Identification of diabetes-related dementia: Longitudinal perfusion SPECT and amyloid PET studies

Biomarkers of Neurodegeneration and Alzheimer's Disease Neuropathology in Adolescents and Young Adults with Youth-Onset Type 1 or Type 2 Diabetes: A Proof-of-Concept Study

Adult-onset diabetes increases one's risk of neurodegenerative disease including Alzheimer's disease (AD); however, the risk associated with youth-onset diabetes (Y-DM) remains underexplored. We quantified plasma biomarkers of neurodegeneration and AD in participants with Y-DM from the SEARCH cohort at adolescence and young adulthood (Type 1, n = 25; Type 2, n = 25; 59% female; adolescence, age = 15 y/o [2.6]; adulthood, age = 27.4 y/o [2.2]), comparing them with controls (adolescence, n = 25, age = 14.8 y/o [2.7]; adulthood, n = 21, age = 24.9 y/o [2.8]). Plasma biomarkers, including glial fibrillary acidic protein (GFAP), neurofilament light chain protein (NfL), phosphorylated tau-181 (pTau181), and amyloid beta (Aβ40, Aβ42), were measured via Simoa. A subset of participants (n = 7; age = 27.5 y/o [5.7]) and six controls (age = 25.1 y/o [4.5]) underwent PET scans to quantify brain amyloid and tau densities in AD sensitive brain regions. Y-DM adolescents exhibited lower plasma levels of Aβ40, Aβ42, and GFAP, and higher pTau181 compared to controls (p < 0.05), a pattern persisting into adulthood (p < 0.001). All biomarkers showed significant increases from adolescence to adulthood in Y-DM (p < 0.01), though no significant differences in brain amyloid or tau were noted between Y-DM and controls in adulthood. Preliminary evidence suggests that preclinical AD neuropathology is present in young people with Y-DM, indicating a potential increased risk of neurodegenerative diseases.

The associations between type 2 diabetes and plasma biomarkers of Alzheimer's disease in the Health and Aging Brain Study: Health Disparities (HABS-HD)

Alzheimer's disease (AD) affects Latinos disproportionately. One of the reasons underlying this disparity may be type 2 diabetes (T2D) that is a risk factor for AD. The purpose of this study was to examine the associations of T2D and AD blood biomarkers and the differences in these associations between Mexican Americans and non-Hispanic Whites. This study was a secondary analysis of baseline data from the observational Health and Aging Brain Study: Health Disparities (HABS-HD) that investigated factors underlying health disparities in AD in Mexican Americans in comparison to non-Hispanic Whites. HABS-HD participants were excluded if they had missing data or were large outliers (z-scores >|4|) on a given AD biomarker. Fasting blood glucose and glycosylated hemoglobin (HbA1c) levels were measured from clinical labs. T2D was diagnosed by licensed clinicians. Plasma amyloid-beta 42 and 40 (Aβ42/42) ratio, total tau (t-tau), and neurofilament light (NfL) were measured via ultra-sensitive Simoa assays. The sample sizes were 1,552 for Aβ42/40 ratio, 1,570 for t-tau, and 1,553 for NfL. Mexican Americans were younger (66.6±8.7 vs. 69.5±8.6) and had more female (64.9% female vs. 55.1%) and fewer years of schooling (9.5±4.6 vs. 15.6±2.5) than non-Hispanic Whites. Mexican Americans differed significantly from non-Hispanic Whites in blood glucose (113.5±36.6 vs. 99.2±17.0) and HbA1c (6.33±1.4 vs. 5.51±0.6) levels, T2D diagnosis (35.3% vs. 11.1%), as well as blood Aβ42/40 ratio (.051±.012 vs. .047±.011), t-tau (2.56±.95 vs. 2.33±.90), and NfL levels (16.3±9.5 vs. 20.3±10.3). Blood glucose, blood HbA1c, and T2D diagnosis were not related to Aβ42/40 ratio and t-tau but explained 3.7% of the variation in NfL (p < .001). Blood glucose and T2D diagnosis were not, while HbA1c was positively (b = 2.31, p < .001, β = 0.26), associated with NfL among Mexican Americans. In contrast, blood glucose, HbA1c, and T2D diagnosis were negatively (b = -0.09, p < .01, β = -0.26), not (b = 0.34, p = .71, β = 0.04), and positively (b = 3.32, p < .01, β = 0.33) associated with NfL, respectively in non-Hispanic Whites. To conclude, blood glucose and HbA1c levels and T2D diagnosis are associated with plasma NfL levels, but not plasma Aβ and t-tau levels. These associations differ in an ethnicity-specific manner and need to be further studied as a potential mechanism underlying AD disparities.

Insulin Resistance and Cognitive Impairment: Evidence From Neuroimaging

Insulin is a peptide well known for its role in regulating glucose metabolism in peripheral tissues. Emerging evidence from human and animal studies indicate the multifactorial role of insulin in the brain, such as neuronal and glial metabolism, glucose regulation, and cognitive processes. Insulin resistance (IR), defined as reduced sensitivity to the action of insulin, has been consistently proposed as an important risk factor for developing neurodegeneration and cognitive impairment. Although the exact mechanism of IR-related cognitive impairment still awaits further elucidation, neuroimaging offers a versatile set of novel contrasts to reveal the subtle cerebral abnormalities in IR. These imaging contrasts, including but not limited to brain volume, white matter (WM) microstructure, neural function and brain metabolism, are expected to unravel the nature of the link between IR, cognitive decline, and brain abnormalities, and their changes over time. This review summarizes the current neuroimaging studies with multiparametric techniques, focusing on the cerebral abnormalities related to IR and therapeutic effects of IR-targeting treatments. According to the results, brain regions associated with IR pathophysiology include the medial temporal lobe, hippocampus, prefrontal lobe, cingulate cortex, precuneus, occipital lobe, and the WM tracts across the globe. Of these, alterations in the temporal lobe are highly reproducible across different imaging modalities. These structures have been known to be vulnerable to Alzheimer's disease (AD) pathology and are critical in cognitive processes such as memory and executive functioning. Comparing to asymptomatic subjects, results are more mixed in patients with metabolic disorders such as type 2 diabetes and obesity, which might be attributed to a multifactorial mechanism. Taken together, neuroimaging, especially MRI, is beneficial to reveal early abnormalities in cerebral structure and function in insulin-resistant brain, providing important evidence to unravel the underlying neuronal substrate that reflects the cognitive decline in IR. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 2.

HMGB1 signaling pathway in diabetes-related dementia: Blood-brain barrier breakdown, brain insulin resistance, and Aβ accumulation

Diabetes contributes to the onset of various diseases, including cancer and cardiovascular and neurodegenerative diseases. Recent studies have highlighted the similarities and relationship between diabetes and dementia as an important issue for treating diabetes-related cognitive deficits. Diabetes-related dementia exhibits several features, including blood-brain barrier disruption, brain insulin resistance, and Aβ over-accumulation. High-mobility group box1 (HMGB1) is a protein known to regulate gene transcription and cellular mechanisms by binding to DNA or chromatin via receptor for advanced glycation end-products (RAGE) and toll-like receptor 4 (TLR4). Recent studies have demonstrated that the interplay between HMGB1, RAGE, and TLR4 can impact both neuropathology and diabetic alterations. Herein, we review the recent research regarding the roles of HMGB1-RAGE-TLR4 axis in diabetes-related dementia from several perspectives and emphasize the importance of the influence of HMGB1 in diabetes-related dementia.

Diabetes-Specific Dementia: A Structured Literature Review of Cognitive Assessment Methods

Diabetes mellitus is a known risk factor for the development of multiple subtypes of dementia and mild cognitive impairment. Recent research identifies a cause-specific diabetes-related dementia with a unique set of characteristics. Currently, there is no standard cognitive assessment battery recommended to specifically assess dementia that is a direct consequence of chronic diabetes, and some evaluations have been used for decades with minimal revisions, regardless of appropriateness. We performed a systematic review of the dementia/cognition evaluation methods most commonly used in the literature for assessing diabetic patients and identified which cognitive domains are typically assessed in this setting, and whether cognitive changes were more reflective of a vascular pathology, Alzheimer's pathology, or something else entirely. Search results yielded 1089 articles. After screening for appropriateness, a total of 11 full-text articles were assessed. In general, subjects in the reviewed studies were assessed using a variety of testing methods, examining different combinations of cognitive domains. A standard, clear definition of which cognitive domains are the most important to assess in diabetic patients is needed in order to determine what combination of assessment tools are most pertinent. Given the growing subset of the US population, careful reconsideration of cognitive assessment methods is needed to create self-care plans that take into account a specific collection of cognitive challenges for those with diabetes.

Cerebral perfusion alterations in type 2 diabetes mellitus - a systematic review

Type 2 diabetes mellitus (T2DM) is related to abnormal brain structure and function, increasing the risk of cognitive impairment and dementia. We systematically reviewed the published literature focusing on cerebral perfusion in patients with T2DM. Although no significant difference was found in global cerebral blood flow (CBF) between the T2DM group and the healthy control group, the regional cerebral perfusion in T2DM was significantly reduced in multiple locations, including the occipital lobe, domains involved in the default mode network and the cerebellum. The decline in regional CBF was associated with a wide range of cognitive disorders in T2DM, including learning, memory, attention, and executive processing, as well as visual function. In addition, diabetes-related biochemical indicators, such as glycated hemoglobin and insulin resistance, were negatively correlated with regional CBF. In general, these functional perfusion imaging studies indicate that decreased CBF in T2DM may be a potential cause of cognitive impairment.

Serine Phosphorylation of IRS1 Correlates with Aβ-Unrelated Memory Deficits and Elevation in Aβ Level Prior to the Onset of Memory Decline in AD

The biological effects of insulin signaling are regulated by the phosphorylation of insulin receptor substrate 1 (IRS1) at serine (Ser) residues. In the brain, phosphorylation of IRS1 at specific Ser sites increases in patients with Alzheimer’s disease (AD) and its animal models. However, whether the activation of Ser sites on neural IRS1 is related to any type of memory decline remains unclear. Here, we show the modifications of IRS1 through its phosphorylation at etiology-specific Ser sites in various animal models of memory decline, such as diabetic, aged, and amyloid precursor protein (APP) knock-in ^NL-G-F (APPKI^NL-G-F) mice. Substantial phosphorylation of IRS1 at specific Ser sites occurs in type 2 diabetes- or age-related memory deficits independently of amyloid-β (Aβ). Furthermore, we present the first evidence that, in APPKI^NL-G-F mice showing Aβ42 elevation, the increased phosphorylation of IRS1 at multiple Ser sites occurs without memory impairment. Our findings suggest that the phosphorylation of IRS1 at specific Ser sites is a potential marker of Aβ-unrelated memory deficits caused by type 2 diabetes and aging; however, in Aβ-related memory decline, the modifications of IRS1 may be a marker of early detection of Aβ42 elevation prior to the onset of memory decline in AD.

Ambulatory glucose profile in diabetes-related dementia

AIM

Diabetes-related dementia (DrD), a dementia subgroup associated with specific diabetes mellitus (DM)-related metabolic abnormalities rather than Alzheimer's disease (AD) pathology or cerebrovascular disease, is characterized by less well-controlled glycemia. We investigated the glucose level, variability and stability, and risk of hypoglycemia in DrD to determine characteristic ambulatory glucose profiles (AGP).

METHODS

We obtained AGP for 14 days of 40 patients with AD associated with DM and 19 patients with DrD using a novel sensor-based flash glucose monitoring system (FreeStyle Libre Pro).

RESULTS

Despite similar mean glucose and estimated A_1c values, the DrD group showed significantly greater glucose variability and higher percentage of time spent in hypoglycemia than the AD associated with DM group. Glucose level and variability correlated significantly and negatively with Mini-Mental State Examination in DrD, but not in AD associated with DM The estimated A_1c levels calculated from the 14 days of AGP data significantly correlated with the HbA_1c levels measured within 2 months of the insertion of the sensor.

CONCLUSIONS

DrD has a distinctively different AGP from that of AD associated with DM. Glucose variability and hypoglycemia are more involved in the pathophysiology of DrD than in that of AD associated with DM. The AGP analysis using the flash glucose monitoring system might provide useful information undetected by HbA_1c values. Geriatr Gerontol Int 2019; 19: 282-286.

Diabetes-Related Dementia

Type 2 diabetes mellitus (DM) has been shown to increase the risk for cognitive decline and dementia, such as in Alzheimer disease (AD) and vascular dementia (VaD). Additionally, there may be a dementia subgroup associated with specific DM-related metabolic abnormalities rather than with AD pathology or cerebrovascular diseases. This type of dementia, not showing hypoperfusion in the parietotemporal lobe on SPECT or cerebrovascular lesions on MRI, was characterized by old age, high hemoglobin A_1c level, long duration of diabetes, high frequency of insulin therapy, low frequency of apolipoprotein E4 carrier, less-severe medial temporal lobe atrophy, impaired attention and executive function, less-impaired word recall, and slow progression of cognitive impairment and might be referred to as "diabetes-related dementia" (DrD). ¹¹C-Pittsburgh compound-B PET shows often negative or equivocal amyloid accumulation in the brain, indicating different from AD pathology. In addition to insulin resistance, elevated inflammatory cytokines, oxidative stress, and advanced glycation end products were associated with cognitive impairment in this type of dementia. Glycemic controls can improve some domains of cognitive function, such as attention and executive functions, in subjects with DrD. Frequencies of frailty and sarcopenia/dynapenia are significantly higher in DrD than in AD, indicating that geriatric interventions are necessary to improve clinical outcomes for patients with DrD. DrD can be considered as a controllable or modifiable dementia. The identification of DrD, as distinct from other types of dementia, may be necessary for considering appropriate therapy and prevention in clinical practice.

p66Shc Signaling Mediates Diabetes-Related Cognitive Decline

Accumlating evidence have suggested that diabetes mellitus links dementia, notably of Alzheimer's disease (AD). However, the underlying mechanism remains unclear. Several studies have shown oxidative stress (OS) to be one of the major factors in the pathogenesis of diabetic complications. Here we show OS involvement in brain damage in a diabetic animal model that is at least partially mediated through an AD-pathology-independent mechanism apart from amyloid-β accumulation. We investigated the contribution of the p66Shc signaling pathway to diabetes-related cognitive decline using p66Shc knockout (-/-) mice. p66Shc (-/-) mice have less OS in the brain and are resistant to diabetes-induced brain damage. Moreover, p66Shc (-/-) diabetic mice show significantly less cognitive dysfunction and decreased levels of OS and the numbers of microglia. This study postulates a p66Shc-mediated inflammatory cascade leading to OS as a causative pathogenic mechanism in diabetes-associated cognitive impairment that is at least partially mediated through an AD-pathology-independent mechanism.

Brain insulin resistance in type 2 diabetes and Alzheimer disease: concepts and conundrums

Considerable overlap has been identified in the risk factors, comorbidities and putative pathophysiological mechanisms of Alzheimer disease and related dementias (ADRDs) and type 2 diabetes mellitus (T2DM), two of the most pressing epidemics of our time. Much is known about the biology of each condition, but whether T2DM and ADRDs are parallel phenomena arising from coincidental roots in ageing or synergistic diseases linked by vicious pathophysiological cycles remains unclear. Insulin resistance is a core feature of T2DM and is emerging as a potentially important feature of ADRDs. Here, we review key observations and experimental data on insulin signalling in the brain, highlighting its actions in neurons and glia. In addition, we define the concept of 'brain insulin resistance' and review the growing, although still inconsistent, literature concerning cognitive impairment and neuropathological abnormalities in T2DM, obesity and insulin resistance. Lastly, we review evidence of intrinsic brain insulin resistance in ADRDs. By expanding our understanding of the overlapping mechanisms of these conditions, we hope to accelerate the rational development of preventive, disease-modifying and symptomatic treatments for cognitive dysfunction in T2DM and ADRDs alike.

Decreased Muscle Strength and Quality in Diabetes-Related Dementia

Background/Aims

Diabetes-related dementia (DrD), a dementia subgroup associated with specific diabetes mellitus (DM)-related metabolic abnormalities, is clinically and pathophysiologically different from Alzheimer disease (AD) and vascular dementia. We determined whether skeletal muscle strength, quality, and mass decrease in individuals with DrD.

Methods

We evaluated grip and knee extension strength, muscle mass, and gait speed in 106 patients with probable AD and without type 2 DM (AD[−DM] group), 74 patients with probable AD and with DM (AD[+DM] group), and 36 patients with DrD (DrD group). Muscle quality was defined as the ratio of muscle strength to muscle mass.

Results

Both female and male subjects with DrD showed significantly decreased muscle strength and quality in the upper extremities compared with the subjects with AD[−DM] or AD[+DM]. Female subjects with DrD showed significantly decreased muscle quality in the lower extremities compared with the subjects with AD[−DM]. Both female and male subjects with DrD had a significantly lower gait speed compared with the subjects with AD[−DM]. However, there were no significant differences in muscle mass and the prevalence of sarcopenia between the groups.

Conclusion

Subjects with DrD showed decreased muscle strength and quality, but not muscle mass, and had a low gait speed.

Cerebrospinal fluid analysis in individuals with diabetes-related dementia

•CSF P-tau and Aβ42 show normal levels in diabetes-related dementia.•Diabetes-related dementia may have a different underlying pathology from AD.•CSF analysis is useful for the differentiation of diabetes-related dementia from AD.