Central regulation of glucose metabolism in an insulin-dependent and -independent manner

Nanoparticle and microparticle-based systems for enhanced oral insulin delivery: A systematic review and meta-analysis

Diabetes mellitus (DM) prevalence is rising worldwide. Current therapies comprising subcutaneous insulin injections can cause adverse effects such as lipodystrophy, local reactions like redness and swelling, fluid retention, and allergic reactions. Nanoparticle carriers for oral insulin are groundbreaking compared to existing methods because they are non-invasive treatments, showing operational convenience, controlled release profile, and ability to simulate the physiological delivery route into the bloodstream. These systems improve patient adherence and have demonstrated the potential to lower blood glucose levels in DM. We present a systematic review and meta-analysis aimed at compiling relevant data to pave the way for developing innovative nano- and microparticles for the oral delivery of insulin. Our analysis of 85 articles revealed that the diminution of glucose levels is not proportional to the administered insulin dosage, which ranged from 1 to 120 International Units (IU). The meta-analysis data indicated that 25 IU of encapsulated porcine insulin did not produce a statistically significant outcome (p = 0.93). In contrast, a dosage of 30 IU was efficacious in eliciting an optimal hypoglycemic effect compared to excipient controls. Parameters such as a high degree of encapsulation (~ 90%), particle size (200-400 nm), and polydispersity index (0.086-0.3) are all associated with lower blood glucose levels. These parameters were also significant in the linear regression analysis. Among the excipients employed, chitosan emerged as a prevalent excipient in formulations due to its biocompatible and biodegradable properties and its ability to establish stable polymeric matrices. Even though oral insulin administration is a promising therapeutic method, it cannot guarantee preclinical safety and therapeutic efficacy yet in regulating glucose levels in diabetic conditions.

Leptin Rs7799039 polymorphism is associated with type 2 diabetes mellitus Egyptian patients

BACKGROUND

Leptin (LEP) is an anti-obesity hormone that regulates food intake, energy expenditure, and glucose metabolism. The genetic variants in LEP and the LEP receptor (LEPR) gene may play an important role in the pathogenesis of type 2 diabetes mellitus (T2DM) and obesity. The current study aimed to investigate the association of serum LEP levels, and LEP polymorphisms in LEP (rs7799039, 2548 G/A) with T2DM in Egyptian patients.

METHODS

A total of 205 subjects were included in the present case-control study, consisting of 100 T2DM patients and 105 healthy controls. The anthropometric, psychometric, and biochemical measurements were taken from all the subjects. The genotyping of LEP gene variants was carried out by polymerase chain reaction TaqMan technology. Serum LEP levels were measured by the ELISA technique.

RESULTS

T2DM patients had significantly elevated levels of glycated haemoglobin (HbA1c), fasting blood sugar (FBS), postprandial blood sugar (PPBS), international normalisation ratio (INR), creatinine, urea, cholesterol, triglyceride (TG), and low-density lipoproteins (LDL) and significantly decreased high-density lipoprotein (HDL) compared to healthy subjects. serum LEP levels were significantly decreased p (<0.001) as compared to the control group. LEP gene SNP rs7799039 was associated with an increased diabetic risk with A allele being more frequent in T2DM patients than control subjects. The distribution of the AA genotype and GA genotype of LEP SNP rs7799039 was higher in the diabetic group than control one. In addition, AA + GA genotype carriers had significantly elevated HbA1c, FBS, PPBS, TG, and LDL levels and on the contrary, decreased serum LEP levels compared to GG homozygotes.

CONCLUSION

The genetic polymorphism rs7799039 showed a highly significant correlation with blood LEP. The co-dominant and dominant models of the LEP genetic polymorphism (rs7799039, 2548 G/A) were shown to have a significant correlation with complicated and uncomplicated diabetes individuals, but we have found that serum LEP levels were inversely related with control and diabetes patients. A positive significant association was found between LEP genetic polymorphism (rs7799039, 2548 G/A) and serum LEP in patients and controls. LEP levels and its rs7799039 genetic variant may play a vital role in increasing T2DM susceptibility.

Insulin resistance as the molecular link between diabetes and Alzheimer's disease

Diabetes mellitus (DM) and Alzheimer's disease (AD) are two major health concerns that have seen a rising prevalence worldwide. Recent studies have indicated a possible link between DM and an increased risk of developing AD. Insulin, while primarily known for its role in regulating blood sugar, also plays a vital role in protecting brain functions. Insulin resistance (IR), especially prevalent in type 2 diabetes, is believed to play a significant role in AD's development. When insulin signalling becomes dysfunctional, it can negatively affect various brain functions, making individuals more susceptible to AD's defining features, such as the buildup of beta-amyloid plaques and tau protein tangles. Emerging research suggests that addressing insulin-related issues might help reduce or even reverse the brain changes linked to AD. This review aims to explore the rela-tionship between DM and AD, with a focus on the role of IR. It also explores the molecular mechanisms by which IR might lead to brain changes and assesses current treatments that target IR. Understanding IR's role in the connection between DM and AD offers new possibilities for treatments and highlights the importance of continued research in this interdisciplinary field.

Adult-Onset CNS Sulfatide Deficiency Causes Sex-Dependent Metabolic Disruption in Aging

The interconnection between obesity and central nervous system (CNS) neurological dysfunction has been widely appreciated. Accumulating evidence demonstrates that obesity is a risk factor for CNS neuroinflammation and cognitive impairment. However, the extent to which CNS disruption influences peripheral metabolism remains to be elucidated. We previously reported that myelin-enriched sulfatide loss leads to CNS neuroinflammation and cognitive decline. In this study, we further investigated the impact of CNS sulfatide deficiency on peripheral metabolism while considering sex- and age-specific effects. We found that female sulfatide-deficient mice gained significantly more body weight, exhibited higher basal glucose levels, and were glucose-intolerant during glucose-tolerance test (GTT) compared to age-matched controls under a normal diet, whereas male sulfatide-deficient mice only displayed glucose intolerance at a much older age compared to female sulfatide-deficient mice. Mechanistically, we found that increased body weight was associated with increased food intake and elevated neuroinflammation, especially in the hypothalamus, in a sex-specific manner. Our results suggest that CNS sulfatide deficiency leads to sex-specific alterations in energy homeostasis via dysregulated hypothalamic control of food intake.

Long-Term Effects of Anxiety on the Metabolic Control of Recently Diagnosed Type 2 Diabetes Patients: Results from the CAIPaDi Cohort Study

INTRODUCTION

Anxiety disorders (AXD) are among the most prevalent mental health conditions in patients with type 2 diabetes (T2D). Previous data have established an association of other psychiatric conditions with poor metabolic control and increased odds of diabetes-related complications. Nonetheless, follow-up information about the effects of AXD on the metabolic control of patients with TD2 is still limited.

OBJECTIVE

Evaluate the effects of AXD on the metabolic parameters of patients with T2D over 12 months of follow-up in a multidisciplinary comprehensive care model.

METHODS

Prospective study of T2D subjects enrolled in a comprehensive care program with follow-up at 3 and 12 months of treatment. Patients were assessed using the Mini-International Neuropsychiatric Interview and the Hospital Anxiety and Depression Scale (HADS). We registered clinical and metabolic characteristics from each visit. Metabolic parameters over time were analyzed with a mixed model of repeated measures using AXD and time as interaction variables.

RESULTS

Our sample included 2703 patients at baseline, and 1161 (43%) subjects continued the follow-up at 12 months. The AXD group had more females, lower age, and fewer years of formal education compared with subjects without AXD at baseline, 3 and 12 months. Patients with AXD also reported higher mean fasting glucose at three months, and higher HbA1c at three and 12 months. Our MMRM for HbA1c reported significant differences over time in subjects with and without AXD. The differences in means between groups increased from 0.17% at three months to 0.31% at 12 months. The variables from the HADS anxiety score, sex, age, years of diagnosis, and insulin treatment were also associated with HbA1c parameters over time.

CONCLUSION

Patients with AXD had the worst glycemic control at 3 and 12 months of follow-up. HbA1c differences in patients with AXD compared with non-AXD subjects increases over time in association with anxiety symptoms.

Central NPFF signalling is critical in the regulation of glucose homeostasis

OBJECTIVE

Neuropeptide FF (NPFF) group peptides belong to the evolutionary conserved RF-amide peptide family. While they have been assigned a role as pain modulators, their roles in other aspects of physiology have received much less attention. NPFF peptides and their receptor NPFFR2 have strong and localized expression within the dorsal vagal complex that has emerged as the key centre for regulating glucose homeostasis. Therefore, we investigated the role of the NPFF system in the control of glucose metabolism and the histochemical and molecular identities of NPFF and NPFFR2 neurons.

METHODS

We examined glucose metabolism in Npff^-/- and wild type (WT) mice using intraperitoneal (i.p.) glucose tolerance and insulin tolerance tests. Body composition and glucose tolerance was further examined in mice after 1-week and 3-week of high-fat diet (HFD). Using RNAScope double ISH, we investigated the neurochemical identity of NPFF and NPFFR2 neurons in the caudal brainstem, and the expression of receptors for peripheral factors in NPFF neurons.

RESULTS

Lack of NPFF signalling in mice leads to improved glucose tolerance without significant impact on insulin excursion after the i.p. glucose challenge. In response to an i.p. bolus of insulin, Npff^-/- mice have lower glucose excursions than WT mice, indicating an enhanced insulin action. Moreover, while HFD has rapid and potent detrimental effects on glucose tolerance, this diet-induced glucose intolerance is ameliorated in mice lacking NPFF signalling. This occurs in the absence of any significant impact of NPFF deletion on lean or fat masses, suggesting a direct effect of NPFF signalling on glucose metabolism. We further reveal that NPFF neurons in the subpostrema area (SubP) co-express receptors for peripheral factors involved in glucose homeostasis regulation such as insulin and GLP1. Furthermore, Npffr2 is expressed in the glutamatergic NPFF neurons in the SubP, and in cholinergic neurons of the dorsal motor nucleus of the vagus (DMV), indicating that central NPFF signalling is likely modulating vagal output to innervated peripheral tissues including those important for glucose metabolic control.

CONCLUSIONS

NPFF signalling plays an important role in the regulation of glucose metabolism. NPFF neurons in the SubP are likely to receive peripheral signals and mediate the control of whole-body glucose homeostasis via centrally vagal pathways. Targeting NPFF and NPFFR2 signalling may provide a new avenue for treating type 2 diabetes and obesity.

The ventromedial hypothalamic nucleus: watchdog of whole-body glucose homeostasis

The brain, particularly the ventromedial hypothalamic nucleus (VMH), has been long known for its involvement in glucose sensing and whole-body glucose homeostasis. However, it is still not fully understood how the brain detects and responds to the changes in the circulating glucose levels, as well as brain-body coordinated control of glucose homeostasis. In this review, we address the growing evidence implicating the brain in glucose homeostasis, especially in the contexts of hypoglycemia and diabetes. In addition to neurons, we emphasize the potential roles played by non-neuronal cells, as well as extracellular matrix in the hypothalamus in whole-body glucose homeostasis. Further, we review the ionic mechanisms by which glucose-sensing neurons sense fluctuations of ambient glucose levels. We also introduce the significant implications of heterogeneous neurons in the VMH upon glucose sensing and whole-body glucose homeostasis, in which sex difference is also addressed. Meanwhile, research gaps have also been identified, which necessities further mechanistic studies in future.

LEAP2 reduces postprandial glucose excursions and ad libitum food intake in healthy men

The gastric hormone ghrelin stimulates food intake and increases plasma glucose through activation of the growth hormone secretagogue receptor (GHSR). Liver-expressed antimicrobial peptide 2 (LEAP2) has been proposed to inhibit actions of ghrelin through inverse effects on GHSR activity. Here, we investigate the effects of exogenous LEAP2 on postprandial glucose metabolism and ad libitum food intake in a randomized, double-blind, placebo-controlled, crossover trial of 20 healthy men. We report that LEAP2 infusion lowers postprandial plasma glucose and growth hormone concentrations and decreases food intake during an ad libitum meal test. In wild-type mice, plasma glucose and food intake are reduced by LEAP2 dosing, but not in GHSR-null mice, pointing to GHSR as a potential mediator of LEAP2’s glucoregulatory and appetite-suppressing effects in mice.

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Exogenous LEAP2 lowers postprandial plasma glucose excursions

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Exogenous LEAP2 suppresses ad libitum food intake

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During fasting, exogenous LEAP2 increases insulin secretion and suppresses lipolysis

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The GHSR is required for eliciting LEAP2 effects in mice

Chronic Antidiabetic Actions of Leptin: Evidence From Parabiosis Studies for a CNS-Derived Circulating Antidiabetic Factor

We used parabiosis to determine whether the central nervous system (CNS)-mediated antidiabetic effects of leptin are mediated by release of brain-derived circulating factors. Parabiosis was surgically induced at 4 weeks of age, and an intracerebroventricular (ICV) cannula was placed in the lateral cerebral ventricle at 12 weeks of age for ICV infusion of leptin or saline vehicle. Ten days after surgery, food intake, body weight, and blood glucose were measured for 5 consecutive days, and insulin-deficiency diabetes was induced in all rats by a single streptozotocin (STZ) injection (40 mg/kg). Five days after STZ injection, leptin or vehicle was infused ICV for 7 days, followed by 5-day recovery period. STZ increased blood glucose and food intake. Chronic ICV leptin infusion restored normoglycemia in leptin-infused rats while reducing blood glucose by ∼27% in conjoined vehicle-infused rats. This glucose reduction was caused mainly by decreased hepatic gluconeogenesis. Chronic ICV leptin infusion also reduced net cumulative food intake and increased GLUT4 expression in skeletal muscle in leptin/vehicle compared with vehicle/vehicle conjoined rats. These results indicate that leptin's CNS-mediated antidiabetic effects are mediated, in part, by release into the systemic circulation of leptin-stimulated factors that enhance glucose utilization and reduce liver gluconeogenesis.