SARS-CoV-2 Spike Protein Intensifies Cerebrovascular Complications in Diabetic hACE2 Mice through RAAS and TLR Signaling Activation

Diabetics are more vulnerable to SARS-CoV-2 neurological manifestations. The molecular mechanisms of SARS-CoV-2-induced cerebrovascular dysfunction in diabetes are unclear. We hypothesize that SARS-CoV-2 exacerbates diabetes-induced cerebrovascular oxidative stress and inflammation via activation of the destructive arm of the renin-angiotensin-aldosterone system (RAAS) and Toll-like receptor (TLR) signaling. SARS-CoV-2 spike protein was injected in humanized ACE2 transgenic knock-in mice. Cognitive functions, cerebral blood flow, cerebrovascular architecture, RAAS, and TLR signaling were used to determine the effect of SARS-CoV-2 spike protein in diabetes. Studies were mirrored in vitro using human brain microvascular endothelial cells treated with high glucose-conditioned media to mimic diabetic conditions. Spike protein exacerbated diabetes-induced cerebrovascular oxidative stress, inflammation, and endothelial cell death resulting in an increase in vascular rarefaction and diminished cerebral blood flow. SARS-CoV-2 spike protein worsened cognitive dysfunction in diabetes compared to control mice. Spike protein enhanced the destructive RAAS arm at the expense of the RAAS protective arm. In parallel, spike protein significantly exacerbated TLR signaling in diabetes, aggravating inflammation and cellular apoptosis vicious circle. Our study illustrated that SAR-CoV-2 spike protein intensified RAAS and TLR signaling in diabetes, increasing cerebrovascular damage and cognitive dysfunction.

Abstract 110: Why Diabetics Are More Vulnerable To Cerebrovascular Complications Of SARS-CoV-2? An In-vivo Animal Study

Diabetics are more vulnerable to SARS-CoV-2 cerebrovascular complications, including brain fog, cognitive impairment, and strokes. This study aims to identify the molecular mechanisms of SARS-CoV-2-induced cerebrovascular dysfunction in diabetes. We hypothesize that SARS-CoV-2 exacerbates diabetes-induced cerebral oxidative stress and inflammation via activation of the destructive arm of the renin-angiotensin system (RAAS) and Toll-Like receptor (TLR) signaling.

Methods: SARS-CoV-2 spike-protein binds to human angiotensin-converting enzyme-2 (ACE2) receptors but not murine Ace2. Therefore, type-2 diabetes was induced in humanized ACE2 (hACE2) knock-in transgenic mice using low-dose streptozotocin followed by eight weeks of a high-fat diet. Recombinant SARS-CoV-2 spike-protein was injected intravenously in control and diabetic mice. Cognitive functions were tested using Y-maze and Barnes maze. RAAS system and TLR signaling were assessed using RT-PCR and western blot analysis. The cerebrovascular architecture was measured using immunohistochemistry.

Results: Diabetes increased cerebrovascular oxidative stress markers NOX1 and NOX5 and inflammatory markers Il-6, Il-1β, and TNF-α gene expression (P<0.05). Diabetes upregulated angiotensin II and angiotensin 1 receptor (AT1R) expression, these effects were amplified by spike-protein (P<0.05). Moreover, spike-protein injection decreased RAAS protective arm, ACE2, and AT2R expression (P<0.05). In parallel, spike-protein exacerbated TLR signaling in diabetes. Spike-protein increased the TLR-8 receptors and its ligands HMGB1 and S100 and downstream adaptor proteins MyD88, TRAF6, and NF-κB expression (P<0.05). Spike-protein significantly increased cerebrovascular rarefaction and cognitive dysfunction in diabetes (P<0.05).

Conclusion: SAR-CoV-2 spike-protein intensified RAAS and TLR signaling in diabetes leading to additional cerebrovascular damage and cognitive dysfunction. Targeting RAAS and TLR singling are possible therapeutic strategies to protect against SAR-CoV-2-induced cerebrovascular dysfunction in diabetes.

GLP-1 receptor nitration contributes to loss of brain pericyte function in a mouse model of diabetes

AIMS/HYPOTHESIS

We have previously shown that diabetes causes pericyte dysfunction, leading to loss of vascular integrity and vascular cognitive impairment and dementia (VCID). Glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1 RAs), used in managing type 2 diabetes mellitus, improve the cognitive function of diabetic individuals beyond glycaemic control, yet the mechanism is not fully understood. In the present study, we hypothesise that GLP-1 RAs improve VCID by preventing diabetes-induced pericyte dysfunction.

METHODS

Mice with streptozotocin-induced diabetes and non-diabetic control mice received either saline (NaCl 154 mmol/l) or exendin-4, a GLP-1 RA, through an osmotic pump over 28 days. Vascular integrity was assessed by measuring cerebrovascular neovascularisation indices (vascular density, tortuosity and branching density). Cognitive function was evaluated with Barnes maze and Morris water maze. Human brain microvascular pericytes (HBMPCs), were grown in high glucose (25 mmol/l) and sodium palmitate (200 μmol/l) to mimic diabetic conditions. HBMPCs were treated with/without exendin-4 and assessed for nitrative and oxidative stress, and angiogenic and blood-brain barrier functions.

RESULTS

Diabetic mice treated with exendin-4 showed a significant reduction in all cerebral pathological neovascularisation indices and an improved blood-brain barrier (p<0.05). The vascular protective effects were accompanied by significant improvement in the learning and memory functions of diabetic mice compared with control mice (p<0.05). Our results showed that HBMPCs expressed the GLP-1 receptor. Diabetes increased GLP-1 receptor expression and receptor nitration in HBMPCs. Stimulation of HBMPCs with exendin-4 under diabetic conditions decreased diabetes-induced vascular inflammation and oxidative stress, and restored pericyte function (p<0.05).

CONCLUSIONS/INTERPRETATION

This study provides novel evidence that brain pericytes express the GLP-1 receptor, which is nitrated under diabetic conditions. GLP-1 receptor activation improves brain pericyte function resulting in restoration of vascular integrity and BBB functions in diabetes. Furthermore, the GLP-1 RA exendin-4 alleviates diabetes-induced cognitive impairment in mice. Restoration of pericyte function in diabetes represents a novel therapeutic target for diabetes-induced cerebrovascular microangiopathy and VCID.

Abstract 53: Covid-19 Spike-protein Causes Cerebrovascular Rarefaction And Deteriorates Cognitive Functions In A Mouse Model Of Humanized ACE2

COVID-19 pandemic has affected our health and economy. Clinical trials confirmed multiple neurological symptoms due to COVID-19, ranging from headaches, insomnia to stroke, and encephalopathy. More studies are required to unravel the cellular and molecular mechanisms to find a cure for these neurological symptoms. Here, we investigate the effect of COVID-19 spike protein (S-protein) on the cerebrovasculature and cognitive functions in two mouse models that express humanized ACE-2 (h ACE2), a receptor essential for cellular infection and COVID-19 internalization. We hypothesize that COVID-19 S-protein causes cognitive dysfunction via the deterioration of cerebrovascular functions.

Methods: S-protein was either injected intravenously or directly into the hippocampus of K-18 (h ACE2 in epithelial cells) or global h-ACE2 knock-in (h ACE2 KI) mice or wild-type mice. Cognitive functions were assessed by Y-maze and Barnes maze. Cerebrovascular density was determined using confocal 3-D image reconstruction. Human brain microvascular endothelial cells (HBMVEC) were treated with S-protein and assessed for apoptosis and inflammatory markers using immunoblotting and RT-PCR. K-18 and h-ACE2 KI mice received intraocular injections of S-protein; retinas were evaluated for vascular cell death and inflammation.

Results: S-protein injections caused significant deterioration in memory and learning function of K-18 and h-ACE2 KI mice but not in the wild-type mice (P<0.05). S-protein significantly increased inflammatory mediators, cytokine production, and apoptosis in the brains and HBMVECs (P<0.05). Significant cerebrovascular rarefaction was detected only in K-18 and h-ACE2 KI mice compared to wild-type mice (P<0.05). Retinal vascular cell death and inflammation were significantly increased after S-protein injection. (P<0.05)

Conclusions: COVID-19 spike protein decreases cognitive function via increased endothelial cell inflammation, apoptosis, and cerebrovascular rarefaction. Humanized ACE2 animal models are excellent and reliable for investigating the neurological symptoms of COVID-19.

Abstract P729: Glp-1 Receptor Nitration Contributes to Brain Pericytes Dysfunction in Diabetes

Brain pericytes are unique, multi-functional mural cells located at the center of the NVU. Pericytes maintain the blood-brain barrier (BBB), promote vascular stability, and control the capillary blood flow. We have previously shown that diabetes alters the functions of the pericytes causing BBB damage and increased cerebrovascular pathological neovascularization. GLP-1 agonists, used in the management of diabetes, showed vascular protective effects. However, the underlying mechanisms are unclear. We hypothesis that GLP-1 receptor nitration contributes to the loss of pericytes functions in diabetes.

Methods: Expression of GLP-1R in pericytes was assessed in the brain of control and diabetic mice and human brain microvascular pericytes using IHC, RT-PCR, and Western blots. BBB was assessed using Western blot/IHC of Occludin, VEGF, and MMPs gelatinase. Vascular integrity was determined by measuring cerebrovascular neovascularization indices (vascular density, tortuosity, and branching density). GLP-1R nitration was determined by immunoprecipitation and slot blotting.

Results: In the present study, we provide novel evidence that the human brain pericytes express the GLP-1R (P<0.05). Moreover, diabetes increased GLP-1R expression in pericytes (P<0.05). Diabetes caused BBB dysfunction, loss of cerebrovascular integrity, and increased all pathological neovascularization indices (P<0.05). Diabetes increased nitration of GLP-1R. Treatment of pericytes with Exendin-4, a GLP-1 agonist, under diabetic conditions, decreased diabetes-induced inflammation, oxidative stress, and pericytes migration, which ameliorated the integrity of the BBB, and prevented the pathological neovascularization (P<0.05).

Conclusion: Our results provide novel evidence that pericytes express GLP-1R and that diabetes increased receptor expression and nitration. Treatment of pericytes with GLP-1R agonist exerts neurovascular protective effects, making it a promising strategy in preventing diabetes- mediated cerebrovascular microangiopathy.

Increased Ephrin-B2 expression in pericytes contributes to retinal vascular death in rodents

AIMS

Diabetes-induced retinal vascular cell death aggravates diabetic retinopathy (DR) to the proliferative stage and blindness. Pericytes play a crucial role in retinal capillaries survival, stability, and angiogenesis. Ephrin-B2 is a tyrosine kinase that regulates pericytes/endothelial cells communication during angiogenesis; yet, its role in DR is still unclear. We hypothesize that diabetes increases Ephrin-B2 signaling in pericytes, which contributes to inflammation and retinal vascular cell death.

METHODS

Selective inhibition of the Ephrin-B2 expression in the retinal pericytes was achieved using an intraocular injection of adeno-associated virus (AAV) with a specific pericyte promotor. Vascular death was determined by retinal trypsin digest. Pathological angiogenesis was assessed using the oxygen-induced retinopathy model in pericyte-Ephrin-B2 knockout mice, wild type, and wild type injected with AAV. Angiogenic properties, inflammatory, and apoptotic markers were measured in human retinal pericytes (HRP) grown under diabetic conditions.

KEY FINDING

Diabetes significantly increased the expression of Ephrin-B2, inflammatory, and apoptotic markers in the diabetic retinas and HRP. These effects were prevented by silencing Ephrin-B2 in HRP. Moreover, Ephrin-B2 silencing in retinal pericytes decreased pathological angiogenesis and acellular capillaries formation in diabetic retinas.

SIGNIFICANCE

Increased Ephrin-B2 expression in the pericytes contributed to diabetes-induced retinal inflammation and vascular death. These results identify pericytes-Ephrin-B2 as a therapeutic target for DR.

Modulating Expression of Thioredoxin Interacting Protein (TXNIP) Prevents Secondary Damage and Preserves Visual Function in a Mouse Model of Ischemia/Reperfusion

Retinal neurodegeneration, an early characteristic of several blinding diseases, triggers glial activation, resulting in inflammation, secondary damage and visual impairment. Treatments that aim only at neuroprotection have failed clinically. Here, we examine the impact of modulating thioredoxin interacting protein (TXNIP) to the inflammatory secondary damage and visual impairment in a model of ischemia/reperfusion (IR). Wild type (WT) and TXNIP knockout (TKO) mice underwent IR injury by increasing intraocular pressure for 40 min, followed by reperfusion. An additional group of WT mice received intravitreal TXNIP-antisense oligomers (ASO, 100 µg/2 µL) 2 days post IR injury. Activation of Müller glial cells, apoptosis and expression of inflammasome markers and visual function were assessed. IR injury triggered early TXNIP mRNA expression that persisted for 14 days and was localized within activated Müller cells in WT-IR, compared to sham controls. Exposure of Müller cells to hypoxia-reoxygenation injury triggered endoplasmic reticulum (ER) stress markers and inflammasome activation in WT cells, but not from TKO cells. Secondary damage was evident by the significant increase in the number of occluded acellular capillaries and visual impairment in IR-WT mice but not in IR-TKO. Intervention with TXNIP-ASO prevented ischemia-induced glial activation and neuro-vascular degeneration, and improved visual function compared to untreated WT. Targeting TXNIP expression may offer an effective approach in the prevention of secondary damage associated with retinal neurodegenerative diseases.

Modulation of the p75 neurotrophin receptor using LM11A-31 prevents diabetes-induced retinal vascular permeability in mice via inhibition of inflammation and the RhoA kinase pathway

AIMS/HYPOTHESIS

Breakdown of the inner blood-retinal barrier (BRB) is an early event in the pathogenesis of diabetic macular oedema, that eventually leads to vision loss. We have previously shown that diabetes causes an imbalance of nerve growth factor (NGF) isoforms resulting in accumulation of its precursor proNGF and upregulation of the p75 neurotrophin receptor (p75^NTR), with consequent increases in the activation of Ras homologue gene family, member A (RhoA). We also showed that genetic deletion of p75^NTR in diabetes preserved the BRB and prevented inflammatory mediators in retinas. This study aims to examine the therapeutic potential of LM11A-31, a small-molecule p75^NTR modulator and proNGF antagonist, in preventing diabetes-induced BRB breakdown. The study also examined the role of p75^NTR/RhoA downstream signalling in mediating cell permeability.

METHODS

Male C57BL/6 J mice were rendered diabetic using streptozotocin injection. After 2 weeks of diabetes, mice received oral gavage of LM11A-31 (50 mg kg^-1 day^-1) or saline (NaCl 154 mmol/l) for an additional 4 weeks. BRB breakdown was assessed by extravasation of BSA-AlexaFluor-488. Direct effects of proNGF were examined in human retinal endothelial (HRE) cells in the presence or absence of LM11A-31 or the Rho kinase inhibitor Y-27632.

RESULTS

Diabetes triggered BRB breakdown and caused significant increases in circulatory and retinal TNF-α and IL-1β levels. These effects coincided with significant decreases in retinal NGF and increases in vascular endothelial growth factor and proNGF expression, as well as activation of RhoA. Interventional modulation of p75^NTR activity through treatment of mouse models of diabetes with LM11A-31 significantly mitigated proNGF accumulation and preserved BRB integrity. In HRE cells, treatment with mutant proNGF (10 ng/ml) triggered increased cell permeability with marked reduction of expression of tight junction proteins, zona occludens-1 (ZO-1) and claudin-5, compared with control, independent of inflammatory mediators or cell death. Modulating p75^NTR significantly inhibited proNGF-mediated RhoA activation, occludin phosphorylation (at serine 490) and cell permeability. ProNGF induced redistribution of ZO-1 in the cell wall and formation of F-actin stress fibres; these effects were mitigated by LM11A-31.

CONCLUSIONS/INTERPRETATION

Targeting p75^NTR signalling using LM11A-31, an orally bioavailable receptor modulator, may offer an effective, safe and non-invasive therapeutic strategy for treating macular oedema, a major cause of blindness in diabetes.

Abstract 105: Obesity Induces Vascular Remodeling and Deteriorates Cognitive Function in Mice: Role of Pericytes

30 million Americans of the United States population have diabetes. Additional 90 million people in the pre-diabetic stage. Insulin resistance and obesity are the hallmarks of prediabetes. Understanding the effect of obesity on cerebrovasculature is crucial to identify novel therapies to prevent cerebrovascular complications of diabetes including vascular cognitive impairment and dementia. We hypothesize that pericyte dysfunction in prediabetes causes vascular remodeling and pathological neovascularization that leads to vascular cognitive impairment and dementia. Methods, male and female mice were fed regular or a high fat diet (HFD) for 12 weeks. Insulin resistance (IR) was confirmed with a glucose tolerance test. Neovascularization indices were measured (Vascular density, tortuosity, and branching density) to assess cerebral integrity. Pericyte count and basement membrane thickness (BMT) were determined in the cerebral cortex. Learning and memory functions were evaluated using Water maze, Y-maze and novel object recognition (NOR). Pericyte (PC) were grown in high glucose (HG) to mimic prediabetes. Pericytes MMP9 activity, TIMP1 and PDGFR beta internalization were measured. Results, male and female mice fed with HFD showed a significant increase in body weight and IR as indicated by impaired glucose tolerance. 3D reconstructed images of cerebral cortex vasculature showed that HFD significantly increases neovascularization indices (P<0.05, n=5). TEM studies showed an increase in cerebrovascular BMT in HFD mice that was associated with significantly decreased in PCs count and TIMP-1 expression in the cerebral cortex. HFD led to significant deterioration of cognitive memory function in Water maze, Y maze, and NOR. (P<0.05, n=5). MMP9 activity and internalization of PDGFR beta were increased in HG-treated PCs that were accompanied by a decrease in TIMP1 expression. (P<0.05, n=4). Conclusion, obesity-induced pericyte dysfunction is associated with pathological cerebral vessel remodeling and impaired cognitive function. These studies illustrate the crucial role of pericyte dysfunction in prediabetes and identify pericytes as a potential therapeutic target for the treatment of cognitive impairment in diabetes.

Inhibition of Ephrin-B2 in brain pericytes decreases cerebral pathological neovascularization in diabetic rats

We have previously shown that diabetes causes dysfunctional cerebral neovascularization that increases the risk for cerebrovascular disorders such as stroke and cognitive impairment. Pericytes (PCs) play a pivotal role in the angiogenic process through their interaction with the endothelial cells (EC). Yet, the role of PCs in dysfunctional cerebral neovascularization in diabetes is unclear. In the present study, we tested the hypothesis that the increased proangiogenic Ephrin-B2 signaling in PCs contributes to the dysfunctional cerebral neovascularization in diabetes. Type-II diabetes was induced by a combination of high fat diet and low dose streptozotocin injection in male Wistar rats. Selective in vivo Ephrin-B2 silencing in brain PCs was achieved using the stereotactic injection of adeno-associated virus (AAV) with NG2-promoter that expresses Ephrin-B2 shRNA. Neovascularization was assessed using vascular fluorescent dye stain. Novel object recognition (NOR) test was used to determine cognitive functions. Human brain microvascular pericytes HBMVPCs were grown in high glucose 25 mM and palmitate 200 uM (HG/Pal) to mimic diabetic conditions. Scratch migration and tube formation assays were conducted to evaluate PC/EC interaction and angiogenic functions in PC/EC co-culture. Diabetes increased the expression of Ephrin-B2 in the cerebrovasculature and pericytes. Concomitant increases in cerebral neovascularization parameters including vascular density, tortuosity and branching density in diabetic rats were accompanied by deterioration of cognitive function. Inhibition of Ephrin-B2 expression in PCs significantly restored cerebral vascularization and improved cognitive functions. HG/Pal increased PC/EC angiogenic properties in co-culture. Silencing Ephrin-B2 in PCs significantly reduced PC migration and PC/EC co-culture angiogenic properties. This study emphasizes the significant contribution of PCs to the pathological neovascularization in diabetes. Our findings introduce Ephrin-B2 signaling as a promising therapeutic target to improve cerebrovascular integrity in diabetes.

Impact of Metabolic Diseases on Cerebral Circulation: Structural and Functional Consequences

Metabolic diseases including obesity, insulin resistance, and diabetes have profound effects on cerebral circulation. These diseases not only affect the architecture of cerebral blood arteries causing adverse remodeling, pathological neovascularization, and vasoregression but also alter the physiology of blood vessels resulting in compromised myogenic reactivity, neurovascular uncoupling, and endothelial dysfunction. Coupled with the disruption of blood brain barrier (BBB) integrity, changes in blood flow and microbleeds into the brain rapidly occur. This overview is organized into sections describing cerebrovascular architecture, physiology, and BBB in these diseases. In each section, we review these properties starting with larger arteries moving into smaller vessels. Where information is available, we review in the order of obesity, insulin resistance, and diabetes. We also tried to include information on biological variables such as the sex of the animal models noted since most of the information summarized was obtained using male animals. © 2018 American Physiological Society. Compr Physiol 8:773-799, 2018.

Abstract 144: Inhibition of EphrinB2 Expression in Pericytes Decreases Cerebrovascular Pathological Neovascularization in Diabetes

We have previously shown that diabetes causes dysfunctional cerebral neovascularization that increases the risk for cerebrovascular disorders such as stroke and cognitive impairment. Pericytes (PC) play a pivotal role in the angiogenic process through interaction with endothelial cells (EC). Yet, the role of PCs in dysfunctional cerebral neovascularization in diabetes is unclear. In the present study, we tested the hypothesis that the increased proangiogenic EphrinB2 signaling in PCs contributes to the dysfunctional cerebral neovascularization in diabetes.

Methods: Type-II diabetes was induced in Wistar rats. Conditional reduction of EphrinB2 expression in rat brain PCs was achieved using stereotactic injection of AAV-virus with NG2-promoter that expresses EphrinB2 shRNA. Neovascularization was assessed using fluorescent space filling model. Novel object recognition (NOR) test was used to assess cognitive functions. Human brain microvascular PCs were grown in glucose 25 mM/palmitate 200 uM (HG/Pal) to mimic diabetic conditions. PC/EC co-culture was used to assess PC/EC interaction and angiogenic functions (scratch migration and tube formation).

Results: Diabetes increased expression of EphrinB2 in the cerebrovasculature (2.2-Fold*) and pericytes (1.4 fold*). Diabetes significantly increased cerebral vascularization (Vascular density 3.1 fold*, tortuosity 1.07 fold* and branching density 1.5 fold*) in Wistar rats that were accompanied by deterioration of cognitive function (40% reduction*). Inhibition of EphrinB2 expression in PC significantly restored cerebral vascularization indices back to normal and improved rat cognitive functions with higher D-2 scores in NOR compared to diabetic rats*. HG/Pal increased PC/EC angiogenic properties in coculture (2-fold*). Silencing Ephrin-B2 in HBMVP significantly reduced PC migration (35 %*) and PC/EC co-culture angiogenic properties. (*p<0.05).

Conclusion: Our findings emphasize the crucial role that PC plays in the pathological neovascularization in diabetes. EphrinB2 signaling is a promising therapeutic target to improve cerebrovascular integrity in diabetes. Yet, the molecular mechanism of the EphrinB2 signaling in PC/EC interaction is to be uncovered.

Enhanced VEGF signalling mediates cerebral neovascularisation via downregulation of guidance protein ROBO4 in a rat model of diabetes

AIMS/HYPOTHESIS

Diabetes promotes cerebral neovascularisation via increased vascular endothelial growth factor (VEGF) angiogenic signalling. Roundabout-4 (ROBO4) protein is an endogenous inhibitor of VEGF signalling that stabilises the vasculature. Yet, how diabetes affects ROBO4 function remains unknown. We hypothesised that increased VEGF signalling in diabetes decreases ROBO4 expression and function via binding of ROBO4 with VEGF-activated β3 integrin and that restoration of ROBO4 expression prevents/repairs cerebral neovascularisation in diabetes.

METHODS

ROBO4 protein expression in a rat model of type 2 diabetes (Goto-Kakizaki [GK] rats) was examined by western blotting and immunohistochemistry. ROBO4 was locally overexpressed in the brain and in primary brain microvascular endothelial cells (BMVECs). GK rats were treated with SKLB1002, a selective VEGF receptor-2 (VEGFR-2) antagonist. Cerebrovascular neovascularisation indices were determined using a FITC vascular space-filling model. Immunoprecipitation was used to determine ROBO4-β3 integrin interaction.

RESULTS

ROBO4 expression was significantly decreased in the cerebral vasculature as well as in BMVECs in diabetes (p < 0.05). Silencing Robo4 increased the angiogenic properties of control BMVECs (p < 0.05). In vivo and in vitro overexpression of ROBO4 inhibited VEGF-induced angiogenic signalling and increased vessel maturation. Inhibition of VEGF signalling using SKLB1002 increased ROBO4 expression (p < 0.05) and reduced neovascularisation indices (p < 0.05). Furthermore, SKLB1002 significantly decreased ROBO4-β3 integrin interaction in diabetes (p < 0.05).

CONCLUSIONS/INTERPRETATION

Our study identifies the restoration of ROBO4 and inhibition of VEGF signalling as treatment strategies for diabetes-induced cerebral neovascularisation.

High fat diet dysregulates microRNA-17-5p and triggers retinal inflammation: Role of endoplasmic-reticulum-stress

AIM

To elucidate how high diet-induced endoplasmic reticulum-stress upregulates thioredoxin interacting protein expression in Müller cells leading to retinal inflammation.

METHODS

Male C57Bl/J mice were fed either normal diet or 60% high fat diet for 4-8 wk. During the 4 wk study, mice received phenyl-butyric acid (PBA); endoplasmic reticulum-stress inhibitor; for 2 wk. Insulin resistance was assessed by oral glucose tolerance. Effects of palmitate-bovine serum albumin (BSA) (400 μmol/L) were examined in retinal Müller glial cell line and primary Müller cells isolated from wild type and thioredoxin interacting protein knock-out mice. Expression of thioredoxin interacting protein, endoplasmic reticulum-stress markers, miR-17-5p mRNA, as well as nucleotide-binding oligomerization domain-like receptor protein (NLRP3) and IL1β protein was determined.

RESULTS

High fat diet for 8 wk induced obesity and insulin resistance evident by increases in body weight and impaired glucose tolerance. By performing quantitative real-time polymerase chain reaction, we found that high fat diet triggered the expression of retinal endoplasmic reticulum-stress markers (P < 0.05). These effects were associated with increased thioredoxin interacting protein and decreased miR-17-5p expression, which were restored by inhibiting endoplasmic reticulum-stress with PBA (P < 0.05). In vitro, palmitate-BSA triggered endoplasmic reticulum-stress markers, which was accompanied with reduced miR-17-5p and induced thioredoxin interacting protein mRNA in retinal Müller glial cell line (P < 0.05). Palmitate upregulated NLRP3 and IL1β expression in primary Müller cells isolated from wild type. However, using primary Müller cells isolated from thioredoxin interacting protein knock-out mice abolished palmitate-mediated increase in NLRP3 and IL1β.

CONCLUSION

Our work suggests that targeting endoplasmic reticulum-stress or thioredoxin interacting protein are potential therapeutic strategies for early intervention of obesity-induced retinal inflammation.

Nox4 contributes to the hypoxia-mediated regulation of actin cytoskeleton in cerebrovascular smooth muscle

Ischemia/reperfusion and the resulting oxidative/nitrative stress impair cerebral myogenic tone via actin depolymerization. While it is known that NADPH oxidase (Nox) family is a major source of vascular oxidative stress; the extent and mechanisms by which Nox activation contributes to actin depolymerization, and equally important, the relative role of Nox isoforms in this response is not clear.

AIM

To determine the role of Nox4 in hypoxia-mediated actin depolymerization and myogenic-tone impairment in cerebral vascular smooth muscle.

MAIN METHODS

Control and Nox4 deficient (siRNA knock-down) human brain vascular smooth muscle cells (HBVSMC) were exposed to 30-min hypoxia/45-min reoxygenation. Nox2, Nox4, inducible and neuronal nitric oxide synthase (iNOS and nNOS) and nitrotyrosine levels as well as F:G actin were determined. Myogenic-tone was measured using pressurized arteriography in middle cerebral artery isolated from rats subjected to sham, 30-min ischemia/45-min reperfusion or ex-vivo oxygen glucose deprivation in the presence and absence of Nox inhibitors.

RESULTS

Nox4 and iNOS expression were significantly upregulated following hypoxia or ischemia/reperfusion. Hypoxia augmented nitrotyrosine levels while reducing F actin. These effects were nullified by inhibiting nitration with epicatechin or pharmacological or molecular inhibition of Nox4. Ischemia/reperfusion impaired myogenic-tone, which was restored by the selective inhibition of Nox4.

CONCLUSION

Nox4 activation in VSMCs contributes to actin depolymerization after hypoxia, which could be the underlying mechanism for myogenic-tone impairment following ischemia/reperfusion.

Linagliptin treatment improves cerebrovascular function and remodeling and restores reduced cerebral perfusion in Type 2 diabetes

The antihyperglycemic agent linagliptin, a dipeptidyl peptidase-4 (DPP-IV) inhibitor, has been shown to reduce inflammation and improve endothelial cell function. In this study, we hypothesized that DPP-IV inhibition with linagliptin would improve impaired cerebral perfusion in diabetic rats, as well as improve insulin-induced cerebrovascular relaxation and reverse pathological cerebrovascular remodeling. We further postulated that these changes would lead to a subsequent improvement of cognitive function. Male Type-2 diabetic and nondiabetic Goto-Kakizaki rats were treated with linagliptin for 4 wk, and blood glucose and DPP-IV plasma levels were assessed. Cerebral perfusion was assessed after treatment using laser-Doppler imaging, and dose response to insulin (10(-13) M-10(-6) M) in middle cerebral arteries was tested on a pressurized arteriograph. The impact of DPP-IV inhibition on diabetic cerebrovascular remodeling was assessed over a physiologically relevant pressure range, and changes in short-term hippocampus-dependent learning were observed using a novel object recognition test. Linagliptin lowered DPP-IV activity but did not change blood glucose or insulin levels in diabetes. Insulin-mediated vascular relaxation and cerebral perfusion were improved in the diabetic rats with linagliptin treatment. Indices of diabetic vascular remodeling, such as increased cross-sectional area, media thickness, and wall-to-lumen ratio, were also ameliorated; however, improvements in short-term hippocampal-dependent learning were not observed. The present study provides evidence that linagliptin treatment improves cerebrovascular dysfunction and remodeling in a Type 2 model of diabetes independent of glycemic control. This has important implications in diabetic patients who are predisposed to the development of cerebrovascular complications, such as stroke and cognitive impairment.

Molecular mechanisms of diabetic retinopathy: potential therapeutic targets

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults in United States. Research indicates an association between oxidative stress and the development of diabetes complications. However, clinical trials with general antioxidants have failed to prove effective in diabetic patients. Mounting evidence from experimental studies that continue to elucidate the damaging effects of oxidative stress and inflammation in both vascular and neural retina suggest its critical role in the pathogenesis of DR. This review will outline the current management of DR as well as present potential experimental therapeutic interventions, focusing on molecules that link oxidative stress to inflammation to provide potential therapeutic targets for treatment or prevention of DR. Understanding the biochemical changes and the molecular events under diabetic conditions could provide new effective therapeutic tools to combat the disease.

Metformin treatment in the period after stroke prevents nitrative stress and restores angiogenic signaling in the brain in diabetes

Diabetes impedes vascular repair and causes vasoregression in the brain after stroke, but mechanisms underlying this response are still unclear. We hypothesized that excess peroxynitrite formation in diabetic ischemia/reperfusion (I/R) injury inactivates the p85 subunit of phosphoinositide 3-kinase (PI3K) by nitration and diverts the PI3K-Akt survival signal to the p38-mitogen-activated protein kinase apoptosis pathway. Nitrotyrosine (NY), Akt and p38 activity, p85 nitration, and caspase-3 cleavage were measured in brains from control, diabetic (GK), or metformin-treated GK rats subjected to sham or stroke surgery and in brain microvascular endothelial cells (BMVECs) from Wistar and GK rats subjected to hypoxia/reoxygenation injury. GK rat brains showed increased NY, caspase-3 cleavage, and p38 activation and decreased Akt activation. Metformin attenuated stroke-induced nitrative signaling in GK rats. GK rat BMVECs showed increased basal nitrative stress compared with controls. A second hit by hypoxia/reoxygenation injury dramatically increased the nitration of p85 and activation of p38 but decreased Akt. These effects were associated with impairment of angiogenic response and were restored by treatment with the peroxynitrite scavenger 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride or the nitration inhibitor epicatechin. Our results provide evidence that I/R-induced peroxynitrite inhibits survival, induces apoptosis, and promotes peroxynitrite as a novel therapeutic target for the improvement of reparative angiogenesis after stroke in diabetes.

Abstract 220: Contralateral Myogenic Dysfunction Contributes to Stroke Outcomes after Acute Hyperglycemic Stroke

Background: Admission hyperglycemia (HG) amplifies vascular injury and neurological deficit in acute ischemic stroke but the mechanism remains controversial. We recently reported that copper/zinc-superoxide dismutase (SOD1) overexpression preserves the myogenic tone of ischemic arteries, achieving neurovascular protection after ischemia/reperfusion (I/R) with or without HG. Experimental studies showed that I/R impairs myogenic response in ischemic and contralateral hemispheres. However, the impact of HG on contralateral vascular reactivity and its role in stroke outcomes still unexplored. Hypothesis: Contralateral myogenic dysfunction worsens stroke outcomes after acute hyperglycemic stroke. Methods: SOD1 adenovirus or an empty vector was stereotaxicly injected in the contralateral hemisphere of control Wistar rats. 2-3 weeks after injection, acute hyperglycemic stroke was induced by injecting saline or 40% glucose solution 10 min before 30 min ischemia/45 min or 24 hr reperfusion. Myogenic tone and neurovascular outcomes were determined. Results: HG exacerbated loss of myogenic tone in contralateral side only (p<0.0001), which was associated with infarct size expansion, increased edema (p<0.05) and more pronounced neurological deficit (p<0.01). Contralateral SOD1 overexpression restored myogenic reactivity in contralateral side only. Cerebral blood flow after reperfusion was increased in both sides (p<0.01), which was accompanied with better neurovascular outcomes (p<0.01). Conclusion: Our results showed that SOD1 overexpression nullified the detrimental effects of HG on contralateral myogenic dysfunction and stroke outcomes, and that contralateral hemisphere may be a novel target for the management of acute hyperglycemic stroke.

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

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.

Cerebrovasculoprotective effects of azilsartan medoxomil in diabetes

We have shown that Goto-Kakizaki (GK) rats, a lean model of type 2 diabetes, develop significant cerebrovascular remodeling by the age of 18 weeks, which is characterized by increased media thickness and matrix deposition. Although early glycemic control prevents diabetes-mediated remodeling of the cerebrovasculature, whether the remodeling can be reversed is unknown. Given that angiotensin II type 1 receptor blockers reverse pathologic vascular remodeling and function independent of changes in blood pressure in other vascular beds, we hypothesized that azilsartan medoxomil, a new angiotensin II type 1 receptor blocker, is vasculoprotective by preventing and reversing cerebrovascular remodeling in diabetes. Control Wistar and diabetic GK rats (n = 6-8 per group) were treated with vehicle (water) or azilsartan medoxomil (3 mg/kg/d) from the age of 14 to 18 or 18 to 22 weeks before or after vascular remodeling is established, respectively. Blood glucose and blood pressure were monitored and middle cerebral artery structure and function were evaluated using pressurized arteriography. Blood glucose was higher in GK rats compared with Wistar rats. Azilsartan treatment lowered blood glucose in diabetic animals with no effect on blood pressure. Diabetic animals exhibited lower myogenic tone, increased wall thickness, and cross-sectional area compared with control group animals, which were corrected by azilsartan treatment when started at the onset of diabetes or later after vascular remodeling is established. Azilsartan medoxomil offers preventive and therapeutic vasculoprotection in diabetes-induced cerebrovascular remodeling and myogenic dysfunction and this is independent of blood pressure.

Abstract W MP77: The Role of Ischemia/Reperfusion Generated Nitrative Stress on VEGF Angiogenic Signaling in Diabetic rats

Diabetes worsens the outcome and impairs recovery after stroke. We have previously shown that diabetes caused a nitration-dependent dysfunctional cerebral neovascularization via increased vascular endothelial growth factor (VEGF) signalling. Our recent study showed that ischemia/reperfusion (I/R) impaired vascular repair in the post-stroke period in diabetes. Yet, the molecular mechanism is unclear. Our present hypothesis is that I/R-mediated excess peroxynitrite formation impairs VEGF survival and angiogenic signal in a nitration-dependent manner.

Methods: Acute ischemic stroke was induced via 90 min middle cerebral artery occlusion in Wistar (Wis) and diabetic Goto-Kakizaki rats (GK). 14 days later brain sections were examined for peroxynitrite generation (nitrotyrosine), survival markers (Akt and P38 activation), and apoptosis markers (caspase-3 and cleaved PARP). Brain micro-vascular endothelial cells (BMVEC) were isolated from Wis and GK rats and subjected to 6 hr hypoxia (0.2% oxygen) followed by 18 h normoxia. Nitrotyrosine, P85 nitration, Akt and P38 activity and caspase-3 cleavage were determined. VEGF signal was assessed via cell proliferation, tube formation and cell migration assay.

Results: There was increased basal tyrosine nitration in diabetes. I/R increased nitrotyrosine in control (*2-fold) and diabetic (*3-fold) rats (*p<0.05). This increase was associated with decreased survival signal (20%, *60%) and increased apoptic signal (1.5-fold and *6-fold in Wis and GK, respectively, *p<0.05). In parallel, BMVEC isolated from GK rats showed increased nitrative stress compared to controls (*p<0.05). A second hit by hypoxia/reoxygenation dramatically increased the nitration of P85 subunit of PI3kinase* and activation of p38 MAPK* while decreased Akt activation* (*p<0.05). These effects were associated with impairment of VEGF-induced migration* and restored by treatments with peroxynitrite scavenger FeTPPS* (5 uM) or nitration inhibitor Epicatechin* (200uM) (*p<0.05).

Conclusion: Our results demonstrate that I/R diverts prosurvial/angiogenic effects of VEGF to a proapoptotic pathway and suggest peroxynitrite as a novel therapeutic target for improvement of reparative angiogenesis after stroke in diabetes.

Abstract W P358: SOD overexpression Accounts for the Neurovascular Protection in Rats Following Ischemic Stroke

Acute hyperglycemic stroke (AHS) is associated with poor stroke outcomes and functional recovery. We recently showed that myogenic response; the ability of blood vessels to maintain adequate blood flow despite changes in pressure; was impaired after AHS. Experimental studies showed that acute elevation of blood glucose at stroke onset enhances oxidative stress that impairs effective reperfusion. Copper/zinc-superoxide dismutase (SOD1), an antioxidant enzyme that catalyzes the dismutation of superoxide into oxygen and hydrogen peroxide, has been shown to be highly protective against ischemia/reperfusion injury (IRI). Yet, the mechanism by which SOD1 improves stroke outcomes is still unresolved.

Hypothesis: SOD1 overexpression improves cerebral myogenic behavior leading to neurovascular protection after AHS

Methods: Wild-type Sprague Dawley (SD) and human SOD1 transgenic rats (n=6-8) were subjected to 30 min middle cerebral artery occlusion (MCAO)/45 min or 24 hr reperfusion. Hyperglycemia was induced by intraperitoneal injection of 40 % glucose solution 10 min before procedure. Myogenic tone of isolated MCAs, infarct size, edema and neurological deficits were determined.

Results: IRI impaired myogenic response of MCAs isolated from SD rats compared to sham (***p<0.001). Normoglycemic and hyperglycemic SOD1 rats maintained a well developed myogenic response after IRI. Infarct size and edema were significantly reduced in the SOD1 transgenic rats compared to SD rats (**p<0.01). SOD1 overexpression significantly improved beam walk score and grip strength deficit compared to SD rats (*p<0.05). Hyperglycemic SOD1 transgenic rats showed smaller infarct size and edema (**p<0.01) and experienced improved neurological behavior (*p<0.05) compared to hyperglycemic SD rats.

Conclusions: We provide evidence that SOD1 overexpression preserves the myogenic behavior of MCAs achieving neurovascular protection in conditions associated with poor stroke outcomes. Further studies are required to unravel the exact mechanism by which SOD exerts its beneficial role on vascular reactivity, and to identify new therapeutic targets for stroke management.

Abstract T P207: Matrix Metalloproteinase 3 (MMP3) Exacerbates the Hemorrhagic Transformation in Hyperglycemic Stroke

Acute hyperglycemia (HG) worsens stroke outcomes and increases the risk of cerebral hemorrhage especially with the co-administration of tissue plasminogen activator (tPA). MMP3 mediates tPA-induced hemorrhagic transformation (HT) after stroke. However, the role of MMP3 in hyperglycemic stroke is unknown. The working hypothesis of the current study is that HG upregulates MMP3 activity and worsens vascular injury after stroke and this response is independent of the method of reperfusion.

Methods: Control and mildly HG rats (160-200 mg/dl, achieved by 30% glucose injection (i.p.) 15 min prior to surgery, n=7-9/group) were subjected to either 90 min middle cerebral artery (MCA) suture occlusion and 22.5 h reperfusion, or to humanized thromboembolic stroke. At 24 h, neurological deficit, infarct size, edema, HT occurrence rate (HT index) and tissue hemoglobin (Hb) were measured. MMP3 activity in isolated cerebral microvasculature and/or brain homogenates was quantified by FRET assay. In addition, MMP-3 expression was assessed in brain microvascular endothelial cells (BVEC) subjected to 90 min hypoxia followed by 22.5 h reoxygenation.

Results: While HG did not increase infarct size when compared to control animals, this mild elevation in blood glucose (BG) significantly increased vascular injury indicated by HT index, edema and Hb content in ischemic hemispheres . This was associated with a significant increase in MMP3 activity in both cerebral micro-vasculature and brain homogenates (Table, *p<0.05 vs control). In vitro, the combination of hypoxia and HG has increased MMP3 expression more than each alone (*p<0.05 vs control).

Conclusion: Even mild elevations in BG increased MMP3 activity and augmented vascular injury following ischemic stroke. Our findings suggest that MMP3 might be playing an important role in worsening the outcomes in hyperglycemic stroke and MMP3 inhibition may be a potential therapeutic target.

Dual endothelin receptor antagonism with bosentan reverses established vascular remodeling and dysfunctional angiogenesis in diabetic rats: relevance to glycemic control

AIMS

We have shown that diabetes causes cerebrovascular remodeling in part by the activation of the endothelin (ET-1) system in a glucose-dependent manner. We also reported increased yet dysfunctional cerebral angiogenesis in diabetes. Here, we tested the hypothesis that dual ET-1 receptor antagonism or glycemic control can reverse already established diabetes-induced vascular remodeling and neovascularization.

MAIN METHODS

18-week non-obese type-2 diabetic Goto-Kakizaki (GK) were treated with vehicle, metformin (300 mg/kg/day) or bosentan (100 mg/kg/day) for 4 weeks by oral gavage and compared to 10 and 18-weeks GK rats. Isolated middle cerebral artery (MCA) lumen diameter (LD), media thickness (MT), media:lumen (M:L) ratio, and cross-sectional area (CSA) were measured using pressurized arteriograph. Assessment of remodeling and angiogenesis in the brain parenchyma was achieved by three-dimensional reconstruction of fluorescently labeled images of the vasculature acquired by confocal microscopy, and measurement of neovascularization indices including vascular volume and surface area, branch density and tortuosity.

KEY FINDINGS

MCA remodeling (increased M:L ratio and CSA, but decreased LD) occurred by 18 weeks and did not progress by 22 weeks in diabetic GK rats. Metformin and bosentan partially corrected large artery remodeling. Both treatments significantly reduced all indices of neovascularization compared to untreated diabetic rats.

SIGNIFICANCE

Glycemic control or ET-1 antagonism can partially reverse diabetes-induced cerebrovascular remodeling and neovascularization. These results strongly suggest that either approach offers a therapeutic benefit and combination treatments need to be tested.

Late dual endothelin receptor blockade with bosentan restores impaired cerebrovascular function in diabetes

AIMS

Up-regulation of the endothelin (ET) system in type-2 diabetes increases contraction and decreases relaxation in basilar artery. We showed that 1) ET-receptor antagonism prevents diabetes-mediated cerebrovascular dysfunction; and 2) glycemic control prevents activation of the ET-system in diabetes. Here, our goal is to determine whether and to what extent glycemic control or ET-receptor antagonism reverses established cerebrovascular dysfunction in diabetes.

MAIN METHODS

Non-obese type-2 diabetic Goto-Kakizaki rats were administered either vehicle, metformin (300 mg/kg/day) or dual ET-receptor antagonist bosentan (100mg/kg) for 4-weeks starting at 18-weeks after established cerebrovascular dysfunction (n=5-6/group). Control group included vehicle-treated aged-matched Wistar rats. Blood glucose and pressure were monitored weekly. At termination, basilar arteries were collected and cumulative dose-response curves to ET-1 (0.1-500 nM), 5-HT (1-1000 nM) and acetylcholine (Ach, 0.1 nM-5 μM) were studied by wire myograph. Middle cerebral artery (MCA) myogenic reactivity and tone were measured using pressurized arteriograph.

KEY FINDINGS

There was no difference in ET-1 and 5-HT-mediated constrictions. Endothelium-dependent relaxation was impaired in diabetes. Bosentan improved sensitivity to Ach as well as the maximum relaxation. Myogenic-tone is decreased over the course of the disease. Both treatments improved the ability of MCAs to develop tone at 80 mm Hg and only bosentan improved the tone at higher pressures.

SIGNIFICANCE

These results suggest that contractile response is not affected by glycemic control or ET-receptor antagonism. Meanwhile, dual ET-receptor blockade is effective in partially improving endothelium-dependent relaxation and myogenic response in a blood pressure-independent manner even after established cerebrovascular dysfunction and offers therapeutic potential.

Protein nitration impairs the myogenic tone of rat middle cerebral arteries in both ischemic and nonischemic hemispheres after ischemic stroke

The myogenic response is crucial for maintaining vascular resistance to achieve constant perfusion during pressure fluctuations. Reduced cerebral blood flow has been reported in ischemic and nonischemic hemispheres after stroke. Ischemia-reperfusion injury and the resulting oxidative stress impair myogenic responses in the ischemic hemisphere. Yet, the mechanism by which ischemia-reperfusion affects the nonischemic side is still undetermined. The goal of the present study was to determine the effect of ischemia-reperfusion injury on the myogenic reactivity of cerebral vessels from both hemispheres and whether protein nitration due to excess peroxynitrite production is the underlying mechanism of loss of tone. Male Wistar rats were subjected to sham operation or 30-min middle cerebral artery occlusion/45-min reperfusion. Rats were administered saline, the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron (III), or the nitration inhibitor epicatechin at reperfusion. Middle cerebral arteries isolated from another set of control rats were exposed to ex vivo oxygen-glucose deprivation with and without glycoprotein 91 tat (NADPH oxidase inhibitor) or N(ω)-nitro-l-arginine methyl ester. Myogenic tone and nitrotyrosine levels were determined. Ischemia-reperfusion injury impaired the myogenic tone of vessels in both hemispheres compared with the sham group (P < 0.001). Vessels exposed to ex vivo oxygen-glucose deprivation experienced a similar loss of myogenic tone. Inhibition of peroxynitrite parent radicals significantly improved the myogenic tone. Peroxynitrite scavenging or inhibition of nitration improved the myogenic tone of vessels from ischemic (P < 0.001 and P < 0.05, respectively) and nonischemic (P < 0.01 and P < 0.05, respectively) hemispheres. Nitration was significantly increased in both hemispheres versus the sham group and was normalized with epicatechin treatment. In conclusion, ischemia-reperfusion injury impairs vessel reactivity in both hemispheres via nitration. We suggest that sham operation rather than the nonischemic side should be used as a control in preclinical stroke studies.

Abstract TP256: Targets of Vascular Protection in Acute Ischemic Stroke Differ in Type 2 Diabetes

Background: Hemorrhagic transformation (HT) is an important complication of acute ischemic stroke particularly in diabetic patients receiving thrombolytic treatment with tissue plasminogen activator (tPA), the only approved drug for the treatment of AIS. The objective of the current study was to determine the effects of acute inhibition of the mediators of HT (i.e., NFkB, peroxynitrite, and matrix metalloproteinases) on vascular injury and functional outcome in a diabetic model of cerebral ischemia.

Methods: Ischemia was induced by middle cerebral artery occlusion in control and type 2 diabetic Goto-Kakizaki rats. Treatment groups received a single dose of peroxynitrite decomposition catalyst FeTPPs, non-specific NFkB inhibitor curcumin, or broad-spectrum matrix metalloproteinase (MMP) inhibitor minocycline at reperfusion. Post-stroke infarct volume, edema, hemorrhage, neurological deficits, and MMP-9 activity were evaluated.

Results: All therapies reduced MMP-9 and HT in diabetic groups. In addition, acute curcumin and minocycline therapy reduced edema in these animals. Improved neurological function was observed in varying degrees with treatment as indicated by beam-walk performance, modified Bederson scores and grip strength; however, infarct size was similar to untreated diabetic animals. In control animals, all treatments reduced MMP-9 activity yet bleeding was not improved. Neuroprotection was only conferred by curcumin and minocycline.

Conclusion: Uncovering underlying mechanisms contributing to the success of acute therapy in diabetes will advance tailored stroke therapies. Table 1 . Summary of experimental stroke data. SE are shown in parentheses. a p<0.05 vs. untreated control, b p<0.05 vs. untreated, c p<0.05 vs. untreated diabetes, d p<0.001 vs. untreated control, e p<0.01 vs. untreated control, * All values in this data set were below detection.

Targets of vascular protection in acute ischemic stroke differ in type 2 diabetes

Hemorrhagic transformation is an important complication of acute ischemic stroke, particularly in diabetic patients receiving thrombolytic treatment with tissue plasminogen activator, the only approved drug for the treatment of acute ischemic stroke. The objective of the present study was to determine the effects of acute manipulation of potential targets for vascular protection [i.e., NF-κB, peroxynitrite, and matrix metalloproteinases (MMPs)] on vascular injury and functional outcome in a diabetic model of cerebral ischemia. Ischemia was induced by middle cerebral artery occlusion in control and type 2 diabetic Goto-Kakizaki rats. Treatment groups received a single dose of the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron (III), the nonspecific NF-κB inhibitor curcumin, or the broad-spectrum MMP inhibitor minocycline at reperfusion. Poststroke infarct volume, edema, hemorrhage, neurological deficits, and MMP-9 activity were evaluated. All acute treatments reduced MMP-9 and hemorrhagic transformation in diabetic groups. In addition, acute curcumin and minocycline therapy reduced edema in these animals. Improved neurological function was observed in varying degrees with treatment, as indicated by beam-walk performance, modified Bederson scores, and grip strength; however, infarct size was similar to untreated diabetic animals. In control animals, all treatments reduced MMP-9 activity, yet bleeding was not improved. Neuroprotection was only conferred by curcumin and minocycline. Uncovering the underlying mechanisms contributing to the success of acute therapy in diabetes will advance tailored stroke therapies.

Cerebral myogenic reactivity and blood flow in type 2 diabetic rats: role of peroxynitrite in hypoxia-mediated loss of myogenic tone

Dysregulation of cerebral vascular function and, ultimately, cerebral blood flow (CBF) may contribute to complications such as stroke and cognitive decline in diabetes. We hypothesized that 1) diabetes-mediated neurovascular and myogenic dysfunction impairs CBF and 2) under hypoxic conditions, cerebral vessels from diabetic rats lose myogenic properties because of peroxynitrite (ONOO(-))-mediated nitration of vascular smooth muscle (VSM) actin. Functional hyperemia, the ability of blood vessels to dilate upon neuronal stimulation, and myogenic tone of isolated middle cerebral arteries (MCAs) were assessed as indices of neurovascular and myogenic function, respectively, in 10- to 12-week control and type 2 diabetic Goto-Kakizaki rats. In addition, myogenic behavior of MCAs, nitrotyrosine (NY) levels, and VSM actin content were measured under normoxic and hypoxic [oxygen glucose deprivation (OGD)] conditions with and without the ONOO(-) decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl) prophyrinato iron (III), chloride (FeTPPs). The percentage of myogenic tone was higher in diabetes, and forced dilation occurred at higher pressures. Functional hyperemia was impaired. Consistent with these findings, baseline CBF was lower in diabetes. OGD reduced the percentage of myogenic tone in both groups, and FeTPPs restored it only in diabetes. OGD increased VSM NY in both groups, and although FeTPPs restored basal levels, it did not correct the reduced filamentous/globular (F/G) actin ratio. Acute alterations in VSM ONOO(-) levels may contribute to hypoxic myogenic dysfunction, but this cannot be solely explained by the decreased F/G actin ratio due to actin nitration, and mechanisms may differ between control and diabetic animals. Our findings also demonstrate that diabetes alters the ability of cerebral vessels to regulate CBF under basal and hypoxic conditions.

The effect of endothelin receptor A antagonism on basilar artery endothelium-dependent relaxation after ischemic stroke

AIMS

Endothelin (ET) receptor A antagonism decreases neuronal damage in experimental models of stroke. Since large arteries like basilar artery contribute significantly to total cerebrovascular resistance and are major determinants of microvascular pressure, dysregulation of basilar artery function may worsen stroke injury. ET-1 is involved in the regulation of basilar constriction. However, whether stroke influences vasoreactivity of basilar artery and to what extent ET-1 contributes to basilar vascular dysfunction after stroke remained unknown. The goal of this study was to test the hypothesis that ET-1 impairs basilar artery vasorelaxation after ischemia/reperfusion (I/R) injury via activation of ET(A) receptor.

MAIN METHODS

Male Wistar rats were subjected to 3h middle cerebral artery occlusion (MCAO) and 21 h reperfusion. One group received ET(A) receptor antagonist atrasentan (5 mg/kg, i.p.) at reperfusion. At 24h, basilar arteries were isolated from control non-stroked, stroked and stroked+atrasentan-treated animals for vascular reactivity measurements using pressurized arteriograph.

KEY FINDINGS

Acetylcholine (Ach)-induced maximum relaxation (R(max)) was decreased in stroked animals as compared to non-stroked group and ET(A) antagonism partially restored it. There was also a trend for decreased EC(50) value for the antagonist treatment group indicating improved Ach sensitivity.

SIGNIFICANCE

These findings suggest that I/R not only affects vessels distal to the occlusion but also impairs relaxation of proximal large vessels. ET-1-mediated basilar artery dysfunction may contribute to neurovascular damage after stroke and early restoration of vascular function by ET receptor antagonism after I/R injury may offer a therapeutic strategy.

Abstract 2487: Ischemia/Reperfusion Injury Impairs Myogenic Tone of Cerebral Vessels in both Ischemic and Nonischemic Hemispheres: Differential Role of Oxidative Stress

Cerebrovascular autoregulation and reactivity are critical to maintain constant perfusion during ischemic brain injury. It is known that ischemia/ reperfusion (I/R) injury and resulting oxidative stress impair vessel reactivity in ischemic hemisphere. Yet the behavior of vessels in nonischemic hemisphere is still unexplored.

Hypothesis: I/R injury impairs myogenic tone of vessels in both ischemic and nonischemic hemispheres via increased peroxynitrite (ONOO - ) generation.

Methods: Middle cerebral arteries (MCA) isolated from age matched male Wistar rats (n=6) subjected to 30 min MCA occlusion (MCAO)/45 min reperfusion, or MCAO followed by treatment with ONOO - scavenger FeTPPs (20mg/kg) at reperfusion were pressurized in arteriograph chamber. In another set of animals, MCA isolated from control Wistar rats were exposed to ex vivo oxygen-glucose deprivation (OGD) then their myogenic tones across the pressure range were determined.

Results: I/R injury impaired myogenic tone of vessels in both ischemic and nonischemic sides albeit to a different degree. Interestingly FeTPPs restored myogenic tone of vessels from ischemic side only ( Table ). Vessels exposed to ex vivo and in vivo hypoxia experienced loss of myogenic tone. The reduction of myogenic tone % by OGD is similar to I/R injury.

Conclusion: Our ex vivo model of hypoxia is a valuable method to assess the ischemic insult on vessel reactivity. Increased ONOO - production is one of the underlying mechanisms of loss of tone under I/R injury in ischemic hemisphere, but the impairment of myogenic tone in nonischemic hemisphere involves other mechanisms. Understanding how I/R alters myogenic tone and ultimately cerebral perfusion in both ischemic and nonischemic hemispheres is vital in improving current preventive and therapeutic strategies for acute stroke. + p<0.001, * p< 0.05 vs Sham, # p<0.001 vs ischemic MCA , ** p<0.01 vs nonischemic MCA