The role of impaired insulin/IGF action in primary diabetic encephalopathy

Affective and Cognitive Impairments in Rodent Models of Diabetes

Diabetes and related acute and long-term complications have a profound impact on cognitive, emotional, and social behavior, suggesting that the central nervous system (CNS) is a crucial substrate for diabetic complications. When anxiety, depression, and cognitive deficits occur in diabetic patients, the symptoms and complications related to the disease worsen, contributing to lower quality of life while increasing health care costs and mortality. Experimental models of diabetes in rodents are a fundamental and valuable tool for improving our understanding of the mechanisms underlying the close and reciprocal link between diabetes and CNS alterations, including the development of affective and cognitive disorders. Such models must reproduce the different components of this pathological condition in humans and, therefore, must be associated with affective and cognitive behavioral alterations. Beyond tight glycemic control, there are currently no specific therapies for neuropsychiatric comorbidities associated with diabetes; animal models are, therefore, essential for the development of adequate therapies. To our knowledge, there is currently no review article that summarizes changes in affective and cognitive behavior in the most common models of diabetes in rodents. Therefore, in this review, we have reported the main evidence on the alterations of affective and cognitive behavior in the different models of diabetes in rodents, the main mechanisms underlying these comorbidities, and the applicable therapeutic strategy.

Impact of lifestyle modification on glycemic control and cognitive function among Type II diabetes mellitus patients

Aim: Assessing impact of lifestyle modification on Type 2 diabetes mellitus (T2DM) glycemic control and cognitive function. Subjects & methods: Prospective study was conducted on T2DM patients (92 patients as interventional group and 92 patients conventional therapy). Results: After 6 months, significant improvements of HbA1c, oxidant and antioxidant, lipid profile, and cognitive function among only the interventional group (p < 0.05). Using logistic analysis, conventional therapy, DM duration >10 years, lower education, HbA1c baseline >7 were significant predictive risks for uncontrolled DM (AOR 4.2, 2.9, 2.7 and 2.2, respectively). While, conventional therapy, baseline mild cognitive impairment (MCI) and females were significant risks for MCI (AOR 11.5, 10.8 and 4.8, respectively). Conclusion: Lifestyle modification is a very important for glycemic control and cognitive function.

Clinical Trial Registration: NCT04891887 ( ClinicalTrials.gov )

Thymoquinone Attenuates Retinal Expression of Mediators and Markers of Neurodegeneration in a Diabetic Animal Model

BACKGROUND

Diabetic retinopathy (DR) is a slow eye disease that affects the retina due to a long-standing uncontrolled diabetes mellitus. Hyperglycemia-induced oxidative stress can lead to neuronal damage leading to DR.

OBJECTIVE

The aim of the current investigation is to assess the protective effects of thymoquinone (TQ) as a potential compound for the treatment and/or prevention of neurovascular complications of diabetes, including DR.

METHODS

Diabetes was induced in rats by the administration of streptozotocin (55 mg/kg intraperitoneally, i.p.). Subsequently, diabetic rats were treated with either TQ (2 mg/kg i.p.) or vehicle on alternate days for three weeks. A healthy control group was also run in parallel. At the end of the treatment period, animals were euthanized, and the retinas were collected and analyzed for the expression levels of brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase (TH), nerve growth factor receptor (NGFR), and caspase-3 using Western blotting techniques in the retina of diabetic rats and compared with the normal control rats. In addition, dichlorofluorescein (DCF) levels in the retina were assessed as a marker of reactive oxygen species (ROS), and blood-retinal barrier breakdown (BRB) was examined for vascular permeability. The systemic effects of TQ treatments on glycemic control, kidney and liver functions were also assessed in all groups.

RESULTS

Diabetic animals treated with TQ showed improvements in the liver and kidney functions compared with control diabetic rats. Normalization in the levels of neuroprotective factors, including BDNF, TH, and NGFR, was observed in the retina of diabetic rats treated with TQ. In addition, TQ ameliorated the levels of apoptosis regulatory protein caspase-3 in the retina of diabetic rats and reduced disruption of the blood-retinal barrier, possibly through a reduction in reactive oxygen species (ROS) generation.

CONCLUSION

These findings suggest that TQ harbors a significant potential to limit the neurodegeneration and retinal damage that can be provoked by hyperglycemia in vivo.

Exercise Training Enhances BDNF/TrkB Signaling Pathway and Inhibits Apoptosis in Diabetic Cerebral Cortex

This study aimed to clarify the therapeutic effects of exercise training on neural BDNF/TrkB signaling and apoptotic pathways in diabetic cerebral cortex. Thirty-six male C57BL/6JNarl mice were randomly divided into three groups: control (CON-G), diabetic group (DM-G, 100 mg/kg streptozotocin, i.p.), and diabetic with exercise training group (DMEX-G, Swim training for 30 min/day, 5 days/week). After 12 weeks, H&E staining, TUNEL staining, and Western blotting were performed to detect the morphological changes, neural apoptosis, and protein levels in the cerebral cortex. The Bcl2, BclxL, and pBad were significant decreased in DM-G compared with CON-G, whereas they (excluded the Ras and pRaf1) were increased in DMEX-G. In addition, interstitial space and TUNEL(+) apoptotic cells found increased in DM-G with increases in Fas/FasL-mediated (FasL, Fas, FADD, cleaved-caspase-8, and cleaved-caspase-3) and mitochondria-initiated (tBid, Bax/Bcl2, Bak/BclxL, Bad, Apaf1, cytochrome c, and cleaved-caspase-9) apoptotic pathways. However, diabetes-induced neural apoptosis was less in DMEX-G than DM-G with observed raises in the BDNF/TrkB signaling pathway as well as decreases in Fas/FasL-mediated and mitochondria-initiated pathways. In conclusion, exercise training provided neuroprotective effects via enhanced neural BDNF/TrkB signaling pathway and prevent Fas/FasL-mediated and mitochondria-initiated apoptotic pathways in diabetic cerebral cortex.

A Pilot Study of Diabetes Mellitus Classification from rs-fMRI Data Using Convolutional Neural Networks

Background. As a chronic progressive disease, diabetes mellitus (DM) has a high incidence worldwide, and it impacts on cognitive and learning abilities in the lifetime even in the early stage, may degenerate memory in middle age, and perhaps increases the risk of Alzheimer’s disease. Method. In this work, we propose a convolutional neural network (CNN) based classification method to help classify diabetes by distinguishing the brains with abnormal functions from the normal ones on resting-state functional magnetic resonance imaging (rs-fMRI). The proposed classification model is based on the Inception-v4-Residual convolutional neural network architecture. In our workflow, the original rs-fMRI data are first mapped to generate amplitude of low-frequency fluctuation (ALFF) images and then fed into the CNN model to get the classification result to indicate the potential existence of DM. Result. We validate our method on a realistic clinical rs-fMRI dataset, and the achieved average accuracy is $89.95$ % in fivefold cross-validation. Our model achieves a 0.8690 AUC with 77.50% and 77.51% sensitivity and specificity using our local dataset, respectively. Conclusion. It has the potential to become a novel clinical preliminary screening tool that provides help for the classification of different categories based on functional brain alteration caused by diabetes, benefiting from its accuracy and robustness, as well as efficiency and patient friendliness.

Quercetin ameliorates diabetic encephalopathy through SIRT1/ER stress pathway in db/db mice

Studies have shown that diabetes is an important risk factor for cognitive dysfunction, also called diabetic encephalopathy (DE). Quercetin has been reported to be effective in improving cognitive dysfunction in DE. But its detailed mechanism is still ambiguous. In this study, we used db/db mice to investigate whether quercetin could activate SIRT1 and inhibit ER pathways to improve DE. Behavioral tests (Morris water maze and new objects) showed that quercetin (70 mg/kg) can effectively improve the learning and memory ability in db/db mice. OGTT and ITT tests indicated that quercetin could alleviate impaired glucose tolerance and insulin resistance in db/db mice. Western blot analysis and Nissl staining showed that quercetin can improve the expression of nerve and synapse-associated proteins (PSD93, PSD95, NGF and BDNF) and inhibit neurodegeneration. Meanwhile, quercetin up-regulates SIRT1 protein expression and inhibits the expression of ER signaling pathway-related proteins (PERK, IRE-1α, ATF6, eIF2α, BIP and PDI). In addition, oxidative stress levels were significantly reduced after quercetin treatment. In conclusion, current experimental results indicated that SIRT1/ER stress is a promising mechanism involved in quercetin-treated diabetic encephalopathy.

Melatonin: new insights on its therapeutic properties in diabetic complications

Diabetes and diabetic complications are considered as leading causes of both morbidity and mortality in the world. Unfortunately, routine medical treatments used for affected patients possess undesirable side effects, including kidney and liver damages as well as gastrointestinal adverse reactions. Therefore, exploring the novel therapeutic strategies for diabetic patients is a crucial issue. It has been recently shown that melatonin, as main product of the pineal gland, despite its various pharmacological features including anticancer, anti-aging, antioxidant and anti-inflammatory effects, exerts anti-diabetic properties through regulating various cellular mechanisms. The aim of the present review is to describe potential roles of melatonin in the treatment of diabetes and its complications.

Metformin and trimetazidine ameliorate diabetes-induced cognitive impediment in status epileptic rats

Patients with diabetes and epilepsy are more prone to cognitive impairment, dementia, and even Alzheimer's disease. Diabetes-induced inflammatory process is one of the main contributing factors; however, the impact on seizure is not clear. The current study is aimed to examine the role of metformin and trimetazidine in the reduction of neuronal damage caused by inflammatory mediators and apoptotic factors in diabetic epileptic rodent model. Diabetic epileptic rats received orally either metformin (100 mg/kg) or trimetazidine (10 mg/kg) for 3 weeks exhibited reduced cognitive function and ameliorated the disturbed brain neurotransmission. Besides, they improved both the inflammatory status and the histopathologic alterations. Administration of metformin or trimetazidine ameliorated the deterioration in cognitive function in Morris water maze (MWM) and reduced seizure score. Furthermore, brain neurotransmitters glutamate and γ-aminobutyric acid (GABA) were reverted back to their normal values. Both treatments reduced the rise in inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), apoptotic markers nuclear factor-κB (NF-κB) and caspase-3, and improved the pathological photomicrograph of the hippocampus of diabetic epileptic rats. Such effects were closely correlated to the observed increase in the adenosine triphosphate and adenosine diphosphate (ATP/ADP) ratio and reduction of death-associated protein (DAP) and mammalian target of rapamycin (mTOR). In conclusion, the current study shed light on the potential neuroprotective role of metformin and trimetazidine in the amelioration of cognitive function via hindering inflammatory processes in diabetic epileptic rats.

Insulin treatment increases brain nitric oxide and oxidative stress, but does not affect memory function in mice

Insulin increases brain nitric oxide (NO) level but the mechanism and the significance of the effect on memory are not fully understood. This study aimed to demonstrate the mechanism of insulin-induced increase in oxidative stress (OS) and its consequences on learning and memory. Twenty four mice were assigned to groups (n = 6) and treated daily for seven days with water (control), insulin, insulin+N^ω-nitro-L-arginine methyl ester hydrochloride (L-NAME) and L-NAME, respectively. Memory was assessed using Y-maze; NO, malondialdehyde (MDA) and glutathione peroxidase (GPx) in brain homogenate were also determined. There was no difference between the groups in the number of entries into the arms and time spent in them, and in number of and percentage alternations performed by the mice, indicating normal memory function of the control and treated mice. NO level in the insulin group was higher compared to the control (p = .018), while those of the other groups were statistically the same compared to the control group. MDA values in the insulin group were higher (p = .001) than those of the control, while those of the other groups were statistically the same compared to those of the control group. GPx activity in the insulin group was lower compared to control (p = .004), while that of the other groups was not significantly different compared to control. It was concluded that insulin treatment increased brain level of NO and OS through increased malondialdehyde level and glutathione peroxidase activity; insulin treatment did not affect long-term visuo-spatial and short-term working memory in the animals. Insulin treatment may have deleterious effects on the brain through increased NO and OS levels.

Chronic Unpredictable Mild Stress Aggravates Mood Disorder, Cognitive Impairment, and Brain Insulin Resistance in Diabetic Rat

Diabetes-induced brain insulin resistance is associated with many mental diseases, including depression. Epidemiological evidences demonstrate the pathophysiologic link between stress, depression, and diabetes. This study was designed to determine whether chronic unpredictable mild stress- (CUMS-) induced changes in brain insulin resistance could contribute to deterioration in mood and cognitive functions in diabetic rats. Male SD rats were randomly assigned to three groups, including standard control group, the diabetes group, and the diabetes with CUMS group. After 7 weeks, emotional behaviors and memory performances as well as metabolic phenotypes were measured. In addition, we examined the changes in protein expression related to brain insulin signaling. Our results show that rats in diabetes with CUMS group displayed a decreased locomotor behavior in open-field test, an increased immobility time in forced swim test, and tail suspension test, and an impaired learning and memory in the Morris water maze when compared to animals in diabetes group. Further, diabetes with CUMS exhibited a significant decrease in phosphorylation of insulin receptor and an increase phosphorylation of IRS-1 in brain. These results suggest that the depression-like behaviors and cognitive function impairments in diabetic rats with CUMS were related to the changes of brain insulin signaling.

Restoration of Rostral Ventrolateral Medulla Cystathionine-γ Lyase Activity Underlies Moxonidine-Evoked Neuroprotection and Sympathoinhibition in Diabetic Rats

We recently demonstrated a fundamental role for cystathionine-γ lyase (CSE)-derived hydrogen sulfide (H₂S) in the cardioprotective effect of the centrally acting drug moxonidine in diabetic rats. Whether a downregulated CSE/H₂S system in the rostral ventrolateral medulla (RVLM) underlies neuronal oxidative stress and sympathoexcitation in diabetes has not been investigated. Along with addressing this question, we tested the hypothesis that moxonidine prevents the diabetes-evoked neurochemical effects by restoring CSE/H₂S function within its major site of action, the RVLM. Ex vivo studies were performed on RVLM tissues of streptozotocin (55 mg/kg, i.p.) diabetic rats treated daily for 3 weeks with moxonidine (2 or 6 mg/kg; gavage), H₂S donor sodium hydrosulfide (NaHS) (3.4 mg/kg, i.p.), CSE inhibitor DL-propargylglycine (DLP) (37.5 mg/kg, i.p.), a combination of DLP with moxonidine, or their vehicle. Moxonidine alleviated RVLM oxidative stress, neuronal injury, and increased tyrosine hydroxylase immunoreactivity (sympathoexcitation) by restoring CSE expression/activity as well as heme oxygenase-1 (HO-1) expression. A pivotal role for H₂S in moxonidine-evoked neuroprotection is supported by the following: 1) NaHS replicated the moxonidine-evoked neuroprotection, and the restoration of RVLM HO-1 expression in diabetic rats; and 2) DLP abolished moxonidine-evoked neuroprotection in diabetic rats, and caused RVLM neurotoxicity, reminiscent of a diabetes-evoked neuronal phenotype, in healthy rats. These findings suggest a novel role for RVLM CSE/H₂S/HO-1 in moxonidine-evoked neuroprotection and sympathoinhibition, and as a therapeutic target for developing new drugs for alleviating diabetes-evoked RVLM neurotoxicity and cardiovascular anomalies.

Protective effects of Huanglian Wendan Decoction aganist cognitive deficits and neuronal damages in rats with diabetic encephalopathy by inhibiting the release of inflammatory cytokines and repairing insulin signaling pathway in hippocampus

Huanglian Wendan decoction (HLWDD) has been used for the treatment of symptom of "Re", one of major causes in diabetes and metabolic disorders, according to the theory of traditional Chinese medicine. The present study aimed at investigating the cerebral protective effects of HLWDD on diabetic encephalopathy (DE), one of the major diabetic complications. The effects of HLWDD and metformin were analyzed in the streptozocin (STZ) + high-glucose-fat (HGF) diet-induced DE rats by gastric intubation. In the present study, the effects of HLWDD on cognition deficits were investigated after 30-day intervention at two daily dose levels (3 and 6 g·kg^-1). To explore the potential mechanisms underlying the effects of HLWDD, we detected the alterations of neuronal damages, inflammatory cytokines, and impaired insulin signaling pathway in hippocampus of the DE rats. Based on our results from the present study, we concluded that the protective effects of HLWDD against the cognitive deficits and neuronal damages through inhibiting the release of inflammatory cytokines and repairing insulin signaling pathway in hippocampus of the DE rats.

Neurotrophins and cognitive functions in T1D compared with healthy controls: effects of a high-intensity exercise

Exercise is known to have beneficial effects on cognitive function. This effect is greatly favored by an exercise-induced increase in neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1), especially with high-intensity exercises (HIE). As a complication of type 1 diabetes (T1D), a cognitive decline may occur, mostly ascribed to hypoglycaemia and chronic hyperglycaemia. Therefore, the purpose of this study was to examine the effects of acute HIE on cognitive function and neurotrophins in T1D and matched controls. Ten trained T1D (8 males, 2 females) participants and their matched (by age, sex, fitness level) controls were evaluated on 2 occasions after familiarization: a maximal test to exhaustion and an HIE bout (10 intervals of 60 s at 90% of their maximal wattage followed by 60 s at 50 W). Cognitive tests and analyses of serum BDNF, IGF-1, and free insulin were performed before and after HIE and following 30 min of recovery. At baseline, cognitive performance was better in the controls compared with the T1D participants (p < 0.05). After exercise, no significant differences in cognitive performance were detected. BDNF levels were significantly higher and IGF-1 levels were significantly lower in T1D compared with the control group (p < 0.05) at all time points. Exercise increased BDNF and IGF-1 levels in a comparable percentage in both groups (p < 0.05). In conclusion, although resting levels of serum BDNF and IGF-1 were altered by T1D, comparable increasing effects on BDNF and IGF-1 in T1D and healthy participants were found. Therefore, regularly repeating acute HIE could be a promising strategy for brain health in T1D.

Inside the Diabetic Brain: Role of Different Players Involved in Cognitive Decline

Diabetes mellitus is the most common metabolic disease, and its prevalence is increasing. A growing body of evidence, both in animal models and epidemiological studies, has demonstrated that metabolic diseases like obesity, insulin resistance, and diabetes are associated with alterations in the central nervous system (CNS), being linked with development of cognitive and memory impairments and presenting a higher risk for dementia and Alzheimer's disease. The rising prevalence of diabetes together with its increasing earlier onset suggests that diabetes-related cognitive dysfunction will increase in the near future, causing substantial socioeconomic impact. Decreased insulin secretion or action, dysregulation of glucose homeostasis, impairment in the hypothalamic-pituitary-adrenal axis, obesity, hyperleptinemia, and inflammation may act independently or synergistically to disrupt neuronal homeostasis and cause diabetes-associated cognitive decline. However, the crosstalk between those factors and the mechanisms underlying the diabetes-related CNS complications is still elusive. During the past few years, different strategies (neuroprotective and antioxidant drugs) have emerged as promising therapies for this complication, which still remains to be preventable or treatable. This Review summarizes fundamental past and ongoing research on diabetes-associated cognitive decline, highlighting potential contributors, mechanistic mediators, and new pharmacological approaches to prevent and/or delay this complication.

Activation of mTOR signaling mediates the increased expression of AChE in high glucose condition: in vitro and in vivo evidences

Acetylcholinesterase (AChE) is impaired in brain of diabetic animals, which may be one of the reasons for diabetes-associated cognitive decline. However, the mechanism is still unknown. The present study was designed to investigate whether the increased expression of AChE in central neurons under high glucose (HG) condition was due to activation of mammalian target of rapamycin (mTOR) signaling. It was found that more production of reactive oxygen species, and higher levels of phospho-Akt, phospho-mTOR, phospho-p70S6K, and AChE were detected in HT-22 cells in HG group than normal glucose group after culture for 24 h, which were all attenuated by an antioxidant N-acetyl-L-cysteine. A PI3K inhibitor LY294002 significantly decreased the levels of phospho-Akt, phospho-mTOR, phospho-p70S6K, and AChE protein expression in HG-cultured HT-22 cells, and an mTOR inhibitor rapamycin markedly reduced the levels of phospho-mTOR, phospho-p70S6K, and AChE expression. Furthermore, compared with normal rats, diabetic rats showed remarkable increases in levels of AChE activity and expression, malondialdehyde, phospho-mTOR, phospho-p70S6K, and a significant decrease in total superoxide dismutase activity in both hippocampus and cerebral cortex. However, much lower levels of phospho-mTOR, phospho-p70S6K, and AChE expression occurred in both brain regions of diabetic rats treated with rapamycin when compared with untreated ones. These results indicated that mTOR signaling was activated through the activation of PI3K/Akt pathway mediated by oxidative stress in HG-cultured HT-22 cells and diabetic rat brains, which contributed to the elevated protein expression of AChE in central neurons under the condition of HG.

Insulin treatment prevents the increase in D-serine in hippocampal CA1 area of diabetic rats

PURPOSE

Diabetes is a high risk factor for dementia. Employing a diabetic rat model, the present study was designed to determine whether the content of D-serine (D-Ser) in hippocampus is associated with the impairment of spatial learning and memory ability.

METHODS

Diabetes was induced by a single intravenous injection of streptozotocin (STZ). The insulin treatment began 3 days after STZ injection.

RESULTS

We found that both water maze learning and hippocampal CA1 long-term potentiation (LTP) were impaired in diabetic rats. The contents of glutamate, D-Ser, and serine racemase in the hippocampus of diabetic rats were significantly higher than those in the control group. Insulin treatment prevented the STZ-induced impairment in water maze learning and hippocampal CA1-LTP in diabetic rats and also maintained the contents of glutamate, D-Ser, and serine racemase at the normal range in hippocampus.

CONCLUSIONS

These results suggest that insulin treatment has a potent protection effect on CA1-LTP, spatial learning and memory ability of the diabetic rats in vivo. Furthermore, insulin may take effect by inhibiting the overactivation of N-methyl-d-aspartate receptors, which play a critical role in neurotoxicity.

Type 1 diabetes-associated cognitive decline: a meta-analysis and update of the current literature

BACKGROUND

Type 1 diabetes (T1D) can have a significant impact on brain structure and function, which is referred to as T1D-associated cognitive decline (T1DACD). Diabetes duration, early onset disease, and diabetes-associated complications are all proposed as factors contributing to T1DACD. However, there have been no comparisons in T1DACD between children and adults with T1D. To obtain a better insight into the occurrence and effects of T1DACD in T1D, the aim of the present meta-analysis was to investigate differences between children and adults and to analyse factors contributing T1DACD.

METHODS

Two electronic databases were consulted: PubMed and ISI Web of Knowledge. Literature published up until the end of 2013 was included in the analysis. Effect sizes (Cohen's d), which are standardized differences between experimental and control groups, were calculated.

RESULTS

There was a small to modest decrease in cognitive performance in T1D patients compared with non-diabetic controls. Children with T1D performed worse while testing for executive function, full intelligence quotient (IQ), and motor speed, whereas adults with T1D performed worse while testing the full, verbal and performance IQ, part of the executive function, memory, spatial memory, and motor speed. Episodes of severe hypoglycemia, chronic hyperglycemia, and age of onset can be significant factors influencing cognitive function in T1D.

CONCLUSIONS

The findings in the literature suggest that T1DACD is more severe in adults than children, indicating that age and diabetes duration contribute to this T1DACD.

The protective effects of insulin and natural honey against hippocampal cell death in streptozotocin-induced diabetic rats

We investigated the effects of insulin and honey as antioxidants to prevent the hippocampal cell death in streptozotocin-induced diabetic rats. We selected sixty Wister rats (5 groups of 12 animals each), including the control group (C), and four diabetic groups (control (D) and 3 groups treated with insulin (I), honey (H), and insulin plus honey (I + H)). Diabetes was induced by streptozotocin injection (IP, 60 mg/kg). Six weeks after the induction of diabetes, the group I received insulin (3-4 U/kg/day, SC), group H received honey (5 mg/kg/day, IP), and group I + H received a combination of the above at the same dose. Groups C and D received normal saline. Two weeks after treatment, rats were sacrificed and the hippocampus was extracted. Neuronal cell death in the hippocampal region was examined using trypan blue assay, "H & E" staining, and TUNEL assay. Cell viability assessment showed significantly lower number of living cells in group D than in group C. Besides, the mean number of living cells was significantly higher in group I, H, and I + H compared to group D. Therefore, it can be concluded that the treatment of the diabetic rats with insulin, honey, and a combination of insulin and honey can prevent neuronal cell death in different hippocampal areas of the studied samples.

Flavonoid, morin inhibits oxidative stress, inflammation and enhances neurotrophic support in the brain of streptozotocin-induced diabetic rats

Diabetes-induced damages in brain are known as diabetic encephalopathy, which is well characterized by cellular, molecular and functional changes in the brain of diabetic subjects and rodents. However, little is known about the mechanism of damages and the therapeutic strategies in ameliorating those damages in the diabetic brain. In this study, we utilized a flavonoid, morin which is emerging as a potent drug against a wide range of free radical-mediated as well as neurodegenerative diseases. Morin (15 and 30 mg/kg body weight/day) was orally administered to two different groups of rats after 1 week of diabetes induction, and continued for five consecutive weeks. Two other untreated groups of diabetic and non-diabetic rats were used to compare with drug-treated groups. After drug treatments, cerebral cortex of the brain harvested and analyzed for different factors. Morin supplementation especially at high dose increased the levels of insulin, reduced glutathione, superoxide dismutase and catalase activities, and decreased fasting glucose and thiobarbituric acid reactive substances in the diabetic brain compared to untreated diabetic rats (P < 0.05). Morin also significantly decreased the level of inflammatory markers (TNFα, IL1β, IL-6) in the diabetic brain compared to untreated diabetic rats. Furthermore, the drug influenced an increase in the level of neurotrophic factors (BDNF, NGF and IGF-1) in the diabetic brain compared to untreated diabetic rats (P < 0.05). Thus, our results indicate a beneficial effect of morin by decreasing oxidative stress, inflammation and increasing the neurotrophic support in the diabetic brain, which may ameliorate diabetic encephalopathy.

Sphingolipid profiles are altered in prefrontal cortex of rats under acute hyperglycemia

Diabetes type 1 is a common autoimmune disease manifesting by insulin deficiency and hyperglycemia, which can lead to dementia-like brain dysfunctions. The factors triggering the pathological processes in hyperglycemic brain remain unknown. We reported in this study that brain areas with different susceptibility to diabetes (prefrontal cortex (PFC), hippocampus, striatum and cerebellum) revealed differential alterations in ceramide (Cer) and sphingomyelin (SM) profiles in rats with streptozotocin-induced hyperglycemia. Employing gas-liquid chromatography, we found that level of total Cer increased significantly only in the PFC of diabetic animals, which also exhibited a broad spectrum of sphingolipid (SLs) changes, such as elevations of Cer-C16:0, -C18:0, -C20:0, -C22:0, -C18:1, -C24:1 and SM-C16:0 and -C18:1. In opposite, only minor changes were noted in other examined structures. In addition, de novo synthesis pathway could play a role in generation of Cer containing monounsaturated fatty acids in PFC during hyperglycemia. In turn, simultaneous accumulation of Cers and their SM counterparts may suggest that overproduced Cers are converted to SMs to avoid excessive Cer-mediated cytotoxicity. We conclude that broad changes in SLs compositions in PFC induced by hyperglycemia may provoke membrane rearrangements in some cell populations, which can disturb cellular signaling and cause tissue damage.

Diabetes alters KIF1A and KIF5B motor proteins in the hippocampus

Diabetes mellitus is the most common metabolic disorder in humans. Diabetic encephalopathy is characterized by cognitive and memory impairments, which have been associated with changes in the hippocampus, but the mechanisms underlying those impairments triggered by diabetes, are far from being elucidated. The disruption of axonal transport is associated with several neurodegenerative diseases and might also play a role in diabetes-associated disorders affecting nervous system. We investigated the effect of diabetes (2 and 8 weeks duration) on KIF1A, KIF5B and dynein motor proteins, which are important for axonal transport, in the hippocampus. The mRNA expression of motor proteins was assessed by qRT-PCR, and also their protein levels by immunohistochemistry in hippocampal slices and immunoblotting in total extracts of hippocampus from streptozotocin-induced diabetic and age-matched control animals. Diabetes increased the expression and immunoreactivity of KIF1A and KIF5B in the hippocampus, but no alterations in dynein were detected. Since hyperglycemia is considered a major player in diabetic complications, the effect of a prolonged exposure to high glucose on motor proteins, mitochondria and synaptic proteins in hippocampal neurons was also studied, giving particular attention to changes in axons. Hippocampal cell cultures were exposed to high glucose (50 mM) or mannitol (osmotic control; 25 mM plus 25 mM glucose) for 7 days. In hippocampal cultures incubated with high glucose no changes were detected in the fluorescence intensity or number of accumulations related with mitochondria in the axons of hippocampal neurons. Nevertheless, high glucose increased the number of fluorescent accumulations of KIF1A and synaptotagmin-1 and decreased KIF5B, SNAP-25 and synaptophysin immunoreactivity specifically in axons of hippocampal neurons. These changes suggest that anterograde axonal transport mediated by these kinesins may be impaired in hippocampal neurons, which may lead to changes in synaptic proteins, thus contributing to changes in hippocampal neurotransmission and to cognitive and memory impairments.

Effects of diabetes on hippocampal neurogenesis: links to cognition and depression

Diabetes often leads to a number of complications involving brain function, including cognitive decline and depression. In addition, depression is a risk factor for developing diabetes. A loss of hippocampal neuroplasticity, which impairs the ability of the brain to adapt and reorganize key behavioral and emotional functions, provides a framework for understanding this reciprocal relationship. The effects of diabetes on brain and behavioral functions in experimental models of type 1 and type 2 diabetes are reviewed, with a focus on the negative impact of impaired hippocampal neurogenesis, dendritic remodeling and increased apoptosis. Mechanisms shown to regulate neuroplasticity and behavior in diabetes models, including stress hormones, neurotransmitters, neurotrophins, inflammation and aging, are integrated within this framework. Pathological changes in hippocampal function can contribute to the brain symptoms of diabetes-associated complications by failing to regulate the hypothalamic-pituitary-axis, maintain learning and memory and govern emotional expression. Further characterization of alterations in neuroplasticity along with glycemic control will facilitate the development and evaluation of pharmacological interventions that could successfully prevent and/or reverse the detrimental effects of diabetes on brain and behavior.

Luteolin attenuates diabetes-associated cognitive decline in rats

Diabetes mellitus can cause dysfunction of the central nervous system called "diabetic encephalopathy". Although various oral drugs are used to treat diabetes, they do not prevent the development of diabetes-associated cognitive decline in rats, and novel strategies for the prevention and treatment are urgently needed. Luteolin, a flavonoid isolated from Cirsium japonicum, has antioxidant, anti-inflammatory and neuroprotective activities. However, no report is available on influence of luteolin on streptozotocin-induced memory impairment. Therefore, we tested its influence against cognitive dysfunction in streptozotocin-induced diabetic rats using Morris water maze test. Nissl's staining, choline esterase (ChE) activity as marker of cholinergic function and oxidative stress were assessed in the cerebral cortex and hippocampus to evaluate the neuropathological changes and the effects of luteolin on diabetic rats. The results showed that streptozotocin-induced diabetes produced obvious neuron damage and cognitive dysfunction coupling with markedly increased oxidative stress and ChE activity in the brain. In contrast, chronic treatment with luteolin (50 and 100mg/kg) improved neuronal injury and cognitive performance by attenuating oxidative stress and ChE activity in diabetic rats. In conclusion, the present study suggested that oral supplementation of luteolin might be a potential therapeutic strategy for the treatment and/or prevention of diabetic encephalopathy.

Crosstalk between diabetes and brain: glucagon-like peptide-1 mimetics as a promising therapy against neurodegeneration

According to World Health Organization estimates, type 2 diabetes (T2D) is an epidemic (particularly in under development countries) and a socio-economic challenge. This is even more relevant since increasing evidence points T2D as a risk factor for Alzheimer's disease (AD), supporting the hypothesis that AD is a "type 3 diabetes" or "brain insulin resistant state". Despite the limited knowledge on the molecular mechanisms and the etiological complexity of both pathologies, evidence suggests that neurodegeneration/death underlying cognitive dysfunction (and ultimately dementia) upon long-term T2D may arise from a complex interplay between T2D and brain aging. Additionally, decreased brain insulin levels/signaling and glucose metabolism in both pathologies further suggests that an effective treatment strategy for one disorder may be also beneficial in the other. In this regard, one such promising strategy is a novel successful anti-T2D class of drugs, the glucagon-like peptide-1 (GLP-1) mimetics (e.g. exendin-4 or liraglutide), whose potential neuroprotective effects have been increasingly shown in the last years. In fact, several studies showed that, besides improving peripheral (and probably brain) insulin signaling, GLP-1 analogs minimize cell loss and possibly rescue cognitive decline in models of AD, Parkinson's (PD) or Huntington's disease. Interestingly, exendin-4 is undergoing clinical trials to test its potential as an anti-PD therapy. Herewith, we aim to integrate the available data on the metabolic and neuroprotective effects of GLP-1 mimetics in the central nervous system (CNS) with the complex crosstalk between T2D-AD, as well as their potential therapeutic value against T2D-associated cognitive dysfunction.

Neuroprotective properties of aucubin in diabetic rats and diabetic encephalopathy rats

In this study, we determined the neuroprotective effect of aucubin on diabetes and diabetic encephalopathy. With the exception of the control group, all rats received intraperitoneal injections of streptozotocin (STZ; 60 mg/kg) to induce type 1 diabetes mellitus (DM). Aucubin (1, 5, 10 mg/kg ip) was used after induction of DM (immediately) and diabetic encephalopathy (65 days after the induction of diabetes). The diabetic encephalopathy treatment groups were divided into short-term and long-term treatment groups. Treatment responses to all parameters were examined (body weight, plasma glucose, Y-maze error rates and proportion of apoptotic cells). In diabetic rats, aucubin controlled blood glucose levels effectively, prevented complications, and improved the quality of life of diabetic rats. In diabetic encephalopathy, aucubin significantly rescued neurons in the hippocampal CA1 subfield and reduced working errors during behavioral testing. The significant neuroprotective effect of aucubin could be seen not only in the short term (15 days) but also in the long term (45 days), which was a highly encouraging finding. These data suggest that aucubin may be a potential neuroprotective agent.

Insulin in central nervous system: more than just a peripheral hormone

Insulin signaling in central nervous system (CNS) has emerged as a novel field of research since decreased brain insulin levels and/or signaling were associated to impaired learning, memory, and age-related neurodegenerative diseases. Thus, besides its well-known role in longevity, insulin may constitute a promising therapy against diabetes- and age-related neurodegenerative disorders. More interestingly, insulin has been also faced as the potential missing link between diabetes and aging in CNS, with Alzheimer's disease (AD) considered as the "brain-type diabetes." In fact, brain insulin has been shown to regulate both peripheral and central glucose metabolism, neurotransmission, learning, and memory and to be neuroprotective. And a future challenge will be to unravel the complex interactions between aging and diabetes, which, we believe, will allow the development of efficient preventive and therapeutic strategies to overcome age-related diseases and to prolong human "healthy" longevity. Herewith, we aim to integrate the metabolic, neuromodulatory, and neuroprotective roles of insulin in two age-related pathologies: diabetes and AD, both in terms of intracellular signaling and potential therapeutic approach.

Genetic polymorphisms of nerve growth factor receptor (NGFR) and the risk of Alzheimer's disease

Background

Loss of basal forebrain cholinergic neurons is attributable to the proapoptotic signaling induced by nerve growth factor receptor (NGFR) and may link to Alzheimer's disease (AD) risk. Only one study has investigated the association between NGFR polymorphisms and the risk of AD in an Italian population. Type 2 diabetes mellitus (DM) may modify this association based on previous animal and epidemiologic studies.

Methods

This was a case-control study in a Chinese population. A total of 264 AD patients were recruited from three teaching hospitals between 2007 to 2010; 389 controls were recruited from elderly health checkup and volunteers of the hospital during the same period of time. Five common (frequency≥5%) haplotype-tagging single nucleotide polymorphisms (htSNPs) were selected from NGFR to test the association between NGFR htSNPs and the risk of AD.

Results

Variant NGFR rs734194 was significantly associated with a decreased risk of AD [GG vs. TT copies: adjusted odds ratio (OR) = 0.43, 95% confidence interval (CI) = 0.20-0.95]. Seven common haplotypes were identified. Minor haplotype GCGCG was significantly associated with a decreased risk of AD (2 vs. 0 copies: adjusted OR = 0.39, 95% CI = 0.17-0.91). Type 2 DM significantly modified the association between rs2072446, rs741072, and haplotype GCTTG and GTTCG on the risk of AD among ApoE ε4 non-carriers (P_interaction < 0.05).

Conclusion

Inherited polymorphisms of NGFR were associated with the risk of AD; results were not significant after correction for multiple tests. This association was further modified by the status of type 2 DM.

Mechanisms of brain aging regulation by insulin: implications for neurodegeneration in late-onset Alzheimer's disease

Insulin and IGF seem to be important players in modulating brain aging. Neurons share more similarities with islet cells than any other human cell type. Insulin and insulin receptors are diffusely found in the brain, especially so in the hippocampus. Caloric restriction decreases insulin resistance, and it is the only proven mechanism to expand lifespan. Conversely, insulin resistance increases with age, obesity, and sedentarism, all of which have been shown to be risk factors for late-onset Alzheimer's disease (AD). Hyperphagia and obesity potentiate the production of oxidative reactive species (ROS), and chronic hyperglycemia accelerates the formation of advanced glucose end products (AGEs) in (pre)diabetes—both mechanisms favoring a neurodegenerative milieu. Prolonged high cerebral insulin concentrations cause microvascular endothelium proliferation, chronic hypoperfusion, and energy deficit, triggering β-amyloid oligomerization and tau hyperphosphorylation. Insulin-degrading enzyme (IDE) seems to be the main mechanism in clearing β-amyloid from the brain. Hyperinsulinemic states may deviate IDE utilization towards insulin processing, decreasing β-amyloid degradation.

Changes in serotoninergic and noradrenergic descending pain pathways during painful diabetic neuropathy: the preventive action of IGF1

Painful diabetic neuropathy (PDN) induces neuronal hyperactivity at the spinal cord and periaqueductal gray (PAG), a key area in descending nociceptive modulation. Since the PAG uses relay stations at serotoninergic and noradrenergic brainstem areas, we determined the serotonin and noradrenaline levels at the spinal cord of streptozotocin-diabetic rats and at those brainstem areas (serotoninergic rostroventromedial medulla and noradrenergic A(5) and A(7) cell groups). Since, during diabetes, the levels of insulin growth factor 1 (IGF1) decrease, reducing its neurotrophic effect in the brain, we also studied the effects of IGF1 treatment. One week after diabetes induction, subcutaneous injections of IGF1 (2.5mg/kg) were performed during 3 weeks. Body weights, glycemia, and mechanical nociception were weekly evaluated until the end of the study, the time when the animals were subjected to a modified formalin test to study chemical allodynia. Serotonin and noradrenaline levels were quantified by ELISA at the spinal cord, whereas at the brainstem, the quantification was performed by immunohistochemistry against, respectively, tryptophan hydroxylase (TpH) or tyrosine hydroxylase (TH). STZ-diabetic rats exhibited mechanical hyperalgesia and chemical allodynia, along with higher spinal levels of serotonin and noradrenaline and higher numbers of neurons expressing TpH at the RVM and TH at the A(5) noradrenergic cell group. Treatment with IGF1 prevented the behavioral signs of PDN and reversed the neuronal hyperactivity at the spinal cord and ventrolateral PAG and the neurochemical changes at the spinal cord and at the brainstem. Based on the facilitatory role of serotoninergic and noradrenergic descending modulation during chronic pain, the increased serotonin and noradrenaline innervation of the dorsal horn in STZ-diabetic rats may probably account for enhanced pain during PDN. The benefits of IGF1 in PDN are probably due to blockade of the increased peripheral input to the somatosensory system, but direct central actions cannot be discarded. The value of IGF1 in PDN treatment deserves further evaluation.

Encephalopathies: the emerging diabetic complications

Diabetic encephalopathies are now accepted complications of diabetes. They appear to differ in type 1 and type 2 diabetes as to underlying mechanisms and the nature of resulting cognitive deficits. The increased incidence of Alzheimer's disease in type 2 diabetes is associated with insulin resistance, hyperinsulinemia and hyperglycemia, and commonly accompanying attributes such as hypercholesterolemia, hypertension and obesity. The relevance of these disorders as to the emergence of dementia and Alzheimer's disease is discussed based on epidemiological studies. The pathobiology of accumulation of β-amyloid and tau the hallmarks of Alzheimer's disease are discussed based on experimental data. Type 1 diabetic encephalopathy is likely to increase as a result of the global increase in the incidence of type 1 diabetes and its occurrence in increasingly younger patients. Alzheimer-like changes and dementia are not prominently increased in type 1 diabetes. Instead, the type 1 diabetic encephalopathy involves learning abilities, intelligence development and memory retrieval resulting in impaired school and professional performances. The major underlying component here appears to be insulin deficiency with downstream effects on the expression of neurotrophic factors, neurotransmitters, oxidative and apoptotic stressors resulting in defects in neuronal integrity, connectivity and loss commonly occurring in the still developing brain. Recent experimental data emphasize the role of impaired central insulin action and provide information as to potential therapies. Therefore, the underlying mechanisms resulting in diabetic encephalopathies are complex and appear to differ between the two types of diabetes. Major headway has been made in our understanding of their pathobiology; however, many questions remain to be clarified. In view of the increasing incidence of both type 1 and type 2 diabetes, intensified investigations are called for to expand our understanding of these complications and to find therapeutic means by which these disastrous consequences can be prevented and modified.

Long-term exposure to high glucose induces changes in the content and distribution of some exocytotic proteins in cultured hippocampal neurons

A few studies have reported the existence of depletion of synaptic vesicles, and changes in neurotransmitter release and in the content of exocytotic proteins in the hippocampus of diabetic rats. Recently, we found that diabetes alters the levels of synaptic proteins in hippocampal nerve terminals. Hyperglycemia is considered the main trigger of diabetic complications, although other factors, such as low insulin levels, also contribute to diabetes-induced changes. Thus, the aim of this work was to evaluate whether long-term elevated glucose per se, which mimics prolonged hyperglycemia, induces significant changes in the content and localization of synaptic proteins involved in exocytosis in hippocampal neurons. Hippocampal cell cultures were cultured for 14 days and were exposed to high glucose (50 mM) or mannitol (osmotic control; 25 mM plus 25 mM glucose), for 7 days. Cell viability and nuclear morphology were evaluated by MTT and Hoechst assays, respectively. The protein levels of vesicle-associated membrane protein-2 (VAMP-2), synaptosomal-associated protein-25 (SNAP-25), syntaxin-1, synapsin-1, synaptophysin, synaptotagmin-1, rabphilin 3a, and also of vesicular glutamate and GABA transporters (VGluT-1 and VGAT), were evaluated by immunoblotting, and its localization was analyzed by immunocytochemistry. The majority of the proteins were not affected. However, elevated glucose decreased the content of SNAP-25 and increased the content of synaptotagmin-1 and VGluT-1. Moreover, there was an accumulation of syntaxin-1, synaptotagmin-1 and VGluT-1 in the cell body of some hippocampal neurons exposed to high glucose. No changes were detected in mannitol-treated cells. In conclusion, elevated glucose per se did not induce significant changes in the content of the majority of the synaptic proteins studied in hippocampal cultures, with the exception of SNAP-25, synaptotagmin-1 and VGluT-1. However, there was an accumulation of some proteins in cell bodies of hippocampal neurons exposed to elevated glucose, suggesting that the trafficking of these proteins to the synapse may be compromised. Moreover, these results also suggest that other factors, in addition to hyperglycemia, certainly contribute to alterations detected in synaptic proteins in diabetic animals.

Insulin and IGF-1 receptors, nitrotyrosin and cerebral neuronal deficits in two young patients with diabetic ketoacidosis and fatal brain edema

Gray and white matter structural deficits may accompany type 1 diabetes. Earlier experimental studies have demonstrated neuronal deficits associated with impaired neurotrophic support, inflammation and oxidative stress. In this study we demonstrate in two patients with histories of poorly controlled type 1 diabetes and fatal brain edema of ketoacidosis neuronal deficits associated with a decreased presence of insulin and IGF-1 receptors and accumulation of nitrotyrosin in neurons of affected areas and the choroid plexus. The findings add support to the suggested genesis of T1DM encephalopathy due to compromised neurotrophic protection, oxidative stress, inflammation and neuronal deficits, as demonstrated in T1DM encephalopathy in the BB/Wor-rat.

Sequential abnormalities in type 1 diabetic encephalopathy and the effects of C-Peptide

Diabetic encephalopathy is a recently recognized complication in type 1 diabetes. In this review, we summarize a series of experimental results obtained longitudinally in the spontaneously type 1 diabetic BB/Wor-rat, and bringing out the beneficial effects of C-peptide replacement. It is increasingly clear that lack of insulin and C-peptide, and perturbations of their signaling cascades in type 1 diabetes are detrimental to the regulation of neurotrophic factors and their receptors. Other consequences of such deficits and perturbations are innate inflammatory responses with effects on synaptogenesis, neurite degeneration, and early behavioral abnormalities. Replacement of C-peptide, which does not effect hyperglycemia, has beneficial effects on a variety of pro-apoptotic stressors, oxidative stressors, and finally on apoptosis. Eventually, this cascade of events leads to neuronal loss and decreased densities of white matter myelinating cells, with more profound deficits in behavioral and cognitive function. Such changes are likely to underlie gray and white matter atrophy in type 1 diabetes, and are significantly prevented by full C-peptide replacement. Present data demonstrate that C-peptide replacement has beneficial effects on numerous sequential and partly interrelated pathogenetic mechanisms, resulting in prevention of neuronal and oligodendroglial cell loss, with significant prevention of neurobehavioral and cognitive functions.

Aucubin prevents loss of hippocampal neurons and regulates antioxidative activity in diabetic encephalopathy rats

In this study, the neuroprotection of aucubin and its mechanism were evaluated in the rat model of diabetic encephalopathy. Diabetes mellitus (DM) rats were stratified by cognitive capability (CC), and assigned to four treatment groups for aucubin treatment (doses of 0, 1, 5 or 10 mg/kg aucubin), with a further two groups of non-DM rats ranked by CC as controls for aucubin (doses of 0 or 5 mg/kg aucubin). Neuroprotection was estimated by the indexes of behavior and histology. Behavioral testing was performed in a Y-maze. The surviving neurons in CA1-CA4 and subiculum (SC) of the hippocampus were counted under a microscope. In addition, the apoptotic neurons in the CA1 of the hippocampus were also examined by using TUNEL staining. In order to clarify the mechanism of aucubin's neuroprotection, the activities of endogenous antioxidants and nitric oxide synthase (NOS) together with the content of lipid peroxide in the hippocampus were assayed. The results proved that aucubin significantly reduced the content of lipid peroxide, regulated the activities of antioxidant enzymatic and decreased the activity of NOS. All these effects indicated that aucubin was a potential neuroprotective agent and its neuroprotective effects were achieved, at least in part, by promoting endogenous antioxidant enzymatic activities.

Zinc-activated C-peptide resistance to the type 2 diabetic erythrocyte is associated with hyperglycemia-induced phosphatidylserine externalization and reversed by metformin

Insulin resistance can broadly be defined as the diminished ability of cells to respond to the action of insulin in transporting glucose from the bloodstream into cells and tissues. Here, we report that erythrocytes (ERYs) obtained from type 2 diabetic rats display an apparent resistance to Zn(2+)-activated C-peptide. Thus, the aims of this study were to demonstrate that Zn(2+)-activated C-peptide exerts potentially beneficial effects on healthy ERYs and that these same effects on type 2 diabetic ERYs are enhanced in the presence of metformin. Incubation of ERYs (obtained from type 2 diabetic BBZDR/Wor-rats) with Zn(2+)-activated C-peptide followed by chemiluminescence measurements of ATP resulted in a 31.2 +/- 4.0% increase in ATP release from these ERYs compared to a 78.4 +/- 4.9% increase from control ERYs. Glucose accumulation in diabetic ERYs, measured by scintillation counting of (14)C-labeled glucose, increased by 35.8 +/- 1.3% in the presence of the Zn(2+)-activated C-peptide, a value significantly lower than results obtained from control ERYs (64.3 +/- 5.1%). When Zn(2+)-activated C-peptide was exogenously added to diabetic ERYs, immunoassays revealed a 32.5 +/- 8.2% increase in C-peptide absorbance compared to a 64.4 +/- 10.3% increase in control ERYs. Phosphatidylserine (PS) externalization and metformin sensitization of Zn(2+)-activated C-peptide were examined spectrofluorometrically by measuring the binding of FITC-labeled annexin to PS. The incubation of diabetic ERYs with metformin prior to the addition of Zn(2+)-activated C-peptide resulted in values that were statistically equivalent to those of controls. Summarily, data obtained here demonstrate an apparent resistance to Zn(2+)-activated C-peptide by the ERY that is corrected by metformin.

Inflammation in Diabetic Encephalopathy is Prevented by C-Peptide

Encephalopathy is an increasingly recognized complication of type 1 diabetes. The underlying mechanisms are not well understood, although insulin deficiency has been implicated. The spontaneously diabetic BB/Wor-rat develops neuro-behavioral deficits and neuronal cell death in hippocampus and frontal cortex, which can be prevented by insulinomimetic C-peptide. Here we examined whether contributing factors such as activation of innate immune mediators are responsive to C-peptide replacement. Seven-month diabetic BB/Wor-rats and those treated with full C-peptide replacement were compared to age-matched control rats. Hippocampi of diabetic rats showed upregulation of RAGE and NF-kappaB, the former being localized to proliferating astrocytes. These changes were associated with increased expression of TNF-alpha, IL-1beta, IL-2 and IL-6 in hippocampi of diabetic rats. Full C-peptide replacement, which did not induce hyperglycemia, resulted in significant prevention of upregulation of RAGE expression, activation of NF-kappaB and activation of pro-inflammatory factors. In conclusion, impaired insulin activity is associated with upregulation of RAGE and pro-inflammatory factors, and these are likely to contribute to previously described oxidative and apoptotic neuronal cell death. Replacement of insulinomimetic C-peptide significantly prevents this cascade of events.

Suppression of NF-kappabeta signaling pathway by tocotrienol can prevent diabetes associated cognitive deficits

OBJECTIVE

The etiology of diabetes associated cognitive decline is multifactorial and involves insulin receptor down regulation, neuronal apoptosis and glutamatergic neurotransmission. The study was designed to evaluate the impact of tocotrienol on cognitive function and neuroinflammatory cascade in streptozotocin-induced diabetes.

RESEARCH DESIGN AND METHOD

Streptozotocin-induced diabetic rats were treated with tocotrienol for 10 weeks. Morris water maze was used for behavioral assessment of memory. Cytoplasmic and nuclear fractions of cerebral cortex and hippocampus were prepared for the quantification of acetylcholinesterase activity, oxidative-nitrosative stress, tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), NFkappabeta and caspase-3.

RESULTS

After 10 weeks of streptozotocin injection, the rats produced significant increase in transfer latency which was coupled with enhanced acetylcholinesterase activity, increased oxidative-nitrosative stress, TNF-alpha, IL-1beta, caspase-3 activity and active p65 subunit of NFkappabeta in different regions of diabetic rat brain. Interestingly, co-administration of tocotrienol significantly and dose-dependently prevented behavioral, biochemical and molecular changes associated with diabetes. Moreover, diabetic rats treated with insulin-tocotrienol combination produced more pronounced effect on molecular parameters as compared to their per se groups.

CONCLUSIONS

Collectively, the data reveal that activation of NFkappabeta signaling pathway is associated with diabetes induced cognitive impairment and point towards the therapeutic potential of tocotrienol in diabetic encephalopathy.

Insulin in combination with other diabetes medication is associated with less Alzheimer neuropathology

OBJECTIVE

To examine the association between treatment for diabetes and Alzheimer disease (AD) neuropathology.

METHODS

This postmortem study matched 124 subjects with diabetes to 124 without diabetes from the Mount Sinai School of Medicine Brain Bank, on age (mean = 81.2 + 9.3), sex (57.3% F), and severity of dementia (Clinical Dementia Rating [CDR] 2.4 + 1.7). Densities of neuritic plaques (NPs) and of neurofibrillary tangles (NFTs) were assessed in several neocortical regions and in the hippocampus, entorhinal cortex, and amygdala. Diabetic subjects were classified according to their recorded lifetime antidiabetic medications: none (n = 29), insulin only (n = 49), diabetes medications other than insulin only (n = 28), or concomitant use of both insulin and any oral antidiabetic medications (n = 18). For each dependent variable, analysis of covariance controlling for age at death, sex, and CDR distinguished among the nondiabetic patients and four diabetic subgroups.

RESULTS

There were differences among the five groups for NP ratings in the entorhinal cortex (p = 0.003), amygdala (p = 0.009), and overall NP (p = 0.014) as well as counts of NPs in all regions examined (p values ranging from 0.009 to 0.04). NP ratings in the hippocampus (p = 0.057) and the combined neocortical measure (p = 0.052) approached significance. In each analysis, the concomitant medication group had significantly fewer NPs (approximately 20%) than any of the other groups, which were relatively similar. No significant NFT differences were found.

CONCLUSION

The results of this study suggest that the combination of insulin with other diabetes medication is associated with substantially lower neuritic plaque density consistent with the effects of both on the neurobiology of insulin.

Increased amyloid beta-peptide (1-40) level in brain of streptozotocin-induced diabetic rats

The aims of the study were to investigate whether the level of amyloid beta-peptide (Abeta) (1-40) was increased in brain of diabetic rats and whether the increase was associated with dysfunction of P-glycoprotein at the blood-brain barrier. A diabetes-like condition was induced by single administration of 65 mg/kg streptozotocin via i.p. injection. Abeta (1-40) levels in brain of the diabetic rats were measured using an enzyme linked immunosorbent assay (ELISA) kit. The in vivo brain-to-blood efflux and blood-to-brain influx transport of [(125)I]-labeled human amyloid-beta-peptide (hAbeta) (1-40) were measured using the brain efflux index and brain permeability coefficient-surface area product, respectively. [(14)C]inulin served as a reference compound. The results showed that Abeta (1-40) levels significantly increased in temporal cortex and hippocampus of the diabetic rats. The brain remaining percentage of [(125)I]hAbeta (1-40) in diabetic rats significantly increased at 30 min after intracerebral microinjection, accompanied by decrease of the brain efflux index. Pretreatment of P-glycoprotein inhibitors verapamil or cyclosporin A significantly increased the brain remaining percentage of [(125)I]hAbeta (1-40). The brain permeability coefficient-surface area product of [(125)I]hAbeta (1-40) was increased in diabetic rats, accompanied by increased Abeta (1-40) levels in plasma. The present study demonstrated that a diabetic state could increase Abeta (1-40) levels in brain, which might be explained, at least in part, by the decline in brain-to-blood efflux of Abeta (1-40) due to deficient cerebral P-glycoprotein function in diabetic rats.

The effects of C-peptide on type 1 diabetic polyneuropathies and encephalopathy in the BB/Wor-rat

Diabetic polyneuropathy (DPN) occurs more frequently in type 1 diabetes resulting in a more severe DPN. The differences in DPN between the two types of diabetes are due to differences in the availability of insulin and C-peptide. Insulin and C-peptide provide gene regulatory effects on neurotrophic factors with effects on axonal cytoskeletal proteins and nerve fiber integrity. A significant abnormality in type 1 DPN is nodal degeneration. In the type 1 BB/Wor-rat, C-peptide replacement corrects metabolic abnormalities ameliorating the acute nerve conduction defect. It corrects abnormalities of neurotrophic factors and the expression of neuroskeletal proteins with improvements of axonal size and function. C-peptide corrects the expression of nodal adhesive molecules with prevention and repair of the functionally significant nodal degeneration. Cognitive dysfunction is a recognized complication of type 1 diabetes, and is associated with impaired neurotrophic support and apoptotic neuronal loss. C-peptide prevents hippocampal apoptosis and cognitive deficits. It is therefore clear that substitution of C-peptide in type 1 diabetes has a multitude of effects on DPN and cognitive dysfunction. Here the effects of C-peptide replenishment will be extensively described as they pertain to DPN and diabetic encephalopathy, underpinning its beneficial effects on neurological complications in type 1 diabetes.

Functional changes in baroreceptor afferent, central and efferent components of the baroreflex circuitry in type 1 diabetic mice (OVE26)

Baroreflex control of heart rate (HR) is impaired in diabetes mellitus. We hypothesized that diabetes mellitus induced functional changes of neural components at multiple sites within the baroreflex arc. Type 1 diabetic mice (OVE26) and FVB control mice were anesthetized. Baroreflex-mediated HR responses to sodium nitroprusside- (SNP) and phenylephrine- (PE) induced mean arterial blood pressure (MAP) changes were measured. Baroreceptor function was characterized by measuring the percent (%) change of baseline integrated aortic depressor nerve activity (Int ADNA) in response to SNP- and PE-induced MAP changes. The HR responses to electrical stimulation of the left aortic depressor nerve (ADN) and the right vagus nerve were assessed. Compared with FVB control mice, we found in OVE26 mice that (1) baroreflex-mediated bradycardia and tachycardia were significantly reduced. (2) The baroreceptor afferent function in response to MAP increase did not differ, as assessed by the parameters of the logistic function curve. But, the inhibition of Int ADNA in response to MAP decrease was significantly attenuated. (3) The maximum amplitude of bradycardic responses to right vagal efferent stimulation was augmented. (4) In contrast, the maximum amplitude of bradycardic responses to left ADN stimulation was decreased. Since Int ADNA was preserved in response to MAP increase and HR responses to vagal efferent stimulation were augmented, we conclude that a deficit of the central mediation of baroreflex HR contributes to the overall attenuation of baroreflex sensitivity in OVE26 mice. The successful conduction of physiological experiments on the ADN in OVE26 mice may provide a foundation for the understanding of cellular and molecular mechanisms of diabetes-induced cardiac neuropathy.