According to recent estimates, over 140 million people from 50 countries regularly get exposed to arsenic through drinking water. The exposure level significantly exceeds the guideline value (10 μg/L) stipulated by the World Health Organization. It is an established fact that chronic arsenic exposure from drinking water causes a variety of cancers including skin cancer. Unfortunately, there is a general paucity of data on the underlying biological mechanisms that regulate arsenic-mediated carcinogenesis. Moreover, methods for the prevention and treatment of arsenic-mediated carcinogenesis have remained elusive thus far.
Researchers at the Shibaura Institute of Technology (SIT) and Nagoya University have recently been able to identify the underlying biological mechanisms of carcinogenesis inhibition. Using in vitro studies, the research team has been able to demonstrate how calcitriol, or activated vitamin D3, inhibits arsenic-mediated carcinogenesis in certain types of skin cells known as “keratinocytes.” These cells are primarily found in the epidermis, the outermost layer of the skin. It is a scientifically established fact that certain signaling molecules—kinase proteins (e.g., MEK or “AKT”) that control the fate of various biological processes—are strongly associated with tumor development.
Professor Ichiro Yajima from the Unit of Molecular and Cellular Toxicology, Department of Bioscience and Engineering, SIT, who led the research team, says, “Our in vitro study in human nontumorigenic HaCaT skin keratinocytes showed that calcitriol, which is also known as activated vitamin D3 or 1,25-dihydroxy-vitamin D3, inhibited arsenic-mediated anchorage-independent growth with downregulations of cancer-related activation of several signaling pathways, including MEK, ERK1/2, and AKT, as well as activity of cell cycle.”
To elucidate the relationship between arsenic uptake and calcitriol treatment, the researchers measured arsenic levels in HaCaT cells— long-lived, spontaneously immortalized human epidermal keratinocytes—treated with calcitriol using an inductively coupled plasma-mass spectrophotometer. Quite interestingly, arsenic levels in HaCaT cells cultured with arsenic significantly decreased when these cells were treated with increasing doses of calcitriol. The findings from their study have been published in the American Journal of Cancer Research.
Dr. Masashi Kato, who serves as a Professor at the Department of Occupational and Environmental Health, Nagoya University, Japan, and is a collaborator on the study, adds, “Calcitriol significantly repressed arsenic uptake in HaCaT cells with the regulation of expressions of aquaporin genes (AQP7, 9, and 10), which were modified by arsenic exposure. Vitamin D receptor expression was significantly increased by arsenic exposure whereas calcitriol had no effect on the expression of the receptor.”
The researchers then sought to understand whether calcitriol had an inhibitory effect on arsenic-induced tumorigenesis in cells other than skin keratinocytes. To this end, they performed anchorage-independent growth assays using a human normal lung epithelial cell line called “Beas-2b.” The results of these assays were equally astonishing: arsenic-mediated anchorage-independent growth of Beas-2b cells treated with calcitriol was suppressed by 21.4–70.0%, suggesting that calcitriol’s potential to suppress arsenic-induced tumorigenesis is not restricted to keratinocytes.
Prof. Yajima muses, “These results suggest that calcitriol suppresses arsenic-induced tumorigenesis not only in keratinocytes, but also in other target cells including lung epithelial cells. Furthermore, the expression pattern of aquaporin genes involved in arsenic uptake, a critical step in arsenic-induced carcinogenesis, is significantly altered by calcitriol treatment. We therefore believe that activated vitamin D3, or calcitriol, may contribute to the prevention and therapy for arsenic-mediated diseases including cancer.”
Environmental toxins such as arsenic contribute significantly to the development of life-threatening diseases such as cancer. However, it may take years, even decades, for cancer to develop from drinking arsenic-contaminated water. The current research clearly indicates that calcitriol could be used as a test compound for validating the safety and efficacy of activated vitamin D3 and/or its analogs in preventing or treating arsenic-triggered cancer. Taking vitamin D3 beforehand in arsenic-contaminated areas may reduce the risk of cancer development 5 or 10 years later and help people maintain good health for a long time. This is certainly welcome news for millions of people forced to survive on polluted water worldwide.
Article link: https://e-century.us/files/ajcr/12/11/ajcr0144719.pdf
About Shibaura Institute of Technology (SIT), Japan
Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained “learning through practice” as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and will receive support from the ministry for 10 years starting from the 2014 academic year. Its motto, “Nurturing engineers who learn from society and contribute to society,” reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 8,000 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.
About Professor Ichiro Yajima from SIT, Japan
Dr. Ichiro Yajima serves as a Professor at the Department of Bioscience and Engineering, Shibaura Institute of Technology (Japan). Using advanced bioscience and technology, his research group primarily focuses on delineating the relationships among environmental factors, aging, and disease. The group also contributes to research in the field of cancer, cosmetology, dermatology, experimental medicine, and toxicology. Prof. Yajima has over 75 publications to his credit. He has received more than 1,600 global citations for his noteworthy research contributions and is affiliated with various reputed academic societies including the Japanese Society of Toxicology, the Molecular Biology Society of Japan and the Japanese Society for Hygiene.
About Professor Masashi Kato from Nagoya University, Japan
Dr. Masashi Kato serves as a Professor at the Department of Occupational and Environmental Health, Nagoya University Graduate School of Medicine (Japan). He has over 200 research publications to his credit. Prof. Kato has received 9 awards for his exemplary research contributions to environmental science and other related areas. He is a vice-president of the Japanese Society of Hygiene. He is also an expert member of Accident Investigation Office in the Consumer Affairs Agency, Japan.
This study was supported in part by Grants-in-Aid for Scientific Research (A) (No. 19H01147 and 17KT0033), (B) (No. 19K22907), (C) (No. 22506148 and 20K06749), Grant-in-Aid for Challenging Research (Exploratory) (No. 19K22907), (B) (16H02962, 24390157 and 24406002), KOSÉ Cosmetology Research Foundation.
METHOD OF RESEARCH
SUBJECT OF RESEARCH
Calcitriol inhibits arsenic-promoted tumorigenesis through regulation of arsenic uptake in a human keratinocyte cell line.
ARTICLE PUBLICATION DATE
The authors declare no conflicting interests.
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