Evaluation of the immunomodulatory potential of diethyl dithiocarbamate derivatives

Toxicological evaluation of the immune function of pesticide workers, a European wide assessment

In this study, the prolonged low-dose exposure of mixtures of pesticides has been examined on hematological parameters and components of the immune defense in occupationally exposed humans. This investigation was carried out in five field studies in: the Netherlands (flower bulb growers, mainly re-entry workers), Italy (vineyard workers), Finland (potato farmers), and Bulgaria (workers from a zineb factory and greenhouse workers). Immunotoxicity was studied by measuring hematological parameters, complement, immunoglobulins, lymphocyte subpopulations, natural killer cells, autoimmunity, and antibody responses to hepatitis B vaccination. The total study population consisted of 248 pesticide-exposed and 231 non-occupationally exposed workers. As a surrogate measure of pesticide exposure the urinary excretion of ethylenethiourea (ETU), the main metabolite ethylenebisdithiocarbamates was measured. A significantly higher level of ETU in occupationally exposed subjects compared with controls (2.7 +/- 8.1 microg/g vs 0.5 +/- 3.7 microg/g creatinine) was found. Statistically significant differences, albeit very low, were found for complement C3 and C4 and the immunoglobulin classes IgG4 and IgA. For complement and IgG4, the levels were slightly increased and the level of IgA was decreased. In the lymphocyte populations, the CD8 subpopulation was increased. No effects were found on autoimmune antibodies and antibody response to hepatitis vaccination. In conclusion, pesticide exposure under various work place conditions in Europe was associated only with some subtle effects on the immune system, which may suggest that occupational exposure to pesticides does not influence the immunologic system in a clinically significant fashion, and does not pose a significant health risk to the exposed subjects.

Changes in serum markers indicative of health effects in vineyard workers following exposure to the fungicide mancozeb: an Italian study

The aim of this study was to investigate the health effects induced by exposure to the fungicide mancozeb in Italian vineyard workers. Ninety-three Italian subjects entered the study - 48 vine-growers intermittently exposed to mancozeb and 45 healthy controls. The subjects were investigated three times: before the seasonal application of pesticides (T0), 30 days after the beginning of the application period (T30), and 45 days after T0 (T45). At T0 the comparison between agricultural workers and controls showed a higher prevalence of cold or flu symptoms, a statistically significant lower percentage of monocytes, higher absolute count of T lymphocytes, CD4 and natural killer cells, and lower plasma levels of IgA and IgM in workers. Such differences were not confirmed at T30 and T45. In fact at T30 in exposed workers, besides a significant increase of urinary ethylenethiourea, confirming mancozeb exposure, T lymphocytes, CD4 and natural killer cells, IgA and IgM returned to values comparable to those observed in controls. Moreover, no other differences in clinical signs, haematological, and immune parameters, such as the immune functional capability evaluated as a response to hepatitis B vaccination, was observed. Altogether the differences between exposed and controls were not consistently correlated to any clinical impairment and suggest that the seasonal application of mancozeb does not pose a significant health risk to exposed subjects.

Molecular mechanisms underlying mancozeb-induced inhibition of TNF-alpha production

Mancozeb, a polymeric complex of manganese ethylenebisdithiocarbamate with zinc salt, is widely used in agriculture as fungicide. Literature data indicate that ethylenebisdithiocarbamates (EBDTCs) may have immunomodulatory effects in humans. We have recently found in agricultural workers occupationally exposed to the fungicide mancozeb a statistically significant decrease in lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha (TNF) production in leukocytes. TNF is an essential proinflammatory cytokine whose production is normally stimulated during an infection. The purpose of this work was to establish an in vitro model reflecting in vivo data and to characterize the molecular mechanism of action of mancozeb. The human promyelocytic cell line THP-1 was used as in vitro model to study the effects of mancozeb and its main metabolite ethylenthiourea (ETU) on LPS-induced TNF release. Mancozeb, but not ETU, at non-cytotoxic concentrations (1-100 microg/ml), induced a dose- and time-dependent inhibition of LPS-induced TNF release, reflecting in vivo data. The modulatory effect observed was not limited to mancozeb but also other EBDTCs, namely zineb and ziram, showed similar inhibitory effects. Mancozeb must be added before or simultaneously to LPS in order to observe the effect, indicating that it acts on early events triggered by LPS. It is known that nuclear factor-kappaB (NF-kappaB) tightly regulates TNF transcription. We could demonstrate that mancozeb, modulating LPS-induced reactive oxygen species generation, prevented IkappaB degradation and NF-kappaB nuclear translocation, which in turn resulted in decreased TNF production. To further understand the mechanism of the effect of mancozeb on TNF transcription, THP-1 cells were transfected with NF-kappaB promoter-luciferase construct, and the effect of mancozeb on luciferase activity was measured. Cells transfected with promoter constructs containing kappaB site showed decreased LPS-induced luciferase activity relative to control after mancozeb treatment, confirming NF-kappaB binding as an intracellular target of mancozeb. Overall, this study contributes to our understanding of the mechanism underlying mancozeb-induced immunotoxicity.

Alleviation of Picryl Chloride-Induced Delayed Type Hypersensitivity Reaction by Saponin Fraction of Gleditsia sinensis

The objective of the present study was to investigate the effects of saponin fraction from anomalous fruits of Gleditsia sinensis (SFGS) on picryl chloride-induced delayed type hypersensitivity (PC-DTH) and functions of T lymphocytes and macrophages in mice. SFGS (100, 200 mg/kg), orally administered during either sensitization stage or effector stage, produced remarkable inhibition of PC-DTH. In vitro, SFGS (1, 2, 4 microg/ml) concentration-dependently attenuated concanavalin A (Con A)-elicited mouse splenocyte proliferation and interleukin 2 (IL-2) production. At concentrations of 10 and 20 microg/ml, SFGS inhibited lipopolysaccharide (LPS)-induced production of nitric oxide and interleukin 1beta (IL-1beta) of mouse peritoneal macrophages. The findings indicate that SFGS attenuates PC-DTH in mice, which is probably mediated by preventing proliferation and differentiation of T cells during the sensitization stage and suppressing activation of macrophages during the effector stage.

Immunomodulatory effects of the fungicide Mancozeb in agricultural workers

Available data suggest that ethylenebisdithiocarbamates (EBDCs) may have immunomodulatory effects. This study aimed to investigate the immunological profile of farmers exposed to Mancozeb, an EBDC fungicide, through the determination of several serum, cellular, and functional immune parameters. Twenty-six healthy subjects entered the study, 13 vineyards exposed to Mancozeb and 13 unexposed controls. Exposure was assessed through the determination of ethylentiourea (ETU) in urine. Complete and differential blood count, serum immunoglobulins, complement fractions, autoantibodies, lymphocyte subpopulations, proliferative response to mitogens, natural killer (NK) activity, and cytokine production were measured. Post-exposure samples showed ETU urine concentration significantly higher than pre-exposure and control groups. A significant increase in CD19+ cells, both percentage and absolute number, and a significant decrease in the percentage of CD25+ cells were found in post-exposure samples compared to controls. A statistically significant increase in the proliferative response to phorbol myristate acetate plus ionomycin (PMA + ionomycin) was observed in the post-exposure group compared to controls and baseline, while a significant reduction in LPS-induced TNF-alpha release in post-exposure samples was observed. Overall, our results suggest that low-level exposure to Mancozeb has slight immunomodulatory effects, and point out a method adequate to reveal immune-modifications in workers occupationally exposed to potential immunotoxic compounds, based on a whole blood assay.

Carbofuran suppresses T-cell-mediated immune responses by the suppression of T-cell responsiveness, the differential inhibition of cytokine production, and NO production in macrophages

The effects of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzo-furanol N-methylcarbamate) on the functions of T cells in splenocytes and peritoneal macrophages were examined in view of T-cell-mediated immune response (CMIR) in male C57BL/6 mice. Intraperitoneal administration of carbofuran (0.075, 0.15 and 0.3 mg/kg body weight) resulted in significant suppression of delayed type hypersensitivity (DTH), indicating that it caused the suppression of CMIR. Carbofuran decreased Concanavalin A (Con A)- and alloantigen-induced proliferation, and interleukin (IL)-2 production of splenocytes. In vitro addition of rIL-2 could not completely restore the suppressed T-cell proliferation, and IL-2-induced proliferation of Con A-activated splenocytes was also suppressed, which implied that carbofuran caused defects in IL-2 production and responsiveness of splenocytes to IL-2, leading to the suppression of T-cell proliferation. Con A-induced production of interferon-gamma (IFN-gamma) was significantly suppressed by carbofuran, while that of IL-4 was not affected. The production of transforming growth factor-beta from splenocytes was also significantly inhibited by carbofuran. Judging from these results, carbofuran might directly suppress the cytokine production in T helper 1 (Th1) cells. In addition, IFN-gamma-induced production of nitric oxide (NO) in macrophages was also inhibited by carbofuran, which might be one of the important mechanisms of carbofuran-induced CMIR suppression in mice. Collectively, the present study suggests that carbofuran might suppress CMIR through the suppression of T-cell responsiveness, IFN-gamma production in Th1 cells, and NO generation in macrophages.

Bone marrow stem cell protection from chemotherapy by low--molecular-weight compounds

The stem cells of the bone marrow have the capacity for both self-renewal and derivation of all the blood cell lineages. Consequently, toxicity to these cells can result in neutropenia, agranulocytosis, thrombocytopenia, pancytopenia, or aplastic anemia. Many anticancer drugs adversely affect the bone marrow, and neutropenia is a common limiting factor in dose escalation. In this review, we discuss agents that appear to have potential as bone marrow sparing agents. Computerized catalogs of the National Library of Medicine and Medline were searched for reports on low-molecular-weight compounds that detailed effects on the hematopoietic progenitor cells. The most promising agents are the endogenous peptides p-glutamic acid-glutamic acid-aspartic acid-cysteine-lysine and acetyl-serine-aspartic acid-lysine-proline, and the exogenous compounds amifostine and ammonium trichloro[dioxoethylene-O,O']tellurate, but several others are also discussed. These compounds preserve stem cell function in the presence of antineoplastic drugs of diverse pharmacological classes, and they do so by various mechanisms of action. Their present status in clinical practice is also detailed. More needs to be learned about their mechanisms of action and therapeutic potential, but the results are encouraging for some of these compounds and more clinical trials should be expected.

Brazilin augments cellular immunity in multiple low dose streptozotocin (MLD-STZ) induced type I diabetic mice

Brazilin, an active principle of Caesalprenia sappan, was examined for its immunopotentiating effects in multiple low dose streptozotocin (MLD-STZ) induced type diabetic mice. Brazilin was intraperitoneally administered for 5 consecutive days to MLD-STZ induced type I diabetic mice. Delayed type hypersensitivity, Con A-induced proliferation of splenocytes and mixed lymphocyte reaction, which had been decreased in diabetic mice, were significantly recovered by the administration of brazilin. Brazilin increased IL-2 production without affecting suppressor cell activity. Con A-induced and IL-2-induced expression of high affinity IL-2 receptors were also enhanced by brazilin. These results indicate that brazilin augments cellular immune responses, which are suppressed in the MLD-STZ induced type I diabetic mice, by increasing IL-2 production and responsiveness of immune cells to IL-2.

Dithiocarbamates inhibit hematopoiesis via a copper-dependent mechanism

Dithiocarbamates (DTC), an important class of therapeutic and industrial chemicals, have alternatively been reported to be either beneficial or toxic to the hematopoietic and immune systems. In the present study, we investigated the potential of dimethyl- and diethyl-dithiocarbamate to alter clonogenic response of primary human CD34(+) bone marrow cells in vitro. Our results demonstrate that both compounds are potent inhibitors of clonogenic response in human CD34(+) bone marrow cells, suppressing cytokine-induced colony formation at concentrations between 100 and 500 nM. Pretreatment of bone marrow cells for 1 h with very high doses of DTC (30 microM) had no effect on colony formation. DTCs are known inhibitors of nuclear factor-kappa B (NF-kappa B); however, data presented herein demonstrate that DTC do not inhibit cytokine activation of NF-kappa B in CD34(+) bone marrow cells. Additional experiments demonstrate that DTCs induce a dose-related increase in apoptosis, potentially acting via a cytotoxic mechanism. We further demonstrate that the addition of copper sulfate greatly potentiates the hematotoxicity of DTC and that the addition of a copper-specific chelator completely abrogates DTC clonogenic suppression. These data support a role for copper in DTC-induced hematotoxicity.

Dimethyldithiocarbamate inhibits in vitro activation of primary human CD4+ T lymphocytes

Dithiocarbamates (DTC), a diverse group of industrial and therapeutic chemicals, have been reported to inhibit, enhance or have no effect on the immune system. These apparent inconsistencies reflect the complexity of the DTCs biological activities and are probably due in part to differences in dose, route of exposure, animal species used and/or specific compound tested. The studies described herein were undertaken to investigate the immunotoxicity of one member of this family, dimethyldithiocarbamate (DMDTC). We demonstrate that 0.1-0.5 microM DMDTC inhibits TNF-alpha-induced activation of NF-kappaB in primary human CD4+ T cells. This inhibition is not accompanied by a loss in viability, and DMDTC-treated T cells retain other active signaling pathways throughout the exposure duration. The inhibition of NF-kappaB is apparently permanent as DMDTC-treated T cells did not regain normal TNF-alpha activation, even after 72 h in culture. DMDTC does not appear to alter NF-kappaB directly as pre-incubation of nuclear extracts with DMDTC does not diminish binding activity of this protein. We further demonstrate that 0.1-0.5 microM DMDTC inhibits intracellular IL-2 production and decreases surface expression of CD25 (the alpha subunit of the IL-2 receptor) in T cells stimulated with phorbol ester. These data demonstrate that DMDTC is a potent immunosuppressive compound in vitro.

Modulation of exercise-induced immunosuppression by dietary polyunsaturated fatty acids in mice

The possible interaction between intense exercise, known to suppress the immune response, and nutritive factors, such as polyunsaturated fatty acids (PUFA), was examined in inbred female C57Bl/6 mice. The animals received for 8 wk either a natural ingredient diet or a diet supplemented with 10 g/100 g linseed oil containing over 50% of 18:3 (n-3) alpha-linoleic acid. Other groups received PUFA containing only traces of 18:3 (n-3) fatty acid; beef tallow, containing mostly 18:1 (n-9) saturated fat, safflower oil, an 18:2 (n-6) PUFA, and fish oil, containing longer chain (n-3) PUFA. Each dietary group was divided into two subgroups: sedentary diet controls and exercised animals. Exercise consisted of continuous swimming at high intensity until exhaustion. It was shown in three separate experiments that (1) the primary humoral response to sheep red blood cells, determined by the plaque-forming cell (PFC) assay, was affected by PUFA diet in sedentary animals in the order beef tallow > control diet > safflower oil > fish oil > linseed oil, and (2) the PFC response was suppressed by the exhaustive exercise, as compared to sedentary controls, except for animals fed 18:3 (n-3) linseed oil, where the normal response was noted. Phagocytosis of fluorescent microspheres by peritoneal macrophages, determined by flow cytometry, was significantly lower in exercised animals receiving the linseed oil diet, whereas other diets either increased or did not significantly change the macrophage phagocytic activity, compared to the sedentary diet controls. Spleen lymphocyte subsets were unchanged in exercised animals except for a marked shift from the lymphoid peak toward the erythroid peak. Generally, our data showed a marked immunomodulatory effect of 18-3 (n-3) alpha-linoleic acid on the exhaustive exercise-related immunosuppression, as compared to the effects of other selected PUFA.

Cytometric profiles of bone marrow and spleen lymphoid cells after mercury exposure in mice

The potential immunotoxic effects of mercury chloride on murine bone marrow (bm) cell subpopulations, including analysis of maturation patterns for B-cells, were evaluated by flow cytometric analysis. CD-1 outbred mice were exposed for 28 days to relatively low doses of 25-100 ppm HgCl2 in drinking water and the mercury-related functional cellular changes were validated in a macrophage phagocytosis assay. Lymphocyte subsets from the bone marrow population were stained with PNA lectin and a panel of monoclonal antibodies against cell surface antigens. The incidence of subset-specific staining was also monitored in spleens and thymuses. A dose-effect correlation was noted for the mercury-related activation of macrophage phagocytosis. Subchronic exposure to mercuric chloride resulted in a transient (7-14 day) decrease of the lymphoid/total bm cell ratio and affected the incidence of splenic T-cell subsets, however, without a clear dose-response correlation. The B-cell population in spleen and maturation patterns of B-cells in bm appeared to be unaffected by the mercury exposure. Overall, cytometric analysis of lymphoid cell subsets in murine bone marrow revealed transient and subset-non-specific cell fluctuations after subchronic exposure to inorganic mercury.

Immunosuppression by chronic exposure to N-nitrosodimethylamine (NDMA) in mice

Immunosuppression of humoral and cellular responses following chronic oral exposure to 1, 5, 10, and 20 ppm N-nitrosodimethylamine (NDMA) was examined in CD-1 mice. Monitoring of cumulative mortality and the incidence of peritoneal ascites in animals showed an NDMA dose-related mortality and hepatotoxicity. No visible changes in immunological parameters were noted at the 1 ppm NDMA dose. Immunosuppression of immunoglobulin M (IgM) antibody response by NDMA to sheep red blood cells (SRBC) was time-related, dose-related, and could be reversed within 30 d by removal of the chemical from the drinking water. Cellular immune response, monitored by allogeneic stimulation of cells in mixed lymphocyte reaction (MLR), was markedly suppressed by 10 and 20 ppm NDMA. Thus, chronic exposure to NDMA, except for the low-hepatotoxic doses of nitrosamine, resulted in a marked and persistent immunosuppression of cellular and humoral responses in CD-1 mice. In conclusion, chronic exposure to the hepatotoxic (ascite-inducing) doses of NDMA suppressed humoral and cellular immunity. The persistent immunosuppression could be reversed after the removal of NDMA from the drinking water. Although no direct NDMA-related cancer was reported in humans, our data point to a potential epigenetic carcinogenicity of nitrosamines due to chronic immunosuppression.

Immunotoxicity of subchronic versus chronic exposure to aldicarb in mice

In this study we compared the immunotoxicity of subchronic vs chronic exposure to the aldicarb insecticide at a relatively low, 0.1-10 ppb, level in drinking water. The immunotoxicity of aldicarb was evaluated in 28- and 90-day studies by determination of the humoral, cellular and nonspecific immunity in inbred C57BL/6 mice. Quantification of splenic plaque-forming cells (PFC) to sheep erythrocytes (SRBC), mitogen activation of spleen lymphocytes, mixed lymphocyte reaction (MLR) and the cytofluorometric assay of the phagocytic uptake of fluorescent beads were among the parameters studied. Neither the cell viability nor the splenic cell count was affected by the insecticide exposure. Immunophenotyping and cytometric determination of L3T4+, Lyt2+ and Ig+ cells revealed no effect of the insecticide exposure on the total count of cell subsets in the ungated splenocyte population. However, a marked shift in the percentages of L3T4+ and Lyt2+ cells was noted after subchronic exposure to 1 and 10 ppb aldicarb, possibly indicating activation of these splenic T-cell subsets. Subchronic aldicarb exposure significantly suppressed the splenic PFC response to SRBC at 1 ppb dose, however, no dose-effect correlation could be concluded. Similarly, no dose-effect correlation was observed for subchronic aldicarb-related changes in mitogen responses. Subchronic exposure to aldicarb had no statistically significant effect on the mixed lymphocyte reaction (MLR) or on the macrophage phagocytosis. Chronic exposure to 0.1-10 ppb aldicarb did not affect any of the parameters measured, including the cell subsets. Thus, aldicarb-related changes in immune parameters, noted after a 28-day exposure, were compensated over chronic exposure to the insecticide.