Effectiveness of PSD95 Inhibitors in Permanent and Transient Focal Ischemia in the Rat

Abstract

Background and Purpose-Postsynaptic density-95 inhibitors reduce ischemic brain damage without inhibiting excitatory neurotransmission, circumventing the negative consequences of glutamatergic inhibition. However, their efficacy in permanent ischemia and in providing permanent neuroprotection and neurobehavioral improvement in a practical therapeutic window is unproven. These were tested here under conditions that included fever, which is a common occurrence in clinical stroke. Methods-Six studies were performed in unfasted Sprague-Dawley rats. Two involved permanent pial vessel occlusion in male and female rats. Two involved permanent middle cerebral artery occlusion, which induced severe hyperthermia, and 2 involved transient middle cerebral artery occlusion. Animals were treated with a single intravenous injection of postsynaptic density-95 inhibitors (Tat-NR2B9c [SDV] or Tat-NR2B9c [TDV] ) 1 hour or 3 hours after stroke. Infarct volumes and neurobehavior were assessed in a blinded manner at 24 hours (pial vessel occlusion and permanent middle cerebral artery occlusion) or at 62 days (transient middle cerebral artery occlusion). Results-Postsynaptic density-95 inhibitors dramatically reduced infarct size in male and female animals exposed to pial vessel occlusion (Ͼ50%), in hyperthermic animals with fever exceeding 39°C exposed to permanent middle cerebral artery occlusion (approximately 50%), and at 62 days poststroke in animals exposed to transient middle cerebral artery occlusion (approximately 80%). Effectiveness of postsynaptic density-95 inhibitors was achieved without the drugs affecting body temperature. In transient middle cerebral artery occlusion, a single dose of postsynaptic density-95 inhibitor given 3 hours after stroke onset permanently maintained reduced infarct size and improved neurobehavior.

A high-affinity, dimeric inhibitor of PSD-95 bivalently interacts with PDZ1-2 and protects against ischemic brain damage

“…Tat-NR2B9c has previously shown robust neuroprotective effects in both transient and permanent focal ischemic stroke models in rats (7,8,16), but these studies cannot be directly compared to the current mouse study due to experimental differences (32). Therefore, whether our results represent generally improved neuroprotective properties across species and types of ischemic stroke models of our compounds relative to Tat-NR2B9c needs confirmation by future studies.…”

“…Accordingly, the most advanced PSD-95 inhibitor is a 20-mer peptide, Tat-NR2B9c (7, 8, 16), composed of nine amino acids corresponding to the C-terminal of the GluN2B subunit of the NMDA receptor, fused to the HIV-1 Tat peptide (17). This peptide has shown promising effects against ischemic brain damage in rats (7,8,16), and is currently investigated in clinical trials (18). However, Tat-NR2B9c suffers from low affinity to PDZ1-2 of PSD-95 (19), which might limit its biological effectiveness and clinical potential.…”

Efficacy of the PSD95 inhibitor Tat-NR2B9c in mice requires dose translation between species

“…One millilitre of saline was injected subcutaneously for post-operative hydration. The initial body temperature was 34.64 AE 0.89 pre-surgery, and the procedure commenced when the rectal temperature was [36][37] . Animals were recovered in a chamber held at 26 C for 2 h post-surgery and were then returned to their cages.…”

Neuroprotection by Freezing Ischemic Penumbra Evolution Without Cerebral Blood Flow Augmentation With a Postsynaptic Density-95 Protein Inhibitor

“…7 Tat-NR2B9c blocks the interactions of postsynaptic density-95 protein, an N-methyl-Daspartate receptor-associated postsynaptic density protein, with other downstream signaling proteins (a postsynaptic density-95 protein inhibitor). This uncouples N-methyl-Daspartate receptors from neurotoxic signaling proteins such as nitric oxide synthase (NOS) 8 and reduces stroke damage in rats.…”

“…This uncouples N-methyl-Daspartate receptors from neurotoxic signaling proteins such as nitric oxide synthase (NOS) 8 and reduces stroke damage in rats. 7,9 We used MRI perfusion-weighted imaging (PWI) to measure the effects of Tat-NR2B9c on cerebral blood flow after pMCAO and combined this with diffusion-weighted imaging (DWI) to characterize the evolution of the ischemic penumbra in vivo. 10 Additionally, we used in vitro measurements of the effect of Tat-NR2B9c on adenosine 5Ј-triphosphate (ATP) levels of neurons exposed to oxygenglucose deprivation (OGD), because this setting is dissociated from blood flow effects.…”