Effects of Fluctuating Glucose Levels on Neuronal Cells In Vitro

Glycaemic level and glycaemic variability in acute ischaemic stroke and functional outcome: An observational continuous glucose monitoring study

INTRODUCTION

Glycaemic variability has been associated with poor outcomes in critically ill patients. We aimed to study the association between glycaemic variability and functional outcome in patients with acute ischaemic stroke using continuous glucose monitoring to ensure all episodes of hyper- and hypoglycaemia were captured.

RESEARCH DESIGN AND METHODS

Participants with acute ischaemic stroke were enrolled and started blinded continuous glucose monitoring (Dexcom G6) between November 2020 and December 2022. Glucose data from the first 72 hours after admission were analysed. Patients were classified into 3 groups based on change in functional status (Modified Rankin Scale) between admission and discharge. These included (i) remained independent (RI); (ii) deteriorated to dependent (DD); and (iii) remained dependent (RD).

RESULTS

Data of 67 patients (mean±SD age 72.1 ± 14 years) were analysed; 19 participants had diabetes. The median (IQR) National Institutes of Health Stroke Scale (NIHSS) was 8 (3,14), and 34.3% received reperfusion therapy. The percentage of patients with RI, DD, and RD was 25.4, 55.2, 19.4%. Patients with DD had older age, higher rate of atrial fibrillation, systolic blood pressure, rate of in-hospital infection, NIHSS at admission and at 24 hours after reperfusion therapy compared to those RI. Continuous glucose monitoring was started at 38.4 (29.5,51) hours after stroke onset. Those with DD had higher mean glucose, %time above 180 mg/dL, and glucose standard deviation than the RI group at discharge. Multivariate analysis showed only an association between NIHSS at admission and deterioration in functional status.

CONCLUSIONS

In this pilot study, an association between glycaemic variability and functional deterioration after acute ischaemic stroke was not observed. Clinical Trial Registration numberNCT04521634.

Glucose metabolism impairment in major depressive disorder

Major depressive disorder (MDD) is a common mental disorder with chronic tendencies that seriously affect regular work, life, and study. However, its exact pathogenesis remains unclear. Patients with MDD experience systemic and localized impairments in glucose metabolism throughout the disease course, disrupting various processes such as glucose uptake, glycoprotein transport, glycolysis, the tricarboxylic acid cycle (TCA), and oxidative phosphorylation (OXPHOS). These impairments may result from mechanisms including insulin resistance, hyperglycemia-induced damage, oxidative stress, astrocyte abnormalities, and mitochondrial dysfunction, leading to insufficient energy supply, altered synaptic plasticity, neuronal cell death, and functional and structural damage to reward networks. These mechanical changes contribute to the pathogenesis of MDD and severely interfere with the prognosis. Herein, we summarized the impairment of glucose metabolism and its pathophysiological mechanisms in patients with MDD. In addition, we briefly discussed potential pharmacological interventions for glucose metabolism to alleviate MDD, including glucagon-like peptide-1 receptor agonists, metformin, topical insulin, liraglutide, and pioglitazone, to encourage the development of new therapeutics.

Association of glycemic variability and prognosis in patients with traumatic brain injury: A retrospective study from the MIMIC-IV database

BACKGROUND

Elevated glycemic variability (GV) often occurs in intensive care unit (ICU) patients and is associated with patient prognosis. However, the association between GV and prognosis in ICU patients with traumatic brain injury (TBI) remains unclear.

METHOD

Clinical data of ICU patients with TBI were obtained from the Medical Information Mart for Intensive Care (MIMIC) -IV database. The coefficient of variation (CV) was utilized to quantify GV, while the Glasgow Coma Scale (GCS) was employed to evaluate the consciousness status of TBI patients. Pearson linear correlation analysis, linear regression, COX regression and restricted cubic spline (RCS) were used to investigate the relationship between CV and consciousness impairment, as well as the risk of in-hospital mortality.

RESULT

A total of 1641 ICU patients with TBI were included in the study from the MIMIC-IV database. Pearson linear correlation and restricted cubic spline (RCS) analysis results showed a negative linear relationship between CV and the last GCS (P = 0.002) with no evidence of nonlinearity (P for nonlinear = 0.733). Multivariable linear regression suggested a higher CV was associated with a lower discharge GCS [β (95 %CI) = -1.86 (-3.08 ∼ -0.65), P = 0.003]. Furthermore, multivariable COX regression indicated that CV ≥ 0.3 was a risk factor for in-hospital death in TBI patients [HR (95 %CI) = 1.74 (1.15-2.62), P = 0.003], and this result was also consistent across sensitivity and subgroup analyses.

CONCLUSION

Higher GV is related to poorer consciousness outcomes and increased risk of in-hospital death in ICU patients with TBI. Additional research is needed to understand the logical relationship between GV and TBI progression.

High blood glucose variability may predict poor outcomes in patients with spontaneous cerebellar hemorrhage undergoing surgical operation: a retrospective study

BACKGROUND

Elevated blood glucose (BG) variability has been reported as an independent risk factor for poor prognosis in a variety of diseases. This study aimed to investigate the association between BG variability and clinical outcomes in patients with spontaneous cerebellar hemorrhage (SCH) undergoing surgical operation.

METHODS

This retrospective cohort study of the consecutive patients admitted to the department of Neurosurgery, the Affiliated Hospital of Qingdao University between January 2014 and June 2022 with the diagnosis of SCH underwent surgical intervention. BG analysis was continuously and routinely performed. BG variability was represented by the standard deviation (SD) of the serial measurements within the first 7 days. The general characteristics, imageological information, blood glucose level, and surgical information were reviewed and compared through medical records.

RESULTS

A total of 115 patients (65 male and 50 female) were enrolled. Out of all 115 patients, the overall clinical outcomes according to the modified Rankin Scale (mRS) were poor (mRS 3-6) in 31 patients (26.96%) and good (mRS 0-2) in 84 patients (73.04%). Twelve of the 115 patients died during hospitalization, and the mortality rate was 10.43%. Multivariate logistic regression analysis showed that SD of BG (odds ratio (OR), 4.717; 95% confidence interval (CI), 1.054-21.115; P = 0.043), GCS (OR, 0.563; 95% CI, 0.330-0.958; P = 0.034), and hematoma volume (OR, 1.395; 95% CI, 1.118-1.748; P = 0.003) were significant predictors. The area under the ROC curve of SD of BG was 0.911 (95% CI, 0.850-0.973; P < 0.001) with a sensitivity and specificity of 90.3% and 83.3%, respectively, and the cut-off value was 1.736.

CONCLUSIONS

High BG Variability is independently correlated with the 6-month poor outcomes in patients with SCH undergoing surgical operation.

Molecular Mechanisms of Neuroprotection after the Intermittent Exposures of Hypercapnic Hypoxia

The review introduces the stages of formation and experimental confirmation of the hypothesis regarding the mutual potentiation of neuroprotective effects of hypoxia and hypercapnia during their combined influence (hypercapnic hypoxia). The main focus is on the mechanisms and signaling pathways involved in the formation of ischemic tolerance in the brain during intermittent hypercapnic hypoxia. Importantly, the combined effect of hypoxia and hypercapnia exerts a more pronounced neuroprotective effect compared to their separate application. Some signaling systems are associated with the predominance of the hypoxic stimulus (HIF-1α, A1 receptors), while others (NF-κB, antioxidant activity, inhibition of apoptosis, maintenance of selective blood-brain barrier permeability) are mainly modulated by hypercapnia. Most of the molecular and cellular mechanisms involved in the formation of brain tolerance to ischemia are due to the contribution of both excess carbon dioxide and oxygen deficiency (ATP-dependent potassium channels, chaperones, endoplasmic reticulum stress, mitochondrial metabolism reprogramming). Overall, experimental studies indicate the dominance of hypercapnia in the neuroprotective effect of its combined action with hypoxia. Recent clinical studies have demonstrated the effectiveness of hypercapnic-hypoxic training in the treatment of childhood cerebral palsy and diabetic polyneuropathy in children. Combining hypercapnic hypoxia with pharmacological modulators of neuro/cardio/cytoprotection signaling pathways is likely to be promising for translating experimental research into clinical medicine.

Glucose Fluctuation Inhibits Nrf2 Signaling Pathway in Hippocampal Tissues and Exacerbates Cognitive Impairment in Streptozotocin-Induced Diabetic Rats

Background

This research investigated whether glucose fluctuation (GF) can exacerbate cognitive impairment in streptozotocin-induced diabetic rats and explored the related mechanism.

Methods

After 4 weeks of feeding with diets containing high fats plus sugar, the rat model of diabetes mellitus (DM) was established by intraperitoneal injection of streptozotocin (STZ). Then, GF was triggered by means of alternating satiety and starvation for 24 h. The weight, blood glucose level, and water intake of the rats were recorded. The Morris water maze (MWM) test was carried out to appraise the cognitive function at the end of week 12. Moreover, the morphological structure of hippocampal neurons was viewed through HE and Nissl staining, and transmission electron microscopy (TEM) was performed for ultrastructure observation. The protein expression levels of Nrf2, HO-1, NQO-1, Bax, Bcl-2, and Caspase-3 in the hippocampal tissues of rats were measured via Western blotting, and the mRNA expressions of Nrf2, HO-1, and NQO-1 were examined using qRT-PCR. Finally, Western blotting and immunohistochemistry were conducted to detect BDNF levels.

Results

It was manifested that GF not only aggravated the impairment of spatial memory in rats with STZ-induced type 2 DM but also stimulated the loss, shrinkage, and apoptosis of hippocampal neurons. Regarding the expressions in murine hippocampal tissues, GF depressed Nrf2, HO-1, NQO-1, Bcl-2, and BDNF but boosted Caspase-3 and Bax.

Conclusions

GF aggravates cognitive impairment by inhibiting the Nrf2 signaling pathway and inducing oxidative stress and apoptosis in the hippocampal tissues.

Associations between HbA1c Reduction and Change in Depressive Symptoms following Glucose-lowering Treatment in Adults: A Systematic Review of Intervention Studies

INTRODUCTION

Hyperglycemia constitutes a likely pathway linking diabetes and depressive symptoms; lowering glycemic levels may help reduce diabetes-comorbid depressive symptoms. Since randomized controlled trials can help understand temporal associations, we systematically reviewed the evidence regarding the potential association of hemoglobin HbA1c lowering interventions with depressive symptoms.

METHODS

PubMed, PsycINFO, CINAHL, and EMBASE databases were searched for randomized controlled trials evaluating HbA1c-lowering interventions and including assessment of depressive symptoms published between 01/2000-09/2020. Study quality was evaluated using the Cochrane Risk of Bias tool. PROSPERO registration: CRD42020215541.

RESULTS

We retrieved 1,642 studies of which twelve met our inclusion criteria. Nine studies had high and three unclear risks of bias. Baseline depressive symptom scores suggest elevated depressive symptoms in five studies. Baseline HbA1c was <8.0% (<64 mmol/mol) in two, 8.0-9.0% (64-75 mmol/mol) in eight, and ≥10.0% (≥86 mmol/mol) in two studies. Five studies found greater HbA1c reduction in the treatment group; three of these found greater depressive symptom reduction in the treatment group. Of four studies analyzing whether the change in HbA1c was associated with the change in depressive symptoms, none found a significant association. The main limitation of these studies was relatively low levels of depressive symptoms at baseline, limiting the ability to show a lowering in depressive symptoms after HbA1c reduction.

CONCLUSIONS

We found insufficient available data to estimate the association between HbA1c reduction and depressive symptom change following glucose-lowering treatment. Our findings point to an important gap in the diabetes treatment literature. Future clinical trials testing interventions to improve glycemic outcomes might consider measuring depressive symptoms as an outcome to enable analyses of this association.

Visit-to-Visit Glucose Variability, Cognition, and Global Cognitive Decline: The Multi-Ethnic Study of Atherosclerosis

CONTEXT

Higher visit-to-visit glucose variability (GV) is associated with dysglycemia and type 2 diabetes (T2D), key risk factors for cognitive decline.

OBJECTIVE

Evaluate the association of GV with cognitive performance and decline in racially/ethnically diverse older populations with and without T2D.

METHODS

We calculated the standard deviation of glucose (SDG), average real variability (ARV), and variability independent of the mean (VIM) among 4367 Multi-Ethnic Study of Atherosclerosis participants over 6 clinical examinations. Participants completed a cognitive assessment at the fifth examination, and a subset completed a second assessment 6 years later. We used multivariable linear regression to estimate the association of intraindividual GV with cognitive test scores after adjustments for cardiovascular risk factors and mean glucose level over the study period.

RESULTS

Two-fold increments in the VIM and SDG were associated with worse Cognitive Abilities Screening Instrument (CASI) performance, while two-fold increments in VIM and ARV were associated with worse Digit Symbol Coding test score. GV measures were not associated with change in CASI performance among 1834 participants with repeat CASI data 6 years later. However, among 229 participants with incident T2D, the SDG and VIM were associated with decline in CASI (-1.7 [95% CI: -3.1, -0.3] and -2.1 [-3.7, -0.5] points, respectively). In contrast, single-timepoint glucose and HbA1c were not associated with CASI decline among participants with or without incident T2D.

CONCLUSION

Higher visit-to-visit GV over 16 to 18 years is associated with worse cognitive performance in the general population, and with modest global cognitive decline in participants with T2D.

Risk of depression and anxiety disorders according to long-term glycemic variability

BACKGROUND

Poor glycemic control has been linked to psychiatric symptoms. However, studies investigating the relationship between glycemic variability (GV) and depression and anxiety disorders are limited. We investigated the association of GV with depression and anxiety disorders. In addition, the relationship between trends in fasting plasma glucose (FPG) levels and these disorders were explored.

METHODS

We analyzed the National Health Insurance Service-National Sample Cohort database (2002-2013) with 151,814 participants who had at least three health screenings between 2002 and 2010. Visit-to-visit FPG variability was measured as variability independent of the mean (VIM). Depression and anxiety disorders were diagnosed using ICD-10 codes (F41 for anxiety and F32 or F33 for depression) after index date. We analyzed the association between GV and incidences of these disorders using Kaplan-Meier and Cox proportional hazards methods. Trajectory analysis was conducted to explore the relationship between FPG trends and these disorders.

RESULTS

During follow-up, 7166 and 14,149 patients were newly diagnosed with depression and anxiety disorders, respectively. The highest quartile group of FPG-VIM had a greater incidence of depression and anxiety than the lowest quartile group, with adjusted hazard ratios of 1.09 (95 % confidence interval [CI]: 1.02-1.17) and 1.08 (95 % CI: 1.03-1.14). Group with persistent hyperglycemia, identified through trajectory clustering of FPG levels, had a 1.43-fold increased risk of depression compared to those with consistently low FPG levels.

LIMITATIONS

Potential selection bias by including participants with at least three health screenings.

CONCLUSIONS

High GV and persistent hyperglycemia are associated with increased incidence of depression and anxiety disorders.

Association of glycemic variability with death and severe consciousness disturbance among critically ill patients with cerebrovascular disease: analysis of the MIMIC-IV database

BACKGROUND

The association of glycemic variability with severe consciousness disturbance and in-hospital all-cause mortality in critically ill patients with cerebrovascular disease (CVD) remains unclear, This study aimed to investigate the association of glycemic variability with cognitive impairment and in-hospital death.

METHOD

We extracted all blood glucose measurements of patients diagnosed with CVD from the Medical Information Mart for Intensive Care IV (MIMIC-IV). Glycemic variability was defined as the coefficient of variation (CV), which was determined using the ratio of standard deviation and the mean blood glucose levels. Cox hazard regression models were applied to analyze the link between glycemic variability and outcomes. We also analyzed non-linear relationship between outcome indicators and glycemic variability using restricted cubic spline curves.

RESULTS

The present study included 2967 patients diagnosed with cerebral infarction and 1842 patients diagnosed with non-traumatic cerebral hemorrhage. Log-transformed CV was significantly related to cognitive impairment and in-hospital mortality, as determined by Cox regression. Increasing log-transformed CV was approximately linearly with the risk of cognitive impairment and in-hospital mortality.

CONCLUSION

High glycemic variability was found to be an independent risk factor for severe cognitive decline and in-hospital mortality in critically ill patients with CVD. Our study indicated that enhancing stability of glycemic variability may reduced adverse outcomes in patients with severe CVD.

Understanding the Combined Effects of High Glucose Induced Hyper-Osmotic Stress and Oxygen Tension in the Progression of Tumourigenesis: From Mechanism to Anti-Cancer Therapeutics

High glucose (HG), a hallmark of the tumour microenvironment, is also a biomechanical stressor, as it exerts hyper-osmotic stress (HG-HO), but not much is known regarding how tumour cells mechanoadapt to HG-HO. Therefore, this study aimed to delineate the novel molecular mechanisms by which tumour cells mechanoadapt to HG/HG-HO and whether phytochemical-based interference in these mechanisms can generate tumour-cell-selective vulnerability to cell death. Mannitol and L-glucose were used as hyper-osmotic equivalents of high glucose. The results revealed that the tumour cells can efficiently mechanoadapt to HG-HO only in the normoxic microenvironment. Under normoxic HG/HG-HO stress, tumour cells polySUMOylate a higher pool of mitotic driver pH3(Ser10), which translocates to the nucleus and promotes faster cell divisions. On the contrary, acute hypoxia dampens HG/HG-HO-associated excessive proliferation by upregulating sentrin protease SENP7. SENP7 promotes abnormal SUMOylation of pH3(Ser10), thereby restricting its nuclear entry and promoting the M-phase arrest and cell loss. However, the hypoxia-arrested cells that managed to survive showed relapse upon reversal to normoxia as well as upregulation of pro-survival-associated SENP1, and players in tumour growth signalling, autophagy, glycolytic pathways etc. Depletion of SENP1 in both normoxia and hypoxia caused significant loss of tumour cells vs undepleted controls. SENP1 was ascertained to restrict the abnormal SUMOylation of pH3(Ser10) in both normoxia and hypoxia, although not so efficiently in hypoxia, due to the opposing activity of SENP7. Co-treatment with Momordin Ic (MC), a natural SENP1 inhibitor, and Gallic Acid (GA), an inhibitor of identified major pro-tumourigenic signalling (both enriched in Momordica charantia), eliminated surviving tumour cells in normal glucose, HG and HG-HO normoxic and hypoxic microenvironments, suggesting that appropriate and enhanced polySUMOylation of pH3(Ser10) in response to HG/HG-HO stress was attenuated by this treatment along with further dampening of other key tumourigenic signalling, due to which tumour cells could no longer proliferate and grow.

A critical review of the relationship between type 1 diabetes mellitus, inhibition, and behavioral management

Type 1 diabetes mellitus (T1DM) is a chronic and lifelong condition that requires adequate behavior management in order to meet desired health outcomes. The effects of T1DM on the neurocognitive functioning of affected individuals raise concerns about how the disease may influence executive functioning. Inhibition is a core component of executive functioning, and plays a vital role in self-regulation and the restriction of impulsive behaviors. Inhibition may thus play a vital role in the behavior management of people with T1DM. The aim of this study was to identify current gaps in existing knowledge regarding the relationship between T1DM, inhibition, and behavior management. This study employed a critical review design to analyze and synthesize the current scientific literature. Twelve studies were identified through an appraisal process, and the data extracted were thematically analyzed and integrated. The findings of this study indicate that a possible cycle arises between these three constructs, in which T1DM affects inhibition, inhibition affects behavior management, and poor behavior management affects inhibition. It is recommended that future research should focus more specifically on this relationship.

Fasting Glucose Variability and the Risk of Dementia in Individuals with Diabetes: A Nationwide Cohort Study

BACKGROUND

We investigated whether fasting glucose (FG) variability could predict the risk of dementia.

METHODS

This cohort study analyzed data from Koreans with diabetes after at least three health examinations by the Korean National Health Insurance Corporation between 2005 and 2010, which included at least one examination between 2009 and 2010. A total of 769,554 individuals were included, excluding those aged <40 years and those with dementia. FG variability was measured using the variability independent of the mean (FG-VIM). The incidence of dementia was defined by the International Classification of Diseases 10th Revision codes and prescription of anti-dementia medication and was subdivided into Alzheimer's disease (AD) and vascular dementia (VD).

RESULTS

During the 6.9-year follow-up, 54,837, 41,032, and 6,892 cases of all-cause dementia, AD, and VD, respectively, were identified. Cox proportional regression analyses showed that as the FG-VIM quartile increased, the risk of dementia serially increased after adjustment for metabolic factors, income status, and diabetes-related characteristics, including the mean FG. Participants in FG-VIM quartile 4 showed a 18%, 19%, and 17% higher risk for all-cause dementia, AD, and VD, respectively, than those in quartile 1; this particularly included non-obese patients with a longer duration of diabetes, high FG levels, dyslipidemia, and those taking glucose-lowering medications. Conversely, the baseline FG status and dementia showed a U-shaped association.

CONCLUSION

Increased FG variability over 5 years can predict the risk of dementia in individuals with diabetes in Korea. This finding was more pronounced in patients with less favorable metabolic profiles.

Impact of glucose metabolism on the developing brain

Glucose is the most important substrate for proper brain functioning and development, with an increased glucose consumption in relation to the need of creating new brain structures and connections. Therefore, alterations in glucose homeostasis will inevitably be associated with changes in the development of the Nervous System. Several studies demonstrated how the alteration of glucose homeostasis - both hyper and hypoglycemia- may interfere with the development of brain structures and cognitivity, including deficits in intelligence quotient, anomalies in learning and memory, as well as differences in the executive functions. Importantly, differences in brain structure and functionality were found after a single episode of diabetic ketoacidosis suggesting the importance of glycemic control and stressing the need of screening programs for type 1 diabetes to protect children from this dramatic condition. The exciting progresses of the neuroimaging techniques such as diffusion tensor imaging, has helped to improve the understanding of the effects, outcomes and mechanisms underlying brain changes following dysglycemia, and will lead to more insights on the physio-pathological mechanisms and related neurological consequences about hyper and hypoglycemia.

Sensitive Oxidation of Sorbitol-Mediated Fe2+ by H2O2: A Reliable TD-NMR Method for Clinical Blood Glucose Detection

The clinical challenge of high-accuracy blood glucose detection schemes is to overcome the detection error caused by the background interferences in different individuals. H₂O₂ as the specific product of glucose oxidation can be involved in the Fe²⁺/Fe³⁺ conversion and detected by the time-domain nuclear magnetic resonance (TD-NMR) method sensitively. But, in clinical applications, the oxidation of Fe²⁺ is susceptible to the complex sample substrates. In this work, we sorted out two kinds of possible interference mechanisms of Fe²⁺ oxidation in the NMR blood glucose detection method and proposed a feasible scheme that uses sorbitol to weaken the adverse effects of interference. We found that sorbitol-mediated Fe²⁺ can greatly enhance the sensitivity of the T₂ value to H₂O₂. The chain reaction caused by sorbitol can significantly amplify the efficiency of Fe²⁺ oxidation at the same concentration of H₂O₂. Thereby, we can achieve the higher dilution multiple of serum samples to reduce the amount of interfering substances involved in the Fe²⁺/Fe³⁺ conversion. We justified the accuracy and availability of our method by successfully detecting and confirming the correlation between the T₂ decrease and glucose concentration of the serum samples collected from 16 subjects. The sorbitol-Fe²⁺ glucose detection method with high sensitivity can be further combined with miniature NMR analyzers to satisfy the calibration requirements of glucose monitoring in diabetic patients instead of frequent medical visits.

Impact of Intensive Glucose Control on Brain Health: Meta-Analysis of Cumulative Data from 16,584 Patients with Type 2 Diabetes Mellitus

INTRODUCTION

Despite growing evidence that type 2 diabetes is associated with dementia, the question of whether intensive glucose control can prevent or arrest cognitive decline remains unanswered. In the analysis reported here, we explored the effect of intensive glucose control versus standard care on brain health, including structural abnormalities of the brain (atrophy, white matter hyperintensities, lacunar infarction, and cerebral microbleeds), cognitive dysfunction, and risk of dementia.

METHODS

We searched the PubMed and Embase databases, the Web of Science website, and the Clinicaltrial.gov registry for studies published in English prior to July 2020. Only studies with a randomized controlled trial (RCT) design were considered. We analyzed structural abnormalities of the brain (atrophy, white matter hyperintensities, lacunar infarction, and cerebral microbleeds), cognitive function (cognitive impairment, executive function, memory, attention, and information-processing speed), and dementia (Alzheimer's disease, vascular dementia, and mixed dementia).

RESULTS

Six studies (5 different RCTs) with 16,584 participants were included in this meta-analysis. One study that compared structural changes between groups receiving intensive versus conventional glucose control measures reported non-significant results. The results of the five studies, comprising four cohorts, indicated a significantly poorer decline in cognitive function in the intensive glucose control group (β - 0.03, 95% confidence interval [CI] - 0.05 to - 0.02) than in the conventional glucose control group. Further subgroup analysis showed a significant difference in the change in cognitive performance in composite cognitive function (β - 0.03, 95% CI - 0.05 to - 0.01) and memory (β  - 0.13, 95% CI - 0.25 to - 0.02). One trial evaluated the prevalence of cognitive impairment and dementia between groups receiving intensive and conventional glucose control, respectively, and the differences were insignificant.

CONCLUSION

This meta-analysis suggests that intensive glucose control in patients with type 2 diabetes can slow down cognitive decline, especially the decline in composite cognition and memory function. However, further studies are necessary to confirm the impact of strict glucose control on structural abnormalities in the brain and the risk of dementia.

miR-129-3p Targeting of MCU Protects Against Glucose Fluctuation-Mediated Neuronal Damage via a Mitochondrial-Dependent Intrinsic Apoptotic Pathway

INTRODUCTION

Glucose fluctuations have an adverse effect on several diabetes-related complications, especially for the nervous system, but the underlying mechanisms are not clear. MicroRNAs are critical regulators of posttranscription in many physiological processes, such as apoptosis. Our study clarified the neuroprotective effects of miR-129-3p targeting mitochondrial calcium uniporter (MCU) in glucose fluctuation-mediated neuronal damage and the specific mechanisms involved.

METHODS

The expression of MCU and miR-129-3p was examined by real-time PCR and Western blot in the glucose fluctuation cell model. Dual-luciferase reporter assay was performed to confirm the transcriptional regulation of miR-129-3p by MCU. Fluorescent probe and assay kit assay was used to determine oxidative stress condition. Mitochondrial-dependent intrinsic apoptotic factors were examined by flow cytometry assay, enzyme-linked immunosorbent assay (ELISA), and gene and protein expression assays.

RESULTS

We found an upregulation of MCU and downregulation of miR-129-3p in glucose fluctuation-treated primary hippocampal neuronal cells, and miR-129-3p directly targeted MCU. miR-129-3p overexpression produced a dramatic reduction in calcium overload, reactive oxygen species (ROS) generation, GSH-to-GSSG ratio, MMP-2 expression in the mitochondrial-dependent intrinsic apoptosis pathway and an increase in MnSOD activity. Increasing MCU expression rescued the effects of miR-129-3p overexpression. miR-129-3p downregulation produced a significant increase in calcium overload, reactive oxygen species (ROS) generation, MMP-2 expression, cytochrome c release and cell apoptosis, and antioxidant N-acetyl cysteine (NAC) rescued the effects of miR-129-3p downregulation.

CONCLUSION

Therefore, miR-129-3p suppressed glucose fluctuation-mediated neuronal damage by targeting MCU via a mitochondrial-dependent intrinsic apoptotic pathway. The miR-129-3p/MCU axis may be a promising therapeutic target for glucose fluctuation-mediated neuronal damage.

Glycemic Variability and CNS Inflammation: Reviewing the Connection

Glucose is the primary energy source for the brain, and exposure to both high and low levels of glucose has been associated with numerous adverse central nervous system (CNS) outcomes. While a large body of work has highlighted the impact of hyperglycemia on peripheral and central measures of oxidative stress, cognitive deficits, and vascular complications in Type 1 and Type 2 diabetes, there is growing evidence that glycemic variability significantly drives increased oxidative stress, leading to neuroinflammation and cognitive dysfunction. In this review, the latest data on the impact of glycemic variability on brain function and neuroinflammation will be presented. Because high levels of oxidative stress have been linked to dysfunction of the blood-brain barrier (BBB), special emphasis will be placed on studies investigating the impact of glycemic variability on endothelial and vascular inflammation. The latest clinical and preclinical/in vitro data will be reviewed, and clinical/therapeutic implications will be discussed.

Resveratrol Prevents GLUT3 Up-Regulation Induced by Middle Cerebral Artery Occlusion

Glucose transporter (GLUT)3 up-regulation is an adaptive response activated to prevent cellular damage when brain metabolic energy is reduced. Resveratrol is a natural polyphenol with anti-oxidant and anti-inflammatory features that protects neurons against damage induced in cerebral ischemia. Since transcription factors sensitive to oxidative stress and inflammation modulate GLUT3 expression, the purpose of this work was to assess the effect of resveratrol on GLUT3 expression levels after ischemia. Male Wistar rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) followed by different times of reperfusion. Resveratrol (1.9 mg/kg; i. p.) was administered at the onset of the restoration of the blood flow. Quantitative-PCR and Western blot showed that MCAO provoked a substantial increase in GLUT3 expression in the ipsilateral side to the lesion of the cerebral cortex. Immunofluorescence assays indicated that GLUT3 levels were upregulated in astrocytes. Additionally, an important increase in GLUT3 occurred in other cellular types (e.g., damaged neurons, microglia, or infiltrated macrophages). Immunodetection of the microtubule-associated protein 2 (MAP2) showed that MCAO induced severe damage to the neuronal population. However, the administration of resveratrol at the time of reperfusion resulted in injury reduction. Resveratrol also prevented the MCAO-induced increase of GLUT3 expression. In conclusion, resveratrol protects neurons from damage induced by ischemia and prevents GLUT3 upregulation in the damaged brain that might depend on AMPK activation.

Visit-to-Visit Fasting Glucose Variability in Young Adulthood and Hippocampal Integrity and Volume at Midlife

OBJECTIVE

To determine whether visit-to-visit fasting glucose (VVFG) variability in young adulthood is associated with midlife hippocampal integrity and volume.

RESEARCH DESIGN AND METHODS

Multivariable-adjusted linear regression models were used to estimate the association between VVFG variability and brain MRI variables in 543 CARDIA study participants. VVFG variability was defined by the SD of FG (SDFG), the coefficient of variation of the mean FG (CVFG), and the average real variability (ARVFG) over 25 years of follow-up. Hippocampal integrity fractional anisotropy (FA) and tissue volume standardized to intracranial volume were measured by 3T MRI at year 25.

RESULTS

After multivariable adjustment, higher FG variability (1-SD increase) was associated with lower hippocampal FA (SDFG -0.015 [95% CI -0.026, -0.004]; CVFG -0.009 [95% CI -0.018, -0.001]; ARVFG -0.011 [95% CI -0.019, -0.002]) and lower hippocampal volume (SDFG -0.012 [95% CI -0.023, -0.001]).

CONCLUSIONS

Higher VVFG variability in young adulthood is associated with lower midlife hippocampal integrity and volume, suggesting its value in predicting risk for hippocampal structural damage.

Clinical Use of Degludec in Children and Adolescents with T1D: A Narrative Review with Fictionalized Case Reports

The use of insulin in children and adolescents with type 1 diabetes (T1D) is a challenge because of the heterogeneity of these patients and their lifestyles, with consequent unpredictability in blood glucose levels. A new ultra-long-acting basal insulin, insulin degludec (degludec), has the potential to mitigate some of these challenges, notably variability in the glucose-lowering action of the basal insulin component of an insulin regimen, and consequent risks of hypo- and hyperglycemia. However, the protracted half-life and steady state pharmacokinetics of degludec potentially bring some new challenges. In particular, the adjustment of therapy in response to commonly encountered clinical situations might require a different approach when degludec is used in place of other currently used basal insulins in this challenging patient population. The purpose of this article is to guide clinicians through a series of case histories in the use of this insulin. These include, but are not limited to, how to initiate, titrate, switch from other basal insulin or pump therapy; how to alleviate difficulties arising as a result of unpredictable lifestyle/habits; and how to maintain treatment following diabetic ketoacidosis. The guidance presented in this review illustrates that degludec is a good option for a diverse range of children and adolescents with T1D, providing much needed flexibility in the treatment of this challenging patient population.Funding Novo Nordisk.

Fasting Glucose Variability in Young Adulthood and Cognitive Function in Middle Age: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

OBJECTIVE

To determine whether intraindividual variability in fasting glucose (FG) below the threshold of diabetes is associated with cognitive function in middle adulthood beyond increasing FG.

RESEARCH DESIGN AND METHODS

We studied 3,307 CARDIA (Coronary Artery Risk Development in Young Adults) Study participants (age range 18-30 years and enrolled in 1985-1986) at baseline and calculated two measures of long-term glucose variability: the coefficient of variation about the mean FG (CV-FG) and the absolute difference between successive FG measurements (average real variability [ARV-FG]) before the onset of diabetes over 25 and 30 years of follow-up. Cognitive function was assessed at years 25 (2010-2011) and 30 (2015-2016) with the Digit Symbol Substitution Test (DSST), Rey-Auditory Verbal Learning Test (RAVLT), Stroop Test, Montreal Cognitive Assessment, and category and letter fluency tests. We estimated the association between glucose variability and cognitive function test score with adjustment for clinical and behavioral risk factors, mean FG level, change in FG level, and diabetes development, medication use, and duration.

RESULTS

After multivariable adjustment, 1-SD increment of CV-FG was associated with worse cognitive scores at year 25: DSST, standardized regression coefficient -0.95 (95% CI -1.54, -0.36); RAVLT, -0.14 (95% CI -0.27, -0.02); and Stroop Test, 0.49 (95% CI 0.04, 0.94). Findings were similar between CV-FG with each cognitive test score at year 30 and when we used an alternative measure of variability (ARV-FG) that captures variability in successive FG values.

CONCLUSIONS

Higher intraindividual FG variability during young adulthood below the threshold of diabetes was associated with worse processing speed, memory, and language fluency in midlife independent of FG levels.

The Glymphatic System in Diabetes-Induced Dementia

The glymphatic system has emerged as an important player in central nervous system (CNS) diseases, by regulating the vasculature impairment, effectively controlling the clearance of toxic peptides, modulating activity of astrocytes, and being involved in the circulation of neurotransmitters in the brain. Recently, several studies have indicated decreased activity of the glymphatic pathway under diabetes conditions such as in insulin resistance and hyperglycemia. Furthermore, diabetes leads to the disruption of the blood-brain barrier and decrease of apolipoprotein E (APOE) expression and the secretion of norepinephrine in the brain, involving the impairment of the glymphatic pathway and ultimately resulting in cognitive decline. Considering the increased prevalence of diabetes-induced dementia worldwide, the relationship between the glymphatic pathway and diabetes-induced dementia should be investigated and the mechanisms underlying their relationship should be discussed to promote the development of an effective therapeutic approach in the near future. Here, we have reviewed recent evidence for the relationship between glymphatic pathway dysfunction and diabetes. We highlight that the enhancement of the glymphatic system function during sleep may be beneficial to the attenuation of neuropathology in diabetes-induced dementia. Moreover, we suggest that improving glymphatic system activity may be a potential therapeutic strategy for the prevention of diabetes-induced dementia.

Insulin deprivation decreases insulin degrading enzyme levels in primary cultured cortical neurons and in the cerebral cortex of rats with streptozotocin-induced diabetes

BACKGROUND

Many studies have indicated a relationship between diabetes and Alzheimer's disease (AD). However, the molecular mechanism underlying this association has not been clarified. Among several factors, insulin degrading enzyme (IDE), which plays roles in the degradation of both insulin and amyloid β (Aβ), has gained interest as a potential target in efforts to solve this puzzle. This study sought to examine the effects of varying insulin and/or glucose concentrations on IDE expression.

METHODS

Experiments were performed on primary cultured rat neurons and cortices of rats with streptozotocin (STZ)-induced diabetes. IDE protein and mRNA expression levels were measured by western blot and RT-PCR, respectively.

RESULTS

In primary cultured cortical neurons, removal of insulin for 5days reduced the expression of IDE. A five-day treatment with a high concentration of glucose in insulin-free media reduced IDE levels, while a high concentration of glucose in the presence of insulin had no effect. In groups treated with glucose or insulin intermittently, the reduction in IDE levels was observed only in neurons exposed to high glucose together with no insulin for 5days. Shorter incubation periods (48h), either continuously or intermittently, did not affect IDE levels. IDE expression in the cortex of rats with STZ-induced diabetes was found to be decreased.

CONCLUSION

Our data suggest that insulin deprivation, rather than high glucose, is a significant determinant of IDE regulation. As evidence indicates potential roles for IDE in diabetes and AD, understanding the mechanisms regulating IDE expression may be important in developing new treatment strategies.

The effects of incretin hormones on cerebral glucose metabolism in health and disease

Incretin hormones, notably glucagon-like peptide-1 (GLP-1), are gluco-regulatory hormones with pleiotropic effects also in the central nervous system. Apart from a local production of GLP-1, systemic administration of the hormone has been shown to influence a number of cerebral pathologies, including neuroinflammation. Given the brains massive dependence on glucose as its major fuel, we here review the mechanistics of cerebral glucose transport and metabolism, focusing on the deleterious effects of both hypo- and hyperglycaemia. GLP-1, when administered as long-acting analogues or intravenously, appears to decrease transport of glucose in normoglycaemic conditions, without affecting the total cerebral glucose content. During hypoglycaemia this effect seems abated, whereas during hyperglycaemia GLP-1 regulates cerebral glucose metabolism towards stable levels resembling normoglycaemia. In Alzheimer's disease, a 6-month intervention with GLP-1 maintained cerebral glucose levels at baseline levels, contrasting the decline otherwise seen in Alzheimer's. Kinetic studies suggest blood-brain barrier (BBB) glucose transport as the key player in GLP-1 mediated effects on cerebral glucose metabolism. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

The additional dose of insulin for high-protein mixed meal provides better glycemic control in children with type 1 diabetes on insulin pumps: randomized cross-over study

BACKGROUND

Delivery of insulin for high-protein low-fat meals with carbohydrates on the basis of carbohydrates leads to higher late postprandial glycemia. Studies with mixed meals demonstrated lower blood glucose level after dual wave bolus. The objective of our study was to assess the impact of additional dose of insulin in dual wave bolus for high-protein mixed meal on the postprandial glycemia.

MATERIALS AND METHODS

We performed a randomized, double-blind, two-way cross-over study, including 58 children with type 1 diabetes, aged 14.7 ± 2.2 years. Participants were randomly assigned into two treatment orders: NORMAL-DUAL or DUAL-NORMAL BOLUS. They consumed standardized high-protein, low-fat meals with carbohydrates. The primary outcome was postprandial glycemia (PPG) based on capillary blood glucose measurements (CBGM). The secondary outcomes were the frequency of hypoglycemia, area under glucose curve, mean amplitude of glycemic excursion (MAGE) and glycemic rise.

RESULTS

PPG assessed at 180 min was significantly lower when dual wave bolus was delivered (NORMAL 162 mg/dL [9 mmol/L] vs DUAL 130.0 mg/dL [7.22 mmol/L]; P = .004). There were no differences in CBGM between both groups at 60 and 120 min. We found differences between the groups in MAGE at 120 min (NORMAL 82.86 mg/dL [4.6 mmol/L] versus DUAL 54.76 mg/dL [3.04 mmol/L]; P = .0008). We observed no differences in the number of hypoglycemic episodes in both groups.

CONCLUSION

Applying an additional dose of insulin in dual wave bolus for high-protein mixed meal improved PPG. We observed no statistically significant increase in the number of hypoglycemic episodes associated with this intervention.

N-Methyl-D aspartate receptor-mediated effect on glucose transporter-3 levels of high glucose exposed-SH-SY5Y dopaminergic neurons

High glucose and insulin lead to neuronal insulin resistance. Glucose transport into the neurons is achieved by regulatory induction of surface glucose transporter-3 (GLUT3) instead of the insulin. N-methyl-D aspartate (NMDA) receptor activity increases GLUT3 expression. This study explored whether an endogenous NMDA receptor antagonist, kynurenic acid (KynA) affects the neuronal cell viability at high glucose concentrations. SH-SY5Y neuroblastoma cells were exposed to 150-250 mg/dL glucose and 40 μU/mL insulin. In KynA and N-nitro-l-arginine methyl ester (L-NAME) supplemented cultures, oxidative stress, mitochondrial metabolic activity (MTT), nitric oxide as nitrite+nitrate (NOx) and GLUT3 were determined at the end of 24 and 48-h incubation periods. Viable cells were counted by trypan blue dye. High glucose-exposed SH-SY5Y cells showed two-times more GLUT3 expression at second 24-h period. While GLUT3-stimulated glucose transport and oxidative stress was increased, total mitochondrial metabolic activity was significantly reduced. Insulin supplementation to high glucose decreased NOx synthesis and GLUT3 levels, in contrast oxidative stress increased three-fold. KynA significantly reduced oxidative stress, and increased MTT by regulating NOx production and GLUT3 expression. KynA is a noteworthy compound, as an endogenous, specific NMDA receptor antagonist; it significantly reduces oxidative stress, while increasing cell viability at high glucose and insulin concentrations.

Uncoupling Protein 2 Inhibition Exacerbates Glucose Fluctuation-Mediated Neuronal Effects

Though glucose fluctuations have been considered as an adverse factor for the development of several diabetes-related complications, their impact in the central nervous system is still not fully elucidated. This study was conducted to evaluate the responses of neuronal cells to different glycemic exposures alongside to elucidate the role of uncoupling protein 2 (UCP2) in regulating such responses. To achieve our goals, primary cortical neurons were submitted to constant high (HG)/low (LG) or glucose level variations (GVs), and the pharmacological inhibition of UCP2 activity was performed using genipin. Results obtained show that GV decreased neuronal cells' viability, mitochondrial membrane potential, and manganese superoxide dismutase activity and increased reactive oxygen species (ROS) production. GV also caused an increase in the glutathione/glutathione disulfide ratio and in the protein expression levels of nuclear factor E2-related factor 2 (NRF2), UCP2, NADH-ubiquinone oxidoreductase chain 1 (ND1), and mitochondrially encoded cytochrome c oxidase I (MTCO1), both mitochondrial DNA encoded subunits of the electron transport chain. Contrariwise, genipin abrogated all those compensations and increased the levels of caspase 3-like activity, potentiated mitochondrial ROS levels, and the loss of neuronal synaptic integrity, decreased the protein expression levels of NRF1, and increased the protein expression levels of UCP5. Further, in the control and LG conditions, genipin increased mitochondrial ROS and the protein expression levels of UCP4, postsynaptic density protein 95 (PSD95), ND1, and MTCO1. Overall, these observations suggest that UCP2 is in the core of neuronal cell protection and/or adaptation against GV-mediated effects and that other isoforms of neuronal UCPs can be upregulated to compensate the inhibition of UCP2 activity.

Glucose Peaks and the Risk of Dementia and 20-Year Cognitive Decline

OBJECTIVE

Hemoglobin A_1c (HbA_1c), a measure of average blood glucose level, is associated with the risk of dementia and cognitive impairment. However, the role of glycemic variability or glucose excursions in this association is unclear. We examined the association of glucose peaks in midlife, as determined by the measurement of 1,5-anhydroglucitol (1,5-AG) level, with the risk of dementia and 20-year cognitive decline.

RESEARCH DESIGN AND METHODS

Nearly 13,000 participants from the Atherosclerosis Risk in Communities (ARIC) study were examined. Dementia was ascertained from surveillance, neuropsychological testing, telephone calls with participants or their proxies, or death certificate dementia codes. Cognitive function was assessed using three neuropsychological tests at three visits over 20 years and was summarized as z scores. We used Cox and linear mixed-effects models. 1,5-AG level was dichotomized at 10 μg/mL and examined within clinical categories of HbA_1c.

RESULTS

Over a median time of 21 years, dementia developed in 1,105 participants. Among persons with diabetes, each 5 μg/mL decrease in 1,5-AG increased the estimated risk of dementia by 16% (hazard ratio 1.16, P = 0.032). For cognitive decline among participants with diabetes and HbA_1c <7% (53 mmol/mol), those with glucose peaks had a 0.19 greater z score decline over 20 years (P = 0.162) compared with those without peaks. Among participants with diabetes and HbA_1c ≥7% (53 mmol/mol), those with glucose peaks had a 0.38 greater z score decline compared with persons without glucose peaks (P < 0.001). We found no significant associations in persons without diabetes.

CONCLUSIONS

Among participants with diabetes, glucose peaks are a risk factor for cognitive decline and dementia. Targeting glucose peaks, in addition to average glycemia, may be an important avenue for prevention.

ROS Production and ERK Activity Are Involved in the Effects of d-β-Hydroxybutyrate and Metformin in a Glucose Deficient Condition

Hypoglycemia, a complication of insulin or sulfonylurea therapy in diabetic patients, leads to brain damage. Furthermore, glucose replenishment following hypoglycemic coma induces neuronal cell death. In this study, we investigated the molecular mechanism underlying glucose deficiency-induced cytotoxicity and the protective effect of d-β-hydroxybutyrate (D-BHB) using SH-SY5Y cells. The cytotoxic mechanism of metformin under glucose deficiency was also examined. Cell viability under 1 mM glucose (glucose deficiency) was significantly decreased which was accompanied by increased production of reactive oxygen species (ROS) and decreased phosphorylation of extracellular signal-regulated kinase (ERK) and glycogen synthase 3 (GSK3β). ROS inhibitor reversed the glucose deficiency-induced cytotoxicity and restored the reduced phosphorylation of ERK and GSK3β. While metformin did not alter cell viability in normal glucose media, it further increased cell death and ROS production under glucose deficiency. However, D-BHB reversed cytotoxicity, ROS production, and the decrease in phosphorylation of ERK and GSK3β induced by the glucose deficiency. ERK inhibitor reversed the D-BHB-induced increase in cell viability under glucose deficiency, whereas GSK3β inhibitor did not restore glucose deficiency-induced cytotoxicity. Finally, the protective effect of D-BHB against glucose deficiency was confirmed in primary neuronal cells. We demonstrate that glucose deficiency-induced cytotoxicity is mediated by ERK inhibition through ROS production, which is attenuated by D-BHB and intensified by metformin.

Lack of insulin results in reduced seladin-1 expression in primary cultured neurons and in cerebral cortex of STZ-induced diabetic rats

Several studies demonstrated that Diabetes mellitus (DM) enhances the risk for Alzheimer's disease (AD). Although hyperglycemia and perturbed function of insulin signaling have been proposed to contribute to AD pathogenesis, the molecular mechanisms behind this association is not clear yet. Seladin-1 is an enzyme catalyzing the last step in cholesterol biosynthesis converting desmosterol to cholesterol. The neuroprotective function of seladin-1 has gained interest in AD research recently. Seladin-1 has anti-apoptotic properties and regulates the expression of β-secretase (BACE-1). Here we measured seladin-1 mRNA and protein expressions in rat primary cultured neurons under diabetic conditions and also in the brains of rats with streptozotocine (STZ)-induced diabetes. We show that constant lack of insulin for 5days decreased seladin-1 levels in cultured rat primary neurons. Similarly, a decrease in seladin-1 was found in the brains of rats with STZ-induced diabetes. However, if the lack of insulin and/or high glucose treatment was intermittent, neuronal seladin-1 levels were not affected in vitro. On the other hand, treatment of neurons with metformin resulted in a significant increase in seladin-1. Constant lack of insulin for 5days, as well as high glucose treatment, increased the neuronal expression of BACE-1 in vitro, but not in the in vivo model. Our study defines insulin as a regulator of seladin-1 expression for the first time. The relevance of these findings for the association of DM with AD is discussed.

Nrf2-Mediated Neuroprotection Against Recurrent Hypoglycemia Is Insufficient to Prevent Cognitive Impairment in a Rodent Model of Type 1 Diabetes

It remains uncertain whether recurrent nonsevere hypoglycemia (Hypo) results in long-term cognitive impairment in type 1 diabetes (T1D). This study tested the hypothesis that specifically in the T1D state, Hypo leads to cognitive impairment via a pathological response to oxidative stress. Wild-type (Control) and nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) null mice were studied. Eight groups of mice (Control and Nrf2(-/-) ± T1D and ± Hypo) were subject to recurrent, twice-weekly, insulin or saline injections over 4 weeks, after which cognitive function was assessed and brain tissue analyzed. Recurrent moderate hypoglycemia in T1D, but not Control, mice significantly impaired cognitive performance, and this was associated with hippocampal oxidative damage and inflammation despite an enhanced expression of Nrf2 and its target genes Hmox1 and Nqo1 In Nrf2(-/-) mice, both T1D and Hypo independently resulted in impaired cognitive performance, and this was associated with oxidative cell damage and marked inflammation. Together, these data suggest that Hypo induces an Nrf2-dependent antioxidant response in the hippocampus, which counteracts oxidative damage. However, in T1D, this neuroprotective mechanism is insufficient to prevent neuronal oxidative damage, resulting in chronic deficits in working and long-term memory.

Fluctuations in glucose levels induce glial toxicity with glutamatergic, oxidative and inflammatory implications

Astrocytes are dynamic cells that maintain brain homeostasis by regulating neurotransmitter systems, antioxidant defenses, inflammatory responses and energy metabolism. Astroglial cells are also primarily responsible for the uptake and metabolism of glucose in the brain. Diabetes mellitus (DM) is a pathological condition characterized by hyperglycemia and is associated with several changes in the central nervous system (CNS), including alterations in glial function. Classically, excessive glucose concentrations are used to induce experimental models of astrocyte dysfunction; however, hypoglycemic episodes may also cause several brain injuries. The main focus of the present study was to evaluate how fluctuations in glucose levels induce cytotoxicity. The culture medium of astroglial cells was replaced twice as follows: (1) from 6mM (control) to 12mM (high glucose), and (2) from 12mM to 0mM (glucose deprivation). Cell viability, mitochondrial function, oxidative/nitrosative stress, glutamate metabolism, inflammatory responses, nuclear factor κB (NFκB) transcriptional activity and p38 mitogen-activated protein kinase (p38 MAPK) levels were assessed. Our in vitro experimental model showed that up and down fluctuations in glucose levels decreased cell proliferation, induced mitochondrial dysfunction, increased oxidative/nitrosative stress with consequent cellular biomolecular damage, impaired glutamate metabolism and increased pro-inflammatory cytokine release. Additionally, activation of the NFκB and p38 signaling pathways were putative mechanisms of the effects of glucose fluctuations on astroglial cells. In summary, for the first time, we show that changes in glucose concentrations, from high-glucose levels to glucose deprivation, exacerbate glial injury.

Impact of glucose fluctuation on acute cerebral infarction in type 2 diabetes

OBJECTIVE

This study aimed to describe the frequency and temporal profile of acute cerebral infarction (ACI) using a continuous glucose monitoring system (CGMS) in patients with and without type 2 diabetes mellitus (T2DM) and explore the impact of blood glucose fluctuations on the short-term prognosis of ACI.

METHODS

The subjects were divided into four groups: T2DM with acute cerebral infarction (DMCI, Group A, n=56); T2DM without acute cerebral infarction (DM-NCI, Group B, n=36); Acute cerebral infarction patients without T2DM (NDM-CI, Group C, n=54); Healthy control group (NG, Group D, n=36). The National Institutes of Health Stoke Scale (NIHSS) and modified Rankin scale (mRs) were collected in Group A and C. All subjects were monitored for 72 hours using the CGMS. Indices such as fasting blood glucose (FBG) and mean amplitude of glycemic excursions (MAGE) were calculated. Glycemic excursions were compared between Group A, B, C and Group D, respectively. Multiple linear regression analysis and logistic analysis was applied.

RESULTS

MAGE is related to NIHSS, homocysteine (HCY), HOMA-IR, FBG, CRP and IMT, while NIHSS is related to CRP, HCY, HOMA-IR, IMT. The factors impacting the short-term prognosis of ACI were NIHSS, HBA1C and MAGE.

CONCLUSION

Larger glucose fluctuations are associated with more stroke risk factors and are associated with a poorer short-term prognosis. More attention should be paid to glucose fluctuations in patients with ACI and a history of T2DM.

[Diabetes mellitus and the central nervous system]

The review considers the current views on the central nervous system (CNS) in diabetes mellitus (DM). It discusses an attitude towards the term 'diabetic encephalopathy'. The data of investigations of cognitive functions in types 1 and 2 DM and the brain structural imaging results obtained using up-to-date technologies are considered. The results of studies of the factors that induce cerebral changes in DM and their associated cognitive impairments are given. There is evidence that hyperglycemia has a more considerable impact on the above processes than hypoglycemia; other possible factors, apart from blood glucose control, are set out. The current views on the function of insulin in the CNS and the relationship of central insulin resistance to Alzheimer's disease are outlined. There are current data on intranasal insulin application that is still exploratory, but, as might be judged from the findings, may by a promising method for the treatment and prevention of cognitive decline in both patients with DM and those without this condition.

Neurorestorative effects of eugenol, a spice bioactive: Evidence in cell model and its efficacy as an intervention molecule to abrogate brain oxidative dysfunctions in the streptozotocin diabetic rat

Eugenol (EU), an active principle of cloves, is also widely distributed in various other plants (eg. basil, cinnamon, etc). While its antioxidant and anti-inflammatory properties are well established, biochemical insights related to its neuromodulatory potential in diabetic conditions are not clear. In the present study, initially we investigated its potential to modulate specific biochemical responses in SHSY5Y cells under experimentally -induced hyperglycemic condition. Co-exposure of cells with EU (5-10 μM) not only enhanced the cell viability, but significantly offset glucose -associated oxidative stress (as evidenced by diminished levels of reactive oxygen species and hydroperoxides). Further EU enhanced the reduced glutathione (GSH) levels and also ameliorated the levels of 3 - nitrotyrosine and expression of HSP70. We subsequently examined its efficacy to attenuate biochemical aberrations in brain regions of a streptozotocin (STZ) diabetic rat employing an intervention approach. Brain regions of EU treated (10 mg/kg bw/d, post 6 weeks of STZ) diabetic rats showed diminished levels of oxidative markers and protein carbonyls in both cytosolic and mitochondrial fractions. EU treatment caused enhanced activities of enzymic antioxidants and diminished both GSH and total thiols. Further, activities of complex I - III, succinate dehydrogenase and citrate synthase in brain regions were also significantly restored. Interestingly, EU treatment differentially attenuated the elevated activity of acetylcholinesterase and levels of calcium in brain regions. Collectively, based on the data obtained in in vitro and in vivo models, we hypothesize that EU may be employed as an adjuvant therapeutic molecule to alleviate complications under diabetic conditions.

The Impact of Diabetes on Brain Function in Childhood and Adolescence

A constant supply of glucose to the brain is critical for normal cerebral metabolism. The dysglycemia of type 1 diabetes (T1D) can affect activity, survival, and function of neural cells. Clinical studies in T1D have shown impairments in brain morphology and function. The most neurotoxic milieu seems to be young age and/or diabetic ketoacidosis at onset, severe hypoglycemia under the age of 6 years followed by chronic hyperglycemia. Adverse cognitive outcomes seem to be associated with poorer mental health outcomes. It is imperative to improve outcomes by investigating the mechanisms of injury so that neuroprotective strategies independent of glycemia can be identified.

Altered glycaemia differentially modulates efflux transporter expression and activity in hCMEC/D3 cell line

The unique phenotype of blood-brain barrier (BBB) endothelium is partly maintained by abundant expression of ATP-binding cassette superfamily of efflux transporters that strictly restrict the CNS access to toxic substances including xenobiotics in circulation. Previously, we have shown that diabetes-related altered glycemic conditions differentially affect and compromise BBB integrity. However, the impact of diabetes on BBB efflux transporters is less understood. In this study, we examined the effects of single or repeated episodes of hypo-and hyperglycemia on major BBB efflux transporters expression/function in human cerebromicrovascular endothelial cell line (hCMEC/D3). Cells were exposed to normal (5.5 mM), hypo (2.2 mM) or hyper (25 or 35 mM)-glycemic media containing D-glucose for 12h (acute) or two 3h episodes/day of hypo- or hyperglycemia with an intercalated 2h normalglycemic exposure for 3 days ("glycemic variability", see Methods). Acute hypoglycemic exposure (12h) up-regulated BBB endothelial mRNA and protein expression of P-glycoprotein, BCRP and other multidrug resistance associated proteins (MRP1 and 4) paralleled by an increase in transporter-specific efflux activity (∼ 2-fold vs. control). Although, 12h hyperglycemia did not affect the efflux transporter expression (except for MRP4), a significant increase in BCRP activity was observed. By contrast, DNA microarray data revealed that repeated hyperglycemic episodes (but not hypoglycemia) significantly up-regulate P-glycoprotein expression and activity. Thus, this study suggests a differential impact of altered glycemic conditions on major BBB drug efflux transporters expression/function, sensitive to the length of exposure (acute vs. repeated), with an implication for altered CNS drug disposition in diabetic population.

Streptozotocin Induced Neurotoxicity Involves Alzheimer's Related Pathological Markers: a Study on N2A Cells

Intracerebroventricular (icv) injection of streptozotocin (STZ) in rat brain causes prolonged impairment of brain energy metabolism and oxidative damage and leads to cognitive dysfunction; however, its mechanistic specific effects on neurons are not known. The present study was conducted to investigate the STZ-induced cellular and molecular alterations in mouse neuronal N2A cells. The N2A cells were treated with STZ (10, 50, 100, 1000 μM) for 48 h, and different assays were performed. STZ treatment caused significant decrease in cell viability, choline levels, increased acetylcholinesterase (AChE) activity, tau phosphorylation and amyloid aggregation. STZ treatment also led to low levels of glucose uptake, elevated mitochondrial stress, translocation of cytochrome c in cytosol, phosphatidylserine externalization, increased expression of caspase-3 and DNA damage. Co-treatment of clinically used drug donepezil (1 μM) offered significant protection against STZ induced neurotoxicity. Donepezil treatment significantly inhibited the STZ induced neurotoxicity, altered choline level, AChE activity, lowered glucose uptake and mitochondrial stress. However, the caspase-3 expression remains unaltered with co-treatment of donepezil. In conclusion, findings showed that STZ treated N2A cells exhibited the Alzheimer's disease (AD) related pathological markers which are attenuated with co-treatment of donepezil. Findings of the study suggested the potent use of STZ treated N2A cells as in vitro experimental test model to study the disease mechanism at cellular level.

Risk factors for decline in IQ in youth with type 1 diabetes over the 12 years from diagnosis/illness onset

OBJECTIVE

This study examined illness-related change in intelligence quotient (IQ) in a cohort of youth with type 1 diabetes studied prospectively from disease onset in childhood to follow-up 12 years later in late adolescence/early adulthood.

RESEARCH DESIGN AND METHODS

Participants included type 1 diabetes patients (n = 95; mean age at follow-up 21.3 years) and healthy control participants (HCs; n = 67; mean age at follow-up 21.0 years) from a cohort followed prospectively. Measures included Wechsler Preschool and Primary Scale of Intelligence-Revised, Wechsler Intelligence Scale for Children-Revised, and Wechsler Abbreviated Scale of Intelligence and prospective collection of data on metabolic control history.

RESULTS

Young people with type 1 diabetes showed greater decline in verbal IQ (VIQ) and full-scale IQ (FSIQ), but not performance IQ (PIQ), than HCs. Within the diabetes group, a younger age at diabetes onset was associated with a decline in PIQ and FSIQ (P ≤ 0.001). A history of hypoglycemic seizures was associated with a decline in VIQ (P = 0.002). Long-term metabolic control was not associated with changes in IQ. Interaction terms were not significant, suggesting no moderating effect of one diabetes-related variable over another.

CONCLUSIONS

The presence of diabetes may negatively influence some aspects of IQ over time. Specific illness risk factors, such as an earlier age of disease onset and a history of hypoglycemic seizures, appear to put the young person at greater risk. Academic progress of children identified as at risk should be monitored and educational supports provided if necessary.

At the centennial of Michaelis and Menten, competing Michaelis-Menten steps explain effect of GLP-1 on blood-brain transfer and metabolism of glucose

Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic incretin hormone with both pancreatic and extrapancreatic effects. Studies of GLP-1 reveal significant effects in regions of brain tissue that regulate appetite and satiety. GLP-1 mimetics are used for the treatment of type 2 diabetes mellitus. GLP-1 interacts with peripheral functions in which the autonomic nervous system plays an important role, and emerging pre-clinical findings indicate a potential neuroprotective role of the peptide, for example in models of stroke and in neurodegenerative disorders. A century ago, Leonor Michaelis and Maud Menten described the steady-state enzyme kinetics that still apply to the multiple receptors, transporters and enzymes that define the biochemical reactions of the brain, including the glucose-dependent impact of GLP-1 on blood-brain glucose transfer and metabolism. This MiniReview examines the potential of GLP-1 as a molecule of interest for the understanding of brain energy metabolism and with reference to the impact on brain metabolism related to appetite and satiety regulation, stroke and neurodegenerative disorders. These effects can be understood only by reference to the original formulation of the Michaelis-Menten equation as applied to a chain of kinetically controlled steps. Indeed, the effects of GLP-1 receptor activation on blood-brain glucose transfer and brain metabolism of glucose depend on the glucose concentration and relative affinities of the steps both in vitro and in vivo, as in the pancreas.

Glycemic extremes in youth with T1DM: the structural and functional integrity of the developing brain

The adult brain accounts for a disproportionally large percentage of the body’s total energy consumption (1). However, during brain development,energy demand is even higher, reaching the adult rate by age 2 and increasing to nearly twice the adult rate by age 10, followed by gradual reduction toward adult levels in the next decade (1,2). The dramatic changes in brain metabolism occurring over the first two decades of life coincide with the initial proliferation and then pruning of synapses to adult levels.The brain derives its energy almost exclusively from glucose and is largely driven by neuronal signaling, biosynthesis, and neuroprotection (3–6).Glucose homeostasis in the body is tightly regulated by a series of hormones and physiologic responses. As a result, hypoglycemia and hyperglycemia are rare occurrences in normal individuals, but they occur commonly inpatients with type 1 diabetes mellitus (T1DM) due to a dysfunction of peripheral glucose-insulin-glucagon responses and non-physiologic doses of exogenous insulin, which imperfectly mimic normal physiology. These extremes can occur more frequently in children and adolescents with T1DM due to the inadequacies of insulin replacement therapy, events leading to the diagnosis [prolonged untreated hyperglycemia and diabetic ketoacidosis (DKA)], and to behavioral factors interfering with optimal treatment. When faced with fluctuations in glucose supply the metabolism of the body and brain change dramatically, largely to conserve resources and, at a cost to other organs, to preserve brain function (7). However,if the normal physiological mechanisms that prevent these severe glucose fluctuations and maintain homeostasis are impaired, neuronal function and potentially viability can be affected (8–11).

Long-term artificial sweetener acesulfame potassium treatment alters neurometabolic functions in C57BL/6J mice

With the prevalence of obesity, artificial, non-nutritive sweeteners have been widely used as dietary supplements that provide sweet taste without excessive caloric load. In order to better understand the overall actions of artificial sweeteners, especially when they are chronically used, we investigated the peripheral and central nervous system effects of protracted exposure to a widely used artificial sweetener, acesulfame K (ACK). We found that extended ACK exposure (40 weeks) in normal C57BL/6J mice demonstrated a moderate and limited influence on metabolic homeostasis, including altering fasting insulin and leptin levels, pancreatic islet size and lipid levels, without affecting insulin sensitivity and bodyweight. Interestingly, impaired cognitive memory functions (evaluated by Morris Water Maze and Novel Objective Preference tests) were found in ACK-treated C57BL/6J mice, while no differences in motor function and anxiety levels were detected. The generation of an ACK-induced neurological phenotype was associated with metabolic dysregulation (glycolysis inhibition and functional ATP depletion) and neurosynaptic abnormalities (dysregulation of TrkB-mediated BDNF and Akt/Erk-mediated cell growth/survival pathway) in hippocampal neurons. Our data suggest that chronic use of ACK could affect cognitive functions, potentially via altering neuro-metabolic functions in male C57BL/6J mice.

Insulin-induced recurrent hypoglycemia exacerbates diabetic brain mitochondrial dysfunction and oxidative imbalance

Intensive insulin therapy can prevent or slow the progression of long-term diabetes complications but, at the same time, it increases the risk for episodes of severe hypoglycemia. In our study, we used a protocol intended to mimic the levels of blood glucose that occur in type 1 diabetic patients under an intensive insulin therapy. Streptozotocin (STZ)-induced diabetic rats were treated subcutaneously with twice-daily insulin injections for 2weeks to induce hypoglycemic episodes. Brain cortical and hippocampal mitochondria were isolated and mitochondrial bioenergetics (respiratory chain and phosphorylation system) and oxidative status parameters (malondialdehyde (MDA) levels, mitochondrial aconitase activity and enzymatic and non-enzymatic antioxidant defenses) were analyzed. The protein levels of synaptophysin, a marker of synaptic integrity, and caspase 9 activity were also evaluated in cortical and hippocampal homogenates. Brain cortical mitochondria isolated from hyper- and recurrent hypoglycemic animals presented higher levels of MDA and α-tocopherol together with an increased glutathione disulfide reductase activity, lower manganese superoxide dismutase (MnSOD) activity and glutathione-to-glutathione disulfide (GSH/GSSG) ratio. No significant alterations were found in cortical mitochondrial respiratory chain and oxidative phosphorylation system. Hippocampal mitochondria from both experimental groups presented an impaired oxidative phosphorylation system characterized by a decreased mitochondrial energization potential and ATP levels and higher repolarization lag phase. In addition, higher MDA levels and decreased GSH/GSSG, α-tocopherol levels, and aconitase, glutathione peroxidase and MnSOD activities were observed in both groups of animals. Hippocampal mitochondria from recurrent hypoglycemic animals also showed an impairment of the respiratory chain characterized by a lower state 3 of respiration, respiratory control ratio and ADP/O index, and a higher state 4 of respiration. Additionally, a non-statistically significant decrease in synaptophysin protein levels was observed in cortical homogenates from recurrent hypoglycemic rats as well as in hippocampal homogenates from hyperglycemic and recurrent hypoglycemic rats. An increase in caspase 9 activity was also observed in hippocampal homogenates from hyperglycemic and recurrent hypoglycemic animals. Our results show that mitochondrial dysfunction induced by long-term hyperglycemic effects is exacerbated by recurrent hypoglycemia, which may compromise the function and integrity of brain cells.