Yi Guo

University of California, San Francisco, San Francisco, California, United States

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Publications (6)19.25 Total impact

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    ABSTRACT: To test the hypothesis that lymphocyte infiltration in brain arteriovenous malformation (bAVM) is not associated with iron deposition (indicator of microhemorrhage). Sections of unruptured, previously untreated bAVM specimens (n=19) were stained immunohistochemically for T-lymphocytes (CD3(+)), B-lymphocytes (CD20(+)), plasma cells (CD138(+)) and macrophages (CD68(+)). Iron deposition was assessed by hematoxylin and eosin and Prussian blue stains. Superficial temporal arteries (STA) were used as control. Both T lymphocytes and macrophages were present in unruptured, previously untreated bAVM specimens, whereas few B cells and plasma cells were detected. Iron deposition was detected in 8 specimens (42%; 95% confidence interval =20-67%). The samples with iron deposition tended to have more macrophages than those without (666±313 vs 478±174 cells/mm(2); P=0.11). T-cells were clustered on the luminal side of the endothelial surface, on the vessel-wall, and in the perivascular regions. There was no correlation between T lymphocyte load and iron deposition (P=0.88). No macrophages and lymphocytes were detected in STA controls. T-lymphocytes were present in bAVM specimens. Unlike macrophages, the load and location of T-lymphocytes were not associated with iron deposition, suggesting the possibility of an independent cell-mediated immunological mechanism in bAVM pathogenesis.
    01/2014; 1(3):147-152. DOI:10.4103/2347-8659.143674
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    ABSTRACT: The absence of safe and reliable methods to harvest vascular tissue in situ limits the discovery of the underlying genetic and pathophysiological mechanisms of many vascular disorders such as aneurysms. We investigated the feasibility and comparable efficacy of endothelial cell collection using a spectrum of endovascular coils. Nine detachable coils ranging in k coefficient (0.15-0.24), diameter (4.0 mm-16.0 mm), and length (8.0 cm-47.0 cm) were tested in pigs. All coils were deployed and retrieved within the iliac artery of pigs (three coils/pig). Collected coils were evaluated under light microscopy. The total and endothelial cells collected by each coil were quantified. The nucleated cells were identified by Wright-Giemsa and DAPI stains. Endothelial and smooth muscle cells were identified by CD31 and α-smooth muscle actin antibody staining. Coils were deployed and retrieved without technical difficulty. Light microscopy demonstrated sheets of cellular material concentrated within the coil winds. All coils collected cellular material while five of nine (55.6%) coils retrieved endothelial cells. Coils collected mean endothelial cell counts of 89.0±101.6. Regression analysis demonstrated a positive correlation between increasing coil diameter and endothelial cell counts (R(2)=0.52, p = 0.029). Conventional detachable coils can be used to harvest endothelial cells. The number of endothelial cells collected by a coil positively correlated with its diameter. Given the widespread use of coils and their well-described safety profile their potential as an endovascular biopsy device would expand the availability of tissue for cellular and molecular analysis.
    Interventional Neuroradiology 12/2013; 19(4):399-408. · 0.73 Impact Factor
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    ABSTRACT: BACKGROUND:: Bone fracture increases alarmins and proinflammatory cytokines in the blood, and provokes macrophage infiltration and proinflammatory cytokine expression in the hippocampus. We recently reported that stroke is an independent risk factor after bone surgery for adverse outcome; however, the impact of bone fracture on stroke outcome remains unknown. We tested the hypothesis that bone fracture, shortly after ischemic stroke, enhances stroke-related injuries by augmenting the neuroinflammatory response. METHODS:: Tibia fracture (bone fracture) was induced in mice one day after permanent occlusion of the distal middle cerebral artery (stroke). High-mobility-group box chromosomal protein-1 (HMGB1) was tested to mimic the bone fracture effects. HMGB1 neutralizing antibody and clodrolip (macrophage depletion) were tested to attenuate the bone fracture effects. Neurobehavioral function (n = 10), infarct volume, neuronal death, and macrophages/microglia infiltration (n = 6-7) were analyzed after 3 days. RESULTS:: We found that mice with both stroke and bone fracture had larger infarct volumes (mean percentage of ipsilateral hemisphere ± SD: 30 ± 7% vs.12 ± 3%, n = 6, P < 0.001), more severe neurobehavioral dysfunction, and more macrophages/microglia in the periinfarct region than mice with stroke only. Intraperitoneal injection of HMGB1 mimicked, whereas neutralizing HMGB1 attenuated, the bone fracture effects and the macrophage/microglia infiltration. Depleting macrophages with clodrolip also attenuated the aggravating effects of bone fracture on stroke lesion and behavioral dysfunction. CONCLUSIONS:: These novel findings suggest that bone fracture shortly after stroke enhances stroke injury via augmented inflammation through HMGB1 and macrophage/microglia infiltration. Interventions to modulate early macrophage/microglia activation could be therapeutic goals to limit the adverse consequences of bone fracture after stroke.
    Anesthesiology 02/2013; 118(6). DOI:10.1097/ALN.0b013e31828c23f8 · 6.17 Impact Factor
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    ABSTRACT: OBJECTIVE: Vessels in brain arteriovenous malformations are prone to rupture. The underlying pathogenesis is not clear. Hereditary hemorrhagic telangiectasia type 2 patients with activin receptor-like kinase 1 (Alk1) mutation have a higher incidence of brain arteriovenous malformation than the general population. We tested the hypothesis that vascular endothelial growth factor impairs vascular integrity in the Alk1-deficient brain through reduction of mural cell coverage. METHODS AND RESULTS: Adult Alk1(1f/2f) mice (loxP sites flanking exons 4-6) and wild-type mice were injected with 2×10(7) PFU Ad-Cre and 2×10(9) genome copies of adeno-associated virus-vascular endothelial growth factor to induce focal homozygous Alk1 deletion (in Alk1(1f/2f) mice) and angiogenesis. Brain vessels were analyzed 8 weeks later. Compared with wild-type mice, the Alk1-deficient brain had more fibrin (99±30×10(3) pixels/mm(2) versus 40±13×10(3); P=0.001), iron deposition (508±506 pixels/mm(2) versus 6±49; P=0.04), and Iba1(+) microglia/macrophage infiltration (888±420 Iba1(+) cells/mm(2) versus 240±104 Iba1(+); P=0.001) after vascular endothelial growth factor stimulation. In the angiogenic foci, the Alk1-deficient brain had more α-smooth muscle actin negative vessels (52±9% versus 12±7%, P<0.001), fewer vascular-associated pericytes (503±179/mm(2) versus 931±115, P<0.001), and reduced platelet-derived growth factor receptor-β expression (26±9%, P<0.001). CONCLUSIONS: Reduction of mural cell coverage in response to vascular endothelial growth factor stimulation is a potential mechanism for the impairment of vessel wall integrity in hereditary hemorrhagic telangiectasia type 2-associated brain arteriovenous malformation.
    Arteriosclerosis Thrombosis and Vascular Biology 12/2012; 33(2). DOI:10.1161/ATVBAHA.112.300485 · 6.34 Impact Factor
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    ABSTRACT: Inflammation cell infiltration and cytokine expression are seen in the vascular walls and intervening stroma of resected brain arteriovenous malformation (bAVM) specimens, even in unruptured and previously untreated lesions. Macrophages may play a critical role in bAVM progression to rupture and could serve as a marker for rupture risk. We assessed feasibility of imaging macrophages within the bAVM nidus using ferumoxytol-enhanced magnetic resonance imaging (MRI) in four patients with already diagnosed bAVMs using iron-sensitive imaging (ISI; T2* GE MRI sequence). Patients were imaged at baseline and at either 1 day (n = 2) or 5 days (n = 2) after infusion of 5 mg/kg of ferumoxytol. Residual intravascular ferumoxytol obscured evaluation for uptake in bAVM vascular walls and stroma at the 1-day time point. The two cases imaged at 5 days showed less intravascular tracer but had signal loss in the nidal region consistent with ferumoxytol localization. One case underwent surgical resection; there was prominent vascular wall CD68 staining. Ferumoxytol-enhanced MRI for assessing bAVM inflammatory cell burden appears feasible and has the potential to be developed as a biomarker to study lesional inflammatory events.
    07/2012; 3(1). DOI:10.1007/s12975-012-0172-y
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    ABSTRACT: We investigated whether brain arteriovenous malformation silent intralesional microhemorrhage, that is, asymptomatic bleeding in the nidal compartment, might serve as a marker for increased risk of symptomatic intracranial hemorrhage (ICH). We evaluated 2 markers to assess the occurrence of silent intralesional microhemorrhage: neuroradiological assessment of evidence of old hemorrhage-imaging evidence of bleeding before the outcome events-and hemosiderin positivity in hematoxylin and eosin-stained paraffin block sections. We identified cases from our brain arteriovenous malformation database with recorded neuroradiological data or available surgical paraffin blocks. Using 2 end points, index ICH or new ICH after diagnosis (censored at treatment, loss to follow-up, or death), we performed logistic or Cox regression to assess evidence of old hemorrhage and hemosiderin positivity adjusting for age, sex, deep-only venous drainage, maximal brain arteriovenous malformation size, deep location, and associated arterial aneurysms. Evidence of old hemorrhage was present in 6.5% (n=975) of patients and highly predictive of index ICH (P<0.001; OR, 3.97; 95% CI, 2.1-7.5) adjusting for other risk factors. In a multivariable model (n=643), evidence of old hemorrhage was an independent predictor of new ICH (hazard ratio, 3.53; 95% CI, 1.35-9.23; P=0.010). Hemosiderin positivity was found in 36.2% (29.6% in unruptured; 47.8% in ruptured; P=0.04) and associated with index ICH in univariate (OR, 2.18; 95% CI, 1.03-4.61; P=0.042; n=127) and multivariable models (OR, 3.64; 95% CI, 1.11-12.00; P=0.034; n=79). The prevalence of silent intralesional microhemorrhage is high and there is evidence for an association with both index and subsequent ICH. Further development of means to detect silent intralesional microhemorrhage during brain arteriovenous malformation evaluation may present an opportunity to improve risk stratification, especially for unruptured brain arteriovenous malformations.
    Stroke 02/2012; 43(5):1240-6. DOI:10.1161/STROKEAHA.111.647263 · 6.02 Impact Factor