Pharmacokinetics and efficacy of PT302, a sustained-release Exenatide formulation, in a murine model of mild traumatic brain injury

The Therapeutic Potential of Glucagon-like Peptide 1 Receptor Agonists in Traumatic Brain Injury

Traumatic brain injury (TBI), which is a global public health concern, can take various forms, from mild concussions to blast injuries, and each damage type has a particular mechanism of progression. However, TBI is a condition with complex pathophysiology and heterogenous clinical presentation, which makes it difficult to model for in vitro and in vivo studies and obtain relevant results that can easily be translated to the clinical setting. Accordingly, the pharmacological options for TBI management are still scarce. Since a wide spectrum of processes, such as glucose homeostasis, food intake, body temperature regulation, stress response, neuroprotection, and memory, were demonstrated to be modulated after delivering glucagon-like peptide 1 (GLP-1) or GLP-1 receptor agonists into the brain, we aimed to speculate on their potential role in TBI management by comprehensively overviewing the preclinical and clinical body of evidence. Based on promising preclinical data, GLP-1 receptor agonists hold the potential to extend beyond metabolic disorders and address unmet needs in neuroprotection and recovery after TBI, but also other types of central nervous system injuries such as the spinal cord injury or cerebral ischemia. This overview can lay the basis for tailoring new research hypotheses for future in vitro and in vivo models in TBI settings. However, large-scale clinical trials are crucial to confirm their safety and efficacy in these new therapeutic applications.

Incretin-Based Multi-Agonist Peptides Are Neuroprotective and Anti-Inflammatory in Cellular Models of Neurodegeneration

Glucagon-like peptide-1 (GLP-1)-based drugs have been approved by the United States Food and Drug Administration (FDA) and are widely used to treat type 2 diabetes mellitus (T2DM) and obesity. More recent developments of unimolecular peptides targeting multiple incretin-related receptors ("multi-agonists"), including the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) and the glucagon (Gcg) receptor (GcgR), have emerged with the aim of enhancing drug benefits. In this study, we utilized human and mouse microglial cell lines, HMC3 and IMG, respectively, together with the human neuroblastoma SH-SY5Y cell line as cellular models of neurodegeneration. Using these cell lines, we studied the neuroprotective and anti-inflammatory capacity of several multi-agonists in comparison with a single GLP-1 receptor (GLP-1R) agonist, exendin-4. Our data demonstrate that the two selected GLP-1R/GIPR dual agonists and a GLP-1R/GIPR/GcgR triple agonist not only have neurotrophic and neuroprotective effects but also have anti-neuroinflammatory properties, as indicated by the decreased microglial cyclooxygenase 2 (COX2) expression, nitrite production, and pro-inflammatory cytokine release. In addition, our results indicate that these multi-agonists have the potential to outperform commercially available single GLP-1R agonists in neurodegenerative disease treatment.

Attenuating mitochondrial dysfunction and morphological disruption with PT320 delays dopamine degeneration in MitoPark mice

BACKGROUND

Mitochondria are essential organelles involved in cellular energy production. Changes in mitochondrial function can lead to dysfunction and cell death in aging and age-related disorders. Recent research suggests that mitochondrial dysfunction is closely linked to neurodegenerative diseases. Glucagon-like peptide-1 receptor (GLP-1R) agonist has gained interest as a potential treatment for Parkinson's disease (PD). However, the exact mechanisms responsible for the therapeutic effects of GLP-1R-related agonists are not yet fully understood.

METHODS

In this study, we explores the effects of early treatment with PT320, a sustained release formulation of the GLP-1R agonist Exenatide, on mitochondrial functions and morphology in a progressive PD mouse model, the MitoPark (MP) mouse.

RESULTS

Our findings demonstrate that administration of a clinically translatable dose of PT320 ameliorates the reduction in tyrosine hydroxylase expression, lowers reactive oxygen species (ROS) levels, and inhibits mitochondrial cytochrome c release during nigrostriatal dopaminergic denervation in MP mice. PT320 treatment significantly preserved mitochondrial function and morphology but did not influence the reduction in mitochondria numbers during PD progression in MP mice. Genetic analysis indicated that the cytoprotective effect of PT320 is attributed to a reduction in the expression of mitochondrial fission protein 1 (Fis1) and an increase in the expression of optic atrophy type 1 (Opa1), which is known to play a role in maintaining mitochondrial homeostasis and decreasing cytochrome c release through remodeling of the cristae.

CONCLUSION

Our findings suggest that the early administration of PT320 shows potential as a neuroprotective treatment for PD, as it can preserve mitochondrial function. Through enhancing mitochondrial health by regulating Opa1 and Fis1, PT320 presents a new neuroprotective therapy in PD.

The GLP-1 receptor agonist exenatide improves recovery from spinal cord injury by inducing macrophage polarization toward the M2 phenotype

Although a wide variety of mechanisms take part in the secondary injury phase of spinal cord injury (SCI), inflammation is the most important factor implicated in the sequelae after SCI. Being central to the inflammation reaction, macrophages and their polarization are a topic that has garnered wide interest in the studies of SCI secondary injury. The glucagon-like peptide 1 (GLP-1) receptor agonist exenatide has been shown to enhance the endoplasmic reticulum stress response and improve motor function recovery after spinal cord injury (SCI). Since exenatide has also been reported to induce the production of M2 cells in models of cerebral infarction and neurodegenerative diseases, this study was conducted to examine the effects of exenatide administration on the inflammation process that ensues after spinal cord injury. In a rat contusion model of spinal cord injury, the exenatide group received a subcutaneous injection of 10 μg exenatide immediately after injury while those in the control group received 1 mL of phosphate-buffered saline. Quantitative RT-PCR and immunohistochemical staining were used to evaluate the effects of exenatide administration on the macrophages infiltrating the injured spinal cord, especially with regard to macrophage M1 and M2 profiles. The changes in hind limb motor function were assessed based on Basso, Beattie, Bresnahan locomotor rating scale (BBB scale) scores. The improvement in BBB scale scores was significantly higher in the exenatide group from day 7 after injury and onwards. Quantitative RT-PCR revealed an increase in the expression of M2 markers and anti-inflammatory interleukins in the exenatide group that was accompanied by a decrease in the expression of M1 markers and inflammatory cytokines. Immunohistochemical staining showed no significant difference in M1 macrophage numbers between the two groups, but a significantly higher number of M2 macrophages was observed in the exenatide group on day 3 after injury. Our findings suggest that exenatide administration promoted the number of M2-phenotype macrophages after SCI, which may have led to the observed improvement in hind limb motor function in a rat model of SCI.

Therapeutic effects of anti-diabetic drugs on traumatic brain injury

AIMS

In this narrative review, we have analyzed and synthesized current studies relating to the effects of anti-diabetic drugs on traumatic brain injury (TBI) complications.

METHODS

Eligible studies were collected from Scopus, Google Scholar, PubMed, and Cochrane Library for clinical, in-vivo, and in-vitro studies published on the impact of anti-diabetic drugs on TBI.

RESULTS

Traumatic brain injury (TBI) is a serious brain disease that is caused by any type of trauma. The pathophysiology of TBI is not yet fully understood, though physical injury and inflammatory events have been implicated in TBI progression. Several signaling pathways are known to play pivotal roles in TBI injuries, including Nuclear factor erythroid 2-related factor 2 (Nrf2), High mobility group box 1 protein/Nuclear factor kappa B (HMGB1/NF-κB), Adiponectin, Mammalian Target of Rapamycin (mTOR), Toll-Like Receptor (TLR), Wnt/β-catenin, Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT), Nod-like receptor protein3 (NLRP3) inflammasome, Phosphoglycerate kinase 1/Kelch-like ECH-associated protein 1 (PGK1/KEAP1)/Nrf2, and Mitogen-activated protein kinase (MAPK) . Recent studies suggest that oral anti-diabetic drugs such as biguanides, thiazolidinediones (TZDs), sulfonylureas (SUs), sodium-glucose cotransporter-2 inhibitors (SGLT2is), dipeptidyl peptidase-4 inhibitors (DPPIs), meglitinides, and alpha-glucosidase inhibitors (AGIs) could have beneficial effects in the management of TBI complications. These drugs may downregulate the inflammatory pathways and induce antioxidant signaling pathways, thus alleviating complications of TBI.

CONCLUSION

Based on this comprehensive literature review, antidiabetic medications might be considered in the TBI treatment protocol. However, evidence from clinical trials in patients with TBI is still warranted.

Administration of the GLP-1 receptor agonist exenatide in rats improves functional recovery after spinal cord injury by reducing endoplasmic reticulum stress

After spinal cord injury (SCI), endoplasmic reticulum (ER) stress has been reported to be an integral part of the secondary injury process that causes apoptosis of glial cells, leading to remyelination failure. This report focuses on exenatide, a glucagon-like peptide-1 (GLP-1) receptor agonist widely used to treat diabetes, as a potential agent to improve functional outcome after SCI by improving the ER stress response. Exenatide administered subcutaneously immediately after injury and 7 days later in a rat model of moderate contusive SCI revealed significant improvement in hindlimb function without any hypoglycemia. Changes in the expression of glucose regulatory protein 78 (GRP78), an endoplasmic reticulum chaperone that protects against ER stress, and C/EBP homologous transcription factor protein (CHOP), a pro-apoptotic transcription factor in the apoptosis pathway were examined as indices of ER stress. We found that administration of exenatide after SCI suppressed CHOP while increasing GRP78 in the injured spinal cord, leading to a significant decrease in tissue damage and a significant increase in oligodendrocyte progenitor cell survival. This study suggests that administration of exenatide after SCI decreases ER stress and improves functional recovery without any apparent side-effects.

Cognitive and Cellular Effects of Combined Organophosphate Toxicity and Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is considered the most common neurological disorder among people under the age of 50. In modern combat zones, a combination of TBI and organophosphates (OP) can cause both fatal and long-term effects on the brain. We utilized a mouse closed-head TBI model induced by a weight drop device, along with OP exposure to paraoxon. Spatial and visual memory as well as neuron loss and reactive astrocytosis were measured 30 days after exposure to mild TBI (mTBI) and/or paraoxon. Molecular and cellular changes were assessed in the temporal cortex and hippocampus. Cognitive and behavioral deficits were most pronounced in animals that received a combination of paraoxon exposure and mTBI, suggesting an additive effect of the insults. Neuron survival was reduced in proximity to the injury site after exposure to paraoxon with or without mTBI, whereas in the dentate gyrus hilus, cell survival was only reduced in mice exposed to paraoxon prior to sustaining a mTBI. Neuroinflammation was increased in the dentate gyrus in all groups exposed to mTBI and/or to paraoxon. Astrocyte morphology was significantly changed in mice exposed to paraoxon prior to sustaining an mTBI. These results provide further support for assumptions concerning the effects of OP exposure following the Gulf War. This study reveals additional insights into the potentially additive effects of OP exposure and mTBI, which may result in more severe brain damage on the modern battlefield.

An injectable PEG-like conjugate forms a subcutaneous depot and enables sustained delivery of a peptide drug

Many biologics have a short plasma half-life, and their conjugation to polyethylene glycol (PEG) is commonly used to solve this problem. However, the improvement in the plasma half-life of PEGylated drugs' is at an asymptote because the development of branched PEG has only had a modest impact on pharmacokinetics and pharmacodynamics. Here, we developed an injectable PEG-like conjugate that forms a subcutaneous depot for the sustained delivery of biologics. The PEG-like conjugate consists of poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) conjugated to exendin, a peptide drug used in the clinic to treat type 2 diabetes. The depot-forming exendin-POEGMA conjugate showed greater efficacy than a PEG conjugate of exendin as well as Bydureon, a clinically approved sustained-release formulation of exendin. The injectable depot-forming exendin-POEGMA conjugate did not elicit an immune response against the polymer, so that it remained effective and safe for long-term management of type 2 diabetes upon chronic administration. In contrast, the PEG conjugate induced an anti-PEG immune response, leading to early clearance and loss of efficacy upon repeat dosing. The exendin-POEGMA depot also showed superior long-term efficacy compared to Bydureon. Collectively, these results suggest that an injectable POEGMA conjugate of biologic drugs that forms a drug depot under the skin, providing favorable pharmacokinetic properties and sustained efficacy while remaining non-immunogenic, offers significant advantages over other commonly used drug delivery technologies.

PT320, a Sustained-Release GLP-1 Receptor Agonist, Ameliorates L-DOPA-Induced Dyskinesia in a Mouse Model of Parkinson's Disease

To determine the efficacy of PT320 on L-DOPA-induced dyskinetic behaviors, and neurochemistry in a progressive Parkinson's disease (PD) MitoPark mouse model. To investigate the effects of PT320 on the manifestation of dyskinesia in L-DOPA-primed mice, a clinically translatable biweekly PT320 dose was administered starting at either 5 or 17-weeks-old mice. The early treatment group was given L-DOPA starting at 20 weeks of age and longitudinally evaluated up to 22 weeks. The late treatment group was given L-DOPA starting at 28 weeks of age and longitudinally observed up to 29 weeks. To explore dopaminergic transmission, fast scan cyclic voltammetry (FSCV) was utilized to measure presynaptic dopamine (DA) dynamics in striatal slices following drug treatments. Early administration of PT320 significantly mitigated the severity L-DOPA-induced abnormal involuntary movements; PT320 particularly improved excessive numbers of standing as well as abnormal paw movements, while it did not affect L-DOPA-induced locomotor hyperactivity. In contrast, late administration of PT320 did not attenuate any L-DOPA-induced dyskinesia measurements. Moreover, early treatment with PT320 was shown to not only increase tonic and phasic release of DA in striatal slices in L-DOPA-naïve MitoPark mice, but also in L-DOPA-primed animals. Early treatment with PT320 ameliorated L-DOPA-induced dyskinesia in MitoPark mice, which may be related to the progressive level of DA denervation in PD.

The pleiotropic of GLP-1/GLP-1R axis in central nervous system diseases

Glucagon-like peptide-1(GLP-1) is a multifunctional polypeptide throughout the lifespan via activating Glucagon-like peptide-1 receptor (GLP-1R).GLP-1 can affect food ingestion, enhance the secretion of insulin from pancreatic islets induced by glucose and be utilized to treat type 2 diabetes mellitus(T2DM).But, accumulating evidences from the decades suggest that activation GLP-1R can not only regulate the blood glucose, but also sustain the homeostasis of intracellular environment and protect neuron from various damaged responses such as oxidative stress, inflammation, excitotoxicity, ischemia and so on. And more and more pre-clinical and clinical studies identified that GLP-1 and its analogues may play a significant role in improving multiple central nervous system (CNS) diseases including neurodegenerative diseases, epilepsy, mental disorders, ischemic stroke, hemorrhagic stroke, traumatic brain injury, spinal cord injury, chronic pain, addictive disorders, other diseases neurological complications and so on. In order to better reveal the relationship between GLP-1/GLP-1R axis and the growth, development and survival of neurons, herein, this review is aimed to summarize the multi-function of GLP-1/GLP-1R axis in CNS diseases.

Glucagon-like peptide-1 (GLP-1) receptor agonists and neuroinflammation: Implications for neurodegenerative disease treatment

Chronic, excessive neuroinflammation is a key feature of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). However, neuroinflammatory pathways have yet to be effectively targeted in clinical treatments for such diseases. Interestingly, increased inflammation and neurodegenerative disease risk have been associated with type 2 diabetes mellitus (T2DM) and insulin resistance (IR), suggesting that treatments that mitigate T2DM pathology may be successful in treating neuroinflammatory and neurodegenerative pathology as well. Glucagon-like peptide-1 (GLP-1) is an incretin hormone that promotes healthy insulin signaling, regulates blood sugar levels, and suppresses appetite. Consequently, numerous GLP-1 receptor (GLP-1R) stimulating drugs have been developed and approved by the US Food and Drug Administration (FDA) and related global regulatory authorities for the treatment of T2DM. Furthermore, GLP-1R stimulating drugs have been associated with anti-inflammatory, neurotrophic, and neuroprotective properties in neurodegenerative disorder preclinical models, and hence hold promise for repurposing as a treatment for neurodegenerative diseases. In this review, we discuss incretin signaling, neuroinflammatory pathways, and the intersections between neuroinflammation, brain IR, and neurodegenerative diseases, with a focus on AD and PD. We additionally overview current FDA-approved incretin receptor stimulating drugs and agents in development, including unimolecular single, dual, and triple receptor agonists, and highlight those in clinical trials for neurodegenerative disease treatment. We propose that repurposing already-approved GLP-1R agonists for the treatment of neurodegenerative diseases may be a safe, efficacious, and cost-effective strategy for ameliorating AD and PD pathology by quelling neuroinflammation.

Protective role of IGF-1 and GLP-1 signaling activation in neurological dysfunctions

Insulin-like growth factor-1 (IGF-1), a pleiotropic polypeptide, plays an essential role in CNS development and maturation. Glucagon-like peptide-1 (GLP-1) is an endogenous incretin hormone that regulates blood glucose levels and fatty acid oxidation in the brain. GLP-1 also exhibits similar functions and growth factor-like properties to IGF-1, which is likely how it exerts its neuroprotective effects. Recent preclinical and clinical evidence indicate that IGF-1 and GLP-1, apart from regulating growth and development, prevent neuronal death mediated by amyloidogenesis, cerebral glucose deprivation, neuroinflammation and apoptosis through modulation of PI3/Akt kinase, mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK/ERK). IGF-1 resistance and GLP-1 deficiency impair protective cellular signaling mechanisms, contributing to the progression of neurodegenerative diseases. Over the past decades, IGF-1 and GLP-1 have emerged as an essential component of the neuronal system and as potential therapeutic targets for several neurodegenerative and neuropsychiatric dysfunctions. There is substantial evidence that IGF-1 and GLP-1 analogues penetrate the blood-brain barrier (BBB) and exhibit neuroprotective functions, including synaptic formation, neuronal plasticity, protein synthesis, and autophagy. Conclusively, this review represents the therapeutic potential of IGF-1 and GLP-1 signaling target activators in ameliorating neurological disorders.

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.

Ketogenic Diet as a potential treatment for traumatic brain injury in mice

Traumatic brain injury (TBI) is a brain dysfunction without present treatment. Previous studies have shown that animals fed ketogenic diet (KD) perform better in learning tasks than those fed standard diet (SD) following brain injury. The goal of this study was to examine whether KD is a neuroprotective in TBI mouse model. We utilized a closed head injury model to induce TBI in mice, followed by up to 30 days of KD/SD. Elevated levels of ketone bodies were confirmed in the blood following KD. Cognitive and behavioral performance was assessed post injury and molecular and cellular changes were assessed within the temporal cortex and hippocampus. Y-maze and Novel Object Recognition tasks indicated that mTBI mice maintained on KD displayed better cognitive abilities than mTBI mice maintained on SD. Mice maintained on SD post-injury demonstrated SIRT1 reduction when compared with uninjured and KD groups. In addition, KD management attenuated mTBI-induced astrocyte reactivity in the dentate gyrus and decreased degeneration of neurons in the dentate gyrus and in the cortex. These results support accumulating evidence that KD may be an effective approach to increase the brain’s resistance to damage and suggest a potential new therapeutic strategy for treating TBI.

Potential new therapeutic target for Alzheimer's disease: Glucagon-like peptide-1

Increasing evidence shows a close relationship between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). Recently, glucagon-like peptide-1 (GLP-1), a gut incretin hormone, has become a well-established treatment for T2DM and is likely to be involved in treating cognitive impairment. In this mini review, the similarities between AD and T2DM are summarised with the main focus on GLP-1-based therapeutics in AD.

The metabolite GLP-1 (9-36) is neuroprotective and anti-inflammatory in cellular models of neurodegeneration

Glucagon-like peptide-1 (GLP-1) is best known for its insulinotropic action following food intake. Its metabolite, GLP-1 (9-36), was assumed biologically inactive because of low GLP-1 receptor (GLP-1R) affinity and non-insulinotropic properties; however, recent studies contradict this assumption. Increased use of FDA approved GLP-1 analogues for treating metabolic disorders and neurodegenerative diseases raises interest in GLP-1 (9-36)'s biological role. We use human SH-SY5Y neuroblastoma cells and a GLP-1R over-expressing variety (#9), in both undifferentiated and differentiated states, to evaluate the neurotrophic/neuroprotective effects of GLP-1 (9-36) against toxic glutamate exposure and other oxidative stress models (via the MTS, LDH or ROS assays). In addition, we examine GLP-1 (9-36)'s signaling pathways, including cyclic-adenosine monophosphate (cAMP), protein kinase-A (PKA), and 5' adenosine monophosphate-activated protein kinase (AMPK) via the use of ELISA, pharmacological inhibitors, or GLP-1R antagonist. Human HMC3 and mouse IMG microglial cell lines were used to study the anti-inflammatory effects of GLP-1 (9-36) against lipopolysaccharide (LPS) (via ELISA). Finally, we applied GLP-1 (9-36) to primary dissociation cultures challenged with α-synuclein or amyloid-β and assessed survival and morphology via immunochemistry. We demonstrate evidence of GLP-1R, cAMP, PKA, and AMPK-mediated neurotrophic and neuroprotective effects of GLP-1 (9-36). The metabolite significantly reduced IL-6 and TNF-α levels in HMC3 and IMG microglial cells, respectively. Lastly, we show mild but significant effects of GLP-1 (9-36) in primary neuron cultures challenged with α-synuclein or amyloid-β. These studies enhance understanding of GLP-1 (9-36)'s effects on the nervous system and its potential as a primary or complementary treatment in pathological contexts.

An extended release GLP-1 analogue increases α-synuclein accumulation in a mouse model of prodromal Parkinson's disease

The repurposing of drugs developed to treat type 2 diabetes for the treatment of Parkinson's disease (PD) was encouraged by the beneficial effect exerted by the glucagon-like peptide 1 (GLP-1) analogue exenatide in a phase 2 clinical trial. The effects of GLP-1 analogues have been investigated extensively using rodent toxin models of PD. However, many of the toxin-based models used lack robust α-synuclein (α-syn) pathology, akin to the Lewy bodies and neurites seen in PD. One prior study has reported a protective effect of a GLP-1 analogue on midbrain dopamine neurons following injection of α-syn preformed fibrils (PFF) into the striatum. Here, we used olfactory bulb injections of PFF as a model of prodromal PD and monitored the effect of a long-acting GLP-1 analogue on the propagation of α-syn pathology in the olfactory system. Thirteen weeks after PFF injection, mice treated with long-acting the GLP-1 analogue had a significant increase in pathological α-syn in brain regions connected to the olfactory bulb, accompanied by signs of microglia activation. Our results suggest that the nature of the neuronal insult and intrinsic properties of the targeted neuronal population markedly influence the effect of GLP-1 analogues.

Sustained Release GLP-1 Agonist PT320 Delays Disease Progression in a Mouse Model of Parkinson's Disease

GLP-1 agonists have become increasingly interesting as a new Parkinson's disease (PD) clinical treatment strategy. Additional preclinical studies are important to validate this approach and define the disease stage when they are most effective. We hence characterized the efficacy of PT320, a sustained release formulation of the long acting GLP-1 agonist, exenatide, in a progressive PD (MitoPark) mouse model. A clinically translatable biweekly PT320 dose was administered starting at 5 weeks of age and longitudinally evaluated to 24 weeks, and multiple behavioral/cellular parameters were measured. PT320 significantly improved spontaneous locomotor activity and rearing in MitoPark PD mice. "Motivated" behavior also improved, evaluated by accelerating rotarod performance. Behavioral improvement was correlated with enhanced cellular and molecular indices of dopamine (DA) midbrain function. Fast scan cyclic voltammetry demonstrated protection of striatal and nucleus accumbens DA release and reuptake in PT320 treated MitoPark mice. Positron emission tomography showed protection of striatal DA fibers and tyrosine hydroxylase protein expression was augmented by PT320 administration. Early PT320 treatment may hence provide an important neuroprotective therapeutic strategy in PD.

Time-dependent cytokine and chemokine changes in mouse cerebral cortex following a mild traumatic brain injury

Traumatic brain injury (TBI) is a serious global health problem, many individuals live with TBI-related neurological dysfunction. A lack of biomarkers of TBI has impeded medication development. To identify new potential biomarkers, we time-dependently evaluated mouse brain tissue and neuronally derived plasma extracellular vesicle proteins in a mild model of TBI with parallels to concussive head injury. Mice (CD-1, 30–40 g) received a sham procedure or 30 g weight-drop and were euthanized 8, 24, 48, 72, 96 hr, 7, 14 and 30 days later. We quantified ipsilateral cortical proteins, many of which differed from sham by 8 hours post-mTBI, particularly GAS-1 and VEGF-B were increased while CXCL16 reduced, 23 proteins changed in 4 or more of the time points. Gene ontology pathways mapped from altered proteins over time related to pathological and physiological processes. Validation of proteins identified in this study may provide utility as treatment response biomarkers.

PT320, Sustained-Release Exendin-4, Mitigates L-DOPA-Induced Dyskinesia in a Rat 6-Hydroxydopamine Model of Parkinson's Disease

Background

We previously demonstrated that subcutaneous administration of PT320, a sustained-release (SR) form of exendin-4, resulted in the long-term maintenance of steady-state exenatide (exendin-4) plasma and target levels in 6-hydroxydopamine (6-OHDA)-pretreated animals. Additionally, pre- or post-treatment with PT320 mitigated the early stage of 6-OHDA-induced dopaminergic neurodegeneration. The purpose of this study was to evaluate the effect of PT320 on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced abnormal involuntary movements (AIMs) in the rat 6-OHDA model of Parkinson’s disease.

Methods

Adult male Sprague–Dawley rats were unilaterally lesioned in the right medial forebrain bundle by 6-OHDA. L-DOPA and benserazide were given daily for 22 days, starting from 4 weeks after lesioning. PT320 was co-administered weekly for 3 weeks. AIM was evaluated on days 1, 16, and 22 after initiating L-DOPA/benserazide + PT320 treatment. Brain tissues were subsequently collected for HPLC measurements of dopamine (DA) and metabolite concentrations.

Results

L-DOPA/benserazide increased AIMs of limbs and axial as well as the sum of all dyskinesia scores (ALO) over 3 weeks. PT320 significantly reduced the AIM scores of limbs, orolingual, and ALO. Although PT320 did not alter DA levels in the lesioned striatum, PT320 significantly attenuated 6-OHDA-enhanced DA turnover.

Conclusion

PT320 attenuates L-DOPA/benserazide-induced dyskinesia in a 6-OHDA rat model of PD and warrants clinical evaluation to mitigate Parkinson’s disease in humans.

Glucagon-like peptide-1 (GLP-1)-based receptor agonists as a treatment for Parkinson's disease

INTRODUCTION

Accumulating evidence supports the evaluation of glucagon-like peptide-1 (GLP-1) receptor (R) agonists for the treatment of the underlying pathology causing Parkinson's Disease (PD). Not only are these effects evident in models of PD and other neurodegenerative disorders but recently in a randomized, double-blind, placebo-controlled clinical trial, a GLP-1R agonist has provided improved cognition motor functions in humans with moderate PD.

AREAS COVERED

In this mini-review, we describe the development of GLP-1R agonists and their potential therapeutic value in treating PD. Many GLP-1R agonists are FDA approved for the treatment of metabolic disorders, and hence can be rapidly repositioned for PD. Furthermore, we present preclinical data offering insights into the use of monomeric dual- and tri-agonist incretin-based mimetics for neurodegenerative disorders. These drugs combine active regions of GLP-1 with those of glucose-dependent insulinotropic peptide (GIP) and/or glucagon (Gcg).

EXPERT OPINION

GLP-1Ragonists offer a complementary and enhanced therapeutic value to other drugs used to treat PD. Moreover, the use of the dual- or tri-agonist GLP-1-based mimetics may provide combinatory effects that are even more powerful than GLP-1R agonism alone. We advocate for further investigations into the repurposing of GLP-1R agonists and the development of classes of multi-agonists for PD treatment.

Neuroprotective Effects and Treatment Potential of Incretin Mimetics in a Murine Model of Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is a commonly occurring injury in sports, victims of motor vehicle accidents, and falls. TBI has become a pressing public health concern with no specific therapeutic treatment. Mild TBI (mTBI), which accounts for approximately 90% of all TBI cases, may frequently lead to long-lasting cognitive, behavioral, and emotional impairments. The incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are gastrointestinal hormones that induce glucose-dependent insulin secretion, promote β-cell proliferation, and enhance resistance to apoptosis. GLP-1 mimetics are marketed as treatments for type 2 diabetes mellitus (T2DM) and are well tolerated. Both GLP-1 and GIP mimetics have shown neuroprotective properties in animal models of Parkinson's and Alzheimer's disease. The aim of this study is to evaluate the potential neuroprotective effects of liraglutide, a GLP-1 analog, and twincretin, a dual GLP-1R/GIPR agonist, in a murine mTBI model. First, we subjected mice to mTBI using a weight-drop device and, thereafter, administered liraglutide or twincretin as a 7-day regimen of subcutaneous (s.c.) injections. We then investigated the effects of these drugs on mTBI-induced cognitive impairments, neurodegeneration, and neuroinflammation. Finally, we assessed their effects on neuroprotective proteins expression that are downstream to GLP-1R/GIPR activation; specifically, PI3K and PKA phosphorylation. Both drugs ameliorated mTBI-induced cognitive impairments evaluated by the novel object recognition (NOR) and the Y-maze paradigms in which neither anxiety nor locomotor activity were confounds, as the latter were unaffected by either mTBI or drugs. Additionally, both drugs significantly mitigated mTBI-induced neurodegeneration and neuroinflammation, as quantified by immunohistochemical staining with Fluoro-Jade/anti-NeuN and anti-Iba-1 antibodies, respectively. mTBI challenge significantly decreased PKA phosphorylation levels in ipsilateral cortex, which was mitigated by both drugs. However, PI3K phosphorylation was not affected by mTBI. These findings offer a new potential therapeutic approach to treat mTBI, and support further investigation of the neuroprotective effects and mechanism of action of incretin-based therapies for neurological disorders.

Pharmacokinetics of Exenatide in nonhuman primates following its administration in the form of sustained-release PT320 and Bydureon

The time-dependent (30 min - day 84) plasma profile of PT320, a sustained-release (SR)-Exenatide formulation under clinical development for treatment of neurodegenerative disorders, was evaluated in nonhuman primates after a single subcutaneous dose and was compared to Bydureon. Exenatide release from PT320 exhibited a triphasic pharmacokinetic profile. An initial peak occurred at 3 hr post-administration, a secondary peak at 5 days, and achievement of Exenatide steady-state plasma levels from day 10–28. Systemic exposure increased across PT320 doses, and Exenatide levels were maintained above the therapeutic threshold prior to achieving a steady-state. In contrast, Exenatide release from Bydureon exhibited a biphasic profile, with an initial plasma peak at 3 hr, followed by a rapid decline to a sub-therapeutic concentration, and a gradual elevation to provide a steady-state from day 35–49. Exenatide total exposure, evaluated from the area under the time-dependent Exenatide concentration curve, was similar for equivalent doses of PT320 and Bydureon. The former, however, reached and maintained steady-state plasma Exenatide levels more rapidly, without dipping to a sub-therapeutic concentration. Both SR-Exenatide formulations proved well-tolerated and, following a well-regulated initial release burst, generated steady-state plasma levels of Exenatide, but with PT320 producing continuous therapeutic Exenatide levels and more rapidly reaching a steady-state.

Neurotrophic and neuroprotective effects of a monomeric GLP-1/GIP/Gcg receptor triagonist in cellular and rodent models of mild traumatic brain injury

A synthetic monomeric peptide triple receptor agonist, termed "Triagonist" that incorporates glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon (Gcg) actions, was previously developed to improve upon metabolic and glucose regulatory benefits of single and dual receptor agonists in rodent models of diet-induced obesity and type 2 diabetes. In the current study, the neurotrophic and neuroprotective actions of this Triagonist were probed in cellular and mouse models of mild traumatic brain injury (mTBI), a prevalent cause of neurodegeneration in both the young and elderly. Triagonist dose- and time-dependently elevated cyclic AMP levels in cultured human SH-SY5Y neuronal cells, and induced neurotrophic and neuroprotective actions, mitigating oxidative stress and glutamate excitotoxicity. These actions were inhibited only by the co-administration of antagonists for all three receptor types, indicating the balanced co-involvement of GLP-1, GIP and Gcg receptors. To evaluate physiological relevance, a clinically translatable dose of Triagonist was administered subcutaneously, once daily for 7 days, to mice following a 30 g weight drop close head injury. Triagonist fully mitigated mTBI-induced visual and spatial memory deficits, evaluated at 7 and 30 days post injury. These results establish Triagonist as a novel neurotrophic/protective agent worthy of further evaluation as a TBI treatment strategy.

(-)-Phenserine and the prevention of pre-programmed cell death and neuroinflammation in mild traumatic brain injury and Alzheimer's disease challenged mice

Mild traumatic brain injury (mTBI) is a risk factor for neurodegenerative disorders, such as Alzheimer's disease (AD) and Parkinson's disease (PD). TBI-derived neuropathologies are promoted by inflammatory processes: chronic microgliosis and release of pro-inflammatory cytokines that further promote neuronal dysfunction and loss. Herein, we evaluated the effect on pre-programmed cell death/neuroinflammation/synaptic integrity and function of (-)-Phenserine tartrate (Phen), an agent originally developed for AD. This was studied at two clinically translatable doses (2.5 and 5.0 mg/kg, BID), in a weight drop (concussive) mTBI model in wild type (WT) and AD APP/PSEN1 transgenic mice. Phen mitigated mTBI-induced cognitive impairment, assessed by Novel Object Recognition and Y-maze behavioral paradigms, in WT mice. Phen fully abated mTBI-induced neurodegeneration, evaluated by counting Fluoro-Jade C-positive (FJC+) cells, in hippocampus and cortex of WT mice. In APP/PSEN1 mice, degenerating cell counts were consistently greater across all experimental groups vs. WT mice. mTBI elevated FJC+ cell counts vs. the APP/PSEN1 control (sham) group, and Phen similarly mitigated this. Anti-inflammatory effects on microglial activation (IBA1-immunoreactivity (IR)) and the pro-inflammatory cytokine TNF-α were evaluated. mTBI increased IBA1-IR and TNF-α/IBA1 colocalization vs. sham, both in WT and APP/PSEN1 mice. Phen decreased IBA1-IR throughout hippocampi and cortices of WT mice, and in cortices of AD mice. Phen, likewise, reduced levels of IBA1/TNF-α-IR colocalization volume across all areas in WT animals, with a similar trend in APP/PSEN1 mice. Actions on astrocyte activation by mTBI were followed by evaluating GFAP, and were similarly mitigated by Phen. Synaptic density was evaluated by quantifying PSD-95+ dendritic spines and Synaptophysin (Syn)-IR. Both were significantly reduced in mTBI vs. sham in both WT and APP/PSEN1 mice. Phen fully reversed the PSD-95+ spine loss in WT and Syn-IR decrease in both WT and APP/PSEN1 mice. To associate immunohistochemical changes in synaptic markers with function, hippocampal long term potentiation (LTP) was induced in WT mice. LTP was impaired by mTBI, and this impairment was mitigated by Phen. In synopsis, clinically translatable doses of Phen ameliorated mTBI-mediated pre-programmed cell death/neuroinflammation/synaptic dysfunction in WT mice, consistent with fully mitigating mTBI-induced cognitive impairments. Phen additionally demonstrated positive actions in the more pathologic brain microenvironment of AD mice, further supporting consideration of its repurposing as a treatment for mTBI.

Incretin Mimetics as Rational Candidates for the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is becoming an increasing public health issue. With an annually estimated 1.7 million TBIs in the United States (U.S) and nearly 70 million worldwide, the injury, isolated or compounded with others, is a major cause of short- and long-term disability and mortality. This, along with no specific treatment, has made exploration of TBI therapies a priority of the health system. Age and sex differences create a spectrum of vulnerability to TBI, with highest prevalence among younger and older populations. Increased public interest in the long-term effects and prevention of TBI have recently reached peaks, with media attention bringing heightened awareness to sport and war related head injuries. Along with short-term issues, TBI can increase the likelihood for development of long-term neurodegenerative disorders. A growing body of literature supports the use of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and glucagon (Gcg) receptor (R) agonists, along with unimolecular combinations of these therapies, for their potent neurotrophic/neuroprotective activities across a variety of cellular and animal models of chronic neurodegenerative diseases (Alzheimer's and Parkinson's diseases) and acute cerebrovascular disorders (stroke). Mild or moderate TBI shares many of the hallmarks of these conditions; recent work provides evidence that use of these compounds is an effective strategy for its treatment. Safety and efficacy of many incretin-based therapies (GLP-1 and GIP) have been demonstrated in humans for the treatment of type 2 diabetes mellitus (T2DM), making these compounds ideal for rapid evaluation in clinical trials of mild and moderate TBI.

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

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