The support of adenosine release from adenosine kinase deficient ES cells by silk substrates

Adenosine kinase deficient (Adk-/-) embryonic stem cells (ESCs) encapsulated in synthetic polymers have previously been shown to provide therapeutic adenosine release and transient seizure suppression in epileptic rats. Here we explored the utility of biopolymer-substrates to promote long-term adenosine release from Adk-/- ESCs. Three different substrates were studied: (1) type I collagen (Col-1), (2) silk-fibroin (SF), and (3) poly(L-ornithine) (PO) coated tissue culture plastic. Adk-/- or wild type (wt) ESC-derived glial precursor cells were seeded on the substrates and cultured either in proliferation medium containing growth factors or in differentiation medium devoid of growth factors. In proliferation medium cell proliferation was higher and metabolic activity lower on Col-1 and PO substrates as compared to SF. Cells from both genotypes readily differentiated into astrocytes after growth factor removal on all substrates. Adk-/- cells cultured on biopolymers released significantly more adenosine than their wt counterparts at all developmental stages. Adenosine release was similar on SF and PO substrates and the amounts released from Adk-/- cells (>20 ng/ml) were considered to be of therapeutic relevance. Taken together, these results suggest that silk matrices are particularly suitable biomaterials for ESC encapsulation and for the design of adenosine releasing bioincubators for the treatment of epilepsy.