PET-MRI nanoparticles imaging of blood-brain barrier damage and modulation after stroke reperfusion

Abstract

In an acute ischaemic stroke, understanding the dynamics of blood-brain barrier injury is of particular importance for the prevention of symptomatic haemorrhagic transformation. However, the available techniques assessing blood-brain barrier permeability are not quantitative and are little used in the context of acute reperfusion therapy. Nanoparticles cross the healthy or impaired blood-brain barrier through combined passive and active processes. Imaging and quantifying their transfer rate could better characterize blood-brain barrier damage and refine the delivery of neuroprotective agents. We previously developed an original endovascular stroke model of acute ischaemic stroke treated by mechanical thrombectomy followed by positron emission tomography-magnetic resonance imaging. Cerebral capillary permeability was quantified for two molecule sizes: small clinical gadolinium Gd-DOTA (<1 nm) and AGuIX^® nanoparticles (∼5 nm) used for brain theranostics. On dynamic contrast-enhanced magnetic resonance imaging, the baseline transfer constant K _trans was 0.94 [0.48, 1.72] and 0.16 [0.08, 0.33] ×10^-3 min^-1, respectively, in the normal brain parenchyma, consistent with their respective sizes, and 1.90 [1.23, 3.95] and 2.86 [1.39, 4.52] ×10^-3 min^-1 in choroid plexus, confirming higher permeability than brain parenchyma. At early reperfusion, K _trans for both Gd-DOTA and AGuIX^® nanoparticles was significantly higher within the ischaemic area compared to the contralateral hemisphere; 2.23 [1.17, 4.13] and 0.82 [0.46, 1.87] ×10^-3 min^-1 for Gd-DOTA and AGuIX^® nanoparticles, respectively. With AGuIX^® nanoparticles, K _trans also increased within the ischaemic growth areas, suggesting added value for AGuIX^®. Finally, K _trans was significantly lower in both the lesion and the choroid plexus in a drug-treated group (ciclosporin A, n = 7) compared to placebo (n = 5). K _trans quantification with AGuIX^® nanoparticles can monitor early blood-brain barrier damage and treatment effect in ischaemic stroke after reperfusion.

Keywords: blood–brain barrier; choroid plexus; ischaemia–reperfusion damage; nanoparticles; stroke.

Graphical Abstract

Figure 1

Experimental set-up and study workflow. Imaging data were acquired on a simultaneous PET-MRI system with T1 mapping, DCE-MRI acquisition with two contrast agents (AGuIX^® NPs and Gd-DOTA) (A). PET and MRI data were analysed (B) using Logan plot model for [⁶⁸Ga]AGuIX^® NPs PET data to obtain parametric distribution volume (V_t) images. AGuIX^® NPs and Gd-DOTA DCE-MRI data were analysed with Extended Tofts model to compute volume transfer constant (K_trans), plasma volume (V_p) and extravascular extracellular volume (V_e) parametric maps. Input function was taken in the sagittal sinus. DCE-MRI = dynamic contrast-enhanced MRI; NPs = nanoparticles.

Figure 2

Representative illustrations of abnormal BBB permeabilities. Illustrations of diffusion-weighted scan (acute infarct), post-contrast T1w scan, T2* and BBB permeability maps (from fourth to sixth row, PET AGuIX^® NPs V_t overlaid on T1 MRI, MRI AGuIX^® NPs K_trans, MRI Gd-DOTA K_trans, respectively) in two animals with focal and limited BBB leakage (A) and extended parenchymal and subarachnoid BBB leakage (B). BBB = blood–brain barrier; NPs = nanoparticles.

Figure 3

Extension of oedema (decreased ADC) and BBB damage (increased permeability) to all compartments, including apparently remote regions at early reperfusion. Boxplot of baseline, per-occlusion, post-recanalization, Day+7 ADC, AGuIX^® NPs K_trans in the five compartments: acute infarct, ischaemic penumbra, final infarct, progression and regression areas (n = 5 animals). Data are normalized by their contralateral value and expressed as ipsilateral/contralateral ratio. *P-value < 0.05 one-way repeated measures non-parametric ANOVA (Friedman test) followed by Dunn's multiple comparisons test. ADC = apparent diffusion coefficient; BBB = blood–brain barrier; NPs = nanoparticles.

Figure 4

Permeability to AGuIX^® NPs is lowered by CsA treatment in brain parenchyma and choroid plexus. Longitudinal progression of normalized BBB permeability (AGuIX^® NPs K_trans) in the acute infarct in the two treatment groups represented as boxplots (A) or individual values (B). Median AGuIX^® NPs K_trans at post-recanalization and Day +7 lateral ventricles in Placebo (n = 5 animals) and CsA (n = 7 animals) groups in choroid plexus (C). Although not significantly, the choroid plexus in the ipsilateral hemisphere showed decreased K_trans in the CsA-treated group post-recanalization (n = 7 animals) compare to the placebo group (n = 5 animals), which persisted and became significantly lower at Day 7 in the group treated with CsA (D). MMP9 levels at the post-recanalization was also significantly lower in the treated group (n = 5 in each group) (E). (A) * P < 0.05 two-way repeated measures ANOVA followed by post hoc Bonferroni test for multiple comparisons. (D, E) * P < 0.05 non-parametric Mann–Whitney test. BBB = blood–brain barrier; CsA = ciclosporin A; NPs = nanoparticles.