The genotoxic potential of mixed nitrosamines in drinking water involves oxidative stress and Nrf2 activation

Nitrosamine by-products in drinking water are designated as probable human carcinogens by the IARC, but the health effects of simultaneous exposure to multiple nitrosamines in drinking water remain unknown. Genotoxicity assays were used to assess the effects of both individual and mixed nitrosamines in finished drinking water produced by a large water treatment plant in Shanghai, China. Cytotoxicity and genotoxicity were measured at 1, 10-, 100- and 1000-fold actual concentrations by the Ames test, Comet assay, γ-H2AX assay, and the cytokinesis-block micronuclei assay; oxidative stress and the Nrf2 pathway were also assessed. Nitrosamines detected in drinking water included NDMA (36.45 ng/L), NDPA (44.68 ng/L), and NEMA (37.27 ng/L). Treatment with a mixture of the three nitrosamines at 1000-fold actual drinking-water concentration induced a doubling of revertants in Salmonella typhimurium strain TA100, DNA and chromosome damage in HepG2 cells, while 1-1000-fold concentrations of compounds applied singly lacked these effects. Treatment with 100- and 1000-fold concentrations increased ROS, GSH, and MDA and decreased SOD activity. Thus, nitrosamine mixtures showed greater genotoxic potential than that of the individual compounds. N-Acetylcysteine protected against the nitrosamine-induced chromosome damage, and Nrf2 pathway activation suggested that oxidative stress played pivotal roles in the genotoxic property of the nitrosamine mixtures.

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.

Many Ways-One Destination: Different Types of Neutrophils Death

Neutrophils constitute the most numerous populations of peripheral blood leukocytes, fulfilling the fundamental role in the development of the innate immune response. As the cells of the first line of defense, they guard the organism against the spread of pathogenic microorganisms. Neutrophils, similar to the other cells of the immune system, enter the path of death after fulfilling their biological function. Depending on the conditions that they are found in, they may undergo different types of cell death which requires the involvement of numerous signaling pathways. In this review article, we summarize the current state of knowledge regarding the different forms of neutrophil death, such as apoptosis, necrosis, necroptosis, autophagy, NETosis and pyroptosis.

Antioxidant properties of Ferulago angulata and its hepatoprotective effect against N-nitrosodimethylamine-induced oxidative stress in rats

CONTEXT

Ferulago angulata (Schlecht.) Boiss. (Apiaceae) (FASB) is used to treat liver diseases and has been used both as food and therapeutics by many cultures for thousands of years because of the natural antioxidant compounds.

OBJECTIVE

This study determines antioxidant properties of FASB flowers, the levels of minerals and vitamins, and also, evaluates the hepatoprotective effect of flowers against N-nitrosodimethylamine (NDMA) induced on liver tissue by assessing antioxidant enzymes and histopathological parameters in Wistar albino rats.

MATERIALS AND METHODS

In the study, the rats were divided into six groups of ten. Control, untreated animals were given 0.9% NaCl. Rats were intraperitoneally given NDMA (10 mg/kg) for the first 7 days. FASB methanol extract (150 and 300 mg/kg) was administered orally for 21 days.

RESULTS

α-Tocopherol, retinol, ascorbic acid, total antioxidant activity, phenolic and flavonoid contents of FASB were 0.70 ± 0.13, 0.29 ± 0.03 μg/g, 139.32 ± 7.06 μg/100 g, 171.61 ± 6.05 mM ascorbic acid/g, 90.47 ± 4.11 mg GA/g and 37.39 ± 2.85 mg QE/g. DPPH and hydroxyl radical scavenging activity was obtained IC₅₀ 67.34 ± 4.14 and 64.87 ± 4.68 μg/mL, respectively.

DISCUSSION AND CONCLUSION

The results of the study indicated that FASB flowers contain high levels of vitamins, minerals, total antioxidant activity, phenolics and flavonoids. Due to the positive effect on significant changes in antioxidant enzymes of liver tissue and histopathological examination, it is thought that the plant could be used as a hepatoprotective.