Brain iron overload, insulin resistance, and cognitive performance in obese subjects: a preliminary MRI case-control study

Iron homeostasis and insulin sensitivity: unraveling the complex interactions

Diabetes has arisen as a noteworthy global health issue, marked by escalating incidence and mortality rates. Insulin, crucial for preserving euglycemia, acts as a vital energy provider for various tissues. Iron metabolism notably plays a significant role in the development of insulin resistance, a key factor in the onset of various metabolic disorders. The intricate interaction between iron and insulin signaling encompasses complex regulatory mechanisms at the molecular level, thereby impacting cellular reactions to insulin. The intricate interplay between insulin and glucagon, essential for precise regulation of hepatic glucose production and systemic glucose levels, may be influenced by certain microelements for instance zinc, copper, iron, boron, calcium, cobalt, chromium, iodine, magnesium and selenium. While significant progress has been achieved in elucidating the pathophysiological connections between iron overload and glucose metabolism, our understanding of the involvement of the Fenton reaction and oxidative stress in insulin resistance influencing many chronical conditions remains limited. Furthermore, the exploration of the multifaceted roles of insulin in the human body continues to be a subject of active investigation by numerous scientific researchers. This review comprehensively outlines the potential adverse impact of iron overload on insulin function and glucose metabolism. Additionally, we provide a synthesis of findings derived from various research domains, encompassing population studies, animal models, and clinical investigations, to scrutinize the multifaceted relationship between iron and insulin sensitivity. Moreover, we delineate instances of correlations between serum iron levels and various medical conditions, including the diabetes also gestational diabetes and obesity.

A high fat diet potentiates neonatal iron overload-induced memory impairments in rats

PURPOSE

The present study aimed at evaluating possible synergistic effects between two risk factors for cognitive decline and neurodegenerative disorders, i.e. iron overload and exposure to a hypercaloric/hyperlipidic diet, on cognition, insulin resistance, and hippocampal GLUT1, GLUT3, Insr mRNA expression, and AKT phosporylation.

METHODS

Male Wistar rats were treated with iron (30 mg/kg carbonyl iron) or vehicle (5% sorbitol in water) from 12 to 14th post-natal days. Iron-treated rats received a standard laboratory diet or a high fat diet from weaning to adulthood (9 months of age). Recognition and emotional memory, peripheral blood glucose and insulin levels were evaluated. Glucose transporters (GLUT 1 and GLUT3) and insulin signaling were analyzed in the hippocampus of rats.

RESULTS

Both iron overload and exposure to a high fat diet induced memory deficits. Remarkably, the association of iron with the high fat diet induced more severe cognitive deficits. Iron overload in the neonatal period induced higher insulin levels associated with significantly higher HOMA-IR, an index of insulin resistance. Long-term exposure to a high fat diet resulted in higher fasting glucose levels. Iron treatment induced changes in Insr and GLUT1 expression in the hippocampus. At the level of intracellular signaling, both iron treatment and the high fat diet decreased AKT phosphorylation.

CONCLUSION

The combination of iron overload with exposure to a high fat diet only led to synergistic deleterious effect on emotional memory, while the effects induced by iron and by the high fat diet on AKT phosphorylation were comparable. These findings indicate that there is, at least to some extent, an additive effect of iron combined with the diet. Further studies investigating the mechanisms associated to deleterious effects on cognition and susceptibility for the development of age-associated neurodegenerative disorders are warranted.

Exploring Potential Mechanisms Accounting for Iron Accumulation in the Central Nervous System of Patients with Alzheimer's Disease

Elevated levels of iron occur in both cortical and subcortical regions of the CNS in patients with Alzheimer's disease. This accumulation is present early in the disease process as well as in more advanced stages. The factors potentially accounting for this increase are numerous, including: (1) Cells increase their uptake of iron and reduce their export of iron, as iron becomes sequestered (trapped within the lysosome, bound to amyloid β or tau, etc.); (2) metabolic disturbances, such as insulin resistance and mitochondrial dysfunction, disrupt cellular iron homeostasis; (3) inflammation, glutamate excitotoxicity, or other pathological disturbances (loss of neuronal interconnections, soluble amyloid β, etc.) trigger cells to acquire iron; and (4) following neurodegeneration, iron becomes trapped within microglia. Some of these mechanisms are also present in other neurological disorders and can also begin early in the disease course, indicating that iron accumulation is a relatively common event in neurological conditions. In response to pathogenic processes, the directed cellular efforts that contribute to iron buildup reflect the importance of correcting a functional iron deficiency to support essential biochemical processes. In other words, cells prioritize correcting an insufficiency of available iron while tolerating deposited iron. An analysis of the mechanisms accounting for iron accumulation in Alzheimer's disease, and in other relevant neurological conditions, is put forward.

Iron overload in hypothalamic AgRP neurons contributes to obesity and related metabolic disorders

Iron overload is closely associated with metabolic dysfunction. However, the role of iron in the hypothalamus remains unclear. Here, we find that hypothalamic iron levels are increased, particularly in agouti-related peptide (AgRP)-expressing neurons in high-fat-diet-fed mice. Using pharmacological or genetic approaches, we reduce iron overload in AgRP neurons by central deferoxamine administration or transferrin receptor 1 (Tfrc) deletion, ameliorating diet-induced obesity and related metabolic dysfunction. Conversely, Tfrc-mediated iron overload in AgRP neurons leads to overeating and adiposity. Mechanistically, the reduction of iron overload in AgRP neurons inhibits AgRP neuron activity; improves insulin and leptin sensitivity; and inhibits iron-induced oxidative stress, endoplasmic reticulum stress, nuclear factor κB signaling, and suppression of cytokine signaling 3 expression. These results highlight the critical role of hypothalamic iron in obesity development and suggest targets for treating obesity and related metabolic disorders.

Iron, glucose and fat metabolism and obesity: an intertwined relationship

A bidirectional relationship exists between adipose tissue metabolism and iron regulation. Total body fat, fat distribution and exercise influence iron status and components of the iron-regulatory pathway, including hepcidin and erythroferrone. Conversely, whole body and tissue iron stores associate with fat mass and distribution and glucose and lipid metabolism in adipose tissue, liver, and muscle. Manipulation of the iron-regulatory proteins erythroferrone and erythropoietin affects glucose and lipid metabolism. Several lines of evidence suggest that iron accumulation and metabolism may play a role in the development of metabolic diseases including obesity, type 2 diabetes, hyperlipidaemia and non-alcoholic fatty liver disease. In this review we summarise the current understanding of the relationship between iron homoeostasis and metabolic disease.

Regional high iron deposition on quantitative susceptibility mapping correlates with cognitive decline in type 2 diabetes mellitus

Objective

To quantitatively evaluate the iron deposition and volume changes in deep gray nuclei according to threshold-method of quantitative susceptibility mapping (QSM) acquired by strategically acquired gradient echo (STAGE) sequence, and to analyze the correlation between the magnetic susceptibility values (MSV) and cognitive scores in type 2 diabetes mellitus (T2DM) patients.

Methods

Twenty-nine patients with T2DM and 24 healthy controls (HC) matched by age and gender were recruited in this prospective study. QSM images were used to evaluate whole-structural volumes (V_wh), regional magnetic susceptibility values (MSV_RII), and volumes (V_RII) in high-iron regions in nine gray nuclei. All QSM data were compared between groups. Receiver operating characteristic (ROC) analysis was used to assess the discriminating ability between groups. The predictive model from single and combined QSM parameters was also established using logistic regression analysis. The correlation between MSV_RII and cognitive scores was further analyzed. Multiple comparisons of all statistical values were corrected by false discovery rate (FDR). A statistically significant P-value was set at 0.05.

Results

Compared with HC group, the MSV_RII of all gray matter nuclei in T2DM were increased by 5.1-14.8%, with significant differences found in bilateral head of caudate nucleus (HCN), right putamen (PUT), right globus pallidus (GP), and left dentate nucleus (DN) (P < 0.05). The V_wh of most gray nucleus in T2DM group were decreased by 1.5-16.9% except bilateral subthalamic nucleus (STN). Significant differences were found in bilateral HCN, bilateral red nucleus (RN), and bilateral substantia nigra (SN) (P < 0.05). V_RII was increased in bilateral GP, bilateral PUT (P < 0.05). V_RII/V_wh was also increased in bilateral GP, bilateral PUT, bilateral SN, left HCN and right STN (P < 0.05). Compared with the single QSM parameter, the combined parameter showed the largest area under curve (AUC) of 0.86, with a sensitivity of 87.5% and specificity of 75.9%. The MSV_RII in the right GP was strongly associated with List A Long-delay free recall (List A LDFR) scores (r = -0.590, P = 0.009).

Conclusion

In T2DM patients, excessive and heterogeneous iron deposition as well as volume loss occurs in deep gray nuclei. The MSV in high iron regions can better evaluate the distribution of iron, which is related to the decline of cognitive function.

Insulin Resistance and Cognitive Impairment: Evidence From Neuroimaging

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

Caveolin-1 Alleviates Diabetes-Associated Cognitive Dysfunction Through Modulating Neuronal Ferroptosis-Mediated Mitochondrial Homeostasis

Aims: Iron metabolism is involved in many biological processes in the brain. Alterations in iron homeostasis have been associated with several neurodegenerative disorders. Instead of stroke and ischemic heart disease, dementia has become the second leading cause of mortality among the type 2 diabetes mellitus (T2DM) population. Therefore, we attempted to investigate the role of ferroptosis in diabetes-associated cognitive dysfunction (DACD). Results: We evaluated ferroptosis hallmarks in the hippocampus of T2DM (high-fat diet/streptozotocin, HFD/STZ) mice, primary hippocampal neurons, as well as in the blood of patients. The results of Gene Set Enrichment Analysis showed significantly differentially expressed genes related to ferroptosis-related pathways between normal control (db/m) and leptin receptor-deficient (db/db) mice. Here, ferroptosis, mitochondrial dysfunction and cognitive impairment were revealed, and caveolin-1 (cav-1) was significantly downregulated in the hippocampus of T2DM (HFD/STZ) mice. In addition, ferrostatin-1 and cav-1 restoration neutralized ferroptosis-related symbolic changes, mitochondrial dysfunction, and improved cognitive dysfunction. Notably, the plasma levels of Fe²⁺ and 4-hydroxynonenal (4-HNE) in T2DM patients showed a tendency to increase compared with those in nondiabetic subjects, and the Fe²⁺ level was negatively correlated with the cognitive ability in T2DM subjects. Innovation: For the first time, this study suggested that ferroptosis promoted the progression of DACD induced by T2DM both in vivo and in vitro, and supported the clinical evidence for the correlation between ferroptosis and T2DM-related DACD, which provided new insights into the potential antioxidant effects of ferroptosis inhibitors and cav-1 on DACD. Conclusions: The overexpression of cav-1 may attenuate DACD by modulating neuronal ferroptosis-mediated mitochondrial homeostasis. We put cav-1 on the spotlight as a promising candidate to prevent DACD. Antioxid. Redox Signal. 37, 867-886.

Heritability of R2* iron in the basal ganglia and cortex

BACKGROUND

While iron is essential for normal brain functioning, elevated concentrations are commonly found in neurodegenerative diseases and are associated with impaired cognition and neurological deficits. Currently, only little is known about genetic and environmental factors that influence brain iron concentrations.

METHODS

Heritability and bivariate heritability of regional brain iron concentrations, assessed by R2* relaxometry at 3 Tesla MRI, were estimated with variance components models in 130 middle-aged to elderly participants of the Austrian Stroke Prevention Family Study.

RESULTS

Heritability of R2* iron ranged from 0.46 to 0.82 in basal ganglia and from 0.65 to 0.76 in cortical lobes. Age and BMI explained up to 12% and 9% of the variance of R2* iron, while APOE ε4 carrier status, hypertension, diabetes, hypercholesterolemia, sex and smoking explained 5% or less. The genetic correlation of R2* iron among basal ganglionic nuclei and among cortical lobes ranged from 0.78 to 0.87 and from 0.65 to 0.97, respectively. R2* rates in basal ganglia and cortex were not genetically correlated.

CONCLUSIONS

Regional brain iron concentrations are mainly driven by genetic factors while environmental factors contribute to a certain extent. Brain iron levels in the basal ganglia and cortex are controlled by distinct sets of genes.

Neuroprotective Effects of Oligosaccharides in Rehmanniae Radix on Transgenic Caenorhabditis elegans Models for Alzheimer’s Disease

Rehmanniae Radix (RR, the dried tuberous roots of Rehmannia glutinosa (Gaertn.) DC.) is an important traditional Chinese medicine distributed in Henan, Hebei, Inner Mongolia, and Northeast in China. RR is frequently used to treat diabetes mellitus, cardiovascular disease, osteoporosis and aging-related diseases in a class of prescriptions. The oligosaccharides and catalpol in RR have been confirmed to have neuroprotective effects. However, there are few studies on the anti-Alzheimer’s disease (AD) effect of oligosaccharides in Rehmanniae Radix (ORR). The chemical components and pharmacological effects of dried Rehmannia Radix (DRR) and prepared Rehmannia Radix (PRR) are different because of the different processing methods. ORR has neuroprotective potential, such as improving learning and memory in rats. Therefore, this study aimed to prove the importance of oligosaccharides in DRR (ODRR) and PRR (OPRR) for AD based on the Caenorhabditis elegans (C. elegans) model and the different roles of ODRR and OPRR in the treatment of AD. In this study, we used paralysis assays, lifespan and stress resistance assays, bacterial growth curve, developmental and behavioral parameters, and ability of learning and memory to explore the effects of ODRR and OPRR on anti-AD and anti-aging. Furthermore, the accumulation of reactive oxygen species (ROS); deposition of Aβ; and expression of amy-1, sir-2.1, daf-16, sod-3, skn-1, and hsp-16.2 were analyzed to confirm the efficacy of ODRR and OPRR. OPRR was more effective than ODRR in delaying the paralysis, improving learning ability, and prolonging the lifespan of C. elegans. Further mechanism studies showed that the accumulation of ROS, aggregation, and toxicity of Aβ were reduced, suggesting that ORR alleviated Aβ-induced toxicity, in part, through antioxidant activity and Aβ aggregation inhibiting. The expression of amy-1 was downregulated, and sir-2.1, daf-16, sod-3, and hsp-16.2 were upregulated. Thus, ORR could have a possible therapeutic effect on AD by modulating the expression of amy-1, sir-2.1, daf-16, sod-3, and hsp-16.2. Furthermore, ORR promoted the nuclear localization of daf-16 and further increased the expression of sod-3 and hsp-16.2, which significantly contributed to inhibiting the Aβ toxicity and enhancing oxidative stress resistance. In summary, the study provided a new idea for the development of ORR.

In vivo brain iron concentration in healthy individuals at 3.0 T magnetic resonance imaging: a prospective cross-sectional study

OBJECTIVE

To quantify iron deposits in the basal ganglia and to evaluate its relation to age, sex, body mass index and brain laterality.

METHODS

Prospective observational study. Data were collected from the patients' electronic medical records. The concentration of iron deposits in the brain was assessed using whole-brain MRI at 3.0 Tesla.

RESULTS

138 participants were selected, 69.6% were female and the mean age was 47 ± 19 years. The κ coefficient was very strong (k = 0.92, p < 0.001). Age showed a moderate correlation between iron deposits in the caudate and putamen nuclei, on both right and left sides. In overall and right-handed individuals, a significantly higher iron concentration was observed on the left side for the caudate nucleus, putamen, thalamus, globus pallidus, and centrum semiovale, and for left-handed individuals, it was also observed in the left side-for the putamen and centrum semiovale. A weak correlation was shown between body mass index and left and right substantia nigra, left caudate nuclei, left putamen and right globus pallidus.

CONCLUSION

Our results showed a significantly higher iron deposit on the left side in most brain regions. In addition, the body mass index may also be related to iron overload, especially in the caudate nucleus.

ADVANCES IN KNOWLEDGE

Brain iron deposits may be normal, owing to aging, or be pathological, such as neurodegeneration. Thus, it is important to know how much is expected of iron deposition in the brain of healthy populations.

Iron Overload in Chronic Kidney Disease: Less Ferritin, More T2*MRI

To date, there is no consensus on the most reliable marker of iron status in patients with chronic kidney disease (CKD). Serum ferritin is used routinely, although it may be a misleading marker for iron overload. The success of T2^* MRI in monitoring iron overload in patients with hemoglobinopathies can be beneficial to monitoring patients with CKD.

Magnetic susceptibility in the deep gray matter may be modulated by apolipoprotein E4 and age with regional predilections: a quantitative susceptibility mapping study

PURPOSE

To examine the relationship between apolipoprotein E gene (APOE) mutation status and iron accumulation in the deep gray matter of subjects with cognitive symptoms using quantitative susceptibility mapping (QSM).

METHODS

A total of 105 patients with cognitive symptoms were enrolled. QSM data were generated from 3D gradient-echo data using an STI Suite algorithm. A region of interest-based analysis with QSM was performed in the deep gray matter. Differences between APOE4 carriers and non-carriers were assessed by analysis of covariance. Multiple regression analysis was performed to identify the factors associated with magnetic susceptibility.

RESULTS

Clinical characters such as age, education, MMSE, vascular risk burden, and systolic blood pressure differ between APOE4 carrier and non-carrier groups. The APOE4 carrier group had higher magnetic susceptibility values than the non-carrier group, with significant differences in the caudate (p = 0.004), putamen (p < 0.0001), and globus pallidus (p < 0.0001) which imply higher iron accumulation. In a multiple regression analysis, APOE4 status was found to be a predictor of magnetic susceptibility value in the globus pallidus (p = 0.03); age for magnetic susceptibility value in the caudate nucleus (p = 0.0064); and age and hippocampal atrophy for magnetic susceptibility value in the putamen (p < 0.05).

CONCLUSION

Our study demonstrates that magnetic susceptibility in globus pallidus is related to APOE4 status while those of caudate and putamen are related to other factors including age. It suggests that brain iron accumulation in the deep gray matter is modulated by APOE4 and age with differential regional predilection.

Gut microbes and health

The human body is populated by myriads of microorganisms throughout its surface and in the cavities connected to the outside. The microbial colonisers of the intestine (microbiota) are a functional and non-expendable part of the human organism: they provide genes (microbiome) and additional functions to the resources of our species and participate in multiple physiological processes (somatic development, nutrition, immunity, etc.). Some chronic non-communicable diseases of developed society (atopias, metabolic syndrome, inflammatory diseases, cancer and some behaviour disorders) are associated with dysbiosis: loss of species richness in the intestinal microbiota and deviation from the ancestral microbial environment. Changes in the vertical transmission of the microbiome, the use of antiseptics and antibiotics, and dietary habits in industrialised society appear to be at the origin of dysbiosis. Generating and maintaining diversity in the microbiota is a new clinical target for health promotion and disease prevention.

Use of 2-dimensional cell monolayers and 3-dimensional microvascular networks on microfluidic devices shows that iron increases transendothelial adiponectin flux via inducing ROS production

BACKGROUND

Iron excess is a risk factor for cardiovascular diseases and it is important to understand the effect of iron on vascular permeability, particularly for the transport of large metabolic hormones such as adiponectin.

METHODS

We used 2-dimensional monolayers of cultured human dermal microvascular endothelial cells (HDMEC) and human umbilical vein endothelial cells (HUVEC) as well as 3-dimensional microvascular networks to measure transendothelial flux.

RESULTS

Iron supplementation reduced transendothelial electric resistance (TEER). Flux analysis indicated that under control conditions permeability of 70 kDa dextran and oligomeric forms of adiponectin were restricted in comparison with a 3 kDa dextran, however upon iron treatment permeability of the larger molecules was increased. The increased permeability and size-dependent trans-endothelial movement in response to iron was also observed in 3-dimensional microvascular networks. Mechanistically, the alteration in barrier functionality was associated with increased oxidative stress in response to iron since alterations in TEER and permeability were rescued when reactive oxygen species production was attenuated by pre-treatment with the antioxidant N-acetyl cysteine.].

CONCLUSIONS

Iron supplementation induced ROS production resulting in increased transendothelial permeability.

GENERAL SIGNIFICANCE

Altogether, this suggests that the oxidative stress associated with iron excess could play an important role in the regulation of endothelial functionality, controlling hormone action in peripheral tissues by regulating the first rate-limiting step controlling hormone access to target tissues.

Does thiamine protect the brain from iron overload and alcohol-related dementia?

Alcohol-related dementia (ARD) is a common and severe co-morbidity in alcohol use disorder (AUD). We propose brain iron overload (BIO) to be an important and previously neglected pathogenic process, accelerating cognitive decline in AUD. Furthermore, we suggest thiamine, which is frequently depleted in AUD, to be a key modulator in this process: Thiamine deficiency impairs the integrity of the blood-brain barrier, thereby enabling iron to pass through and accumulate in the brain. This hypothesis is based on findings from animal, translational, and neuroimaging studies, discussed in this article. To validate this hypothesis, translational studies focusing on brain iron homeostasis in AUD, as well as prospective clinical studies investigating prevalence and clinical impact of BIO in AUD, should be conducted. If proven right, this would change the understanding of ARD and may lead to novel therapeutic interventions in prevention and treatment of ARD.

The impact of brain iron accumulation on cognition: A systematic review

Iron is involved in many processes in the brain including, myelin generation, mitochondrial function, synthesis of ATP and DNA and the cycling of neurotransmitters. Disruption of normal iron homeostasis can result in iron accumulation in the brain, which in turn can partake in interactions which amplify oxidative damage. The development of MRI techniques for quantifying brain iron has allowed for the characterisation of the impact that brain iron has on cognition and neurodegeneration. This review uses a systematic approach to collate and evaluate the current literature which explores the relationship between brain iron and cognition. The following databases were searched in keeping with a predetermined inclusion criterion: Embase Ovid, PubMed and PsychInfo (from inception to 31st March 2020). The included studies were assessed for study characteristics and quality and their results were extracted and summarised. This review identified 41 human studies of varying design, which statistically assessed the relationship between brain iron and cognition. The most consistently reported interactions were in the Caudate nuclei, where increasing iron correlated poorer memory and general cognitive performance in adulthood. There were also consistent reports of a correlation between increased Hippocampal and Thalamic iron and poorer memory performance, as well as, between iron in the Putamen and Globus Pallidus and general cognition. We conclude that there is consistent evidence that brain iron is detrimental to cognitive health, however, more longitudinal studies will be required to fully understand this relationship and to determine whether iron occurs as a primary cause or secondary effect of cognitive decline.

Glycated Hemoglobin, but not Insulin Sensitivity, is Associated with Memory in Subjects with Obesity

OBJECTIVE

Obesity has been related to later-life dementia. Serum glucose levels and insulin resistance are known to influence cognition in individuals with diabetes. This study aimed to evaluate memory function in middle-aged individuals with obesity in association with glucose metabolism and brain iron content.

METHODS

This was a cross-sectional case-control study including 121 participants aged 27.2 to 66.6 years (56 without obesity, 65 with obesity) stratified according to sex and menopausal status. Insulin sensitivity, body composition, brain iron content, and memory function were evaluated by euglycemic hyperinsulinemic clamp, dual-energy x-ray absorptiometry, magnetic resonance relaxometry (R2*), and California Verbal Learning Test, respectively.

RESULTS

Women with obesity, but not men, had lower scores in some California Verbal Learning Tests in association with metabolic parameters and increased brain iron content compared with controls. Fasting plasma glucose, glycated hemoglobin (HbA1c; within normal range), and R2* were negatively associated with memory scores, whereas insulin sensitivity showed positive associations. Remarkably, only HbA1c levels and R2* in the right inferior fronto-orbital region remained significant after controlling for age, sex, education, and BMI.

CONCLUSIONS

Impairments in memory function in middle-aged women with obesity are associated with HbA1c levels and brain iron content independently of insulin sensitivity. These results may have implications in the design of therapeutic strategies in women with obesity.

MRI imaging and histopathological study of brain iron overload of β-thalassemic mice

Brain iron overload is chronic and slow progressing and plays an important role in the pathogenesis of neurodegenerative disorders. Magnetic resonance imaging (MRI) is a useful noninvasive tool for determining liver iron content, but it has not been proven to be adequate for evaluating brain iron overload. We evaluated the usefulness of MRI-derived parameters to determine brain iron concentration in β-thalassemic mice and the effects of the membrane permeable iron chelator, deferiprone. Sixteen β-thalassemic mice underwent 1.5T MRI of the brain that included a multiecho T2*-weighted sequence. Brain T2* values ranged from 28 to 31ms for thalassemic mice. For the iron overloaded thalassemic mice, brain T2* values decreased, ranging from 8 to 12ms, which correlated with the iron overload status of the animals. In addition, brain T2* values increased in the group with the treatment of deferiprone, ranging from 18 to 24ms. Our results may be useful to understand brain pathology in iron overload. Moreover, data could lead to an earlier diagnosis, assist in following disease progression, and demonstrate the benefits of iron chelation therapy.

Distribution of brain iron accrual in adolescence: Evidence from cross-sectional and longitudinal analysis

To track iron accumulation and location in the brain across adolescence, we repurposed diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) data acquired in 513 adolescents and validated iron estimates with quantitative susceptibility mapping (QSM) in 104 of these subjects. DTI and fMRI data were acquired longitudinally over 1 year in 245 male and 268 female, no-to-low alcohol-consuming adolescents (12-21 years at baseline) from the National Consortium on Alcohol and NeuroDevelopment in Adolescence (NCANDA) study. Brain region average signal values were calculated for susceptibility to nonheme iron deposition: pallidum, putamen, dentate nucleus, red nucleus, and substantia nigra. To estimate nonheme iron, the corpus callosum signal (robust to iron effects) was divided by regional signals to generate estimated R2 (edwR2 for DTI) and R2 * (eR2 * for fMRI). Longitudinal iron deposition was measured using the normalized signal change across time for each subject. Validation using baseline QSM, derived from susceptibility-weighted imaging, was performed on 46 male and 58 female participants. Normalized iron deposition estimates from DTI and fMRI correlated with age in most regions; both estimates indicated less iron in boys than girls. QSM results correlated highly with DTI and fMRI results (adjusted R2 = 0.643 for DTI, 0.578 for fMRI). Cross-sectional and longitudinal analyses indicated an initial rapid increase in iron, notably in the putamen and red nucleus, that slowed with age. DTI and fMRI data can be repurposed for identifying regional brain iron deposition in developing adolescents as validated with high correspondence with QSM.

Region-specific susceptibility change in cognitively impaired patients with diabetes mellitus

Emerging evidence suggests that diabetes mellitus (DM) is associated with iron and calcium metabolism. However, few studies have investigated the presence of DM in cognitively impaired patients and its effect on brain iron and calcium accumulation. Therefore, we assessed the effects of DM on cognitively impaired patients using quantitative susceptibility mapping (QSM). From June 2012 to Feb 2014, 92 eligible cognitively impaired patients underwent 3T magnetic resonance imaging (MRI). There were 46 patients with DM (DM+) and 46 aged matched patients without DM (DM-). QSM was obtained from gradient echo data and analyzed by drawing regions of interest around relevant anatomical structures. Clinical factors and vascular pathology were also evaluated. Measurement differences between DM+ and DM- patients were assessed by t tests. A multiple regression analysis was performed to identify independent predictors of magnetic susceptibility. DM+ patients showed lower susceptibility values, indicative of lower brain iron content, than DM- patients, which was significant in the hippocampus (4.80 ± 8.31 ppb versus 0.22 ± 10.60 ppb, p = 0.024) and pulvinar of the thalamus (36.30 ± 19.88 ppb versus 45.90 ± 20.02 ppb, p = 0.023). On multiple regression analysis, microbleed number was a predictor of susceptibility change in the hippocampus (F = 4.291, beta = 0.236, p = 0.042) and DM was a predictor of susceptibility change in the pulvinar of the thalamus (F = 4.900, beta = - 0.251, p = 0.030). In cognitively impaired patients, presence of DM was associated with lower susceptibility change in the pulvinar of the thalamus and hippocampus. This suggests that there may be region-specific alterations of calcium deposition in cognitively impaired subjects with DM.

Iron metabolism in diabetes-induced Alzheimer's disease: a focus on insulin resistance in the brain

Alzheimer's disease (AD) is characterized by an excessive accumulation of toxic amyloid beta (Aβ) plaques and memory dysfunction. The onset of AD is influenced by age, genetic background, and impaired glucose metabolism in the brain. Several studies have demonstrated that diabetes involving insulin resistance and glucose tolerance could lead to AD, ultimately resulting in cognitive dysfunction. Even though the relationship between diabetes and AD was indicated by significant evidences, the critical mechanisms and metabolic alterations in diabetes induced AD are not clear until now. Recently, iron metabolism has been shown to play multiple roles in the central nervous system (CNS). Iron deficiency and overload are associated with neurodegenerative diseases. Iron binds to Aβ and subsequently regulates Aβ toxicity in the CNS. In addition, previous studies have shown that iron is involved in the aggravation of insulin resistance. Considering these effects of iron metabolism in CNS, we expect that iron metabolism may play crucial roles in diabetic AD brain. Thus, we review the recent evidence regarding the relationship between diabetes-induced AD and iron metabolism.

Prion protein modulates glucose homeostasis by altering intracellular iron

The prion protein (PrP^C), a mainly neuronal protein, is known to modulate glucose homeostasis in mouse models. We explored the underlying mechanism in mouse models and the human pancreatic β-cell line 1.1B4. We report expression of PrP^C on mouse pancreatic β-cells, where it promoted uptake of iron through divalent-metal-transporters. Accordingly, pancreatic iron stores in PrP knockout mice (PrP^-/-) were significantly lower than wild type (PrP^+/+) controls. Silencing of PrP^C in 1.1B4 cells resulted in significant depletion of intracellular (IC) iron, and remarkably, upregulation of glucose transporter GLUT2 and insulin. Iron overloading, on the other hand, resulted in downregulation of GLUT2 and insulin in a PrP^C-dependent manner. Similar observations were noted in the brain, liver, and neuroretina of iron overloaded PrP^+/+ but not PrP^-/- mice, indicating PrP^C-mediated modulation of insulin and glucose homeostasis through iron. Peripheral challenge with glucose and insulin revealed blunting of the response in iron-overloaded PrP^+/+ relative to PrP^-/- mice, suggesting that PrP^C-mediated modulation of IC iron influences both secretion and sensitivity of peripheral organs to insulin. These observations have implications for Alzheimer's disease and diabetic retinopathy, known complications of type-2-diabetes associated with brain and ocular iron-dyshomeostasis.

Correlations between working memory impairment and neurometabolites of prefrontal cortex and lenticular nucleus in patients with major depressive disorder

BACKGROUND

The mechanism of working memory (WM) impairment in MDD remains unclear. We aimed to find out the mechanism by using neuropsychological tests and proton magnetic resonance spectroscopy (1H-MRS).

METHODS

31 MDD patients and 31 healthy controls were recruited in our study. The WM performance and neurometabolite ratios of prefrontal cortex (PFC) and lenticular nucleus (LN) between two groups were evaluated and compared. And the correlations between abnormal neurometabolite ratios and WM dysfunction were computed.

RESULTS

Scores of SDMT, DST(forwards), VRS and 2-back Task(accuracy rate) in MDD were lower than HCs. NAA/Cr ratios of bilateral PFC in MDD were significantly lower than HCs, while no significant differences showed in NAA/Cr ratios of LN and Cho/Cr, mI/Cr values of the bilateral PFC and LN between two groups. And for MDD patients, NAA/Cr ratios in the right PFC were positively correlated with scores of DST (Forwards).

CONCLUSIONS

Our findings suggest that depressed patients may have impairments in working memory, including phonological loop, visual-spatial sketchpad, episodic buffer and central executive. And the impairment of verbal WM and WM capacity may be associated with the abnormal neurometabolites in the right PFC.

Ferric Citrate Supplementation Reduces Red-Blood-Cell Aggregation and Improves CD163+ Macrophage-Mediated Hemoglobin Metabolism in a Rat Model of High-Fat-Diet-Induced Obesity

SCOPE

In adults, >90% of the daily iron requirement is derived from macrophage-mediated heme iron, recycling from senescent red blood cells (RBCs) or free hemoglobin (Hb). Currently, the effects of pharmacological doses of iron supplementation on RBCs and heme iron recycling in obesity are unclear.

METHODS AND RESULTS

Sprague Dawley rats are fed a standard diet or a 50% high-fat diet (HFD) with (0.25, 1, and 2 g of ferric iron per kg diet) or without ferric citrate supplementation for 12 weeks. Ferric iron increases hepatic iron accumulation in macrophages and hepatocyte-like cells. Compared with rats that received the standard diet, HFD-fed rats exhibit higher RBC aggregation and serum-free Hb levels but lower LVV-hemorphin-7 levels. These effects are reversed by ferric citrate supplementation. Immunofluorescent staining reveals that ferric iron increases the expression of hepatic CD163+ macrophages and heme oxygenase (HO)-1. A further analysis reveals the dose-related effects of ferric iron on hepatic globin degradation proteins (cathepsin D and glyoxalase 1), cytochrome p450 reductase expression, and HO-1 enzyme activity.

CONCLUSIONS

Ferric citrate supplementation reduces RBC aggregation and improves CD163+ macrophage-mediated Hb metabolism in HFD-induced obese rats. These findings suggest that ferric citrate may be explored as an alternative treatment method for RBC dysfunction.

Obesity status influences the relationship among serum osteocalcin, iron stores and insulin sensitivity

BACKGROUND & AIMS

Increased iron stores significantly influence the clinical course of several chronic metabolic diseases. Recent studies have shown that iron overload decreases osteocalcin. We aimed to explore the relationship among osteocalcin, iron stores and insulin sensitivity.

METHODS

Extensive clinical and laboratory measurements, including serum ferritin, cross-linked C-telopeptide of type I collagen (CTX) and osteocalcin (OC) concentrations, were analyzed in 250 adult consecutive Caucasian men. Insulin sensitivity was evaluated through frequently sampled intravenous glucose tolerance tests with minimal model analysis.

RESULTS

Circulating serum ferritin were negatively associated with serum OC and CTX (p = 0.004 and p = 0.045 respectively). In all subjects as a whole, BMI and ferritin contributed to explain 5.2% of OC variance after controlling for age and smoking status. However, the association between OC and insulin sensitivity remained significant only in lean subjects (BMI < 25 kg/m², r = 0.468; p = 0.006) whereas the link between serum ferritin concentration and OC and CTX were significant only in overweight/obese subjects (BMI ≥ 25 kg/m², r = -0.229; p = 0.002 and r = -0.196; p = 0.008, respectively).

CONCLUSIONS

The association of circulating osteocalcin with parameters of insulin sensitivity and iron stores were dependent on obesity status. Increased iron stores could contribute to the detrimental metabolic effects of overweight and obesity on bone.

The Gut Metagenome Changes in Parallel to Waist Circumference, Brain Iron Deposition, and Cognitive Function

CONTEXT

Microbiota perturbations seem to exert modulatory effects on emotional behavior, stress-, and pain-modulation systems in adult animals; however, limited information is available in humans.

OBJECTIVE

To study potential relationships among the gut metagenome, brain microstructure, and cognitive performance in middle-aged, apparently healthy, obese and nonobese subjects after weight changes.

DESIGN

This is a longitudinal study over a 2-year period.

SETTING

A tertiary public hospital.

PATIENTS OR OTHER PARTICIPANTS

Thirty-five (18 obese) apparently healthy subjects.

INTERVENTION(S)

Diet counseling was provided to all subjects. Obese subjects were followed every 6 months.

MAIN OUTCOME MEASURE(S)

Brain relaxometry (using magnetic resonance R2*), cognitive performance (by means of cognitive tests), and gut microbiome composition (shotgun).

RESULTS

R2* increased in both obese and nonobese subjects, independent of weight variations. Changes in waist circumference, but not in body mass index, were associated with brain iron deposition (R2*) in the striatum, amygdala, and hippocampus in parallel to visual-spatial constructional ability and circulating beta amyloid Aβ42 levels. These changes were linked to shifts in gut microbiome in which the relative abundance of bacteria belonging to Caldiserica and Thermodesulfobacteria phyla were reciprocally associated with raised R2* in different brain nuclei. Of note, the increase in bacteria belonging to Tenericutes phylum was parallel to decreased R2* gain in the striatum, serum Aβ42 levels, and spared visual-spatial constructional ability. Interestingly, metagenome functions associated with circulating and brain iron stores are involved in bacterial generation of siderophores.

CONCLUSIONS

Changes in the gut metagenome are associated longitudinally with cognitive function and brain iron deposition.

Increased adipose tissue heme levels and exportation are associated with altered systemic glucose metabolism

Iron status is known to be associated with the physiology of adipose tissue (AT). We aimed to investigate AT heme and expression of heme exporter (FLVCR1) in association with obesity and type 2 diabetes (T2D). Substantial amounts of FLVCR1 mRNA and protein levels were detected in AT, being significantly increased in subjects with T2D, and positively correlated with fasting glucose, fasting triglycerides and with circulating markers of iron stores (serum ferritin, blood hemoglobin and hematocrit). In both visceral (VAT) and subcutaneous AT (SAT), increased heme levels were found in subjects with T2D. Reinforcing these associations, FLVCR1 mRNA levels were positively linked to fasting glucose in an independent cohort. Longitudianlly, the percent change of FLVCR1 positively correlated with the percent change in fasting glucose (r = 0.52, p = 0.03) after bariatric surgery-induced weight loss. High-fat diet-induced weight gain in rats did not result in significant changes in AT Flvcr1 mRNA but, remarkably, the expression of this gene positively correlated with fasting glucose and negatively with insulin sensitivity (QUICKI). Altogether, these findings showed a direct association between FLVCR1 mRNA levels and hyperglycemia, suggesting that increased adipose tissue heme exportation might disrupt, or is the consequence of, impaired systemic glucose metabolism during the progression to T2D.

Impact of high iron intake on cognition and neurodegeneration in humans and in animal models: a systematic review

Context

Accumulation of brain iron is linked to aging and protein-misfolding neurodegenerative diseases. High iron intake may influence important brain health outcomes in later life.

Objective

The aim of this systematic review was to examine evidence from animal and human studies of the effects of high iron intake or peripheral iron status on adult cognition, brain aging, and neurodegeneration.

Data Sources

MEDLINE, Scopus, CAB Abstracts, the Cochrane Central Register of Clinical Trials, and OpenGrey databases were searched.

Study Selection

Studies investigating the effect of elevated iron intake at all postnatal life stages in mammalian models and humans on measures of adult brain health were included.

Data Extraction

Data were extracted and evaluated by two authors independently, with discrepancies resolved by discussion. Neurodegenerative disease diagnosis and/or behavioral/cognitive, biochemical, and brain morphologic findings were used to study the effects of iron intake or peripheral iron status on brain health. Risk of bias was assessed for animal and human studies. PRISMA guidelines for reporting systematic reviews were followed.

Results

Thirty-four preclinical and 14 clinical studies were identified from database searches. Thirty-three preclinical studies provided evidence supporting an adverse effect of nutritionally relevant high iron intake in neonates on brain-health-related outcomes in adults. Human studies varied considerably in design, quality, and findings; none investigated the effects of high iron intake in neonates/infants.

Conclusions

Human studies are needed to verify whether dietary iron intake levels used in neonates/infants to prevent iron deficiency have effects on brain aging and neurodegenerative disease outcomes.

Exercise and dietary program-induced weight reduction is associated with cognitive function among obese adolescents: a longitudinal study

Objective

The present study was to determine the effect of a combined exercise and dietary program on cognitive function as well as the relationship between the program-induced weight change and cognitive function alterations.

Design

The study applies a quasi-experimental design.

Methods

Fifty-eight adolescents with obese status (body mass index, BMI >28 kg/m²) were assigned to either an experiment (n = 30) or control group (n = 28). Participants in the experiment group received a scheduled program with a specific exercise protocol (two sessions per day, six days per week) and diet plan for four consecutive weeks; the control group was instructed to maintain their normal school activities. The primary outcome measures were anthropometric data and flanker task performance.

Results

The combined program led to reduced BMI with maintenance of the incongruent accuracy in the experiment group, but the incongruent accuracy decreased in the control group after the four-week period. Additionally, the change in weight status between post- and pre-test measurements was inversely correlated with the change in incongruent accuracy.

Conclusion

The combined exercise and dietary program resulted in decreased weight and enhanced executive function in the obese adolescents, and the weight alteration may be considered the mediator between the intervention and executive function.

Insulin resistance in Alzheimer's disease

The links between systemic insulin resistance (IR), brain-specific IR, and Alzheimer's disease (AD) have been an extremely productive area of current research. This review will cover the fundamentals and pathways leading to IR, its connection to AD via cellular mechanisms, the most prominent methods and models used to examine it, an introduction to the role of extracellular vesicles (EVs) as a source of biomarkers for IR and AD, and an overview of modern clinical studies on the subject. To provide additional context, we also present a novel analysis of the spatial correlation of gene expression in the brain with the aid of Allen Human Brain Atlas data. Ultimately, examining the relation between IR and AD can be seen as a means of advancing the understanding of both disease states, with IR being a promising target for therapeutic strategies in AD treatment. In conclusion, we highlight the therapeutic potential of targeting brain IR in AD and the main strategies to pursue this goal.

Brain-derived neurotrophic factor plasma levels and premature cognitive impairment/dementia in type 2 diabetes

AIM

To assess the relationship of brain-derived neurotrophic factor (BDNF) with cognitive impairment in patients with type 2 diabetes.

METHODS

The study included 40 patients with diabetes mellitus type 2 (DM2), 37 patients with chronic kidney disease in hem dialysis hemodialysis therapy (HD) and 40 healthy subjects. BDNF in serum was quantified by ELISA. The Folstein Mini-Mental State Examination was used to evaluate cognitive impairment.

RESULTS

The patients with DM2 and the patients in HD were categorized into two groups, with cognitive impairment and without cognitive impairment. The levels of BDNF showed significant differences between patients with DM2 (43.78 ± 9.05 vs 31.55 ± 10.24, P = 0.005). There were no differences between patients in HD (11.39 ± 8.87 vs 11.11 ± 10.64 P = 0.77); interestingly, ferritin levels were higher in patients with cognitive impairment (1564 ± 1335 vs 664 ± 484 P = 0.001). The comparison of BDNF values, using a Kruskal Wallis test, between patients with DM2, in HD and healthy controls showed statistical differences (P < 0.001).

CONCLUSION

Low levels of BDNF are associated with cognitive impairment in patients with DM2. The decrease of BDNF occurs early and progressively in patients in HD.

Hepatic iron content is independently associated with serum hepcidin levels in subjects with obesity

BACKGROUND & AIMS

Serum hepcidin concentration is known to increase in parallel to circulating markers of iron stores. We aimed to investigate whether this is reflected at the tissue level in subjects with obesity.

METHODS

Serum hepcidin and ferritin levels (ELISA) and hepatic iron content (using magnetic resonance imaging) were analyzed longitudinally in 44 participants (19 without obesity and 25 with obesity). In a subgroup of 16 participants with obesity, a weight loss intervention was performed.

RESULTS

Serum hepcidin, ferritin and hepatic iron content (HIC) were significantly increased in participants with obesity. Age- and gender-adjusted serum hepcidin was positively correlated with BMI, hsCRP, ferritin and HIC. In addition, age- and gender-adjusted serum hepcidin was positively correlated with ferritin and HIC in both non-obese and obese participants. In multivariate regression analysis, hepatic iron content (p < 0.01) and serum ferritin (p < 0.001) contributed independently to circulating hepcidin concentration variation after controlling for age, gender, BMI and hsCRP. Diet intervention-induced weight loss led to decreased serum hepcidin (p = 0.01), serum ferritin concentration (p = 0.01) and HIC (p = 0.002). Of note, the percent change of serum hepcidin strongly correlated with the percent change of serum ferritin (r = 0.69, p = 0.01) and HIC (r = 0.61, p = 0.03) even after controlling for age and gender.

CONCLUSIONS

Serum hepcidin is a reliable marker of the hepatic iron content in subjects with obesity.

Vascular Damage in Patients with Nonalcoholic Fatty Liver Disease: Possible Role of Iron and Ferritin

Non Alcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in Western countries. Recent data indicated that NAFLD is a risk factor by itself contributing to the development of cardiovascular disease independently of classical known risk factors. Hyperferritinemia and mild increased iron stores are frequently observed in patients with NAFLD and several mechanisms have been proposed to explain the role of iron, through oxidative stress and interaction with insulin metabolism, in the development of vascular damage. Moreover, iron depletion has been shown to decrease atherogenesis in experimental models and in humans. This review presents the recent evidence on epidemiology, pathogenesis, and the possible explanation of the role of iron and ferritin in the development of cardiovascular damage in patients with NAFLD, and discusses the possible interplay between metabolic disorders associated with NAFLD and iron in the development of cardiovascular disease.

Iron Regulation of Pancreatic Beta-Cell Functions and Oxidative Stress

Dietary advice is the cornerstone in first-line treatment of metabolic diseases. Nutritional interventions directed at these clinical conditions mainly aim to (a) improve insulin resistance by reducing energy-dense macronutrient intake to obtain weight loss and (b) reduce fluctuations in insulin secretion through avoidance of rapidly absorbable carbohydrates. However, even in the majority of motivated patients selected for clinical trials, massive efforts using this approach have failed to achieve lasting efficacy. Less attention has been given to the role of micronutrients in metabolic diseases. Here, we review the evidence that highlights (a) the importance of iron in pancreatic beta-cell function and dysfunction in diabetes and (b) the integrative pathophysiological effects of tissue iron levels in the interactions among the beta cell, gut microbiome, hypothalamus, innate and adaptive immune systems, and insulin-sensitive tissues. We propose that clinical trials are warranted to clarify the impact of dietary or pharmacological iron reduction on the development of metabolic disorders.

Lower serum osteocalcin concentrations are associated with brain microstructural changes and worse cognitive performance

OBJECTIVE

Rodent models have found that osteocalcin crosses the blood-brain barrier and regulates behaviour. No data are available on osteocalcin's effects on brain microstructure and cognitive performance in humans. We evaluated the association between serum osteocalcin concentrations and (i) brain microstructural changes on magnetic resonance imaging (MRI) and (ii) neuropsychological performance.

DESIGN, PATIENTS AND MEASUREMENTS

We studied 24 consecutive obese subjects (13 women; age, 49·8 ± 8·1 years; body mass index [BMI], 43·9 ± 4·54 kg/m(2) ) and 20 healthy volunteers (10 women; age, 48·8 ± 9·5 years; BMI, 24·3 ± 3·54 kg/m(2) ) in a cross-sectional study within the multicentre FLORINASH Project. FLAIR signal intensity and DTI-metrics (primary (λ1 ), secondary (λ2 ) and tertiary (λ3 ) eigenvalues; fractional anisotropy (FA); and mean diffusivity) in the caudate, hypothalamus, thalamus and putamen, and in subcortical white matter were assessed. Cognitive performance evaluated by neuropsychological test battery.

RESULTS

Lower osteocalcin concentrations were associated with BMI, higher λ1, λ2 and λ3 values at the caudate and lower FLAIR signal intensity at the caudate and putamen. Obese patients with lower osteocalcin concentrations had higher FA at putamen and thalamus. Lower osteocalcin concentrations were associated with higher Iowa Gambling Task (IGT) scores. FLAIR signal intensity at the caudate <601·832 yielded 85·7% sensitivity, 64·3% specificity, 70·6% negative predictive value and 81·8% positive predictive value for IGT score. Lower osteocalcin was an independent predictor of worse cognitive performance on multivariate analysis (F = 3·551, P = 0·01343; R(2) = 0·103). Bayesian information criterion demonstrated that osteocalcin had the predominant role in predicting IGT score.

CONCLUSIONS

Lower serum osteocalcin concentrations are associated with brain microstructural changes and worse cognitive performance.

Accumulation of iron in the putamen predicts its shrinkage in healthy older adults: A multi-occasion longitudinal study

Accumulation of non-heme iron is believed to play a major role in neurodegeneration of the basal ganglia. In healthy aging, however, the temporal relationship between change in brain iron content and age-related volume loss is unclear. Here, we present the first long-term longitudinal multi-occasion investigation of changes in iron content and volume in the neostriatum in a sample of healthy middle-aged and older adults (N=32; ages 49-83years at baseline). Iron content, estimated via R2* relaxometry, increased in the putamen, but not the caudate nucleus. In the former, the rate of accumulation was coupled with change in volume. Moreover, greater baseline iron content predicted faster shrinkage and smaller volumes seven years later. Older age partially accounted for individual differences in neostriatal iron content and volume, but vascular risk did not. Thus, brain iron content may be a promising biomarker of impending decline in normal aging.

Examining the Influence of Measures of Adiposity on Cognitive Function in Middle Age and Older African Americans

The objectives of the study were to examine whether measures of total obesity (body mass index [BMI]) and central obesity (waist circumference [WC] and waist-to-hip ratio [WHR]) are associated with cognitive function in African Americans, and whether sex moderates these associations. A sample of 194 African Americans, with a mean age of 58.97 years, completed a battery of cognitive tests and a self-reported health questionnaire. Height, weight, waist and hip circumference, and blood pressure were assessed. Linear regression analyses were run. Results suggested lower performance on measures of verbal fluency and complex attention/cognitive flexibility was accounted for by higher levels of central adiposity. Among men, higher WHR was more strongly related to complex attention/cognitive flexibility performance, but for women, WC was a salient predictor. Higher BMI was associated with poorer verbal memory performance among men, but poorer nonverbal memory performance among women. Findings suggest a need for healthy lifestyle interventions for African Americans to maintain healthy weight and cognitive function.

Gut Microbiota Interacts With Brain Microstructure and Function

CONTEXT

Evidence from animals suggests that gut microbiota affects brain structure and function but evidence in humans is scarce.

OBJECTIVE

This study sought to evaluate potential interactions among gut microbiota composition, brain microstructure, and cognitive tests in obese and nonobese subjects.

DESIGN, SETTING, AND PARTICIPANTS

This was a cross-sectional study at a tertiary hospital including 20 consecutive obese and 19 nonobese subjects similar in age and sex.

MAIN OUTCOME MEASURES

Gut microbiota (16S bacterial gene pyrosequencing), brain microstructure (diffusion tensor imaging of brain white and gray matter and R2* sequences in magnetic resonance imaging) and cognitive tests.

RESULTS

Hierarchical clustering revealed a specific gut microbiota-brain map profile for obese individuals who could be discriminated from nonobese subjects (accuracy of 0.81). Strikingly, Shannon index was linked to R2* and fractional anisotropy of the hypothalamus, caudate nucleus, and hippocampus, suggesting sparing of these brain structures with increased bacterial biodiversity. Microbiota profile also clustered with cognitive function. The relative abundance of Actinobacteria phylum was linked not only to magnetic resonance imaging diffusion tensor imaging variables in the thalamus, hypothalamus, and amygdala but also to cognitive test scores related to speed, attention, and cognitive flexibility.

CONCLUSIONS

In sum, obesity status affects microbiota-brain microstructure and function crosstalk.

Mechanisms of divalent metal toxicity in affective disorders

Metals are required for proper brain development and play an important role in a number of neurobiological functions. The divalent metal transporter 1 (DMT1) is a major metal transporter involved in the absorption and metabolism of several essential metals like iron and manganese. However, non-essential divalent metals are also transported through this transporter. Therefore, altered expression of DMT1 can modify the absorption of toxic metals and metal-induced toxicity. An accumulating body of evidence has suggested that increased metal stores in the brain are associated with elevated oxidative stress promoted by the ability of metals to catalyze redox reactions, resulting in abnormal neurobehavioral function and the progression of neurodegenerative diseases. Metal overload has also been implicated in impaired emotional behavior, although the underlying mechanisms are not well understood with limited information. The current review focuses on psychiatric dysfunction associated with imbalanced metabolism of metals that are transported by DMT1. The investigations with respect to the toxic effects of metal overload on behavior and their underlying mechanisms of toxicity could provide several new therapeutic targets to treat metal-associated affective disorders.

Appraising the Role of Iron in Brain Aging and Cognition: Promises and Limitations of MRI Methods

Age-related increase in frailty is accompanied by a fundamental shift in cellular iron homeostasis. By promoting oxidative stress, the intracellular accumulation of non-heme iron outside of binding complexes contributes to chronic inflammation and interferes with normal brain metabolism. In the absence of direct non-invasive biomarkers of brain oxidative stress, iron accumulation estimated in vivo may serve as its proxy indicator. Hence, developing reliable in vivo measurements of brain iron content via magnetic resonance imaging (MRI) is of significant interest in human neuroscience. To date, by estimating brain iron content through various MRI methods, significant age differences and age-related increases in iron content of the basal ganglia have been revealed across multiple samples. Less consistent are the findings that pertain to the relationship between elevated brain iron content and systemic indices of vascular and metabolic dysfunction. Only a handful of cross-sectional investigations have linked high iron content in various brain regions and poor performance on assorted cognitive tests. The even fewer longitudinal studies indicate that iron accumulation may precede shrinkage of the basal ganglia and thus predict poor maintenance of cognitive functions. This rapidly developing field will benefit from introduction of higher-field MRI scanners, improvement in iron-sensitive and -specific acquisition sequences and post-processing analytic and computational methods, as well as accumulation of data from long-term longitudinal investigations. This review describes the potential advantages and promises of MRI-based assessment of brain iron, summarizes recent findings and highlights the limitations of the current methodology.

Striatal iron content predicts its shrinkage and changes in verbal working memory after two years in healthy adults

The accumulation of non-heme iron in the brain has been proposed as a harbinger of neural and cognitive decline in aging and neurodegenerative disease, but support for this proposal has been drawn from cross-sectional studies, which do not provide valid estimates of change. Here, we present longitudinal evidence of subcortical iron accumulation in healthy human adults (age 19-77 at baseline). We used R2* relaxometry to estimate regional iron content twice within a 2 year period, measured volumes of the striatum and the hippocampus by manual segmentation, and assessed cognitive performance by working memory tasks. Two-year change and individual differences in the change of regional volumes, regional iron content, and working memory were examined by latent change score models while taking into account the age at baseline and metabolic risk indicators. Over the examined period, volume reduction occurred in the caudate nucleus and hippocampus, but iron content increased only in the striatum, where it explained shrinkage. Higher iron content in the caudate nucleus at baseline predicted lesser improvement in working memory after repeat testing. Although advanced age and elevated metabolic syndrome risk were associated with greater iron content in the putamen at baseline, neither age nor metabolic risk influenced change in any variable. Thus, longitudinal evidence supports the notion that accumulation of subcortical iron is a risk factor for neural and cognitive decline in normal aging.