New targets in spontaneous intracerebral hemorrhage

Abstract

Purpose of review

Intracerebral hemorrhage (ICH) is a devastating stroke with limited medical treatments; thus, timely exploration of emerging therapeutic targets is essential. This review focuses on the latest strategies to mitigate secondary brain injury post-ICH other than targeting surgery or hemostasis, addressing a significant gap in clinical practice and highlighting potential improvements in patient outcomes.

Recent findings

Promising therapeutic targets to reduce secondary brain injury following ICH have recently been identified, including attenuation of iron toxicity and inhibition of ferroptosis, enhancement of endogenous resorption of hematoma, and modulation of perihematomal inflammatory responses and edema. Additionally, novel insights suggest the lymphatic system of the brain may potentially play a role in hematoma clearance and edema management. Various experimental and early-phase clinical trials have demonstrated these approaches may potentially offer clinical benefits, though most research remains in the preliminary stages.

Summary

Continued research is essential to identify multifaceted treatment strategies for ICH. Clinical translation of these emerging targets could significantly enhance the efficacy of therapeutic interventions and potentially reduce secondary brain damage and improve neurological recovery. Future efforts should focus on large-scale clinical trials to validate these approaches, to pave the way for more effective treatment protocols for spontaneous ICH.

INTRODUCTION

Intracerebral hemorrhage (ICH) is a devastating form of stroke with a poor prognosis, and despite ongoing research, effective treatments remain limited. Stroke unit care benefits all ICH patients in general, though the individual effect is probably small. Hematoma volume and growth are key determinants of ICH outcomes, as early brain damage is primarily caused by the mass effect of the hematoma. Aggressive blood pressure control and hemostatic agents are currently considered the main treatment approaches for acute ICH, with modest effects on reducing mortality and dependency [1^▪▪,2]. Minimally invasive surgery may be beneficial for a highly selected group of patients, particularly those with lobar ICH [3^▪▪], but conventional surgery has not consistently shown benefit, underscoring the need for new treatment strategies.

After an ICH occurs, the blood products from the hematoma gradually lead to secondary brain injuries due to increased oxidative stress and related inflammatory responses [4]. Management of the consequences of secondary brain injuries has not been extensively investigated. Most of the related targets have only been investigated at the preclinical stage in experimental models of ICH. Some promising targets have been successfully translated to clinical trials but have only reached early-phase studies (Table 1); therefore, more research is needed to identify targets that may help to reduce secondary brain damage after an ICH occurs. 

Table 1.

Therapeutic targets in intracerebral hemorrhage that enter phase I/II trials

Drug	n	Study design	Status	ClinicalTrials. gov number	Outcomes in completed trials
Deferoxamine (i-DEF) [28,35]	291	Phase II; randomized, double-blind, placebo-controlled	Completed	NCT02175225	No improvement of mRS score at day 90. Post hoc analysis suggested that drug accelerated and altered the trajectory of recovery up to 6 months
Pioglitazone (SHRINC) [12,13]	84	Phase II; randomized, double-blind, placebo-controlled	Completed	NCT00827892	No difference in mortality, cerebral edema, and functional outcomes
Remote ischemic conditioning (RICH) [15▪]	40	Phase I; randomized, open-label, evaluator-blind	Completed	NCT03930940	No difference in hematoma size and absolute PHE at day 7, but higher hematoma resolution rate and lower relative PHE in RIC group were observed
Minocycline (MACH) [22]	16	Phase I/II; randomized, open-label, evaluator-blind	Completed	NCT01805895	No difference in mRS, inflammatory biomarkers, hematoma volume, or PHE at 90 days
Minocycline (MITCH) [23]	20	Phase I/II; randomized, double-blind, placebo-controlled	Completed	NCT03040128	No difference in clinical and radiological outcomes. Drug was associated with a decrease in MMP-9 level
Minocycline (BATMAN) [27]		Phase I/II; randomized, double-blind, placebo-controlled	Recruiting	NCT05680389
Anakinra (BLOC-ICH) [29]	25	Phase II; randomized, double-blind, placebo-controlled	Completed	NCT03737344	No difference in oedema extension distance and mRS at 3 months. Post hoc analysis indicated reduced IL-6 levels with anakinra
Anakinra (ACTION) [30]	75	Phase II; randomized, open-label, evaluator-blind, three-armed	Recruiting	NCT04834388
Fingolimod (FITCH)	28	Phase I; randomized, double-blind, placebo-controlled	Completed	NCT04088630	Pending
Siponimod [42▪]	32	Phase II; randomized, double-blind, placebo-controlled	Completed	NCT03338998	No difference in absolute PHE volume
Glibenclamide (GATE-ICH) [66]	200	Phase II; randomized, open-label, evaluator-blind	Completed	NCT03741530	Drug did not improve functional outcome at day 90
Celecoxib	60	Phase II; randomized, open-label	Recruiting	NCT05434065
Statin discontinuation vs. continuation (SATURN) [77]	1456	Phase III; randomized, open-label, evaluator-blind	Recruiting	NCT03936361
Atorvastatin (STATIC) [78]	98	Phase II/III; randomized, open-label, evaluator-blind	Recruiting	NCT04857632
Conivaptan [83]	7	Phase I; open-label	Completed	NCT03000283	Drug was well tolerated, with no change in cardiac or renal function

IL, interleukin; MMP, matrix metalloproteinase; mRS, modified Rankin Scale; PHE, perihematomal edema; RIC, remote ischemic conditioning.

Box 1.

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This review summaries the recent advances for various therapeutic targets that may reduce secondary brain injury after ICH, including reduction of toxicity from blood components, promotion of endogenous hematoma resorption, modulation of perihematomal inflammatory responses, and alleviation of perihematomal edema (PHE). We also discuss the emerging knowledge on the role of the lymphatic system, which may participate in hematoma clearance and contribute to the formation of PHE after ICH. Important trials of these novel therapeutic targets are summarized in Table 1.

IRON TOXICITY AND FERROPTOSIS

After an ICH occurs, neurotoxins from the hematoma, such as hemoglobin and heme, are released into the brain parenchyma and metabolized into ferrous (Fe²⁺) or ferric ion (Fe³⁺) [5]. This process induces iron toxicity that involves the overproduction of reactive oxygen species (ROS) and iron-dependent nonapoptotic cell death, also called ferroptosis [6,7]. Ferroposis is a form of programmed cell death that is characterized by morphological changes in mitochondria and iron-dependent lipid peroxidation [7,8].

Attenuation of iron toxicity or inhibition of ferroptosis has been considered as a potential therapeutic target to reduce secondary brain injury following ICH. Infusion of the iron chelator agent deferoxamine mesylate within 24 h of the onset of ICH was investigated in a phase II clinical trial (i.e. deferoxamine mesylate in patients with ICH, iDEF trial), which confirmed this approach was well tolerated but potentially had low efficacy in terms of 90-day functional outcomes [9]. However, a more recently published post hoc analysis of the iDEF trial for long-term recovery suggested that deferoxamine accelerated recovery and altered the trajectory of functional outcomes in the 6 months after ICH [10].

Targets that inhibit heme-induced ferroptosis have been found to have beneficial effects after ICH; however, most of these findings were based on preclinical studies [11]. Increased expression of heme oxygenase-1 (HO-1), which catalyzes heme to release Fe²⁺, is observed after ICH, especially in the peri-hematoma area [12,13]. Recent advances suggest that targeting pathways that alter HO-1-related signaling could effectively attenuate ferroptosis-induced brain injury [14^▪–16^▪]. However, further research is required to determine how ferroptosis interacts with other traditional cell death pathways and elucidate its contribution to brain injury [17].

ENDOGENOUS HEMATOMA RESORPTION

Currently, minimally invasive removal of the hematoma is the primary treatment approach for rapid hematoma clearance; however, this treatment is restricted to patients with hematoma located in the lobar regions and is only effective within the early time window [3^▪▪,18]. In addition, surgical approaches are more frequently employed for patients with larger hematoma, and therefore the role of surgery in minor ICH remains uncertain. Acceleration of endogenous absorption of hematoma has been suggested as a potential strategy to reduce secondary brain injury due to hemolytic blood products, especially for patients who are ineligible for surgical hematoma removal.

Erythrophagocytosis by microglia/macrophages is an important endogenous mechanism that removes red blood cells, detoxifies hemolytic products, and facilitates neurological recovery [19]. Enhancement of peroxisome proliferator-activated receptor (PPAR)-γ or NRF2-related signaling though controlling the expression of scavenger receptor genes, which promotes erythrophagocytosis by microglia/macrophages, has been found to increase hematoma resorption [20–22]. Bexarotene, a retinoid X receptor agonist that may promote activation of PPAR-γ, and vitamin D have been found to potentially enhance hematoma clearance in experimental ICH models [23,24]. Drugs targeting PPAR-γ or related pathways may potentially improve patient outcomes; however, a phase II clinical trial of pioglitazone, a potent PPAR-γ agonist, demonstrated no difference in mortality, cerebral edema, or functional outcomes (SHRINC, n = 84) [25,26].

Remote ischemic conditioning (RIC), a maneuver that involves repetitive inflation–deflation of a blood pressure cuff on a limb, has been shown to promote clot resolution and attenuate cerebral edema in an animal model via AMPK-dependent immune regulation [27]. Repeated daily RIC for 7 days was evaluated in a phase I trial (RICH, n = 40) and was found to be well tolerated in patients with ICH. It may potentially improve the rate of hematoma resolution [28].

INFLAMMATORY RESPONSES

Following an ICH, various inflammatory pathways are activated around the hematoma. These processes involve activation of microglia and astrocytes, as well as leukocyte infiltration. The resulting neuroinflammation, which begins within hours and persists for weeks, provides a window for therapeutic intervention [29,30,31].

Microglia and macrophages exist in either a proinflammatory (M1) state, producing cytokines like TNF-α and IL-1β, or a regulatory (M2) state, releasing anti-inflammatory cytokines such as TGF-β and IL-10 [29,30]. Minocycline, a second-generation tetracycline, has been reported to exert several nonantimicrobial properties that may be beneficial for ICH treatment, including inhibition of pro-inflammatory microglia/macrophages and matrix metalloproteases (MMPs), antioxidant effects, and reduction of neuronal apoptotic signaling [32–34]. Small phase I/II trials (MACH [35], n = 16; MITCH [36], n = 20) reported that minocycline reduced serum MMP-9 levels in patients with ICH, although no significant differences in clinical outcomes were observed. A retrospective cohort study of patients with clinically aggressive cerebral amyloid angiopathy (CAA) demonstrated that minocycline was associated with a reduced risk of ICH recurrence [37^▪]. A phase I/II study of minocycline for CAA is currently underway (BATMAN, NCT05680389) [38^▪].

Cytokines play pivotal roles in the polarization and functional regulation of microglia. Anakinra, a recombinant human IL-1 receptor antagonist, was evaluated in a phase II study (BLOC-ICH [39^▪▪], n = 25); although no significant improvements in radiological or clinical outcomes were observed, a post hoc analysis indicated reduced IL-6 levels with anakinra at day 2 after ICH. Another phase II trial of Anakinra (ACTION [40^▪], NCT04834388) is currently ongoing. TGF-β1 modulates microglia-mediated neuroinflammation and supports functional recovery, as demonstrated in animal studies, and therefore may also have therapeutic potential for ICH [41,42^▪].

Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator that acts through the S1P receptors (S1PR1–S1PR5) [30,43]. Activation of the S1P receptors inhibits the egress of lymphocytes from lymph nodes and their recirculation [44], and also appears to reduce pro-inflammatory responses and enhance regulatory functions in microglia [45]. Fingolimod, an S1PR agonist, was demonstrated to reduce PHE and neurological deficits in a small proof-of-concept clinical study (n = 23) [46]. A phase I study of fingolimod (FITCH, NCT04088630) in 28 patients with ICH has been completed; however, the results are pending. Siponimod, another S1PR modulator, was tested in a phase II trial (NCT03338998) that was halted because of the COVID-19 pandemic, with no significant differences in edema volume observed in the final 29 patients [47].

Moreover, ICH activates the Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, which amplifies inflammation by promoting the release of IL-1β and neutrophil infiltration, which in turn worsen brain edema [48]. In animal models, inhibition of NLRP3 reduced cerebral edema and neurological deficits [49^▪,50,51]. The 18 kDa translocator protein (TSPO), which is upregulated in peri-hematomal regions post-ICH, is primarily observed in microglia/macrophages and regulates the release of pro-inflammatory cytokines [52]. TSPO ligands such as etifoxine have been shown to reduce neurodeficits and brain edema in animal models [53]. In addition, the complement system is activated at an early stage in ICH, and triggers microglial activation and subsequent neuroinflammation [54]. C3a and C5a receptor antagonists have been found to improve brain edema and neurological function [54], and the complement inhibitor N-acetyl heparin (NAH) reduced brain injury and iron accumulation postintraventricular hemorrhage in animal models [55^▪].

Reactive astrocytes, which are classified as the proinflammatory A1 and reparative A2 subtypes, also play crucial roles in neuroinflammation [31]. The aquaporin-4 (AQP4) water channel protein is located in astrocyte foot processes and is essential for maintenance of blood–brain barrier integrity. Enhancing the expression of AQP4 reduced PHE [56]. Moreover, edaravone, which maintains the polarity of AQP4, alleviated brain edema and injury [57^▪]. IL-15, which colocalizes with astrocytes, exacerbated neurological deficits and cerebral edema and modulated microglia towards a pro-inflammatory phenotype in GFAP-IL-15^tg mice [58]. Conversely, IL-33, which is expressed in astrocytes, suppressed pro-inflammatory cytokines, reduced cerebral water content, and improved neurological function post-ICH in mice ICH model [59].

Neutrophil-driven inflammation and cytotoxicity are generally believed to worsen ICH injury. IL-27, which is produced by microglia/macrophages, increased production of lactoferrin by neutrophils and reduced brain edema, neuronal death, and functional deficits [60]. Lastly, activation of the PD-1/PD-L1 pathway, which inhibits T-cell activity, reduced neurologic deficits, cerebral edema, and the hemorrhage volume in ICH [61], and also potentially shifted microglia to an anti-inflammatory phenotype [62].

PERIHEMATOMAL EDEMA

PHE is a significant secondary injury after ICH that contributes to the mass effect and increased intracranial pressure [63]. The standard management of cerebral edema includes osmolar therapies such as mannitol or hypertonic saline [63]. Thrombin, which breaks down the blood–brain barrier and promotes inflammation, is a key factor in brain edema [64]. In a rat ICH model, inhibition of thrombin using argatroban reduced secondary brain damage, including edema and inflammation [65]. However, thrombin is a crucial component of the coagulation cascade, and thus is a challenging therapeutic target for ICH.

Glibenclamide (glyburide), a sulfonylurea, inhibits Sur1-TRMP4 channels and has been shown to reduce PHE in animal models [66]. For ischemic stroke, a phase II trial (GAMES-RP [67], n = 77) of patients with large hemispheric infarcts showed glyburide reduced cerebral edema and mortality due to edema compared with the placebo, despite both groups achieving similar functional outcomes. The terminated phase III CHARM trial (NCT02864953, n = 585) of glibenclamide reported no overall functional improvement at 3 months [68], though patients with stroke volumes 120 ml or less had favorable outcomes in subgroup analysis [69]. For hemorrhagic stroke, the phase II GATE-ICH trial (n = 200) of patients with ICH found glibenclamide had no functional benefit at day 90 and was associated with a higher incidence of hypoglycemia [70], whereas the phase II ASTRAL trial (NCT03954041, n = 92) in patients with brain contusion showed no significant difference in contusion volume or functional outcomes [71].

Cyclo-oxygenase 2 (COX2) expression increases following ICH [72]. Celecoxib, a selective COX2 inhibitor, was found to reduce ICH-induced edema in animal models and in a case–control study [73,74]. The ACE-ICH pilot study (n = 44) indicated that treatment with celecoxib within 24 h was associated with reduced PHE expansion within the first 7 days post-ICH [75]. A phase II clinical trial (NCT05434065) is currently investigating the effects of administering celecoxib within 6 h of the onset of ICH.

Statins inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and exert anti-inflammatory properties. In rodent ICH models, statins reduced PHE, decreased blood–brain barrier permeability, and improved functional outcomes and mortality [76]. Retrospective studies in humans have reported mixed results regarding prior statin use and PHE [77,78]. Analysis of a single-center prospective registry that included 1275 patients found initiation of statins post-ICH was linked to larger peak cerebral edema, while the continuation of prior statin use was not associated with a significant difference in peak edema compared with discontinuation [79]. Current trials investigating the role of statins in ICH include the phase III SATURN (NCT03936361) and phase II/III STATIC (NCT04857632) trials [80^▪,81^▪].

Vasopressin receptor antagonists, such as conivaptan and tolvaptan, increase plasma osmolarity and sodium levels. In experimental models of ICH, tolvaptan reduced brain edema and improved functional outcomes [82,83]. An open-label phase I trial of seven patients with ICH found conivaptan was well tolerated and did not lead to adverse cardiac or renal effects [84]. However, sodium overcorrection, hypotension, and hypokalemia were observed in another cohort study of patients treated with conivaptan or tolvaptan in neurocritical care [85].

EMERGING TARGET: THE BRAIN LYMPHATIC SYSTEM

The lymphatic system of the brain, including the glymphatics and meningeal lymphatics, plays a pivotal role in brain clearance of solutes, interstitial fluid, and metabolic waste [86]. As in other central nervous system (CNS) disorders, the lymphatic system has emerged as new target to alleviate secondary brain injury and to improve neurological recovery after ICH.

Perivascular spaces, which are surrounded by astrocytic endfeet, are key structures involved in cerebrospinal fluid (CSF) and interstitial fluid exchange and therefore regulate the function of the glymphatics [87]. Previous studies have suggested an association between enlarged PVS and increased risk of ICH recurrence, which implies a pathogenic role for the glymphatics in hemorrhagic stroke [88,89]. Within the PVS, AQP4 water channels expressed in the astrocytic endfeet have been investigated as potential targets to modulate water movement and the function of the glymphatics in ICH. Upregulation of AQP4 may protect the blood–brain barrier and help to resolve PHE (as mentioned above), whereas downregulation of AQP4 was associated with glymphatic dysfunction and had detrimental effects on neurological deficits following ICH in more recent studies [60,61,90].

The discovery of the meningeal lymphatic vessels (mLVs) generated broad research interest and has prompted investigation of their roles in various CNS diseases, including ICH. The mLVs are embedded within the dura mater and the vessel branches extend into the subarachnoid space, where they make direct contact with the CSF, and carry macromolecules away from the brain parenchyma and transport CSF to the cervical lymph nodes [91]. One study demonstrated the meningeal lymphatic system was involved in hematoma resolution, red blood cell drainage, and neurological recovery in an animal model of ICH [92]. Additionally, cilostazol, a drug that has been found to promote lymphatic flow, improved lymphatic function and hematoma clearance in an experimental model [92]. Therefore, targeting the lymphatic systems within the brain, including the glymphatics or meningeal lymphatics, may hold substantial therapeutic potential; however, more research is needed before these findings can be translated into clinical treatments.

CONCLUSION

The exploration of new therapeutic targets for spontaneous ICH is both timely and necessary, given the current lack of effective medical treatments. Recent advancements in our understanding of how to mitigate secondary brain injury post-ICH, such as reducing iron toxicity, enhancing endogenous resorption of hematoma, modulating inflammatory responses, and addressing PHE, offer promising avenues to improve patient outcomes. The lymphatic system of the brain also presents a novel area for therapeutic intervention. Despite the promising results obtained in experimental model and early-phase trials, further large-scale studies are essential to validate and translate these novel therapeutic targets into clinical practice. Continued research and innovation in this field are necessary to develop effective management protocols and ultimately improve the prognosis of patients with ICH.

Acknowledgements

None.

Financial support and sponsorship

This article is supported by funding from the National Science and Technology Council (Tsai HH, 113-2628-B-002-013-MY3 and 112-2923-B-002-001-MY3).

Conflicts of interest

There are no conflicts of interest.

REFERENCES AND RECOMMENDED READING

Papers of particular interest, published within the annual period of review, have been highlighted as:

• ▪ of special interest

• ▪▪ of outstanding interest