Evolution of cerebral ischaemia induced by thromboembolism in rats detected by early sequential MR imaging

Imaging neural stem cell graft-induced structural repair in stroke

Stem cell therapy ameliorates motor deficits in experimental stroke model. Multimodal molecular imaging enables real-time longitudinal monitoring of infarct location, size, and transplant survival. In the present study, we used magnetic resonance imaging (MRI) and positron emission tomography (PET) to track the infarct evolution,tissue repair, and the fate of grafted cells. We genetically engineered embryonic stem cell-derived neural stem cells (NSCs) with a triple fusion reporter gene to express monomeric red fluorescence protein and herpes simplex virus-truncated thymidine kinase for multimodal molecular imaging and SPIO labeled for MRI. The infarct size as well as fate and function of grafted cells were tracked in real time for 3 months using MRI and PET. We report that grafted NSCs reduced the infarct size in animals with less than 0.1 cm(3) initial infarct in a dose-dependent manner, while larger stroke was not amenable to such beneficial effects. PET imaging revealed increased metabolic activity in grafted animals and visualized functioning grafted cells in vivo. Immunohistopathological analysis demonstrated that, after a 3-month survival period, grafted NSCs dispersed in the stroke-lesioned parenchyma and differentiated into neurons, astrocytes, and oligodendrocytes. Longitudinal multimodal imaging provides insights into time course dose-dependent interactions between NSC grafts and structural changes in infarcted tissue.

Why Does Acute Hyperglycemia Worsen the Outcome of Transient Focal Cerebral Ischemia?

Background and Purpose— Hyperglycemia adversely affects the outcome of stroke. Global ischemia data support that the harmful effect of hyperglycemia is mediated by glucose-induced elevated plasma glucocorticoids. Here we sought to evaluate the negative effects of hyperglycemia on transient focal ischemia in the rat, and to test whether these could be prevented by inhibition of either corticosteroid production or neutrophil infiltration.

Methods— Sprague-Dawley rats (n=217) were used. Ischemia was induced by 1 hour middle cerebral artery occlusion (n=196). Acute hyperglycemia was induced by IP injection of dextrose 30 minutes before ischemia. Neutrophil infiltration was blocked by neutropenia with vinblastine. Corticosterone synthesis was inhibited by chemical adrenalectomy with metyrapone. We measured MRI lesion and tissue infarct volumes, evaluated the neurological function, brain myeloperoxidase and matrix metalloproteinase-9 activities, and protein O-glycosylation.

Results— Hyperglycemia significantly enhanced MRI diffusion-weighted imaging alterations, increased cortical, but not subcortical, infarct volume, worsened neurological score, and enhanced brain myeloperoxidase and matrix metalloproteinase-9 activities. Metyrapone did not prevent hyperglycemic brain damage despite successful reduction of plasma corticosterone. Yet, metyrapone tended to reduce cortical infarction and apparent diffusion coefficient lesion volume, indicating some negative contribution of corticosterone. Blocking neutrophil infiltration was also ineffective to prevent the harmful effect of hyperglycemia. A new finding was that O-linked glycosylation of cerebral proteins was increased under hyperglycemia.

Conclusions— In transient middle cerebral artery occlusion, the hyperglycemia-exacerbated brain damage cannot be fully explained by the negative effects of plasma corticosteroids or neutrophil infiltration. The contribution of other intrinsic effects of high glucose, such as brain protein O-glycosylation, deserves further investigation.

The Evolution of Cerebral Ischemia in a Rat Model of Complete Unilateral Carotid Artery Occlusion With Severe Hypotension as Detected By Diffusion-, T2-, and Postcontrast T1-Weighted Magnetic Resonance Images

Severe internal carotid artery stenosis or occlusion is considered to be one of the important causes of stroke. The authors created a complete unilateral carotid artery occlusion model in 15 Sprague-Dawley rats, induced severe hypotension for at least 36 minutes by exsanguination with the target mean arterial pressure being equal or less than 35 mmHg, and investigated the temporal and spatial evolution of cerebral ischemia by diffusion-, T2-, and postcontrast T1-weighted magnetic resonance images. Cerebral ischemia was detected in most regions of the right middle cerebral artery territory during exsanguination. There was no significant relationship between ischemic lesion volume detected on apparent diffusion coefficient (ADC) map (ADC lesion volume) and infarction volume found on histopathology. However, there was a linear relationship between the change in ADC lesion volume at blood reinfusion (after reinfusion minus before reinfusion) and the enlargement of the lesion volume during the postreinfusion period (Y = 0.4X + 161.7, P = 0.0066) and a significant logarithmic correlation between the volume of vasogenic edema found on postcontrast T1-weighted image at 1 hour of the postreinfusion period and the enlargement of the lesion volume during the postreinfusion period (Y = 62.1 x logX - 115.4, P = 0.022). In conclusion, although it may be difficult to predict the outcome of cerebral ischemia (infarction volume) from the lesion volume during exsanguination, the evolution of cerebral ischemia may be partly predicted by lesion volume changes seen on the ADC maps at the time of the blood reinfusion or by the severity of blood-brain barrier disruption at the early stage of the postreinfusion period.

Apparent diffusion coefficient mapping predicts mortality and outcome in rats with intracerebral haemodynamic disturbance: potential role of intraoperative diffusion and perfusion weighted magnetic resonance imaging to detect cerebral ischaemia

BACKGROUND

Usefulness and ability of diffusion and perfusion weighted magnetic resonance images (DWI and PWI) to detect intracerebral haemodynamic disturbance have not been fully evaluated.

METHODS

After the right common carotid artery had been ligated, rats were exsanguinated to maintain a mean arterial pressure of 35, 42, or 50 mm Hg (n=6, each group). Apparent diffusion coefficient (ADC) maps were calculated from DWIs and lesion volume (area) was defined based on ADC values (ADC lesion volume (area)).

RESULTS

ADC lesion volume during exsanguination in the 35 mm Hg group (417 (111) mm(3), P<0.01) was significantly larger than in the 42 mm Hg group (87 (84) mm(3)) and 50 mm Hg group (42 (58) mm(3)). The low relative cerebral blood flow area, calculated from PWI, was significantly larger during exsanguination in the 35 mm Hg group than in the other groups. ADC lesion volume in the six rats that died within 3 days of the MRI study was significantly larger (median 421 mm(3), range 205-476 mm(3), P<0.005) than in the 12 rats that survived for 3 days (median 26 mm(3), range 3-517 mm(3)). Rats with an ADC lesion area over 14 mm(2) on the coronal slice including the caudate putamen during exsanguination died within 3 days or revealed a more severe histopathological outcome than those that survived for 3 days.

CONCLUSIONS

Incomplete cerebral ischaemia created by the combination of common carotid artery occlusion and exsanguination could be detected by DWI and PWI both qualitatively and quantitatively. The size of the lesion on ADC mapping was found to correlate with mortality and outcome.