Effect of an intravitreal cyclosporine implant on experimental uveitis in horses.

The study explores the effect of a device releasing cyclosporine A (CsA) in mitigating recurring inflammation episodes caused by uveitis in horses. The researchers discovered that CsA reduced the intensity and duration of inflammation, cellular infiltration, tissue damage, and pro-inflammatory cytokine RNA levels, but did not entirely prevent a second inflammatory episode.

Research Design and Experiment

• The study involved immunizing nine healthy horses with the H37RA-mTB antigen twice. Upon immunization, 25 micrograms of the antigen were inserted intravitreally in the right eye and balanced salt solution introduced in a similar manner in the left eye.
• Two weeks later, either a device releasing cyclosporine A (CsA) or a polymer implant (without CsA) was chosen randomly and implanted into both eyes of each horse. Seven days post implantation, each horse’s right eye received another injection of 25 micrograms of H37RA-mTB antigen.
• Symptoms of eye inflammation were graded following the injections and the implantation.
• Aqueous and vitreous humor protein concentrations were measured.
• The horses were euthanized at three time points – 3, 14, and 28 days after the second injection to determine the presence, number, and type of infiltrating inflammatory cells, plus the amount of tissue destruction.
• Total RNA was isolated and quantitative reverse transcriptase-polymerase chain reaction was performed for equine specific interleukin (IL) 2 and 4, interferon-gamma (IFN gamma) and beta-actin.
• At the conclusion of the experiment, aqueous, vitreous humor, and peripheral blood were collected and CsA concentration was analyzed via high-performance liquid chromatography (HPLC).

Results of the Study

• The experiment noted that within four hours of the first intravitreal H37RA-mTB antigen injection, each horse developed symptoms such as epiphora (excessive tear production), blepharospasm (persistent, uncontrolled spasms of the periorbital muscles), mild corneal edema, aqueous flare, myosis (pupillary constriction) and vitreous opacity.
• However, following the second injection, the clinical signs in the eyes with the CsA implant were less severe and significantly shorter in duration compared to eyes with the polymer-only implant.
• In addition, quantifiable reductions were noted in aqueous and vitreous humor protein levels, number of infiltrating cells, total T-lymphocytes, and IL-2 and IFN gamma-mRNA levels with the CsA implant.
• Despite these results, it was observed that the CsA implants did not completely prevent the development of a second (recurring) experimental inflammatory episode in the horses.
• However, the duration and severity of inflammation, cellular infiltration, tissue destruction, and pro-inflammatory cytokine RNA transcript levels were significantly reduced in eyes implanted with the CsA device.