Suppression of kindled seizures by paracrine adenosine release from stem cell-derived brain implants.

PURPOSE: Stem cells and their derivatives have emerged as a promising tool for cell-based drug delivery because of (a) their unique ability to differentiate into various somatic cell types, (b) the virtually unlimited donor source for transplantation, and (c) the advantage of being amenable to a wide spectrum of genetic manipulations. Previously, adenosine-releasing embryonic stem (ES) cells have been generated by disruption of both alleles of adenosine kinase (Adk-/-). Lack of ADK did not compromise the cells' differentiation potential into embryoid bodies or glial precursor cells. The aim of the present study was to investigate the potential of differentiated Adk-/- ES cell progeny for seizure suppression by paracrine adenosine release. METHODS: To isolate paracrine effects of stem cell-derived implants from effects caused by network integration, ES cell-derived embryoid bodies and glial precursor cells were encapsulated into semipermeable polymer membranes and grafted into the lateral brain ventricles of kindled rats. RESULTS: While seizure activity in kindled rats with wild-type Adk+/+ implants remained unaltered, rats with adenosine-releasing Adk-/- ES cell-derived implants displayed transient protection from convulsive seizures and a profound reduction of afterdischarge activity in EEG recordings. Long-term seizure suppression was precluded by limited viability of the encapsulated cells. CONCLUSIONS: We thereby provide a proof-of-principle that Adk-/- ES cell-derived brain implants can suppress seizure activity by a paracrine mode of action. Adk-deficient stem cells therefore represent a potential tool for the treatment of epileptic disorders.

Seizure suppression and lack of adenosine A1 receptor desensitization after focal long-term delivery of adenosine by encapsulated myoblasts.

Adenosine is an important inhibitory modulator of brain activity. In a previous ex vivo gene therapy approach, local release of adenosine by encapsulated fibroblasts implanted into the vicinity of an epileptic focus, was sufficient to provide transient protection from seizures (Huber, A., Padrun, V., Deglon, N., Aebischer, P., Mohler, H., Boison, D., 2001. Grafts of adenosine-releasing cells suppress seizures in kindling epilepsy. Proc. Natl. Acad. Sci. U. S. A. 98, 7611-7616). Long-term seizure suppression beyond 2 weeks was precluded by limited life expectancy of the encapsulated fibroblasts. To study the feasibility for long-term seizure suppression by adenosine releasing brain implants, in the present contribution, mouse C2C12 myoblasts were engineered to release adenosine by genetic inactivation of adenosine kinase. After encapsulation, the myoblasts were grafted into the lateral brain ventricles of epileptic rats kindled in the hippocampus. While seizure activity in animals with wild-type implants remained unaltered, 1 week after grafting all rats with adenosine-releasing implants (n = 25) displayed complete protection from convulsive seizures and a corresponding reduction of afterdischarges in EEG-recordings. The duration of seizure suppression was maintained for a period of 3 weeks in 50% of the animals ranging to a maximum of 8 weeks in one animal. During the course of these experiments, adenosine A1 receptors remained responsive to selective agonists and antagonists indicating a lack of desensitization of A1 receptors after local long-term exposure to adenosine. Furthermore, local release of adenosine did not affect locomotor activity, whereas systemic application of the A1 agonist 2-chloro-N6-cyclopentyladenosine caused strong sedation. Thus, the local release of adenosine by cellular implants provides a feasible option for a potential side-effect free approach for the long-term treatment of focal epilepsies.