Mechanisms involved in methylmercuric chloride (MeHgCl)-induced suppression of human neutrophil apoptosis

Human eosinophils are direct targets to nanoparticles: Zinc oxide nanoparticles (ZnO) delay apoptosis and increase the production of the pro-inflammatory cytokines IL-1β and IL-8

Zinc oxide NPs (ZnO) have been recently proposed as novel candidates for the treatment of allergic inflammatory diseases. Paradoxically, recent data suggested that ZnO could cause eosinophilic airway inflammation in rodents. Despite the above observations, there are currently no studies reporting direct interaction between a given NP and human eosinophils themselves. In this study, freshly isolated human eosinophils were incubated with ZnO and several cellular functions were studied. We found that ZnO delay human eosinophil apoptosis, partially by inhibiting caspases and by preventing caspase-4 and Bcl-xL degradation. ZnO do not induce production of reactive oxygen species but increase de novo protein synthesis. In addition, ZnO were found to increase the production of the proinflammatory IL-1β and IL-8 cytokines. Using a pharmacological approach, we demonstrated that inhibition of caspase-1 reversed the ability of ZnO to induce IL-1β and IL-8 production, whereas inhibition of caspase-4 only reversed that of IL-8. Our results indicate the necessity of conducting studies to determine the potential of using NP as nanotherapies, particularly in diseases in which eosinophils may be involved. We conclude that, indeed, human eosinophils represent potential new direct targets to NPs, ZnO in the present case.

Silver nanoparticles of 70 nm and 20 nm affect differently the biology of human neutrophils

The influence of size of nanoparticles (NP), especially in regard to pulmonary toxicity, has been widely investigated. In general, NP with smaller diameters are more pro-inflammatory in vivo, at least in terms of neutrophil influx. Nevertheless, the influence of size of NP on polymorphonuclear neutrophil (PMN) cell biology is poorly documented. In the study here, it was decided to determine if AgNP with a diameter of 70 nm (AgNP70) will alter the biology of human PMN similarly to AgNP20 previously reported to induce apoptosis and inhibit de novo protein synthesis. The results here indicated that, in contrast to AgNP20, AgNP70 delayed PMN apoptosis. However, both AgNP20 and AgNP70 inhibited de novo protein synthesis. Both forms of AgNP did not significantly increase reactive oxygen species (ROS) production, but AgNP20 significantly increased the cell production of the CXCL8 chemokine (IL-8). In addition, AgNP20, but not AgNP70, induced the release of albumin and matrix metalloproteinase-9 (MMP-9/gelatinase B) into culture supernatants. Consistent with this latter observation, gelatinase activity was increased by AgNP20, as assessed by zymography. From these outcomes, it is concluded that two NP with different initial diameters can possess similar - as well as distinct - biological properties in modulating human PMN functions. These outcomes are testimony to the complexity of the modes of action of NP at the cellular level.

Mercury immune toxicity in harbour seals: links to in vitro toxicity

BACKGROUND

Mercury is known to bioaccumulate and to magnify in marine mammals, which is a cause of great concern in terms of their general health. In particular, the immune system is known to be susceptible to long-term mercury exposure. The aims of the present study were (1) to determine the mercury level in the blood of free-ranging harbour seals from the North Sea and (2) to examine the link between methylmercury in vitro exposure and immune functions using seal and human mitogen-stimulated peripheral blood mononuclear cells (T-lymphocytes).

METHODS

Total mercury was analysed in the blood of 22 harbour seals. Peripheral blood mononuclear cells were isolated from seals (n = 11) and from humans (n = 9). Stimulated lymphocytes of both species were exposed to functional tests (proliferation, metabolic activity, radioactive precursor incorporation) under increasing doses of methylmercury (0.1 to 10 microM). The expression of cytokines (IL-2, IL-4 and TGF-beta) was investigated in seal lymphocytes by RT-PCR and by real time quantitative PCR (n = 5) at methylmercury concentrations of 0.2 and 1 microM. Finally, proteomics analysis was attempted on human lymphocytes (cytoplasmic fraction) in order to identify biochemical pathways of toxicity at concentration of 1 microM (n = 3).

RESULTS

The results showed that the number of seal lymphocytes, viability, metabolic activity, DNA and RNA synthesis were reduced in vitro, suggesting deleterious effects of methylmercury concentrations naturally encountered in free-ranging seals. Similar results were found for human lymphocytes. Functional tests showed that a 1 microM concentration was the critical concentration above which lymphocyte activity, proliferation and survival were compromised. The expression of IL-2 and TGF-beta mRNA was weaker in exposed seal lymphocytes compared to control cells (0.2 and 1 microM). Proteomics showed some variation in the protein expression profile (e.g. vimentin).

CONCLUSION

Our results suggest that seal and human PBMCs react in a comparable way to MeHg in vitro exposure with, however, larger inter-individual variations. MeHg could be an additional cofactor in the immunosuppressive pollutant cocktail generally described in the blood of seals and this therefore raises the possibility of additional additive effects in the marine mammal immune system.

Cell surface expression of intermediate filament proteins vimentin and lamin B1 in human neutrophil spontaneous apoptosis

Neutrophils represent an important source of autoantigens for antineutrophil cytoplasmic antibody associated with vasculitis. To date, two cytoskeletal proteins, vinculin and vimentin, have been reported to be expressed on the cell surfaces of activated macrophages, platelets, and apoptotic T lymphocytes. However, such cell surface expression has never been studied in human neutrophils. As we recently demonstrated that different cytoskeletal proteins were cleaved in apoptotic neutrophils, we hypothesized that some of these were expressed on the cell surface of apoptotic neutrophils. Herein, we found that among vinculin, paxillin, gelsolin, vimentin, lamin B1, alpha-tubulin, and beta-tubulin, only the two intermediate filament (INFIL) proteins, vimentin and lamin B1, are expressed on the cell surface of 24-h aged neutrophils [spontaneous apoptosis (SA)]. By monitoring intracellular expression of vimentin and lamin B1 during SA, we found that these two proteins were cleaved and that such cleavage was reversed by the pan caspase inhibitor N-benzyloxy-carbonyl-V-A-D-O-methylfluoromethyl ketone (z-VAD-fmk). When neutrophil apoptosis was delayed or suppressed by lipopolysaccharide or the cytokines granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage (GM)-CSF, or interleukin-4, the loss of intracellular expression of vimentin and lamin B1 was prevented. The INFIL proteins were absent from the cell surface when neutrophil apoptosis was delayed. Addition of z-VAD-fmk significantly decreased the cell surface expression of vimentin and lamin B1 during SA. This study provides the first evidence that apoptotic neutrophils express cytoskeletal proteins on their surface, opening the possibility that these cells may participate in the development of autoantibodies directed against cytoskeletal proteins, a condition frequently reported in several inflammatory diseases.