Role of neutrophils in acrylonitrile-induced gastric mucosal damage

Acrylonitrile induction of rodent neoplasia: Potential mechanism of action and relevance to humans

Acrylonitrile, an industrial chemical, is a multisite carcinogen in rats and mice, producing tumors in four tissues with barrier function, that is, brain, forestomach, Zymbal’s gland, and Harderian gland. To assess mechanism(s) of action (MoA) for induction of neoplasia and to evaluate whether the findings in rodents are indicative of human hazard, data on the potential key effects produced by acrylonitrile in the four rodent target tissues of carcinogenicity were evaluated. A notable finding was depletion of glutathione in various organs, including two target tissues, the brain, and forestomach, suggesting that this effect could be a critical initiating event. An additional combination of oxidative DNA damage and cytotoxic effects of acrylonitrile and its metabolites, cyanide, and 2-cyanoethylene oxide, could initiate pro-inflammatory signaling and sustained cell and tissue injury, leading to compensatory cell proliferation and neoplastic development. The in vivo DNA-binding and genotoxicity of acrylonitrile has been studied in several target tissues with no compelling positive results. Thus, while some mutagenic effects were reported in acrylonitrile-exposed rodents, data to determine whether this mutagenicity stems from direct DNA reactivity of acrylonitrile are insufficient. Accordingly, the induction of tumors in rodents is consistent primarily with a non-genotoxic MoA, although a contribution from weak mutagenicity cannot be ruled out. Mechanistic data to support conclusions regarding human hazard from acrylonitrile exposure is weak. Comparison of metabolism of acrylonitrile between rodents and humans provide little support for human hazard. Three of the tissues affected in bioassays (forestomach, Zymbal’s gland, and Harderian gland) are present only in rodents, while the brain is anatomically different between rodents and humans, diminishing relevance of tumor induction in these tissues to human hazard. Extensive epidemiological data has not revealed causation of human cancer by acrylonitrile.

Differential response to acrylonitrile toxicity in rat primary astrocytes and microglia

Acrylonitrile (ACN) is a widely used chemical in the production of plastics, resins, nitriles, acrylic fibers, synthetic rubber and acrylamide. While acute high level exposures to ACN are known to be lethal, chronic low dose exposures causes glial cell tumors in rats. Recently, these glial tumors have been characterized as microglial in origin. While effects of ACN on astrocytes, the more numerous glial cell, have been investigated, the effects on microglia are unknown. This study was conducted to compare the responses of astrocytes and microglia to ACN treatment in vitro to address differential sensitivities and adaptive responses to this toxic chemical. Cell viability, ACN uptake, lipid peroxidation byproducts (F2-isoprostanes), glutathione (GSH) levels and expression of NF-E2-related factor 2 (Nrf2) were evaluated in primary rat microglia and astrocytes following ACN treatment. Results indicate that microglia are more sensitive to ACN than astrocytes, accumulating less ACN while demonstrating higher F2-isoprostane levels. GSH levels were up-regulated in both cell types, as a protective mechanism against ACN-induced oxidative stress, while Nrf2 levels were only induced in microglia. Our data suggest that microglia and astrocytes exhibit different sensitivities and responses to ACN, which are linked to the intracellular thiol status inherent to each of these cell types.

Gastroduodenal mucosal defense

PURPOSE OF REVIEW

To review recent developments in the field of gastroduodenal mucosal defense.

RECENT FINDINGS

Research in the field of gastroduodenal mucosal defense is shifting from animal models of mucosal injury towards the elucidation of molecular mechanisms that protect the mucosa at the cellular level. Accordingly, the recent literature is focused on endogenous antioxidants such as mitochondrial superoxide dismutase (SOD), and heme oxygenase-1, mucosal receptors such as the Toll-like receptors and protease-activated receptors, endogenous proteins with protective effects such as the matrix metalloproteinases, heat-inducible factors and trefoil factors, protective functions of submucosal mononuclear cells, junctional proteins affecting mucosal permeability, and hormone-mediated protective mechanisms mediated by estrogens, vasoactive peptides, and other hormones.

SUMMARY

These new published findings contribute to our overall understanding of gastroduodenal defense and suggest innovative avenues of future research and possible novel therapeutic targets.