Ganglion cell death in glaucoma is caused by a variety of insults that include ischemia, insufficient neurotrophic support and oxidative stress. Experimental studies were therefore conducted on cell cultures to determine how serum deprivation (to mimic insufficient neurotrophic support) or oxidative glutamate toxicity (GB), cause oxidative stress and induce retinal cell death. Moreover, studies were carried out to deduce whether selected sulphur containing compounds can blunt any negative influences to cells in culture and/or a defined ischaemic insult to the rat retina in situ, as this might suggest their use for the treatment of glaucoma. Serum deprivation and GB caused generation of reactive oxygen species (ROS) and apoptosis-like death to transformed retinal ganglion cells (RGC-5 cells). RGC-5 cells were more susceptible to the detrimental effects of GB than serum deprivation. RGC-5 cells subjected to serum deprivation appear to die by mechanisms that resemble classical apoptosis more closely than that caused by GB and the phase between the maximal generation of ROS and cell death were different. Cell death caused by serum deprivation was caspase-dependent but this was not the case for GB. Moreover, of the two sulphur compounds sulbutiamine and N-acetyl cysteine (NAC), sulbutiamine blunts the effect of serum deprivation more effectively. In addition, the pan caspase inhibitor z-VAD-fmk attenuated the negative effect of serum deprivation to RGC-5 cells while the necroptosis inhibitor (necrostsatin-1) counteracted solely the insult of GB. The sulphur containing compounds, ACS1 and ACS 67 which release hydrogen sulphide (H2S) slowly and NAC (a pro-cysteine GSH precursor) attenuated GB-induced cell death of RGC-5 cells. In contrast, sulbutiamine (a lipophilic thiolic thiamine derivative) was particularly effective in protecting RGC-5 cells from an insult of serum deprivation. Moreover, all of the sulphur compounds directly sequestered different types of ROS but with varying efficiency. Common features by which all tested sulphur containing agents seem to elicit a mode of action include the stimulation of GSH and the antioxidant enzyme glutathione-S-transferase (GST) as well as to scavenge excess free radicals. Moreover, the slow release of H<sub>2</sub>S from the ACS compounds appears to protect cells from oxidative stress through increasing the level of GSH, modulation of the cystine uptake transporter xCT, stimulation of the oxidative stress related transcription factor Nrf2 and the stimulation of pro-survival signalling pathways. The slow releasing H<sub>2</sub>S sulphur compound ACS67 also counteracts a number of detrimental influences to the rat retina in situ because of ischemia/reperfusion that includes damage to their ganglion cells. This suggests that such sulphur compounds might find a use in the treatment of glaucoma where ischemia probably plays a part in the disease process.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:547441 |
| Date | January 2011 |
| Creators | Abdul Majid, Aman Shah Bin |
| Contributors | Osborne, Neville |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:bfb5ec82-9141-4784-94a8-0df3ce9d9471 |
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