Kazuo Washida

Nonhypotensive Dose of Telmisartan Attenuates Cognitive Impairment Partially Due to Peroxisome Proliferator-Activated Receptor-γ Activation in Mice With Chronic Cerebral Hypoperfusion

Background and Purpose— The effect of telmisartan, an angiotensin II Type 1 receptor blocker with peroxisome proliferator-activated receptor-&ggr;-modulating activity, was investigated against spatial working memory disturbances in mice subjected to chronic cerebral hypoperfusion. Methods— Adult C57BL/6J male mice were subjected to bilateral common carotid artery stenosis using external microcoils. Mice received a daily oral administration of low-dose telmisartan (1 mg/kg per day), high-dose telmisartan (10 mg/kg per day), or vehicle with or without peroxisome proliferator-activated receptor-&ggr; antagonist GW9662 (1 mg/kg per day) for all treatments for 30 days after bilateral common carotid artery stenosis. Cerebral mRNA expression of monocyte chemoattractant protein-1 and tumor necrosis factor-&agr; was measured 30 days after bilateral common carotid artery stenosis, and postmortem brains were analyzed for demyelinating change with Klüver-Barrera staining and immunostained for glial, oxidative stress, and vascular endothelial cell markers. Spatial working memory was assessed by the Y-maze test. Results— Mean systolic blood pressure and cerebral blood flow did not decrease with low-dose telmisartan but significantly decreased with high-dose telmisartan. Low-dose telmisartan significantly attenuated, but high-dose telmisartan provoked, spatial working memory impairment with glial activation, oligodendrocyte loss, and demyelinating change in the white matter. Such positive effects of low-dose telmisartan were partially offset by cotreatment with GW9662. Consistent with this, low-dose telmisartan reduced the degree of oxidative stress of vascular endothelial cells and the mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-&agr; compared with vehicle. Conclusions— Anti-inflammatory and antioxidative effects of telmisartan that were exerted in part by peroxisome proliferator-activated receptor-&ggr; activation, but not its blood pressure-lowering effect, have protective roles against cognitive impairment and white matter damage after chronic cerebral hypoperfusion.

Angiogenic and Vasoprotective Effects of Adrenomedullin on Prevention of Cognitive Decline After Chronic Cerebral Hypoperfusion in Mice

Background and Purpose— Although subcortical vascular dementia, the major subtype of vascular dementia, is caused by a disruption in white matter integrity after cerebrovascular insufficiency, no therapy has been discovered that will restore cerebral perfusion or functional cerebral vessels. Because adrenomedullin (AM) has been shown to be angiogenic and vasoprotective, the purpose of the study was to investigate whether AM may be used as a putative treatment for subcortical vascular dementia. Methods— A model of subcortical vascular dementia was reproduced in mice by placing microcoils bilaterally on the common carotid arteries. Using mice overexpressing circulating AM, we assessed the effect of AM on cerebral perfusion, cerebral angioarchitecture, oxidative stress, white matter change, cognitive function, and brain levels of cAMP, vascular endothelial growth factor, and basic fibroblast growth factor. Results— After bilateral common carotid artery stenosis, mice overexpressing circulating AM showed significantly faster cerebral perfusion recovery due to substantial growth of the capillaries, the circle of Willis, and the leptomeningeal anastomoses and reduced oxidative damage in vascular endothelial cells compared with wild-type mice. Vascular changes were preceded by upregulation of cAMP, vascular endothelial growth factor, and basic fibroblast growth factor. White matter damage and working memory deficits induced by bilateral common carotid artery stenosis were subsequently restored in mice overexpressing circulating AM. Conclusions— These data indicate that AM promotes arteriogenesis and angiogenesis, inhibits oxidative stress, preserves white matter integrity, and prevents cognitive decline after chronic cerebral hypoperfusion. Thus, AM may serve as a strategy to tackle subcortical vascular dementia.

Selective white matter abnormalities in a novel rat model of vascular dementia.

Rats subjected to bilateral common carotid artery (CCA) occlusion or 2-vessel occlusion (2VO) have been used as animal models of subcortical ischemic vascular dementia. However, this model possesses an inherent limitation in that cerebral blood flow (CBF) drops too sharply and substantially after ligation of CCAs. To circumvent such hypoxic-ischemic conditions, we tested implantation of the ameroid constrictor device on bilateral CCAs of male Wistar-Kyoto rats and more precisely replicated chronic cerebral hypoperfusion by gradual narrowing of the CCAs (2-vessel gradual occlusion; 2VGO). The acute cerebral blood flow reduction and resultant inflammatory responses observed in the 2VO rats were eliminated in the 2VGO rats. Thus, chronic cerebral hypoperfusion was segregated, and induced selective white matter changes with relatively preserved neurovascular coupling and substantially less metabolic and histological derangements in the gray matter including the hippocampus. This led to significant spatial working memory impairment of a magnitude similar to the 2VO rats at 28 days postoperation. The 2VGO model may more closely mimic cognitive impairment subsequent to selective white matter damage.

The Influence of Chronic Cerebral Hypoperfusion on Cognitive Function and Amyloid β Metabolism in APP Overexpressing Mice

Background and Purpose Cognitive impairment resulting from cerebrovascular insufficiency has been termed vascular cognitive impairment, and is generally accepted to be distinct from Alzheimers disease resulting from a neurodegenerative process. However, it is clear that this simple dichotomy may need revision in light of the apparent occurrence of several shared features between Alzheimers disease and vascular cognitive impairment. Nevertheless, it still remains largely unknown whether the burden of vascular- and Alzheimer-type neuropathology are independent or interdependent. Therefore, we investigated whether chronic cerebral hypoperfusion influences cognitive ability or amyloid β deposition in amyloid precursor protein (APP) overexpressing transgenic mice. Methods Two months old mice overexpressing a mutant form of the human APP bearing both the Swedish and Indiana mutations (APPSw/Ind-Tg mice), or their wild-type littermates, were subjected to chronic cerebral hypoperfusion with bilateral common carotid artery stenosis (BCAS) using microcoils or sham operation. Barnes maze test performance and histopathological findings were analyzed at eight months old by 2×2 factorial experimental designs with four groups. Results BCAS-operated APPSw/Ind-Tg mice showed significantly impaired learning ability compared to the other three groups of mice. Two-way repeated measures analysis of variance showed a synergistic interaction between the APP genotype and BCAS operation in inducing learning impairment. The cognitive performances were significantly correlated with the neuronal densities. BCAS significantly reduced the density of Nissl-stained neurons and silver-stained cored plaques in the hippocampus of APPSw/Ind-Tg mice but increased the amount of filter-trap amyloid β in the extracellular-enriched soluble brain fraction, compared to those from sham operated mice. Conclusions The results suggest interaction between chronic cerebral hypoperfusion and APPSw/Ind overexpression in cognitive decline in mice through enhanced neuronal loss and altered amyloid β metabolism.

Cilostazol, a phosphodiesterase inhibitor, prevents no-reflow and hemorrhage in mice with focal cerebral ischemia.

BACKGROUND AND PURPOSE The Cilostazol Stroke Prevention Study II has shown a similar efficacy in stroke prevention but markedly fewer hemorrhagic events with the phosphodiesterase inhibitor cilostazol versus aspirin. The purpose of this study is therefore to investigate how cilostazol affects cerebral hemodynamics and whether it prevents hemorrhagic transformation induced by recombinant tissue plasminogen activator (rtPA) in a mouse model of focal ischemia/reperfusion. Particular emphasis will be placed on the plasma-microvessel interface. METHODS After receiving food containing 0.3% cilostazol or standard food for 7 days, adult C57BL/6J mice were subjected to middle cerebral artery occlusion/reperfusion with or without rtPA (10mg/kg) intravenously administered prior to reperfusion. Cerebral blood flow was monitored at several time points by laser speckle imaging in the 24 hour period post reperfusion, before neurobehavioral and histological assessment. The long-term effect of cilostazol on cerebral ischemia was analyzed in the non-rtPA cohort. RESULTS In the non-rtPA cohort, pretreatment by cilostazol significantly decreased the endothelial expression of adhesion molecules (P-selectin and intercellular adhesion molecule-1) and prevented platelet aggregation and leukocyte plugging in the microvessels after cerebral ischemia/reperfusion in the acute phase. Cilostazol significantly reduced mortality rate and improved motor function at 7 days post-ischemia/reperfusion. In the rtPA cohort, cilostazol significantly suppressed edema formation and hemorrhagic transformation with reduced density of microglial cells positive for matrix metalloproteinase-9 in the cerebral cortex and the striatum. In both cohorts, cilostazol significantly suppressed focal no-reflow, mitigated cerebral infarct, and improved neurological outcome. CONCLUSIONS Cilostazol may possess protective properties against cerebral ischemic injury by preventing no-reflow and hemorrhagic transformation, via maintenance of microvascular integrity.

Frontal white matter hyperintensities, clasmatodendrosis and gliovascular abnormalities in ageing and post-stroke dementia

White matter hyperintensities are associated with post-stroke cognitive dysfunction, but the underlying mechanisms are unclear. Chen et al. provide evidence from human and experimental studies that clasmatodendrosis – a marker of irreversible astrocyte damage – and gliovascular abnormalities are increased in the frontal white matter of subjects who succumb to vascular dementia.

Mechanisms of Axonal Damage and Repair after Central Nervous System Injury

Central nervous system (CNS) injury initiates spatial and temporal neurodegeneration. Under pathologic conditions, damaged glial cells cannot supply sufficient metabolites to neurons, leading to energy deficiency for neuronal axons. The widespread disruption of cellular membranes causes disturbed intracellular signaling via dysregulated ionic gradients in neurons. Although several deleterious cascades are activated during the acute phase of CNS injury, some compensatory responses may tend to promote axonal repair during the chronic/remodeling phase. Because it may not be easy to block all multifactorial neurodegenerative pathways after CNS injury, supporting or boosting endogenous regenerative mechanisms would be an important therapeutic approach for CNS diseases. In this mini-review, we briefly but broadly introduce basic mechanisms that trigger axonal degeneration and then discuss potential targets for promoting axonal regeneration after CNS injury.

A mouse model of chronic cerebral hypoperfusion characterizing features of vascular cognitive impairment.

Vascular dementia or vascular cognitive impairment occurs as a result of persistently compromised blood flow to the brain and represents the second most common type of dementia after Alzheimers disease. In order to investigate its underlying mechanisms, a mouse model of chronic cerebral hypoperfusion has been developed, which involves the narrowing of the bilateral common carotid arteries with newly designed microcoils. This mouse model provides a unique platform to investigate the mechanisms of angiogenesis following chronic cerebral hypoperfusion and to explore potential drugs or cell therapies designed to enhance angiogenesis as a preclinical step toward developing novel treatments for dementia of vascular origin.

Vascular Function in Alzheimer's Disease and Vascular Dementia.

We investigated vascular functioning in patients with a clinical and radiological diagnosis of either Alzheimer’s disease (AD) or vascular dementia (VaD) and examined a possible relationship between vascular function and cognitive status. Twenty-seven patients with AD, 23 patients with VaD, and 26 healthy control patients underwent measurements of flow-mediated dilation (FMD), ankle–brachial index (ABI), cardioankle vascular index (CAVI), and intima–media thickness (IMT). The FMD was significantly lower in patients with AD or VaD compared to controls. There were no significant differences in ABI, CAVI, or IMT among the 3 groups. A significant correlation was found between Mini-Mental State Examination (MMSE) scores and FMD. Furthermore, a multiple regression analysis revealed that FMD was significantly predicted by MMSE scores. These results suggest that endothelial involvement plays a role in AD pathogenesis, and FMD may be more sensitive than other surrogate methods (ABI, CAVI, and IMT) for detecting early-stage atherosclerosis and/or cognitive decline.

Endothelial Progenitor Cell Secretome and Oligovascular Repair in a Mouse Model of Prolonged Cerebral Hypoperfusion

Background and Purpose— Endothelial progenitor cells (EPCs) have been extensively investigated as a therapeutic approach for repairing the vascular system in cerebrovascular diseases. Beyond vascular regeneration per se, EPCs may also release factors that affect the entire neurovascular unit. Here, we aim to study the effects of the EPC secretome on oligovascular remodeling in a mouse model of white matter injury after prolonged cerebral hypoperfusion. Methods— The secretome of mouse EPCs was analyzed with a proteome array. In vitro, the effects of the EPC secretome and its factor angiogenin were assessed on primary oligodendrocyte precursor cells and mature human cerebral microvascular endothelial cells (hCMED/D3). In vivo, mice were subjected to permanent bilateral common carotid artery stenosis, then treated with EPC secretome at 24 hours and at 1 week, and cognitive outcome was evaluated with the Y maze test together with oligodendrocyte precursor cell proliferation/differentiation and vascular density in white matter at 4 weeks. Results— Multiple growth factors, cytokines, and proteases were identified in the EPC secretome, including angiogenin. In vitro, the EPC secretome significantly enhanced endothelial and oligodendrocyte precursor cell proliferation and potentiated oligodendrocyte precursor cell maturation. Angiogenin was proved to be a key factor since pharmacological blockade of angiogenin signaling negated the positive effects of the EPC secretome. In vivo, treatment with the EPC secretome increased vascular density, myelin, and mature oligodendrocytes in white matter and rescued cognitive function in the mouse hypoperfusion model. Conclusions— Factors secreted by EPCs may ameliorate white matter damage in the brain by boosting oligovascular remodeling.