Silk polymer-based adenosine release: Therapeutic potential for epilepsy

Abstract

Adenosine augmentation therapies (AAT) make rational use of the brain's own adenosine-based seizure control system and hold promise for the therapy of refractory epilepsy. In an effort to develop an AAT compatible with future clinical application, we developed a novel silk protein-based release system for adenosine. Adenosine releasing brain implants with target release doses of 0, 40, 200, and 1,000 ng adenosine/day were prepared by embedding adenosine-containing microspheres into nanofilm-coated silk fibroin scaffolds. In vitro, the respective polymers released 0, 33.4, 170.5, and 819.0 ng adenosine/day over 14 days. The therapeutic potential of the implants was validated in a dose-response study in the rat model of kindling epileptogenesis. Four days prior to the onset of kindling, adenosine-releasing polymers were implanted into the infrahippocampal cleft and progressive acquisition of kindled seizures was monitored over a total of 48 stimulations. We document a dose-dependent retardation of seizure acquisition. In recipients of polymers releasing 819 ng adenosine/day, kindling epileptogenesis was delayed by one week corresponding to 18 kindling stimulations. Histological analysis of brain samples confirmed correct location of implants and electrodes. We conclude that silk-based delivery of around 1,000 ng adenosine/day is a safe and efficient strategy to suppress seizures.

Caffeine and Adenosine

“…Therefore, attention is now focused on the development of biocompatible materials for adenosine-releasing intrahippocampal implants [92]. In line with the evidence for the antiepileptic role of A1 ARs, A1 AR KO mice are more susceptible to seizures and develop lethal status epilepticus after experimental traumatic brain injury [93].…”

The Antiepileptic Potential of Nucleosides

“…Adenosine-releasing silk-base polymers may be a more suitable strategy for drug delivery than synthetic polymers because of their biocompatibility and slow biodegradation, thus avoiding the need for removal of the synthetic polymer which limits their clinical application [33,67,405,406]. Wilz et al [407] developed silk-based polymers that release 0-1000 ng/day and 0-819 ng/day of Ado in vivo and in vitro, respectively. Based on kindled rats, which were intrahippocampally implanted with silk-based polymers, they concluded that approximately 1000 ng/day Ado effectively decrease seizures, which could provide an opportunity for a safe decrease of epileptic seizures (Table 4) [407,408].…”

“…Wilz et al [407] developed silk-based polymers that release 0-1000 ng/day and 0-819 ng/day of Ado in vivo and in vitro, respectively. Based on kindled rats, which were intrahippocampally implanted with silk-based polymers, they concluded that approximately 1000 ng/day Ado effectively decrease seizures, which could provide an opportunity for a safe decrease of epileptic seizures (Table 4) [407,408]. These results suggest that focal synthetic-polymer-based and silk-based-polymer drug-delivery systems may release sufficient amounts of Ado to decrease epileptic activity.…”

Epigenetic changes induced by adenosine augmentation therapy prevent epileptogenesis

“…To investigate the therapeutic potential of ADO, we used ADO-releasing silk-based polymer implants to alter DNA methylation. We previously generated and characterized silk-based biodegradable brain implants able to deliver local doses of 8 to 1000 ng ADO per day (27,28). These implants successfully suppressed seizures in kindled rats (27) with no adverse effects.…”