Insulin-degrading enzyme higher in subjects with metabolic syndrome

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.

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.

APOE-Genotype and Insulin Modulate Estimated Effect of Dietary Macronutrients on Cognitive Performance: Panel Analyses in Nondiabetic Older Adults at Risk of Dementia

BACKGROUND

The apolipoprotein E gene (APOE ε-2/3/4, combined as 6 different genotypes: ε-22/23/24/33/34/44) and insulin status modulate dementia risk and play a role in the metabolism of macronutrients.

OBJECTIVES

We aimed to examine APOE-genotype and fasting insulin as effect modifiers of the slopes between dietary macronutrients and cognitive performance among older adults at risk of dementia.

METHODS

Panel analyses-with diet and cognition measured at baseline and follow-up at years 1 and 2-were performed in a sub-sample from the FINGER (Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability) trial (n = 676, 60-77 y, 46% females, all nondiabetics). The associations between macronutrients (3-d food records, z-scores) and global cognition (modified Neuropsychological Test Battery, z-score) were analyzed in mixed regression models adjusted for confounders selected a priori. After a gradient was implied by the point estimates in categorical APOE analyses, we investigated a continuous APOE variable [APOE-gradient, coded -1 (for ε-23), -0.5 (ε-24), 0 (ε-33), 1 (ε-34), 2 (ε-44)] as an effect-modifier.

RESULTS

At increasing levels of the APOE-gradient, a relatively more favorable slope between diet and cognition was observed for a lower carbohydrate/fat ratio [β = -0.040, 95% confidence interval (CI): -0.074, -0.006; P = 0.020 for interaction diet × APOE-gradient), and higher protein (β = 0.075, 95% CI: 0.042, 0.109; P = 9.4 × 10-6). Insulin concentration (log-linear) modulated the association between the carbohydrate/fat ratio and cognition by a quadratic interaction (β = -0.016, P = 0.039). Coherent findings for exploratory predictors (fiber, fat subtypes, composite score, metabolic biomarkers) were compatible with published hypotheses of differential dietary adaptation by APOE, with cognition among ε-33 being relatively independent of dietary parameters-implying "metabolic flexibility." Antagonistic slopes to cognition for ε-23 (positive) compared with ε-34 and ε-44 (negative) were found for a Higher-carbohydrates-fiber-Lower-fat-protein composite score, even as within-subjects effects.

CONCLUSIONS

APOE-based precision nutrition appears conceptually promising, but replications in wider samples are warranted, as well as support from trials. Both relative hyper- and hypoinsulinemia might modulate the effect of diet on cognition.

Ghrelin proteolysis increases in plasma of men, but not women, with obesity

AIMS

Since plasma ghrelin can undergo des-acylation and proteolysis, the aim of this study was to investigate the extent to which an enhancement of these reactions is associated to the decrease of ghrelin in plasma after food intake or in individuals with obesity.

MAIN METHODS

we performed an intervention cross-sectional study, in which levels of ghrelin, desacyl-ghrelin (DAG), glucose, insulin, ghrelin des-acylation and ghrelin proteolysis were assessed in plasma before and after a test meal in 40 people (n = 21 males) with normal weight (NW, n = 20) or overweight/obesity (OW/OB, n = 20).

KEY FINDINGS

Preprandial ghrelin and DAG levels were lower, whereas preprandial ghrelin proteolysis was ∼4.6-fold higher in plasma of males with OW/OB. In males, ghrelin proteolysis positively correlated with glycemia. Ghrelin and DAG levels were also lower in females with OW/OB, but preprandial ghrelin proteolysis was not different between females with NW or OW/OB. Ghrelin and DAG levels decreased postprandially in males and females, independently of BMI, and ghrelin proteolysis increased postprandially ∼2 folds only in individuals with NW. Ghrelin des-acylation remained unaffected by BMI or feeding status in both sexes.

SIGNIFICANCE

Current study shows that ghrelin proteolysis increases in males with obesity as well as after meal in lean individuals. Therefore, ghrelin proteolysis may be an important checkpoint and, consequently, a putative pharmacological target to control circulating ghrelin levels in humans.

Increased levels of plasma neudesin in adult growth hormone deficiency and their relationship with plasma liver-expressed antimicrobial peptide-2 levels: a cross-sectional study

PURPOSE

Adult growth hormone deficiency (aGHD) is characterized by an altered metabolic profile and increased cardiovascular risk. Neudesin is a newly discovered protein mainly secreted from adipose tissue and brain, under evaluation for its possible activity as a negative regulator of energy expenditure. Liver-expressed antimicrobial peptide (LEAP)-2 is a competitive antagonist of ghrelin on its receptor. An observational cross-sectional study was performed to test the hypothesis that plasma neudesin levels may be modified in aGHD. Given the role played in the energy balance, any possible relationships between neudesin, LEAP-2 and metabolic and anthropometric parameters were evaluated.

SUBJECTS AND METHODS

Thirty-eight patients were included: 18 aGHD patients (7 females and 11 males, aged 59.7 ± 2.6 years, BMI 30.2 ± 2.2 kg/m²); 20 healthy controls (12 females and 8 males, aged 47.1 ± 2.5 years, BMI 24.1 ± 0.9 kg/m²). All patients were evaluated for glucose, insulin, HOMA and QUICKI index, total/LDL/HDL cholesterol, triglycerides, uric acid, and IGF-1. Plasma neudesin, LEAP-2, and ghrelin were measured by ELISA. Fat mass was evaluated by DEXA.

RESULTS

Neudesin levels were significantly higher in aGHD versus controls. We confirmed the finding of significantly lower ghrelin levels and significantly higher LEAP-2/ghrelin ratio in aGHD patients and found a significant direct correlation between neudesin and LEAP-2 levels. A significant direct correlation between neudesin and fat mass percentage was found in the whole population.

CONCLUSION

These results suggest the onset of adaptive responses to an altered metabolic picture in aGHD. The changes in two distinct pathways that modulate food intake and the still limited knowledge about neudesin suggest future developments in this field.

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

PURPOSE

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.

METHOD

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.

RESULTS

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.

CONCLUSION

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.

Prevalence and Characteristics of Prediabetes and Metabolic Syndrome in Seemingly Healthy Persons at a Health Check-Up Clinic

Purpose

This study investigated the prevalence and characteristics of prediabetes (PreDM) and metabolic syndrome (MetS) in seemingly healthy persons attending a health check-up clinic at a tertiary care hospital.

Patients and Methods

This was a cross-sectional study that enrolled 1213 subjects (339 male, 874 female) who underwent an annual health check-up at Siriraj Hospital, Bangkok, Thailand from 2009 to 2019. Factors that independently related to PreDM were analyzed using unconditional logistic regression analysis with adjustments for age, BMI, and gender.

Results

The prevalence of PreDM and MetS was 54.3% and 19.7% respectively. Participants with impaired fasting glucose (IFG) and glycated hemoglobin (HbA_1c) 38.8–46.4 mmol/mol had significantly higher waist circumference (WC) and blood pressure (BP) compared to those with IFG or HbA_1c 38.8–46.4 mmol/mol alone (P < 0.05). Among three PreDM subgroups, the average age was lowest in the HbA_1c 38.8–46.4 mmol/mol subgroup (P < 0.001). PreDM participants with MetS were older (p = 0.03), had higher WC, BP, fasting plasma glucose and serum triglyceride level (all P < 0.001) but had lower serum high-density lipoprotein (HDL) cholesterol level (P < 0.001). Multivariate analysis revealed high MetS score, obesity, and low serum HDL cholesterol level to be independently associated with PreDM with odds ratios of 9.02 (95% confidence interval [CI]: 4.03–20.18), 1.8 (95% CI: 1.07–3.04), and 1.42 (95% CI: 1.02–1.96), respectively.

Conclusion

The prevalence of PreDM and MetS was relatively high in seemingly healthy persons. Distinct PreDM subgroups with or without MetS exhibited diverse clinical and biochemical features suggesting dissimilar pathogenesis.

Sirtuins as therapeutic targets for improving delayed wound healing in diabetes

Sirtuins are a vast family of histone deacetylases, which are NAD⁺ dependent enzymes, consisting of seven members, namely SIRT 1, SIRT 6 and SIRT 7 located within the nucleus, SIRT 2 in the cytoplasm and SIRT 3, SIRT 4, and SIRT 5 in the mitochondria. They have vital roles in regulating various biological functions such as age-related metabolic disorders, inflammation, stress response, cardiovascular and neuronal functions. Delayed wound healing is one of the complication of diabetes, which can lead to lower limb amputation if not treated timely. SIRT 1, 3 and 6 are potent targets for diabetic wound healing. SIRT 1 deficiency reduces recruitment of fibroblasts, macrophages, mast cells, neutrophils to wound site and delays wound healing; negatively expressing MMP-9. The SIRT 1 mediated signalling pathway in diabetic wound healing is the SIRT 1-foxo-C-Myc pathway. On the contrary SIRT 3 deficiency, impairs proliferation and migration of fibroblasts and SIRT 6 deficiency impairs wound closure rate and interrupts the vascular remodelling. This review focuses on the role of sirtuins in improving delayed wound healing in diabetes and its natural modulators with their specific functions towards healing diabetic wounds.

Antibody-Mediated Inhibition of Insulin-Degrading Enzyme Improves Insulin Activity in a Diabetic Mouse Model

Diabetes is a metabolic disease that may lead to different life-threatening complications. While insulin constitutes a beneficial treatment, its use may be limited due to increased degradation and an increase in side effects such as weight gain and hypoglycemia. Small molecule inhibitors to insulin-degrading enzyme (IDE) have been previously suggested as a potential treatment for diabetes through their ability to reduce insulin degradation and thus increase insulin activity. Nevertheless, their tendency to bind to the zinc ion in the catalytic site of IDE may affect other important metalloproteases and limit their clinical use. Here, we describe the isolation of an IDE-specific antibody that specifically inhibits insulin degradation by IDE. Using phage display, we generated a human IDE-specific antibody that binds human and mouse IDE with high affinity and specificity and can differentiate between active IDE to a mutated IDE with reduced catalytic activity in the range of 30 nM. We further assessed the ability of that IDE-inhibiting antibody to improve insulin activity in vivo in an STZ-induced diabetes mouse model. Since human antibodies may stimulate the mouse immune response to generate anti-human antibodies, we reformatted our inhibitory antibody to a “reverse chimeric” antibody that maintained the ability to inhibit IDE in vitro, but consisted of mouse constant regions, for reduced immunogenicity. We discovered that one intraperitoneal (IP) administration of the IDE-specific antibody in STZ-induced diabetic mice improved insulin activity in an insulin tolerance test (ITT) assay and reduced blood glucose levels. Our results suggest that antibody-mediated inhibition of IDE may be beneficial on improving insulin activity in a diabetic environment.

Palmitic and Stearic Acids Inhibit Chaperone-Mediated Autophagy (CMA) in POMC-like Neurons In Vitro

The intake of food with high levels of saturated fatty acids (SatFAs) is associated with the development of obesity and insulin resistance. SatFAs, such as palmitic (PA) and stearic (SA) acids, have been shown to accumulate in the hypothalamus, causing several pathological consequences. Autophagy is a lysosomal-degrading pathway that can be divided into macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA). Previous studies showed that PA impairs macroautophagy function and insulin response in hypothalamic proopiomelanocortin (POMC) neurons. Here, we show in vitro that the exposure of POMC neurons to PA or SA also inhibits CMA, possibly by decreasing the total and lysosomal LAMP2A protein levels. Proteomics of lysosomes from PA- and SA-treated cells showed that the inhibition of CMA could impact vesicle formation and trafficking, mitochondrial components, and insulin response, among others. Finally, we show that CMA activity is important for regulating the insulin response in POMC hypothalamic neurons. These in vitro results demonstrate that CMA is inhibited by PA and SA in POMC-like neurons, giving an overview of the CMA-dependent cellular pathways that could be affected by such inhibition and opening a door for in vivo studies of CMA in the context of the hypothalamus and obesity.

Plasma Levels of Neudesin and Glucose Metabolism in Obese and Overweight Children

Childhood overweight and obesity are among the major health problems of modern times, especially in Western countries, due to their association with increased cardiovascular and cancer risk in adulthood. Neudesin, a recently discovered peptide secreted mainly in the brain and adipose tissue, is being investigated for its possible activity as a negative regulator of energy expenditure. We conducted a cross-sectional observational preliminary study with the aim of testing the hypothesis that plasma levels of neudesin can be modified in obese and overweight children and to evaluate any possible relationship between plasma neudesin levels and metabolic and anthropometric parameters. 34 Children (Tanner's stage 1) were included and divided in two groups according to Cole's criteria. Group A included obese and overweight children (23 patients, 17 females and 6 males, aged 4-10 years); Group B included healthy normal-weight children (11 subjects, 7 females and 4 males, aged 3-10 years). Metabolic (glucose and insulin, total, LDL- and HDL-cholesterol, triglycerides, uric acid) and hormonal (fT3, fT4, TSH, IGF-1, leptin) parameters were evaluated. HOMA-IR and QUICKI index and the area under the curve (AUC) of glucose and insulin after oral glucose load were calculated in obese and overweight children. Neudesin was measured by ELISA. Neudesin levels were significantly higher in obese/overweight children than in controls. In obese and overweight children, plasma neudesin levels were significantly directly correlated with blood glucose and glucose AUC. Taken together, these results, although preliminary, may suggest a possible age-related role of neudesin in glucose homeostasis in obese/overweight children.

Effects of Fasting and Feeding on Transcriptional and Posttranscriptional Regulation of Insulin-Degrading Enzyme in Mice

Insulin-degrading enzyme (IDE) is a highly conserved and ubiquitously expressed Zn²⁺-metallopeptidase that regulates hepatic insulin sensitivity, albeit its regulation in response to the fasting-to-postprandial transition is poorly understood. In this work, we studied the regulation of IDE mRNA and protein levels as well as its proteolytic activity in the liver, skeletal muscle, and kidneys under fasting (18 h) and refeeding (30 min and 3 h) conditions, in mice fed a standard (SD) or high-fat (HFD) diets. In the liver of mice fed an HFD, fasting reduced IDE protein levels (~30%); whereas refeeding increased its activity (~45%) in both mice fed an SD and HFD. Likewise, IDE protein levels were reduced in the skeletal muscle (~30%) of mice fed an HFD during the fasting state. Circulating lactate concentrations directly correlated with hepatic IDE activity and protein levels. Of note, L-lactate in liver lysates augmented IDE activity in a dose-dependent manner. Additionally, IDE protein levels in liver and muscle tissues, but not its activity, inversely correlated (R² = 0.3734 and 0.2951, respectively; p < 0.01) with a surrogate marker of insulin resistance (HOMA index). Finally, a multivariate analysis suggests that circulating insulin, glucose, non-esterified fatty acids, and lactate levels might be important in regulating IDE in liver and muscle tissues. Our results highlight that the nutritional regulation of IDE in liver and skeletal muscle is more complex than previously expected in mice, and that fasting/refeeding does not strongly influence the regulation of renal IDE.

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.

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.