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Marlyn P. Langford, Jordan M. Burnham, Thomas B. Redens, Donald E. Texada; Intravenous Muramyl Dipeptide Injection Increases Gamma-Glutamyl Transpeptidase Activity in Tears. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2914.
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To investigate the effects of intravenous injection of bacterial cell wall component muramyl dipeptide (MDP) on tear levels of the ectoenzyme gamma-glutamyl transpeptidase (GGT) as a model to study the mechanisms of elevated GGT in human tears (IOVS 1999;40:S27 Poster #143-B103).
Adult New Zealand White rabbits were injected intravenously with a uveitogenic dose of MDP (2mg/kg) and tear fluid collected via Schirmer’s strips or by micro-capillary tubes through 6 d. GGT activity was measured by standard colorimetric assay and expressed as GGT/strip or /ml. Western blot analysis of tear fluid was performed using monoclonal anti-GGT antibody.
Anterior uveitis, mild conjunctivitis with increased tearing was detected at 4-5 h post injection. The tear fluid GGT activity paralleled the GGT activity detected on Schirmer’s strips. The increased tear fluid GGT activity was associated with increased immunoreactive GGT proteins as well as total proteins. The GGT activity in control tears (20-40 units) remained constant through 8 h, increased to maximal levels by 12 h and remained elevated through 36 h (60-180 units). The GGT activity declined to the low pre-treatment levels by 72 h and remained low through 6 d.
Intravenous MDP injection increased GGT activity in tears. The mechanism(s) responsible for the MDP-induced GGT increase in tear at 12-36 h post intravenous injection is unknown, but could be due to increased conjunctival blood vessel/epithelium permeability, leukocyte infiltration and/or release from apoptotic conjunctival epithelial cells. The detection of elevated GGT in rabbit tear post intravenous MDP is novel and introduces the possibility that the mechanism may play a role in other bacterial associated diseases.
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