Evaluation of immunotoxic and immunodisruptive effects of inorganic arsenite on human monocytes/macrophages

Chronic arsenic exposure impairs macrophage functions in the exposed individuals

INTRODUCTION

Owing to the established roles of human macrophages in immune defense, we investigated the effect of chronic arsenic exposure upon these major hematopoietic cells in 70 arsenic-exposed individuals with skin lesions and 64 unexposed individuals.

METHODS

Human monocyte-derived macrophages were prepared from peripheral blood mononuclear cells, by culture of the adherent cells for 6 days in medium supplemented with granulocyte-monocyte colony stimulating factor. Parameters studied included cell adhesion capacity, expression of CD54 and F-actin, nitric oxide production, phagocytic capacity, and effect of arsenic on Rho A-ROCK pathway.

RESULTS

In macrophages of exposed individuals when compared to unexposed group, there was cell rounding accompanied with a significant (p < 0.001) loss of cell adhesion capacity, decrease in nitric oxide production, impaired phagocytic capacity, and decreased CD 54 and F-actin expression. Additionally, chronic arsenic exposure affected Rho A-ROCK pathway which in turn impaired macrophage functions.

DISCUSSION AND CONCLUSION

These altogether could contribute significantly to arsenic-induced immunosuppression observed in the arsenic-exposed individuals.

Arsenic trioxide induces apoptosis of human monocytes during macrophagic differentiation through nuclear factor-kappaB-related survival pathway down-regulation

Arsenic trioxide (As(2)O(3)) is known to be toxic toward leukemia cells. In this study, we determined its effects on survival of human monocytic cells during macrophagic differentiation, an important biological process involved in the immune response. As(2)O(3) used at clinically relevant pharmacological concentrations induced marked apoptosis of human blood monocytes during differentiation with either granulocyte-macrophage colony-stimulating factor or macrophage colony-stimulating factor. Apoptosis of monocytes was associated with increased caspase activities and decreased DNA binding of p65 nuclear factor-kappaB (NF-kappaB); like As(2)O(3), the selective NF-kappaB inhibitor (E)-3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (Bay 11-7082) strongly reduced survival of differentiating monocytes. The role of NF-kappaB in arsenic toxicity was also studied in promonocytic U937 cells during phorbol 12-myristate 13-acetate-induced macrophagic differentiation. In these cells, As(2)O(3) first reduced DNA binding of p65 NF-kappaB and subsequently induced apoptosis. In addition, overexpression of the p65 NF-kappaB subunit, following stable infection with a p65 retroviral expressing vector, increased survival of As(2)O(3)-treated U937 cells. As(2)O(3) specifically decreased protein levels of X-linked inhibitor of apoptosis protein and FLICE-inhibitory protein, two NF-kappaB-regulated genes in both U937 cells and blood monocytes during their differentiations. Finally, As(2)O(3) was found to inhibit macrophagic differentiation of monocytic cells when used at cytotoxic concentrations; however, overexpression of the p65 NF-kappaB subunit in U937 cells reduced its effects toward differentiation. In contrast to monocytes, well differentiated macrophages were resistant to low concentrations of As(2)O(3). Altogether, our study demonstrates that clinically relevant concentrations of As(2)O(3) induced marked apoptosis of monocytic cells during in vitro macrophagic differentiation likely through inhibition of NF-kappaB-related survival pathways.

Effects of glutamine on adhesion molecule expression and leukocyte transmigration in endothelial cells exposed to arsenic

This study evaluated whether glutamine (GLN) concentration was related to endothelial surface molecule expression and the migration of polymorphonuclear neutrophils (PMNs) through endothelial cells (ECs) stimulated by arsenic. Human umbilical vein endothelial cells (HUVECs) and PMNs were treated with different GLN concentrations (0, 300, 600 and 1000 microM) for 24 h. After that, we stimulated HUVECs for 3 h with 0.5 microM arsenic, and PMNs were allowed to transmigrate to ECs for 2 h. HUVEC surface expressions of cell adhesion molecules and integrin (CD11b) and interleukin (IL)-8 receptor expressions on PMNs were measured. The transendothelial migration of PMNs was also analyzed. The results showed that cell adhesion molecule (CAM) and integrin expressions in arsenic groups were higher than in those without arsenic. Among the arsenic groups, the expression of CAMs on ECs and CD11b, and IL-8 receptor on PMNs was lowest with 0 microM compared with the other GLN concentrations. Vascular CAM-1 on ECs and CD11b on PMN expression were higher with 300 microM than with 600 and 1000 microM GLN. IL-8 secretions from ECs and PMNs were higher with 300 muM than with 600 and 1000 microM GLN, and this was consistent with the expression of the IL-8 receptor on PMNs. Polymorphonuclear neutrophil transmigration was significantly higher with 300 muM GLN than with other GLN concentrations. These results suggest that ECs and PMNs were activated after arsenic stimulation. Cell adhesion molecule expressions on ECs and PMNs were suppressed in the absence of GLN. A low GLN concentration comparable to catabolic conditions resulted in higher adhesion molecule expression and greater transendothelial migration of neutrophils. Glutamine administration at levels similar to or higher than physiological concentrations reduced IL-8 and adhesion molecule expression; PMN transmigration was also decreased after stimulation with arsenic.