Niaspan enhances vascular remodeling after stroke in type 1 diabetic rats

Abstract

We investigated the changes and the molecular mechanisms of cerebral vascular damage and tested the therapeutic effects of Niaspan in type-1 streptozotocin induced diabetic (T1DM) rats after stroke. T1DM-rats were subjected to transient middle cerebral artery occlusion (MCAo) and treated without or with Niaspan. Non-streptozotocin rats (WT) were also subjected to MCAo. Functional outcome, blood-brain-barrier (BBB) leakage, brain hemorrhage, immunostaining, and rat brain microvascular endothelial cell (RBEC) culture were performed. Compared to WT-MCAo-rats, T1DM-MCAo-rats did not show an increase lesion volume, but exhibited significantly increased brain hemorrhage, BBB leakage and vascular damage as well as decreased functional outcome after stroke. Niaspan treatment of stroke in T1DM-MCAo-rats significantly attenuated BBB damage, promoted vascular remodeling and improved functional outcome after stroke. T1DM-MCAo-rats exhibited significantly increased Angiopoietin 2 (Ang2) expression, but decreased Ang1 expression in the ischemic brain compared to WT-MCAo-rats. Niaspan treatment attenuated Ang2, but increased Ang1 expression in the ischemic brain in T1DM-MCAo-rats. In vitro data show that the capillary-like tube formation in the WT-RBECs marginally increased compared to T1DM-RBEC. Niaspan and Ang1 treatment significantly increased tube formation compared to non-treatment control. Inhibition of Ang1 attenuated Niacin-induced tube formation in T1DM-RBECs. Niaspan treatment of stroke in T1DM-rats promotes vascular remodeling and improves functional outcome. The Ang1/Ang2 pathway may contribute to Niaspan induced brain plasticity. Niaspan warrants further investigation as a therapeutic agent for the treatment of stroke in diabetics.

Fig. 1

Lesion volume is not increased in T1DM rats after stroke, but functional outcome is significantly attenuated after stroke compared to WT-MCAo rats. Niaspan treatment promotes functional outcome after stroke in T1DM rats. A–C: mNSS test (A), adhesive removal-test (B) and foot-fault test (C) were measured before MCAo and at 1, 7 and 14 days after MCAo. D: Seven sections of HE staining for lesion volume measurement and quantitative data 14 days after MCAo. E: Mortality rate.

Fig. 2

Brain hemorrhage, BBB leakage and vascular damage are increased in T1DM-MCAo rats compared to WT-MCAo rats. Niaspan treatment of T1DM-MCAo rats decreases BBB leakage, brain hemorrhage and vascular damage. A: HE staining for brain hemorrhage rate and hemorrhage volume measurement. B: Evans blue assay for BBB leakage (n=4/group). C–E: ZO1, EBA and Desmin expression in the IBZ (n=8/group).

Fig. 3

T1DM-MCAo rats have increased vascular density, but decreased vascular perimeter, arterial diameter compared to WT-MCAo rats. Niaspan treatment of stroke increases vascular remodeling in the ischemic brain in T1DM-MCAo rats. A–B: Vascular density and vascular perimeter were measured by vWF immunostaining in the IBZ (n=8/group). C–D: Artery density and arterial diameter was measured by α-SMA immunostaining in the IBZ (n=8/group). The total number of α-SMA positive coated vessels per mm² area is presented. E–F: BrdU-positive VECs and quantatitive data. G: rCBF was measured before MCAo, after MCAo and Niaspan treatment in WT-MCAo, T1DM-MCAo and T1DM-MCAo+Niaspan treatment rats. The data are presented as percentage of baseline (before MCAo in WT rats).

Fig. 4

T1DM-MCAo rats show decreased Ang1 and increased Ang2 expression in the ischemic brain compared to WT-MCAo rats. Niaspan treatment increases Ang1 and decreases Ang2 expression in the ischemic brain compared to non-Niaspan treatment T1DM-MCAo rats. A: Ang1 expression in the IBZ (n=8/group). B: Ang2 expression in the IBZ (n=8/group). C: Schematic map shows ischemic brain tissue extraction from IC and IBZ for Western blot assay and Western blot quantitative data (n=4/group). D: Correlation Ang1 expression in the IBZ and mNSS. E: Capillary-like tube formation measurements in the rat brain endothelial cells (RBECs) in vitro.