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L. Srur, M. P. Langford; Caspase Mediated Apoptosis of Conjunctival Cells Associated With Muramyl Dipeptide Induced Conjunctivitis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1925.
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To investigate the role of apoptosis in conjunctivitis induced by topical application of muramyl dipeptide (MDP) (N-acetylmuramyl-L-alanyl-D-isoglutamine; gram positive and gram negative bacterial cell wall component) in rabbits.
Schirmer tear tests were performed and tear samples were collected in capillary pipettes from rabbits at hourly intervals following topical application of 50 µl of phosphate buffered saline containing 100 µg of MDP. Tear samples were centrifuged to remove cell debris and analyzed for gamma-glutamyl transpeptidase (GGT) (i.e., index of cell membrane shedding), apoptotic DNA ladders and caspase-2, 3, 6 and 9 activity.
. The initial clinical signs and symptoms of conjunctivitis were detected at 3 to 4 hr post MDP application, peaked at 7 h and declined through 24 h. Tear production increased 2-fold and GGT activity increased 5-fold in tears collected 4 to 12 h post application of MDP. Caspase-2 and 3 activities were detected in tears at 4 to 7 h post MDP. Caspase-6 and 9 activities were detected in tears collected at 6 and 7 h post MDP. Apoptotic DNA ladders were detected in tears collected 4 to 7 h post MDP. All caspase-activities declined by 12 h post MDP.
MDP has been shown to cause caspase-3 mediated apoptosis in rabbit kidney cells in vitro and rabbit ciliary body epithelial cells in vivo. Here, we show that the topical application of MDP induces conjunctivitis and that the onset of conjunctivitis coincided with activation of caspase-2, 3, 6 and 9, release of GGT and the appearance of apoptotic DNA in tears. The results suggest that the signs and symptoms of bacterial induced conjunctivitis could be due to the apoptogenic effects of bacterial cell wall peptidoglycan.
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