Sitagliptin and liraglutide reversed nigrostriatal degeneration of rodent brain in rotenone-induced Parkinson’s disease

Impact of alogliptin on lipopolysaccharide-induced experimental Parkinson's disease: Unrevealing neurochemical and histopathological alterations in rodents

BACKGROUND

Degeneration of the nigrostriatal dopaminergic pathway has been seen as a significant cause of movement disability in Parkinson's disease (PD) patients. However, the exact reason for these degenerative changes has remained obscure. In recent years, incretins have been neuroprotective in various pathologies. In the current study, we have investigated the neuroprotective potential of alogliptin (Alo), a dipeptidyl peptidase-IV (DPP-IV) inhibitor, in a lipopolysaccharide (LPS) induced experimental model of PD.

EXPERIMENTAL APPROACH

LPS (5μg/5 μl) was infused intranigrally to induce PD in experimental rats. Post-LPS infusion, these animals were treated with Alo for 21 days in three successive dosages of 10, 20, and 40 mg/kg/day/per oral. The study is well supported with the determinations of motor functions biochemical, neurochemical, and histological analysis.

KEY RESULTS

Intranigral infusion of LPS in rats produced motor deficit. It was accompanied by oxidative stress, elevation in neuroinflammatory cytokines, altered neurochemistry, and degenerative changes in the striatal brain region. While Alo abrogated LPS-induced biochemical/neurochemical alterations, improved motor functions, and preserved neuronal morphology in LPS-infused rats.

CONCLUSION

The observed neuroprotective potential of Alo may be due to its antioxidant and anti-inflammatory actions and its ability to modulate monoaminergic signals. Nonetheless, current findings suggest that improving the availability of incretins through DPP-IV inhibition is a promising strategy for treating Parkinson's disease.

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

DPP-4 inhibitors sitagliptin and PF-00734,200 mitigate dopaminergic neurodegeneration, neuroinflammation and behavioral impairment in the rat 6-OHDA model of Parkinson's disease

Epidemiological studies report an elevated risk of Parkinson's disease (PD) in patients with type 2 diabetes mellitus (T2DM) that is mitigated in those prescribed dipeptidyl peptidase 4 (DPP-4) inhibitors. With an objective to characterize clinically translatable doses of DPP-4 inhibitors (gliptins) in a well-characterized PD rodent model, sitagliptin, PF-00734,200 or vehicle were orally administered to rats initiated either 7-days before or 7-days after unilateral medial forebrain bundle 6-hydroxydopamine (6-OHDA) lesioning. Measures of dopaminergic cell viability, dopamine content, neuroinflammation and neurogenesis were evaluated thereafter in ipsi- and contralateral brain. Plasma and brain incretin and DPP-4 activity levels were quantified. Furthermore, brain incretin receptor levels were age-dependently evaluated in rodents, in 6-OHDA challenged animals and human subjects with/without PD. Cellular studies evaluated neurotrophic/neuroprotective actions of combined incretin administration. Pre-treatment with oral sitagliptin or PF-00734,200 reduced methamphetamine (meth)-induced rotation post-lesioning and dopaminergic degeneration in lesioned substantia nigra pars compacta (SNc) and striatum. Direct intracerebroventricular gliptin administration lacked neuroprotective actions, indicating that systemic incretin-mediated mechanisms underpin gliptin-induced favorable brain effects. Post-treatment with a threefold higher oral gliptin dose, likewise, mitigated meth-induced rotation, dopaminergic neurodegeneration and neuroinflammation, and augmented neurogenesis. These gliptin-induced actions associated with 70-80% plasma and 20-30% brain DPP-4 inhibition, and elevated plasma and brain incretin levels. Brain incretin receptor protein levels were age-dependently maintained in rodents, preserved in rats challenged with 6-OHDA, and in humans with PD. Combined GLP-1 and GIP receptor activation in neuronal cultures resulted in neurotrophic/neuroprotective actions superior to single agonists alone. In conclusion, these studies support further evaluation of the repurposing of clinically approved gliptins as a treatment strategy for PD.

GLP-1 Receptor Agonists: A New Treatment in Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Recent data highlight similarities between neurodegenerative diseases, including PD and type 2 diabetes mellitus (T2DM), suggesting a crucial interplay between the gut-brain axis. Glucagon-like peptide-1 receptor (GLP-1R) agonists, known for their use in T2DM treatment, are currently extensively studied as novel PD modifying agents. For this narrative review article, we searched PubMed and Scopus databases for peer-reviewed research, review articles and clinical trials regarding GLP-1R agonists and PD published in the English language with no time restrictions. We also screened the references of the selected articles for possible additional articles in order to include most of the key recent evidence. Many data on animal models and preclinical studies show that GLP1-R agonists can restore dopamine levels, inhibit dopaminergic loss, attenuate neuronal degeneration and alleviate motor and non-motor features of PD. Evidence from clinical studies is also very promising, enhancing the possibility of adding GLP1-R agonists to the current armamentarium of drugs available for PD treatment.

Sitagliptin elevates plasma and CSF incretin levels following oral administration to nonhuman primates: relevance for neurodegenerative disorders

The endogenous incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) possess neurotrophic, neuroprotective, and anti-neuroinflammatory actions. The dipeptidyl peptidase 4 (DPP-4) inhibitor sitagliptin reduces degradation of endogenous GLP-1 and GIP, and, thereby, extends the circulation of these protective peptides. The current nonhuman primate (NHP) study evaluates whether human translational sitagliptin doses can elevate systemic and central nervous system (CNS) levels of GLP-1/GIP in naive, non-lesioned NHPs, in line with our prior rodent studies that demonstrated sitagliptin efficacy in preclinical models of Parkinson's disease (PD). PD is an age-associated neurodegenerative disorder whose current treatment is inadequate. Repositioning of the well-tolerated and efficacious diabetes drug sitagliptin provides a rapid approach to add to the therapeutic armamentarium for PD. The pharmacokinetics and pharmacodynamics of 3 oral sitagliptin doses (5, 20, and 100 mg/kg), equivalent to the routine clinical dose, a tolerated higher clinical dose and a maximal dose in monkey, were evaluated. Peak plasma sitagliptin levels were aligned both with prior reports in humans administered equivalent doses and with those in rodents demonstrating reduction of PD associated neurodegeneration. Although CNS uptake of sitagliptin was low (cerebrospinal fluid (CSF)/plasma ratio 0.01), both plasma and CSF concentrations of GLP-1/GIP were elevated in line with efficacy in prior rodent PD studies. Additional cellular studies evaluating human SH-SY5Y and primary rat ventral mesencephalic cultures challenged with 6-hydroxydopamine, established cellular models of PD, demonstrated that joint treatment with GLP-1 + GIP mitigated cell death, particularly when combined with DPP-4 inhibition to maintain incretin levels. In conclusion, this study provides a supportive translational step towards the clinical evaluation of sitagliptin in PD and other neurodegenerative disorders for which aging, similarly, is the greatest risk factor.

Acute and Chronic Exposure to Linagliptin, a Selective Inhibitor of Dipeptidyl Peptidase-4 (DPP-4), Has an Effect on Dopamine, Serotonin and Noradrenaline Level in the Striatum and Hippocampus of Rats

Linagliptin is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor that indirectly elevates the glucagon-like peptide-1 (GLP-1) level. The aim of the present study was to check whether linagliptin has an influence on neurotransmission in rat brain. Rats were acutely and chronically exposed to linagliptin (10 and 20 mg/kg, intraperitoneally (i.p.)). Twenty-four hours later, the striatum and hippocampus were selected for further studies. In neurochemical experiments, using high-performance liquid chromatography with electrochemical detection (HPLC-ED), the concentrations of three major neurotransmitters-dopamine, serotonin and noradrenaline-and their metabolites were measured. The analysis of mRNA expression of dopamine (D1 and D2), serotonin (5-HT-1 and 5-HT-2) and noradrenaline (α1 and α2a) receptors was also investigated using real-time quantitative reverse transcription polymerase chain reaction (RQ-PCR) in the same brain areas. Linagliptin has the ability to influence the dopaminergic system. In the striatum, the elevation of dopamine and its metabolites was observed after repeated administration of that linagliptin, and in the hippocampus, a reduction in dopamine metabolism was demonstrated. Acute linagliptin exposure increases the serotonin level in both areas, while after chronic linagliptin administration a tendency for the mRNA expression of serotoninergic receptors (5-HT1A and 5-HT2A) to increase was observed. A single instance of exposure to linagliptin significantly modified the noradrenaline level in the striatum and intensified noradrenaline turnover in the hippocampus. The recognition of the interactions in the brain between DPP-4 inhibitors and neurotransmitters and/or receptors is a crucial step for finding novel discoveries in the pharmacology of DPP-4 inhibitors and raises hope for further applications of DPP-4 inhibitors in clinical practices.

Dopamine in the Regulation of Glucose Homeostasis, Pathogenesis of Type 2 Diabetes, and Chronic Conditions of Impaired Dopamine Activity/Metabolism: Implication for Pathophysiological and Therapeutic Purposes

Dopamine regulates several functions, such as voluntary movements, spatial memory, motivation, sleep, arousal, feeding, immune function, maternal behaviors, and lactation. Less clear is the role of dopamine in the pathophysiology of type 2 diabetes mellitus (T2D) and chronic complications and conditions frequently associated with it. This review summarizes recent evidence on the role of dopamine in regulating insular metabolism and activity, the pathophysiology of traditional chronic complications associated with T2D, the pathophysiological interconnection between T2D and chronic neurological and psychiatric disorders characterized by impaired dopamine activity/metabolism, and therapeutic implications. Reinforcing dopamine signaling is therapeutic in T2D, especially in patients with dopamine-related disorders, such as Parkinson's and Huntington's diseases, addictions, and attention-deficit/hyperactivity disorder. On the other hand, although specific trials are probably needed, certain medications approved for T2D (e.g., metformin, pioglitazone, incretin-based therapy, and gliflozins) may have a therapeutic role in such dopamine-related disorders due to anti-inflammatory and anti-oxidative effects, improvement in insulin signaling, neuroinflammation, mitochondrial dysfunction, autophagy, and apoptosis, restoration of striatal dopamine synthesis, and modulation of dopamine signaling associated with reward and hedonic eating. Last, targeting dopamine metabolism could have the potential for diagnostic and therapeutic purposes in chronic diabetes-related complications, such as diabetic retinopathy.

A Dual GLP-1/GIP Receptor Agonist Is More Effective than Liraglutide in the A53T Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a complex syndrome with many elements, such as chronic inflammation, oxidative stress, mitochondrial dysfunction, loss of dopaminergic neurons, build-up of alpha-synuclein (α-syn) in cells, and energy depletion in neurons, that drive the disease. We and others have shown that treatment with mimetics of the growth factor glucagon-like peptide 1 (GLP-1) can normalize energy utilization, neuronal survival, and dopamine levels and reduce inflammation. Liraglutide is a GLP-1 analogue that recently showed protective effects in phase 2 clinical trials in PD patients and in Alzheimer disease patients. We have developed a novel dual GLP-1/GIP receptor agonist that can cross the blood-brain barrier and showed good protective effects in animal models of PD. Here, we test liraglutide against the dual GLP-1/GIP agonist DA5-CH (KP405) in the A53T tg mouse model of PD which expresses a human-mutated gene of α-synuclein. Drug treatment reduced impairments in three different motor tests, reduced levels of α-syn in the substantia nigra, reduced the inflammation response and proinflammatory cytokine levels in the substantia nigra and striatum, and normalized biomarker levels of autophagy and mitochondrial activities in A53T mice. DA5-CH was superior in almost all parameters measured and therefore may be a better drug treatment for PD than liraglutide.

Liraglutide modulates adhesion molecules and enhances cell properties in three-dimensional cultures of olfactory ensheathing cells

Cell transplantation using olfactory ensheathing cells (OECs) is a promising approach for nerve repair but there are numerous limitations with their delivery method. Three-dimensional (3D) cell culture systems potentially offer a powerful approach for cell production and delivery options. To further optimise the use of OECs, strategies to promote cell viability and maintain cell behaviours in 3D cultures become important. We previously demonstrated an anti-diabetic drug, liraglutide, could modulate OEC migration and re-model extracellular matrix in two-dimensional (2D) cultures. In the present study, we further investigated its beneficial effects in our 3D culture system using primary OECs. OECs treated with liraglutide at 100 nM showed improved cell viability and had modulated expression of N-cadherin and β1-integrin (two important cell adhesion molecules). When formed into 3D spheroids, the pre-treated OECs generated spheroids with an increased volume and a decreased cell density compared to control spheroids. OECs that subsequently migrated out of the liraglutide pre-treated spheroids had higher capacity for migration with increased duration and length, which was attributed to a reduction in the pauses during the migration. Moreover, OECs that migrated out from liraglutide spheroids had a more bipolar morphology consistent with higher migratory capacity. In summary, liraglutide improved the viability of OECs, modulated cell adhesion molecules, and resulted in stable 3D cell constructs which conferred enhanced migratory capacity on the OECs. Overall, liraglutide may potentially improve the therapeutic use of OECs for neural repair by enhancing the generation of stable 3D constructs and increasing the migratory behaviour of OECs.

The Molecular Mechanisms of the Relationship between Insulin Resistance and Parkinson's Disease Pathogenesis

Parkinson's disease (PD) is a degenerative condition resulting from the loss of dopaminergic neurons. This neuronal loss leads to motor and non-motor neurological symptoms. Most PD cases are idiopathic, and no cure is available. Recently, it has been proposed that insulin resistance (IR) could be a central factor in PD development. IR has been associated with PD neuropathological features like α-synuclein aggregation, dopaminergic neuronal loss, neuroinflammation, mitochondrial dysfunction, and autophagy. These features are related to impaired neurological metabolism, neuronal death, and the aggravation of PD symptoms. Moreover, pharmacological options that involve insulin signaling improvement and dopaminergic and non-dopaminergic strategies have been under development. These drugs could prevent the metabolic pathways involved in neuronal damage. All these approaches could improve PD outcomes. Also, new biomarker identification may allow for an earlier PD diagnosis in high-risk individuals. This review describes the main pathways implicated in PD development involving IR. Also, it presents several therapeutic options that are directed at insulin signaling improvement and could be used in PD treatment. The understanding of IR molecular mechanisms involved in neurodegenerative development could enhance PD therapeutic options and diagnosis.

Exploring Molecular Targets for Mitochondrial Therapies in Neurodegenerative Diseases

The progressive deterioration of function and structure of brain cells in neurodegenerative diseases is accompanied by mitochondrial dysfunction, affecting cellular metabolism, intracellular signaling, cell differentiation, morphogenesis, and the activation of programmed cell death. However, most of the efforts to develop therapies for Alzheimer's and Parkinson's disease have focused on restoring or maintaining the neurotransmitters in affected neurons, removing abnormal protein aggregates through immunotherapies, or simply treating symptomatology. However, none of these approaches to treating neurodegeneration can stop or reverse the disease other than by helping to maintain mental function and manage behavioral symptoms. Here, we discuss alternative molecular targets for neurodegeneration treatments that focus on mitochondrial functions, including regulation of calcium ion (Ca2+) transport, protein modification, regulation of glucose metabolism, antioxidants, metal chelators, vitamin supplementation, and mitochondrial transference to compromised neurons. After pre-clinical evaluation and studies in animal models, some of these therapeutic compounds have advanced to clinical trials and are expected to have positive outcomes in subjects with neurodegeneration. These mitochondria-targeted therapeutic agents are an alternative to established or conventional molecular targets that have shown limited effectiveness in treating neurodegenerative diseases.

DPP-4 inhibitors and type 2 diabetes mellitus in Parkinson's disease: a mutual relationship

Parkinson's disease (PD) usually occurs due to the degeneration of dopaminergic neurons in the substantia nigra (SN). Management of PD is restricted to symptomatic improvement. Consequently, a novel treatment for managing motor and non-motor symptoms in PD is necessary. Abundant findings support the protection of dipeptidyl peptidase 4 (DPP-4) inhibitors in PD. Consequently, this study aims to reveal the mechanism of DPP-4 inhibitors in managing PD. DPP-4 inhibitors are oral anti-diabetic agents approved for managing type 2 diabetes mellitus (T2DM). T2DM is linked with an increased chance of the occurrence of PD. Extended usage of DPP-4 inhibitors in T2DM patients may attenuate the development of PD by inhibiting inflammatory and apoptotic pathways. Thus, DPP-4 inhibitors like sitagliptin could be a promising treatment against PD neuropathology via anti-inflammatory, antioxidant, and anti-apoptotic impacts. DPP-4 inhibitors, by increasing endogenous GLP-1, can also reduce memory impairment in PD. In conclusion, the direct effects of DPP-4 inhibitors or indirect effects through increasing circulating GLP-1 levels could be an effective therapeutic strategy in treating PD patients through modulation of neuroinflammation, oxidative stress, mitochondrial dysfunction, and neurogenesis.

Beyond Weight Loss: Added Benefits Could Guide the Choice of Anti-Obesity Medications

PURPOSE OF REVIEW

To highlight the added benefits of approved and upcoming, centrally-acting, anti-obesity drugs, focusing not only on the most common metabolic and cardiovascular effects but also on their less explored clinical benefits and drawbacks, in order to provide clinicians with a tool for more comprehensive, pharmacological management of obesity.

RECENT FINDINGS

Obesity is increasingly prevalent worldwide and has become a challenge for healthcare systems and societies. Reduced life expectancy and cardiometabolic complications are some of the consequences of this complex disease. Recent insights into the pathophysiology of obesity have led to the development of several promising pharmacologic targets, so that even more effective drugs are on the horizon. The perspective of having a wider range of treatments increases the chance to personalize therapy. This primarily has the potential to take advantage of the long-term use of anti-obesity medication for safe, effective and sustainable weight loss, and to concomitantly address obesity complications/comorbidities when already established. The evolving scenario of the availability of anti-obesity drugs and the increasing knowledge of their added effects on obesity complications will allow clinicians to move into a new era of precision medicine.

Neuroprotective Role of DPP-4 Inhibitor Linagliptin Against Neurodegeneration, Neuronal Insulin Resistance and Neuroinflammation Induced by Intracerebroventricular Streptozotocin in Rat Model of Alzheimer's Disease

Alzheimer's disease (AD) is an age-related, multifactorial progressive neurodegenerative disorder manifested by cognitive impairment and neuronal death in the brain areas like hippocampus, yet the precise neuropathology of AD is still unclear. Continuous failure of various clinical trial studies demands the utmost need to explore more therapeutic targets against AD. Type 2 Diabetes Mellitus and neuronal insulin resistance due to serine phosphorylation of Insulin Receptor Substrate-1 at 307 exhibits correlation with AD. Dipeptidyl Peptidase-4 inhibitors (DPP-4i) have also indicated therapeutic effects in AD by increasing the level of Glucagon-like peptide-1 in the brain after crossing Blood Brain Barrier. The present study is hypothesized to examine Linagliptin, a DPP-4i in intracerebroventricular streptozotocin induced neurodegeneration, and neuroinflammation and hippocampal insulin resistance in rat model of AD. Following infusion on 1st and 3rd day, animals were treated orally with Linagliptin (0.513 mg/kg, 3 mg/kg, and 5 mg/kg) and donepezil (5 mg/kg) as a standard for 8 weeks. Neurobehavioral, biochemical and histopathological analysis was done at the end of treatment. Dose-dependently Linagliptin significantly reversed behavioral alterations done through locomotor activity (LA) and morris water maze (MWM) test. Moreover, Linagliptin augmented hippocampal GLP-1 and Akt-ser473 level and mitigated soluble Aβ (1-42), IRS-1 (s307), GSK-3β, TNF-α, IL-1β, IL-6, AchE and oxidative/nitrosative stress level. Histopathological analysis also exhibited neuroprotective and anti-amylodogenic effect in Hematoxylin and eosin and Congo red staining respectively. The findings of our study concludes remarkable dose-dependent therapeutic potential of Linagliptin against neuronal insulin resistance via IRS-1 and AD-related complication. Thus, demonstrates unique molecular mechanism that underlie AD.

Type 2 Diabetes and Parkinson's Disease: A Focused Review of Current Concepts

Highly reproducible epidemiological evidence shows that type 2 diabetes (T2D) increases the risk and rate of progression of Parkinson's disease (PD), and crucially, the repurposing of certain antidiabetic medications for the treatment of PD has shown early promise in clinical trials, suggesting that the effects of T2D on PD pathogenesis may be modifiable. The high prevalence of T2D means that a significant proportion of patients with PD may benefit from personalized antidiabetic treatment approaches that also confer neuroprotective benefits. Therefore, there is an immediate need to better understand the mechanistic relation between these conditions and the specific molecular pathways affected by T2D in the brain. Although there is considerable evidence that processes such as insulin signaling, mitochondrial function, autophagy, and inflammation are involved in the pathogenesis of both PD and T2D, the primary aim of this review is to highlight the evidence showing that T2D-associated dysregulation of these pathways occurs not only in the periphery but also in the brain and how this may facilitate neurodegeneration in PD. We also discuss the challenges involved in disentangling the complex relationship between T2D, insulin resistance, and PD, as well as important questions for further research. © 2022 International Parkinson and Movement Disorder Society.

Dipeptidyl peptidase 4(DPP4) inhibitors stride up the management of Parkinson's disease

Parkinson's disease (PD) is the 2^nd most common age-related hypokinetic disorder, characterized by dopaminergic degeneration and movement abnormalities. Dopaminergic degeneration in the basal ganglia is primarily seen in PD patients. The therapeutic strategies currently under investigation are to rescue dopaminergic degeneration and promote neuronal regeneration, which could halt disease progression. On the other hand, the therapeutic efficacy of existing drugs used in other disorders has been repurposed in neurodegenerative pathologies. DPP4 inhibitors widely used in treating diabetes have been considered viable target sites and are being tested for efficacy in neurodegenerative pathologies. DPP4 inhibitors have been reported to rescue neuronal degeneration and improve motor functions in various preclinical and clinical PD studies. The current review is focused on the neuroprotective potential, molecular mechanisms and therapeutic potential of DPP4 inhibitors in PD pathology.

Sitagliptin attenuates neuronal apoptosis via inhibiting the endoplasmic reticulum stress after acute spinal cord injury

Regulation of endoplasmic reticulum stress (ER) stress-induced apoptosis and nerve regeneration is a hopeful way for acute spinal cord injury (SCI). Sitagliptin (Sita) is one of dipeptidyl peptidase-4 (DPP-4) inhibitor, which is beneficial neurons damaged diseases. However, its protective mechanisms of avoiding nerve injury remain unclear. In this study, we further investigated the mechanism of the anti-apoptotic and neuroprotective effects of Sita in promoting locomotor recovery from SCI. In vivo results showed that Sita treatment reduced neural apoptosis caused by SCI. Moreover, Sita effectively attenuated the ER tress and associated apoptosis in rats with SCI. A striking feature was the occurrence of nerve fiber regeneration at the lesion site, which eventually led to significant locomotion recovery. In vitro results showed that the PC12 cell injury model induced by Thapsigargin (TG) also showed similar neuroprotective effects. Overall, sitagliptin showed potent neuroprotective effects by targeting the ER stress-induced apoptosis both in vivo and vitro, thus facilitating the regeneration of the injured spinal cord.

Alternative role of glucagon-like Peptide-1 receptor agonists in neurodegenerative diseases

Aging is a crucial risk factor for common neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Limited options are available for the treatment of age-related, multiple pathogenic mechanism-contributed diseases that usually advance to irreversible conditions with severe neurological deficits and result in a heavy socioeconomic burden on patients, families, and society. A therapy that decelerates disease progression and reduces the socioeconomic burden stemming from these diseases is required. Glucagon-like peptide-1 receptor (GLP-1R) is an important class of medication for type 2 diabetes mellitus (T2DM). Through pancreatic effects, GLP-1R agonists can stimulate insulin secretion, increase β-cell proliferation, reduce β-cell apoptosis, and inhibit glucagon secretion in patients with T2DM. Currently, seven clinically approved GLP-1R agonists are used for T2DM: exenatide, liraglutide, lixisenatide, extended-release exenatide, albiglutide, dulaglutide, and semaglutide. Besides the pancreas, GLP-1Rs are also expressed in organs, such as the gastrointestinal tract, heart, lung, kidney, and brain, indicating their potential use in diseases other than T2DM. Emerging evidence reveals that GLP-1R agonists possess pleiotropic effects that enrich neurogenesis, diminish apoptosis, preclude neurons from oxidative stress, and reduce neuroinflammation in various neurological conditions. These favorable effects may also be employed in neurodegenerative diseases. Herein, we reviewed the recent progress, both in preclinical studies and clinical trials, regarding these clinically used GLP-1R agonists in aging-related neurodegenerative diseases, mainly AD and PD. We stress the pleiotropic characteristics of GLP-1R agonists as repurposing drugs to target multiple pathological mechanisms and for use in the future for these devastating neurodegenerative conditions.

Association between Parkinson's Disease and Diabetes Mellitus: From Epidemiology, Pathophysiology and Prevention to Treatment

Diabetes mellitus (DM) and Parkinson's disease (PD) are both age-related diseases of global concern being among the most common chronic metabolic and neurodegenerative diseases, respectively. While both diseases can be genetically inherited, environmental factors play a vital role in their pathogenesis. Moreover, DM and PD have common underlying molecular mechanisms, such as misfolded protein aggregation, mitochondrial dysfunction, oxidative stress, chronic inflammation, and microbial dysbiosis. Recently, epidemiological and experimental studies have reported that DM affects the incidence and progression of PD. Moreover, certain antidiabetic drugs have been proven to decrease the risk of PD and delay its progression. In this review, we elucidate the epidemiological and pathophysiological association between DM and PD and summarize the antidiabetic drugs used in animal models and clinical trials of PD, which may provide reference for the clinical translation of antidiabetic drugs in PD treatment.

AmyP53, a Therapeutic Peptide Candidate for the Treatment of Alzheimer’s and Parkinson’s Disease: Safety, Stability, Pharmacokinetics Parameters and Nose-to Brain Delivery

Neurodegenerative disorders are a major public health issue. Despite decades of research efforts, we are still seeking an efficient cure for these pathologies. The initial paradigm of large aggregates of amyloid proteins (amyloid plaques, Lewis bodies) as the root cause of Alzheimer’s and Parkinson’s diseases has been mostly dismissed. Instead, membrane-bound oligomers forming Ca²⁺-permeable amyloid pores are now considered appropriate targets for these diseases. Over the last 20 years, our group deciphered the molecular mechanisms of amyloid pore formation, which appeared to involve a common pathway for all amyloid proteins, including Aβ (Alzheimer) and α-synuclein (Parkinson). We then designed a short peptide (AmyP53), which prevents amyloid pore formation by targeting gangliosides, the plasma membrane receptors of amyloid proteins. Herein, we show that aqueous solutions of AmyP53 are remarkably stable upon storage at temperatures up to 45 °C for several months. AmyP53 appeared to be more stable in whole blood than in plasma. Pharmacokinetics studies in rats demonstrated that the peptide can rapidly and safely reach the brain after intranasal administration. The data suggest both the direct transport of AmyP53 via the olfactory bulb (and/or the trigeminal nerve) and an indirect transport via the circulation and the blood–brain barrier. In vitro experiments confirmed that AmyP53 is as active as cargo peptides in crossing the blood–brain barrier, consistent with its amino acid sequence specificities and physicochemical properties. Overall, these data open a route for the use of a nasal spray formulation of AmyP53 for the prevention and/or treatment of Alzheimer’s and Parkinson’s diseases in future clinical trials in humans.

Type 2 diabetes mellitus augments Parkinson's disease risk or the other way around: Facts, challenges and future possibilities

About 10% of the adult population is living with type 2 diabetes mellitus (T2DM) and 1% of the population over 60 years of age is suffering from Parkinson's disease (PD). A school of thought firmly believes that T2DM, an age-related disease, augments PD risk. Such relationship is reflected from the severity of PD symptoms in drug naive subjects possessing T2DM. Onset of Parkinsonian feature in case controls possessing T2DM corroborates the role of hyperglycemia in PD. A few cohort, meta-analysis and animal studies have shown an increased PD risk owing to insulin resistance. High fat diet and role of insulin signaling in the regulation of sugar metabolism, oxidative stress, α-synuclein aggregation and accumulation, inflammatory response and mitochondrial function in PD models and sporadic PD further connect the two. Although little is reported about the implication of PD in hyperglycemia and T2DM, a few studies have also contradicted. Ameliorative effect of anti-diabetic drugs on Parkinsonian symptoms and vague outcome of anti-PD medications in T2DM patients also suggest a link. The article reviews the literature supporting augmented risk of one by the other, analysis of proof of the concept, facts, challenges, future possibilities and standpoint on the subject.

Vesicles of yeast cell wall-sitagliptin to alleviate neuroinflammation in Alzheimer's disease

A cell-based drug delivery system based on yeast-cell wall loaded with sitagliptin, a drug with an anti-inflammatory effect, was developed to control neuroinflammation associated with Alzheimer's disease. The optimized nanoparticles had a spherical shape with a negative surface charge, and were shown to be less toxic than the carrier and sitagliptin. Moreover, the nanoparticles caused anti-inflammatory effects against tumor necrosis factor-alpha in mice model of neuroinflammation. The pharmacokinetics study showed the brain concentration of drug in the nanoparticles group was much higher than in the control group. To evaluate the effect of P-glycoprotein on brain entry of sitagliptin, the experiment was repeated with verapamil, as a P-glycoprotein inhibitor. Brain concentration of the nanoparticles group remained approximately unchanged, proving the "Trojan Horse" effect of the developed nanocarriers. The results are promising for using yeast-cell wall as a carrier for targeted delivery to immune cells for the management of inflammation.

Update to the Treatment of Parkinson's Disease Based on the Gut-Brain Axis Mechanism

Gastrointestinal (GI) symptoms represented by constipation were significant non-motor symptoms of Parkinson’s disease (PD) and were considered early manifestations and aggravating factors of the disease. This paper reviewed the research progress of the mechanism of the gut-brain axis (GBA) in PD and discussed the roles of α-synuclein, gut microbiota, immune inflammation, neuroendocrine, mitochondrial autophagy, and environmental toxins in the mechanism of the GBA in PD. Treatment of PD based on the GBA theory has also been discussed, including (1) dietary therapy, such as probiotics, vitamin therapy, Mediterranean diet, and low-calorie diet, (2) exercise therapy, (3) drug therapy, including antibiotics; GI peptides; GI motility agents, and (4) fecal flora transplantation can improve the flora. (5) Vagotomy and appendectomy were associated but not recommended.

Deciphering Intertwined Molecular Pathways Underlying Metabolic Syndrome Leading to Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that gradually develops over time in a progressive manner. The main culprit behind the disease pathology is dopaminergic deficiency in Substantia nigra Pars Compacta (SNpc) due to neuronal degeneration. However, there are other factors that are not only associated with it but also somehow responsible for inception of pathology. Metabolic syndrome is one such risk factor for PD. Metabolic syndrome is a cluster of diseases mainly including diabetes, hypertension, obesity, and hyperlipidemia which pose a risk for developing cardiovascular disorders. All of these disorders have their own pathological pathways that intertwine with PD pathology. This leads to alpha-synuclein aggregation, neuroinflammation, mitochondrial dysfunction, and oxidative stress which are facets in initiating PD pathology. Although few reports are available, this area is underexplored and has contradictory views. Hence, further studies are needed in order to establish a definite relationship between PD and metabolic syndrome. In this review, we aim to elucidate the molecular mechanisms to confirm the association between them and pave the way for potential repurposing of therapies.

GLP-1 Receptor Agonists in Neurodegeneration: Neurovascular Unit in the Spotlight

Defects in brain energy metabolism and proteopathic stress are implicated in age-related degenerative neuronopathies, exemplified by Alzheimer’s disease (AD) and Parkinson’s disease (PD). As the currently available drug regimens largely aim to mitigate cognitive decline and/or motor symptoms, there is a dire need for mechanism-based therapies that can be used to improve neuronal function and potentially slow down the underlying disease processes. In this context, a new class of pharmacological agents that achieve improved glycaemic control via the glucagon-like peptide 1 (GLP-1) receptor has attracted significant attention as putative neuroprotective agents. The experimental evidence supporting their potential therapeutic value, mainly derived from cellular and animal models of AD and PD, has been discussed in several research reports and review opinions recently. In this review article, we discuss the pathological relevance of derangements in the neurovascular unit and the significance of neuron–glia metabolic coupling in AD and PD. With this context, we also discuss some unresolved questions with regard to the potential benefits of GLP-1 agonists on the neurovascular unit (NVU), and provide examples of novel experimental paradigms that could be useful in improving our understanding regarding the neuroprotective mode of action associated with these agents.

Type 2 diabetes mellitus-associated cognitive dysfunction: Advances in potential mechanisms and therapies

Type 2 diabetes (T2D) and its target organ injuries cause distressing impacts on personal health and put an enormous burden on the healthcare system, and increasing attention has been paid to T2D-associated cognitive dysfunction (TDACD). TDACD is characterized by cognitive dysfunction, delayed executive ability, and impeded information-processing speed. Brain imaging data suggest that extensive brain regions are affected in patients with T2D. Based on current findings, a wide spectrum of non-specific neurodegenerative mechanisms that partially overlap with the mechanisms of neurodegenerative diseases is hypothesized to be associated with TDACD. However, it remains unclear whether TDACD is a consequence of T2D or a complication that co-occurs with T2D. Theoretically, anti-diabetes methods are promising neuromodulatory approaches to reduce brain injury in patients with T2D. In this review, we summarize potential mechanisms underlying TDACD and promising neurotropic effects of anti-diabetes methods and some neuroprotective natural compounds. Constructing screening or diagnostic tools and developing targeted treatment and preventive strategies would be expected to reduce the burden of TDACD.

Gut-Brain Communication in Parkinson's Disease: Enteroendocrine Regulation by GLP-1

PURPOSE OF REVIEW

Defective gut-brain communication has recently been proposed as a promoter of neurodegeneration, but mechanisms mediating communication remain elusive. In particular, the Parkinson's disease (PD) phenotype has been associated with both dysbiosis of intestinal microbiota and neuroinflammation. Here, we review recent advances in the PD field that connect these two concepts, providing an explanation based on enteroendocrine signaling from the gut to the brain.

RECENT FINDINGS

There have been several recent accounts highlighting the importance of the microbiota-gut-brain axis in PD. The objective of this review is to discuss the role of the neuroendocrine system in gut-brain communication as it relates to PD pathogenesis, as this system has not been comprehensively considered in prior reviews. The incretin hormone glucagon-like peptide 1 (GLP-1) is secreted by enteroendocrine cells of the intestinal epithelium, and there is evidence that it is neuroprotective in animal models and human subjects with PD. Agonists of GLP-1 receptors used in diabetes appear to be useful for preventing neurodegeneration. New tools and models have enabled us to study regulation of GLP-1 secretion by intestinal microbiota, to understand how this process may be defective in PD, and to develop methods for therapeutically modifying disease development or progression using the enteroendocrine system. GLP-1 secretion by enteroendocrine cells may be a key mediator of neuroprotection in PD, and new findings in this field may offer unique insights into PD pathogenesis and therapeutic strategies.

Therapeutic application of GLP-1 and GIP receptor agonists in Parkinson's disease

INTRODUCTION

Diabetes is a risk factor for Parkinson's disease (PD) and shares similar dysregulated insulin pathways. Glucagon-like peptide-1 (GLP-1) analogs originally designed to treat diabetes have shown potent neuroprotective activity in preclinical studies of PD. They are neuroprotective by inhibiting inflammation, improving neuronal survival, maintenance of synapses, and dopaminergic transmission in the brain. Building on this, three clinical studies have reported impressive effects in patients with PD, testing exendin-4 (Exenatide, Bydureon) or liraglutide (Victoza, Saxenda). Glucose-dependent insulinotropic peptide (GIP) is another peptide hormone that has shown good effects in animal models of PD. Novel dual GLP-1/GIP agonists have been developed that can penetrate the blood-brain barrier (BBB) and show superior effects in animal models compared to GLP-1 drugs.

AREAS COVERED

The review summarizes preclinical and clinical studies testing GLP-1R agonists and dual GLP-1/GIPR agonists in PD and discusses possible mechanisms of action.

EXPERT OPINION

Current strategies to treat PD by lowering the levels of alpha-synuclein have not shown effects in clinical trials. It is time to move on from the 'misfolding protein' hypothesis. Growth factors such as GLP-1 that can cross the BBB have already shown impressive effects in patients and are the future of drug discovery in PD.

Omarigliptin attenuates rotenone-induced Parkinson's disease in rats: Possible role of oxidative stress, endoplasmic reticulum stress and immune modulation

The current study aimed to explore the potential neuroprotective effect of omarigliptin (OG), an antidiabetic drug that crosses the blood-brain barrier (BBB), in a Parkinson's disease (PD) rotenone-based rat-model. Results showed that OG attenuated motor impairment, histological aberrations, α-synuclein accumulation, and rescued the dopaminergic neurons in rotenone-administered rats. Furthermore, OG halted rotenone-induced oxidative stress; as shown by reduced lipid peroxidation, decline in the oxidative stress sensor (nuclear factor erythroid 2-related factor 2) and its downstream heme oxygenase-1. In addition, OG abrogated neuroinflammation and apoptosis in rotenone-treated rats. Moreover, OG ameliorated endoplasmic reticulum (ER) stress in rotenone-administered rats; as evidenced by reduced levels of ER resident proteins such as glucose-regulated protein 78, C/EBP homologous protein and apoptotic caspase-12. In conclusion, this study implies repurposing of OG, as a novel neuroprotective agent due to its antioxidant properties, its effects on ER stress in addition to its anti-inflammatory and anti-apoptotic activities.

Neuroprotective effect of liraglutide in an experimental mouse model of multiple sclerosis: role of AMPK/SIRT1 signaling and NLRP3 inflammasome

The heterogeneous nature of multiple sclerosis (MS) and the unavailability of treatments addressing its intricate network and reversing the disease state is yet an area that needs to be elucidated. Liraglutide, a glucagon-like peptide-1 analogue, recently exhibited intriguing potential neuroprotective effects. The currents study investigated its potential effect against mouse model of MS and the possible underlying mechanisms. Demyelination was induced in C57Bl/6 mice by cuprizone (400 mg/kg/day p.o.) for 5 weeks. Animals received either liraglutide (25 nmol/kg/day i.p.) or dorsomorphin, an AMPK inhibitor, (2.5 mg/Kg i.p.) 30 min before the liraglutide dose, for 4 weeks (starting from the second week). Liraglutide improved the behavioral profile in cuprizone-treated mice. Furthermore, it induced the re-myelination process through stimulating oligodendrocyte progenitor cells differentiation via Olig2 transcription activation, reflected by increased myelin basic protein and myelinated nerve fiber percentage. Liraglutide elevated the protein content of p-AMPK and SIRT1, in addition to the autophagy proteins Beclin-1 and LC3B. Liraglutide halted cellular damage as manifested by reduced HMGB1 protein and consequently TLR-4 downregulation, coupled with a decrease in NF-κB. Liraglutide also suppressed NLRP3 transcription. Dorsomorphin pre-administration indicated a possible interplay between AMPK/SIRT1 and NLRP3 inflammasome activation as it partially reversed liraglutide’s effects. Immunohistochemical examination of Iba⁺ microglia emphasized these findings. In conclusion, liraglutide exerts neuroprotection against cuprizone-induced demyelination via anti-inflammatory, autophagic flux activation, NLRP3 inflammasome suppression, and anti-apoptotic mechanisms, possibly mediated, at least in part, via AMPK/SIRT1, autophagy, TLR-4/ NF-κB/NLRP3 signaling.

Dysmetabolism and Neurodegeneration: Trick or Treat?

Accumulating evidence suggests the existence of a strong link between metabolic syndrome and neurodegeneration. Indeed, epidemiologic studies have described solid associations between metabolic syndrome and neurodegeneration, whereas animal models contributed for the clarification of the mechanistic underlying the complex relationships between these conditions, having the development of an insulin resistance state a pivotal role in this relationship. Herein, we review in a concise manner the association between metabolic syndrome and neurodegeneration. We start by providing concepts regarding the role of insulin and insulin signaling pathways as well as the pathophysiological mechanisms that are in the genesis of metabolic diseases. Then, we focus on the role of insulin in the brain, with special attention to its function in the regulation of brain glucose metabolism, feeding, and cognition. Moreover, we extensively report on the association between neurodegeneration and metabolic diseases, with a particular emphasis on the evidence observed in animal models of dysmetabolism induced by hypercaloric diets. We also debate on strategies to prevent and/or delay neurodegeneration through the normalization of whole-body glucose homeostasis, particularly via the modulation of the carotid bodies, organs known to be key in connecting the periphery with the brain.

Fluoxetine ameliorates Alzheimer's disease progression and prevents the exacerbation of cardiovascular dysfunction of socially isolated depressed rats through activation of Nrf2/HO-1 and hindering TLR4/NLRP3 inflammasome signaling pathway

Depression is a risk factor for Alzheimer's (AD) and cardiovascular diseases (CVD). Therefore, depression treatment restricts its deteriorating effects on mood, memory and CV system. Fluoxetine is the most widely used antidepressant drug, it has neuroprotective effect through its antioxidant/anti-inflammatory properties. The current study investigated for the first-time the cross link between depression, AD and CVD besides, role of fluoxetine in mitigating such disorders. Depression was induced in rats by social isolation (SI) for 12 weeks, AlCL3 (70 mg/kg/day, i.p.) was used to induce AD which was administered either in SI or normal control (NC) grouped rats starting at 8th week till the end of the experiment, fluoxetine (10 mg/kg/day, p.o) treatment also was started at 8th week. SI and AD showed a statistically significant deteriorated effect on behavioral, neurochemical and histopathological analysis which was exaggerated when two disorder combined than each alone. Fluoxetine treatment showed protective effect against SI, AD and prevents exacerbation of CVD. Fluoxetine improved animals' behavior, increased brain monoamines, BDNF besides increased antioxidant defense mechanism of SOD, TAC contents and increased protein expression of Nrf2/HO-1 with significant decrease of AChE activity, β-amyloid, Tau protein, MDA, TNF-α, IL1β contents as well as decreased protein expression of NF-kB, TLR4, NLRP3 and caspase1. It also showed cardioprotective effects as it improved lipid profile with pronounced decrease of cardiac enzymes of CK-MB, troponin and MEF2. In conclusion, fluoxetine represents as a promising drug against central and peripheral disorders through its anti-inflammatory/antioxidant effects via targeting antioxidant Nrf2/HO-1 and hindering TLR4/NLRP3 inflammasome signaling pathways.

Neuroprotective effects of liraglutide against inflammation through the AMPK/NF-κB pathway in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease with increasing incidence in aged populations, second only to Alzheimer's disease. Increasing evidence has shown that inflammation plays an important role in the occurrence and development of Parkinson's disease. Growing evidence has shown that AMP-activated protein kinase (AMPK) and NF-κB are closely related to inflammation. Glucagon-like peptide 1 (GLP-1) is a hormone that is primarily secreted by intestinal endocrine L cells, and it has a variety of physiology through binding to GLP-1 receptor. GLP-1can be used for treatment of type 2 diabetes. In addition, GLP-1 also has anti-neuroinflammation activity. However, the exact mechanism behind how GLP-1 regulates neuroinflammation remains unclear. This study was designed to examine the effect of liraglutide on 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-induced injury in mice and its potential mechanism of action. Results showed that liraglutide dose-dependently ameliorated mouse behavior including swimming time and locomotor activity, increased the number of tyrosine hydroxylase (TH)-positive neurons and protein level, and reduced Iba1 and GFAP expression in the substantia nigra (SN). Liraglutide treatment also increased p-AMPK expression and reduced NF-κB protein level. Applying the AMPK inhibitor Dorsomorphin (Compound C) reversed the effect of liraglutide-reducing p-AMPK and increasing NF-κB expression. Finally, GFAP protein level increased, along with a decrease in TH expression. In conclusion, these results suggest that liraglutide can suppress neuroinflammation. Moreover, this effect is mediated through the AMPK/NF-κB signaling pathway.

The effect of GLP-1 receptor agonists in pre-clinical rodent models of Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

Parkinson's Disease (PD) is a progressive neurodegenerative condition associated with significant morbidity. Currently, there are limited pharmacological options and none of the therapies available are disease-modifying. This systematic review and meta-analysis considers a novel drug class through the research question - in pre-clinical rodent models of PD, is GLP-1 receptor agonist therapy neuroprotective when compared to vehicle controls?

METHODS

A literature search was conducted to locate relevant pre-clinical studies. Two separate outcomes were considered. The primary outcome was indicators of dopaminergic neurotransmission. The secondary outcome was indicators of motor symptoms. Untreated PD models were compared to PD-models treated with GLP-1 receptor agonists. The final meta-analysis was conducted using the Cochrane RevMan software and represented continuous data using the inverse variance statistical method and random effects analysis model. The final study statistic was represented as an SMD value with a p-value < 0.05 considered statistically significant. Study heterogeneity and publication bias was assessed using I2 values and funnel plots respectively.

RESULTS

Eleven studies fit the inclusion criteria and were included in the final analysis. For the primary outcome (n = 128), there was a statistically significant relative improvement of dopaminergic neurotransmission (SMD 1.71, 95% CI = 0.74-2.68, p = 0.0005, I2 = 76%). For the secondary outcome (n = 280), there was a statistically significant improvement in motor outcomes (SMD 2.11, 95% CI = 1.14-3.09, p < 0.0001, I2 = 89%).

CONCLUSIONS

GLP-1 receptor agonist therapy is neuroprotective in pre-clinical models of PD. This study provides the clinical foundation and research support for the design of rigorous clinical trials to further investigate these results in human PD populations.

Astrocytes as Key Regulators of Brain Energy Metabolism: New Therapeutic Perspectives

Astrocytes play key roles in the regulation of brain energy metabolism, which has a major impact on brain functions, including memory, neuroprotection, resistance to oxidative stress and homeostatic tone. Energy demands of the brain are very large, as they continuously account for 20–25% of the whole body’s energy consumption. Energy supply of the brain is tightly linked to neuronal activity, providing the origin of the signals detected by the widely used functional brain imaging techniques such as functional magnetic resonance imaging and positron emission tomography. In particular, neuroenergetic coupling is regulated by astrocytes through glutamate uptake that triggers astrocytic aerobic glycolysis and leads to glucose uptake and lactate release, a mechanism known as the Astrocyte Neuron Lactate Shuttle. Other neurotransmitters such as noradrenaline and Vasoactive Intestinal Peptide mobilize glycogen, the reserve for glucose exclusively localized in astrocytes, also resulting in lactate release. Lactate is then transferred to neurons where it is used, after conversion to pyruvate, as a rapid energy substrate, and also as a signal that modulates neuronal excitability, homeostasis, and the expression of survival and plasticity genes. Importantly, glycolysis in astrocytes and more generally cerebral glucose metabolism progressively deteriorate in aging and age-associated neurodegenerative diseases such as Alzheimer’s disease. This decreased glycolysis actually represents a common feature of several neurological pathologies. Here, we review the critical role of astrocytes in the regulation of brain energy metabolism, and how dysregulation of astrocyte-mediated metabolic pathways is involved in brain hypometabolism. Further, we summarize recent efforts at preclinical and clinical stages to target brain hypometabolism for the development of new therapeutic interventions in age-related neurodegenerative diseases.

Liraglutide Improves Cognitive and Neuronal Function in 3-NP Rat Model of Huntington's Disease

Huntington’s disease (HD) is an autosomal dominant inherited neurodegenerative disease characterized by progressive motor, psychiatric, and cognitive abnormalities. The antidiabetic drug liraglutide possesses a neuroprotective potential against several neurodegenerative disorders; however, its role in Huntington’s disease (HD) and the possible mechanisms/trajectories remain elusive, which is the aim of this work. Liraglutide (200 μg/kg, s.c) was administered to rats intoxicated with 3-nitropropionic acid (3-NP) for 4 weeks post HD model induction. Liraglutide abated the 3-NP-induced neurobehavioral deficits (open field and elevated plus maze tests) and histopathological changes. Liraglutide downregulated the striatal mRNA expression of HSP 27, PBR, and GFAP, while it upregulated that of DARPP32. On the molecular level, liraglutide enhanced striatal miR-130a gene expression and TrKB protein expression and its ligand BDNF, while it reduced the striatal protein content and mRNA expression of the death receptors sortilin and p75NTR, respectively. It enhanced the neuroprotective molecules cAMP, p-PI3K, p-Akt, and p-CREB, besides modulating the p-GSK-3β/p-β-catenin axis. Liraglutide enhanced the antioxidant transcription factor Nrf2, abrogated TBARS, upregulated both Bcl2 and Bcl-XL, and downregulated Bax along with decreasing caspase-3 activity. Therefore, liraglutide exerts a neurotherapeutic effect on 3-NP-treated rats that is, besides the upturn of behavioral and structural findings, it at least partially, increased miR-130a and modulated PI3K/Akt/CREB/BDNF/TrKB, sortilin, and p75NTR, and Akt/GSK-3β/p-β-catenin trajectories besides its capacity to decrease apoptosis and oxidative stress, as well as its neurotrophic activity.

Neuroprotective effects of linagliptin in a rotenone-induced rat model of Parkinson's disease

The present study investigates the antiParkinsonian activity of dipeptidyl peptidase-4 (DPP-IV) inhibitor, linagliptin. The experimental Parkinson's disease (PD) was induced by administration of rotenone at a dose of 1.5 mg/kg at alternate day subcutaneously for 21 days. Standard drug (levodopa-200 mg/kg and carbidopa-50 mg/kg) and treatment drug (linagliptin-5 mg/kg, 10 mg/kg, and 20mg/kg) were administered orally daily 1 h before rotenone administration. In a rat rotenone model, linagliptin improved muscle coordination, motor performance, and corrected akinesia. Pretreatment with linagliptin showed significant higher levels of superoxide dismutase, catalase, and glutathione in brain homogenate of animals. Linagliptin significantly elevated the levels of striatal DA and active glucagon-like peptide 1 in brain homogenate of animals. Furthermore, linagliptin amended alterations induced by rotenone in the thiobarbituric acid reactive substances and inflammatory marker such as tumor necrosis factor-α level. The results of the present study indicate the neuroprotective potential of linagliptin for the management of PD might be due to remarkable improvement in motor functions, antioxidant, anti-inflammatory, anti-apoptotic, and neuroprotective mechanisms.

Brain Imaging of the GLP-1 Receptor in Obesity Using 68Ga-NODAGA-Exendin-4 PET

Stimulation of glucagon-like peptide-1 (GLP-1) receptors increases the insulin release in the pancreas during high glucose levels, and also stimulates a feeling of satiety. Likewise, synthetic GLP-1 receptor agonists derived from exendin are used successfully in the treatment of type-2 diabetes mellitus and obesity. Interestingly, preclinical and clinical studies further suggest that GLP-1 receptor agonists may decrease motor, behavioral, and cognitive symptoms in (animal models) Parkinson’s disease and Alzheimer’s disease and may slow down neurodegeneration. These observations suggest stimulation of GLP-1 receptors in the brain. The GLP-1 positron emission tomography (PET) tracer ⁶⁸Ga-NODAGA-exendin-4 has been developed and successfully used for imaging in humans. In an ongoing study on the effects of bariatric surgery on GLP-1 receptor expression, we performed ⁶⁸Ga-NODAGA-exendin-4 PET in obese subjects. Here we evaluated whether GLP-1 receptor binding could be visualized in the central nervous system in 10 obese subjects (seven woman; body mass index: mean ± SD: 39 ± 4.4 kg/m²) before bariatric surgery. Although we observed clear uptake in the pituitary area (mean SUV_max 4.3 ± 2.3), we found no significant uptake in other parts of the brain. We conclude that ⁶⁸Ga-NODAGA-exendin-4 PET cannot be used to analyze GLP-1 receptors in the brain of obese subjects.

Novel mechanistic insights towards the repositioning of alogliptin in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease that impairs people's lives tremendously. The development of innovative treatment modalities for PD is a significant unmet medical need. The critical function of glucagon-like peptide-1 (GLP-1) in neurodegenerative diseases has raised impetus in investigating the repositioning of a dipeptidyl peptidase IV inhibitor, alogliptin (ALO), as an effective treatment for PD. As a result, the focus of this research was to assess the effect of ALO in a rat rotenone (ROT) model of PD. For 21 days, ROT (1.5 mg/kg) was delivered subcutaneously every other day. ALO (30 mg/kg/day), delivered by gavage for 21 days, recovered motor performance and improved motor coordination in the open-field and rotarod testing. These impacts were highlighted by restoring striatal dopamine content and correcting histological changes that occurred concurrently. The ALO molecular signaling was determined by increasing the quantity of GLP-1 and the protein expression of its downstream signaling pathway, pT172-AMPK/SIRT1/PGC-1α. Furthermore, it curbed neuroinflammation via hampering HMGB1/TLR4/NLRP3 inflammasome activation and conquered striatal microglia activation. Pre-administration of dorsomorphin reversed the neuroprotective effects. In conclusion, the promising neuroprotective effect of ALO highlights the repositioning of ALO as a prospective revolutionary candidate for combating PD.

L-dopa-Dependent Effects of GLP-1R Agonists on the Survival of Dopaminergic Cells Transplanted into a Rat Model of Parkinson Disease

Cell therapy is a promising treatment for Parkinson's disease (PD), however clinical trials to date have shown relatively low survival and significant patient-to-patient variability. Glucagon Like Peptide-1 receptor (GLP-1R) agonists have potential neuroprotective effects on endogenous dopaminergic neurons. This study explores whether these agents could similarly support the growth and survival of newly transplanted neurons. 6-OHDA lesioned Sprague Dawley rats received intra-striatal grafts of dopaminergic ventral mesencephalic cells from embryonic day 14 Wistar rat embryos. Transplanted rats then received either saline or L-dopa (12 mg/kg) administered every 48 h prior to, and following cell transplantation. Peripheral GLP-1R agonist administration (exendin-4, 0.5 μg/kg twice daily or liraglutide, 100 μg/kg once daily) commenced immediately after cell transplantation and was maintained throughout the study. Graft survival increased under administration of exendin-4, with motor function improving significantly following treatment with both exendin-4 and liraglutide. However, this effect was not observed in rats administered with L-dopa. In contrast, L-dopa treatment with liraglutide increased graft volume, with parallel increases in motor function. However, this improvement was accompanied by an increase in leukocyte infiltration around the graft. The co-administration of L-dopa and exendin-4 also led to indicators of insulin resistance not seen with liraglutide, which may underpin the differential effects observed between the two GLP1-R agonists. Overall, there may be some benefit to the supplementation of grafted patients with GLP-1R agonists but the potential interaction with other pharmacological treatments needs to be considered in more depth.

Liraglutide ameliorates diabetes-associated cognitive dysfunction via rescuing autophagic flux

The incidence of diabetes-associated cognitive dysfunction is increasing. However, few clinical interventions are available to prevent the disorder. Several researches have shown that liraglutide, as a glucagon-like peptide-1 analog, has protective effects on various neurodegenerative diseases, but its roles in diabetic cognitive dysfunction are rarely reported. This study aims to investigate the protective effects of liraglutide on diabetic cognitive dysfunction and its underlying mechanisms. In vivo, the effects of liraglutide treatment were investigated in a mouse model of type 2 diabetes mellitus (T2DM). In vitro, we investigated the effects of liraglutide on the high-glucose-induced rat primary neurons. The results showed that liraglutide reduced the escape latency and increased the time in effective area in the Morris water maze test, improved the damage of hippocampal and synaptic ultrastructure, and decreased the accumulation of amyloid β protein in hippocampus of T2DM mice. Furthermore, liraglutide increased the ratio of microtubule-associated protein light 1 chain Ⅱ/Ⅰ, the expression of Beclin1 protein and Lysosome-associated membrane protein 2 in vivo and vitro. Additionally, Bafilomycin A1 which can inhibit the fusion of autophagosome and lysosome partially abolished the effects of liraglutide. These findings indicate liraglutide ameliorates diabetes-associated cognitive dysfunction by rescuing autophagic flux.

Activation of microglial GLP-1R in the trigeminal nucleus caudalis suppresses central sensitization of chronic migraine after recurrent nitroglycerin stimulation

Background

Central sensitization is considered a critical pathogenic mechanism of chronic migraine (CM). Activation of microglia in the trigeminal nucleus caudalis (TNC) contributes to this progression. Microglial glucagon-like peptide-1 receptor (GLP-1R) activation can alleviate pain; however, whether it is involved in the mechanism of CM has not been determined. Thus, this study aims to investigate the precise role of GLP-1R in the central sensitization of CM.

Methods

Repeated nitroglycerin injection-treated mice were used as a CM animal model in the experiment. To identify the distribution and cell localization of GLP-1R in the TNC, we performed immunofluorescence staining. Changes in the expression of GLP-1R, Iba-1, PI3K and p-Akt in the TNC were examined by western blotting. To confirm the effect of GLP-1R and PI3K/Akt in CM, a GLP-1R selective agonist (liraglutide) and antagonist (exendin(9–39)) and a PI3K selective antagonist (LY294002) were administered. Mechanical hypersensitivity was measured through von Frey filaments. To investigate the role of GLP-1R in central sensitization, calcitonin gene-related peptide (CGRP) and c-fos were determined using western blotting and immunofluorescence. To determine the changes in microglial activation, IL-1β and TNF-α were examined by western blotting, and the number and morphology of microglia were measured by immunofluorescence. We also confirmed the effect of GLP-1R on microglial activation in lipopolysaccharide-treated BV-2 microglia.

Results

The protein expression of GLP-1R was increased in the TNC after nitroglycerin injection. GLP-1R was colocalized with microglia and astrocytes in the TNC and was fully expressed in BV-2 microglia. The GLP-1R agonist liraglutide alleviated basal allodynia and suppressed the upregulation of CGRP, c-fos and PI3K/p-Akt in the TNC. Similarly, the PI3K inhibitor LY294002 prevented nitroglycerin-induced hyperalgesia. In addition, activating GLP-1R reduced Iba-1, IL-1β and TNF-α release and inhibited TNC microglial number and morphological changes (process retraction) following nitroglycerin administration. In vitro, the protein levels of IL-1β and TNF-α in lipopolysaccharide-stimulated BV-2 microglia were also decreased by liraglutide.

Conclusions

These findings suggest that microglial GLP-1R activation in the TNC may suppress the central sensitization of CM by regulating TNC microglial activation via the PI3K/Akt pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-021-01302-x.

Diabetes, insulin and new therapeutic strategies for Parkinson's disease: Focus on glucagon-like peptide-1 receptor agonists

Parkinson's disease and diabetes mellitus are two chronic disorders associated with aging that are becoming increasingly prevalent worldwide. Parkinson is a multifactorial progressive condition with no available disease modifying treatments at the moment. Over the last few years there is growing interest in the relationship between diabetes (and impaired insulin signaling) and neurodegenerative diseases, as well as the possible benefit of antidiabetic treatments as neuroprotectors, even in non-diabetic patients. Insulin regulates essential functions in the brain such as neuronal survival, autophagy of toxic proteins, synaptic plasticity, neurogenesis, oxidative stress and neuroinflammation. We review the existing epidemiological, experimental and clinical evidence that supports the interplay between insulin and neurodegeneration in Parkinson's disease, as well as the role of antidiabetic treatments in this disease.

Linagliptin, a DPP-4 inhibitor, ameliorates Aβ (1-42) peptides induced neurodegeneration and brain insulin resistance (BIR) via insulin receptor substrate-1 (IRS-1) in rat model of Alzheimer's disease

Alzheimer's disease (AD) is the most devastating neurodegenerative disorder, accounting over 46 million cases of dementia globally. Evidence supports that Brain Insulin Resistance (BIR) due to serine phosphorylation of Insulin Receptor Substrate-1 (IRS-1) has an association with AD. GLP-1 an incretin hormone, rapidly degraded by Dipeptidyl Peptidase-4 (DPP-4) has also confirmed its efficacious role in AD. Linagliptin, a DPP-4 inhibitor is hypothesized to increase GLP-1 level, which then crosses Blood Brain Barrier (BBB), decreases Amyloid-beta (Aβ) and insulin resistance in hippocampus. Thus, the present study was designed to evaluate Linagliptin in Aβ (1-42) peptides induced rat model of AD. Following 1 week of induction, rats were administered with Linagliptin (0.513 mg/kg, 3 mg/kg, and 5 mg/kg) orally for 8 weeks and donepezil (5 mg/kg) as a reference standard. At the end of scheduled treatment neurobehavioral parameters were assessed. After this, rats were sacrificed, hippocampus was isolated from the whole brain for histopathological analysis and biochemical parameters estimation. Linagliptin dose-dependently and significantly reversed motor and cognitive impairment, assessed through locomotor activity (LA) and Morris water maze (MWM) test respectively. Moreover, Linagliptin augmented GLP-1 level and attenuated soluble Aβ (1-42), IRS-1 (s307), GSK-3β, TNF-α, IL-1β, IL-6, AchE and oxidative/nitrosative stress level in hippocampus. H&E and Congo red staining also exhibited neuroprotective and anti-amylodogenic effect respectively. Our study findings implies the significant effect of Linagliptin in reversing the behavioural and biochemical deficits by altering Aβ (1-42) and BIR via IRS-1 confirming one of the mechanism underlying the pathophysiology of AD.

Simultaneous Quantification of Pioglitazone and Omarigliptin in Rat Plasma by UHPLC-MS/MS and Its Application to Pharmacokinetic Study after Coadministration of the Two Drugs

Combination therapy is a common approach for clinical treatment of type 2 diabetes mellitus, especially for patients with poor monotherapy. Meta-analysis suggested that omarigliptin, a long-acting DPP-4 inhibitor, combined with pioglitazone might improve the side effects of pioglitazone. However, little is known about the pharmacokinetic properties after a coadministration. In this study, a rapid and reliable method for the simultaneous determination of the pioglitazone and omarigliptin in rat plasma by UHPLC-MS/MS was established and validated for the first time. An exsil mono C18 column (2.0 × 50 mm, 3 μm) was used to separate the analytes and the column temperature was kept at 30°C. Sitagliptin was selected as the internal standard. 0.02% formic acid aqueous solution (A) and methanol-acetonitrile (B) were used as mobile phases with gradient elution at a flow rate of 0.3 mL/min. The elution procedure was as follows: 20%B (0-0.1 min), 80%B (0.1-0.3 min), 80%B (0.3-2.0 min), and 20%B (2.1-3.0 min). A multiple reaction monitor (MRM) was used under positive ionization mode with electrospray ion source to detect pioglitazone (357.1 ⟶ 134.1), omarigliptin (399.2 ⟶ 153.0), and sitagliptin (408.2 ⟶ 235.0). The linear ranges of pioglitazone and omarigliptin were 5-2000 ng/mL and 10-4000 ng/mL, respectively. Good linear relationships were exhibited in the corresponding linear ranges (r ≥ 0.9944). The bioanalytical method was validated, and the selectivity, linearity, sensitivity, accuracy, precision, stability, recovery, and matrix effect were acceptable. The validated method was then successfully applied to pharmacokinetic study of pioglitazone combined with omarigliptin in rats. Results suggested that the combination of the two drugs had little effect on the pharmacokinetic parameters of each other in rats.

Beneficial effects of dipeptidyl peptidase-4 inhibitors in diabetic Parkinson's disease

Dipeptidyl peptidase 4 (DPP4) inhibitors are widely used hypoglycaemic agents and improve glucose metabolism by enhancing the bioavailability of active glucagon-like peptide-1. In this study, we hypothesized that treatment with DPP4 inhibitors may have beneficial effects on nigrostriatal dopamine and longitudinal motor performance in diabetic patients with Parkinson's disease. We classified 697 drug naive patients with de novo Parkinson's disease who had undergone dopamine transporter imaging into three groups according to a prior diagnosis of diabetes and use of DPP4 inhibitors: diabetic patients with Parkinson's disease being treated with (n = 54) or without DPP4 inhibitors (n = 85), and non-diabetic patients with Parkinson's disease (n = 558). Diabetic patients with Parkinson's disease being treated with DPP4 inhibitors had a higher baseline dopamine transporter availability in the anterior (2.56 ± 0.74 versus 2.10 ± 0.50; P = 0.016), posterior (1.83 ± 0.69 versus 1.40 ± 0.50; P < 0.001), and ventral putamina (1.72 ± 0.58 versus 1.35 ± 0.37; P = 0.001) than that in diabetic patients with Parkinson's disease without DPP4 inhibitors. Additionally, diabetic patients with Parkinson's disease being treated with DPP4 inhibitors had higher dopamine transporter availability in the posterior putamen than that in non-diabetic patients with Parkinson's disease (1.83 ± 0.69 versus 1.43 ± 0.59; P < 0.001). After adjusting for age, sex, disease duration, and vascular risk factors, linear regression models showed that a prior treatment of DPP4 inhibitors remained independently and significantly associated with dopamine transporter availability in the anterior (β = -0.186, P = 0.012; β = -0.207, P = 0.003), posterior (β = -0.336, P < 0.001; β = -0.286, P < 0.001), and ventral putamina (β = -0.204, P = 0.005; β = -0.250, P < 0.001). A linear mixed model revealed that the diabetic group with Parkinson's disease being treated with DPP4 inhibitors had a slower longitudinal increase in levodopa-equivalent dose than the other groups (P = 0.003). Survival analyses showed that the rate of levodopa-induced dyskinesia was significantly lower in the diabetic group with a prior treatment with DPP4 inhibitors than the diabetic group without DPP4 inhibitors (hazard ratio = 0.194, P = 0.037). These findings suggest that DPP4 inhibitors may confer beneficial effects on the baseline nigrostriatal dopamine degeneration and long-term motor outcomes in diabetic patients with Parkinson's disease and may extend its role into non-diabetic patients with Parkinson's disease.

Repurposing Immunomodulatory Imide Drugs (IMiDs) in Neuropsychiatric and Neurodegenerative Disorders

Neuroinflammation represents a common trait in the pathology and progression of the major psychiatric and neurodegenerative disorders. Neuropsychiatric disorders have emerged as a global crisis, affecting 1 in 4 people, while neurological disorders are the second leading cause of death in the elderly population worldwide (WHO, 2001; GBD 2016 Neurology Collaborators, 2019). However, there remains an immense deficit in availability of effective drug treatments for most neurological disorders. In fact, for disorders such as depression, placebos and behavioral therapies have equal effectiveness as antidepressants. For neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease, drugs that can prevent, slow, or cure the disease have yet to be found. Several non-traditional avenues of drug target identification have emerged with ongoing neurological disease research to meet the need for novel and efficacious treatments. Of these novel avenues is that of neuroinflammation, which has been found to be involved in the progression and pathology of many of the leading neurological disorders. Neuroinflammation is characterized by glial inflammatory factors in certain stages of neurological disorders. Although the meta-analyses have provided evidence of genetic/proteomic upregulation of inflammatory factors in certain stages of neurological disorders. Although the mechanisms underpinning the connections between neuroinflammation and neurological disorders are unclear, and meta-analysis results have shown high sensitivity to factors such as disorder severity and sample type, there is significant evidence of neuroinflammation associations across neurological disorders. In this review, we summarize the role of neuroinflammation in psychiatric disorders such as major depressive disorder, generalized anxiety disorder, post-traumatic stress disorder, and bipolar disorder, as well as in neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease, and introduce current research on the potential of immunomodulatory imide drugs (IMiDs) as a new treatment strategy for these disorders.