Preliminary evidence for brain complications in obese adolescents with type 2 diabetes mellitus

Impact of metabolic syndrome on cognition and brain: a selected review of the literature

Metabolic syndrome (MetS), a clustering of risk factors for type 2 diabetes mellitus and cardiovascular disease, has been associated with cognitive dysfunction and brain abnormalities. This review describes the literature on the impact of MetS on brain and cognition and suggests directions for future research. A literature search for reports of MetS and cognition and brain imaging was conducted for both nonelderly adults and adolescents. No studies were found describing MetS and brain or cognition among adolescents; therefore, we also included studies investigating individual components of MetS in this age group. Most studies found associations between MetS and cognitive dysfunction. Multiple cognitive domains were affected by MetS in adults. In adolescents, the majority of findings were in executive functioning. Brain imaging literature in adults implicated MetS in ischemic stroke, white matter alterations, and altered brain metabolism. For adolescents, individual MetS factors were linked to volume losses in the hippocampus and frontal lobes. MetS negatively impacts cognitive performance and brain structure. Potential explanatory models include impaired vascular reactivity, neuroinflammation, oxidative stress, and abnormal brain lipid metabolism. We posit that insulin resistance-associated impairment in cerebrovascular reactivity is an important mechanism underlying brain deficits seen in MetS.

Risk of future depression in people who are obese but metabolically healthy: the English longitudinal study of ageing

There is some evidence to suggest that obesity is a risk factor for the development of depression, although this is not a universal finding. This discordance might be ascribed to the existence of a 'healthy obese phenotype'--that is, obesity in the absence of the associated burden of cardiometabolic risk factors. We examined whether the association of obesity with depressive symptoms is dependent on the individual's metabolic health. Participants were 3851 men and women (aged 63.0±8.9 years, 45.1% men) from the English Longitudinal Study of Ageing, a prospective study of community dwelling older adults. Obesity was defined as body mass index ≥30 kg m(-2). Based on blood pressure, high-density lipoprotein cholesterol, triglycerides, glycated haemoglobin and C-reactive protein, participants were classified as 'metabolically healthy' (0 or 1 metabolic abnormality) or 'unhealthy' (≥2 metabolic abnormalities). Depressive symptoms were assessed at baseline and at 2 years follow-up using the 8-item Centre of Epidemiological Studies Depression (CES-D) scale. Obesity prevalence was 27.5%, but 34.3% of this group was categorized as metabolically healthy at baseline. Relative to non-obese healthy participants, after adjustment for baseline CES-D score and other covariates, the metabolically unhealthy obese participants had elevated risk of depressive symptoms at follow-up (odds ratio (OR)=1.50; 95% confidence interval (CI), 1.05-2.15), although the metabolically healthy obese did not (OR=1.38; 95% CI, 0.88-2.17). The association between obesity and risk of depressive symptoms appears to be partly dependent on metabolic health, although further work is required to confirm these findings.

Understanding migraine through the lens of maladaptive stress responses: a model disease of allostatic load

The brain and body respond to potential and actual stressful events by activating hormonal and neural mediators and modifying behaviors to adapt. Such responses help maintain physiological stability ("allostasis"). When behavioral or physiological stressors are frequent and/or severe, allostatic responses can become dysregulated and maladaptive ("allostatic load"). Allostatic load may alter brain networks both functionally and structurally. As a result, the brain's responses to continued/subsequent stressors are abnormal, and behavior and systemic physiology are altered in ways that can, in a vicious cycle, lead to further allostatic load. Migraine patients are continually exposed to such stressors, resulting in changes to central and peripheral physiology and function. Here we review how changes in brain states that occur as a result of repeated migraines may be explained by a maladaptive feedforward allostatic cascade model and how understanding migraine within the context of allostatic load model suggests alternative treatments for this often-debilitating disease.

Diabetes and cognitive dysfunction

Cognitive dysfunction in type 1 and type 2 diabetes share many similarities, but important differences do exist. A primary distinguishing feature of type 2 diabetes is that people with this disorder often (but not invariably) do poorly on measures of learning and memory, whereas deficits in these domains are rarely seen in people with type 1 diabetes. Chronic hyperglycaemia and microvascular disease contribute to cognitive dysfunction in both type 1 and type 2 diabetes, and both disorders are associated with mental and motor slowing and decrements of similar magnitude on measures of attention and executive functioning. Additionally, both types are characterised by neural slowing, increased cortical atrophy, microstructural abnormalities in white matter tracts, and similar, but not identical, changes in concentrations of brain neurometabolites. Disconcertingly, the rapid rise in obesity and type 2 diabetes in all age groups might result in a substantial increase in prevalence of diabetes-related cognitive dysfunction.

Liraglutide improves hippocampal synaptic plasticity associated with increased expression of Mash1 in ob/ob mice

OBJECTIVE

Consumption of high-fat diet exerts adverse effects on learning and memory formation, which is linked to impaired hippocampal function. Activation of glucagon-like peptide-1 (GLP-1) signalling ameliorates detrimental effects of obesity-diabetes on cognitive function; however, mechanisms underlying these beneficial actions remain unclear. This study examined effects of daily subcutaneous treatment with GLP-1 mimetic, Liraglutide, on synaptic plasticity, hippocampal gene expression and metabolic control in adult obese diabetic (ob/ob) mice.

RESULTS

Long-term potentiation (LTP) induced by area CA1 was completely abolished in ob/ob mice compared with lean controls. Deleterious effects on LTP were rescued (P<0.001) with Liraglutide. Indeed, Liraglutide-treated mice exhibited superior LTP profile compared with lean controls (P<0.01). Expression of hippocampal brain-derived neurotropic factor and neurotrophic tyrosine kinase receptor-type 2 were not significantly different, but synaptophysin and Mash1 were decreased in ob/ob mice. Treatment with Liraglutide over 21 days increased expression of Mash1 in ob/ob mice (2.0-fold; P<0.01). These changes were associated with significantly reduced plasma glucose (21% reduction; P<0.05) and markedly improved plasma insulin concentrations (2.1- to 3.3-fold; P<0.05 to P<0.01). Liraglutide also significantly reduced the glycaemic excursion following an intraperitonal glucose load (area under curve (AUC) values: 22%; P<0.05) and markedly enhanced the insulin response to glucose (AUC values: 1.6-fold; P<0.05). O2 consumption, CO2 production, respiratory exchange ratio and energy expenditure were not altered by Liraglutide therapy. On day 21, accumulated food intake (32% reduction; P<0.05) and number of feeding bouts (32% reduction; P<0.05) were significantly reduced but simple energy restriction was not responsible for the beneficial actions of Liraglutide.

CONCLUSION

Liraglutide elicits beneficial effects on metabolic control and synaptic plasticity in mice with severe obesity and insulin resistance mediated in part through increased expression of Mash1 believed to improve hippocampal neurogenesis and cell survival.

[Association between SUMO4 polymorphisms and type 2 diabetes mellitus]

This study investigated the association between small ubiquitin-like modifier 4 (SUMO4) gene polymorphisms and type 2 diabetes mellitus (T2DM) in Chinese Han of Beijing area. Using the case-control method, we included 404 T2DM patients in T2DM group and 500 age- and gender- matched healthy subjects in control group. We detected the distribution of alleles and genotypes of the three single nucleotide polymorphisms (SNPs, rs237025, rs237024 and rs600739) with the polymerase chain reaction-high resolution melting curve (PCR-HRM) combined with gene sequencing, analysed the differences of glycosylated hemoglobin A1c (HbA1c) among different genotypes carriers in T2DM group, and conducted a haplotype analysis. In this study, the results showed that the frequency of the G allele of rs237025 was significantly higher in T2DM group than that of control group (0.334 vs. 0.282, P = 0.017). Compared with control group, the GA genotype carriers of T2DM patients had 1.563 times more susceptibility to T2DM [P =0.001; odds ratio (OR), 1.563; 95% confidence interval (CI), 1.189-2.053]. Meanwhile, the G allele carriers (GG+GA) of T2DM patients had 1.525 times more susceptibility to T2DM in the dominant model (GG+GA vs. AA, P = 0.002; OR,1.525; 95% CI,1.169-1.989). However, as for rs237024 and rs600739, no significant differences were found in the distribution of the genotypes and alleles between two groups (P >0.05).Although our study didn't observe any statistically significant results, we found that T2DM patients with GG and GA genotypes of rs237025, TT genotype of rs237024 and GG genotype of rs600739 had a higher level of HbA1c than counterparts in control group. In addition, the AAC, AGC and GGT haplotypes might contribute to susceptibility to T2DM (OR>1) , while the AAT and GAC haplotypes might be considered as protective factors against T2DM (OR<1). The results suggested that rs237025 polymorphisms was associated with susceptibility to T2DM, but rs237024 and rs600739 were not.

Calorie restriction reduces the influence of glucoregulatory dysfunction on regional brain volume in aged rhesus monkeys

Insulin signaling dysregulation is related to neural atrophy in hippocampus and other areas affected by neurovascular and neurodegenerative disorders. It is not known if long-term calorie restriction (CR) can ameliorate this relationship through improved insulin signaling or if such an effect might influence task learning and performance. To model this hypothesis, magnetic resonance imaging was conducted on 27 CR and 17 control rhesus monkeys aged 19-31 years from a longitudinal study. Voxel-based regression analyses were used to associate insulin sensitivity with brain volume and microstructure cross-sectionally. Monkey motor assessment panel (mMAP) performance was used as a measure of task performance. CR improved glucoregulation parameters and related indices. Higher insulin sensitivity predicted more gray matter in parietal and frontal cortices across groups. An insulin sensitivity × dietary condition interaction indicated that CR animals had more gray matter in hippocampus and other areas per unit increase relative to controls, suggesting a beneficial effect. Finally, bilateral hippocampal volume adjusted by insulin sensitivity, but not volume itself, was significantly associated with mMAP learning and performance. These results suggest that CR improves glucose regulation and may positively influence specific brain regions and at least motor task performance. Additional studies are warranted to validate these relationships.

Actions of incretin metabolites on locomotor activity, cognitive function and in vivo hippocampal synaptic plasticity in high fat fed mice

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) improve markers of cognitive function in obesity-diabetes, however, both are rapidly degraded to their major metabolites, GLP-1(9-36)amide and GIP(3-42), respectively. Therefore, the present study investigated effects of GLP-1(9-36)amide and GIP(3-42) on locomotor activity, cognitive function and hippocampal synaptic plasticity in mice with diet-induced obesity and insulin resistance. High-fat fed Swiss TO mice treated with GLP-1(9-36)amide, GIP(3-42) or exendin(9-39)amide (twice-daily for 60 days) did not exhibit any changes in bodyweight, non-fasting plasma glucose and plasma insulin concentrations or glucose tolerance compared with high-fat saline controls. Similarly, locomotor and feeding activity, O(2) consumption, CO(2) production, respiratory exchange ratio and energy expenditure were not altered by chronic treatment with incretin metabolites. Administration of the truncated metabolites did not alter general behavior in an open field test or learning and memory ability as recorded during an object recognition test. High-fat mice exhibited a significant impairment in hippocampal long-term potentiation (LTP) which was not affected by treatment with incretin metabolites. These data indicate that incretin metabolites do not influence locomotor activity, cognitive function and hippocampal synaptic plasticity when administered at pharmacological doses to mice fed a high-fat diet.

Brain glycogen and its role in supporting glutamate and GABA homeostasis in a type 2 diabetes rat model

The number of people suffering from diabetes is hastily increasing and the condition is associated with altered brain glucose homeostasis. Brain glycogen is located in astrocytes and being a carbohydrate reservoir it contributes to glucose homeostasis. Furthermore, glycogen has been indicated to be important for proper neurotransmission under normal conditions. Previous findings from our laboratory suggested that glucose metabolism was reduced in type 2 diabetes, and thus we wanted to investigate more specifically how brain glycogen metabolism contributes to maintain energy status in the type 2 diabetic state. Also, our objective was to elucidate the contribution of glycogen to support neurotransmitter glutamate and GABA homeostasis. A glycogen phosphorylase (GP) inhibitor was administered to Sprague-Dawley (SprD) and Zucker Diabetic Fatty (ZDF) rats in vivo and after one day of treatment [1-¹³C]glucose was used to monitor metabolism. Brain levels of ¹³C labeling in glucose, lactate, alanine, glutamate, GABA, glutamine and aspartate were determined. Our results show that inhibition of brain glycogen metabolism reduced the amounts of glutamate in both the control and type 2 diabetes models. The reduction in glutamate was associated with a decrease in the pyruvate carboxylase/pyruvate dehydrogenase ratio in the control but not the type 2 diabetes model. In the type 2 diabetes model GABA levels were increased suggesting that brain glycogen serves a role in maintaining a proper ratio between excitatory and inhibitory neurotransmitters in type 2 diabetes. Both the control and the type 2 diabetic states had a compensatory increase in glucose-derived ¹³C processed through the TCA cycle following inhibition of glycogen degradation. Finally, it was indicated that the type 2 diabetes model might have an augmented necessity for compensatory upregulation at the glycolytic level.

Diabetes management and hyperglycemia in safety sensitive jobs

The chronic and acute effects of hyperglycemia affecting cognition and work are as important as those of hypoglycemia. Its impact, considering that majority of diabetic patients fail to reach therapeutic targets, would be potentially significant. Self monitoring of blood glucose, recognition of body cues and management interventions should be geared not only towards avoidance of disabling hypoglycemia, but also towards unwanted hyperglycemia. Over the long term, chronic hyperglycemia is a risk for cognitive decline. Acute episodes of hyperglycemia, above 15 mmol/L have also been shown to affect cognitive motor tasks. Maintaining blood sugar to avoid hyperglycemia in diabetic workers will help promote safety at work.

Abnormal Cholesterol is Associated with Prefrontal White Matter Abnormalities among Obese Adults: A Diffusion Tensor Imaging Study

The brain is the most cholesterol-rich organ in the body. Although most of the cholesterol in the brain is produced endogenously, some studies suggest that systemic cholesterol may be able to enter the brain. We investigated whether abnormal cholesterol profiles correlated with diffusion-tensor-imaging-based estimates of white matter microstructural integrity of lean and overweight/obese (o/o) adults. Twenty-two lean and 39 obese adults underwent magnetic resonance imaging, kept a three-day food diary, and had a standardized assessment of fasting blood lipids. The lean group ate less cholesterol-rich food than o/o although both groups ate equivalent servings of food per day. Voxelwise correlational analyses controlling for age, diabetes, and white matter hyperintensities, resulted in two significant clusters of negative associations between abnormal cholesterol profile and fractional anisotropy, located in the left and right prefrontal lobes. When the groups were split, the lean subjects showed no associations, whereas the o/o group expanded the association to three significant clusters, still in the frontal lobes. These findings suggest that cholesterol profile abnormalities may explain some of the reductions in white matter microstructural integrity that are reported in obesity.

Weight gain and metabolic risks associated with antipsychotic medications in children and adolescents

BACKGROUND

Antipsychotic-related weight gain and metabolic adverse effects have become a major focus, especially in youth.

METHODS

Review of randomized, cohort, and pharmacoepidemiologic studies of antipsychotic-related weight gain and metabolic adverse effects and of interventions for their reduction in youth.

RESULTS

Across 34 published head-to-head and placebo-controlled studies in youth with psychotic and bipolar disorders, weight gain ranged from 3.8 to 16.2 kg with olanzapine (n=353), 0.9-9.5 kg with clozapine (n=97), 1.9-7.2 kg with risperidone (n=571), 2.3-6.1 kg with quetiapine (n=133), and 0-4.4 kg with aripiprazole (n=451). In 24 placebo-controlled trials, the numbers-needed-to-harm for weight gain ≥7% in youth with bipolar disorder and schizophrenia were 39 (confidence interval [CI]: -1 to +6, not significant) for aripiprazole, 36 (CI: -1 to +7, not significant) for ziprasidone, 9 (CI: 7-14) for quetiapine, 6 (CI: 5-8) for risperidone, and 3 (CI: 3-4) for olanzapine. Data in youth with autism and disruptive behavior disorders, available only for some antipsychotics, suggest greater weight gain, possibly due to less prior antipsychotic exposure. Three-month results from a large cohort study in antipsychotic-naïve youth indicated that metabolic effects differ among second-generation antipsychotics, despite significant weight gain with all studied agents, suggesting additional, weight-independent effects. Further, pharmacoepidemiologic work indicates that antipsychotic polypharmacy increases the risk for obesity (odds ratio [OR]: 2.28 [CI: 1.49-3.65]) or any cardiovascular, cerebrovascular, or hypertensive adverse event (OR: 1.72 [CI: 1.10-2.69]). However, despite marked weight gain and its greater impact on youth, monitoring rates are low and studies of pharmacologic and behavioral interventions are extremely limited.

CONCLUSIONS

More research is needed to develop strategies to minimize antipsychotic-related weight gain and metabolic effects in youth and to discover treatments with lower risk potential.

Abnormal cholesterol is associated with prefrontal white matter abnormalities among obese adults, a diffusion tensor imaging study

The brain is the most cholesterol-rich organ in the body. Although most of the cholesterol in the brain is produced endogenously, some studies suggest that systemic cholesterol may be able to enter the brain. We investigated whether abnormal cholesterol profiles correlated with diffusion-tensor-imaging-based estimates of white matter microstructural integrity of lean and overweight/obese (o/o) adults. Twenty-two lean and 39 obese adults underwent magnetic resonance imaging, kept a 3-day food diary, and had a standardized assessment of fasting blood lipids. The lean group ate less cholesterol rich food than o/o although both groups ate equivalent servings of food per day. Voxelwise correlational analyses controlling for age, diabetes, and white matter hyperintensities, resulted in two significant clusters of negative associations between abnormal cholesterol profile and fractional anisotropy, located in the left and right prefrontal lobes. When the groups were split, the lean subjects showed no associations, whereas the o/o group expanded the association to three significant clusters, still in the frontal lobes. These findings suggest that cholesterol profile abnormalities may explain some of the reductions in white matter microstructural integrity that are reported in obesity.

Metabolic syndrome: links to social stress and socioeconomic status

Socioeconomic stress associated with financial and psychosocial stress is widespread in society. A comprehensive body of research indicates that low socioeconomic status and social stress is associated with a broad spectrum of health risks. This paper reviews epidemiological evidence demonstrating the association between chronic social stress and development of obesity and symptoms leading to metabolic syndrome. The cumulative effects of socioeconomic stress on health and well being are evident throughout the lifespan, affecting children, adolescents, and adults. While the links between stress and metabolic disease are documented, the mechanisms remain less well understood. Animal models are well established and have provided opportunities to systematically investigate contributing mechanisms that may be targeted to develop treatment and prevention strategies against metabolic disorders arising from exposure to chronic social stress.

Systematic differences between lean and obese adolescents in brain spin-lattice relaxation time: a quantitative study

BACKGROUND AND PURPOSE

Emerging evidence suggests that obese adolescents show changes in brain structure compared with lean adolescents. In addition, obesity impacts body development during adolescence. We tested a hypothesis that T1, a marker of brain maturation, can show brain differences associated with obesity.

MATERIALS AND METHODS

Adolescents similar in sex, family income, and school grade were recruited by using strict entry criteria. We measured brain T1 in 48 obese and 31 lean adolescents by quantitative MR imaging at 1.5T. We combined MPRAGE and inversion-recovery sequences with normalization to standard space and automated skull stripping to obtain T1 maps with a symmetric voxel volume of 1 mm(3).

RESULTS

Sex, income, triglycerides, total cholesterol, and fasting glucose did not differ between groups, but obese adolescents had significantly lower HDL, higher LDL, and higher fasting insulin levels than lean adolescents. Intracranial vault volume did not differ between groups, but obese adolescents had smaller intracranial vault-adjusted brain parenchymal volumes. Obese adolescents had 4 clusters (>100 contiguous voxels) of T1 relaxation that were significantly different (P < .005) from those in lean adolescents. Three of these clusters had longer T1s in obese adolescents (in the orbitofrontal and parietal regions), and 1 cluster had shorter T1s, compared with lean adolescents.

CONCLUSIONS

Our results suggest that obesity may have a significant impact on brain development, especially in the frontal and parietal lobes. It is unclear if these changes persist into adulthood or whether they indicate that obese subjects follow a different developmental trajectory during adolescence.

Effects of stress on the developing brain

In a complementary article, Judge Cindy Lederman explains the importance of using science to inform family court decisions. Here, Dr. Bruce S. McEwen looks at that science in depth, discussing how early-life stress can lead to long-lasting behavioral, mental, and physical consequences. Fortunately, preventive measures can improve health outcomes, and while interventions for those who have already experienced debilitating early-life stress require considerable effort, they remain possible, thanks to the brain's plasticity.

Haemoglobin A1c, fasting glucose and future risk of elevated depressive symptoms over 2 years of follow-up in the English Longitudinal Study of Ageing

BACKGROUND

The cross-sectional association between impaired glucose/diabetes and depression is inconsistent. We examined the longitudinal associations between diabetes, indicators of glucose metabolism and depressive symptoms over 2 years of follow-up.

METHOD

Participants were 4338 men and women from the English Longitudinal Study of Ageing, a prospective study of community-dwelling older adults [aged 62.9 (s.d.=9.0) years, 45.2% men]. Depressive symptoms were assessed at baseline and after 2 years of follow-up using the eight-item Centre of Epidemiological Studies--Depression (CES-D) scale. Glycated haemoglobin (HbA1c) levels, fasting glucose and other biological and behavioural risk factors were also assessed at baseline.

RESULTS

Approximately 11.5% of the sample were categorized with elevated depressive symptoms at follow-up (a score ≥ 4 on the CES-D). There was an association between HbA1c and depressive symptoms at follow-up [per unit increase, odds ratio (OR) 1.17, 95% confidence interval (CI) 1.03-1.33] after adjustment for age and baseline CES-D. Cross-sectionally, the probability of depressive symptoms increased with increasing HbA1c levels until the value of 8.0% after which there was a plateau [p(curve)=0.03]. Compared with those with normal fasting glucose, participants with diabetes (confirmed through self-report or elevated fasting blood glucose) at baseline had an elevated risk of depressive symptoms at follow-up (OR 1.52, 95% CI 1.01-2.30) after adjusting for depressive symptoms at baseline, behavioural and sociodemographic variables, adiposity and inflammation.

CONCLUSIONS

These data suggest that poor glucose metabolism and diabetes are risk factors for future depression in older adults. There was no evidence of a U-shaped association.

Cognitive function in 6- to 12-year-old offspring of women with Type 1 diabetes

AIMS

Maternal diabetes is a recognized risk factor for congenital malformation, perinatal morbidity and obesity in later childhood. The aim of this study is to assess the impact of maternal diabetes on cognitive function in offspring.

METHODS

Participants were 6- to 12-year-old offspring of women with Type 1 diabetes. All women received their antenatal care and delivered at one university hospital. HbA(1c) was monitored monthly throughout pregnancy and cognitive function was assessed using the Wechsler Intelligence Scale for Children, version 4.

RESULTS

We present results in 40 offspring. There was no difference in overall full-scale IQ compared with UK normative data. However, working memory was poorer than other parts of the Wechsler Intelligence Scale for Children version 4 test and significantly lower compared with UK normative data [8.4 (2.2) vs. 10.1 (3.2), P < 0.01]. We found no correlation between measurement of digit span or HbA(1c) at any stage during pregnancy (r = -0.225 to 0.002), gestational age at delivery (r = -0.178) or infant birthweight ratio (r = -0.176). There was no relationship between working memory score and maternal hypoglycaemia episodes or maternal duration of diabetes. Comparing infants born before (n = 9) or after 37 weeks' gestation, digit span was non-significantly lower [7.9 (1.8) vs. 8.6 (2.4)].

DISCUSSION

These results suggest offspring of women with Type 1 diabetes have normal overall cognitive function but poorer working memory. We have been unable to identify specific risk factors. Further larger studies are required to increase the understanding of this memory defect and identify any modifiable risk factors.

Disinhibited eating in obese adolescents is associated with orbitofrontal volume reductions and executive dysfunction

In adults, obesity has been associated with disinhibited eating, decreased cortical gray matter (GM) volume, and lower performance on cognitive assessments. Much less is known about these relationships in adolescence and there are no studies assessing behavioral, cognitive, and neurostructural measures in the same group of study participants. This study examined the relationship between obesity, executive function, disinhibition, and brain volumes in relatively healthy youth. Participants included 54 obese and 37 lean adolescents. Participants received a cognitive battery, questionnaires of eating behaviors, and magnetic resonance imaging (MRI). Neuropsychological assessments included tasks targeting frontal lobe function. Eating behaviors were determined using the Three Factor Eating Questionnaire (TFEQ), and structural MRIs were performed on a 1.5 T Siemens Avanto MRI System (Siemens, Erlangen, Germany) to determine brain GM volumes. Lean and obese adolescents were matched on age, years of education, gender, and socioeconomic status. Relative to lean adolescents, obese participants had significantly higher ratings of disinhibition on the TFEQ, lower performance on the cognitive tests, and lower orbitofrontal cortex (OFC) volume. Disinhibition significantly correlated with BMI, Stroop color-word score, and OFC volume. This is the first report of these associations in adolescents and point to the importance of better understanding the associations between neurostructural deficits and obesity.

Central nervous system: a conductor orchestrating metabolic regulations harmed by both hyperglycaemia and hypoglycaemia

Recent evidence suggests that the brain has a key role in the control of energy metabolism, body fat content and glucose metabolism. Neuronal systems, which regulate energy intake, energy expenditure, and endogenous glucose production, sense and respond to input from hormonal and nutrient-related signals that convey information regarding both body energy stores and current energy availability. In response to this input, adaptive changes occur that promote energy homeostasis and the maintenance of blood glucose levels in the normal range. Defects in this control system are implicated in the link between obesity and type 2 diabetes mellitus. The central nervous system may be considered the conductor of an orchestra involving many peripheral organs involved in these homeostatic processes. However, the brain is mainly a glucose-dependent organ, which can be damaged by both hypoglycaemia and hyperglycaemia. Hypoglycaemia unawareness is a major problem in clinical practice and is associated with an increased risk of coma. Stroke is another acute complication associated with diabetes mellitus, especially in elderly people, and the control of glucose level in this emergency situation remains challenging. The prognosis of stroke is worse in diabetic patients and both its prevention and management in at-risk patients should be improved. Finally, chronic diabetic encephalopathies, which may lead to cognitive dysfunction and even dementia, are also recognized. They may result from recurrent hypoglycaemia and/or from chronic hyperglycaemia leading to cerebral vascular damage. Functional imaging is of interest for exploring diabetes-associated cerebral abnormalities. Thus, the intimate relationship between the brain and diabetes is increasingly acknowledged in both research and clinical practice.

Vascular pathology and blood-brain barrier disruption in cognitive and psychiatric complications of type 2 diabetes mellitus

Vascular pathology is recognized as a principle insult in type 2 diabetes mellitus (T2DM). Co-morbidities such as structural brain abnormalities, cognitive, learning and memory deficits are also prevailing in T2DM patients. We previously suggested that microvascular pathologies involving blood-brain barrier (BBB) breakdown results in leakage of serum-derived components into the brain parenchyma, leading to neuronal dysfunction manifested as psychiatric illnesses. The current postulate focuses on the molecular mechanisms controlling BBB permeability in T2DM, as key contributors to the pathogenesis of mental disorders in patients. Revealing the mechanisms underlying BBB dysfunction and inflammatory response in T2DM and their role in metabolic disturbances, abnormal neurovascular coupling and neuronal plasticity, would contribute to the understanding of the mechanisms underlying psychopathologies in diabetic patients. Establishing this link would offer new targets for future therapeutic interventions.

Diabetes as a chronic metabolic stressor: causes, consequences and clinical complications

Diabetes mellitus is an endocrine disorder resulting from inadequate insulin release and/or reduced insulin sensitivity. The complications of diabetes are well characterized in peripheral tissues, but there is a growing appreciation that the complications of diabetes extend to the central nervous system (CNS). One of the potential neurological complications of diabetes is cognitive deficits. Interestingly, the structural, electrophysiological, neurochemical and anatomical underpinnings responsible for cognitive deficits in diabetes are strikingly similar to those observed in animals subjected to chronic stress, as well as in patients with stress-related psychiatric illnesses such as major depressive disorder. Since diabetes is a chronic metabolic stressor, this has led to the suggestion that common mechanistic mediators are responsible for neuroplasticity deficits in both diabetes and depression. Moreover, these common mechanistic mediators may be responsible for the increase in the risk of depressive illness in diabetes patients. In view of these observations, the aims of this review are (1) to describe the neuroplasticity deficits observed in diabetic rodents and patients; (2) to summarize the similarities in the clinical and preclinical studies of depression and diabetes; and (3) to highlight the diabetes-induced neuroplasticity deficits in those brain regions that have been implicated as important pathological centers in depressive illness, namely, the hippocampus, the amygdala and the prefrontal cortex.

Obese Adolescents with Type 2 Diabetes Mellitus Have Hippocampal and Frontal Lobe Volume Reductions

The rates of type 2 diabetes (T2DM) continue to parallel the rising rates of obesity in the United States, increasingly affecting adolescents as well as adults. Hippocampal and frontal lobe reductions have been found in older adults with type 2 diabetes, and we sought to ascertain if these brain alterations were also present in obese adolescents with T2DM. In a cross-sectional study we compared MRI-based regional brain volumes of 18 obese adolescents with T2DM and 18 obese controls without evidence of marked insulin resistance. Groups were matched on age, sex, school grade, ethnicity, socioeconomic status, body mass index, and waist circumference. Relative to obese controls, adolescents with T2DM had significantly reduced hippocampal and prefrontal volumes, and higher rates of global cerebral atrophy. Hemoglobin A1c, an index of long-term glycemic control, was inversely associated with prefrontal volume and positively associated with global cerebral atrophy (both p < 0.05). Brain integrity is negatively impacted by T2DM already during adolescence, long before the onset of overt macrovascular disease. Paralleling the findings of greater vascular and renal complications among obese adolescents with severe insulin resistance and T2DM relative to their age-matched peers with type 1 diabetes, we find clear evidence of possible brain complications. Our findings call for aggressive and early intervention to limit the negative impact of obesity-associated insulin resistance leading to T2DM on the developing brains of adolescents.