Student Research: Emily Schneider
Arsenic distributes throughout the body, able to pass the placental barrier and reach the developing fetal brain. High-dose inorganic arsenic exposure to animals during development has been associated with neural tube defects, exencephaly and other disorders, although the molecular mechanisms underlying potential effects from low-dose exposure are uncertain. Although many mechanisms including cell cycle disruption, altered gene expression, and induction of apoptosis have been proposed for AS3+ toxicity, the effects on cell proliferation during embryonic/fetal development has not been extensively studied.
In this study, gestation day 12 primary rat midbrain neuroepithelial cells were exposed to As3+ (0,2,4, and 5mM, 0-48 hr) in vitro. Effects of As3+ on cell cycle kinetics were determined by continuous BrdU labeling and bivariate flow cytometric Hoechst-ethidium bromide analysis. We observed a time- and concentration- dependent inhibition of mitosis as early as 12 hours after exposure. After 24 hours, the fraction of cell in S phase treated with As3+ were significantly higher than untreated controls. In later rounds of cell division, significantly fewer treated cells were present, due to inhibition in earlier phases and/or cell death. Significant inhibition of cell cycle entry from G0/G1 was not seen until 36 hours of treatment. Although cell proliferation was inhibited, cell cycle progression was observed to occur under all exposure conditions.
The present study confiRMS previous observations of As3+ induced cell cycle inhibition found in other cell types. Taken as a whole, As3+ caused time- and concentration- dependent effects on Ga, S, and G2/M phases. These effects likely contribute to its neurodevelopmental toxicity. Further studies investigating changes in gene expression during development will provide a better understanding of the As3+ induced disruption of the cell cycle.