Insulin and leptin as potential cognitive enhancers in metabolic disorders and Alzheimer's disease

Obesity-induced chronic low-grade inflammation in adipose tissue: A pathway to Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of cognitive impairment worldwide. Overweight and obesity are strongly associated with comorbidities, such as hypertension, diabetes, and insulin resistance (IR), which contribute substantially to the development of AD and subsequent morbidity and mortality. Adipose tissue (AT) is a highly dynamic organ composed of a diverse array of cell types, which can be classified based on their anatomic localization or cellular composition. The expansion and remodeling of AT in the context of obesity involves immunometabolic and functional shifts steered by the intertwined actions of multiple immune cells and cytokine signaling within AT, which contribute to the development of metabolic disorders, IR, and systemic markers of chronic low-grade inflammation. Chronic low-grade inflammation, a prolonged, low-dose stimulation by specific immunogens that can progress from localized sites and affect multiple organs throughout the body, leads to neurodystrophy, increased apoptosis, and disruption of homeostasis, manifesting as brain atrophy and AD-related pathology. In this review, we sought to elucidate the mechanisms by which AT contributes to the onset and progression of AD in obesity through the mediation of chronic low-grade inflammation, particularly focusing on the roles of adipokines and AT-resident immune cells.

Putative Molecular Mechanisms Underpinning the Inverse Roles of Mitochondrial Respiration and Heme Function in Lung Cancer and Alzheimer's Disease

Mitochondria are the powerhouse of the cell. Mitochondria serve as the major source of oxidative stress. Impaired mitochondria produce less adenosine triphosphate (ATP) but generate more reactive oxygen species (ROS), which could be a major factor in the oxidative imbalance observed in Alzheimer's disease (AD). Well-balanced mitochondrial respiration is important for the proper functioning of cells and human health. Indeed, recent research has shown that elevated mitochondrial respiration underlies the development and therapy resistance of many types of cancer, whereas diminished mitochondrial respiration is linked to the pathogenesis of AD. Mitochondria govern several activities that are known to be changed in lung cancer, the largest cause of cancer-related mortality worldwide. Because of the significant dependence of lung cancer cells on mitochondrial respiration, numerous studies demonstrated that blocking mitochondrial activity is a potent strategy to treat lung cancer. Heme is a central factor in mitochondrial respiration/oxidative phosphorylation (OXPHOS), and its association with cancer is the subject of increased research in recent years. In neural cells, heme is a key component in mitochondrial respiration and the production of ATP. Here, we review the role of impaired heme metabolism in the etiology of AD. We discuss the numerous mitochondrial effects that may contribute to AD and cancer. In addition to emphasizing the significance of heme in the development of both AD and cancer, this review also identifies some possible biological connections between the development of the two diseases. This review explores shared biological mechanisms (Pin1, Wnt, and p53 signaling) in cancer and AD. In cancer, these mechanisms drive cell proliferation and tumorigenic functions, while in AD, they lead to cell death. Understanding these mechanisms may help advance treatments for both conditions. This review discusses precise information regarding common risk factors, such as aging, obesity, diabetes, and tobacco usage.

Tauroursodeoxycholic acid: a bile acid that may be used for the prevention and treatment of Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disease that has become one of the main factors affecting human health. It has serious impacts on individuals, families, and society. With the development of population aging, the incidence of AD will further increase worldwide. Emerging evidence suggests that many physiological metabolic processes, such as lipid metabolism, are implicated in the pathogenesis of AD. Bile acids, as the main undertakers of lipid metabolism, play an important role in the occurrence and development of Alzheimer's disease. Tauroursodeoxycholic acid, an endogenous bile acid, has been proven to possess therapeutic effects in different neurodegenerative diseases, including Alzheimer's disease. This review tries to find the relationship between bile acid metabolism and AD, as well as explore the therapeutic potential of bile acid taurocursodeoxycholic acid for this disease. The potential mechanisms of taurocursodeoxycholic acid may include reducing the deposition of Amyloid-β protein, regulating apoptotic pathways, preventing tau hyperphosphorylation and aggregation, protecting neuronal synapses, exhibiting anti-inflammatory properties, and improving metabolic disorders. The objective of this study is to shed light on the use of tauroursodeoxycholic acid preparations in the prevention and treatment of AD, with the aim of identifying effective treatment targets and clarifying various treatment mechanisms involved in this disease.

Exercise Reshapes the Brain: Molecular, Cellular, and Structural Changes Associated with Cognitive Improvements

Physical exercise is well known as a non-pharmacological and holistic therapy believed to prevent and mitigate numerous neurological conditions and alleviate ageing-related cognitive decline. To do so, exercise affects the central nervous system (CNS) at different levels. It changes brain physiology and structure, promoting cognitive improvements, which ultimately improves quality of life. Most of these effects are mediated by neurotrophins release, enhanced adult hippocampal neurogenesis, attenuation of neuroinflammation, modulation of cerebral blood flow, and structural reorganisation, besides to promote social interaction with beneficial cognitive outcomes. In this review, we discuss, based on experimental and human research, how exercise impacts the brain structure and function and how these changes contribute to cognitive improvements. Understanding the mechanisms by which exercise affects the brain is essential to understand the brain plasticity following exercise, guiding therapeutic approaches to improve the quality of life, especially in obesity, ageing, neurodegenerative disorders, and following traumatic brain injury.

Recent progress in leptin signaling from a structural perspective and its implications for diseases

As a multi-potency cytokine, leptin not only plays a crucial role in controlling weight and energy homeostasis but also participates in the metabolic balance in the human body. Leptin is a small helical protein with a molecular weight of 16 kDa. It can interact with multiple subtypes of its receptors to initiate intracellular signal transduction and exerts physiological effects. Disturbances in leptin signaling may lead to obesity and a variety of metabolic diseases. Leptin was also found to be a critical factor in many diseases of the elderly. In this review, we focus on recent advances in the structural and molecular mechanisms of leptin signaling through its receptors with the aim of a deeper understanding of leptin-related diseases.

Recent Advances in the Knowledge of the Mechanisms of Leptin Physiology and Actions in Neurological and Metabolic Pathologies

Excess body weight is frequently associated with low-grade inflammation. Evidence indicates a relationship between obesity and cancer, as well as with other diseases, such as diabetes and non-alcoholic fatty liver disease, in which inflammation and the actions of various adipokines play a role in the pathological mechanisms involved in these disorders. Leptin is mainly produced by adipose tissue in proportion to fat stores, but it is also synthesized in other organs, where leptin receptors are expressed. This hormone performs numerous actions in the brain, mainly related to the control of energy homeostasis. It is also involved in neurogenesis and neuroprotection, and central leptin resistance is related to some neurological disorders, e.g., Parkinson's and Alzheimer's diseases. In peripheral tissues, leptin is implicated in the regulation of metabolism, as well as of bone density and muscle mass. All these actions can be affected by changes in leptin levels and the mechanisms associated with resistance to this hormone. This review will present recent advances in the molecular mechanisms of leptin action and their underlying roles in pathological situations, which may be of interest for revealing new approaches for the treatment of diseases where the actions of this adipokine might be compromised.

Association of Adipokines with Alzheimer's Disease in a Chinese Cohort

BACKGROUND

The correlation between plasma adipose factor levels and Alzheimer's patients is not entirely clear.

OBJECTIVE

We aimed to investigate associations between AD and plasma levels of three adipokines including plasma adiponectin, leptin, and resistin.

METHODS

A single-center, cross-sectional study recruited AD patients (n = 148) and cognitively normal (CN) controls (n = 110). The multivariate logistic regression analysis was applied to determine associations of adiponectin, leptin, and resistin with the presence of AD. The receiver operating characteristic (ROC) analysis was employed to determine the diagnostic power of adiponectin, leptin and resistin for AD.

RESULTS

After adjusted for the conventional risk factors, plasma levels of leptin (OR = 0.417, 95% CI: 0.272-0.638, p < 0.0001) and adiponectin (OR = 1.249, 95% CI: 1.151-1.354, p < 0.0001) were associated with the presence of AD. In total participants, the plasma adiponectin level was negatively correlated with MMSE scores (p < 0.0001) and was positively with CDR scores (p < 0.0001) and age (p < 0.0001). The plasma level of leptin was negatively correlated with CDR scores (p < 0.0001) and positively correlated with MMSE scores (p < 0.0001). Both adiponectin (p < 0. 0001) and leptin (p < 0. 0001) featured higher AUC than the random chance.

CONCLUSIONS

Plasma adiponectin and leptin were associated with the presence, symptomatic severity, and diagnostic power of AD, suggesting a potential role of adipokines in the pathogenesis of AD.

Increased ghrelin and decreased leptin levels in patients with antisocial personality disorder

OBJECTIVE

The study aimed to compare acyl ghrelin (AG), des-acyl ghrelin (DAG), and leptin levels considered to be used as biological markers in the etiopathogenesis of antisocial personality disorder (ASPD) with healthy controls, and to investigate the relationship between these hormones and aggression and impulsivity.

METHOD

The study included 45 patients with ASPD and 61 healthy people in the control group. Sociodemographic data form, Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Barratt Impulsiveness Scale (BIS-11), and Buss-Durkee Aggression Scale (BDAS) were applied to all participants. Fasting venous blood samples were taken from all participants at the same time of the day and the height and weight of the participants were measured.

RESULTS

It was found that the mean serum AG and DAG levels were significantly higher than that of healthy controls whereas leptin hormone levels were significantly lower in patients compared to healthy controls. BDI, BAI, BIS-11, and BDAS scores of the patients were significantly higher compared to healthy controls. There was a positive correlation between AG and DAG hormone levels and impulsivity and aggression.

DISCUSSION

The present study is the first in the literature to examine AG, DAG, and leptin hormone levels of patients diagnosed with ASPD. According to the results of the study, it is believed that changes in serum leptin and ghrelin levels will bring a new perspective in terms of understanding the pathophysiological mechanism of ASPD. Further studies are required to explain the definitive roles of these hormones in ASPD.

Can Alzheimer's Disease Be Secondary to Type-2 Diabetes Mellitus?

Alzheimer's disease and insulin resistance are prevalent in older adults. Insulin's ability to effectively affect target tissues is diminished by IR. Hyperglycemia, higher blood pressure, elevated triglyceride levels, decreased HDL levels and central obesity are the outcomes of a condition, namely metabolic syndrome. Cognitive impairment and abnormalities of the brain have been linked to metabolic syndrome (MetS), a grouping of risk factors for type 2 diabetes mellitus. Type-2 diabetes mellitus and its relationship to other conditions have been investigated on the assorted extent in the pair of, human and animal subjects. First, it was shown that insulin receptors are present in the brain, namely the hippocampus. Most insulin is delivered to the brain by crossing the blood-brain barrier. Second, numerous research revealed that insulin impacts various neurotransmitters in a way that enhances memory and cognition. Thirdly, several pathological research has also shown that beta-amyloid plaques, hyperphosphorylated tau protein, and brain shrinkage, particularly in the hippocampus, are shared brain lesions between insulin and Alzheimer's disease. In light of this, type 2 diabetes mellitus may be viewed as a liability for dementia and Alzheimer's disease.

Targeted Mitochondrial Epigenetics: A New Direction in Alzheimer’s Disease Treatment

Mitochondrial epigenetic alterations are closely related to Alzheimer’s disease (AD), which is described in this review. Reports of the alteration of mitochondrial DNA (mtDNA) methylation in AD demonstrate that the disruption of the dynamic balance of mtDNA methylation and demethylation leads to damage to the mitochondrial electron transport chain and the obstruction of mitochondrial biogenesis, which is the most studied mitochondrial epigenetic change. Mitochondrial noncoding RNA modifications and the post-translational modification of mitochondrial nucleoproteins have been observed in neurodegenerative diseases and related diseases that increase the risk of AD. Although there are still relatively few mitochondrial noncoding RNA modifications and mitochondrial nuclear protein post-translational modifications reported in AD, we have reason to believe that these mitochondrial epigenetic modifications also play an important role in the AD process. This review provides a new research direction for the AD mechanism, starting from mitochondrial epigenetics. Further, this review summarizes therapeutic approaches to targeted mitochondrial epigenetics, which is the first systematic summary of therapeutic approaches in the field, including folic acid supplementation, mitochondrial-targeting antioxidants, and targeted ubiquitin-specific proteases, providing a reference for therapeutic targets for AD.

Brain effect of bariatric surgery in people with obesity

BACKGROUND/OBJECTIVES

The link between obesity and brain function is a fascinating but still an enigmatic topic. We evaluated the effect of Roux-en-Y gastric bypass (RYGB) on peripheral glucose metabolism, insulin sensitivity, brain glucose utilization and cognitive abilities in people with obesity.

SUBJECTS/METHODS

Thirteen subjects with obesity (F/M 11/2; age 44.4 ± 9.8 years; BMI 46.1 ± 4.9 kg/m²) underwent 75-g OGTT during a [18F]FDG dynamic brain PET/CT study at baseline and 6 months after RYGB. At the same timepoints, cognitive performance was tested with Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), Trail making test (TMT) and Token test (TT). Glucose, insulin, C-peptide, GLP-1, GIP, and VIP levels were measured during OGTT. Leptin and BDNF levels were measured before glucose ingestion.

RESULTS

RYGB resulted in significant weight loss (from 46.1 ± 4.9 to 35.3 ± 5.0 kg/m²; p < 0.01 vs baseline). Insulin sensitivity improved (disposition index: from 1.1 ± 0.2 to 2.9 ± 1.1; p = 0.02) and cerebral glucose metabolic rate (CMRg) declined in various brain areas (all p ≤ 0.01). MMSE and MoCA score significantly improved (p = 0.001 and p = 0.002, respectively). TMT and TT scores showed a slight improvement. A positive correlation was found between CMRg change and HOMA-IR change in the caudate nucleus (ρ = 0.65, p = 0.01). Fasting leptin decreased (from 80.4 ± 13.0 to 16.1 ± 2.4 ng/dl; p = 0.001) and correlated with CMRg change in the hippocampus (ρ = 0.50; p = 0.008). CMRg change was correlated with cognitive scores changes on the TMT and TT (all p = 0.04 or less).

CONCLUSIONS

Bariatric surgery improves CMRg directly related to a better cognitive testing result. This study highlights the potential pleiotropic effects of bariatric surgery.

TRIAL REGISTRY NUMBER

NCT03414333.

Integrated Analyses of Microbiomics and Metabolomics Explore the Effect of Gut Microbiota Transplantation on Diabetes-Associated Cognitive Decline in Zucker Diabetic Fatty Rats

Diabetes-associated cognitive decline (DACD), one of the complications of type 2 diabetes (T2DM), correlates significantly with the disorder in glycolipid metabolism, insulin/leptin resistance, and accumulation of β-amyloid (Aβ). Although gut microbiota transplantation (GMT), a novel non-invasive physiotherapy strategy, has been a promising intervention to alleviate the symptoms of T2DM, its protective effect on progressive cognitive decline remains elusive. Here, we transplanted the gut microbiota of healthy or cognitive decline donor rats into ZDF or LZ rats, and integrated microbiomics and metabolomics to evaluate the directional effect of the gut microbiota on the recipient rats. The basal metabolism phenotype changed in ZDF rats instead of in LZ rats. One possible mechanism is that the microbiota and metabolites alter the structure of the intestinal tract, stimulate the brain insulin and leptin signaling pathways, and regulate the deposition of Aβ in the brain. It is worth noting that 10 species of genera, such as Parabacteroides, Blautia, and Lactobacillus, can regulate 20 kinds of metabolites, such as propanoic acid, acetic acid, and citramalic acid, and having a significant improvement on the cognitive behavior of ZDF rats. In addition, the correlation analysis indicated the gut microbiota and metabolites are highly associated with host phenotypes affected by GMT. In summary, our study indicates that altering the microbiota-gut-brain axis by reshaping the composition of gut microbiota is a viable strategy that has great potential for improving cognitive function and combatting DACD.

Obesity as a Risk Factor for Dementia and Alzheimer's Disease: The Role of Leptin

Obesity is a growing worldwide health problem, affecting many people due to excessive saturated fat consumption, lack of exercise, or a sedentary lifestyle. Leptin is an adipokine secreted by adipose tissue that increases in obesity and has central actions not only at the hypothalamic level but also in other regions and nuclei of the central nervous system (CNS) such as the cerebral cortex and hippocampus. These regions express the long form of leptin receptor LepRb, which is the unique leptin receptor capable of transmitting complete leptin signaling, and are the first regions to be affected by chronic neurocognitive deficits, such as mild cognitive impairment (MCI) and Alzheimer's Disease (AD). In this review, we discuss different leptin resistance mechanisms that could be implicated in increasing the risk of developing AD, as leptin resistance is frequently associated with obesity, which is a chronic low-grade inflammatory state, and obesity is considered a risk factor for AD. Key players of leptin resistance are SOCS3, PTP1B, and TCPTP whose signalling is related to inflammation and could be worsened in AD. However, some data are controversial, and it is necessary to further investigate the underlying mechanisms of the AD-causing pathological processes and how altered leptin signalling affects such processes.

Potentials of Neuropeptides as Therapeutic Agents for Neurological Diseases

Despite recent leaps in modern medicine, progress in the treatment of neurological diseases remains slow. The near impermeable blood-brain barrier (BBB) that prevents the entry of therapeutics into the brain, and the complexity of neurological processes, limits the specificity of potential therapeutics. Moreover, a lack of etiological understanding and the irreversible nature of neurological conditions have resulted in low tolerability and high failure rates towards existing small molecule-based treatments. Neuropeptides, which are small proteinaceous molecules produced by the body, either in the nervous system or the peripheral organs, modulate neurological function. Although peptide-based therapeutics originated from the treatment of metabolic diseases in the 1920s, the adoption and development of peptide drugs for neurological conditions are relatively recent. In this review, we examine the natural roles of neuropeptides in the modulation of neurological function and the development of neurological disorders. Furthermore, we highlight the potential of these proteinaceous molecules in filling gaps in current therapeutics.

Metabolic determinants of Alzheimer's disease: A focus on thermoregulation

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease, associated with central and peripheral metabolic anomalies, such as impaired glucose utilization and insulin resistance. These observations led to a considerable interest not only in lifestyle-related interventions, but also in repurposing insulin and other anti-diabetic drugs to prevent or treat dementia. Body temperature is the oldest known metabolic readout and mechanisms underlying its maintenance fail in the elderly, when the incidence of AD rises. This raises the possibility that an age-associated thermoregulatory deficit contributes to energy failure underlying AD pathogenesis. Brown adipose tissue (BAT) plays a central role in thermogenesis and maintenance of body temperature. In recent years, the modulation of BAT activity has been increasingly demonstrated to regulate energy expenditure, insulin sensitivity and glucose utilization, which could also provide benefits for AD. Here, we review the evidence linking thermoregulation, BAT and insulin-related metabolic defects with AD, and we propose mechanisms through which correcting thermoregulatory impairments could slow the progression and delay the onset of AD.

Infection and Immunometabolism in the Central Nervous System: A Possible Mechanistic Link Between Metabolic Imbalance and Dementia

Metabolic syndromes are frequently associated with dementia, suggesting that the dysregulation of energy metabolism can increase the risk of neurodegeneration and cognitive impairment. In addition, growing evidence suggests the link between infections and brain disorders, including Alzheimer's disease. The immune system and energy metabolism are in an intricate relationship. Infection triggers immune responses, which are accompanied by imbalance in cellular and organismal energy metabolism, while metabolic disorders can lead to immune dysregulation and higher infection susceptibility. In the brain, the activities of brain-resident immune cells, including microglia, are associated with their metabolic signatures, which may be affected by central nervous system (CNS) infection. Conversely, metabolic dysregulation can compromise innate immunity in the brain, leading to enhanced CNS infection susceptibility. Thus, infection and metabolic imbalance can be intertwined to each other in the etiology of brain disorders, including dementia. Insulin and leptin play pivotal roles in the regulation of immunometabolism in the CNS and periphery, and dysfunction of these signaling pathways are associated with cognitive impairment. Meanwhile, infectious complications are often comorbid with diabetes and obesity, which are characterized by insulin resistance and leptin signaling deficiency. Examples include human immunodeficiency virus (HIV) infection and periodontal disease caused by an oral pathogen Porphyromonas gingivalis. This review explores potential interactions between infectious agents and insulin and leptin signaling pathways, and discuss possible mechanisms underlying the relationship between infection, metabolic dysregulation, and brain disorders, particularly focusing on the roles of insulin and leptin.

The Potential Effect of Insulin on AChE and Its Interactions with Rivastigmine In Vitro

There is no definite cure for Alzheimer’s disease (AD) due to its multifactorial origin. Drugs that inhibit acetylcholinesterase (AChE), such as rivastigmine, are promising symptomatic treatments for AD. Emerging evidence suggests that insulin therapy can hinder several aspects of AD pathology. Insulin has been shown to modify the activity of AChE, but it is still unknown how insulin and AChE interact. Combination therapy, which targets several features of the disease based on existing medications, can provide a worthy therapy option for AD management. However, to date, no studies have examined the potential interaction of insulin with AChE and/or rivastigmine in vitro. In the present study, we employed the Response Surface Methodology (RSM) as an in vitro assessment to investigate the effect of insulin on both AChE activity and rivastigmine inhibitory action using a common spectrophotometric assay for cholinesterase activity, Ellman’s method. Our results showed that insulin, even at high concentrations, has an insignificant effect on both the activity of AChE and rivastigmine’s inhibitory action. The variance of our data is near zero, which means that the dispersion is negligible. However, to improve our understanding of the possible interaction of insulin and rivastigmine, or its target AChE, more in silico modelling and in vivo studies are needed.

Body Mass Index and Polygenic Risk for Alzheimer's Disease Predict Conversion to Alzheimer's Disease

Body mass index (BMI) is a risk factor for Alzheimer's disease (AD) although the relationship is complex. Obesity in midlife is associated with increased risk for AD, whereas evidence supports both higher and lower BMI increasing risk for AD in late life. This study examined the influence of individual differences in genetic risk for AD to further clarify the relationship between late-life BMI and conversion to AD. Participants included 52 individuals diagnosed as having mild cognitive impairment (MCI) at baseline who converted to AD within 24 months and 52 matched MCI participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. BMI was measured at baseline. Genetic risk for AD was assessed via genome-wide polygenic risk scores. Conditional logistic regression models were run to determine if BMI and polygenic risk predicted conversion to AD. Results showed an interaction between BMI and genetic risk, such that individuals with lower BMI and higher polygenic risk were more likely to convert to AD relative to individuals with higher BMI. These results remained significant after adjusting for cerebrospinal fluid biomarkers of AD. Exploratory sex-stratified analyses revealed this relationship only remained significant in males. These results show that higher genetic risk in the context of lower BMI predicts conversion to AD in the next 24 months, particularly among males. These findings suggest that genetic risk for AD in the context of lower BMI may serve as a prodromal risk factor for future conversion to AD.

Anti-Obesity Effect of Pine Needle Extract on High-Fat Diet-Induced Obese Mice

Background: Obesity due to an excessive intake of nutrient disturbs the hypothalamus-mediated energy metabolism subsequently develops metabolic disorders. In this study, we investigated the effect of pine needle extract (PNE) on the hypothalamic proopiomelanocortin (POMC) neurons involved in the regulation of energy balance via melanocortin system and fat tissue metabolism. Methods: We performed electrophysiological and immunohistochemical analyses to determine the effect of PNE on POMC neurons. Mice were fed a normal or high-fat diet for 12 weeks, then received PNE for the last 2 weeks to measure the following physiological indices: Body weight, food intake, fat/lean mass, glucose metabolism, and plasma leptin levels. In addition, changes of thermogenic, lipolytic, and lipogenetic markers were evaluated in brown adipose tissue (BAT) and white adipose tissue (WAT) by western blotting, respectively. Results: PNE increased hypothalamic POMC neuronal activity, and the effect was abolished by blockade of melanocortin 3/4 receptors (MC3/4Rs). PNE decreased body weight, fat mass, plasma leptin levels, and improved glucose metabolism after high-fat-induced obesity. However, PNE did not change the expression of thermogenic markers of the BAT in HFD fed groups, but decreased only the lipogenetic markers of WAT. This study suggests that PNE has a potent anti-obesity effect, inhibiting lipogenesis in WAT, even though HFD-induced leptin resistance-mediated disruption of POMC neuronal activity.

AMPK: A bridge between diabetes mellitus and Alzheimer's disease

The pathogenesis and etiology of diabetes mellitus (DM) and Alzheimer's disease (AD) share many common cellular and molecular themes. Recently, a growing body of research has shown that AMP-activated protein kinase (AMPK), a biomolecule that regulates energy balance and glucose and lipid metabolism, plays key roles in DM and AD. In this review, we summarize the relevant research on the roles of AMPK in DM and AD, including its functions in gluconeogenesis and insulin resistance (IR) and its relationships with amyloid β-protein (Aβ), Tau and AMPK activators. In DM, AMPK is involved in the regulation of glucose metabolism and IR. AMPK is closely related to gluconeogenesis, which can not only be activated by the upstream kinases liver kinase B1 (LKB1), transforming growth factor β-activated kinase 1 (TAK1), and Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) but also regulate the downstream kinases glucose-6-phosphatase (G-6-Pase) and phosphoenolpyruvate carboxy kinase (PEPCK), thereby affecting gluconeogenesis and ameliorating DM. Moreover, AMPK can regulate glucose transporter 4 (GLUT4) and free fatty acids to improve IR. In AD, AMPK can ameliorate abnormal brain energy metabolism, not only by reduces Aβ deposition through β-secretase but also reduces tau hyperphosphorylation through sirtuin 1 (SIRT1) and protein phosphatase 2A (PP2A). Therefore, AMPK is a bridge between DM and AD.

Plasma Leptin Reflects Progression of Neurofibrillary Pathology in Animal Model of Tauopathy

The close relationship between Alzheimer's disease (AD) and obesity was recognized many years ago. However, complete understanding of the pathological mechanisms underlying the interactions between degeneration of CNS and fat metabolism is still missing. The leptin a key adipokine of white adipose tissue has been suggested as one of the major mediators linking the obesity and AD. Here we investigated the association between peripheral levels of leptin, general metabolic status and stage of the pathogenesis in rat transgenic model of AD. We demonstrate significantly decreased levels of plasma leptin in animals with experimentally induced progressive neurofibrillary pathology, which represents only 62.3% (P = 0.0015) of those observed in normal wild type control animals. More detailed analysis showed a strong and statistically significant inverse correlation between the load of neurofibrillary pathology and peripheral levels of leptin (r = - 0.7248, P = 0.0177). We also observed a loss of body weight during development of neurodegeneration (about 14% less than control animals, P = 0.0004) and decrease in several metabolic parameters such as glucose, insulin, triglycerides and VLDL in plasma of the transgenic animals. Our data suggest that plasma leptin could serve as a convenient peripheral biomarker for tauopathies and Alzheimer's disease. Decrease in gene expression of leptin in fat tissue and its plasma level was found as one of the consequences of experimentally induced neurodegeneration. Our data may help to design rational diagnostic and therapeutic strategies for patients suffering from Alzheimer's disease or other forms of tauopathy.

Insulin resistance and bioenergetic manifestations: Targets and approaches in Alzheimer's disease

AIM

Insulin has a well-established role in cognition, neuronal detoxification and synaptic plasticity. Insulin transduction affect neurotransmitter functions, influence bioenergetics and regulate neuronal survival through regulating glucose energy metabolism and downward pathways.

METHODS

A systematic literature review of PubMed, Medline, Bentham, Scopus and EMBASE (Elsevier) databases was carried out with the help of the keywords like "Alzheimer's disease; Hypometabolism; Oxidative stress; energy failure in AD, Insulin; Insulin resistance; Bioenergetics" till June 2020. The review was conducted using the above keywords to collect the latest articles and to understand the nature of the extensive work carried out on insulin resistance and bioenergetic manifestations in Alzheimer's disease.

KEY FINDINGS

The article sheds light on insulin resistance mediated hypometabolic state on pathological progression of AD. The disrupted insulin signaling has pathological outcome in form of disturbed glucose homeostasis, altered bioenergetic state which increases build-up of senile plaques (Aβ), neurofibrillary tangles (τ), decline in transportation of glucose and activation of inflammatory pathways. The mechanistic link of insulin resistant state with therapeutically explorable potential transduction pathways is the focus of the reviewed work.

SIGNIFICANCE

The present work opines that the mechanism by which the insulin resistance mediates dysregulation of bioenergetics and progresses to neurodegenerative state holds the tangible potential to succeed in the development of novel dementia therapies. Further, hypometabolic complications and altered insulin signaling may be explored as a mechanistic relation between bioenergetic deficits and AD.

New hopes for disease modification in Parkinson's Disease

To date, despite numerous clinical trials, no intervention has been demonstrated to modify the progression of Parkinson's disease (PD). However, over the past decades encouraging progress has been made towards a better understanding of molecular pathways relevant for the neurodegenerative process in PD. This is also based on new insights into the genetic architecture of the disease, revealing multiple novel targets for potentially disease-modifying interventions. Important achievements have also been made in the field of risk markers and combinations thereof, in the form of risk algorithms, will hopefully soon provide the possibility to identify affected individuals at yet prediagnostic or prodromal stages of the illness. Such phases of the disease would provide an ideal window for neuroprotection trials. Taken together, these developments offer hope that a breakthrough towards modifying the course of PD might be reached. In this article we summarize various approaches currently pursued in this quest. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.