Tacrolimus (FK506), a widely used immunosuppressant drug, has neurite-promoting activity in cultured PC12 cells and peripheral neurons. The present study investigated whether tacrolimus affects the expression of the neuronal growth-associated protein, GAP-43, as well as functional recovery after photothrombotic spinal cord injury in the rat. In injured animals receiving tacrolimus, the number of neurons expressing GAP-43 mRNA and protein approximately doubled compared to that in injured animals receiving vehicle alone. This increase in GAP-43-positive cells was paralleled by a significant improvement in neurological function evaluated by open-field and inclined plane tests. Another FKBP-12 ligand (V-10,367) had similar effects on GAP-43 expression and functional outcome, indicating that the observed effects of tacrolimus do not involve inhibition of the phosphatase calcineurin. Thus, tacrolimus, a drug which is already approved for use in humans, as well as other FKBP-12 ligands which do not inhibit calcineurin, could potentially enhance functional outcome after CNS injury in humans.
Copyright 1998 Academic Press.