SOD1 overexpression prevents acute hyperglycemia-induced cerebral myogenic dysfunction: relevance to contralateral hemisphere and stroke outcomes

Abstract

Admission hyperglycemia (HG) amplifies vascular injury and neurological deficits in acute ischemic stroke, but the mechanisms remain controversial. We recently reported that ischemia-reperfusion (I/R) injury impairs the myogenic response in both hemispheres via increased nitration. However, whether HG amplifies contralateral myogenic dysfunction and whether loss of tone in the contralateral hemisphere contributes to stroke outcomes remain to be determined. Our hypothesis was that contralateral myogenic dysfunction worsens stroke outcomes after acute hyperglycemic stroke in an oxidative stress-dependent manner. Male wild-type or SOD1 transgenic rats were injected with saline or 40% glucose solution 10 min before surgery and then subjected to 30 min of ischemia/45 min or 24 h of reperfusion. In another set of animals (n = 5), SOD1 was overexpressed only in the contralateral hemisphere by stereotaxic adenovirus injection 2-3 wk before I/R. Myogenic tone and neurovascular outcomes were determined. HG exacerbated myogenic dysfunction in contralateral side only, which was associated with infarct size expansion, increased edema, and more pronounced neurological deficit. Global and selective SOD1 overexpression restored myogenic reactivity in ipsilateral and contralateral sides, respectively, and enhanced neurovascular outcomes. In conclusion, our results show that SOD1 overexpression nullified the detrimental effects of HG on myogenic tone and stroke outcomes and that the contralateral hemisphere may be a novel target for the management of acute hyperglycemic stroke.

Keywords: admission hyperglycemia; contralateral hemisphere; ischemia-reperfusion injury; myogenic tone; stroke outcomes; superoxide dismutase.

Fig. 1.

Acute hyperglycemia (HG) at the time of stroke exacerbated contralateral myogenic dysfunction. A: ischemia-reperfusion (I/R) with or without HG led to complete loss of the myogenic response in middle cerebral arteries (MCAs) isolated from the ischemic (IS) hemisphere compared with sham-operated (sham) right (RT) and sham RT with HG sides. B: the myogenic response was significantly reduced in the left (LT) hemisphere after I/R injury [nonischemic (NIS) side] or HG alone (sham LT + HG) compared with the sham LT side. Contralateral myogenic dysfunction was aggravated when I/R injury was superimposed with acute HG. ^a,b,cDifferent letters for pairs of means are significantly different (P < 0.05 by Tukey's test, n = 5–8). C: blood glucose levels at baseline, MCA occlusion (MCAO), and reperfusion in sham, sham + HG, stroked Wistar (Wis MCAO), and Wis MCAO + HG rats. #P < 0.001 vs. sham and Wis MCAO rats (n = 4).

Fig. 2.

SOD1 transgenic rats maintained well-developed vascular reactivity after acute hyperglycemic stroke. Sprague-Dawley (SD) and SOD1 rats were subjected to 30 min of MCAO/45 min of reperfusion with or without HG. A: I/R injury with or without HG led to loss of the myogenic response in ipsilateral MCAs isolated from SD rats compared with sham SD rats. ^a,bDifferent letters for pairs of means are significantly different (P < 0.05 by Tukey's test, n = 5–6). B: SOD1 transgenic rats maintained a well-developed myogenic response after I/R injury with or without HG (n = 4–6). C: representative images acquired by the Pim3 laser Doppler at baseline, MCAO, and after reperfusion (Post Rep). D: percent cerebral blood flow (CBF) reduction during MCAO was similar among all groups. E: percent CBF after reperfusion was improved in SOD transgenic rats exposed to MCAO, which was significantly reduced after acute hyperglycemic stroke. **P < 0.01 vs. SOD1 MCAO (n = 4–6).

Fig. 3.

Physiological parameters of SOD1 transgenic rats. A: increased total SOD1 expression in brain homogenates of SOD1 transgenic rats compared with SD rats. **P < 0.01 vs. SD rats (n = 4). B: increased total SOD activity in brain homogenates of SOD1 transgenic rats compared with SD rats. *P < 0.05 vs. SD rats (n = 7). C: blood glucose levels at baseline, MCAO, and reperfusion in SD, SD + HG, SOD1, and SOD1 + HG groups. ***P < 0.001 vs. SD MCAO and SOD1 MCAO (n = 3–8). D: nitration was significantly upregulated after I/R injury with and without HG in SD rats, whereas global SOD1 overexpression blunted that increase. ^a,bDifferent letters for pairs of means are significantly different (P < 0.05 by Tukey's test, n = 4).

Fig. 4.

Global SOD1 overexpression improved stroke outcomes after acute hyperglycemic stroke. SD and SOD1 rats were subjected to 30 min of MCAO/24 h of reperfusion with or without HG. A and B: acute HG at time of stroke led to infarct size and edema expansion in SD rats, whereas normoglycemic and hyperglycemic SOD1 transgenic rats showed smaller infarct size and edema compared with SD rats exposed to I/R injury with or without HG. C: hyperglycemic SD rats showed poor beam walk performance compared with normoglycemic SD rats after I/R injury, whereas normoglycemic and hyperglycemic SOD1 transgenic rats experienced better performance compared with stroked SD rats with or without HG. D: acute HG at the time of stroke exacerbated grip strength deficits in SD rats but had no additional effect on SOD1 rats. P values indicate an interaction such that HG affects infarct size, edema, and neurological tests differently in SD vs. SOD rats. ^a,b,cDifferent letters on pairs of means are significantly different by Tukey's post hoc pairwise comparison test (n = 5–8).

Fig. 5.

Contralateral SOD1 overexpression in control Wistar rats. Wistar rats were subjected to a stereotaxic injection of SOD1 adenovirus (AD) or an empty vector in the LT hemisphere 2–3 wk before acute hyperglycemic stroke. A: representative image of the stereotaxic injection of SOD1 AD in the contralateral hemisphere. B: focal contralateral SOD1 overexpression significantly improved contralateral myogenic dysfunction compared with NIS + HG and with acutely hyperglycemic stroked rats injected with an empty vector. C: contralateral SOD1 overexpression did not improve the myogenic response of vessels obtained from IS hemisphere (IS + HG SOD1 AD) after acute hyperglycemic stroke compared with IS + HG and with rats injected with an empty vector. ^a,bDifferent letters on pairs of means are significantly different (P < 0.05 by Tukey's test, n = 3–6). D: focal contralateral SOD1 overexpression increased lumen diameter under active conditions while maintaining a well-developed autoregulatory response in the contralateral hemisphere compared with acute hyperglycemic stroke with and without the empty vector injection. E: focal contralateral SOD1 overexpression improved passive vasodilation in the contralateral hemisphere compared with the effect of an empty vector injection and with MCAs isolated from rats exposed to acute hyperglycemic stroke. *P < 0.001 vs. NIS + HG and NIS + HG empty vector (n = 3–6). F: SOD1 expression was significantly upregulated after stereotaxic injection of SOD1 AD in the LT hemisphere compared with the RT uninjected (unij) side, LT side injected with an empty vector, and control Wistar rats. *P < 0.05 vs. RT uninjected side; **P < 0.01 vs. control and LT empty vector (n = 4–5). G: SOD activity was significantly upregulated after stereotaxic injection of SOD1 AD in the LT hemisphere compared with the RT uninjected side, LT side injected with an empty vector, and control Wistar rats. ***P < 0.001 vs. control, RT uninjected side, and LT empty vector (n = 3–6). H: blood glucose levels at baseline, MCAO, and reperfusion in hyperglycemic stroked Wistar rats (Wis MCAO + HG), Wistar rats injected with SOD1 AD (SOD1 AD MCAO + HG), or Wistar rats injected with empty vector before hyperglycemic stroke (MCAO + HG empty vector) (n = 3–6).

Fig. 6.

Contralateral SOD1 overexpression improved CBF after acute hyperglycemic stroke. Wistar rats were subjected to a stereotaxic injection of SOD1 AD or an empty vector in the LT hemisphere 2–3 wk before acute hyperglycemic stroke. A and B: mean percent CBF was significantly decreased in both hemispheres during MCAO and postreperfusion after acute hyperglycemic stroke compared with baseline. Contralateral SOD1 overexpression improved CBF after reperfusion in both IS and NIS hemispheres. C: percent CBF reduction during MCAO in IS and NIS hemispheres was similar between the two groups. D: contralateral SOD1 overexpression improved postreperfusion CBF in IS and NIS hemispheres after acute hyperglycemic stroke. P^ < 0.001, **P < 0.01, and *P < 0.05 vs. baseline; ***P < 0.001 vs. postreperfusion and baseline; #P < 0.001 vs. IS + HG vehicle; ∼P < 0.01 vs. NIS + HG vehicle (n = 5–6).

Fig. 7.

Contralateral SOD1 overexpression improved stroke outcomes after acute hyperglycemic stroke. Wistar rats were subjected to a stereotaxic injection of SOD1 AD in the Lt hemisphere 2–3 wk before acute hyperglycemic stroke. A and B: acute HG at the time of stroke led to infarct size and edema expansion in Wistar rats (MCAO + HG), which were significantly reduced by contralateral SOD1 overexpression (SOD1 AD + HG). C and D: hyperglycemic Wistar rats showed poor beam walk performance and grip strength deficits compared with normoglycemic SD rats after I/R injury. Contralateral SOD1 overexpression (SOD1 AD + HG) significantly enhanced behavioral outcomes compared with MCAO + HG. ^a,bDifferent letters on pairs of means are significantly different (P < 0.05 by Tukey's test, n = 5–7).