Insulin-degrading Enzyme Levels Research Articles

PFOS sub-chronic exposure selectively activates Aβ clearance pathway to improve the cognitive ability of AD mice

Perfluorooctane sulfonate (PFOS), an emerging persistent organic pollutant, has been controversial in its impact on cognitive functions. Our previous research has confirmed that the sub-chronic PFOS exposure leads to neuronal apoptosis in the cerebral cortex, impairing cognitive functions in normal mice. However, our current study presents a surprising finding: sub-chronic exposure to PFOS effectively reduces cognitive impairments in Alzheimer's disease (AD) mice and significantly retards the disease's progression. Our results indicate that PFOS exposure upregulates the expression level of insulin-degrading enzyme (IDE) in the prefrontal cortex (PFC) of AD mice, thereby selectively enhancing the amyloid-beta (Aβ) clearance pathway without affecting the Aβ production. Moreover, PFOS exposure inhibits microglial proliferation and reduces inflammatory cytokines levels in the PFC of AD mice, providing further supporting for the pivotal role of IDE in attenuating AD progression under PFOS exposure. Collectively, our study is the first to demonstrate that sub-chronic PFOS exposure can alleviates cognitive impairments in AD pathology, with the IDE-mediated Aβ clearance pathway potentially playing a critical role.

Sustained feeding of a diet high in fat resulted in a decline in the liver's insulin-degrading enzyme levels in association with the induction of oxidative and endoplasmic reticulum stress in adult male rats: Evaluation of 4-phenylbutyric acid

The current study explored the impact of high fat diet (HFD) on hepatic oxidative and endoplasmic reticulum (ER) stress and its insulin degrading enzyme (IDE) content with the injection of 4-phenyl butyric acid (4-PBA) in adult male rats.Following the weaning period, male offspring were distributed among six distinct groups. The corresponding diet was used for 20 weeks, subsequently 4-PBA was administered for three consecutive days. Plasma glucose and insulin levels, HOMA-β (homeostasis model assessment of β-cell), hepatic ER and oxidative stress biomarkers and IDE protein content were assessed.Long-term ingestion of HFD (31 % cow butter) induced oxidative and ER stress in the liver tissue. Accordingly, a rise in the malondialdehyde (MDA) content and catalase enzyme activity and a decrease in the glutathione (GSH) content were detected within the liver of the HFD and HFD + DMSO groups. Consumption of this diet elevated the liver expression of binding immunoglobulin protein (BIP) and C/enhancer-binding protein homologous protein (CHOP) levels while reduced its IDE content. The HOMA-β decreased significantly. The injection of the 4-PBA moderated all the induced changes.Findings from this study indicated that prolonged HFD consumption led to a reduction in plasma insulin levels, likely attributed to pancreatic β cell malfunction, as evidenced by a decline in the HOMA-β index. Also, the HFD appears to have triggered oxidative and ER stress in the liver, along with a decrease in its IDE content.

Acute Hyperglycemia Induced by Hyperglycemic Clamp Affects Plasma Amyloid-β in Type 2 Diabetes.

Individuals with type 2 diabetes (T2D) have an increased risk of cognitive symptoms and Alzheimer's disease (AD). Mis-metabolism with aggregation of amyloid-β peptides (Aβ) play a key role in AD pathophysiology. Therefore, human studies on Aβ metabolism and T2D are warranted. The objective of this study was to examine whether acute hyperglycemia affects plasma Aβ1-40 and Aβ1-42 concentrations in individuals with T2D and matched controls. Ten participants with T2D and 11 controls (median age, 69 years; range, 66-72 years) underwent hyperglycemic clamp and placebo clamp (saline infusion) in a randomized order, each lasting 4 hours. Aβ1-40, Aβ1-42, and insulin-degrading enzyme (IDE) plasma concentrations were measured in blood samples taken at 0 and 4 hours of each clamp. Linear mixed-effect regression models were used to evaluate the 4-hour changes in Aβ1-40 and Aβ1-42 concentrations, adjusting for body mass index, estimated glomerular filtration rate, and 4-hour change in insulin concentration. At baseline, Aβ1-40 and Aβ1-42 concentrations did not differ between the two groups. During the hyperglycemic clamp, Aβ decreased in the control group, compared to the placebo clamp (Aβ1-40: p = 0.034, Aβ1-42: p = 0.020), IDE increased (p = 0.016) during the hyperglycemic clamp, whereas no significant changes in either Aβ or IDE was noted in the T2D group. Clamp-induced hyperglycemia was associated with increased IDE levels and enhanced Aβ40 and Aβ42 clearance in controls, but not in individuals with T2D. We hypothesize that insulin-degrading enzyme was inhibited during hyperglycemic conditions in people with T2D.

Reduction in Hippocampal Amyloid-β Peptide (Aβ) Content during Glycine-Proline-Glutamate (Gly-Pro-Glu) Co-Administration Is Associated with Changes in Inflammation and Insulin-like Growth Factor (IGF)-I Signaling.

Alzheimer's disease (AD) is characterized by the deposition in the brain of senile plaques composed of amyloid-β peptides (Aβs) that increase inflammation. An endogenous peptide derived from the insulin-like growth factor (IGF)-I, glycine-proline-glutamate (GPE), has IGF-I-sensitizing and neuroprotective actions. Here, we examined the effects of GPE on Aβ levels and hippocampal inflammation generated by the intracerebroventricular infusion of Aβ25-35 for 2 weeks (300 pmol/day) in ovariectomized rats and the signaling-related pathways and levels of Aβ-degrading enzymes associated with these GPE-related effects. GPE prevented the Aβ-induced increase in the phosphorylation of p38 mitogen-activated protein kinase and the reduction in activation of signal transducer and activator of transcription 3, insulin receptor substrate-1, and Akt, as well as on interleukin (IL)-2 and IL-13 levels in the hippocampus. The functionality of somatostatin, measured as the percentage of inhibition of adenylate cyclase activity and the levels of insulin-degrading enzyme, was also preserved by GPE co-treatment. These findings indicate that GPE co-administration may protect from Aβ insult by changing hippocampal cytokine content and somatostatin functionality through regulation of leptin- and IGF-I-signaling pathways that could influence the reduction in Aβ levels through modulation of levels and/or activity of Aβ proteases.

Exploring the in vitro stability of insulin degrading enzyme as a potential biomarker for neurocognitive disorders and Alzheimer's disease risk

Insulin degrading enzyme (IDE) plays a critical role in degrading insulin and beta-forming proteins, implicating its significance as a biomarker in metabolic dysfunction and neurocognitive disorders, including Alzheimer's disease (AD). Understanding the impact of pre-analytic conditions of in vitro IDE levels is imperative for reliable biomarker assessment. This study explored the influence of freeze-thaw cycles, storage temperature, and storage time on IDE levels in human serum.Serum samples from seven healthy volunteers were subjected to various storage conditions, including refrigeration (4 °C) and freezing (−20 °C and −80 °C) for 24 h and six months, with differing freeze-thaw cycles. In vitro IDE levels were measured at 24 h and after 6 months using ELISA.Results indicate that while short-term storage at either −20 °C or −80 °C yielded similar IDE levels, prolonged storage and multiple freeze-thaw cycles significantly impacted IDE stability, with colder temperatures exhibiting better preservation.Although further research with larger cohorts and longer storage time is warranted to establish clinical significance, our study suggests preferential use of unthawed samples or consistent freeze-thaw conditions for accurate IDE assessment. Thus, optimizing sample storage conditions is paramount for reliable IDE biomarker analysis in clinical and research settings.

Correlations between insulin-degrading enzyme and metabolic markers in patients diagnosed with type 2 diabetes, Alzheimer’s disease, and healthy controls: a comparative study

PurposeThis study aimed to explore correlations between insulin-degrading enzyme (IDE) and markers of metabolic function in a group of patients diagnosed with type 2 diabetes mellitus (T2DM) or Alzheimer’s disease (AD) and metabolically healthy volunteers.MethodWe included 120 individuals (47 with T2DM, 9 with AD, and 64 healthy controls). Serum levels of IDE were measured with commercial kits for ELISA. Differences in IDE levels between groups were analyzed with non-parametric ANCOVA, and correlations were analyzed with Spearman’s rank correlations. We also investigated the influence of age, sex, and the use of insulin on the correlation using a non-parametric version of partial correlation.ResultsPatients diagnosed with T2DM had higher IDE levels than patients diagnosed with AD and healthy controls after adjustment for age and sex. IDE was increasingly associated with body mass index (BMI), fasting blood glucose, C-peptide, hemoglobin A1c (HbA1c), insulin resistance, and triglycerides. In stratified analyses, we found a decreasing partial correlation between IDE and HbA1c in patients diagnosed with AD and a decreasing partial correlation between IDE and C-peptide in healthy controls. In patients diagnosed with T2DM, we found no partial correlations.ConclusionThese results indicate that IDE is essential in metabolic function and might reflect metabolic status, although it is not yet a biomarker that can be utilized in clinical practice. Further research on IDE in human blood may provide crucial insights into the full function of the enzyme.

SGLT2 and DPP4 inhibitors improve Alzheimer’s disease–like pathology and cognitive function through distinct mechanisms in a T2D–AD mouse model

Alzheimer’s disease (AD) and type 2 diabetes mellitus (T2D) share common features, including insulin resistance. Brain insulin resistance has been implicated as a key factor in the pathogenesis of AD. Recent studies have demonstrated that anti-diabetic drugs sodium–glucose cotransporter-2 inhibitor (SGLT2-i) and dipeptidyl peptidase-4 inhibitor (DPP4-i) improve insulin sensitivity and provide neuroprotection. However, the effects of these two inhibitors on the brain metabolism and insulin resistance remain uninvestigated. We developed a T2D–AD mouse model using a high-fat diet (HFD) for 19 weeks along with a single dose of streptozotocin (100 mg/kg, intraperitoneally) at the fourth week of HFD initiation. Subsequently, the animals were treated with SGLT2-i (empagliflozin, 25 mg/kg/day orally [p.o.]) and DPP4-i (sitagliptin, 100 mg/kg/day p.o.) for 7 weeks. Subsequently, behavioral tests were performed, and the expression of insulin signaling, AD-related, and other signaling pathway proteins in the brain were examined. T2D–AD mice not only showed increased blood glucose levels and body weight but also insulin resistance. SGLT2-i and DPP4-i effectively ameliorated insulin sensitivity and reduced body weight in these mice. Furthermore, SGLT2-i and DPP4-i significantly improved hippocampal-dependent learning, memory, and cognitive functions in the T2D–AD mouse model. Interestingly, SGLT2-i and DPP4-i reduced the hyperphosphorylated tau (pTau) levels and amyloid β (Aβ) accumulation and enhanced brain insulin signaling. SGLT2-i reduced pTau accumulation through the angiotensin converting enzyme-2/angiotensin (1−7)/ mitochondrial assembly receptor axis, whereas DPP4-i reduced Aβ accumulation by increasing insulin-degrading enzyme levels. These findings suggest that SGLT2-i and DPP4-i prevent AD-like pathology and cognitive dysfunction in T2D mice potentially through affecting brain insulin signaling via different mechanisms.

200-OR: Role of Insulin-Degrading Enzyme (IDE) in the Tubulin–Primary Cilium Axis to Regulate Glucagon Secretion

Hyperglucagonemia is a hallmark of T2D, although molecular mechanisms underlying glucagon secretion dysregulation are poorly understood. We have recently reported that genetic ablation of IDE in α-cells (A-IDE-KO mouse) leads to constitutive glucagon secretion, hypertrophy, hyperplasia and increased proliferation. αTC1.9-KD-IDE cells (~30% IDE-knock-down) displayed reduced tubulin and acetylated-α-tubulin protein levels, impaired primary cilium and increased proliferation. Thus, we aimed to elucidate the role of IDE in α-cells tubulin network and ciliogenesis, and how this axis may be part of the glucagon secretion machinery. We have studied by western-blot IDE, tubulin, acetylated-α-tubulin and Arl13b (primary cilium marker) levels in αTC1.9 cells under low- and high-glucose conditions. We have found that high-glucose lowers IDE protein levels by 50% compared to low-glucose conditions, leading to a similar decrease in tubulin, acetylated-α-tubulin and Arl13b protein levels. These findings agree with our previous results using αTC1.9-KD-IDE cells, suggesting a relevant role of IDE in microtubule dynamics to control glucagon granules exocytosis. On the other hand, αTC1.9-KD-Arl13b cells (~70% Arl13b-knock-down) were used as a model of impaired ciliogenesis, showing 50% decrease in tubulin, and dysregulated glucagon secretion, mimicking αTC1.9-KD-IDE cells phenotype. In parallel, insulin-mediated inhibition of glucagon secretion is lost and insulin receptor protein levels were decreased by 40% in both, αTC1.9-KD-IDE and αTC1.9-KD-Arl13b cells, showing the relevance of IDE and primary cilium in the paracrine regulation of α-cells. Furthermore, these results have been reproduced in A-IDE-KO mice isolated islets. In conclusion, our results show that IDE-tubulin-primary cilium axis is regulated during glucose-stimulated glucagon secretion, this axis is also required for the paracrine action of insulin on α-cells to inhibit glucagon secretion. Disclosure E.Casanueva-alvarez: None. A.Sanz-gonzález: None. B.Merino: None. G.Perdomo: None. I.Cozar-castellano: None. Funding Ministerio de Ciencia e Innovación-Spain (PID2019-110496RB-C21)

Ginsenoside ompound K reduces neuronal damage and improves neuronal synaptic dysfunction by targeting Aβ.

Background: Alzheimer's disease (AD) is the most common neurodegenerative condition worldwide, with amyloid ß (Aβ) fibrils presenting as its main pathological feature. This study investigated whether Ginsenoside Compound K (CK) has activity against Aβ and its mechanism in reducing synaptic damage and cognitive impairment. Methods: The binding capacity of CK to Aβ42 and Nrf2/Keap1 was determined using molecular docking. Transmission electron microscopy was used to monitor CK-mediated degradation of Aβ fibrils. The effect of CK on the survival of Aβ42-damaged HT22 cells was determined using a CCK-8 assay. The therapeutic efficacy of CK in a scopoletin hydrobromide (SCOP) induced cognitive dysfunction mouse model was measured using a step-down passive avoidance test. GO enrichment analysis of mouse brain tissue was peformed using Genechip. Hydroxyl radical scavenging and reactive oxygen species assays were performed to verify the antioxidant activity of CK. The effects of CK on the expression of Aβ42, the Nrf2/Keap1 signaling pathway, and other proteins were determined by western blotting, immunofluorescence, and immunohistochemistry. Results: Molecular docking results showed that CK interacts with Lys16 and Glu3 of Aβ42. CK reduced the aggregation of Aβ42 as observed using transmission electron microscopy. CK increased the level of insulin-degrading enzyme and decreased the levels ß-secretase and γ-secretase; therefore, it can potentially inhibit the accumulation of Aβ in neuronal extracellular space in vivo. CK improved cognitive impairment and increased postsynaptic density protein 95 and synaptophysin expression levels in mice with SCOP-induced cognitive dysfunction. Further, CK inhibited the expression of cytochrome C, Caspase-3, and cleaved Caspase-3. Based on Genechip data, CK was found to regulate molecular functions such as oxygen binding, peroxidase activity, hemoglobin binding, and oxidoreductase activity, thus affecting the production of oxidative free radicals in neurons. Further, CK regulated the expression of the Nrf2/Keap1 signaling pathway through its interaction with the Nrf2/Keap1 complex. Conclusion: Our findings show that CK regulates the balance between Aβ monomers production and clearance, CK binds to Aβ monomer to inhibits the accumulation of Aβ, increases the level of Nrf2 in neuronal nuclei, reduces oxidative damage of neurons, improves synaptic function, thus ultimately protecting neurons.

Altered Surface Expression of Insulin-Degrading Enzyme on Monocytes and Lymphocytes from COVID-19 Patients Both at Diagnosis and after Hospital Discharge.

Although the COVID-19 disease has developed into a worldwide pandemic, its pathophysiology remains to be fully understood. Insulin-degrading enzyme (IDE), a zinc-metalloprotease with a high affinity for insulin, has been found in the interactomes of multiple SARS-CoV-2 proteins. However, the relevance of IDE in the innate and adaptative immune responses elicited by circulating peripheral blood mononuclear cells is unknown. Here, we show that IDE is highly expressed on the surface of circulating monocytes, T-cells (both CD4+ and CD4−), and, to a lower extent, in B-cells from healthy controls. Notably, IDE’s surface expression was upregulated on monocytes from COVID-19 patients at diagnosis, and it was increased in more severe patients. However, IDE’s surface expression was downregulated (relative to healthy controls) 3 months after hospital discharge in all the studied immune subsets, with this effect being more pronounced in males than in females, and thus it was sex-dependent. Additionally, IDE levels in monocytes, CD4+ T-cells, and CD4− T-cells were inversely correlated with circulating insulin levels in COVID-19 patients (both at diagnosis and after hospital discharge). Of note, high glucose and insulin levels downregulated IDE surface expression by ~30% in the monocytes isolated from healthy donors, without affecting its expression in CD4+ T-cells and CD4− T-cells. In conclusion, our studies reveal the sex- and metabolism-dependent regulation of IDE in monocytes, suggesting that its regulation might be important for the recruitment of immune cells to the site of infection, as well as for glucometabolic control, in COVID-19 patients.

Is there a role of insulin degrading enzyme in Parkinson’s disease?

Objectives: Alpha-synucleins are the basic structural components of Lewy bodies, which are the pathognomonic feature of Parkinson’s disease (PD). It is propounded that alpha-synucleins interact with the insulin-degrading enzyme (IDE). In this study, it was aimed to evaluate the relationship between the insulin-degrading enzyme (IDE) level and the disease and the symptomatology of the disease in patients with PD. Methods: A total of 98 individuals, including 57 patients with PD and 41 healthy controls, were enrolled in this cross-sectional, case-control study. The clinical characteristics of the patients with PD, modified Hoehn and Yahr (mHY) stages, and Unified Parkinson’s Disease Rating Scale (UPDRS) scores were recorded. The mini-mental state examination (MMSE) was applied to all participants. Serum samples were collected for the level of IDE. Results: No significant difference was found in terms of IDE between PD patients and the control group with similar sociodemographic characteristics (p>0.05). No statistically significant difference was revealed between the level of IDE and the age of onset of disease, initial symptom, disease subtype, mHY stage, LED dose, MMSE score, UPDRS part II, III and IV. In PD patients, a weak negative correlation was found between IDE, duration of disease, and UPDRS part I (p=0.049, r=-0.299 and p=0.003, r=-0.431, respectively). Conclusion: No significant difference was determined in the level of IDE between PD patients and the controls. There was no relationship between IDE level and onset symptom, disease subtype, disease stage. It was suggested that the serum level of IDE was related to a longer duration of disease and the affected mentation, behavior and mood. The confirmation of these results with larger patient series will contribute to clarifying the role of IDE in the pathogenesis of PD.

Increased levels of insulin-degrading enzyme in patients with type 2 diabetes mellitus

Decreasing levels of serum insulin-degrading enzyme (IDE) have been associated with an increased risk for Alzheimer´s disease (AD) in patients with type 2 diabetes mellitus (T2DM). Research on serum IDE levels in patients with T2DM is sparse and the aim of this study was to explore serum levels of IDE in patients with T2DM. Blood serum samples were obtained from a biobank. Samples from subjects with T2DM and without metabolic disease were divided into subgroups; lifestyle treatment (n = 10), oral antidiabetic treatment (n = 17), insulin treatment (n = 20) and metabolically healthy controls (n = 18). Serum levels of IDE were analysed using specific ELISA assays. Serum levels of IDE were elevated in subjects with T2DM compared to metabolically healthy individuals (p = 0.033). No significant differences were detected between treatment subgroups. The present study indicates that patients with T2DM have increased serum IDE levels, compared to metabolically healthy individuals. However, for IDE to be clinically useful as a biomarker, its full function and possible use needs to be further elucidated in larger studies showing reproducible outcomes.

Diosmetin Targeted at Peroxisome Proliferator-Activated Receptor Gamma Alleviates Advanced Glycation End Products Induced Neuronal Injury.

The present study aimed to evaluate the role of diosmetin in alleviating advanced glycation end products (AGEs)-induced Alzheimer’s disease (AD)-like pathology and to clarify the action mechanisms. Before stimulation with AGEs (200 μg/mL), SH-SY5Y cells were treated with diosmetin (10 μmol/L), increasing cell viability. The induction of AGEs on the reactive oxygen species overproduction and downregulation of antioxidant enzyme activities, including superoxide dismutase, glutathione peroxidase, and catalase, were ameliorated by diosmetin. Amyloid precursor protein upregulation, accompanied by increased production of amyloid-β, caused by AGEs, was reversed by diosmetin. In the presence of diosmetin, not only β-site amyloid precursor protein cleaving enzyme1 expression was lowered, but the protein levels of insulin-degrading enzyme and neprilysin were elevated. Diosmetin protects SH-SY5Y cells from endoplasmic reticulum (ER) stress response to AGEs by suppressing ER stress-induced glucose regulated protein 78, thereby downregulating protein kinase R-like endoplasmic reticulum kinase, eukaryotic initiation factor 2 α, activating transcription factor 4, and C/EBP homologous protein. Diosmetin-pretreated cells had a lower degree of apoptotic DNA fragmentation; this effect may be associated with B-cell lymphoma (Bcl) 2 protein upregulation, Bcl-2-associated X protein downregulation, and decreased activities of caspase-12/-9/-3. The reversion of diosmetin on the AGEs-induced harmful effects was similar to that produced by pioglitazone. The peroxisome proliferator-activated receptor (PPAR)γ antagonist T0070907 (5 μmol/L) abolished the beneficial effects of diosmetin on AGEs-treated SH-SY5Y cells, indicating the involvement of PPARγ. We conclude that diosmetin protects neuroblastoma cells against AGEs-induced ER injury via multiple mechanisms and may be a potential option for AD.

Possible Role of Insulin-Degrading Enzyme in the Physiopathology of Retinitis Pigmentosa.

Insulin-degrading enzyme (IDE) was named after its role as a proteolytic enzyme of insulin. However, recent findings suggest that IDE is a widely expressed, multitask protein, with both proteolytic and non-proteolytic functions. Here, we characterize the expression of IDE in the mammalian retina in both physiological and pathological conditions. We found that IDE was enriched in cone inner segments. IDE levels were downregulated in the dystrophic retina of several mouse models of retinitis pigmentosa carrying distinct mutations. In rd10 mice, a commonly studied mouse model of retinitis pigmentosa, treatment with an IDE activator (a synthetic peptide analog of preimplantation factor) delayed loss of visual function and preserved photoreceptor cells. Together, these results point to potential novel roles for IDE in retinal physiology and disease, further extending the list of diverse functions attributed to this enzyme.

Caloric restriction overcomes pre-diabetes and hypertension induced by a high fat diet and renal artery stenosis.

Calorie restriction (CR) is a type of dietary intervention that is essential in weight loss through modulation of critical metabolic control pathways, is well established and understood in cases of systemic arterial hypertension, however, its role in renovascular hypertension is still unclear. Rats were divided into three groups: SHAM, and two groups that underwent surgery to clip the left renal artery and induce renovascular hypertension (OH and OHR). The SHAM diet was as follows: 14weeks normolipidic diet; OH: 2weeks normolipidic diet + 12weeks hyperlipidic diet, both ad libitum; OHR, 2weeks normolipidic diet + 8weeks ad libitum high-fat diet + 4weeks 40% calorie-restricted high-fat diet. Rats in the OHR group had decreased blood pressure, body weight, and glucose levels. Reductions in insulinemia and in lipid and islet fibrotic areas in the OHR group were observed, along with increased insulin sensitivity and normalization of insulin-degrading enzyme levels. The expression of nicotinamide phosphoribosyltransferase (NAMPT), insulin receptor (IR), sirtuin 1 (SIRT1), and complex II proteins were increased in the liver tissue of the OHR group. Strong correlations, whether positive or negative, were evaluated via Spearman's model between SIRT1, AMPK, NAMPT, PGC-1α, and NNMT expressions with the restoration of normal blood pressure, weight loss, glycemic and lipid panel, and mitochondrial adaptation. CR provided short-term beneficial effects to recover the physiological parameters induced by a high-fat diet and renal artery stenosis in obese and hypertensive animals. These benefits, even in the short term, can provide physiological benefits in the long term.

Polymorphism Rs2421943 of the Insulin-Degrading Enzyme Gene and the Risk of Late-Onset Alzheimer's Disease.

Insulin-degrading enzyme (IDE) is a widely distributed Zn2+-binding metalloprotease that cleaves multiple short and medium-sized peptides prone to form β-structures. These include insulin and amyloid-β peptides. Accumulation and fibrillation of amyloid-β peptides leading to the formation of amyloid plaques is a characteristic sign of Alzheimer's disease (AD) pathology. The study investigated the rs2421943 single nucleotide polymorphism (SNP) of the IDE gene as a risk factor for MCI (mild cognitive impairment) and AD. Two independent groups of 1670 patients and controls were included. The AD group consisted of 595 patients and 400 controls; the MCI group involved 135 patients and 540 matched controls. PCR and restriction fragment length analysis were used to analyze the rs2421943 polymorphism. Using the miRBase and RNA22 prediction tools in silico indicated that the rs2421943 polymorphism is a potential target for a specific miRNA (hsa-miR-7110-5p). AG and GG genotypes of rs2421943 significantly increased the risk of AD, and the AG genotype increased the risk of MCI. It seems the G allele both increases the risk of AD and accelerates the transition through the MCI phase. In silico study revealed that rs2421943 is inside the sequence binding miRNA hsa-miR-7110-5p. The polymorphism could affect the rate of IDE pre-RNA (heterogeneous nuclear RNA, hnRNA) processing, resulting in slower translation, lower levels of IDE, deficient removal of amyloid-β fragments, and greater risk of and/or accelerated progression of AD. GG and AG genotypes of the single nucleotide polymorphism rs2421943 of insulindegrading enzyme gene increase the risk of AD and MCI.

Ginsenoside F1 Protects the Brain against Amyloid Beta-Induced Toxicity by Regulating IDE and NEP.

Ginsenoside F1, the metabolite of Rg1, is one of the most important constituents of Panax ginseng. Although the effects of ginsenosides on amyloid beta (Aβ) aggregation in the brain are known, the role of ginsenoside F1 remains unclear. Here, we investigated the protective effect of ginsenoside F1 against Aβ aggregation in vivo and in vitro. Treatment with 2.5 μM ginsenoside F1 reduced Aβ-induced cytotoxicity by decreasing Aβ aggregation in mouse neuroblastoma neuro-2a (N2a) and human neuroblastoma SH-SY5Y neuronal cell lines. Western blotting, real-time PCR, and siRNA analysis revealed an increased level of insulin-degrading enzyme (IDE) and neprilysin (NEP). Furthermore, liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis confirmed that ginsenoside F1 could pass the blood–brain barrier within 2 h after administration. Immunostaining results indicate that ginsenoside F1 reduces Aβ plaques in the hippocampus of APPswe/PSEN1dE9 (APP/PS1) double-transgenic Alzheimer’s disease (AD) mice. Consistently, increased levels of IDE and NEP protein and mRNA were observed after the 8-week administration of 10 mg/kg/d ginsenoside F1. These data indicate that ginsenoside F1 is a promising therapeutic candidate for AD.

Effect of Global Brain Ischemia on Amyloid Precursor Protein Metabolism and Expression of Amyloid-Degrading Enzymes in Rat Cortex: Role in Pathogenesis of Alzheimer's Disease.

The incidence of Alzheimer's disease (AD) increases significantly following chronic stress and brain ischemia which, over the years, cause accumulation of toxic amyloid species and brain damage. The effects of global 15-min ischemia and 120-min reperfusion on the levels of expression of the amyloid precursor protein (APP) and its processing were investigated in the brain cortex (Cx) of male Wistar rats. Additionally, the levels of expression of the amyloid-degrading enzymes neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), and insulin-degrading enzyme (IDE), as well as of some markers of oxidative damage were assessed. It was shown that the APP mRNA and protein levels in the rat Cx were significantly increased after the ischemic insult. Protein levels of the soluble APP fragments, especially of sAPPβ produced by β-secretase, (BACE-1) and the levels of BACE-1 mRNA and protein expression itself were also increased after ischemia. The protein levels of APP and BACE-1 in the Cx returned to the control values after 120-min reperfusion. The levels of NEP and ECE-1 mRNA also decreased after ischemia, which correlated with the decreased protein levels of these enzymes. However, we have not observed any changes in the protein levels of insulin-degrading enzyme. Contents of the markers of oxidative damage (di-tyrosine and lysine conjugates with lipid peroxidation products) were also increased after ischemia. The obtained data suggest that ischemia shifts APP processing towards the amyloidogenic β-secretase pathway and accumulation of the neurotoxic Aβ peptide as well as triggers oxidative stress in the cells. These results are discussed in the context of the role of stress and ischemia in initiation and progression of AD.

Dietary Curcumin Systemically Maintains Insulin Homeostasis in Diet-Induced Aged Obese Mice via Liver-Pancreas-Brain Axis

Abstract Objectives Aging is a condition in which we gradually lose the ability to maintain homeostasis due to dysfunction. There continues to be a knowledge gap in implicating how dietary intervention affects the mechanisms delaying or preventing aging-related chronic diseases. Although curcumin (CUR), a natural antioxidant, shows the putative therapeutic properties such as reinstating insulin homeostasis in obese mice, an aging-associated mechanism in which CUR regulates insulin levels largely remains unclear. Thus, the objective of this study is to determine effects of CUR on anti-aging under obese condition mediated by maintaining insulin homeostasis via cross-talk among liver, pancreas and brain. Methods We examine how dietary CUR improves insulin clearance and maintains a proper range of circulating insulin level in the aged diet-induced obesity (DIO) mouse model. Old male C57BL/6J mice were fed a normal chow diet (NCD) or a NCD containing 0.4% (w/w) curcumin (NCD + CUR), a high fat/high sugar diet (HFHSD) or a HFHSD + CUR (N = 7–9 per group) for 16 weeks. Results Old male C57BL/6J mice were fed a normal chow diet (NCD) or a NCD containing 0.4% (w/w) curcumin (NCD + CUR), a high fat/high sugar diet (HFHSD) or a HFHSD + CUR (N = 7–9 per group) for 16 weeks. Mice given HFHSD + CUR had reduced body weight gain (4.7 ± 1.8 vs 7.8 ± 1.6g) and had lower blood insulin levels (2.24 ± 0.3 vs. 1.53 ± 0.3 ng/ml) under fasting conditions compared to mice on HFHSD alone, resulting from significantly improved insulin clearance via upregulation of hepatic insulin-degrading enzyme (IDE) and circulating IDE levels in serum. On the other hand, the expression of IDE gene in hypothalamus was significantly lower in HFHSD + CUR mice (1.3 folds) than HFHSD animals. Obesity induces hyperglycemic condition in brain by higher IDE expression to excessively break down insulin. We also observed significantly smaller islets of Langerhans (4.53 ± 0.72 vs 7.90 ± 0.34 a.u.) in HFSD + CUR fed mice and increased glucagon contents compared to HFS fed mice, indicating less secretion of insulin in pancreas under obese condition. Conclusions The conclusion of this study is that curcumin is a potent, natural therapeutic agent that can systemically regulate insulin levels in a multifaceted manner to protect against insulin resistance in aged mice. Funding Sources Intramural Research Program of NIAThe OTTOGI HAM TAIHO Foundation

Short-Term Calorie Restriction Maintains Plasma Insulin Concentrations along with a Reduction in Hepatic Insulin-Degrading Enzyme Levels in db/db Mice.

Maintaining blood insulin levels is important for patients with diabetes because insulin secretion capacity declines with the development of the disease. Calorie restriction (CR) is effective for the improvement of glucose tolerance, but it is not clear whether CR can maintain insulin levels in the late stage of diabetes. We examined the effect of CR on whole-body glucose tolerance and fasting blood insulin concentrations in the late stage of diabetes. Male db/db mice were subjected to either a standard laboratory diet ad libitum for 3 weeks (dbdb group) or 40% CR (dbdb+CR group). CR significantly decreased body mass and epididymal fat weight. Glucose tolerance and fasting glucose levels were significantly improved with 3-week CR. Fasting insulin concentrations were decreased in the dbdb group but were maintained in the dbdb+CR group. CR significantly reduced insulin-degrading enzyme (IDE) levels in the liver, and hepatic IDE levels were significantly positively and negatively correlated with plasma glucose concentrations (area under the curve) after glucose administration and after fasting insulin concentrations, respectively. Therefore, 3-week CR maintained blood insulin levels and improved glucose tolerance with decreased hepatic IDE levels in an animal model of late-stage diabetes.