Different impacts of acylated and non-acylated long-acting insulin analogs on neural functions in vitro and in vivo

C-terminal peptide of preproorexin enhances brain-derived neurotrophic factor expression in rat cerebrocortical cells and recognition memory in mice

During the production of orexin A and B from preproorexin, a common precursor protein, in hypothalamic orexin neurons, C-terminal peptide (herein called preproorexin C-peptide) is concomitantly produced via post-translational processing. The predicted three-dimensional structure of preproorexin C-peptide is similar among mammalian species, suggestive of a conserved function in the mammalian brain. However, C-peptide has long been regarded as a non-functional peptide. We herein examined the effects of rat and/or mouse preproorexin C-peptide on gene expression and cell viability in cultured rat cerebrocortical cells and on memory behavior in C57BL/6J mice. Rat and mouse C-peptides both increased brain-derived neurotrophic factor (Bdnf) mRNA levels. Moreover, C-peptide enhanced high K+-, glutamate-, and BDNF-induced increases in Bdnf mRNA levels without affecting forskolin-induced Bdnf expression. H-89, a protein kinase A inhibitor, blocked C-peptide-induced Bdnf expression, whereas rolipram, a phosphodiesterase inhibitor, enhanced this effect. Intracellular cyclic AMP concentrations were elevated by C-peptide. These results demonstrate that preproorexin C-peptide promoted Bdnf mRNA expression by a cyclic AMP-dependent mechanism. Eleven amino acids at the N terminus of rat preproorexin C-peptide exerted similar effects on Bdnf expression as full-length preproorexin C-peptide. Preproorexin C-peptide also exerted protective effects against CoCl2-induced neuronal cell death. An intracerebroventricular injection of mouse preproorexin C-peptide induced c-fos and Bdnf expression in the cerebral cortex and hippocampus and enhanced novel object recognition memory in mice. Collectively, the present results show that preproorexin C-peptide is a functional substance, at least in some pharmacological and neuronal settings.

Resting phase-administration of lemborexant ameliorates sleep and glucose tolerance in type 2 diabetic mice

Sleep disorders are associated with increased risk of obesity and type 2 diabetes. Lemborexant, a dual orexin receptor antagonist (DORA), is clinically used to treat insomnia. However, the influence of lemborexant on sleep and glucose metabolism in type 2 diabetic state has remained unknown. In the present study, we investigated the effect of lemborexant in type 2 diabetic db/db mice exhibiting both sleep disruption and glucose intolerance. Single administration of lemborexant at the beginning of the light phase (i.e., resting phase) acutely increased total time spent in non-rapid eye movement (NREM) and REM sleep in db/db mice. Durations of NREM sleep-, REM sleep-, and wake-episodes were also increased by this administration. Daily resting-phase administration of lemborexant for 3-6 weeks improved glucose tolerance without changing body weight and glucose-stimulated insulin secretion in db/db mice. Similar improvement of glucose tolerance was caused by daily resting-phase administration of lemborexant in obese C57BL/6J mice fed high fat diet, whereas no such effect was observed in non-diabetic db/m+ mice. Diabetic db/db mice treated daily with lemborexant exhibited increased locomotor activity in the dark phase (i.e., awake phase), although they did not show any behavioral abnormality in the Y-maze, elevated plus maze, and forced swim tests. These results suggest that timely promotion of sleep by lemborexant improved the quality of wakefulness in association with increased physical activity during the awake phase, and these changes may underlie the amelioration of glucose metabolism under type 2 diabetic conditions.

Food odor perception promotes systemic lipid utilization

Food cues during fasting elicit Pavlovian conditioning to adapt for anticipated food intake. However, whether the olfactory system is involved in metabolic adaptations remains elusive. Here we show that food-odor perception promotes lipid metabolism in male mice. During fasting, food-odor stimulation is sufficient to increase serum free fatty acids via adipose tissue lipolysis in an olfactory-memory-dependent manner, which is mediated by the central melanocortin and sympathetic nervous systems. Additionally, stimulation with a food odor prior to refeeding leads to enhanced whole-body lipid utilization, which is associated with increased sensitivity of the central agouti-related peptide system, reduced sympathetic activity and peripheral tissue-specific metabolic alterations, such as an increase in gastrointestinal lipid absorption and hepatic cholesterol turnover. Finally, we show that intermittent fasting coupled with food-odor stimulation improves glycemic control and prevents insulin resistance in diet-induced obese mice. Thus, olfactory regulation is required for maintaining metabolic homeostasis in environments with either an energy deficit or energy surplus, which could be considered as part of dietary interventions against metabolic disorders.

New Horizons: Next-Generation Insulin Analogues: Structural Principles and Clinical Goals

Design of "first-generation" insulin analogues over the past 3 decades has provided pharmaceutical formulations with tailored pharmacokinetic (PK) and pharmacodynamic (PD) properties. Application of a molecular tool kit-integrating protein sequence, chemical modification, and formulation-has thus led to improved prandial and basal formulations for the treatment of diabetes mellitus. Although PK/PD changes were modest in relation to prior formulations of human and animal insulins, significant clinical advantages in efficacy (mean glycemia) and safety (rates of hypoglycemia) were obtained. Continuing innovation is providing further improvements to achieve ultrarapid and ultrabasal analogue formulations in an effort to reduce glycemic variability and optimize time in range. Beyond such PK/PD metrics, next-generation insulin analogues seek to exploit therapeutic mechanisms: glucose-responsive ("smart") analogues, pathway-specific ("biased") analogues, and organ-targeted analogues. Smart insulin analogues and delivery systems promise to mitigate hypoglycemic risk, a critical barrier to glycemic control, whereas biased and organ-targeted insulin analogues may better recapitulate physiologic hormonal regulation. In each therapeutic class considerations of cost and stability will affect use and global distribution. This review highlights structural principles underlying next-generation design efforts, their respective biological rationale, and potential clinical applications.

Structural principles of insulin formulation and analog design: A century of innovation

BACKGROUND

The discovery of insulin in 1921 and its near-immediate clinical use initiated a century of innovation. Advances extended across a broad front, from the stabilization of animal insulin formulations to the frontiers of synthetic peptide chemistry, and in turn, from the advent of recombinant DNA manufacturing to structure-based protein analog design. In each case, a creative interplay was observed between pharmaceutical applications and then-emerging principles of protein science; indeed, translational objectives contributed to a growing molecular understanding of protein structure, aggregation and misfolding.

SCOPE OF REVIEW

Pioneering crystallographic analyses-beginning with Hodgkin's solving of the 2-Zn insulin hexamer-elucidated general features of protein self-assembly, including zinc coordination and the allosteric transmission of conformational change. Crystallization of insulin was exploited both as a step in manufacturing and as a means of obtaining protracted action. Forty years ago, the confluence of recombinant human insulin with techniques for site-directed mutagenesis initiated the present era of insulin analogs. Variant or modified insulins were developed that exhibit improved prandial or basal pharmacokinetic (PK) properties. Encouraged by clinical trials demonstrating the long-term importance of glycemic control, regimens based on such analogs sought to resemble daily patterns of endogenous β-cell secretion more closely, ideally with reduced risk of hypoglycemia.

MAJOR CONCLUSIONS

Next-generation insulin analog design seeks to explore new frontiers, including glucose-responsive insulins, organ-selective analogs and biased agonists tailored to address yet-unmet clinical needs. In the coming decade, we envision ever more powerful scientific synergies at the interface of structural biology, molecular physiology and therapeutics.

Metabolic and sympathovagal effects of bolus insulin glulisine versus basal insulin glargine therapy in people with type 2 diabetes: A randomized controlled study

AIMS/INTRODUCTION

This study compares the effects of two different insulin regimens - basal versus bolus insulin - on metabolic and cardiovascular autonomic function in Japanese participants with type 2 diabetes.

MATERIALS AND METHODS

Participants were randomly assigned to groups for therapy with insulin glulisine (IGlu) or insulin glargine (IGla). The primary efficacy end-point was glycemic variability, including M-values, mean of glucose levels, and a blood glucose profile of seven time points before and after the intervention. The secondary end-points included pleiotropic effects, including endothelial and cardiac autonomic nerve functions.

RESULTS

Blood glucose levels at all time points significantly decreased in both groups. Post-lunch, post-dinner, and bedtime blood glucose levels were significantly lower in the IGlu group than in the IGla group. Nadir fasting blood glucose levels at the end-point were significantly lower in the IGla group than in the IGlu group. The M-value and mean blood glucose levels were significantly decreased from baseline in both groups, although the former was significantly lower in the IGlu group than in the IGla group. IGla, but not IGlu, was found to elevate 24-h parasympathetic tone, especially during night-time, and it decreased 24-h sympathetic nerve activity, especially at dawn.

CONCLUSIONS

Both IGlu and IGla regimens reduced glucose variability, with IGlu bringing a greater reduction in M-value. IGla, but not IGlu, increased parasympathetic tone during night-time and decreased sympathetic nerve activity at dawn. These findings shed light on the previously unrecognized role of night-time basal insulin supplementation on sympathovagal activity in type 2 diabetes patients.

Meta-analysis of cognitive and behavioral tests in leptin- and leptin receptor-deficient mice

Leptin is a hormone produced by adipocytes that regulates food intake and metabolism. Leptin-related gene-deficient mice, such as db/db and ob/ob mice, are widely used to study diabetes and its related diseases. However, broad effects of leptin appear to cause variability in behavioral test results. We performed a meta-analysis of major behavioral tests in db/db and ob/ob mice. These mice exhibited significant impairments in the Morris water maze, forced swim, novel object recognition, Y-maze, tail suspension, and light-dark box tests, whereas the elevated plus maze and open field tests did not reveal significant changes. We also performed correlation and regression analyses between the animals' performances and the experimental protocols and conditions. The memory-related tests were characterized by the correlations of their results with animal age, while the performances in the elevated plus-maze and forced swim tests were affected by the width of the devices used. In conclusion, db/db and ob/ob mice mainly exhibit memory deficits and depression-like behavior, although experimenters should be aware of animal age and device size in conducting experiments.

Diabetes and dementia - the two faces of Janus

Patients with type 2 diabetes are at high risk for cognitive decline and dementia. Despite the limited data on the possible pathogenetic mechanisms, evidence suggests that cognitive decline, and thus dementia and Alzheimer’s disease, might arise from a complex interplay between type 2 diabetes and the aging brain, including decreased insulin signalling and glucose metabolism, mitochondrial dysfunction, neuroinflammation, and vascular disease. Furthermore, there is increasing interest on the effects of antidiabetic agents on cognitive decline. There are many studies showing that antidiabetic agents might have beneficial effects on the brain, mainly through inhibition of oxidative stress, inflammation, and apoptosis. In addition, experimental studies on patients with diabetes and Alzheimer’s disease have shown beneficial effects on synaptic plasticity, metabolism of amyloid-β, and microtubule-associated protein tau. Therefore, in the present review, we discuss the effects of antidiabetic agents in relation to cognitive decline, and in particular dementia and Alzheimer’s disease, in patients with type 2 diabetes.

Potential role of insulin on the pathogenesis of depression

The regulation of insulin on depression and depression-like behaviour has been widely reported. Insulin and activation of its receptor can promote learning and memory, affect the hypothalamic-pituitary-adrenal axis (HPA) balance, regulate the secretion of neurotrophic factors and neurotransmitters, interact with gastrointestinal microbiome, exert neuroprotective effects and have an impact on depression. However, the role of insulin on depression remains largely unclear. Therefore, in this review, we summarized the potential role of insulin on depression. It may provide new insight for clarifying role of insulin on the pathogenesis of depression.

Antidiabetic treatment on memory and spatial learning: From the pancreas to the neuron

The detrimental effects of constant hyperglycemia on neural function have been quantitatively and qualitatively evaluated in the setting of diabetes mellitus. Some of the hallmark features of diabetic encephalopathy (DE) are impaired synaptic adaptation and diminished spatial learning capacity. Chronic and progressive cognitive dysfunction, perpetuated by several positive feedback mechanisms in diabetic subjects, facilitates the development of early-onset dementia and Alzheimer's disease. Despite the numerous clinical manifestations of DE having been described in detail and their pathophysiological substrate having been elucidated in both type 1 and type 2 diabetes mellitus, an effective therapeutic approach is yet to be proposed. Therefore, the aim of this review is to summarize the growing body of evidence concerning the effect of current antidiabetic treatment options on diabetic and non-DE.