Unmasking Silent Endothelial Activation in the Cardiovascular System Using Molecular Magnetic Resonance Imaging

Immuno-MRI for Stroke Diagnosis and Prognosis

Following a stroke, an inflammatory response occurs, characterized by an increased blood-brain barrier permeability, expression of endothelial trafficking molecules, and infiltration of immune cells. Adhesion molecules expressed on activated brain endothelial cells are potential biomarkers of intraparenchymal inflammation. However, in current clinical practice, it is not possible to measure endothelial activation using clinically available imaging. Using targeted micro-sized particles of iron oxide (MPIO), immuno-MRI enables the detection of endothelial adhesion molecules at high resolution and, consequently, facilitates the detection of stroke-induced brain inflammation. In this review, we highlight the most recent studies that used immuno-MRI in models of neurovascular disorders, including transient ischemic attack, ischemic stroke, intracranial hemorrhage, and subarachnoid hemorrhage. We also discuss the potential of immuno-MRI in clinical practice and the necessary next steps for its implementation in patients.

Targeted Radiation Exposure Induces Accelerated Aortic Valve Remodeling in ApoE-/- Mice

Thoracic radiation therapy may result in accelerated atherosclerosis and in late aortic valve stenosis (AS). In this study, we assessed the feasibility of inducing radiation-induced AS using a targeted aortic valve irradiation (10 or 20 Grays) in two groups of C57Bl6/J (WT) and ApoE-/- mice compared to a control (no irradiation). Peak aortic jet velocity was evaluated by echocardiography to characterize AS. T2*-weighted magnetic resonance imaging after injection of MPIO-αVCAM-1 was used to examine aortic inflammation resulting from irradiation. A T2* signal void on valve leaflets and aortic sinus was considered positive. Valve remodeling and mineralization were assessed using von Kossa staining. Finally, the impact of radiation on cell viability and cycle from aortic human valvular interstitial cells (hVICs) was also assessed. The targeted aortic valve irradiation in ApoE-/- mice resulted in an AS characterized by an increase in peak aortic jet velocity associated with valve leaflet and aortic sinus remodeling, including mineralization process, at the 3-month follow-up. There was a linear correlation between histological findings and peak aortic jet velocity (r = 0.57, p < 0.01). In addition, irradiation was associated with aortic root inflammation, evidenced by molecular MR imaging (p < 0.01). No significant effect of radiation exposure was detected on WT animals. Radiation exposure did not affect hVICs viability and cell cycle. We conclude that targeted radiation exposure of the aortic valve in mice results in ApoE-/-, but not in WT, mice in an aortic valve remodeling mimicking the human lesions. This preclinical model could be a useful tool for future assessment of therapeutic interventions.

Use of metal-based contrast agents for in vivo MR and CT imaging of phagocytic cells in neurological pathologies

The activation of phagocytic cells is a hallmark of many neurological diseases. Imaging them in their 3-dimensional cerebral environment over time is crucial to better understand their role in disease pathogenesis and to monitor their potential therapeutic effects. Phagocytic cells have the ability to internalize metal-based contrast agents both in vitro and in vivo and can thus be tracked by magnetic resonance imaging (MRI) or computed tomography (CT). In this review article, we summarize the different labelling strategies, contrast agents, and in vivo imaging modalities that can be used to monitor cells with phagocytic activity in the central nervous system using MRI and CT, with a focus on clinical applications. Metal-based nanoparticle contrast agents such as gadolinium, gold and iron are ideal candidates for these applications as they have favourable magnetic and/or radiopaque properties and can be fine-tuned for optimal uptake by phagocytic cells. However, they also come with downsides due to their potential toxicity, especially in the brain where they might accumulate. We therefore conclude our review by discussing the pitfalls, safety and potential for clinical translation of these metal-based neuroimaging techniques. Early results in patients with neuropathologies such as multiple sclerosis, stroke, trauma, cerebral aneurysm and glioblastoma are promising. If the challenges represented by safety issues are overcome, phagocytic cells imaging will be a very valuable tool for studying and understanding the inflammatory response and evaluating treatments that aim at mitigating this response in patients with neurological diseases.

Tracking the immune response by MRI using biodegradable and ultrasensitive microprobes

Molecular magnetic resonance imaging (MRI) holds great promise for diagnosis and therapeutic monitoring in a wide range of diseases. However, the low intrinsic sensitivity of MRI to detect exogenous contrast agents and the lack of biodegradable microprobes have prevented its clinical development. Here, we synthetized a contrast agent for molecular MRI based on a previously unknown mechanism of self-assembly of catechol-coated magnetite nanocrystals into microsized matrix-based particles. The resulting biodegradable microprobes (M3P for microsized matrix-based magnetic particles) carry up to 40,000 times higher amounts of superparamagnetic material than classically used nanoparticles while preserving favorable biocompatibility and excellent water dispersibility. After conjugation to monoclonal antibodies, targeted M3P display high sensitivity and specificity to detect inflammation in vivo in the brain, kidneys, and intestinal mucosa. The high payload of superparamagnetic material, excellent toxicity profile, short circulation half-life, and widespread reactivity of the M3P particles provides a promising platform for clinical translation of immuno-MRI.

Molecular MRI of Neuroinflammation: Time to Overcome the Translational Roadblock

The ability to detect a molecular target in the central nervous system non-invasively and at high spatial resolution using magnetic resonance imaging (MRI) has attracted the interest of researchers for several decades. Yet, molecular MRI studies remain restricted to the preclinical stage and the path to clinical translation remains unclear. The focus of molecular MRI of neuroinflammation has moved from parenchymal to vascular targets, that are more easily reachable by intravenously injected probes. This has allowed the use of large superparamagnetic probes, such as micro-sized particles of iron oxide (MPIO), that dramatically improved the sensitivity of molecular MRI compared to smaller contrast agents. In particular, recent studies demonstrated the feasibility of unraveling inflammation in the brain by MRI using MPIO able to bind activated endothelial cells with potential applications in neurovascular, neuroinflammatory and neurodegenerative disorders. In the present review, we present the most striking advances in the field and the remaining challenges that must be overcome before clinical use of molecular MRI of neuroinflammation.

New Approaches in Nanomedicine for Ischemic Stroke

Ischemic stroke, caused by the interruption of blood flow to the brain and subsequent neuronal death, represents one of the main causes of disability in developed countries. Therapeutic methods such as recanalization approaches, neuroprotective drugs, or recovery strategies have been widely developed to improve the patient's outcome; however, important limitations such as a narrow therapeutic window, the ability to reach brain targets, or drug side effects constitute some of the main aspects that limit the clinical applicability of the current treatments. Nanotechnology has emerged as a promising tool to overcome many of these drug limitations and improve the efficacy of treatments for neurological diseases such as stroke. The use of nanoparticles as a contrast agent or as drug carriers to a specific target are some of the most common approaches developed in nanomedicine for stroke. Throughout this review, we have summarized our experience of using nanotechnology tools for the study of stroke and the search for novel therapies.

Kidney function and dementia risk in community-dwelling older adults: the Shanghai Aging Study

BACKGROUND

Association between kidney dysfunction and dementia has been studied in western cohorts, but with inconsistent conclusions which may be due to the different measurements of kidney function. We aim to verify the hypothesis that lower levels of kidney function would be associated with increased risk of incident dementia in Chinese elderly.

METHODS

One thousand four hundred twelve dementia-free participants aged 60 years or older from the Shanghai Aging Study were enrolled and followed up for 5.3 years on average. Glomerular filtration rate (GFR) was calculated by using combined creatinine-cystatin C CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. Diagnoses of incident dementia and Alzheimer's disease (AD) were established using DSM-IV and NINCDS-ADRDA criteria based on medical, neurological, and neuropsychological examinations to each participant. Cox proportional regression was used to analyze the association of baseline GFR_crcys levels with incident dementia/AD, adjusting age, gender, education years, APOE-ε4, diabetes, hypertension, baseline Mini-Mental State Examination score, and proteinuria.

RESULTS

A total of 113 (8%) and 84 (7%) participants developed dementia and AD. Comparing to participants with high GFR_crcys (≥ 80 ml/min/1.73 m²), participants with low (< 67 ml/min/1.73 m²) and moderate GFR_crcys (67 ≤ GFR < 80 ml/min/1.73 m²) had increased risk of incident dementia with hazard ratios (HRs) of 1.87 (95% CI 1.02-3.44) and 2.19 (95% CI 1.21-3.95) after adjustment for confounders, respectively. Low (HR = 2.27 [95%CI 1.10-4.68]) and moderate (HR = 2.14 [95% CI 1.04-4.40]) GFR_crcys at baseline was also independently associated with incident AD after adjustments when comparing to high GFR_crcys. The significant association between GFR_crcys and dementia risk was observed in female but not in male participants.

CONCLUSIONS

GFR_crcys may be considered as a marker of an individual's vulnerability to the increased risk of cognitive decline.

Ultrasensitive molecular imaging of intestinal mucosal inflammation using leukocyte-mimicking particles targeted to MAdCAM-1 in mice

Mucosal tissues play critical roles in health and disease as the primary barrier between the external world and the inner body, lining the digestive, respiratory, urinary, mammary, and reproductive tracts. Clinical evaluation of mucosal tissues is currently performed using endoscopy, such as ileocolonoscopy for the intestinal mucosa, which causes substantial patient discomfort and can lead to organ damage. Here, we developed a contrast agent for molecular magnetic resonance imaging (MRI) that is targeted to mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1), an adhesion molecule overexpressed by inflamed mucosal tissues. We investigated the diagnostic performance of molecular MRI of MAdCAM-1 to detect mucosal inflammation in several models of acute and chronic intestinal inflammation in mice. We demonstrated that molecular MRI of MAdCAM-1 reveals disease activity and can evaluate the response to inflammatory treatments along the whole intestinal mucosa in clinically relevant models of inflammatory bowel diseases. We also provide evidence that this technique can detect low, subclinical mucosal inflammation. Molecular MRI of MAdCAM-1 has potential applications in early diagnosis, longitudinal follow-up, and therapeutic response monitoring in diseases affecting mucosal tissues, such as inflammatory bowel diseases.

Molecular imaging of endothelial activation and mineralization in a mouse model of accelerated atherosclerosis

PURPOSE

Preclinical imaging of endothelial activation and mineralization using both positron emission tomography (PET) and magnetic resonance (MR) remains scarce.

PROCEDURES

A group of uremic ApoE-/- (Ur), non-uremic ApoE-/- (NUr), and control C57Bl/6 J mice (Ctl) were investigated. Mineralization process was assessed using sodium fluoride ([18F]NaF) PET, and MR imaging combined with intravenous injection of MPIO-αVCAM-1 was used to evaluate endothelial activation. Micro- and macrocalcifications were evaluated by flame atomic absorption spectroscopy and von Kossa staining, respectively.

RESULTS

Ur mice showed an active and sustained mineralization process compared to Ctl mice (p = 0.002) using [18F]NaF PET imaging. Calcium plasma level was increased in Ur (2.54 ± 0.09 mM, n = 17) compared to NUr and Ctl mice (2.24 ± 0.01, n = 22, and 2.14 ± 0.02, n = 27, respectively; p < 0.0001). Likewise, vascular calcium content was increased in Ur (0.51 ± 0.06 μg Ca2+ per milligram of dry weight aorta, n = 11) compared to NUr (0.27 ± 0.05, n = 9, p = 0.013) and Ctl (0.28 ± 0.05, n = 11, p = 0.014). Ur mice also had a higher inflammatory state using MPIO-αVCAM-1 MR (p global = 0.01, post hoc analysis Ur vs. Ctl p = 0.003) associated with increased VCAM-1 expression (p global = 0.02). Aortic remodeling at the level of the brachiocephalic trunk, brachiocephalic trunk itself, and aortic arch in Ur mice was also demonstrated using MR.

CONCLUSIONS

Preclinical molecular imaging allowed in vivo characterization of the early phase of atherosclerosis. [18F]NaF PET showed early and sustained vascular mineralization in uremic ApoE-/- mice. MPIO-αVCAM-1 MR imaging demonstrated aortic endothelial activation, predominantly in segments with vascular remodeling.

Molecular Magnetic Resonance Imaging of Endothelial Activation in the Central Nervous System

Endothelial cells of the central nervous system over-express surface proteins during neurological disorders, either as a cause, or a consequence, of the disease. Since the cerebral vasculature is easily accessible by large contrast-carrying particles, it constitutes a target of choice for molecular magnetic resonance imaging (MRI). In this review, we highlight the most recent advances in molecular MRI of brain endothelial activation and focus on the development of micro-sized particles of iron oxide (MPIO) targeting adhesion molecules including intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), P-Selectin and E-Selectin. We also discuss the perspectives and challenges for the clinical application of this technology in neurovascular disorders (ischemic stroke, intracranial hemorrhage, subarachnoid hemorrhage, diabetes mellitus), neuroinflammatory disorders (multiple sclerosis, brain infectious diseases, sepsis), neurodegenerative disorders (Alzheimer's disease, vascular dementia, aging) and brain cancers (primitive neoplasms, metastasis).

Age-, Gender-, and in Vivo Different Doses of Isoproterenol Modify in Vitro Aortic Vasoreactivity and Circulating VCAM-1

Different human-like cardiomyopathies associated to β-adrenergic stimulation are experimentally modeled in animals through variations in dose, route, and duration of administration of different cardiotoxic drugs. However, associated changes in the vasculature and their relation to systemic inflammation, and the influence of cardiovascular diseases risk factors (gender and age) upon them are seldom analyzed. Here we studied the effect of age and gender on the vasoreactivity of aortas from mice subjected to in vivo repeated β-adrenergic stimulation with different doses of isoproterenol (ISO) in association with circulating inflammatory cytokines. Young (2 months) and old (18 months) male and female mice received 0 (control), 5, 40, 80 or 160 μg/g/d of ISO (7 days, s.c.). IL-1α, IL-4 and vascular cell adhesion molecule-1 (VCAM-1) were quantified in plasma. In vitro, norepinephrine-induced vasoconstriction and acetylcholine-induced relaxation were measured in aortas. No differences in contraction, relaxation, IL-1α, and IL-4 were found between control young males and females. Age decreased contraction in males and relaxation was lower in females and abolished in males. VCAM-1 was higher in young males than in females and increased in old mice. Vasoconstriction in ISO-treated mice results as a bell-shaped curve on contraction in young and old males, with lower values in the latter. In females, ISO-160 increased contraction in young females but decreased it in old females. Vasorelaxation was reduced in ISO-treated young males and females. ISO-80 and 160 reduced vasorelaxation in old females, and intermediate doses relaxed aortas from old males. VCAM-1 was higher in young and old males with ISO-80 and 160; while VCAM-1 was higher only with ISO-160 in old females. Our results demonstrate that repeated β-adrenergic stimulation modifies vascular reactivity depending on gender, age, and dose. Females were less sensitive to alterations in vasoreactivity, and young females required a higher amount of the adrenergic stimuli than old females to show vascular alterations. Changes were independent of IL-1α and IL-4. VCAM-1 only changed in old females stimulated with ISO 160. Our results highlight the relevance of considering and comparing in the same study females and aged organisms to improve the accuracy of applications to clinical studies.

PET Imaging of VCAM-1 Expression and Monitoring Therapy Response in Tumor with a 68Ga-Labeled Single Chain Variable Fragment

Vascular cell adhesion molecule-1 (VCAM-1) is a transmembrane glycoprotein closely related to tumorigenicity as well as tumor metastasis. It is also a well-known candidate for detecting tumors. LY2409881, an IKKβ inhibitor, could induce apoptosis of VCAM-1 positive cells. Our purpose is to prepare a novel tracer to evaluate its feasibility of detecting VCAM-1 expression and monitoring LY2409881 tumor curative effect. The tracer was prepared by conjugating the single chain variable fragment (scFv) of VCAM-1 and NOTA-NHS-ester and then labeled with ⁶⁸Ga. ⁶⁸Ga-NOTA-VCAM-1_scFv was successfully prepared with high radiochemical yield. VCAM-1 overexpression and underexpression melanoma cell lines, B16F10 and A375m, were used in this study. The results of microPET/CT imaging in small animals indicated that the uptake of ⁶⁸Ga-NOTA-VCAM-1_scFv in B16F10 tumor was much higher than that of A375m, which was also confirmed by the biodistribution and autoradiography results. LY2409881 inhibits the growth of B16F10 melanoma in vivo by inducing dose- and time-dependent growth inhibition and apoptosis of the cells. The LY2409881 treated group and DMSO control group were established and imaged by microPET/CT. In the LY2409881 group, uptake of the tracer in tumor was decreased at the first week, and then gradually recovered to the initial level. In DMSO control, the uptake of the tracer remained at the same level during the whole time. The results suggested that LY2409881 inhibits the expression of VCAM-1 and suppresses tumor growth. ⁶⁸Ga-NOTA-VCAM-1_scFv, an easily synthesized probe, has a potential clinical application in the visual monitoring of IKKβ inhibitor intervention on VCAM-1 positive tumors.

Molecular Magnetic Resonance Imaging (mMRI)

Molecular magnetic resonance imaging (mMRI) enables the detection of a protein of interest in vivo, in a noninvasive manner. The general concept of mMRI is to target a contrast agent to a protein of interest, and to perform a contrast-sensitive MRI sequence. Typically, contrast agents are made of a "contrastophore" (the part of the construct responsible for the contrast on the images) and a targeting moiety ("pharmacophore"). Recently, the development of a new family of contrastophore carrying a high payload of iron oxide (micro-sized particles of iron oxide, MPIO) has led to a dramatic increase in the sensitivity of mMRI. Here, we describe the production of targeted MPIO using commercially available reagents and the MRI protocols to allow their detection in vivo.

General Anesthesia Inhibits the Activity of the "Glymphatic System"

INTRODUCTION: According to the "glymphatic system" hypothesis, brain waste clearance is mediated by a continuous replacement of the interstitial milieu by a bulk flow of cerebrospinal fluid (CSF). Previous reports suggested that this cerebral CSF circulation is only active during general anesthesia or sleep, an effect mediated by the dilatation of the extracellular space. Given the controversies regarding the plausibility of this phenomenon and the limitations of currently available methods to image the glymphatic system, we developed original whole-brain in vivo imaging methods to investigate the effects of general anesthesia on the brain CSF circulation. METHODS: We used magnetic resonance imaging (MRI) and near-infrared fluorescence imaging (NIRF) after injection of a paramagnetic contrast agent or a fluorescent dye in the cisterna magna, in order to investigate the impact of general anesthesia (isoflurane, ketamine or ketamine/xylazine) on the intracranial CSF circulation in mice. RESULTS:In vivo imaging allowed us to image CSF flow in awake and anesthetized mice and confirmed the existence of a brain-wide CSF circulation. Contrary to what was initially thought, we demonstrated that the parenchymal CSF circulation is mainly active during wakefulness and significantly impaired during general anesthesia. This effect was especially significant when high doses of anesthetic agent were used (3% isoflurane). These results were consistent across the different anesthesia regimens and imaging modalities. Moreover, we failed to detect a significant change in the brain extracellular water volume using diffusion weighted imaging in awake and anesthetized mice. CONCLUSION: The parenchymal diffusion of small molecular weight compounds from the CSF is active during wakefulness. General anesthesia has a negative impact on the intracranial CSF circulation, especially when using a high dose of anesthetic agent.

Prediction of disease activity in models of multiple sclerosis by molecular magnetic resonance imaging of P-selectin

New strategies for detecting disease activity in multiple sclerosis are being investigated to ameliorate diagnosis and follow-up of patients. Today, although magnetic resonance imaging (MRI) is widely used to diagnose and monitor multiple sclerosis, no imaging tools exist to predict the evolution of disease and the efficacy of therapeutic strategies. Here, we show that molecular MRI targeting the endothelial adhesion molecule P-selectin unmasks the pathological events that take place in the spinal cord of mice subjected to chronic or relapsing experimental autoimmune encephalomyelitis. This approach provides a quantitative spatiotemporal follow-up of disease course in relation to clinical manifestations. Moreover, it predicts relapse in asymptomatic mice and remission in symptomatic animals. Future molecular MRI targeting P-selectin may be used to improve diagnosis, follow-up of treatment, and management of relapse/remission cycles in multiple sclerosis patients by providing information currently inaccessible through conventional MRI techniques.

Hyperfibrinolysis increases blood–brain barrier permeability by a plasmin- and bradykinin-dependent mechanism

Hydrodynamic transfection of plasmids encoding for plasminogen activators leads to a hyperfibrinolytic state in mice. Hyperfibrinolysis increases BBB permeability via a plasmin- and bradykinin-dependent mechanism.

Plaque angiogenesis and its relation to inflammation and atherosclerotic plaque destabilization

PURPOSE OF REVIEW

The review discusses the recent literature on plaque angiogenesis and its relation to inflammation and plaque destabilization. Furthermore, it discusses how plaque angiogenesis can be used to monitor atherosclerosis and serve as a therapeutic target.

RECENT FINDINGS

Histopathologic studies have shown a clear relationship between plaque angiogenesis, intraplaque hemorrhage (IPH), plaque vulnerability, and cardiovascular events. Hypoxia is a main driver of plaque angiogenesis and the mechanism behind angiogenesis is only partly known. IPH, as the result of immature neovessels, is associated with increased influx of inflammatory cells in the plaques. Experimental models displaying certain features of human atherosclerosis such as plaque angiogenesis or IPH are developed and can contribute to unraveling the mechanism behind plaque vulnerability. New imaging techniques are established, with which plaque angiogenesis and vulnerability can be detected. Furthermore, antiangiogenic therapies in atherosclerosis gain much attention.

SUMMARY

Plaque angiogenesis, IPH, and inflammation contribute to plaque vulnerability. Histopathologic and imaging studies together with specific experimental studies have provided insights in plaque angiogenesis and plaque vulnerability. However, more extensive knowledge on the underlying mechanism is required for establishing new therapies for patients at risk.

Cardiovascular Risk Evaluated With the Use of Heartscore in Kidney Transplant Recipients-Three Years of Follow-up

BACKGROUND

Cardiovascular (CV) complications are the major cause of death in kidney transplant (KT) patients.

METHODS

During a 3-year follow-up, 112 KT recipients, from living (LD KTRs; n = 54), and deceased (DD KTRs; n = 58) donors, were assessed for 10-year risk of fatal CV events with the use of the Heartscore tool (www.heartscore.org). In post-KT months 6, 12, and 36, current and optimum (target) CV risks (CVRs) were estimated.

RESULTS

Current risk was lower in the LD KTRs and remained stable. In DD KTRs, the risk was at the highest level in months 6 and 12 of follow-up and decreased in month 36. Change in CVR, ie, the difference between the current and target risk, was the highest in DD KTRs in month 36 of follow-up (P = .014). In the increased-CVR group, recipients were older (P < .01), primarily male (P = .08), and more frequently smokers (P < .01) and had a higher systolic blood pressure (P < .05) despite taking more hypotensive medicines (P < .01), and had higher total cholesterol (P < .01) and low-density lipoprotein (P < .01) levels. In this group, body mass index (BMI) was higher (P < .01) and metabolic syndrome was diagnosed significantly more often (P < .01). The high-risk group (estimated CVR, ≥5) was different also in longer durations of pre-transplantation dialysis (P < .05) and higher rates of CV episodes before transplantation (P < .05). In logistic regression, higher BMI and lower estimated glomerular filtration rate (eGFR) were the parameters strongly correlated with higher CVR.

CONCLUSIONS

Mean CVR applicable to all kidney transplant recipients was stable throughout the follow-up. Changes in the risk affected mainly DD KTRs. In months 6 and 12, CVR was the highest in this group and was substantially reduced in the 3rd year of follow-up, probably owing to medical interventions. In the high-CVR group, impaired function of the transplanted kidney was recorded. CVR scores in patients with renal conditions and after kidney transplantation should additionally account for eGFR.

Nano-zymography Using Laser-Scanning Confocal Microscopy Unmasks Proteolytic Activity of Cell-Derived Microparticles

Cell-derived microparticles (MPs) are nano-sized vesicles released by activated cells in the extracellular milieu. They act as vectors of biological activity by carrying membrane-anchored and cytoplasmic constituents of the parental cells. Although detection and characterization of cell-derived MPs may be of high diagnostic and prognostic values in a number of human diseases, reliable measurement of their size, number and biological activity still remains challenging using currently available methods. In the present study, we developed a protocol to directly image and functionally characterize MPs using high-resolution laser-scanning confocal microscopy. Once trapped on annexin-V coated micro-wells, we developed several assays using fluorescent reporters to measure their size, detect membrane antigens and evaluate proteolytic activity (nano-zymography). In particular, we demonstrated the applicability and specificity of this method to detect antigens and proteolytic activities of tissue-type plasminogen activator (tPA), urokinase and plasmin at the surface of engineered MPs from transfected cell-lines. Furthermore, we were able to identify a subset of tPA-bearing fibrinolytic MPs using plasma samples from a cohort of ischemic stroke patients who received thrombolytic therapy and in an experimental model of thrombin-induced ischemic stroke in mice. Overall, this method is promising for functional characterization of cell-derived MPs.

The "inflammatory penumbra" in ischemic stroke: From clinical data to experimental evidence

Purpose

The objective of the present review is to provide an overview of the available clinical and preclinical data supporting the existence of an "inflammatory penumbra" in ischemic stroke.

Findings

Recent data from clinical trials suggest the existence of an inflammatory area at risk, surrounding the initial ischemic lesion and secondarily infiltrated by lymphocytes, that is ultimately recruited by the ischemic core: called the "inflammatory penumbra." Experimental results support this concept. Lymphocytes, especially T-cells, enter the brain in the perilesional area in a vascular-cell adhesion molecule-1 dependent manner and participate in delayed neuronal cell death.

Methods

For writing this review, we used the more recent publications in the field, including the preclinical and clinical studies. We have also used our own experise in the field of in vivo imaging of inflammatory processes.

Discussion

Consequently, the intensity of the inflammatory reaction and the size of the inflammatory penumbra may vary considerably in patients, as it is the case in experimental stroke models in mice. By analogy with the ischemic penumbra of the acute phase of stroke, this secondary inflammatory penumbra represents a therapeutic opportunity during the subacute phase of stroke. Large clinical trials that target lymphocyte trafficking are currently taking place. However, to improve the benefit of such therapeutic strategies, adequate patient selection may be mandatory.

Conclusion

In this context, innovative imaging methods including magnetic resonance imaging of adhesion molecules may contribute to noninvasively detect this inflammatory penumbra and thus to select patients eligible for such therapy.