New views and possibilities of antidiabetic drugs in treating and/or preventing mild cognitive impairment and Alzheimer's Disease

Metformin Prevents NDEA-Induced Memory Impairments Associated with Attenuating Beta-Amyloid, Tumor Necrosis Factor-Alpha, and Interleukin-6 Levels in the Hippocampus of Rats

N-nitrosodiethylamine (NDEA) is a potential carcinogen known to cause liver tumors and chronic inflammation, diabetes, cognitive problems, and signs like Alzheimer's disease (AD) in animals. This compound is classified as probably carcinogenic to humans. Usual sources of exposure include food, beer, tobacco, personal care products, water, and medications. AD is characterized by cognitive decline, amyloid-β (Aβ) deposit, tau hyperphosphorylation, and cell loss. This is accompanied by neuroinflammation, which involves release of microglial cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin 1β (IL-1β), by nuclear factor kappa B (NF-κB) upregulation; each are linked to AD progression. Weak PI3K/Akt insulin-signaling inhibits IRS-1 phosphorylation, activates GSK3β and promotes tau hyperphosphorylation. Metformin, an antihyperglycemic agent, has potent anti-inflammatory efficacy. It reduces proinflammatory cytokines such as IL-6, IL-1β, and TNF-α via NF-κB inhibition. Metformin also reduces reactive oxidative species (ROS) and modulates cognitive disorders reported due to brain insulin resistance links. Our study examined how NDEA affects spatial memory in Wistar rats. We found that all NDEA doses tested impaired memory. The 80 µg/kg dose of NDEA increased levels of Aβ1-42, TNF-α, and IL-6 in the hippocampus, which correlated with memory loss. Nonetheless, treatment with 100 mg/kg of metformin attenuated the levels of pro-inflammatory cytokines and Aβ1-42, and enhanced memory. It suggests that metformin may protect against NDEA-triggered memory issues and brain inflammation.

Angiotensin II Receptor Blockers Reduce Tau/Aß42 Ratio: A Cerebrospinal Fluid Biomarkers’ Case-Control Study

(1) Background: The role of antihypertensives in Alzheimer’s Disease (AD) prevention is controversial. This case-control study aims to assess whether antihypertensive medication has a protective role by studying its association with amyloid and tau abnormal levels. Furthermore, it suggests a holistic view of the involved pathways between renin-angiotensin drugs and the tau/amyloidß42 ratio (tau/Aß42 ratio); (2) Methods: The medical records of the participant patients were reviewed, with a focus on prescribed antihypertensive drugs and clinical variables, such as arterial blood pressure. The Anatomical Therapeutic Chemical classification was used to classify each drug. The patients were divided into two groups: patients with AD diagnosis (cases) and cognitively healthy patients (control); (3) Results: Age and high systolic blood pressure are associated with a higher risk of developing AD. In addition, combinations of angiotensin II receptor blockers are associated with a 30% lower t-tau/Aß42 ratio than plain angiotensin-converting enzyme inhibitor consumption; (4) Conclusions: Angiotensin II receptor blockers may play a potential role in neuroprotection and AD prevention. Likewise, several mechanisms, such as the PI3K/Akt/GSK3ß or the ACE1/AngII/AT1R axis, may link cardiovascular pathologies and AD presence, making its modulation a pivotal point in AD prevention. The present work highlights the central pathways in which antihypertensives may affect the presence of pathological amyloid and tau hyperphosphorylation.

Repositioning of antidiabetic drugs for Alzheimer's disease: possibility of Wnt signaling modulation by targeting LRP6 an in silico based study

Alzheimer disease (AD) is the most common, irreversible and progressive form of dementia for which the exact pathology and cause are still not clear. At present, we are only confined to symptomatic treatment, and the lack of disease-modifying therapeutics is worrisome. Alteration of Wnt signaling has been linked to metabolic diseases as well as AD. The crosstalk between Canonical Wnt signaling and insulin signaling pathway has been widely studied and accepted from several clinical and preclinical studies that have proven the beneficial effect of antidiabetic medications in the case of memory and cognition loss. This structure-based in silico study was focused on exploring the link between the currently available FDA approved antidiabetic drugs and the Wnt signaling pathway. The library of antidiabetics was obtained from drug bank and was screened for their binding affinity with protein (PDB ID: 3S2K) LRP6, a coreceptor of the Wnt signaling pathway using GLIDE module of Schrodinger. The top molecules, with higher docking score, binding energy and stable interactions, were subjected to energy-based calculation using MMGBSA, followed by a molecular dynamics-based simulation study. Drugs of class α-glucosidase inhibitors and peroxisome proliferator-activated receptors (PPARs) agonists were found to have a strong affinity towards LRP6 proteins, highlighting the possibility of the modulation of Wnt signaling by antidiabetics as one of the possible mechanisms for use in AD. However, further experimental based in vitro and in vivo studies are warranted for verification and support.Communicated by Ramaswamy H. Sarma.

Metabolic Syndrome, Cognitive Impairment and the Role of Diet: A Narrative Review

Background: This narrative review presents the association between metabolic syndrome (MetS), along with its components, and cognition-related disorders, as well as the potential reversal role of diet against cognitive impairment by modulating MetS. Methods: An electronic research in Medline (Pubmed) and Scopus was conducted. Results: MetS and cognitive decline share common cardiometabolic pathways as MetS components can trigger cognitive impairment. On the other side, the risk factors for both MetS and cognitive impairment can be reduced by optimizing the nutritional intake. Clinical manifestations such as dyslipidemia, hypertension, diabetes and increased central body adiposity are nutrition-related risk factors present during the prodromal period before cognitive impairment. The Mediterranean dietary pattern stands among the most discussed predominantly plant-based diets in relation to cardiometabolic disorders that may prevent dementia, Alzheimer’s disease and other cognition-related disorders. In addition, accumulating evidence suggests that the consumption of specific dietary food groups as a part of the overall diet can improve cognitive outcomes, maybe due to their involvement in cardiometabolic paths. Conclusions: Early MetS detection may be helpful to prevent or delay cognitive decline. Moreover, this review highlights the importance of healthy nutritional habits to reverse such conditions and the urgency of early lifestyle interventions.

A Tale of Two Diseases: Exploring Mechanisms Linking Diabetes Mellitus with Alzheimer's Disease

Dementias, including the type associated with Alzheimer's disease (AD), are on the rise worldwide. Similarly, type 2 diabetes mellitus (T2DM) is one of the most prevalent chronic diseases globally. Although mechanisms and treatments are well-established for T2DM, there remains much to be discovered. Recent research efforts have further investigated factors involved in the etiology of AD. Previously perceived to be unrelated diseases, commonalities between T2DM and AD have more recently been observed. As a result, AD has been labeled as "type 3 diabetes". In this review, we detail the shared processes that contribute to these two diseases. Insulin resistance, the main component of the pathogenesis of T2DM, is also present in AD, causing impaired brain glucose metabolism, neurodegeneration, and cognitive impairment. Dysregulation of insulin receptors and components of the insulin signaling pathway, including protein kinase B, glycogen synthase kinase 3β, and mammalian target of rapamycin are reported in both diseases. T2DM and AD also show evidence of inflammation, oxidative stress, mitochondrial dysfunction, advanced glycation end products, and amyloid deposition. The impact that changes in neurovascular structure and genetics have on the development of these conditions is also being examined. With the discovery of factors contributing to AD, innovative treatment approaches are being explored. Investigators are evaluating the efficacy of various T2DM medications for possible use in AD, including but not limited to glucagon-like peptide-1 receptor agonists, and peroxisome proliferator-activated receptor-gamma agonists. Furthermore, there are 136 active trials involving 121 therapeutic agents targeting novel AD biomarkers. With these efforts, we are one step closer to alleviating the ravaging impact of AD on our communities.

Therapeutic Potential of Phytoconstituents in Management of Alzheimer's Disease

Since primitive times, herbs have been extensively used in conventional remedies for boosting cognitive impairment and age-associated memory loss. It is mentioned that medicinal plants have a variety of dynamic components, and they have become a prominent choice for synthetic medications for the care of cognitive and associated disorders. Herbal remedies have played a major role in the progression of medicine, and many advanced drugs have already been developed. Many studies have endorsed practicing herbal remedies with phytoconstituents, for healing Alzheimer's disease (AD). All the information in this article was collated from selected research papers from online scientific databases, such as PubMed, Web of Science, and Scopus. The aim of this article is to convey the potential of herbal remedies for the prospect management of Alzheimer's and related diseases. Herbal remedies may be useful in the discovery and advancement of drugs, thus extending new leads for neurodegenerative diseases such as AD. Nanocarriers play a significant role in delivering herbal medicaments to a specific target. Therefore, many drugs have been described for the management of age-linked complaints such as dementia, AD, and the like. Several phytochemicals are capable of managing AD, but their therapeutic claims are restricted due to their lower solubility and metabolism. These limitations of natural therapeutics can be overcome by using a targeted nanocarrier system. This article will provide the primitive remedies as well as the development of herbal remedies for AD management.

The effects of dipeptidyl peptidase-4 inhibitors and glucagon-like peptide 1 receptor agonists on cognitive functions in adults with type 2 diabetes mellitus: a systematic review and meta-analysis

AIMS

The effects of dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors/DPP-4I) and glucagon-like peptide 1 receptor agonists (GLP-1 RA) on cognition in patients with type 2 diabetes mellitus (T2DM) remain controversial. We aimed to explore this clinical issue through a systematic review and meta-analysis.

METHODS

PubMed, EMBASE and the Cochrane Library were searched, and data were expressed as mean difference (MD) or hazard ratio (HR)/odds ratio (OR) with a 95% confidence interval (CI). Heterogeneity was assessed using the Chi-squared test and the I² statistic. The study was registered with PROSPERO (ID: CRD42019138777).

RESULTS

Eleven studies (n = 304,258 T2DM patients) were included in our review. In the DPP-4I group, six studies were enrolled to estimate ΔMini-Mental State Examination (MMSE) scores from baseline to the final evaluations after DPP-4I treatment, which showed no statistical difference (MD 0.20; 95% CI - 0.75 to 1.15, p = 0.68). ΔMMSE scores in the DPP-4I group and the other antidiabetic groups were compared, revealing no statistical difference (MD 0.57; 95% CI - 0.05 to 1.19, p = 0.07). Two cohort studies were pooled to determine the HRs for dementia, showing a lower risk of dementia after DPP-4I treatment (HR 0.52; 95% CI 0.29-0.93, p = 0.03). In the GLP-1 analogs group, two studies were included, one of which revealed a downward trend in the risk of dementia after GLP-1 analog treatment, while the other revealed no significant difference after incretins treatment.

CONCLUSIONS

Currently there is not enough irrefutable evidence to support the hypothesis of positive effects of incretins on cognition. Further clinical studies need to be performed.

Repositioning medication for cardiovascular and cerebrovascular disease to delay the onset and prevent progression of Alzheimer's disease

Alzheimer's disease (AD) is a complex, progressive, neurodegenerative disorder. As with other common chronic diseases, multiple risk factors contribute to the onset and progression of AD. Many researchers have evaluated the epidemiologic and pathophysiological association between AD, cardiovascular diseases (CVDs), and cerebrovascular diseases (CBVDs), including commonly reported risk factors such as diabetes, hypertension, and dyslipidemia. Relevant therapies of CVDs/CBVDs for the attenuation of AD have also been empirically investigated. Considering the challenges of new drug development, in terms of cost and time, multifactorial approaches such as therapeutic repositioning of CVD/CBVD medication should be explored to delay the onset and progression of AD. Thus, in this review, we discuss our current understanding of the association between cardiovascular risk factors and AD, as revealed by clinical and non-clinical studies, as well as the therapeutic implications of CVD/CBVD medication that may attenuate AD. Furthermore, we discuss future directions by evaluating ongoing trials in the field.

5-lipoxygenase pathway and its downstream cysteinyl leukotrienes as potential therapeutic targets for Alzheimer's disease

5-lipoxygenase (ALOX5) is an enzyme involved in arachidonic acid (AA) metabolism, a metabolic pathway in which cysteinyl leukotrienes (CysLTs) are the resultant metabolites. Both ALOX5 and CysLTs are clinically significant in a number of inflammatory diseases, such as in asthma and allergic rhinitis, and drugs antagonizing the effect of these molecules have long been successfully used to counter these diseases. Interestingly, recent advances in 'neuroinflammation' research has led to the discovery of several novel inflammatory pathways regulating many cerebral pathologies, including the ALOX5 pathway. By means of pharmacological and genetic studies, both ALOX5 and CysLTs receptors have been shown to be involved in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative/neurological diseases, such as in Parkinson's disease, multiple sclerosis, and epilepsy. In both transgenic and sporadic models of AD, it has been shown that the levels of ALOX5/CysLTs are elevated, and that genetic/pharmacological interventions of these molecules can alleviate AD-related behavioral and pathological conditions. Clinical relevance of these molecules has also been found in AD brain samples. In this review, we aim to summarize such important findings on the role of ALOX5/CysLTs in AD pathophysiology, from both the cellular and the molecular aspects, and also discuss the potential of their blockers as possible therapeutic choices to curb AD-related conditions.

Combination Drug Therapy for the Management of Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of dementia worldwide. Even though the number of AD patients is rapidly growing, there is no effective treatment for this neurodegenerative disorder. At present, implementation of effective treatment approaches for AD is vital to meet clinical needs. In AD research, priorities concern the development of disease-modifying therapeutic agents to be used in the early phases of AD and the optimization of the symptomatic treatments predominantly dedicated to the more advanced AD stages. Until now, available therapeutic agents for AD treatment only provide symptomatic treatment. Since AD pathogenesis is multifactorial, use of a multimodal therapeutic intervention addressing several molecular targets of AD-related pathological processes seems to be the most practical approach to modify the course of AD progression. It has been demonstrated through numerous studies, that the clinical efficacy of combination therapy (CT) is higher than that of monotherapy. In case of AD, CT is more effective, mostly when started early, at slowing the rate of cognitive impairment. In this review, we have covered the major studies regarding CT to combat AD pathogenesis. Moreover, we have also highlighted the safety, tolerability, and efficacy of CT in the treatment of AD.

Metformin Promotes Anxiolytic and Antidepressant-Like Responses in Insulin-Resistant Mice by Decreasing Circulating Branched-Chain Amino Acids

Epidemiological studies indicate that insulin resistance (IR), a hallmark of type 2 diabetes, is associated with an increased risk of major depression. Here, we demonstrated that male mice fed a high-fat diet (HFD) exhibited peripheral metabolic impairments reminiscent of IR accompanied by elevated circulating levels of branched-chain amino acids (BCAAs), whereas both parameters were normalized by chronic treatment with metformin (Met). Given the role of BCAAs in the regulation of tryptophan influx into the brain, we then explored the activity of the serotonin (5-HT) system. Our results indicated that HFD-fed mice displayed impairment in the electrical activity of dorsal raphe 5-HT neurons, attenuated hippocampal extracellular 5-HT concentrations and anxiety, one of the most visible and early symptoms of depression. On the contrary, Met stimulated 5-HT neurons excitability and 5-HT neurotransmission while hindering HFD-induced anxiety. Met also promoted antidepressant-like activities as observed with fluoxetine. In light of these data, we designed a modified HFD in which BCAA dietary supply was reduced by half. Deficiency in BCAAs failed to reverse HFD-induced metabolic impairments while producing antidepressant-like activity and enhancing the behavioral response to fluoxetine. Our results suggest that Met may act by decreasing circulating BCAAs levels to favor serotonergic neurotransmission in the hippocampus and promote antidepressant-like effects in mice fed an HFD. These findings also lead us to envision that a diet poor in BCAAs, provided either alone or as add-on therapy to conventional antidepressant drugs, could help to relieve depressive symptoms in patients with metabolic comorbidities.SIGNIFICANCE STATEMENT Insulin resistance in humans is associated with increased risk of anxiodepressive disorders. Such a relationship has been also found in rodents fed a high-fat diet (HFD). To determine whether insulin-sensitizing strategies induce anxiolytic- and/or antidepressant-like activities and to investigate the underlying mechanisms, we tested the effects of metformin, an oral antidiabetic drug, in mice fed an HFD. Metformin reduced levels of circulating branched-chain amino acids, which regulate tryptophan uptake within the brain. Moreover, metformin increased hippocampal serotonergic neurotransmission while promoting anxiolytic- and antidepressant-like effects. Moreover, a diet poor in these amino acids produced similar beneficial behavioral property. Collectively, these results suggest that metformin could be used as add-on therapy to a conventional antidepressant for the comorbidity between metabolic and mental disorders.

A Review and Hypothesized Model of the Mechanisms That Underpin the Relationship Between Inflammation and Cognition in the Elderly

Age is associated with increased risk for several disorders including dementias, cardiovascular disease, atherosclerosis, obesity, and diabetes. Age is also associated with cognitive decline particularly in cognitive domains associated with memory and processing speed. With increasing life expectancies in many countries, the number of people experiencing age-associated cognitive impairment is increasing and therefore from both economic and social terms the amelioration or slowing of cognitive aging is an important target for future research. However, the biological causes of age associated cognitive decline are not yet, well understood. In the current review, we outline the role of inflammation in cognitive aging and describe the role of several inflammatory processes, including inflamm-aging, vascular inflammation, and neuroinflammation which have both direct effect on brain function and indirect effects on brain function via changes in cardiovascular function.