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Hoi Lam Li, Ashim Dey, Shasha Yu, Sze Wan Shan, W Daniel Stamer, Henry Ho-lung Chan, Chi-ho To, Kin Chiu, Chi-wai Do; Effects of intravitreal administration of baicalein on intraocular pressure and retinal thickness in Sprague-Dawley rats. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4466.
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© ARVO (1962-2015); The Authors (2016-present)
Baicalein (5,6,7-trihydroxyflavone) is a natural flavone extracted from the roots of Scutellaria baicalensis. We have previously demonstrated that topical administration of 10mM baicalein causes a transient (up to 6 hours) intraocular pressure (IOP) reduction by 1.5±0.3 and 2.2±0.4 mmHg under daytime and nighttime, respectively, in rodents. In this study, we investigated whether intravitreal administration of baicalein altered the ocular hypotensive responses and retinal thickness in Sprague-Dawley (SD) rats.
Thirty-six adult male SD rats were used. They were kept at room temperature with 12-hour light/dark cycles. 2µL of baicalein (at 7.5, 75 or 750µM) or phosphate buffered saline (PBS) was injected intravitreally to the experimental eye while the fellow untreated eye was used as control. IOP was measured by rebound tonometry under awake condition for 9 days after treatment. Comparisons were made between the drug-injected eye and the contralateral untreated eye of the same animal. The retinal thickness was measured by spectral domain optical coherence tomography.
In the first experiment, intravitreal administration of 2µL baicalein at 7.5, 75 or 750µM had no effects on retinal thickness 9 days after injection (n=6 in each group, p>0.05). Likewise, no significant changes in IOP were observed at 3-, 6- and 9-day after drug treatment (n=6, p>0.05). At 750µM, baicalein lowered the IOP by 2.8±1.2 mmHg after 3 days, and that was equivalent to 17% IOP reduction compared with the fellow untreated eye. In the second experiment, IOP was monitored once every 12 hours for 3 days after a single intravitreal injection of either 750µM baicalein or PBS. A significant IOP reduction was detected up to 60 hours after baicalein treatment. The maximum IOP-lowering effects were 2.4±0.5 and 9.3±1.2 mmHg under daytime and nighttime, respectively. These ocular hypotensive responses were equivalent to 24% and 48% reduction over the daytime and nighttime IOP values in the untreated eye.
Intravitreal injection of baicalein triggered a sustained IOP reduction for 2-3 days. The IOP-lowering effect was more pronounced during nighttime than daytime, contributing to a reduced diurnal IOP variation after baicalein treatment. No changes in retinal thickness after drug treatment suggested the absence of retinal toxicity caused by baicalein.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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