Mechanisms of the Apoptotic and Necrotic Actions of Trimethyltin in Cerebellar Granule Cells

Abstract

In evaluating mechanisms of trimethyltin (TMT)-initiated neuronal damage, the present study focused on involvement of reactive oxygen species, protein kinase C (PKC), and glutamate receptors. Exposure of cerebellar granule cells to TMT (0.01-0.1 microM) produced primarily apoptosis, but higher concentrations were associated with cellular lactate dehydrogenase efflux and necrosis. TMT increased generation of cellular reactive oxygen species, which was inhibited by either L-NAME (inhibitor of nitric oxide synthase, NOS) or catalase, indicating that both NO and H(2)O(2) are formed on TMT exposure. Since chelerythrine (selective PKC inhibitor) also inhibited oxidative species generation, PKC appears to play a significant role in TMT-induced oxidative stress. The metabotropic glutamate receptor antagonist, MCPG, (but not MK-801) prevented oxidative species generation, indicating significant involvement of metabotropic receptors (but not NMDA receptors) in TMT-induced oxidative stress. NOS involvement in the action of TMT was confirmed through measurement of nitrite, which increased concentration dependently. Nitrite accumulation was blocked by L-NAME, chelerythrine, or MCPG, showing that NO is generated by TMT and that associated changes in NOS are regulated by a PKC-mediated mechanism. Oxidative damage by TMT was demonstrated by detection of elevated malondialdehyde levels. It was concluded that low concentrations of TMT (0.01-0.1 microM) cause apoptotic cell death in which oxidative signaling is an important event. Higher concentrations of TMT initiate necrotic death, which involves both an oxidative and a non-oxidative component. TMT-induced necrosis but not apoptosis in granule cells is mediated by glutamate receptors.

Equivalent effect of DNA damage-induced apoptotic cell death or long-term cell cycle arrest on colon carcinoma cell proliferation and tumour growth

“…Necrotic cell death, measured as the efflux of lactate dehydrogenase (LDH) into the culture medium (Gunasekar et al, 2001), was negligible after SN-38 treatment in the cell cycle-arrested p53 wt cell lines as well as in the apoptotic HT-29 cell line, whereas necrosis in the HCT116p53 À/À cells was evident (Figure 6e and j). Heat shock treatment, used as a standard necrosis inducer, caused necrosis in all cell lines in a timedependent manner.…”

Dysregulation of intracellular calcium homeostasis is responsible for neuronal death in an experimental model of selective hippocampal degeneration induced by trimethyltin

“…It is noteworthy that TMT-induced cell death has also been shown to be linked to the above mentioned mechanisms (Philbert et al 2000;Gunasekar et al 2001;Geloso et al 2002;Jenkins and Barone 2004;Misiti et al 2008). All above commented data are consistent with the possibility that hippocampal neuronal death is mediated by TMTinduced intracellular Ca 2+ overload activating apoptotic pathways.…”

Hypoxia‐like transcriptional activation in TMT‐induced degeneration: microarray expression analysis on PC12 cells

“…TMT interacts with cell membranes because of its high lipophilicity, thus being able to alter the membrane properties of pyramidal neurons in vitro and impair the transport of neurotransmitters (Harkins and Armstrong 1992;Ortiz et al 2005). TMT is also able to impair cell signaling by interfering with different signal transduction pathways, such as those mediated by the activation of protein kinase C (Pavlakovic et al 1995;Kane et al 1998;Gunasekar et al 2001), phospholipase A2 (Kafer and Krug 1994) and JNK (Ogita et al 2004). Several other mechanisms have been reported to be implicated in the in vivo and in vitro effects of organotins, including the alteration of energy-related metabolic processes (Lock 1976;Thompson et al 1996).…”