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  1. Assessment of polyethylene glycol (PEG) on spinal cord injury repair by means of lactate dehydrogenase (LDH) release Iman Rad 1, SogolieKouhzaei1 and Hamid Mobasheri 1, 21 Laboratory of membrane Biophysics and Macromolecules, Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran2 Biomaterials Research Centre (BRC), University of Tehran, Tehran, IranThursday,April 18,2013 (14-18) Material and Methods: Membrane disintegration was monitored by means of the release of common cytoplasmic enzymes like lactate dehydrogenase (LDH) that is considered as a membrane permeability marker. An aneurism clip exerting 650 kpa lateral pressures applied on isolated spinal cord to cause and mimic spinal cord injury (SCI). The collected spinal cord strips were then incubated for 5, 10 and 60 minutes in PEGs (200, 400, 600 and 1000 Da) at 10, 30, 50 and 70 mM concentrations. The level of LDH specific activity in media was measured in different time courses using NADH absorbance spectrometry at 340 nm. LDH catalysis occurs via NADH consumption. NADH absorbance at 340 nm declines concurrent to LDH activity increment. The repairing ability of PEG1000 (70 mM) measured by means of LDH release assay is shown below. Abstract: Mechanical damages cause great pressure on membranes that lead to partial or complete disruption of membrane and have to be manifested at nano-scale level. Polyethylene glycol (PEG) is a well-studied non-toxic, hydrophilic polymer used for cell membrane repair. Different forms of PEG have been administrated intravenously in animal models or incubated with isolated spinal cord strip in experimental spinal cord injury (SCI) models. It has been reported that PEG repairs injured spinal fibers immediately after its application while, its longevity of action in time, effects of its differential size and concentration have not been fully addressed. Here, different concentrations of PEGs ( 200, 400, 600 and 1000 Da) were applied on isolated spinal cord strips and their corresponding repair ability in intentional SCI was monitored ex-vivo in double sucrose gap (DSG) by means of lactate dehydrogenase (LDH) release assay. Different concentrations of PEG 200 showed the most decrease in the LDH release by 33.53% on average. The results indicate the feasibility of PEGs at concentrations of 30 – 50 mM would reinforce the reintegration of the lipids and their interaction contribution to cytoskeleton which introduce their therapeutic property in the treatment of SCI at early stages. Keywords:SCI, LDH release assay, PEG, DSG. Conclusion: According to our results, treatment of SCI with PEG200 at 10mM caused less LDH release than at 30 and 50 mM (p-values of 0.0025 and 0.012, respectively). However, this situation did not repeated when strips were treated in PEG 400, 600 and 1000 in different concentrations. PEG is considered to be effective in immediate sealing of membrane following SCI in RattusNorvegicus models via its interactions with membrane or cytoplasm. Based on LDH release assay, repairing ability of PEG200 tends to follows dynamic patterns of adsorption/desorption interactions with neural fibers in spinal cord strips. The ultimate aggregation of PEGs molecules leads to the formation of certain structures (e.g. dendrimers and polymerosomes), that reveals the effects of geometry, packing parameter, hydration and physico-chemical condition on the arrangement and integration of molecules in the resulted lipid-PEG-cytoskeleton complexes References: Cho, Youngnam, Riyi Shi, Richard Borgens, and AlbenaIvanisevic. "Repairing the damaged spinal cord and brain with nanomedicine." small 4, no. 10 (2008): 1676-1681. Luo, Jian, Richard Borgens, and Riyi Shi. "Polyethylene glycol immediately repairs neuronal membranes and inhibits free radical production after acute spinal cord injury." Journal of neurochemistry 83, no. 2 (2002): 471-480. Kouhzaei, Sogolie, Iman Rad, Sara Mousavidoust, and Hamid Mobasheri. "Protective effect of low molecular weight polyethylene glycol on the repair of experimentally damaged neural membranes in rat's spinal cord." (2013).

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