Exploring the effects of PHD inhibition and antioxidants in a rat hippocampal slice model of oxygen and glucose deprivation

Several complex mechanisms contribute to acute ischemic stroke, ultimately leading to neuronal damage and impairment of synaptic signalling. Emerging evidence supports the neuroprotective role of pharmacological inhibition of prolyl hydroxylase domain enzymes in experimental models of ischemia, such as oxygen-glucose deprivation (OGD). Therefore, this study explored the effects of two prolyl hydroxylase inhibitors (PHDIs), JNJ-42041935 and roxadustat on synaptic signalling during OGD in isolated rat hippocampal slices. In slices treated with the PHDIs, there was an increase in fEPSP recovery following OGD. These compounds exhibited neuroprotective effects on cell viability for up to 24 h in in vitro organotypic hippocampal slice cultures exposed to OGD. However, acute hippocampal slices pre-treated with the inhibitors showed impaired synaptic potentiation in normoxic conditions. Increased production in reactive oxygen species (ROS) is an additional factor that contributes to neuronal damage during ischemia. Previous studies have demonstrated that antioxidant compounds exhibit neuroprotective effects against ischemic insults. It has been reported that application of the superoxide scavenger, MnTMPyP, had a neuroprotective effect following ischemia in isolated hippocampal slices. The neuroprotection was reported to be achieved by the specific pharmacological scavenging of O2-. In this study the effects of MnTMPyP on synaptic signalling during OGD in isolated rat hippocampal slices were investigated. In the CA1 region of acute hippocampal slices, pre-treatment with MnTMPyP induced an extensive inhibition of fEPSP during and after OGD. This effect was associated with increased neuronal viability in organotypic hippocampal slices exposed to ischemic-like conditions. The complex molecular changes supporting cellular adaptation to metabolic stress, and how these are modulated by MnTMPyP, were also investigated. In OGD, mass spectrometry protein enrichment analysis highlighted impairments in pathways involved in cell proliferation and differentiation, such as TGF-β1 and CDKN1B signalling, in addition to downregulation of mitochondrial dysfunction and an increased expression of CAMKII. These new findings may help to understand the complex interaction between synaptic signalling and ischemia informing novel therapies for the treatment of ischemic stroke.