Vascular recovery promoted by atorvastatin and simvastatin after experimental intracerebral hemorrhage: magnetic resonance imaging and histological study

Abstract

Object: Longitudinal multiparametric MR imaging and histological studies were performed on simvastatin- or atorvastatin-treated rats to evaluate vascular repair mechanisms after experimental intracerebral hemorrhage (ICH).

Methods: Primary ICH was induced in adult Wistar rats by direct infusion of 100 μl of autologous blood into the striatal region adjacent to the subventricular zone. Atorvastatin (2 mg/kg), simvastatin (2 mg/kg), or phosphate-buffered saline was given orally at 24 hours post-ICH and continued daily for 7 days. The temporal evolution of ICH in each group was assessed by MR imaging measurements of T2, T1(sat), and cerebral blood flow in brain areas corresponding to the bulk of the hemorrhage (core) and edematous border (rim). Rats were killed after the final MR imaging examination at 28 days, and histological studies were performed. A small group of sham-operated animals was also studied. Neurobehavioral testing was performed in all animals. Analysis of variance methods were used to compare results from the treatment and control groups, with significance inferred at p ≤ 0.05.

Results: Using histological indices, animals treated with simvastatin and atorvastatin had significantly increased angiogenesis and synaptogenesis in the hematoma rim compared with the control group (p ≤ 0.05). The statin-treated animals exhibited significantly increased cerebral blood flow in the hematoma rim at 4 weeks, while blood-brain barrier permeability (T1(sat)) and edema (T2) in the corresponding regions were reduced. Both statin-treated groups showed significant neurological improvement from 2 weeks post-ICH onward.

Conclusions: The results of the present study demonstrate that simvastatin and atorvastatin significantly improve the recovery of rats from ICH, possibly via angiogenesis and synaptic plasticity. In addition, in vivo multiparametric MR imaging measurements over time can be effectively applied to the experimental ICH model for longitudinal assessment of the therapeutic intervention.

Fig. 1

Examples of quantitative cerebral blood flow, T₂, and T_1sat maps at various times before and after experimental ICH in representative atorvastatin-treated rats. The CBF maps (top row) indicate normal flow before ICH that decreases severely after ICH, particularly in the central core region. The T₂ maps (middle row) show a dark central core region (low T₂) and adjacent surrounding bright rim (high T₂) acutely that reverses in intensity at 24 hours and beyond. Increased blood-brain barrier permeability was noted in both core and rim areas at 24 hours that increased further in the core while stabilizing or decreasing slightly in the rim in the T_1sat maps (bottom row).

Fig. 2

T_1sat ratios (ipsilateral/contralateral) plotted as a function of time after ICH. T_1sat values in the core region decreased initially and then became significantly elevated at later times. Only minor T_1sat changes were seen in the rim. However, at 4 weeks, the simvastatin/atorvastatin intervention decreased T_1sat values in the rim as compared to the control group.

Fig. 3

Plot of T₂ ratios (ipsilateral/contralateral) as a function of time after ICH onset for regions in the central core and surrounding rim of the lesion. In the core, T₂ declined significantly at the acute stage and then became significantly elevated at later times relative to the corresponding contralateral region. Conversely, T₂ ratios in the rim were elevated acutely and then decreased at later times. Simvastatin/atorvastatin therapies significantly lowered T₂ values in the core and rim at 4 weeks after ICH.

Fig. 4

Cerebral blood flow (CBF) ratios (ipsilateral/contralateral) plotted as a function of time. CBF in both the core and rim regions decreased significantly relative to contralateral regions at all time points. Treatment with either simvastatin or atorvastatin significantly increased CBF in the hematoma rim at 4 weeks.

Fig. 5

Representative immunostaining and quantitative immunoreactivities of _vWF in the the ICH border zone. Upper panels show BrdU (left) and _vWF (center) immunostaining and colocalization of BrdU-_vWF (right) for a subpopulation of cells located near the injured site for a simvastatin-treated animal. Arrows indicate cells that stained positively for both BrdU and _vWF. _vWF results are shown in the lower panels for control (left) and simvastatin (center) treatment groups, respectively. Quantitative immunoreactivities for all three groups are presented as bar graphs in the lower right panel.

Fig. 6

Representative immunostaining and quantitative immunoreactivities of synaptophysin are shown for the ICH border zone of control and simvastatin-treated rats (left and center panels, respectively). A higher percentage per area of cells positively reacting to synaptophysin is seen in the sections derived from simvastatin-treated vs control rats. Quantitative immunoreactivities for all three groups are presented as a bar graph on the right side.