Aβ-Degrading Proteases: Therapeutic Potential in Alzheimer Disease

Alzheimer's Disease: Models and Molecular Mechanisms Informing Disease and Treatments

Alzheimer's Disease (AD) is a complex neurodegenerative disease resulting in progressive loss of memory, language and motor abilities caused by cortical and hippocampal degeneration. This review captures the landscape of understanding of AD pathology, diagnostics, and current therapies. Two major mechanisms direct AD pathology: (1) accumulation of amyloid β (Aβ) plaque and (2) tau-derived neurofibrillary tangles (NFT). The most common variants in the Aβ pathway in APP, PSEN1, and PSEN2 are largely responsible for early-onset AD (EOAD), while MAPT, APOE, TREM2 and ABCA7 have a modifying effect on late-onset AD (LOAD). More recent studies implicate chaperone proteins and Aβ degrading proteins in AD. Several tests, such as cognitive function, brain imaging, and cerebral spinal fluid (CSF) and blood tests, are used for AD diagnosis. Additionally, several biomarkers seem to have a unique AD specific combination of expression and could potentially be used in improved, less invasive diagnostics. In addition to genetic perturbations, environmental influences, such as altered gut microbiome signatures, affect AD. Effective AD treatments have been challenging to develop. Currently, there are several FDA approved drugs (cholinesterase inhibitors, Aß-targeting antibodies and an NMDA antagonist) that could mitigate AD rate of decline and symptoms of distress.

Coupling of Alzheimer's Disease Genetic Risk Factors with Viral Susceptibility and Inflammation

Alzheimer's disease (AD) is a neurodegenerative disease characterized by persistent cognitive decline. Amyloid plaque deposition and neurofibrillary tangles are the main pathological features of AD brain, though mechanisms leading to the formation of lesions remain to be understood. Genetic efforts through genome-wide association studies (GWAS) have identified dozens of risk genes influencing the pathogenesis and progression of AD, some of which have been revealed in close association with increased viral susceptibilities and abnormal inflammatory responses in AD patients. In the present study, we try to present a list of AD candidate genes that have been shown to affect viral infection and inflammatory responses. Understanding of how AD susceptibility genes interact with the viral life cycle and potential inflammatory pathways would provide possible therapeutic targets for both AD and infectious diseases.

Suppression of Fli-1 protects against pericyte loss and cognitive deficits in Alzheimer's disease

Brain pericytes regulate cerebral blood flow, maintain the integrity of the blood-brain barrier (BBB) and facilitate the removal of amyloid β (Aβ) which is critical to healthy brain activity. Pericyte loss has been observed in brains from patients with Alzheimer's disease (AD) and animal models. Our previous data demonstrated that friend leukemia virus integration 1 (Fli-1), an ETS transcription factor, governs pericyte viability in murine sepsis; however, the role of Fli-1 and its impact on pericyte loss in AD remains unknown. Here, we demonstrated that Fli-1 expression was up-regulated in postmortem brains from a cohort of human AD donors and in 5xFAD mice, which corresponded with a decreased pericyte number, elevated inflammatory mediators, and increased Aβ accumulation as compared to cognitively normal individuals and WT mice. Antisense oligonucleotide Fli-1 Gapmer administrated via intrahippocampal injection decelerated pericyte loss, decreased inflammatory response, ameliorated cognitive deficits, improved BBB dysfunction, and reduced Aβ deposition in 5xFAD mice. Fli-1 Gapmer-mediated inhibition of Fli-1 protected against Aβ accumulation-induced human brain pericyte apoptosis in vitro. Overall, these studies indicate that Fli-1 contributes to pericyte loss, inflammatory response, Aβ deposition, vascular dysfunction and cognitive decline, and suggest that inhibition of Fli-1 may represent novel therapeutic strategies for AD.

Insulin-Degrading Enzyme: Paradoxes and Possibilities

More than seven decades have passed since the discovery of a proteolytic activity within crude tissue extracts that would become known as insulin-degrading enzyme (IDE). Certainly much has been learned about this atypical zinc-metallopeptidase; at the same time, however, many quite fundamental gaps in our understanding remain. Herein, I outline what I consider to be among the most critical unresolved questions within the field, many presenting as intriguing paradoxes. For instance, where does IDE, a predominantly cytosolic protein with no signal peptide or clearly identified secretion mechanism, interact with insulin and other extracellular substrates? Where precisely is IDE localized within the cell, and what are its functional roles in these compartments? How does IDE, a bowl-shaped protein that completely encapsulates its substrates, manage to avoid getting “clogged” and thus rendered inactive virtually immediately? Although these paradoxes are by definition unresolved, I offer herein my personal insights and informed speculations based on two decades working on the biology and pharmacology of IDE and suggest specific experimental strategies for addressing these conundrums. I also offer what I believe to be especially fruitful avenues for investigation made possible by the development of new technologies and IDE-specific reagents. It is my hope that these thoughts will contribute to continued progress elucidating the physiology and pathophysiology of this important peptidase.

Racemization in Post-Translational Modifications Relevance to Protein Aging, Aggregation and Neurodegeneration: Tip of the Iceberg

Homochirality of DNA and prevalent chirality of free and protein-bound amino acids in a living organism represents the challenge for modern biochemistry and neuroscience. The idea of an association between age-related disease, neurodegeneration, and racemization originated from the studies of fossils and cataract disease. Under the pressure of new results, this concept has a broader significance linking protein folding, aggregation, and disfunction to an organism's cognitive and behavioral functions. The integrity of cognitive function is provided by a delicate balance between the evolutionarily imposed molecular homo-chirality and the epigenetic/developmental impact of spontaneous and enzymatic racemization. The chirality of amino acids is the crucial player in the modulation the structure and function of proteins, lipids, and DNA. The collapse of homochirality by racemization is the result of the conformational phase transition. The racemization of protein-bound amino acids (spontaneous and enzymatic) occurs through thermal activation over the energy barrier or by the tunnel transfer effect under the energy barrier. The phase transition is achieved through the intermediate state, where the chirality of alpha carbon vanished. From a thermodynamic consideration, the system in the homo-chiral (single enantiomeric) state is characterized by a decreased level of entropy. The oscillating protein chirality is suggesting its distinct significance in the neurotransmission and flow of perceptual information, adaptive associative learning, and cognitive laterality. The common pathological hallmarks of neurodegenerative disorders include protein misfolding, aging, and the deposition of protease-resistant protein aggregates. Each of the landmarks is influenced by racemization. The brain region, cell type, and age-dependent racemization critically influence the functions of many intracellular, membrane-bound, and extracellular proteins including amyloid precursor protein (APP), TAU, PrP, Huntingtin, α-synuclein, myelin basic protein (MBP), and collagen. The amyloid cascade hypothesis in Alzheimer's disease (AD) coexists with the failure of amyloid beta (Aβ) targeting drug therapy. According to our view, racemization should be considered as a critical factor of protein conformation with the potential for inducing order, disorder, misfolding, aggregation, toxicity, and malfunctions.

Quantitative, High-Throughput Assays for Proteolytic Degradation of Amylin

Amylin is a pancreatic peptide hormone that regulates glucose homeostasis but also aggregates to form islet amyloid in type-2 diabetes. Given its role in both health and disease, there is renewed interest in proteolytic degradation of amylin by insulin-degrading enzyme (IDE) and other proteases. Here, we describe the development and detailed characterization of three novel assays for amylin degradation, two based on a fluoresceinated and biotinylated form of rodent amylin (fluorescein-rodent amylin-biotin, FrAB), which can be used for any amylin protease, and another based on an internally quenched fluorogenic substrate (FRET-based amylin, FRAM), which is more specific for IDE. The FrAB-based substrate can be used in a readily implemented fluorescence-based protocol or in a fluorescence polarization (FP)-based protocol that is more amenable to high-throughput screening (HTS), whereas the FRAM substrate has the advantage of permitting continuous monitoring of proteolytic activity. All three assays yield highly quantitative data and are resistant to DMSO, and the FRAM and FP-based FrAB assay are ideally suited to HTS applications.

Shenqi Xingnao Granules ameliorates cognitive impairments and Alzheimer’s disease-like pathologies in APP/PS1 mouse model

Objective

Alzheimer's disease (AD) is along with cognitive decline due to amyloid-β (Aβ) plaques, tau hyperphosphorylation, and neuron loss. Shenqi Xingnao Granules (SQXN), a traditional Chinese medicine, significantly ameliorated the cognitive function and daily living abilities of patients with AD. However, till date, no study has investigated the mechanism of action of SQXN on AD. The present study aimed to verify the effects of SQXN treatment on cognitive impairments and AD-like pathologies in APP/PS1 mice.

Methods

Four-month-old APP/PS1 transgenic (Tg) mice were randomly divided into a model group and SQXN-treated (3.5, 7, 14 g/kg per day) groups. Learning-memory abilities were determined by Morris water maze and object recognition test. All mice were sacrificed and the brain samples were collected after 75 d. The soluble Aβ contents were detected by Elisa kit; The levels of expression of NeuN, APP, phosphorylated tau and related protein were measured by Western blotting; The inflammation factors were detected by the proinflammatory panel kit.

Results

Four-month-old APP/PS1 mice were administered SQXN by oral gavage for 2.5 months. Using the Morris water maze tests and Novel object recognition, we found that SQXN restored behavioral deficits in the experimental group of Tg mice when compared with the controls. SQXN also inhibited neuronal loss (NeuN marker). SQXN treatment decreased soluble Aβ42 through inhibiting the expression of sAPPβ and BACE-1 without regulating full-length amyloid precursor protein (FL APP). Insulin degrading enzyme (IDE), the Aβ degrading enzyme, were increased by SQXN. In addition, SQXN reduced hyperphosphorylated tau protein levels and prevented excessive activation of p-GSK-3β in the brain of APP/PS1 mice. Compared with APP/PS1 transgenic negative mice, IFN-γ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-12p70, KC/GRO and TNF-α were not obviously changed in the brain of 6.5-month-old APP/PS1 transgenic (Tg) mice. However, SQXN could inhibited the expression of IL-2.

Conclusion

These results demonstrate that SQXN ameliorates the cognitive impairments in APP/PS1 mice. The possible mechanisms involve its inhibition of neuronal loss, soluble Aβ deposition, tau hyperphosphorylation and inflammation.

Kai-Xin-San, a Chinese Herbal Decoction, Accelerates the Degradation of β-Amyloid by Enhancing the Expression of Neprilysin in Rats

This study aimed to investigate the mechanisms of Kai-Xin-San (KXS, a famous Chinese herbal decoction used to treat amnesia) on the degradation of Aβ and further elucidate the mechanism of KXS on Aβ-induced memory dysfunction. After pretreatment with KXS (1.08 g/kg/day) for two weeks, Aβ₄₂ (2 μL, 200 μM) was injected into rat hippocampus to induce cognitive dysfunction. Morris water maze (MWM) test was developed to evaluate cognitive performance in rats. Hippocampal neurons were observed by histological staining using Hematoxylin-Eosin (HE) methods. Levels of exogenous Aβ₄₂, which was injected into the hippocampus, were continually measured through a special Enzyme-linked immunoassay (ELISA) kit to observe the catabolic process of Aβ in the brain. Similarly, Aβ degradation in PC12 cells was also investigated using the ELISA kit. The expressions of Aβ degeneration enzymes, including neprilysin (NEP), angiotensin-converting enzyme (ACE), and endothelin-converting enzyme (ECE), were detected by western blotting to elucidate Aβ reduction mechanism. Our results showed that KXS prevented Aβ₄₂-induced cognitive impairment and attenuated hippocampus neuronal damage caused by Aβ₄₂. Moreover, KXS could accelerate Aβ₄₂ degradation in Aβ₄₂ injected rats. Furthermore, NEP, an Aβ degradation enzyme, was increased in the hippocampus while ECE and ACE, other two Aβ-degrading enzymes, were not changed. KXS accelerated Aβ degradation in PC12 cells. Our findings revealed that KXS facilitated the degradation of Aβ₄₂ by increasing the expression of NEP in rat hippocampus. By reducing the Aβ burdens, KXS protected hippocampal neurons, leading to the improvement of cognitive function in rats.

Anti-Alzheimer's disease activity of secondary metabolites from Xanthoceras sorbifolia Bunge

Xanthoceras sorbifolia Bunge is an edible oil tree species peculiar to China and it has long been used as a traditional medicine for enuresis in children. In this study, we investigated the active components in X. sorbifolia and eight barrigenol-type triterpenoids were isolated and identified. All the isolated compounds were tested first for H₂O₂-induced oxidative stress on human SH-SY5Y cells. Then Y-maze, Morris water maze, novel object recognition and passive avoidance tests were conducted to evaluate the improved effect of selected compounds with neuroprotective activity on ICV Aβ_1-42 mice. Among all the tested compounds, XS-8 exhibited significant protective effects against learning and memory impairments induced by ICV-Aβ_1-42. The XS-8 treatment significantly altered Aβ-induced hippocampal oxidative defense (increased MDA, nitrite and decreased SOD, glutathione) and pro-inflammatory levels (increased IL-1β and IL-18). The present study strongly suggests that X. sorbifolia is a promising plant resource for AD use and other neurodegenerative diseases.

Molecular Mechanism of Autophagy: Its Role in the Therapy of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder of progressive dementia that is characterized by the accumulation of beta-amyloid (Aβ)-containing neuritic plaques and intracellular Tau protein tangles. This distinctive pathology indicates that the protein quality control is compromised in AD. Autophagy functions as a "neuronal housekeeper" that eliminates aberrant protein aggregates by wrapping then into autophagosomes and delivering them to lysosomes for degradation. Several studies have suggested that autophagy deficits in autophagy participate in the accumulation and propagation of misfolded proteins (including Aβ and Tau). In this review, we summarize current knowledge of autophagy in the pathogenesis of AD, as well as some pathways targeting the restoration of autophagy. Moreover, we discuss how these aspects can contribute to the development of disease-modifying therapies in AD.

Oleanolic Acid Ameliorates Aβ25-35 Injection-induced Memory Deficit in Alzheimer's Disease Model Rats by Maintaining Synaptic Plasticity

Background:

Abnormal amyloid β (Aβ) accumulation and deposition in the hippocampus is an essential process in Alzheimer’s disease (AD).

Objective:

To investigate whether Oleanolic acid (OA) could improve memory deficit in AD model and its possible mechanism.

Methods:

Forty-five SD rats were randomly divided into sham operation group, model group, and OA group. AD models by injection of Aβ25-35 were built. Morris water maze (MWM) was applied to inves-tigate learning and memory, transmission electron microscope (TEM) to observe the ultrastructure of synapse, western blot to the proteins, electrophysiology for long-term potentiation (LTP), and Ca2+ con-centration in synapse was also measured.

Results:

The latency time in model group was significantly longer than that in sham operation group (P=0.0001); while it was significantly shorter in the OA group than that in model group (P=0.0001); compared with model group, the times of cross-platform in OA group significantly increased (P=0.0001). TEM results showed OA could alleviate neuron damage and synapses changes induced by Aβ25-35. The expressions of CaMKII, PKC, NMDAR2B, BDNF, TrkB, and CREB protein were signif-icantly improved by OA (P=0.0001, 0.036, 0.041, 0.0001, 0.0001, 0.026, respectively) compared with that in model group; the concentration of Ca2+ was significantly lower in OA group (1.11±0.42) than that in model group (1.68±0.18); and the slope rate (P=0.0001) and amplitude (P=0.0001) of f-EPSP significantly increased in OA group.

Conclusion:

The present results support that OA could ameliorate Aβ-induced memory loss of AD rats by maintaining synaptic plasticity of the hippocampus

Mass spectrometry is a multifaceted weapon to be used in the battle against Alzheimer's disease: Amyloid beta peptides and beyond

Amyloid-β peptide (Aβ) accumulation and aggregation have been considered for many years the main cause of Alzheimer's disease (AD), and therefore have been the principal target of investigation as well as of the proposed therapeutic approaches (Grasso [2011] Mass Spectrom Rev. 30: 347-365). However, the amyloid cascade hypothesis, which considers Aβ accumulation the only causative agent of the disease, has proven to be incomplete if not wrong. In recent years, actors such as metal ions, oxidative stress, and other cofactors have been proposed as possible co-agents or, in some cases, main causative factors of AD. In this scenario, MS investigation has proven to be fundamental to design possible diagnostic strategies of this elusive disease, as well as to understand the biomolecular mechanisms involved, in the attempt to find a possible therapeutic solution. We review the current applications of MS in the search for possible Aβ biomarkers of AD to help the diagnosis of the disease. Recent examples of the important contributions that MS has given to prove or build theories on the molecular pathways involved with such terrible disease are also reviewed.

Blood-brain barrier-associated pericytes internalize and clear aggregated amyloid-β42 by LRP1-dependent apolipoprotein E isoform-specific mechanism

BACKGROUND

Clearance at the blood-brain barrier (BBB) plays an important role in removal of Alzheimer's amyloid-β (Aβ) toxin from brain both in humans and animal models. Apolipoprotein E (apoE), the major genetic risk factor for AD, disrupts Aβ clearance at the BBB. The cellular and molecular mechanisms, however, still remain unclear, particularly whether the BBB-associated brain capillary pericytes can contribute to removal of aggregated Aβ from brain capillaries, and whether removal of Aβ aggregates by pericytes requires apoE, and if so, is Aβ clearance on pericytes apoE isoform-specific.

METHODS

We performed immunostaining for Aβ and pericyte biomarkers on brain capillaries (< 6 μm in diameter) on tissue sections derived from AD patients and age-matched controls, and APPSwe/0 mice and littermate controls. Human Cy3-Aβ42 uptake by pericytes was studied on freshly isolated brain slices from control mice, pericyte LRP1-deficient mice (Lrplox/lox;Cspg4-Cre) and littermate controls. Clearance of aggregated Aβ42 by mouse pericytes was studied on multi-spot glass slides under different experimental conditions including pharmacologic and/or genetic inhibition of the low density lipoprotein receptor related protein 1 (LRP1), an apoE receptor, and/or silencing mouse endogenous Apoe in the presence and absence of human astrocyte-derived lipidated apoE3 or apoE4. Student's t-test and one-way ANOVA followed by Bonferroni's post-hoc test were used for statistical analysis.

RESULTS

First, we found that 35% and 60% of brain capillary pericytes accumulate Aβ in AD patients and 8.5-month-old APPSw/0 mice, respectively, compared to negligible uptake in controls. Cy3-Aβ42 species were abundantly taken up by pericytes on cultured mouse brain slices via LRP1, as shown by both pharmacologic and genetic inhibition of LRP1 in pericytes. Mouse pericytes vigorously cleared aggregated Cy3-Aβ42 from multi-spot glass slides via LRP1, which was inhibited by pharmacologic and/or genetic knockdown of mouse endogenous apoE. Human astrocyte-derived lipidated apoE3, but not apoE4, normalized Aβ42 clearance by mouse pericytes with silenced mouse apoE.

CONCLUSIONS

Our data suggest that BBB-associated pericytes clear Aβ aggregates via an LRP1/apoE isoform-specific mechanism. These data support the role of LRP1/apoE interactions on pericytes as a potential therapeutic target for controlling Aβ clearance in AD.

Noradrenergic Dysfunction in Alzheimer's and Parkinson's Diseases-An Overview of Imaging Studies

Noradrenergic dysfunction contributes to cognitive impairment in Alzheimer's Disease (AD) and Parkinson's Disease (PD). Conventional therapeutic strategies seek to enhance cholinergic and dopaminergic neurotransmission in AD and PD, respectively, and few studies have examined noradrenergic dysfunction as a target for medication development. We review the literature of noradrenergic dysfunction in AD and PD with a focus on human imaging studies that implicate the locus coeruleus (LC) circuit. The LC sends noradrenergic projections diffusely throughout the cerebral cortex and plays a critical role in attention, learning, working memory, and cognitive control. The LC undergoes considerable degeneration in both AD and PD. Advances in magnetic resonance imaging have facilitated greater understanding of how structural and functional alteration of the LC may contribute to cognitive decline in AD and PD. We discuss the potential roles of the noradrenergic system in the pathogenesis of AD and PD with an emphasis on postmortem anatomical studies, structural MRI studies, and functional MRI studies, where we highlight changes in LC connectivity with the default mode network (DMN). LC degeneration may accompany deficient capacity in suppressing DMN activity and increasing saliency and task control network activities to meet behavioral challenges. We finish by proposing potential and new directions of research to address noradrenergic dysfunction in AD and PD.

Transcriptional Effects of ApoE4: Relevance to Alzheimer's Disease

The major genetic risk factor for sporadic Alzheimer's disease (AD) is the lipid binding and transporting carrier protein apolipoprotein E, epsilon 4 allele (ApoE4). One of the unsolved mysteries of AD is how the presence of ApoE4 elicits this age-associated, currently incurable neurodegenerative disease. Recently, we showed that ApoE4 acts as a transcription factor and binds to the promoters of genes involved in a range of processes linked to aging and AD disease pathogenesis. These findings point to novel therapeutic strategies for AD and aging, resulting in an extension of human healthspan, the disease-free and functional period of life. Here, we review the effects and implications of the putative transcriptional role of ApoE4 and propose a model of Alzheimer's disease that focuses on the transcriptional nature of ApoE4 and its downstream effects, with the aim that this knowledge will help to define the role ApoE4 plays as a risk factor for AD, aging, and other processes such as inflammation and cardiovascular disease.

Extra-virgin olive oil ameliorates cognition and neuropathology of the 3xTg mice: role of autophagy

OBJECTIVE

Consumption of extra virgin olive oil (EVOO), a major component of the Mediterranean diet, has been associated with reduced incidence of Alzheimer's disease (AD). However, the mechanisms involved in this protective action remain to be fully elucidated.

METHODS

Herein, we investigated the effect of daily consumption of EVOO on the AD-like phenotype of a mouse mode of the disease with plaques and tangles.

RESULTS

Triple transgenic mice (3xTg) received either regular chow or a chow diet supplemented with EVOO starting at 6 months of age for 6 months, then assessed for the effect of the diet on the AD-like neuropathology and behavioral changes. Compared with controls, mice receiving the EVOO-rich diet had an amelioration of their behavioral deficits, and a significant increase in the steady state levels of synaptophysin, a protein marker of synaptic integrity. In addition, they had a significant reduction in insoluble Aβ peptide levels and deposition, lower amount of phosphorylated tau protein at specific epitopes, which were secondary to an activation of cell autophagy.

INTERPRETATION

Taken together, our findings support a beneficial effect of EVOO consumption on all major features of the AD phenotype (behavioral deficits, synaptic pathology, Aβ and tau neuropathology), and demonstrate that autophagy activation is the mechanism underlying these biological actions.

Haplodeficiency of Cathepsin D does not affect cerebral amyloidosis and autophagy in APP/PS1 transgenic mice

Autophagy and lysosomal function are important for protein homeostasis and their dysfunction have been associated with Alzheimer's disease (AD). Increased immunoreactivities of an important lysosomal protease, cathepsin D (Cat D), are evident in amyloid plaques and neurons in patients with AD. This study tests the hypothesis that deleting one allele of the cathepsin D gene (Ctsd) impacts cerebral β-amyloidosis in amyloid-β precursor protein (APP)sw/PS1dE9 (APP/PS1) double transgenic mice. Despite a significant 38% decrease in Cat D level in APP/PS1/Ctsd+/- compared with APP/PS1/Ctsd+/+ mice, no changes in steady state levels and deposition of Aβ were found in the brain. There were also no differences in APP processing, the levels of two other Aβ-degrading proteases, the levels of autophagy related protein, such as LAMP2, P62, LC3-I, LC3-II, and Beclin-1, or the markers of neuroinflammation, observed between the APP/PS1/Ctsd+/+ and APP/PS1/Ctsd+/- mice. Our findings demonstrate that in wild-type mice, Cat D protein levels are either in excess or redundant with other factors in the brain, and at least one allele of Ctsd is dispensable for cerebral β-amyloidosis and autophagy in APP/PS1 transgenic mice.

Neurologic Diseases and Sleep

Sleep disorders and neurologic illness are common and burdensome in their own right; when combined, they can have tremendous negative impact at an individual level as well as societally. The socioeconomic burden of sleep disorders and neurologic illness can be identified, but the real cost of these conditions lies far beyond the financial realm. There is an urgent need for comprehensive care and support systems to help with the burden of disease. Further research in improving patient outcomes in those who suffer with these conditions will help patients and their families, and society in general.

Neuroprotective mechanism of Kai Xin San: upregulation of hippocampal insulin-degrading enzyme protein expression and acceleration of amyloid-beta degradation

Kai Xin San is a Chinese herbal formula composed of Radix Ginseng, Poria, Radix Polygalae and Acorus Tatarinowii Rhizome. It has been used in China for many years for treating amnesia. Kai Xin San ameliorates amyloid-β (Aβ)-induced cognitive dysfunction and is neuroprotective in vivo, but its precise mechanism remains unclear. Expression of insulin-degrading enzyme (IDE), which degrades Aβ, is strongly correlated with cognitive function. Here, we injected rats with exogenous Aβ₄₂ (200 μM, 5 μL) into the hippocampus and subsequently administered Kai Xin San (0.54 or 1.08 g/kg/d) intragastrically for 21 consecutive days. Hematoxylin-eosin and Nissl staining revealed that Kai Xin San protected neurons against Aβ-induced damage. Furthermore, enzyme-linked immunosorbent assay, western blot and polymerase chain reaction results showed that Kai Xin San decreased Aβ₄₂ protein levels and increased expression of IDE protein, but not mRNA, in the hippocampus. Our findings reveal that Kai Xin San facilitates hippocampal Aβ degradation and increases IDE expression, which leads, at least in part, to the alleviation of hippocampal neuron injury in rats.