Blood-brain barrier stabilization effects of agmatine assessed by dynamic contrast-enhanced MRI in a rat model of transient cerebral ischemia

Abstract

Purpose: Blood-brain barrier (BBB) disruption after acute ischemic stroke and subsequent permeability increase may be enhanced by reperfusion. Agmatine has been reported to attenuate BBB disruption. Therefore, the aim of this study was to evaluate BBB stabilization effect of agmatine in a rat model of transient cerebral ischemia using permeability (dynamic contrast-enhanced, DCE) MRI at early stages, and to demonstrate the feasibility of DCE-MRI for the investigation of new therapies.Materials and Methods: Thirty male Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion for 90 min. Immediately after reperfusion, agmatine (100 mg/kg) was injected intraperitoneally in the agmatine-treated group (n=15) and normal saline in the control group. MRI was performed at 4 hours and 30 hours after reperfusion in 18 rats (n=9 agmatine-treated, n=9 control) and only at 4 hours after reperfusion in 12 rats (n=6 agmatine-treated, n=6 control) before obtaining the specimens. Infarct volumes were calculated on diffusion-weighted imaging. For quantitative analysis, regions of interest were defined within the infarct area and ADC, FA, volume transfer constant (Ktrans), rate transfer coefficient (Kep), and volume fraction of extravascular extracellular space (Ve) values were obtained from MRI. Immunohistochemical staining was performed and the numbers of factor VIII positive cells were counted. Infarct volume, infarct growth, quantitative imaging parameters, and numbers of factor VIII positive cells were compared between the control and the agmatine-treated groups.Results: Agmatine reduced infarct volume (36.1±10.8% vs. 54.2±7.1%, P<0.001) and infarct growth (60±44.4 mm3 vs. 130±55.2 mm3, P=0.009). There was no significant difference in ADC and FA between the two groups. Ktrans was significantly lower in the agmatine-treated group compared to the control group (0.05±0.02 min-1 vs. 0.08±0.03 min-1, P=0.012) at 4 hour-reperfusion. Other permeability parameters were not significantly different between the groups. The number of factor VIII positive cells was less in the agmatine-treated group than in the control group (3-fold vs. 4-fold compared to contralateral hemisphere, P=0.037).Conclusion: Agmatine protects the BBB in ischemic stroke, which can be monitored in vivo by quantification of permeability with DCE-MRI. Therefore, DCE-MRI provides imaging biomarkers for assessing the BBB stabilization properties of pharmacological agents to reduce the complications associated with thrombolytic therapy in ischemic stroke.