Induction of cytochrome P450 1A1 in human hepatoma HepG2 cells by 6-nitrochrysene

Nitro-PAHs: Occurrences, ecological consequences, and remediation strategies for environmental restoration

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are persistent pollutants that have been introduced into the environment as a result of human activities. They are produced when PAHs undergo oxidation and are highly resistant to degradation, resulting in prolonged exposure and significant health risks for wildlife and humans. Nitro-PAHs' potential to induce cancer and mutations has raised concerns about their harmful effects. Furthermore, their ability to accumulate in the food chain seriously threatens the ecosystem and human health. Moreover, nitro-PAHs can disrupt the normal functioning of the endocrine system, leading to reproductive and developmental problems in humans and other organisms. Reducing nitro-PAHs in the environment through source management, physical removal, and chemical treatment is essential to mitigate the associated environmental and human health risks. Recent studies have focused on improving nitro-PAHs' phytoremediation by incorporating microorganisms and biostimulants. Microbes can break down nitro-PAHs into less harmful substances, while biostimulants can enhance plant growth and metabolic activity. By combining these elements, the effectiveness of phytoremediation for nitro-PAHs can be increased. This study aimed to investigate the impact of introducing microbial and biostimulant agents on the phytoremediation process for nitro-PAHs and identify potential solutions for addressing the environmental risks associated with these pollutants.

Azithromycin attenuates cigarette smoke extract-induced oxidative stress injury in human alveolar epithelial cells

Cigarette smoking has been verified to be one of the most important etiological factors causing the development of bronchogenic carcinoma and chronic obstructive pulmonary disease. Azithromycin (AZM) has been demonstrated to have antioxidant capacity. In the present study, whether AZM is able to attenuate cigarette smoke extract (CSE)-induced A549 cell oxidative stress injury was investigated. Cells were incubated with CSE in the presence or absence of AZM. Cell viability was measured using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The expression of vascular endothelial growth factor (VEGF) was analyzed using western blotting and ELISA. The expression of epithelial cell structural proteins, zona occludens (ZO)-1 and occludin was determined using western blotting and immunofluorescence staining. Reactive oxygen species (ROS) production was examined by flow cytometry and fluorescence staining. The results demonstrated that the exposure of A549 cells to CSE decreased cell viability in a dose- and time-dependent manner. AZM significantly attenuated the CSE-induced decreases in the expression of VEGF and epithelial cell structural proteins, including ZO-1 and occludin. CSE also stimulated ROS production in the A549 cell, while AZM significantly reversed the effects of CSE. In addition, the inhibition of ROS by N-acetyl-L-cysteine had similar effects as AZM on the expression of VEGF and epithelial cell structural proteins and also enhanced cell proliferation. In conclusion, AZM attenuated CSE-induced oxidative stress injury in A549 cells and may be a promising therapeutic agent for smoking-associated pulmonary diseases.

Apoptotic insults to human HepG2 cells induced by S-(+)-ketamine occurs through activation of a Bax-mitochondria-caspase protease pathway

BACKGROUND

Ketamine is widely used as an i.v. anaesthetic agent and as a drug of abuse. Hepatocytes contribute to the metabolism of endogenous and exogenous substances. This study evaluated the toxic effects of S-(+)-ketamine and possible mechanisms using human hepatoma HepG2 cells as the experimental model.

METHODS

HepG2 cells were exposed to S-(+)-ketamine. Cell viability and the release of lactate dehydrogenase (LDH) and gamma-glutamyl transpeptidase (GPT) were measured to determine the toxicity of S-(+)-ketamine to HepG2 cells. Cell morphology, DNA fragmentation, and apoptotic cells were analysed to evaluate the mechanism of S-(+)-ketamine-induced cell death. Amounts of Bax, an apoptotic protein, and cytochrome c in the cytoplasm or mitochondria were quantified by immunoblotting. Cellular adenosine triphosphate levels were analysed using a bioluminescence assay. Caspases-3, -9, and -6 were measured fluorometrically.

RESULTS

Exposure of HepG2 cells to S-(+)-ketamine increased the release of LDH and GPT, but decreased cell viability (all P<0.01). S-(+)-Ketamine time-dependently caused shrinkage of HepG2 cells. Exposure to S-(+)-ketamine led to significant DNA fragmentation and cell apoptosis (P=0.003 and 0.002). S-(+)-Ketamine increased translocation of Bax from the cytoplasm to mitochondria, but decreased the mitochondrial membrane potential and cellular adenosine triphosphate levels (all P<0.01). Sequentially, cytosolic cytochrome c levels and activities of caspases-9, -3, and -6 were augmented after S-(+)-ketamine administration (all P<0.001). Z-VEID-FMK, an inhibitor of caspase-6, alleviated the S-(+)-ketamine-induced augmentation of caspase-6 activity, DNA fragmentation, and cell apoptosis (all P<0.001).

CONCLUSIONS

This study shows that S-(+)-ketamine can induce apoptotic insults to human HepG2 cells via a Bax-mitochondria-caspase protease pathway. Thus, we suggest that S-(+)-ketamine at a clinically relevant or an abused concentration may induce liver dysfunction possibly due to its toxicity to hepatocytes.

Cytoskeleton interruption in human hepatoma HepG2 cells induced by ketamine occurs possibly through suppression of calcium mobilization and mitochondrial function

Ketamine is an intravenous anesthetic agent often used for inducing and maintaining anesthesia. Cytoskeletons contribute to the regulation of hepatocyte activity of drug biotransformation. In this study, we attempted to evaluate the effects of ketamine on F-actin and microtubular cytoskeletons in human hepatoma HepG2 cells and its possible molecular mechanisms. Exposure of HepG2 cells to ketamine at <or=100 microM, which corresponds to clinically relevant concentrations for 1, 6, and 24 h, did not affect cell viability. Meanwhile, administration of therapeutic concentrations of ketamine obviously interrupted F-actin and microtubular cytoskeletons. In parallel, levels of intracellular calcium concentration- and time-dependently decreased after ketamine administration. Analysis by confocal microscopy further revealed that ketamine suppressed calcium mobilization from an extracellular buffer into HepG2 cells. Exposure to ketamine decreased cellular ATP levels. The mitochondrial membrane potential and complex I NADH dehydrogenase activity were both reduced after ketamine administration. Ketamine did not change the production of actin or microtubulin mRNA in HepG2 cells. Consequently, ketamine-caused cytoskeletal interruption led to suppression of CYP3A4 expression and its metabolizing activity. Therefore, this study shows that therapeutic concentrations of ketamine can disrupt F-actin and microtubular cytoskeletons possibly through suppression of intracellular calcium mobilization and cellular ATP synthesis due to down-regulation of the mitochondrial membrane potential and complex I enzyme activity. Such disruption of the cytoskeleton may lead to reductions in CYP3A4 activity in HepG2 cells.

Effects of the environmental mammary carcinogen 6-nitrochrysene on p53 and p21(Cip1) protein expression and cell cycle regulation in MCF-7 and MCF-10A cells

The environmental pollutant 6-nitrochrysene (6-NC) is a potent mammary carcinogen in rats; it is more potent than numerous classical mammary carcinogens such as benzo[a]pyrene (BaP). The mechanisms that account for the remarkable carcinogenicity of 6-NC remain elusive. Similar to BaP, 6-NC is also known to induce DNA damage in rodents and in human breast tissues. As an initial investigation, we reasoned that DNA damage induced by 6-NC may alter the expression of p53 protein in a manner that differs from other DNA damaging carcinogens (e.g. BaP). Using human breast adenocarcinoma MCF-7 cells and immortalized human mammary epithelial MCF-10A cells, we determined the effects of 6-NC on the expression of p53 protein and its direct downstream target cyclin-dependent kinase inhibitor p21(Cip1) as well as on the cell cycle progression. Western blot analysis demonstrated that treatments of MCF-7 and MCF-10A cells with 6-NC for 12, 24 or 48h did not increase the level of total p53 protein; however, an increase of p21(Cip1) protein and a commitment increase of G(1) phase were observed in MCF-10A cells but not in MCF-7 cells. Further studies using 1,2-dihydroxy-1,2-dihydro-6-hydroxylaminochrysene (1,2-DHD-6-NHOH-C), the putative ultimate genotoxic metabolite of 6-NC, was conducted and showed a significant induction of p53 (p<0.05) in MCF-7 cells; however, this effect was not evident in MCF-10A cells, indicating the varied DNA damage responses between the two cell lines. By contrast to numerous DNA damaging agents such as BaP which is known to stimulate p53 expression, the lack of p53 response by 6-NC imply the lack of protective functions mediated by p53 (e.g. DNA repair machinery) after exposure to 6-NC and this may, in part, account for its remarkable carcinogenicity in the mammary tissue.

Benzo[a]pyrene-induced elevation of GSH level protects against oxidative stress and enhances xenobiotic detoxification in human HepG2 cells

Glutathione (GSH) is one of the most important antioxidants in mammalian cells. It also plays an important role in chemical detoxification. Some evidence showed that polycyclic aromatic hydrocarbons, such as benzo[a]pyrene (B[a]P [50-32-8]), could increase GSH content as a defense mechanism against oxidative stress as well as to promote its detoxification. However, there has been very little study on clarifying the role GSH plays in antioxidation and detoxification actions. Therefore, the present study aims to analyze intracellular glutathione metabolism in the human hepatoma cells (HepG2) upon exposure to B[a]P. Exposure of the cells to B[a]P (1-100 microM) for 24 h did not cause significant cell death in this cell line. By selecting the sublethal concentration of 10 microM, B[a]P caused a significant increase in GSH and a small (13%) but significant decrease in glutathione reductase activity. However, there was no change in the activity of glutathione peroxidase, and no detectable increase in reactive oxygen species (ROS) production. Treatment with B[a]P caused up to 1.5 folds increase in gamma-glutamylcysteine synthatase (gamma-GCS) activity over control. Buthioneine sulfoximine (BSO), an inhibitor of gamma-GCS, could suppress GSH increase in a dose-dependent manner. Assessment of the oxidative state of the cells indicated that the increase in GSH caused the cells to become more reduced. Thus, the results concluded that cells were not suffering from oxidative stress at 24 h after treatment with 10 microM B[a]P. Upon analyzing the activities of detoxification enzymes, there was an increase in the activity of CYP1A subfamily monooxygenases and glutathione S-transferase. Both changes occurred prior to the changes in gamma-GCS activity and the increase in GSH. In summary, results of the present study demonstrate that B[a]P caused an activation of detoxification enzymes. The increase in intracellular GSH level was due to activation of gamma-GCS activities. Oxidative stress may not be an important risk factor for B[a]P (at 10 microM of up to 24 h) induced injury.

Nitric oxide modulates pro- and anti-inflammatory cytokines in lipopolysaccharide-activated macrophages

BACKGROUND

Sepsis is a serious and life-threatening syndrome that occurs in intensive care unit patients. Lipopolysaccharide (LPS) has been implicated as one of major causes of sepsis. Nitric oxide (NO) and cytokines are involved in sepsis-induced inflammatory responses. This study is aimed at evaluating the effects of NO on the modulation of pro- and anti-inflammatory cytokines in LPS-activated macrophages and its possible mechanism.

METHODS

N-Monomethyl arginine (NMMA), an inhibitor of NO synthase, was used in this study to suppress NO production. Mouse macrophage-like Raw 264.7 cells were exposed to LPS, NMMA, or a combination of NMMA and LPS. Cell viability was determined by the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-di-phenyltetrazolium bromide assay. The amounts of nitrite, an oxidative product of NO, in the culture medium were quantified according to the Griess reaction method. Enzyme-linked immunosorbent assay and reverse-transcriptase polymerase chain reaction were carried out to determine the expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, and IL-10 in macrophages.

RESULTS

Exposure of macrophages to LPS, NMMA, and a combination of NMMA and LPS for 24 hours did not affect cell viability. LPS significantly increased the amounts of nitrite in macrophages (p < 0.01). Treatment with NMMA decreased LPS-enhanced nitrite (p < 0.01) in a concentration-dependent manner. Analyses of enzyme-linked immunosorbent assays and reverse-transcriptase polymerase chain reaction revealed that LPS significantly induced TNF-alpha, IL-1 beta, and IL-10 proteins and mRNA (p < 0.01). A combined treatment with NMMA and LPS significantly blocked LPS-induced TNF-alpha and IL-1 beta (p < 0.01), but synergistically enhanced LPS-induced IL-10 (p < 0.05) protein and RNA.

CONCLUSION

This study has shown that NO suppression can inhibit LPS-induced TNF-alpha and IL-1 beta but enhance IL-10, and the modulation occurs at a pretranslational level.

Nitric oxide induces osteoblast apoptosis through the de novo synthesis of Bax protein

Nitric oxide (NO) plays a crucial role in the physiological and pathophysiological regulations of osteoblast functions. This study is designed to evaluate the toxic effects of NO released by sodium nitroprusside (SNP), an NO donor, on neonatal Wistar rat calvarial osteoblasts from the analyses of cell viability, alkaline phosphatase (ALP) activity, cell morphology, apoptotic cells, terminal deoxynucleotidyl transferase-mediated dUTP nick end-label (TUNEL) assay, DNA ladder, and immunocytochemistry and Western blot for proapoptotic Bax protein. SNP increased the levels of nitrite, an oxidative product of NO, in the culture medium of osteoblasts in concentration- and time-dependent manners, and altered cell morphologies to round and shrinkage shapes. Administration of osteoblasts with SNP resulted in concentration- and time-dependent decreases of cell viability and ALP activity. Analysis of apoptotic cells revealed that SNP increased the percentages of osteoblasts processing apoptosis. Analyses of TUNEL and DNA ladder showed that SNP caused DNA fragmentation. Pretreatment with cycloheximide, an inhibitor of protein synthesis, partially blocked SNP-induced osteoblast apoptosis. Imunocytochemical and immunoblotting analyses revealed that SNP increased Bax protein in osteoblasts. This study suggests that SNP could increase the levels of NO in osteoblasts, and cause osteoblast apoptosis possibly through the de novo synthesis of proapoptotic Bax protein.

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.