Tacrolimus (FK506) limits accumulation of granulocytes and platelets and protects against brain damage after transient focal cerebral ischemia in rat.

We investigated the neuroprotective effect of tacrolimus (FK506) on the ischemia-reperfusion injury caused by transient focal brain ischemia induced by middle cerebral artery (MCA) occlusion for 60 min in rats. Neuronal damage visualized as a decrease of MAP2 immunoreactivity was observed in the cerebral cortex at 9 h after MCA occlusion and further expanded at 24 h. Hypoxic areas visualized with an immunohistochemical reaction for 2-nitroimidazole, a hypoxia marker (hypoxyprobe-1), and accumulation of granulocytes and platelets were also observed at 9 h and 24 h after MCA occlusion. Tacrolimus (1 mg/kg, i.v.), administered immediately after MCA occlusion, attenuated cortical damage and decreased the hypoxyprobe-1 positive area, as well as the number of granulocytes and platelets at 24 h after MCA occlusion. Immunohistochemical analysis showed that tacrolimus reduced the number of blood vessels positively stained for ICAM-1, E-selectin and P-selection. These results suggested that tacrolimus limited attachment of granulocytes and platelets to blood vessels by inhibiting the expression of adhesion molecules and protected neuronal tissue from hypoxic insults.

Temporal and topographic profiles of tissue hypoxia following transient focal cerebral ischemia in rats.

Intravascular accumulation of blood cells after brain ischemia-reperfusion can cause obstruction of cerebral blood flow and tissue hypoxia/ischemia as a consequence. In the present study, we examined temporal and topographic changes of tissue hypoxia/ischemia after occlusion of the middle cerebral artery (MCA) for 60 min in rats with immunohistochemical staining for hypoxia (2-nitroimidazole hypoxia marker: hypoxyprobe-1 adducts). Our results showed that tissue hypoxia expressed as positive staining for hypoxyprobe-1 adducts preceded neuronal degeneration. Platelets and granulocytes were detected close to the hypoxyprobe-1 adducts positive area. These results suggested that the hypoxic environment could persist even after reperfusion of MCA, because of vascular obstruction with accumulation of platelets and granulocytes.

FK1706, a novel non-immunosuppressive immunophilin: neurotrophic activity and mechanism of action.

Immunophilin ligands are neuroregenerative agents, characterized by binding to FK506 binding proteins (FKBPs), which stimulate recovery of neurons in a variety of injury paradigms. Here we report the discovery of a novel, non-immunosuppressive immunophilin ligand, FK1706. FK1706, a derivative of FK506, showed similarly high affinity for two FKBP subtypes, FKBP-12 and FKBP-52, but inhibited T-cell proliferation and interleukin-2 cytokine production with much lower potency and efficacy than FK506. FK1706 (0.1 to 10 nM) significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in SH-SY5Y cells, as did FK506. This neurite potentiation could be blocked by an anti-FKBP-52 antibody, as well as by specific pharmacological inhibitors of phospholipase C (PLC), phosphatidylinositol 3-kinase (PI3K), and the Ras/Raf/Mitogen-Activated Protein Kinase (MAPK) signaling pathway. FK1706 also potentiated NGF-induced MAPK activation, with a similar dose-dependency to that necessary for potentiating neurite outgrowth. Taken together, these data suggest that FK1706 is a non-immunosuppressive immunophilin ligand with significant neurotrophic effects, putatively mediated via FKBP-52 and the Ras/Raf/MAPK signaling pathway, and therefore that FK1706 may have therapeutic potential in a variety of neurological disorders.

Neuroprotective effect of tacrolimus (FK506) on ischemic brain damage following permanent focal cerebral ischemia in the rat.

We investigated the neuroprotective effect of tacrolimus (FK506) on the ischemic cell death with respect to cytochrome c translocation and DNA fragmentation, which are pivotal events in the necrotic and apoptotic signaling pathway, using permanent focal cerebral ischemia in rats. Immunohistochemically, cytochrome c was observed in the cytoplasm as early as 1 h after middle cerebral artery (MCA) occlusion in the infarcted hemisphere. Cytosolic release of cytochrome c after MCA occlusion was also confirmed by Western blot analysis and enzyme immunoassay. Terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL) showed DNA fragmentation evolving in the ipsilateral cortex and the caudate putamen after 3 and 6 h, respectively, following MCA occlusion. Tacrolimus (1 mg/kg, i.v.), administered immediately after MCA occlusion, significantly attenuated the release of cytochrome c in the ischemic region, the number of TUNEL-positive cells in the ischemic penumbra zone, and the size of cortical ischemic lesions. This study demonstrated that tacrolimus ameliorated the accumulation of cytochrome c in the cytosol and the increase of TUNEL-positive cells induced by cerebral ischemia, indicating that the neuroprotective action of tacrolimus on ischemic brain injury caused by permanent focal cerebral ischemia could partially be attributed to the attenuation of the activation of the apoptotic execution machinery.

Multiple modes of action of tacrolimus (FK506) for neuroprotective action on ischemic damage after transient focal cerebral ischemia in rats.

While the immunosuppressant tacrolimus (FK506) is known to be neuroprotective following cerebral ischemia, the mechanisms underlying its neuroprotective properties are not fully understood. To determine the mode of action by which tacrolimus ameliorates neurodegeneration after transient focal ischemia, we therefore evaluated the effect of tacrolimus on DNA damage, release of cytochrome c, activation of microglia and infiltration of neutrophils following a 60-min occlusion of the middle cerebral artery (MCA) in rats. In this model, cortical brain damage gradually expanded until 24 h after reperfusion, whereas brain damage in the caudate putamen was fully developed within 5 h. Tacrolimus (1 mg/kg) administered immediately after MCA occlusion significantly reduced ischemic damage in the cerebral cortex, but not in the caudate putamen. Tacrolimus decreased both apoptotic and necrotic cell death at 24 h and reduced the number of cytochrome c immunoreactive cells at 8 h after reperfusion in the ischemic penumbra in the cerebral cortex. In contrast, tacrolimus did not show significant neuroprotection for necrotic cell death and reduction of cytochrome c immunoreactive cells in the caudate putamen. Tacrolimus also significantly decreased microglial activation at 8 h and inflammatory markers (cytokine-induced neutrophil chemoattractant and myeloperoxidase [MPO] activity) at 24 h after reperfusion in the ischemic cortex but not in the caudate putamen. These results collectively suggest that tacrolimus ameliorates the gradually expanded brain damage by inhibiting both apoptotic and necrotic cell death, as well as suppressing inflammatory reactions.