Master Thesis

In vitro toxicity of arsenite in human urothelial cells: Effects of garlic and leek

Sinikka Hinrichsen (03/2010-12/2010)

Support: Britta Planer-Friedrich, Sasan Rabieh

Arsenic is a widespread, toxic pollutant in water, air, and soil known to cause among others cancer of the bladder and liver. Trivalent arsenic species are known to be more toxic than pentavalent species. Worldwide, about 100 million of people are affected by arsenic exposure. Therefore, it is extremely important to investigate what might counteract arsenic toxicity. A previous study could show the reduction of arsenic toxicity for human skin cells by the addition of aqueous garlic extract (AGE). The positive effect of garlic can be traced back to its antioxidant and anti-clastogenic property, and its ability to oxidize trivalent arsenic species to less toxic pentavalent species. Besides different active sulfur compounds, selenium is an essential micronutrient in garlic and also is assessed to have an anticarcinogenic potential. In the present study, human urothelial cells (UROtsa) and human hepatoma cells (HepG2) were exposed for 24 h to arsenite and arsenate with and without the addition of AGE, garlic powder extract (GPE), aqueous leek extract (ALE), individual sulfur compounds contained in garlic (alliin, allylsulfide (AS), allyldisulfide (ADS), dimethyldisulfide (DMDS)), selenite, and selenate. Cell viabilities (CVs) were measured by the spectrophotometric MTT assay.

For UROtsa cells, the addition of the two garlic extracts and ALE did not reduce arsenite toxicity, GPE was even shown to be enormously cytotoxic. AS, ADS, and DMDS were cytotoxic due to the solvent ethanol. Alliin initially showed a slight increase in CVs but this effect could not be reproduced. Selenite increased CVs at different concentrations of arsenite (25, 50, and 75 µM) with the best effect at 5 µM selenite (reversion of cytotoxicity of up to 35 %). A reduction of arsenate cytotoxicity up to 40 % could be achieved by adding 10 µM selenite to 250, 500, and 750 µM arsenate. For HepG2 cells, AGE had no influence on arsenite toxicity. In contrast to the experiments with UROtsa cells, GPE was not cytotoxic for HepG2 cells and the addition of ALE showed a concentration-dependent negative effect on CVs. Selenite in concentrations of 10, 25, and 50 µM increased arsenic toxicity. This can be explained by the toxic effect of selenite alone in these concentrations. Selenate did not influence arsenic toxicity for both cell lines. It is questionable whether the two cell lines of the present study can be compared to the skin cells used in the previously published study concerning their response to arsenic and garlic or leek extract exposure. Moreover, different extraction methods in the two studies might have influenced the chemical composition and concentrations of sulfur and selenium compounds in the garlic extracts.

Further experiments with different cell lines and different breeds of garlic are needed to get to a better knowledge about the influence of garlic, especially concerning the effect of individual sulfur compounds, on arsenic cytotoxicity. Selenite was shown to be most effective in reducing arsenite toxicity. Therefore, investigations on the interaction between selenium and arsenic are a promising field of future research in the context of arsenic cytotoxicity.