Effects of halogenated substances on testicular cells - : Risk assessment and DNA damage

Abstract This study investigates four halogenated substances; three polyfluorinated compounds and one brominated substance. The polyfluorinated compounds, namely 6:2 fluorotelomer alcohol (6:2 FTOH), 8:2 fluorotelomer alcohol (8:2 FTOH) and perfluorooctanoic acid (PFOA), are widespread anthropogenic compounds, used in a variety of consumer products due to their water-, grease- and stain-repellent property. Levels of PFOA in human blood are typically around 5 ppb (0.01 μM), while FTOHs so far not have been measured in human samples due to technical difficulties. One of the main effect of PFOA in laboratory animals and in in vitro experiments is an induction of peroxisomal proliferation, leading to increased oxidation of fat, changed expression of a variety of genes, and increased cell proliferation, possibly inducing cancer development, both in the liver and in the pancreas and testicle. PFOA is also a reproductive toxicant, changes membrane architecture, and inhibits the effluent transporter Pgp. Several of the effects of the FTOHs are similar to those observed after PFOA exposure and several of the genes that show altered expression after PFOA exposure are also changed after exposure to 8:2 FTOH. Effects of 8:2 FTOH exposure include hepatocellular necrosis and peroxisomal proliferation, as well as detrimental effects on development in mice. Both 6:2 and 8:2 FTOH have been shown to act as xenoestrogens in vitro. We evaluated the effect of 6:2, 8:2 FTOH and PFOA on testicular cells from Wistar rats. Testicular cells were exposed in vitro to concentrations up to 300 μM for one hour. No signs of cytotoxicity were observed. The level of single strand breaks, abasic sites and oxidized purines was not increased, either. Whether the expression of the breast cancer resistant protein (Bcrp1) was altered, remains unsure due to high variability between experimental runs. One major weakness in these experiments is the use of a relatively short exposure time, making it very difficult to draw conclusions. Since the tested concentrations are many magnitudes higher than exposure in the general population, the data have nonetheless predictive value. Taken together, the results suggest that the tested PFCs do not exhibit testicular toxicity. The brominated compound 1,2-dibromo-3-chloropropane (DBCP) is known to induce permanent or temporary infertility in men, in addition to being a renal toxicant. It also induced DNA damage and acts as a clastogen and mutagen, inducing cancer development. The DNA inducing effect of DBCP on three testicular cell types was evaluated; Sertoli cells and other somatic cells seem to be the most sensitive cell type, spermatogonia the least sensitive, and spermatids seem to have a medium sensitivity. However whether the results obtained in experiments with somatic cells are correct is quite uncertain due to prolonged perincubation time. The repair capacity in spermatogonia and spermatids was also examined; spermatogonia were found to repair DNA damage induced by DBCP somehow faster than spermatids. Taken together, the results suggest that it may be the supporting cells like Sertoli cells that get heaviest damaged by DBCP. The damage in these cells can then lead to impaired germ cell development by interfering with the supply of nutrition, testosterone and other supporting functions. Spermatogonia appear to be least sensitive and repair the induced DNA damage relatively effectively. Since these cells are located outside of the blood-testis barrier these efficient defense mechanisms are very meaningful.