Induction of differentiation in human myeloblastic leukemia ML-1 cells by heptachlor, a chlorinated hydrocarbon insecticide

Exposure to p,p'-DDE Induces Morphological Changes and Activation of the PKCα-p38-C/EBPβ Pathway in Human Promyelocytic HL-60 Cells

Dichlorodiphenyldichloroethylene (p,p′-DDE), the most persistent metabolite of dichlorodiphenyltrichloroethane (DDT), is still present in the human population. Both are present in the bone marrow of patients with bone marrow disorders, but thus far there are no studies that assess the capability of p,p′-DDE to affect myeloid cells. The aim of this study was to determine the effect of p,p′-DDE on promyelocytic cell differentiation and intracellular pathways related to this event. p,p′-DDE induced morphological changes compatible with promyelocytic differentiation in a concentration-dependent manner. The p,p′-DDE effect on [Ca²⁺]_i, C/EBPβ protein levels, PKCα and p38 activation, and the role of oxidative stress or PLA2 was assayed. Exposure to 1.9 μg/mL of p,p′-DDE increased [Ca²⁺]_i, PKCα, p38, and C/EBPβ protein levels; the increase of nuclear C/EBPβ protein was dependent on p38. PKCα phosphorylation was dependent on PLA2 and p,p′-DDE-induced oxidative stress. p38 phosphorylation induced by p,p′-DDE was dependent on PLA2, PKC activation, and oxidative stress. These effects of p,p′-DDE at concentrations found in human bone marrow may induce alterations in immature myeloid cells and could affect their cellular homeostasis. In order to establish the risk from exposure to p,p′-DDE on the development of bone marrow disorders in humans, these effects deserve further study.

Occupational exposure to pesticides and risk of hematopoietic cancers: meta-analysis of case–control studies

OBJECTIVE

In this study we conducted a meta-analysis of 13 case-control studies that examined the occurrence of hematopoietic cancers in pesticide related occupations in order to undertake a qualitative and quantitative evaluation of a possible relationship.

METHODS

Pubmed databases were searched for case-control studies published between 1990 and 2005 investigating the relation between hematopoietic cancers and occupational exposure to pesticides. Fixed and random effect meta-analysis models were used depending on the presence of heterogeneity between studies.

RESULTS

The overall meta-odds ratio obtained after pooling 44 ORs from 13 studies was 1.3 (95% CI: 1.3-1.5). We realized stratified analysis on three different types of hematopoietic cancers (non-Hodgkin lymphoma (NHL), leukemia and multiple myeloma). A significant increased risk of NHL was found (OR = 1.35; 95% CI = 1.2-1.5). Moreover, increased risks of Leukemia (OR = 1.35; 95% CI = 0.9-2) and multiple myeloma (OR = 1.16; 95% CI = 0.99-1.36) were also detected but these results were not statistically significant. Significant heterogeneity existed among the different studies and a publication bias was detected. Therefore, a meta-regression was carried out. Our results showed that a long period of exposure (more than 10 years) provided an increase in the risk of all hematopoietic cancers and for NHL by fractions of 2.18 (95% CI = 1.43-3.35) and 1.65 (95% CI = 1.08-2.51), respectively.

CONCLUSIONS

The overall meta-odds ratio suggests that there is a significantly positive association between occupational exposure to pesticides and all hematopoietic cancers as well as NHL. A major limitation of our meta-analysis is the lack of sufficient data about exposure information and other risk factors for hematopoietic cancer (genetic predisposition, ethnic origin, immunodepression...). In addition, data concerning specific subtypes of hematopoietic cancers are often confusing. Thus, future epidemiological studies should undertake a major effort to assess the identity and the level of pesticides exposure and should control for the most likely potential confounders.

Possible mechanisms underlying the mitogenic actionof heptachlor in rat hepatocytes

The worldwide use of the organochlorine pesticide heptachlor has led to widespread contamination in the environment. Like many other organochlorine pesticides, heptachlor is considered to pose a threat to human health. It has been shown that heptachlor is a tumor-promoting agent, but the mechanisms involved still remain unclear. The negative response of heptachlor in in vitro genotoxicity test suggests that this pesticide displays its carcinogenicity through epigenetic pathways. With the growing evidence that proliferation accounts for the tumor-promoting effects of many agents, the purpose of this work was to investigate the mechanisms involved in the mitogenic activity of heptachlor in quiescent rat hepatocytes and to understand the properties of this compound as a tumor promoter in the liver. Heptachlor triggered significant proliferation in quiescent rat hepatocytes. Two mechanisms were delineated to support the mitogenic effect in the hepatocyte: activation of key kinases in signaling pathways and inhibition of apoptosis. Exposure to heptachlor led to activation of protein kinase C mitogenactivated protein kinases. Moreover, these results indicate that like many tumor promoters, heptachlor strongly inhibited TGFbeta-induced apoptosis and cytochrome c release into the cytosol. The levels of the anti-apoptotic protein Bcl-2 were also increased in the presence of heptachlor. In conclusion, these results indicate that heptachlor alters basic cell function by interfering with key cellular signaling pathways.

Modulation of CPP32 activity and induction of apoptosis in Human CEM X 174 lymphocytes by heptachlor, a chlorinated hydrocarbon insecticide

Heptachlor is an organochlorine insecticide used worldwide for the control of pests both agriculturally and domestically. Its lipophilic structure allows it to bioaccumulate and pass through the food chain, exposing those who come in contact with it to its tumor promoting and possible carcinogenic effects. As a mechanism of tumor promotion, we explored the possibility of heptachlor suppressing the apoptotic process in human CEM x 174 lymphocytes. In this article, we describe the effect of heptachlor on the activity of the apoptosis protease CPP32. We show that heptachlor by itself was able to stimulate CPP32 activity at relatively high concentrations. When combined with the chemotherapeutic agent doxorubicin, a known CPP32 activator, a dual effect was observed. Low concentrations of heptachlor (5 microM-10 microM) suppressed doxorubicin-induced CPP32 activity, and high concentrations of heptachlor (80 microM-120 microM) augmented it. We also showed that heptachlor alone at relatively high concentrations induced apoptosis-associated changes in CEM x 174 cells including high molecular weight (HMW) DNA cleavage and chromatin condensation. From these results, it appears that heptachlor has tumor promoting-like effects at lower concentrations, and at higher concentrations induces apoptosis as a mechanism of cytotoxicity.

Effect of the chlorinated hydrocarbons heptachlor, chlordane, and toxaphene on retinoblastoma tumor suppressor in human lymphocytes

Organochlorine use over the past 50 years has resulted in the contamination of soil, water, plant and animal species. This contamination has created a long-lasting environmental problem, as the members of the organochlorine class of pesticides are resistant to degradation and have been labeled as persistent bioaccumulators. Studies have shown certain organochlorines to be tumor promoters, liver toxicants and to induce immune cell dysfunction in rats and mice. Our laboratory has shown that the organochlorines heptachlor and chlordane affect leukocytic gene expression and differentiation. In this study, experiments with CEM x 174 cells, a hybrid of human T and B cells, were performed to investigate the effects of the tumor promoter heptachlor and its congeners chlordane and toxaphene on retinoblastoma (Rb) gene expression. The results indicated that heptachlor, chlordane or toxaphene, in the range of 10-50 microM, were able to reduce Rb protein levels in a concentration-dependent manner. In the case of heptachlor, the reduction could be seen as early as 12 h and was time-dependent. Analysis of Rb mRNA levels revealed no detectable difference over the same concentration range. These results suggest that members of the organochlorine class are able to downregulate Rb expression at the post-transcriptional level, an effect similar to that on p53 tumor suppressor previously reported by our laboratory.

Heptachlor and the mitogen-activated protein kinase module in human lymphocytes

The organochlorine pesticide heptachlor constitutes a potential health hazard because of its persistence in nature, its reported contamination in food and milk, and its possible carcinogenic effects. As a tumor promoter, heptachlor induces human myeloblastic leukemia cells to differentiate, and also down-regulates the tumor suppressor gene p53 in human immune cells. In this study, the heptachlor signaling pathway in human lymphocytes was studied. Addition of heptachlor to human CEM x174 lymphocytic cells reduced the cellular levels of MAP kinase (MAPK, mitogen-activated protein kinase) cascade proteins, including ERK1 (a 44-kDa MAPK), ERK2 (a 42-kDa MAPK), a 85-kDa and a 54-kDa MAP kinase, MEK1 (a 45-kDa ERK kinase) and MEKK (a 78-kDa MEK kinase). However, heptachlor treatment caused a marked increase in the expression of the activated (Thr- and Tyr-dually phosphorylated) ERK1 and ERK2 in the cells. These studies indicate that mitogen-activated protein kinases are important intermediates in the signal transduction pathway of immune cells upon heptachlor exposure, and the observation of stimulation of activated MAP kinases without a simultaneous accumulation of basal enzymes may suggest the involvement of a negative feedback control mechanism in the pathway.

The effect of heptachlor, a chlorinated hydrocarbon insecticide, on p53 tumor suppressor in human lymphocytes

Previous studies have shown that heptachlor, a chlorinated hydrocarbon insecticide, is a liver tumor promoter in rats and mice and induces tumor promoting-like alterations in human myeloblastic leukemia cells. The nature of tumor promotion is multifaceted and has recently been shown to include suppression of programmed cell death (apoptosis) as a mechanism by which a tumor promoter can prolong cell viability. The ability of tumor promoters to suppress apoptosis prompted us to address the question of whether heptachlor is capable of effecting the expression of genes involved in lymphocyte apoptosis, in particular, the p53 tumor suppressor gene. Experiments with a CEM x 174 cell line, a hybrid of human T and B cells, revealed that heptachlor downregulated p53 gene expression at the post-transcriptional level without changing levels of mRNA in the cells. The heptachlor-induced reduction in the basal levels of expression of this gene was both in a concentration and time-dependent manner.

Characterization of quinone reductase, glutathione and glutathione S-transferase in human myeloid cell lines: induction by 1,2-dithiole-3-thione and effects on hydroquinone-induced cytotoxicity

In this study, we have characterized quinone reductase (QR), glutathione (GSH), glutathione S-transferase (GST) and their induction by a chemoprotector, 1,2-dithiole-3-thione (D3T), in the human myeloid cell lines ML-1 and HL-60. In addition, we also examined the toxicity of hydroquinone (HQ), a benzene metabolite, to these two cell lines. Both of the cell lines contain a basal level of cellular GSH, which is similar in the two cell lines. Although ML-1 cells contain much higher QR specific activity than HL-60 cells, which are relatively QR deficient, the GST specific activity of ML-1 cells is 1.8 times less than that of HL-60 cells. Immunoblot experiments showed that the GST in these two cell lines is GST pi. In addition, HL-60 cells exhibit 4.5 times more myeloperoxidase specific activity than ML-1 cells. Inclusion of D3T in the cultures could induce significant increases in cellular GSH content and QR activity, but not GST activity in either cell line. Treatment with HQ caused both inhibition of cell proliferation and loss of cell viability in these two myeloid cell lines. HQ treatment also resulted in a significant depletion of cellular GSH, which preceded the loss of cell viability. Pretreatment of both cell lines with buthionine sulfoximine, an inhibitor of GSH biosynthesis, markedly increased HQ-induced toxicity. In contrast, the presence of dicumarol, a QR inhibitor, failed to potentiate HQ-induced toxicity in ML-1 cells. On the other hand, pretreatment of these two myeloid cell lines with D3T significantly protected against HQ-induced inhibition of cell proliferation and cell death. Therefore, the above results suggest that GSH but not QR is an important factor involved in the toxicodynamics of HQ in these myeloid cells.

The effect of the insecticide heptachlor on ras proto-oncogene expression in human myeloblastic leukemia (ML-1) cells

Expression of the ras proto-oncogene mRNA in human myeloblastic leukemia (ML-1) cells was analyzed as a function of cDNA amplification by polymerase chain reaction (PCR). By using a pair of oligonucleotides that flank exon-2 from opposite strands (5' and 3') of H-ras cDNA for PCR amplification, ML-1 cells were found to express a 112 bp segment of the ras transcript. A rapid decline in the expression of this transcript was seen in cells treated with heptachlor, a chlorinated hydrocarbon insecticide. Expression of the same ras segment was not affected by treatment of ML-1 with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Furthermore, addition of serum to quiescent, heptachlor-treated cultures of ML-1 cells inhibited the effect of heptachlor and restored the expression of the ras protooncogene mRNA.