Combination treatment with low-dose Niaspan and tissue plasminogen activator provides neuroprotection after embolic stroke in rats

Abstract

Introduction: Niaspan, an extended-release formulation of niacin (vitamin B3), has been widely used to increase high density lipoprotein (HDL) cholesterol and to prevent cardiovascular diseases and stroke. We have previously demonstrated that Niaspan (40 mg/kg) administered at 2h after stroke induces neuroprotection, while low dose Niaspan (20mg/kg) does not reduce infarct volume. Tissue plasminogen activator (tPA) is an effective therapy for acute stroke, but its use remains limited by a narrow therapeutic window. We have previously demonstrated that intravenous administration of tPA 4h after stroke in rats does not reduce infarct volume. In this study, we tested whether combination treatment with low-dose Niaspan (20mg/kg) and tPA administered 4h after embolic stroke in a rat model reduces infarct volume and provides neuroprotection.

Methods: Adult male Wistar rats were subjected to embolic middle cerebral artery occlusion (MCAo) and treated with low-dose Niaspan (20mg/kg) alone (n = 7), tPA (10mg/kg) alone (n = 7), combination of low-dose Niaspan and tPA (n = 7), or saline control (n = 9), 4h after stroke. A battery of functional outcome tests was performed. Rats were sacrificed at 7 days after MCAo and lesion volumes were measured. To investigate the underlying mechanism of combination treatment neuroprotective effect, deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), cleaved caspase-3, tumor necrosis factor alpha (TNF-alpha), and toll-like receptor 4 (TLR-4) immunostaining were performed.

Results: Combination treatment with low-dose Niaspan and tPA significantly improved functional outcome compared to the saline control group (p<0.05), while treatment with Niaspan or tPA alone did not significantly improve functional outcome compared to saline control group. Additionally, combination treatment significantly reduced infarct volume compared to saline control group (p = 0.006) and infarct volume was significantly correlated with functional outcome (p = 0.0008; r = 0.63). Monotherapy with Niaspan or tPA did not significantly decrease infarct volume compared to saline control group. Combination treatment reduced apoptosis as measured by significant reduction in the number of TUNEL-positive cells and cleaved caspase-3 expression in the ischemic brain compared to saline control group (p<0.05). Combination treatment also significantly reduced the expression of TNF-alpha and TLR-4 in the ischemic brain compared to Niaspan, tPA and saline treatment groups (p<0.05). A significant interaction between Niaspan and tPA on the TNF-alpha expression was detected (p<0.05), indicating a synergy effect in the combination treatment group.

Conclusion: Treatment of stroke with combination of low-dose Niaspan and tPA at 4h after embolic stroke reduces infarct volume, improves neurological outcome and provides neuroprotection. The neuroprotective effects of combination treatment were associated with reduction of apoptosis and attenuation of TNF-alpha and TLR-4 expression.