Effect of thiazolidinediones and insulin on cognitive outcomes in ACCORD-MIND

Anti-diabetics and the Prevention of Dementia: A Systematic Review

Type 2 diabetes mellitus (T2DM) is a worldwide epidemic that is only increasing as the years progress, and as of 2019, affecting over 37 million. T2DM is a chronic condition caused by reduced insulin secretion and increased insulin resistance. Due to insulin not operating at optimal conditions, blood glucose rises and remains high, thus disturbing metabolic hemostasis. Many complications can arise from T2DM, such as coronary vascular disease, kidney damage, eye damage, and, quite significantly, dementia. It is theorized that dementia from T2DM stems from the fact that the brain is susceptible to hyperglycemic conditions, which are promoted by the increase in insulin resistance of target cells in the central nervous system. This directly affects cognitive processes and memory, which correlates to decreased temporal and front lobes volume. The risk of diabetic complications can be minimized with therapeutic interventions such as oral-antidiabetic (OAD) agents and insulin. Several OADs are on the market, but the first-line agent is metformin, a biguanide that decreases glucose production and increases insulin sensitivity. This paper aims to determine if currently prescribed OADs can help slow cognitive decline and reduce the risk and incidence of dementia as a complication of T2DM. Studies found that, for the most part, all OADs except sulfonylureas (SU) significantly slowed the decline of cognitive function and reduced the risk and incidence of dementia. SU's were shown to increase the risk of dementia in most studies. Of all the OADs, thiazolidinediones may be the most beneficial drug class for reducing the risk of dementia in T2DM patients. Future research should focus on whether early intervention with specific classes of OADs can not only improve glycemic control, leading to decreased hyperglycemia but also prevent the build-up of damaged brain tissue and help to reduce the risk and incidence of dementia in patients with T2DM.

Drug Repositioning of Pioglitazone in Management and Improving the Cognitive Function among the Patients With Mild to Moderate Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background

Disease-modifying agents like Pioglitazone have shown promising effects on neuroinflammation and homeostasis of amyloid plaques, but there is a lack of research papers providing conclusive evidence.

Objectives

This study is aimed to determine the safety and efficacy of Pioglitazone in improving cognitive function in patients with mild-moderate Alzheimer's disease (AD).

Materials and Methods

Trials published in the last 12 years were identified from PubMed, Scopus, Cochrane Central, and other trial registries. Five hundred twenty-five records were obtained, from which five studies were included for quantitative analysis. Studies comparing Pioglitazone with a suitable placebo or other oral hypoglycemic agent were considered for review. Data was extracted using a pretested form, which was followed by a risk of bias assessment (ROB) with Cochrane's ROB assessment tool.

Results

This meta-analysis included studies where Pioglitazone (15-30 mg) was compared to other oral hypoglycemic agents, placebo, or diabetic diet for a minimum duration of 6 months. Pioglitazone did not show a statistically significant improvement in Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) scores [mean difference (MD): -1.16; 95% confidence interval (CI): -4.14-1.81]. By conducting sensitivity analysis with the removal of one study, significant efficacy was obtained [MD: -2.75; 95% CI: -4.84--0.66]. The Wechsler Memory Scale-Revised logical memory I (WMS-R) scores had a significant improvement in the Pioglitazone group [MD: 2.02; 95% CI: 0.09-3.95].

Conclusion

Pioglitazone is a safe medication that has a promising effect in slowing the advancement of AD.

Glucose-lowering drugs, cognition, and dementia: The clinical evidence

Type 2 diabetes mellitus (T2DM) is an important risk factor for dementia. The possibility to mitigate this risk by controlling T2DM is compelling; however, different glucose-lowering drugs have different effects on the brain by virtue of their different mechanisms of action. The clinical and epidemiological data appear mixed, warranting careful critical evaluation of the human studies. Here we examine the evidence in the context of dementia prevention and treatment, both for people with and without T2DM. We discuss the evidence on this scaffold of research directions, identifying methodological complexities in the extant literature (e.g. comparator discrepancies, changes in the therapeutic landscape), and the implications of different outcome measures (e.g. neuropsychological). We consider possible implications of cerebrovascular protection vs. effects on progression of neurodegenerative proteinopathy, and we present a research roadmap for glucose-lowering drugs in cognitive neurology, including neuroimaging, and fluid biomarkers. We conclude that there is great potential to advance personalized strategies to prevent and treat dementia with glucose-lowering drugs.

Expert Consensus on Cognitive Dysfunction in Diabetes

The incidence of diabetes is gradually increasing in China, and diabetes and associated complications, such as cognitive dysfunction have gained much attention in recent time. However, the concepts, clinical treatment, and prevention of cognitive dysfunction in patients with diabetes remain unclear. The Chinese Society of Endocrinology investigated the current national and overseas situation of cognitive dysfunction associated with diabetes. Based on research both in China and other countries worldwide, the Expert Consensus on Cognitive Dysfunction in Diabetes was established to guide physicians in the comprehensive standardized management of cognitive dysfunction in diabetes and to improve clinical outcomes in Chinese patients. This consensus presents an overview, definition and classification, epidemiology and pathogenesis, risk factors, screening, diagnosis, differential diagnosis, treatment, and prevention of cognitive dysfunction in patients with diabetes.

Relationships between memory decline and the use of metformin or DPP4 inhibitors in people with type 2 diabetes with normal cognition or Alzheimer's disease, and the role APOE carrier status

INTRODUCTION

Few studies have examined memory decline among patients with type 2 diabetes using different oral hypoglycemic drugs.

METHODS

Participants with normal cognition (NC) or Alzheimer's disease (AD) dementia using a hypoglycemic medication (2005 to 2019) were identified from the National Alzheimer's Coordinating Center database. Delayed memory was assessed using the Wechsler Memory Scale Revised-Logical Memory test. Associations between oral drug classes and memory over time were examined using mixed-effects models with inverse probability treatment weights.

RESULTS

In NC (n = 1192), metformin use was associated with better memory performance over time, whereas in AD (n = 807), dipeptidyl peptidase-4 (DPP4) inhibitor use was associated with a slower rate of memory decline. Interaction effects suggested greater benefit associated with DPP4 inhibitor use among APOE ε4 carriers.

DISCUSSION

Associations between different oral hypoglycemic drugs and memory change were not consistent between cognitively normal elderly and those with AD dementia. APOE ε4 genotype modified some relationships.

Clinical Evidence of Antidepressant Effects of Insulin and Anti-Hyperglycemic Agents and Implications for the Pathophysiology of Depression-A Literature Review

Close connections between depression and type 2 diabetes (T2DM) have been suggested by many epidemiological and experimental studies. Disturbances in insulin sensitivity due to the disruption of various molecular pathways cause insulin resistance, which underpins many metabolic disorders, including diabetes, as well as depression. Several anti-hyperglycemic agents have demonstrated antidepressant properties in clinical trials, probably due to their action on brain targets based on the shared pathophysiology of depression and T2DM. In this article, we review reports of clinical trials examining the antidepressant effect of these medications, including insulin, metformin, glucagon like peptide-1 receptor agonists (GLP-1RA), and peroxisome proliferator-activated receptor (PPAR)-γ agonists, and briefly consider possible molecular mechanisms underlying the associations between amelioration of insulin resistance and improvement of depressive symptoms. In doing so, we intend to suggest an integrative perspective for understanding the pathophysiology of depression.

Neuromodulatory effects of anti-diabetes medications: A mechanistic review

Diabetes mellitus is a potent upstream event in the molecular pathophysiology which gives rise to various diabetes-related complications. There are several classes of anti-diabetic medications that have been developed to normalize blood glucose concentrations through a variety of molecular mechanisms. Beyond glucose-lowering effects, these agents may also provide further therapeutic potential. For instance, there is a high incidence of diabetes-induced neuronal disorders among patients with diabetes, who may also develop neurodegenerative and psychological complications. If anti-diabetic agents can modify the molecular mechanisms involved in the pathophysiology of neuronal comorbidities, this could potentially be translated to reducing the risk of other neurological conditions such as Alzheimer's disease, Parkinson's disease, depression, memory deficits and cognition impairments among patients with diabetes. This review aimed to shed light on some of the potentially beneficial aspects of anti-diabetic agents in lowering the risk or treating neuronal disorders by reviewing the molecular mechanisms by which these agents can potentially modulate neuronal behaviors.

Therapeutic Strategies for Alzheimer's Disease in the View of Diabetes Mellitus

Recently, Alzheimer's disease (AD) is understood as "diabetes of the brain" or "type 3 diabetes." Recent clinical trials of anti-amyloid β-protein (Aβ) therapies have not proved to be successful. Thus, glucose-insulin metabolism in the brain is thought to be an alternative therapeutic target. Various types of antidiabetic drugs such as insulin, thiazolidinediones, dipeptidyl peptidase-4 (DPP4) inhibitors, glucagon-like peptide-1 (GLP-1) agonists, biguanides, and others have been reported to be effective on cognitive impairment in animal models and patients with DM or AD. Here, recent reports are reviewed. While we identified apomorphine (APO) as a novel drug that promoted intracellular Aβ degradation and improved memory function in an AD mouse model, more recently, we have revealed that APO treatment improves neuronal insulin resistance and activates insulin-degrading enzyme (IDE), a major Aβ-degrading enzyme. In this context, recovery of impaired insulin signaling in AD neurons may be a promising therapeutic strategy for AD dementia.

Probucol prevents blood-brain barrier dysfunction and cognitive decline in mice maintained on pro-diabetic diet

An emerging body of evidence consistently suggests that compromised blood-brain barrier integrity may be causally associated with cognitive decline induced by type-2 diabetes. Our previous studies demonstrated that selected anti-inflammatory/anti-oxidative agents can preserve the integrity of blood-brain barrier and prevent neuroinflammation in mouse models of dysfunctional blood-brain barrier. Therefore, we have tested whether the previously proven blood-brain barrier protective agent, probucol, can prevent blood-brain barrier breakdown and cognitive decline in a dietary-induced murine model of diabetic insulin resistance. After 6-month chronic ingestion of a diet high in fat and fructose, the mice became insulin resistant. The high-fat and high-fructose-fed mice showed significant cognitive decline assessed by Morris water maze, concomitant with significant elevations in cortical and hippocampal glial acidic fibrillary protein and Fluoro Jade-C staining, indicating heightened neuroinflammation and neurodegeneration, respectively. The integrity of blood-brain barrier in high-fat and high-fructose-fed mice was substantially compromised, and this showed a significant association with heightened neurodegeneration. Co-provision of probucol with high-fat and high-fructose diet completely prevented the cognitive decline and blood-brain barrier dysfunction. Similarly, metformin was able to restore the cognitive function in high-fat and high-fructose-fed mice, while its blood-brain barrier protective effects were modest. These data suggest that probucol may prevent cognitive decline induced by insulin resistance by preserving the integrity of blood-brain barrier, whereas metformin's neuroprotective effects may be mediated through a separate pathway.

Cognitive impairment in patients with type 2 diabetes mellitus: prevalence, pathogenetic mechanisms, the effect of antidiabetic drugs

In recent years, a large amount of data has been accumulated on the relationship between cognitive impairment, dementia and diabetes mellitus. This article presents an overview of modern literature, including the definition of cognitive functions, the modern classification of cognitive impairment, pathogenetic mechanisms of diabetes mellitus influence on the development of cognitive impairment and dementia (neurogenesis, integrity of the blood-brain barrier, systemic inflammatory reactions, hyper- and hypoglycemia, insulin resistance, vascular dysfunction of the microvasculature and increase in glucocorticosteroids). The influence of anti-diabetic medications on cognitive functions has been examined in detail: insulin preparations, oral hypoglycemic agents of the biguanide group (metformin), thiazolidinediones (rosiglitazone and pioglitazone), sulfonylurea derivatives (glycazide, glipizide), a-glucosidase (acarbose) inhibitors, incretin-directed therapy (receptor agonists glucan-like peptide (exenatide and liraglutide) and inhibitors of dipeptidylpeptidase type 4 (sitagliptin, vildagliptin and alogliptin)), sodium glucose inhibitors cotransporter type 2. The data demonstrating a multidirectional effect on the cognitive functions of various antidiabetic drugs is presented, the possible influence on the rate of progression of cognitive impairment and the risk of dementia of intensive control of plasma glucose level in comparison with the standard decrease in patients with type 2 diabetes is analyzed.

[Treatment of type 2 diabetes mellitus in elderly patients]

The prevalence of type 2 diabetes mellitus (DM2) increases markedly with age. Antidiabetic treatment and the objectives of glycaemic control in elderly patients with DM2 should be individualised according to their biopsychosocial characteristics. In elderly patients for whom the benefits of intensive antidiabetic treatment are limited, the basic objectives should be to improve the quality of life, preserve functionality and avoid adverse effects, especially hypoglycaemia. Treatment of DM2 in the elderly was the subject of a consensus document published in 2012 and endorsed by several Spanish scientific societies. Since then, new therapeutic groups and evidence have emerged that warrant an update to this consensus document. The present document focuses on the therapeutic aspects of DM2 in elderly patients, understood as being older than 75 years or frail.

Treatment of type 2 diabetes mellitus in elderly patients

The prevalence of type 2 diabetes mellitus (DM2) increases markedly with age. Antidiabetic treatment and the objectives of glycaemic control in elderly patients with DM2 should be individualised according to their biopsychosocial characteristics. In elderly patients for whom the benefits of intensive antidiabetic treatment are limited, the basic objectives should be to improve the quality of life, preserve functionality and avoid adverse effects, especially hypoglycaemia. Treatment of DM2 in the elderly was the subject of a consensus document published in 2012 and endorsed by several Spanish scientific societies. Since then, new therapeutic groups and evidence have emerged that warrant an update to this consensus document. The present document focuses on the therapeutic aspects of DM2 in elderly patients, understood as being older than 75 years or frail.

Effects of pioglitazone on cognitive function in patients with a recent ischaemic stroke or TIA: a report from the IRIS trial

INTRODUCTION

Patients with cerebrovascular disease are at increased risk for cognitive dysfunction. Modification of vascular risk factors, including insulin resistance, could improve poststroke cognitive function.

METHODS

In the Insulin Resistance Intervention after Stroke (IRIS) trial, patients with a recent ischaemic stroke or transient ischaemic attack (TIA) were randomised to pioglitazone (target 45 mg daily) or placebo. All patients were insulin resistant based on a Homeostasis Model Assessment-Insulin Resistance score >3.0. For this preplanned analysis of cognitive function, we examined the Modified Mini-Mental State Examination (3MS) score (maximum score, 100) during follow-up. Patients were tested at baseline and annually for up to 5 years. Longitudinal mixed model methods were used to compare changes in the 3MS over time.

RESULTS

Of the 3876 IRIS participants, 3398 had a 3MS score at baseline and at least once during follow-up and were included in the analysis. Median 3MS score at baseline was 97 (IQR 93-99). The average overall least squared mean 3MS score increased by 0.27 in the pioglitazone group and by 0.29 in the placebo group (mean difference between treatment groups -0.02; 95% CI -0.33 to 0.28, p=0.88).

CONCLUSIONS

Among insulin-resistant patients with a recent ischaemic stroke or TIA, pioglitazone did not affect cognitive function, as measured by the 3MS, over 5 years.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00091949; Results.

Vascular Contributions to Cognitive Impairment in Late Life

Cerebrovascular disease (CVD) is the second leading cause of cognitive impairment in late life. Structural neuroimaging offers the most sensitive and specific biomarkers for hemorrhages and infarcts, but there are significant limitations in its ability to detect microvascular disease, microinfarcts, dynamic changes in the blood-brain barrier, and preclinical cerebrovascular disease. Autopsy studies disclose the common co-occurrence of vascular and neurodegenerative conditions, suggesting that in late life, a multifactorial approach to cognitive impairment may be more appropriate than traditional dichotomous classifications. Management of vascular risk factors remains a proven and practical approach to reducing acute and progressive cognitive impairment and dementia.

The impact of diabetes on cognitive decline: potential vascular, metabolic, and psychosocial risk factors

Older people with type 2 diabetes are at increased risk of developing cognitive impairment, for which several potential risk factors have been proposed. The present article reviews evidence in people with type 2 diabetes for associations of cognitive impairment with a range of vascular, metabolic, and psychosocial risk factors, many of which have a higher prevalence in people with type 2 diabetes than in non-diabetic adults of a similar age. Definitive research studies in this field are few in number. The risk factors may be involved in causal pathways or may act as useful markers of cerebrovascular damage (or both), and for which relatively consistent evidence is available, include poor glycemic control, hypoglycemia, microvascular disease, inflammation, and depression. For macrovascular disease, the strength of the association with cognitive impairment appears to depend on which vascular system has been examined. A role for pre-morbid ability in young adulthood as influencing the risk of both diabetes and cognitive impairment has also been suggested. The importance of considering inter-relationships between risk factors when investigating their potential contribution to cognitive impairment in future investigations is discussed.

Glucose regulation, cognition, and brain MRI in type 2 diabetes: a systematic review

Type 2 diabetes is associated with cognitive dysfunction and structural brain changes. Abnormalities in glucose regulation are involved in several complications related to type 2 diabetes, but their role in these cerebral complications is unclear. We systematically reviewed studies of the association between glucose regulation (glycaemia, hypoglycaemic events, insulin concentration, insulin resistance, and glucose-lowering treatment) and cognitive function and brain abnormalities on MRI in people with type 2 diabetes. The 86 papers included showed that glycaemia, particularly high HbA1c concentration and glucose variability, are negatively associated with cognitive function in people with type 2 diabetes without dementia. However, the strength of this association is weak, and HbA1c generally accounted for less than 10% of the variance in cognition. Importantly, few studies have measured long-term cerebral outcomes, such as dementia and structural brain changes on MRI, and the effect of glucose-lowering treatment on these outcomes. More randomised controlled trials are needed to establish the effect of glucose-lowering treatment on long-term cognitive function in people with type 2 diabetes.

Achieving glycemic control in elderly patients with type 2 diabetes: a critical comparison of current options

The prevalence of type 2 diabetes mellitus (T2DM) is increasing in the elderly. Because of the unique characteristics of elderly people with T2DM, therapeutic strategy and focus should be tailored to suit this population. This article reviews the guidelines and studies related to older people with T2DM worldwide. A few important themes are generalized: 1) the functional and cognitive status is critical for older people with T2DM considering their life expectancy compared to younger counterparts; 2) both severe hypoglycemia and persistent hyperglycemia are deleterious to older adults with T2DM, and both conditions should be avoided when determining therapeutic goals; 3) recently developed guidelines emphasize the avoidance of hypoglycemic episodes in older people, even in the absence of symptoms. In addition, we raise the concern of glycemic variability, and discuss the rationale for the selection of current options in managing this patient population.

Diabetes and the brain: issues and unmet needs

Diabetes mellitus (DM) is associated with an increased risk of mild cognitive impairment, dementia and stroke. The association between DM and dementia appears to be stronger for vascular cognitive impairment than for Alzheimer’s disease, suggesting cerebrovascular disease may be an important factor in cognitive impairment in DM. Although the exact mechanisms by which DM affects the brain remain unclear, changes to brain vasculature, disturbances of cerebral insulin signaling, insulin resistance, glucose toxicity, oxidative stress, accumulation of advanced glycation end products, hypoglycemic episodes, and alterations in amyloid metabolism may all be involved. Cognitive impairment and dementia associated with DM may also be mediated via vascular risk factors, in particular brain ischemia, the occurrence of which can have an additive or synergistic effect with concomitant neurodegenerative processes. To date, no drug has been approved for the treatment of vascular dementia and there are no specific pharmacological treatments for preventing or reducing cognitive decline in patients with DM. Most focus has been on tighter management of vascular risk factors, although evidence of reduced cognitive decline through reducing blood pressure, lipid-lowering or tighter glycemic control is inconclusive. Tailored, multimodal therapies may be required to reduce the risk of cognitive dysfunction and decline in patients with DM. The use of pleiotropic drugs with multimodal mechanisms of action (e.g., cerebrolysin, Actovegin) may have a role in the treatment of cognitive dysfunction and their use may warrant further investigation in diabetic populations.

The impact of glucose disorders on cognition and brain volumes in the elderly: the Sydney Memory and Ageing Study

Type 2 diabetes predicts accelerated cognitive decline and brain atrophy. We hypothesized that impaired fasting glucose (IFG) and incident glucose disorders have detrimental effects on global cognition and brain volume. We further hypothesized that metabolic and inflammatory derangements accompanying hyperglycaemia contribute to change in brain structure and function. This was a longitudinal study of a community-dwelling elderly cohort with neuropsychological testing (n = 880) and brain volumes by magnetic resonance imaging (n = 312) measured at baseline and 2 years. Primary outcomes were global cognition and total brain volume. Secondary outcomes were cognitive domains (processing speed, memory, language, visuospatial and executive function) and brain volumes (hippocampal, parahippocampal, precuneus and frontal lobe). Participants were categorised as normal, impaired fasting glucose at both assessments (stable IFG), baseline diabetes or incident glucose disorders (incident diabetes or IFG at 2 years). Measures included inflammatory cytokines and oxidative metabolites. Covariates were age, sex, education, non-English speaking background, smoking, blood pressure, lipid-lowering or antihypertensive medications, mood score, apolipoprotein E genotype and baseline cognition or brain volume. Participants with incident glucose disorders had greater decline in global cognition and visuospatial function compared to normal, similar to that observed in baseline diabetes. Homocysteine was independently associated with the observed effect of diabetes on executive function. Apolipoprotein E genotype did not influence the observed effects of diabetes on cognition. Incident glucose disorders and diabetes were also associated with greater 2-year decline in total brain volume, compared to normal (40.0 ± 4.2 vs. 46.7 ± 5.7 mm(3) vs. 18.1 ± 6.2, respectively, p < 0.005). Stable IFG did not show greater decline in global cognition or brain volumes compared to normal. Incident glucose disorders, like diabetes, are associated with accelerated decline in global cognition and brain volumes in non-demented elderly, whereas stable IFG is not. Preventing deterioration in glucose metabolism in the elderly may help preserve brain structure and function.

Diabetes drugs and neurological disorders: new views and therapeutic possibilities

Type 2 diabetes is a metabolic disease characterised by insulin resistance with hyperglycaemia and dyslipidaemia. It is associated with increased risk of stroke and vascular dementia, and might contribute to the development of Alzheimer's disease. Recent studies have shown that several antidiabetic drugs can promote neuronal survival and lead to a significant clinical improvement of memory and cognition in different clinical settings. We discuss these emerging data, with a focus on metformin, thiazolidinediones, and the more recently developed compounds targeting the glucagon-like peptide-1 receptor. Data show that these antidiabetic drugs affect brain metabolism, neuroinflammation, and regeneration. Evidence thus far strongly indicates that these antidiabetic drugs could be developed as disease-modifying therapies for human brain diseases in patients with and without diabetes.

Dementia and cognitive decline in type 2 diabetes and prediabetic stages: towards targeted interventions

Type 2 diabetes is associated with dementia, and also with more slight cognitive decrements. In this Review we discuss trajectories from normal cognition to dementia in people with type 2 diabetes, and explore opportunities for treatment. Slight diabetes-associated cognitive decrements and dementia affect different age groups and show a different evolution. These cognitive entities should therefore not be regarded as a continuum, although their effects might be additive. Vascular damage is a key underlying process in both entities. Glucose-mediated processes and other metabolic disturbances might also have a role. No treatment has been established, but management of vascular risk factors and optimisation of glycaemic control could have therapeutic benefit. We identify possible opportunities for intervention to improve cognitive outcomes in people with type 2 diabetes, and suggest how treatment can be tailored to individual risk profiles and comorbidities.