Advancements in Therapy for Alzheimer’s Disease Based on the Cerebral Lymphatic System

Late onset Alzheimer’s Disease (AD) is the most common form of dementia, affecting 40 million patients and countless families worldwide. AD is characterized by accumulation of amyloid beta (Aß) in the brain and central nervous system (CNS). A growing body of evidence indicates that while Aß production is unchanged, its clearance from the CNS is attenuated in late onset AD. Therefore, it is critical to determine how Aβ is cleared from the brain and if these processes differ in healthy and AD patients. Recently, two groups independently reported that a network of meningeal lymphatic vasculature participates in the clearance of solutes and macromolecules from the brain and cerebrospinal fluid of mice. However the presence of meningeal lymphatic vessels and their potential role in the clearance of Aß has not yet been defined in humans. Therefore, to determine if human meningeal lymphatic vessels absorb Aβ, we used immunofluorescence to examine superior sagittal sinus-associated dura mater tissue in a cohort of 21 patient samples including 6 subjects with no diagnosed dementia (control), 7 subjects with histopathologically confirmed AD, and 8 with diagnosis of mixed or other dementia. We found podoplanin (PDPN) positive, lumenized vessels in 19/21 patient samples, with 5/6 in control patients, 7/7 in AD patients and 7/8 in other or mixed dementia patients. These vessels were located in the dura mater, lateral to the superior sagittal sinus, and ranged from approximately 10 to 500 microns in diameter. Trace Aβ immunoreactivity was colocalized with podoplanin-positive vessels in 1/5 control, 1/7 AD, and 1/7 other or mixed dementia patients. Aß reactivity was found in meningeal blood vessels of 0/6 control, 1/7 AD, and 0/7 other or mixed dementia patients. To our knowledge, these data are the first to robustly support the existence of lymphatic vasculature in the human meninges. The data further suggest that Aß does not appear to widely deposit along wither these meningeal lymphatic or blood vessels, even among AD subjects.

The amyloid hypothesis states that the buildup of ß-amyloid in the brain is the main factor for Alzheimer's disease (AD) pathogenesis. An imbalance between ß-amyloid production and ß-amyloid clearance causes the advanced stages of the disease, including the development of neurofibrillary tangles containing tau protein.1 Many medications that aim to reduce ß-amyloid in AD are not clinically effective. FDA has approved aducanumab, one of four anti-ß-amyloid antibodies that have been demonstrated to mediate the removal of amyloid plaque from the brains of AD patients. FDA accepted the decrease of amyloid plaque as a surrogate endpoint for aducanumab. But there is intense disagreement over the justification for approval and the scope of the clinical benefit provided by antiamyloid antibodies.2 One side effect of the antibodies is brain edema, effusion, and hemorrhages, so called amyloid-related imaging abnormalities (ARIA). ARIA occurs in aged squirrel monkeys as well as in humans.3 Lecanemab, an antiamyloid monoclonal antibody, was associated with edema or effusions in 12.4% of subjects, including three fatal brain hemorrhages; the placebo group had 1.7% brain edema.4-9 In the case of donanemab, another anti-amyloid monoclonal antibody, if edema or effusion occurred with the first three doses of the drug, the dosage was not increased.10 A serious clinical condition, brain edema is defined by a pathological swelling of the brain tissue brought on by an increase in the water content of the brain. In humans11 and in a mouse model, APOE isoform affects neurological prognosis following intracerebral hemorrhage. Poor functional outcome and more cerebral edema are linked to APOE4.12 Three SNPs of the ABCC8 gene, rs2283261, rs3819521, and rs2283258, are significantly associated with brain edema, measured by increased intracranial pressure and CT imaging. Haptoglobin type, Hp2 versus Hp1, may also influence brain edema.13 Aquaporins, a family of water channel proteins that have been found in animals, may provide an explanation for AD brain edema. Aquaporin-4 (AQP4), the most significant form of aquaporin in the central nervous system, mediates water homeostasis in healthy and pathological settings, such as severe brain injury.13, 14 Because brain edema has occurred during clinical trials of most anti-amyloid antibodies, we hypothesize that ß-amyloid might be an important element in brain water homeostasis. Removing ß-amyloid could cause brain edema and bleeding in some AD patients. To investigate this idea, we analyzed structures of aquaporin-4 and ß-amyloid from the RCSB protein data bank. To help identify the brain regions where anti-amyloid antibodies may act, we used the Allen Brain Atlas and the Human Protein Atlas to examine AQP4 and APP (amyloid ß precursor protein) RNA expression in the brain.15, 16 2D57: Double layered 2D crystal structure of Aquaporin-4 (AQP4M23) at 3.2 Å resolution by electron crystallography.17 1 × 45: Solution structure of the first PDZ domain of ß-amyloid A4 precursor protein-binding family A, member 1. The PDZ domain is a common structural domain of 80–90 amino acids found in the signaling proteins of bacteria, yeast, plants, viruses, and animals. The protein structures were superimposed and aligned on PYMOL v 2.5.0 with the Super command, which super aligns two protein selections. Super does a sequence-independent structure-based dynamic programming alignment (unlike the align command) followed by a series of refinement cycles intended to improve the fit by eliminating pairing with high relative variability. The Super command is more reliable than the align command for proteins with low sequence similarity. AQP4 expression (Allen Brain Atlas) is shown in Figure 1. AQP4 RNA is strongly and broadly expressed in a variety of brain areas, including the hippocampal and parahippocampal regions where AD originates. Figure 2 shows AQP4 RNA expression diagrammatically. AQP4 RNA is strongly and broadly expressed in a variety of brain areas in both the human and mouse (not shown). The donor was a 24-year-old Male Black or African American (Allen Brain Atlas). Amyloid precursor protein (APP) RNA expression is in Figure 3. Like AQP4, APP is strongly expressed throughout the brain (Human Protein Atlas). Pymol performed five cycles of calculations on 29 aligned atoms of aquaporin-4 and ß-amyloid proteins, with a final root mean square deviation of atomic positions (RMSD) of 0.300 Å for 21 atoms (Figure 4). Pymol automatically determines the optimum number of cycles to calculate. Lower values of RMSD indicate that alignment is validated with higher accuracy. RMSD values of 1 Å or less indicate very good alignment. The two aligned molecules aquaporin-4 and ß-amyloid are shown in Figure 5. The 21-atom alignment is excellent. The arrow indicates isoleucine 77 of ß-amyloid overlying valine 162 in exon 3 of aquaporin 4. Alignments are a powerful way to compare related protein sequences. They can be used to record a variety of information about matched sequences, such as shared structural function or common evolutionary ancestry. Over the past few decades, protein sequence alignment analyses have become an essential stage in bioinformatics analytic research. Numerous protein databases with information on protein families were created using sequence alignments.18 Our analysis indicates that AQP4 and ß-amyloid may have shared functions, including maintenance of brain water homeostasis and prevention of brain edema. The similarities in brain expression of AQP4 and APP (Figures 2 and 3) reinforce this conclusion. The most widespread CNS aquaporin channel, AQP4, is frequently seen in the astrocytic end feet. AQP4 RNA is strongly and broadly expressed in a variety of brain areas in both the human and mouse. Additionally, the entire mouse brain exhibits significant AQP4 intensity and broad immunolabelling of astrocyte end-feet, with this pattern representing the vasculature and capillary walls. AQP4 variants may be a risk factor for AD vasogenic edema. A direct result of tight junction breakdown between vascular endothelial cells, vasogenic edema develops because of a disturbance of blood–brain barrier integrity. The extracellular compartment of the brain enlarges because fluid and proteins from the vasculature penetrate the interstitial space. Vasogenic edema results in increased intracranial pressure, decreased cerebral blood flow, brain herniation, and ultimately death. Vasogenic edema can follow trauma, arterial hypertension, tumor-released vasoactive substances, or endothelium-damaging substances, for example, arachidonic acid, excitatory neurotransmitters, eicosanoids, bradykinin, histamine, and free radicals.13, 14 Vasogenic edema is a common side effect of anti-amyloid AD drugs19 and may be a sign that amyloid is being cleared from the brain.20 One study of AQP4 exon 4 did not find mutations. But in another, seven tag single nucleotide polymorphisms (SNPs) were detected along the AQP4 gene region in a study that examined clinical, neuroimaging, and genetic data from 363 traumatic brain injury patients. A tag SNP is a SNP in a region of the genome with high linkage disequilibrium, part of a group of SNPs called a haplotype. Two tag SNPs, rs3763043, associated with schizophrenia,21 and rs3875089, associated with intracerebral hemorrhage,22 were connected to poor clinical outcomes as assessed 6 months after traumatic brain injury.23 Our finding that AQP4 aligns closely with ß-amyloid may indicate that ß-amyloid, like AQP4, might be important in maintaining brain water homeostasis and preventing brain edema. ß-amyloid structure has been highly conserved throughout mammalian evolution, indicating one or more vital functions. For example, ß-amyloid is antimicrobial and may be an inherited defense against herpes simplex type 1.24 The results of the current study have two notable implications: (1) Screening for AQP4 polymorphisms SNPs rs3763043, rs3875089, and APOE4 isoform before antiamyloid AD treatment could identify patients at high risk of brain edema and hemorrhage. Screening for ABCC8 polymorphisms and haptoglobin form could be of value as well. (2) Screening for the same in children could detect those with increased vulnerability to traumatic brain injury in certain sports: football, hockey, basketball, and baseball. APOE2, APOE4, AQP4, and antiamyloid antibodies are not the only substances associated with AD vasogenic edema. The Alzheimer's drug, avagacestat, a small molecule gamma-secretase inhibitor that reduces ß-amyloid levels, also caused vasogenic edema.25 Moreover, asymptomatic vasogenic edema has been found in AD patients who have received no treatment at all.19 Therefore, focal, localized vasogenic edema may be part of the AD pathologic process. Since APOE and ABCC8 genes are associated with cerebral edema, it would be worthwhile to evaluate the alignment and other similarities of these protein structures with AQP4. We conclude that ß-amyloid may be involved in brain water homeostasis and protect against vasogenic brain edema. Removing ß-amyloid from AD patients may promote vasogenic brain edema and bleeding. Screening for AQP4 and ABCC8 polymorphisms, APOE2 and APOE4 isoforms, and haptoglobin form could identify patients at high risk of brain edema and hemorrhage from anti-amyloid treatment. Further studies are warranted. Preprint posted https://doi.org/10.21203/rs.3.rs-2350250/v1 Dr. Steven Lehrer and Dr. Peter H. Rheinstein contributed equally to this work. None. The authors declare no conflict of interest. Not applicable, all data from publicly available sources. All data from publicly available sources.

Central nervous system lymphatic drainage system (CNSLDS) is composed of glymphatic system, perivascular lymphatic drainage pathways and meningeal lymphatic vessels. Based on new findings of structures and functions of CNSLDS, CNSLDS is one of the mechanisms for promoting the clearance of β-amyloid (Aβ). CNSLDS functions physiologically as a route of drainage for Aβ from glymphatic system or perivascular lymphatic drainage pathways to meningeal lymphatic vessels, and the meningeal lymphatic vessels helps Aβ drainage to the nearby lymph nodes. In this review, we summarize the key component elements (structure and function) in the clearance of Aβ during the CNS lymphatic drainage. Also, we highlight their potential roles in the pathogenesis of Alzheimer's disease and their clinical importance in diagnosis and treatment of neurologic diseases associated with Aβ, including Alzheimer's disease. Key words: Central nervous system; Lymphatic drainage system; Glymphatic system; Meningeal lymphatic vessel; β-amyloid protein

Yuanzhi powder facilitated Aβ clearance in APP/PS1 mice: Target to the drainage of glymphatic system and meningeal lymphatic vessels

Accumulation of toxic protein aggregates-amyloid-β (Aβ) plaques and hyperphosphorylated tau tangles-is the pathological hallmark of Alzheimer disease (AD). Aβ accumulation has been hypothesized to result from an imbalance between Aβ production and clearance; indeed, Aβ clearance seems to be impaired in both early and late forms of AD. To develop efficient strategies to slow down or halt AD, it is critical to understand how Aβ is cleared from the brain. Extracellular Aβ deposits can be removed from the brain by various clearance systems, most importantly, transport across the blood-brain barrier. Findings from the past few years suggest that astroglial-mediated interstitial fluid (ISF) bulk flow, known as the glymphatic system, might contribute to a larger portion of extracellular Aβ (eAβ) clearance than previously thought. The meningeal lymphatic vessels, discovered in 2015, might provide another clearance route. Because these clearance systems act together to drive eAβ from the brain, any alteration to their function could contribute to AD. An understanding of Aβ clearance might provide strategies to reduce excess Aβ deposits and delay, or even prevent, disease onset. In this Review, we describe the clearance systems of the brain as they relate to proteins implicated in AD pathology, with the main focus on Aβ.

Thermodynamic and kinetic origins of Alzheimer's and related diseases: A chemical engineer's perspective

Alzheimer's disease (AD) is the main neurodegenerative disease leading to dementia and cognitive impairment in the elderly. Considering AD to be an epidemic, an increase from the current 50 million to more than 150 million patients is expected by the year 2050. AD is characterized by a slow, progressive and asymptomatic onset; making it difficult to decipher the precise etiology. It is well established that AD presents two characteristic features, extracellular β-amyloid plaques and intracellular tau tangles, that eventually lead to the impairment of cognitive functions. Unfortunately, AD symptomatology shares many similarities with other dementias once is present, which makes it difficult an accurate premortem diagnosis. Although AD is mainly considered an aging-related condition that affects cognitive function, several cardio- and cerebrovascular comorbidities such as hypertension or diabetes are also risk factors for cognitive impairment. Accordingly, brain vascular-associated alterations underlie many pathophysiological mechanisms of AD. We have recently reviewed the latest evidence supporting the detrimental role of vascular and angiogenic alterations during AD (Custodia et al., 2022). Remarkably, cerebral blood-brain barrier (BBB) leakage and microbleeds are associated with cognitive decline in patients with mild cognitive impairment (MCI) and early AD. Accordingly, the two-hit vascular hypothesis points at initial damage in cerebral vasculature (hit one) that eventually induces the accumulation of β-amyloid (Aβ) in the brain (hit two; Zlokovic, 2005). CD34+ bone marrow-derived progenitor cells (BMPCs) define a group of stem and progenitor cell populations released by the bone marrow that covers different subpopulations of cells from the hematopoietic linage, including endothelial progenitor cells (EPCs). EPCs exhibit characteristics of both endothelial and stem cells, and, accordingly, proangiogenic early EPCs expressing both CD34 and CD133 (a progenitor surface marker) can be distinguished from late EPCs additionally expressing KDR and/or CD146 (endothelial markers), which participate in the process of angiogenesis and vasculogenesis (Figure 1). Therefore, EPCs participate in angiogenesis and the maintenance of the endothelium by acting as a cellular reservoir for the replacement of dysfunctional endothelial cells, or by the secretion of angiogenic growth factors.Figure 1: Beneficial roles of CD34+ BMPCs following CNS injury.CD34+ BMPCs and the EPCs subtypes, early and late, can promote both angiogenesis and vasculogenesis following CNS injury by specializing in endothelial cells, and/or indirectly by secreting free and exosome-enveloped growth factors. G-CSF is a glycoprotein that acts in the bone marrow to mobilize both EPCs and CD34+ BMPCs after damage. BMPCs: Bone marrow progenitor cells; CNS: central nervous system; EPCs: endothelial progenitor cells; G-CSF: granulocyte colony-stimulating factor. Created with BioRender.com.Given that both dysfunctional angiogenesis and compromised BBB integrity seem critical in the onset and/or progression of AD, CD34+ progenitor cells, primarily EPCs, appear as potential targets for the early diagnosis and/or treatment of the disease. In this way, early and late EPCs would work synergistically: early EPCs reach the site of injury due to the high concentration of angiogenic factors and inflammatory cytokines, from which they paracrinally release different factors promoting angiogenesis and recruiting late EPCs, which either restore the endothelium or form new vessels guided by the early EPCs. Here, we discuss recent work and ongoing human clinical trials testing the feasibility of CD34+ BMPCs and EPCs as early biomarkers of AD and pharmacological targets for future treatments. Association of circulating levels of CD34+ BMPCs and cognitive decline in healthy and MCI subjects: Several cross-sectional studies have shown that the number of circulating CD34+ BMPCs decreases with age, and this may impact cognition. In this regard, a longitudinal study regarding cognition and CD34+ BMPCs levels reported that older healthy subjects had lower levels of CD34+ BMPCs than younger counterparts at baseline measurements (Hajjar et al., 2016). Moreover, this investigation revealed that subjects with higher baseline levels of several subgroups of CD34+ BMPCs such as early and late EPCs, and CD34+/KDR+ cells, among others, had better executive-derived and working memory scores over 4 years of follow-up (Hajjar et al., 2016). Recently, a large transverse study has shown the association between CD34+ BMPCs and different memory-related tests in cognitively normal subjects with coronary artery disease (Moazzami et al., 2020). Notably, circulating numbers of late EPCs were positively correlated with a better performance in tasks assessing visual, logical, and verbal immediate/delayed memory. Therefore, the amount of circulating CD34+ BMPCs subtypes appears to be negatively correlated to the cognitive decline of both healthy subjects and patients with vascular-associated conditions. Although more longitudinal clinical studies are needed to fully confirm the harmful effect of low levels of CD34+ BMPCs on the cognitive state, and other factors may be also taking part in this cognitive decline, it is still plausible that larger amounts of circulating endothelial progenitors exert a protective effect, probably by the maintenance of vascular endothelium integrity. MCI often precedes clinical symptoms of AD, and MCI patients show an increased risk of developing dementia in the future. Thus, it is very interesting to study CD34+ BMPCs/EPCs levels in patients with MCI in order to test whether such levels can be used as potential non-invasive diagnostic biomarkers to detect cognitive decline or its progression from MCI to dementia. Some studies have observed a decrease in CD34+ BMPCs and EPCs populations from MCI patients (Nation et al., 2018; Callahan et al., 2020). In this sense, MCI patients with lower levels of circulating CD34+ BMPCs and both subtypes of EPCs exhibited worse scores in memory tests and reduced cortical thickness compared to control subjects (Nation et al., 2018). Considering the angiogenesis ratio (pro-angiogenic/non-angiogenic BMPCs, including early and late EPCs), Callahan et al. (2020) showed a positive association between angiogenesis ratio and white matter hyperintensities, but not with global cerebral blood flow, hippocampal volume, or accumulation of tau and Aβ. By contrast, measurements in an older cohort of MCI patients did not show significant changes in CD34+, early EPCs, and late EPCs circulating levels compared to control subjects (Breining et al., 2016). This discrepancy may highlight that aging decreases CD34+ BMPCs to such a reduced level that is no longer different in controls compared to MCI. In summary, it seems that the reduction in CD34+ BMPCs is directly related to vascular dysfunction, increasing brain white matter microlesions and impairing cognition in MCI patients. Association of circulating levels of CD34+ BMPCs and AD: Several studies have been performed in order to determine the relationship between CD34+ BMPCs/EPCs circulating levels and the progression of AD (Maler et al., 2006; Lee et al., 2009; Stellos et al., 2010; Bigalke et al., 2011; Kong et al., 2011; Breining et al., 2016; Callahan et al., 2020; Haiyuan et al., 2020). In this way, AD patients in the early symptomatic phase already showed lower levels of CD34+ and CD34+/KDR+ cells compared to their control counterparts (Maler et al., 2006; Haiyuan et al., 2020). Notably, CD34+ BMPCs counts have negatively correlated with levels of Aβ1–42 in cerebrospinal fluid and the Aβ ratio 42/40, two well-known biomarkers for AD, as well as with age, only in the early AD group (Maler et al., 2006). Furthermore, the homing capacity of EPCs from early AD patients was already impaired (Haiyuan et al., 2020). Overall, it is becoming clear that dysfunctional CD34+ BMPCs are related to a reduced ability to repair brain endothelial cells, which appears to mediate neurotoxicity by affecting the BBB permeability. On the other hand, different outcomes were described in studies assessing the number of progenitor cells during AD progression. Specifically, lower counts of CD34+ BMPCs and EPCs have been observed in moderate and severe AD patients compared to both early AD stage (Haiyuan et al., 2020) and control subjects (Lee et al., 2009; Kong et al., 2011; Haiyuan et al., 2020). Such studies also revealed that homing and adhesion features of EPCs from AD patients were impaired (Haiyuan et al., 2020), as well as EPCs levels were inversely correlated with the mini-mental state exam (MMSE) score (Lee et al., 2009; Stellos et al., 2010; Kong et al., 2011). Furthermore, moderate to severe AD patients displayed a reduced flow velocity of the middle cerebral artery (Kong et al., 2011). In contrast, other studies reported higher levels of CD34+ BMPCs and EPCs compared to controls (Stellos et al., 2010; Bigalke et al., 2011), or even no changes (Breining et al., 2016). Intriguingly, the work from Stellos and colleagues reported an increase in both CD34+ BMPCs and early EPCs counting when comparing moderate to severe AD patients versus control subjects; however, within the AD group, there was an inverse correlation between CD34+ BMPCs and early EPCs counting and the MMSE score. Although these results seem contrary to each other, it is noteworthy that most AD patients from this study (Stellos et al., 2010) were treated with cholinesterase inhibitor; a drug involved in EPCs proliferation. Therefore, this fact may bias the results and it could explain why cell counting in the AD group was higher than in controls, but they were inversely correlated with MMSE scores. The other study that showed increased levels of CD34+ BMPCs/EPCs (Bigalke et al., 2011) only measured the numbers of CD34+ BMPCs in early to moderate AD compared to controls, with no information regarding cholinesterase inhibitor treatment. In summary, most of the studies in later AD stages support the studies performed on MCI and early AD stages. Therefore, AD-mediated loss of CD34+ BMPCs/EPCs, as well as loss of EPCs-intrinsic features, are likely present in AD patients and may constitute novel diagnostic and therapeutic targets. Potential therapy with granulocyte colony-stimulating factor (G-CSF) in AD: The G-CSF is a glycoprotein secreted by endothelial and immune cells that acts as a hematopoietic growth factor (Figure 1). Among other beneficial mechanisms following vascular injury, the G-CSF can promote angiogenesis by mobilizing EPCs (Figure 1). Therefore, G-CSF may be a potential target to enhance vascular repair in AD patients. Indeed, it has been recently shown that a G-CSF treatment improved memory as well as reduced blood levels of amyloid and tau in mild to moderate patients of AD (Potter et al., 2021). Based on these achievements, it is currently conducting a phase2b clinical trial in order to evaluate the long-term treatment of G-CSF in AD patients (NCT04902703; ClinicalTrials.gov). It would be interesting to look at CD34+ BMPCs and EPCs levels from those clinical trials in order to elucidate whether such potential benefits promoted by G-CSF therapy are totally or partially mediated by increasing CD34+ BMPCs/EPCs mobilization. Future challenges: The body of evidence supporting a vascular component underlying AD onset and/or progression is growing. However, further studies are mandatory to elucidate whether such vascular component triggers AD, is a consequence of AD, or both. Moreover, longitudinal studies are needed to confirm the relationship between CD34+ BMPCs/EPCs levels and AD progression. Given that vascular-related diseases may influence the amount of circulating progenitor cells, especially in AD patients, comorbidities present in those subjects deserve special attention when interpreting the results. Likewise, pharmacological treatments, such as a cholinesterase inhibitor, may bias the results from studies giving uncorrected information. Despite the promising results in animal models of AD, the number of published results and clinical trials regarding the direct application of EPCs as a potential therapy in AD patients is absent. This is remarkable when there is compelling evidence that supports the role of endothelial dysfunction in the onset and progression of AD, and the potential of EPCs as a diagnostic biomarker and/or therapeutic target (Custodia et al., 2022). However, we were unable to find published data or ongoing clinical trials in humans using the application of EPCs to treat AD; as already seen in a stroke clinical trial (NCT01468064). Moreover, several recent studies have highlighted the beneficial role of EPCs secretome/exosomes by protecting and repairing the BBB following damage without using a cell-based therapy. So, clinical trials based on EPCs-derived secretome/exosomes might be a safer and more promising approach in AD research. Finally, only the GCSF-based treatment is being tested in AD patients at later stages, with modest but promising results. Given that endothelium-related impairments are already seen in MCI patients, it would be really interesting to test this GCSF-based treatment in those subjects in order to increase the benefits and protect against the progression to AD. This work was partially supported by grants from the Xunta de Galicia (IN607A2018/3 to TS, IN607D 2020/09 to TS, IN606A-2021/015 to AC; IN606B-2021/010 to DRS), and Science Ministry of Spain (RTI2018-102165-B-I00 to TS, RTC2019-007373-1 to TS). Furthermore, this work was also supported by grants from the INTERREG Atlantic Area (EAPA_791/2018_ NEUROATLANTIC project to TS), INTER-REG V A España Portugal (POCTEP) (0624_2IQBIONEURO_6_E to TS), and the European Regional Development Fund (ERDF). Moreover, DRS (CD21/00166) and TS (CPII17/00027) are recipients of research contracts from the Sara Borrell and Miguel Servet Programs, respectively, from the Instituto de Salud Carlos III. Availability of data and materials:All data generated or analyzed during this study are included in this published article and its supplementary information files. Open peer reviewers:Yali Jia, Beijing Institute of Radiation Medicine, China; Rongcan Luo, Kunming Institute of Zoology Chinese Academy of Sciences, China. Additional file:Open peer review reports 1 and 2.P-Reviewers: Jia Y, Luo R; C-Editors: Zhao M, Liu WJ, Wang Lu; T-Editor: Jia Y

High Activities of BACE1 in Brains with Mild Cognitive Impairment

Psychosis in Alzheimer’s Disease

New cerebrospinal fluid biomarkers in Alzheimer’s disease

Intrinsic Connectivity Identifies the Hippocampus as a Main Crossroad between Alzheimer’s and Semantic Dementia-Targeted Networks

The potential existence and roles of the meningeal lymphatic system in normal and pathological brain function have been a long-standing enigma. Recent evidence suggests that meningeal lymphatic vessels are present in both the mouse and human brain; in mice, they seem to play a role in clearing toxic amyloid-beta peptides, which have been connected with Alzheimer disease (AD). Here, we review the evidence linking the meningeal lymphatic system with human AD. Novel findings suggest that the recently described meningeal lymphatic vessels could be linked to, and possibly drain, the efferent paravascular glial lymphatic (glymphatic) system carrying cerebrospinal fluid, after solute and immune cell exchange with brain interstitial fluid. In so doing, the glymphatic system could contribute to the export of toxic solutes and immune cells from the brain (an exported fluid we wish to describe as glymph, similarly to lymph) to the meningeal lymphatic system; the latter, by being connected with downstream anatomic regions, carries the glymph to the conventional cervical lymphatic vessels and nodes. Thus, abnormal function in the meningeal lymphatic system could, in theory, lead to the accumulation, in the brain, of amyloid-beta, cellular debris, and inflammatory mediators, as well as immune cells, resulting in damage of the brain parenchyma and, in turn, cognitive and other neurologic dysfunctions. In addition, we provide novel insights into APOE4—the leading genetic risk factor for AD—and its relation to the meningeal lymphatic system. In this regard, we have reanalyzed previously published RNA-Seq data to show that induced pluripotent stem cells (iPSCs) carrying the APOE4 allele (either as APOE4 knock-in or stemming from APOE4 patients) express lower levels of (a) genes associated with lymphatic markers, and (b) genes for which well-characterized missense mutations have been linked to peripheral lymphedema. Taking into account this evidence, we propose a new conceptual framework, according to which APOE4 could play a novel role in the premature shrinkage of meningeal lymphatic vessels (meningeal lymphosclerosis), leading to abnormal meningeal lymphatic functions (meningeal lymphedema), and, in turn, reduction in the clearance of amyloid-beta and other macromolecules and inflammatory mediators, as well as immune cells, from the brain, exacerbation of AD manifestations, and progression of the disease. Altogether, these findings and their potential interpretations may herald novel diagnostic tools and therapeutic approaches in patients with AD.

Review of research advances in the cerebral lymphatic system and neurological disorders.

Lecanemab is a humanized murine IgG1 antibody. Recent Phase 3 clinical trials have demonstrated its ability to reduce brain amyloid-β (Aβ) load and slow cognitive decline in patients with early Alzheimer's disease (AD). However, since its approval, reports on adverse effects (AEs) associated with lecanemab have been limited. To better understand the AEs related to lecanemab and provide guidance for future clinical use, we analyzed lecanemab-associated AEs using data from the United States Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS). We extracted all AEs reports from the FAERS database for the period from the first quarter of 2023 to the third quarter of 2024. Using the Reporting Odds Ratio (ROR), Proportional Reporting Ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), and Multi-item Gamma Poisson Shrinker (MGPS) algorithms, we conducted a comprehensive analysis of lecanemab-related AEs, restricting the analysis to AEs with the role code of primary suspect (PS). A total of 811 AEs reports related to lecanemab used in AD patients and 506 AEs in Non-AD patients were included. The preferred terms (PTs) identified as positive across all four algorithms included headache, Amyloid Related Imaging Abnormalities-oedema/effusion (ARIA-E), chills, Amyloid Related Imaging Abnormalities-haemosiderosis/microhaemorrhage (ARIA-H), fatigue, infusion-related reaction, nausea, pyrexia, pain, influenza like illness, and so on. Among these, ARIA-E, ARIA-H, brain oedema and status epilepticus were associated with Important Medical Events (IMEs) for AD patients, and brain oedema, cerebral haemorrhage, cerebral microhaemorrhage, subdural haematoma, ischaemic stroke, cerebral infarction were associated with IMEs for Non-AD patients. At the system organ class (SOC) level, the highest signal detection for lecanemab was observed in nervous system disorders among AD and Non-AD patients [ROR for AD: 2.42 (2.2-2.65); ROR for Non-AD: 6.97 (6.12-7.95)]. The median time to the occurrence of these AEs was 44 days after administration in AD patients and 30 days for Non-AD patients. This study utilized the FAERS database to evaluate lecanemab-associated AEs in AD and non-AD patients, along with their temporal patterns post-marketing authorization, thereby establishing a foundation for subsequent clinical pharmacovigilance. A biweekly 10mg/kg was identified as the optimal therapeutic dosage. ARIA emerged as frequent treatment-related AEs, with APOEɛ4 carriers demonstrating heightened susceptibility. This necessitates serial brain MRI surveillance for all patients during treatment, aimed not only at early ARIA detection but also vigilant monitoring of IMEs including cerebral haemorrhage, cerebral microhaemorrhages, subdural haematoma, cerebral edema, ischaemic stroke, and cerebral infarction. While AD patients predominantly exhibited non-specific clinical manifestations, non-AD cohorts showed elevated risks of stroke-related complications. Consequently, dynamic neurological deficit monitoring is indispensable for non-AD populations receiving lecanemab to mitigate adverse outcomes. Finally, comprehensive reassessment of anticoagulant or antiplatelet therapy indications is warranted in both AD and non-AD patients to reduce hemorrhagic risks.

Editorial: New drugs for Alzheimer's disease in Japan