Nonylphenol-induced Ca 2+ elevation and Ca 2+-independent cell death in human osteosarcoma cells

Abstract

The effect of the environmental toxicant nonylphenol on cytosolic free Ca 2+ concentration ([Ca 2+] i ) and proliferation has not been explored in human osteoblast-like cells. This study examined whether nonylphenol alters Ca 2+ levels and causes cell death in MG63 human osteosarcoma cells. [Ca 2+] i and cell death were measured using the fluorescent dyes fura-2 and WST-1 respectively. Nonylphenol at concentrations above 3 μM increased [Ca 2+] i in a concentration-dependent manner. The Ca 2+ signal was reduced by 90% by removing extracellular Ca 2+. The nonylphenol-induced Ca 2+ influx was insensitive to blockade of L-type Ca 2+ channel blockers. After pretreatment with 10 μM nonylphenol, 1 μM thapsigargin (an endoplasmic reticulum Ca 2+ pump inhibitor) failed to induce [Ca 2+] i rises. Inhibition of phospholipase C with 2 μM U73122 did not change nonylphenol-induced [Ca 2+] i rises. The nonylphenol-induced [Ca 2+] i rises were enhanced or inhibited by phorbol myristate acetate or GF 109203X, respectively. At concentrations of 10 and 20 μM nonylphenol killed 55% and 100% cells, respectively. The cytotoxic effect of 10 μM nonylphenol was unaltered by pre-chelating cytosolic Ca 2+ with BAPTA. Collectively, in MG63 cells, nonylphenol induced [Ca 2+] i rises by causing Ca 2+ release from intracellular stores and Ca 2+ influx from extracellular space. Furthermore, nonylphenol can cause Ca 2+-unrelated cytotoxicity in a concentration-dependent manner.