Safety and efficacy of factor XIa inhibition with milvexian for secondary stroke prevention (AXIOMATIC-SSP): a phase 2, international, randomised, double-blind, placebo-controlled, dose-finding trial.

BACKGROUND: People with factor XI deficiency have lower rates of ischaemic stroke than the general population and infrequent spontaneous bleeding, suggesting that factor XI has a more important role in thrombosis than in haemostasis. Milvexian, an oral small-molecule inhibitor of activated factor XI, added to standard antiplatelet therapy, might reduce the risk of non-cardioembolic ischaemic stroke without increasing the risk of bleeding. We aimed to estimate the dose-response of milvexian for recurrent ischaemic cerebral events and major bleeding in patients with recent ischaemic stroke or transient ischaemic attack (TIA). METHODS: AXIOMATIC-SSP was a phase 2, randomised, double-blind, placebo-controlled, dose-finding trial done at 367 hospitals in 27 countries. Eligible participants aged 40 years or older, with acute (<48 h) ischaemic stroke or high-risk TIA, were randomly assigned by a web-based interactive response system in a 1:1:1:1:1:2 ratio to receive one of five doses of milvexian (25 mg once daily, 25 mg twice daily, 50 mg twice daily, 100 mg twice daily, or 200 mg twice daily) or matching placebo twice daily for 90 days. All participants received clopidogrel 75 mg daily for the first 21 days and aspirin 100 mg daily for the first 90 days. Investigators, site staff, and participants were masked to treatment assignment. The primary efficacy endpoint was the composite of ischaemic stroke or incident covert brain infarct on MRI at 90 days, assessed in all participants allocated to treatment who completed a follow-up MRI brain scan, and the primary analysis assessed the dose-response relationship with Multiple Comparison Procedure-Modelling (MCP-MOD). The main safety outcome was major bleeding at 90 days, assessed in all participants who received at least one dose of the study drug. This trial is registered with ClinicalTrials.gov (NCT03766581) and the EU Clinical Trials Register (2017-005029-19). FINDINGS: Between Jan 27, 2019, and Dec 24, 2021, 2366 participants were randomly allocated to placebo (n=691); milvexian 25 mg once daily (n=328); or twice-daily doses of milvexian 25 mg (n=318), 50 mg (n=328), 100 mg (n=310), or 200 mg (n=351). The median age of participants was 71 (IQR 62-77) years and 859 (36%) were female. At 90 days, the estimates of the percentage of participants with either symptomatic ischaemic stroke or covert brain infarcts were 16·8 (90·2% CI 14·5-19·1) for placebo, 16·7 (14·8-18·6) for 25 mg milvexian once daily, 16·6 (14·8-18·3) for 25 mg twice daily, 15·6 (13·9-17·5) for 50 mg twice daily, 15·4 (13·4-17·6) for 100 mg twice daily, and 15·3 (12·8-19·7) for 200 mg twice daily. No significant dose-response was observed among the five milvexian doses for the primary composite efficacy outcome. Model-based estimates of the relative risk with milvexian compared with placebo were 0·99 (90·2% CI 0·91-1·05) for 25 mg once daily, 0·99 (0·87-1·11) for 25 mg twice daily, 0·93 (0·78-1·11) for 50 mg twice daily, 0·92 (0·75-1·13) for 100 mg twice daily, and 0·91 (0·72-1·26) for 200 mg twice daily. No apparent dose-response was observed for major bleeding (four [1%] of 682 participants with placebo, two [1%] of 325 with milvexian 25 mg once daily, two [1%] of 313 with 25 mg twice daily, five [2%] of 325 with 50 mg twice daily, five [2%] of 306 with 100 mg twice daily, and five [1%] of 344 with 200 mg twice daily). Five treatment-emergent deaths occurred, four of which were considered unrelated to the study drug by the investigator. INTERPRETATION: Factor XIa inhibition with milvexian, added to dual antiplatelet therapy, did not substantially reduce the composite outcome of symptomatic ischaemic stroke or covert brain infarction and did not meaningfully increase the risk of major bleeding. Findings from our study have informed the design of a phase 3 trial of milvexian for the prevention of ischaemic stroke in patients with acute ischaemic stroke or TIA. FUNDING: Bristol Myers Squibb and Janssen Research & Development.

Brain parenchymal TNF-α and IL-1ß induction in experimental pneumococcal meningitis.

Triggers of brain inflammation in pneumococcal meningitis are unknown. TNF-α and IL-1ß were upregulated (real time PCR and in situ hybridization) in neurons and astrocytes time-dependently and maximally in the hippocampus during murine pneumococcal meningitis. Upregulation of TNF-α and IL-1ß mRNA in the brain parenchyma was independent of cerebrospinal fluid leukocytosis, pneumococcal pneumolysin and H2O2, but it was potently induced by pneumococcal cell wall (PCW) fragments. Brain TNF-α mRNA was downregulated by a matrix metalloproteinases inhibitor. PCW fragments were located in the brain parenchyma. In conclusion, PCW fragments and matrix metalloproteinases trigger cytokine induction in the brain parenchyma during pneumococcal meningitis.

Bacterial pore-forming cytolysins induce neuronal damage in a rat model of neonatal meningitis.

BACKGROUND: Group B Streptococcus (GBS) and Streptococcus pneumoniae (SP) are leading causes of bacterial meningitis in neonates and children. Each pathogen produces a pore-forming cytolytic toxin, ß-hemolysin/cytolysin (ß-h/c) by GBS and pneumolysin by SP. The aim of this study was to understand the role of these pore-forming cytotoxins, in particular of the GBS ß-h/c, as potential neurotoxins in experimental neonatal meningitis. METHODS: Meningitis was induced in 7- and 11-day-old rats by intracisternal injection of wild type (WT) GBS or SP and compared with isogenic ß-h/c- or pneumolysin-deficient mutants, or a double mutant of SP deficient in pneumolysin and hydrogen peroxide production. RESULTS: GBS ß-h/c and SP pneumolysin contributed to neuronal damage, worsened clinical outcome and weight loss, but had no influence on the early kinetics of leukocyte influx and bacterial growth in the cerebrospinal fluid. In vitro, ß-h/c-induced neuronal apoptosis occurred independently of caspase-activation and was not preventable by the broad spectrum caspase-inhibitor z-VAD-fmk. CONCLUSIONS: These data suggest that both cytolytic toxins, the GBS ß-h/c and SP pneumolysin, contribute to neuronal damage in meningitis and extend the concept of a key role for bacterial pore-forming cytolysins in the pathogenesis and sequelae of neonatal meningitis.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) in central nervous system inflammation.

In a wide variety of acute and chronic central nervous system (CNS) disorders, inflammatory processes contribute to the damage of brain cells and progression of the disease. Along with other regulatory cytokines, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is involved in the pathology of multiple sclerosis (MS) and murine experimental autoimmune encephalomyelitis (EAE), bacterial meningitis (BM), HIV encephalitis (HIVE), stroke and Alzheimer's disease (AD). In these conditions, TRAIL is released within the brain mainly by activated microglia and leukocytes infiltrating from the blood stream. TRAIL promotes apoptosis of parenchymal cells in MS/EAE, HIVE, AD and stroke through interaction with TRAIL death receptors expressed on these cells. Frequently, cells in the diseased brain display increased susceptibility to apoptosis induction by TRAIL due to upregulation of death receptors and downregulation of decoy receptors. On the other hand, TRAIL inhibits the proliferation of encephalitogenic T cells in EAE, and it is involved in the clearance of infected brain macrophages in HIVE and of activated neutrophils in BM by interaction with their death receptors. Especially in BM, the ability of TRAIL to limit an acute granulocyte-driven inflammation carries significant neuroprotective potential. Given the diversity of beneficial and harmful effects in the immune and nervous system, TRAIL is a double-edged sword in diseases involving CNS inflammation.

Heterogeneous effects of distinct tocopherol analogues on NO release, cell volume, and cell death in microglial cells.

Tocopherols (vitamin E) are potent antioxidants as well as modulators of enzymes involved in signal transduction, like nitric oxide synthase (NOS). In primary murine microglial cells and in the microglial cell line BV-2, alpha-, gamma-, and delta-tocopherol and alpha-tocopherol acid succinate, respectively, promote nitric oxide (NO) release. The NOS inhibitors aminoguanidine and N(G)-methyl-L-arginine (L-NMMA) suppressed alpha- and gamma-tocopherol-induced NO release, but had no significant effect on delta-tocopherol- and alpha-tocopherol acid succinate-induced NO release. In BV-2 cells, but not in primary microglial cells, gamma- and delta-tocopherol and alpha-tocopherol acid succinate, respectively, led to cell death, characterized by exposition of phosphatidylserine on the cell surface, chromatin condensation, changes in cell volume, and formation of blebs on the cell surface. Aminoguanidine, L-NMMA, and the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) enhanced apoptosis in gamma-tocopherol-exposed cells and suppressed apoptosis in delta-tocopherol-treated cells, but had no effect on cells supplemented with alpha-tocopherol acid succinate. The NO donors sodium nitroprusside and 2-(N,N-diethylamino)-diazenolate 2-oxide enhanced apoptosis in gamma- or delta-tocopherol-treated cells, but rescued cells from alpha-tocopherol acid succinate-induced cell death.

A vicious cycle involving release of heat shock protein 60 from injured cells and activation of toll-like receptor 4 mediates neurodegeneration in the CNS.

Infection, ischemia, trauma, and neoplasia elicit a similar inflammatory response in the CNS characterized by activation of microglia, the resident CNS monocyte. The molecular events leading from CNS injury to the activation of innate immunity is not well understood. We show here that the intracellular chaperone heat shock protein 60 (HSP60) serves as a signal of CNS injury by activating microglia through a toll-like receptor 4 (TLR4)-dependent and myeloid differentiation factor 88 (MyD88)-dependent pathway. HSP60 is released from CNS cells undergoing necrotic or apoptotic cell death and specifically binds to microglia. HSP60-induced synthesis of neurotoxic nitric oxide by microglia is dependent on TLR4. HSP60 induces extensive axonal loss and neuronal death in CNS cultures from wild-type but not TLR4 or MyD88 loss-of-function mutant mice. This is the first evidence of an endogenous molecular pathway common to many forms of neuronal injury that bidirectionally links CNS inflammation with neurodegeneration.

TLR2 and caspase-8 are essential for group B Streptococcus-induced apoptosis in microglia.

Microglia, the resident innate immune cells of the CNS, detect invading pathogens via various receptors, including the TLR. Microglia are involved in a number of neurodegenerative diseases in which their activation may be detrimental to neurons. It is largely unknown how this potentially deleterious action can be countered on a cellular level. We previously found that the interaction of TLR2 with group B Streptococcus (GBS), the most important pathogen in neonatal bacterial meningitis, activates microglia that in turn generate neurotoxic NO. We report in this study that GBS not only activates microglia, but also induces apoptosis in these cells via TLR2 and the TLR-adaptor molecule MyD88. Soluble toxic mediators, such as NO, are not responsible for this form of cell death. Instead, interaction of GBS with TLR2 results in formation and activation of caspase-8, a process that involves the transcription factor family Ets. Whereas caspase-8 plays an essential role in GBS-induced microglial apoptosis, caspase-3 is dispensable in this context. We suggest that TLR2- and caspase-8-mediated microglial apoptosis constitutes an autoregulatory mechanism that limits GBS-induced overactivation of the innate immune system in the CNS.

Toll-like receptor 2 mediates CNS injury in focal cerebral ischemia.

Toll-like receptors (TLR) recognize molecular structures associated with pathogens as well as host-derived components and initiate an inflammatory innate immune response. Microglia represent the resident immune host defense and are the major inflammatory cell type in the central nervous system (CNS). We show here that TLR2-deficient mice develop a decreased CNS injury compared to wild type mice in a model of focal cerebral ischemia. TLR2 mRNA is up-regulated in wild type mice during cerebral ischemia. In ischemic brains, TLR2 protein is expressed in lesion-associated microglia. Absence of TLR2 does not affect the recruitment of granulocytes to the infarct region. We conclude that TLR2 in microglia propagates stroke-induced CNS injury.

TRAIL limits excessive host immune responses in bacterial meningitis.

Apart from potential roles in anti-tumor surveillance, the TNF-related apoptosis-inducing ligand (TRAIL) has important regulatory functions in the host immune response. We studied antiinflammatory effects of endogenous and recombinant TRAIL (rTRAIL) in experimental meningitis. Following intrathecal application of pneumococcal cell wall, a TLR2 ligand, we found prolonged inflammation, augmented clinical impairment, and increased apoptosis in the hippocampus of TRAIL(-/-) mice. Administration of rTRAIL into the subarachnoid space of TRAIL(-/-) mice or reconstitution of hematopoiesis with wild-type bone marrow cells reversed these effects, suggesting an autoregulatory role of TRAIL within the infiltrating leukocyte population. Importantly, intrathecal application of rTRAIL in wild-type mice with meningitis also decreased inflammation and apoptosis. Moreover, patients suffering from bacterial meningitis showed increased intrathecal synthesis of TRAIL. Our findings provide what we believe is the first evidence that TRAIL may act as a negative regulator of acute CNS inflammation. The ability of TRAIL to modify inflammatory responses and to reduce neuronal cell death in meningitis suggests that it may be used as a novel antiinflammatory agent in invasive infections.

Pneumolysin causes neuronal cell death through mitochondrial damage.

Bacterial toxins such as pneumolysin are key mediators of cytotoxicity in infections. Pneumolysin is a pore-forming toxin released by Streptococcus pneumoniae, the major cause of bacterial meningitis. We found that pneumolysin is the pneumococcal factor that accounts for the cell death pathways induced by live bacteria in primary neurons. The pore-forming activity of pneumolysin is essential for the induction of mitochondrial damage and apoptosis. Pneumolysin colocalized with mitochondrial membranes, altered the mitochondrial membrane potential, and caused the release of apoptosis-inducing factor and cell death. Pneumolysin induced neuronal apoptosis without activating caspase-1, -3, or -8. Wild-type pneumococci also induced apoptosis without activation of caspase-3, whereas pneumolysin-negative pneumococci activated caspase-3 through the release of bacterial hydrogen peroxide. Pneumolysin caused upregulation of X-chromosome-linked inhibitor of apoptosis protein and inhibited staurosporine-induced caspase activation, suggesting the presence of actively suppressive mechanisms on caspases. In conclusion, our results indicate additional functions of pneumolysin as a mitochondrial toxin and as a determinant of caspase-independent apoptosis. Considering this, blocking of pneumolysin may be a promising cytoprotective strategy in pneumococcal meningitis and other infections.

Pneumococcal cell wall-induced meningitis impairs adult hippocampal neurogenesis.

Bacterial meningitis is a major infectious cause of neuronal degeneration in the hippocampus. Neurogenesis, a continuous process in the adult hippocampus, could ameliorate such loss. Yet the high rate of sequelae from meningitis suggests that this repair mechanism is inefficient. Here we used a mouse model of nonreplicative bacterial meningitis to determine the impact of transient intracranial inflammation on adult neurogenesis. Experimental meningitis resulted in a net loss of neurons, diminished volume, and impaired neurogenesis in the dentate gyrus for weeks following recovery from the insult. Inducible nitric oxide synthase (iNOS) immunoreactivity was prominent in microglia in nonproliferating areas of the dentate gyrus and hilus region after meningitis induction. Treatment with the specific iNOS inhibitor N6-(1-iminoethyl)-L-lysine restored neurogenesis in experimental meningitis. These data suggest that local central nervous system inflammation in and of itself suppresses adult neurogenesis by affecting both proliferation and neuronal differentiation. Repair of cognitive dysfunction following meningitis could be improved by intervention to interrupt these actively suppressive effects.

TLR2 mediates neuroinflammation and neuronal damage.

Innate immunity relies on pattern recognition receptors to detect the presence of infectious pathogens. In the case of Gram-positive bacteria, binding of bacterial lipopeptides to TLR2 is currently regarded as an important mechanism. In the present study, we used the synthetic bacterial lipopeptide Pam3CysSK4, a selective TLR2 agonist, to induce meningeal inflammation in rodents. In a 6-h rat model, intrathecal application of Pam3CysSK4 caused influx of leukocytes into the cerebrospinal fluid (CSF) and induced a marked increase of regional cerebral blood flow and intracranial pressure. In wild-type mice, we observed CSF pleocytosis and an increased number of apoptotic neurons in the dentate gyrus 24 h after intrathecal challenge. Inflammation and associated neuronal loss were absent in TLR2 knockout mice. In purified neurons, cytotoxicity of Pam3CysSK4 itself was not observed. Exposure of microglia to Pam3CysSK4 induced neurotoxic properties in the supernatant of wild-type, but not TLR2-deficient microglia. We conclude that TLR2-mediated signaling is sufficient to induce the host-dependent key features of acute bacterial meningitis. Therefore, synthetic lipopeptides are a highly specific tool to study mechanisms of TLR2-driven neurodegeneration in vivo.

Bacterial hydrogen peroxide contributes to cerebral hyperemia during early stages of experimental pneumococcal meningitis.

Alterations of blood flow contribute to major clinical complications in invasive infections such as sepsis and bacterial meningitis. As a unique feature streptococci -- in particular, Streptococcus pneumoniae, the most frequent pathogen in bacterial meningitis -- release hydrogen peroxide (H(2)O(2)) because of the absence of functional catalase. In a 6 h rat model of experimental meningitis, we studied the impact of bacterial H(2)O(2) production on regional cerebral blood flow (rCBF) and intracranial pressure (ICP). Compared to wild-type D39 pneumococci, the increase of rCBF was diminished in meningitis induced by the H(2)O(2) defective SpxB(-) mutant (maximum increase, 135% +/- 17% versus 217% +/- 23% of the individual baseline; P<0.01) or after treatment of D39-induced meningitis with H(2)O(2)-degrading catalase or with tetraethylammonium (TEA), a blocker of calcium-sensitive potassium channels, which mediate H(2)O(2)-induced vasodilation. Catalase did not significantly reduce the remaining rCBF increase caused by SpxB(-), supporting the predominant role of bacterial H(2)O(2). We conclude that in addition to host-sided mediators, bacterial-derived H(2)O(2) acts as a potent vasodilator, which accounts for a certain proportion of the early cerebral hyperperfusion in pneumococcal meningitis.

Cellular damage in bacterial meningitis: an interplay of bacterial and host driven toxicity.

Bacterial meningitis is still an important infectious disease causing death and disability. Invasive bacterial infections of the CNS generate some of the most powerful inflammatory responses known in medicine. Although the components of bacterial cell surfaces are now chemically defined in exquisite detail and the interaction with several receptor pathways has been discovered, it is only very recently that studies combining these advanced biochemical and cell biological tools have been done. Additional to the immunological response direct bacterial toxicity has been identified as an important contributor to neuronal damage. A detailed understanding of the complex interaction of bacterial toxicity and host response may generate opportunities for innovative and specific neuroprotective therapies.

Platelet-activating factor receptor and innate immunity: uptake of gram-positive bacterial cell wall into host cells and cell-specific pathophysiology.

The current model of innate immune recognition of Gram-positive bacteria suggests that the bacterial cell wall interacts with host recognition proteins such as TLRs and Nod proteins. We describe an additional recognition system mediated by the platelet-activating factor receptor (PAFr) and directed to the pathogen-associated molecular pattern phosphorylcholine that results in the uptake of bacterial components into host cells. Intravascular choline-containing cell walls bound to endothelial cells and caused rapid lethality in wild-type, Tlr2(-/-), and Nod2(-/-) mice but not in Pafr(-/-) mice. The cell wall exited the vasculature into the heart and brain, accumulating within endothelial cells, cardiomyocytes, and neurons in a PAFr-dependent way. Physiological consequences of the cell wall/PAFr interaction were cell specific, being noninflammatory in endothelial cells and neurons but causing a rapid loss of cardiomyocyte contractility that contributed to death. Thus, PAFr shepherds phosphorylcholine-containing bacterial components such as the cell wall into host cells from where the response ranges from quiescence to severe pathophysiology.

Interplay of pneumococcal hydrogen peroxide and host-derived nitric oxide.

Reactive oxygen and nitrogen species are released by immune-competent cells and contribute to cellular damage. On the other hand, certain pathogens, including Streptococcus pneumoniae, are known to produce hydrogen peroxide (H2O2), while production of nitrogen radicals by bacteria presumably occurs but has been poorly studied. We determined the relative contributions of bacterial versus host-derived oxygen and nitrogen radicals to cellular damage in pneumococcal infection. A special focus was placed on peroxynitrite as a hypothetical common product formed by the reaction of H2O2 and NO. In microglial cultures, reduction of the formation of 3-nitrotyrosine and cellular damage required H2O2-deficient (DeltaspxB or DeltacarB) pneumococci and inhibition of host NO synthesis with aminoguanidine. In infected C57BL/6 mice, neuronal loss and immunopositivity for nitrotyrosine in the dentate gyrus were markedly reduced with DeltaspxB or DeltacarB bacterial mutants and in inducible nitric oxide synthase knockout mice. We conclude that although host and bacteria both produce oxygen and nitrogen radicals, the interplay of prokaryotic H2O2 and eukaryotic NO is a major contributor to cellular damage in pneumococcal meningitis.

A mechanism for neurodegeneration induced by group B streptococci through activation of the TLR2/MyD88 pathway in microglia.

Group B Streptococcus (GBS) is a major cause of bacterial meningitis and neurological morbidity in newborn infants. The cellular and molecular mechanisms by which this common organism causes CNS injury are unknown. We show that both heat-inactivated whole GBS and a secreted proteinaceous factor from GBS (GBS-F) induce neuronal apoptosis via the activation of murine microglia through a TLR2-dependent and MyD88-dependent pathway in vitro. Microglia, astrocytes, and oligodendrocytes, but not neurons, express TLR2. GBS as well as GBS-F induce the synthesis of NO in microglia derived from wild-type but not TLR2(-/-) or MyD88(-/-) mice. Neuronal death in neuronal cultures complemented with wild-type microglia is NO-dependent. We show for the first time a TLR-mediated mechanism of neuronal injury induced by a clinically relevant bacterium. This study demonstrates a causal molecular relationship between infection with GBS, activation of the innate immune system in the CNS through TLR2, and neurodegeneration. We suggest that this process contributes substantially to the serious morbidity associated with neonatal GBS meningitis and may provide a potential therapeutic target.

The role of lipopolysaccharide-binding protein in modulating the innate immune response.

Lipopolysaccharide-binding protein (LBP) has a well-established role in Gram-negative infection. New data suggest a more expanded role for LBP as a general recognition molecule. Several bacterial surface components from Gram-positive pathogens are also recognized by this molecule. LBP may also serve as a clinical marker in severe infections and may carry therapeutic potential.

Bacterial programmed cell death of cerebral endothelial cells involves dual death pathways.

Major barriers separating the blood from tissue compartments in the body are composed of endothelial cells. Interaction of bacteria with such barriers defines the course of invasive infections, and meningitis has served as a model system to study endothelial cell injury. Here we report the impressive ability of Streptococcus pneumoniae, clinically one of the most important pathogens, to induce 2 morphologically distinct forms of programmed cell death (PCD) in brain-derived endothelial cells. Pneumococci and the major cytotoxins H2O2 and pneumolysin induce apoptosis-like PCD independent of TLR2 and TLR4. On the other hand, pneumococcal cell wall, a major proinflammatory component, causes caspase-driven classical apoptosis that is mediated through TLR2. These findings broaden the scope of bacterial-induced PCD, link these effects to innate immune TLRs, and provide insight into the acute and persistent phases of damage during meningitis.

Dual phases of apoptosis in pneumococcal meningitis.

Significant injury during bacterial meningitis arises from mechanisms of neuronal apoptosis, particularly in the hippocampus. Apoptosis can involve both the caspase-dependent and the caspase-independent pathway, and, although both pathways have been implicated in pneumococcus-induced neuronal cell death, their relative contributions in vivo are unclear. We used mice deficient in the activation of caspase-3, ATM, and p53 to examine the role that caspase-dependent apoptosis plays in neuronal death in the context of pneumococcal meningitis. The overall symptomatology of acute infection was similar in all mice tested, indicating that late sequelae are the clinical manifestations of neuronal death. Two phases of apoptosis were discernible: neuronal injury at 18 h after infection was independent of the caspase-3 pathway, and neuronal cell death at 24 h after infection was attenuated in the absence of the caspase-3 pathway. We conclude that treatments to increase the survival rate of neurons in patients with meningitis will need to take into account at least these 2 mechanisms of damage.