The influence of very low doses of N-nitrosodimethylamine (NDMA) on the apoptosis of rat neutrophils in vivo. The role of reactive oxygen species

Metabolomics-based molecular signatures reveal the toxic effect of co-exposure to nitrosamines in drinking water

Nitrosamines, a group of emerging nitrogenous pollutants, are ubiquitously found in the drinking water system. However, less is known about how systemic biological responses resist or tolerate nitrosamines, especially long-term co-exposure at low concentrations. In this study, untargeted metabolomics was used to investigate the metabolic perturbations in human esophageal epithelial Het-1A cells induced by a mixture of nine common nitrosamines in drinking water at environmentally relevant, human-internal-exposure, and genotoxic concentrations. Generally, the disrupted metabolic spectrum became complicated with nitrosamines dose increasing. Notably, two inflammation-associated pathways, namely, cysteine (Cys) and methionine (MET) metabolism, and nicotinate and nicotinamide metabolism, changed significantly under the action of nitrosamines, even at the environmentally relevant level. Furthermore, targeted metabolomics and molecular biology indicators in cells were identified in mice synchronously. For one thing, the up-regulated Cys and MET metabolism provided methyl donors for histone methylation in the context of pro-inflammatory response. For another, the down-regulated NAD⁺/NADH ratio inhibited the deacetylation of NF-кB p65 and eventually activated the NF-кB signaling pathway. Taken collectively, the metabolomics molecular signatures were important indicative markers for nitrosamines-induced inflammation. The potential crosstalk between the inflammatory cascade and metabolic regulation also requires further studies. These findings suggest that more attention should be paid to long-term co-exposure at low concentrations in the control of nitrosamines pollution in drinking water. Additionally, this study also highlights a good prospect of the combined metabolomic-molecular biology approach in environmental toxicology.

Accelerated apoptosis, oxidative stress, and cholinergic inflammation in blood of metalworkers

Metalworkers are exposed to numerous chemicals in their workplace environment, such as solvents, heavy metals, and metalworking fluids, that have a negative impact on their health. Furthermore, there is an increase in the prevalence of chronic diseases among metalworkers; however, the molecular mechanisms involved in this increased predisposition to chronic diseases are unclear. Considering that occupational exposure represents a potential risk for metalworkers, the aim of this study was to measure biomarkers of oxidative stress, inflammation, and cytotoxicity in the peripheral blood of metalworkers from Southern Brazil. The study included 40 metalworkers and 20 individuals who did not perform activities with any recognized exposure to chemical substances, such as those working in administration, commerce, and education, as controls. Cellular and molecular biomarkers as leukocyte viability, intracellular production of reactive species, mitochondrial mass and membrane potential and plasma lipid peroxidation, sulfhydryl groups, total antioxidant capacity, and butyrylcholinesterase activity were evaluated in the blood of metalworkers and controls. Metalworkers were found to have higher rates of apoptosis, increased production of reactive species, and increased mitochondrial potential and mass in leukocytes associated with decreased antioxidant defenses and increased activity of the butyrylcholinesterase enzyme in their plasma. It can be concluded that cytotoxicity, oxidative stress, and inflammation are involved in the multiplicity of health outcomes related to chemical exposure in the metalworking industry.

Carcinogenesis: Failure of resolution of inflammation?

Inflammation in the tumor microenvironment is a hallmark of cancer and is recognized as a key characteristic of carcinogens. However, the failure of resolution of inflammation in cancer is only recently being understood. Products of arachidonic acid and related fatty acid metabolism called eicosanoids, including prostaglandins, leukotrienes, lipoxins, and epoxyeicosanoids, critically regulate inflammation, as well as its resolution. The resolution of inflammation is now appreciated to be an active biochemical process regulated by endogenous specialized pro-resolving lipid autacoid mediators which combat infections and stimulate tissue repair/regeneration. Environmental and chemical human carcinogens, including aflatoxins, asbestos, nitrosamines, alcohol, and tobacco, induce tumor-promoting inflammation and can disrupt the resolution of inflammation contributing to a devastating global cancer burden. While mechanisms of carcinogenesis have focused on genotoxic activity to induce mutations, nongenotoxic mechanisms such as inflammation and oxidative stress promote genotoxicity, proliferation, and mutations. Moreover, carcinogens initiate oxidative stress to synergize with inflammation and DNA damage to fuel a vicious feedback loop of cell death, tissue damage, and carcinogenesis. In contrast, stimulation of resolution of inflammation may prevent carcinogenesis by clearance of cellular debris via macrophage phagocytosis and inhibition of an eicosanoid/cytokine storm of pro-inflammatory mediators. Controlling the host inflammatory response and its resolution in carcinogen-induced cancers will be critical to reducing carcinogen-induced morbidity and mortality. Here we review the recent evidence that stimulation of resolution of inflammation, including pro-resolution lipid mediators and soluble epoxide hydrolase inhibitors, may be a new chemopreventive approach to prevent carcinogen-induced cancer that should be evaluated in humans.

N-nitrosodimethylamine (NDMA) induced apoptosis dependent on Fas/FasL complex in human leukocytes

Objective:

To investigate the mechanism of apoptosis dependent on the Fas/FasL (Fas ligand) complex in the presence of N-nitrosodimethylamine (NDMA) in human leukocytes.

Methods:

Polymorphonuclear neutrophils (PMNs) and peripheral blood mononuclear cells (PBMCs) were isolated form whole blood by density centrifugation. The concentration of NDMA was assessed by cellular toxicity assay. Apoptotic cells were assessed with flow cytometry and the expression of pro- and antiapoptotic proteins was investigated by Western blotting in PMNs and PBMCs treated with NDMA and/or FasL.

Results:

PMNs showed a higher ratio of apoptotic cells than PBMCs after exposure to NDMA and/or FasL. Enhanced apoptosis was related to the increased expression of proapoptotic proteins in neutrophils following exposure to either NDMA or FasL. In PBMCs, the relation was observed after exposure to FasL only. PMNs and PBMCs incubated with NDMA and FasL simultaneously demonstrated the highest increase in protein expression.

Conclusions:

NDMA shows a stronger proapoptotic effect with PMNs than with PBMCs. The Fas/FasL complex, along with other proapoptotic proteins of the receptor (Fas, FADD) and mitochondrial pathway (Noxa, Puma, Bim), plays a key role in the induction of neutrophil apoptosis. Synergic effects of NDMA and FasL which lead to higher induction of apoptosis in PMNs than in PBMCs indicates a multistage and varied regulation of apoptosis in different populations of leukocytes.

Expression of selected proteins of the extrinsic and intrinsic pathways of apoptosis in human leukocytes exposed to N-nitrosodimethylamine

N-nitrosodimethylamine (NDMA) is a xenobiotic widespread in human environment capable of regulating the lifespan of immune cells. In this study, we examined the roles of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/death receptor 5 (DR5) complex and the Fas molecule in the induction of the extrinsic apoptosis pathway in human neutrophils (polymorphonuclear neutrophils (PMNs)) and peripheral blood mononuclear cells (PBMCs) exposed to NDMA. Also we assessed these proteins ability to trigger the intrinsic apoptosis pathway in those cells. For this purpose, we examined the expression of Fas-associated protein with death domain, truncated Bid (tBid) proteins, and apoptogenic factors such as apoptosis-inducing factor, Smac/Diablo, Omi/HtrA2, and caspase-3 as an indication of accomplished apoptosis phenomenon. PMNs and PBMCs were isolated from whole blood by density gradient centrifugation using Polymorphrep. Apoptotic cells were assessed with flow cytometry using a ready-made kit. The expression of proapoptotic molecules was investigated by Western blot analysis of PMNs and PBMCs treated with NDMA and/or rhTRAIL. The obtained results confirm the proapoptotic effects of NDMA on the examined human leukocytes and indicate an active participation of the TRAIL/DR5 complex and Fas protein in the process of apoptosis. Moreover, the research revealed distinct mechanisms of intrinsic apoptosis pathway activation between PMNs and PBMCs exposed to NDMA, as confirmed by the different levels of tBid, Smac/Diablo, Omi/HtrA2, and caspase-3 expression in those cells.

Role of AP-1 family proteins in regulation of inducible nitric oxide synthase (iNOS) in human neutrophils

The aim of the study was to assess the activity of AP-1 family proteins, e.g. Fra-1, Fra-2, JunB, JunD, and FosB, engaged in the regulation of inducible nitric oxide synthase (iNOS) expression and the production of NO by neutrophils (PMN) exposed to N-nitrosodimethylamine (NDMA) xenobiotic. Isolated human PMN were incubated in the presence of NDMA. iNOS mRNA expression was then analyzed using Northern blot and the expression of other proteins in the cytoplasmic and nuclear fractions were assessed using Western blot. The obtained results indicate that NDMA increased iNOS mRNA and protein expression in human PMN. Furthermore, it increased the expression of Fra-1, Fra-2, JunB, and JunD in the cytoplasmic fraction, and FosB expression in the fractions of analyzed cells. As a consequence of inhibiting p38 pathway and JNK, reduced iNOS expression and NO production was noted in PMN exposed to NDMA. Inhibition of the p38 pathway resulted in reduced expression of all analyzed proteins in the cytoplasmic fraction of PMN exposed to NDMA. Furthermore, increased Fra-2 expression and reduced FosB expression were found in the nuclear fraction of those cells. Inhibiting ERK5 pathway resulted in increased JunB expression in both fractions of the analyzed cells. Therefore, no changes in the expression of analyzed proteins in the presence of NDMA were observed in PMN pre-incubated with JNK pathway inhibitor. In conclusion, the results here indicate a role of Fra-1, Fra-2, JunB, JunD, and FosB transcription factors in the regulation of iNOS expression and NO production by human neutrophils exposed to NDMA.

The effect of N-nitrosodimethylamine (NDMA) on Bax and Mcl-1 expression in human neutrophils

In the present study we examined a role of pro-apoptotic Bax and anti-apoptotic Mcl-1 proteins, participating in the regulation of intrinsic apoptosis pathway in human neutrophils (PMNs) exposed to N-nitrosodimethylamine (NDMA), the environmental xenobiotic. For the purpose comparison, the same studies were conducted in autologous peripheral blood mononuclear cells (PBMCs). The production of cytochrome c by PMNs was also determined. A deficit of anti-apoptotic Mcl-1 and overexpression of the pro-apoptotic protein Bax suggest that the apoptosis process in human neutrophils exposed to NDMA is dependent on changes in the expression of these proteins. PMNs were more sensitive to NDMA than PBMCs.

The Effect of N-Nitrosodimethylamine on TRAIL and DR5 Expression in Human Neutrophils—Preliminary Study

The intracellular mechanisms of NDMA-induced apoptosis of neutrophils have not yet been fully understood. The aim of this study was to explain whether the TRAIL/DR5 system is implicated in NDMA-induced apoptosis of human neutrophils. The expression of TRAIL and DR5 was examined, as well as the secretion of sTRAIL and sDR5 by human neutrophils treated with NDMA confronted with intensity apoptosis of these cells. For comparative purposes similar examinations in autologous peripheral blood mononuclear cells (PBMC) were performed. Decreased expression and secretion of TRAIL and increased expression and secretion of DR5 associated with increased intensity of apoptosis of polymorphonuclear leukocytes (PMNs) suggest that NDMA-induced apoptosis in these cells may be depend on TRAIL/DR5 system. Autologous PBMCs no exerted that changes in the expression and secretion of TRAIL as well as in the intensity of apoptosis. However, the expression and secretion of DR5 by PBMCs were similar to those by PMNs. Differences above suggest that PMNs are more sensitive to unfavorable action of NDMA than PBMCs.