Chronic alcohol consumption, via several processes, is a risk factor for many cancers, including liver cancer. Iron overload is also a risk factor for liver cancer. RATIONALE. Alcohol is known to have an impact on s-adenosyl methionine (SAMe) synthesis, via pleotropic effects. We posit that iron and its potential to exacerbate oxidant stress generation may also perturb SAMe synthesis through drawing carbon to replenish glutathione (GSH) via the transsulfuration pathway. Such an impact on the methyl donor pool in cells has the potential to affect epigenetic regulation, specifically by attenuating DNA methylation. Epigenetic changes that result in altered expression of critical genes involved in control of proliferation, apoptosis, DNA integrity, angiogenesis and other processes are important to cancer progression. Thus, we hypothesize that changes in GSH levels brought about through exposure to iron derived oxidant stress will stress the pool of homocysteine, potentiating ethanol's inhibition of SAMe leading to alterations in epigenetic regulation reactions that depend on this methyl donor. Homocysteine provides both methionine to produce SAMe and cystathionine to produce GSH. The OBJECTIVE of this exploratory R21 proposal is to conduct key experiments to elucidate the relationship between iron induced oxidant stress and epigenetic regulation in alcohol-related cancer development. In doing so, critical data to support a subsequent R01 application in this area will be generated. Our results will determine the extent to which iron and ethanol converge to impact a fundamentally important pathway and indicate if this in turn may affect processes that are involved with heritable changes in gene regulation.
Specific Aim : to determine if ethanol and iron combine to affect methyl donor availability and epigenetic regulation in liver cells in vitro and in vivo. Our preliminary data with a tet-inducible Ferritin H transgenic model indicate we can alter iron availability in a tissue specific manner in vivo. We also demonstrate the capacity to evaluate SAMe and SAH levels in liver tissue, and to analyze alterations in DNA methylation. We will use this expertise in vivo, to test the impact of ethanol and iron independently and together on: A) the formation of pre-neoplastic lesions in the liver;B) SAMe and GSH availability;C) global and gene promoter specific (e-cadherin and HAI-2/PB) DNA methylation;D) oxidant stress as 4-HNE and carbonyl adduct formation, oxidized to reduced GSH ratios, and reductive stress as NAD+/NADH ratios. By answering the question of whether iron and ethanol affect epigenetic regulation, we increase our understanding of the mechanisms by which the microenvironment influences the cell. Given the importance of oxidant stress and epigenetic gene regulation in oncogene stimulation and chromosomal instability, such progress may ultimately help us design strategies to prevent and treat the occurrence of ethanol related cancer development.

Public Health Relevance

Alcohol drinking is known to place the drinker at increased risk for many types of cancer. Individuals that have iron overload disease are at much higher risk of developing liver cancer if they drink alcohol regularly. In addition, how cells handle iron can be influenced by alcohol, making iron an important factor in the development of alcohol associated cancer. Iron acts by causing an increase in a process that damages the cell, called oxidant stress. We think this process may affect a chemical that cells make that is responsible for regulating genes through modifying DNA. We propose to find out if this occurs in liver cells in mice. If this is the case, then we will have identified a mechanism by which iron and oxidant stress may help to drive the formation of cancer in alcohol drinkers. Discovering such a mechanism would give us targets that may help prevent alcohol associated cancer formation.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Exploratory/Developmental Grants (R21)
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Cancer Etiology Study Section (CE)
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Okano, Paul
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Marshall University
Schools of Medicine
United States
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Belalcázar, Andrea D; Ball, John G; Frost, Leslie M et al. (2014) Transsulfuration Is a Significant Source of Sulfur for Glutathione Production in Human Mammary Epithelial Cells. ISRN Biochem 2013:637897