Treatment of experimentally induced transient cerebral ischemia with low energy laser inhibits nitric oxide synthase activity and up-regulates the expression of transforming growth factor-beta 1

Background and Objectives: Nitric oxide (NO) has been shown to be neurotoxic while transforming growth factor-beta 1 (TGF-β1) is neuroprotective in the stroke model. The present study investigates the effects of low energy laser on nitric oxide synthase (NOS) and TGF-β1 activities after cerebral ischemia and reperfusion injury. Study Design/Materials and Methods: Cerebral ischemia was induced for 1 hour in male adult Sprague-Dawley (S.D.) rats with unilateral occlusion of middle cerebral artery (MCAO). Low energy laser irradiation was then applied to the cerebrum at different durations (1, 5, or 10 minutes). The activity of NOS and the expression of TGF-β1 were evaluated in groups with different durations of laser irradiation. Results: After ischemia, the activity of NOS was gradually increased from day 3, became significantly higher from day 4 to 6 (P < 0.001), but returned to the normal level after day 7. The activity and expression of the three isoforms of NOS were significantly suppressed (P < 0.001) to different extents after laser irradiation. In addition, laser irradiation was shown to trigger the expression of TGF-β1 (P < 0.001). Conclusions: Low energy laser could suppress the activity of NOS and up-regulate the expression of TGF-β1 after stroke in rats. © 2002 Wiley-Liss, Inc.link_to_subscribed_fulltex

Total retinal nitric oxide level is increased under elevated intra-ocular pressure

Purpose: Nitric oxide (NO) is a well-known vaso-dilator but its modulation in the retina is unclear. This study was conducted to quantify the total NO level and retinal ganglion cell (RGC) loss in an experimental glaucoma model. Methods: Three quarters of the episcleral drainage vessels (right eyes) of SD rats were thermally blocked using laser irradiation while the left eyes served as controls. We measured the intra-ocular pressure (IOP) using a digital tonometer (TonopenTM) 21 days, 28 days and 35 days after the laser treatment. We also measured total NO levels of the retina and the eyecup using a spectro-photometric assay, and RGC numbers by counting the retro-grade fluoro-gold stained cell bodies for the laser-treated and control eyes after 35 days. Results: The laser treatment significantly increased the IOP by approximately two-folds throughout the whole period of measurements (p<0.0001). The mean total RGC number decreased significantly from 98 7255383 (SEM) to 69 2765592 (p=0.008), or 29.8% reduction, in the laser-treated eyes after 35 days. The mean total NO level in the laser-treated retina was significantly increased by 2.4x compared with controls (p=0.016), but no significant difference was found in the eyecups (p≷0.05). Conclusion: Laser treatment resulted in significant IOP elevation and RGC loss, suggesting that thermal coagulation of drainage vessels provides an alternate model for glaucoma study. Retinal NO level is increased by about 2 times on Day 35 post-laser treatment. Since NO is capable of producing powerful peroxynitrite anion and hydroxyl radical, increasing NO production has a potential oxidative role for RGC loss in glaucoma

Total retinal nitric oxide production is increased in intraocular pressure-elevated rats

Nitric oxide (NO) is a well-known vaso-dilator but its regulation in the retina is unclear. This study was conducted to quantify total NO production and retinal ganglion cell (RGC) loss in an experimental glaucoma model. Three quarters of the peri-limbal/episcleral drainage vessels and anterior angle (right eyes) of Sprague-Dawley rats were thermally blocked using laser irradiation, while the left eyes served as controls. We measured the intraocular pressure (IOP) of both eyes using a digital tonometer (Tonopen) 21, 28 and 35 days after the laser treatment. After 35 days, we determined the total NO level in retinas and remaining ocular tissues for the laser-treated and control eyes using a spectro-photometric assay. The viable RGC numbers were also determined by counting the cell bodies stained retrogradely by fluoro-gold. The laser treatment significantly increased the lOP 2.0-2.6× throughout the whole period of measurements (P 0.05). Laser treatment resulted in significant IOP elevation and RGC loss, suggesting that thermal coagulation of the perilimbal region may provide an alternate protocol for glaucoma study. NO level was increased by two-fold in the retina but not in other ocular tissues. Since NO is capable of producing powerful peroxynitrite anions and hydroxyl radicals, elevated level of NO has a potential role in glaucoma. © 2002 Elsevier Science Ltd.link_to_subscribed_fulltex

Endogenous Anti-apoptotic Mechanism in Axotomized Retinal Ganglion Cells: the Involvement of Elevated Akt Phosphorylation

Purpose:We have previously shown that axotomy induced an early release of cytochrome c in axotomized retinal ganglion cells (RGCs) at 1 day post-axotomy (dpa). Interestingly, activation of caspase-9, caspase-3 and nuclear fragmentation were not observed in axotomized RGCs until 3 dpa. We hypothesize that endogenous neuroprotective pathways exist to temporarily halt the progress of apoptosis at a site downstream of cytochrome c release. Methods:Unilateral optic nerve transection 1.5 mm from the optic disc was performed on adult hamster. Operated animals were sacrificed at various time-points after axotomy to investigate the levels of phospho-Akt (Ser 473) in axotomized retinas using western blotting. Alternatively, the operated eyes were injected intravitreally with wortmannin, an inhibitor of PI3K, at 0 and 1 dpa. Animals were sacrificed at 2 dpa to examine the effect of wortmannin injections on phospho-Akt levels, caspase-3 and -9 activation and nuclear fragmentation in axotomized retinas. Results:We found that axotomy induced a rapid but transient increase in Akt phosphorylation in axotomized retinas. Akt activation markedly increased as early as 3 hours post-axotomy and returned to control level at 3 dpa, coinciding with the onset of caspase activation and RGC loss. In addition, attenuating the increase in Akt phosphorylation following axotomy by intravitreal injections of wortmannin induced the presence of activated caspase-3 and -9-positive apoptotic cells in the ganglion cell layer. Conclusion:Our data suggest that axotomy resulted in an increase in Akt phosphorylation, which delayed the onset of apoptotic machinery downstream of cytochrome c release by inhibiting the activation of caspase-9 or -3. Akt may hence serve as an endogenous neuroprotective pathway to limit RGC death following axotomy

Regulation of caspase activation in axotomized retinal ganglion cells

Transection of the optic nerve initiates massive death of retinal ganglion cells (RGCs). Interestingly, despite the severity of the injury, RGC loss was not observed until several days after axotomy. The mechanisms responsible for this initial lack of RGC death remained unknown. In the current study, immunohistochemical analysis revealed that caspases-3 and -9 activation in the RGCs were not detected until day 3 post-axotomy, coinciding with the onset of axotomy-induced RGC loss. Interestingly, elevated Akt phosphorylation was observed in axotomized retinas during the absence of caspase activation. Inhibiting the increase in Akt phosphorylation by intravitreal injection of wortmannin and LY294002, inhibitors of PI3K, resulted in premature nuclear fragmentation, caspases-3 and -9 activation in the ganglion cell layer. Our findings thus indicate that the PI3K/Akt pathway may serve as an endogenous regulator of caspase activation in axotomized RGCs, thereby, contributing to the late onset of RGC death following axotomy. © 2004 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Endogenous Neuroprotective Mechanism of Retinal Ganglion Cells following Transection of the Optic Nerve

Optic nerve transection has been shown to induce retinal ganglion cell (RGC) death mediated by caspase-3 and -9 activation. In this study, we examined the possible role of cytochrome c release in axotomized RGC death. Axotomized RGCs are proposed to die via apoptosis. Caspase-3 activation after axotomy has been shown, and caspase-3 inhibitors or Bcl-2 over-expression has been observed to enhance RGC survival. These studies suggest that caspase-3 may participate in the loss of axotomized RGCs. One of the upstream initiators of the apoptotic pathway is cytochrome c release from the intermembrane space of mitochondria. Released cytochrome c binds to Apaf-1 and activates caspase-9. Activated caspase-9 in turn activates caspase-3. To examine the involvement of the cytochrome c pathway in the apoptosis of axotomized RGCs, the release of cytochrome c post-axotomy was analyzed using immunohistochemistry. At 1, 2, 3, 5, 7, 10 and 14 days post-axotomy (dpa), animals were sacrificed and their eyeballs sectioned. Ten-micrometer retinal sections where the RGCs were prelabeled with retrograde transport of fluoro-Gold were used. The sections were counter-stained with DAPI to reveal nuclear morphology. We found that by 1 dpa, there was a significant increase in cytochrome c immunoreactivity compared to normal, undamaged retinas. The increase peaked at 3 dpa, and declined thereafter. By 10 dpa, cytochrome c immunoreactivity has returned to control level. Based on the findings from other apoptosis studies, this upregulation of cytochrome c immunoreactivity may contribute to axotomized RGC death. Interestingly, all the RGCs that were stained positive for cytochrome c exhibited normal nuclear morphology. Immunohistochemical staining of activated caspase-3 revealed that no caspase-3 activation was observed until 3 dpa. This suggests that cytochrome c release may act upstream of caspase-3 activation and precede any visible nuclear changes. Double immunohistochemical analysis for cytochrome c and activated caspase-3 showed that the two staining exhibit no co-localization. The lack of co-localization and the lag between the onset of cytochrome c and activated caspase- 3 staining suggests that there is a temporal gap between the two events. To examine the mechanism underlying the apparent temporal gap between cytochrome c release and caspase activation, the effect of axotomy on Akt activation was investigated. We found that axotomy induced a rapid increase in Akt phosphorylation at 3 h postaxotomy. Phospho-Akt content returned to control level at 3 dpa, coinciding with the onset of caspase activation and RGC loss. Our data suggest that this transient increase may contribute to the delayed activation of caspase-3/9 in axotomized retinas. Attenuating the increase in Akt phosphorylation following axotomy by intravitreal injections of wortmannin, a PI3K inhibitor, resulted in the presence of activated caspase-3 and -9-positive apoptotic cells in the ganglion cell layer. The activation of PI3K/Akt pathway following axotomy may serve as an endogenous protective machinery to counteract the death signals initiated by axotomy

Developing a prototype for the rapid demountable platform (RDP) : stage II of CII-HK research on "construction safety involving working at height for residential building repair and maintenance" : research summary

Author name used in this publication: Esther W. K. ChoyAuthor name used in this publication: Tracy S. K. ChungAuthor name used in this publication: W. C. LeeAuthor name used in this publication: C. H. LiuAuthor name used in this publication: Paul C. H. LoAuthor name used in this publication: Michael K. W. SiuAuthor name used in this publication: Pete C. W. WongAuthor name used in this publication: Michael C. H. YamConstruction Industry Institute-Hong Kong Report, no. 14E-publishing2008-2009 > Academic research: not refereed > Research book or monograph (author)Version of RecordPublishe

Developing a prototype for a rapid demountable platform (RDP) : stage 2 of construction safety involving working at height for residential building repair and maintenance : draft final report of the CII-HK research project

Author name used in this publication: Michael C. H. YamAuthor name used in this publication: Albert W. K. KwokAuthor name used in this publication: Michael K. W. SiuAuthor name used in this publication: C. H. LiuAuthor name used in this publication: Edmond W. M. LamAuthor name used in this publication: Pete C. W. WongAuthor name used in this publication: W. C. LeeAuthor name used in this publication: Esther W. K. ChoyAuthor name used in this publication: C. H. Paul LoAuthor name used in this publication: Tracy S. K. ChungConstruction Industry Institute-Hong Kong Report, no. 14Other Versio