Hydroquinone inhibits PMA-induced activation of NFkappaB in primary human CD19+ B lymphocytes

Benzene and its effects on cell signaling pathways related to hematopoiesis and leukemia

Benzene is an environmental toxicant found in many consumer products. It is an established human carcinogen and is known to cause acute myeloid leukemia in adults. Epidemiological evidence has since shown that benzene can cross the placenta and affect the fetal liver. Animal studies have shown that in utero exposure to benzene can increase tumor incidence in offspring. Although there have been risk factors established for acute myeloid leukemia, they still do not account for many of the cases. Clearly then, current efforts to elucidate the mechanism by which benzene exerts its carcinogenic properties have been superficial. Owing to the critical role of cell signaling pathways in the development of an organism and its various organ systems, it seems plausible to suspect that these pathways may have a role in leukemogenesis. This review article assesses current evidence of the effects of benzene on critical hematopoietic signaling pathways. Pathways discussed included Hedgehog, Notch/Delta, Wingless/Integrated, nuclear factor-kappaB and others. Following a review of the literature, it seems that current evidence about the effects of benzene on these critical signaling pathways remains limited. Given the important role of these pathways in hematopoiesis, more attention should be given to them.

Hydroquinone Exhibits In Vitro and In Vivo Anti-Cancer Activity in Cancer Cells and Mice

Hydroquinone (HQ, 1,4-benzenediol) is a hydroxylated benzene metabolite with various biological activities, including anti-oxidative, neuroprotective, immunomodulatory, and anti-inflammatory functions. However, the anti-cancer activity of HQ is not well understood. In this study, the in vitro and in vivo anti-cancer activity of HQ was investigated in various cancer cells and tumor-bearing mouse models. HQ significantly induced the death of A431, SYF, B16F10, and MDA-MB-231 cells and also showed a synergistic effect on A431 cell death with other anti-cancer agents, such as adenosine-2′,3′-dialdehyde and buthionine sulfoximine. In addition, HQ suppressed angiogenesis in fertilized chicken embryos. Moreover, HQ prevented lung metastasis of melanoma cells in mice in a dose-dependent manner without toxicity and adverse effects. HQ (10 mg/kg) also suppressed the generation of colon and reduced the thickness of colon tissues in azoxymethane/dextran sodium sulfate-injected mice. This study strongly suggests that HQ possesses in vitro and in vivo anti-cancer activity and provides evidence that HQ could be developed as an effective and safe anti-cancer drug.

Hydroquinone suppresses IFN-β expression by targeting AKT/IRF3 pathway

Previous studies have demonstrated the role of hydroquinone (HQ), a hydroxylated benzene metabolite, in modulating various immune responses; however, its role in macrophage-mediated inflammatory responses is not fully understood. In this study, the role of HQ in inflammatory responses and the underlying molecular mechanism were explored in macrophages. HQ down-regulated the expression of interferon (IFN)-β mRNA in LPS-stimulated RAW264.7 cells without any cytotoxicity and suppressed interferon regulatory factor (IRF)-3-mediated luciferase activity induced by TIR-domain-containing adapter-inducing interferon-β (TRIF) and TANK-binding kinase 1 (TBK1). A mechanism study revealed that HQ inhibited IRF-3 phosphorylation induced by lipopolysaccharide (LPS), TRIF, and AKT by suppressing phosphorylation of AKT, an upstream kinase of the IRF-3 signaling pathway. IRF-3 phosphorylation is highly induced by wild-type AKT and poorly induced by an AKT mutant, AKT C310A, which is mutated at an inhibitory target site of HQ. We also showed that HQ inhibited IRF-3 phosphorylation by targeting all three AKT isoforms (AKT1, AKT2, and AKT3) in RAW264.7 cells and suppressed IRF-3-mediated luciferase activities induced by AKT in HEK293 cells. Taken together, these results strongly suggest that HQ inhibits the production of a type I IFN, IFN-β, by targeting AKTs in the IRF-3 signaling pathway during macrophage-mediated inflammation.

JS-III-49, a hydroquinone derivative, exerts anti-inflammatory activity by targeting Akt and p38

Since previous studies have reported that hydroquinone (HQ) exerted immunosuppressive and anti-inflammatory activity, various HQ derivatives have been synthesized and their biological activities investigated. In this study, we explored the anti-inflammatory activity of JS-III-49, a novel HQ derivative, in macrophage-mediated inflammatory responses. JS-III-49 suppressed the production of the inflammatory mediators nitric oxide (NO) and prostaglandin E₂ (PGE₂) and down-regulated the mRNA expression of the inflammatory enzymes cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) as well as the expression of the pro-inflammatory cytokines interleukin-6 (IL-6) and IL-1b without cytotoxicity in LPS-stimulated RAW264.7 cells. JS-III-49 inhibited nuclear translocation of the NF-kB transcription factors p65 and p50 by directly targeting Akt, an upstream kinase of the NF-kB pathway, in LPS-stimulated RAW264.7 cells. However, JS-III-49 did not directly inhibit the kinase activities of Src and Syk, which are upstream kinases of Akt, in LPS-stimulated RAW264.7 cells. Moreover, JS-III-49 suppressed the nuclear translocation of c-Fos, one of the components of AP-1, by specifically targeting p38, an upstream mitogen-activated protein kinase (MAPK) in the AP-1 pathway in LPS-stimulated RAW264.7 cells. These results suggest that JS-III-49 plays an anti-inflammatory role in LPS-stimulated macrophages by targeting Akt and p38 in the NF-kB and AP-1 pathways, respectively.

Tetrachlorobenzoquinone exhibits neurotoxicity by inducing inflammatory responses through ROS-mediated IKK/IκB/NF-κB signaling

Tetrachlorobenzoquinone (TCBQ) is a joint metabolite of persistent organic pollutants (POPs), hexachlorobenzene (HCB) and pentachlorophenol (PCP). Previous studies have been reported that TCBQ contributes to acute hepatic damage due to its pro-oxidative nature. In the current study, TCBQ showed the highest capacity on the cytotoxicity, ROS formation and inflammatory cytokines release among four compounds, i.e., HCB, PCP, tetrachlorohydroquinone (TCHQ, reduced form of TCBQ) and TCBQ, in PC 12 cells. Further mechanistic study illustrated TCBQ activates nuclear factor-kappa B (NF-κB) signaling. The activation of NF-κB was identified by measuring the protein expressions of inhibitor of nuclear factor kappa-B kinase (IKK) α/β, p-IKKα/β, an inhibitor of NF-κB (IκB) α, p-IκBα, NF-κB (p65) and p-p65. The translocation of NF-κB was assessed by Western blotting of p65 in nuclear/cytosolic fractions, electrophoretic mobility shift assay (EMSA) and luciferase reporter gene assay. In addition, TCBQ significantly induced protein and mRNA expressions of inflammatory cytokines and mediators, such as interleukin-1 beta (IL-1β), IL-6, tumor necrosis factor-alpha (TNF-α), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and the production of nitric oxide (NO) and prostaglandin E2 (PGE2). Pyrrolidine dithiocarbamate (PDTC), a specific NF-κB inhibitor inhibited these effects efficiently, further suggested TCBQ-induced inflammatory responses involve NF-κB signaling. Moreover, antioxidants, i.e., N-acetyl-l-cysteine (NAC), Vitamin E and curcumin, ameliorated TCBQ-induced ROS generation as well as the activation of NF-κB, which implied that ROS serve as the upstream molecule of NF-κB signaling. In summary, TCBQ exhibits a neurotoxic effect by inducing oxidative stress-mediated inflammatory responses via the activation of IKK/IκB/NF-κB pathway in PC12 cells.

Hydroquinone regulates hemeoxygenase-1 expression via modulation of Src kinase activity through thiolation of cysteine residues

The hydroxylated benzene metabolite hydroquinone (HQ) is mainly generated from benzene, an important industrial chemical, and is also a common dietary component. Although numerous papers have addressed the potential role of HQ in tumorigenic responses, the immunosuppressive and anti-inflammatory effects of hydroquinone have also been considered. In this study, we characterized the mechanism of the induction of hemeoxygenase (HO)-1 and other phase 2 enzymes by HQ and its derivatives. HQ upregulated the mRNA and protein levels of HO-1 by increasing the antioxidant-response element-dependent transcriptional activation of Nrf-2. Src knockdown or deficiency induced via siRNA treatment and infection with a retrovirus expressing shRNA targeting Src, as well as exposure to PP2, a Src kinase inhibitor, strongly abrogated HO-1 expression. Interestingly, HQ directly targeted and bound to the sulfhydryl group of cysteine-483 (C483) and C400 residues of Src, potentially leading to disruption of intracellular disulfide bonds. Src kinase activity was dramatically enhanced by mutation of these cysteine sites, implying that these sites may play an important role in the regulation of Src kinase activity. Therefore, our data suggest that Src and, particularly, its C483 target site can be considered as prime molecular targets of the HQ-mediated induction of phase 2 enzymes, which is potentially linked to HO-1-mediated cellular responses such as immunosuppressive and anti-inflammatory actions.

Utilization of IκB-EGFP Chimeric Gene as an Indicator to Identify Microbial Metabolites with NF-κB Inhibitor Activity

NF-κB regulates several important expressions, such as cytokine release, anti-apoptosis, adhesion molecule expression, and cell cycle processing. Several NF-κB inhibitors have been discovered as an anti-tumor or anti-inflammatory drug. The activity of NF-κB transcription factor is negatively regulated by IκB binding. In this study, IκB assay system was established and IκB–EGFP fusion protein was used as an indicator to monitor the effects of substances on the IκB degradation. The results indicated that the chosen hydroquinone could inhibit the IκB degradation and cause the cell de-attachment from the bottom of culture plate. In addition, this system could also monitor the IκB degradation of microbial metabolite of natural mixtures of propolis. Thus, the IκB assay system may be a good system for drug discovery related to microbial metabolite.

Akt Cys-310-targeted inhibition by hydroxylated benzene derivatives is tightly linked to their immunosuppressive effects

The hydroxylated benzene metabolite hydroquinone (HQ) is mainly generated from benzene, an important industrial chemical, and is also a common dietary component. Although numerous reports have addressed the tumorigenesis-inducing effects of HQ, few papers have explored its molecular regulatory mechanism in immunological responses. In this study we characterized Akt (protein kinase B)-targeted regulation by HQ and its derivatives, in suppressing inflammatory responses using cellular, molecular, biochemical, and immunopharmacological approaches. HQ down-regulated inflammatory responses such as NO production, surface levels of pattern recognition receptors, and cytokine gene expression with IC(50) values that ranged from 5 to 10 microm. HQ inhibition was mediated by blocking NF-kappaB activation via suppression of its translocation pathway, which is composed of Akt, I kappaB alpha kinase beta, and I kappaB alpha. Of the targets in this pathway, HQ directly targeted and bound to the sulfhydryl group of Cys-310 of Akt and sequentially interrupted the phosphorylation of both Thr-308 and Ser-473 by mediation of beta-mercaptoethanol, according to the liquid chromatography/mass spectroscopy analysis of the interaction of HQ with an Akt-derived peptide. Therefore, our data suggest that Akt and its target site Cys-310 can be considered as a prime molecular target of HQ-mediated immunosuppression and for novel anti-Akt-targeted immunosuppressive drugs.

Relationships between metabolic and non-metabolic susceptibility factors in benzene toxicity

Reactive metabolites formed from benzene include benzene oxide, trans,trans muconaldehyde, quinones, thiol adducts, phenolic metabolites and oxygen radicals. Susceptibility to the toxic effects of benzene has been suggested to occur partly because of polymorphisms in enzymes involved in benzene metabolism which include cytochrome P450 2E1, epoxide hydrolases, myeloperoxidase, glutathione-S-transferases and quinone reductases. However, susceptibility factors not directly linked to benzene metabolism have also been associated with its toxicity and include p53, proteins involved in DNA repair, genomic stability and expression of cytokines and/or cell adhesion molecules. In this work, we examine potential relationships between metabolic and non-metabolic susceptibility factors using the enzyme NAD(P)H:quinone oxidoreductase (NQO1) as an example. NQO1 may also impact pathways in addition to metabolism of quinones due to protein-protein interactions or other mechanisms related to NQO1 activity. NQO1 has been implicated in stabilizing p53 and in maintaining microtubule integrity. Inhibition or knockdown of NQO1 in bone marrow endothelial cells has been found to lead to deficiencies of E-selectin, ICAM-1 and VCAM-1 adhesion molecule expression after TNFalpha stimulation. These examples illustrate how the metabolic susceptibility factor NQO1 may influence non-metabolic susceptibility pathways for benzene toxicity.

Suppressive effect of hydroquinone, a benzene metabolite, on in vitro inflammatory responses mediated by macrophages, monocytes, and lymphocytes

We investigated the inhibitory effects of hydroquinone on cytokine release, phagocytosis, NO production, ROS generation, cell-cell/cell fibronectin adhesion, and lymphocyte proliferation. We found that hydroquinone suppressed the production of proinflammatory cytokines [tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6], secretion of toxic molecules [nitric oxide (NO) and reactive oxygen species (ROS)], phagocytic uptake of FITC-labeled dextran, upregulation of costimulatory molecules, U937 cell-cell adhesion induced by CD18 and CD29, and the proliferation of lymphocytes from the bone marrow and spleen. Considering that (1) environmental chemical stressors reduce the immune response of chronic cigarette smokers and children against bacterial and viral infections and that (2) workers in petroleum factories are at higher risk for cancer, our data suggest that hydroquinone might pathologically inhibit inflammatory responses mediated by monocytes, macrophages, and lymphocytes.

Effect of in vivo phenol or hydroquinone exposure on events related to neutrophil delivery during an inflammatory response

Phenol (PHE) and hydroquinone (HQ) are metabolites of benzene that affect leukocytes after solvent intoxication. Hence, we investigated the effects of PHE or HQ exposure on neutrophil mobilization during an inflammatory response. Male Wistar rats received intraperitoneal injections of PHE, HQ or vehicle only and assays were performed 24 h after the last dose. Quantifications of bone marrow or circulating leukocytes showed that only HQ exposure induced neutrophilia, probably due to the accelerated mobilization from the bone marrow compartment, since reduced numbers of segmented cells in the last phase of maturation were detected there. Intravital microscopy showed that circulating leukocytes of HQ-exposed rats increased their rolling behavior and adherence to the mesenteric postcapillary venule wall in vivo. The enhanced leukocyte-endothelium interaction was not dependent on microvascular reactivity or perivascular mast cell degranulation. Instead, it was the result of neutrophil activation, demonstrated by a decrease in L-selectin and an increase in beta2 integrin expression on neutrophil membranes. This pattern of neutrophil activation may have contributed to the higher number of neutrophils in the subcutaneous inflammatory response of HQ-exposed rats after oyster glycogen injection. Taken together, our results indicate that HQ exposure alters neutrophil mobilization, which results in an exacerbated response after an injury. Although PHE is endogenously metabolized to HQ, PHE exposure only induced an increment in rolling behavior, which was not sufficient to alter the inflammatory response.

Inhibition of NF-kappaB by hydroquinone sensitizes human bone marrow progenitor cells to TNF-alpha-induced apoptosis

Suppression of hematopoiesis is an important mechanism governing blood cell formation. Factors such as tumor necrosis factor alpha (TNF-alpha) inhibit proliferation and colony-forming activity of bone marrow cells and activate nuclear factor kappa B (NF-kappaB) in multiple cell types. Activated NF-kappaB is required for many cells to escape apoptosis, including hematopoietic progenitor cells (HPC). The benzene metabolite hydroquinone (HQ) alters cytokine response and induces cell death in HPC, and inhibits NF-kappaB activation in T and B cells. Therefore, we studied the potential role of HQ-induced NF-kappaB inhibition in a hematopoietic cell line (TF-1) and primary HPC in rendering these cells susceptible to TNF-alpha-induced apoptosis. We demonstrate in both cell types that TNF-alpha activates NF-kappaB, and HQ exposure inhibits activation of NF-kappaB by TNF-alpha in a dose dependent manner. We further investigated the ability of HQ to potentiate TNF-alpha-induced apoptosis in these cells, and found that HQ sensitized the cells to the pro-apoptotic effect of TNF-alpha. These results suggest that NF-kappaB plays a key role in HPC survival, and that HQ-induced inhibition of NF-kappaB leaves these cells susceptible to cytokine-induced apoptosis. These effects may play a role in the suppression of hematopoiesis seen in some benzene exposed individuals.