Kyoungju Choi - Academia.edu (original) (raw)

Papers by Kyoungju Choi

Applied In Vitro Toxicology, 2015

Toxicology letters, Jan 18, 2015

In vitro cell culture systems are a useful tool to rapidly assess the potential safety or toxicit... more In vitro cell culture systems are a useful tool to rapidly assess the potential safety or toxicity of chemical constituents of food. Here, we investigated oxidative stress and organ-specific antioxidant responses by 7 potential dietary ingredients using canine in vitro culture of hepatocytes, proximal tubule cells (CPTC), bone marrow-derived mesenchymal stem cells (BMSC) and enterocyte-like cells (ELC). Cellular production of free radical species by denatonium benzoate (DB), epigallocatechin gallate (EPI), eucalyptol (EUC), green tea catechin extract (GTE) and sodium copper chlorophyllin (SCC), tetrahydroisohumulone (TRA) as well as xylitol (XYL) were continuously measured for reactive oxygen/nitrogen species (ROS/RNS) and superoxide (SO) for up to 24 hr. DB and TRA showed strong prooxidant activities in hepatocytes and to a lesser degree in ELC. DB was a weak prooxidant in BMSC. In contrast DB and TRA were antioxidants in CPTC. EPI was prooxidant in hepatocytes and BMSC but showed ...

Pesticide Biochemistry and Physiology, 2010

Atrazine (ATZ) metabolism by human liver microsomes (HLM), cytochrome P450 (CYP) isoforms, and hu... more Atrazine (ATZ) metabolism by human liver microsomes (HLM), cytochrome P450 (CYP) isoforms, and human liver (HL) S9 fractions, was investigated using HPLC/PDA and LC/MS/MS. CYP-dependent metabolites from pooled HLM are desethylatrazine (DEA), desisopropylatrazine (DIA), 1-hydroxyisopropylatrazine (HIATZ), and 2-hydroxyethyl atrazine (HEATZ). DEA and DIA were major metabolites in pooled HLM. CYP1A2 and 2C19, respectively, were major isoforms for DEA and DIA production. CYP3A4, while less active, is generally at high concentrations, produces both DEA and DIA and is significant. The percent total normalized rates (%TNR) for CYP1A2 and 3A4 in pooled HLM were 63% and 24% for DEA, and 35% and 56% for DIA production. Single donor HLM samples, showed correlations for CYP1A2 (r = 0.92) and 3A4 (r = 0.81) for DEA and DIA production, while variations in production of DEA and DIA were 8.5-and 6.0-fold, respectively. Pooled S9 fractions also mediate glutathione conjugation of atrazine, DEA and DIA.

Toxicology in Vitro, 2013

In vitro metabolism of DEHP by subcellular fractions of human brain, intestine, kidney, liver, lu... more In vitro metabolism of DEHP by subcellular fractions of human brain, intestine, kidney, liver, lung, skin, testis, rat liver and recombinant CYP isoforms of human and rat was investigated using LC-MS/MS. DEHP was rapidly hydrolyzed to mono(2-ethylhexyl) phthalate (MEHP) in 12 microsomal/cytosolic fractions of selected 7 human organs and rat liver but not in microsomal fractions of human brain and human female skin. MEHP was metabolized to CYP-mediated oxidative and dealkylated metabolites in human and rat liver and at a lower rate in human intestine. Measurable amounts of mono(2-ethyl-5-hydroxyhexyl) phthalate (5-OH MEHP), mono(2-ethyl-5-oxohexyl) phthalate (5-Oxo MEHP), mono(2-ethyl-5-carboxypentyl) phthalate (5-carboxy MEPP), mono(2-carboxymethyl-hexyl) phthalate (2-carboxy MMHP) and phthalic acid (PA) were formed by human liver fractions. Human CYP2C9 ⁄ 1, CYP2C19 and rat CYP2C6 were the major CYP isoforms producing 5-OH MEHP and 5-Oxo MEHP metabolites; however, only human CYP2C9 ⁄ 1 and 2C9 ⁄ 2 produced 5-carboxy MEPP from MEHP. Additionally, human CYP3A4 and rat CYP3A2 were the primary enzymes for PA production via heteroatom dealkylation of MEHP. Percent total normalized rates (%TNR) by CYP2C9 ⁄ 1 in human liver microsomes (HLM) were 94%, 98% and 100%, respectively, for 5-OH MEHP, 5-Oxo MEHP, 5-carboxy MEPP, and 76% for PA production by CYP3A4.

Toxicology in Vitro, 2012

Tissue Engineering Part C: Methods, 2014

Primary and cryopreserved hepatocytes and immortalized hepatic cell lines in static two-dimension... more Primary and cryopreserved hepatocytes and immortalized hepatic cell lines in static two-dimensional monolayer culture format have been widely used as in vitro liver models for studies of xenobiotic metabolism, enzyme induction, hepatocyte regeneration, and hepatotoxicity. However, the tissue structure and metabolic capacity in these liver models are often ill-defined and are not well preserved compared to in vivo liver-specific architecture and functions. For this reason, we developed a three-dimensional (3D) dynamic flow model with primary human hepatocytes, which was optimized for cell seeding density, medium composition, and extracellular matrix proteins. Human hepatocytes cultured in this system were maintained for up to 7 weeks and reproducibly recapitulated in vivo liver-like structure and important liver-specific functions, such as albumin/ total protein production, glucose utilization, lactate production, and cytochrome P450 (CYP) 3A4 activity across multiple tissue donors. The in vitro intrinsic clearance (CL int ) of 7-ethoxycoumarin (7-EC) was determined from human hepatocytes cultured in the 3D dynamic flow model and compared to that in hepatocyte suspension. The 7-EC CL int values varied among individual batches and/or the two different in vitro liver models used in this study. The 3D flow model appeared to give more reproducible and stable estimates of clearance that is similar to previously published values. Overall, the results from these studies demonstrate that this culture system could be a valuable tool for making more accurate predictions of the metabolic clearance and long-term effects of chemicals and their metabolites in a complex 3D environment under dynamic flow.

Journal of Biochemical and Molecular Toxicology, 2006

The metabolism of chlorpyrifos (CPS) and chlorpyrifos oxon (CPO) by human hepatocytes and human l... more The metabolism of chlorpyrifos (CPS) and chlorpyrifos oxon (CPO) by human hepatocytes and human liver S9 fractions was investigated using LC-MS/MS. Cytochrome P450 (CYP)-dependent and phase II-related products were determined following incubation with CPS and CPO. CYP-related products, 3,5,6-trichloro-2-pyridinol (TCP), diethyl thiophosphate, and dealkylated CPS, were found following CPS treatment and dealkylated CPO following CPO treatment. Diethyl phosphate was not identified because of its high polarity and lack of retention with the chromatographic conditions employed. Phase IIrelated conjugates, including O-and S-glucuronides as well as 11 GSH-derived metabolites, were identified in CPS-treated human hepatocytes, although the O-sulfate of TCP conjugate was found only when human liver S9 fractions were used as the enzyme source. O-Glucuronide of TCP was also identified in CPO-treated hepatocytes. CPS and CPO were identified using HPLC-UV after CPS metabolism by the human liver S9 fraction. However, CPO was not found following treatment of human hepatocytes with either CPS or CPO. These results suggest that human liver plays an important role in detoxification, rather than activation,

Journal of Biochemical and Molecular Toxicology, 2007

Previous studies have established that chlorpyrifos (CPS), fipronil, and nonane can all be metabo... more Previous studies have established that chlorpyrifos (CPS), fipronil, and nonane can all be metabolized by human liver microsomes (HLM) and a number of cytochrome P450 (CYP) isoforms. However, metabolic interactions between these three substrates have not been described. In this study the effect of either coincubation or preincubation of CPS with HLM or CYP isoforms with either fipronil or nonane as substrate was investigated. In both co-and preincubation experiments, CPS significantly inhibited the metabolism of fipronil or nonane by HLM although CPS inhibited the metabolism of fipronil more effectively than that of nonane. CPS significantly inhibited the metabolism of fipronil by CYP3A4 as well as the metabolism of nonane by CYP2B6. In both cases, preincubation with CPS caused greater inhibition than coincubation, suggesting that the inhibition is mechanism based. C 2007 Wiley Periodicals, Inc.

Journal of Biochemical and Molecular Toxicology, 2014

The new paradigms proposed for human health risk assessment stress the need for the use of human ... more The new paradigms proposed for human health risk assessment stress the need for the use of human and human-derived cell lines, and this review summarizes the use of primary human hepatocytes and hepatocyte subcellular preparations for the investigation of the metabolism and metabolic interactions of environmental chemicals. This includes interactions based on inhibition, induction, and activation. The role of cytotoxicity is also considered. The use of hepatocytes and hepatocyte preparations provides especially important information for the investigation of human variation and is summarized. This area is, at present, relatively neglected but will in the future be essential for accurate assessment of human health risk. A detailed summary of an initial attempt to utilize microarray technology for the study of genomewide effects is included. C 2013 Wiley Periodicals, Inc.

Inhalation Toxicology, 2012