Ca²⁺ movement and cytotoxicity induced by the pyrethroid pesticide bifenthrin in human prostate cancer cells

Bifenthrin, a commonly used pyrethroid pesticide, evokes various toxicological effects in different models. However, the effect of bifenthrin on cytosolic-free Ca²⁺ level ([Ca²⁺] _i) and cytotoxicity in human prostate cancer cells is unclear. This study examined whether bifenthrin altered Ca²⁺ homeostasis and cell viability in PC3 human prostate cancer cells. [Ca²⁺] _i in suspended cells were measured using the fluorescent Ca²⁺-sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 assay. Bifenthrin (100–400 μM) concentration-dependently induced [Ca²⁺] _i rises. Ca²⁺ removal reduced the signal by approximately 30%. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished bifenthrin-evoked [Ca²⁺] _i rises. Conversely, treatment with bifenthrin abolished BHQ-evoked [Ca²⁺] _i rises. Inhibition of phospholipase C (PLC) with U73122 significantly inhibited bifenthrin-induced [Ca²⁺] _i rises. Mn²⁺ has been shown to enter cells through similar mechanisms as Ca²⁺ but quenches fura-2 fluorescence at all excitation wavelengths. Bifenthrin (400 μM)-induced Mn²⁺ influx implicates that Ca²⁺ entry occurred. Bifenthrin-induced Ca²⁺ entry was inhibited by 30% by protein kinase C (PKC) activator (phorbol 12-myristate 13 acetate) and inhibitor (GF109203X) and three inhibitors of store-operated Ca²⁺ channels: nifedipine, econazole, and SKF96365. Bifenthrin at 175–275 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetra acetic acid-acetoxymethyl ester. Together, in PC3 cells, bifenthrin-induced [Ca²⁺] _i rises by evoking PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. Bifenthrin also caused Ca²⁺-independent cell death.