Nitric Oxide Inhibits Cell Death Induced by Photodynamic Therapy Through a Caspase S-Nitrosylation-Independent Mechanism

Abstract

Ancona . ItalyMelatonin, the principal hormone of the pineal gland, elicits potent anti-stress, anti-aging and oncostatic properties and influences various immunological and endocrinological functions. The mechanism of most pharmacological effects of melatonin seems straightforward. It was found to be the most potent physiological free radical scavenger playing also a role in the regulation of apoptosis. Moreover melatonin receptor gene expression in the thymus and spleen supports the motion of the immunomodulatory role of this hormone. Since melatonin has previously been reported to influence cell differentiation and growth in a number of cell culture systems in vitro, in this report we describe the effects of melatonin at different concentrations on cell growth and cell death in human lymphoblastoid cell lines at various stage of differentiation. Pre-T RPMI-8402, pre-B KM-3, differentiated T cells MOLT-3 and B cells RAMOS-1 cell lines were treated up to 72 hours with different concentrations of melatonin. Cell growth, cell death, morphological and biochemical modifications were analysed. The results obtained display that the effects of melatonin are cell type and dose dependent and that the response is in terms of cell growth inhibition in RPMI-8402, KM-3 and RAMOS-1 and apoptosis induction in RPMI-8402 and RAMOS-1. These data appears to encourage the studies showing that the melatonin may be an important endogenous cell death modulator and a potential therapeutic agent. 337 Virus induced apoptosis in PC12 rat phaeochromocytoma cells w , B. Torocsik MD1, K. Kiss MD1, J. Tigyil, A. Freeman2, L. K. Csatary3, C. M. Csatary3, V. Liszka3 and Jozsef Szeberenyi MD, PhD, DScl Pics, Szigeti st): 12. 7624 HungaryThe attenuated Newcastle disease virus (NDV) vaccine MTH-68/H was found previously to cause regression of various tumors including certain types of human neoplasms. The mechanism of its oncolytic action is poorly understood, but it appears to affect specific signaling pathways in the target cell. The cellular effects of NDV were studied in PCl2 rat phaeochromocytoma cells, a widely used model system to analyze differentiation, proliferation and apoptosis signalling. The MTH-68/H vaccine was found to be cytotoxic on PC12 cells; it caused internucleosomal DNA fragmentation, a characteristic feature of apoptotic cell death. A very brief exposure (30 min) of cells to the virus was sufficient to produce a full-blown apoptotic response. Major mitogen-activated protein kinase pathways (including the stress inducible c-Jun N-terminal kinase pathway and p38 pathway) or mechanisms regulated by reactive oxygen species appear to have no role in virus-induced cell death. The apoptosis-inducing effect of MTH-68/H could not be prevented by simultaneous treatment of the cells with growth factors, second messenger analogs stimulating protein kinase C or Ca++-mediated pathways, or inhibitors of intracellular phosphatases, MEK, or NGF receptor. In contrast, a cyclic AMP analog partially protected the cells from virus-induced apopto...