Dithiocarbamate fungicides increase intracellular Zn2+ levels by increasing influx of Zn2+ in rat thymic lymphocytes

Abstract

Dithiocarbamate fungicides are used as alternative antifouling agents to highly toxic organotin antifouling agents, such as tri-n-butyltin and triphenyltin. There are some concerns regarding their environmental and health risks. It has been shown that tri-n-butyltin increases intracellular Zn2+ levels of mammalian lymphocytes. Therefore, we examined the effects of dithiocarbamate fungicides (Ziram, Thiram, and Zineb) on rat thymic lymphocytes using a flow-cytometric technique to elucidate how these fungicides affect intracellular Zn2+ levels. We further determined whether the agents increase intracellular Zn2+ and/or Ca2+, because both Zn2+ and Ca2+ are intracellular signals in lymphocytes, and excessive increases in their intracellular concentrations can have adverse effects. Dithiocarbamate fungicides increased intracellular Zn2+ levels, without affecting intracellular Ca2+ levels. Ziram was the most potent compound, increasing intracellular Zn2+ levels via Zn2+ influx. Ziram (1μM) greatly decreased the cellular nonprotein thiol content, and Zn2+ chelators attenuated the Ziram-induced decrease. Ziram increased the population of annexin V-positive cells in a Zn2+-dependent manner. Therefore, we propose that dithiocarbamate fungicides induce Zn2+ influx, resulting in an excessive elevation of intracellular Zn2+ levels, leading to the induction of apoptosis. This study gives a basic insight into the mechanisms of dithiocarbamate fungicide-induced adverse events.