Purpose
Ischemic retinal vascular diseases such as diabetic retinopathy are characterized by decreased oxygen to retinal photoreceptors. This localized tissue hypoxia in turn leads to photoreceptor damage and death. This study tests the hypothesis that a bioimplant containing oxigenic unicellular organisms can be encapsulated and used as a device to deliver oxygen using in vitro models.
Methods
Prototype devices consisting of dialysis membranes with a silicone endcap were constructed. These allow passage of light and small molecules such as oxygen, carbon dioxide, and sugars, but restrict passage of cells. Three devices were filled with Synechococcus cyanobacteria and three control devices filled with saline. Each device was then placed in a 50 mL closed container of saline and continuous oxygen recordings taken for nine hours. The main outcome measure was the difference in the initial and final oxygen partial pressure (pO2) of the saline, and the two groups compared using a paired t-test.
Results
At baseline, there was no difference in the pO2 between the active group (108.9 +/-1.37 mmHg) and the control (110.73 +/- 0.65 mmHg, p = 0.11). After nine hours, the p02 in the Synechoccocus group increased 28% from baseline (138.99 +/- 1.71 mmHg, p = 0.0005) and the control group increased by 2% (112.4 +/- 1.10 mmHg, p = 0.07). This slight increase was thought to be artifact from exposure of the saline to room air from placement of the oxygen sensor. The difference in the final pO2 concentration between the two groups was statistically significant (p = 0.001).
Conclusions
These results are consistent with the hypothesis that oxygen producing Synechoccocus cyanobacteria can be encapsulated in a device and used to produce oxygen in vitro. Further ex vivo and in vivo testing is needed, but such a device implanted in the vitreous cavity may prove useful in ischemic retinopathies to reverse the local tissue hypoxemia.