Cell death induced by physical agents: morphological features

The aim of this work is to present and discuss in vitro cell death appearing after exposure to physical conditions such as UVB radiation, static magnetic fields, hyperthermia and hypothermia. UVB radiation induces oxidative stress, leading, in most experimental models, to apoptotic death. Generally death occurs through the intrinsic apoptotic pathway, even if the extrinsic one cannot be excluded. UVB radiation also appears effective on cell systems which are normally apoptosis-resistant, such as muscle cells. Static magnetic fields mostly induce plasma membrane and microvilli alterations; occasionally apoptotic cell death appears. Hyperthermic conditions applied were mild, i.e. variable exposures to 43°C, as well as hypothermia, consisting of variable exposures to 0-6°C. Both treatments were followed by incubation at physiological conditions. Heat exposure is a powerful apoptotic inducer in a variety of cells, where it induces classical apoptotic changes and the well known biochemical pathways. The effect of hyperthermia has been described in adherent human tumor cells, which undergo cell rounding and progressively detach from the substrate, in close correlation with the down-regulation of adhesion molecules. Hypothermia, only occasionally triggers apoptosis, more frequently inducing cell necrosis. Therefore, cell death can be induced by physical agents dependently on the treatment and cell model. In particular, UVB and hyperthermia can be considered reliable and reproducible apoptotic triggers.