Insulin, C-peptide, hyperglycemia, and central nervous system complications in diabetes

Psychological and personality factors in type 2 diabetes mellitus, presenting the rationale and exploratory results from The Maastricht Study, a population-based cohort study

BACKGROUND

Strong longitudinal evidence exists that psychological distress is associated with a high morbidity and mortality risk in type 2 diabetes. Little is known about the biological and behavioral mechanisms that may explain this association. Moreover, the role of personality traits in these associations is still unclear. In this paper, we first describe the design of the psychological part of The Maastricht Study that aims to elucidate these mechanisms. Next, we present exploratory results on the prevalence of depression, anxiety and personality traits in type 2 diabetes. Finally, we briefly discuss the importance of these findings for clinical research and practice.

METHODS

We measured psychological distress and depression using the MINI diagnostic interview, the PHQ-9 and GAD-7 questionnaires in the first 864 participants of The Maastricht Study, a large, population-based cohort study. Personality traits were measured by the DS14 and Big Five personality questionnaires. Type 2 diabetes was assessed by an oral glucose tolerance test. Logistic regression analyses were used to estimate the associations of depression, anxiety and personality with type 2 diabetes, adjusted for age, sex and education level.

RESULTS

Individuals with type 2 diabetes had higher levels of depressive and anxiety symptoms, odds ratios (95 % CI) were 3.15 (1.49; 6.67), 1.73 (0.83-3.60), 1.50 (0.72-3.12), for PHQ-9 ≥ 10, current depressive disorder and GAD-7 ≥ 10, respectively. Type D personality, social inhibition and negative affectivity were more prevalent in type 2 diabetes, odds ratios were 1.95 (1.23-3.10), 1.35 (0.93-1.94) and 1.70 (1.14-2.51), respectively. Individuals with type 2 diabetes were less extraverted, less conscientious, less agreeable and less emotionally stable, and similar in openness to individuals without type 2 diabetes, although effect sizes were small.

CONCLUSIONS

Individuals with type 2 diabetes experience more psychological distress and have different personality traits compared to individuals without type 2 diabetes. Future longitudinal analyses within The Maastricht Study will increase our understanding of biological and behavioral mechanisms that link psychological distress to morbidity and mortality in type 2 diabetes.

[Pathogenetic approaches to treatment of cognitive disorders in patients with diabetes mellitus]

The article presents the currents concepts on the mechanisms of brain lesions and development of cognitive impairment in diabetes mellitus (DM) including DM type 2. Metabolic and vascular mechanisms, oxidative stress, hyperglycemia, glutamate excitotoxicity, insulin insufficiency and brain insulin resistance, general vascular and microcirculatory disturbances, death of cortical neurons, decrease in the newly synthesized acetylcholine, activation of lipid peroxidation are considered. A review of the main domestic and international drugs used in clinical practice for treatment of cognitive impairment in patients with DM is presented.

Clinical Characteristics for the Relationship between Type-2 Diabetes Mellitus and Cognitive Impairment: A Cross-Sectional Study

We explored the potential differences in cognitive status, lipid and glucose metabolism, ApoEε4 alleles and imaging between diabetic and non-diabetic subjects. 83 subjects with normal cognitive function and 114 mild cognitive impaired patients were divided into four groups by history of diabetes. General demographics was collected from all participants followed by MRI scan, biochemical examinations and a series of neuropsychological tests. Student's t test, multiple regressions and one-way ANOVA were applied to investigate the differences between groups. Comparing diabetic patients with non-diabetic subjects in the mild cognitive impaired group, we found several decreased items in recall of three words in MMSE (p=0.020), AVLT and SCWT (p<0.050). The multiple linear regression revealed that two-hour glucose level (B= -0.255, p<0.001) and fasting C-peptide (B= -0.466, p=0.001) had negative effects on the score of MMSE. In addition, diabetic patients treated with insulin and other diabetes medication performed better in part of the AVLT (p<0.050) compared to patients with insulin treatment or oral antidiabetic medication only. Patients with metformin medication had a better memory outcome compared to patients with sulphonylurea medication in the AVLT long delay free recall (p =0.010). These findings show that patients of mild cognitive impairment with diabetes mellitus have a worse outcome in attention, information processing speed and memory compared to non-diabetic patients. Higher two-hour glucose level and C-peptide level may be risk factors for severe cognitive impairment in type-2 diabetes mellitus patients. The results of this study also suggest that medication may have effects on cognitive function.

Alterations in Hippocampal Oxidative Stress, Expression of AMPA Receptor GluR2 Subunit and Associated Spatial Memory Loss by Bacopa monnieri Extract (CDRI-08) in Streptozotocin-Induced Diabetes Mellitus Type 2 Mice

Bacopa monnieri extract has been implicated in the recovery of memory impairments due to various neurological disorders in animal models and humans. However, the precise molecular mechanism of the role of CDRI-08, a well characterized fraction of Bacopa monnieri extract, in recovery of the diabetes mellitus-induced memory impairments is not known. Here, we demonstrate that DM2 mice treated orally with lower dose of CDRI-08 (50- or 100 mg/kg BW) is able to significantly enhance spatial memory in STZ-DM2 mice and this is correlated with a significant decline in oxidative stress and up regulation of the AMPA receptor GluR2 subunit gene expression in the hippocampus. Treatment of DM2 mice with its higher dose (150 mg/kg BW or above) shows anti-diabetic effect in addition to its ability to recover the spatial memory impairment by reversing the DM2-induced elevated oxidative stress and decreased GluR2 subunit expression near to their values in normal and CDRI-08 treated control mice. Our results provide evidences towards molecular basis of the memory enhancing and anti diabetic role of the Bacopa monnieri extract in STZ-induced DM2 mice, which may have therapeutic implications.

ASK1 modulates the expression of microRNA Let7A in microglia under high glucose in vitro condition

Hyperglycemia results in oxidative stress and leads to neuronal apoptosis in the brain. Diabetes studies show that microglia participate in the progression of neuropathogenesis through their involvement in inflammation in vivo and in vitro. In high-glucose-induced inflammation, apoptosis signal regulating kinase 1 (ASK1) triggers the release of apoptosis cytokines and apoptotic gene expression. MicroRNA-Let7A (miR-Let7A) is reported to be a regulator of inflammation. In the present study, we investigated whether miR-Let7A regulates the function of microglia by controlling ASK1 in response to high-glucose-induced oxidative stress. We performed reverse transcription (RT) polymerase chain reaction, Taqman assay, real-time polymerase chain reaction, and immunocytochemistry to confirm the alteration of microglia function. Our results show that miR-Let7A is associated with the activation of ASK1 and the expression of anti-inflammatory cytokine (interleukin (IL)-10) and Mycs (c-Myc and N-Myc). Thus, the relationship between Let-7A and ASK1 could be a novel target for enhancing the beneficial function of microglia in central nervous system (CNS) disorders.

Glucose regulation, cognition, and brain MRI in type 2 diabetes: a systematic review

Type 2 diabetes is associated with cognitive dysfunction and structural brain changes. Abnormalities in glucose regulation are involved in several complications related to type 2 diabetes, but their role in these cerebral complications is unclear. We systematically reviewed studies of the association between glucose regulation (glycaemia, hypoglycaemic events, insulin concentration, insulin resistance, and glucose-lowering treatment) and cognitive function and brain abnormalities on MRI in people with type 2 diabetes. The 86 papers included showed that glycaemia, particularly high HbA1c concentration and glucose variability, are negatively associated with cognitive function in people with type 2 diabetes without dementia. However, the strength of this association is weak, and HbA1c generally accounted for less than 10% of the variance in cognition. Importantly, few studies have measured long-term cerebral outcomes, such as dementia and structural brain changes on MRI, and the effect of glucose-lowering treatment on these outcomes. More randomised controlled trials are needed to establish the effect of glucose-lowering treatment on long-term cognitive function in people with type 2 diabetes.

Severity of Type 2 Diabetes, Cognitive Function, and Self-Care

Type 2 diabetes mellitus (T2DM) is associated with poorer performance on certain measures of cognitive function. However, little is known about the associations among working memory (WM), executive function (EF), and self-care in those with severe T2DM. This investigation explored these relationships among 67 middle-aged and older individuals with T2DM (mean age of 62.9 years). Severity of T2DM was measured with a health status composite (HSC) score from the Diabetes Care Profile, the number of prescribed medications, and the number of comorbid conditions. Cognitive assessments included the Working Memory Index and the Executive Interview 25 (EXIT 25). Self-care was measured using the Self-Care Inventory-Revised (SCI-R) and hemoglobin A1c (HgbA1c). WM was significantly correlated with all measures of severity of T2DM (HSC, r = .542, p < . 01; number of comorbidities, r = -.476, p < .01; and number of prescription medications, r = -.344, p < .01). EF was significantly correlated with all measures of severity of T2DM (HSC, r = -.504, p < .01; number of comorbidities, r = .492, p < .01; and number of prescription medications, r = .326, p < .01). The self-care measure HgbA1c was significantly correlated with WM (r = -.352, p < .01) and EF (r = .510, p < .01). The EXIT 25 score fully mediated the relationship between severity of T2DM and self-care as measured by HgbA1c (β = .431, p < .001). These findings provide preliminary evidence for the associations among severity of T2DM, WM, EF, and self-care.

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.

Rosmarinic acid prevents lipid peroxidation and increase in acetylcholinesterase activity in brain of streptozotocin-induced diabetic rats

We investigated the efficacy of rosmarinic acid (RA) in preventing lipid peroxidation and increased activity of acetylcholinesterase (AChE) in the brain of streptozotocin-induced diabetic rats. The animals were divided into six groups (n = 8): control, ethanol, RA 10 mg/kg, diabetic, diabetic/ethanol and diabetic/RA 10 mg/kg. After 21 days of treatment with RA, the cerebral structures (striatum, cortex and hippocampus) were removed for experimental assays. The results demonstrated that the treatment with RA (10 mg/kg) significantly reduced the level of lipid peroxidation in hippocampus (28%), cortex (38%) and striatum (47%) of diabetic rats when compared with the control. In addition, it was found that hyperglycaemia caused significant increased in the activity of AChE in hippocampus (58%), cortex (46%) and striatum (30%) in comparison with the control. On the other hand, the treatment with RA reversed this effect to the level of control after 3 weeks. In conclusion, the present findings showed that treatment with RA prevents the lipid peroxidation and consequently the increase in AChE activity in diabetic rats, demonstrating that this compound can modulate cholinergic neurotransmission and prevent damage oxidative in brain in the diabetic state. Thus, we can suggest that RA could be a promising compound in the complementary therapy in diabetes.

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.

Protection of neurons from high glucose-induced injury by deletion of MAD2B

Diabetic encephalopathy may lead to cognitive deficits in diabetic patients and diminish quality of life. It has been shown that protracted hyperglycaemia is directly associated with neuronal apoptosis, which is involved in diabetic encephalopathy. The anaphase-promoting complex (APC) is essential for the survival of post-mitotic neurons. In our previous study, we found that the mitotic arrest deficient protein MAD2B, one of APC inhibitors, was expressed in neurons in central nervous system. However, whether MAD2B is involved in hyperglycaemia-induced apoptosis and thus takes part in diabetic encephalopathy is still unknown. To address this issue, we first explored the expression of MAD2B and cyclin B1 detected by immunofluorescence and Western blot. It was found that hyperglycaemia remarkably increased the expression of MAD2B and accumulation of cyclin B1 in cortices of diabetes mellitus rat model and in cultured primary neurons. To further explore the role of MAD2B in hyperglycaemia-induced neuronal injury, we depleted MAD2B expression by a specifically targeted shRNA against MAD2B. We observed that MAD2B deficiency alleviated cyclin B1 expression and apoptotic neuronal death. These results demonstrate that MAD2B expression is the main culprit for accumulation of cyclin B1 and apoptosis in neurons under high glucose. Moreover, inhibition of the expression of MAD2B prevented neurons from entering an aberrant S phase that led differentiated neurons into apoptotic cell death. These results suggest that hyperglycaemia induced neuronal apoptosis through inducing expression of MAD2B, which represents a novel mechanism of diabetic encephalopathy.

Brain effect of insulin and clonazepam in diabetic rats under depressive-like behavior

Diabetes mellitus is characterized by hyperglycemia resulting from defects on insulin secretion, insulin action, or both. It has recently become clear that the central nervous system is not spared from the deleterious effects of diabetes, since diabetic encephalopathy was recognized as a complication of this heterogeneous metabolic disorder. There is a well recognized association between depression and diabetes, once prevalence of depression in diabetic patients is higher than in general population, and clonazepam is being used to treat this complication. Oxidative stress is widely accepted as playing a key mediatory role in the development and progression of diabetes and its complications. In this work we analyzed DNA damage by comet assay and lipid damage in prefrontal cortex, hippocampus and striatum of streptozotocin-induced diabetic rats submitted to the forced swimming test. It was verified that the diabetic group presented DNA and lipid damage in the brain areas evaluated, when compared to the control groups. Additionally, a significant reduction of the DNA and lipid damage in animals treated with insulin and/or clonazepam was observed. These data suggest that the association of these two drugs could protect against DNA and lipid damage in diabetic rats submitted to the forced swimming test, an animal model of depression.

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).

Association of attention-deficit/hyperactivity disorder with diabetes: a population-based study

BACKGROUND

Cognitive impairment has been documented in adult diabetes but is unclear in pediatric diabetes. No study had been conducted to explore the relationship between attention-deficit/hyperactivity disorder (ADHD) and diabetes. Using a population-based data set, we aimed to examine the association between ADHD and a prior diagnosis of diabetes mellitus (DM) in Taiwan.

METHODS

A total of 4,302 patients with ADHD were selected as cases and 21,510 randomly selected subjects as controls. We used conditional logistic regression to calculate the odds ratio (OR) for having previously received a diagnosis of DM between subjects with and without ADHD.

RESULTS

In this study, 116 of the 25,812 sampled subjects (0.5%) had received a diagnosis of DM prior to their index date. Subjects with ADHD had a higher proportion of prior DM diagnoses than controls (0.9% vs. 0.4%, P < 0.001). After adjusting for age, sex, index year, geographic location, and obesity, ADHD was significantly associated with a prior diagnosis of type 2 DM (OR = 2.75, 95% confidence interval (CI) = 1.82-4.16). However, no significant association was observed between ADHD and type 1 DM.

CONCLUSION

The findings suggest that ADHD was associated with a previous diagnosis of type 2 DM.

Comparison of the clinical manifestations of type 2 diabetes mellitus between rhesus monkey (Macaca mulatta lasiotis) and human being

OBJECTIVES

Type 2 diabetes mellitus (T2DM) is the most common form of diabetes. To determine the similarities of development of T2DM between rhesus monkey [Macaca mulatta lasiotis (M. m. lasiotis)] and human being, the clinical parameters were determined during a period of 2 years in 60 adult male rhesus monkeys (M. m. lasiotis).

METHODS

Sixty male monkeys whose fasting plasma glucose (FPG) level less than or equal to 5 mmol/L (90 mg/dL) were enrolled in this study. Of these, 50 monkeys aged 7 to 20 years were fed with high-fat diet and 10 aged 4 to 10 years fed with standard diet as normal monkeys. Body weight, body mass index, FPG, fasting plasma insulin, and hemoglobin A1c levels were measured and calculated. The responses of insulin and glucose levels to intravenous glucose tolerance test were analyzed.

RESULTS

Of 50 monkeys fed with high-fat diet, 8 developed overt T2DM, 26 experienced impaired glucose tolerance and impaired fasting glucose, and FPG of 16 monkeys was normal. All monkeys with impaired glucose tolerance experienced obesity, compensatory increase of fasting plasma insulin, significant decline of postprandial glucose clearance rate (KGluc5-20), and decreased insulin secretion.

CONCLUSIONS

In conclusion, rhesus monkey (M. m. lasiotis) has many similarities with human beings in terms of clinical manifestations and risk factors at different diabetes stages.

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.

Effect of Acute Administration of loganin on Spatial Memory in Diabetic Male Rats

PURPOSE

Diabetes is associated with memory and learning disorder. The purpose of this study is to determine the effect of acute oral administration of loganin on memory in diabetic male rats.

METHODS

42 male Wistar rats (250-300 g) were divided into six groups: Control, Diabetic (1 week), Diabetic (12 weeks), Loganin, Diabetic (1 week) + Loganin, Diabetic (12 weeks) + Loganin. Diabetes was induced by IP injection of Streptozotocin (60 mg/kg). Loganin (40 mg/kg, po) was administrated 1 hour before test. Then, spatial memory was compared between groups with Morris Water Maze tests.

RESULTS

Administration of loganin during acquisition, significantly (p<0.05) decreased both escape latency and traveled distance to find hidden platform in 1 and 12 weeks diabetic rats. In evaluation of recall phase of memory, loganin significantly (p<0.05) increased time and distance spent in the target quadrant in 1 and 12 weeks diabetic rats.

CONCLUSION

Acute administration of loganin could improve spatial memory in diabetic rats.

Neurodegeneration in streptozotocin-induced diabetic rats is attenuated by treatment with resveratrol

AIM

Diabetes mellitus-associated hyperglycemia and oxidative stress have been shown to have detrimental effects on the brain and may lead to impairment of cognitive functions. Resveratrol (Rsv), a polyphenolic antioxidant, has been shown to have moderate hypoglycemic and prominent hypolipidemic effects in diabetic rats. In the present study, we examined if Rsv improves the diabetic encephalopathy and explored its possible underlying mechanisms.

METHODS

Male SD rats were treated with streptozotocin (65 mg/kg), and the diabetic rats were orally fed with Rsv (0.75 mg/kg, every 8 h) or normal saline for 4 weeks. Animals were then sacrificed and the brain tissues (hippocampus) processed for biochemical and histological studies.

RESULTS

Neurodegeneration and astrocytic activation were noted in the hippocampus of the diabetic rats. Tumor necrosis factor-α, IL-6 transcripts and nuclear factor-κB expression were increased in the brain. In addition, neuropathic alterations in the hippocampus were evident in diabetic rats, including increased blood vessel permeability and VEGF expression, decreased mitochondrial number and AMP-activated protein kinase activity. In Rsv-treated diabetic rats, the aforementioned abnormalities were all attenuated.

CONCLUSION

These observations suggest that Rsv significantly attenuated neurodegeneration and astrocytic activation in the hippocampus of diabetic rats. Our results suggested that Rsv could potentially be a new therapeutic agent for diabetic encephalopathy and neurodegeneration.

Guizhi-Fuling-Wan, a Traditional Chinese Herbal Medicine, Ameliorates Memory Deficits and Neuronal Apoptosis in the Streptozotocin-Induced Hyperglycemic Rodents via the Decrease of Bax/Bcl2 Ratio and Caspase-3 Expression

Brain neuronal apoptosis and cognitive impairment are associated with hyperglycemia and diabetes mellitus. The present study determined if the Chinese herbal medicine Guizhi-Fuling-Wan (GFW) would reduce memory loss and neuronal apoptosis in streptozotocin- (STZ-) induced hyperglycemic rodents. Two weeks after STZ induction, GFW was orally administered once daily for 7 days. GFW significantly improved spatial memory deficits in STZ-induced hyperglycemic mice. GFW decreased TUNEL-positive cells and caspase-3 positive cells in STZ-induced hyperglycemic rats. It also was found that GFW treatment reduced caspase-3 protein levels and increased levels of the antiapoptotic protein Bcl-2 that were indicative of neuroprotection. The protective therapeutic effects of GFW on neuronal apoptosis and cognition deficits caused by STZ-induced hyperglycemia may be due in part to inhibition of the cellular apoptosis pathway. GFW may have therapeutic effects in patients with diabetes-mellitus-induced neuropathology.

Participation of antioxidant and cholinergic system in protective effect of naringenin against type-2 diabetes-induced memory dysfunction in rats

Naringenin is a flavone flavonoid possessing antidiabetic, antioxidant and memory improving effects. Therefore, we studied the influence of naringenin against type-2 diabetes-induced memory dysfunction in rats. Type-2 diabetes was induced by high-fat diet and high-fat emulsion for two weeks and a low dose of streptozotocin (35 mg/kg). The memory deficit was assessed by using a novel object recognition paradigm. The changes in oxidative markers and cholinesterase (ChE) levels were evaluated in the hippocampal region. After confirmation of diabetes, naringenin (50mg/kg) treatment was given to animals as a preventive and in another set of experiments naringenin (25 and 50mg/kg) or pioglitazone (5mg/kg) or donepezil (3mg/kg) treatments were started after long-standing diabetes (4 weeks after confirmation). Both the treatment schedules show significant protection and improvement in cognitive behavior against diabetes-induced memory dysfunction and biochemical changes. Also, treatment with pioglitazone and donepezil improved memory performance in rats. Naringenin was found to decrease oxidative stress by depleting elevated lipid peroxide and nitric oxide and elevating reduced glutathione levels. Cholinergic function was improved by naringenin through the inhibition of elevated ChE activity. In conclusion, the present study suggests that naringenin acts as an antioxidant and ChE inhibitor against type-2 diabetes-induced memory dysfunction.

Agmatine, an endogenous ligand of imidazoline receptor protects against memory impairment and biochemical alterations in streptozotocin-induced diabetic rats

Agmatine, a polycationic amine synthesized via decarboxylation of l-arginine by arginine decarboxylase is reported to exhibit anti-hyperglycemic, antioxidant and memory enhancing effects. Therefore, we tested its influence against cognitive dysfunction in streptozotocin-induced diabetic rats using Morris water maze and object recognition paradigm. Lipid peroxidation and glutathione levels as parameters of oxidative stress and choline esterase (ChE) activity as a marker of cholinergic function were assessed in the cerebral cortex and hippocampus. Thirty days after diabetes induction rats showed a severe deficit in learning and memory associated with increased lipid peroxidation, decreased reduced glutathione, and elevated ChE activity. In contrast, chronic treatment with agmatine (5-10mg/kg, i.p. for 30 days) improved cognitive performance, lowered hyperglycemia, oxidative stress, and ChE activity in diabetic rats. Further, memory improving effects of agmatine were independent of adrenal I(2) imidazoline receptors. In a separate set, agmatine treatment for an initial 15 days after diabetes confirmation also significantly reduced memory impairment during training trials after 30 days of diabetes confirmation. Moreover, treatment during training trials (30 days after diabetes) also significantly reduced memory impairment in diabetic rats. In conclusion, the present study demonstrates that treatment with agmatine prevents changes in oxidative stress and ChE activity, and probably consequent memory impairment in diabetic rats.

Reduced gap junctional communication among astrocytes in experimental diabetes: contributions of altered connexin protein levels and oxidative-nitrosative modifications

Experimental diabetes increases production of reactive oxygen-nitrogen species and inhibits astrocytic gap junctional communication in tissue culture and brain slices from streptozotocin (STZ)-diabetic rats by unidentified mechanisms. Relative connexin (Cx) protein levels were assessed by Western blotting using extracts from cultured astrocytes grown in high (25 mmol/liter) or low (5.5 mmol/liter) glucose for 2-3 weeks and STZ-diabetic rat brain. Chemiluminescent signals for diabetic samples were normalized to those of controls on the same blot and same protein load. Growth in high glucose did not alter relative Cx26 level, whereas Cx30 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were reduced by ∼30%, and Cx43 increased ∼1.9-fold. In the inferior colliculus of STZ-diabetic rats, Cx30 and Cx43 levels in three of four rats were half those of controls, whereas GAPDH and actin were unaffected. Diabetes did not affect levels of Cx30, Cx43, or GAPDH in cerebral cortex, but actin level rose 24%. Cx43 was predominantly phosphorylated in control and diabetic samples, so the reduced dye transfer is not due to overall dephosphorylation of Cx43. Astrocytic growth in high glucose reduced the dye-labeled area by 75%, but 10 min of treatment with dithiothreitol restored normal dye transfer. In contrast, nitric oxide donors inhibited dye transfer among astrocytes grown in low glucose by 50-65% within 1 hr. Thus, modifications arising from oxidative-nitrosative stress, not altered connexin levels, may underlie the reduced dye transfer among severely hyperglycemic cultured astrocytes, whereas both oxidative-nitrosative stress and regionally selective down-regulation of connexin protein content may affect gap junctional communication in the brains of STZ-diabetic rats.

High glucose stimulates TNFα and MCP-1 expression in rat microglia via ROS and NF-κB pathways

AIM

To investigate whether high glucose stimulates the expression of inflammatory cytokines and the possible mechanisms involved.

METHODS

ELISA and real-time PCR were used to determine the expression of the inflammatory factors, and a chemiluminescence assay was used to measure the production of reactive oxygen species (ROS).

RESULTS

Compared to low glucose (10 mmol/L), treatment with high glucose (35 mmol/L) increased the secretion of tumor necrosis factor (TNF)α and monocyte chemotactic protein-1 (MCP-1), but not interleukin (IL)-1β and IL-6, in a time-dependent manner in primary cultured rat microglia. The mRNA expression of TNFα and MCP-1 also increased in response to high glucose. This upregulation was specific to high glucose because it was not observed in the osmotic control. High-glucose treatment stimulated the formation of ROS. Furthermore, treatment with the ROS scavenger NAC significantly reduced the high glucose-induced TNFα and MCP-1 secretion. In addition, the nuclear factor kappa B (NF-κB) inhibitors MG132 and PDTC completely blocked the high glucose-induced TNFα and MCP-1 secretion.

CONCLUSION

We found that high glucose induces TNFα and MCP-1 secretion as well as mRNA expression in rat microglia in vitro, and this effect is mediated by the ROS and NF-κB pathways.

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.

Cognitive dysfunction in patients with type 2 diabetes

People with diabetes mellitus are at increased risk of cognitive dysfunction and dementia. This review explores the nature and severity of cognitive changes in patients with type 2 diabetes. Possible risk factors such as hypo- and hyperglycemia, vascular risk factors, micro- and macrovascular complications, depression and genetic factors will be examined, as well as findings from brain imaging and autopsy studies. We will show that type 2 diabetes is associated with modest cognitive decrements in non-demented patients that evolve only slowly over time, but also with an increased risk of more severe cognitive deficits and dementia. There is a dissociation between these two 'types' of cognitive dysfunction with regard to affected age groups and course of development. Therefore, we hypothesize that the mild and severe cognitive deficits observed in patients with type 2 diabetes reflect separate processes, possibly with different risk factors and aetiologies.

Protein and lipid oxidative damage in streptozotocin-induced diabetic rats submitted to forced swimming test: the insulin and clonazepam effect

Diabetes may modify central nervous system functions and is associated with moderate cognitive deficits and changes in the brain, a condition that may be referred to as diabetic encephalopathy. The prevalence of depression in diabetic patients is higher than in the general population, and clonazepam is being used to treat this complication. Oxidative stress may play a role in the development of diabetes complications. We investigated oxidative stress parameters in streptozotocin-induced diabetic rats submitted to forced swimming test (STZ) and evaluated the effect of insulin (STZ-INS) and/or clonazepam (STZ-CNZ and STZ-INS-CNZ) acute treatment on these animal model. Oxidative damage to proteins measured as carbonyl content in plasma was significantly increased in STZ group compared to STZ treated groups. Malondialdehyde plasma levels were significantly reduced in STZ-INS and STZ-INS-CNZ groups when compared to STZ rats, being significantly reduced in STZ-INS-CNZ than STZ-INS rats. The activities of the antioxidant enzymes catalase, superoxide dismutase and glutathione peroxidase showed no significant differences among all groups of animals. These findings showed that protein and lipid damage occurs in this diabetes/depression animal model and that the associated treatment of insulin and clonazepam is capable to protect against oxidative damage in this experimental model.

Protective effects of grape seed proanthocyanidin extracts on cerebral cortex of streptozotocin-induced diabetic rats through modulating AGEs/RAGE/NF-kappaB pathway

Diabetic encephalopathy is a severe complication in patients with long-term hyperglycemia. Oxidative stress is thought to be closely implicated in this disorder, so in this study, we examined whether grape seed proanthocyanidin extract (GSPE), a naturally occurring antioxidant derived from grape seeds, could reduce the injuries in the cerebral cortex of diabetic rats by modulating advanced glycation end products (AGEs)/the receptor for AGEs (RAGE)/nuclear factor-kappa B p65 (NF-kappaB p65) pathway, which is crucial in oxidative stress. Body weight and serum AGEs were tested; cerebral cortexes were isolated for morphological observations and the pyramidal cell layers were immunohistochemically stained for the detection of RAGE, NF-kappaB p65, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) as well. For RAGE and NF-kappaB p65, quantitative reverse transcriptase coupled to polymerase chain reaction (RT-PCR) was employed for determination of mRNA levels, and western blot was used to detect protein expression. Our results showed that long term hyperglycemia in diabetic rats caused the degeneration of neurons and the up-regulation of serum AGEs, and also the up-regulation of RAGE, NF-kappaB p65, VCAM-1 and ICAM-1 in the brain. We found that GSPE treatment improved the pathological changes of diabetic rats by modulating the AGEs/RAGE/NF-kappaB p65 pathway. This study enables us to further understand the key role that the AGEs/RAGE/NF-kappaB pathway plays in the pathogenesis of diabetic encephalopathy, and confirms that GSPE might be a therapeutical means to the prevention and treatment of this disorder.

Hyperglycaemia and diabetes impair gap junctional communication among astrocytes

Sensory and cognitive impairments have been documented in diabetic humans and animals, but the pathophysiology of diabetes in the central nervous system is poorly understood. Because a high glucose level disrupts gap junctional communication in various cell types and astrocytes are extensively coupled by gap junctions to form large syncytia, the influence of experimental diabetes on gap junction channel-mediated dye transfer was assessed in astrocytes in tissue culture and in brain slices from diabetic rats. Astrocytes grown in 15–25 mmol/l glucose had a slow-onset, poorly reversible decrement in gap junctional communication compared with those grown in 5.5 mmol/l glucose. Astrocytes in brain slices from adult STZ (streptozotocin)-treated rats at 20–24 weeks after the onset of diabetes also exhibited reduced dye transfer. In cultured astrocytes grown in high glucose, increased oxidative stress preceded the decrement in dye transfer by several days, and gap junctional impairment was prevented, but not rescued, after its manifestation by compounds that can block or reduce oxidative stress. In sharp contrast with these findings, chaperone molecules known to facilitate protein folding could prevent and rescue gap junctional impairment, even in the presence of elevated glucose level and oxidative stress. Immunostaining of Cx (connexin) 43 and 30, but not Cx26, was altered by growth in high glucose. Disruption of astrocytic trafficking of metabolites and signalling molecules may alter interactions among astrocytes, neurons and endothelial cells and contribute to changes in brain function in diabetes. Involvement of the microvasculature may contribute to diabetic complications in the brain, the cardiovascular system and other organs.

Proinsulin C-peptide prevents type-1 diabetes-induced decrease of renal Na+-K+-ATPase alpha1-subunit in rats

AIMS/HYPOTHESIS

C-peptide reduces renal damage in diabetic patients and experimental animal models. In vitro studies suggest that the renal effects of C-peptide may, in part, be explained by stimulation of Na(+)/K(+)-ATPase activity. However, the responses of Na(+)/K(+)-ATPase expression in the kidney of diabetic animals to C-peptide administration remain unclear. The aim of this study was to clarify the responses.

METHODS

Type 1 diabetic rats were produced by injecting streptozotocin (STZ), and some of the rats were treated with either C-peptide or insulin by the aid of an osmotic pump for 1 week. The mRNA expression and immunohistochemical localization of Na(+)/K(+)-ATPase alpha1-, alpha2- and beta3-subunits were investigated in the kidney of these rats.

RESULTS

Na(+)/K(+)-ATPase alpha1-subunit was abundantly expressed in the medullary collecting ducts of control animals, but the expression was markedly decreased in the diabetic state with concomitant decrease in its mRNA expression. Similar decreases were observed in the insulin-treated diabetic rats, whereas in the C-peptide-treated diabetic rats, there was no reduction in the alpha1-expression. The beta3-subunit was expressed in podocytes and parietal cells in the glomeruli, vascular endothelial cells, and cortical collecting ducts, but lesser signals were observed in the proximal and distal tubules. However, the beta3-subunit did not appear to be affected by the diabetic state.

CONCLUSIONS

Diabetes selectively reduced Na(+)/K(+)-ATPase alpha1-subunit expression and abundance. Chronic administration of C-peptide prevented this decrease. This implies a role for C-peptide in the long-term regulation of Na(+)/K(+)-ATPase function.

Presence of the APOE epsilon4 allele modifies the relationship between type 2 diabetes and cognitive performance: the Maine-Syracuse Study

AIMS/HYPOTHESIS

The primary aim of this study was to determine whether the presence of one or more APOE epsilon4 alleles modifies the association between diabetes (defined by glucose > or =7 mmol/l or treatment) and cognitive function.

METHODS

Diabetic status and APOE genotype interactions were assessed cross-sectionally for 826 community-dwelling, stroke-free, non-demented individuals (526 non-diabetic non-APOE epsilon4 carriers, 174 non-diabetic APOE epsilon4 carriers, 87 diabetic APOE epsilon4 non-carriers, 39 diabetic APOE epsilon4 carriers) ranging in age from 50 to 98 years. Cognitive function was assessed using the Mini-Mental State Examination (MMSE), the similarities subtest from the Wechsler Adult Intelligence Scale, and four composite scores derived from 17 additional neuropsychological tests. Multiple linear regression analyses were employed to relate diabetes and APOE genotype to cognitive performance and to examine the interaction between these two risk factors as they relate to cognitive performance. Multiple cardiovascular disease risk factors were statistically controlled.

RESULTS

With adjustment for age, education, sex, race/ethnicity and APOE genotype, performance level was lower for the diabetic than for the non-diabetic group for the MMSE, the similarities subtest and each of the cognitive composites with the exception of the verbal memory composite. Interactions (p < 0.05) between diabetes and APOE genotype were found for all but the visual-spatial memory/organisation composite. The negative association between diabetes and cognitive performance was of a higher magnitude for individuals who carry one or more APOE epsilon4 alleles. Results were similar with additional adjustment for cardiovascular disease and associated risk factors.

CONCLUSIONS/INTERPRETATION

The presence of one or more APOE epsilon4 alleles modifies the association between diabetes and cognitive function.

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.

The beneficial effects of C-Peptide on diabetic polyneuropathy

Diabetic polyneuropathy (DPN) is a common complication in diabetes. At present, there is no adequate treatment, and DPN is often debilitating for patients. It is a heterogeneous disorder and differs in type 1 and type 2 diabetes. An important underlying factor in type 1 DPN is insulin deficiency. Proinsulin C-peptide is a critical element in the cascade of events. In this review, we describe the physiological role of C-peptide and how it provides an insulin-like signaling function. Such effects translate into beneficial outcomes in early metabolic perturbations of neural Na+/K+-ATPase and nitric oxide (NO) with subsequent preventive effects on early nerve dysfunction. Further corrective consequences resulting from this signaling cascade have beneficial effects on gene regulation of early gene responses, neurotrophic factors, their receptors, and the insulin receptor itself. This may lead to preventive and corrective results to nerve fiber degeneration and loss, as well as, promotion of nerve fiber regeneration with respect to sensory somatic fibers and small nociceptive nerve fibers. A characteristic abnormality of type 1 DPN is nodal and paranodal degeneration with severe consequences for myelinated fiber function. This review deals in detail with the underlying insulin-deficiency-related molecular changes and their correction by C-peptide. Based on these observations, it is evident that continuous maintenance of insulin-like actions by C-peptide is needed in peripheral nerve to minimize the sequences of metabolic and molecular abnormalities, thereby ameliorating neuropathic complications. There is now ample evidence demonstrating that C-peptide replacement in type 1 diabetes promotes insulin action and signaling activities in a more enhanced, prolonged, and continuous fashion than does insulin alone. It is therefore necessary to replace C-peptide to physiological levels in diabetic patients. This will have substantial beneficial effects on type 1 DPN.

Combined effects of hyperglycemic conditions and HIV-1 Nef: a potential model for induced HIV neuropathogenesis

Hyperglycemic conditions associated with diabetes mellitus (DM) or with the use of antiretroviral therapy may increase the risk of central nervous system (CNS) disorders in HIV-1 infected patients. In support of this hypothesis, we investigated the combined effects of hyperglycemic conditions and HIV-1 accessory protein Nef on the CNS using both in vitro and in vivo models. Astrocytes, the most abundant glial cell type required for normal synaptic transmission and other functions were selected for our in vitro study. The results show that in vitro hyperglycemic conditions enhance the expression of proinflammatory cytokines including caspase-3, complement factor 3 (C3), and the production of total nitrate and 8-iso-PGF2 α as reactive oxygen species (ROS) in human astrocytes leading to cell death in a dose-dependent manner. Delivery of purified recombinant HIV-1 Nef protein, or Nef expressed via HIV-1-based vectors in astrocytes showed similar results. The expression of Nef protein delivered via HIV-1 vectors in combination with hyperglycemia further augmented the production of ROS, C3, activation of caspase-3, modulation of filamentous protein (F-protein), depolarization of the mitochondria, and loss of astrocytes. To further verify the effects of hyperglycemia and HIV-1 Nef protein on CNS individually or in combination, in vivo studies were performed in streptozotocin (STZ) induced diabetic mice, by injecting HIV-1 Nef expressing viral particles into the sub-cortical region of the brain. Our in vivo results were similar to in vitro findings indicating an enhanced production of caspases-3, ROS (lipid oxidation and total nitrate), and C3 in the brain tissues of these animals. Interestingly, the delivery of HIV-1 Nef protein alone caused similar damage to CNS as augmented by hyperglycemia conditions. Taken together, the data suggests that HIV-1 infected individuals with hyperglycemia could potentially be at a higher risk of developing CNS related complications.

Efficacy and safety of insulin glulisine in Japanese patients with type 1 diabetes mellitus

AIM

The rapid-acting insulin analogue insulin glulisine (glulisine) was compared with insulin lispro (lispro) for efficacy and safety in Japanese patients with type 1 diabetes mellitus (T1DM), using insulin glargine (glargine) as basal insulin.

METHODS

This was an open, randomized, parallel-group, comparative non-inferiority study. The primary efficacy measure was change in adjusted mean haemoglobin A1c (HbA1c) from baseline to endpoint. Safety and treatment satisfaction using the Diabetes Treatment Satisfaction Questionnaire (DTSQ) were also assessed. Patients were treated for 28 weeks with either glulisine or lispro administered 0-15 min before a meal. Doses were titrated to obtain 2-h postprandial plasma glucose (2h-PPG) of 7.11-9.55 mmol/l (128-172 mg/dl). All patients were concomitantly treated with glargine at bedtime, titrated to obtain a fasting (prebreakfast) plasma glucose level of 5.27-7.11 mmol/l (95-128 mg/dl).

RESULTS

Baseline mean HbA1c values were similar for the glulisine (n = 132) and lispro (n = 135) groups (7.44 and 7.50% respectively). From baseline to endpoint, adjusted mean HbA1c increased by 0.10% in the glulisine group and by 0.04% in the lispro group. Non-inferiority of glulisine compared with lispro was shown. There were no significant differences between glulisine and lispro in adjusted mean 2h-PPG [glulisine, 9.06 mmol/l (163 mg/dl) vs. lispro, 8.13 mmol/l (146 mg/dl); p = 0.065] and change in adjusted mean daily rapid-acting insulin dose (glulisine, 0.26 U vs. lispro, 0.26 U; p = 0.994) at study endpoint. There was a significant difference for change in adjusted mean daily basal insulin dose from baseline to study endpoint (glulisine, -0.54 U vs. lispro, 0.26 U; p = 0.013). The most common serious adverse events were hypoglycaemia-related events (hypoglycaemia, hypoglycaemic seizure and hypoglycaemic coma) with no difference observed between the two groups [glulisine, 6.8% (9/132) vs. lispro, 4.4% (6/135); p = 0.437]. No noteworthy differences were observed for change in insulin antibodies from baseline to endpoint. Assessment of treatment satisfaction score and perceived frequency of hyperglycaemia and hypoglycaemia by DTSQ showed no changes from baseline in either group.

CONCLUSIONS

Glulisine was as effective as lispro with respect to change in HbA1c and was well tolerated when used in combination with glargine in Japanese patients with T1DM.

Ectonucleotidase and acetylcholinesterase activities in synaptosomes from the cerebral cortex of streptozotocin-induced diabetic rats and treated with resveratrol

The aim of the present study was to investigate the effects of resveratrol (RV), an important neuroprotective compound on NTPDase, 5'-nucleotidase and acetylcholinesterase (AChE) activities in cerebral cortex synaptosomes of streptozotocin (STZ)-induced diabetic rats. The animals were divided into six groups (n=8): control/saline; control/RV 10mg/kg; control/RV 20mg/kg; diabetic/saline; diabetic/RV 10mg/kg; diabetic/RV 20mg/kg. After 30 days of treatment with resveratrol the animals were sacrificed and the cerebral cortex was removed for synaptosomes preparation and enzymatic assays. The results demonstrated that NTPDase and 5'-nucleotidase activities were significantly increased in the diabetic/saline group (p<0.05) compared to control/saline group. Treatment with resveratrol significantly increased NTPDase, 5'-nucleotidase activities in the diabetic/RV10 and diabetic/RV20 groups (p<0.05) compared to diabetic/saline group. When resveratrol was administered per se there was also an increase in the activities of these enzymes in the control/RV10 and control/RV20 groups (p<0.05) compared to control/saline group. AChE activity was significantly increased in the diabetic/saline group (p<0.05) compared to control/saline group. The treatment with resveratrol prevented this increase in the diabetic/RV10 and diabetic/RV20 groups. In conclusion, this study demonstrated that the resveratrol interfere with the purinergic and cholinergic neurotransmission by altering NTPDase, 5'-nucleotidase and AChE activities in cerebral cortex synaptosomes of diabetic rats. In this context, we can suggest that resveratrol should be considered potential therapeutics and scientific tools to be investigated in brain disorders associated with the diabetes.

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.

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.

Resveratrol prevents memory deficits and the increase in acetylcholinesterase activity in streptozotocin-induced diabetic rats

The objective of the present study was to investigate the effect of the administration of resveratrol (RV) on memory and on acetylcholinesterase (AChE) activity in the cerebral cortex, hippocampus, striatum, hypothalamus, cerebellum and blood in streptozotocin-induced diabetic rats. The animals were divided into six groups (n=6-13): Control/saline; Control/RV 10 mg/kg; Control/RV 20 mg/kg; Diabetic/saline; Diabetic/RV 10 mg/kg; Diabetic/RV 20 mg/kg. One day after 30 days of treatment with resveratrol the animals were submitted to behavioral tests and then submitted to euthanasia and the brain structures and blood were collected. The results showed a decrease in step-down latency in diabetic/saline group. Resveratrol (10 and 20 mg/kg) prevented the impairment of memory induced by diabetes. In the open field test, no significant differences were observed between the groups. In relation to AChE activity, a significant increase in diabetic/saline group (P<0.05) was observed in all brain structures compared to control/saline group. However, AChE activity decreased significantly in control/RV10 and control/RV20 (P<0.05) groups in cerebral cortex, hippocampus and striatum, while no significant differences were observed in diabetic/RV10 and diabetic/RV20 groups in all brain structures compared to control/saline group. Blood AChE activity increased significantly in diabetic/saline group (P<0.05) decreased in control/RV10, control/RV20 and diabetic/RV20 groups (P<0.05) compared to control/saline group. In conclusion, the present findings showed that treatment with resveratrol prevents the increase in AChE activity and consequently memory impairment in diabetic rats, demonstrating that this compound can modulate cholinergic neurotransmission and consequently improve cognition.

Neuroprotective effect of N-acetylcysteine in the development of diabetic encephalopathy in streptozotocin-induced diabetes

Diabetic encephalopathy is characterized by impaired cognitive functions that involve neuronal damage triggered by glucose driven oxidative stress. The objective of the present study was to determine whether N-acetylcysteine (NAC) supplementation ameliorates learning and memory deficits caused by hyperglycemia-induced oxidative stress in experimental diabetes. Male Wistar rats (200-250 g) were rendered diabetic by a single intraperitoneal injection of streptozotocin (50 mg/kg). Cognitive deficits were observed in diabetic animals assessed using elevated plus maze test after 8 weeks of induction of diabetes. Acetylcholinesterase activity, a marker of cholinergic function, was decreased by 15.6% in the cerebral cortex, 20.9% in cerebellum and 14.9% in brain stem of diabetic rats compared to control rats. There was an increase in lipid peroxidation in cerebral cortex (21.97%), cerebellum (20.4%) and brain stem (25.5%) of diabetic rats. This was accompanied by decrease in glutathione and total thiol content along with decrease in the activities of superoxide dismutase, catalase and glutathione reductase. However, glutathione peroxidase activity increased by 11.2%, 13.6% and 23.1% in cerebral cortex, cerebellum and brain stem respectively, while the activity of glutathione-s-transferase decreased only in cerebral cortex (21.7%). Supplementation with NAC (1.4 g/kg/day in drinking water) significantly attenuated cognitive deficits and oxidative stress in diabetic rats. Our results emphasize the involvement of increased oxidative stress in cognitive impairment in diabetic animals and point towards the potential beneficial role of NAC as an adjuvant therapy to conventional anti-hyperglycemic regimens for the prevention and treatment of diabetic encephalopathy.