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Daniel Schwartz, Yoshihiro Fukuoka; Brimonidine, like vancomycin, directly activates mast cells to degranulate, releasing preformed mediators. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6407.
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© ARVO (1962-2015); The Authors (2016-present)
The effect of glaucoma medicines and their preservatives on conjunctival mast cells is unclear. Alphagan (brimonidine 0.2% and its preservative benzalkonium chloride (BAK)) is known to cause local reactions, including follicular conjunctivitis. We examined whether brimonidine, like vancomycin, directly degranulates mast cells in vitro.
Degranulation was determined by β-hexosaminidase release from mast cells exposed to various stimulants: alphagan, alphagan-P, vancomycin (MRGPR-X2 positive control), benzalkonium chloride, brimonidine, 22E7 (anti-FcεRI antibody positive control) and Phosphate Buffer Solution (PBS, negative control). Mast cells were dispersed from fresh surgical skin obtained from the Cooperative Human Tissue Network, placed into culture with Stem Cell Factor (100 ng/ml), removed after 6-12 weeks, suspended at 1 x 10^6 cells/ml, preincubated at 37°C x 5 min, stimulated for 15 min at 37°C, and stopped by adding two-volumes of ice-cold Ca/Mg-free medium. Releasates were separated from retentates by centrifugation. The pellet was combined with a detergent (TX100) to extract β-hexosaminidase, and the activity of released and retained enzyme was measured by cleavage of pnitrophenyl-hexosamine; %degranulation being 100 x releasate/(releasate + retentate). Viablity was determined by trypan blue exclusion.
Brimonidine (0.17%, n=6) reproducibly caused mast cell degranulation without evidence of cell toxicity, %degranulation ranging from 4.5 to 14.0. Alphagan (0.033% Brimonidine) and alphagan P (0.025% Brimonidine) caused no detectable degranulation (n=6). 22E7 consistently degranulated mast cells, %degranulation ranging from 26.8 to 65.6. Vancomycin (8.3 μM to 83 μM), n=1 degranulated mast cells in a dose-dependent manner. There was no spontaneous release to PBS alone in all experiments.
Our results show that brimonidine, at a pharmacologic concentration of 0.17%, when applied topically to the eye, directly stimulates mast cells to degranulate in vitro. The lower concentrations of Brimonidine in Alphagan and Alphagan P did not do so. Whether brimonidine concentrations applied to the eye remain high enough after dilution with tears and diffusion through conjunctiva to where mast cells reside is uncertain, but could result in conjunctival pruritis in some patients.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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