Lecanemab blocks the effects of the Aß/fibrinogen complex on blood clots and synapse toxicity in organotypic culture.

Proteinaceous brain inclusions, neuroinflammation, and vascular dysfunction are common pathologies in Alzheimer's disease (AD). Vascular deficits include a compromised blood-brain barrier, which can lead to extravasation of blood proteins like fibrinogen into the brain. Fibrinogen's interaction with the amyloid-beta (Aß) peptide is known to worsen thrombotic and cerebrovascular pathways in AD. Lecanemab, an FDA-approved antibody therapy for AD, clears Aß plaque from the brain and slows cognitive decline. Here, we show that lecanemab blocks fibrinogen's binding to Aß protofibrils, preventing Aß/fibrinogen-mediated delayed fibrinolysis and clot abnormalities in vitro and in human plasma. Additionally, we show that lecanemab dissociates the Aß/fibrinogen complex and prevents fibrinogen from exacerbating Aß-induced synaptotoxicity in mouse organotypic hippocampal cultures. These findings reveal a possible protective mechanism by which lecanemab may slow disease progression in AD.

A possible mechanism for the enhanced toxicity of beta-amyloid protofibrils in Alzheimer's disease.

The amyloid-beta peptide (Aß) is a driver of Alzheimer's disease (AD). Aß monomers can aggregate and form larger soluble (oligomers/protofibrils) and insoluble (fibrils) forms. There is evidence that Aß protofibrils are the most toxic form, but the reasons are not known. Consistent with a critical role for this form of Aß in AD, a recently FDA-approved therapeutic antibody targeted against protofibrils, lecanemab, slows the progression of AD in patients. The plasma contact system, which can promote coagulation and inflammation, has been implicated in AD pathogenesis. This system is activated by Aß which could lead to vascular and inflammatory pathologies associated with AD. We show here that the contact system is preferentially activated by protofibrils of Aß. Aß protofibrils bind to coagulation factor XII and high molecular weight kininogen and accelerate the activation of the system. Furthermore, lecanemab blocks Aß protofibril activation of the contact system. This work provides a possible mechanism for Aß protofibril toxicity in AD and why lecanemab is therapeutically effective.

Plasmin-mediated cleavage of high-molecular-weight kininogen contributes to acetaminophen-induced acute liver failure.

Acetaminophen (APAP)-induced liver injury is associated with activation of coagulation and fibrinolysis. In mice, both tissue factor-dependent thrombin generation and plasmin activity have been shown to promote liver injury after APAP overdose. However, the contribution of the contact and intrinsic coagulation pathways has not been investigated in this model. Mice deficient in individual factors of the contact (factor XII [FXII] and prekallikrein) or intrinsic coagulation (FXI) pathway were administered a hepatotoxic dose of 400 mg/kg of APAP. Neither FXII, FXI, nor prekallikrein deficiency mitigated coagulation activation or hepatocellular injury. Interestingly, despite the lack of significant changes to APAP-induced coagulation activation, markers of liver injury and inflammation were significantly reduced in APAP-challenged high-molecular-weight kininogen-deficient (HK-/-) mice. Protective effects of HK deficiency were not reproduced by inhibition of bradykinin-mediated signaling, whereas reconstitution of circulating levels of HK in HK-/- mice restored hepatotoxicity. Fibrinolysis activation was observed in mice after APAP administration. Western blotting, enzyme-linked immunosorbent assay, and mass spectrometry analysis showed that plasmin efficiently cleaves HK into multiple fragments in buffer or plasma. Importantly, plasminogen deficiency attenuated APAP-induced liver injury and prevented HK cleavage in the injured liver. Finally, enhanced plasmin generation and HK cleavage, in the absence of contact pathway activation, were observed in plasma of patients with acute liver failure due to APAP overdose. In summary, extrinsic but not intrinsic pathway activation drives the thromboinflammatory pathology associated with APAP-induced liver injury in mice. Furthermore, plasmin-mediated cleavage of HK contributes to hepatotoxicity in APAP-challenged mice independently of thrombin generation or bradykinin signaling.

An antibody against HK blocks Alzheimer's disease peptide ß-amyloid-induced bradykinin release in human plasma.

Bradykinin is a proinflammatory factor that mediates angioedema and inflammation in many diseases. It is a key player in some types of hereditary angioedema and is involved in septic shock, traumatic injury, Alzheimer's disease (AD), and stroke, among others. Activation of the plasma contact system leads to elevated levels of plasma kallikrein, which cleaves high molecular weight kininogen (HK) to release bradykinin. Drug development for bradykinin-meditated pathologies has focused on designing inhibitors to the enzymes that cleave HK (to prevent bradykinin release) or antagonists of endothelial bradykinin receptors (to prevent downstream bradykinin action). Here we show a strategy to block bradykinin generation by using an HK antibody that binds to HK, preventing its cleavage and subsequent bradykinin release. We show that this antibody blocks dextran sodium sulfate-induced HK cleavage and bradykinin production. Moreover, while the pathogenic AD peptide ß-amyloid (Aß)42 cleaves HK and induces a dramatic increase in bradykinin production, our HK antibody blocked these events from occurring. These results may provide strategies for developing treatments for bradykinin-driven pathologies.

Blood-derived plasminogen drives brain inflammation and plaque deposition in a mouse model of Alzheimer's disease.

Two of the most predominant features of the Alzheimer's disease (AD) brain are deposition of ß-amyloid (Aß) plaques and inflammation. The mechanism behind these pathologies remains unknown, but there is evidence to suggest that inflammation may predate the deposition of Aß. Furthermore, immune activation is increasingly being recognized as a major contributor to the pathogenesis of the disease, and disorders involving systemic inflammation, such as infection, aging, obesity, atherosclerosis, diabetes, and depression are risk factors for the development of AD. Plasminogen (PLG) is primarily a blood protein synthesized in the liver, which when cleaved into its active form, plasmin (PL), plays roles in fibrinolysis, wound healing, cell signaling, and inflammatory regulation. Here we show that PL in the blood is a regulator of brain inflammatory action and AD pathology. Depletion of PLG in the plasma of an AD mouse model through antisense oligonucleotide technology dramatically improved AD pathology and decreased glial cell activation in the brain, whereas an increase in PL activity through α-2-antiplasmin (A2AP) antisense oligonucleotide treatment exacerbated the brain's immune response and plaque deposition. These studies suggest a crucial role for peripheral PL in mediating neuroimmune cell activation and AD progression and could provide a link to systemic inflammatory risk factors that are known to be associated with AD development.

Increased plasma bradykinin level is associated with cognitive impairment in Alzheimer's patients.

Alzheimer's disease (AD) is characterized by the presence of proteinaceous brain deposits, brain atrophy, vascular dysfunction, and chronic inflammation. Along with cerebral inflammation, peripheral inflammation is also evident in many AD patients. Bradykinin, a proinflammatory plasma peptide, is also linked to AD pathology. For example, bradykinin infusion into the hippocampus causes learning and memory deficits in rats, and blockade of the bradykinin receptor lessens cognitive impairment in AD mouse models. Even though it has been hypothesized that plasma bradykinin could contribute to inflammation in AD, the level of plasma bradykinin and its association with beta-amyloid (Aß) pathology in AD patients had not been explored. Here, we assessed plasma bradykinin levels in AD patients and age-matched non-demented (ND) control individuals. We found significantly elevated plasma bradykinin levels in AD patients compared to ND subjects. Additionally, changes in plasma bradykinin levels were more profound in many AD patients with severe cognitive impairment, suggesting that peripheral bradykinin could play a role in dementia most likely via inflammation. Bradykinin levels in the cerebrospinal fluid (CSF) were reduced in AD patients and exhibited an inverse correlation with the CSF Aß40/Aß42 ratio. We also report that bradykinin interacts with the fibrillar form of Aß and co-localizes with Aß plaques in the post-mortem human AD brain. These findings connect the peripheral inflammatory pathway to cerebral abnormalities and identify a novel mechanism of inflammatory pathology in AD.

Plasminogen mediates communication between the peripheral and central immune systems during systemic immune challenge with lipopolysaccharide.

BACKGROUND: Systemic inflammation has been implicated in the progression of many neurodegenerative diseases and may be an important driver of the disease. Dementia and cognitive decline progress more rapidly following acute systemic infection, and systemic inflammation midlife is predictive of the degree of cognitive decline. Plasmin, the active form of the serine protease plasminogen (PLG), is a blood protein that plays physiological roles in fibrinolysis, wound healing, cell signaling, extracellular matrix degradation, and inflammatory regulation. METHODS: Mice were treated with an antisense oligonucleotide to deplete liver-produced PLG prior to systemic challenge with lipopolysaccharide (LPS), a major component of the outer membrane of gram-negative bacteria, known to induce a strong immune response in animals. Following treatment, the innate immune response in the brains of these animals was examined. RESULTS: Mice that were PLG-deficient had dramatically reduced microgliosis and astrogliosis in their brains after LPS injection. We found that blood PLG regulates the brain's innate immune response to systemic inflammatory signaling, affecting the migration of perivascular macrophages into the brain after challenge with LPS. CONCLUSIONS: Depletion of plasma PLG with an antisense oligonucleotide dramatically reduced glial cell activation and perivascular macrophage migration into the brain following LPS injection. This study suggests a critical role for PLG in mediating communication between systemic inflammatory mediators and the brain.

Depletion of coagulation factor XII ameliorates brain pathology and cognitive impairment in Alzheimer disease mice.

Vascular abnormalities and inflammation are found in many Alzheimer disease (AD) patients, but whether these changes play a causative role in AD is not clear. The factor XII (FXII) -initiated contact system can trigger both vascular pathology and inflammation and is activated in AD patients and AD mice. We have investigated the role of the contact system in AD pathogenesis. Cleavage of high-molecular-weight kininogen (HK), a marker for activation of the inflammatory arm of the contact system, is increased in a mouse model of AD, and this cleavage is temporally correlated with the onset of brain inflammation. Depletion of FXII in AD mice inhibited HK cleavage in plasma and reduced neuroinflammation, fibrinogen deposition, and neurodegeneration in the brain. Moreover, FXII-depleted AD mice showed better cognitive function than untreated AD mice. These results indicate that FXII-mediated contact system activation contributes to AD pathogenesis, and therefore this system may offer novel targets for AD treatment.

Activation of the factor XII-driven contact system in Alzheimer's disease patient and mouse model plasma.

Alzheimer's disease (AD) is characterized by accumulation of the ß-amyloid peptide (Aß), which likely contributes to disease via multiple mechanisms. Increasing evidence implicates inflammation in AD, the origins of which are not completely understood. We investigated whether circulating Aß could initiate inflammation in AD via the plasma contact activation system. This proteolytic cascade is triggered by the activation of the plasma protein factor XII (FXII) and leads to kallikrein-mediated cleavage of high molecular-weight kininogen (HK) and release of proinflammatory bradykinin. Aß has been shown to promote FXII-dependent cleavage of HK in vitro. In addition, increased cleavage of HK has been found in the cerebrospinal fluid of patients with AD. Here, we show increased activation of FXII, kallikrein activity, and HK cleavage in AD patient plasma. Increased contact system activation is also observed in AD mouse model plasma and in plasma from wild-type mice i.v. injected with Aß42. Our results demonstrate that Aß42-mediated contact system activation can occur in the AD circulation and suggest new pathogenic mechanisms, diagnostic tests, and therapies for AD.

Interactions of ß-amyloid peptide with fibrinogen and coagulation factor XII may contribute to Alzheimer's disease.

PURPOSE OF REVIEW: To review the evidence that the Alzheimer peptide ß-amyloid interacts with the blood coagulation system and influences the pathophysiology of the disease. RECENT FINDINGS: ß-amyloid can interact with fibrinogen and blood coagulation factor XII and trigger ischemia and inflammation. SUMMARY: ß-amyloid interacts with fibrinogen and factor XII. These interactions can lead to increased clotting, abnormal clot formation, persistent fibrin deposition, and generation of proinflammatory molecules. These events can damage neurons and could contribute to the cognitive decline in Alzheimer's disease patients.

Schwann cell myelination requires integration of laminin activities.

Laminins promote early stages of peripheral nerve myelination by assembling basement membranes (BMs) on Schwann cell surfaces, leading to activation of ß1 integrins and other receptors. The BM composition, structural bonds and ligands needed to mediate this process, however, are not well understood. Mice hypomorphic for laminin γ1-subunit expression that assembled endoneurial BMs with reduced component density exhibited an axonal sorting defect with amyelination but normal Schwann cell proliferation, the latter unlike the null. To identify the basis for this, and to dissect participating laminin interactions, LAMC1 gene-inactivated dorsal root ganglia were treated with recombinant laminin-211 and -111 lacking different architecture-forming and receptor-binding activities, to induce myelination. Myelin-wrapping of axons by Schwann cells was found to require higher laminin concentrations than either proliferation or axonal ensheathment. Laminins that were unable to polymerize through deletions that removed critical N-terminal (LN) domains, or that lacked cell-adhesive globular (LG) domains, caused reduced BMs and almost no myelination. Laminins engineered to bind weakly to α6ß1 and/or α7ß1 integrins through their LG domains, even though they could effectively assemble BMs, decreased myelination. Proliferation depended upon both integrin binding to LG domains and polymerization. Collectively these findings reveal that laminins integrate scaffold-forming and cell-adhesion activities to assemble an endoneurial BM, with myelination and proliferation requiring additional α6ß1/α7ß1-laminin LG domain interactions, and that a high BM ligand/structural density is needed for efficient myelination.

Non-redundant function of dystroglycan and ß1 integrins in radial sorting of axons.

Radial sorting allows the segregation of axons by a single Schwann cell (SC) and is a prerequisite for myelination during peripheral nerve development. Radial sorting is impaired in models of human diseases, congenital muscular dystrophy (MDC) 1A, MDC1D and Fukuyama, owing to loss-of-function mutations in the genes coding for laminin α2, Large or fukutin glycosyltransferases, respectively. It is not clear which receptor(s) are activated by laminin 211, or glycosylated by Large and fukutin during sorting. Candidates are αß1 integrins, because their absence phenocopies laminin and glycosyltransferase deficiency, but the topography of the phenotypes is different and ß1 integrins are not substrates for Large and fukutin. By contrast, deletion of the Large and fukutin substrate dystroglycan does not result in radial sorting defects. Here, we show that absence of dystroglycan in a specific genetic background causes sorting defects with topography identical to that of laminin 211 mutants, and recapitulating the MDC1A, MDC1D and Fukuyama phenotypes. By epistasis studies in mice lacking one or both receptors in SCs, we show that only absence of ß1 integrins impairs proliferation and survival, and arrests radial sorting at early stages, that ß1 integrins and dystroglycan activate different pathways, and that the absence of both molecules is synergistic. Thus, the function of dystroglycan and ß1 integrins is not redundant, but is sequential. These data identify dystroglycan as a functional laminin 211 receptor during axonal sorting and the key substrate relevant to the pathogenesis of glycosyltransferase congenital muscular dystrophies.

Renal collecting system growth and function depend upon embryonic γ1 laminin expression.

In order to understand the functions of laminins in the renal collecting system, the Lamc1 gene was inactivated in the developing mouse ureteric bud (UB). Embryos bearing null alleles exhibited laminin deficiency prior to mesenchymal tubular induction and either failed to develop a UB with involution of the mesenchyme, or developed small kidneys with decreased proliferation and branching, delayed renal vesicle formation and postnatal emergence of a water transport deficit. Embryonic day 12.5 kidneys revealed an almost complete absence of basement membrane proteins and reduced levels of α6 integrin and FGF2. mRNA levels for fibroblast growth factor 2 (FGF2) and mediators of the GDNF/RET and WNT11 signaling pathway were also decreased. Furthermore, collecting duct cells derived from laminin-deficient kidneys and grown in collagen gels were found to proliferate and branch slowly. The laminin-deficient cells exhibited decreased activation of growth factor- and integrin-dependent pathways, whereas heparin lyase-treated and ß1 integrin-null cells exhibited more selective decreases. Collectively, these data support a requirement of γ1 laminins for assembly of the collecting duct system basement membrane, in which immobilized ligands act as solid-phase agonists to promote branching morphogenesis, growth and water transport functions.

A small-scale silica gel column chromatography method for separating carbazole compounds from highly mature crude oil.

The concentration of carbazoles in highly mature crude oil is quite low, making it challenging to separate carbazole compounds for the gas chromatography-mass spectrometry (GC-MS) detection. This study presents a small-scale column chromatography method for separating carbazoles from highly mature crude oil using silica gel as a solid phase adsorbent and a Pasteur pipette as a separation device. The carbazole-rich crude oil from the Pearl River Mouth Basin was selected to explore the impact of reagent polarity and injection mode on the separation of carbazoles. The oil sample was eluted with solvents mixed with different volume proportions of n-hexane and dichloromethane and each eluted fraction was collected for GC-MS testing. The results indicated that increasing the reagent polarity caused the aromatic hydrocarbons and carbazole compounds in crude oil to be eluted sequentially. Most aromatic compounds in the crude oil could be selectively eluted using a reagent polarity ratio of 9:1 (Vn-hexane: Vdichloromethane), with no carbazole compounds. A significant amount of carbazole compounds were eluted in the polar segments of 8:2-6:4, with the eluted carbazoles concentration accounting for more than 98 % of the total concentration. Moreover, the concentration and recovery of carbazoles eluted by direct injection mode were about 10 % higher than those after adsorption by silica gel. The standard deviation of the parameter ratio for the separated carbazole compounds in the three groups of repeatable parallel experiments was less than 0.2 %. Our method is superior to traditional two-step method and C18 column method in separation efficiency and damage to human body. This method can be applied to both highly mature crude oil and other kinds of oils including biodegradable oil. It could be a versatile method for the carbazoles separation and provide technical support in unveiling the geochemical implications of these compounds in complex areas.

Lecanemab Blocks the Effects of the Aß/Fibrinogen Complex on Blood Clots and Synapse Toxicity in Organotypic Culture.

Proteinaceous brain inclusions, neuroinflammation, and vascular dysfunction are common pathologies in Alzheimer's disease (AD). Vascular deficits include a compromised blood-brain barrier, which can lead to extravasation of blood proteins like fibrinogen into the brain. Fibrinogen's interaction with the amyloid-beta (Aß) peptide is known to worsen thrombotic and cerebrovascular pathways in AD. Lecanemab, an FDA-approved antibody therapy for AD, shows promising results in facilitating reduction of Aß from the brain and slowing cognitive decline. Here we show that lecanemab blocks fibrinogen's binding to Aß protofibrils, normalizing Aß/fibrinogen-mediated delayed fibrinolysis and clot abnormalities in vitro and in human plasma. Additionally, we show that lecanemab dissociates the Aß/fibrinogen complex and prevents fibrinogen from exacerbating Aß-induced synaptotoxicity in mouse organotypic hippocampal cultures. These findings reveal a possible protective mechanism by which lecanemab may slow disease progression in AD.

A small-scale neutral alumina column chromatography method for carbon isotope determination of hopanes in crude oils or rock extracts.

This paper presents a small-scale column chromatography method for separating hopanes in crude oil or rock extracts using neutral alumina as a solid phase adsorbent and a Pasteur pipette as a separation device. Three oil samples were selected to study the effect of solid phase adsorbent type and column length on the separation of hopanes. The oil samples were eluted with mixed reagents (V hexane: V petroleum ether = 8:2) and collected at intervals of 0.5 ml. Ten Fractions were collected and tested for the compounds using GC-MS. A quantitative approach was used to reveal distribution characteristics of compounds in each eluted Fraction. Experimental results showed that 100-200 um neutral alumina exhibited significant differences in the adsorptive capacity of biomarkers from oil samples and rock extracts. The elution order of the biomarkers in the chromatographic column (the length is 180 mm) was n-alkanes, steranes and hopanes. The separation of hopanes could be realized by collecting the eluted Fractions 4 and 5. Compared with the urea complexation, the purity of hopanes separated by column chromatography was higher. The concentration of n-alkanes (nC16-nC34) could be reduced from 1.99 to 4.83 mg/ml to 0.79-0.94 mg/ml, and the content of steranes can be reduced from the original 12% to 0.45%. Residual n-alkanes and steranes were not visible in the GC-MS detection. The Total Ion Chromatography (TIC) of hopanes was consistent with the distribution characteristics of the m/z191 mass chromatogram. The isolated hopanes could meet the detection requirements of isotope ratio mass spectrometry. The C29Ts/C29αß ratio of hopanes decreased gradually from 1.63 to 0.73 as the column length increased. It is speculated that the variation of the C29Ts/C29αß ratio is not only affected by maturity but also by the oil and gas migration. This method is a new attempt in the field of compound purification and can be widely used in the study of stable carbon isotopes of hopanes monomeric hydrocarbons.

Anti-HK antibody inhibits the plasma contact system by blocking prekallikrein and factor XI activation in vivo.

A dysregulated plasma contact system is involved in various pathological conditions, such as hereditary angioedema, Alzheimer disease, and sepsis. We previously showed that the 3E8 anti-high molecular weight kininogen (anti-HK) antibody blocks HK cleavage and bradykinin generation in human plasma ex vivo. Here, we show that 3E8 prevented not only HK cleavage but also factor XI (FXI) and prekallikrein (PK) activation by blocking their binding to HK in mouse plasma in vivo. 3E8 also inhibited contact system-induced bradykinin generation in vivo. Interestingly, FXII activation was also inhibited, likely because of the ability of 3E8 to block the positive feedback activation of FXII by kallikrein (PKa). In human plasma, 3E8 also blocked PK and FXI binding to HK and inhibited both thrombotic (FXI activation) and inflammatory pathways (PK activation and HK cleavage) of the plasma contact system activation ex vivo. Moreover, 3E8 blocked PKa binding to HK and dose-dependently inhibited PKa cleavage of HK. Our results reveal a novel strategy to inhibit contact system activation in vivo, which may provide an effective method to treat human diseases involving contact system dysregulation.

Striatal fibrinogen extravasation and vascular degeneration correlate with motor dysfunction in an aging mouse model of Alzheimer's disease.

Introduction: Alzheimer's Disease (AD) patients exhibit signs of motor dysfunction, including gait, locomotion, and balance deficits. Changes in motor function often precede other symptoms of AD as well as correlate with increased severity and mortality. Despite the frequent occurrence of motor dysfunction in AD patients, little is known about the mechanisms by which this behavior is altered. Methods and Results: In the present study, we investigated the relationship between cerebrovascular impairment and motor dysfunction in a mouse model of AD (Tg6799). We found an age-dependent increase of extravasated fibrinogen deposits in the cortex and striatum of AD mice. Interestingly, there was significantly decreased cerebrovascular density in the striatum of the 15-month-old as compared to 7-month-old AD mice. We also found significant demyelination and axonal damage in the striatum of aged AD mice. We analyzed striatum-related motor function and anxiety levels of AD mice at both ages and found that aged AD mice exhibited significant impairment of motor function but not in the younger AD mice. Discussion: Our finding suggests an enticing correlation between extravasated fibrinogen, cerebrovascular damage of the striatum, and motor dysfunction in an AD mouse model, suggesting a possible mechanism underlying motor dysfunction in AD.

Blocking domain 6 of high molecular weight kininogen to understand intrinsic clotting mechanisms.

Background: The contact system is initiated by factor (F) XII activation and the assembly of high molecular weight kininogen (HK) with either FXI or prekallikrein (PK) on a negatively charged surface. Overactivation of this system contributes to thrombosis and inflammation in numerous diseases. To develop effective therapeutics for contact system disorders, a detailed understanding of this pathway is needed. Methods: We performed coagulation assays in normal human plasma and various factor-deficient plasmas. To evaluate how HK-mediated PK and FXI activation contributes to coagulation, we used an anti-HK antibody to block access to domain 6 of HK, the region required for efficient activation of PK and FXI. Results: FXI's binding to HK and its subsequent activation by activated FXII contributes to coagulation. We found that the 3E8 anti-HK antibody can inhibit the binding of FXI or PK to HK, delaying clot formation in human plasma. Our data show that in the absence of FXI, however, PK can substitute for FXI in this process. Addition of activated FXI (FXIa) or activated PK (PKa) abolished the inhibitory effect of 3E8. Moreover, the requirement of HK in intrinsic coagulation can be largely bypassed by adding FXIa. Like FXIa, exogenous PKa shortened the clotting time in HK-deficient plasma, which was not due to feedback activation of FXII. Conclusions: This study improves our understanding of HK-mediated coagulation and provides an explanation for the absence of bleeding in HK-deficient individuals. 3E8 specifically prevented HK-mediated FXI activation; therefore, it could be used to prevent contact activation-mediated thrombosis without altering hemostasis.

Anti-HK antibody reveals critical roles of a 20-residue HK region for Aß-induced plasma contact system activation.

Alzheimer's disease (AD) is a neurodegenerative disorder and the leading cause of dementia. Vascular abnormalities and neuroinflammation play roles in AD pathogenesis. Plasma contact activation, which leads to fibrin clot formation and bradykinin release, is elevated in many AD patients, likely due to the ability of AD's pathogenic peptide ß-amyloid (Aß) to induce its activation. Since overactivation of this system may be deleterious to AD patients, the development of inhibitors could be beneficial. Here, we show that 3E8, an antibody against a 20-amino acid region in domain 6 of high molecular weight kininogen (HK), inhibits Aß-induced intrinsic coagulation. Mechanistically, 3E8 inhibits contact system activation by blocking the binding of prekallikrein (PK) and factor XI (FXI) to HK, thereby preventing their activation and the continued activation of factor XII (FXII). The 3E8 antibody can also disassemble HK/PK and HK/FXI complexes in normal human plasma in the absence of a contact system activator due to its strong binding affinity for HK, indicating its prophylactic ability. Furthermore, the binding of Aß to both FXII and HK is critical for Aß-mediated contact system activation. These results suggest that a 20-amino acid region in domain 6 of HK plays a critical role in Aß-induced contact system activation, and this region may provide an effective strategy to inhibit or prevent contact system activation in related disorders.