Intraocular cell‐based production of glucagon‐like peptide‐1 in the anterior chamber (2009)

Editor, By the intravitreal application of drugs such as antivascular endothelial growth factor drugs, pronounced improvements in the therapy of intraocular oedematous and neovascular diseases have been achieved (Jonas 2005; Rosenfeld et al. 2006). The disadvantage of this new type of intraocular drug application is that it usually has to be repeated. Attempts have, therefore, been made to either develop intravitreal slow-release devices or to develop an intraocular cell-based therapy by intravitreally implanting cells which continuously produce the drug in the eye (Tao et al. 2002; Lee et al. 2009). While previous studies on the intraocular encapsulated cell-based drug therapy have been focused on the vitreous cavity as site of implantation, we examined whether it is possible to produce a drug in the anterior chamber. As substance to be produced we choose glucagon-like peptide-1 (GLP-1), which has shown some neuroprotective effects in previous experimental studies (During et al. 2003), We used cells from a human mesenchymal stromal cell line and transfected them with plasmid DNA, so that they produced GLP-1. The experimental study included 12 New Zealand white rabbits with a body weight of 2.5–3 kg. All experiments were carried out in accordance with the statements of the Association for Research in Vision and Ophthalmology ARVO for the use of animals in ophthalmic and vision research. For the study, we used a GLP-1 fusion peptide secreting cell line encapsulated into beads by sodium alginate. The cells were entrapped in an alginate matrix, which was generated by cross-linking of alginate with barium ions. The cells were cryopreserved. Before use, the GLP-1 CellBeads were thawed and washed in Ringer’s solution. For the injection, the GLP-1 CellBeads were aspirated into a sterile 1- ml syringe and injected into the anterior chamber through a paracentesis under sterile conditions. Before, an aqueous humour sample was aspirated. The group of animals was divided into three subgroups receiving 5, 10 or 20 CellBeads per animal, respectively. Aqueous humour (100–200 μl) was sampled at the time of the implantation of the CellBeads and during the follow-up at 1 and 2 weeks after implantation. The samples were immediately stored at −20°C without adding an inhibitor. The aqueous humour was analysed for active GLP-1 using the GLP-1 active ELISA (Biotrend Chemikalien GmbH, 50933 Köln, Germany). One of the rabbits of the third subgroup died during the implantation procedure, probably because of an intolerability of the anaesthetics. All other animals were healthy and did not show any signs of postoperative intraocular inflammation. Compared with the baseline value, the GLP-1 concentration in the aqueous humour samples increased significantly (p = 0.001) from values below the detectability level of 2 pm at baseline to 20.7 ± 15.4 pm at 1 week after the implantation and decreased significantly (p = 0.001) to a concentration of 8.9 ± 7.9 pm at 2 weeks after the implantation (Fig. 1). That value was still significantly (p = 0.002) higher than the baseline value. The concentration of GLP-1 in the aqueous humour increased significantly with the number of beads implanted (p = 0.01; correlation coefficient r = 0.73). Boxplots showing the distribution of the concentration of glucagon-like peptide-1 (GLP-1) in the aqueous humour of rabbits after the implantation alginate-encoated beads of cells producing GLP-1. Limitations of our study should be mentioned. First, no inhibitor was added to the aqueous humour samples, so that a biodegradation of GLP-1 may have occurred before it was measured. The measured values may, therefore, be higher in reality than as determined in the study. Second, the follow-up was relatively short. Third, the number of animals included into the study was relatively small. These limitations may serve, however, only to underline the conclusion, that GLP-1 can be produced by cells embedded in an alginate hydrogel and implanted into the anterior chamber. The intracameral cell-encoated drug therapy with GLP-1 producing CellBeads appears feasible. Dr Jonas and Dr Wallrapp hold a patent on the technique; Dr C. Wallrapp is an employee of CellMed AG.