Cytotoxicity of Bismuth Compounds to Cultured Cancer Cells

Bismuth (Bi) is a ubiquitous metal, but its effects on human health are unknown. We examined the cytotoxicity of Bi compounds to cultured 8505C human thyroid cancer cells. Treatments of 0.05–0.1 mM of Bi subgallate and free gallic acid resulted in cell death in approximately 100% of cells. *Corresponding author: Jun Kobayashi, School of Veterinary Nursing and Technology, Faculty of Veterinary Medicine, Nippon Veterinary and Life Science University, 1-7-1 Kyonan-cho, Musashino, Tokyo 180-8602, Japan, Tel: +81422314151; Fax: +81422332094; E-mail: junkoba@nvlu.ac.jp Received March 21, 2017; Accepted April 26, 2017; Published April 29, 2017 Citation: Kobayashi J, Ikeda K, Sugiyama H (2017) Cytotoxicity of Bismuth Compounds to Cultured Cancer Cells. J Environ Anal Toxicol 7: 462. doi: 10.4172/2161-0525.1000462 Copyright: © 2017 Kobayashi J, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Citation: Kobayashi J, Ikeda K, Sugiyama H (2017) Cytotoxicity of Bismuth Compounds to Cultured Cancer Cells. J Environ Anal Toxicol 7: 462. doi: 10.4172/2161-0525.1000462


Introduction
Bismuth (Bi) occurs in the earth's crust at a concentration of approximately 100 μg/kg, and is a Group 15 metal element with properties similar to those of lead and mercury [1]. Humans ingest 5-20 μg/day of Bi, mainly through food, and some Bi is thought to be absorbed and accumulated locally in the body. Whether Bi is an essential nutrient in humans is unknown [1,2]. Environmental pollution of Bi has not been a problem, as it is only used in small amounts in industrial settings, and is very low in environmental emissions. In Japan, Bi is not included in any regulatory criteria such as water quality standards or monitoring item guidelines. Entities such as the World Health Organization (WHO), European Union (EU), and the United States Environmental Protection Agency (USEPA) have likewise published no regulatory provisions regarding bismuth [3]. Bismuth is known to exert toxicity when administered in large quantities or for an extended period [1,2,4,5]. Bi subgallate has been used as a medicine for syphilis, peptic ulcer, and skin diseases for decades, and Bi subsalicylate and Bi citrate are used as anti-gastritis and antidiarrheal agents [1,5,6]. In recent years, Bi compounds have been used in cosmetic products, bactericides, dyes, and alloy materials. In addition, the use of Bi in semiconductor manufacturing, the chemical industry, and the nuclear fuel industry is increasing [5,7], potentially resulting in environmental release. However, there are few published reports on the toxicity of Bi compounds.
In this study, we assessed the cytotoxicity of a Bi compound standard product to cultured cells.
Twenty-four-well plates (Iwaki, Tokyo, Japan; bottom area of each well: 1.9 cm 2 ) were used for culturing and experiments. All glassware were disposable or autoclaved to sterilize.

Bi cytotoxicity assay
The 8505C cells were cultured to a subconfluent state in an incubator (37°C, 5% carbon dioxide, humidified) and stripped from the culture plates with trypsin/EDTA. Cells were centrifuged at 800 rpm for 5 min and the supernatant removed. The medium was replaced with RPMI-1640 containing 10% fetal bovine serum (FBS). One milliliter of the cell suspension (5 × 10 4 cells/ml) was added to each well of a 24-well plate. After overnight incubation, the supernatant of culture medium was replaced with the experimental medium (RPMI-1640 containing no FBS) and Bi (0-0.1 mM Bi subgallate, Bi subsalicylate, Bi acetate, and Bi chloride). After 24 h, live cells were measured using the MTT assay [8].

Results and Discussion
Cell death was observed only in cells treated with Bi subgallate (Figure 1). To ascertain whether the cytotoxicity was attributable to Bi or gallic acid, or to a synergistic effect of both, we investigated the cytotoxicity of gallic acid alone and gallic acid in combination with Bi chloride or Bi subgallate. Gallic acid displayed substantial toxicity, followed by the toxicity of Bi subgallate combined with gallic acid ( Figure  2). This finding indicates that Bi can mitigate the cytotoxicity of gallic acid; perhaps ionic Bi forms a complex with free gallic acid, regulating its permeation of the cell membrane [8,9]. It seems that not contrary to the fact that the ratio of free Bi ions in the culture solution is low in the case of organic acid salts such as subgallate. Bi can be detoxified by chelation [10,11], although some amino acids and soil fungi have been shown to enhance its toxicity [8,9]. In this study, we conducted only a very basic examination of cytotoxicity in a human thyroid cancer cell line. Experiments using free gallic acid and other cell lines are necessary to identify the molecular effects of Bi compounds.