Data regarding
tellurium (Te) toxicity are scarce. Studies on its metabolism, performed mainly in bacteria, underline a major role of
reactive oxygen species (ROS). We investigated whether
tellurite undergoes redox cycling leading to ROS formation and
cancer cell death. The murine hepatocarcinoma Transplantable Liver
Tumor (TLT) cells were challenged with
tellurite either in the presence or in the absence of different compounds as
N-acetylcysteine (NAC),
3-methyladenine,
BAPTA-AM, and
catalase. NAC inhibition of
tellurite-mediated toxicity suggested a major role of oxidative stress.
Tellurite also decreased both
glutathione (GSH) and
ATP content by 57 and 80%, respectively. In the presence of NAC however, the levels of such markers were almost fully restored.
Tellurite-mediated ROS generation was assessed both by using the fluorescent, oxidation-sensitive probe dichlorodihydrofluorescein diacetate (DCHF-DA) and electron spin resonance (ESR) spectroscopy to detect
hydroxyl radical formation. Cell death occurs by a
caspase-independent mechanism, as shown by the lack of
caspase-3 activity and no cleavage of
poly(ADP-ribose)polymerase (PARP). The presence of gamma-H2AX suggests
tellurite-induced
DNA strand breaking, NAC being unable to counteract it. Although the
calcium chelator BAPTA-AM did show no effect, the rapid phosphorylation of eIF2alpha suggests that, in addition to oxidative stress, an endoplasmic reticulum (ER) stress may be involved in the mechanisms leading to cell death by
tellurite.