Neuroprotective effects of an immunosuppressant agent on diffusion/perfusion mismatch in transient focal ischemia

From cartoon to real time MRI: in vivo monitoring of phagocyte migration in mouse brain

Recent studies have demonstrated that immune cells play an important role in the pathogenesis of many neurological conditions. Immune cells constantly survey the brain microvasculature for irregularities in levels of factors that signal homeostasis. Immune responses are initiated when necessary, resulting in mobilisation of the microglial cells resident in the central nervous system (CNS) and/or of infiltrating peripheral cells. However, little is known about the kinetics of immune cells in healthy and diseased CNS, because it is difficult to perform long-term visualisation of cell motility in live tissue with minimal invasion. Here, we describe highly sensitive in vivo MRI techniques for sequential monitoring of cell migration in the CNS at the single-cell level. We show that MRI combined with intravenous administration of super-paramagnetic particles of iron oxide (SPIO) can be used to monitor the transmigration of peripheral phagocytes into healthy or LPS-treated mouse brains. We also demonstrate dynamic cell migration in live animal brains with time-lapse MRI videos. Time-lapse MRI was used to visualise and track cells with low motility in a control mouse brain. High-sensitivity MRI cell tracking using SPIO offers new insights into immune cell kinetics in the brain and the mechanisms of CNS homeostasis.

The cyclic AMP effects and neuroprotective activities of PACAP and VIP in cultured astrocytes and neurons exposed to oxygen-glucose deprivation

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are endogenous peptides, widely expressed in the central and peripheral nervous system. The adenylyl cyclase (AC)/cyclic AMP (cAMP) is their main intracellular signal transduction pathway. Numerous data suggest that PACAP and VIP have considerable neuroprotective potential, indicating the possibility for their use as new therapeutic strategies in stroke treatment. The aim of this study was to evaluate the effect of oxygen-glucose deprivation (OGD) - an established in vitro model for ischemic cell stress - on PACAP and VIP-evoked receptor-mediated cAMP generation in glial and neuronal cells, and to determine whether PACAP and VIP have neuroprotective activity under these conditions.

METHODS

The formation of [(3)H]cAMP by PACAP, VIP and forskolin (a direct activator of AC) was measured in [(3)H]adenine prelabeled primary rat glial and neuronal cells under normoxia and OGD conditions. The effects of PACAP and VIP on cell viability were measured using the MTT conversion method, and were compared to tacrolimus (FK506), a well known neuroprotective agent.

RESULTS

The OGD model inhibited the PACAP and VIP-induced cAMP formation in rat astrocytes and neurons. Incubation of neuronal cells with PACAP prevented OGD-induced cell death, more efficiently than VIP and FK506.

CONCLUSION

The obtained results showed that hypoxia/ischemia may trigger down-regulation of the brain AC-coupled PACAP/VIP receptors, with a consequent decrease of PACAP- and/or VIP-ergic-dependent cAMP-driven signaling. Moreover, our findings indicate that PACAP and VIP can prevent the deleterious effect of OGD on rat neuronal cells.

Discovery of a novel neuroprotective compound, AS1219164, by high-throughput chemical screening of a newly identified apoptotic gene marker

We have reported that tacrolimus (FK506), an immunosuppressive drug, and diclofenac, a non-steroidal anti-inflammatory drug, possess different modes of neuroprotective action. FK506 suppresses only thapsigargin-induced apoptosis in neuroblastoma SH-SY5Y cells while diclofenac reverses tunicamycin-induced as well as thapsigargin-induced apoptosis. The aim of this study is to discover novel compounds that exert neuroprotective properties by using the transcriptional response of a newly identified gene, which was regulated by both FK506 and diclofenac, as a surrogate screening marker in high-throughput chemical screening and characterize the compounds in comparison with FK506 and diclofenac. Using a microarray with 4504 human cDNAs and quantitative RT-PCR, two genes as apoptotic markers, transmembrane protein 100 (TMEM100) and limb-bud and heart (LBH), were identified because the thapsigargin-induced elevations in their mRNA levels were reversed by both FK506 and diclofenac. A luciferase reporter assay with a TMEM100 promoter region was applied to high-throughput chemical screening. AS1219164, {3-[(E)-2-{5-[(E)-2-pyridin-4-ylvinyl]pyridin-3-yl} vinyl]aniline}, suppressed thapsigargin-induced transactivation of the TMEM100 gene and reversed thapsigargin-induced increases in TMEM100 and LBH mRNA levels in SH-SY5Y cells, similar to the effects of FK506 and diclofenac. Furthermore, AS1219164 protected against SH-SY5Y cell death induced by four apoptotic agents including thapsigargin, similar to diclofenac, but was more potent than diclofenac, while FK506 only showed protective effects against thapsigargin-induced cell death. In conclusion, a novel neuroprotecitve compound, AS1219164, was discovered by high-throughput chemical screening using a reporter assay with the TMEM100 gene promoter regulated by both FK506 and diclofenac. Reporter assay using the promoter region of a gene under pharmacological and physiological transcriptional regulation would be well suit for use in high-throughput chemical screening.

The mechanisms of brain ischemic insult and potential protective interventions

The mechanisms of brain ischemic insult include glutamate excitoxicity, calcium toxicity, free radicals, nitric oxide, inflammatory reactions, as well as dysfunctions of endoplasmic reticulum and mitochondrion. These injury cascades are interconnected in complex ways, thus it is hard to compare their pathogenic importances in ischemia models. And the research in cellular and molecular pathways has spurred the studies in potential neuroprotections mainly in pharmacological fields, such as anti-excitotoxic treatment, calcium-channel antagonism, approaches for inhibition of oxidation, inflammation and apoptosis, etc. Besides, other protective interventions including thrombolysis, arteriogenesis, regeneration therapy, and ischemia preconditioning or postconditioning, are also under investigations. Despite the present difficulties, we are quite optimistic towards future clinical applications of neuroprotective agents, by optimizing experimental approaches and clinical trials.

Future of neuroprotection for acute stroke: in the aftermath of the SAINT trials

The concept of neuroprotective therapy for acute ischemic stroke to salvage tissue at risk and improve functional outcome is based on sound scientific principles and extensive preclinical animal studies demonstrating efficacy. The failure of most neuroprotective drugs in clinical trials has been due to inadequate preclinical testing and flawed clinical development programs. The Stroke Therapy Academic Industry Roundtable (STAIR) group has outlined rational approaches to preclinical and clinical studies. The positive results from the first Stroke-Acute-Ischaemic-NXY-Treatment (SAINT-I) trial of the free-radical spin-trap drug, NXY-059, which followed many of the STAIR guidelines, reinvigorated enthusiasm in neuroprotection, but the SAINT-II trial did not replicate the positive effect on the same primary prespecified outcome measure. This has led to concerns about the future of neuroprotection as a therapeutic strategy for acute ischemic stroke. We discuss new suggestions to bridge the chasm between preclinical animal modeling and acute human stroke trials to potentially enhance the future assessment of novel neuroprotective drugs.

Time Course in the Development of Cerebral Vasospasm after Experimental Subarachnoid Hemorrhage: Clinical and Neuroradiological Assessment of the Rat Double Hemorrhage Model

OBJECTIVE

The "double hemorrhage" model in the rat is frequently used to simulate delayed cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) in humans. However, an exact neurological and angiographic characterization of the CVS is not available for this model so far and is provided in the present investigation. Additionally, perfusion weighted imaging (PWI) at 3 tesla magnetic resonance (MR) tomography was implemented to assess the reduction in cerebral blood flow (CBF).

METHODS

In a prospective, randomized setting CVS was induced by injection of 0.2 ml autologous blood twice in the cisterna magna of 45 male Sprague-Dawley rats. The surviving animals were examined on Days 2, 3, 5, 7 and 9 and compared to a sham operated control group (n = 9). Rats were neurologically graded between 0 and 3, followed by MRI and selective digital subtraction angiography (DSA). The relative CBF was set in relation to the perfusion of the masseter muscle.

RESULTS

The neurological state was significantly worsened on Day 2 (Grade 3), 3 (Grade 3), and 5 (Grade 2) (medians). The relative CBF/muscle BF ratio (2.5 +/- 0.8 (SAH) versus 9.2 +/- 1.3 (sham) (mean +/- SEM) and the basilar artery (BA) diameter (0.15 +/- 0.02 mm (SAH) versus 0.32 +/- 0.01 mm (sham) were significantly decreased on Day 5. Correlation between relative CBF/muscle BF ratio and BA diameter was 0.70.

CONCLUSION

A valid and reproducible CVS simulation was proven by neurological score, DSA, and PWI on Day 5. Furthermore, our data demonstrate the practicability and validity of MR PWI for the monitoring of CVS in a rat SAH model.

Perfusion and diffusion imaging in acute focal cerebral ischemia: temporal vs. spatial resolution

High-resolution diffusion- (DWI) and perfusion-weighted (PWI) imaging may provide substantial benefits in accurate delineation of normal, ischemic, and at-risk tissue. We compared the capability of low (400 x 400 microm(2)) and high (200 x 200 microm(2)) spatial resolution imaging in characterizing the spatiotemporal evolution of the ischemic lesion in a permanent middle artery occlusion (MCAO) model in rats. Serial measurements of cerebral blood flow (CBF) and the apparent diffusion coefficient (ADC) were performed. Lesion volumes were calculated by using viability thresholds or by visual inspection, and correlated with infarct volume defined by TTC staining at 24 h after MCAO. At the very early phase of ischemia, high-resolution resulted in a significantly larger ADC-derived lesion volume and a smaller PWI/DWI mismatch. At 3 h after MCAO, ADC and CBF lesions showed similar robust correlations with TTC-defined infarct volumes for both groups using previously established thresholds. When lesions were determined visually, low-resolution resulted in a substantial overestimation of TTC-defined infarct volume and a lower inter-observer reliability (r = 0.75), whereas high-resolution produced an excellent correlation with TTC-defined infarct volume and inter-observer reliability (r = 0.96). In conclusion, high-resolution MRI resulted in substantial temporal averaging of the ischemic lesion during the early phase, but was clearly superior in visual determination of final infarct size. Low-resolution reasonably evaluated the temporal and spatial evolution of ischemia when thresholds were used.