DPP-4 Inhibitor Linagliptin is Neuroprotective in Hyperglycemic Mice with Stroke via the AKT/mTOR Pathway and Anti-apoptotic Effects

Geroprotective interventions in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is an age-associated neurodegenerative disease. As the population ages, the increasing prevalence of AD threatens massive healthcare costs in the coming decades. Unfortunately, traditional drug development efforts for AD have proven largely unsuccessful. A geroscience approach to AD suggests that since aging is the main driver of AD, targeting aging itself may be an effective way to prevent or treat AD. Here, we discuss the effectiveness of geroprotective interventions on AD pathology and cognition in the widely utilized triple-transgenic mouse model of AD (3xTg-AD) which develops both β-amyloid and tau pathologies characteristic of human AD, as well as cognitive deficits. We discuss the beneficial impacts of calorie restriction (CR), the gold standard for geroprotective interventions, and the effects of other dietary interventions including protein restriction. We also discuss the promising preclinical results of geroprotective pharmaceuticals, including rapamycin and medications for type 2 diabetes. Though these interventions and treatments have beneficial effects in the 3xTg-AD model, there is no guarantee that they will be as effective in humans, and we discuss the need to examine these interventions in additional animal models as well as the urgent need to test if some of these approaches can be translated from the lab to the bedside for the treatment of humans with AD.

Linagliptin counteracts rotenone's toxicity in non-diabetic rat model of Parkinson's disease: Insights into the neuroprotective roles of DJ-1, SIRT-1/Nrf-2 and implications of HIF1-α

While all current therapies' main focus is enhancing dopaminergic effects and remission of symptoms, delaying Parkinson's disease (PD) progression remains a challenging mission. Linagliptin, a Dipeptidyl Peptidase-4 (DPP-4) Inhibitor, exhibited neuroprotection in various neurodegenerative diseases. This study aims to evaluate the neuroprotective effects of Linagliptin in a rotenone-induced rat model of PD and investigate the possible underlying mechanisms of Linagliptin's actions. The effects of two doses of Linagliptin (5 and 10 mg/kg) on spontaneous locomotion, catalepsy, coordination and balance, and histology were assessed. Then, after Linagliptin showed promising results, it was further tested for its potential anti-inflammatory, antiapoptotic effects, and different pathways for oxidative stress. Linagliptin prevented rotenone-induced motor deficits and histological damage. Besides, it significantly inhibited the rotenone-induced increase in pro-inflammatory cytokines: Tumor Necrosis Factor-α (TNF-α) and Interleukin-6 (IL-6) and decrease in caspase 3 levels. These effects were associated with induction in the levels of Protein deglycase also known as DJ-1, Hypoxia-inducible factor 1-alpha (HIF-1α), potentiation in the Sirtuin 1 (SIRT-1)/Nuclear factor erythroid-2-related factor 2 (Nrf-2)/Heme oxygenase-1 (HO-1) pathway, and an increase in the antioxidant activity of catalase which provided neuroprotection to the neurons from rotenone-induced PD. Collectively, these results suggest that Linagliptin might be a suitable candidate for the management of PD.

The many facets of CD26/dipeptidyl peptidase 4 and its inhibitors in disorders of the CNS - a critical overview

Dipeptidyl peptidase 4 is a serine protease that cleaves X-proline or X-alanine in the penultimate position. Natural substrates of the enzyme are glucagon-like peptide-1, glucagon inhibiting peptide, glucagon, neuropeptide Y, secretin, substance P, pituitary adenylate cyclase-activating polypeptide, endorphins, endomorphins, brain natriuretic peptide, beta-melanocyte stimulating hormone and amyloid peptides as well as some cytokines and chemokines. The enzyme is involved in the maintenance of blood glucose homeostasis and regulation of the immune system. It is expressed in many organs including the brain. DPP4 activity may be effectively depressed by DPP4 inhibitors. Apart from enzyme activity, DPP4 acts as a cell surface (co)receptor, associates with adeosine deaminase, interacts with extracellular matrix, and controls cell migration and differentiation. This review aims at revealing the impact of DPP4 and DPP4 inhibitors for several brain diseases (virus infections affecting the brain, tumours of the CNS, neurological and psychiatric disorders). Special emphasis is given to a possible involvement of DPP4 expressed in the brain.While prominent contributions of extracerebral DPP4 are evident for a majority of diseases discussed herein; a possible role of "brain" DPP4 is restricted to brain cancers and Alzheimer disease. For a number of diseases (Covid-19 infection, type 2 diabetes, Alzheimer disease, vascular dementia, Parkinson disease, Huntington disease, multiple sclerosis, stroke, and epilepsy), use of DPP4 inhibitors has been shown to have a disease-mitigating effect. However, these beneficial effects should mostly be attributed to the depression of "peripheral" DPP4, since currently used DPP4 inhibitors are not able to pass through the intact blood-brain barrier.

Effect of new glucose-lowering drugs on stroke in patients with type 2 diabetes: A systematic review and Meta-analysis

AIMS

People with diabetes tend to face a higher risk of stroke. Randomized controlled trials (RCTs) have demonstrated the different outcomes of new glucose-lowering drugs marketed in recent years on cardiovascular outcome events. The effects of glucagon-like peptide-1 (GLP-1) agonists, sodium-glucose cotransporter-2 (SGLT-2) inhibitors, and dipeptidyl peptidase-4 (DPP-4) inhibitors on stroke risk were evaluated in published RCTs.

METHODS

A search of Embase, Cochrane Library, and PubMed databases identified studies with stroke as an outcome event up to 3 December 2021. Risk ratios for stroke outcomes were analyzed using a fixed-effects model. I² was used to assess the heterogeneity of the study.

RESULTS

19 RCTs with 155,027 participants with type 2 diabetes were identified. Pooled analysis showed that compared to placebo, GLP-1 agonists reduced non-fatal stroke by 15 % (RR = 0.85, 95%CI 0.77-0.94, P = 0.002, I² = 0 %) and total stroke (RR = 0.84, 95%CI 0.77-0.93, P = 0.000, I² = 0 %) by 16 %. SGLT-2 inhibitors and DPP-4 inhibitors were not significantly associated with lower stroke risk.

CONCLUSIONS

This meta-analysis indicates that GLP-1 agonists have potential benefits for stroke. However, further studies are needed if GLP-1 agonists are to be used to reduce the risk of stroke in patients with type 2 diabetes. More research is also needed to investigate the effects of new glucose-lowering drugs on different stroke subtypes.

SYSTEMATIC REVIEW REGISTRATION

This protocol was registered on the International Prospective Register of Systematic Reviews (https://www.crd.york.ac.uk/PROSPERO/; registration number: CRD42022326382).

A review of stress-induced hyperglycaemia in the context of acute ischaemic stroke: Definition, underlying mechanisms, and the status of insulin therapy

The transient elevation of blood glucose produced following acute ischaemic stroke (AIS) has been described as stress-induced hyperglycaemia (SIH). SIH is common even in patients with AIS who have no previous diagnosis of diabetes mellitus. Elevated blood glucose levels during admission and hospitalization are strongly associated with enlarged infarct size and adverse prognosis in AIS patients. However, insulin-intensive glucose control therapy defined by admission blood glucose for SIH has not achieved the desired results, and new treatment ideas are urgently required. First, we explore the various definitions of SIH in the context of AIS and their predictive value in adverse outcomes. Then, we briefly discuss the mechanisms by which SIH arises, describing the dual effects of elevated glucose levels on the central nervous system. Finally, although preclinical studies support lowering blood glucose levels using insulin, the clinical outcomes of intensive glucose control are not promising. We discuss the reasons for this phenomenon.

Cardiovascular protection by DPP-4 inhibitors in preclinical studies: an updated review of molecular mechanisms

Dipeptidyl peptidase 4 (DPP4) inhibitors are a class of antidiabetic medications that cause glucose-dependent increase in incretins in diabetic patients. One of the two incretins, glucagon-like peptide-1 (GLP-1), beside its insulinotropic activity, has been studied for extra pancreatic effects. Most of DPP4 inhibitors (DPP4i) have been investigated in in vivo and in vitro models of diabetic and nondiabetic cardiovascular diseases including heart failure, hypertension, myocardial ischemia or infarction, atherosclerosis, and stroke. Results of preclinical studies proved prominent therapeutic potential of DPP4i in cardiovascular diseases, regardless the presence of diabetes. This review aims to present an updated summary of the cardiovascular protective and therapeutic effects of DPP4 inhibitors through the past 5 years focusing on the molecular mechanisms beneath these effects. Additionally, based on the results summary presented here, future studies may be conducted to elucidate or illustrate some of these findings which can add clinical benefits towards management of diabetic cardiovascular complications.

Plasma-Soluble Dipeptidyl Peptidase 4 and Risk of Major Cardiovascular Events After Ischemic Stroke: Secondary Analysis of China Antihypertensive Trial in Acute Ischemic Stroke (CATIS)

BACKGROUND AND OBJECTIVES

Recent studies have suggested that plasma soluble dipeptidyl peptidase-4 (sDPP4) have important physiological effects, which may influence the prognosis of ischemic stroke. Our study aimed to examine the relationship between plasma sDDP4 levels and long-term clinical outcomes among acute ischemic stroke patients.

METHODS

Secondary analysis was conducted among 3,564 participants (2,270 men and 1,294 women) from the China Antihypertensive Trial in Acute Ischemic Stroke with baseline measurement of plasma sDPP4 levels. We evaluated the associations between plasma sDPP4 levels and 2-year clinical outcomes using logistic regression and Cox regression models. We further investigated the predictive utility of sDPP4 by calculating net reclassification index (NRI) and integrated discrimination improvement (IDI).

RESULTS

The highest plasma sDPP4 quartile was associated with lower risk of cardiovascular events (HR 0.62, 95% CI 0.45-0.87), recurrent stroke (HR 0.70, 95% CI 0.49-0.99), all-cause mortality (HR 0.62, 95% CI 0.44-0.87), stroke-specific mortality (HR 0.65, 95% CI 0.44-0.94) and poor functional outcomes (OR 0.66, 95% CI 0.53-0.82) at 2 years compared with the lowest sDPP4 category in multivariable models. The addition of plasma sDPP4 to conventional risk factors model significantly improved risk prediction of all outcomes.

DISCUSSION

In this study, we found that higher plasma sDPP4 levels in acute ischemic stroke patients were associated with decreased risks of cardiovascular events, recurrent stroke, all-cause mortality, and poor functional outcomes after ischemic stroke. These findings suggest that plasma sDPP4 may be a potential prognostic marker for initial risk stratification in patients with acute ischemic stroke.

Role of Dipeptidyl Peptidase 4 Inhibitors in Antidiabetic Treatment

In recent years, important changes have occurred in the field of diabetes treatment. The focus of the treatment of diabetic patients has shifted from the control of blood glucose itself to the overall management of risk factors, while adjusting blood glucose goals according to individualization. In addition, regulators need to approve new antidiabetic drugs which have been tested for cardiovascular safety. Thus, the newest class of drugs has been shown to reduce major adverse cardiovascular events, including sodium-glucose transporter 2 (SGLT2) and some glucagon like peptide 1 receptor (GLP1) analog. As such, they have a prominent place in the hyperglycemia treatment algorithms. In recent years, the role of DPP4 inhibitors (DPP4i) has been modified. DPP4i have a favorable safety profile and anti-inflammatory profile, do not cause hypoglycemia or weight gain, and do not require dose escalation. In addition, it can also be applied to some types of chronic kidney disease patients and elderly patients with diabetes. Overall, DPP4i, as a class of safe oral hypoglycemic agents, have a role in the management of diabetic patients, and there is extensive experience in their use.

Total Flavonoids of Chuju Decrease Oxidative Stress and Cell Apoptosis in Ischemic Stroke Rats: Network and Experimental Analyses

Background: Pharmacological research results showed that total flavonoids of Chuju (TFCJ) could be used to treat acute myocardial ischemia and myocardial ischemia-reperfusion injury. In this study, we explored the protective effect of TFCJ on ischemic stroke (IS) in the IS rat model. We hypothesized that TFCJ might exert its neuroprotective effects by suppressing apoptosis and oxidative stress that are closely related to PI3K/Akt/mTOR signaling pathway. Method: TFCJ (10, 20, and 40 mg/kg) was administered for 7 days. Rats (260 ± 20 g) were subjected to middle cerebral artery occlusion (MCAO) for 2 h and reperfusion for 24 h. The neuroprotective effect of TFCJ was substantiated in terms of neurological deficits, oxidative stress (superoxide dismutase, glutathione peroxidase, catalase, and malondialdehyde), pathomorphological changes (HE staining and TUNEL staining), and neurobehavioral functions in the rats. Then, we employed network pharmacology to reveal the potential mechanism of TFCJ against IS. Western blot was used to determine the levels of PI3K/AKT/mTOR pathway proteins. The expression of BCL-2, BAX, and cleaved-Caspase-3 was also measured by Western blots and RT-PCR. Results: The histopathological assessment showed that TFCJ reduced MCAO-induced brain damage. Besides, TFCJ exerted a protective role in MCAO rats by alleviating cell apoptosis and oxidative stress. Network pharmacology showed that TFCJ might be used against IS through the PI3K/AKT signaling pathway. TFCJ reduced cell apoptosis and oxidative stress by increasing the level of p-AKT and p-mTOR in MCAO rats, while the effect of TFCJ was significantly reversed when applying LY294002 (PI3k inhibitor). Conclusion: These results indicated that TFCJ might decrease oxidative stress and apoptosis that are closely related to PI3K/Akt/mTOR pathway in IS. TFCJ is a promising authentic traditional Chinese medicine for the management of IS.

SET8, a novel regulator to ameliorate vascular calcification via activating PI3K/Akt mediated anti-apoptotic effects

Previous studies have shown that the apoptosis of vascular smooth muscle cells (VSMCs) underlies the mechanism of pathological calcification in patients with chronic kidney disease (CKD). SET domain-containing protein 8 (SET8) is an efficient protein that modulates apoptosis in hepatocellular carcinoma cells, esophageal squamous cells, and neuronal cells by regulating pathological processes, such as cell cycle progression and transcription regulation. However, whether SET8 is involved in high phosphorus-induced vascular calcification by mediating apoptosis remains unclear. Here, we report that SET8 is located both in the nucleus and cytoplasm and is significantly downregulated in calcification models. SET8 deficiency promoted apoptosis of VSMCs, as indicated by the increased Bax/Bcl-2 and cleaved caspase-3/total caspase-3 ratios. Mechanistically, the PI3K/Akt pathway was mediated by SET8, and inhibition of the PI3K/Akt signaling pathway by administering LY294002 or transfecting the Akt phosphorylation-inactivated mutation plasmid increased apoptosis and calcification. Akt phosphorylation constitutively activated mutations can reduce the apoptosis and calcification of VSMCs. Furthermore, exogenous overexpression of SET8 reversed the effect of PI3K/Akt inhibition on VSMC apoptosis and calcification. In summary, our research suggests that SET8 overexpression ameliorates high phosphorus-induced calcification of VSMCs by activating PI3K/Akt mediated anti-apoptotic effects.

Endothelial Thioredoxin-Interacting Protein Depletion Reduces Hemorrhagic Transformation in Hyperglycemic Mice after Embolic Stroke and Thrombolytic Therapy

We hypothesize that endothelial-specific thioredoxin-interacting protein knock-out (EC-TXNIP KO) mice will be more resistant to the neurovascular damage (hemorrhagic-transformation-HT) associated with hyperglycemia (HG) in embolic stroke. Adult-male EC-TXNIP KO and wild-type (WT) littermate mice were injected with-streptozotocin (40 mg/kg, i.p.) for five consecutive days to induce diabetes. Four-weeks after confirming HG, mice were subjected to embolic middle cerebral artery occlusion (eMCAO) followed by tissue plasminogen activator (tPA)-reperfusion (10 mg/kg at 3 h post-eMCAO). After the neurological assessment, animals were sacrificed at 24 h for neurovascular stroke outcomes. There were no differences in cerebrovascular anatomy between the strains. Infarct size, edema, and HT as indicated by hemoglobin (Hb)-the content was significantly higher in HG-WT mice, with or without tPA-reperfusion, compared to normoglycemic WT mice. Hyperglycemic EC-TXNIP KO mice treated with tPA tended to show lower Hb-content, edema, infarct area, and less hemorrhagic score compared to WT hyperglycemic mice. EC-TXNIP KO mice showed decreased expression of inflammatory mediators, apoptosis-associated proteins, and nitrotyrosine levels. Further, vascular endothelial growth factor-A and matrix-metalloproteinases (MMP-9/MMP-3), which degrade junction proteins and increase blood-brain-barrier permeability, were decreased in EC-TXNIP KO mice. Together, these findings suggest that vascular-TXNIP could be a novel therapeutic target for neurovascular damage after stroke.

ubtor Mutation Causes Motor Hyperactivity by Activating mTOR Signaling in Zebrafish

Mechanistic target of rapamycin (mTOR) signaling governs important physiological and pathological processes key to cellular life. Loss of mTOR negative regulators and subsequent over-activation of mTOR signaling are major causes underlying epileptic encephalopathy. Our previous studies showed that UBTOR/KIAA1024/MINAR1 acts as a negative regulator of mTOR signaling, but whether UBTOR plays a role in neurological diseases remains largely unknown. We therefore examined a zebrafish model and found that ubtor disruption caused increased spontaneous embryonic movement and neuronal activity in spinal interneurons, as well as the expected hyperactivation of mTOR signaling in early zebrafish embryos. In addition, mutant ubtor larvae showed increased sensitivity to the convulsant pentylenetetrazol, and both the motor activity and the neuronal activity were up-regulated. These phenotypic abnormalities in zebrafish embryos and larvae were rescued by treatment with the mTORC1 inhibitor rapamycin. Taken together, our findings show that ubtor regulates motor hyperactivity and epilepsy-like behaviors by elevating neuronal activity and activating mTOR signaling.

CD26/DPP-4: Type 2 Diabetes Drug Target with Potential Influence on Cancer Biology

Simple Summary

Dipeptidyl peptidase (DPP)-4 inhibitor is widely used for type 2 diabetes. Although DPP-4/CD26 has been recognized as both a suppressor and inducer in tumor biology due to its various functions, how DPP-4 inhibitor affects cancer progression in diabetic patients is still unknown. The aim of this review is to summarize one unfavorable aspect of DPP-4 inhibitor in cancer-bearing diabetic patients.

Abstract

DPP-4/CD26, a membrane-bound glycoprotein, is ubiquitously expressed and has diverse biological functions. Because of its enzymatic action, such as the degradation of incretin hormones, DPP-4/CD26 is recognized as the significant therapeutic target for type 2 diabetes (T2DM); DPP-4 inhibitors have been used as an anti-diabetic agent for a decade. The safety profile of DPP-4 inhibitors for a cardiovascular event in T2DM patients has been widely analyzed; however, a clear association between DPP-4 inhibitors and tumor biology is not yet established. Previous preclinical studies reported that DPP-4 suppression would impact tumor progression processes. With regard to this finding, we have shown that the DPP-4 inhibitor induces breast cancer metastasis and chemoresistance via an increase in its substrate C-X-C motif chemokine 12, and the consequent induction of epithelial-mesenchymal transition in the tumor. DPP-4/CD26 plays diverse pivotal roles beyond blood glucose control; thus, DPP-4 inhibitors can potentially impact cancer-bearing T2DM patients either favorably or unfavorably. In this review, we primarily focus on the possible undesirable effect of DPP-4 inhibition on tumor biology. Clinicians should note that the safety of DPP-4 inhibitors for diabetic patients with an existing cancer is an unresolved issue, and further mechanistic analysis is essential in this field.

Targeting AGE-RAGE signaling pathway by Saxagliptin prevents myocardial injury in isoproterenol challenged diabetic rats

The role of Saxagliptin in diabetes-associated cardiovascular complications is controversial. This study aimed to investigate whether Saxagliptin could prevent Isoproterenol-induced myocardial changes in diabetic rats and to identify the possible mechanism as well. The high-fat diet/low-dose Streptozotocin-induced type 2 diabetic rats were divided into 3 groups: the control group (0.25% CMC for 28 days), the Isoproterenol group (85 mg/kg Isoproterenol for the last 2 days plus 0.25% CMC for 28 days), and the treatment group (10 mg/kg Saxagliptin for 28 days plus 85 mg/kg Isoproterenol for the last 2 days). Hemodynamic measurements were performed, and samples were examined for RAGE and NF-κB expressions, histopathological and ultrastructural changes, AGEs level, myocardial injury markers, oxidative stress, and apoptosis. Saxagliptin significantly recovered cardiac function (p < .001), reverted myocardial injury and oxidative stress levels back to the control value (p < .05 to p < .001). Saxagliptin alleviates Isoproterenol-induced myocardial injury in diabetic rats by suppressing AGE-RAGE pathway.