Benzene and the hemopoietic stem cell

Nonlinear low dose hematotoxicity of benzene; a pooled analyses of two studies among Chinese exposed workers

BACKGROUND

Impairment of the hematopoietic system is one of the primary adverse health effects from exposure to benzene. We previously have shown that exposure to benzene at low levels (<1 ppm) affects the blood forming system and that these effects were proportionally stronger at lower versus higher levels of benzene exposure. This observation is potentially explained by saturation of enzymatic systems.

METHODS

Here we extend these analyses by detailed modeling of the exposure response association of benzene and its major metabolites (i.e. catechol, muconic acid, phenol, and hydroquinone) on peripheral white blood cell (WBC) counts and its major cell-subtypes (i.e. granulocytes, lymphocytes, and monocytes) using two previously published cross-sectional studies among occupationally exposed Chinese workers.

RESULTS

Supra-linear exposure response associations were observed between air benzene concentrations (range ∼ 0.1 - 100 ppm) and WBC counts and its cell-subtypes, with a larger than proportional decrease in cell counts at lower than at higher levels of benzene exposure. The hematotoxicity associations were largely similar in shape when the analyses were repeated with benzene urinary metabolites suggesting that enzymatic saturation is not a full explanation of the observed non-linearity with WBC endpoints.

DISCUSSION

We hypothesize that the flattening of the exposure response curve especially at higher benzene exposure levels may reflect a response by the bone marrow to maintain hematopoietic homeostasis. Toxicity to the bone marrow and an induced hyper-proliferative response could both contribute to risk of subsequently developing a hematopoietic malignancy. Additional work is needed to explore this hypothesis.

Immunosuppression characterized by increased Treg cell and IL-10 levels in benzene-induced hematopoietic toxicity mouse model

Benzene is a typical hematopoietic toxic substance, that can cause serious blood and circulatory system diseases such as aplastic anemia, myelodysplastic syndrome and acute myeloid leukemia, but the immunological mechanism by which this occurs is not clear. T helper cells play a key role in regulating the immune balance in the body. In this study, benzene-induced hematopoietic toxicity BALB/c mice model was established, and changes in immune organs and T helper cell subsets (Th1, Th2, Th17 and Treg cells) were explored. At 28 days after subcutaneous injection of 150 mg/kg benzene, mice showed pancytopenia and obvious pathological damage to the bone marrow, spleen, and thymus. Flow cytometry revealed that the number of CD4⁺CD25⁺Foxp3⁺ Treg cells in the spleen increased significantly. The level of IL-10 in the spleen, serum, and bone marrow increased, while the levels of IL-17 in the spleen and serum decreased. Furthermore, the levels of CD4 and CD8 proteins in the spleen decreased. Immunofluorescence results showed that levels of Foxp3, a specific transcription factor that induced the differentiation of Treg cells, increased after exposure to benzene. Our results demonstrate that immunosuppression occurred in the benzene-induced hematopoietic toxicity model mice, and Treg cells and secreted IL-10 may play a key role in the process.

Lipidomic analysis reveals disturbances in glycerophospholipid and sphingolipid metabolic pathways in benzene-exposed mice

Benzene, a known occupational and environmental contaminant, has been recognized as the hematotoxin and human carcinogen. Lipids have a variety of important physiological functions and the abnormal lipid metabolism has been reported to be closely related to the occurrence and development of many diseases. In the present study, we aim to utilize LC-MS/MS lipidomic platform to identify novel biomarkers and provide scientific clues for mechanism study of benzene hematotoxicity. Results showed that a total of 294 differential metabolites were obtained from the comparison of benzene-treated group and control group. The glycerophospholipid pathway was altered involving the down-regulation of the levels of phosphatidylcholine and phosphatidylserine. In addition, phosphatidylethanolamine (PE) and 1-Acyl-sn-glycero-3-phosphocholine levels were increased in benzene-treated group. Based on the relationship between PE and autophagy, we then found that effective biomarker of autophagy, Beclin1 and LC3B, were increased remarkably. Furthermore, following benzene treatment, significant decreases in glucosylceramide (GlcCer) and phytosphingosine (PHS) levels in sphingolipid pathway were observed. Simultaneously, the levels of proliferation marker (PCNA and Ki67) and apoptosis regulator (Bax and Caspase-3) showed clear increases in benzene-exposed group. Based on our results, we speculate that disturbances in glycerophospholipid pathway play an important role in the process of benzene-induced hematopoietic toxicity by affecting autophagy, while sphingolipid pathway may also serve as a vital role in benzene-caused toxicity by regulating proliferation and apoptosis. Our study provides basic study information for the future biomarker and mechanism research underlying the development of benzene-induced blood toxicity.

Proteome Changes of Human Bone Marrow Mesenchymal Stem Cells Induced by 1,4-Benzoquinone

Benzene is metabolized to hydroquinone in liver and subsequently transported to bone marrow for further oxidization to 1,4-benzoquinone (1,4-BQ), which may be related to the leukemia and other blood disorders. In the present study, we investigated the proteome profiles of human primary bone marrow mesenchymal stem cells (hBM-MSCs) treated by 1,4-BQ. We identified 32 proteins that were differentially expressed. Two of them, HSP27 and Vimentin, were verified at both mRNA and protein levels and their cellular localization was examined by immunofluorescence. We also found increased mRNA level of RAP1GDS1, a critical factor of metabolism that has been identified as a fusion partner in various hematopoietic malignancies. Therefore, these differentially expressed proteins can play important roles in benzene-mediated hematoxicity.

Immunosuppressive therapy in patients with aplastic anemia: a single-center retrospective study

BACKGROUND

Aplastic anemia (AA) is a rare disease in which hematopoietic stem cells are severely diminished resulting in hypocellular bone marrow and pancytopenia. Etiology of AA includes auto immunity, toxins, infection, ionizing radiation, drugs and rare genetic disorders, but in the majority of cases no cause can be identified. In the present study we assessed response rate, survival, relapse and clonal evolution in patients with AA treated with immunosuppressive therapy.

METHODS

Patients with AA who received immunosuppressive therapy between May 1998 and September 2013 were included in this study. Patients with non-severe AA (NSAA) were treated with cyclosporine (CsA) and danazol while patients with severe AA (SAA) as well as patients with NSAA who progressed to SAA after beginning of the treatment, were candidates for receiving antithymocyte globulin in addition to CsA and danazol.

RESULTS

Among the 63 studied patients, 29 (46%) had NSAA and 34 (54%) had SAA. Three months after treatment, overall response was 58.6% in NSAA and 12.9% in patients with SAA. Survival of all patients at 5, 10 and 15 years were 73%, 55% and 49%, respectively. Survival rates were significantly higher in patients with NSAA compared to patients with SAA as well as in patients who responded at 6 months compared to non-responders. The relapse risk was 39.7% at 10 years. Relapse occurred in patients who discontinued the therapy more than those who continued taking CsA (p value<0.01). The risk of clonal evolution was 9.9% at 10 years and 22.8% at 15 years after treatment.

CONCLUSION

This long-term retrospective study indicated that immunosuppressive therapy should be recommended to patients with AA. Also, our experience indicated that immunosuppressive therapy should not be discontinued after response to therapy in patients with both NSAA and SAA due to high risk of relapse. Low dose of CsA should be continued indefinitely.

Metabolic polymorphisms and biomarkers of effect in the biomonitoring of occupational exposure to low-levels of benzene: state of the art

Current levels of occupational exposure to benzene, a genotoxic human carcinogen, in Western countries are reduced by two-three orders of magnitude (from ppm to ppb) as compared to the past. However, as benzene toxicity is strongly dependent on biotransformation and recent evidence underlines a higher efficiency of bio-activation pathways at lower levels of exposure, toxic effects at low doses could be higher than expected, particularly in susceptible individuals. Currently, biological monitoring can allow accurate exposure assessment, relying on sensitive and specific enough biomarkers of internal dose. The availability of similarly reliable biomarkers of early effect or susceptibility could greatly improve the risk assessment process to such an extent that risk could even be assessed at the individual level. As to susceptibility biomarkers, functional genetic polymorphisms of relevant biotransformation enzymes may modulate the risk of adverse effects (NQO1) and the levels of biomarkers of internal dose, in particular S-phenylmercapturic acid (GSTM1, GSTT1, GSTA1). Among biomarkers of early effect, genotoxicity indicators, although sensitive in some cases, are too aspecific for routine use in occupational health surveillance programmes. Currently only the periodical blood cell count seems suitable enough to be applied in the longitudinal monitoring of effects from benzene exposure. Novel biomarkers of early effect are expected from higher collaboration among toxicologists and clinicians, also using advanced "omics" techniques.

Diagnosis and treatment of acquired aplastic anaemia in adults: 142 cases from a multicentre, prospective cohort study in Shanghai, China

To improve diagnosis and therapy for aplastic anaemia (AA) in Shanghai, clinical and laboratory data for patients with AA (n = 142) and hypocellular myelodysplastic syndrome (MDS; n = 22) were comparatively analysed (follow-up 2 - 6 years). Red blood cell distribution width and absolute lymphocyte and reticulocyte counts were significantly different between the two groups. AA was diagnosed in 54.2% of patients using a single bone marrow aspirate smear plus peripheral haemogram results, and in 95.1% using an additional bone marrow biopsy; 4.9% required multiple-site bone marrow examination. Clonal chromosomal abnormalities occurred in 3.9% and 31.8% of patients with AA and MDS, respectively. In patients with severe AA, 12.0% received antithymocyte globulin (ATG) + cyclosporin A (CSA; effectiveness rate 77.8%; 5-year survival 74.1%), 45.3% received CSA + androgen therapy (effectiveness rate 58.8%; 5-year survival 76.5%) and 26.7% received androgen monotherapy (effectiveness rate 25.0%). Multivariate analysis of prognostic factors indicated that therapy regimen and blood platelet count affected survival. Peripheral blood smears, bone marrow spicule classification and biopsy are important diagnostic factors. Standardization of evidence-based therapy and promotion of ATG + CSA would improve general therapeutic effects in AA.

Temozolomide-induced myelodysplasia

A patient who had received temozolomide (TMZ) as a single agent in treatment of malignant glioma developed therapy-induced myelodysplasia (T-MDS). TMZ is an orally active imidazotetrazine which methylates guanine residues in DNA, ultimately causing single and double-strand DNA breaks leading to apoptotic cell death. TMZ does not chemically cross-link DNA and is considered a nonclassical alkylating agent, similar in structure and activity to dacarbazine. Observations on this patient, and on similarly treated others, suggest that the cumulative dose threshold (CDT) for TMZ that predisposes to T-MDS and which may potentially lead to acute myeloid leukemia (T-AML) is around 18000 to 20000 mg/sq m. Although the incidence of T-MDS and the predisposing CDT of TMZ may differ from that of other potentially leukemogenic compounds currently and formerly used as chemotherapeutic agents, all alkylating agents, including TMZ, should be considered potentially leukemogenic when administered long term.

Advances in understanding benzene health effects and susceptibility

Benzene is a ubiquitous chemical in our environment that causes acute leukemia and probably other hematological cancers. Evidence for an association with childhood leukemia is growing. Exposure to benzene can lead to multiple alterations that contribute to the leukemogenic process, indicating a multimodal mechanism of action. Research is needed to elucidate the different roles of multiple metabolites in benzene toxicity and the pathways that lead to their formation. Studies to date have identified a number of polymorphisms in candidate genes that confer susceptibility to benzene hematotoxicity. However, a genome-wide study is needed to truly assess the role of genetic variation in susceptibility. Benzene affects the blood-forming system at low levels of occupational exposure, and there is no evidence of a threshold. There is probably no safe level of exposure to benzene, and all exposures constitute some risk in a linear, if not supralinear, and additive fashion.

ATSDR evaluation of health effects of benzene and relevance to public health

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the Toxicological Profile for Benzene. The primary purpose of this article is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of benzene. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.

Formaldehyde exposure and leukemia: a new meta-analysis and potential mechanisms

Formaldehyde is an economically important chemical, to which more than 2 million U.S. workers are occupationally exposed. Substantially more people are exposed to formaldehyde environmentally, as it is generated by automobile engines, is a component of tobacco smoke and is released from household products, including furniture, particleboard, plywood, and carpeting. The International Agency for Research on Cancer (IARC) recently classified formaldehyde as a human carcinogen that causes nasopharyngeal cancer and also concluded that there is "strong but not sufficient evidence for a causal association between leukemia and occupational exposure to formaldehyde". Here, we review the epidemiological studies published to date on formaldehyde-exposed workers and professionals in relation to lymphohematopoietic malignances. In a new meta-analysis of these studies, focusing on occupations known to have high formaldehyde exposure, we show that summary relative risks (RRs) were elevated in 15 studies of leukemia (RR=1.54; confidence interval (CI), 1.18-2.00) with the highest relative risks seen in the six studies of myeloid leukemia (RR=1.90; 95% CI, 1.31-2.76). The biological plausibility of this observed association is discussed and potential mechanisms proposed. We hypothesize that formaldehyde may act on bone marrow directly or, alternatively, may cause leukemia by damaging the hematopoietic stem or early progenitor cells that are located in the circulating blood or nasal passages, which then travel to the bone marrow and become leukemic stem cells. To test these hypotheses, we recommend that future studies apply biomarkers validated for other chemical leukemogens to the study of formaldehyde.

Inorganic arsenic induces necrosis of human CD34-positive haematopoietic stem cells

Inorganic arsenic is a major environmental contaminant known to exert immunosuppressive effects. In this study, we report toxicity of As2O3, a trivalent inorganic form, toward isolated human hematopoietic CD34+ progenitor cells. Our results demonstrate that low concentrations of As2O3 (0.1-5 microM) inhibit in vitro proliferation of CD34+ cells and their differentiation into various hematological cell lineages. These effects were associated with the induction of a necrotic process independent of caspases and likely related to mitochondrial damage. We conclude that As2O3 can impair in vitro human hematopoiesis by decreasing survival of CD34+ progenitor cells.

Benzene exposure and refractory sideroblastic erythropoiesis: is there an association?

The myelodysplastic syndromes (MDS) consist of a group of diverse hematological disorders that carry an increased risk of transforming into acute myeloid leukemia. They may appear de novo and without obvious cause (primary or de novo MDS) or be induced by certain mutagenic environmental or therapeutic toxins (secondary MDS). Excessive exposures to benzene are generally considered to be a potential environmental risk factor for both MDS and acute myeloid leukemia. However, such risk is unproven for each disease component within the MDS classification. A critical review of the refractory sideroblastic disorders strongly suggests that benzene exposure is not a potential cause of this distinct and still-evolving subset of MDS. The widely disparate nature of MDS suggests that epidemiologic studies can only provide meaningful data on associations and potential causation of its component syndromes by a disease-specific analysis, as is currently advocated for other hematological malignancies.

Benzene-induced acute myeloid leukemia: a clinician's perspective

Benzene-induced acute myeloid leukemia (AML) is considered a secondary form of AML, based both in theory and on limited cohort observations. Its latency, cytogenetic aberrations, and clinical features are thought similar to, or identical with, AML resulting from the use of modern day cytotoxic agents for chemotherapy and immunotherapy. Although distinction between secondary AML and the far more common de novo AML is difficult to establish with certainty in any given case, latency from toxic therapeutic and environmental exposure and certain clinical and pathological features generally separate these two entities. AML is the only human neoplasm proven to be potentially caused by benzene, which actually is an obsolete form of chemotherapy. Despite many years of environmental regulation, alleged toxic exposure to this ubiquitous chemical has become an expanding area of litigation. A review of benzene-induced AML suggests that, in developed countries, this entity should no longer merit serious consideration among workers in the modern petrochemical industry and related fields.

Repeated administration of diphenyl ditelluride induces hematological disorders in rats

In the present study, we investigated potential toxic effects of diphenyl ditelluride, as measured by biochemical and hematological parameters. Rats were given a daily dose of 0.3 micromol/kg diphenyl ditelluride by subcutaneous route and sacrificed at different times (24 and 48 h). Hepatic and renal TBARS levels were changed by diphenyl ditelluride exposure at the dose 0.9 micromol/Kg in rats. Diphenyl ditelluride exposure demonstrated an increase in AST (aspartate aminotransferase), ALT (alanine aminotransferase) and LDH (lactate dehydrogenase) activities. Plasma creatinine and urea levels increase after diphenyl ditelluride exposure. Diphenyl ditelluride also produced a significant decrease in plasma triglyceride and cholesterol levels. In contrast, this compound, at all doses tested, induced a marked increase in total leukocyte counts. The present study suggests that diphenyl ditelluride induces hematological disorders and provides evidence for renal and hepatic toxicity in rats.

Fluorescent in situ hybridization (FISH) in bone marrow and peripheral blood of leukemia patients: implications for occupational surveillance

Although there has been a rapid rise in the application of fluorescent in situ hybridization (FISH) analysis of bone marrow tissue for the staging and prognosis determination of hematopoietic malignacies such as the chronic and acute leukemias, it's application as a surveillance tool for leukemogen exposed high risk occupational cohorts is understandably limited by the invasiveness of sample collection. While some small occupational studies have been performed using FISH in peripheral blood with promising results, some of the basic assumptions made in utilizing the FISH technique have not been fully explored. These include selection of the correct hematopoietic cell to assay (myeloid or lymphoid); selection of appropriate chromosomal markers and the sensitivity of peripheral blood FISH in detecting unbalanced genomic abnormalities. In this study, we performed a pilot 'validation' exercise utilizing the FISH technique and standard metaphase cytogenetics, comparing results in tandem pairs of peripheral blood with bone marrow cells, where clonal abnormalities arise. Samples were taken from patients with known chromosomal lesions associated with active leukemia. We carefully chose markers most frequently associated with leukemogen-inducing DNA damage and probes that have been utilized successfully in clinical practice. Ten de novo or therapy-related acute myeloid leukemia (t-AML) patients underwent bone marrow cell karyotyping and fluorescent in situ hybridization (FISH) analysis. Parallel peripheral blood samples were concommitently drawn and evaluated with FISH using the same probes. In six of eight paired samples treated with a 3-day phytohemagglutinin (PHA) stimulation, typically used to assay lymphocytes and their progenitors, we detected abnormal clones. In one of the two remaining cases, we identified an abnormal clone in both bone marrow and PHA-stimulated peripheral blood, although at a level in the peripheral blood sample that would typically be reported as "non-diagnostic" for clinical purposes. These results suggest that use of FISH in PHA stimulated peripheral blood samples with probes commonly employed in t-AML evaluations (chromosomes 5q, 7q, 8, 11q) to detect cytogenetic abnormalities in peripheral blood represents a potentially promising though as yet, under-utilized approach for the occupational surveillance of workers exposed to leukemogens, especially if it could be linked to automated high-throughput assays for increased sensitivity.

Current concepts in the pathophysiology and treatment of aplastic anemia

Aplastic anemia, an unusual hematologic disease, is the paradigm of the human bone marrow failure syndromes. Almost universally fatal just a few decades ago, aplastic anemia can now be cured or ameliorated by stem-cell transplantation or immunosuppressive drug therapy. The pathophysiology is immune mediated in most cases, with activated type 1 cytotoxic T cells implicated. The molecular basis of the aberrant immune response and deficiencies in hematopoietic cells is now being defined genetically; examples are telomere repair gene mutations in the target cells and dysregulated T-cell activation pathways. Immunosuppression with antithymocyte globulins and cyclosporine is effective at restoring blood-cell production in the majority of patients, but relapse and especially evolution of clonal hematologic diseases remain problematic. Allogeneic stem-cell transplant from histocompatible sibling donors is curative in the great majority of young patients with severe aplastic anemia; the major challenges are extending the benefits of transplantation to patients who are older or who lack family donors. Recent results with alternative sources of stem cells and a variety of conditioning regimens to achieve their engraftment have been promising, with survival in small pediatric case series rivaling conventional transplantation results.