Overexpression of Insulin Degrading Enzyme could Greatly Contribute to Insulin Down-regulation Induced by Short-Term Swimming Exercise

Exercise and inactivity as modifiers of β cell function and type 2 diabetes risk

Exercise and regular physical activity are beneficial for the prevention and management of metabolic diseases such as obesity and type 2 diabetes, whereas exercise cessation, defined as deconditioning from regular exercise or physical activity that has lasted for a period of months to years, can lead to metabolic derangements that drive disease. Adaptations to the insulin-secreting pancreatic β-cells are an important benefit of exercise, whereas less is known about how exercise cessation affects these cells. Our aim is to review the impact that exercise and exercise cessation have on β-cell function, with a focus on the evidence from studies examining glucose-stimulated insulin secretion (GSIS) using gold-standard techniques. Potential mechanisms by which the β-cell adapts to exercise, including exerkine and incretin signaling, autonomic nervous system signaling, and changes in insulin clearance, will also be explored. We will highlight areas for future research.

The Effect of Melatonin and Exercise on Social Isolation-Related Behavioral Changes in Aged Rats

Social isolation (SI) is well established as an environmental factor that negatively influences different behavioral parameters, including cognitive function, anxiety, and social interaction, depending on the age of isolation. Aging is a physiological process that is associated with changes in cognitive function, locomotor activity, anxiety and emotional responses. Few studies have investigated the effect of SI in senescence, or possible interventions. In the current study, we investigated the possible complementary effects of melatonin (MLT) and exercise (Ex) in improving SI-related behavioral changes in aged rats. Forty aged Wistar rats (24 months old) were randomly divided into five groups (n = 8 per group): Control (group housing), SI (individual housing for 7 weeks), SI + MLT (SI rats treated with 0.4 mg MLT/ml in drinking water), SI + Ex (SI rats treated with 60 min of swimming), and SI + MLT + Ex (SI rats treated with both MLT and Ex). Different behavioral tasks were conducted in the following sequence: open field test, elevated plus maze test, sucrose preference test, Y maze test, and Morris water maze test. Locomotor activities measured by total distance moved and velocity revealed that SI + Ex (P = 0.0038; P = 0.0015) and SI + MLT + Ex (P = 0.0001; P = 0.0003) significantly improved the locomotor activity compared with SI rats but SI + MLT (P = 0.0599; P = 0.0627) rats showed no significant change. Anxiety index score was significantly improved in SI + MLT + Ex (P = 0.0256) compared with SI rats while SI + MLT (P > 0.9999) and SI + Ex (P = 0.2943) rats showed no significant change. Moreover, latency to reach the platform in Morris water maze was significantly reduced at day 5 in SI + MLT + Ex (P = 0.0457) compared with SI rats but no change was detected in SI + MLT (P = 0.7314) or SI + Ex (P = 0.1676) groups. In conclusion, this study supports the possible potential of MLT in combination with Ex in improving physical activity, anxiety, and cognitive functions in aging population.

Reviewing physical exercise in non-obese diabetic Goto-Kakizaki rats

There is a high incidence of non-obese type 2 diabetes mellitus (non-obese-T2DM) cases, particularly in Asian countries, for which the pathogenesis remains mainly unclear. Interestingly, Goto-Kakizaki (GK) rats spontaneously develop insulin resistance (IR) and non-obese-T2DM, making them a lean diabetes model. Physical exercise is a non-pharmacological therapeutic approach to reduce adipose tissue mass, improving peripheral IR, glycemic control, and quality of life in obese animals or humans with T2DM. In this narrative review, we selected and analyzed the published literature on the effects of physical exercise on the metabolic features associated with non-obese-T2DM. Only randomized controlled trials with regular physical exercise training, freely executed physical activity, or skeletal muscle stimulation protocols in GK rats published after 2008 were included. The results indicated that exercise reduces plasma insulin levels, increases skeletal muscle glycogen content, improves exercise tolerance, protects renal and myocardial function, and enhances blood oxygen flow in GK rats.

Aging Reduces Insulin Clearance in Mice

Hyperinsulinemia is frequently associated with aging and may cause insulin resistance in elderly. Since insulin secretion and clearance decline with age, hyperinsulinemia seems to be maintained, primarily, due to a decrease in the insulin clearance. To investigate these aging effects, 3- and 18-month-old male C57BL/6 mice were subjected to intraperitoneal glucose and insulin tolerance tests (ipGTT and ipITT) and, during the ipGTT, plasma c-peptide and insulin were measure to evaluate in vivo insulin clearance. Glucose-stimulated insulin secretion in isolated pancreatic islets was also assessed, and liver samples were collected for molecular analyses (western blot). Although insulin sensitivity was not altered in the old mice, glucose tolerance, paradoxically, seems to be increased, accompanied by higher plasma insulin, during ipGTT. While insulin secretion did not increase, insulin clearance was reduced in the old mice, as suggested by the lower c-peptide:insulin ratio, observed during ipGTT. Carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) and insulin-degrading enzyme (IDE), as well as the activity of this enzyme, were reduced in the liver of old mice, justifying the decreased insulin clearance observed in these mice. Therefore, loss of hepatic CEACAM1 and IDE function may be directly related to the decline in insulin clearance during aging.

Low fasting serum insulin and dementia in nondiabetic women followed for 34 years

Objective

In a representative population of women followed over 34 years, we investigated the prospective association between fasting serum insulin and dementia, taking into account the incidence of diabetes mellitus.

Methods

Fasting values for serum insulin and blood glucose were obtained in 1,212 nondiabetic women 38 to 60 years of age at the 1968 baseline. Risk of dementia was assessed by Cox proportional hazard regression with adjustment for insulin, glucose, and other covariates and, in a second model, after censoring for incident cases of diabetes mellitus. Incident diabetes mellitus was considered as a third endpoint for comparison with dementia.

Results

Over 34 years, we observed 142 incident cases of dementia. The low tertile of insulin displayed excess risk for dementia (hazard ratio [HR] 2.34, 95% confidence interval [CI] 1.52–3.58) compared to the medium tertile, but the high tertile of insulin did not (HR 1.28, 95% CI 0.81–2.03). These associations were also seen for dementia without diabetes comorbidity. In contrast, high but not low insulin predicted incident diabetes mellitus (115 cases) (HR 1.70, 95% CI 1.08–2.68 and HR 0.76, 95% CI 0.43–1.37, respectively).

Conclusion

A previous study reported a U-shaped association between fasting insulin and dementia in a 5-year follow-up of elderly men. Our results confirmed a nonlinear association in a female population, with high risk at low insulin values that was not attributable to preclinical dementia or impaired insulin secretion. This condition suggests a new pathway to dementia, which differs from the metabolic pathway involving diabetes mellitus.

Physical activity and beta-amyloid pathology in Alzheimer's disease: A sound mind in a sound body

Alzheimer's disease (AD) is the most common type of dementia worldwide. Since curative treatment has not been established for AD yet and due to heavy financial and psychological costs of patients' care, special attention has been paid to preventive interventions such as physical activity. Evidence shows that physical activity has protective effects on cognitive function and memory in AD patients. Several pathologic factors are involved in AD-associated cognitive impairment some of which are preventable by physical activity. Also, various experimental and clinical studies are in progress to prove exercise role in the beta-amyloid (Aβ) pathology as a most prevailing hypothesis explaining AD pathogenesis. This study aims to review the role of physical activity in Aβ-related pathophysiology in AD.

Bioactivity of food peptides: biological response of rats to bovine milk whey peptides following acute exercise

Background: Several physiologically beneficial effects of consuming a whey protein hydrolysate (WPH) have been attributed to the greater availability of bioactive peptides.

Aims: The aim was to investigate the effect of four branched-chain amino acid- (BCAA-)containing dipeptides, present in WPH, on immune modulation, stimulation of HSP expression, muscle protein synthesis, glycogen content, satiety signals and the impact of these peptides on the plasma free amino acid profiles.

Methods: The animals were divided in groups: control (rest, without gavage), vehicle (water), L-isoleucyl-L-leucine (lle-Leu), L-leucyl-L-isoleucine (Leu-lle), L-valyl-Lleucine (Val-Leu), L-leucyl-L-valine (Leu-Val) and WPH. All animals were submitted to acute exercise, except for control.

Results: lle-Leu stimulated immune response, hepatic and muscle glycogen and HSP60 expression, whereas Leu-Val enhanced HSP90 expression. All dipeptides reduced glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, no changes were observed on leptin. All peptides inhibited NF-kB expression. The plasma amino acid time-course showed peptide-specific and isomer-specific metabolic features, including increases of the BCAAs.

Conclusion: The data indicate that lle-Leu was effective to attenuate immune-suppression exercise-induced, promoted glycogen content and stimulated anti-stress effect (HSP). Furthermore, Leu-Val increased HSP90, p-4EBP1, p-mTOR and p-AMPK expression. The data suggest the involvement of these peptides in various beneficial functions of WPH consumption.

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.