Investigating potentially salvageable penumbra tissue in an in vivo model of transient ischemic stroke using sodium, diffusion, and perfusion magnetic resonance imaging

Background: Diffusion magnetic resonance imaging (MRI) is the current-state-of-the-art technique to clinically investigate acute (0–24 h) ischemic stroke tissue. However, reduced apparent diffusion coefficient (ADC)—considered a marker of tissue damage—was observed to reverse spontaneously during the subacute stroke phase (24–72 h) which means that low ADC cannot be used to reflect the damaged tissue after 24 h in experimental and clinical studies. One reason for the change in ADC is that ADC values drop with cytotoxic edema (acute phase) and rise when vasogenic edema begins (subacute phase). Recently, combined 1H- and 23Na-MRI was proposed as a more accurate approach to improve delineation between reversible (penumbra) and irreversible ischemic injury (core). The aim of this study was to investigate the effects of reperfusion on the ADC and the sodium MRI signal after experimental ischemic stroke in rats in well-defined areas of different viability levels of the cerebral lesion, i.e. core and penumbra as defined via perfusion and histology. Transient middle cerebral artery occlusion was induced in male rats by using the intraluminal filament technique. MRI sodium, perfusion and diffusion measurement was recorded before reperfusion, shortly after reperfusion and 24 h after reperfusion. The animals were reperfused after 90 min of ischemia. Results: Sodium signal in core did not change before reperfusion, increased after reperfusion while sodium signal in penumbra was significantly reduced before reperfusion, but showed no changes after reperfusion compared to control. The ADC was significantly decreased in core tissue at all three time points compared to contralateral side. This decrease recovered above commonly applied viability thresholds in the core after 24 h. Conclusions: Reduced sodium-MRI signal in conjunction with reduced ADC can serve as a viability marker for penumbra detection and complement hydrogen diffusion- and perfusion-MRI in order to facilitate time-independent assessment of tissue fate and cellular bioenergetics failure in stroke patients

Stimulating brain recovery after stroke using theranostic albumin nanocarriers loaded with nerve growth factor in combination therapy

For many years, delivering drug molecules across the blood brain barrier has been a major challenge. The neuropeptide nerve growth factor is involved in the regulation of growth and differentiation of cholinergic neurons and holds great potential in the treatment of stroke. However, as with many other compounds, the biomolecule is not able to enter the central nervous system. In the present study, nerve growth factor and ultrasmall particles of iron oxide were co-encapsulated into a chemically crosslinked albumin nanocarrier matrix which was modified on the surface with apolipoprotein E. These biodegradable nanoparticles with a size of 212 ± 1 nm exhibited monodisperse size distribution and low toxicity. They delivered NGF through an artificial blood brain barrier and were able to induce neurite outgrowth in PC12 cells in vitro. In an animal model of stroke, the infarct size was significantly reduced compared to the vehicle control. The combination therapy of NGF and the small-molecular MEK inhibitor U0126 showed a slight but not significant difference compared to U0126 alone. However, further in vivo evidence suggests that successful delivery of the neuropeptide is possible as well as the synergism between those two treatments

Inhibition of cerebrovascular raf activation attenuates cerebral blood flow and prevents upregulation of contractile receptors after subarachnoid hemorrhage

<p>Abstract</p> <p>Background</p> <p>Late cerebral ischemia carries high morbidity and mortality after subarachnoid hemorrhage (SAH) due to reduced cerebral blood flow (CBF) and the subsequent cerebral ischemia which is associated with upregulation of contractile receptors in the vascular smooth muscle cells (SMC) via activation of mitogen-activated protein kinase (MAPK) of the extracellular signal-regulated kinase (ERK)1/2 signal pathway. We hypothesize that SAH initiates cerebrovascular ERK1/2 activation, resulting in receptor upregulation. The raf inhibitor will inhibit the molecular events upstream ERK1/2 and may provide a therapeutic window for treatment of cerebral ischemia after SAH.</p> <p>Results</p> <p>Here we demonstrate that SAH increases the phosphorylation level of ERK1/2 in cerebral vessels and reduces the neurology score in rats in additional with the CBF measured by an autoradiographic method. The intracisternal administration of SB-386023-b, a specific inhibitor of raf, given 6 h after SAH, aborts the receptor changes and protects the brain from the development of late cerebral ischemia at 48 h. This is accompanied by reduced phosphorylation of ERK1/2 in cerebrovascular SMC. SAH per se enhances contractile responses to endothelin-1 (ET-1), 5-carboxamidotryptamine (5-CT) and angiotensin II (Ang II), upregulates ET_B, 5-HT_1Band AT₁receptor mRNA and protein levels. Treatment with SB-386023-b given as late as at 6 h but not at 12 h after the SAH significantly decreased the receptor upregulation, the reduction in CBF and the neurology score.</p> <p>Conclusion</p> <p>These results provide evidence for a role of the ERK1/2 pathway in regulation of expression of cerebrovascular SMC receptors. It is suggested that raf inhibition may reduce late cerebral ischemia after SAH and provides a realistic time window for therapy.</p

Protein Kinase Inhibition in Late Cerebral Ischemia after Subarachnoid Hemorrhage

The cerebral ischemia that occur after a subarachnoid hemorrhage (SAH) often results in death or severe disability and is a significant cause of stroke. Our hypothesis is that cerebral ischemia leads to pathophysiological receptor changes on the vascular smooth muscle cells. The changes may lead to a stronger vasoconstriction than normal in response to endogenous ligands. We are focusing on the endothelin (ET), 5-hydroxytryptamine (5-HT) and angiotensin II receptor-ligand systems. Previous studies have shown an upregulation of contractile ETB, 5-HT1B and AT1 receptors in cerebral arteries following experimental induced SAH. There is data to suggest that the intracellular pathways responsible for this upregulation involve protein kinase C (PKC) and mitogen activated protein kinase (MAPK). The aim of this thesis was to determine in detail the intracellular signaling mechanisms involved in the receptor changes in SAH. The results show that SAH induce upregulation of the contractile ETB, 5-HT1B and AT1 receptors in a time-dependent manner both at functional and molecular levels. We also showed that the PKC and MAPK pathways are involved in the late cerebral ischemia after SAH. By administrating inhibitors of PKC or ERK1/2 to the SAH rats we were able to prevent the upregulation of contractile receptors, the associated reduction in the regional CBF and neurological deterioration. Similar results were seen when the ERK1/2 inhibitor was given 6 h after the induced SAH. The main findings of this thesis, suggest that kinase inhibition is a novel target for treatment of cerebrovascular disorders such as cerebral ischemia after SAH

Equal contribution of increased intracranial pressure and subarachnoid blood to cerebral blood flow reduction and receptor upregulation after subarachnoid hemorrhage.

Object Cerebral ischemia remains the key cause of disability and death in the late phase after subarachnoid hemorrhage (SAH), and its pathogenesis is still poorly understood. The purpose of this study was to examine whether the change in intracranial pressure or the extravasated blood causes the late cerebral ischemia and the upregulation of receptors or the cerebral vasoconstriction observed following SAH. Methods Rats were allocated to 1 of 3 experimental conditions: 1) cisternal injection of 250 mul blood (SAH Group), 2) cisternal injection of 250 mul NaCl (Saline Group), or 3) the same procedure but without fluid injection (Sham Group). Two days after the procedure, the basilar and middle cerebral arteries were harvested, and contractile responses to endothelin (ET)-1 and 5-carboxamidotryptamine (5-CT) were investigated by means of myography. In addition, real-time polymerase chain reaction was used to determine the mRNA levels for ET(A), ET(B), and 5-HT(1) receptors. Regional and global cerebral blood flow (CBF) were quantified by means of an autoradiographic technique. Results Compared with the sham condition, both SAH and saline injection resulted in significantly enhanced contraction of cerebral arteries in response to ET-1 and 5-CT. Regional and global CBF were reduced both in the Saline and SAH groups compared with the Sham Group. The mRNA levels for ET(B) and 5-HT(1B) receptors were upregulated after SAH and saline injection compared with the sham procedure. The effects in all parameters were more pronounced for SAH than for saline injection. Conclusions This study revealed that both the elevation of intracranial pressure and subarachnoid blood per se contribute approximately equally to the late CBF reductions and receptor upregulation following SAH

Elevated intracranial pressure or subarachnoid blood responsible for reduction in cerebral blood flow after SAH

Background. The pathogenesis of cerebral ischemia after subarachnoid hemorrhage (SAH) still remains elusive. The purpose of the present study was to examine whether it is the change in intracranial pressure (ICP) or the extravasated blood that is responsible for cerebral ischemia and cerebral vasoconstriction observed following SAH. Method. Three groups of animals were studied; (1) cisternal injection of 250 mu l blood (SAH), (2) injection of 250 mu l NaCl (saline) or (3) same procedure in every detail but no fluid injection (sham). Two days after the treatment, an autoradiographic technique was used to investigate the cerebral blood flow (CBF). Findings. Both SAH (blood+ ICP) and saline injection (ICP only) resulted in significantly reduced regional and global CBF after as compared to sham/control. Conclusions. This study revealed that both the elevation of ICP and A Subarachnoid blood per se contribute approximately equally to the SAH induced effects