-1}\;min{-1})$. These studies employed several methods of altering activities of specific isozymes present in pulmonary microsomes, including the use of the isozyme2 and 6 specific inhibitor $\alpha$-methylbenzyl ABT, metabolite inhibitors, norbenzphetamine and N-hydroxyamphetamine. TCDD induction and Arochlor 1260 pretreatment. These results support the conclusion that nicotine metabolism by rabbit lung microsomes is mediated primarily by cytochrome P-450 isozyme 2.

• Toxicological Research
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• 제23권3호
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• pp.189-196
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• 2007

Cytochrome P450 (P450) enzymes are the major catalysts involved in the biotransformation of various drugs, pollutants, carcinogens, and many endogenous compounds. Most of chemical carcinogens are not active by themselves but they require metabolic activation. P450 isozymes playa pivotal role in the metabolic activation. The activation of arylamines and heterocyclic arylamines (HAAs) involves critical N-hydroxylation, usually by P450. CYP1A2 plays an important role in these reactions. Broad exposure to many of these compounds might cause carcinogenicity in animals and humans. On the other hand, P450s can be also involved in the bioactivation of other chemicals including alcohols, aflatoxin B1, acetaminophen, and trichloroethylene, both in humans and in experimental animals. Understanding the P450 metabolic activation of many chemicals is necessary to develop rational strategies for prevention of their toxicities in human health. An important part is the issues of extrapolation between species in predicting risks and variation of P450 enzyme activities in humans.