Exendin-4 protects pancreatic beta cells from human islet amyloid polypeptide-induced cell damage: potential involvement of AKT and mitochondria biogenesis

New fraternine analogues: Evaluation of the antiparkinsonian effect in the model of Parkinson's disease

Venom-derived peptides are important sources for the development of new therapeutic molecules, especially due to their broad pharmacological activity. Previously, our research group identified a novel natural peptide, named fraternine, with promising effects for the treatment of Parkinson's disease. In the present paper, we synthesized three peptides bioinspired in fraternine: fra-10, fra-14, and fra-24. They were tested in the 6-OHDA-induced model of parkinsonism, quantifying motor coordination, levels of TH+ neurons in the substantia nigra pars compacta (SN), and inflammation mediators TNF-α, IL-6, and IL-1ß in the cortex. Peptides fra-14 and fra-10 improved the motor coordination in relation to 6-OHDA lesioned animals. However, most of the peptides were toxic in the doses applied. All three peptides reduced the intensity of the lesion induced rotations in the apomorphine test. Fra-24 higher dose increased the number of TH+ neurons in SN and reduced the concentration of TNF-α in the cortex of 6-OHDA lesioned mice. Overall, only the peptide fra-24 presented a neuroprotection effect on dopaminergic neurons of SN and a reduction of cytokine TNF-α levels, making it worthy of consideration for the treatment of PD.

Targeting mitochondrial quality control for diabetic cardiomyopathy: Therapeutic potential of hypoglycemic drugs

Diabetic cardiomyopathy is a chronic cardiovascular complication caused by diabetes that is characterized by changes in myocardial structure and function, ultimately leading to heart failure and even death. Mitochondria serve as the provider of energy to cardiomyocytes, and mitochondrial dysfunction plays a central role in the development of diabetic cardiomyopathy. In response to a series of pathological changes caused by mitochondrial dysfunction, the mitochondrial quality control system is activated. The mitochondrial quality control system (including mitochondrial biogenesis, fusion and fission, and mitophagy) is core to maintaining the normal structure of mitochondria and performing their normal physiological functions. However, mitochondrial quality control is abnormal in diabetic cardiomyopathy, resulting in insufficient mitochondrial fusion and excessive fission within the cardiomyocyte, and fragmented mitochondria are not phagocytosed in a timely manner, accumulating within the cardiomyocyte resulting in cardiomyocyte injury. Currently, there is no specific therapy or prevention for diabetic cardiomyopathy, and glycemic control remains the mainstay. In this review, we first elucidate the pathogenesis of diabetic cardiomyopathy and explore the link between pathological mitochondrial quality control and the development of diabetic cardiomyopathy. Then, we summarize how clinically used hypoglycemic agents (including sodium-glucose cotransport protein 2 inhibitions, glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, thiazolidinediones, metformin, and α-glucosidase inhibitors) exert cardioprotective effects to treat and prevent diabetic cardiomyopathy by targeting the mitochondrial quality control system. In addition, the mechanisms of complementary alternative therapies, such as active ingredients of traditional Chinese medicine, exercise, and lifestyle, targeting mitochondrial quality control for the treatment of diabetic cardiomyopathy are also added, which lays the foundation for the excavation of new diabetic cardioprotective drugs.

Phycocyanin as a nature-inspired antidiabetic agent: A systematic review

BACKGROUND

Nutraceuticals have been important for more than two decades for their safety, efficacy, and outstanding effects. Diabetes is a major metabolic syndrome, which may be improved using nutritional pharmaceuticals. Some microalgae species, such as spirulina, stand out by providing biomass with exceptional nutritional properties. Spirulina has a wide range of pharmacological effects, mostly related to phycocyanin. Phycocyanin is a protein compound with antidiabetic properties, known as a nutraceutical.

OBJECTIVE

This review delves into phycocyanin applications in diabetes and its complications and ascertains the mechanisms involved.

METHODS

Scopus, PubMed, Cochrane Library, Web of Science, and ProQuest databases were systematically reviewed (up to April 30, 2023), in which only animal and cellular studies were found.

RESULTS

According to animal studies, the administration of phycocyanin affected biochemical parameters (primary outcome) related to diabetes. These results showed an increase in fasting insulin serum and a decrease in fasting blood glucose, glycosylated serum protein, and glycosylated hemoglobin. In cellular studies, though, phycocyanin prevented methylglyoxal and human islet amyloid polypeptide-induced dysfunction in β-cells and induced apoptosis through different molecular pathways (secondary outcome), including activation of Nrf2, PI3K/Akt, and suppression of JNK and p38. Also, phycocyanin exerted its antidiabetic effect by affecting the pathways regulating hepatic glucose metabolism.

CONCLUSIONS

Thus, based on the available information and literature, targeting these pathways by phycocyanin may unleash an array of benefits, including positive outcomes of the antidiabetic effects of phycocyanin as a nutraceutical.

OTHER

This systematic review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) at the National Institute of Health. The registration number is CRD42022307522.

Exendin-4 protects against high glucose-induced mitochondrial dysfunction and oxidative stress in SH-SY5Y neuroblastoma cells through GLP-1 receptor/Epac/Akt signaling

Mitochondrial dysfunction under diabetic condition leads to the development and progression of neurodegenerative complications. Recently, the beneficial effects of glucagon-like peptide-1 (GLP-1) receptor agonists on diabetic neuropathies have been widely recognized. However, molecular mechanisms underlying the neuroprotective effects of GLP-1 receptor agonists against high glucose (HG)-induced neuronal damages is not completely elucidated. Here, we investigated the underlying mechanisms of GLP-1 receptor agonist treatment against oxidative stress, mitochondrial dysfunction, and neuronal damages under HG-conditions mimicking a diabetic hyperglycemic state in SH-SY5Y neuroblastoma cells. We revealed that treatment with exendin-4, a GLP-1 receptor agonist, not only increased the expression of survival markers, phospho-Akt/Akt and Bcl-2, but also decreased the expression of pro-apoptotic marker, Bax, and reduced the levels of reactive oxygen species (ROS) defense markers (catalase, SOD-2, and HO-1) under HG conditions. The expressions of mitochondrial function associated genes, MCU and UCP3, and mitochondrial fission genes, DRP1 and FIS1, were decreased by exendin-4 compared to non-treated levels, while the protein expression levels of mitochondrial homeostasis regulators, Parkin and PINK1, were enhanced. In addition, blockade of Epac and Akt activities was able to antagonize these neuroprotective effects of exendin-4. Collectively, we demonstrated that stimulation of GLP-1 receptor propagates a neuroprotective cascade against the oxidative stresses and mitochondrial dysfunctions as well as augments survival through the Epac/Akt-dependent pathway. Therefore, the revealed mechanisms underlying GLP-1 receptor pathway by preserving mitochondrial homeostasis would be a therapeutic candidate to alleviate neuronal dysfunctions and delay the progression of diabetic neuropathies.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer's and Parkinson's disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer's and Parkinson's disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

Metabolic Adaptions/Reprogramming in Islet Beta-Cells in Response to Physiological Stimulators—What Are the Consequences

Irreversible pancreatic β-cell damage may be a result of chronic exposure to supraphysiological glucose or lipid concentrations or chronic exposure to therapeutic anti-diabetic drugs. The β-cells are able to respond to blood glucose in a narrow concentration range and release insulin in response, following activation of metabolic pathways such as glycolysis and the TCA cycle. The β-cell cannot protect itself from glucose toxicity by blocking glucose uptake, but indeed relies on alternative metabolic protection mechanisms to avoid dysfunction and death. Alteration of normal metabolic pathway function occurs as a counter regulatory response to high nutrient, inflammatory factor, hormone or therapeutic drug concentrations. Metabolic reprogramming is a term widely used to describe a change in regulation of various metabolic enzymes and transporters, usually associated with cell growth and proliferation and may involve reshaping epigenetic responses, in particular the acetylation and methylation of histone proteins and DNA. Other metabolic modifications such as Malonylation, Succinylation, Hydroxybutyrylation, ADP-ribosylation, and Lactylation, may impact regulatory processes, many of which need to be investigated in detail to contribute to current advances in metabolism. By describing multiple mechanisms of metabolic adaption that are available to the β-cell across its lifespan, we hope to identify sites for metabolic reprogramming mechanisms, most of which are incompletely described or understood. Many of these mechanisms are related to prominent antioxidant responses. Here, we have attempted to describe the key β-cell metabolic adaptions and changes which are required for survival and function in various physiological, pathological and pharmacological conditions.

Effect of free fatty acids on insulin secretion, insulin sensitivity and incretin effect - a narrative review

Deleterious effects of free fatty acids, FFAs, on insulin sensitivity are observed in vivo studies in humans. Mechanisms include impaired insulin signaling, oxidative stress, inflammation, and mitochondrial dysfunction, but the effects on insulin secretion are less well known. Our aim was to review the relationship of increased FFAs with insulin resistance, secretion and mainly with the incretin effect in humans. Narrative review. Increased endogenous or administered FFAs induce insulin resistance. FFAs effects on insulin secretion are debatable; inhibition and stimulation have been reported, depending on the type and duration of lipids exposition and the study subjects. Chronically elevated FFAs seem to decrease insulin biosynthesis, glucose-stimulated insulin secretion and β-cell glucose sensitivity. Lipids infusion decreases the response to incretins with unchanged incretin levels in volunteers with normal glucose tolerance. In contrast, FFAs reduction by acipimox did not restore the incretin effect in type-2 diabetes, probably due to the dysfunctional β-cell. Possible mechanisms of FFAs excess on incretin effect include reduction of the expression and levels of GLP-1 (glucagon like peptide-1) receptor, reduction of connexin-36 expression thus the coordinated secretory activity in response to GLP-1, and GIP (glucose-dependent insulinotropic polypeptide) receptors downregulation in islets cells. Increased circulating FFAs impair insulin sensitivity. Effects on insulin secretion are complex and controversial. Deleterious effects on the incretin-induced potentiation of insulin secretion were reported. More investigation is needed to better understand the extent and mechanisms of β-cell impairment and insulin resistance induced by increased FFAs and how to prevent them.

Islet amyloid toxicity: From genesis to counteracting mechanisms

Islet amyloid polypeptide (IAPP or amylin) is a hormone co-secreted with insulin by pancreatic β-cells and is the major component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes (T2D) and may be involved in β-cell dysfunction and death, observed in this disease. Thus, investigating the aspects related to amyloid formation is relevant to the development of strategies towards β-cell protection. In this sense, IAPP misprocessing, IAPP overproduction, and disturbances in intra- and extracellular environments seem to be decisive for IAPP to form islet amyloid. Islet amyloid toxicity in β-cells may be triggered in intra- and/or extracellular sites by membrane damage, endoplasmic reticulum stress, autophagy disruption, mitochondrial dysfunction, inflammation, and apoptosis. Importantly, different approaches have been suggested to prevent islet amyloid cytotoxicity, from inhibition of IAPP aggregation to attenuation of cell death mechanisms. Such approaches have improved β-cell function and prevented the development of hyperglycemia in animals. Therefore, counteracting islet amyloid may be a promising therapy for T2D treatment.

Electrocardiographic, hemodynamic, and biochemical evidence on the protective effects of exenatide against phosphine-induced cardiotoxicity in rat model

Aluminum phosphide (AlP) poisoning can be deadly in most cases targeting the heart. To overcome AlP toxicity, exenatide has been studied in the present study due to its pleiotropic effects on cardiac damages. In this study, the rats were exposed to LD₅₀ of AlP (10 mg/kg) by gavage, and exenatide at doses (0.05, 0.1, and 0.2 mg/kg) injected intraperitoneally 30 min after poisoning. The cardiac parameters including heart rate (HR), blood pressure (BP), QRS, corrected QT (QT_c), and ST were monitored for 180 min. Blood glucose level was measured in the study groups 30 min after exenatide injection. Evaluation of biochemical parameters including mitochondrial complexes I, II, and IV activities, adenosine diphosphate (ADP)/adenosine triphosphate (ATP) ratio, malondialdehyde (MDA), apoptosis, lactate, troponin I, and brain natriuretic peptide (BNP) was done on heart tissues after 12 and 24 h. Additionally, the tissues were analyzed for any pathological damages including necrosis, hemorrhage, or hyperemia 24 h post-treatment. Our results showed that AlP-induced HR, BP, and electrocardiographic changes were improved by exenatide at all doses. The blood glucose levels of poisoned animals reached control levels after exenatide treatment. Besides, treatment with exenatide at all doses improved complexes I and IV activity, ADP/ATP ratio, and apoptosis. Malondialdehyde, lactate, troponin I, and BNP levels were also diminished after exenatide co-treatment in poisoned animals. On the other hand, administration of exenatide doses improved the histopathology of AlP-induced tissues. Based on our findings, exenatide has a protective effect against phosphine-induced cardiotoxicity in an almost dose-dependent way. However, further investigations are needed on the potential clinical use of exenatide in this poisoning.

Mechanisms of Beta-Cell Apoptosis in Type 2 Diabetes-Prone Situations and Potential Protection by GLP-1-Based Therapies

Type 2 diabetes (T2D) is characterized by chronic hyperglycemia secondary to the decline of functional beta-cells and is usually accompanied by a reduced sensitivity to insulin. Whereas altered beta-cell function plays a key role in T2D onset, a decreased beta-cell mass was also reported to contribute to the pathophysiology of this metabolic disease. The decreased beta-cell mass in T2D is, at least in part, attributed to beta-cell apoptosis that is triggered by diabetogenic situations such as amyloid deposits, lipotoxicity and glucotoxicity. In this review, we discussed the molecular mechanisms involved in pancreatic beta-cell apoptosis under such diabetes-prone situations. Finally, we considered the molecular signaling pathways recruited by glucagon-like peptide-1-based therapies to potentially protect beta-cells from death under diabetogenic situations.

The Future of Incretin-Based Approaches for Neurodegenerative Diseases in Older Adults: Which to Choose? A Review of their Potential Efficacy and Suitability

The current treatment options for neurodegenerative diseases in older adults rely mainly on providing symptomatic relief. Yet, it remains imperative to identify agents that slow or halt disease progression to avoid the most disabling features often associated with advanced disease stages. A potential overlap between the pathological processes involved in diabetes and neurodegeneration has been established, raising the question of whether incretin-based therapies for diabetes may also be useful in treating neurodegenerative diseases in older adults. Here, we review the different agents that belong to this class of drugs (GLP-1 receptor agonists, dual/triple receptor agonists, DPP-4 inhibitors) and describe the data supporting their potential role in treating neurodegenerative conditions including Parkinson's disease and Alzheimer's disease. We further discuss whether there are any distinctive properties among them, particularly in the context of safety or tolerability and CNS penetration, that might facilitate their successful repurposing as disease-modifying drugs. Proof-of-efficacy data will obviously be of the greatest importance, and this is most likely to be demonstrable in agents that reach the central nervous system and impact on neuronal GLP-1 receptors. Additionally, however, the long-term safety and tolerability (including gastrointestinal side effects and unwanted weight loss) as well as the route of administration of this class of agents may also ultimately determine success and these aspects should be considered in prioritising which approaches to subject to formal clinical trial evaluations.

Novel targeted therapies for Parkinson's disease

Parkinson’s disease (PD) is the second more common neurodegenerative disease with increasing incidence worldwide associated to the population ageing. Despite increasing awareness and significant research advancements, treatment options comprise dopamine repleting, symptomatic therapies that have significantly increased quality of life and life expectancy, but no therapies that halt or reverse disease progression, which remain a great, unmet goal in PD research. Large biomarker development programs are undertaken to identify disease signatures that will improve patient selection and outcome measures in clinical trials. In this review, we summarize PD-related mechanisms that can serve as targets of therapeutic interventions aiming to slow or modify disease progression, as well as previous and ongoing clinical trials in each field, and discuss future perspectives.

Targeting Mitochondrial Impairment in Parkinson's Disease: Challenges and Opportunities

The underlying pathophysiology of Parkinson's disease is complex, but mitochondrial dysfunction has an established and prominent role. This is supported by an already large and rapidly growing body of evidence showing that the role of mitochondrial (dys)function is central and multifaceted. However, there are clear gaps in knowledge, including the dilemma of explaining why inherited mitochondriopathies do not usually present with parkinsonian symptoms. Many aspects of mitochondrial function are potential therapeutic targets, including reactive oxygen species production, mitophagy, mitochondrial biogenesis, mitochondrial dynamics and trafficking, mitochondrial metal ion homeostasis, sirtuins, and endoplasmic reticulum links with mitochondria. Potential therapeutic strategies may also incorporate exercise, microRNAs, mitochondrial transplantation, stem cell therapies, and photobiomodulation. Despite multiple studies adopting numerous treatment strategies, clinical trials to date have generally failed to show benefit. To overcome this hurdle, more accurate biomarkers of mitochondrial dysfunction are required to detect subtle beneficial effects. Furthermore, selecting study participants early in the disease course, studying them for suitable durations, and stratifying them according to genetic and neuroimaging findings may increase the likelihood of successful clinical trials. Moreover, treatments involving combined approaches will likely better address the complexity of mitochondrial dysfunction in Parkinson's disease. Therefore, selecting the right patients, at the right time, and using targeted combination treatments, may offer the best chance for development of an effective novel therapy targeting mitochondrial dysfunction in Parkinson's disease.

Downregulation of the GLP-1/CREB/adiponectin pathway is partially responsible for diabetes-induced dysregulated vascular tone and VSMC dysfunction

BACKGROUND

The dysfunction of vasculature is observed in diabetes and might be responsible for the increased incidence of vascular events. Previous studies indicated that supplementation of GLP-1 analogues is beneficial to the cardiovascular functions in diabetic patients, but the mechanisms are not clear.

METHODS

A type 1 diabetic model was constructed. Vascular constrictions were measured using wire myograph. Western blotting and quantitative PCR were adopted to analyze the expression profiles of key molecules. Mitochondrial functions were analyzed in both vascular tissues or vascular smooth muscle cells (VSMCs). Dual-luciferase reporter assay was used to investigate the mechanism of adiponectin regulation.

RESULTS

In this study, abnormal vascular hypertrophy and increased vascular tones were observed in both diabetic patients and animals. ROS productions were increased in vessels and VSMCs from diabetic patients and animals, and the ROS scavenger mitoTEMPO partially attenuated the abnormal vascular tones and hypertension. In addition, decreased GLP-1 levels were observed, while GLP-1 supplementation improved the mitochondrial functions and vascular tones. Furthermore, it was shown that GLP-1 supplementation enhanced adiponectin expressions, while adiponectin facilitated the phosphorylation of AMPK and Sirt1 expressions. Also, CREB phosphorylation was enhanced upon GLP-1 supplementation and promoted the transcriptions of adiponectin. Finally, CREB inhibition partially attenuated the effects of GLP-1 on mitochondrial functions and adiponectin expressions.

CONCLUSION

GLP-1 downregulation might be an important mechanism of abnormal mitochondrial function and vascular tone in diabetes. Targeting GLP-1/CREB/adiponectin axis might become a promising therapeutic strategy in alleviating diabetes-related cardiovascular dysfunctions.

Stimulation of GLP-1 Receptor Inhibits Methylglyoxal-Induced Mitochondrial Dysfunctions in H9c2 Cardiomyoblasts: Potential Role of Epac/PI3K/Akt Pathway

Accumulation of methylglyoxal (MG) contributes to oxidative stress, apoptosis, and mitochondrial dysfunction, leading to the development of type 2 diabetes and cardiovascular diseases. Inhibition of mitochondrial abnormalities induced by MG in the heart may improve and delay the progression of heart failure. Although glucagon-like peptide-1 receptor (GLP-1R) agonists have been used as anti-diabetic drugs and GLP-1R has been detected in the heart, the cardioprotective effects of GLP-1R agonists on the inhibition of MG-induced oxidative stress and mitochondrial abnormalities have not been elucidated. Stimulation of GLP-1Rs leads to cAMP elevation and subsequently activates PKA- and/or Epac-dependent signaling pathway. However, the signaling pathway involved in the prevention of MG-induced mitochondrial dysfunctions in the heart has not been clarified so far. In the present study, we demonstrated that stimulation of GLP-1Rs with exendin-4 inhibited MG-induced intracellular and mitochondrial reactive oxygen species (ROS) production and apoptosis in H9c2 cardiomyoblasts. GLP-1R stimulation also improved the alterations of mitochondrial membrane potential (MMP) and expressions of genes related to mitochondrial functions and dynamics induced by MG. In addition, stimulation of GLP-1R exhibits antioxidant and antiapoptotic effects as well as the improvement of mitochondrial functions through cAMP/Epac/PI3K/Akt signaling pathway in H9c2 cells. Our study is the first work demonstrating a novel signaling pathway for cardioprotective effects of GLP-1R agonist on inhibition of oxidative stress and prevention of mitochondrial dysfunction. Thus, GLP-1R agonist represents a potential therapeutic target for inhibition of oxidative stress and modulation of mitochondrial functions in the heart.

RNA-seq-based identification of Star upregulation by islet amyloid formation

Aggregation of islet amyloid polypeptide (IAPP) into islet amyloid results in β-cell toxicity in human type 2 diabetes. To determine the effect of islet amyloid formation on gene expression, we performed ribonucleic acid (RNA) sequencing (RNA-seq) analysis using cultured islets from either wild-type mice (mIAPP), which are not amyloid prone, or mice that express human IAPP (hIAPP), which develop amyloid. Comparing mIAPP and hIAPP islets, 5025 genes were differentially regulated (2439 upregulated and 2586 downregulated). When considering gene sets (reactomes), 248 and 52 pathways were up- and downregulated, respectively. Of the top 100 genes upregulated under two conditions of amyloid formation, seven were common. Of these seven genes, only steroidogenic acute regulatory protein (Star) demonstrated no effect of glucose per se to modify its expression. We confirmed this differential gene expression using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and also demonstrated the presence of STAR protein in islets containing amyloid. Furthermore, Star is a part of reactomes representing metabolism, metabolism of lipids, metabolism of steroid hormones, metabolism of steroids and pregnenolone biosynthesis. Thus, examining gene expression that is differentially regulated by islet amyloid has the ability to identify new molecules involved in islet physiology and pathology applicable to type 2 diabetes.

The Association Between Type 2 Diabetes Mellitus and Parkinson's Disease

In recent years, an emerging body of evidence has forged links between Parkinson's disease (PD) and type 2 diabetes mellitus (T2DM). In observational studies, those with T2DM appear to be at increased risk of developing PD, as well as experiencing faster progression and a more severe phenotype of PD, with the effects being potentially mediated by several common cellular pathways. The insulin signalling pathway, for example, may be responsible for neurodegeneration via insulin dysregulation, aggregation of amyloids, neuroinflammation, mitochondrial dysfunction and altered synaptic plasticity. In light of these potential shared disease mechanisms, clinical trials are now investigating the use of established diabetes drugs targeting insulin resistance in the management of PD. This review will discuss the epidemiological links between T2DM and PD, the potential shared cellular mechanisms, and assess the relevant treatment options for disease modification of PD.

Nutrient Sensor mTOR and OGT: Orchestrators of Organelle Homeostasis in Pancreatic β-Cells

The purpose of this review is to integrate the role of nutrient-sensing pathways into β-cell organelle dysfunction prompted by nutrient excess during type 2 diabetes (T2D). T2D encompasses chronic hyperglycemia, hyperlipidemia, and inflammation, which each contribute to β-cell failure. These factors can disrupt the function of critical β-cell organelles, namely, the ER, mitochondria, lysosomes, and autophagosomes. Dysfunctional organelles cause defects in insulin synthesis and secretion and activate apoptotic pathways if homeostasis is not restored. In this review, we will focus on mTORC1 and OGT, two major anabolic nutrient sensors with important roles in β-cell physiology. Though acute stimulation of these sensors frequently improves β-cell function and promotes adaptation to cell stress, chronic and sustained activity disturbs organelle homeostasis. mTORC1 and OGT regulate organelle function by influencing the expression and activities of key proteins, enzymes, and transcription factors, as well as by modulating autophagy to influence clearance of defective organelles. In addition, mTORC1 and OGT activity influence islet inflammation during T2D, which can further disrupt organelle and β-cell function. Therapies for T2D that fine-tune the activity of these nutrient sensors have yet to be developed, but the important role of mTORC1 and OGT in organelle homeostasis makes them promising targets to improve β-cell function and survival.

Repurposing anti-diabetic drugs for the treatment of Parkinson's disease: Rationale and clinical experience

The most pressing need in Parkinson's disease (PD) clinical practice is to identify agents that might slow down, stop or reverse the neurodegenerative process of Parkinson's disease and therefore avoid the onset of the most disabling, dopa-refractory symptoms of the disease. These include dementia, speech and swallowing problems, poor balance and falling. To date, there have been no agents which have yet had robust trial data to confirm positive effects at slowing down the neurodegenerative disease process of PD. In this chapter we will review the reasons why there is growing interest in drugs currently licensed for the treatment of diabetes as agents which may slow down disease progression in PD, including a review of the published trials regarding exenatide, a GLP-1 receptor agonist licensed to treat type 2 diabetes, and recently shown to be associated with reduced severity of PD in a randomized, placebo controlled washout design trial of 60 patients treated for 48 weeks. This subject is now a major area of interest for multiple pharmaceutical companies hoping to bring GLP-1 receptor agonists forward as treatment options in PD.

Animal Venom Peptides as a Treasure Trove for New Therapeutics Against Neurodegenerative Disorders

BACKGROUND

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and cerebral ischemic stroke, impose enormous socio-economic burdens on both patients and health-care systems. However, drugs targeting these diseases remain unsatisfactory, and hence there is an urgent need for the development of novel and potent drug candidates.

METHODS

Animal toxins exhibit rich diversity in both proteins and peptides, which play vital roles in biomedical drug development. As a molecular tool, animal toxin peptides have not only helped clarify many critical physiological processes but also led to the discovery of novel drugs and clinical therapeutics.

RESULTS

Recently, toxin peptides identified from venomous animals, e.g. exenatide, ziconotide, Hi1a, and PcTx1 from spider venom, have been shown to block specific ion channels, alleviate inflammation, decrease protein aggregates, regulate glutamate and neurotransmitter levels, and increase neuroprotective factors.

CONCLUSION

Thus, components of venom hold considerable capacity as drug candidates for the alleviation or reduction of neurodegeneration. This review highlights studies evaluating different animal toxins, especially peptides, as promising therapeutic tools for the treatment of different neurodegenerative diseases and disorders.

Mitochondrial dysfunction in diabetes and the regulatory roles of antidiabetic agents on the mitochondrial function

The prevalence of type 2 diabetes mellitus (T2DM) is increasing rapidly with its associated morbidity and mortality. Many pathophysiological pathways such as oxidative stress, inflammatory responses, adipokines, obesity‐induced insulin resistance, improper insulin signaling, and beta cell apoptosis are associated with the development of T2DM. There is increasing evidence of the role of mitochondrial dysfunction in the onset of T2DM, particularly in relation to the development of diabetic complications. Here, the role of mitochondrial dysfunction in T2DM is reviewed together with its modulation by antidiabetic therapeutic agents, an effect that may be independent of their hypoglycemic effect.

Exendin-4 attenuates brain mitochondrial toxicity through PI3K/Akt-dependent pathway in amyloid beta (1-42)-induced cognitive deficit rats

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory loss, disorientation and gradual deterioration of intellectual ability. In the pharmacotherapy of AD, the mitochondrial protective activity of Exendin-4 in experimental studies is yet to be established though its effectiveness is demonstrated in these patients. Therefore, the mitochondria protective activity of Exendin-4 (5 μg/kg, i.p.) was investigated in hippocampus and pre-frontal cortex (PFC) of AD-like animals. The amyloid beta (Aβ) was injected through bilateral intracerebroventricular route into lateral ventricles to induce AD-like manifestations in the male rats. Exendin-4 significantly attenuated Aβ-induced memory-deficits in the Morris water maze and Y-maze test protocols. Exendin-4 significantly decreased Aβ-induced increase in the level of Aβ in both brain regions. Exendin-4 significantly increased Aβ-induced decrease in acetylcholine level and activity of cholineacetyl transferase in all brain regions. Moreover, Exendin-4 significantly decreased Aβ-induced increase in the activity of acetylcholinestrase in both the brain regions. E4 significantly increased Aβ-induced decrease in mitochondrial function, integrity, respiratory control rate and ADP/O in all brain regions. Further, Exendin-4 significantly decreased Aβ-induced increase in the mitochondrial complex enzyme-I, IV and V activities in all brain regions. Furthermore, Exendin-4 significantly increased Aβ-induced decrease in the level of phosphorylated Akt and the ratio of phosphorylated Akt to Akt in both brain regions. However, LY294002 diminished the therapeutic effects of Exendin-4 on behavioral, biochemical and molecular observations in AD-like animals. Pearson's analysis showed that the attributes of mitochondrial dysfunction (MMP and RCR) exhibited significant correlation to the loss in memory formation, level of Aβ and cholinergic dysfunction in these animals. Thus, it can be speculated that Exendin-4 may mitigate AD-like manifestations including mitochondrial toxicity perhaps through PI3K/Akt-mediated pathway in the experimental animals. Hence, Exendin-4 could be a potential therapeutic alternative candidate in the management of AD.

A GLP‑1 receptor agonist attenuates human islet amyloid polypeptide‑induced autophagy and apoptosis in MIN6 cells

Type 2 diabetes mellitus (T2DM) is characterized by the dysfunction and loss of pancreatic islet β‑cells, in part due to islet amyloid deposits derived from islet amyloid polypeptide (IAPP). The glucagon‑like peptide‑1 (GLP‑1) receptor agonist exendin‑4 enhances the insulin secretory response by increasing β‑cell mass in T2DM. However, it is unknown whether exendin‑4 protects β‑cells from IAPP‑mediated autophagy and apoptosis. In the present study, reverse transcription‑quantitative polymerase chain reaction, ELISA and western blotting were used to detected the mRNA and protein expression of insulin/hIAPP and other signaling molecules, while the mechanisms underlying these effects were also determined. Exendin‑4 increased the level of insulin secretion, which was greater than that of IAPP, leading to a beneficial IAPP/insulin secretion pattern. In MIN6 cells incubated with 25 mM glucose, exendin‑4 decreased the ratio of light chain 3 (LC3)‑II/I, which was accompanied by an increase in p62 protein. In a hIAPP‑overexpressing MIN6 cell model, exendin‑4 prevented the hIAPP‑induced increase in the LC3II/I ratio and decrease in p62 expression. In addition, exendin‑4 pretreatment reduced hIAPP‑induced activation of cleaved caspase‑3, suggesting that exendin‑4 may protect MIN6 cells against apoptosis. Taken together, the results highlight hIAPP as a critical mediator of β‑cell loss and suggest that the GLP‑1 receptor agonist exendin‑4 may be a potential therapeutic agent for hIAPP‑induced β‑cell damage.

Neuroprotective exendin-4 enhances hypothermia therapy in a model of hypoxic-ischaemic encephalopathy

Hypoxic-ischaemic encephalopathy remains a global health burden. Despite medical advances and treatment with therapeutic hypothermia, over 50% of cooled infants are not protected and still develop lifelong neurodisabilities, including cerebral palsy. Furthermore, hypothermia is not used in preterm cases or low resource settings. Alternatives or adjunct therapies are urgently needed. Exendin-4 is a drug used to treat type 2 diabetes mellitus that has also demonstrated neuroprotective properties, and is currently being tested in clinical trials for Alzheimer's and Parkinson's diseases. Therefore, we hypothesized a neuroprotective effect for exendin-4 in neonatal neurodisorders, particularly in the treatment of neonatal hypoxic-ischaemic encephalopathy. Initially, we confirmed that the glucagon like peptide 1 receptor (GLP1R) was expressed in the human neonatal brain and in murine neurons at postnatal Day 7 (human equivalent late preterm) and postnatal Day 10 (term). Using a well characterized mouse model of neonatal hypoxic-ischaemic brain injury, we investigated the potential neuroprotective effect of exendin-4 in both postnatal Day 7 and 10 mice. An optimal exendin-4 treatment dosing regimen was identified, where four high doses (0.5 µg/g) starting at 0 h, then at 12 h, 24 h and 36 h after postnatal Day 7 hypoxic-ischaemic insult resulted in significant brain neuroprotection. Furthermore, neuroprotection was sustained even when treatment using exendin-4 was delayed by 2 h post hypoxic-ischaemic brain injury. This protective effect was observed in various histopathological markers: tissue infarction, cell death, astrogliosis, microglial and endothelial activation. Blood glucose levels were not altered by high dose exendin-4 administration when compared to controls. Exendin-4 administration did not result in adverse organ histopathology (haematoxylin and eosin) or inflammation (CD68). Despite initial reduced weight gain, animals restored weight gain following end of treatment. Overall high dose exendin-4 administration was well tolerated. To mimic the clinical scenario, postnatal Day 10 mice underwent exendin-4 and therapeutic hypothermia treatment, either alone or in combination, and brain tissue loss was assessed after 1 week. Exendin-4 treatment resulted in significant neuroprotection alone, and enhanced the cerebroprotective effect of therapeutic hypothermia. In summary, the safety and tolerance of high dose exendin-4 administrations, combined with its neuroprotective effect alone or in conjunction with clinically relevant hypothermia make the repurposing of exendin-4 for the treatment of neonatal hypoxic-ischaemic encephalopathy particularly promising.

Drug Repurposing in Parkinson's Disease

The development of an intervention to slow or halt disease progression remains the greatest unmet therapeutic need in Parkinson's disease. Given the number of failures of various novel interventions in disease-modifying clinical trials in combination with the ever-increasing costs and lengthy processes for drug development, attention is being turned to utilizing existing compounds approved for other indications as novel treatments in Parkinson's disease. Advances in rational and systemic drug repurposing have identified a number of drugs with potential benefits for Parkinson's disease pathology and offer a potentially quicker route to drug discovery. Here, we review the safety and potential efficacy of the most promising candidates repurposed as potential disease-modifying treatments for Parkinson's disease in the advanced stages of clinical testing.

Current perspective of mitochondrial biology in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorder characterized by preferential loss of dopaminergic neurons of the substantia nigra pars compacta and the presence of Lewy bodies containing α-synuclein. Although the cause of PD remains elusive, remarkable advances have been made in understanding the possible causative mechanisms of PD pathogenesis. An explosion of discoveries during the past two decades has led to the identification of several autosomal dominant and recessive genes that cause familial forms of PD. The investigations of these familial PD gene products have shed considerable insights into the molecular pathogenesis of the more common sporadic PD. A growing body of evidence suggests that the etiology of PD is multifactorial and involves a complex interplay between genetic and environmental factors. Substantial evidence from human tissues, genetic and toxin-induced animal and cellular models indicates that mitochondrial dysfunction plays a central role in the pathophysiology of PD. Deficits in mitochondrial functions due to bioenergetics defects, alterations in the mitochondrial DNA, generation of reactive oxygen species, aberrant calcium homeostasis, and anomalies in mitochondrial dynamics and quality control are implicated in the underlying mechanisms of neuronal cell death in PD. In this review, we discuss how familial PD-linked genes and environmental factors interface the pathways regulating mitochondrial functions and thereby potentially converge both familial and sporadic PD at the level of mitochondrial integrity. We also provide an overview of the status of therapeutic strategies targeting mitochondrial dysfunction in PD. Unraveling potential pathways that influence mitochondrial homeostasis in PD may hold the key to therapeutic intervention for this debilitating neurodegenerative movement disorder.

Liraglutide ameliorates early renal injury by the activation of renal FoxO1 in a type 2 diabetic kidney disease rat model

AIMS

The aim of this study was to investigate the effects of liraglutide on renal injury and the renal expression of FoxO1 in type 2 diabetic rats.

METHODS

Type 2 diabetic rats model was induced by a high-sugar and high-fat diet and intraperitoneal injection of low-dose Streptozotocin (STZ) (30 mg/kg). Five weeks after STZ injection, diabetic rats were randomly treated with or without subcutaneous injection of liraglutide (0.2 mg/kg/12 h) for eight weeks. Diabetes-related physical and biochemical indicators, renal histopathological and ultrastructural changes, the expression of renal transforming growth factor beta-1 (TGF-β1), fibronectin (FN), type IV collagen (Col IV), protein kinase B (Akt), forkhead box protein O1 (FoxO1) and manganese superoxide dismutase (MnSOD) were measured.

RESULTS

Rats in DN group showed a significant increase in fasting blood glucose, HbA1c, kidney to body weight index, serum creatinine (Scr), blood urea nitrogen (BUN), urinary albumin excretion, mesangial matrix index, glomerular basement membrane (GBM) thickening, podocyte foot process fusion, the mRNA and protein levels of renal TGF-β1, FN and Col IV and a dramatic decrease in the mRNA and protein levels of renal MnSOD, all of which were significantly ameliorated by liraglutide. In addition, liraglutide also increased the expression of FoxO1 mRNA and reduced renal phosphorylation levels of Akt and FoxO1 protein.

CONCLUSIONS

These results suggest that liraglutide may exert a renoprotective effect by a FoxO1-mediated upregulation of renal MnSOD expression in the early DKD.

Exenatide exerts cognitive effects by modulating the BDNF-TrkB neurotrophic axis in adult mice

Modulation of insulin-dependent signaling is emerging as a valuable therapeutic tool to target neurodegeneration. In the brain, the activation of insulin receptors promotes cell growth, neuronal repair, and protection. Altered brain insulin signaling participates in the cognitive decline seen in Alzheimer's disease patients and the aging brain. Glucagon-like peptide-1 (GLP-1) regulates insulin secretion and, along with GLP-1 analogues, enhances neurotrophic signaling and counteracts cognitive deficits in preclinical models of neurodegeneration. Moreover, recent evidence indicates that GLP-1 modulates the activity of the brain-derived neurotrophic factor (BDNF). In this study, in adult wild-type mice, here employed as a model of mid-life brain aging, we evaluated the effects of a 2-month treatment with exenatide, a GLP-1 analogue. We found that exenatide promotes the enhancement of long-term memory performances. Biochemical and imaging analyses show that the drug promotes the activation of the BDNF-TrkB neurotrophic axis and inhibits apoptosis by decreasing p75NTR-mediated signaling. The study provides preclinical evidence for the use of exenatide to delay age-dependent cognitive decline.

Vildagliptin prevents cognitive deficits and neuronal apoptosis in a rat model of Alzheimer's disease

Diabetes has been identified to be a risk factor for Alzheimer's disease (AD). Vildagliptin, a novel oral hypoglycemic agent, has been demonstrated to exert protective effects on the pancreas and cardiovascular system. The present study examined the potential protective effects of vildagliptin on neurons in an AD rat model. Treatment with vildagliptin improved memory deficits and decreased neuronal apoptosis in the hippocampus. The expression levels of B cell lymphoma 2 (Bcl‑2) were increased, and the expression levels of caspase‑3, Bcl‑2 associated X protein and AD‑associated proteins were decreased in the hippocampus following treatment with vildagliptin. Additionally, the AD model‑induced decrease in phosphorylated (p) protein kinase B (p‑Akt), p‑glycogen synthase kinase 3β (p‑GSK3β), post‑synaptic density 95 and synaptophysin expression was reversed. These results indicate that vildagliptin administration exerts a protective effect against cognitive deficits by reducing tau phosphorylation and increasing the expression of proteins associated with synaptic plasticity in the hippocampus. Targeting of the Akt/GSK3β signaling pathway may be a key mechanism in preventing the disease progression of AD.

Insulin upregulates GRIM-19 and protects cardiac mitochondrial morphology in type 1 diabetic rats partly through PI3K/AKT signaling pathway

Insulin is involved in the development of diabetic heart disease and is important in the activities of mitochondrial complex I. However, the effect of insulin on cardiac mitochondrial nicotinamide adenine dinucleotide dehydrogenase (ubiquinone) 1 subunit of retinoic-interferon-induced mortality 19 (GRIM-19) has not been characterized. The aim of this study was to investigate the effect of insulin on the mitochondrial GRIM-19 in the hearts of rats with streptozotocin (STZ)-induced type 1 diabetes. Protein changes of GRIM-19 were evaluated by western blotting and reverse transcription-quantitative polymerase chain reaction. Furthermore, the effects of insulin on mitochondrial complex I were detected in HeLa cells and H9C2 cardiac myocytes. During the development of diabetic heart disease, the cardiac function did not change within the 8 weeks, but the mitochondrial morphology was altered. The hearts from the rats with STZ-induced diabetes exhibited reduced expression of GRIM-19. Prior to the overt cardiac dilatation, mitochondrial alterations were already present. Following subcutaneous insulin injection, it was demonstrated that GRIM-19 protein was altered, as well as the mitochondrial morphology. The phosphoinositide 3-kinase inhibitor LY294002 had an effect on insulin signaling in H9C2 cardiacmyocytes, and decreased the level of GRIM-19 by half compared with that in the insulin group. The results indicate that insulin is essential for the control of cardiac mitochondrial morphology and the GRIM-19 expression partly via PI3K/AKT signaling pathways.

Successful Glycemic Control Decreases the Elevated Serum FGF21 Level without Affecting Normal Serum GDF15 Levels in a Patient with Mitochondrial Diabetes

Mitochondrial diabetes mellitus is a subtype of diabetes linked to mutations in mitochondrial DNA. In patients with mitochondrial diabetes mellitus, the effect of glycemic control on the serum concentrations of fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) has not been evaluated. FGF21 and GDF15 have been reported to be useful biomarkers for the diagnosis and severity assessment of mitochondrial diseases like mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Recent studies have shown FGF21 acts in an endocrine fashion to regulate glucose and lipid metabolism in type 2 diabetes mellitus, while the exact biological functions of GDF15 remain unknown. Although mitochondrial diabetes mellitus is commonly found in cases with mitochondrial diseases, the comparison of FGF21 and GDF15 levels between those with and without diabetes has not been performed. Here, we report a 24-year-old woman with mitochondrial diabetes mellitus, who showed a high level of serum FGF21, but not serum GDF15, at diagnosis. In our case, liraglutide, a glucagon-like peptide-1 receptor agonist, added to insulin glargine was effective for her glycemic control and showed no adverse effects, including gastrointestinal symptoms and hypoglycemia, during a 14-week observation. The successful glycemic control caused a decrease in the FGF21 level, without affecting the GDF15 level. Thus, we should consider patients' glycemic control levels in using FGF21 values for the diagnosis of mitochondrial diseases. In addition, sustained GDF15 levels during glycemic treatment in our case suggest the usefulness of GDF15 as a marker for clinical severity of muscle-manifested mitochondrial diseases.

Tat-biliverdin reductase A protects INS-1 cells from human islet amyloid polypeptide-induced cytotoxicity by alleviating oxidative stress and ER stress

Human islet amyloid polypeptide (hIAPP), a major constituent of islet amyloid deposits, induces pancreatic β-cell apoptosis and eventually contributes to β-cell deficit in patients with type 2 diabetes mellitus (T2DM). In this study, Tat-mediated transduction of biliverdin reductase A (BLVRA) was investigated in INS-1 cells to examine whether exogenous supplementation of BLVRA prevented hIAPP-induced apoptosis and dysfunction in insulin secretion in β-cells. Tat-BLVRA fusion protein was efficiently delivered into INS-1 cells in a time- and dose-dependent manner. Exposure of cells to hIAPP induced apoptotic cell death, which was dose-dependently inhibited by pre-treatment with Tat-BLVRA for 1 h. Transduced Tat-BLVRA reduced hIAPP-evoked generation of reactive oxygen species, a crucial mediator of β-cell destruction. Immunoblot analysis showed that Tat-BLVRA suppressed hIAPP-induced increase in the levels of proteins involved in endoplasmic reticulum (ER) stress and apoptosis signaling. Transduced Tat-BLVRA also recovered hIAPP-induced dysfunction in basal and glucose-stimulated insulin secretions. These results suggested that transduced Tat-BLVRA enhanced the tolerance of β-cells against IAPP-induced cytotoxicity by alleviating oxidative stress and ER stress. Therefore, Tat-mediated transduction of BLVRA may provide a potential tool to ameliorate β-cell deficit in pancreas with T2DM.

The anti-diabetic drug exenatide, a glucagon-like peptide-1 receptor agonist, counteracts hepatocarcinogenesis through cAMP-PKA-EGFR-STAT3 axis

Epidemiological studies have demonstrated a close association of type 2 diabetes and hepatocellular carcinoma (HCC). Exenatide (Ex-4), a potent diabetes drug targeting glucagon-like peptide-1 receptor (GLP-1R), is protective against non-alcoholic fatty liver disease (NAFLD). However, the Ex-4 function and GLP-1R status have yet been explored in HCC. Herein we investigated the effect of Ex-4 in diethylnitrosamine (DEN)-treated mice consuming control or high-fat high-carbohydrate diet. Administration of Ex-4 significantly improved obesity-induced hyperglycemia and hyperlipidemia and reduced HCC multiplicity in obese DEN-treated mice, in which suppressed proliferation and induced apoptosis were confined to tumor cells. The tumor suppression effects of Ex-4 were associated with high expression of GLP-1R and activation of cyclic AMP (cAMP) and protein kinase A (PKA). Importantly, Ex-4 also downregulated epidermal growth factor receptor (EGFR) and signal transducer and activator of transcription 3 (STAT3), which lie downstream of cAMP-PKA signaling, resulting in suppression of multiple STAT3-targeted genes including c-Myc, cyclin D1, survivin, Bcl-2 and Bcl-xl. The growth inhibitory effects of Ex-4 were consistent in GLP-1R-abundant hepatoma cell lines and xenograft mouse model, wherein both PKA and EGFR had obligatory roles in mediating Ex-4 functions. In addition, Ex-4 also effectively suppressed inflammatory and fibrotic phenotypes in mice fed with methionine-choline-deficient (MCD) diet and choline-deficient ethionine-supplemented (CDE) diet, respectively. In summary, Ex-4 elicits protective functions against NAFLD and obesity-associated HCC through cAMP-PKA-EGFR-STAT3 signaling, suggesting its administration as a novel approach to reduce HCC risk in diabetic patients.

Islet amyloid polypeptide: Another key molecule in Alzheimer's pathogenesis?

Recent epidemiological evidence reveals that patients suffering from type 2 diabetes mellitus (T2DM) often experience a significant decline in cognitive function, and approximately 70% of those cases eventually develop Alzheimer's disease (AD). Although several pathological processes are shared by AD and T2DM, the exact molecular mechanisms connecting these two diseases are poorly understood. Aggregation of human islet amyloid polypeptide (hIAPP), the pathological hallmark of T2DM, has also been detected in brain tissue and is associated with cognitive decline and AD development. In addition, hIAPP and amyloid β protein (Aβ) share many biophysical and physiological properties as well as exert similar cytotoxic mechanisms. Therefore, it is important to examine the possible role of hIAPP in the pathogenesis of AD. In this article, we introduce the basics on this amyloidogenic protein. More importantly, we discuss the potential mechanisms of hIAPP-induced AD development, which will be beneficial for proposing novel and feasible strategies to optimize AD prevention and/or treatment in diabetics.

Enhanced-autophagy by exenatide mitigates doxorubicin-induced cardiotoxicity

OBJECTIVES

Exenatide is a glucagon-like peptide-1 analogue that mitigates myocardial injury caused by ischemia-reperfusion injury via the survival signaling pathway. We hypothesized that exenatide would provide a protective effect in doxorubicin-induced cardiotoxicity.

METHODS

H9c2 cardiomyocytes were pre-treated with exenatide followed by doxorubicin (DOX), and cell viability and intracellular reactive oxygen species (ROS) were subsequently measured. In order to determine the role of autophagy, we performed western blot as well as TUNEL and autophagosome staining. Additionally, rats were treated with exenatide 1h prior to every DOX treatment. Left ventricular (LV) function and performance were then assessed by echocardiography. Myocardial and serum ROS was measured with DHE fluorescence and ROS/RNS assay.

RESULTS

DOX-induced caspase-3 activation decreased after pre-treatment with exenatide both in vivo and in vitro. Oxidative stress was attenuated by exenatide in H9c2 cells, as well as in cardiac tissue and serum. The number of autophagosomes and autophagic markers were further increased by exenatide in the DOX-treated H9c2 cells, which mediated AMPK activation. Suppression of the autophagosome abolished exenatide-induced anti-apoptotic effect. Echocardiography showed that pre-treatment with exenatide significantly improved LV dysfunction that is induced by DOX treatment. Exenatide inhibits the DOX-induced production of intracellular ROS and apoptosis in the myocardium. The autophagic markers increased in exenatide pre-treated cardiac tissue.

CONCLUSION

Exenatide reduces DOX-induced apoptosis of cardiomyocytes by upregulating autophagy and improving cardiac dysfunction. These novel results highlight the therapeutic potential of exenatide to prevent doxorubicin cardiotoxicity.

Glucagon-like peptide-1 prevents methylglyoxal-induced apoptosis of beta cells through improving mitochondrial function and suppressing prolonged AMPK activation

Accumulation of methylglyoxal (MG) contributes to glucotoxicity and mediates beta cell apoptosis. The molecular mechanism by which GLP-1 protects MG-induced beta cell apoptosis remains unclear. Metformin is a first-line drug for treating type 2 diabetes associated with AMPK activation. However, whether metformin prevents MG-induced beta cell apoptosis is controversial. Here, we explored the signaling pathway involved in the anti-apoptotic effect of GLP-1, and investigated whether metformin had an anti-apoptotic effect on beta cells. MG treatment induced apoptosis of beta cells, impaired mitochondrial function, and prolonged activation of AMP-dependent protein kinase (AMPK). The MG-induced pro-apoptotic effects were abolished by an AMPK inhibitor. Pretreatment of GLP-1 reversed MG-induced apoptosis, and mitochondrial dysfunction, and suppressed prolonged AMPK activation. Pretreatment of GLP-1 reversed AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR)-induced apoptosis, and suppressed prolonged AMPK activation. However, metformin neither leads to beta cell apoptosis nor ameliorates MG-induced beta cell apoptosis. In parallel, GLP-1 also prevents MG-induced beta cell apoptosis through PKA and PI3K-dependent pathway. In conclusion, these data indicates GLP-1 but not metformin protects MG-induced beta cell apoptosis through improving mitochondrial function, and alleviating the prolonged AMPK activation. Whether adding GLP-1 to metformin provides better beta cell survival and delays disease progression remains to be validated.

Saxagliptin restores vascular mitochondrial exercise response in the Goto-Kakizaki rat

Cardiovascular disease risk and all-cause mortality are largely predicted by physical fitness. Exercise stimulates vascular mitochondrial biogenesis through endothelial nitric oxide synthase (eNOS), sirtuins, and PPARγ coactivator 1α (PGC-1α), a response absent in diabetes and hypertension. We hypothesized that an agent regulating eNOS in the context of diabetes could reconstitute exercise-mediated signaling to mitochondrial biogenesis. Glucagon-like peptide 1 (GLP-1) stimulates eNOS and blood flow; we used saxagliptin, an inhibitor of GLP-1 degradation, to test whether vascular mitochondrial adaptation to exercise in diabetes could be restored. Goto-Kakizaki (GK) rats, a nonobese, type 2 diabetes model, and Wistar controls were exposed to an 8-day exercise intervention with or without saxagliptin (10 mg·kg⁻¹·d⁻¹). We evaluated the impact of exercise and saxagliptin on mitochondrial proteins and signaling pathways in aorta. Mitochondrial protein expression increased with exercise in the Wistar aorta and decreased or remained unchanged in the GK animals. GK rats treated with saxagliptin plus exercise showed increased expression of mitochondrial complexes, cytochrome c, eNOS, nNOS, PGC-1α, and UCP3 proteins. Notably, a 3-week saxagliptin plus exercise intervention significantly increased running time in the GK rats. These data suggest that saxagliptin restores vascular mitochondrial adaptation to exercise in a diabetic rodent model and may augment the impact of exercise on the vasculature.

The value of nature's natural product library for the discovery of New Chemical Entities: the discovery of ingenol mebutate

In recent decades, 'Big Pharma' has invested billions of dollars into ingenious and innovative strategies designed to develop drugs using high throughput screening of small molecule libraries generated on the laboratory bench. Within the same time frame, screening of natural products by pharmaceutical companies has suffered an equally significant reduction. This is despite the fact that the complexity, functional diversity and druggability of nature's natural product library are considered by many to be superior to any library any team of scientists can prepare. It is therefore no coincidence that the number of New Chemical Entities reaching the market has also suffered a substantial decrease, leading to a productivity crisis within the pharmaceutical sector. In fact, the current dearth of New Chemical Entities reaching the market in recent decades might be a direct consequence of the strategic decision to move away from screening of natural products. Nearly 700 novel drugs derived from natural product New Chemical Entities were approved between 1981 and 2010; more than 60% of all approved drugs over the same time. In this review, we use the example of ingenol mebutate, a natural product identified from Euphorbia peplus and later approved as a therapy for actinic keratosis, as why nature's natural product library remains the most valuable library for discovery of New Chemical Entities and of novel drug candidates.

Linked clinical trials--the development of new clinical learning studies in Parkinson's disease using screening of multiple prospective new treatments

Finding new therapies for Parkinson’s disease (PD) is a slow process. We assembled an international committee of experts to examine drugs potentially suitable for repurposing to modify PD progression. This committee evaluated multiple drugs currently used, or being developed, in other therapeutic areas, as well as considering several natural, non-pharmaceutical compounds. The committee prioritized which of these putative treatments were most suited to move immediately into pilot clinical trials. Aspects considered included known modes of action, safety, blood-brain-barrier penetration, preclinical data in animal models of PD and the possibility to monitor target engagement in the brain. Of the 26 potential interventions, 10 were considered worth moving forward into small, parallel ‘learning’ clinical trials in PD patients. These trials could be funded in a multitude of ways through support from industry, research grants and directed philanthropic donations. The committee-based approach to select the candidate compounds might help rapidly identify new potential PD treatment strategies for use in clinical trials.

Common defects of mitochondria and iron in neurodegeneration and diabetes (MIND): a paradigm worth exploring

A popular, if not centric, approach to the study of an event is to first consider that of the simplest cause. When dissecting the underlying mechanisms governing idiopathic diseases, this generally takes the form of an ab initio genetic approach. To date, this genetic 'smoking gun' has remained elusive in diabetes mellitus and for many affected by neurodegenerative diseases. With no single gene, or even subset of genes, conclusively causative in all cases, other approaches to the etiology and treatment of these diseases seem reasonable, including the correlation of a systems' predisposed sensitivity to particular influence. In the cases of diabetes mellitus and neurodegenerative diseases, overlapping themes of mitochondrial influence or dysfunction and iron dyshomeostasis are apparent and relatively consistent. This mini-review discusses the influence of mitochondrial function and iron homeostasis on diabetes mellitus and neurodegenerative disease, namely Alzheimer's disease. Also discussed is the incidence of diabetes accompanied by neuropathy and neurodegeneration along with neurodegenerative disorders prone to development of diabetes. Mouse models containing multiple facets of this overlap are also described alongside current molecular trends attributed to both diseases. As a way of approaching the idiopathic and complex nature of these diseases we are proposing the consideration of a MIND (mitochondria, iron, neurodegeneration, and diabetes) paradigm in which systemic metabolic influence, iron homeostasis, and respective genetic backgrounds play a central role in the development of disease.

Microenvironmental stimuli for proliferation of functional islet β-cells

Diabetes is characterized by high blood glucose level due to either autoimmune destruction of islet β-cells or insufficient insulin secretion or glucose non-responsive production of insulin by β-cells. It is highly desired to replace biological functional β-cells for the treatment of diabetes. Unfortunately, β-cells proliferate with an extremely low rate. This cellular property hinders cell-based therapy for clinical application. Many attempts have been made to develop techniques that allow production of large quantities of clinically relevant islet β-cells in vitro. A line of studies evidently demonstrate that β-cells can proliferate under certain circumstances, giving the hopes for generating and expanding these cells in vitro and transplanting them to the recipient. In this review, we discuss the requirements of microenvironmental stimuli that stimulate β-cell proliferation in cell cultures. We highlight advanced approaches for augmentation of β-cell expansion that have recently emerged in this field. Furthermore, knowing the signaling pathways and molecular mechanisms would enable manipulating cell proliferation and optimizing its insulin secretory function. Thus, signaling pathways involved in the enhancement of cell proliferation are discussed as well.

Exendin-4 protects murine MIN6 pancreatic β-cells from interleukin-1β-induced apoptosis via the NF-κB pathway

BACKGROUND

Glucagon-like peptide-1 (GLP-1) and its potent analog, exendin-4, are well known to inhibit β- cell apoptosis and promote β-cell proliferation. Meanwhile, cytokines, such as interleukin-1β (IL-1β), stimulate inducible nitric oxide synthase (iNOS) expression and nitric oxide overproduction leading to β-cell damage. However, the protective mechanisms of GLP-1 in β-cells exposed to cytokines have not been fully elucidated.

AIMS

In this study, the protective effects of exendin-4 on IL-1β-induced apoptosis were investigated in murine MIN6 pancreatic β-cells. The role of nuclear factor-κB (NF-κB) signaling in this process was also explored.

METHODS

The effects of exendin-4 pre-treatment on IL-1β-induced apoptosis were investigated by Hoechst/PI and Annexin V/PI staining. Levels of iNOS and NF-κB proteins were investigated by Western blotting and cytoplasmic nitrite levels were determined using Griess reagent.

RESULTS

IL-1β treatment (range, 5-40 ng/ml) for 24 h was positively correlated with nitrite production (R2=0.9668, p<0.01), a significant increase in the percentage of apoptotic cells (p<0.01) and a concomitant dose-dependent increase in cytoplasmic levels of iNOS and NF-κB p65 activation. N-acetyl- L-cysteine (NAC), NG-nitro-L-arginine methyl ester (L-NAME) and pyrrolidine dithiocarbamate (PDTC), partially rescued apoptotic β-cells, suggesting involvement of NF-κB-iNOS-nitrite in this process. Exendin-4 (100 nM) treatment significantly decreased IL-1β-induced apoptosis (p<0.01), downregulated NF-κB activation and subsequently decreased iNOS and nitrite levels in IL-1β-induced β-cells (p<0.001), in a similar manner to L-NAME, PDTC and NAC.

CONCLUSIONS

These results suggest that exendin-4 protects against IL-1β- induced apoptosis in β-cells via downregulation of the NF- κB-iNOS-nitrite pathway.

Differential protective effects of exenatide, an agonist of GLP-1 receptor and Piragliatin, a glucokinase activator in beta cell response to streptozotocin-induced and endoplasmic reticulum stresses

Background

Agonists of glucagon-like peptide-1 receptor (GLP-1R) and glucokinase activators (GKA) act as antidiabetic agents by their ability protect beta cells, and stimulate insulin secretion. Oxidative and endoplasmic reticulum (ER) stresses aggravate type 2 diabetes by causing beta cell loss. It was shown that GLP-1R agonists protect beta cells from oxidative and ER stresses. On the other hand, little is known regarding how GKAs protect beta cells. We hypothesized that GKAs protect beta cells by mechanisms distinct from those underlying GLP-1R agonist and tested our hypothesis by comparing the molecular effects of exenatide, a GLP-1R agonist, and piragliatin, a GKA, on INS-1 cells under oxidative and ER-induced stresses.

Methods

Beta cells were treated with streptozotocin (STZ) to induce oxidative stress and with palmitate or thapsigargin (Tg) to induce ER stress respectively, and the effects of exenatide and piragliatin on these cells were investigated by: a) characterizing the kinases involved employing specific kinase inhibitors, and b) by identifying the differentially regulated proteins in response to stresses with proteomic analysis.

Results

Exenatide protected INS-1 cells from both ER and STZ-induced death. In contrast, piragliatin rescued the cells only from STZ-induced stress. Akt activation by exenatide appeared to contribute to its protective effects of beta cells while enhanced glucose utilization was the contributing factor in the case of piragliatin. Also, exenatide, not piragliatin, blocked changes in proteins 14-3-3β, ε and θ, and preserved the 14-3-3θ levels under the ER stress. Isoform-specific modifications of 14-3-3, and the reduction of 14-3-3θ, commonly associated with beta cell death were assessed.

Conclusions

Exenatide and piragliatin exert distinct effects on beta cell survival and thus on type 2 diabetes. This study which confirmed our hypothesis is also the first to observe specific modulation of 14-3-3 isoform in stress-induced beta cell death associated with progressive deterioration of type 2 diabetes.