Article

Chronic oral exposure to inorganic arsenate interferes with methylation status of p16INK4a and RASSF1A and induces lung cancer in A/J mice.

Environmental Health Sciences Division, National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan.
Toxicological Sciences (Impact Factor: 4.48). 07/2006; 91(2):372-81. DOI: 10.1093/toxsci/kfj159
Source: PubMed

ABSTRACT Although inorganic arsenate (iAs(V)) or arsenite (iAs(III)) is clearly a human carcinogen, it has been difficult to produce tumors in rodents. In the present study, we orally administered iAs(V) to A/J mice to examine arsenic carcinogenicity in rodent. A/J mice (male, n = 120) assigned to four groups were given drinking water containing 0, 1, 10, and 100 ppm iAs(V) for 18 months. At the end of experiment, the complete lungs were removed and used for examining histopathology and extracting RNA and DNA. Epigenetic effects of iAs(V) on DNA methylation patterns of p16INK4a and RASSF1A genes were determined by methylation-specific polymerase chain reaction. Changes of p16INK4a and RASSF1A at mRNA and protein levels were examined by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Arsenic was accumulated dose dependently in the lung tissues of iAs(V)-exposed mice. Increase in lung tumor number and lung tumor size was observed in iAs(V)-exposed mice compared to the control. Histopathological examination showed that the rate of poorly differentiated lung adenocarcinoma was much higher in iAs(V)-exposed mice than in the control. Methylation rates appeared to be higher in a dose-related tendency in lung tumors from iAs(V)-exposed mice compared to the control. Lower or loss of p16INK4a and RASSF1A expression was found in lung tumors from iAs(V)-exposed mice, compared to that in nontumor lung tissues from both control and iAs(V)-exposed mice, and this reduced or lost expression was in accordance with hypermethylation of the genes. In conclusion, iAs(V) exposure increased lung tumor incidence and multiplicity in A/J mice. Epigenetic changes of tumor suppressor genes such as p16INK4a and RASSF1A are involved in the iAs(V)-induced lung carcinogenesis.

0 Bookmarks
 · 
65 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Occupational and environmental exposure to inorganic arsenic leads to development of cancer and represents a significant health hazard in more than 70 countries. The underlying mechanism for arsenic-induced carcinogenesis remains unclear. Laboratory studies suggest that arsenic is a poor mutagen but may cause epigenetic silencing of key tumor suppressor genes such as p16 through DNA hypermethylation. However, the evidence for an association between human arsenic exposure and abnormal DNA methylation of tumor suppressor genes is lacking. Paired case-control studies were conducted involving 40 individuals with high arsenic exposure and arsenicosis, 40 individuals with similarly high exposure to arsenic but without arsenicosis, and 40 individuals with normal exposure to arsenic. DNA methylation status of p16 was determined using methylation-specific PCR. Conditional logistic regression analysis showed that DNA hypermethylation of p16 gene was significantly associated with high arsenic exposure (Odds Ratio = 10.0, P = 0.0019) independently of the development of arsenicosis (Odds Ratio = 2.0, P = 0.1343). High exposure of arsenic in human is positively linked to DNA hypermethylation of p16 gene, suggesting that epigenetic silencing of key tumor suppressor may be an important mechanism by which arsenic promotes cancer initiation.
    Journal of occupational medicine and toxicology (London, England). 01/2014; 9(1):42.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Heavy metals and their derivatives can cause various diseases. Numerous studies have evaluated the possible link between exposure to heavy metals and various cancers. Recent data show a correlation between heavy metals and aberration of genetic and epigenetic patterns. From a literature search we noticed few experimental and epidemiological studies that evaluate a possible correlation between heavy metals and brain tumors. Gliomas arise due to genetic and epigenetic alterations of glial cells. Changes in gene expression result in the alteration of the cellular division process. Epigenetic alterations in brain tumors include the hypermethylation of CpG group, hypomethylation of specific genes, aberrant activation of genes, and changes in the position of various histones. Heavy metals are capable of generating reactive oxygen assumes that key functions in various pathological mechanisms. Alteration of homeostasis of metals could cause the overproduction of reactive oxygen species and induce DNA damage, lipid peroxidation, and alteration of proteins. In this study we summarize the possible correlation between heavy metals, epigenetic alterations and brain tumors. We report, moreover, the review of relevant literature.
    Current Genomics 12/2014; 15(6). · 2.87 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Exposure to toxic metals poses a serious human health hazard based on ubiquitous environmental presence, the extent of exposure, and the toxicity and disease states associated with exposure. This global health issue warrants accurate and reliable models derived from the risk assessment process to predict disease risk in populations. There has been considerable interest recently in the impact of environmental toxicants such as toxic metals on the epigenome. Epigenetic modifications are alterations to an individual's genome without a change in the DNA sequence, and include, but are not limited to, three commonly studied alterations: DNA methylation, histone modification, and non-coding RNA expression. Given the role of epigenetic alterations in regulating gene and thus protein expression, there is the potential for the integration of toxic metal-induced epigenetic alterations as informative factors in the risk assessment process. In the present review, epigenetic alterations induced by five high priority toxic metals/metalloids are prioritized for analysis and their possible inclusion into the risk assessment process is discussed.
    Frontiers in Genetics 07/2014; 5:201.

Full-text (2 Sources)

Download
12 Downloads
Available from
May 31, 2014