Insulin action in brain regulates systemic metabolism and brain function

Okra-supplemented diet prevents hypothalamic inflammation in early overfeeding-programmed obese rats

BACKGROUND

Early overnutrition programs long-term metabolic dysfunctions. Owing to their benefits, functional foods have been used to treat metabolic diseases. We aimed to test the hypothesis that a diet supplemented with okra (Abelmoschus esculentus L.) mitigates energy metabolism impairment and glucose dyshomeostasis in early overfeeding-programmed rat offspring.

METHODS

At postnatal Day 3, the litters were adjusted to 3 (small litter, SL) or 8 (normal litter, NL) pups. During lactation, milk collection and milk intake were performed. At 22 days-old, the pups were weaned and fed a standard diet (NL-SD and SL-SD groups) or an okra-supplemented diet (1.5 % A. esculentus; NL-AE and SL-AE groups). Body weight and food and water intake were measured every two days. Intraperitoneal glucose tolerance and intracerebroventricular insulin (10-3 mmol/L) tests were performed, and then the offspring were euthanized. Blood, hypothalamus, and visceral fat pads were collected and lean body mass was measured.

RESULTS

Milk from SL mothers had higher triglyceride and energy contents (P < 0.05), and milk consumption by SL offspring was greater than that by NL rats. SL-SD rats were obese, hyperphagic, hypertriglyceridemic, hyperglycemic and glucose intolerant (P < 0.05) and presented central insulin resistance and increased levels of hypothalamic proinflammatory [tumor necrosis factor alpha (TNF-α), 43.5 %; interleukin 6 (IL-6), 78.5 %; and interleukin 1 beta (IL-1β), 50.1 %, P < 0.05] cytokines. On the other hand, the consumption of an okra-supplemented diet prevented all metabolic impairments.

CONCLUSION

In summary, dietary supplementation with okra prevents obesity and glucose deregulation in early-overfeeding rats, which is associated with improved hypothalamic inflammation and insulin resistance.

Glucagon-like peptide-1 receptor agonists in neurodegenerative diseases: Promises and challenges

Glucagon-like peptide-1 (GLP-1) receptor agonists (GRA) belong to a class of compounds that reduce blood glucose and energy intake by simulating actions of endogenous incretin hormone GLP-1 after it is released by the gut following food consumption. They are used to treat type 2 diabetes mellitus (T2DM) and obesity and have systemic effects on various organs, including the brain, liver, pancreas, heart, and the gut. Patients with T2DM have a higher risk of developing neurodegenerative diseases (NDs), including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD), accompanied by more severe motor deficits and faster disease progression, suggesting dysregulation of insulin signaling in these diseases. Experimental studies have shown that GRA have protective effects to modulate neuroinflammation, oxidative stress, mitochondrial and autophagic functions, and protein misfolding. Hence the compounds have generated enormous interest as novel therapeutic agents against NDs. To date, clinical trials have shown that three GRA, exenatide, liraglutide and lixisenatide can improve motor deficits as an add-on therapy in PD patients and liraglutide can improve cognitive function in AD patients. The neuroprotective effects of these and other GRA, such as PT320 (a sustained-released exenatide) and semaglutide, are still under investigation. The dual GLP-1/gastric inhibitory polypeptide (GIP) receptor agonists have been demonstrated to have beneficial effects in AD and PD mice models. Overall, GRA are highly promising novel drugs, but future clinical studies should identify which subsets of patients should be targeted as potential candidates for their symptomatic and/or neuroprotective benefits, investigate whether combinations with other classes of drugs can further augment their efficacy, and evaluate their long-term disease-modifying and adverse effects.

The protective effects of insulin on the developing of dementia in chronic kidney disease patients with hypertension and diabetes: a population-based nationwide study

BACKGROUND

Chronic kidney disease (CKD), hypertension, and diabetes are associated with dementia, and insulin resistance promotes vascular dysfunction resulting in dementia. However, the study of insulin use in preventing dementia in CKD patients with diabetes and hypertension is limited. We aim to assess the effects of insulin use on the incidence of dementia in patients with CKD with hypertension and diabetes.

DESIGN, SETTING AND PARTICIPANTS

A retrospective cohort study using the nationwide database from Taiwan's National Health Insurance Research Database. We selected 11,758 CKD patients with diabetes and hypertension in 2006, including 5,864 insulin users and 5,894 non-insulin users. Moreover, their medication possession ratios (MPR) were calculated.

MAIN OUTCOMES

We used the competing risk model to estimate the hazard ratio (HR) for the incidence of dementia for insulin use in the target population.

RESULTS

In a follow-up period of 11 years, 1285 events of dementia were recorded, and the multivariate-adjusted HR for dementia by insulin usage (yes vs. no) and insulin usage per MPR is 0.652 (95% confidence interval [CI]: 0.552 to 0.771) and 0.995 (95% CI: 0.993 to 0.998) respectively. Such a significant negative association was consistent in almost all subgroups. Moreover, a dose-dependent effect of insulin was noted, where patients with higher insulin MPRs were less likely to have dementia.

CONCLUSION

The CKD patients with hypertension and diabetes who received insulin therapy had a 35% decreased risk of dementia.

Insulin resistance in Alzheimer's disease: signalling mechanisms and therapeutics strategies

BACKGROUND

Alzheimer's disease (AD), one of the most common neurodegenerative disorders, is characterised by hallmark abnormalities such as amyloid-β plaques and neurofibrillary tangles (NFTs). Emerging evidence suggests that faulty insulin signalling contributes to these pathological features, impairing critical cellular and metabolic processes.

OBJECTIVE

This review aims to elucidate the role of insulin signalling in the central nervous system (CNS) under normal and pathological conditions and to explore therapeutic approaches targeting insulin pathways in AD and other neurodegenerative diseases.

METHODS

We reviewed studies highlighting the involvement of insulin-signalling pathways in neuronal health, with a particular focus on the key components-IRS, PI3K, Akt, and GSK-3β-predominantly expressed in cortical and hippocampal regions.

RESULTS

Insulin, an essential growth factor, regulates numerous cellular functions, including glucose metabolism, mitochondrial activity, oxidative stress response, autophagy, synaptic plasticity, and cognitive processes. Altered phosphorylation of signalling molecules in insulin pathways contributes to oxidative stress, inflammation, and the formation of AD hallmarks. Indirect modulators such as NF-κB and caspases further exacerbate neuronal damage, linking impaired insulin signalling to neurodegeneration.

CONCLUSION

Insulin signalling plays a crucial role in maintaining neuronal health and mitigating neurodegenerative processes. Targeting insulin pathways and associated molecules offers promising therapeutic avenues for AD and other neurodegenerative disorders.

Controlled induction of type 2 diabetes in mice using high fat diet and osmotic-mini pump infused streptozotocin

Type 2 diabetes (T2D) is a progressive metabolic disorder characterised by obesity, insulin resistance, impaired glucose tolerance, and hyperglycaemia. The long time-course of T2D in humans makes accurate modelling of sustained T2D in animal models difficult. The goal of this study was to develop and characterise an accurate and reproducible, non-transgenic model of sustained T2D in mice. Adult, male C57BL/6 mice were placed on a high-fat diet (HFD) for 17 weeks. From weeks 3-5, osmotic mini-pumps were implanted subcutaneously to slowly infuse streptozotocin (STZ; 200-350 mg/kg) for 14-days after which mini-pumps were removed. Body weight, blood glucose concentration, and glucose tolerance were monitored for 12 weeks post STZ treatment. Our data demonstrate that the combination of HFD and 200 mg/kg STZ delivered by mini-pump leads to increased blood glucose concentrations and impaired glucose tolerance, while maintaining obesity and hepatic dyslipidaemia. In week 17, plasma insulin concentration was assessed and showed that with STZ treatment, mice still produce insulin, but that this is reduced compared with mice on HFD only. Lastly, we examined pancreas sections using immunohistochemistry and show that there is no overt loss of beta cell mass. In conclusion, we demonstrate development of a reproducible in vivo model of T2D in mice that replicates a number of key pathophysiological changes seen in humans with T2D.

Astrocyte involvement in metabolic regulation and disease

Astrocytes, the predominant glial cell type in the mammalian brain, influence a wide variety of brain parameters including neuronal energy metabolism. Exciting recent studies have shown that obesity and diabetes can impact on astrocyte function. We review evidence that dysregulation of astrocytic lipid metabolism and glucose sensing contributes to dysregulation of whole-body energy balance, thermoregulation, and insulin sensitivity. In addition, we consider the overlooked topic of the sex-specific roles of astrocytes and their response to hormonal fluctuations that provide insights into sex differences in metabolic regulation. Finally, we provide an update on potential ways to manipulate astrocyte function, including genetic targeting, optogenetic and chemogenetic techniques, transplantation, and tailored exosome-based therapies, which may lead to improved treatments for metabolic disease.

Intranasal insulin administration affecting perioperative neurocognitive dysfunction by regulating calcium transport protein complex IP3R/GRP75/VDAC1 on MAMs

Perioperative neurocognitive disorders (PND) are common complications following surgery and anesthesia, especially in the elderly. These disorders are associated with disruptions in neuronal energy metabolism and mitochondrial function. This study explores the potential of intranasal insulin administration as a therapeutic strategy to prevent PND by targeting the calcium transport protein complex IP3R/GRP75/VDAC1 on mitochondria-associated endoplasmic reticulum membranes (MAMs).

METHODS

Male C57BL/6J mice underwent partial hepatectomy to induce PND and were subsequently treated with either intranasal insulin or saline. Cognitive function was evaluated using the Morris water maze test, and hippocampal tissue was analyzed for calcium transport protein complex IP3R/GRP75/VDAC1 expression and apoptosis markers. In vitro, HT22 and BV2 cell co-cultures were utilized to simulate surgical injury, with IP3R knockdown employed to assess its effects on oxidative stress and apoptosis.

RESULTS

Intranasal insulin effectively alleviated cognitive impairment as demonstrated by improved performance in the Morris water maze. It significantly reduced neuronal apoptosis and modulated the expression of the IP3R/GRP75/VDAC1 complex, enhancing mitochondrial ATP production and stabilizing MAMs. Furthermore, insulin administration also increased PI3K/AKT signaling, counteracting the impact of surgical stress. In vitro experiments confirmed that IP3R knockdown mitigated inflammation-induced oxidative stress and neuronal apoptosis, while insulin's beneficial effects were blocked by inhibition of the PI3K/AKT pathway.

CONCLUSION

Intranasal insulin mitigates PND by modulating the IP3R/GRP75/VDAC1 complex and enhancing mitochondrial function through the PI3K/AKT signaling pathway. This study supports the potential of intranasal insulin as a promising therapeutic strategy for preventing and managing PND, potentially leading to improved surgical outcomes for elderly patients.

Targeting Ferroptosis in Parkinson's: Repurposing Diabetes Drugs as a Promising Treatment

This review explores the promising potential of repurposing type 2 diabetes (T2D) medications for the treatment of Parkinson's disease (PD), highlighting the shared pathophysiological mechanisms between these two age-related conditions, such as oxidative stress, mitochondrial dysfunction, and ferroptosis. The overlap suggests that existing diabetes drugs could target the common pathways involved in both conditions. Specifically, the review discusses how T2D medications, including metformin (Met), peroxisome-proliferator-activated receptor gamma (PPAR-γ) agonists, sodium-glucose cotransporter-2 (SGLT2) inhibitors, incretins, and dipeptidyl-peptidase 4 (DPP-4) inhibitors, can improve mitochondrial function, reduce neuroinflammation and oxidative stress, and potentially inhibit ferroptosis. The connection between ferroptosis and existing treatments, including diabetes medication, are only beginning to be explored. The limited data can be attributed also to the complexity of mechanisms involved in ferroptosis and Parkinson's disease and to the fact that the specific role of ferroptosis in Parkinson's disease pathogenesis has not been a primary focus until recent. Despite the promising preclinical evidence, clinical findings are mixed, underscoring the need for further research to elucidate these drugs' roles in neurodegeneration. Repurposing existing diabetes medications that have well-established safety profiles for Parkinson's disease treatment could significantly reduce the time and cost associated with drug development and could offer a more comprehensive approach to managing Parkinson's disease compared to treatments targeting a single mechanism.

High-fat diet and neuroinflammation: The role of mitochondria

In recent years, increasing evidence has supported that high-fat diet (HFD) can induce the chronic, low-grade neuroinflammation in the brain, which is closely associated with the impairment of cognitive function. As the key organelles responsible for energy metabolism in the cell, mitochondria are believed to involved in the pathogenesis of a variety of neurological disorders. This review summarizes the current progress in the field of the relationship between HFD exposure and neurodegenerative diseases, and outline the major routines of HFD induced neuroinflammation and its pathological significance in the pathogenesis of neurodegenerative diseases. Furthermore, the article highlights the pivotal role of mitochondrial dysfunction in driving the neuroinflammation in the setting of HFD. Danger-associated molecular patterns (DAMPs) from damaged mitochondria can activate innate immune signaling pathways, while mitochondrial dysfunction itself can lead to metabolic remodeling of inflammatory cells, thus inducing neuroinflammation. More importantly, mitochondrial damage, neuroinflammation, and insulin resistance caused by HFD form a mutually reinforcing vicious cycle, ultimately leading to the death of neurons and promoting the progression of neurodegenerative diseases. Thus, in-depth elucidation of the role and underlying mechanisms of mitochondrial dysfunction in HFD-induced metabolic disorders may not only expand our understanding of the mechanistic linkages between HFD and etiology of neurodegenerative diseases, but also help develop the specific strategies for the prevention and treatment of neurodegenerative diseases.

Glucose metabolism impairment in major depressive disorder

Major depressive disorder (MDD) is a common mental disorder with chronic tendencies that seriously affect regular work, life, and study. However, its exact pathogenesis remains unclear. Patients with MDD experience systemic and localized impairments in glucose metabolism throughout the disease course, disrupting various processes such as glucose uptake, glycoprotein transport, glycolysis, the tricarboxylic acid cycle (TCA), and oxidative phosphorylation (OXPHOS). These impairments may result from mechanisms including insulin resistance, hyperglycemia-induced damage, oxidative stress, astrocyte abnormalities, and mitochondrial dysfunction, leading to insufficient energy supply, altered synaptic plasticity, neuronal cell death, and functional and structural damage to reward networks. These mechanical changes contribute to the pathogenesis of MDD and severely interfere with the prognosis. Herein, we summarized the impairment of glucose metabolism and its pathophysiological mechanisms in patients with MDD. In addition, we briefly discussed potential pharmacological interventions for glucose metabolism to alleviate MDD, including glucagon-like peptide-1 receptor agonists, metformin, topical insulin, liraglutide, and pioglitazone, to encourage the development of new therapeutics.

The mechanism underlying streptozotocin injection for the development of a nontransgenic Alzheimer's disease animal model

Streptozotocin (STZ) is a widely used chemical agent in biomedical research. It is primarily known for its ability to induce high blood glucose levels in animal models by selectively destroying pancreatic beta cells. Nonetheless, many studies have also used STZ to generate animal models of diabetic complications, such as Alzheimer's disease (AD) animal models. STZ induction promotes hyperglycemia, which activates numerous mechanism pathways that result in the production of pathogenic AD characteristics, including beta-amyloid accumulation and neurofibrillary tangles. Numerous theories exist to elucidate the mechanisms underlying diabetes and AD; however, studies on the potential of an animal model of STZ-induced AD remain limited. Thus, this review summarizes the pathogenesis associated with STZ exposure, particularly in AD animal model studies related to diabetes. More specifically, this study will discuss the relationship between increased blood glucose levels after STZ injection and the process of beta-amyloid formation and insulin dysfunction in the brain.

Side-Stream Based Marine Solubles From Atlantic Cod (Gadus morhua) Modulate Appetite and Dietary Nutrient Utilization in Atlantic Salmon (Salmo salar L.) and can Replace Fish Meal

Whitefish fisheries' side-stream biomass is an abundant underutilized resource that can be valorized to benefit future aquaculture sustainability. Four novel ingredients based on side-streams from Atlantic cod (Gadus morhua) fileting were produced. FM-hb, a fish meal (FM), and FPH-hb, a fish protein hydrolysate based on heads (h) and backbones (b); FM-hbg, a FM based on heads, backbones, and viscera/guts (g); and FPC-g, a fish protein concentrate based on viscera preserved in formic acid. Four diets were prepared containing one of the ingredients replacing 50% of the dietary FM protein, in addition to a positive (FM10) and a negative (FM5) control. The six diets were fed to triplicate tanks with Atlantic salmon (Salmo salar L.; 113 ± 1 g) over 8 weeks. Besides general performance, gut and brain gene expression for selected hormones and key neuropeptides involved in the control of appetite and digestive processes were studied during feeding and postprandial, and possible reference levels for Atlantic salmon were established. All side-stream-added diets performed well, with no significant differences in performance and biometrics between the treatments. Some gene expression differences were observed, but no well-defined patterns emerged supporting clear dietary effects related to digestive performance or appetite. However, in the brain, a short-time upregulation of agouti-related protein-1 (agrp1), corresponded to higher cumulative feed intake (FI) for the FM10 diet supporting notions that this may be a candidate biomarker for appetite in salmon. Expression of stomach ghrelin-1 (ghrl1) was higher than ghrelin-2 (ghrl2) and membrane-bound O-acyltransferase domain-containing 4 (mboat4), and midgut peptide YYa-2 (pyya2) and glucagon-a (gcga) were higher than peptide YYb-1 (pyyb1). A comparison showed that midgut peptide YYa-1 (pyya1), pyya2, and gcga expressions were higher than in the hindgut, which is opposite of what is found in mammals. In conclusion, this study shows that sustainable side-stream raw materials with different characteristics can partly replace high-quality commercial FMs giving similar performance.

The interface of depression and diabetes: treatment considerations

This state-of-the-art review explores the relationship between depression and diabetes, highlighting the two-way influences that make treatment challenging and worsen the outcomes of both conditions. Depression and diabetes often co-occur and share genetic, lifestyle, and psychosocial risk factors. Lifestyle elements such as diet, physical activity, and sleep patterns play a role on the development and management of both conditions, highlighting the need for integrated treatment strategies. The evidence suggests that traditional management strategies focusing on either condition in isolation fall short of addressing the intertwined nature of diabetes and depression. Instead, integrated care models encompassing psychological support and medical management are recommended to improve treatment efficacy and patient adherence. Such models require collaboration across multiple healthcare disciplines, including endocrinology, psychiatry, and primary care, to offer a holistic approach to patient care. This review also identifies significant patient-related barriers to effective management, such as stigma, psychological resistance, and health literacy, which need to be addressed through patient-centered education and support systems. Future directions for research include longitudinal studies in diverse populations to further elucidate causal relationships and the exploration of novel therapeutic targets, as well as the effectiveness of healthcare models aimed at preventing the onset of one condition in individuals diagnosed with the other.

Genetically predicted brain cortical structure mediates the causality between insulin resistance and cognitive impairment

Background

Insulin resistance is tightly related to cognition; however, the causal association between them remains a matter of debate. Our investigation aims to establish the causal relationship and direction between insulin resistance and cognition, while also quantifying the mediating role of brain cortical structure in this association.

Methods

The publicly available data sources for insulin resistance (fasting insulin, homeostasis model assessment beta-cell function and homeostasis model assessment insulin resistance, proinsulin), brain cortical structure, and cognitive phenotypes (visual memory, reaction time) were obtained from the MAGIC, ENIGMA, and UK Biobank datasets, respectively. We first conducted a bidirectional two-sample Mendelian randomization (MR) analysis to examine the susceptibility of insulin resistance on cognitive phenotypes. Additionally, we applied a two-step MR to assess the mediating role of cortical surficial area and thickness in the pathway from insulin resistance to cognitive impairment. The primary Inverse-variance weighted, accompanied by robust sensitivity analysis, was implemented to explore and verify our findings. The reverse MR analysis was also performed to evaluate the causal effect of cognition on insulin resistance and brain cortical structure.

Results

This study identified genetically determined elevated level of proinsulin increased reaction time (beta=0.03, 95% confidence interval [95%CI]=0.01 to 0.05, p=0.005), while decreasing the surface area of rostral middle frontal (beta=-49.28, 95%CI=-86.30 to -12.27, p=0.009). The surface area of the rostral middle frontal mediated 20.97% (95%CI=1.44% to 40.49%) of the total effect of proinsulin on reaction time. No evidence of heterogeneity, pleiotropy, or reverse causality was observed.

Conclusions

Briefly, our study noticed that elevated level of insulin resistance adversely affected cognition, with a partial mediation effect through alterations in brain cortical structure.

The Crucial Role of the Blood-Brain Barrier in Neurodegenerative Diseases: Mechanisms of Disruption and Therapeutic Implications

The blood-brain barrier (BBB) is a crucial structure that maintains brain homeostasis by regulating the entry of molecules and cells from the bloodstream into the central nervous system (CNS). Neurodegenerative diseases such as Alzheimer's and Parkinson's disease, as well as ischemic stroke, compromise the integrity of the BBB. This leads to increased permeability and the infiltration of harmful substances, thereby accelerating neurodegeneration. In this review, we explore the mechanisms underlying BBB disruption, including oxidative stress, neuroinflammation, vascular dysfunction, and the loss of tight junction integrity, in patients with neurodegenerative diseases. We discuss how BBB breakdown contributes to neuroinflammation, neurotoxicity, and the abnormal accumulation of pathological proteins, all of which exacerbate neuronal damage and facilitate disease progression. Furthermore, we discuss potential therapeutic strategies aimed at preserving or restoring BBB function, such as anti-inflammatory treatments, antioxidant therapies, and approaches to enhance tight junction integrity. Given the central role of the BBB in neurodegeneration, maintaining its integrity represents a promising therapeutic approach to slow or prevent the progression of neurodegenerative diseases.

Insulin Resistance Is a Modifying Factor for Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is the second most common, and the fastest-growing neurodegenerative disorder with unclear etiology in most cases. Therefore, the identification of non-genetic risk factors for PD pathology is crucial to develop effective preventative or therapeutic strategies. An increasing number of evidence suggests that central insulin resistance might have an essential role in PD pathology. Nevertheless, it is not clear whether insulin resistance arises from external factors/lifestyle, comorbidities such as type 2 diabetes or it can occur in a PD patient's brain independently from peripheral insulin resistance.

OBJECTIVE

We aimed to investigate insulin resistance and its role in GBA1 mutation-associated PD pathogenesis and phenotype severity.

METHODS

Midbrain organoids, generated from induced pluripotent stem cells (iPSCs) of PD patients carrying the GBA1-N370S heterozygous mutation (GBA-PD) and healthy donors, were exposed to different insulin concentrations to modify insulin signaling function. Transcriptomics analysis was performed to explore insulin signaling gene expression patterns in GBA-PD and to find a potential target for GBA-PD-associated phenotype rescue.

RESULTS

The insulin signaling pathway genes show dysregulation in GBA-PD. Particularly, we highlight that a knockdown of FOXO1 mitigates the loss of dopaminergic neurons and cellular death in GBA-PD. Additionally, our findings suggest a promising therapeutic potential of the anti-diabetic drug Pioglitazone in decreasing dopaminergic neuron loss associated with GBA-PD.

CONCLUSION

Local insulin signaling dysfunction plays a substantial role in GBA-PD pathogenesis, exacerbating dopaminergic neuron death. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Predictive model in silicon and pathogenicity mechanism of metabolic syndrome: Impacts of heavy metal exposure

Although the association between heavy metals in human and the development of metabolic syndrome (MetS) have been extensively studied, the pathogenic mechanism of MetS affected by metals is not clear to date. In this study, a predictive model was developed with machine learning base on the large-scale dataset. These proposed models were evaluated via comparatively analysis of their accuracy and robustness. With the optimal model, two metals significantly correlated with MetS were screened and were employed to infer the pathogenicity mechanism of MetS via molecular docking. Significant associations between heavy metals and MetS were found. Molecular docking provided insights into the interactions between metal ions and key protein receptors involved in metabolic regulation, suggesting a mechanism by which heavy metals interfere with metabolic functions. Specifically, Ba and Cd affect the development of MetS thru their interactions with insulin and estrogen receptors. This study attempted to explore heavy metals' potential roles in MetS at the molecular level. These findings emphasize the importance of addressing environmental exposures in the prevention and treatment of MetS.

DEP-1 is a brain insulin receptor phosphatase that prevents the simultaneous activation of counteracting metabolic pathways

A healthy metabolism relies on precise regulation of anabolic and catabolic pathways. While insulin deficiency impairs anabolism, insulin resistance in obesity causes metabolic dysfunction, especially via altered brain insulin receptor (IR) activity. Density-enhanced phosphatase 1 (DEP-1) negatively modulates the IR in peripheral tissues. Our study shows that DEP-1 is an insulin-regulated gene, dysregulated in obesity, and uncovers its role in brain insulin signaling, impacting both anabolic and catabolic pathways. Neuro-2a cells lacking DEP-1 demonstrated heightened IR phosphorylation upon acute insulin stimulation. This coincided with simultaneous AMP-activated protein kinase (AMPK) activation, which governs catabolic pathways, due to increased phospholipase C-gamma 1 signaling. These opposing pathways in male DEP-1 forebrain-specific knockout mice resulted in elevated lipolysis in white adipose tissue and fat oxidation in brown adipose tissue, with enhanced sympathetic activation and β-adrenergic receptor expression. In conclusion, DEP-1 deficiency causes the simultaneous activation of IR and AMPK signaling in the brain, with enhanced sympathetic activity in adipose tissues.

STZ-induced hyperglycemia differentially influences mitochondrial distribution and morphology in the habenulointerpeduncular circuit

Introduction

Diabetes is a metabolic disorder of glucose homeostasis that is a significant risk factor for neurodegenerative diseases, such as Alzheimer's disease, as well as mood disorders, which often precede neurodegenerative conditions. We examined the medial habenulainterpeduncular nucleus (MHb-IPN), as this circuit plays crucial roles in mood regulation, has been linked to the development of diabetes after smoking, and is rich in cholinergic neurons, which are affected in other brain areas in Alzheimer's disease.

Methods

This study aimed to investigate the impact of streptozotocin (STZ)-induced hyperglycemia, a type 1 diabetes model, on mitochondrial and lipid homeostasis in 4% paraformaldehyde-fixed sections from the MHb and IPN of C57BL/6 J male mice, using a recently developed automated pipeline for mitochondrial analysis in confocal images. We examined different time points after STZ-induced diabetes onset to determine how the brain responded to chronic hyperglycemia, with the limitation that mitochondria and lipids were not examined with respect to cell type or intracellular location.

Results

Mitochondrial distribution and morphology differentially responded to hyperglycemia depending on time and brain area. Six weeks after STZ treatment, mitochondria in the ventral MHb and dorsal IPN increased in number and exhibited altered morphology, but no changes were observed in the lateral habenula (LHb) or ventral IPN. Strikingly, mitochondrial numbers returned to normal dynamics at 12 weeks. Both blood glucose level and glycated hemoglobin (HbA1C) correlated with mitochondrial dynamics in ventral MHb, whereas only HbA1C correlated in the IPN. We also examined lipid homeostasis using BODIPY staining for neutral lipids in this model given that diabetes is associated with disrupted lipid homeostasis. BODIPY staining intensity was unchanged in the vMHb of STZ-treated mice but increased in the IPN and VTA and decreased in the LHb at 12 weeks. Interestingly, areas that demonstrated changes in mitochondria had little change in lipid staining and vice versa.

Discussion

This study is the first to describe the specific impacts of diabetes on mitochondria in the MHb-IPN circuit and suggests that the cholinergic MHb is uniquely sensitive to diabetesinduced hyperglycemia. Further studies are needed to understand the functional and behavioral implications of these findings.

Effects of ketamine on metabolic parameters in depressive disorders: A systematic review

BACKGROUND

Persons with Major Depressive Disorder (MDD), notably treatment-resistant depression (TRD), are differentially affected by type 2 diabetes mellitus and associated morbidity. Ketamine is highly efficacious in the treatment of adults living with MDD, notably TRD. Herein, we sought to determine the effect of ketamine on metabolic parameters in animal stress paradigms and human studies.

METHODS

We performed a comprehensive search on PubMed, OVID, and Scopus databases for primary research articles from inception to May 5, 2024. Study screening and data extraction were performed by two reviewers (S.W. and G.H.L.). Both preclinical and clinical studies were included in this review.

RESULTS

Results from the preclinical studies indicate that in experimental diabetic conditions, ketamine does not disrupt glucose-insulin homeostasis. Within adults with MDD, ketamine is associated with GLUT3 transporter upregulation and differentially affects metabolomic signatures. In adults with TRD, ketamine induces increased brain glucose uptake in the prefrontal cortex. Available evidence suggests that ketamine does not adversely affect metabolic parameters.

LIMITATIONS

There are a paucity of clinical studies evaluating the effects of ketamine on glucose-insulin homeostasis in adults with MDD.

CONCLUSIONS

Our results indicate that ketamine is not associated with significant and/or persistent disruptions in metabolic parameters. Available evidence indicates that ketamine does not adversely affect glucose-insulin homeostasis. These results underscore ketamine's efficacy and safety as an antidepressant treatment that is not associated with metabolic disturbances commonly reported with current augmentation therapies.

Autonomic neuromodulation for cardiomyopathy associated with metabolic syndrome - Prevention of precursors for heart failure with preserved ejection fraction

Metabolic syndrome (MetS) induces a systemic inflammatory state which can lead to cardiomyopathy, manifesting clinically as heart failure (HF) with preserved ejection fraction (HFpEF). MetS components are intricately linked to the pathophysiologic processes of myocardial remodeling. Increased sympathetic nervous system activity, which is noted as an upstream factor of MetS, has been linked to adverse myocardial structural changes. Since renal denervation and vagus nerve stimulation have a sympathoinhibitory effect, attention has been paid to the cardioprotective effects of autonomic neuromodulation. In this review, the pathophysiology underlying the relationship between MetS and HF is elucidated, and the evidence regarding autonomic neuromodulation in HFpEF is summarized.

The gut-brain-metabolic axis: exploring the role of microbiota in insulin resistance and cognitive function

The gut-brain-metabolic axis has emerged as a critical area of research, highlighting the intricate connections between the gut microbiome, metabolic processes, and cognitive function. This review article delves into the complex interplay between these interconnected systems, exploring their role in the development of insulin resistance and cognitive decline. The article emphasizes the pivotal influence of the gut microbiota on central nervous system (CNS) function, demonstrating how microbial colonization can program the hypothalamic-pituitary-adrenal (HPA) axis for stress response in mice. It further elucidates the mechanisms by which gut microbial carbohydrate metabolism contributes to insulin resistance, a key factor in the pathogenesis of metabolic disorders and cognitive impairment. Notably, the review highlights the therapeutic potential of targeting the gut-brain-metabolic axis through various interventions, such as dietary modifications, probiotics, prebiotics, and fecal microbiota transplantation (FMT). These approaches have shown promising results in improving insulin sensitivity and cognitive function in both animal models and human studies. The article also emphasizes the need for further research to elucidate the specific microbial species and metabolites involved in modulating the gut-brain axis, as well as the long-term effects and safety of these therapeutic interventions. Advances in metagenomics, metabolomics, and bioinformatics are expected to provide deeper insights into the complex interactions within the gut microbiota and their impact on host health. Overall, this comprehensive review underscores the significance of the gut-brain-metabolic axis in the pathogenesis and treatment of metabolic and cognitive disorders, offering a promising avenue for the development of novel therapeutic strategies targeting this intricate system.

Targeting Glucose Metabolism: A Novel Therapeutic Approach for Parkinson's Disease

Glucose metabolism is essential for the maintenance and function of the central nervous system. Although the brain constitutes only 2% of the body weight, it consumes approximately 20% of the body's total energy, predominantly derived from glucose. This high energy demand of the brain underscores its reliance on glucose to fuel various functions, including neuronal activity, synaptic transmission, and the maintenance of ion gradients necessary for nerve impulse transmission. Increasing evidence shows that many neurodegenerative diseases, including Parkinson's disease (PD), are associated with abnormalities in glucose metabolism. PD is characterized by the progressive loss of dopaminergic neurons in the substantia nigra, accompanied by the accumulation of α-synuclein protein aggregates. These pathological features are exacerbated by mitochondrial dysfunction, oxidative stress, and neuroinflammation, all of which are influenced by glucose metabolism disruptions. Emerging evidence suggests that targeting glucose metabolism could offer therapeutic benefits for PD. Several antidiabetic drugs have shown promise in animal models and clinical trials for mitigating the symptoms and progression of PD. This review explores the current understanding of the association between PD and glucose metabolism, emphasizing the potential of antidiabetic medications as a novel therapeutic approach. By improving glucose uptake and utilization, enhancing mitochondrial function, and reducing neuroinflammation, these drugs could address key pathophysiological mechanisms in PD, offering hope for more effective management of this debilitating disease.

Alzheimer's Disease as Type 3 Diabetes: Understanding the Link and Implications

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are two prevalent conditions that present considerable public health issue in aging populations worldwide. Recent research has proposed a novel conceptualization of AD as "type 3 diabetes", highlighting the critical roles of insulin resistance and impaired glucose metabolism in the pathogenesis of the disease. This article examines the implications of this association, exploring potential new avenues for treatment and preventive strategies for AD. Key evidence linking diabetes to AD emphasizes critical metabolic processes that contribute to neurodegeneration, including inflammation, oxidative stress, and alterations in insulin signaling pathways. By framing AD within this metabolic context, we can enhance our understanding of its etiology, which in turn may influence early diagnosis, treatment plans, and preventive measures. Understanding AD as a manifestation of diabetes opens up the possibility of employing novel therapeutic strategies that incorporate lifestyle modifications and the use of antidiabetic medications to mitigate cognitive decline. This integrated approach has the potential to improve patient outcomes and deepen our comprehension of the intricate relationship between neurodegenerative diseases and metabolic disorders.

Role of Peripheral and Central Insulin Resistance in Neuropsychiatric Disorders

Insulin acts on different organs, including the brain, which helps it regulate energy metabolism. Insulin signaling plays an important role in the function of different cell types. In this review, we have summarized the key roles of insulin and insulin receptors in healthy brains and in different brain disorders. Insulin signaling, as well as insulin resistance (IR), is a major contributor in the regulation of mood, behavior, and cognition. Recent evidence showed that both peripheral and central insulin resistance play a role in the pathophysiology, clinical presentation, and management of neuropsychiatric disorders like Cognitive Impairment/Dementia, Depression, and Schizophrenia. Many human studies point out Insulin Resistance/Metabolic Syndrome can increase the risk of dementia especially Alzheimer's dementia (AD). IR has been shown to play a role in AD development but also in its progression. This review article discusses the pathophysiological pathways and mechanisms of insulin resistance in major neuropsychiatric disorders. The extent of insulin resistance can be quantified using IR biomarkers like insulin levels, HOMA-IR index, and Triglyceride glucose-body mass index (TyG-BMI) levels. IR has been shown to precede neurodegeneration. Human trials showed current treatment with certain antidiabetic drugs, as well as life style management, like weight loss and exercise for IR, have shown promise in the management of cognitive/neuropsychiatric disorders. This may pave the pathway to the development of new therapeutic approaches to these challenging disorders of dementia and psychiatric diseases. Recent clinical trials are showing some encouraging evidence for these pharmacological and nonpharmacological approaches for IR in psychiatric and cognitive disorders, even though more research is needed to apply this evidence into clinical practice. Early identification and management of IR may help as a strategy to potentially alter neuropsychiatric disorders onset as well as its progression.

Chronically Increased Levels of Circulating Insulin Secondary to Insulin Resistance: A Silent Killer

Despite all the progress made by science in the prevention and treatment of cardiovascular diseases and cancers, these are still the main reasons for hospitalizations and death in the Western world. Among the possible causes of this situation, disorders related to hyperinsulinemia and insulin resistance (Hyperin/IR) are still little-known topics. An analysis of the literature shows that this condition is a multiple risk factor for type 2 diabetes, cardiovascular diseases, cellular senescence and cancer, and neurodegenerative diseases. Hyperin/IR is progressively increasing worldwide, and its prevalence has now exceeded 50% of the general population and in overweight children. Asymptomatic or poorly symptomatic, it can last for many years before manifesting itself as diabetes, cardiovascular disease, neoplasm, cognitive deficit, or dementia, therefore leading to enormous social and healthcare costs. For these reasons, a screening plan for this pathology should be implemented for the purpose of identifying people with Hyperin/IR and promptly starting them on preventive treatment.

Insulin-inspired hippocampal neuron-targeting technology for protein drug delivery

Hippocampal neurons can be the first to be impaired with neurodegenerative disorders, including Alzheimer's disease (AD). Most drug candidates for causal therapy of AD cannot either enter the brain or accumulate around hippocampal neurons. Here, we genetically engineered insulin-fusion proteins, called hippocampal neuron-targeting (Ht) proteins, for targeting protein drugs to hippocampal neurons because insulin tends to accumulate in the neuronal cell layers of the hippocampus. In vitro examinations clarified that insulin and Ht proteins were internalized into the cultured hippocampal neurons through insulin receptor-mediated macropinocytosis. Cysteines were key determinants of the delivery of Ht proteins to hippocampal neurons, and insulin B chain mutant was most potent in delivering cargo proteins. In vivo accumulation of Ht proteins to hippocampal neuronal layers occurred after intracerebroventricular administration. Thus, hippocampal neuron-targeting technology can provide great help for developing protein drugs against neurodegenerative disorders.

Biologically Informed Polygenic Scores for Brain Insulin Receptor Network Are Associated with Cardiometabolic Risk Markers and Diabetes in Women

BACKGRUOUND

To investigate associations between variations in the co-expression-based brain insulin receptor polygenic score and cardiometabolic risk factors and diabetes mellitus.

METHODS

This cross-sectional study included 1,573 participants from the Helsinki Birth Cohort Study. Biologically informed expression-based polygenic risk scores for the insulin receptor gene network were calculated for the hippocampal (hePRS-IR) and the mesocorticolimbic (mePRS-IR) regions. Cardiometabolic markers included body composition, waist circumference, circulating lipids, insulin-like growth factor 1 (IGF-1), and insulin-like growth factor-binding protein 1 and 3 (IGFBP-1 and -3). Glucose and insulin levels were measured during a standardized 2-hour 75 g oral glucose tolerance test and impaired glucose regulation status was defined by the World Health Organization 2019 criteria. Analyzes were adjusted for population stratification, age, smoking, alcohol consumption, socioeconomic status, chronic diseases, birth weight, and leisure-time physical activity.

RESULTS

Multinomial logistic regression indicated that one standard deviation increase in hePRS-IR was associated with increased risk of diabetes mellitus in all participants (adjusted relative risk ratio, 1.17; 95% confidence interval, 1.01 to 1.35). In women, higher hePRS-IR was associated with greater waist circumference and higher body fat percentage, levels of glucose, insulin, total cholesterol, low-density lipoprotein cholesterol, triglycerides, apolipoprotein B, insulin, and IGFBP-1 (all P≤0.02). The mePRS-IR was associated with decreased IGF-1 level in women (P=0.02). No associations were detected in men and studied outcomes.

CONCLUSION

hePRS-IR is associated with sex-specific differences in cardiometabolic risk factor profiles including impaired glucose regulation, abnormal metabolic markers, and unfavorable body composition in women.

Hyperglycemia and cognitive impairments anticipate the onset of an overt type 2 diabetes-like phenotype in TALLYHO/JngJ mice

Type 2 Diabetes mellitus (T2DM) is a metabolic disorder characterized by chronic hyperglycemia, resulting from deficits in insulin secretion, insulin action, or both. Whilst the role of insulin in the peripheral nervous system has been ascertained in countless studies, its role in the central nervous system (CNS) is emerging only recently. Brain insulin has been lately associated with brain disorders like Alzheimer's disease, obsessive compulsive disorder, and attention deficit hyperactivity disorder. Thus, understanding the role of insulin as a common risk factor for mental and somatic comorbidities may disclose novel preventative and therapeutic approaches. We evaluated general metabolism (glucose tolerance, insulin sensitivity, energy expenditure, lipid metabolism, and polydipsia) and cognitive capabilities (attention, cognitive flexibility, and memory), in adolescent, young adult, and adult male and female TALLYHO/JngJ mice (TH, previously reported to constitute a valid experimental model of T2DM due to impaired insulin signaling). Adult TH mice have also been studied for alterations in gut microbiota diversity and composition. While TH mice exhibited profound deficits in cognitive flexibility and altered glucose metabolism, we observed that these alterations emerged either much earlier (males) or independent of (females) a comprehensive constellation of symptoms, isomorphic to an overt T2DM-like phenotype (insulin resistance, polydipsia, higher energy expenditure, and altered lipid metabolism). We also observed significant sex-dependent alterations in gut microbiota alpha diversity and taxonomy in adult TH mice. Deficits in insulin signaling may represent a common risk factor for both T2DM and CNS-related deficits, which may stem from (partly) independent mechanisms.

Advancing the understanding of diabetic encephalopathy through unravelling pathogenesis and exploring future treatment perspectives

Diabetic encephalopathy (DE), a significant micro-complication of diabetes, manifests as neurochemical, structural, behavioral, and cognitive alterations. This condition is especially dangerous for the elderly because aging raises the risk of neurodegenerative disorders and cognitive impairment, both of which can be made worse by diabetes. Despite its severity, diagnosis of this disease is challenging, and there is a paucity of information on its pathogenesis. The pivotal roles of various cellular pathways, activated or influenced by hyperglycemia, insulin sensitivity, amyloid accumulation, tau hyperphosphorylation, brain vasculopathy, neuroinflammation, and oxidative stress, are widely recognized for contributing to the potential causes of diabetic encephalopathy. We also reviewed current pharmacological strategies for DE encompassing a comprehensive approach targeting metabolic dysregulations and neurological manifestations. Antioxidant-based therapies hold promise in mitigating oxidative stress-induced neuronal damage, while anti-diabetic drugs offer neuroprotective effects through diverse mechanisms, including modulation of insulin signaling pathways and neuroinflammation. Additionally, tissue engineering and nanomedicine-based approaches present innovative strategies for targeted drug delivery and regenerative therapies for DE. Despite significant progress, challenges remain in translating these therapeutic interventions into clinical practice, including long-term safety, scalability, and regulatory approval. Further research is warranted to optimize these approaches and address remaining gaps in the management of DE and associated neurodegenerative disorders.

Insulin Resistance, a Risk Factor for Alzheimer's Disease: Pathological Mechanisms and a New Proposal for a Preventive Therapeutic Approach

Peripheral insulin resistance (IR) is a well-documented, independent risk factor for the development of type 2 diabetes, cardiovascular disease, cancer and cellular senescence. Recently, the brain has also been identified as an insulin-responsive region, where insulin acts as regulator of the brain metabolism. Despite the clear link between IR and the brain, the exact mechanisms underlying this relationship remain unclear. Therapeutic intervention in patients showing symptoms of neurodegenerative diseases has produced little or no results. It has been demonstrated that insulin resistance plays a significant role in the pathogenesis of neurodegenerative diseases, particularly cognitive decline. Peripheral and brain IR may represent a modifiable state that could be used to prevent major brain disorders. In this review, we will analyse the scientific literature supporting IR as a risk factor for Alzheimer's disease and suggest some therapeutic strategies to provide a new proposal for the prevention of brain IR and its consequences.

Association between triglyceride glucose index and cognitive decline: A meta-analysis

BACKGROUND

The triglyceride glucose (TyG) index, a novel surrogate indicator for insulin resistance (IR), is believed to be associated with various diseases. However, its connection with cognitive decline remains controversy.

METHODS

The PubMed, EMBASE, Cochrane Library, Web of Science, and Medline databases were systematically searched up to October 2023 to assess the association between the TyG index and the risk of cognitive decline. Effect estimates and 95 % confidence intervals (CIs) were calculated using a random-effects model.

RESULTS

Our review included 3 cohort studies and 9 case-control/cross-sectional studies with a total of 5,603,350 participants. In comparison to a low TyG index, a higher TyG index was connected to an elevated risk of cognitive decline (RR/HR = 1.14, 95 % CI [1.11, 1.17], P < 0.05; OR = 1.75, 95 % CI [1.34, 2.29], P < 0.05). Furthermore, the dose-response analysis from the case-control/cross-sectional studies revealed a 1.42 times higher risk of cognitive decline per 1 mg/dl increment of the TyG index (OR = 1.42, 95 % CI [1.19, 1.69], P < 0.05).

LIMITATIONS

The inclusion of observational studies in the meta-analysis demonstrated a lower hierarchy of evidence compared to randomized controlled trials. Moreover, we incorporated a restricted number of studies and identified significant heterogeneity among them, potentially attributed to the presence of numerous confounding variables.

CONCLUSION

TyG index is related to cognitive decline. In view of some of the limitations of this study, further research will be necessary to confirm this relationship.

Insulin enhances acid-sensing ion channel currents in rat primary sensory neurons

Insulin has been shown to modulate neuronal processes through insulin receptors. The ion channels located on neurons may be important targets for insulin/insulin receptor signaling. Both insulin receptors and acid-sensing ion channels (ASICs) are expressed in dorsal root ganglia (DRG) neurons. However, it is still unclear whether there is an interaction between them. Therefore, the purpose of this investigation was to determine the effects of insulin on the functional activity of ASICs. A 5 min application of insulin rapidly enhanced acid-evoked ASIC currents in rat DRG neurons in a concentration-dependent manner. Insulin shifted the concentration-response plot for ASIC currents upward, with an increase of 46.2 ± 7.6% in the maximal current response. The insulin-induced increase in ASIC currents was eliminated by the insulin receptor antagonist GSK1838705, the tyrosine kinase inhibitor lavendustin A, and the phosphatidylinositol-3 kinase antagonist wortmannin. Moreover, insulin increased the number of acid-triggered action potentials by activating insulin receptors. Finally, local administration of insulin exacerbated the spontaneous nociceptive behaviors induced by intraplantar acid injection and the mechanical hyperalgesia induced by intramuscular acid injections through peripheral insulin receptors. These results suggested that insulin/insulin receptor signaling enhanced the functional activity of ASICs via tyrosine kinase and phosphatidylinositol-3 kinase pathways. Our findings revealed that ASICs were targets in primary sensory neurons for insulin receptor signaling, which may underlie insulin modulation of pain.

The mitochondrial quality control system: a new target for exercise therapeutic intervention in the treatment of brain insulin resistance-induced neurodegeneration in obesity

Obesity is a major global health concern because of its strong association with metabolic and neurodegenerative diseases such as diabetes, dementia, and Alzheimer's disease. Unfortunately, brain insulin resistance in obesity is likely to lead to neuroplasticity deficits. Since the evidence shows that insulin resistance in brain regions abundant in insulin receptors significantly alters mitochondrial efficiency and function, strategies targeting the mitochondrial quality control system may be of therapeutic and practical value in obesity-induced cognitive decline. Exercise is considered as a powerful stimulant of mitochondria that improves insulin sensitivity and enhances neuroplasticity. It has great potential as a non-pharmacological intervention against the onset and progression of obesity associated neurodegeneration. Here, we integrate the current knowledge of the mechanisms of neurodegenration in obesity and focus on brain insulin resistance to explain the relationship between the impairment of neuronal plasticity and mitochondrial dysfunction. This knowledge was synthesised to explore the exercise paradigm as a feasible intervention for obese neurodegenration in terms of improving brain insulin signals and regulating the mitochondrial quality control system.

Sustained insulin treatment restoring metabolic status, body weight, and cognition in an anorexia nervosa-like animal model in mice

INTRODUCTION

Anorexia Nervosa (AN) is a psycho-socio-biological disease characterized by severe weight loss as result of dieting and hyperactivity. Effective treatments are scarce, despite its significant prevalence and mortality. AN patients show lower basal insulin levels and increased metabolic clearance, leading to weight loss, cognitive deficits, and hormonal imbalances. Low-dose polymer insulin could potentially reverse these effects by restoring brain function, reducing fear of weight gain, encouraging food intake, and restoring fat depots. This study evaluates an insulin delivery system designed for sustained release and AN treatment.

METHODS

AN-like model was established through dietary restriction (DR). On days 1-25, mice were on DR, and on days 26-31 they were on ad libitum regimen. An insulin-loaded delivery system was administered subcutaneously (1% w/w insulin). The impact of insulin treatment on gene expression in the hippocampus (cognition, regulation of stress, neurogenesis) and hypothalamus (eating behavior, mood) was assessed. Behavioral assays were conducted to evaluate motor activity and cognitive function.

RESULTS

The delivery system demonstrated sustained insulin release, maintaining therapeutic plasma levels. Diet restriction mice treated with the insulin delivery system showed body weight restoration. Gene expression analysis revealed enhanced expression of CB1 and CB2 genes associated with improved eating behavior and cognition, while POMC expression was reduced. Insulin-polymer treatment restored cognitive function and decreased hyperactivity in the AN-like model.

CONCLUSION

The PSA-RA-based insulin delivery system effectively restores metabolic balance, body weight, and cognitive function in the AN model. Its ability to steadily release insulin makes it a promising candidate for AN treatment."

Exploring the Role of Metabolic Hormones in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by progressive loss of motor neurons. Emerging evidence suggests a potential link between metabolic dysregulation and ALS pathogenesis. This study aimed to investigate the relationship between metabolic hormones and disease progression in ALS patients. A cross-sectional study was conducted involving 44 ALS patients recruited from a tertiary care center. Serum levels of insulin, total amylin, C-peptide, active ghrelin, GIP (gastric inhibitory peptide), GLP-1 active (glucagon-like peptide-1), glucagon, PYY (peptide YY), PP (pancreatic polypeptide), leptin, interleukin-6, MCP-1 (monocyte chemoattractant protein-1), and TNFα (tumor necrosis factor alpha) were measured, and correlations with ALSFRS-R, evolution scores, and biomarkers were analyzed using Spearman correlation coefficients. Subgroup analyses based on ALS subtypes, progression pattern of disease, and disease progression rate patterns were performed. Significant correlations were observed between metabolic hormones and ALS evolution scores. Insulin and amylin exhibited strong correlations with disease progression and clinical functional outcomes, with insulin showing particularly robust associations. Other hormones such as C-peptide, leptin, and GLP-1 also showed correlations with ALS progression and functional status. Subgroup analyses revealed differences in hormone levels based on sex and disease evolution patterns, with male patients showing higher amylin and glucagon levels. ALS patients with slower disease progression exhibited elevated levels of amylin and insulin. Our findings suggest a potential role for metabolic hormones in modulating ALS progression and functional outcomes. Further research is needed to elucidate the underlying mechanisms and explore the therapeutic implications of targeting metabolic pathways in ALS management.

Brain energy metabolism: A roadmap for future research

Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD+, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research.

Dietary restriction alters insulin signaling pathway in the brain

Insulin is known to be a key hormone in the regulation of peripheral glucose homeostasis, but beyond that, its effects on the brain are now undisputed. Impairments in insulin signaling in the brain, including changes in insulin levels, are thought to contribute significantly to declines in cognitive performance, especially during aging. As one of the most widely studied experimental interventions, dietary restriction (DR) is considered to delay the neurodegenerative processes associated with aging. Recently, however, data began to suggest that the onset and duration of a restrictive diet play a critical role in the putative beneficial outcome. Because the effects of DR on insulin signaling in the brain have been poorly studied, we decided to examine the effects of DR that differed in onset and duration: long-term DR (LTDR), medium-term DR (MTDR), and short-term DR (STDR) on the expression of proteins involved in insulin signaling in the hippocampus of 18- and 24-month-old male Wistar rats. We found that DR-induced changes in insulin levels in the brain may be independent of what happens in the periphery after restricted feeding. Significantly changed insulin content in the hippocampus, together with altered insulin signaling were found under the influence of DR, but the outcome was highly dependent on the onset and duration of DR.

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.

Lycium Barbarum Polysaccharides Improves Cognitive Functions in ICV-STZ-Induced Alzheimer's Disease Mice Model by Improving the Synaptic Structural Plasticity and Regulating IRS1/PI3K/AKT Signaling Pathway

Lycium barbarum polysaccharide (LBP) have a certain curative effect on hypoglycemic and neuroprotective effects, but the specific mechanism is unclear and needs to be further explored. This study aimed to clarify the mechanisms of LBP in the treatment of ICV-STZ mice model of AD from the perspectives of insulin resistance, IRS1/PI3K/AKT signaling pathway, and synaptic protein expression. We used male C57BL/6J mice injected with STZ (3 mg/kg) in the lateral ventricle as an AD model. After treatment with LBP, the learning and memory abilities of ICV-STZ mice were enhanced, and the pathological changes in brain tissue were alleviated. LBP can regulate the expression of proteins related to the IRS1/PI3K/AKT signaling pathway and thereby reducing Aβ deposition and tau protein phosphorylation in the brain of ICV-STZ mice. In addition, LBP also can up-regulate the expression of synaptic proteins. The results indicated that LBP played a neuroprotective role by regulating the IRS1/PI3K/AKT pathway, inhibiting tau protein hyperphosphorylation and improving the expression levels of synapse-related proteins.

Role of the Insulin-like Growth Factor System in Neurodegenerative Disease

The insulin-like growth factor (IGF) system has paracrine and endocrine roles in the central nervous system. There is evidence that IGF signalling pathways have roles in the pathophysiology of neurodegenerative disease. This review focusses on Alzheimer's disease and Parkinson's disease, the two most common neurodegenerative disorders that are increasing in prevalence globally in relation to the aging population and the increasing prevalence of obesity and type 2 diabetes. Rodent models used in the study of the molecular pathways involved in neurodegeneration are described. However, currently, no animal model fully replicates these diseases. Mice with triple mutations in APP, PSEN and MAPT show promise as models for the testing of novel Alzheimer's therapies. While a causal relationship is not proven, the fact that age, obesity and T2D are risk factors in both strengthens the case for the involvement of the IGF system in these disorders. The IGF system is an attractive target for new approaches to management; however, there are gaps in our understanding that first need to be addressed. These include a focus beyond IGF-I on other members of the IGF system, including IGF-II, IGF-binding proteins and the type 2 IGF receptor.

Differential DNA methylation associated with delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage: a systematic review

Recent studies suggest that differential DNA methylation could play a role in the mechanism of cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH). Considering the significance of this matter and a lack of effective prophylaxis against DCI, we aim to summarize the current state of knowledge regarding their associations with DNA methylation and identify the gaps for a future trial. PubMed MEDLINE, Scopus, and Web of Science were searched by two authors in three waves for relevant DNA methylation association studies in DCI after aSAH. PRISMA checklist was followed for a systematic structure. STROBE statement was used to assess the quality and risk of bias within studies. This research was funded by the National Science Centre, Poland (grant number 2021/41/N/NZ2/00844). Of 70 records, 7 peer-reviewed articles met the eligibility criteria. Five studies used a candidate gene approach, three were epigenome-wide association studies (EWAS), one utilized bioinformatics of the previous EWAS, with two studies using more than one approach. Methylation status of four cytosine-guanine dinucleotides (CpGs) related to four distinct genes (ITPR3, HAMP, INSR, CDHR5) have been found significantly or suggestively associated with DCI after aSAH. Analysis of epigenetic clocks yielded significant association of lower age acceleration with radiological CVS but not with DCI. Hub genes for hypermethylation (VHL, KIF3A, KIFAP3, RACGAP1, OPRM1) and hypomethylation (ALB, IL5) in DCI have been indicated through bioinformatics analysis. As none of the CpGs overlapped across the studies, meta-analysis was not applicable. The identified methylation sites might potentially serve as a biomarker for early diagnosis of DCI after aSAH in future. However, a lack of overlapping results prompts the need for large-scale multicenter studies. Challenges and prospects are discussed.

The Role Played by Mitochondria in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) refers to an endocrine disorder syndrome that are correlated with multiple organs and systems. PCOS has an effect on women at all stages of their lives, and it has an incidence nearly ranging from 6% to 20% worldwide. Mitochondrial dysfunctions (e.g., oxidative stress, dynamic imbalance, and abnormal quality control system) have been identified in patients and animal models of PCOS, and the above processes may play a certain role in the development of PCOS and its associated complications. However, their specific pathogenic roles should be investigated in depth. In this review, recent studies on the mechanisms of action of mitochondrial dysfunction in PCOS and its associated clinical manifestations are summarized from the perspective of tissues and organs, and some studies on the treatment of the disease by improving mitochondrial function are reviewed to highlight key role of mitochondrial dysfunction in this syndrome.

Unravelling the effect of renal denervation on glucose homeostasis: more questions than answers?

Renal Denervation (RDN) is an interventional, endovascular procedure used for the management of hypertension. The procedure itself aims to ablate the renal sympathetic nerves and to interrupt the renal sympathetic nervous system overactivation, thus decreasing blood pressure (BP) levels and total sympathetic drive in the body. Recent favorable evidence for RDN resulted in the procedure being included in the recent European Guidelines for the management of Hypertension, while RDN is considered the third pillar, along with pharmacotherapy, for managing hypertension. Sympathetic overactivation, however, is associated with numerous other pathologies, including diabetes, metabolic syndrome and glycemic control, which are linked to adverse cardiovascular health and outcomes. Therefore, RDN, via ameliorating sympathetic response, could be also proven beneficial for maintaining an euglycemic status in patients with cardiovascular disease, alongside its BP-lowering effects. Several studies have aimed, over the years, to provide evidence regarding the pathophysiological effects of RDN in glucose homeostasis as well as investigate the potential clinical benefits of the procedure in glucose and insulin homeostasis. The purpose of this review is, thus, to analyze the pathophysiological links between the autonomous nervous system and glycemic control, as well as provide an overview of the available preclinical and clinical data regarding the effect of RDN in glycemic control.

Changes in Cells Associated with Insulin Resistance

Insulin is a polypeptide hormone synthesized and secreted by pancreatic β-cells. It plays an important role as a metabolic hormone. Insulin influences the metabolism of glucose, regulating plasma glucose levels and stimulating glucose storage in organs such as the liver, muscles and adipose tissue. It is involved in fat metabolism, increasing the storage of triglycerides and decreasing lipolysis. Ketone body metabolism also depends on insulin action, as insulin reduces ketone body concentrations and influences protein metabolism. It increases nitrogen retention, facilitates the transport of amino acids into cells and increases the synthesis of proteins. Insulin also inhibits protein breakdown and is involved in cellular growth and proliferation. On the other hand, defects in the intracellular signaling pathways of insulin may cause several disturbances in human metabolism, resulting in several chronic diseases. Insulin resistance, also known as impaired insulin sensitivity, is due to the decreased reaction of insulin signaling for glucose levels, seen when glucose use in response to an adequate concentration of insulin is impaired. Insulin resistance may cause, for example, increased plasma insulin levels. That state, called hyperinsulinemia, impairs metabolic processes and is observed in patients with type 2 diabetes mellitus and obesity. Hyperinsulinemia may increase the risk of initiation, progression and metastasis of several cancers and may cause poor cancer outcomes. Insulin resistance is a health problem worldwide; therefore, mechanisms of insulin resistance, causes and types of insulin resistance and strategies against insulin resistance are described in this review. Attention is also paid to factors that are associated with the development of insulin resistance, the main and characteristic symptoms of particular syndromes, plus other aspects of severe insulin resistance. This review mainly focuses on the description and analysis of changes in cells due to insulin resistance.

A review of the mechanisms of abnormal ceramide metabolism in type 2 diabetes mellitus, Alzheimer's disease, and their co-morbidities

The global prevalence of type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) is rapidly increasing, revealing a strong association between these two diseases. Currently, there are no curative medication available for the comorbidity of T2DM and AD. Ceramides are structural components of cell membrane lipids and act as signal molecules regulating cell homeostasis. Their synthesis and degradation play crucial roles in maintaining metabolic balance in vivo, serving as important mediators in the development of neurodegenerative and metabolic disorders. Abnormal ceramide metabolism disrupts intracellular signaling, induces oxidative stress, activates inflammatory factors, and impacts glucose and lipid homeostasis in metabolism-related tissues like the liver, skeletal muscle, and adipose tissue, driving the occurrence and progression of T2DM. The connection between changes in ceramide levels in the brain, amyloid β accumulation, and tau hyper-phosphorylation is evident. Additionally, ceramide regulates cell survival and apoptosis through related signaling pathways, actively participating in the occurrence and progression of AD. Regulatory enzymes, their metabolites, and signaling pathways impact core pathological molecular mechanisms shared by T2DM and AD, such as insulin resistance and inflammatory response. Consequently, regulating ceramide metabolism may become a potential therapeutic target and intervention for the comorbidity of T2DM and AD. The paper comprehensively summarizes and discusses the role of ceramide and its metabolites in the pathogenesis of T2DM and AD, as well as the latest progress in the treatment of T2DM with AD.

Blood-brain barrier transporters: An overview of function, dysfunction in Alzheimer's disease and strategies for treatment

The blood-brain-barrier (BBB) has a major function in maintaining brain homeostasis by regulating the entry of molecules from the blood to the brain. Key players in BBB function are BBB transporters which are highly expressed in brain endothelial cells (BECs) and critical in mediating the exchange of nutrients and waste products. BBB transporters can also influence drug delivery into the brain by inhibiting or facilitating the entry of brain targeting therapeutics for the treatment of brain disorders, such as Alzheimer's disease (AD). Recent studies have shown that AD is associated with a disrupted BBB and transporter dysfunction, although their roles in the development in AD are not fully understand. Modulation of BBB transporter activity may pose a novel approach to enhance the delivery of drugs to the brain for enhanced treatment of AD. In this review, we will give an overview of key functions of BBB transporters and known changes in AD. In addition, we will discuss current strategies for transporter modulation for enhanced drug delivery into the brain.

Association of Triglyceride-Glucose Index With Cognitive Function and Brain Atrophy: A Population-Based Study

OBJECTIVE

To investigate the associations of triglyceride-glucose (TyG) index, a reliable surrogate marker for insulin resistance, with the function of various cognitive domains and brain structures among older adults.

DESIGN

A population-based cross-sectional study.

SETTING

Older adults living in the rural communities in China.

PARTICIPANTS

About 4,541 rural-dwelling dementia-free participants (age ≥65 years; 56.37% women) undertook examinations in March-September 2018 for MIND-China.

MEASUREMENTS

TyG index was calculated as ln[fasting triglyceride (mg/dL) × fasting glucose (mg/dL)/2]. A neuropsychological test battery was used to assess memory, attention, verbal fluency, and executive function. Volumetric brain measures were assessed on magnetic resonance imaging (MRI) in a subsample (n = 1,019). Data were analyzed with restricted cubic spline and multivariable general linear models.

RESULTS

An inverted J-shaped association was observed between TyG index and z-scores of multiple cognitive domains, such that among individuals with TyG index ≥8.57 (median), a higher TyG index was significantly associated with lower z-scores of memory, attention, verbal fluency, executive function, and global cognition (all p < 0.05); among people with TyG index <8.57, a higher TyG index was significantly associated with a higher executive function z-score (p < 0.05), but not with any of the other examined cognitive domains. In the MRI subsample, a higher TyG index was significantly associated with lower volumes of total brain tissue, gray matter, and white matter as well as greater cerebrospinal fluid volume (p < 0.05), but not with white matter hyperintensity volume.

CONCLUSIONS

Insulin resistance, as indicated by a high TyG index, was associated with poor function in multiple cognitive domains and global brain atrophy.

Dietary Marine Oils Selectively Decrease Obesogenic Diet-Derived Carbonylation in Proteins Involved in ATP Homeostasis and Glutamate Metabolism in the Rat Cerebellum

The regular intake of diets high in saturated fat and sugars increases oxidative stress and has been linked to cognitive decline and premature brain aging. The cerebellum is highly vulnerable to oxidative stress and thus, obesogenic diets might be particularly detrimental to this tissue. However, the precise molecular mechanisms behind obesity-related brain damage are still not clear. Since protein carbonylation, a biomarker of oxidative stress, influences protein functions and is involved in metabolic control, the current investigation addressed the effect of long-term high-fat and high-sucrose diet intake on the cerebellum of Sprague-Dawley rats by deciphering the changes caused in the carbonylated proteome. The antioxidant effects of fish oil supplementation on cerebellar carbonylated proteins were also investigated. Lipid peroxidation products and carbonylated proteins were identified and quantified using immunoassays and 2D-LC-MS/MS in the cerebellum. After 21 weeks of nutritional intervention, the obesogenic diet selectively increased carbonylation of the proteins that participate in ATP homeostasis and glutamate metabolism in the cerebellum. Moreover, the data demonstrated that fish oil supplementation restrained carbonylation of the main protein targets oxidatively damaged by the obesogenic diet, and additionally protected against carbonylation of several other proteins involved in amino acid biosynthesis and neurotransmission. Therefore, dietary interventions with fish oils could help the cerebellum to be more resilient to oxidative damage. The results could shed some light on the effect of high-fat and high-sucrose diets on redox homeostasis in the cerebellum and boost the development of antioxidant-based nutritional interventions to improve cerebellum health.