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Erdener ŞE, Dalkara T. Small Vessels Are a Big Problem in Neurodegeneration and Neuroprotection. Front Neurol 2019; 10:889. [PMID: 31474933 PMCID: PMC6707104 DOI: 10.3389/fneur.2019.00889] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Accepted: 08/01/2019] [Indexed: 12/11/2022] Open
Abstract
The cerebral microcirculation holds a critical position to match the high metabolic demand by neuronal activity. Functionally, microcirculation is virtually inseparable from other nervous system cells under both physiological and pathological conditions. For successful bench-to-bedside translation of neuroprotection research, the role of microcirculation in acute and chronic neurodegenerative disorders appears to be under-recognized, which may have contributed to clinical trial failures with some neuroprotectants. Increasing data over the last decade suggest that microcirculatory impairments such as endothelial or pericyte dysfunction, morphological irregularities in capillaries or frequent dynamic stalls in blood cell flux resulting in excessive heterogeneity in capillary transit may significantly compromise tissue oxygen availability. We now know that ischemia-induced persistent abnormalities in capillary flow negatively impact restoration of reperfusion after recanalization of occluded cerebral arteries. Similarly, microcirculatory impairments can accompany or even precede neural loss in animal models of several neurodegenerative disorders including Alzheimer's disease. Macrovessels are relatively easy to evaluate with radiological or experimental imaging methods but they cannot faithfully reflect the downstream microcirculatory disturbances, which may be quite heterogeneous across the tissue at microscopic scale and/or happen fast and transiently. The complexity and size of the elements of microcirculation, therefore, require utilization of cutting-edge imaging techniques with high spatiotemporal resolution as well as multidisciplinary team effort to disclose microvascular-neurodegenerative connection and to test treatment approaches to advance the field. Developments in two photon microscopy, ultrafast ultrasound, and optical coherence tomography provide valuable experimental tools to reveal those microscopic events with high resolution. Here, we review the up-to-date advances in understanding of the primary microcirculatory abnormalities that can result in neurodegenerative processes and the combined neurovascular protection approaches that can prevent acute as well as chronic neurodegeneration.
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Affiliation(s)
- Şefik Evren Erdener
- Institute of Neurological Sciences and Psychiatry, Hacettepe University, Ankara, Turkey
| | - Turgay Dalkara
- Institute of Neurological Sciences and Psychiatry, Hacettepe University, Ankara, Turkey.,Department of Neurology, Faculty of Medicine, Hacettepe University, Ankara, Turkey
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Bellapart J, Cuthbertson K, Dunster K, Diab S, Platts DG, Raffel C, Gabrielian L, Barnett A, Paratz J, Boots R, Fraser JF. The effects of normovolemic anemia and blood transfusion on cerebral microcirculation after severe head injury. Intensive Care Med Exp 2018; 6:46. [PMID: 30411308 PMCID: PMC6223395 DOI: 10.1186/s40635-018-0210-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 10/18/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Cerebral regional microcirculation is altered following severe head injury. In addition to tissue disruption, partial pressure of tissue oxygenation is impaired due to an increase in the oxygen tissue gradient. The heterogenic distribution of cerebral microcirculation is multifactorial, and acute anemia challenges further the delivery of oxygen to tissues. Currently, a restrictive transfusion threshold is globally applied; however, it is unclear how anemia modifies regional cerebral microcirculation; hence, it is unclear if by aiming to a global endpoint, specific anatomical regions undergo ischemia. This study aims to quantify the temporal changes in cerebral microcirculation after severe head injury, under the effect of anemia and transfusion. It also aims to assess its effects specifically at the ischemic penumbra compared to contralateral regions and its interactions with axonal integrity in real time. Twelve ovine models were subjected to a severe contusion and acceleration-deceleration injury. Normovolemic anemia to a restrictive threshold was maintained after injury, followed by autologous transfusion. Direct quantification of cerebral microcirculation used cytometric count of color-coded microspheres. Axonal injury was assessed using amyloid precursor protein staining. RESULTS A mixed-effect regression model from pre-transfusion to post-transfusion times with a random intercept for each sheep was used. Cerebral microcirculation amongst subjects with normal intracranial pressure was maintained from baseline and increased further after transfusion. Subjects with high intracranial pressure had a consistent reduction of their microcirculation to ischemic thresholds (20-30 ml/100 g/min) without an improvement after transfusion. Cerebral PtiO2 was reduced when exposed to anemia but increased in a 9.6-fold with transfusion 95% CI 5.6 to 13.6 (p value < 0.001). CONCLUSIONS After severe head injury, the exposure to normovolemic anemia to a restrictive transfusion threshold, leads to a consistent reduction on cerebral microcirculation below ischemic thresholds, independent of cerebral perfusion pressure. Amongst subjects with raised intracranial pressure, microcirculation does not improve after transfusion. Cerebral oxymetry is impaired during anemia with a statistically significant increase after transfusion. Current transfusion practices in neurocritical care are based on a rigid hemoglobin threshold, a view that excludes cerebral metabolic demands and specific needs. An RCT exploring these concepts is warranted.
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Affiliation(s)
- Judith Bellapart
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia. .,Intensive Care Department, Royal Brisbane and Women's Hospital, Butterfield Street, Herston, QLD, 4025, Australia.
| | - Kylie Cuthbertson
- Histopathology Department, Royal Brisbane and Women's Hospital, Herston, QLD, 4025, Australia
| | - Kimble Dunster
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia.,Medical Engineering Research Facility, Queensland University of Technology, Stafford Heights, QLD, 4053, Australia
| | - Sara Diab
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia.,Medical Engineering Research Facility, Queensland University of Technology, Stafford Heights, QLD, 4053, Australia
| | - David G Platts
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia.,Department of Cardiology, The Prince Charles Hospital, Chermside, QLD, 4032, Australia
| | - Christopher Raffel
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia.,Department of Cardiology, The Prince Charles Hospital, Chermside, QLD, 4032, Australia
| | - Levon Gabrielian
- Medical School Research Centre, Frome road, Adelaide, SA, 5005, Australia
| | - Adrian Barnett
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia.,Institute of Health and Biomedical Innovation and School of Public Health and Social Work, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, QLD, 4059, Australia
| | - Jennifer Paratz
- School of Medicine, University of Queensland, Brisbane, Queensland, 4025, Australia.,Griffith University, Parkland Drive, Southport, 4215, Australia
| | - Rob Boots
- Intensive Care Department, Royal Brisbane and Women's Hospital, Butterfield Street, Herston, QLD, 4025, Australia
| | - John F Fraser
- Critical Care Research Group, University of Queensland, Brisbane, Queensland, Australia.,Intensive Care Department, The Prince Charles Hospital, Rode road, Chermside, QLD, 4032, Australia
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Bellapart J, Cuthbertson K, Dunster K, Diab S, Platts DG, Raffel OC, Gabrielian L, Barnett A, Paratz J, Boots R, Fraser JF. Cerebral Microcirculation and Histological Mapping After Severe Head Injury: A Contusion and Acceleration Experimental Model. Front Neurol 2018; 9:277. [PMID: 29867710 PMCID: PMC5949334 DOI: 10.3389/fneur.2018.00277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Accepted: 04/09/2018] [Indexed: 11/21/2022] Open
Abstract
Background Cerebral microcirculation after severe head injury is heterogeneous and temporally variable. Microcirculation is dependent upon the severity of injury, and it is unclear how histology relates to cerebral regional blood flow. Objective This study assesses the changes of cerebral microcirculation blood flow over time after an experimental brain injury model in sheep and contrasts these findings with the histological analysis of the same regions with the aim of mapping cerebral flow and tissue changes after injury. Methods Microcirculation was quantified using flow cytometry of color microspheres injected under intracardiac ultrasound to ensure systemic and homogeneous distribution. Histological analysis used amyloid precursor protein staining as a marker of axonal injury. A mapping of microcirculation and axonal staining was performed using adjacent layers of tissue from the same anatomical area, allowing flow and tissue data to be available from the same anatomical region. A mixed effect regression model assessed microcirculation during 4 h after injury, and those results were then contrasted to the amyloid staining qualitative score. Results Microcirculation values for each subject and tissue region over time, including baseline, ranged between 20 and 80 ml/100 g/min with means that did not differ statistically from baseline flows. However, microcirculation values for each subject and tissue region were reduced from baseline, although their confidence intervals crossing the horizontal ratio of 1 indicated that such reduction was not statistically significant. Histological analysis demonstrated the presence of moderate and severe score on the amyloid staining throughout both hemispheres. Conclusion Microcirculation at the ipsilateral and contralateral site of a contusion and the ipsilateral thalamus and medulla showed a consistent decline over time. Our data suggest that after severe head injury, microcirculation in predefined areas of the brain is reduced from baseline with amyloid staining in those areas reflecting the early establishment of axonal injury.
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Affiliation(s)
- Judith Bellapart
- Department of Intensive Care, Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia
| | - Kylie Cuthbertson
- Department of Histopathology, Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia
| | - Kimble Dunster
- Critical Care Research Group, University of Queensland, Brisbane, QLD, Australia.,Medical Engineering Research Facility, Queensland University of Technology, Brisbane, QLD, Australia
| | - Sara Diab
- Critical Care Research Group, University of Queensland, Brisbane, QLD, Australia.,Medical Engineering Research Facility, Queensland University of Technology, Brisbane, QLD, Australia
| | - David G Platts
- Critical Care Research Group, University of Queensland, Brisbane, QLD, Australia.,Department of Cardiology, The Prince Charles Hospital, Chermside, QLD, Australia
| | - Owen Christopher Raffel
- Critical Care Research Group, University of Queensland, Brisbane, QLD, Australia.,Department of Cardiology, The Prince Charles Hospital, Chermside, QLD, Australia
| | - Levon Gabrielian
- Medical School, University of South Australia, Adelaide, SA, Australia.,Medical Research Centre, Adelaide, SA, Australia
| | - Adrian Barnett
- Critical Care Research Group, University of Queensland, Brisbane, QLD, Australia.,Institute of Health and Biomedical Innovation & School of Public Health and Social Work, Queensland University of Technology, Brisbane, QLD, Australia
| | - Jenifer Paratz
- Department of Intensive Care, Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia
| | - Rob Boots
- Department of Intensive Care, Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia
| | - John F Fraser
- Critical Care Research Group, University of Queensland, Brisbane, QLD, Australia.,Medical Engineering Research Facility, Queensland University of Technology, Brisbane, QLD, Australia.,Institute of Health and Biomedical Innovation & School of Public Health and Social Work, Queensland University of Technology, Brisbane, QLD, Australia.,Department of Intensive Care, The Prince Charles Hospital, Chermside, QLD, Australia
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