Polymorphisms within insulin-degrading enzyme (IDE) gene determine insulin metabolism and risk of type 2 diabetes

Ide Copy Number Variant Does Not Influence Stroke Severity in 2 C57BL/6J Mouse Models nor in Humans: An Exploratory Study

BACKGROUND

Contrary to the common belief, the most commonly used laboratory C57BL/6J mouse inbred strain presents a distinctive genetic and phenotypic variability, and for several traits, the genotype-phenotype link remains still unknown. Recently, we characterized the most important stroke survival factor such as brain collateral plasticity in 2 brain ischemia C57BL/6J mouse models (bilateral common carotid artery stenosis and middle cerebral artery occlusion) and observed a Mendelian-like fashion of inheritance of the posterior communicating artery (PcomA) patency. Interestingly, a copy number variant (CNV) spanning Ide locus was reported to segregate in an analogous Mendelian-like pattern in the C57BL/6J colonies of the Jackson Laboratory. Given IDE critical role in vascular plasticity, we hypothesized Ide CNV may have explained PcomA variability in C57BL/6J inbred mice.

METHODS

We applied a combination of techniques (T2-weighted magnetic resonance imaging, time-of-flight angiography, cerebral blood flow imaging, and histology) to characterize the collaterome in 77 C57BL/6J bilateral common carotid artery stenosis, middle cerebral artery occlusion, naive, and sham mice and performed on these Taqman genotyping, exome sequencing, and RNA sequencing. We then investigated the hypothesis that IDE structural variants (CNVs, gain/loss of function mutations) may have influenced the cerebrovascular phenotype in a large cohort of 454 040 cases and controls (UK Biobank, Genomics England).

RESULTS

We detected an Ide CNV in a bilateral common carotid artery stenosis mouse with 2 patent PcomAs (minor allele frequency, 1.3%), not segregating with the PcomA patency phenotype. In addition, 2 heterozygous IDE CNVs, resulting in loss of function were found in 1 patient with hereditary ataxia, a patient with hereditary congenital heart disease, and 2 healthy individuals (minor allele frequency 9×10-6). Moreover, we report 4 IDE loss of function point mutations (p.Leu5X, p.Met394ValfsX29, p.Pro14SerfsX26, p.Leu889X, minor allele frequency 0.02%) present also in controls or inherited from healthy parents.

CONCLUSIONS

Ide CNV and loss of function variants are rare, do not crucially influence PcomA variability in C57BL/6J inbred mice, and do not cause a vascular phenotype in humans.

Insulin-degrading enzyme inhibition increases the unfolded protein response and favours lipid accumulation in the liver

BACKGROUND AND PURPOSE

Nonalcoholic fatty liver disease refers to liver pathologies, ranging from steatosis to steatohepatitis, with fibrosis ultimately leading to cirrhosis and hepatocellular carcinoma. Although several mechanisms have been suggested, including insulin resistance, oxidative stress, and inflammation, its pathophysiology remains imperfectly understood. Over the last decade, a dysfunctional unfolded protein response (UPR) triggered by endoplasmic reticulum (ER) stress emerged as one of the multiple driving factors. In parallel, growing evidence suggests that insulin-degrading enzyme (IDE), a highly conserved and ubiquitously expressed metallo-endopeptidase originally discovered for its role in insulin decay, may regulate ER stress and UPR.

EXPERIMENTAL APPROACH

We investigated, by genetic and pharmacological approaches, in vitro and in vivo, whether IDE modulates ER stress-induced UPR and lipid accumulation in the liver.

KEY RESULTS

We found that IDE-deficient mice display higher hepatic triglyceride content along with higher inositol-requiring enzyme 1 (IRE1) pathway activation. Upon induction of ER stress by tunicamycin or palmitate in vitro or in vivo, pharmacological inhibition of IDE, using its inhibitor BDM44768, mainly exacerbated ER stress-induced IRE1 activation and promoted lipid accumulation in hepatocytes, effects that were abolished by the IRE1 inhibitors 4μ8c and KIRA6. Finally, we identified that IDE knockout promotes lipolysis in adipose tissue and increases hepatic CD36 expression, which may contribute to steatosis.

CONCLUSION AND IMPLICATIONS

These results unravel a novel role for IDE in the regulation of ER stress and development of hepatic steatosis. These findings pave the way to innovative strategies modulating IDE to treat metabolic diseases.

Islet cell stress induced by insulin-degrading enzyme deficiency promotes regeneration and protection from autoimmune diabetes

Tuning of protein homeostasis through mobilization of the unfolded protein response (UPR) is key to the capacity of pancreatic beta cells to cope with variable demand for insulin. Here, we asked how insulin-degrading enzyme (IDE) affects beta cell adaptation to metabolic and immune stress. C57BL/6 and autoimmune non-obese diabetic (NOD) mice lacking IDE were exposed to proteotoxic, metabolic, and immune stress. IDE deficiency induced a low-level UPR with islet hypertrophy at the steady state, rapamycin-sensitive beta cell proliferation enhanced by proteotoxic stress, and beta cell decompensation upon high-fat feeding. IDE deficiency also enhanced the UPR triggered by proteotoxic stress in human EndoC-βH1 cells. In Ide-/- NOD mice, islet inflammation specifically induced regenerating islet-derived protein 2, a protein attenuating autoimmune inflammation. These findings establish a role of IDE in islet cell protein homeostasis, demonstrate how its absence induces metabolic decompensation despite beta cell proliferation, and UPR-independent islet regeneration in the presence of inflammation.

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

PURPOSE

This 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.

METHOD

We 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.

RESULTS

Patients 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.

CONCLUSION

These 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.

The interaction between insulin resistance and Alzheimer's disease: a review article

Insulin serves multiple functions as a growth-promoting hormone in peripheral tissues. It manages glucose metabolism by promoting glucose uptake into cells and curbing the production of glucose in the liver. Beyond this, insulin fosters cell growth, drives differentiation, aids protein synthesis, and deters degradative processes like glycolysis, lipolysis, and proteolysis. Receptors for insulin and insulin-like growth factor-1 are widely expressed in the central nervous system. Their widespread presence in the brain underscores the varied and critical functions of insulin signaling there. Insulin aids in bolstering cognition, promoting neuron extension, adjusting the release and absorption of catecholamines, and controlling the expression and positioning of gamma-aminobutyric acid (GABA). Importantly, insulin can effortlessly traverse the blood-brain barrier. Furthermore, insulin resistance (IR)-induced alterations in insulin signaling might hasten brain aging, impacting its plasticity and potentially leading to neurodegeneration. Two primary pathways are responsible for insulin signal transmission: the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway, which oversees metabolic responses, and the mitogen-activated protein kinase (MAPK) pathway, which guides cell growth, survival, and gene transcription. This review aimed to explore the potential shared metabolic traits between Alzheimer's disease (AD) and IR disorders. It delves into the relationship between AD and IR disorders, their overlapping genetic markers, and shared metabolic indicators. Additionally, it addresses existing therapeutic interventions targeting these intersecting pathways.

Insulin Clearance at the Pubertal Transition in Youth with Obesity and Steatosis Liver Disease

No data are available on insulin clearance (ClI) trends during the pubertal transition. The aim of this study was to investigate in 973 youths with obesity whether ClI in fasting and post-oral glucose challenge (OGTT) conditions varies at the pubertal transition in relation to the severity of obesity and the presence of steatosis liver disease (SLD). The severity of obesity was graded according to the Centers for Disease Control. SLD was graded as absent, mild and severe based on alanine amino transferase levels. ClI was defined as the molar ratio of fasting C-peptide to insulin and of the areas under the insulin to glucose curves during an OGTT. In total, 35% of participants were prepubertal, 72.6% had obesity class II, and 52.6% had mild SLD. Fasting ClI (nmol/pmol × 10-2) was significantly lower in pubertal [0.11 (0.08-0.14)] than in prepubertal individuals [0.12 (0.09-0.16)] and higher in class III [0.15 (0.11-0.16)] than in class I obesity [0.11 (0.09-0.14)]. OGTT ClI was higher in boys [0.08 (0.06-0.10)] than in girls [0.07 (0.06-0.09)]; in prepubertal [0.08 (0.06-0.11)] than in pubertal individuals [0.07 (0.05-0.09)]; in class III [0.14 (0.08-0.17)] than in class I obesity [0.07 (0.05-0.10)]; and in severe SLD [0.09 (0.04-0.14)] than in no steatosis [0.06 (0.04-0.17)]. It was lower in participants with prediabetes [0.06 (0.04-0.07)]. OGTT ClI was lower in youths with obesity at puberty along with insulin sensitivity and greater secretion. The findings suggest that the initial increase in ClI in youth with severe obesity and SLD is likely to compensate for hyperinsulinemia and its subsequent decrease at the onset of prediabetes and other metabolic abnormalities.

Pancreatic islet cell stress induced by insulin-degrading enzyme deficiency promotes islet regeneration and protection from autoimmune diabetes

Appropriate tuning of protein homeostasis through mobilization of the unfolded protein response (UPR) is key to the capacity of pancreatic beta cells to cope with highly variable demand for insulin synthesis. An efficient UPR ensures a sufficient beta cell mass and secretory output but can also affect beta cell resilience to autoimmune aggression. The factors regulating protein homeostasis in the face of metabolic and immune challenges are insufficiently understood. We examined beta cell adaptation to stress in mice deficient for insulin-degrading enzyme (IDE), a ubiquitous protease with high affinity for insulin and genetic association with type 2 diabetes. IDE deficiency induced a low-level UPR in both C57BL/6 and autoimmune non-obese diabetic (NOD) mice, associated with rapamycin-sensitive beta cell proliferation strongly enhanced by proteotoxic stress. Moreover, in NOD mice, IDE deficiency protected from spontaneous diabetes and triggered an additional independent pathway, conditional on the presence of islet inflammation but inhibited by proteotoxic stress, highlighted by strong upregulation of regenerating islet-derived protein 2, a protein attenuating autoimmune inflammation. Our findings establish a key role of IDE in islet cell protein homeostasis, identify a link between low-level UPR and proliferation, and reveal an UPR-independent anti-inflammatory islet cell response uncovered in the absence of IDE of potential interest in autoimmune diabetes.

Association between polymorphism rs2421943 of the insulin-degrading enzyme and schizophrenia: Preliminary report

BACKGROUND

Insulin-degrading enzyme (IDE) is an important gene in studies of the pathophysiology of type 2 diabetes mellitus (T2DM). Recent studies have suggested a possible link between type 2 diabetes mellitus (T2DM) and the pathophysiology of schizophrenia (SZ). At the same time, significant changes in insulin-degrading enzyme (IDE) gene expression have been found in the brains of people with schizophrenia. These findings highlight the need to further investigate the role of IDE in schizophrenia pathogenesis.

METHODS

We enrolled 733 participants from the Czech Republic, including 383 patients with schizophrenia and 350 healthy controls. Our study focused on the single nucleotide polymorphism (SNP) rs2421943 in the IDE gene, which has previously been associated with the pathogenesis of Alzheimer's disease. The SNP was analyzed using the PCR-RFLP method.

RESULTS

The G allele of the rs2421943 polymorphism was found to significantly increase the risk of developing SZ (p < 0.01) when a gender-based analysis showed that both AG and GG genotypes were associated with a more than 1.55 times increased risk of SZ in females (p < 0.03) but not in males. Besides, we identified a potential binding site at the G allele locus for has-miR-7110-5p, providing a potential mechanism for the observed association.

CONCLUSION

Our results confirm the role of the IDE gene in schizophrenia pathogenesis and suggest that future research should investigate the relationship between miRNA and estrogen influence on IDE expression in schizophrenia pathogenesis.

Long-Term High-Fat Diet Decreases Renal Insulin-Degrading Enzyme Expression and Function by Inhibiting the PPARγ Pathway

SCOPE

Long-term high-fat diet (HFD) causes insulin resistance, which is a primary etiological factor in the development of obesity and type 2 diabetes mellitus. Impaired insulin clearance is not only a consequence but also a cause of insulin resistance. The kidney is a major site of insulin clearance, where the insulin-degrading enzyme (IDE) plays a vital role in the proximal tubule. Thus, the study investigates the role of renal IDE in the regulation of insulin resistance in HFD-induced obese mice.

METHODS AND RESULTS

Twenty four-weeks of HFD in C57BL/6 mice causes insulin resistance and impaires insulin clearance, accompanied by a decrease in renal IDE expression and activity. Palmitic acid decreases IDE mRNA and protein expressions in HK-2 cells. RNA-Seq analysis found that the PPAR pathway is involved. 24-weeks of HFD decreases renal PPARγ, but not PPARα or PPARβ/δ mRNA expression. The inhibition of IDE expression by palmitic acid is prevented by the PPARγ agonist rosiglitazone. The amount of PPARγ bound to the promoters of IDE is decreased in palmitic acid-treated cells. Rosiglitazone improves insulin clearance and insulin resistance and increases renal IDE expression in HFD fed-mice.

CONCLUSION

Long-term HFD decreases renal IDE expression and activity, and causes insulin resistance, which involves PPARγ.

Insulin resistance in Alzheimer's disease: The genetics and metabolomics links

Alzheimer's disease (AD) is a neurodegenerative disease with significant socioeconomic burden worldwide. Although genetics and environmental factors play a role, AD is highly associated with insulin resistance (IR) disorders such as metabolic syndrome (MS), obesity, and type two diabetes mellitus (T2DM). These findings highlight a shared pathogenesis. The use of metabolomics as a downstream systems' biology (omics) approach can help to identify these shared metabolic traits and assist in the early identification of at-risk groups and potentially guide therapy. Targeting the shared AD-IR metabolic trait with lifestyle interventions and pharmacological treatments may offer promising AD therapeutic approach. In this narrative review, we reviewed the literature on the AD-IR pathogenic link, the shared genetics and metabolomics biomarkers between AD and IR disorders, as well as the lifestyle interventions and pharmacological treatments which target this pathogenic link.

Butyrate-Producing Bacteria and Insulin Homeostasis: The Microbiome and Insulin Longitudinal Evaluation Study (MILES)

Gut microbiome studies have documented depletion of butyrate-producing taxa in type 2 diabetes. We analyzed associations between butyrate-producing taxa and detailed measures of insulin homeostasis, whose dysfunction underlies diabetes in 224 non-Hispanic Whites and 129 African Americans, all of whom completed an oral glucose tolerance test. Stool microbiome was assessed by whole-metagenome shotgun sequencing with taxonomic profiling. We examined associations among 36 butyrate-producing taxa (n = 7 genera and 29 species) and insulin sensitivity, insulin secretion, disposition index, insulin clearance, and prevalence of dysglycemia (prediabetes plus diabetes, 46% of cohort), adjusting for age, sex, BMI, and race. The genus Coprococcus was associated with higher insulin sensitivity (β = 0.14; P = 0.002) and disposition index (β = 0.12; P = 0.012) and a lower rate of dysglycemia (odds ratio [OR] 0.91; 95% CI 0.85-0.97; P = 0.0025). In contrast, Flavonifractor was associated with lower insulin sensitivity (β = -0.13; P = 0.004) and disposition index (β = -0.11; P = 0.04) and higher prevalence of dysglycemia (OR 1.22; 95% CI 1.08-1.38; P = 0.0013). Species-level analyses found 10 bacteria associated with beneficial directions of effects and two bacteria with adverse associations on insulin homeostasis and dysglycemia. Although most butyrate producers analyzed appear to be metabolically beneficial, this is not the case for all such bacteria, suggesting that microbiome-directed therapeutic measures to prevent or treat diabetes should be targeted to specific butyrate-producing taxa rather than all butyrate producers.

Insulin-Degrading Enzyme Is a Non Proteasomal Target of Carfilzomib and Affects the 20S Proteasome Inhibition by the Drug

Carfilzomib is a last generation proteasome inhibitor (PI) with proven clinical efficacy in the treatment of relapsed/refractory multiple myeloma. This drug is considered to be extremely specific in inhibiting the chymotrypsin-like activity of the 20S proteasome, encoded by the β5 subunit, overcoming some bortezomib limitations, the first PI approved for multiple myeloma therapy which is however burdened by a significant toxicity profile, due also to its off-target effects. Here, molecular approaches coupled with molecular docking studies have been used to unveil that the Insulin-Degrading Enzyme, a ubiquitous and highly conserved Zn2+ peptidase, often found to associate with proteasome in cell-based models, is targeted by carfilzomib in vitro. The drug behaves as a modulator of IDE activity, displaying an inhibitory effect over 10-fold lower than for the 20S. Notably, the interaction of IDE with the 20S enhances in vitro the inhibitory power of carfilzomib on proteasome, so that the IDE-20S complex is an even better target of carfilzomib than the 20S alone. Furthermore, IDE gene silencing after delivery of antisense oligonucleotides (siRNA) significantly reduced carfilzomib cytotoxicity in rMC1 cells, a validated model of Muller glia, suggesting that, in cells, the inhibitory activity of this drug on cell proliferation is somewhat linked to IDE and, possibly, also to its interaction with proteasome.

Effects of Early vs. Late Time-Restricted Eating on Cardiometabolic Health, Inflammation, and Sleep in Overweight and Obese Women: A Study Protocol for the ChronoFast Trial

Background: Time-restricted eating is a promising dietary strategy for weight loss, glucose and lipid metabolism improvements, and overall well-being. However, human studies demonstrated contradictory results for the restriction of food intake to the beginning (early TRE, eTRE) or to the end of the day (late TRE, lTRE) suggesting that more carefully controlled studies are needed.

Objective: The aim of the ChronoFast trial study is to determine whether eTRE or lTRE is a better dietary approach to improve cardiometabolic health upon minimized calorie deficits and nearly stable body weight.

Methods: Here, we present the study protocol of the randomized cross-over ChronoFast clinical trial comparing effects of 2 week eTRE (8:00 to 16:00 h) and lTRE (13:00 to 21:00 h) on insulin sensitivity and other glycemic traits, blood lipids, inflammation, and sleep quality in 30 women with overweight or obesity and increased risk of type 2 diabetes. To ensure timely compliance and unchanged dietary composition, and to minimize possible calorie deficits, real-time monitoring of dietary intake and body weight using a smartphone application, and extensive nutritional counseling are performed. Continuous glucose monitoring, oral glucose tolerance test, 24 h activity tracking, questionnaires, and gene expression analysis in adipose tissue and blood monocytes will be used for assessment of study outcomes.

Discussion: The trial will determine whether eTRE or lTRE is more effective to improve cardiometabolic health, elucidate underlying mechanisms, and contribute to the development of recommendations for medical practice and the wider population.

Clinical Trial Registration:www.ClinicalTrials.gov, Identifier [NCT04351672]

Alzheimer's Disease and Diabetes Mellitus in Comparison: The Therapeutic Efficacy of the Vanadium Compound

Alzheimer’s disease (AD) is an intractable neurodegenerative disease that leads to dementia, primarily in elderly people. The neurotoxicity of amyloid-beta (Aβ) and tau protein has been demonstrated over the last two decades. In line with these findings, several etiological hypotheses of AD have been proposed, including the amyloid cascade hypothesis, the oxidative stress hypothesis, the inflammatory hypothesis, the cholinergic hypothesis, et al. In the meantime, great efforts had been made in developing effective drugs for AD. However, the clinical efficacy of the drugs that were approved by the US Food and Drug Association (FDA) to date were determined only mild/moderate. We recently adopted a vanadium compound bis(ethylmaltolato)-oxidovanadium (IV) (BEOV), which was originally used for curing diabetes mellitus (DM), to treat AD in a mouse model. It was shown that BEOV effectively reduced the Aβ level, ameliorated the inflammation in brains of the AD mice, and improved the spatial learning and memory activities of the AD mice. These finding encouraged us to further examine the mechanisms underlying the therapeutic effects of BEOV in AD. In this review, we summarized the achievement of vanadium compounds in medical studies and investigated the prospect of BEOV in AD and DM treatment.

Dipeptidyl peptidase-4 inhibitor, anagliptin, alters hepatic insulin clearance in relation to the glycemic status in Japanese individuals with type 2 diabetes

AIMS/INTRODUCTION

This study investigated the impact of the dipeptidyl peptidase-4 inhibitor, anagliptin, on hepatic insulin clearance (HIC) in Japanese type 2 diabetes patients and explored its relationship to glycemic status.

MATERIALS AND METHODS

Data on 765 participants in anagliptin phase 2 and 3 studies were analyzed. Adjusted changes in variables during 12 weeks of anagliptin therapy were compared with a placebo. HIC was calculated as the ratio, C-peptide area under the curve 0-120 min to insulin area under the curve 0-120 min, after a meal tolerance test. To explore the effects of baseline HIC levels on variables, participants receiving anagliptin were divided according to quartiles of baseline HIC. Furthermore, multivariate analysis investigated the association between baseline HIC levels and glycemic status.

RESULTS

Anagliptin significantly reduced glycosylated hemoglobin levels (P < 0.001 vs placebo) and HIC levels (P < 0.01). Longer duration of diabetes, lower body mass index, higher glycosylated hemoglobin and lower insulin secretion capacity were observed with increases in baseline HIC levels. Improvements in glycosylated hemoglobin, glycoalbumin and 1,5-anhydroglucitol levels were greater in the relatively higher HIC group (baseline HIC levels ≥median) than in the lower HIC group (

CONCLUSIONS

Anagliptin affected HIC levels according to HIC baseline levels. Higher baseline HIC values might result in improved hyperglycemia through reduced HIC.

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Key Words

• Dipeptidyl peptidase-4 inhibitor
• Hepatic insulin clearance
• Meal tolerance test

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MESH Headings

• Aged
• Asian People
• Diabetes Mellitus, Type 2/drug therapy
• Diabetes Mellitus, Type 2/metabolism
• Dipeptidyl-Peptidase IV Inhibitors/pharmacology
• Dipeptidyl-Peptidase IV Inhibitors/therapeutic use
• Double-Blind Method
• Female
• Humans
• Insulin/metabolism
• Liver/metabolism
• Male
• Middle Aged
• Pyrimidines/pharmacology
• Pyrimidines/therapeutic use

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Grants

• Sanwa Kagaku Kenkyusho Co., Ltd.
• Kowa Co., Ltd

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Affiliation(s)

Takahiro Abe Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan
Yasuhiro Matsubayashi Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan
Sayaka Muragishi Kowa Co., Ltd.TokyoJapan
Akihiro Yoshida Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan Kowa Co., Ltd.TokyoJapan
Hideki Suganami Kowa Co., Ltd.TokyoJapan
Kenichi Furusawa Sanwa Kagaku Kenkyusho Co., Ltd.NagoyaJapan
Kazuya Fujihara Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan
Shiro Tanaka Department of Clinical BiostatisticsGraduate School of Medicine Kyoto UniversityKyotoJapan
Kohei Kaku Kawasaki Medical SchoolOkayamaJapan
Hirohito Sone Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan

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Short-Term SGLT2 Inhibitor Administration Does Not Alter Systemic Insulin Clearance in Type 2 Diabetes

Background: Decreased insulin clearance could be a relatively upstream abnormality in obesity, metabolic syndrome, and nonalcoholic fatty liver disease. Previous studies have shown that sodium-glucose cotransporter 2 inhibitor (SGLT2i) increases insulin–C-peptide ratio, a marker of insulin clearance, and improves metabolic parameters. We evaluated the effects of the SGLT2i tofogliflozin on metabolic clearance rate of insulin (MCRI) with a hyperinsulinemic euglycemic clamp study, the gold standard for measuring systemic insulin clearance. Methods: Study participants were 12 Japanese men with type 2 diabetes. We evaluated MCRI and tissue-specific insulin sensitivity with a hyperinsulinemic euglycemic clamp (insulin infusion rate, 40 mU/m²·min) before and immediately after a single dose (n = 12) and 8 weeks (n = 9) of tofogliflozin. We also measured ectopic fat in muscle and liver and the abdominal fat area using ¹H-magnetic resonance spectroscopy and magnetic resonance imaging, respectively, before and after 8 weeks of tofogliflozin. Results: MCRI did not change after a single dose of tofogliflozin (594.7 ± 67.7 mL/min·m² and 608.3 ± 90.9 mL/min·m², p = 0.61) or after 8 weeks (582.5 ± 67.3 mL/min·m² and 602.3 ± 67.0 mL/min·m², p = 0.41). The 8-week treatment significantly improved glycated hemoglobin and decreased body weight (1.7%) and the subcutaneous fat area (6.4%), whereas insulin sensitivity and ectopic fat in muscle and liver did not change significantly. Conclusions: MCRI did not change after a single dose or 8 weeks of tofogliflozin. Increased MCRI does not precede a decrease in body fat or improved glycemic control.

Insulin-degrading enzyme: an ally against metabolic and neurodegenerative diseases

Insulin-degrading enzyme (IDE) function goes far beyond its known proteolytic role as a regulator of insulin levels. IDE has a wide substrate promiscuity, degrading several proteins such as amyloid-β peptide, glucagon, islet amyloid polypeptide (IAPP) and insulin-like growth factors, that have diverse physiological and pathophysiological functions. Importantly, IDE plays other non-proteolytical functions such as a chaperone/dead-end chaperone, an E1-ubiquitin activating enzyme, and a proteasome modulator. It also responds as a heat shock protein, regulating cellular proteostasis. Notably, amyloidogenic proteins such as IAPP, amyloid-β and α-synuclein have been reported as substrates for IDE chaperone activity. This is of utmost importance as failure of IDE may result in increased protein aggregation, a key hallmark in the pathogenesis of beta cells in type 2 diabetes mellitus and of neurons in neurodegenerative diseases such as Alzheimer's and Parkinson's disease. In this review, we focus on the biochemical and biophysical properties of IDE and the regulation of its physiological functions. We further raise the hypothesis that IDE plays a central role in the pathological context of dysmetabolic and neurodegenerative diseases and discuss its potential as a therapeutic target. This article is protected by copyright. All rights reserved.

From virus to diabetes therapy: Characterization of a specific insulin-degrading enzyme inhibitor for diabetes treatment

Inhibition of insulin-degrading enzyme (IDE) is a possible target for treating diabetes. However, it has not yet evolved into a medical intervention, mainly because most developed inhibitors target the zinc in IDE's catalytic site, potentially causing toxicity to other essential metalloproteases. Since IDE is a cellular receptor for the varicella-zoster virus (VZV), we constructed a VZV-based inhibitor. We computationally characterized its interaction site with IDE showing that the peptide specifically binds inside IDE's central cavity, however, not in close proximity to the zinc ion. We confirmed the peptide's effective inhibition on IDE activity in vitro and showed its efficacy in ameliorating insulin-related defects in types 1 and 2 diabetes mouse models. In addition, we suggest that inhibition of IDE may ameliorate the pro-inflammatory profile of CD4⁺ T-cells toward insulin. Together, we propose a potential role of a designed VZV-derived peptide to serve as a selectively-targeted and as an efficient diabetes therapy.

Defining the Relative Role of Insulin Clearance in Early Dysglycemia in Relation to Insulin Sensitivity and Insulin Secretion: The Microbiome and Insulin Longitudinal Evaluation Study (MILES)

Insulin resistance and insufficient insulin secretion are well-recognized contributors to type 2 diabetes. A potential role of reduced insulin clearance has been suggested, but few studies have investigated the contribution of insulin clearance while simultaneously examining decreased insulin sensitivity and secretion. The goal of this study was to conduct such an investigation in a cohort of 353 non-Hispanic White and African American individuals recruited in the Microbiome and Insulin Longitudinal Evaluation Study (MILES). Participants underwent oral glucose tolerance tests from which insulin sensitivity, insulin secretion, insulin clearance, and disposition index were calculated. Regression models examined the individual and joint contributions of these traits to early dysglycemia (prediabetes or newly diagnosed diabetes). In separate models, reduced insulin sensitivity, reduced disposition index, and reduced insulin clearance were associated with dysglycemia. In a joint model, only insulin resistance and reduced insulin secretion were associated with dysglycemia. Models with insulin sensitivity, disposition index, or three insulin traits had the highest discriminative value for dysglycemia (area under the receiver operating characteristics curve of 0.82 to 0.89). These results suggest that in the race groups studied, insulin resistance and compromised insulin secretion are the main independent underlying defects leading to early dysglycemia.

Loss of postprandial insulin clearance control by Insulin-degrading enzyme drives dysmetabolism traits

Systemic insulin availability is determined by a balance between beta-cell secretion capacity and insulin clearance (IC). Insulin-degrading enzyme (IDE) is involved in the intracellular mechanisms underlying IC. The liver is a major player in IC control yet the role of hepatic IDE in glucose and lipid homeostasis remains unexplored. We hypothesized that IDE governs postprandial IC and hepatic IDE dysfunction amplifies dysmetabolic responses and prediabetes traits such as hepatic steatosis. In a European/Portuguese population-based cohort, IDE SNPs were strongly associated with postprandial IC in normoglycemic men but to a considerably lesser extent in women or in subjects with prediabetes. Liver-specific knockout-mice (LS-IDE KO) under normal chow diet (NCD), showed reduced postprandial IC with glucose intolerance and under high fat diet (HFD) were more susceptible to hepatic steatosis than control mice. This suggests that regulation of IC by IDE contributes to liver metabolic resilience. In agreement, LS-IDE KO hepatocytes revealed reduction of Glut2 expression levels with consequent impairment of glucose uptake and upregulation of CD36, a major hepatic free fatty acid transporter. Together these findings provide strong evidence that dysfunctional IC due to abnormal IDE regulation directly impairs postprandial hepatic glucose disposal and increases susceptibility to dysmetabolic conditions in the setting of Western diet/lifestyle.

Reduced insulin sensitivity and increased β/α cell mass is associated with reduced hepatic insulin-degrading enzyme activity in pregnant rats

AIMS

Pregnancy is associated with the development of a transitory insulin resistance that parallels with the upregulation of pancreatic β-cell function and mass. These metabolic adaptations guarantee the higher insulin demand, but there is no evidence of whether insulin clearance contributes to this process. Thus, we investigated some of the hepatic parameters related to insulin clearance during rat pregnancy. We also investigated some molecular parameters in the hypothalamus.

MAIN METHODS

We evaluated the body mass and food intake, insulin sensitivity, β- and α-cell masses, insulin clearance based on an exogenous insulin load, hepatic insulin-degrading enzyme (IDE) activity, and hepatic and hypothalamic protein content of IDE and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM-1) in three periods of gestation in Wistar rats.

KEY FINDINGS

In the first week of pregnancy, both insulin sensitivity and clearance increased, a pattern that inverted in the third week of gestation (reduced insulin sensitivity and clearance). Diminished insulin clearance was associated with lower hepatic IDE activity and higher pancreatic β- and α-cell masses. No alteration in the hepatic IDE and CEACAM protein content was observed throughout pregnancy, but hypothalamic IDE protein content was significantly reduced in the late gestation period.

SIGNIFICANCE

In conclusion, elevated insulin demand in the late period of gestation occurs not only as a result of increased β-cell mass and function but also by a potential reduction in hepatic insulin clearance. Knowing this physiological process may be valuable when considering gestational diabetes mellitus results from a failure in insulin supply during pregnancy.

Targeting Insulin-Degrading Enzyme in Insulin Clearance

Hepatic insulin clearance, a physiological process that in response to nutritional cues clears ~50–80% of circulating insulin, is emerging as an important factor in our understanding of the pathogenesis of type 2 diabetes mellitus (T2DM). Insulin-degrading enzyme (IDE) is a highly conserved Zn²⁺-metalloprotease that degrades insulin and several other intermediate-size peptides. Both, insulin clearance and IDE activity are reduced in diabetic patients, albeit the cause-effect relationship in humans remains unproven. Because historically IDE has been proposed as the main enzyme involved in insulin degradation, efforts in the development of IDE inhibitors as therapeutics in diabetic patients has attracted attention during the last decades. In this review, we retrace the path from Mirsky’s seminal discovery of IDE to the present, highlighting the pros and cons of the development of IDE inhibitors as a pharmacological approach to treating diabetic patients.

Bilberry (Vaccinium myrtillus L.) Extracts Comparative Analysis Regarding Their Phytonutrient Profiles, Antioxidant Capacity along with the In Vivo Rescue Effects Tested on a Drosophila melanogaster High-Sugar Diet Model

Bilberries (Vaccinium myrtillus L.) have been reported to hold a plentitude of health-promoting properties beyond basic nutrition, mainly attributed to their anthocyanin content and antioxidant activity. In this article, we built the phytochemical profile of three wild bilberry fruit extract formulations (aqueous, methanolic, and hydro-methanolic) using UHPLC-ESI-MS/MS putative analysis, identifying 88 individual phytochemicals, mainly flavonoids (total content 8.41 ± 0.11 mg QE/g dw), free amino acids, polyphenols (total content 21.68 ± 0.19 mg GAE/g dw), carboxylic acids, and vitamins. Furthermore, the antioxidant activity of the extract was assessed, reaching 78.03 ± 0.16% DPPH free radical scavenging activity, comparable to literature values determined for bilberry extracts of other origin. Due to the increased prevalence of metabolic syndrome and based on the reviewed benefits of bilberries, we tested the most potent formulation of our bilberry extracts in this biological context. The in vivo rescue effect of a bilberry extract supplemented diet on Drosophila melanogaster was assessed by monitoring biochemical and genomic markers. Hemolymph trehalose levels were halved upon addition of 3% hydro-methanolic bilberry extract to a high-sugar (1.5 M sucrose) diet, as compared to the non-supplemented high-sugar diet. Noteworthy, the rescue seen for flies kept on the bilberry extract supplemented high-sugar diet appeared to parallel the trehalose levels observed in the case of the control diet (50 mM sucrose) flies. Moreover, next to the trehalose-lowering type of in vivo effects, other gene expression related rescues were also detected for genes such as InR, Akh, AstA, AstC, Irk, Npc2g, and CCHa2 upon supplementation of the high-sugar diet with our hydro-methanolic bilberry fruit extract. Our findings suggest that such a bilberry fruit extract could generate physiological and genomic type of compensatory mechanisms so that further translational approaches would advance the understanding of some human specific pathological conditions.

Determinants of longitudinal change in insulin clearance: the Prospective Metabolism and Islet Cell Evaluation cohort

OBJECTIVE

To evaluate multiple determinants of the longitudinal change in insulin clearance (IC) in subjects at high risk for type 2 diabetes (T2D).

RESEARCH DESIGN AND METHODS

Adults (n=492) at risk for T2D in the Prospective Metabolism and Islet Cell Evaluation cohort, a longitudinal observational cohort, had four visits over 9 years. Values from oral glucose tolerance tests collected at each assessment were used to calculate the ratios of both fasting C peptide-to-insulin (IC_FASTING) and areas under the curve of C peptide-to-insulin (IC_AUC). Generalized estimating equations (GEE) evaluated multiple determinants of longitudinal changes in IC.

RESULTS

IC declined by 20% over the 9-year follow-up period (p<0.05). Primary GEE results indicated that non-European ethnicity, as well as increases in baseline measures of waist circumference, white cell count, and alanine aminotransferase, was associated with declines in IC_FASTING and IC_AUC over time (all p<0.05). There were no significant associations of IC with sex, age, physical activity, smoking, or family history of T2D. Both baseline and longitudinal IC were associated with incident dysglycemia.

CONCLUSIONS

Our findings suggest that non-European ethnicity and components of the metabolic syndrome, including central obesity, non-alcoholic fatty liver disease, and subclinical inflammation, may be related to longitudinal declines in IC.

Postprandial Insulin Response and Clearance Among Black and White Women: The Federal Women's Study

CONTEXT

Postprandial hyperinsulinemia might be an important cardiometabolic risk determinant in black compared with white women. However, the contributions of insulin clearance and β-cell function to racial differences in postprandial insulin response are unknown.

OBJECTIVE

To compare, by race and menopause, early insulin response to oral and intravenous glucose and to measure postprandial intact glucagon-like peptide 1 (GLP-1) concentrations, insulin clearance, and β-cell function.

DESIGN AND PARTICIPANTS

119 federally employed women without diabetes [87 premenopausal (52 black, 35 white) and 32 postmenopausal (19 black, 13 white)] underwent an oral glucose tolerance test, insulin-modified frequently sampled intravenous glucose test (IM-FSIGT), and mixed meal tolerance test (MMTT).

OUTCOME MEASURES

Early insulin response was measured as follows: (i) insulinogenic index (oral glucose tolerance test); (ii) acute insulin response to glucose (IM-FSIGT); and (iii) ratio of incremental insulin/glucose area under the curve in the first 30 minutes of the MMTT. Insulin clearance was assessed during the IM-FSIGT and MMTT. During the MMTT, intact GLP-1 was measured and β-cell function assessed using the insulin secretion rate and β-cell responsivity indexes.

RESULTS

Black pre-menopausal and postmenopausal women had a greater insulin response and lower insulin clearance and greater dynamic β-cell responsivity (P ≤ 0.05 for all). No differences were found in the total insulin secretion rates or intact GLP-1 concentrations.

CONCLUSIONS

Greater postprandial hyperinsulinemia in black pre-menopausal and postmenopausal women was associated with lower hepatic insulin clearance and heightened β-cell capacity to rapid changes in glucose, but not to higher insulin secretion. The relationship of increased β-cell secretory capacity, reduced insulin clearance, and ambient hyperinsulinemia to the development of cardiometabolic disease requires further investigation.

Vitamin E supplementation and caloric restriction promotes regulation of insulin secretion and glycemic homeostasis by different mechanisms in rats

Vitamin E and caloric restriction have antioxidant effects in mammals. The aim of this study was to evaluate effects of vitamin E supplementation and caloric restriction upon insulin secretion and glucose homeostasis in rats. Male Wistar rats were distributed among the following groups: C, control group fed ad libitum; R, food quantity reduction of 40%; CV, control group supplemented with vitamin E [30 mg·kg^-1·day^-1]; and RV, food-restricted group supplemented with vitamin E. The experiments ran for 21 days. Glucose tolerance and insulin sensitivity was higher in the CV, R, and RV groups. Insulin secretion stimulated with different glucose concentrations was lower in the R and RV groups, compared with C and CV. In the presence of glucose and secretagogues, insulin secretion was higher in the CV group and was lower in the R and RV groups. An increase in insulin receptor occurred in the fat pad and muscle tissue of groups CV, R, and RV. Levels of hepatic insulin receptor and phospho-Akt protein were higher in groups R and RV, compared with C and CV, while muscle phospho-Akt was increased in the CV group. There was a reduction in hepatic RNA levels of the hepatocyte growth factor gene and insulin degrading enzyme in the R group, and increased levels of insulin degrading enzyme in the CV and RV groups. Thus, vitamin E supplementation and caloric restriction modulate insulin secretion by different mechanisms to maintain glucose homeostasis.

Draft genome of the Marco Polo Sheep (Ovis ammon polii)

Background

The Marco Polo Sheep (Ovis ammon polii), a subspecies of argali (Ovis ammon) that is distributed mainly in the Pamir Mountains, provides a mammalian model to study high altitude adaptation mechanisms. Due to over-hunting and subsistence poaching, as well as competition with livestock and habitat loss, O. ammon has been categorized as an endangered species on several lists. It can have fertile offspring with sheep. Hence, a high-quality reference genome of the Marco Polo Sheep will be very helpful in conservation genetics and even in exploiting useful genes in sheep breeding.

Findings

A total of 1022.43 Gb of raw reads resulting from whole-genome sequencing of a Marco Polo Sheep were generated using an Illumina HiSeq2000 platform. The final genome assembly (2.71 Gb) has an N50 contig size of 30.7 Kb and a scaffold N50 of 5.49 Mb. The repeat sequences identified account for 46.72% of the genome, and 20 336 protein-coding genes were predicted from the masked genome. Phylogenetic analysis indicated a close relationship between Marco Polo Sheep and the domesticated sheep, and the time of their divergence was approximately 2.36 million years ago. We identified 271 expanded gene families and 168 putative positively selected genes in the Marco Polo Sheep lineage.

Conclusions

We provide the first genome sequence and gene annotation for the Marco Polo Sheep. The availability of these resources will be of value in the future conservation of this endangered large mammal, for research into high altitude adaptation mechanisms, for reconstructing the evolutionary history of the Caprinae, and for the future conservation of the Marco Polo Sheep.

The core sequence of PIF competes for insulin/amyloid β in insulin degrading enzyme: potential treatment for Alzheimer's disease

The central pathological feature of Alzheimer's disease (AD) is the sequential proteolytic processing of amyloid precursor protein (APP) to amyloid-β peptides (Aβ) agglomeration. The clearance of Aβ may be induced by the large zinc-binding protease insulin degrading enzyme (IDE). IDE is the common link between AD and Type II diabetes as insulin is an IDE target as well. Not surprisingly, the search for safe and effective drugs modulating IDE is ongoing. A new pregnancy derived peptide, PreImplantation Factor (PIF), inhibits neuro-inflammation and crosses the blood-brain-barrier. Importantly, we report that the (R3I4K5P6) core sequence of the PIF peptide modulates IDE function and results in decreased Aβ agglomeration in neuronal cells. Using bioinformatics we show that PIF binds to the IDE complex and sterically competes for the same place as insulin or Aβ. The predicted RIKP sequence and especially the specific I4 and P6 amino acids are essential for hydrophobic interactions with the IDE complex. In terms of potential AD treatment, PIF was successfully tested in neurodegenerative animal models of perinatal brain injury and experimental autoimmune encephalitis. Importantly, sPIF received a FDA Fast Track Approval and orphan drug designation for first-in-human trial in autoimmunity.

Variability of Directly Measured First-Pass Hepatic Insulin Extraction and Its Association With Insulin Sensitivity and Plasma Insulin

Although the β-cells secrete insulin, the liver, with its first-pass insulin extraction (FPE), regulates the amount of insulin allowed into circulation for action on target tissues. The metabolic clearance rate of insulin, of which FPE is the dominant component, is a major determinant of insulin sensitivity (SI). We studied the intricate relationship among FPE, SI, and fasting insulin. We used a direct method of measuring FPE, the paired portal/peripheral infusion protocol, where insulin is infused stepwise through either the portal vein or a peripheral vein in healthy young dogs (n = 12). FPE is calculated as the difference in clearance rates (slope of infusion rate vs. steady insulin plot) between the paired experiments. Significant correlations were found between FPE and clamp-assessed SI (r_s = 0.74), FPE and fasting insulin (r_s = -0.64), and SI and fasting insulin (r_s = -0.67). We also found a wide variance in FPE (22.4-77.2%; mean ± SD 50.4 ± 19.1) that is reflected in the variability of plasma insulin (48.1 ± 30.9 pmol/L) and SI (9.4 ± 5.8 × 10⁴ dL · kg^-1 · min^-1 · [pmol/L]^-1). FPE could be the nexus of regulation of both plasma insulin and SI.

Loss of renal SNX5 results in impaired IDE activity and insulin resistance in mice

AIMS/HYPOTHESIS

We hypothesised that renal sorting nexin 5 (SNX5) regulates the insulin-degrading enzyme (IDE) and, thus, circulating insulin levels. We therefore studied the dynamic interaction between SNX5 and IDE in human renal proximal tubule cells (hRPTCs), as well as in rat and mouse kidneys.

METHODS

The regulation of IDE by SNX5 expressed in the kidney was studied in vitro and in vivo. Snx5 or mock siRNA was added to immortalised hRPTCs (passage <20) in culture or selectively infused, via osmotic mini-pump, into the remnant kidney of uninephrectomised mice and rats.

RESULTS

SNX5 co-localised with IDE at the plasma membrane and perinuclear area of hRPTCs and in the brush border membrane of proximal tubules of human, rat, and mouse kidneys. Insulin increased the co-localisation and co-immunoprecipitation of SNX5 and IDE in hRPTCs. Silencing SNX5 in hRPTCs decreased IDE expression and activity. Renal-selective silencing of Snx5 (SNX5 protein: 100 ± 25 vs 29 ± 10, p < 0.05 [% of control]) in C57Bl/6J mice decreased IDE protein (100 ± 13 vs 57 ± 6, p < 0.05 [% of control]) and urinary insulin excretion, impaired the responses to insulin and glucose, and increased blood insulin and glucose levels. Spontaneously hypertensive rats (SHRs) had increased blood insulin and glucose levels and decreased renal SNX5 (100 ± 27 vs 29 ± 6, p < 0.05 [% of control]) and IDE (100 ± 5 vs 75 ± 4, p < 0.05 [% of control]) proteins, compared with normotensive Wistar-Kyoto (WKY) rats. Kidney Snx5-depleted WKY rats also had increased blood insulin and glucose levels. The expression of SNX5 and IDE was decreased in RPTCs from SHRs and hypertensive humans compared with cells from normotensive volunteers, indicating a common cause for hyperinsulinaemia and hypertension.

CONCLUSIONS/INTERPRETATION

Renal SNX5 positively regulates IDE expression and function. This study is the first to demonstrate the novel and crucial role of renal SNX5 in insulin and glucose metabolism.

Alzheimer's disease and metabolic syndrome: A link from oxidative stress and inflammation to neurodegeneration

Alzheimer's disease (AD) is the most common cause of dementia and one of the most important causes of morbidity and mortality among the aging population. AD diagnosis is made post-mortem, and the two pathologic hallmarks, particularly evident in the end stages of the illness, are amyloid plaques and neurofibrillary tangles. Currently, there is no curative treatment for AD. Additionally, there is a strong relation between oxidative stress, metabolic syndrome, and AD. The high levels of circulating lipids and glucose imbalances amplify lipid peroxidation that gradually diminishes the antioxidant systems, causing high levels of oxidative metabolism that affects cell structure, leading to neuronal damage. Accumulating evidence suggests that AD is closely related to a dysfunction of both insulin signaling and glucose metabolism in the brain, leading to an insulin-resistant brain state. Four drugs are currently used for this pathology: Three FDA-approved cholinesterase inhibitors and one NMDA receptor antagonist. However, wide varieties of antioxidants are promissory to delay or prevent the symptoms of AD and may help in treating the disease. Therefore, therapeutic efforts to achieve attenuation of oxidative stress could be beneficial in AD treatment, attenuating Aβ-induced neurotoxicity and improve neurological outcomes in AD. The term inflammaging characterizes a widely accepted paradigm that aging is accompanied by a low-grade chronic up-regulation of certain pro-inflammatory responses in the absence of overt infection, and is a highly significant risk factor for both morbidity and mortality in the elderly.

Multiple functions of insulin-degrading enzyme: a metabolic crosslight?

Insulin-degrading enzyme (IDE) is a ubiquitous zinc peptidase of the inverzincin family, which has been initially discovered as the enzyme responsible for insulin catabolism; therefore, its involvement in the onset of diabetes has been largely investigated. However, further studies on IDE unraveled its ability to degrade several other polypeptides, such as β-amyloid, amylin, and glucagon, envisaging the possible implication of IDE dys-regulation in the "aggregopathies" and, in particular, in neurodegenerative diseases. Over the last decade, a novel scenario on IDE biology has emerged, pointing out a multi-functional role of this enzyme in several basic cellular processes. In particular, latest advances indicate that IDE behaves as a heat shock protein and modulates the ubiquitin-proteasome system, suggesting a major implication in proteins turnover and cell homeostasis. In addition, recent observations have highlighted that the regulation of glucose metabolism by IDE is not merely based on its largely proposed role in the degradation of insulin in vivo. There is increasing evidence that improper IDE function, regulation, or trafficking might contribute to the etiology of metabolic diseases. In addition, the enzymatic activity of IDE is affected by metals levels, thus suggesting a role also in the metal homeostasis (metallostasis), which is thought to be tightly linked to the malfunction of the "quality control" machinery of the cell. Focusing on the physiological role of IDE, we will address a comprehensive vision of the very complex scenario in which IDE takes part, outlining its crucial role in interconnecting several relevant cellular processes.

Bridging Type 2 Diabetes and Alzheimer's Disease: Assembling the Puzzle Pieces in the Quest for the Molecules With Therapeutic and Preventive Potential

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two age-related amyloid diseases that affect millions of people worldwide. Broadly supported by epidemiological data, the higher incidence of AD among type 2 diabetic patients led to the recognition of T2D as a tangible risk factor for the development of AD. Indeed, there is now growing evidence on brain structural and functional abnormalities arising from brain insulin resistance and deficiency, ultimately highlighting the need for new approaches capable of preventing the development of AD in type 2 diabetic patients. This review provides an update on overlapping pathophysiological mechanisms and pathways in T2D and AD, such as amyloidogenic events, oxidative stress, endothelial dysfunction, aberrant enzymatic activity, and even shared genetic background. These events will be presented as puzzle pieces put together, thus establishing potential therapeutic targets for drug discovery and development against T2D and diabetes-induced cognitive decline-a heavyweight contributor to the increasing incidence of dementia in developed countries. Hoping to pave the way in this direction, we will present some of the most promising and well-studied drug leads with potential against both pathologies, including their respective bioactivity reports, mechanisms of action, and structure-activity relationships.

Insulin-degrading enzyme: new therapeutic target for diabetes and Alzheimer's disease?

Insulin-degrading enzyme (IDE) is a major enzyme responsible for insulin degradation. In addition to insulin, IDE degrades many targets including glucagon, atrial natriuretic peptide, and beta-amyloid peptide, regulates proteasomal degradation and other cell functions. IDE represents a pathophysiological link between type 2 diabetes (T2DM) and late onset Alzheimer's disease (AD). Potent and selective modulators of IDE activity are potential drugs for therapies of both diseases. Acute treatment with a novel IDE inhibitor was recently tested in a mouse study as a therapeutic approach for the treatment of T2DM. In contrast, effective IDE activators can be used for the AD treatment. However, because of the pleiotropic IDE action, the sustained treatment with systemic IDE modulators should be carefully tested in animal studies. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets. KEY MESSAGES Insulin-degrading enzyme (IDE) represents a pathophysiological link between type 2 diabetes (T2DM) and Alzheimer's disease (AD). Selective modulators of IDE activity are potential drugs for both T2DM and AD treatment. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets.

COMBINED TREATMENT WITH SAXAGLIPTIN PLUS DAPAGLIFLOZIN REDUCES INSULIN LEVELS BY INCREASED INSULIN CLEARANCE AND IMPROVES β-CELL FUNCTION

OBJECTIVE

To determine if reduction in serum insulin with dapagliflozin plus saxagliptin or dapagliflozin add-on to metformin contributed to increased insulin clearance and to assess the effects of these treatments on β-cell function.

METHODS

Patients (glycated hemoglobin, 8 to 12%; 64 to 108 mmol/mol) were randomized to 24-week, double-blind treatment with saxagliptin 5 mg/day plus dapagliflozin 10 mg/day (n = 179), saxagliptin 5 mg/day plus placebo (n = 176), or dapagliflozin 10 mg/day plus placebo (n = 179) added to metformin. C-peptide to insulin ratio was used as an index of insulin clearance during a meal tolerance test, and β-cell function was evaluated by Homeostasis Model Assessment 2.

RESULTS

At 24 weeks, compared with baseline, saxagliptin + dapagliflozin and saxagliptin + placebo increased mean (95% confidence interval [CI]) C-peptide area under the curve (AUC_{0-180 min}) (40.2 [9.2 to 71.3] ng/mL and 95.4 [63.4 to 127.4] ng/mL, respectively); no change was noted with dapagliflozin + placebo (14.5 [-17.6 to 46.8] ng/mL). Insulin AUC was reduced from baseline with saxagliptin + dapagliflozin (-1,120.4 [-1,633.9 to -606.9] μU/mL) and dapagliflozin + placebo (-1,018.6 [-1550.5 to -486.8] μU/mL) but increased with saxagliptin + placebo (661.2 [131.1 to 1,191.3] μU/mL). C-peptide to insulin ratio did not change versus baseline with saxagliptin + placebo but increased after saxagliptin + dapagliflozin and dapagliflozin + placebo, largely due to decreased insulin AUC with dapagliflozin. All treatments improved β-cell function (mean change [95% CI] from baseline, saxagliptin+dapagliflozin: 20.6% [16.5% to 24.8%]; dapagliflozin + placebo: 17.0% [12.7% to 21.4%]; saxagliptin + placebo: 11.0% [6.6% to 15.5%]).

CONCLUSION

Increased C-peptide to insulin ratio with saxagliptin + dapagliflozin and dapagliflozin + placebo add-on to metformin compared with saxagliptin + placebo add-on to metformin suggests that dapagliflozin increases insulin clearance and may contribute to lower circulating insulin. All treatments improved β-cell function, with the greatest improvements with saxagliptin + dapagliflozin and dapagliflozin + placebo.

ABBREVIATIONS

A1c = glycated hemoglobin AUC_{0-180 min} = area under the curve from 0 to 180 minutes HOMA-2β = homeostasis model assessment-2 β-cell function SGLT-2 = sodium-glucose cotransporter-2 T2D = type 2 diabetes.

Acute Exercise Improves Insulin Clearance and Increases the Expression of Insulin-Degrading Enzyme in the Liver and Skeletal Muscle of Swiss Mice

The effects of exercise on insulin clearance and IDE expression are not yet fully elucidated. Here, we have explored the effect of acute exercise on insulin clearance and IDE expression in lean mice. Male Swiss mice were subjected to a single bout of exercise on a speed/angle controlled treadmill for 3-h at approximately 60-70% of maximum oxygen consumption. As expected, acute exercise reduced glycemia and insulinemia, and increased insulin tolerance. The activity of AMPK-ACC, but not of IR-Akt, pathway was increased in the liver and skeletal muscle of trained mice. In an apparent contrast to the reduced insulinemia, glucose-stimulated insulin secretion was increased in isolated islets of these mice. However, insulin clearance was increased after acute exercise and was accompanied by increased expression of the insulin-degrading enzyme (IDE), in the liver and skeletal muscle. Finally, C2C12, but not HEPG2 cells, incubated at different concentrations of 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) for 3-h, showed increased expression of IDE. In conclusion, acute exercise increases insulin clearance, probably due to an augmentation of IDE expression in the liver and skeletal muscle. The elevated IDE expression, in the skeletal muscle, seems to be mediated by activation of AMPK-ACC pathway, in response to exercise. We believe that the increase in the IDE expression, comprise a safety measure to maintain glycemia at or close to physiological levels, turning physical exercise more effective and safe.

Acute exercise restores insulin clearance in diet-induced obese mice

The aim of this study was to investigate the insulin clearance in diet-induced obese (DIO) mice submitted to acute endurance exercise (3h of treadmill exercise at 60-70% VO2max). Glucose-stimulated insulin secretion in isolated islets; ipGTT; ipITT; ipPTT; in vivo insulin clearance; protein expression in liver, skeletal muscle, and adipose tissue (insulin degrading enzyme (IDE), insulin receptor subunitβ(IRβ), phospho-Akt (p-Akt) and phospho-AMPK (p-AMPK)), and the activity of IDE in the liver and skeletal muscle were accessed. In DIO mice, acute exercise reduced fasting glycemia and insulinemia, improved glucose and insulin tolerance, reduced hepatic glucose production, and increased p-Akt protein levels in liver and skeletal muscle and p-AMPK protein levels in skeletal muscle. In addition, insulin secretion was reduced, whereas insulin clearance and the expression of IDE and IRβ were increased in liver and skeletal muscle. Finally, IDE activity was increased only in skeletal muscle. In conclusion, we propose that the increased insulin clearance and IDE expression and activity, primarily, in skeletal muscle, constitute an additional mechanism, whereby physical exercise reduces insulinemia in DIO mice.

Genes, Genetics, and Environment in Type 2 Diabetes: Implication in Personalized Medicine

Type 2 diabetes (T2D) is a multifactorial anomaly involving 57 genes located on 16 different chromosomes and 136 single nucleotide polymorphisms (SNPs). Ten genes are located on chromosome 1, followed by seven genes on chromosome 11 and six genes on chromosomes 3. Remaining chromosomes harbor two to five genes. Significantly, chromosomes 13, 14, 16, 18, 21, 22, X, and Y do not have any associated diabetogenic gene. Genetic components have their own pathways encompassing insulin secretion, resistance, signaling, and β-cell dysfunction. Environmental factors include epigenetic changes, nutrition, intrauterine surroundings, and obesity. In addition, ethnicity plays a role in conferring susceptibility to T2D. This scenario poses a challenge toward the development of biomarker for quick disease diagnosis or for generating a consensus to delineate different categories of T2D patients. We believe, before prescribing a generic drug, detailed genotypic information with the background of ethnicity and environmental factors may be taken into consideration. This nonconventional approach is envisaged to be more robust in the context of personalized medicine and perhaps would cause lot less burden on the patient ensuring better management of T2D.

The insulin degrading enzyme activates ubiquitin and promotes the formation of K48 and K63 diubiquitin

We report an ATP-dependent ubiquitin conjugation with IDE which, in turn, promotes Ub-Ub linkages in tube tests. We propose a novel function for IDE as a non-canonical ubiquitin activating enzyme.

An Extended Polyanion Activation Surface in Insulin Degrading Enzyme

Insulin degrading enzyme (IDE) is believed to be the major enzyme that metabolizes insulin and has been implicated in the degradation of a number of other bioactive peptides, including amyloid beta peptide (Aβ), glucagon, amylin, and atrial natriuretic peptide. IDE is activated toward some substrates by both peptides and polyanions/anions, possibly representing an important control mechanism and a potential therapeutic target. A binding site for the polyanion ATP has previously been defined crystallographically, but mutagenesis studies suggest that other polyanion binding modes likely exist on the same extended surface that forms one wall of the substrate-binding chamber. Here we use a computational approach to define three potential ATP binding sites and mutagenesis and kinetic studies to confirm the relevance of these sites. Mutations were made at four positively charged residues (Arg 429, Arg 431, Arg 847, Lys 898) within the polyanion-binding region, converting them to polar or hydrophobic residues. We find that mutations in all three ATP binding sites strongly decrease the degree of activation by ATP and can lower basal activity and cooperativity. Computational analysis suggests conformational changes that result from polyanion binding as well as from mutating residues involved in polyanion binding. These findings indicate the presence of multiple polyanion binding modes and suggest the anion-binding surface plays an important conformational role in controlling IDE activity.

HHEX_23 AA Genotype Exacerbates Effect of Diabetes on Dementia and Alzheimer Disease: A Population-Based Longitudinal Study

BACKGROUND

Research has suggested that variations within the IDE/HHEX gene region may underlie the association of type 2 diabetes with Alzheimer disease (AD). We sought to explore whether IDE genes play a role in the association of diabetes with dementia, AD, and structural brain changes using data from two community-based cohorts of older adults and a subsample with structural MRI.

METHODS AND FINDINGS

The first cohort, which included dementia-free adults aged ≥75 y (n = 970) at baseline, was followed for 9 y to detect incident dementia (n = 358) and AD (n = 271) cases. The second cohort (for replication), which included 2,060 dementia-free participants aged ≥60 y at baseline, was followed for 6 y to identify incident dementia (n = 166) and AD (n = 121) cases. A subsample (n = 338) of dementia-free participants from the second cohort underwent MRI. HHEX_23 and IDE_9 were genotyped, and diabetes (here including type 2 diabetes and prediabetes) was assessed. In the first cohort, diabetes led to an adjusted hazard ratio (HR) of 1.73 (95% CI 1.19-2.32) and 1.66 (95% CI 1.06-2.40) for dementia and AD, respectively, among all participants. Compared to people carrying the GG genotype without diabetes, AA genotype carriers with diabetes had an adjusted HR of 5.54 (95% CI 2.40-7.18) and 4.81 (95% CI 1.88-8.50) for dementia and AD, respectively. There was a significant interaction between HHEX_23-AA and diabetes on dementia (HR 4.79, 95% CI 1.63-8.90, p = 0.013) and AD (HR 3.55, 95% CI 1.45-9.91, p = 0.025) compared to the GG genotype without diabetes. In the second cohort, the HRs were 1.68 (95% CI 1.04-2.99) and 1.64 (1.02-2.33) for the diabetes-AD and dementia-AD associations, respectively, and 4.06 (95% CI 1.06-7.58, p = 0.039) and 3.29 (95% CI 1.02-8.33, p = 0.044) for the interactions, respectively. MRI data showed that HHEX_23-AA carriers with diabetes had significant structural brain changes compared to HHEX_23-GG carriers without diabetes. No joint effects of IDE_9 and diabetes on dementia were shown. As a limitation, the sample sizes were small for certain subgroups.

CONCLUSIONS

A variant in the HHEX_23 gene interacts with diabetes to be associated with a substantially increased risk of dementia and AD, and with structural brain changes among dementia-free elderly people.

Candidate genes for Alzheimer's disease are associated with individual differences in plasma levels of beta amyloid peptides in adults with Down syndrome

We examined the contribution of candidates genes for Alzheimer's disease (AD) to individual differences in levels of beta amyloid peptides in adults with Down syndrom, a population at high risk for AD. Participants were 254 non-demented adults with Down syndrome, 30-78 years of age. Genomic deoxyribonucleic acid was genotyped using an Illumina GoldenGate custom array. We used linear regression to examine differences in levels of Aβ peptides associated with the number of risk alleles, adjusting for age, sex, level of intellectual disability, race and/or ethnicity, and the presence of the APOE ε4 allele. For Aβ42 levels, the strongest gene-wise association was found for a single nucleotide polymorphism (SNP) on CAHLM1; for Aβ40 levels, the strongest gene-wise associations were found for SNPs in IDE and SOD1, while the strongest gene-wise associations with levels of the Aβ42/Aβ40 ratio were found for SNPs in SORCS1. Broadly classified, variants in these genes may influence amyloid precursor protein processing (CALHM1, IDE), vesicular trafficking (SORCS1), and response to oxidative stress (SOD1).

Modulation of insulin degrading enzyme activity and liver cell proliferation

Diabetes mellitus type 2 (T2DM), insulin therapy, and hyperinsulinemia are independent risk factors of liver cancer. Recently, the use of a novel inhibitor of insulin degrading enzyme (IDE) was proposed as a new therapeutic strategy in T2DM. However, IDE inhibition might stimulate liver cell proliferation via increased intracellular insulin concentration. The aim of this study was to characterize effects of inhibition of IDE activity in HepG2 hepatoma cells and to analyze liver specific expression of IDE in subjects with T2DM. HepG2 cells were treated with 10 nM insulin for 24 h with or without inhibition of IDE activity using IDE RNAi, and cell transcriptome and proliferation rate were analyzed. Human liver samples (n = 22) were used for the gene expression profiling by microarrays. In HepG2 cells, IDE knockdown changed expression of genes involved in cell cycle and apoptosis pathways. Proliferation rate was lower in IDE knockdown cells than in controls. Microarray analysis revealed the decrease of hepatic IDE expression in subjects with T2DM accompanied by the downregulation of the p53-dependent genes FAS and CCNG2, but not by the upregulation of proliferation markers MKI67, MCM2 and PCNA. Similar results were found in the liver microarray dataset from GEO Profiles database. In conclusion, IDE expression is decreased in liver of subjects with T2DM which is accompanied by the dysregulation of p53 pathway. Prolonged use of IDE inhibitors for T2DM treatment should be carefully tested in animal studies regarding its potential effect on hepatic tumorigenesis.

Endurance training inhibits insulin clearance and IDE expression in Swiss mice

INTRODUCTION

Endurance training improves peripheral insulin sensitivity in the liver and the skeletal muscle, but the mechanism for this effect is poorly understood. Recently, it was proposed that insulin clearance plays a major role in both glucose homeostasis and insulin sensitivity. Therefore, our goal was to determine the mechanism by which endurance training improves insulin sensitivity and how it regulates insulin clearance in mice.

METHODS

Mice were treadmill-trained for 4 weeks at 70-80% of maximal oxygen consumption (VO2 max) for 60 min, 5 days a week. The glucose tolerance and the insulin resistance were determined using an IPGTT and an IPITT, respectively, and the insulin decay rate was calculated from the insulin clearance. Protein expression and phosphorylation in the liver and the skeletal muscle were ascertained by Western blot.

RESULTS

Trained mice exhibited an increased VO2 max, time to exhaustion, glucose tolerance and insulin sensitivity. They had smaller fat pads and lower plasma concentrations of insulin and glucose. Endurance training inhibited insulin clearance and reduced expression of IDE in the liver, while also inhibiting insulin secretion by pancreatic islets. There was increased phosphorylation of both the canonical (IR-AKT) and the non-canonical (CaMKII-AMPK-ACC) insulin pathways in the liver of trained mice, whereas only the CaMKII-AMPK pathway was increased in the skeletal muscle.

CONCLUSION

Endurance training improved glucose homeostasis not only by increasing peripheral insulin sensitivity but also by decreasing insulin clearance and reducing IDE expression in the liver.

Reduced insulin clearance and lower insulin-degrading enzyme expression in the liver might contribute to the thrifty phenotype of protein-restricted mice

Nutrient restriction during the early stages of life usually leads to alterations in glucose homeostasis, mainly insulin secretion and sensitivity, increasing the risk of metabolic disorders in adulthood. Despite growing evidence regarding the importance of insulin clearance during glucose homeostasis in health and disease, no information exists about this process in malnourished animals. Thus, in the present study, we aimed to determine the effect of a nutrient-restricted diet on insulin clearance using a model in which 30-d-old C57BL/6 mice were exposed to a protein-restricted diet for 14 weeks. After this period, we evaluated many metabolic variables and extracted pancreatic islet, liver, gastrocnemius muscle (GCK) and white adipose tissue samples from the control (normal-protein diet) and restricted (low-protein diet, LP) mice. Insulin concentrations were determined using RIA and protein expression and phosphorylation by Western blot analysis. The LP mice exhibited lower body weight, glycaemia, and insulinaemia, increased glucose tolerance and altered insulin dynamics after the glucose challenge. The improved glucose tolerance could partially be explained by an increase in insulin sensitivity through the phosphorylation of the insulin receptor/protein kinase B and AMP-activated protein kinase/acetyl-CoA carboxylase in the liver, whereas the changes in insulin dynamics could be attributed to reduced insulin secretion coupled with reduced insulin clearance and lower insulin-degrading enzyme (IDE) expression in the liver and GCK. In summary, protein-restricted mice not only produce and secrete less insulin, but also remove and degrade less insulin. This phenomenon has the double benefit of sparing insulin while prolonging and potentiating its effects, probably due to the lower expression of IDE in the liver, possibly with long-term consequences.

Genetics of Alzheimer's disease in Caribbean Hispanic and African American populations

Late-onset Alzheimer's disease (LOAD), which is characterized by progressive deterioration in cognition, function, and behavior, is the most common cause of dementia and the sixth leading cause of all deaths, placing a considerable burden on Western societies. Most studies aiming to identify genetic susceptibility factors for LOAD have focused on non-Hispanic white populations. This is, in part related to differences in linkage disequilibrium and allele frequencies between ethnic groups that could lead to confounding. However, in addition, non-Hispanic white populations are simply more widely studied. As a consequence, minorities are genetically underrepresented despite the fact that in several minority populations living in the same community as whites (including African American and Caribbean Hispanics), LOAD incidence is higher. This review summarizes the current knowledge on genetic risk factors associated with LOAD risk in Caribbean Hispanics and African Americans and provides suggestions for future research. We focus on Caribbean Hispanics and African Americans because they have a high LOAD incidence and a body of genetic studies on LOAD that is based on samples with genome-wide association studies data and reasonably large effect sizes to yield generalizable results.

The Drosophila insulin-degrading enzyme restricts growth by modulating the PI3K pathway in a cell-autonomous manner

The Drosophila insulin-degrading enzyme (dIDE) is a negative modulator of the PI3K pathway that restrains tissue growth in an autonomous manner. Larvae reared in high sucrose exhibit reduced growth and delayed developmental timing due to insulin resistance; dIDE loss of function exacerbates these phenotypes.

Mammalian insulin-degrading enzyme (IDE) cleaves insulin, among other peptidic substrates, but its function in insulin signaling is elusive. We use the Drosophila system to define the function of IDE in the regulation of growth and metabolism. We find that either loss or gain of function of Drosophila IDE (dIDE) can restrict growth in a cell-autonomous manner by affecting both cell size and cell number. dIDE can modulate Drosophila insulin-like peptide 2 levels, thereby restricting activation of the phosphatidylinositol-3-phosphate kinase pathway and promoting activation of Drosophila forkhead box, subgroup O transcription factor. Larvae reared in high sucrose exhibit delayed developmental timing due to insulin resistance. We find that dIDE loss of function exacerbates this phenotype and that mutants display increased levels of circulating sugar, along with augmented expression of a lipid biosynthesis marker. We propose that dIDE is a modulator of insulin signaling and that its loss of function favors insulin resistance, a hallmark of diabetes mellitus type II.

Hepatic insulin clearance is closely related to metabolic syndrome components

OBJECTIVE

Insulin clearance is decreased in type 2 diabetes mellitus (T2DM) for unknown reasons. Subjects with metabolic syndrome are hyperinsulinemic and have an increased risk of T2DM. We aimed to investigate the relationship between hepatic insulin clearance (HIC) and different components of metabolic syndrome and tested the hypothesis that HIC may predict the risk of metabolic syndrome.

RESEARCH DESIGN AND METHODS

Individuals without diabetes from the Metabolic Syndrome Berlin Brandenburg (MeSyBePo) study (800 subjects with the baseline examination and 189 subjects from the MeSyBePo recall study) underwent an oral glucose tolerance test (OGTT) with assessment of insulin secretion (insulin secretion rate [ISR]) and insulin sensitivity. Two indices of HIC were calculated.

RESULTS

Both HIC indices showed lower values in subjects with metabolic syndrome (P < 0.001) at baseline. HIC indices correlate inversely with waist circumference, diastolic blood pressure, fasting glucose, triglycerides, and OGTT-derived insulin secretion index. During a mean follow-up of 5.1 ± 0.9 years, 47 individuals developed metabolic syndrome and 33 subjects progressed to impaired glucose metabolism. Both indices of HIC showed a trend of an association with increased risk of metabolic syndrome (HICC-peptide odds ratio 1.13 [95% CI 0.97-1.31], P = 0.12, and HICISR 1.38 [0.88-2.17], P = 0.16) and impaired glucose metabolism (HICC-peptide 1.12 [0.92-1.36], P = 0.26, and HICISR 1.31 [0.74-2.33] P = 0.36), although point estimates reached no statistical significance.

CONCLUSIONS

HIC was associated with different components of metabolic syndrome and markers of insulin secretion and insulin sensitivity. Decreased HIC may represent a novel pathophysiological mechanism of the metabolic syndrome, which may be used additionally for early identification of high-risk subjects.

Cafeteria diet inhibits insulin clearance by reduced insulin-degrading enzyme expression and mRNA splicing

Insulin clearance plays a major role in glucose homeostasis and insulin sensitivity in physiological and/or pathological conditions, such as obesity-induced type 2 diabetes as well as diet-induced obesity. The aim of the present work was to evaluate cafeteria diet-induced obesity-induced changes in insulin clearance and to explain the mechanisms underlying these possible changes. Female Swiss mice were fed either a standard chow diet (CTL) or a cafeteria diet (CAF) for 8 weeks, after which we performed glucose tolerance tests, insulin tolerance tests, insulin dynamics, and insulin clearance tests. We then isolated pancreatic islets for ex vivo glucose-stimulated insulin secretion as well as liver, gastrocnemius, visceral adipose tissue, and hypothalamus for subsequent protein analysis by western blot and determination of mRNA levels by real-time RT-PCR. The cafeteria diet induced insulin resistance, glucose intolerance, and increased insulin secretion and total insulin content. More importantly, mice that were fed a cafeteria diet demonstrated reduced insulin clearance and decay rate as well as reduced insulin-degrading enzyme (IDE) protein and mRNA levels in liver and skeletal muscle compared with the control animals. Furthermore, the cafeteria diet reduced IDE expression and alternative splicing in the liver and skeletal muscle of mice. In conclusion, a cafeteria diet impairs glucose homeostasis by reducing insulin sensitivity, but it also reduces insulin clearance by reducing IDE expression and alternative splicing in mouse liver; however, whether this mechanism contributes to the glucose intolerance or helps to ameliorate it remains unclear.