Cerebral hypometabolism mediates the effect of stroke volume on cognitive impairment in heart failure patients

AIMS

The present study aimed to phenotype the cerebral structural and glucose metabolic alterations in patients with heart failure (HF) using simultaneous positron emission tomography (PET)/magnetic resonance (MR) and to investigate their relationship to cardiac biomarkers and cognitive performance.

METHODS AND RESULTS

Forty-two HF patients caused by ischaemic heart disease (mean age 67.2 ± 10.4, 32 males) and 32 age- and sex-matched healthy volunteers (mean age 61.3 ± 4.8, 18 males) were included in this study. Participants underwent simultaneous cerebral fluorine-18 (18 F) fluorodeoxyglucose PET/MR followed by cardiac MR scan, and neuropsychological scores were obtained to assess cognitive performance. The grey matter volume (GMV) and standardized uptake value ratio (SUVR) were calculated to examine cerebral structural and metabolic alterations. Cardiac biomarkers included cardiac MR parameters and cardiac serum laboratory tests. Mediation analysis was performed to explore the associations among cerebral alterations, cardiac biomarkers, and cognitive performance. HF patients demonstrated notable cognitive impairment compared with normal controls (P < 0.001). Furthermore, HF patients exhibited regional brain hypometabolism in the bilateral calcarine cortex, caudate nucleus, thalamus, hippocampus, precuneus, posterior cingulate cortex, lingual and olfactory cortex, and GMV reduction in bilateral thalamus and hippocampus (cluster level at P < 0.05, Gaussian random field correction). The SUVR of the hypometabolic brain regions was correlated with the Montreal Cognitive Assessment (MoCA) scores (r = 0.55, P = 0.038) and cardiac stroke volume (r = 0.49, P = 0.002). Cerebral hypometabolism played a key role in the relationship between the decreased stroke volume and MoCA scores, with a mediation effect of 33.2%.

CONCLUSIONS

HF patients suffered cerebral metabolic and structural alterations in regions associated with cognition. The observed correlation between cardiac stroke volume and cognitive impairment underscored the potential influence of cerebral hypometabolism, suggesting that cerebral hypometabolism due to chronic systemic hypoperfusion may significantly contribute to cognitive impairment in HF patients.

Early cerebral amyloid-β accumulation and hypermetabolism are associated with subtle cognitive deficits before accelerated cerebral atrophy

AIMS

Alzheimer's disease (AD) is characterized by the accumulation of amyloid beta (Aβ) in the brain. The deposition of Aβ is believed to initiate a detrimental cascade, including cerebral hypometabolism, accelerated brain atrophy, and cognitive problems-ultimately resulting in AD. However, the timing and causality of the cascade resulting in AD are not yet fully established. Therefore, we examined whether early Aβ accumulation affects cerebral glucose metabolism, atrophy rate, and age-related cognitive decline before the onset of neurodegenerative disease.

METHODS

Participants from the Metropolit 1953 Danish Male Birth Cohort underwent brain positron emission tomography (PET) imaging using the radiotracers [11C]Pittsburgh Compound-B (PiB) (N = 70) and [18F]Fluorodeoxyglucose (FDG) (N = 76) to assess cerebral Aβ accumulation and glucose metabolism, respectively. The atrophy rate was calculated from anatomical magnetic resonance imaging (MRI) scans conducted presently and 10 years ago. Cognitive decline was examined from neurophysiological tests conducted presently and ten or 5 years ago.

RESULTS

Higher Aβ accumulation in AD-critical brain regions correlated with greater visual memory decline (p = 0.023). Aβ accumulation did not correlate with brain atrophy rates. Increased cerebral glucose metabolism in AD-susceptible regions correlated with worse verbal memory performance (p = 0.040).

CONCLUSIONS

Aβ accumulation in known AD-related areas was associated with subtle cognitive deficits. The association was observed before hypometabolism or accelerated brain atrophy, suggesting that Aβ accumulation is involved early in age-related cognitive dysfunction. The association between hypermetabolism and worse memory performance may be due to early compensatory mechanisms adapting for malfunctioning neurons by increasing metabolism.

In vivo imaging of cerebral glucose metabolism informs on subacute to chronic post-stroke tissue status - A pilot study combining PET and deuterium metabolic imaging

Recanalization therapy after acute ischemic stroke enables restoration of cerebral perfusion. However, a significant subset of patients has poor outcome, which may be caused by disruption of cerebral energy metabolism. To assess changes in glucose metabolism subacutely and chronically after recanalization, we applied two complementary imaging techniques, fluorodeoxyglucose (FDG) positron emission tomography (PET) and deuterium (2H) metabolic imaging (DMI), after 60-minute transient middle cerebral artery occlusion (tMCAO) in C57BL/6 mice. Glucose uptake, measured with FDG PET, was reduced at 48 hours after tMCAO and returned to baseline value after 11 days. DMI revealed effective glucose supply as well as elevated lactate production and reduced glutamate/glutamine synthesis in the lesion area at 48 hours post-tMCAO, of which the extent was dependent on stroke severity. A further decrease in oxidative metabolism was evident after 11 days. Immunohistochemistry revealed significant glial activation in and around the lesion, which may play a role in the observed metabolic profiles. Our findings indicate that imaging (altered) active glucose metabolism in and around reperfused stroke lesions can provide substantial information on (secondary) pathophysiological changes in post-ischemic brain tissue.

Regional differences in the reduction in cerebral FDG uptake induced by the ketogenic diet

BACKGROUND

The postulated benefits of the ketogenic diet in the management of multiple medical conditions have seen more patients who are in therapeutic ketosis attending 18F-FDG PET scans. This study aimed to investigate the effect of ketosis on cerebral glucose metabolism in a clinical PET scanning environment using 18F-FDG uptake as a surrogate marker.

METHODS

A retrospective audit was conducted of the brain 18F-FDG uptake in 52 patients who underwent PET scans for possible cardiac sarcoidosis or suspected intracardiac infection, following a ketogenic diet and prolonged fasting. SUVbw for whole brain and separate brain regions was compared with serum glucose and serum ketone body (beta-hydroxybutyrate) levels.

RESULTS

The expected negative association between serum glucose levels and whole brain 18F-FDG uptake was confirmed. A reduction in SUVbw due to increasing serum ketones levels was also observed that was independent of and in addition to the effects of glucose. The magnitude of the reduction in SUVbw related to serum glucose level and serum ketone level was found to be greater in the precuneus than in the cerebellum or whole brain.

CONCLUSION

In a real-world clinical PET setting, cerebral 18F-FDG uptake appears to be affected by glycaemia and ketonaemia. This means when assessing the brain, both serum glucose and ketone levels need to be considered when SUVs are used to distinguish between pathologic and physiologic states. The magnitude of this effect appears to vary between different brain regions. This regional difference should be taken into consideration when selecting the appropriate brain region for SUV normalisation, particularly when undertaking database comparison in the assessment of dementia.

The associations of serum valine with mild cognitive impairment and Alzheimer's disease

BACKGROUND

The introduction of metabolomics makes it possible to study the characteristic changes of peripheral metabolism in Alzheimer's disease (AD). Recent studies have found that the levels of valine are related to mild cognitive impairment (MCI) and AD.

AIMS

This study aimed to further clarify the characteristics of valine levels in MCI and AD.

METHODS

A total of 786 participants from the Alzheimer's Disease Neuroimaging Initiative-1 (ADNI-1) cohort were selected to evaluate the relationships between serum valine and cerebrospinal fluid (CSF) biomarkers, brain structure (magnetic resonance imaging, MRI), cerebral glucose metabolism (¹⁸F-fluorodeoxyglucose-positron emission tomography, FDG-PET), and cognitive declines, through different cognitive subgroups.

RESULTS

Serum valine was decreased in patients with AD compared with cognitive normal (CN) and stable MCI (sMCI), and in progressive MCI (pMCI) compared with CN. Serum valine was negatively correlated with CSF total tau (t-tau) and phosphorylated tau (p-tau) in pMCI. Serum valine significantly predicted conversion from MCI to AD. In addition, serum valine was related to the rate of change of cerebral glucose metabolism during the follow-up period in pMCI.

CONCLUSIONS

Serum valine may be a peripheral biomarker of pMCI and AD, and its level predicts the progression of MCI to AD. Our study may help to reveal the metabolic changes during AD disease trajectory and its relationship to clinical phenotype.

Non-invasive quantification of cerebral glucose metabolism using Gjedde-Patlak plot and image-derived input function from the aorta

INTRODUCTION

We aimed at evaluating a Gjedde-Patlak plot and non-invasive image-derived input functions (IDIF) from the aorta to quantify cerebral glucose metabolic rate (CMRglc) in comparison to the reference standard based on sampling the arterial input function (AIF).

METHOD

Six healthy subjects received 200 MBq [¹⁸F]FDG simultaneously with the initiation of a three-part dynamic PET recording consisting of a 15 min-recording of the aorta, a 40 min-recording of the brain and finally 2 min-recording of the aorta. Simultaneously, the arterial ¹⁸F concentration was measured via arterial cannulation. Regions of interest were drawn in the aorta and the brain and time-activity curves extracted. The IDIF was obtained by fitting a triple exponential function to the aorta time-activity curve after the initial peak including the late aorta frame, thereby interpolating the arterial blood activity concentration during the brain scan. CMRglc was calculated from Gjedde-Patlak plots using AIF and IDIF, respectively and the predictive value was examined. Results from frontal cortex, insula, hippocampus and cerebellum were compared by paired t-test and agreement between the methods was analyzed by Bland-Altman plot statistics.

RESULTS

There was a strong linear relationship and an excellent agreement between the methods (mean±SD of CMRglcIDIF (μmol 100 g^-1 min^-1), mean difference, mean relative difference, 95% limits of agreement): frontal cortex: 30.8 ± 3.3, 0.5, 2.2%, [-1,6:2.5], insula: 25.4 ± 2.2, 0.4, 2.4%, [-1.4:2.2], hippocampus: 16.9 ± 1.2, 0.4, 3.8%, [-1.1:2.0] and cerebellum: 23.4 ± 1.9, 0.5, 3.1%, [-1.4:2.5]).

CONCLUSION

We found excellent agreement between CMRglc obtained with an IDIF from the aorta and the reference standard with AIF. A non-invasive three-part dynamic [¹⁸F]FDG PET recording is feasible as a non-invasive alternative for reliable quantification of cerebral glucose metabolism in all scanner systems. This is useful in patients with presumed global cerebral changes owing to systemic disease or for the monitoring of treatment effects.

The relationship of glucose-stimulated insulin secretion to cerebral glucose metabolism and cognition in healthy middle-aged and older adults

Insulin resistance (IR) has been related to reduced cerebral glucose metabolism in regions identified as hypometabolic in Alzheimer's clinical syndrome. Insulin secretion (IS) has been less studied than IR despite findings that decreased IS is an early indicator of future type 2 diabetes and a potential predictor of Alzheimer's clinical syndrome. We investigated whether higher IR and lower IS would be associated with greater age-related reductions in regional cerebral glucose metabolism and worse cognitive performance. Two-hour oral glucose tolerance testing and 18F-fluorodeoxyglucose positron emission tomography were performed on 1-2 occasions on a sample of healthy middle-aged and older adults from the Wisconsin Alzheimer's Disease Research Center. Neuropsychological tests were completed during Alzheimer's Disease Research Center Clinical Core visits. Pattern of findings suggested that lower (not higher) IS was related to higher regional cerebral glucose metabolism in middle aged but not older adults, and lower (not higher) IS was also related to better immediate recall. In the context of healthy insulin sensitivity, lower IS may be beneficial to brain health.

Association between the Onset of Idiopathic Normal Pressure Hydrocephalus Symptoms and Reduced Default Mode Network Connectivity

OBJECTIVE

The aim was to examine the association between connectivity changes in the default mode network (DMN) and the progression of idiopathic normal pressure hydrocephalus (iNPH).

METHODS

We retrospectively recruited cases of preclinical and clinical iNPH from 2,196 patients who had received whole-body 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) scanning. We included 31 cases with asymptomatic ventriculomegaly with features of iNPH on MRI (AVIM; reported as preclinical iNPH) and 12 with iNPH. We performed a voxel-based analysis of the brain FDG-PET images of the AVIM and iNPH groups as well as for each background-matched normal control (NC) group, using Statistical Parametric Mapping 12. Volume of interest (VOI)-based analysis was also performed. We set the VOI as the region from the precuneus to the posterior cingulate cortices (PCC), and compared the mean regional standardized uptake value ratio (SUVR) between the AVIM and iNPH group FDG-PET/CT images and each corresponding NC group.

RESULTS

The voxel-based analysis showed a greater decreased FDG uptake in the PCC in the iNPH group than in the AVIM group. The VOI-based analysis revealed no significant difference in the mean SUVR of the AVIM group and the corresponding NC group, but that of the iNPH group was significantly lower than that of its corresponding NC group.

CONCLUSIONS

DMN connectivity was reduced in the clinical iNPH group but not in the preclinical group. These data suggest that alterations in the functional connectivity of the DMN are related to the onset of iNPH symptoms.

Longitudinal [18F]FDG-PET/CT analysis of the glucose metabolism in ApoE-deficient mice

Background

Strong line of evidence suggests that the increased risk to develop AD may at least be partly mediated by cholesterol metabolism. A key regulator of cholesterol transport is the Apolipoprotein E4 (ApoE4), which plays a fundamental role in neuronal maintenance and repair. Impaired function of ApoE4 may contribute to altered cerebral metabolism leading to higher susceptibility to neurodegeneration.

Methods

To determine a possible link between ApoE function and alterations in AD in the brain of Apolipoprotein E-deficient mice (ApoE−/−) in a longitudinal manner metabolic and neurochemical parameters were analyzed. Cortical metabolism was measured by 2-deoxy-2-[¹⁸F]fluoroglucose ([¹⁸F]FDG)-PET/CT and proton magnetic resonance spectroscopy (¹H-MRS) served to record neurochemical status.

Results

By using [¹⁸F]FDG-PET/CT, we showed that brain metabolism declined significantly stronger with age in ApoE−/− versus wild type (wt) mice. This difference was particularly evident at the age of 41 weeks in almost each analyzed brain region. In contrast, the ¹H-MRS-measured N-acetylaspartate to creatine ratio, a marker of neuronal viability, did not decline with age and did not differ between ApoE−/− and wt mice.

Conclusion

In summary, this longitudinal in vivo study shows for the first time that ApoE−/− mice depict cerebral hypometabolism without neurochemical alterations.

Antidiabetic drugs for Alzheimer's and Parkinson's diseases: Repurposing insulin, metformin, and thiazolidinediones

Medical and scientific communities have been striving to disentangle the complexity of neurodegenerative diseases, particularly Alzheimer's disease (AD) and Parkinson's disease (PD), in order to develop a cure or effective treatment for these diseases. Along this journey, it has become important to identify the early events occurring in the prodromal phases of these diseases and the disorders that increase the risk of neurodegeneration highlighting common pathological features. This strategy has led to a wealth of evidence identifying diabetes, mainly type 2 diabetes mellitus (T2DM) as a main risk factor for the onset and progression of AD and PD. Impaired glucose metabolism, insulin resistance, and mitochondrial dysfunction are features common to both type 2 diabetes mellitus (T2DM), and AD and PD, and they appear before clinical diagnosis of the two neurodegenerative diseases. These could represent the strategic nodes of therapeutic intervention. Following this line of thought, a conceivable approach is to repurpose antidiabetic drugs as valuable agents that may prevent or reduce the risk of cognitive decline and neurodegeneration. This review summarizes the past and current findings that link AD and PD with T2DM, emphasizing the common pathological mechanisms. The efficacy of antidiabetic drugs, namely intranasal insulin, metformin, and thiazolidinediones, in the prevention and/or treatment of AD and PD is also discussed.

Impaired Sensorimotor Processing During Complex Gait Precedes Behavioral Changes in Middle-aged Adults

Gait impairment during complex walking in older adults is thought to result from a progressive failure to compensate for deteriorating peripheral inputs by central neural processes. It is the primary hypothesis of this article that failure of higher cerebral adaptations may already be present in middle-aged adults who do not present observable gait impairments. We, therefore, compared metabolic brain activity during steering of gait (ie, complex locomotion) and straight walking (ie, simple locomotion) in young and middle-aged individuals. Cerebral distribution of [18F]-fluorodeoxyglucose, a marker of brain synaptic activity, was assessed during over ground straight walking and steering of gait using positron emission tomography in seven young adults (aged 24 ± 3) and seven middle-aged adults (aged 59 ± 3). Brain regions involved in steering of gait (posterior parietal cortex, superior frontal gyrus, and cerebellum) are retained in middle age. However, despite similar walking performance, there are age-related differences in the distribution of [18F]-fluorodeoxyglucose during steering: middle-aged adults have (i) increased activation of precentral and fusiform gyri, (ii) reduced deactivation of multisensory cortices (inferior frontal, postcentral, and fusiform gyri), and (iii) reduced activation of the middle frontal gyrus and cuneus. Our results suggest that preclinical decline in central sensorimotor processing in middle age is observable during complex walking.

Transient gain of function of cannabinoid CB1 receptors in the control of frontocortical glucose consumption in a rat model of Type-1 diabetes

Here we aimed to unify some previous controversial reports on changes in both cannabinoid CB₁ receptor (CB₁R) expression and glucose metabolism in the forebrain of rodent models of diabetes. We determined how glucose metabolism and its modulation by CB₁R ligands evolve in the frontal cortex of young adult male Wistar rats, in the first 8 weeks of streptozotocin-induced type-1 diabetes (T1D). We report that frontocortical CB₁R protein density was biphasically altered in the first month of T1D, which was accompanied with a reduction of resting glucose uptake ex vivo in acute frontocortical slices that was normalized after eight weeks in T1D. This early reduction of glucose uptake in slices was also restored by ex vivo treatment with both the non-selective CB₁R agonists, WIN55212-2 (500 nM) and the CB₁R-selective agonist, ACEA (3 μM) while it was exacerbated by the CB₁R-selective antagonist, O-2050 (500 nM). These results suggest a gain-of-function for the cerebrocortical CB₁Rs in the control of glucose uptake in diabetes. Although insulin and IGF-1 receptor protein densities remained unaffected, phosphorylated GSKα and GSKβ levels showed different profiles 2 and 8 weeks after T1D induction in the frontal cortex. Altogether, the biphasic response in frontocortical CB₁R density within a month after T1D induction resolves previous controversial reports on forebrain CB₁R levels in T1D rodent models. Furthermore, this study also hints that cannabinoids may be useful to alleviate impaired glucoregulation in the diabetic cortex.

Personality factors and cerebral glucose metabolism in community-dwelling older adults

Personality factors have been associated with Alzheimer's disease (AD) and dementia, but they have not been examined against markers of regional brain glucose metabolism (a primary measure of brain functioning) in older adults without clinically diagnosed cognitive impairment. The relationship between personality factors derived from the five-factor model and cerebral glucose metabolism determined using positron emission tomography (PET) with [18F]-2-fluoro-2-deoxy-D-glucose (18F-FDG-PET) was examined in a cohort of 237 non-demented, community-dwelling older adults aged 60-89 years (M ± SD = 73.76 ± 6.73). Higher neuroticism and lower scores on extraversion and conscientiousness were significantly associated with decreased glucose metabolism in brain regions typically affected by AD neuropathological processes, including the hippocampus and entorhinal cortex. Furthermore, while there were significant differences between apolipoprotein E (APOE) ε4 allele carriers and non-carriers on ¹⁸F-FDG-PET results in the neocortex and other brain regions (p < 0.05), there was no significant difference between carriers and non-carriers on personality factors and no significant interactions were found between APOE ε4 carriage and personality factors on brain glucose metabolism. In conclusion, we found significant relationships between personality factors and glucose metabolism in neural regions more susceptible to AD neuropathology in older adults without clinically significant cognitive impairment. These findings support the need for longitudinal research into the potential mechanisms underlying the relationship between personality and dementia risk, including measurement of change in other AD biomarkers (amyloid and tau imaging) and how they correspond to change in personality factors. Future research is also warranted to determine whether timely psychological interventions aimed at personality facets (specific aspects or characteristics of personality factors) can affect imaging or other biomarkers of AD resulting in delay or ideally preventing the onset of the cognitive impairment.

Shared cerebral metabolic pathology in non-transgenic animal models of Alzheimer's and Parkinson's disease

Parkinson's disease (PD) and Alzheimer's disease (AD) are the most common chronic neurodegenerative disorders, characterized by motoric dysfunction or cognitive decline in the early stage, respectively, but often by both symptoms in the advanced stage. Among underlying molecular pathologies that PD and AD patients have in common, more attention is recently paid to the central metabolic dysfunction presented as insulin resistant brain state (IRBS) and altered cerebral glucose metabolism, both also explored in animal models of these diseases. This review aims to compare IRBS and alterations in cerebral glucose metabolism in representative non-transgenic animal PD and AD models. The comparison is based on the selectivity of the neurotoxins which cause experimental PD and AD, towards the cellular membrane and intracellular molecular targets as well as towards the selective neurons/non-neuronal cells, and the particular brain regions. Mitochondrial damage and co-expression of insulin receptors, glucose transporter-2 and dopamine transporter on the membrane of particular neurons as well as astrocytes seem to be the key points which are further discussed in a context of alterations in insulin signalling in the brain and its interaction with dopaminergic transmission, particularly regarding the time frame of the experimental AD/PD pathology appearance and the correlation with cognitive and motor symptoms. Such a perspective provides evidence on IRBS being a common underlying metabolic pathology and a contributor to neurodegenerative processes in representative non-transgenic animal PD and AD models, instead of being a direct cause of a particular neurodegenerative disorder.

Changes in cerebral glucose metabolism caused by morphologic features of prodromal idiopathic normal pressure hydrocephalus

Background

Decreased cerebral glucose metabolism has been reported in idiopathic normal pressure hydrocephalus (iNPH). However, the timing of appearance in the preclinical stage of iNPH remains unknown. Herein, we evaluated the changes in regional cerebral glucose metabolism with respect to the characteristic morphologic features of iNPH.

Methods

We performed a cross-sectional study in > 2000 elderly patients who received a whole body 18F-fluorodeoxyglucose-positron emission tomography/computed tomography scanning and recruited subjects with clinical and preclinical iNPH. We included 12 subjects with iNPH, 32 subjects with asymptomatic ventriculomegaly with features of iNPH on magnetic resonance imaging (AVIM), and 33 subjects with preclinical morphologic features of DESH (PMD). We previously reported that iNPH develops in the order of PMD (asymptomatic subjects with incomplete DESH), AVIM (asymptomatic subjects with DESH), and iNPH (symptomatic subjects with DESH). We measured the median regional standardized uptake value ratio (SUVR) on 18F-fluorodeoxyglucose-positron emission tomography/computed tomography images between the three groups and compared them with background-matched normal controls in the frontal lobes, temporal lobes, medial parietal lobes, striata, and thalami.

Results

In the frontal and temporal lobes, the SUVR distributions of the PMD, AVIM, and PMD groups were significantly lower than for each NC (p < 0.05 for all). In the medial parietal lobes, the SUVR distributions were significantly higher in PMD and AVIM groups (p < 0.05 for all). In the thalami and striata, the SUVR distributions were significantly lower in the iNPH group (p < 0.05 for all).

Conclusions

Changes in brain glucose metabolism in the cortices are observed in preclinical iNPH, while metabolic decline in the basal ganglia is only detected in clinical iNPH.

Cerebral glucose metabolism changes in chronic ischemia patients following subcranial-intracranial bypass

The use of the internal maxillary artery (IMA) in intracranial artery bypass or subcranial-intracranial (SC-IC) bypass has recently been described as an alternative to traditional bypass. This study explores cerebral glucose metabolism characteristics of SC-IC bypass. Ten crescendo transient ischemic attack (TIA) patients with chronic occlusion of the middle cerebral artery (MCA) received bypass surgery of IMA with the radial artery graft (RAG) to the branch of MCA. The graft's flow volume (FV) was measured by operative intraoperative duplex ultrasonography. Positron emission tomography (PET)/computed tomography (CT) was used to calculate the preoperational and postoperational average of the standard uptake value (SUVavg) of the 18-fluoro-2-deoxy-D-glucose (18F-FDG) in the region of interest (ROI). The asymmetric index (AI) is recommended to reflect the SUVavg changes, and subsequently, cerebral glucose metabolism changes are supposedly clarified. Patent IMA-RAG-MCA bypass in ten chronic ischemia patients was confirmed by angiography after surgery. The intraoperative FV measurement value was 65.64 ± 10.52 (58.11-73.17) ml/min. Before the operation, the SUVavg of the ROI in the ischemic hemisphere (4.76 ± 2.35 (3.08-6.04)) clearly decreased compared to the one (5.99 ± 2.63 (4.11-7.87)) in the contralateral mirror region (P = 0.003). The result of AI of preoperation minus AI of postoperation was more than 10% (P = 0.031), which indicated suspicious significant changes in cerebral metabolism. All symptoms of study patients having crescendo ischemia were resolved in 1 month after the operation. In the cerebral hypoperfusion territory, uptake of ¹⁸F-FDG deceased. Improving the flow volume via SC-IC bypass makes available an elevated uptake of ¹⁸F-FDG.

Temporal changes in neuroinflammation and brain glucose metabolism in a rat model of viral vector-induced α-synucleinopathy

Rat models based on viral vector-mediated overexpression of α-synuclein are regarded as highly valuable models that closely mimic cardinal features of human Parkinson's disease (PD) such as L-DOPA-dependent motor impairment, dopaminergic neurodegeneration and α-synuclein inclusions. To date, the downstream effects of dopaminergic cell loss on brain glucose metabolism, including the neuroinflammation component, have not been phenotyped in detail for this model. Cerebral glucose metabolism was monitored throughout different stages of the disease using in vivo 2-[¹⁸F]-fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) positron emission tomography (PET) and was combined with in vitro [¹⁸F]DPA-714 autoradiography to assess concomitant inflammation. Rats were unilaterally injected with recombinant adeno-associated viral vector serotype 2/7 (rAAV2/7) encoding either A53T α-synuclein or eGFP. Brain [¹⁸F]FDG microPET was performed at baseline, 1, 2, 3, 4, 6, and 9 weeks post-surgery, in combination with behavioral tests. As a second experiment, [¹⁸F]DPA-714 autoradiography was executed across the same timeline. Voxel-based analysis of relative [¹⁸F]FDG uptake showed a dynamic pattern of PD-related metabolic changes throughout the disease progression (weeks 2-9). Glucose hypermetabolism covering a large bilateral area reaching from the insular, motor- and somatosensory cortex to the striatum was observed at week 2. At week 4, hypermetabolism presented in a cluster covering the ipsilateral nigra-thalamic region, whereas hypometabolism was noted in the ipsilateral striatum at week 6. Elevated [¹⁸F]FDG uptake was seen in a cluster extending across the contralateral striatum, motor- and somatosensory cortex at week 9. Increased [¹⁸F]FDG in the region of the substantia nigra was associated with increased [¹⁸F]DPA-714 binding, and correlated significantly with motor symptoms. These findings point to disease-associated metabolic and neuroinflammatory changes taking place in the primary area of dopaminergic neurodegeneration but also closely interconnected motor and somatosensory brain regions.

Region-specific association between basal blood insulin and cerebral glucose metabolism in older adults

Background

Although previous studies have suggested that insulin plays a role in brain function, it still remains unclear whether or not insulin has a region-specific association with neuronal and synaptic activity in the living human brain. We investigated the regional pattern of association between basal blood insulin and resting-state cerebral glucose metabolism (CMglu), a proxy for neuronal and synaptic activity, in older adults.

Method

A total of 234 nondiabetic, cognitively normal (CN) older adults underwent comprehensive clinical assessment, resting-state 18F-fluodeoxyglucose (FDG)-positron emission tomography (PET) and blood sampling to determine overnight fasting blood insulin and glucose levels, as well as apolipoprotein E (APOE) genotyping.

Results

An exploratory voxel-wise analysis of FDG-PET without a priori hypothesis demonstrated a positive association between basal blood insulin levels and resting-state CMglu in specific cerebral cortices and hippocampus, rather than in non-specific overall cerebral regions, even after controlling for the effects of APOE e4 carrier status, vascular risk factor score, body mass index, fasting blood glucose, and demographic variables. Particularly, a positive association of basal blood insulin with CMglu in the right posterior hippocampus and adjacent parahippocampal region as well as in the right inferior parietal region remained significant after multiple comparison correction. Conversely, no region showed negative association between basal blood insulin and CMglu.

Conclusions

Our finding suggests that basal fasting blood insulin may have association with neuronal and synaptic activity in specific cerebral regions, particularly in the hippocampal/parahippocampal and inferior parietal regions.

•

We investigated regional pattern of association between basal blood insulin and resting-state cerebral glucose metabolism.

•

Significant clusters with positive associations were found mainly in the hippocampal and inferior parietal regions.

•

Our finding suggests a region-specific association of basal blood insulin with resting-state cerebral glucose metabolism.

•

Further studies to elucidate underlying mechanism and implication of this region-specific association will be necessary.

Synergistic interaction between APOE and family history of Alzheimer's disease on cerebral amyloid deposition and glucose metabolism

Background

Recently, the field of gene-gene or gene-environment interaction research appears to have gained growing interest, although it is seldom investigated in Alzheimer’s disease (AD). Hence, the current study aims to investigate interaction effects of the key genetic and environmental risks—the apolipoprotein ε4 allele (APOE4) and family history of late-onset AD (FH)—on AD-related brain changes in cognitively normal (CN) middle-aged and older adults.

Methods

[¹¹C] Pittsburg compound-B (PiB) positron emission tomography (PET) imaging as well as [¹⁸F] fluoro-2-deoxyglucose (FDG) PET that were simultaneously taken with T1-weighted magnetic resonance imaging (MRI) were obtained from 268 CNs from the Korean Brain Aging Study for Early Diagnosis and Prediction of AD (KBASE). Composite standardized uptake value ratios were obtained from PiB-PET and FDG-PET images in the AD signature regions of interests (ROIs) and analyzed. Voxel-wise analyses were also performed to examine detailed regional changes not captured by the ROI analyses.

Results

A significant synergistic interaction effect was found between the APOE4 and FH on amyloid-beta (Aβ) deposition in the AD signature ROIs as well as other regions. Synergistic interaction effects on cerebral glucose metabolism were observed in the regions not captured by the AD signature ROIs, particularly in the medial temporal regions.

Conclusions

Strong synergistic effects of APOE4 and FH on Aβ deposition and cerebral glucose metabolism in CN adults indicate possible gene-to-gene or gene-to-environment interactions that are crucial for pathogenesis of AD involving Aβ. Other unspecified risk factors—genes and/or environmental—that are captured by the positive FH status might either coexpress or interact with APOE4 to alter AD-related brain changes in CN. Healthy people with both FH and APOE4 need more attention for AD prevention.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0411-x) contains supplementary material, which is available to authorized users.

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

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

Cerebral glucose metabolism in adults with neurofibromatosis type 1

Previous studies with positron emission tomography (PET) and the glucose analog F-18-fluorodeoxyglucose (FDG) in patients with neurofibromatosis type 1 (NF1) suggest reduced cerebral glucose metabolism in NF1 specifically in the thalamus. The latter is distinguished by extensive neural circuitry connections which makes thalamic hypoactivity in NF1 an interesting finding. Yet it is not very well confirmed, since previous studies were limited by small sample size and/or poorly matched control groups. Primary aim of the present study therefore was to compare brain FDG PET between a large sample of NF1 patients and a well-matched control group. Secondary aim was to test for an NF1-associated FDG effect in the amygdala, as increased blood flow in the amygdala has recently been detected in a mouse model of NF1. Fifty adult NF1 patients and 50 gender- and age-matched control subjects were included retrospectively. Voxel-wise comparison of brain FDG uptake was performed using the statistical parametric mapping (SPM8). Additional region-of-interest (ROI) analysis was performed using standard ROI templates. Voxel-based testing revealed a single 11.2 ml cluster of reduced FDG uptake in the thalamus of NF1 patients. There was no further significant cluster throughout the whole brain including the amygdala, neither hypo nor hyper. ROI-analysis confirmed reduction of thalamic FDG uptake in the NF1 group (p<0.0005) with a magnitude of 7.6%. In conclusion, adults with NF1 show reduced brain activity specifically in thalamus. There is no indication of abnormal brain activity in the amygdala in humans with NF1.

The change in cerebral glucose metabolism after electroacupuncture: a possible marker to predict the therapeutic effect of deep brain stimulation for refractory anorexia nervosa

Some reports have demonstrated that deep brain stimulation (DBS) is a promising treatment for patients who suffer from intractable anorexia nervosa. However, the nature of DBS may not be viewed as a standard clinical treatment option for anorexia nervosa because of the unpredictable outcome before DBS. Just like DBS in the brain, electroacupuncture at acupoints is also efficient in treating refractory anorexia nervosa. Some neuroimaging studies using functional magnetic resonance imaging, single-photon emission computed tomography (SPECT), and positron emission tomography (PET) had revealed that both DBS and electroacupuncture at acupoints with electrical stimulation are related to the changes in cerebral glucose metabolism. Therefore, we hypothesize that the changes in cerebral glucose metabolism after electroacupuncture might be useful to predict the therapeutic effect of deep brain stimulation for refractory anorexia nervosa.

Combat-related blast exposure and traumatic brain injury influence brain glucose metabolism during REM sleep in military veterans

Traumatic brain injury (TBI), a signature wound of Operations Enduring and Iraqi Freedom, can result from blunt head trauma or exposure to a blast/explosion. While TBI affects sleep, the neurobiological underpinnings between TBI and sleep are largely unknown. To examine the neurobiological underpinnings of this relationship in military veterans, [(18)F]-fluorodeoxyglucose positron emission tomography (FDG PET) was used to compare mTBI-related changes in relative cerebral metabolic rate of glucose (rCMRglc) during wakefulness, Rapid Eye Movement (REM) sleep, and non-REM (NREM) sleep, after adjusting for the effects of posttraumatic stress (PTS). Fourteen veterans with a history of blast exposure and/or mTBI (B/mTBI) (age 27.5±3.9) and eleven veterans with no history (No B/mTBI) (age 28.1±4.3) completed FDG PET studies during wakefulness, REM sleep, and NREM sleep. Whole-brain analyses were conducted using Statistical Parametric Mapping (SPM8). Between group comparisons revealed that B/mTBI was associated with significantly lower rCMRglc during wakefulness and REM sleep in the amygdala, hippocampus, parahippocampal gyrus, thalamus, insula, uncus, culmen, visual association cortices, and midline medial frontal cortices. These results suggest that alterations in neurobiological networks during wakefulness and REM sleep subsequent to B/mTBI exposure may contribute to chronic sleep disturbances and differ in individuals with acute symptoms.

Default mode network hypometabolism in epileptic encephalopathies with CSWS

Previous studies investigating cerebral metabolic changes associated with continuous spike-waves during sleep (CSWS) compared the metabolism of children with CSWS with that of healthy adults, precluding any assessment in brain areas showing physiologic age-related metabolic changes. Here, we investigated the metabolic and connectivity changes characterizing the acute phase of CSWS activity by comparing awake brain metabolism of children with CSWS with that of pediatric pseudo-controls. Positron emission tomography using [18F]-fluorodeoxyglucose (FDG-PET) was performed in 17 awake children with cryptogenic CSWS (5 girls, age: 5-11 years). Voxel-based analyses identified significant metabolic changes in CSWS patients compared with 18 pediatric pseudo-controls (12 girls, age: 6-11 years, non-CSWS focal cryptogenic epilepsy with normal FDG-PET). CSWS-induced changes in the contribution of brain areas displaying metabolic changes to the level of metabolic activity in other brain areas were investigated using pathophysiological interaction. Hypermetabolism in perisylvian regions bilaterally and hypometabolism in lateral and mesial prefrontal cortex, precuneus, posterior cingulate cortex and parahippocampal gyri characterized the acute phase of CSWS (p<0.05 FWE). No change in thalamic metabolism was disclosed. Altered functional connectivity was found between hyper- and hypometabolic regions in CSWS patients compared with pediatric pseudo-controls. This study demonstrates hypometabolism in key nodes of the default mode network (DMN) in awake patients with CSWS, in relation with a possible phenomenon of sustained remote inhibition from the epileptic foci. This hypometabolism might account for some of the acquired cognitive or behavioral features of CSWS epileptic encephalopathies. This study failed to find any evidence of thalamic metabolic changes, which supports the primary involvement of the cortex in CSWS genesis.

Alzheimer disease and cognitive impairment associated with diabetes mellitus type 2: associations and a hypothesis

INTRODUCTION

Epidemiological studies have demonstrated that patients with diabetes mellitus have an increased risk of developing Alzheimer disease, but the relationship between the 2 entities is not clear.

DEVELOPMENT

Both diseases exhibit similar metabolic abnormalities: disordered glucose metabolism, abnormal insulin receptor signalling and insulin resistance, oxidative stress, and structural abnormalities in proteins and β-amyloid deposits. Different hypotheses have emerged from experimental work in the last two decades. One of the most comprehensive relates the microvascular damage in diabetic polyneuritis with the central nervous system changes occurring in Alzheimer disease. Another hypothesis considers that cognitive impairment in both diabetes and Alzheimer disease is linked to a state of systemic oxidative stress. Recently, attenuation of cognitive impairment and normalisation of values in biochemical markers for oxidative stress were found in patients with Alzheimer disease and concomitant diabetes. Antidiabetic drugs may have a beneficial effect on glycolysis and its end products, and on other metabolic alterations.

CONCLUSIONS

Diabetic patients are at increased risk for developing Alzheimer disease, but paradoxically, their biochemical alterations and cognitive impairment are less pronounced than in groups of dementia patients without diabetes. A deeper understanding of interactions between the pathogenic processes of both entities may lead to new therapeutic strategies that would slow or halt the progression of impairment.

Positive Correlation between Severity of Blepharospasm and Thalamic Glucose Metabolism

A 43-year-old woman with drug-related blepharospasm was followed up for 22 months. She had undergone etizolam treatment for 19 years for indefinite complaints. We examined her cerebral glucose metabolism 5 times (between days 149 and 688 since presentation), using positron emission tomography, and identified regions of interest in the thalamus, caudate nucleus, putamen, and primary somatosensory area on both sides. The severity of the blepharospasm was evaluated by PET scanning using the Wakakura classification. Sixteen women (mean age 42.4 ± 11.7 years) were examined as normal controls. The thalamic glucose metabolism in our patient was significantly increased on days 149, 212, and 688. The severity of the blepharospasm was positively correlated with the thalamic glucose metabolism, suggesting that the severity of blepharospasms reflects thalamic activity.

Influence of emotional factors on cerebral glucose metabolism in patients with functional dyspepsia

AIM: To observe the influence of depression and anxiety on cerebral glucose metabolism in patients with functional dyspepsia (FD).

METHODS: Seven FD patients with mild depression and anxiety (AD group) and eight patients without depression and anxiety (non-AD group) were enrolled in the study. All the patients were examined by positron emission tomography-computed tomography (PET-CT) with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) to detect glucose metabolism in different brain regions. The difference in cerebral glucose metabolism was compared between the two groups using a semiquantitative method.

RESULTS: Compared with patients in the non-AD group, those in the AD group showed decreased cerebral glucose metabolism mainly in the temporal and frontal lobes and the limbic system in the right cerebral hemisphere and the inferior frontal gyrus and precentral gyrus in the left cerebral hemisphere, and increased cerebral glucose metabolism mainly in the temporal and occipital lobes in the right cerebral hemisphere and the parietal and occipital lobes and limbic system in the left cerebral hemisphere.

CONCLUSION: The emotion processing and regulation in FD patients with depression and anxiety involve multiple cerebral regions in bilateral cerebral hemispheres, mainly including the frontal and temporal lobes, the limbic system, and the parietal and occipital lobes.

PET study in a patient with spinocerebellar degeneration before and after long-term administration of thyrotropin releasing hormone

We studied the chronic effect of thyrotropin releasing hormone (TRH) in a patient with spinocerebellar degeneration by measuring cerebral metabolic rate for glucose (CMRG1c) using 2-[18F]fluoro-2-deoxy-D-glucose (18FDG) and positron emission tomography (PET). A 56-year-old female, who had suffered from progressive ataxia for 2 years, was treated by intravenous administration of 2 mg TRH for 3 weeks, and CMRG1c of the brain was measured before and after treatment. CMRG1c was markedly decreased in the cerebellum and there was no significant difference before and after the treatment, i.e. mean CMRG1c values were 4.92 and 4.90 mg/100 g/min, and the ratios of the cerebellum versus the frontal cortex were 0.50 and 0.51, respectively. The degree of disequilibrium of her body examined with stabilography became better by the 19th day and further improved by the 26th day after the start of TRH treatment. Based on the present study we conclude that long-term administration of TRH did not improve CMRG1c in the cerebellum, but evidently improved the sway of gravity center by stabilography. We speculate that the chronic effect of TRH was not necessarily due to an improvement of cerebellar function, because TRH receptors are widely distributed throughout the central nervous system.