Vildagliptin, a DPP4 inhibitor, alleviates diabetes-associated cognitive deficits by decreasing the levels of apoptosis-related proteins in the rat hippocampus

Neuroprotective effects of dipeptidyl peptidase 4 inhibitor on Alzheimer's disease: a narrative review

Insulin resistance in brain and amyloidogenesis are principal pathological features of diabetes-related cognitive decline and development of Alzheimer's disease (AD). A growing body of evidence suggests that maintaining glucose under control in diabetic patients is beneficial for preventing AD development. Dipeptidyl peptidase 4 inhibitors (DDP4is) are a class of novel glucose-lowering medications through increasing insulin excretion and decreasing glucagon levels that have shown neuroprotective potential in recent studies. This review consolidates extant evidence from earlier and new studies investigating the association between DPP4i use, AD, and other cognitive outcomes. Beyond DPP4i's benefits in alleviating insulin resistance and glucose-lowering, underlying mechanisms for the potential neuroprotection with DPP4i medications were categorized into the following sections: (Ferrari et al., Physiol Rev, 2021, 101, 1,047-1,081): the benefits of DPP4is on directly ameliorating the burden of β-amyloid plaques and reducing the formation of neurofibrillary tangles; DPP4i increasing the bioactivity of neuroprotective DPP4 substrates including glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and stromal-derived factor-1α (SDF-1α) etc.; pleiotropic effects of DPP4is on neuronal cells and intracerebral structure including anti-inflammation, anti-oxidation, and anti-apoptosis. We further revisited recently published epidemiological studies that provided supportive data to compliment preclinical evidence. Given that there remains a lack of completed randomized trials that aim at assessing the effect of DPP4is in preventing AD development and progression, this review is expected to provide a useful insight into DPP4 inhibition as a potential therapeutic target for AD prevention and treatment. The evidence is helpful for informing the rationales of future clinical research and guiding evidence-based clinical practice.

Dipeptidyl peptidase-4 inhibitors alleviate cognitive dysfunction in type 2 diabetes mellitus

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) are commonly at high risk for developing cognitive dysfunction. Antidiabetic agents might be repurposed for targeting cognitive dysfunction in addition to modulation on glucose homeostasis. This study aimed to evaluate the impact of dipeptidyl peptidase-4 inhibitors (DPP-4i) on cognitive function in T2DM.

METHODS

PubMed, Embase, Cochrane Library and Web of Science were systematically searched from inception to September 30, 2023. Weighted mean differences were calculated using the Mantel-Haenszel (M-H) fixed or random effects model based on the degree of heterogeneity among studies. Heterogeneity was evaluated using a Chi-squared test and quantified with Higgins I2. Sensitivity analysis was performed with the leave-one-out method, and publication bias was evaluated according to Begg's and Egger's tests.

RESULTS

Six clinical trials involving 5,178 participants were included in the pooled analysis. Administration of DPP-4i generally correlated with an increase of Mini-Mental State Examination (MMSE) scores (1.09, 95% CI: 0.22 to 1.96). DPP-4i alleviated cognitive impairment in the copying skill subdomain of MMSE (0.26, 95% CI: 0.12 to 0.40). Treatment with DPP-4i also resulted in an increase of Instrumental Activities of Daily Living (IADL) scores (0.82, 95% CI: 0.30 to 1.34). However, DPP-4i produced no significant effects on Barthel Activities of Daily Living (BADL) scores (0.37, 95% CI: -1.26 to 1.99) or other test scores.

CONCLUSIONS

DPP-4i treatment favourably improved cognitive function in patients with T2DM. Further trials with larger samples should be performed to confirm these estimates and investigate the association of different DPP-4i with cognitive function among diabetic patients.

TRIAL REGISTRATION IN PROSPERO

CRD42023430873.

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

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

In silico analysis of novel dipeptidyl peptidase-IV inhibitory peptides released from Macadamia integrifolia antimicrobial protein 2 (MiAMP2) and the possible pathways involved in diabetes protection

The aim of the present study was to screen novel dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from Macadamia integrifolia antimicrobial protein 2 (MiAMP2) and evaluate the potential antidiabetic targets and involved signaling pathways using in silico approaches. In silico digestion of MiAMP2 with pepsin, trypsin and chymotrypsin was performed with ExPASy PeptideCutter and the generated peptides were subjected to BIOPEP-UWM, iDrug, INNOVAGEN and Autodock Vina for further analyses. Six novel peptides EQVR, EQVK, AESE, EEDNK, EECK, and EVEE were predicted to possess good DPP-IV inhibitory potentials, water solubility, and absorption, distribution, metabolism, excretion, and toxicity properties. Molecular dynamic simulation and molecular docking displayed that AESE was the most potent DPP-IV inhibitory peptide and can bind with the active sites of DPP-IV through hydrogen bonding and van der Waals forces. The potential antidiabetic targets of AESE were retrieved from SwissTargetPrediction and GeneCards databases. Protein-protein interaction analysis identified BIRC2, CASP3, MMP7 and BIRC3 to be the hub targets. Moreover, the KEGG pathway enrichment analysis showed that AESE prevented diabetes through the apoptosis and TNF signaling pathways. These results will provide new insights into utilization of MiAMP2 as functional food ingredients for the prevention and treatment of diabetes.

New agents and perspectives in the pharmacological treatment of major depressive disorder

Despite the important advances in the understanding of the pathophysiology of MDD, a large proportion of depressed patients do not respond well to currently available pharmacological agents. The present review focuses on new targets and future directions in the pharmacological treatment of MDD. Novel agents and their efficacy in the treatment of depression are discussed, with a focus on the respectively target pathophysiological pathways and the level of available evidence. Although it is expected that classic antidepressants will remain the cornerstone of MDD treatment, at least for the near future, a large number of novel compounds is currently under investigation as for their efficacy in the treatment of MDD, many of which with promising results.

Targeting Insulin Resistance to Treat Cognitive Dysfunction

Dementia is a devastating disease associated with aging. Alzheimer's disease is the most common form of dementia, followed by vascular dementia. In addition to clinically diagnosed dementia, cognitive dysfunction has been reported in diabetic patients. Recent studies are now beginning to recognize type 2 diabetes mellitus, characterized by chronic hyperglycemia and insulin resistance, as a risk factor for Alzheimer's disease and other cognitive disorders. While studies on insulin action have remained traditionally in the domain of peripheral tissues, the detrimental effects of insulin resistance in the central nervous system on cognitive dysfunction are increasingly being reported by recent clinical and preclinical studies. The findings from these studies suggest that antidiabetic drugs have the potential to be used to treat dementia. In this review, we discuss the physiological functions of insulin in the brain, studies on the evaluation of cognitive function under conditions of insulin resistance, and reports on the beneficial actions of antidiabetic drugs in the brain. This review covers clinical studies as well as investigations in animal models and will further highlight the emerging link between insulin resistance and neurodegenerative disorders.

Vildagliptin Has a Neutral Association With Dementia Risk in Type 2 Diabetes Patients

BACKGROUND AND AIMS

Animal studies suggested that vildagliptin might exert a beneficial effect on cognitive function. The present study evaluated whether the use of vildagliptin in patients with type 2 diabetes mellitus might affect dementia risk.

METHODS

The database of Taiwan's National Health Insurance was used to enroll an unmatched cohort and a propensity score-matched-pair cohort of ever and never users of vildagliptin from patients with newly diagnosed diabetes mellitus during 2002-2014. The patients should be alive on January 1, 2015 and were followed up for dementia diagnosis until December 31, 2016. Unadjusted and multivariate-adjusted hazard ratios (HR) and their 95% confidence intervals (CI) were estimated for vildagliptin ever versus never users, for cumulative duration and cumulative dose of vildagliptin therapy categorized into tertiles versus never users, and for cumulative duration and cumulative dose treated as continuous variables.

RESULTS

There were 355610 never users and 43196 ever users in the unmatched cohort and 40489 never users and 40489 ever users in the matched cohort. In the unmatched cohort, unadjusted HR (95% CI) was 0.929 (0.683-1.264) and the multivariate-adjusted HR (95% CI) was 0.922 (0.620-1.372). In the matched cohort, the unadjusted HR (95% CI) was 0.930 (0.616-1.402) and the multivariate-adjusted HR (95% CI) was 0.825 (0.498-1.367). None of the analyses conducted for cumulative duration and cumulative dose was significant, either being treated as tertile cutoffs or as continuous variables, in either the unmatched cohort or the matched cohort.

CONCLUSIONS

This study showed a neutral effect of vildagliptin on dementia risk.

Link Between Diabetes and Alzheimer's Disease due to the Shared Amyloid Aggregation and Deposition Involving both Neurodegenerative Changes and Neurovascular Damages

Diabetes and Alzheimer’s disease are two highly prevalent diseases among the aging population and have become major public health concerns in the 21st century, with a significant risk to each other. Both of these diseases are increasingly recognized to be multifactorial conditions. The terms “diabetes type 3” or “brain diabetes” have been proposed in recent years to provide a complete view of the potential common pathogenic mechanisms between these diseases. While insulin resistance or deficiency remains the salient hallmarks of diabetes, cognitive decline and non-cognitive abnormalities such as impairments in visuospatial function, attention, cognitive flexibility, and psychomotor speed are also present. Furthermore, amyloid aggregation and deposition may also be drivers for diabetes pathology. Here, we offer a brief appraisal of social impact and economic burden of these chronic diseases and provide insight into amyloidogenesis through considering recent advances of amyloid-β aggregates on diabetes pathology and islet amyloid polypeptide on Alzheimer’s disease. Exploring the detailed knowledge of molecular interaction between these two amyloidogenic proteins opens new opportunities for therapies and biomarker development.

Vildagliptin Attenuates Huntington's Disease through Activation of GLP-1 Receptor/PI3K/Akt/BDNF Pathway in 3-Nitropropionic Acid Rat Model

Vildagliptin (Vilda), a dipeptidyl peptidase-4 (DPP-4) inhibitor, has been highlighted as a promising therapeutic agent for neurodegenerative diseases as Alzheimer's and Parkinson's diseases. Vilda's effect is mostly linked to PI3K/Akt signaling in CNS. Moreover, PI3K/Akt activation reportedly enhanced survival and dampened progression of Huntington's disease (HD). However, Vilda's role in HD is yet to be elucidated. Thus, the aim of the study is to uncover the potentiality of Vilda in HD and unfold its link with PI3K/Akt pathway in 3-nitropropionic acid (3NP) rat model. Rats were randomly assigned into 4 groups; group 1 received saline, whereas, groups 2, 3 and 4 received 3NP (10 mg/kg/day; i.p.) for 14 days, concomitantly with Vilda (5 mg/kg/day; p.o.) in groups 3 and 4, and wortmannin (WM), a PI3K inhibitor, (15 μg/kg/day; i.v.) in group 4. Vilda improved cognitive and motor perturbations induced by 3NP, as confirmed by striatal histopathological specimens and immunohistochemical examination of GFAP. The molecular signaling of Vilda was estimated by elevation of GLP-1 level and protein expressions of survival proteins; p85/p55 (pY458/199)-PI3K, pS473-Akt. Together, it boosted striatal neurotrophic factors and receptor; pS133-CREB, BDNF, pY515-TrKB, which subsequently maintained mitochondrial integrity, as indicated by enhancing both SDH and COX activities, and the redox modulators; Sirt1, Nrf2. Such neuroprotection restored imbalance of neurotransmitters through increasing GABA and suppressing glutamate as well PDE10A. These effects were reversed by WM pre-administration. In conclusion, Vilda purveyed significant anti-Huntington effect which may be mediated, at least in part, via activation of GLP-1/PI3K/Akt pathway in 3NP rat model.

Abelmoschus esculentus subfractions attenuate beta amyloid-induced neuron apoptosis by regulating DPP-4 with improving insulin resistance signals

The association of Alzheimer disease (AD) and Diabetes (DM) is less clear. Accumulation of beta amyloid (Aβ) and presence of hyperphosphorylated tau (p-tau) are hallmarks of AD, spreading in the region where insulin receptors are also found. Aβ exerts neuron toxicity, and could disturb insulin signaling of phosphatidylinositol 3-kinase (PI3K), glycogen synthase kinase (GSK)-3β and AMP-activated protein kinase (AMPK), but increase IRS-1-Ser307 phosphorylation which is viewed as insulin resistance marker. Previously we reported dipeptidyl peptidase-4 (DPP-4) mediate insulin resistance signals, and Abelmoschus esculentus (AE) subfractions F1 (rich in quercetin glucosides and triterpene ester) and F2 (containing large amount of polysaccharides) attenuate DPP-4-mediated apoptosis. In the present study, we aim to investigate if Aβ induce neuron death by regulating DPP-4 and insulin resistance signals, and the putative effect of F1 and F2. By MTT, microscopy, and Western blotting, we demonstrate treatment of appropriate doses of AE subfractions prevent Aβ-induced neuron apoptosis. F1 attenuate Aβ-induced caspase 3 expression especially at 25 μg/mL, while F2 attenuate caspase 3 activation even at the low dose of 1 μg/mL. Both AE subfractions decrease Aβ-enhanced DPP-4, but increase Aβ-reduced p-AMPK and p-PI3K. The activity analysis reveals that F2 is more valid than F1 to reduce DPP-4 activity. The inhibition of DPP-4 demonstrates it plays the pivotal role in Aβ-induced neuron apoptosis. Moreover, although both F1 and F2 are effective to inhibit p-IRS-1-Ser307, F2 takes advantage to reduce p-Tau while F1 is superior to enhance p-GSK-3β. This implies AE subfractions act on different targets, and could be developed respectively. In conclusion, we demonstrate AE is potential to prevent Aβ-induced neuron damage by regulating DPP-4 and the insulin resistance cascades. AE could be an adjuvant to protect neuron degenerative disease related to Aβ and insulin resistance.

Dipeptidyl Peptidase-4 Inhibitors for the Potential Treatment of Brain Disorders; A Mini-Review With Special Focus on Linagliptin and Stroke

Cerebral stroke is a leading cause of death and persistent disability of elderly in the world. Although stroke prevention by targeting several risk factors such as diabetes and hypertension has decreased the stroke incidence, the total number of strokes is increasing due to the population aging and new preventive therapies are needed. Moreover, post-stroke acute pharmacological strategies aimed to reduce stroke-induced brain injury have failed in clinical trials despite being effective in animal models. Finally, approximately 30% of surviving stroke patients do not recover from stroke and remain permanently dependent on supportive care in activities of daily living. Therefore, strategies to improve stroke recovery in the post-acute phase are highly needed. Linagliptin is a dipeptidyl peptidase-4 inhibitor which is clinically approved to reduce hyperglycemia in type 2 diabetes. The regulation of glycemia by dipeptidyl peptidase-4 inhibition is mainly achieved by preventing endogenous glucagon-like peptide-1 (GLP-1) degradation. Interestingly, linagliptin has also shown glycaemia-independent beneficial effects in animal models of stroke, Parkinson's disease and Alzheimer's disease. In some case the preclinical data have been supported with some clinical data. Although potentially very interesting for the development of new strategies against stroke and neurodegenerative disorders, the mode of action of linagliptin in the brain is still largely unknown and seems to occur in a GLP-1R-independent manner. The purpose of this mini-review is to summarize and discuss the recent experimental and clinical work regarding the effects of linagliptin in the central nervous system, with special emphasis on acute neuroprotection, stroke prevention and post-stroke recovery. We also highlight the main questions in this research field that need to be addressed in clinical perspective.

GLP-1's role in neuroprotection: a systematic review

Glucagon-like peptide 1 (GLP-1) is a target for treatment of diabetes; however, its function in the brain is not well studied. In this systematic review, we aimed to analyze the neuroprotective role of GLP-1 and its defined mechanisms. Methods: We searched 'Web of Science' and 'Pubmed' to identify relevant studies using GLP-1 as the keyword. Two hundred and eighty-nine clinical and preclinical studies have been included. Data have been presented by grouping neurodegenerative, neurovascular and specific cell culture models. Results: Recent literature shows that GLP-1 and its agonists, DPP-4 inhibitors and combined GLP-1/GIP molecules are effective in partially or fully reversing the effects of neurotoxic compounds, neurovascular complications of diabetes, neuropathological changes related with Alzheimer's disease, Parkinson's disease or vascular occlusion. Possible mechanisms that provide neuroprotection are enhancing the viability of the neurons and restoring neurite outgrowth by increased neurotrophic factors, increasing subventricular zone progenitor cells, decreasing apoptosis, decreasing the level of pro-inflammatory factors, and strengthening blood-brain barrier. Conclusion: Based on the preclinical studies, GLP-1 modifying agents are promising targets for neuroprotection. On the other hand, the number of clinical studies that investigate GLP-1 as a treatment is low and further clinical trials are needed for a benchside to bedside translation of recent findings.

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

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

Protective Effects of Oleuropein Against Cerebral Ischemia/Reperfusion by Inhibiting Neuronal Apoptosis

BACKGROUND In this study, we investigated the potential neuroprotective effect of oleuropein (OLE) on apoptotic changes via modulating Akt/glycogen synthase kinase 3 beta (Akt/GSK-3b) signaling in a rat model of cerebral ischemia/reperfusion injury (IRI). MATERIAL AND METHODS Sprague-Dawley male rats (12 weeks, n=200) were randomly assigned to 5 groups: sham group, vehicle (IRI+ vehicle) group, OLE (IRI+OLE) group, OLE+LY294002 (IRI+OLE+LY294002) group, and LY294002(IRI+LY294002) group. The rats were subjected to cerebral ischemia/reperfusion injury (IRI) model and treated once daily for 5 days with vehicle and OLE (100 mg/kg via intraperitoneal injection) after IRI injury. LY294002 (0.3 mg/kg) was intraperitoneally injected once at 30 min after IRI injury. Brain edema, neurological deficit, rotarod latencies, and Morris water maze (MWM) performance were evaluated after IRI. The number of dead cells were assayed by TUNEL staining. Western blot was used to detect the expression of Bcl-2, Bax, cleaved caspase-3 (CC3), neurotrophic factors, and the phosphorylation levels of Akt and GSK-3β. RESULTS Compared with the vehicle group, brain water content, neurological deficits, rotarod latencies, and escape latency following IRI were reduced in the OLE group. Cell apoptosis and reduced neurotrophic factor caused by IRI was also attenuated by OLE. Furthermore, increased p-Akt and decreased p-GSK-3β were caused by OLE, which were associated with decrease of Bax/Bcl-2 ratio and the suppression of Caspase-3 activity after IRI. Importantly, all the beneficial effects of OLE in the vehicle group were abrogated by PI3K inhibitor LY294002. CONCLUSIONS Cerebral ischemia was protected by OLE via suppressing apoptosis through the Akt/GSK-3β pathway and upregulating neurotrophic factor after IRI.