Liraglutide prevents metabolic side-effects and improves recognition and working memory during antipsychotic treatment in rats

Liraglutide alleviated alpha-pyrrolidinovalerophenone (α-PVP) induced cognitive deficits in rats by modifying brain mitochondrial impairment

The use of NPS compounds is increasing, and impairment in spatial learning and memory is a growing concern. Alpha-pyrrolidinovalerophenone (α-PVP) consumption, as a commonly used NPS, can impair spatial learning and memory via the brain mitochondrial dysfunction mechanism. Liraglutide isone of the most well-known Glucagon-Like Peptide 1 (GLP-1) agonists that is used as an anti-diabetic and anti-obesity drug. According to current research, Liraglutide likely ameliorates cognitive impairment in neurodegenerative conditions and substance use disorders. Hence, the purpose of this study is examining the effect of Liraglutide on α-PVP-induced spatial learning and memory problems due to brain mitochondrial dysfunction. Wistar rats (8 in each group) received α-PVP (20 mg/kg/d for 10 consecutive days, intraperitoneally (I.P.)). Then, Liraglutide was administered at 47 and 94 μg/kg/d, I.P., for 4 weeks following the α-PVP administration. The Morris Water Maze (MWM) task evaluated spatial learning and memory 24 h after Liraglutide treatment. Bedside, brain mitochondrial activity parameters, including reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP), cytochrome c release, mitochondrial outer membrane damage and swelling, and brain ADP/ATP ratio, were studied. Our results showed that Liraglutide ameliorated α-PVP-induced spatial learning and memory impairments through alleviating brain mitochondrial dysfunction (which is indicated by increasing ROS formation, collapsed MMP, mitochondrial outer membrane damage, cytochrome c release, mitochondrial swelling, and increased brain ADP/ATP ratio). This study could be used as a starting point for future studies about the possible role of Liraglutide in ameliorating mitochondrial dysfunction leading to substance use disorder- induced cognitive impairment.

Targeting GLP-1 receptors to reduce nicotine use disorder: Preclinical and clinical evidence

Nicotine use disorder (NUD) remains a leading cause of preventable death in the U.S. Unfortunately, current FDA-approved pharmacotherapies for smoking cessation have limited efficacy and are associated with high rates of relapse. One major barrier to long-term smoking abstinence is body weight gain during withdrawal. Nicotine withdrawal-induced body weight gain can also lead to development of chronic disease states like obesity and type II diabetes mellitus. Therefore, it is critical to identify novel pharmacotherapies for NUD that decrease relapse and nicotine withdrawal symptoms including body weight gain. Recent studies demonstrate that glucagon-like peptide-1 receptor (GLP-1R) agonists attenuate voluntary nicotine taking and seeking and prevent withdrawal-induced hyperphagia and body weight gain. Emerging evidence also suggests that GLP-1R agonists improve cognitive deficits, as well as depressive- and anxiety-like behaviors, which contribute to smoking relapse during withdrawal. While further studies are necessary to fully characterize the effects of GLP-1R agonists on NUD and understand the mechanisms by which GLP-1R agonists decrease nicotine withdrawal-mediated behaviors, the current literature supports GLP-1R-based approaches to treating NUD.

Potent synergistic effects of dulaglutide and food restriction in prevention of olanzapine-induced metabolic adverse effects in a rodent model

BACKGROUND

Antipsychotics are indispensable in the treatment of severe mental illneses, however adverse metabolic effects including diabetes, weight gain, dyslipidemia, and related cardiovascular morbidity are common, and current pharmacological strategies for their management are unsatisfactory. Glucagon-like 1 peptide receptor agonists (GLP-1 RAs) are approved for the treatment of type 2 diabetes and obesity hold promise for the management of antipsychotic-associated adverse metabolic effects.

METHODS

To characterize the molecular effects and identify biomarkers for GLP-1 RA preventive treatment, Sprague-Dawley female rats were treated with long-acting formulations of the antipsychotic olanzapine and the GLP-1 RA dulaglutide for 8 days. A pair-feeding protocol evaluated the combined effects of dulaglutide and food restriction on an olanzapine-induced metabolic phenotype. Body weight and food consumption were recorded. Biochemical analysis included a lipid profile, a spectrum of gastrointestinal and adipose tissue-derived hormones, and fibroblast growth factor 21 serum levels.

RESULTS

Olanzapine induced hyperphagia, weight gain, increased serum triglycerides and HDL cholesterol. Food restriction affected the OLA-induced phenotype but not serum markers. Dulaglutide led to a modest decrease in food intake, with no effect on weight gain, and did not reverse the OLA-induced changes in serum lipid parameters. Concomitant dulaglutide and food restriction resulted in weight loss, decreased feed efficiency, and lower total and HDL cholesterol.

CONCLUSIONS

A combined strategy of dulaglutide and food restriction manifested a massive synergistic benefit. GLP-1RAs represent a promising strategy and deserve thorough future research. Our findings underline the potential importance of lifestyle intervention in addition to GLP-1 RA treatment.

A systematic review of preclinical studies exploring the role of insulin signalling in executive function and memory

Beside its involvement in somatic dysfunctions, altered insulin signalling constitutes a risk factor for the development of mental disorders like Alzheimer's disease and obsessive-compulsive disorder. While insulin-related somatic and mental disorders are often comorbid, the fundamental mechanisms underlying this association are still elusive. Studies conducted in rodent models appear well suited to help decipher these mechanisms. Specifically, these models are apt to prospective studies in which causative mechanisms can be manipulated via multiple tools (e.g., genetically engineered models and environmental interventions), and experimentally dissociated to control for potential confounding factors. Here, we provide a narrative synthesis of preclinical studies investigating the association between hyperglycaemia - as a proxy of insulin-related metabolic dysfunctions - and impairments in working and spatial memory, and attention. Ultimately, this review will advance our knowledge on the role of glucose metabolism in the comorbidity between somatic and mental illnesses.

Targeting Autophagy, Apoptosis, and Oxidative Perturbations with Dapagliflozin Mitigates Cadmium-Induced Cognitive Dysfunction in Rats

Cognitive decline and Alzheimer-like neuropathology are common manifestations of cadmium toxicity. Thanks to its antioxidant/anti-apoptotic features, dapagliflozin has demonstrated promising neuroprotective actions. However, its effect on cadmium-induced neurotoxicity is lacking. The present work aimed to examine whether dapagliflozin could protect rats from cadmium-evoked cognitive decline. In this study, the behavioral disturbances and hippocampal biomolecular alterations were studied after receiving dapagliflozin. Herein, cadmium-induced memory/learning decline was rescued in the Morris water maze, novel object recognition task, and Y-shaped maze by dapagliflozin. Meanwhile, the hippocampal histopathological abnormalities were mitigated. The molecular mechanisms revealed that dapagliflozin lowered hippocampal expression of p-tau and Aβ42 neurotoxic proteins while augmenting acetylcholine. The cognitive enhancement was triggered by hippocampal autophagy stimulation, as indicated by decreased SQSTM-1/p62 and Beclin 1 upregulation. Meanwhile, a decrease in p-mTOR/total mTOR and an increase in p-AMPK/total AMPK ratio were observed in response to dapagliflozin, reflecting AMPK/mTOR cascade stimulation. Dapagliflozin, on the other hand, dampened the pro-apoptotic processes in the hippocampus by downregulating Bax, upregulating Bcl-2, and inactivating GSK-3β. The hippocampal oxidative insult was mitigated by dapagliflozin as seen by lipid peroxide lowering, antioxidants augmentation, and SIRT1/Nrf2/HO-1 pathway activation. In conclusion, dapagliflozin's promising neuroprotection was triggered by its pro-autophagic, anti-apoptotic, and antioxidant properties.

The Involvement of PGRMC1 Signaling in Cognitive Impairment Induced by Long-Term Clozapine Treatment in Rats

INTRODUCTION

Progesterone receptor component 1 (PGRMC1) has been identified as a potential target in atypical antipsychotic drug-induced metabolic disturbances as well as neuroprotection in the central nervous system. In our study, we aimed to figure out the essential role of PGRMC1 signaling pathway underlying clozapine-induced cognitive impairment.

METHODS

In male SD rats, we utilized recombinant adeno-associated viruses (BBB 2.0) and the specific inhibitor of PGRMC1 (AG205) to regulate the expression of PGRMC1 in the brain, with a special focus on the hippocampus. Treatments of clozapine and AG205 were conducted for 28 days, and subsequent behavioral tests including modified elevated plus maze and Morris water maze were conducted to evaluate the cognitive performance. Hippocampal protein expressions were measured by Western blotting.

RESULTS

Our study showed that long-term clozapine administration led to cognitive impairment as confirmed by behavioral tests as well as histopathological examination in the hippocampus. Clozapine inhibited neural survival through the PGRMC1/EGFR/GLP1R-PI3K-Akt signaling pathway, leading to a decrease in the downstream survival factor, brain-derived neurotrophic factor (BDNF), and simultaneously promoted neural apoptosis in the rat hippocampus. Intriguingly, by targeting at the hippocampal PGRMC1, we found that inhibiting PGRMC1 mimics, while its upregulation notably mitigates clozapine-induced cognitive impairment through PGRMC1 and its downstream signaling pathways.

CONCLUSION

PGRMC1-overexpression could protect hippocampus-dependent cognitive impairment induced by clozapine. This effect appears to arise, in part, from the upregulated expression of PGRMC1/EGFR/GLP1R and the activation of downstream PI3K-Akt-BDNF and caspase-3 signaling pathways.

Therapeutic management of atypical antipsychotic‑related metabolic dysfunctions using GLP‑1 receptor agonists: A systematic review

Metabolic disorders (MDs) like obesity, dyslipidemia, and type 2 diabetes are more frequently observed in patients diagnosed with psychiatric disorders undergoing treatment with antipsychotics, particularly atypical agents, than in the general population. The second generation of antidiabetics (SGAD) has been associated with cardiovascular benefits in large clinical trials which represent an important advantage over first-generation agents and might be of interest in the psychiatric population where multiple risk factors for cardiovascular disease (e.g., smoking, lack of exercise, and lack of healthy diet) are common occurrences. Therefore, this systematic review focused on the evaluation of the glucagon-like peptide-1 receptor agonists (GLP1-RAs), as a representative of the SGAD, to determine whether these agents may be recommended in patients with psychiatric disorders and MDs. For analysis, three electronic databases and clinical trial registers were explored for papers published between January 2000 and November 2022. After applying the inclusion and exclusion criteria, 20 clinical and preclinical trials, therapeutic guidelines, and meta-analyses were reviewed, and clinical recommendations were formulated. The large majority of the reviewed data (nine papers) were graded 'moderate' based on the GRADE criteria. The efficacy and tolerability of liraglutide and exenatide in the management of antipsychotic-induced MDs were supported by evidence of average quality, while the results regarding other GLP-1RAs were not sufficient to formulate a recommendation for their administration in this specific population. Clozapine and olanzapine had the most negative consequences on body weight, glycemic, and lipid metabolism. Therefore, careful monitoring of metabolic parameters is required when these are prescribed. Liraglutide and exenatide may be recommended as augmentative agents to metformin therapy, especially in patients receiving these two atypical antipsychotics, but most of the reviewed data supported the efficacy of GLP-1RAs only during the treatment administration. The two follow-up studies retrieved in the literature reported modest effects after GLP-1RA discontinuation after 1 year; therefore, long-term monitoring of metabolic parameters is required. More research is needed, and three randomized clinical trials are already ongoing, to evaluate the effects of GLP-1RAs in decreasing body weight, but also on other important metabolic variables, such as HbA1c status, fasting glucose levels, and lipid levels in patients receiving antipsychotic treatment.

Augmentation Therapies as Treatments for Coexisting Somatic Problems in Schizophrenia-A Systematic Review

The aim of this review is to appraise the data from available randomized clinical trials (RCT) regarding the possible combinations of neuroleptic and non-antipsychotic treatment which could enhance antipsychotic therapy efficacy whilst simultaneously addressing somatic symptoms in individuals with schizophrenia. A systematic search of the PubMed database up to February 2022 was conducted. Inclusion criteria: randomized controlled trials using augmentation therapy in chronic schizophrenia in adults, written in English, and only studies with psychometric assessments of schizophrenia were incorporated. Exclusion criteria: non-clinical, first episode of schizophrenia, patients on medication other than antipsychotics augmented, and not adjunctive therapy. Overall, 37 studies of 1931 patients with schizophrenia who received a combination of antipsychotic medication with other drugs were selected. A statistically significant reduction of negative and positive symptoms of schizophrenia, measured with the PANSS scale, when using a combination of antipsychotic treatment along with aspirin, simvastatin, N-acetylcysteine, or pioglitazone was found. A combination of antipsychotic medication with aspirin, simvastatin, N-acetylcysteine, or pioglitazone seems to be effective in the reduction of symptoms of schizophrenia in adults, but long-term studies are required to confirm this effect.

GLP-1 agonist Liraglutide prevents MK‑801-induced schizophrenia‑like behaviors and BDNF, CREB, p-CREB, Trk-B expressions in the hippocampus and prefrontal cortex in Balb/c mice

Glucagon-like peptide 1 (GLP-1) agonists are among the agents that can be used to treat type 2 diabetes mellitus, and they have also been reported to have neuroprotective effects. This study examined the effects of GLP-1 agonist Liraglutide on CREB, BDNF, Trk-B expression and emotional/cognitive behaviors in an experimental schizophrenia-like behavior model induced by MK-801. MK-801 (0.25 mg/kg, 0.1 ml/kg body weight) and/or Liraglutide (300 mcg/kg) were injected intraperitoneally once a day for 7 weeks into 8-10 weeks old male Balb/c mice (n = 78). Mice were randomly divided into 5 groups: Saline+Saline, MK-801 +Saline, Liraglutide+Saline, MK-801 +Liraglutide co-treatment, and Liraglutide+MK-801 co-treatment. A Morris water maze test, an elevated plus maze test, and an open field test were performed after injection. Western blots were performed on mice' hippocampus and PFC for BDNF, Trk-B, CREB, and p-CREB expression. Our study found that MK-801 impaired emotional and cognitive functions in mice. MK-801 administration did not affect Liraglutide's positive effects on spatial learning and memory activity in the Liraglutide+MK-801 group. Liraglutide administration (Liraglutide+MK-801 group) improved the BDNF/Trk-B and p-CREB/CREB ratio in the hippocampus, and the p-CREB/CREB ratio in the PFC to the control group level. The negative effects of MK-801 on cognitive behavior were not reversed by Liraglutide in the MK-801 +Liraglutide group. In conclusion, Liraglutide does not affect NMDA receptor blockade-induced emotional and cognitive behaviors. However, it has a protective effect against cognitive impairment. Furthermore, it is possible that the GLP-1 receptors in the hippocampus and PFC are involved in the modulation of NMDA receptor activity through CREB activation/deactivation.

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.

GLP-1 agonists: superior for mind and body in antipsychotic-treated patients?

Antipsychotics (APDs) represent a core treatment for severe mental disorders (SMEs). Providing symptomatic relief, APDs do not exert therapeutic effects on another clinically significant domain of serious mental disorders, cognitive impairment. Moreover, adverse metabolic effects (diabetes, weight gain, dyslipidemia, and increased cardiovascular risk) are common during treatment with APDs. Among pharmacological candidates reversing APD-induced metabolic adverse effects, glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1 RAs), approved for both diabetes and recently for obesity treatment, stand out due to their favorable effects on peripheral metabolic parameters. Interestingly, GLP-1 RAs are also proposed to have pro-cognitive effects. Particularly in terms of dual therapeutic mechanisms potentially improving both central nervous system (CNS) deficits and metabolic burden, GLP-1 RAs open a new perspective and assume a clinically advantageous position.

Neuroprotective effects of glucagon-like peptide-1 (GLP-1) analogues in epilepsy and associated comorbidities

Epilepsy is a common neurological condition induced by losing equilibrium of different pathway as well as neurotransmitters that affects over 50 million people globally. Furthermore, long-term administration of anti-seizure medications has been associated with psychological adverse effects. Also, epilepsy has been related to an increased prevalence of obesity and called type 2 diabetes mellitus. On the other hand, GLP-1 receptors are located throughout the brain, including the hippocampus, which have been associated to majority of neurological conditions, such as epilepsy and psychiatric disorders. Moreover, the impact of different GLP-1 analogues on diverse neurotransmitter systems and associated cellular and molecular pathways as a potential therapeutic target for epilepsy and associated comorbidities has piqued curiosity. In this regard, the anticonvulsant effects of GLP-1 analogues have been investigated in various animal models and promising results such as anticonvulsants as well as cognitive improvements have been observed. For instance, GLP-1 analogues like liraglutide in addition to their possible anticonvulsant benefits, could be utilized to alleviate mental cognitive problems caused by both epilepsy and anti-seizure medication side effects. In this review and growing protective function of GLP-1 in epilepsy induced by disturbed neurotransmitter pathways and the probable mechanisms of action of GLP-1 analogues as well as the GLP-1 receptor in these effects have been discussed.

Effect of Co-Treatment of Olanzapine with SEP-363856 in Mice Models of Schizophrenia

Olanzapine is a commonly used drug in the treatment of schizophrenia, but its clinical application has been restricted by metabolic-related side effects. In order to mitigate the weight gain side effects caused by olanzapine, other drugs with different targets were selected for combined use and evaluated in animal models of schizophrenia. SEP-363856 is a novel psychotropic agent which is under phase III clinical trials for schizophrenia treatment. The aim of the research was to evaluate whether co-administration of olanzapine and SEP-363856 exerts synergistic anti-schizophrenic effects in the apomorphine (APO)-induced climbing test, the MK-801-induced hyperactivity test, and the Morris water maze test, and therefore reduces the weight gain side effects induced by olanzapine. Through isobolographic analysis, the results showed a synergistic interaction in the climbing test; the experimental ED30 (3 mg/kg) was significantly smaller (p < 0.05) than the theoretical ED30 (5 mg/kg). Additionally, such potentiating effects appeared additive in the MK-801 challenge experiment. Co-treatment with an effective dose of olanzapine and a low dose of SEP-363856 reversed MK-801-induced cognitive impairment symptoms in mice. Moreover, combination treatment with olanzapine and SEP-363856 controls sustained weight gain in mice with chronic exposure to olanzapine. These results support further clinical trials to test the effectiveness of co-treatment of olanzapine and SEP-363856 for controlling symptoms and weight gain in patients with schizophrenia during antipsychotic treatments.

Antipsychotic Drug-Induced Increases in Peripheral Catecholamines are Associated With Glucose Intolerance

The second-generation antipsychotic drugs are widely used in the field of psychiatry, for an expanding number of different conditions. While their clinical efficacy remains indispensable, many of the drugs can cause severe metabolic side-effects, resulting in an increased risk of developing cardiometabolic disorders. The physiological basis of these side-effects remains an ongoing area of investigation. In the present study, we examined the potential role of peripheral catecholamines in antipsychotic-induced glucose intolerance. Adult female rats were acutely treated with either the first-generation antipsychotic drug haloperidol (0.1, 0.5 or 1 mg/kg) or the second-generation drugs risperidone (0.25, 1.0 or 2.5 mg/kg), olanzapine (1.5, 7.5 or 15 mg/kg) or clozapine (2, 10 or 20 mg/kg) or vehicle. Fasting glucose levels were measured and then animals were subjected to the intraperitoneal glucose tolerance test. Levels of peripheral norepinephrine, epinephrine and dopamine were concurrently measured in the same animals 75, 105 and 135 min after drug treatment. All antipsychotics caused glucose intolerance, with strongest effects by clozapine > olanzapine > risperidone > haloperidol. Plasma catecholamines were also increased by drug treatment, with greatest effects for norepinephrine and epinephrine caused by clozapine > risperidone > olanzapine > haloperidol. Importantly, there were strong and statistically significant associations between norepinephrine/epinephrine levels and glucose intolerance for all drugs. These findings confirm that increases in peripheral catecholamines co-occur in animals that exhibit antipsychotic-induced glucose intolerance, and these effects are strongly associated with each other, providing further evidence for elevated catecholamines as a substrate for antipsychotic metabolic side-effects.

Antipsychotic Drug Development: From Historical Evidence to Fresh Perspectives

Schizophrenia is a complex disorder of varied etiology, manifesting symptoms that can differ between patients and change throughout an individual's lifespan. Antipsychotic drugs have evolved through first (e.g., haloperidol), second (olanzapine and clozapine) and a possible third (aripiprazole) generation of drugs in an attempt to improve efficacy and tolerability, with minimal side-effects. Despite robust scientific efforts over the past 70 years, there remains a need to develop drugs with greater efficacy, particularly in relation to the negative and cognitive symptoms of schizophrenia, addressing treatment resistance, with a lower side-effects profile compared to existing antipsychotic drugs. Identifying and investigating novel therapeutic targets remains an important component of future antipsychotic drug discovery; however, mounting evidence demonstrates neurobiological, neuroanatomical and functional heterogeneity in cohorts of individuals with schizophrenia. This presents an opportunity to refresh the approach to drug trials to a more targeted strategy. By increasing understanding of the basic science and pharmacological mechanisms underlying the potential antipsychotic efficacy of novel therapeutics prior to clinical trials, new drugs may be appropriately directed to a target population of schizophrenia subjects based on the drug mechanisms and correlating biological sub-groupings of patient characteristics. Improving the lives of sub-populations of people with schizophrenia that share common biological characteristics and are likely to be responsive to a particular compound may be more achievable than aiming to treat the complexities of schizophrenia as a homogenous disorder. This approach to clinical trials in antipsychotic research is discussed in the present review.

Brexpiprazole caused glycolipid metabolic disorder by inhibiting GLP1/GLP1R signaling in rats

Brexpiprazole (Bre) is a new multi-target antipsychotic drug (APD) approved by the US FDA in 2015, and shows good therapeutic potential. But it lacks assessments on the metabolic side effects, which obstructs the treatment of schizophrenia. Glucagon-like peptide 1 (GLP1), an incretin associated with insulin action and metabolism, is involved in the metabolic syndrome (MS) caused by most APDs. In this study, we examined the adverse effects of Bre on glycolipid metabolism in rats and determined whether GLP1 was involved in Bre-caused MS. In the first part of experiments, rats were orally administered Bre (0.5 mg· kg^-1· d^-1) for 28 days with aripiprazole (1.0 mg· kg^-1· d^-1) or olanzapine (1.0 mg· kg^-1· d^-1) as the controls. Compared to vehicle, Bre administration significantly increased the weight gain, serum lipid (TG, TC, LDL, FFA), and blood glucose levels accompanied by the hormonal (insulin, glucagon, GLP1) imbalance, and the impaired glucose tolerance and insulin sensitivity. Moreover, we demonstrated that Bre administration significantly decreased the protein and mRNA levels of GLP1 in pancreas and small intestine by suppressing CaMKIIα, AMPK, and β-catenin; Bre administration also caused islet dysfunction with decreased GLP1R, PI3K, IRβ expression in pancreas, and the interference of IRS1, PI3K, p-AKT, and GLUT4 expression in the liver and skeletal muscle that represented the insulin resistance. In the second part of experiments, rats were orally administered Bre (0.5 mg· kg^-1· d^-1) for 42 days. We showed that co-administration with the GLP1 receptor (GLP1R) agonist liraglutide (0.125 mg· kg^-1· d^-1, ip) could ameliorate Bre-caused metabolic abnormalities. Our results demonstrate that GLP1/GLP1R signaling is involved in Bre-induced glycolipid metabolic disorders and co-treatment with liraglutide is an effective intervention against those abnormal metabolisms.

Treating cognitive impairment in schizophrenia with GLP-1RAs: an overview of their therapeutic potential

INTRODUCTION

Schizophrenia is a neuropsychiatric disorder that affects approximately 1% of individuals worldwide. There are no available medications to treat cognitive impairment in this patient population currently. Preclinical evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve cognitive function. There is a need to evaluate how GLP-1 RAs alter specific domains of cognition and whether they will be of therapeutic benefit in individuals with schizophrenia.

AREAS COVERED

This paper summarizes the effects of GLP-1 RAs on metabolic processes in the brain and how these mechanisms relate to improved cognitive function. We provide an overview of preclinical studies that demonstrate GLP-1 RAs improve cognition and comment on their potential therapeutic benefit in individuals with schizophrenia.

EXPERT OPINION

To understand the benefits of GLP-1 RAs in individuals with schizophrenia, further preclinical research with rodent models relevant to schizophrenia symptomology are needed. Moreover, preclinical studies must focus on using a wider range of behavioral assays to understand whether important aspects of cognition such as executive function, attention, and goal-directed behavior are improved using GLP-1 RAs. Further research into the specific mechanisms of how GLP-1 RAs affect cognitive function and their interactions with antipsychotic medication commonly prescribed is necessary.

Repurposing of Anti-Diabetic Agents as a New Opportunity to Alleviate Cognitive Impairment in Neurodegenerative and Neuropsychiatric Disorders

Cognitive impairment is a shared abnormality between type 2 diabetes mellitus (T2DM) and many neurodegenerative and neuropsychiatric disorders, such as Alzheimer’s disease (AD) and schizophrenia. Emerging evidence suggests that brain insulin resistance plays a significant role in cognitive deficits, which provides the possibility of anti-diabetic agents repositioning to alleviate cognitive deficits. Both preclinical and clinical studies have evaluated the potential cognitive enhancement effects of anti-diabetic agents targeting the insulin pathway. Repurposing of anti-diabetic agents is considered to be promising for cognitive deficits prevention or control in these neurodegenerative and neuropsychiatric disorders. This article reviewed the possible relationship between brain insulin resistance and cognitive deficits. In addition, promising therapeutic interventions, especially current advances in anti-diabetic agents targeting the insulin pathway to alleviate cognitive impairment in AD and schizophrenia were also summarized.

Targeting the microbiome-gut-brain axis for improving cognition in schizophrenia and major mood disorders: A narrative review

Cognitive impairment has been consistently found to be a core feature of serious mental illnesses such as schizophrenia and major mood disorders (major depression and bipolar disorder). In recent years, a great effort has been made in elucidating the biological causes of cognitive deficits and the search for new biomarkers of cognition. Microbiome and gut-brain axis (MGB) hormones have been postulated to be potential biomarkers of cognition in serious mental illnesses. The main aim of this review was to synthesize current evidence on the association of microbiome and gut-brain hormones on cognitive processes in schizophrenia and major mood disorders and the association of MGB hormones with stress and the immune system. Our review underscores the role of the MGB axis on cognitive aspects of serious mental illnesses with the potential use of agents targeting the gut microbiota as cognitive enhancers. However, the current evidence for clinical trials focused on the MGB axis as cognitive enhancers in these clinical populations is scarce. Future clinical trials using probiotics, prebiotics, antibiotics, or faecal microbiota transplantation need to consider potential mechanistic pathways such as the HPA axis, the immune system, or gut-brain axis hormones involved in appetite control and energy homeostasis.

Effect of liraglutide on neural and peripheral markers of metabolic function during antipsychotic treatment in rats

BACKGROUND

Liraglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist that prevents metabolic side effects of the antipsychotic drugs (APDs) olanzapine and clozapine through unknown mechanisms.

AIM

This study aimed to investigate the effect of chronic APD and liraglutide co-treatment on key neural and peripheral metabolic signals, and acute liraglutide co-treatment on clozapine-induced hyperglycaemia.

METHODS

In study 1, rats were administered olanzapine (2 mg/kg), clozapine (12 mg/kg), liraglutide (0.2 mg/kg), olanzapine + liraglutide co-treatment, clozapine + liraglutide co-treatment or vehicle for six weeks. Feeding efficiency was examined weekly. Examination of brain tissue (dorsal vagal complex (DVC) and mediobasal hypothalamus (MBH)), plasma metabolic hormones and peripheral (liver and kidney) cellular metabolism and oxidative stress was conducted. In study 2, rats were administered a single dose of clozapine (12 mg/kg), liraglutide (0.4 mg/kg), clozapine + liraglutide co-treatment or vehicle. Glucose tolerance and plasma hormone levels were assessed.

RESULTS

Liraglutide co-treatment prevented the time-dependent increase in feeding efficiency caused by olanzapine, which plateaued by six weeks. There was no effect of chronic treatment on melanocortinergic, GABAergic, glutamatergic or endocannabionoid markers in the MBH or DVC. Peripheral hormones and cellular metabolic markers were unaltered by chronic APD treatment. Acute liraglutide co-treatment was unable to prevent clozapine-induced hyperglycaemia, but it did alter catecholamine levels.

CONCLUSION

The unexpected lack of change to central and peripheral markers following chronic treatment, despite the presence of weight gain, may reflect adaptive mechanisms. Further studies examining alterations across different time points are required to continue to elucidate the mechanisms underlying the benefits of liraglutide on APD-induced metabolic side effects.

A Focused Review of the Metabolic Side-Effects of Clozapine

The second generation antipsychotic drug clozapine represents the most effective pharmacotherapy for treatment-resistant psychosis. It is also associated with low rates of extrapyramidal symptoms and hyperprolactinemia compared to other antipsychotic drugs. However, clozapine tends to be underutilized in clinical practice due to a number of disabling and serious side-effects. These are characterized by a constellation of metabolic side-effects which include dysregulation of glucose, insulin, plasma lipids and body fat. Many patients treated with clozapine go on to develop metabolic syndrome at a higher rate than the general population, which predisposes them for Type 2 diabetes mellitus and cardiovascular disease. Treatments for the metabolic side-effects of clozapine vary in their efficacy. There is also a lack of knowledge about the underlying physiology of how clozapine exerts its metabolic effects in humans. In the current review, we focus on key studies which describe how clozapine affects each of the main symptoms of the metabolic syndrome, and cover some of the treatment options. The clinical data are then discussed in the context of preclinical studies that have been conducted to identify the key biological substrates involved, in order to provide a better integrated overview. Suggestions are provided about key areas for future research to better understand how clozapine causes metabolic dysregulation.

Peripheral mechanisms of acute olanzapine induced metabolic dysfunction: A review of in vivo models and treatment approaches

Antipsychotic (AP) medications are associated with an increased risk for developing metabolic side effects including weight gain, dyslipidemia, hypertension, type 2 diabetes (T2D), and cardiovascular disease. Previous reviews have focused on the chronic metabolic side effects associated with AP use. However, an underappreciated aspect of APs are the rapid perturbations in glucose and lipid metabolism that occur with each dose of drug. The purpose of this narrative review is to summarize work examining the peripheral mechanisms of acute olanzapine-induced related metabolic disturbances. We also discuss recent studies that have attempted to elucidate treatment approaches to mitigate AP-induced impairments in fuel metabolism.

GLP1 receptor agonism protects against acute olanzapine-induced hyperglycemia

Olanzapine is a second-generation antipsychotic (SGA) used in the treatment of schizophrenia and a number of off-label conditions. Although effective in reducing psychoses, acute olanzapine treatment causes hyperglycemia. Pharmacological agonists of the glucagon-like peptide 1 (GLP1) receptor have been shown to offset weight gain associated with chronic SGA administration. It is not known whether GLP1 receptor agonism would mitigate the acute metabolic side effects of SGAs. Within this context, we sought to determine whether pharmacological targeting of the GLP1 receptor would be sufficient to protect against acute olanzapine-induced impairments in glucose and lipid homeostasis. Male C57BL/6J mice were treated with olanzapine and/or the GLP1 receptor agonists liraglutide and exendin 4, and the blood glucose response was measured. We found that liraglutide or exendin 4 completely protected male mice against olanzapine-induced hyperglycemia in parallel with increases in circulating insulin (liraglutide, exendin 4) and reductions in glucagon (liraglutide only). In additional experiments, female mice, which are protected from acute olanzapine-induced hyperglycemia, displayed hyperglycemia, increases in glucagon, and reductions in insulin when treated with olanzapine and the GLP1 receptor antagonist exendin 9-39 compared with olanzapine treatment alone. Although in some instances the pharmacological targeting of the GLP1 receptor attenuated indexes of olanzapine-induced lipolysis, increases in liver triglyceride accumulation were not impacted. Our findings provide evidence that signaling through the GLP1 receptor can remarkably influence acute olanzapine-induced hyperglycemia, and from the standpoint of protecting against acute excursions in blood glucose, GLP1 receptor agonists should be considered as an adjunct treatment approach.NEW & NOTEWORTHY Antipsychotic drugs cause rapid perturbations in glucose and lipid metabolism. In the present study we have demonstrated that cotreatment with glucagon-like peptide 1 (GLP1) receptor agonists, such as liraglutide, protects against metabolic dysregulation caused by the antipsychotic drug olanzapine. These findings suggest that pharmacological targeting of the GLP1 receptor could be an effective adjunct approach to mitigate the harmful acute metabolic side effects of antipsychotic drugs.

Treatment With Liraglutide Exerts Neuroprotection After Hypoxic-Ischemic Brain Injury in Neonatal Rats via the PI3K/AKT/GSK3β Pathway

Neonatal hypoxic–ischemic (HI) brain injury is a detrimental disease, which results in high mortality and long-term neurological deficits. Nevertheless, the treatment options for this disease are limited. Thus, the aim of the present study was to assess the role of liraglutide in neonatal HI brain injury in rats and investigate the associated mechanisms. The results showed that treatment with liraglutide significantly reduced infarct volume and ameliorated cerebral edema, decreased inflammatory response, promoted the recovery of tissue structure, and improved prognosis following HI brain injury. Moreover, treatment with liraglutide inhibited apoptosis and promoted neuronal survival both in the rat model and following oxygen-glucose deprivation (OGD) insult. LY294002, an inhibitor of phosphoinositide 3-kinase (PI3K), partially reversed these therapeutic effects, suggesting that the PI3K/protein kinase B (Akt) pathway was involved. In conclusion, our data revealed that treatment with liraglutide exerts neuroprotection after neonatal HI brain injury via the PI3K/Akt/glycogen synthase kinase-3β (GSK3β) pathway and may be a promising therapy for this disease.

Differential Effects of Acute Treatment With Antipsychotic Drugs on Peripheral Catecholamines

Antipsychotic drugs represent the most effective treatment for chronic psychotic disorders. The newer second generation drugs offer the advantage of fewer neurological side-effects compared to prior drugs, but many cause serious metabolic side-effects. The underlying physiology of these side-effects is not well-understood, but evidence exists to indicate that the sympathetic nervous system may play an important role. In order to examine this possibility further, we treated separate groups of adult female rats acutely with either the first generation antipsychotic drug haloperidol (0.1 or 1 mg/kg) or the second generation drugs risperidone (0.25 or 2.5 mg/kg), clozapine (2 or 20 mg/kg), olanzapine (3 or 15 mg/kg) or vehicle by intraperitoneal injection. Blood samples were collected prior to drug and then 30, 60, 120, and 180 mins after treatment. Plasma samples were assayed by HPLC-ED for levels of norepinephrine, epinephrine, and dopamine. Results confirmed that all antipsychotics increased peripheral catecholamines, although this was drug and dose dependent. For norepinephrine, haloperidol caused the smallest maximum increase (+158%], followed by risperidone (+793%), olanzapine (+952%) and clozapine (+1,684%). A similar pattern was observed for increases in epinephrine levels by haloperidol (+143%], olanzapine (+529%), risperidone (+617%) then clozapine (+806%). Dopamine levels increased moderately with olanzapine [+174%], risperidone [+271%], and clozapine [+430%]. Interestingly, levels of the catecholamines did not correlate strongly with each other prior to treatment at baseline, but were increasingly correlated after treatment as time proceeded. The results demonstrate antipsychotics can potently regulate peripheral catecholamines, in a manner consistent with their metabolic liability.

Pro-cognitive effect of 1MeTIQ on recognition memory in the ketamine model of schizophrenia in rats: the behavioural and neurochemical effects

RATIONALE

Schizophrenia is a mental illness which is characterised by positive and negative symptoms and by cognitive impairments. While the major prevailing hypothesis is that altered dopaminergic and/or glutamatergic transmission contributes to this disease, there is evidence that the noradrenergic system also plays a role in its major symptoms.

OBJECTIVES

In the present paper, we investigated the pro-cognitive effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) an endogenous neuroprotective compound, on ketamine-modelled schizophrenia in rats.

METHODS

We used an antagonist of NMDA receptors (ketamine) to model memory deficit symptoms in rats. Using the novel object recognition (NOR) test, we investigated the pro-cognitive effect of 1MeTIQ. Additionally, olanzapine, an atypical antipsychotic drug, was used as a standard to compare the pro-cognitive effects of the substances. In vivo microdialysis studies allowed us to verify the changes in the release of monoamines and their metabolites in the rat striatum.

RESULTS

Our study demonstrated that 1MeTIQ, similarly to olanzapine, exhibits a pro-cognitive effect in NOR test and enhances memory disturbed by ketamine treatment. Additionally, in vivo microdialysis studies have shown that ketamine powerfully increased noradrenaline release in the rat striatum, while 1MeTIQ and olanzapine completely antagonised this neurochemical effect.

CONCLUSIONS

1MeTIQ, as a possible pro-cognitive drug, in contrast to olanzapine, expresses beneficial neuroprotective activity in the brain, increasing concentration of the extraneuronal dopamine metabolite, 3-methoxytyramine (3-MT), which plays an important physiological role in the brain as an inhibitory regulator of catecholaminergic activity. Moreover, we first demonstrated the essential role of noradrenaline release in memory disturbances observed in the ketamine-model of schizophrenia, and its possible participation in negative symptoms of the schizophrenia.

Cannabidiol improves behavioural and neurochemical deficits in adult female offspring of the maternal immune activation (poly I:C) model of neurodevelopmental disorders

Cognitive impairment is a major source of disability in schizophrenia and current antipsychotic drugs (APDs) have minimal efficacy for this symptom domain. Cannabidiol (CBD), the major non-intoxicating component of Cannabis sativa L., exhibits antipsychotic and neuroprotective properties. We recently reported the effects of CBD on cognition in male offspring of a maternal immune activation (polyinosinic-polycytidilic acid (poly I:C)) model relevant to the aetiology of schizophrenia; however, the effects of CBD treatment in females are unknown. Sex differences are observed in the onset of schizophrenia symptoms and response to APD treatment. Furthermore, the endogenous cannabinoid system, a direct target of CBD, is sexually dimorphic in humans and rodents. Therefore, the present work aimed to assess the therapeutic impact of CBD treatment on behaviour and neurochemical signalling markers in female poly I:C offspring. Time-mated pregnant Sprague-Dawley rats (n = 16) were administered poly I:C (4 mg/kg; i.v.) or saline (control) on gestational day 15. From postnatal day 56, female offspring received CBD (10 mg/kg, i.p.) or vehicle treatment for approximately 3 weeks. Following 2 weeks of CBD treatment, offspring underwent behavioural testing, including the novel object recognition, rewarded alternation T-maze and social interaction tests to assess recognition memory, working memory and sociability, respectively. After 3 weeks of CBD treatment, the prefrontal cortex (PFC) and hippocampus (HPC) were collected to assess effects on endocannabinoid, glutamatergic and gamma-aminobutyric acid (GABA) signalling markers. CBD attenuated poly I:C-induced deficits in recognition memory, social interaction and glutamatergic N-methyl-d-aspartate receptor (NMDAR) binding in the PFC of poly I:C offspring. Working memory performance was similar between treatment groups. CBD also increased glutamate decarboxylase 67, the rate-limiting enzyme that converts glutamate to GABA, and parvalbumin protein levels in the HPC. In contrast to the CBD treatment effects observed in poly I:C offspring, CBD administration to control rats reduced social interaction, cannabinoid CB1 receptor and NMDAR binding density in the PFC, suggesting that CBD administration to healthy rats may have negative consequences on social behaviour and brain maturation in adulthood. Overall, the findings of this study support the therapeutic benefits of CBD on recognition memory and sociability in female poly I:C offspring, and provide insight into the neurochemical changes that may underlie the therapeutic benefits of CBD in the poly I:C model.

Clinical Trials and Therapeutic Rationale for Drug Repurposing in Schizophrenia

There is a paucity of efficacious novel drugs to address high rates of treatment resistance and refractory symptoms in schizophrenia. The identification of novel therapeutic indications for approved drugs-drug repurposing-has the potential to expedite clinical trials and reduce the costly risk of failure which currently limits central nervous system drug discovery efforts. In the present Review we discuss the historical role of drug repurposing in schizophrenia drug discovery and review the main classes of repurposing candidates currently in clinical trials for schizophrenia in terms of their therapeutic rationale, mechanisms of action, and preliminary results from clinical trials. Subsequently we outline the challenges and limitations which face the clinical repurposing pipeline and how novel technologies might serve to address these.

Liraglutide for psychiatric disorders: clinical evidence and challenges

Obesity and diabetes are both risk factors and consequences of psychiatric disorders. Glucagon like peptide 1 (GLP-1) receptor agonists such as liraglutide are widely used in the treatment of diabetes and obesity. There are considerable amounts of preclinical studies showing the effects of liraglutide on promotion of neurogenesis, while preventing apoptosis and oxidation. Preliminary clinical evidence has suggested that liraglutide could decrease weight gain, improve cognition and prevent cognitive decline. Accordingly, liraglutide has been regarded as a potential candidate for the management of psychiatric disorders. Herein, we will discuss the association between obesity/diabetes and psychiatric disorders, and the emerging use of liraglutide in psychiatry.

Disrupted sphingolipid metabolism following acute clozapine and olanzapine administration

Background

Second generation antipsychotics (SGAs) induce glucometabolic side-effects, such as hyperglycemia and insulin resistance, which pose a therapeutic challenge for mental illness. Sphingolipids play a role in glycaemic balance and insulin resistance. Endoplasmic reticulum (ER) stress contributes to impaired insulin signalling and whole-body glucose intolerance. Diabetogenic SGA effects on ER stress and sphingolipids, such as ceramide and sphingomyelin, in peripheral metabolic tissues are unknown. This study aimed to investigate the acute effects of clozapine and olanzapine on ceramide and sphingomyelin levels, and protein expression of key enzymes involved in lipid and glucose metabolism, in the liver and skeletal muscle.

Methods

Female rats were administered olanzapine (1 mg/kg), clozapine (12 mg/kg), or vehicle (control) and euthanized 1-h later. Ceramide and sphingomyelin levels were examined using electrospray ionization (ESI) mass spectrometry. Expression of lipid enzymes (ceramide synthase 2 (CerS2), elongation of very long-chain fatty acid 1 (ELOVL1), fatty acid synthase (FAS) and acetyl CoA carboxylase 1 (ACC1)), ER stress markers (inositol-requiring enzyme 1 (IRE1) and eukaryotic initiation factor (eIF2α) were also examined.

Results

Clozapine caused robust reductions in hepatic ceramide and sphingolipid levels (p < 0.0001), upregulated CerS2 (p < 0.05) and ELOVL1 (+ 37%) and induced significant hyperglycemia (vs controls). In contrast, olanzapine increased hepatic sphingomyelin levels (p < 0.05 vs controls). SGAs did not alter sphingolipid levels in the muscle. Clozapine increased (+ 52.5%) hepatic eIF2α phosphorylation, demonstrating evidence of activation of the PERK/eIF2α ER stress axis. Hepatic IRE1, FAS and ACC1 were unaltered.

Conclusions

This study provides the first evidence that diabetogenic SGAs disrupt hepatic sphingolipid homeostasis within 1-h of administration. Sphingolipids may be key candidates in the mechanisms underlying the diabetes side-effects of SGAs; however, further research is required.