Ischemic stroke is the most prevalent neurological disease worldwide (1). Intravenous administration of recombinant tissue plasminogen activator (rt-PA) and endovascular thrombectomy (EVT) are the only two United States Food and Drug Administration (FDA)-approved reperfusion therapies for treating patients with acute ischemic stroke (AIS) (2). However, the therapeutic benefits of administering rt-PA 4.5 h after the onset of a stroke are overshadowed by the risks of hemorrhagic transformation (HT) (3). EVT, a more recently FDA-approved procedure, can be carried out within 24 h of the manifestation of symptoms and is primarily intended for AIS caused by large-vessel occlusions (4). Importantly, EVT can only be performed in stroke centers equipped with adequate resources and expertise (5). These constraints contribute to the estimation that less than 10% of stroke patients benefit from reperfusion therapies (6).

HT is a severe complication arising after reperfusion therapy that results in profound neurological impairment and significant mortality risk (3). Our clinical objective is to enhance early diagnosis, diminish the likelihood of cerebral hemorrhage, and ultimately augment the overall effectiveness of reperfusion therapies (7, 8). Matrix metalloproteinase-9 (MMP-9) belongs to the matrix metalloproteinase family and plays a role in proteolyzing cerebrovascular basement membrane and tight junction proteins (9, 10). Elevated expression of MMP-9 has been associated with breakdown of the blood–brain barrier (BBB) and development of HT following rt-PA treatments (11). However, these study results were acquired prior to the widespread adoption of EVT. One recent study determined the levels of serum biomarkers (MMP-9, APP770, ET-1, S100B, and Claudin-5) of venous blood collected from AIS patients at admission, yet predictive value of these biomarkers for HT following EVT was not demonstrated (12). The inability of serum biomarkers collected before EVT to predict HT could stem from factors intrinsic to the EVT procedure. During mechanical thrombectomy, direct vessel wall damage from endovascular procedures may exceed the BBB impairment resulting from ischemia (13). After three stent retriever passes during EVT, the rate of symptomatic intracranial hemorrhage or parenchymal hematoma increased exponentially post-puncture (14). Therefore, instead of relying on venous blood, we specifically collected arterial blood from the EVT puncture site to mitigate the influence of systemic factors. The arterial levels of MMP-9 collected both before and after EVT were analyzed to consider factors inherent in the EVT process. Our findings indicate that the increased levels of arterial MMP-9 post-EVT were associated with incidence of HT and could potentially function as a predictive biomarker for HT following EVT.

Our results demonstrate that the upregulation of arterial MMP-9 following EVT is associated with the occurrence of HT and may serve as a predictive biomarker for HT after EVT. To the best of our knowledge, this study represents the first research, to date, evaluating the prognostic role of temporal changes in arterial biomarkers after EVT.

Our main finding was partly in line with the large retrospective study where higher admission neutrophil-to-lymphocyte ratio (NLR) was an independent predictor of symptomatic intracranial hemorrhage (sICH) in AIS patients treated with EVT (17). AIS has been shown to trigger a strong immune system response in animal models of MCA occlusion by enhancing neutrophil migration into the brain. Neutrophils are a key source of MMP-9 within the first 24 h after AIS, potentially linking admission NLR to sICH in LVO patients post-EVT, given the association of MMP-9 with BBB disruption and sICH after thrombolysis (17). However, several factors can influence admission NLR, including infections, inflammatory conditions, stress, and certain medications (18).

Several studies indicated that higher levels of MMP-9 before thrombolytic therapies were associated with the development of HT after rt-PA administration (10). The median MMP-9 values detected in blood plasma before rt-PA treatments ranged from 54 to 225 ng/mL (11), a range akin to the MMP-9 levels (100.1–195 ng/mL) observed in our study utilizing blood plasma. A recent study revealed that high MMP-9 levels in blood sera (>775 ng/mL) at 6 h from admission were associated with HT following EVT (19). Conversely, another recent study utilizing blood sera failed to establish a connection between MMP-9 levels (15–46 ng/mL) and HT following EVT (12). MMP-9 levels vary significantly across studies, likely due to the utilization of different ELISA kits sourced from various companies and differences in sample types, such as serum versus plasma (20, 21). The processing of blood samples to obtain sera versus plasma can contribute to differences in MMP-9 levels. Serum is obtained by allowing blood to clot and then centrifuging to separate the liquid portion (serum) from the clot. Plasma, on the other hand, is obtained by centrifuging blood without allowing it to clot, resulting in a liquid portion containing clotting factors and cellular components. Neutrophils are known to be a significant source of MMP-9, and their activation and degranulation can lead to increased MMP-9 secretion (20, 21). During the clotting process in serum preparation, neutrophils may release MMP-9 into the serum, contributing to higher MMP-9 levels compared to plasma samples, where neutrophils are not activated (20, 21).

Personalized medicine, also known as precision medicine, represents an innovative paradigm in medical treatment and healthcare (22). Rather than adopting a one-size-fits-all approach, personalized medicine aims to tailor medical decisions, interventions, and treatments to the specific characteristics of each patient (23). In this study, we embraced the personalized medicine approach by examining the percentage changes in arterial MMP-9 levels before and after EVT in individual patients to identify those at high risk of HT. Although potential gender-related differences in MMP-9 levels in cardiovascular and central nervous system conditions have been reported (24), no significant gender difference of arterial MMP-9 changes was found in this study.

By concentrating resources on individuals at a heightened risk of HT resulting from these interventions, we aim to optimize the utilization of resources and improve patient outcomes. For example, several small-molecule inhibitors targeting MMP-9 have been developed (25). Recently, an anti-MMP-9 neutralizing antibody was isolated based on a functional selection strategy (26). This antibody demonstrated the ability to reduce BBB breakdown in mice following a stroke (27). Our study may assist in identifying and prioritizing patients who would derive the greatest benefits from MMP-9 inhibitors, aiming to prevent or minimize the occurrence of hemorrhagic complications (28).

A major limitation of our study was its relatively small sample size. Nonetheless, the upregulation of MMP-9 showed clear associations with the occurrence of HT following EVT. The application of personalized medicine supported by our study can be substantiated through broader and more extensive investigations. However, a limitation preventing practical clinical use of MMP-9 as a biomarker is the length of time required to obtain results from existing MMP-9 ELISA assays; the current assays require over 3 h to produce results. The development of more rapid MMP-9 assays is crucial for practical clinical application.

In conclusion, the results from this single-center prospective study demonstrate an association between MMP-9 upregulation following EVT and the occurrence of HT. We are the first to show that the upregulation of MMP-9 may act as a biomarker for HT following EVT. The idea of biomarker-guided therapy, as suggested in this study, has been explored and applied using the association between various other biomarkers and the clinical status of patients (29, 30). This approach may foster more personalized and targeted strategies in stroke care, ultimately enhancing patient outcomes.

The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.

This study protocol was approved by the Institutional Review Board (IRB) of Taichung Veterans General Hospital (TCVGH, CE22262B) and by National Health Research Institutes (NHRI, EC1110609-E). The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

J-AH: Writing – review & editing, Writing – original draft, Supervision, Project administration, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Y-HW: Writing – review & editing, Writing – original draft, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. P-LC: Writing – review & editing, Writing – original draft, Supervision, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Y-CW: Writing – review & editing, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. I-CC: Writing – review & editing, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Y-TH: Writing – review & editing, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. W-HC: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.