Contributing Factors to Diabetic Brain Injury and Cognitive Decline

New insights toward molecular and nanotechnological approaches to antidiabetic agents for Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder affecting a major class of silver citizens. The disorder shares a mutual relationship on account of its cellular and molecular pathophysiology with type-II diabetes mellitus (DM). Chronic DM increases the risk for AD. Emerging evidence recommended that resistance in insulin production develops cognitive dysfunction, which generally leads to AD. Repurposing of antidiabetic drugs can be effective in preventing and treatment of the neurodegenerative disorder. Limitations of antidiabetic drugs restrict the repurposing of the drugs for other disorders. Therefore, nanotechnological intervention plays a significant role in the treatment of neurological disorders. In this review, we discuss the common cellular and molecular pathophysiologies between AD and type-II DM, the relevance of in vivo models of type II DM in the study of AD, and the repurposing of antidiabetic drugs and the nanodelivery systems of antidiabetic drugs against AD.

Nicotinamide Prevents Diabetic Brain Inflammation via NAD+-Dependent Deacetylation Mechanisms

This study investigated the effect of nicotinamide (NAM) supplementation on the development of brain inflammation and microglial activation in a mouse model of type 1 diabetes mellitus. C57BL/6J male mice, which were made diabetic with five consecutive, low-dose (55 mg/kg i.p.) streptozotocin (STZ) injections. Diabetic mice were randomly distributed in different experimental groups and challenged to different doses of NAM (untreated, NAM low-dose, LD, 0.1%; NAM high-dose, HD, 0.25%) for 25 days. A control, non-diabetic group of mice was used as a reference. The NAD+ content was increased in the brains of NAM-treated mice compared with untreated diabetic mice (NAM LD: 3-fold; NAM HD: 3-fold, p-value < 0.05). Immunohistochemical staining revealed that markers of inflammation (TNFα: NAM LD: -35%; NAM HD: -46%; p-value < 0.05) and microglial activation (IBA-1: NAM LD: -29%; NAM HD: -50%; p-value < 0.05; BDKRB1: NAM LD: -36%; NAM HD: -37%; p-value < 0.05) in brains from NAM-treated diabetic mice were significantly decreased compared with non-treated T1D mice. This finding was accompanied by a concomitant alleviation of nuclear NFκB (p65) signaling in treated diabetic mice (NFκB (p65): NAM LD: -38%; NAM HD: -53%, p-value < 0.05). Notably, the acetylated form of the nuclear NFκB (p65) was significantly decreased in the brains of NAM-treated, diabetic mice (NAM LD: -48%; NAM HD: -63%, p-value < 0.05) and inversely correlated with NAD+ content (r = -0.50, p-value = 0.03), suggesting increased activity of NAD+-dependent deacetylases in the brains of treated mice. Thus, dietary NAM supplementation in diabetic T1D mice prevented brain inflammation via NAD+-dependent deacetylation mechanisms, suggesting an increased action of sirtuin signaling.

The association between renal accumulation of pancreatic amyloid-forming amylin and renal hypoxia

Chronic kidney disease (CKD) is increasing worldwide and is associated with diabetic states (obesity, prediabetes and type-2 diabetes mellitus). The kidney is intrinsically susceptible to low oxygen (hypoxia) and renal hypoxia plays a vital role in the progression of CKD. Recent studies suggest an association between CKD and renal deposition of amyloid-forming amylin secreted from the pancreas. Renal accumulation of amyloid-forming amylin is associated with hypertension, mitochondrial dysfunction, increased production of reactive oxygen species (ROS) and activation of hypoxia signaling in the kidney. In this review we will discuss potential associations between renal amylin amyloid accumulation, hypertension, and mechanism of hypoxia-induced kidney dysfunction, including activation of hypoxia-inducible factors (HIFs) and mitochondrial dysfunction.

Ipriflavone as a non-steroidal glucocorticoid receptor antagonist ameliorates diabetic cognitive impairment in mice

Diabetic cognitive impairment (DCI) is a common diabetic complication with hallmarks of loss of learning ability and disorders of memory and behavior. Glucocorticoid receptor (GR) dysfunction is a main reason for neuronal impairment in brain of diabetic patients. Here, we determined that ipriflavone (IP) a clinical anti-osteoporosis drug functioned as a non-steroidal GR antagonist and efficiently ameliorated learning and memory dysfunction in both type 1 and 2 diabetic mice. The underlying mechanism has been intensively investigated by assay against the diabetic mice with GR-specific knockdown in the brain by injection of adeno-associated virus (AAV)-ePHP-si-GR. IP suppressed tau hyperphosphorylation through GR/PI3K/AKT/GSK3β pathway, alleviated neuronal inflammation through GR/NF-κB/NLRP3/ASC/Caspase-1 pathway, and protected against synaptic impairment through GR/CREB/BDNF pathway. To our knowledge, our work might be the first to expound the detailed mechanism underlying the amelioration of non-steroidal GR antagonist on DCI-like pathology in mice and report the potential of IP in treatment of DCI.

The role of traditional Chinese medicine in the treatment of cognitive dysfunction in type 2 diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic cognitive dysfunction (DCD) is mainly one of the complications of type 2 diabetes mellitus (T2DM) with complex and obscure pathogenesis. Extensive evidence has demonstrated the effectiveness and safety of traditional Chinese medicine (TCM) for DCD management.

AIM OF THE STUDY

This review attempted to systematically summarize the possible pathogenesis of DCD and the current Chinese medicine on the treatment of DCD.

MATERIALS AND METHODS

We acquired information of TCM on DCD treatment from PubMed, Web of Science, Science Direct and CNKI databases. We then dissected the potential mechanisms of currently reported TCMs and their active ingredients for the treatment of DCD by discussing the deficiencies and giving further recommendations.

RESULTS

Most TCMs and their active ingredients could improve DCD through alleviating insulin resistance, microvascular dysfunction, abnormal gut microbiota composition, inflammation, and the damages of the blood-brain barrier, cerebrovascular and neurons under hyperglycemia conditions.

CONCLUSIONS

TCM is effective in the treatment of DCD with few adverse reactions. A large number of in vivo and in vitro, and clinical trials are still needed to further reveal the potential quality markers of TCM on DCD treatment.

The Association Between Second-Line Oral Antihyperglycemic Medication on Types of Dementia in Type 2 Diabetes: A Nationwide Real-World Longitudinal Study

BACKGROUND

There are few reports that evaluated the association between various types of dementia and dual oral therapy with antihyperglycemic medication.

OBJECTIVE

The goal of this study was to investigate the association between treatment of dual antihyperglycemic medication and dementia subclass in type 2 diabetes mellitus using the Korean National Health Insurance System.

METHODS

This study included 701,193 individuals with diabetes prescribed dual oral therapy between 2009 and 2012 from the Korean National Health Insurance Service Database, which were tracked until 2017. All-cause, Alzheimer's (AD) and vascular dementia (VaD) were investigated by dual oral therapy. Adjustments were made for age, sex, income, diabetes duration, hypertension, dyslipidemia, smoking, drinking, exercise, body mass index, glucose level, and estimated glomerular filtration rate.

RESULTS

Dual therapy with metformin (Met) + dipeptidyl peptidase-4 inhibitor (DPP-4i), Met + thiazolidinedione (TZD), and sulfonylurea (SU) + thiazolidinediones (TZD) were significantly associated with all-cause dementia (HR = 0.904, 0.804, and 0.962, respectively) and VaD (HR = 0.865, 0.725, and 0.911, respectively), compared with Met + SU. Met + DPP-4i and Met + TZD were associated with significantly lower risk of AD (HR = 0.922 and 0.812), compared with Met + SU. Dual therapy with TZD was associated with a significantly lower risk of all-cause dementia, AD, and VaD than nonusers of TZD (HR = 0.918, 0.925 and 0.859, respectively).

CONCLUSION

Adding TZD or DPP-4i instead of SU as second-line anti-diabetic treatment may be considered for delaying or preventing dementia. Also, TZD users relative to TZD non-users on dual oral therapy were significantly associated with lower risk of various types of dementia.

Effects of linagliptin vs glimepiride on cognitive performance in type 2 diabetes: results of the randomised double-blind, active-controlled CAROLINA-COGNITION study

AIMS/HYPOTHESIS

Type 2 diabetes, particularly with concomitant CVD, is associated with an increased risk of cognitive impairment. We assessed the effect on accelerated cognitive decline (ACD) of the DPP-4 inhibitor linagliptin vs the sulfonylurea glimepiride in individuals with type 2 diabetes.

METHODS

The CAROLINA-COGNITION study was part of the randomised, double-blind, active-controlled CAROLINA trial that evaluated the cardiovascular safety of linagliptin vs glimepiride in individuals with age ≥40 and ≤85 years and HbA1c 48-69 mmol/mol (6.5-8.5%) receiving standard care, excluding insulin therapy. Participants were randomised 1:1 using an interactive telephone- and web-based system and treatment assignment was determined by a computer-generated random sequence with stratification by center. The primary cognitive outcome was occurrence of ACD at end of follow-up, defined as a regression-based index score ≤16th percentile on either the Mini-Mental State Examination (MMSE) or a composite measure of attention and executive functioning, in participants with a baseline MMSE score ≥24. Prespecified additional analyses included effects on ACD at week 160, in subgroups (sex, age, race, ethnicity, depressive symptoms, cardiovascular risk, duration of type 2 diabetes, albuminuria), and absolute changes in cognitive performance. Participants, caregivers, and people involved in measurements, examinations or adjudication, were all masked to treatment assignment.

RESULTS

Of 6033 participants recruited from hospital and primary care sites, 3163 (38.0% female, mean age/diabetes duration 64/7.6 years, MMSE score 28.5, HbA1c 54 mmol/mol [7.1%]) represent the CAROLINA-COGNITION cohort. Over median 6.1 years, ACD occurred in 27.8% (449/1618, linagliptin) vs 27.6% (426/1545, glimepiride), OR 1.01 (95% CI 0.86, 1.18). Also, no differences in ACD were observed at week 160 (OR 1.07 [0.91, 1.25]), between treatments across subgroups, or for absolute cognitive changes.

CONCLUSIONS/INTERPRETATION

In a large, international outcome trial in people with relatively early type 2 diabetes at elevated cardiovascular risk, no difference in risk for ACD was observed between linagliptin and glimepiride over 6.1 years.

FUNDING

This study was sponsored by Boehringer Ingelheim.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01243424.

Diabetes and dementia - the two faces of Janus

Patients with type 2 diabetes are at high risk for cognitive decline and dementia. Despite the limited data on the possible pathogenetic mechanisms, evidence suggests that cognitive decline, and thus dementia and Alzheimer’s disease, might arise from a complex interplay between type 2 diabetes and the aging brain, including decreased insulin signalling and glucose metabolism, mitochondrial dysfunction, neuroinflammation, and vascular disease. Furthermore, there is increasing interest on the effects of antidiabetic agents on cognitive decline. There are many studies showing that antidiabetic agents might have beneficial effects on the brain, mainly through inhibition of oxidative stress, inflammation, and apoptosis. In addition, experimental studies on patients with diabetes and Alzheimer’s disease have shown beneficial effects on synaptic plasticity, metabolism of amyloid-β, and microtubule-associated protein tau. Therefore, in the present review, we discuss the effects of antidiabetic agents in relation to cognitive decline, and in particular dementia and Alzheimer’s disease, in patients with type 2 diabetes.