The effects of benzene and the metabolites phenol and catechol on c-Myb and Pim-1 signaling in HD3 cells

CXCR2 Activated JAK3/STAT3 Signaling Pathway Exacerbating Hepatotoxicity Associated with Tacrolimus

Purpose

Tacrolimus could induce hepatotoxicity during clinical use, and the mechanism was still unclear, which posed new challenge for the prevention and treatment of tacrolimus-induced hepatotoxicity. The aim of this study was to investigate the mechanism of tacrolimus-induced hepatotoxicity and provide reference for drug development target.

Methods

In this study, biochemical analysis, pathological staining, immunofluorescent staining, immunohistochemical staining, transcriptomic analysis, Western blotting was used to investigate the mechanism of tacrolimus-induced hepatotoxicity in gene knockout mice and Wistar rats.

Results

In gene knockout mice, compared to wild-type mice, CXCR2-deficiency alleviated tacrolimus-induced hepatotoxicity (P < 0.05 or P < 0.01). In Wistar rats, compared to control group, CXCL2-CXCR2, JAK3/STAT3 signaling pathway (phosphorylation of JAK3 and STAT3) were up-regulated, the expression of CIS was lowered and the expression of PIM1 was raised, inducing liver pathological change (P < 0.05 or P < 0.01); Inversely, blocking CXCR2 could reverse the expression of p-JAK3/p-STAT3 and tacrolimus-induced hepatotoxicity (P < 0.05 or P < 0.01).

Conclusion

CXCR2 activated JAK3/STAT3 signaling pathway (phosphorylation of JAK3 and STAT3) exacerbating hepatotoxicity associated with tacrolimus, meanwhile the expression of CIS was down-regulated, the expression of PIM1 was up-regulated. Blocking CXCR2 could reverse the expression of p-JAK3/p-STAT3, CIS, PIM1, and tacrolimus-induced hepatotoxicity.

Phenolic metabolites of benzene inhibited the erythroid differentiation of K562 cells

Benzene is a common occupational hazard and a ubiquitous environmental pollutant. Benzene exposure at the levels even below 1ppm still showed hematotoxicity. It is widely accepted that the metabolites of benzene play important roles in the benzene toxicity to the hematopoietic system, but little is known about the effects of benzene metabolites on erythropoiesis. In present study, erythroid progenitor-like K562 cells were used to determine the effects of phenolic metabolites of benzene, including phenol, hydroquinone and 1,2,4-benzenetriol, on the erythroid differentiation. After the treatment with these benzene metabolites at the concentrations with no obvious cytotoxicity, the hemin-induced hemoglobin synthesis in K562 cells decreased in a concentration- and time-dependent manner, and the expression of CD71 and GPA protein on the surface of K562 cells was also inhibited. The reverse transcription-PCR was used to determine the mRNA level of the erythroid related genes in the K562 cells that were treated with benzene metabolites. The hemin-induced expression of globin genes, including α-, β- and γ-globin genes, and the gene encoding the heme synthesis enzyme porphobilinogen deaminase was inhibited by benzene metabolites. When the K562 cells were pretreated with benzene metabolites, the hemin-induced expression of two transcription factor genes GATA-1 and NF-E2 was distinctly reduced, and the pre-treatment with benzene metabolites promoted the decrease of the mRNA level of transcription factor gene GATA-2 by hemin. These results indicated that benzene metabolites inhibited the hemin-induced erythroid differentiation through affecting the transcription of the erythroid related genes.

The effects of 1,4-benzoquinone on c-Myb and topoisomerase II in K-562 cells

Exposure to benzene, a ubiquitous environmental pollutant, has been linked to leukemia, although the mechanism of benzene-initiated leukemogenesis remains unclear. Benzene can be bioactivated to toxic metabolites such as 1,4 benzoquinone (BQ), which can alter signaling pathways and affect chromosomal integrity. BQ has been shown to increase the activity of c-Myb, which is an important transcription factor involved in hematopoiesis, cell proliferation, and cell differentiation. The c-Myb protein has also been shown to increase topoisomerase IIalpha (Topo IIalpha) promoter activity specifically in cell lines with hematopoietic origin. Topo IIalpha is a critical nuclear enzyme that removes torsional strain by cleaving, untangling and religating double-stranded DNA. Since Topo IIalpha mediates DNA strand breaks, aberrant Topo IIalpha activity or increased protein levels may increase the formation of DNA strand breaks, leaving the cell susceptible to mutational events. We hypothesized that BQ can increase c-Myb activity, which in turn increases Topo IIalpha promoter activity resulting in increased DNA strand breaks. Using luciferase reporter assays in K-562 cells we demonstrated that BQ (25 and 37microM) exposure caused an increase in c-Myb activity after 24h. Contradictory to previous findings, overexpression of exogenous c-Myb or a polypeptide consisting of c-Myb's DNA binding domain (DBD), which competitively inhibits the binding of endogenous c-Myb to DNA, did not affect Topo IIalpha promoter activity. However, BQ (37microM for 24h) exposure caused a significant increase in Topo IIalpha promoter activity, which could be blocked by the overexpression of the DBD polypeptide, suggesting that BQ exposure increases Topo IIalpha promoter activity through the c-Myb signaling pathway.

A review of the role of benzene metabolites and mechanisms in malignant transformation: summative evidence for a lack of research in nonmyelogenous cancer types

The aromatic hydrocarbon benzene is a well-recognised haematotoxin and carcinogen associated with malignancy in occupational environments. Primary benzene metabolites phenol, catechol, and hydroquinone are implicated in the progression from cytotoxicity to carcinogenicity, and malignant transformation in myelogenous cell lineage is hypothesised to encompass a complex multistep process involving gene mutations in cell signalling and mitosis, oncogene activation, downregulated immune-mediated tumour surveillance, anti-apoptotic activities, and genetic susceptibility. Several mechanisms of carcinogenicity are proposed but none are accepted widely as causative. Involvement of covariables such as duration and frequency of benzene exposure, metabolite concentration, and degree of biological interactions provides a theoretical framework for a multiple mechanistic model to explain cytotoxic-malignant transformation. Despite significant research in myeloid leukaemias, limited biological and epidemiological studies on benzene and its metabolites in nonhaematopoietic malignancies suggests more research is needed to determine its role in contributing to other cancer types.

Comparison of the effect of phenol and its derivatives on protein and free radical formation in human erythrocytes (in vitro)

The effect of phenolic compounds: phenol, 2,4-dichlorophenol (2,4-DCP), 2,4-dimethylphenol (2,4-DMP) and catechol on human erythrocytes was studied. The level of fluorescent label - 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (H(2)DCFDA) oxidation by phenolic compounds in erythrocytes as well as the carbonyl group content and hemoglobin denaturation were monitored. H(2)DCFDA has been utilized extensively as a marker for studies of oxidative stress at the cellular level. We noted that 2,4-DCP, 2,4-DMP and catechol induced an increase in the concentration- and time-dependent H(2)DCFDA oxidation. We also observed an increase in carbonyl group content and the changes in parameter T (denaturation of hemoglobin) in erythrocytes incubated with 2,4-DCP, catechol and 2,4-DMP. The highest level of H(2)DCFDA oxidation was provoked by 2,4-DCP. The biggest changes of proteins in erythrocytes measured as the carbonyl group content were induced by 2,4-DMP, but measured as parameter T they were induced by catechol. It was observed that phenol did not oxidize H(2)DCFDA up to the concentration of 2.5 mM after 3 h of incubation. Phenol did not affect the carbonyl group content but decreased parameter T (induced denaturation of hemoglobin). To sum up, the kind of the substituent in a phenolic ring determines the molecular mechanism of action of the individual compound and the capacity of reactive oxygen species generation and thus damages the specified structures in human erythrocytes.

Inhibitory effects of catechol accumulation on benzene biodegradation in Pseudomonas putida F1 cultures

The influence of benzene concentration on the specific growth rate (mu), CO(2) and metabolite production, and cellular energetic content (i.e., ATP content), during benzene biodegradation by Pseudomonas putida F1 was investigated. Within the concentration range tested (5-130mg benzene l(-1)) the mu, the specific CO(2) production, and the ATP content remained constant at 0.42-0.48h(-1), 1.86+/-0.21g CO(2) g(-1) biomass, and 5.3+/-0.4x10(-6)mol ATP g(-1) biomass, respectively. Catechol accumulated during process start-up at all tested concentrations. Catechol specific production increased with increasing benzene inlet concentrations. This confirms that the transformation of this intermediate was the limiting step during benzene degradation. It was shown that catechol inhibited both the conversion of benzene to catechol and its further transformation. In addition, catechol concentrations higher than 10mgl(-1) significantly decreased both benzene and catechol associated respiration, confirming the highly inhibitory effect of this intermediate. This inhibitory threshold concentration was approximately two orders of magnitude lower than the concentrations present in the culture medium during process start-up, suggesting that cellular activity was always far below its maximum. Thus, due to its toxic and inhibitory nature and its tendency to accumulate at high benzene loading, catechol must be carefully monitored during process operation.

In utero-initiated cancer: the role of reactive oxygen species

It is becoming more evident that not only can drugs and environmental chemicals interfere with normal fetal development by causing structural malformations, such as limb defects, but that xenobiotic exposure during development can also cause biochemical and functional abnormalities that may ultimately lead to cancer later on in life. Fetal toxicity may be partly mediated by the embryonic bioactivation of xenobiotics to free radical intermediates that can lead to oxidative stress and potentially lead, in some cases, to carcinogenesis. Using a number of examples, this review will focus on the role of reactive oxygen species (ROS) in the mechanisms pertaining to in utero initiated cancers.

The role of c-MYB in benzene-initiated toxicity

Chronic exposure to benzene has been correlated with increased oxidative stress and leukemia. Oncogene activation, including c-Myb activation, is one of the earliest steps leading to the formation of leukemic cells, however the molecular mechanisms involved in these events are poorly understood. Given that oxidative stress can alter the activity and fate of cell signaling pathways we hypothesize that the bioactivation of benzene leads to the formation of reactive oxygen species (ROS), which if not detoxified can alter the c-Myb signaling pathway. Using chicken erythroblast HD3 cells we have shown that exposure to the benzene metabolites catechol, benzoquinone, and hydroquinone leads to increased c-Myb activity, increased phosphorylation of c-Myb and increased production of ROS supporting our hypothesis. Activation of the aryl hydrocarbon receptor (AhR) by environmental contaminants has also been associated with carcinogenesis and mice lacking this receptor are resistant to benzene-initiated hematotoxicity. Using wild type and AhR deficient cells we are investigating the role of this receptor in benzene-initiated alterations in the c-Myb signaling pathway. We have found that both wild type and AhR deficient cells are sensitive to catechol and hydroquinone-initiated increases in c-Myb activity while both cell types are resistant to benzene-initiated alterations leaving the role of the AhR still undetermined. Interestingly, protein expression of c-Myb is increased after catechol exposure in AhR deficient cells while decreased in wild-type cells. Further studies on the role of the AhR in benzene-initiated alterations on the c-Myb signaling pathway are on going.