Blood–Brain Barrier Disruption in Humans Is Independently Associated With Increased Matrix Metalloproteinase-9
Background and Purpose— Matrix metalloproteinases (MMP) may play a role in blood–brain barrier (BBB) disruption after ischemic stroke. We hypothesized that plasma concentrations of MMP-9 are associated with a marker of BBB disruption in patients evaluated for acute stroke.
Methods— Patients underwent MRI on presentation and ≈24 hours later. The MRI marker, termed hyperintense acute reperfusion injury marker (HARM), is gadolinium enhancement of cerebrospinal fluid on fluid-attenuated inversion recovery MRI. Plasma MMP-9 and tissue inhibitor of matrix metalloproteinase-1 were measured by enzyme-linked immunosorbent assay. Logistic regression models tested for predictors of HARM on 24-hour follow-up scans separately for MMP-9 and the ratio of MMP-9 to TIMP-1.
Results— For the 41 patients enrolled, diagnoses were: acute ischemic cerebrovascular syndrome, 33 (80.6%); intracerebral hemorrhage, 6 (14.6%); stroke mimic, 1 (2.4%); and no stroke, 1 (2.4%). HARM was present in 17 (41.5%) patients. In model 1, HARM was associated with baseline plasma MMP-9 concentration (odds ratio [OR], 1.01; 95% confidence interval [CI], 1.001–1.019; P=0.033). In model 2, HARM was associated with the ratio of MMP-9 to tissue inhibitor of matrix metalloproteinase-1 (OR, 4.94; 95% CI, 1.27–19.14; P=0.021).
Conclusions— Baseline MMP-9 was a significant predictor of HARM at 24-hour follow-up, supporting the hypothesis that MMP-9 is associated with BBB disruption. If the association between MMP-9 and BBB disruption is confirmed in future studies, HARM may be a useful imaging marker to evaluate MMP-9 inhibition in ischemic stroke and other populations with BBB disruption.
Blood–brain barrier (BBB) disruption after ischemic brain injury initiates a series of detrimental events, escalating secondary injury and the likelihood of poor outcome.1–3⇓⇓ Proteolytic breakdown of the BBB vasculature increases the permeability of the barrier within hours of ischemia, resulting in vasogenic edema, leukocyte infiltration, and hemorrhagic transformation (HT). The identification of factors contributing to and associated with impaired BBB integrity in humans after ischemia and reperfusion may be crucial to developing stroke therapies that can improve the safety of thrombolytics. There is evidence, in human and animal stroke models, that activation of matrix metalloproteinase (MMP) and, specifically, MMP-9 may contribute to proteolysis of the BBB basal lamina.4,5⇓ However, a direct association between MMP-9 and the presence of imaging-identified BBB disruption has yet to be demonstrated in humans.
MMP are critical regulators of the extracellular matrix. Extracellular matrix homeostasis is maintained by a balance between proteolytic and antiproteolytic factors, including MMP-9 and its natural inhibitor tissue inhibitor of matrix metalloproteinase-1 (TIMP-1). Because it is the balance of these proteolytic and antiproteolytic factors that contributes to impairment of the BBB, the MMP-9/TIMP-1 ratio has been used to provide an in vivo assessment of the proteolytic potential of MMP-9 to degrade the extracellular matrix.6 In stroke patients, the MMP-9/TIMP-1 ratio has been shown to have a more significant association with injury and the volume of perihematomal edema than when MMP-9 and TIMP-1 are considered independently.7 In addition, the MMP-9/TIMP-1 ratio has been identified as a significant predictor of total anterior circulation infarct stroke subtype.8 Therefore, the balance between MMP-9 and TIMP-1 is likely to play a role in BBB injury.9
BBB disruption after acute ischemic stroke can be visualized on fluid-attenuated inversion recovery MRI. This phenomenon has been previously described and termed HARM (hyperintense acute reperfusion injury marker).1,2⇓ HARM is gadolinium-diethylene triamine penta-acetic acid (Gd-DTPA) enhancement of the cerebrospinal fluid space, primarily the subarachnoid cerebrospinal fluid space in the hemispheric sulci. Gd-DTPA does not readily cross an intact BBB; therefore, its presence within the cerebrospinal fluid space implies an impaired BBB.
After Gd-DTPA, fluid-attenuated inversion recovery identification of HARM has been confirmed in subsequent studies of stroke and multiple sclerosis, identifying its utility in clinical practice as a marker of BBB disruption.10,11⇓ HARM has been observed in 33% of ischemic stroke patients imaged at 24 hours after injury and is significantly associated with reperfusion, HT, and poor clinical outcome.1,2⇓ Treatment with thrombolytic agents significantly increases the prevalence of HARM in this population.12
Recombinant tissue plasminogen activator (rt-PA) is a physiological activator of MMP and is the only FDA-approved treatment for ischemic stroke. The administration of rt-PA for the treatment of ischemic stroke can increase circulating MMP-9 by direct and indirect mechanisms13 contributing to the initiation of extracellular matrix remodeling.13–15⇓⇓ This process ultimately results in barrier disruptions with subsequent HT. HT after ischemic stroke has important implications for clinical outcome; however, the molecular underpinnings of the process are not completely understood. Stroke severity,16 age,17 and thrombolytic administration17 have been associated with the development of HT. Elevated plasma MMP-9 has emerged as a predictor of HT,18,19⇓ particularly after rt-PA administration.20
BBB disruption is a primary event initiating HT, and given associations between plasma MMP-9 and the occurrence of HT, we hypothesized that plasma MMP-9 would be associated with HARM, a marker of BBB disruption. The goal of this study was to identify predictors of BBB disruption through regression models containing MMP-9 and the MMP-9/TIMP-1 ratio with previously identified covariates of HARM.
Materials and Methods
This was a prospective study of acute stroke patient referrals admitted to Washington Hospital Center, DC, between May 2006 and June 2007. This study was approved by the National Institute of Neurological Disorders and Stroke and Washington Hospital Center Institutional Review Boards. Written informed consent was obtained from patients with suspected acute cerebrovascular events or their authorized representatives. Patients were included in this study if MRI and blood samples were available at the time of presentation and ≈24 hours later. Patients were excluded if they were younger than 18 years of age, had a contraindication to MRI, or were pregnant. The time of stroke symptom onset was determined as the time the patient was last known to be free of the acute stroke symptoms. Patient evaluations and management were standardized. Thrombolytic therapy with rt-PA was administered to patients who met standard eligibility criteria.
Patients evaluated for suspected stroke in the emergency room underwent MRI on presentation and ≈24 hours later on a 3-Tesla clinical MRI system. The scanning protocol was standardized for sequence parameters and order of acquisition: diffusion-weighted imaging, T2*-weighted gradient-recalled echo (GRE), T2-weighted fluid-attenuated inversion recovery, contrast-enhanced MRA, and perfusion-weighted imaging, performed in that order. Gd-DTPA was administered on the acute and follow-up scans at a dosing of 0.1 mmol/kg for contrast-enhanced MRA of the head and neck and for perfusion-weighted imaging. Maps of mean transit time obtained at baseline were viewed along side of acute diffusion-weighted imaging, blinded to all other series and time points, and evaluated for the existence of a perfusion deficit. For those patients found to have a perfusion deficit, follow-up mean transit time maps were reviewed to determine whether reperfusion had occurred with respect to baseline, by consensus. A visually obvious improvement in the mean transit time maps, typically representing a volume difference of at least 30%, was considered evidence of reperfusion.
Baseline and 24-hour follow-up images were presented to expert readers in a randomized order, absent of patient identifiers and clinical outcome. All image interpretations were by visual inspection and performed jointly by consensus, with a third blinded investigator resolving disagreement. All fluid-attenuated inversion recovery images were reviewed sequentially in time to allow for the comparison before and after Gd-DTPA between baseline and 24-hour scans. Presence of HARM (BBB disruption) was identified as positive if the cerebrospinal fluid intensity in the sulci, ventricles, background, or vitreous appeared hyperintense and continuous across >10 slices. The 24-hour scan was used as the criterion for analysis to allow for the maximum accumulation of enhancement.
MMP-9 and TIMP-1 Determination
Peripheral blood samples were collected during the baseline work-up and ≈24 hours later in sodium heparin sampling tubes, placed immediately on ice, and centrifuged within 15 minutes at 2000g for 10 minutes. The plasma was transferred to cryo vials for storage at −80°C until analysis.
Plasma MMP-9 and TIMP-1 concentrations were determined by a commercially available sandwich enzyme-linked immunosorbent assay obtained from R&D Systems. The MMP-9 enzyme-linked immunosorbent assay is designed to measure total MMP-9 (92 kDa pro and 82 kDa active forms). Per manufacturer, detectable ranges for MMP-9 and TIMP-1 in healthy controls are 13.2 to 105 ng/mL and 39 to 279 ng/mL, respectively. Patient samples were prepared according to manufacturer recommendations, and freeze–thaw cycles were avoided. All enzyme-linked immunosorbent assay microplates were read by the SPECTRAmax Ms ROM v2.00b73. Known standards were included on all plates and unknown samples were assayed in duplicate. Concentration values with coefficients of variation >10% were re-assayed. MMP-9/TIMP-1 ratios were calculated to provide a representation of the net proteolytic activity present in the plasma sample of each patient.
Descriptive and frequency analysis was obtained for all data. Because MMP-9 and TIMP-1 were not normally distributed, data for the biomarkers are presented as median with range. Statistical significance between groups for univariate analysis was determined by χ2 for categorical variables, Student t test, or ANOVA for continuous variables, and Mann-Whitney tests as appropriate, using a criterion of P<0.05. Binary logistic regression models were tested to determine whether baseline MMP-9 or MMP-9/TIMP-1 ratio were predictors of HARM. The models were entered as forward conditional, with an entry and exit criterion of 0.15, to test the relationship between HARM at 24 hours and these covariates: baseline MMP-9 or baseline MMP-9/TIMP-1 ratio, baseline diffusion-weighted imaging lesion volume, age, baseline NIHSS, hours from onset to baseline gadolinium injection, rt-PA administration (yes/no), whether rt-PA was administered before the baseline blood sampling (yes/no), and reperfusion (yes/no). All statistical analyses were performed using SPSS v15.
A total of 41 patients met inclusion criteria. Diagnoses included acute ischemic cerebrovascular syndrome (33; 80.6%), intracerebral hemorrhage (6; 14.6%), stroke mimic (1; 2.4%), and no stroke (1; 2.4%). Results are presented as mean±SD and median. Mean age of the sample was 62±13.9 years (range, 34–85 years). Median NIHSS score on admission was 4 (range, 0–27). Median time from onset to first blood draw was 9.8 hours, median time from onset to baseline imaging was 5 hours, and median time from baseline blood draw to follow-up MRI was 23 hours. Eight patients were treated with intravenous rt-PA within 3 hours of symptom onset and 1 intra-arterial rt-PA patient was treated at 3 hours and 45 minutes after symptom onset. Of the 33 stroke patients, 30 patients had readable mean transit time scans at baseline and 20 had a perfusion deficit. Of these 20 patients, 18 patients had readable mean transit time scans at follow-up and 12 patients had reperfusion.
Of the 41 patients, 17 (41.5%) had HARM present on the 24-hour follow-up scan. Eight (47%) of those patients had hemorrhage present on the 24-hour GRE (χ2=2.2; P=0.14). Two of the 8 patients with a positive GRE had primary hemorrhages diagnosed. Refer to the Figure for examples of HARM.
Table 1 provides the univariate associations between clinical variables and the presence of HARM. Acute severity of injury as measured by the baseline NIHSS (P=0.015), baseline diffusion-weighted imaging lesion volume (P=0.036), and age (P<0.001) were significantly different between patients with and without HARM at 24 hours. Patients who were older, with larger lesion volumes, and had higher NIHSS scores were more likely to have HARM. For the 33 ischemic stroke patients, these relationships with HARM also remained significantly associated with age (P<0.001), baseline NIHSS (P=0.055), and rt-PA administration (P=0.001). Eight of 9 patients treated with rt-PA presented with HARM on the 24-hour scan (χ2=10.7; P=0.001). There was no relationship between HARM and reperfusion at follow-up; however, there was a trend for an association with a perfusion deficit on the baseline MRI and the presence of HARM on the follow-up MRI (χ2=5.66; P=0.059).
Biomarkers and Relationship to HARM
Median plasma MMP-9 concentration was 36.8 ng/mL (range, 0–714.03 ng/mL) and median TIMP-1 concentration was 129.3 ng/mL (range, 0–539.52 ng/mL) on the baseline blood draw for the entire sample. MMP-9 values were significantly lower at 24 hours compared to baseline (Wilcoxon Z=−2.216; P=0.027), and TIMP-1 values were significantly higher at 24 hours compared to baseline (Wilcoxon Z=−2.757; P=0.006). Baseline plasma MMP-9 concentrations were not significantly different between patients with and without HARM at 24 hours (Mann-Whitney U=183; P=0.58). However, baseline TIMP-1 concentrations were slightly higher for those patients in whom HARM developed (Mann-Whitney U=126; P=0.04). When the sample was dichotomized by groups based on acute ischemic cerebrovascular syndrome criteria,21 definite acute ischemic cerebrovascular syndrome patients also had higher baseline TIMP-1 values associated with the presence of HARM at 24 hours (Mann-Whitney U=74; P=0.03).
On univariate analysis, the baseline MMP-9/TIMP-1 ratio was not statistically associated with the presence of HARM for either the entire population or definite acute ischemic cerebrovascular syndrome patients alone; however, there was a trend for higher MMP-9/TIMP-1 ratios in patients with HARM. There was no relationship between MMP-9, TIMP-1, or the MMP-9/TIMP-1 ratio with the presence of a perfusion deficit on the baseline MRI or reperfusion at follow-up.
A logistic regression analysis was performed to identify whether MMP-9 or the MMP-9/TIMP-1 ratio were predictors of HARM, controlling for previously known covariates and those shown to be significant in univariate analysis. Table 2 provides the regression coefficients, odds ratios, 95% confidence intervals for the odds ratios, and probability values for the significant variables in each model. In model 1, HARM was associated with baseline MMP-9 (P=0.03), age (P=0.005), and rt-PA administration (P=0.019). In model 2, HARM on the 24-hour follow-up scan was associated with baseline MMP-9/TIMP-1 ratio (P=0.021), age (P=0.005), and rt-PA administration (P=0.021).
This study demonstrates a relationship between plasma MMP-9 and the presence of HARM, a neuroimaging marker of BBB disruption in humans. This finding is consistent with preclinical animal studies9,18,22–24⇓⇓⇓⇓ and supports previous clinical data suggesting relationships between HARM and BBB disruption1,2⇓ and between MMP-9 and BBB disruption18,19,24–26,27⇓⇓⇓⇓⇓ If further validation of this finding is achieved in a larger cohort of patients, then it may be clinically significant to monitor plasma MMP-9 for the early detection of BBB impairment after stroke. In addition, HARM may be a useful imaging marker to evaluate MMP-9 inhibition for the treatment of BBB disruption in stroke and other neurological diseases.
MMP-9 expression is the result of activated leukocytes (particularly neutrophils);23 it results in IL-1β activation28 and initiation of the inflammatory cascade,29 further contributing to BBB impairment. MMP are closely related to endogenous tPA concentrations22,30–32⇓⇓⇓ such that endogenous tPA enhances MMP-9 expression and plays a role in MMP-9/heparin-induced HT.14 Early inhibition of MMP-9 and MMP-9 gene knockout mice models consistently demonstrate decreased infarct volumes and attenuation of BBB disruption and inflammation.28,33,34⇓⇓ However, the timing of inhibition is critical and late inhibition of MMP-9 can be detrimental, suggesting a role for MMP-9 in neurovascular remodeling and recovery after ischemic brain injury.35 The timing associated with this switch from deleterious to beneficial is relatively unstudied, which complicates the use of MMP-9 inhibition clinically. However, there is a scientific case for the use of MMP-9 inhibition to offset the negative effects associated with rt-PA therapy (eg, HT). Published data suggest that early MMP-9 inhibition (possibly within the same time window as that accepted for rt-PA therapy) in stroke may be beneficial, especially when used in combination with thrombolytic therapy to attenuate inflammation and BBB disruption.
In stroke patients, MMP-9 has been shown to have an association with NIHSS36 and severity of injury,8,37⇓ lesion volume growth,25,38⇓ rt-PA administration,39,40⇓ and other peripheral biomarker proteins (cellular fibronectin,19 F2IP,41 and IL-642). Overwhelming evidence identifies a risk between elevated baseline MMP-9 concentrations and subsequent HT and parenchymal hematoma for ischemic stroke patients.18–20,26⇓⇓⇓ Similarly, we found a significant association between the baseline MMP-9 and the NIHSS for patients with HARM (P=0.025). Postmortem studies validate that MMP-9 is increased in infarct and peri-infarct human brain tissue of stroke patients.24,27,43⇓⇓ The potential of peripheral blood measurements of MMP-9 as a biomarker of proteolytic activity within the cerebral environment is promising.
Given that the median time of baseline blood sampling was ≈10 hours from onset of symptoms (≈18 hours for the mean of the sample), it is possible that the initial increase of MMP-9 in response to the cerebrovascular event was missed with the later blood draw. This would explain why we can identify a significant univariate relationship between TIMP-1 and HARM and not MMP-9 and HARM. TIMP-1 levels are increased acutely in response to an increase in MMP-9, and TIMP-1 levels continue to increase at 24 hours.39 When the baseline MMP-9 concentration is entered into a multivariate model that controls for the effects of other significant covariates, the association between MMP-9 and HARM is revealed.
There are other potential limitations to this study. It is well-known that plasma MMP-9 may be elevated in patients with hypertension,44 dyslipidemia,45 inflammatory/infectious processes,46 diabetes,44 and in patients who smoke.47 Atherosclerotic disease involves matrix remodeling and MMP-9 activation for each of these disorders.48 Patients in this study presented with differing degrees of comorbidities and were not adequately screened for the presence of heart disease or infectious processes. However, the patient groups were not significantly different from one another based on medical history. In addition, 4 out of the 9 (44.4%) patients who received rt-PA had their blood draw after rt-PA administration, which could lead to a false increase in plasma MMP-9. Some studies report results of plasma MMP-9 isolated from whole blood drawn after rt-PA administration.41 Because this was found to be significant in our population, it was used as a covariate in the logistic regression analysis. Last, our patient population was small, and replication of the results on a larger independent sample is required.
Disruption of the BBB is a serious complication of ischemic stroke that may contribute to subsequent edema, initiation of the inflammatory cascade, HT, and poor clinical outcome. Identification of the factors resulting in BBB disruption may ultimately aid in therapeutic drug discovery for the treatment of ischemic stroke. Data presented here are among the first to validate preclinical studies suggesting a significant relationship between MMP-9 and the presence of BBB disruption in humans. The significant associations presented here between MMP-9 and the MMP-9/TIMP-1 ratio with HARM provides further evidence of the relationship between MMP-9 and BBB disruption. It remains to be determined whether MMP-9 is an active player in BBB disruption or is a marker of the severity of the ongoing damage to the BBB after ischemic stroke. Future studies should be designed to elucidate whether MMP-9 plays a causative role in BBB disruption after stroke.
The authors thank Dace Klimanis for her technical assistance.
Sources of Funding
Taura Barr’s contributions were supported by a pre-doctoral Intramural Research Training Award via the Graduate Partnerships Program through the National Institute of Nursing Research, National Institutes of Health. This research was supported by the Division of Intramural Research of the National Institute of Neurological Disorders and Stroke, National Institutes of Health.
- Received October 20, 2009.
- Accepted November 4, 2009.
- ↵Warach S, Latour LL. Evidence of reperfusion injury, exacerbated by thrombolytic therapy, in human focal brain ischemia using a novel imaging marker of early blood-brain barrier disruption. Stroke. 2004; 35: 2659–2661.
- ↵Pfefferkorn T, Rosenberg GA. Closure of the blood-brain barrier by matrix metalloproteinase inhibition reduces rtpa-mediated mortality in cerebral ischemia with delayed reperfusion. Stroke. 2003; 34: 2025–2030.
- ↵Alvarez-Sabin J, Delgado P, Abilleira S, Molina CA, Arenillas J, Ribo M, Santamarina E, Quintana M, Monasterio J, Montaner J. Temporal profile of matrix metalloproteinases and their inhibitors after spontaneous intracerebral hemorrhage: Relationship to clinical and radiological outcome. Stroke. 2004; 35: 1316–1322.
- ↵Rosenberg GA, Estrada EY, Dencoff JE. Matrix metalloproteinases and TIMPs are associated with blood-brain barrier opening after reperfusion in rat brain. Stroke. 1998; 29: 2189–2195.
- ↵Cuadrado E, Ortega L, Hernandez-Guillamon M, Penalba A, Fernandez-Cadenas I, Rosell A, Montaner J. Tissue plasminogen activator (t-PA) promotes neutrophil degranulation and mmp-9 release. J Leukoc Biol. 2008; 84: 207–214.
- ↵Zhao BQ, Ikeda Y, Ihara H, Urano T, Fan W, Mikawa S, Suzuki Y, Kondo K, Sato K, Nagai N, Umemura K. Essential role of endogenous tissue plasminogen activator through matrix metalloproteinase 9 induction and expression on heparin-produced cerebral hemorrhage after cerebral ischemia in mice. Blood. 2004; 103: 2610–2616.
- ↵Thomalla G, Sobesky J, Kohrmann M, Fiebach JB, Fiehler J, Zaro Weber O, Kruetzelmann A, Kucinski T, Rosenkranz M, Rother J, Schellinger PD. Two tales: Hemorrhagic transformation but not parenchymal hemorrhage after thrombolysis is related to severity and duration of ischemia: MRI study of acute stroke patients treated with intravenous tissue plasminogen activator within 6 hours. Stroke. 2007; 38: 313–318.
- ↵Larrue V, von Kummer R, del Zoppo G, Bluhmki E. Hemorrhagic transformation in acute ischemic stroke. Potential contributing factors in the European cooperative acute stroke study. Stroke. 1997; 28: 957–960.
- ↵Castellanos M, Leira R, Serena J, Pumar JM, Lizasoain I, Castillo J, Davalos A. Plasma metalloproteinase-9 concentration predicts hemorrhagic transformation in acute ischemic stroke. Stroke. 2003; 34: 40–46.
- ↵Castellanos M, Sobrino T, Millan M, Garcia M, Arenillas J, Nombela F, Brea D, Perez de la Ossa N, Serena J, Vivancos J, Castillo J, Davalos A. Serum cellular fibronectin and matrix metalloproteinase-9 as screening biomarkers for the prediction of parenchymal hematoma after thrombolytic therapy in acute ischemic stroke: A multicenter confirmatory study. Stroke. 2007; 38: 1855–1859.
- ↵Montaner J, Fernandez-Cadenas I, Molina CA, Monasterio J, Arenillas JF, Ribo M, Quintana M, Chacon P, Andreu AL, Alvarez-Sabin J. Safety profile of tissue plasminogen activator treatment among stroke patients carrying a common polymorphism (c-1562t) in the promoter region of the matrix metalloproteinase-9 gene. Stroke. 2003; 34: 2851–2855.
- ↵Kidwell CS, Warach S. Acute ischemic cerebrovascular syndrome. Diagnostic criteria. Stroke. 2003.
- ↵Sumii T, Lo EH. Involvement of matrix metalloproteinase in thrombolysis-associated hemorrhagic transformation after embolic focal ischemia in rats. Stroke. 2002; 33: 831–836.
- ↵Gidday JM, Gasche YG, Copin JC, Shah AR, Perez RS, Shapiro SD, Chan PH, Park TS. Leukocyte-derived matrix metalloproteinase-9 mediates blood-brain barrier breakdown and is proinflammatory after transient focal cerebral ischemia. Am J Physiol Heart Circ Physiol. 2005; 289: H558–568.
- ↵Rosell A, Ortega-Aznar A, Alvarez-Sabin J, Fernandez-Cadenas I, Ribo M, Molina CA, Lo EH, Montaner J. Increased brain expression of matrix metalloproteinase-9 after ischemic and hemorrhagic human stroke. Stroke. 2006; 37: 1399–1406.
- ↵Rosell A, Alvarez-Sabin J, Arenillas JF, Rovira A, Delgado P, Fernandez-Cadenas I, Penalba A, Molina CA, Montaner J. A matrix metalloproteinase protein array reveals a strong relation between MMP-9 and MMP-13 with diffusion-weighted image lesion increase in human stroke. Stroke. 2005.
- ↵Montaner J, Molina CA, Monasterio J, Abilleira S, Arenillas JF, Ribo M, Quintana M, Alvarez-Sabin J. Matrix metalloproteinase-9 pretreatment level predicts intracranial hemorrhagic complications after thrombolysis in human stroke. Circulation. 2003; 107: 598–603.
- ↵Russo R, Siviglia E, Gliozzi M, Amantea D, Paoletti A, Berliocchi L, Bagetta G, Corasaniti MT. Evidence implicating matrix metalloproteinases in the mechanism underlying accumulation of il-1beta and neuronal apoptosis in the neocortex of hiv/gp120-exposed rats. Int Rev Neurobiol. 2007; 82: 407–421.
- ↵Wang S, Lee SR, Guo SZ, Kim WJ, Montaner J, Wang X, Lo EH. Reduction of tissue plasminogen activator-induced matrix metalloproteinase-9 by simvastatin in astrocytes. Stroke. 2006; 37: 1910–1912.
- ↵Kahles T, Foerch C, Sitzer M, Schroeter M, Steinmetz H, Rami A, Neumann-Haefelin T. Tissue plasminogen activator mediated blood-brain barrier damage in transient focal cerebral ischemia in rats: Relevance of interactions between thrombotic material and thrombolytic agent. Vascul Pharmacol. 2005; 43: 254–259.
- ↵Svedin P, Hagberg H, Savman K, Zhu C, Mallard C. Matrix metalloproteinase-9 gene knock-out protects the immature brain after cerebral hypoxia-ischemia. J Neurosci. 2007; 27: 1511–1518.
- ↵Montaner J, Alvarez-Sabin J, Molina C, Angles A, Abilleira S, Arenillas J, Gonzalez MA, Monasterio J. Matrix metalloproteinase expression after human cardioembolic stroke: Temporal profile and relation to neurological impairment. Stroke. 2001; 32: 1759–1766.
- ↵Serena J, Blanco M, Castellanos M, Silva Y, Vivancos J, Moro MA, Leira R, Lizasoain I, Castillo J, Davalos A. The prediction of malignant cerebral infarction by molecular brain barrier disruption markers. Stroke. 2005; 36: 1921–1926.
- ↵Ning M, Furie KL, Koroshetz WJ, Lee H, Barron M, Lederer M, Wang X, Zhu M, Sorensen AG, Lo EH, Kelly PJ. Association between tPA therapy and raised early matrix metalloproteinase-9 in acute stroke. Neurology. 2006; 66: 1550–1555.
- ↵Horstmann S, Kalb P, Koziol J, Gardner H, Wagner S. Profiles of matrix metalloproteinases, their inhibitors, and laminin in stroke patients: Influence of different therapies. Stroke. 2003; 34: 2165–2170.
- ↵Kelly PJ, Morrow JD, Ning M, Koroshetz W, Lo EH, Terry E, Milne GL, Hubbard J, Lee H, Stevenson E, Lederer M, Furie KL. Oxidative stress and matrix metalloproteinase-9 in acute ischemic stroke: The biomarker evaluation for antioxidant therapies in stroke (beat-stroke) study. Stroke. 2008; 39: 100–104.
- ↵Tayebjee MH, Lim HS, MacFadyen RJ, Lip GY. Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 and -2 in type 2 diabetes: Effect of 1 year’s cardiovascular risk reduction therapy. Diabetes Care. 2004; 27: 2049–2051.
- ↵Sundstrom J, Evans JC, Benjamin EJ, Levy D, Larson MG, Sawyer DB, Siwik DA, Colucci WS, Sutherland P, Wilson PW, Vasan RS. Relations of plasma matrix metalloproteinase-9 to clinical cardiovascular risk factors and echocardiographic left ventricular measures: The Framingham heart study. Circulation. 2004; 109: 2850–2856.