The ganglioside GD3 (Neu5Aca8Neu5Aca3Galb4GlcCer) is an intracellular lipid messenger that induces apoptosis by targeting mitochondria in various cell types. GD3 can also promote apoptosis when externally added to cells. Previous studies showed that the proapoptotic effects of GD3 can be counteracted by 9-O-acetylation. To determine whether 9-O-acetyl GD3 (acGD3) has a general antiapoptotic potential, the apoptosis-sensitive Jurkat cell line and an apoptosis-sensitive variant of the cell line Molt-4 were preincubated with micromolar concentrations of acGD3 and then treated with inducers of apoptosis. A reduced apoptotic index and an increased cell viability were observed. On the other hand, when the Jurkat cells were treated with GD3 for extended periods of time, a population was selected that was resistant to apoptosis induction by N-acetyl sphingosine as well as by the anti-leukemic drug daunorubicin. Comparative analysis of gangliosides revealed the formation of acGD3 in the resistant Jurkat cells that was not found in the apoptosis-sensitive cells. Conversely, exposing the acGD3 positive and apoptosis-resistant cell line Molt-4 to the Odeacetylating activity of salicylate resulted in a complete disappearance of acGD3 and an enhanced sensitivity to N-acetyl sphingosine-mediated apoptosis. Formation of acGD3 might thus represent a new mechanism how tumor cells can escape apoptosis. ' 2006 Wiley-Liss, Inc.Key words: apoptosis; 9-O-acetyl GD3; gangliosideThe intracellular ganglioside GD3 (Neu5Aca8Neu5Aca3Galb 4GlcCer) has been shown to serve as a second lipid messenger in the apoptotic pathway induced by FAS/FASL, TNF-a or b-amyloid in diverse lymphoid and myeloid cell types.1-3 Various effects have been ascribed to GD3, such as production of reactive oxygen species (ROS), 4 opening of the mitochondrial permeability transition pore (PTP), 4 release of cytochrome C, 1,4,5 activation of caspases 6 and inhibition of the translocation of NFjB to the nucleus. 7 The importance of ROS and PTP in the GD3-mediated apoptotic pathway is stressed by the finding that GD3-induced mitochondrial changes are prevented by antioxidants such as butylated hydroxytoluene (BHT) 2 and by preincubation of the cells with cyclosporin A, an inhibitor of the PTP.8 Despite the obvious involvement of mitochondria, the exact mechanism how GD3 promotes apoptosis still remains elusive.Accumulation of GD3 has been reported in a variety of tumors.9-11 The concomitant presence of an acetylated modification of GD3, 9-O-acetyl GD3 (acGD3), was observed in some tumors such as melanoma 12,13 and breast cancer, 14,15 as well as in tumor cell lines like MOLT 4 16 and SKMel28. 17In a previous report, we have shown that the proapoptotic activity of GD3 is suppressed by acetylation. 18 However, it remained unclear whether the observed resistance to apoptosis is due to inactivation of GD3 by acetylation or, rather, to an antiapoptotic potential of acGD3 on its own. To approach this question, more information is needed about the effects of acGD3 when applied ...

No abstract

Dorzolamide reduced the damage inflicted on retinal neural cells by agents that induced apoptosis and, therefore, can be considered a neuroprotectant.

The ability of glyoxal to induce apoptosis was confirmed by our findings demonstrating the time- and dose-dependent acidification of retinal cells. The onset of acidification is a hallmark because acidification is a measurable cytosolic event that follows the mitochondrial change but precedes caspase activation. Therefore, monitoring of pHi can allow one to assess cell stresses such as hypoxia, and metabolic stress (AGEs), and to test whether these stresses have a cumulative effect on apoptosis induction. Our study showed that intracellular pH and mitochondrial potential in living retinal cells are useful parameters for monitoring metabolic status in retinal tissue. These findings may be relevant in the study of retinal cell death mechanisms associated with age-related diabetic retinopathy and macular degeneration.

Retinal ganglion cell degeneration is supposed to be mediated by reactive oxygen species (ROS) and advanced glycation end products (AGEs). The alpha2‐adrenergic agonist, 5‐bromo‐N‐(4,5‐dihydro‐1H‐imidazol‐2‐yl)‐6‐quinoxalinamine (brimonidine; UK‐14,304), is said to exert a neuroprotective effect. To investigate these mechanisms in detail, we exposed rat whole mounts to glyoxal or H2O2 and treated them with either UK‐14,304 alone or additionally with the phosphatidylinositide 3 kinase (PI3) kinase inhibitor, 2‐(4‐Morpholinyl)‐8‐phenyl‐4H‐1‐benzopyran‐4‐one (Ly 294002). The accumulation of Nε‐[carboxymethyl] lysine (CML) was assessed immunohistochemically and changes in intracellular pH (pHi), mitochondrial transmembrane potential (MTMP) and ROS production in cell bodies of multipolar ganglion cell layer were studied by intravital fluorescence microscopy and confocal laser scanning microscopy. Ultrastructural changes in mitochondria of multipolar ganglion cell layer cell bodies were determined by transmission electron microscopy. We found that glyoxal and H2O2 increased accumulation of CML‐modified proteins and ROS production and decreased pHi and MTMP in cell bodies of multipolar ganglion cell layer. UK‐14,304 could prevent production of ROS, accumulation of CML‐modified proteins, ameliorate acidification, preserve MTMP and attenuate ultrastructural damages of ganglion cell mitochondria. Ly 294002 reversed the UK‐14,304‐mediated attenuation of CML and ROS production. We conclude that the protective effects of UK‐14,304 seem partly to be mediated by PI3 kinase‐dependent pathways.