In vivo analysis of neuroinflammation in the late chronic phase after experimental stroke
Graphical abstract
USPIO-MRI revealed macrophages after stroke (red). Combined analysis with [11C]PK11195-PET presented dominance of non-phagocytic neuroinflammation in the acute phase and increasing phagocytic activity in the chronic phase after stroke. Tissue affected by phagocytic activity, was associated with severe injury and necrosis.
Introduction
Cerebral ischemia is accompanied by various cellular and molecular processes, which contribute to restoration of brain function after stroke (Wieloch and Nikolich, 2006, Murphy and Corbett, 2009). Especially inflammation impacts on neuroplasticity and long-term recovery (del Zoppo, 2010, Morrison and Filosa, 2013, Ruscher et al., 2013). In vivo visualization of inflammatory reactions may facilitate translation of novel therapies into clinical studies (Fumagalli et al., 2013, Heiss, 2014, Quattromani et al., 2014). Among others, magnetic resonance imaging (MRI) using ultra small supraparamagnetic iron oxide particles (USPIO) (Deddens et al., 2012, Marinescu et al., 2013) and positron emission tomography (PET) with the radiotracer [11C]PK11195 (Schroeter et al., 2009, Jacobs et al., 2012) represent attractive approaches.
The lipophilic tracer [11C]PK11195 binds to the 18-kDa translocator protein (TSPO), a cholesterol-transporter found on the membrane of mitochondria (Papadopoulos et al., 2006). After brain injury, its expression on microglia, astrocytes and macrophages increases, representing a target for imaging (Stephenson et al., 1995, Chen and Guilarte, 2008). Unfortunately the method is limited due to short half-life of 11C and low signal-to-noise ratio (Jucaite et al., 2012, Dickens et al., 2014). Moreover radiosynthesis of [11C]PK11195 is very time consuming and expensive.
In MRI, intravenously applied USPIOs lead to hypointense T2∗-signal changes in the lesioned central nervous system (CNS) by invasion of USPIO-loaded macrophages (Nighoghossian et al., 2007, Desestret et al., 2013). This was shown to occur independently of a potentially associated blood–brain barrier breakdown (Stoll and Bendszus, 2010, Yang et al., 2013). Translational approaches demonstrated USPIO+ phagocytes also in the human CNS after stroke (Saleh et al., 2004, Saleh et al., 2007). However, these findings have been questioned by studies using transient stroke models in high-field MRI (Desestret et al., 2009, Farr et al., 2011, Harms et al., 2013). In addition dysregulation of natural neuroinflammatory responses by USPIOs has been discussed (Siglienti et al., 2006, Hsiao et al., 2008). Recent results furthermore suggest that iron deposition naturally occurs after stroke (Danielisova et al., 2004, Li et al., 2009, Hagemeier et al., 2012) and other diseases associated with persistent microglia activation (Zivadinov et al., 2011).
The present study was conducted to evaluate the validity of combined imaging by USPIO-MRI and [11C]PK11195-PET as a method to longitudinally and intraindividually analyze stroke-induced inflammatory processes in the living organism.
Section snippets
Experimental design
Thirteen male Wistar rats underwent permanent middle cerebral artery occlusion (pMCAO) by the macrosphere model, which closely resembles the dynamic patterns of neuroinflammatory procedures in human stroke (Gerriets et al., 2003, Walberer et al., 2010). At day 6 (d6), d27, and d55, animals were subjected to both MRI (T2, T2∗) and PET, using the tracer [11C]PK11195 to investigate neuroinflammatory processes. Directly afterward, USPIOs (300 μmol Fe/kg) were injected intravenously (iv) followed by
Dynamics of post-stroke inflammation
During the observation period of 56 days, the inflammatory signal by [11C]PK11195, decreased over time and moved from regions directly adjacent to the infarct toward the thalamus (d28), and further toward midbrain and pons (d56) (Fig. 2A, B). In line with previous results, post-stroke inflammation peaked at d7.
Immunohistochemistry
Focal signals for iron (Fe) were present in all USPIO+ areas corresponding to the infarct-margin and periinfarct region (Fig. 2C). Iba1-stained tissue confirmed the presence of microglia
Discussion
To date, the detailed pathomechanisms underlying stroke-induced inflammatory processes still remain elusive and especially the distinction of various cellular subtypes contributing to postischemic reactions is matter of vivid debates (Prinz et al., 2011). Cellular and genetic labeling as well as functional studies have shown that in particular the microglia/macrophage population is highly heterogeneous in respect to origin, activity and marker expression (Morrison and Filosa, 2013, Perego et
Conclusion
The combination of USPIO-MRI and [11C]PK11195-PET allows longitudinal and intra-individual analysis of inflammatory processes in the chronic post-stroke phase, facilitating valid predictions about regional tissue fate. Hereby valuable information about mechanisms of repair and recovery after stroke is provided. As both methods have successfully been applied in humans, translation of this multi-modal imaging protocol into clinical routine is feasible and may help to monitor new therapeutic
Sources of funding
This study was supported by the Köln-Fortune-Programme and the European Community’s Seventh Framework Programme, project number 2780006, “NeuroFGL”.
Disclosures
The authors declare no competing financial interests.
Acknowledgment
None.
References (58)
- et al.
Translocator protein 18 kDa (TSPO): molecular sensor of brain injury and repair
Pharmacol Ther
(2008) - et al.
Fast and robust registration of PET and MR images of human brain
Neuroimage
(2004) - et al.
High-resolution intravital imaging reveals that blood-derived macrophages but not resident microglia facilitate secondary axonal dieback in traumatic spinal cord injury
Exp Neurol
(2014) - et al.
Magnetic labeling of activated microglia in experimental gliomas
Neoplasia
(2001) - et al.
The macrosphere model: evaluation of a new stroke model for permanent middle cerebral artery occlusion in rats
J Neurosci Methods
(2003) - et al.
Microglia: new roles for the synaptic stripper
Neuron
(2013) - et al.
Simplified reference tissue model for PET receptor studies
Neuroimage
(1996) - et al.
Quantitative analysis of iron concentration and expression of ferroportin 1 in the cortex and hippocampus of rats induced by cerebral ischemia
J Clin Neurosci
(2009) - et al.
Translocator protein (18 kDa): new nomenclature for the peripheral-type benzodiazepine receptor based on its structure and molecular function
Trends Pharmacol Sci
(2006) - et al.
Enriched housing down-regulates the Toll-like receptor 2 response in the mouse brain after experimental stroke
Neurobiol Dis
(2014)
Predominant phagocytic activity of resident microglia over hematogenous macrophages following transient focal cerebral ischemia: an investigation using green fluorescent protein transgenic bone marrow chimeric mice
Exp Neurol
Effects of monocyte chemoattractant protein 1 on blood-borne cell recruitment after transient focal cerebral ischemia in mice
Neuroscience
Synthesis of the enantiomers of [N-methyl-11C]PK 11195 and comparison of their behaviours as radioligands for PK binding sites in rats
Nucl Med Biol
Cytokine profile of iron-laden macrophages: implications for cellular magnetic resonance imaging
J Neuroimmunol
Migration of enhanced green fluorescent protein expressing bone marrow-derived microglia/macrophage into the mouse brain following permanent focal ischemia
Neuroscience
Mechanisms of neural plasticity following brain injury
Curr Opin Neurobiol
Iron deposition in the brain following the ischemia in a rat model of ischemic tolerance
Acta Medica (Hradec Kralove)
Imaging neuroinflammation after stroke: current status of cellular and molecular MRI strategies
Cerebrovasc Dis
Acute anti-inflammatory approaches to ischemic stroke
Ann N Y Acad Sci
Early-stage investigations of ultrasmall superparamagnetic iron oxide-induced signal change after permanent middle cerebral artery occlusion in mice
Stroke
In vitro and in vivo models of cerebral ischemia show discrepancy in therapeutic effects of M2 macrophages
PLoS One
Detection of microglial activation in an acute model of neuroinflammation using PET and radiotracers 11C-(R)-PK11195 and 18F-GE-180
J Nucl Med
Challenges towards MR imaging of the peripheral inflammatory response in the subacute and chronic stages of transient focal ischemia
NMR Biomed
CX3CR1 deficiency induces an early protective inflammatory environment in ischemic mice
Glia
Molecular magnetic resonance imaging of brain–immune interactions
Front Cell Neurosci
Brain iron accumulation in aging and neurodegenerative disorders
Expert Rev Neurother
Efficient stereospecific synthesis of no-carrier-added 2-[18F]-fluoro-2-deoxy-d-glucose using aminopolyether supported nucleophilic substitution
J Nucl Med
Certain types of iron oxide nanoparticles are not suited to passively target inflammatory cells that infiltrate the brain in response to stroke
J Cereb Blood Flow Metab
PET imaging in ischemic cerebrovascular disease: current status and future directions
Neurosci Bull
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Both authors contributed equally to this study.