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Victoria Kearns, Helen Cauldbeck, Maude Le Hellaye, Steve Rannard; Accurate Solubility and Release Measurements of Retinoic Acid (RA) in Silicone Oil (SiO). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):219.
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© ARVO (1962-2015); The Authors (2016-present)
SiO tamponades are a potential reservoir for extended delivery of drugs, such as RA, for the treatment of proliferative vitreoretinopathy such as RA. The accurate measurement of drugs in oil is crucial for developing these systems. This study used radiochemistry and UV-vis to measure SiO solubility and release of all-trans RA from silicone oil in vitro. The cytotoxicity of all-trans RA when dosed to ARPE-19 cells over extended periods was also studied.
Standard RA or tritium-labelled RA (3H-RA) was stirred in SiO-1000 for 2 weeks then filtered. RA-SiO mixtures were analysed by UV-Vis, following extraction with methanol and acetone. 3H RA mixtures were measured directly using a scintillation counter. Release of RA from SiO into culture medium (DMEM:F12 inc. 10% foetal calf serum) was investigated by the same methods. ARPE-19 cells were seeded for 1d or 7d, then exposed to RA at concentrations of 10-4M-10-8M for up to 7d. Cytotoxicity was assessed by assessment of cell number, morphology and metabolic activity.
The maximum solubility of RA in SiO is reported as approximately 20µg/mL (Araiz, IOVS, 1993). Here, with SiO-1000, UV-vis gave results in the same order of magnitude (mean 26.7µg/mL, s.d. 3 µg/mL, n=6). Using 3H-RA, 25 times the reported amount (450.6µg/mL, s.d. 40, n=4) was measured. In release studies, UV-vis recorded complete release within 10 days. Using radiochemistry, release was measured for over 60 days (Fig.1), and at much higher levels than previously reported. After 1d seeding then 7d RA exposure, cytotoxicty was observed at concentrations above 10-6M. In all other conditions, this increased to concentrations above 10-5M. These cytotoxicity results are similar to those previously reported (Wu, Journal Of Ocular Pharmacology And Therapeutics, 2005).
An accurate method to measure solubility of RA in SiO was established and identified a fundamental inaccuracy in the published literature. The cytotoxicity of the drug depended on the level of confluence of the cells. These data will be used in the development of extended drug delivery systems using SiO.
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