Pharmacokinetics, electrophysiological, and morphological effects of the intravitreal injection of mycophenolic acid in rabbits

Abstract

Purpose: To determine the half-life of mycophenolic acid (MPA) in the vitreous of New Zealand albino rabbits after intravitreal injection and the retinal toxicity of different doses of MPA.

Methods: Ten micrograms of MPA (Roche Bioscience, Palo Alto, CA) was injected in the vitreous of 16 rabbits, animals were sacrificed at different time-points, and vitreous samples underwent high-performance liquid chromatography. For functional and morphological studies, 5 doses of MPA (0.05, 0.5, 2, 10, and 100 μg) were injected in the vitreous of 20 rabbits. As control, contralateral eyes were injected with aqueous vehicle. Electroretinograms (ERGs) were recorded before injection and at days 7, 15, and 30. Animals were sacrificed on day 30 and retinas were analyzed under light microscopy.

Results: MPA half-life in the vitreous was 5.0±0.3 days. ERG revealed photoreceptor functional impairment in eyes injected with 0.5 μg and higher on day 30, while eyes injected with 100 μg presented the same changes already from day 15. No morphological change was found.

Conclusions: MPA vitreous half-life is 5.0 days. Intravitreal injection of 0.5 μg MPA and higher causes dose- and time-related photoreceptor sensitivity decrease in rabbits. The MPA dose of 0.05 μg may be safe for intravitreal use in rabbits.

FIG. 1.

Linear regression of concentrations of mycophenolic acid (MPA) in the vitreous after intravitreal injection of 10 μg (4 eyes in each time-point).

FIG. 2.

Representative ERG records of 1 animal at different time-points after intravitreal injection of 100 μg MPA. (A) Dark-adapted state (stimulus of 30 cd·s/m²); (B) light-adapted state (stimulus of 3 cd·s/m²); (C) light-adapted flicker (stimulus of 3 cd·s/m² at 30 Hz).

FIG. 3.

Log b-wave amplitude versus flash intensity curves of eyes injected with different doses of MPA. Gray areas represent the mean±standard deviation of 4 eyes before intravitreal injection. Dots and error bars represent mean±standard deviation of the 4 eyes after intravitreal injection. Contralateral eyes, injected with aqueous vehicle, did not present differences from baseline.

FIG. 4.

b-Wave to a-wave amplitude correlations in eyes injected with different doses of MPA at different time-points (dark-adapted state, stimulus of 30 cd·s/m²). Baseline data are represented as linear regression±standard deviation. Dots represent the a- and b-wave amplitudes of each animal, and lines represent the linear regression for each group. Contralateral eyes, injected with aqueous vehicle, did not present differences from baseline.

FIG. 5.

Flicker results of eyes injected with 5 doses of MPA for stimulus frequency and time-point after intravitreal injection. Differences between the MPA and vehicle normalized FFT first-harmonic amplitude values are plotted.

FIG. 6.

Light micrographs 30 days after intravitreal injection of different doses of MPA showing well-preserved retinal morphology.