Association of Type 1 Diabetes and Hypoglycemic and Hyperglycemic Events and Risk of Dementia

Age-dependent impact of streptozotocin on metabolic endpoints and Alzheimer's disease pathologies in 3xTg-AD mice

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease with a complex origin, thought to involve a combination of genetic, biological and environmental factors. Insulin dysfunction has emerged as a potential factor contributing to AD pathogenesis, particularly in individuals with diabetes, and among those with insulin deficiency or undergoing insulin therapy. The intraperitoneal administration of streptozotocin (STZ) is widely used in rodent models to explore the impact of insulin deficiency on AD pathology, although prior research predominantly focused on young animals, with no comparative analysis across different age groups. Our study aimed to fill this gap by analyzing the impact of insulin dysfunction in 7 and 23 months 3xTg-AD mice, that exhibit both amyloid and tau pathologies. Our objective was to elucidate the age-specific consequences of insulin deficiency on AD pathology. STZ administration led to insulin deficiency in the younger mice, resulting in an increase in cortical amyloid-β (Aβ) and tau aggregation, while tau phosphorylation was not significantly affected. Conversely, older mice displayed an unexpected resilience to the peripheral metabolic impact of STZ, while exhibiting an increase in both tau phosphorylation and aggregation without significantly affecting amyloid pathology. These changes were paralleled with alterations in signaling pathways involving tau kinases and phosphatases. Several markers of blood-brain barrier (BBB) integrity declined with age in 3xTg-AD mice, which might have facilitated a direct neurotoxic effect of STZ in older mice. Overall, our research confirms the influence of insulin signaling dysfunction on AD pathology, but also advises careful interpretation of data related to STZ-induced effects in older animals.

Barriers and Facilitators of Self-Management in Older People with Type 1 Diabetes: A Narrative Review Focusing on Cognitive Impairment

Over the past decades, life expectancy of people with type 1 diabetes has increased considerably, which brings potential challenges due to the process of aging. Cognitive aging and dementia, as well as reductions in visual acuity, hearing and dexterity, can influence the frequency and quality of daily self-management activities, including medication taking and insulin dosing, glucose self-monitoring, and healthy eating. This can increase the risk for hypo- and hyperglycemic events, which, in turn, may contribute to cognitive decline. Because there is a gap in understanding the barriers and facilitators of self-management in older adults with type 1 diabetes and the relationship to cognitive functioning, the authors 1) review the available literature on cognitive aging and type 1 diabetes, 2) describe what self-management in later adulthood entails and the cognitive functions required for effective self-management behaviors, 3) analyze the interaction between type 1 diabetes, cognition, aging, and self-management behaviors, and 4) describe the barriers and facilitators for self-management throughout the life span and how they may differ for older people. Potential evidence-based practices that could be developed for older adults with type 1 diabetes are discussed. There is need for further studies that clarify the impact of aging on T1D self-management, ultimately to improve diabetes care and quality of life.

Risk factors associated with cognitive performance and cognitive impairment in older adults with type 1 diabetes: Data from the Wireless Innovation for Seniors with Diabetes Mellitus (WISDM) study

BACKGROUND

Adults with type 1 diabetes (T1D) are considered at increased risk for cognitive impairment and accelerated brain aging. However, longitudinal data on cognitive impairment and dementia in this population are scarce.

OBJECTIVE

To identify risk factors associated with cognitive performance and cognitive impairment in a longitudinal sample of older adults with T1D.

METHODS

We analyzed data collected as part of the Wireless Innovation for Seniors with Diabetes Mellitus (WISDM) Study, in which 22 endocrinology practices participated. Randomized participants with T1D ≥60 years of age who completed at least one cognitive assessment were included in this study (n = 203). Cognitive impairment was classified using published recommendations.

RESULTS

Older age, male sex, non-private health insurance, worse daily functioning, diagnosis of neuropathy, and longer duration of diabetes were associated with worse cognitive performance, but not cognitive impairment. 49 % and 39 % of the sample met criteria for cognitive impairment at baseline and 52 weeks respectively. Of the participants that had data at both time points, 10 % were normal at baseline and impaired at 52 weeks and 22 % of participants (44 % of those classified with cognitive impairment at baseline) reverted to normal over 52 weeks.

CONCLUSION

This study indicated that several demographic and clinical characteristics are associated with worse cognitive performance in older adults with T1D, but there were no associations between these characteristics and cognitive impairment defined by NIH Toolbox cognitive impairment criteria. Caution is warranted when assessing cognition in older adults with T1D, as a large percentage of those identified as having cognitive impairment at baseline reverted to normal after 52 weeks. There is need for future studies on the interrelationship of cognition and aging to better understand the effects of T1D on cognitive health, to improve clinical monitoring and help mitigate the risk of dementia in this population.

Causal relationships between type 1 diabetes mellitus and Alzheimer's disease and Parkinson's disease: a bidirectional two-sample Mendelian randomization study

BACKGROUND

Previous compelling evidence suggests an association between Type 2 diabetes (T2D) and neurodegenerative diseases. However, it remains uncertain whether Type 1 diabetes mellitus (T1DM) exerts a causal influence on the risk of Alzheimer's disease (AD) and Parkinson's disease (PD). Consequently, this study employed a bidirectional two-sample Mendelian Randomization (MR) approach to investigate the causal relationship between T1DM and the genetic susceptibility to AD and PD.

METHODS

We utilized large-scale cohorts derived from publicly available genome-wide association study datasets involving European populations to perform MR analyses. The primary analytical method employed was the inverse-variance weighted (IVW) approach. Furthermore, sensitivity analyses, including assessments of heterogeneity and horizontal pleiotropy, were carried out using Cochran's Q, MR-Egger intercept, and MR-PRESSO tests to enhance the robustness of our conclusions.

RESULTS

Using the IVW-based method, the MR analysis indicated no significant association between genetically determined T1DM and AD (OR = 0.984, 95% CI: 0.958-1.011, p = 0.247). Conversely, T1DM appeared to be associated with a reduced risk of genetic susceptibility to PD (IVW: OR = 0.958, 95% CI: 0.928-0.989, p = 0.001). In the reverse direction, no evidence of reverse causality was observed between AD (OR = 1.010, 95% CI: 0.911-1.116, p = 0.881) or PD (OR = 1.164, 95% CI: 0.686-2.025, p = 0.5202) and T1DM. Additionally, our analysis found no indications of the results being influenced by horizontal pleiotropy.

CONCLUSION

This MR study reveals that T1DM is associated with a reduced genetic susceptibility to PD, whereas no significant genetic susceptibility is observed between T1DM and AD. These findings suggest that T1DM may have a distinct role in the development of neurodegenerative diseases compared to T2D. Further investigations are warranted to elucidate the underlying mechanisms and provide a more comprehensive understanding of this relationship.

A Comprehensive Review of the Effects of Glycemic Carbohydrates on the Neurocognitive Functions Based on Gut Microenvironment Regulation and Glycemic Fluctuation Control

Improper glycemic carbohydrates (GCs) consumption can be a potential risk factor for metabolic diseases such as obesity and diabetes, which may lead to cognitive impairment. Although several potential mechanisms have been studied, the biological relationship between carbohydrate consumption and neurocognitive impairment is still uncertain. In this review, the main effects and mechanisms of GCs' digestive characteristics on cognitive functions are comprehensively elucidated. Additionally, healthier carbohydrate selection, a reliable research model, and future directions are discussed. Individuals in their early and late lives and patients with metabolic diseases are highly susceptible to dietary-induced cognitive impairment. It is well known that gut function is closely related to dietary patterns. Unhealthy carbohydrate diet-induced gut microenvironment disorders negatively impact cognitive functions through the gut-brain axis. Moreover, severe glycemic fluctuations, due to rapidly digestible carbohydrate consumption or metabolic diseases, can impair neurocognitive functions by disrupting glucose metabolism, dysregulating calcium homeostasis, oxidative stress, inflammatory responses, and accumulating advanced glycation end products. Unstable glycemic status can lead to more severe neurological impairment than persistent hyperglycemia. Slow-digested or resistant carbohydrates might contribute to better neurocognitive functions due to stable glycemic response and healthier gut functions than fully gelatinized starch and nutritive sugars.

SIRT3 ameliorates diabetes-associated cognitive dysfunction via regulating mitochondria-associated ER membranes

BACKGROUND

Diabetes is associated with an increased risk of cognitive decline and dementia. These diseases are linked with mitochondrial dysfunction, most likely as a consequence of excessive formation of mitochondria-associated membranes (MAMs). Sirtuin3 (SIRT3), a key mitochondrial NAD⁺-dependent deacetylase, is critical responsible for mitochondrial functional homeostasis and is highly associated with neuropathology. However, the role of SIRT3 in regulating MAM coupling remains unknown.

METHODS

Streptozotocin-injected diabetic mice and high glucose-treated SH-SY5Y cells were established as the animal and cellular models, respectively. SIRT3 expression was up-regulated in vivo using an adeno-associated virus in mouse hippocampus and in vitro using a recombinant lentivirus vector. Cognitive function was evaluated using behavioural tests. Hippocampus injury was assessed using Golgi and Nissl staining. Apoptosis was analysed using western blotting and TUNEL assay. Mitochondrial function was detected using flow cytometry and confocal fluorescence microscopy. The mechanisms were investigated using co-immunoprecipitation of VDAC1-GRP75-IP3R complex, fluorescence imaging of ER and mitochondrial co-localisation and transmission electron microscopy of structural analysis of MAMs.

RESULTS

Our results demonstrated that SIRT3 expression was significantly reduced in high glucose-treated SH-SY5Y cells and hippocampal tissues from diabetic mice. Further, up-regulating SIRT3 alleviated hippocampus injuries and cognitive impairment in diabetic mice and mitigated mitochondrial Ca²⁺ overload-induced mitochondrial dysfunction and apoptosis. Mechanistically, MAM formation was enhanced under high glucose conditions, which was reversed by genetic up-regulation of SIRT3 via reduced interaction of the VDAC1-GRP75-IP3R complex in vitro and in vivo. Furthermore, we investigated the therapeutic effects of pharmacological activation of SIRT3 in diabetic mice via honokiol treatment, which exhibited similar effects to our genetic interventions.

CONCLUSIONS

In summary, our findings suggest that SIRT3 ameliorates cognitive impairment in diabetic mice by limiting aberrant MAM formation. Furthermore, targeting the activation of SIRT3 by honokiol provides a promising therapeutic candidate for diabetes-associated cognitive dysfunction. Overall, our study suggests a novel role of SIRT3 in regulating MAM coupling and indicates that SIRT3-targeted therapies are promising for diabetic dementia patients.

Type 1 Diabetes and Aging

The number of older adults with type 1 diabetes (T1D) is increasing due to an overall increase in life expectancy and improvement in diabetes management and treatment of complications. They are a heterogeneous cohort due to the dynamic process of aging and the presence of comorbidities and diabetes-related complications. A high risk for hypoglycemia unawareness and severe hypoglycemia has been described. Periodic assessment of health status and adjustment of glycemic goals to mitigate hypoglycemia is imperative. Continuous glucose monitoring, insulin pump, and hybrid closed-loop systems are promising tools to improve glycemic control and mitigate hypoglycemia in this age group.

MoCA Intraindividual Cognitive Variability in Older Adults With Type 1 Diabetes

Older adults with type 1 diabetes (T1D) may have an elevated risk of developing Alzheimer disease and related dementia. Higher intraindividual cognitive variability (IICV) has been proposed as a novel risk factor of Alzheimer disease and related dementia. Here, we examined the association between cross-domain IICV measured using the Montreal Cognitive Assessment (MoCA) and cognitive impairment measured using traditional neuropsychological tests in older individuals with T1D. Participants with T1D (N=201) completed both the MoCA and a battery of traditional neuropsychological tests. Participants with cognitive impairment, determined using traditional tests, had significantly higher IICV scores and significantly lower total MoCA scores ( P <0.001). However, the effect of the total score was greater than that of the IICV score on the likelihood of cognitive impairment (total odds ratio=3.50, IICV odds ratio=2.03, P <0.001). The MoCA total score performed better than the MoCA IICV score in identifying T1D individuals classified with cognitive impairment.

The Correlation between Diabetes Mellitus and Neurodegenerative Diseases

Today there is no longer any doubt that diabetes mellitus is associated with cognitive impairment and neurodegenerative diseases. The two most common forms of diabetes mellitus are type 1 and type 2. Type 1 diabetes mellitus is characterized by an absolute insulin deficiency that is associated with a large number of metabolic changes. This type of diabetes requires insulin therapy. Without insulin, this disease is fatal. The far more common form of diabetes mellitus nowadays is type 2 diabetes mellitus. It is characterized by insulin resistance. For a number of years drugs have been available that can be used to treat this form of diabetes in a multimodal manner. These therapy options can not only improve metabolic control, but also prevent cardiovascular events. Different cognitive alterations associated with diabetes mellitus can be distinguished. On the one hand, the change in glucose homeostasis itself leads to cognitive alterations, i.e. blood sugar levels that are too high or acutely too low are regularly associated with significant impairments in mental performance, including loss of consciousness. But not only the momentary blood sugar levels, but also long-term changes in glucose metabolism might lead to neurodegeneration and even dementia in a way that has not yet been fully understood. Insulin or insulin-like molecules have important effects in the central nervous system. In the last decades, it has been shown that insulin receptors themselves are expressed in many regions of the brain and e.g. regulate food intake and memory formation in humans and in animal models. In the animal model, disturbances in insulin signal transduction influence the development of pathologies typical of Alzheimer's disease (AD). In humans, central insulin resistance is at least part of the formal pathogenesis of AD. Vascular changes (macroangiopathy) in patients with diabetes mellitus often lead to cerebral insults, microangiopathies and vascular dementia.

Advances in the roles and mechanisms of lignans against Alzheimer’s disease

Background: Alzheimer’s disease (AD) is a serious neurodegenerative disease associated with the memory and cognitive impairment. The occurrence of AD is due to the accumulation of amyloid β-protein (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain tissue as well as the hyperphosphorylation of Tau protein in neurons, doing harm to the human health and even leading people to death. The development of neuroprotective drugs with small side effects and good efficacy is focused by scientists all over the world. Natural drugs extracted from herbs or plants have become the preferred resources for new candidate drugs. Lignans were reported to effectively protect nerve cells and alleviate memory impairment, suggesting that they might be a prosperous class of compounds in treating AD.

Objective: To explore the roles and mechanisms of lignans in the treatment of neurological diseases, providing proofs for the development of lignans as novel anti-AD drugs.

Methods: Relevant literature was extracted and retrieved from the databases including China National Knowledge Infrastructure (CNKI), Elsevier, Science Direct, PubMed, SpringerLink, and Web of Science, taking lignan, anti-inflammatory, antioxidant, apoptosis, nerve regeneration, nerve protection as keywords. The functions and mechanisms of lignans against AD were summerized.

Results: Lignans were found to have the effects of regulating vascular disorders, anti-infection, anti-inflammation, anti-oxidation, anti-apoptosis, antagonizing NMDA receptor, suppressing AChE activity, improving gut microbiota, so as to strengthening nerve protection. Among them, dibenzocyclooctene lignans were most widely reported and might be the most prosperous category in the develpment of anti-AD drugs.

Conclusion: Lignans displayed versatile roles and mechanisms in preventing the progression of AD in in vitro and in vivo models, supplying potential candidates for the treatment of nerrodegenerative diseases.

Immune-mediated diseases are associated with a higher incidence of dementia: a prospective cohort study of 375,894 individuals

BACKGROUND

Immune system dysregulation plays a vital role in the pathogenesis of neurodegenerative diseases, even considered to be as important as classical pathological protein aggregation assumption. However, the associations of immune-mediated diseases with incident dementia are unclear and need to be clarified in prospective studies with a large population and long follow-up time.

METHODS

We investigated the relationship between any or individual immune-mediated diseases and incident dementia based on a prospective cohort UK Biobank. The risk for dementia was assessed with multivariable hazard ratio (HR) and 95% confidence interval (CI) after adjusting for various potential confounders using time-varying Cox proportional hazards regression. We also performed the subgroup Cox analysis stratified by time since immune-mediated diseases and gender. Causal mediation analyses with 1000 bootstrapped iterations were conducted to explore the mediation effects of peripheral immune cells on the associations of immune-mediated diseases with dementia.

RESULTS

A total of 375,894 participants were included in the study, among which 5291 developed dementia during a median follow-up of 9.08 years. Immune-mediated diseases were associated with an increased risk of dementia (HR, 1.10; 95% CI, 1.00-1.21), and the risk was highest between 1 and 2 years after immune-mediated diseases onset (HR, 2.74; 95% CI, 1.86-4.04). Females who suffered from immune-mediated diseases were more prone to AD, while males were more susceptible to VD. Four of the individual immune-mediated diseases including type I diabetes mellitus (HR, 2.49; 95% CI, 1.97-3.15), rheumatic fever or rheumatic heart diseases (HR, 1.36; 95% CI, 1.05-1.77), multiple sclerosis (HR, 2.87; 95% CI, 1.92-4.30), and necrotizing vasculopathies (HR, 1.71; 95%CI, 1.03-2.85) were significantly related to higher dementia incidence. The relationship between immune-mediated diseases and dementia was partially mediated by peripheral immune cells including neutrophils and lymphocytes.

CONCLUSIONS

In this large cohort study, immune-mediated diseases were proven to be significantly associated with an increased risk of incident dementia, especially for type I diabetes mellitus which was observed to be related to the higher incidence of all types of dementia. Our findings could provide new sights on dementia pathogenesis and intervention from the perspective of systemic immunology and immune-mediated diseases.

Association between hypoglycemia and dementia in patients with diabetes: a systematic review and meta-analysis of 1.4 million patients

BACKGROUND

Diabetes mellitus (DM) is known to be a risk factor for dementia. However, it is unclear if hypoglycemic events play a role in the risk of dementia. We aimed to systematically review evidence on the risk of dementia in DM patients based on prior hypoglycemic events.

METHODS

PubMed, Embase, ScienceDirect, CENTRAL, and Google Scholar databases were searched till 15th November 2021 for cohort studies assessing the risk of dementia based on prior hypoglycemic events in DM patients. Adjusted data were pooled in a random-effects model.

RESULTS

Ten studies with a total of 1,407,643 patients were included. Pooled analysis of all ten studies indicated that hypoglycemic episodes were associated with a statistically significant increase in the risk of dementia in DM patients as compared to those not experiencing hypoglycemic episodes (HR: 1.44 95% CI: 1.26, 1.65 I² = 89% p < 0.00001). The results did not change on the exclusion of any study. Sub-group analysis based on the study population, type of study, adjustment for glycated hemoglobin, gender, and the number of hypoglycemic episodes also presented similar results.

CONCLUSIONS

Evidence from observational studies with a large sample size indicates that DM patients with hypoglycemic episodes are at increased risk of dementia. Anti-hyperglycemic drugs should be adequately tailored in these patients to avoid the risk of dementia.

Amino Acid Nanofibers Improve Glycemia and Confer Cognitive Therapeutic Efficacy to Bound Insulin

Diabetes poses a high risk for debilitating complications in neural tissues, regulating glucose uptake through insulin-dependent and predominantly insulin-independent pathways. Supramolecular nanostructures provide a flexible strategy for combinatorial regulation of glycemia. Here, we compare the effects of free insulin to insulin bound to positively charged nanofibers comprised of self-assembling amino acid compounds (AACs) with an antioxidant-modified side chain moiety (AAC2) in both in vitro and in vivo models of type 1 diabetes. Free AAC2, free human insulin (hINS) and AAC2-bound-human insulin (AAC2-hINS) were tested in streptozotocin (STZ)-induced mouse model of type 1 diabetes. AAC2-hINS acted as a complex and exhibited different properties compared to free AAC2 or hINS. Mice treated with the AAC2-hINS complex were devoid of hypoglycemic episodes, had improved levels of insulin in circulation and in the brain, and increased expression of neurotransmitter taurine transporter, Slc6a6. Consequently, treatment with AAC2-hINS markedly advanced both physical and cognitive performance in mice with STZ-induced and genetic type 1 diabetes compared to treatments with free AAC2 or hINS. This study demonstrates that the flexible nanofiber AAC2 can serve as a therapeutic platform for the combinatorial treatment of diabetes and its complications.

Hypoglycemia, Vascular Disease and Cognitive Dysfunction in Diabetes: Insights from Text Mining-Based Reconstruction and Bioinformatics Analysis of the Gene Networks

Hypoglycemia has been recognized as a risk factor for diabetic vascular complications and cognitive decline, but the molecular mechanisms of the effect of hypoglycemia on target organs are not fully understood. In this work, gene networks of hypoglycemia and cardiovascular disease, diabetic retinopathy, diabetic nephropathy, diabetic neuropathy, cognitive decline, and Alzheimer's disease were reconstructed using ANDSystem, a text-mining-based tool. The gene network of hypoglycemia included 141 genes and 2467 interactions. Enrichment analysis of Gene Ontology (GO) biological processes showed that the regulation of insulin secretion, glucose homeostasis, apoptosis, nitric oxide biosynthesis, and cell signaling are significantly enriched for hypoglycemia. Among the network hubs, INS, IL6, LEP, TNF, IL1B, EGFR, and FOS had the highest betweenness centrality, while GPR142, MBOAT4, SLC5A4, IGFBP6, PPY, G6PC1, SLC2A2, GYS2, GCGR, and AQP7 demonstrated the highest cross-talk specificity. Hypoglycemia-related genes were overrepresented in the gene networks of diabetic complications and comorbidity; moreover, 14 genes were mutual for all studied disorders. Eleven GO biological processes (glucose homeostasis, nitric oxide biosynthesis, smooth muscle cell proliferation, ERK1 and ERK2 cascade, etc.) were overrepresented in all reconstructed networks. The obtained results expand our understanding of the molecular mechanisms underlying the deteriorating effects of hypoglycemia in diabetes-associated vascular disease and cognitive dysfunction.