Eva M. del Amo1, John R. Griffiths2, Izabela P Klaska3, Anne White4, Leon Aarons1, James W B Bainbridge3, Richard J. Unwin2, Paul N Bishop4
(1) School of Health Sciences, (2) School of Medical Sciences and (4) School of Biological Sciences, Faculty of Biology, Medicine & Health, University of Manchester, Manchester, United Kingdom; (3) UCL Institute of Ophthalmology, London, United Kingdom
Introduction and objectives:
Proliferative diabetic retinopathy (PDR) is the more advanced form of diabetic retinopathy disease, with formation of new retinal vessels and oedema, at the back of the eye, that may lead to vision loss and scarring of the retina. An endogenous molecule of the eye, opticin, has potential therapeutic value as an anti-angiogenic agent inhibiting the formation of new blood vessels (1). It is an extracellular glycoprotein that binds to collagen fibrils in the vitreous, gel-like substance that occupies the space inside the eye between the lens and the retina. The objective of this study was to investigate the pharmacokinetic (PK) profile of exogenous opticin injected into the vitreous of rabbit eyes.
Methods:
In vivo PK studies were carried out with eighteen New Zealand rabbits that received an intravitreal injection in both eyes with 40 µg of human opticin (50 µl). Eyes were enucleated at different time points: 5 h, 24 h, 72 h, 7 days, 14 days, 28 days (n=5-6). The vitreous was extracted and the free and bound forms of human opticin were measured in the supernatant and in the collagen-containing pellet respectively. The measurement were done by mass spectrometry using selected reaction monitoring. Additionally, the concentration of free and bound endogenous opticin in rabbit vitreous were also measured using the same method at the same time points. The basal concentrations of both endogenous forms were also obtained from nine uninjected rabbit eyes.
The concentration profiles of the human opticin were analysed by Nonlinear Mixed Effects (Monolix software®) using a one compartmental model. The interplay between the exogenous and endogenous opticin in the vitreous was also investigated.
Results:
The injected free human opticin presented a first-order elimination profile with an intravitreal volume of distribution of 3.18 ml, clearance of 0.022 ml/h and half-life of 4 days, whereas the bound human opticin had a longer half-life of 7.5 days.
Regarding the endogenous opticin, the concentrations of the free form (in the vitreous supernatant) was relatively constant during the whole time profile, 19 nM (0.67 µg/ml) (n=5 per time point) and similar to the basal levels in the uninjected rabbit eyes, 17 nM (0.60 µg/ml) (n=9). Assuming that the elimination rate constant of the free rabbit opticin is similar to the one for human (0.168 days-1), the rabbit opticin synthesis rate was calculated as 0.15 µg of opticin/day. The basal bound endogenous opticin was 1.12 nM (0.04 µg /ml, n=9). The injected human opticin reached concentration 20-fold greater than free rabbit opticin, with an apparent partial replacement of the bound rabbit opticin by the human one. This effect was reversed as the human opticin was cleared from the eye.
Conclusions:
Free opticin presents a similar half-life to the antiangiogenic therapeutic drug, aflibercept (Eylea®), while the bound form has a longer half-life, binding to the collagen fibrils and possible some other inner ocular tissue sites. Reversible displacement of the natural bound opticin was observed and the apparent synthesis rate of the endogenous opticin was calculated for the first time.
References:
[1] Le Goff MM, Sutton MJ, Slevin M, Latif A, Humphries MJ, Bishop PN. Opticin exerts its anti-angiogenic activity by regulating extracellular matrix adhesiveness. J Biol Chem. 2012 Aug 10;287(33):28027-36.
Reference: PAGE 28 (2019) Abstr 9030 [www.page-meeting.org/?abstract=9030]
Poster: Drug/Disease Modelling - Other Topics