Reduction in polyamine catabolism leads to spermine-mediated airway epithelial injury and induces asthma features.

BACKGROUND: Airway epithelial injury is a crucial component of acute and severe asthma pathogenesis and a promising target for treatment of refractory asthma. However, the underlying mechanism of epithelial injury remains poorly explored. Although high levels of polyamines, mainly spermine, have been found in asthma and comorbidity, their role in airway epithelial injury and the cause of their altered levels in asthma have not been explored. METHODS: We measured key polyamine metabolic enzymes in lung samples from normal and asthmatic subjects and in mice with OVA-induced allergic airway inflammation (AAI). Polyamine metabolism was modulated using pharmacologic/genetic modulators. Epithelial stress and apoptosis were measured by TSLP levels and TUNEL assay, respectively. RESULTS: We found loss of the polyamine catabolic enzymes spermidine/spermine-N (1)-acetyltransferase-1 (SAT1) and spermine oxidase (SMOX) predominantly in bronchial epithelial cells (BECs) of human asthmatic lung samples and mice with AAI. In naïve mice, SAT1 or SMOX knockdown led to airway hyper-responsiveness, remodeling, and BEC apoptosis. Conversely, in mice with AAI, overexpression of either SAT1 or SMOX alleviated asthmatic features and reduced TSLP levels and BEC apoptosis. Similarly, while pharmacological induction of SAT1 and SMOX using the polyamine analogue bis(ethyl)norspermine (BENSPM) alleviated asthmatic features with reduced TSLP levels and BEC apoptosis, pharmacological inhibition of these enzymes using BERENIL or MDL72527, respectively, worsened them. Spermine accumulation in lungs correlated with BEC apoptosis, and spermine treatment caused apoptosis of human BEAS-2B cells in vitro. CONCLUSIONS: Spermine induces BEC injury. Induction of polyamine catabolism may represent a novel therapeutic approach for asthma via reversing BEC stress.

Epigenetic silencing of miR-124 prevents spermine oxidase regulation: implications for Helicobacter pylori-induced gastric cancer.

Chronic inflammation contributes to the development of various forms of cancer. The polyamine catabolic enzyme spermine oxidase (SMOX) is induced in chronic inflammatory conditions, including Helicobacter pylori-associated gastritis, where its production of hydrogen peroxide contributes to DNA damage and subsequent tumorigenesis. MicroRNA expression levels are also altered in inflammatory conditions; specifically, the tumor suppressor miR-124 becomes silenced by DNA methylation. We sought to determine if this repression of miR-124 is associated with elevated SMOX activity and concluded that miR-124 is indeed a negative regulator of SMOX. In gastric adenocarcinoma cells harboring highly methylated and silenced mir-124 gene loci, 5-azacytidine treatment allowed miR-124 re-expression and decreased SMOX expression. Overexpression of an exogenous miR-124-3p mimic repressed SMOX mRNA and protein expression as well as H2O2 production by >50% within 24 h. Reporter assays indicated that direct interaction of miR-124 with the 3'-untranslated region of SMOX mRNA contributes to this negative regulation. Importantly, overexpression of miR-124 before infection with H. pylori prevented the induction of SMOX believed to contribute to inflammation-associated tumorigenesis. Compelling human in vivo data from H. pylori-positive gastritis tissues indicated that the mir-124 gene loci are more heavily methylated in a Colombian population characterized by elevated SMOX expression and a high risk for gastric cancer. Furthermore, the degree of mir-124 methylation significantly correlated with SMOX expression throughout the population. These results indicate a protective role for miR-124 through the inhibition of SMOX-mediated DNA damage in the etiology of H. pylori-associated gastric cancer.

Inhibitors of DNA Methylation, Histone Deacetylation, and Histone Demethylation: A Perfect Combination for Cancer Therapy.

Epigenetic silencing and inappropriate activation of gene expression are frequent events during the initiation and progression of cancer. These events involve a complex interplay between the hypermethylation of CpG dinucleotides within gene promoter and enhancer regions, the recruitment of transcriptional corepressors and the deacetylation and/or methylation of histone tails. These epigenetic regulators act in concert to block transcription or interfere with the maintenance of chromatin boundary regions. However, DNA/histone methylation and histone acetylation states are reversible, enzyme-mediated processes and as such, have emerged as promising targets for cancer therapy. This review will focus on the potential benefits and synergistic/additive effects of combining DNA-demethylating agents and histone deacetylase inhibitors or lysine-specific demethylase inhibitors together in epigenetic therapy for solid tumors and will highlight what is known regarding the mechanisms of action that contribute to the antitumor response.

Increased Helicobacter pylori-associated gastric cancer risk in the Andean region of Colombia is mediated by spermine oxidase.

Helicobacter pylori infection causes gastric cancer, the third leading cause of cancer death worldwide. More than half of the world's population is infected, making universal eradication impractical. Clinical trials suggest that antibiotic treatment only reduces gastric cancer risk in patients with non-atrophic gastritis (NAG), and is ineffective once preneoplastic lesions of multifocal atrophic gastritis (MAG) and intestinal metaplasia (IM) have occurred. Therefore, additional strategies for risk stratification and chemoprevention of gastric cancer are needed. We have implicated polyamines, generated by the rate-limiting enzyme ornithine decarboxylase (ODC), in gastric carcinogenesis. During H. pylori infection, the enzyme spermine oxidase (SMOX) is induced, which generates hydrogen peroxide from the catabolism of the polyamine spermine. Herein, we assessed the role of SMOX in the increased gastric cancer risk in Colombia associated with the Andean mountain region when compared with the low-risk region on the Pacific coast. When cocultured with gastric epithelial cells, clinical strains of H. pylori from the high-risk region induced more SMOX expression and oxidative DNA damage, and less apoptosis than low-risk strains. These findings were not attributable to differences in the cytotoxin-associated gene A oncoprotein. Gastric tissues from subjects from the high-risk region exhibited greater levels of SMOX and oxidative DNA damage by immunohistochemistry and flow cytometry, and this occurred in NAG, MAG and IM. In Mongolian gerbils, a prototype colonizing strain from the high-risk region induced more SMOX, DNA damage, dysplasia and adenocarcinoma than a colonizing strain from the low-risk region. Treatment of gerbils with either α-difluoromethylornithine, an inhibitor of ODC, or MDL 72527 (N(1),N(4)-Di(buta-2,3-dien-1-yl)butane-1,4-diamine dihydrochloride), an inhibitor of SMOX, reduced gastric dysplasia and carcinoma, as well as apoptosis-resistant cells with DNA damage. These data indicate that aberrant activation of polyamine-driven oxidative stress is a marker of gastric cancer risk and a target for chemoprevention.

Inflammation and polyamine catabolism: the good, the bad and the ugly.

The induction of polyamine catabolism by specific anti-tumour polyamine analogues has increased interest in the roles polyamine catabolism play in cell growth, death and response to various anti-tumour agents. The relatively recent finding of an inducible mammalian spermine oxidase (SMO/PAOh1), in addition to the two-step spermidine/spermine N(1)-acetyltransferanse (SSAT)/N(1)-acetylpolyamine oxidase (APAO) catabolic pathway, underscores the complexities of the regulation of polyamine catabolism by various stimuli. Furthermore, recent data indicate that infectious agents and mediators of inflammation can also up-regulate polyamine catabolism. Induction of SSAT by these agents can reduce intracellular polyamine concentrations and cell growth rate, thus providing a beneficial mechanism by which cells may adapt to inflammatory stress. However, increased polyamine catabolism can also result in substantial increases in intracellular reactive oxygen species (ROS) through the production of H(2)O(2) as a by-product of either APAO or SMO/PAOh1 activity. This increased generation of ROS can have different results, depending on the mechanism of induction and cell types involved. Targeted killing of tumour cells by agents that stimulate SSAT/APAO and/or SMO/PAOh1 is obviously a 'good' effect. However, induction of SMO/PAOh1 by inflammation or infectious agents has the potential to produce sufficient ROS in normal, non-tumour cells to lead to DNA damage, mutation and, potentially, carcinogenic transformation ('bad'). The variation in the induction of these polyamine catabolic enzymes, as well as the level and timing of this induction will dictate the cellular outcome in the presence of both desirable and undesirable effects ('ugly'). Here we discuss the relative role of each of the steps in polyamine catabolism in response to inflammatory stress.