Peripheral administration of a novel diketopiperazine, NNZ 2591, prevents brain injury and improves somatosensory-motor function following hypoxia–ischemia in adult rats

The current study describes the neuroprotective effects of an endogenous diketopiperazine, cyclo-glycyl-proline (cyclic GP), in rats with hypoxic–ischemic brain injury and the pre-clinical development of an analogue, cyclo-l-glycyl-l-2-allylproline (NNZ 2591), modified for improved bioavailability. The compounds were given either intracerebroventricularly or subcutaneously 2 h after hypoxia–ischemia. Histology, immunohistochemistry and behavior were used to evaluate treatment effects. The central uptake of NNZ 2591 was also examined in normal and hypoxic–ischemic injured rats by HPLC–mass spectrometry. Central administration of cyclic GP or NNZ 2591 reduced the extent of brain damage in the lateral cortex, the hippocampus and the striatum (p < 0.001), with NNZ 2591 being more potent. NNZ 2591 was stable in the plasma and crossed the blood–brain barrier independent of hypoxic–ischemic injury. The level of NNZ 2591 in the CSF was maintained for 2 h after a single subcutaneous dose, and modest neuroprotection was seen after a bolus subcutaneous administration (overall p < 0.001). Treatment with NNZ 2591 for 5 d subcutaneously improved somatosensory-motor function (p < 0.05) and long-term histological outcome (overall p < 0.0001). NNZ 2591 treatment not only reduced both caspase-3 mediated apoptosis and microglial activation but also enhanced astrocytic reactivity, which may mediate its protective effect. The pharmacokinetic profile and potent long-term protective effects of NNZ 2591 suggests its utility for the treatment of ischemic brain injury and other neurological conditions requiring chronic intervention.