Evidence of fatigue, disordered sleep and peripheral inflammation, but not increased brain TSPO expression, in seasonal allergy: A [(11)C]PBR28 PET study

Uncovering a Severe Patient Group With Pollen-Related Extrarespiratory Allergic Symptoms: A Year-Long Diary Survey in Japan

BACKGROUND

The most common symptoms of pollen allergy are rhinitis and conjunctivitis. However, in real-world clinical practice, we sometimes encounter patients with pollen allergy suffering from severe extrarespiratory symptoms including skin, gastrointestinal, or flu-like symptoms in relation to exposure to sensitized pollen.

OBJECTIVE

To elucidate the extrarespiratory symptoms in patients with pollen allergy.

METHODS

We performed a non-drug-focused prospective study of patients with pollen allergy (n = 384). During the 1-year observational period, they were asked to complete a weekly electronic diary consisting of visual analog scale (VAS) scores to assess all symptoms experienced in various organs over the past week. An association between seasonal pollen levels and seasonal increase in VAS scores was evaluated using a mixed-effects model for repeated measures. A k-means cluster analysis was performed to identify a group of patients experiencing stronger extrarespiratory symptoms.

RESULTS

In patients sensitized to grass or birch pollen, higher seasonal levels of these pollen grains were associated with higher VAS scores for headache, gastrointestinal symptoms, skin symptoms, and fatigue. A cluster analysis identified a group of severe pollen-allergic patients with higher extrarespiratory symptoms (n = 42). This group was characterized by a higher frequency of comorbid food allergy/atopic dermatitis, higher rate of IgE sensitization to pollens, and higher impaired activity and work productivity.

CONCLUSIONS

This 1-year survey identified a small but nonnegligible group of patients with pollen-related extrarespiratory symptoms. More attention should be paid to this patient group considering their impaired activity and work productivity.

Does seasonal variation affect the neuroimmune system? A retrospective [11C]PBR28 PET study in healthy individuals

INTRODUCTION

The neuroimmune system performs a wide range of functions in the brain and the central nervous system. The microglial translocator protein (TSPO) has an established role as a cell marker in identification of the neuroimmune system. Previously, human studies have shown TSPO differences in neuropsychiatric disorders. Seasonal variability has also been demonstrated in multiple systems of healthy individuals. Therefore, in this study, we attempt to understand whether seasonal changes affect brain TSPO levels using [11C]PBR28 positron emission tomography (PET) imaging.

METHODS

46 healthy subjects (mean age ± SD = 32.5 ± 10); sex (M/F) = 32/14)) underwent PET imaging with [11C]PBR28 in a retrospectively conducted analysis. All PET scans were performed on the HRRT scanner. Volume of distribution (VT) values were generated for cortical and subcortical regions and the cerebellum. Spring/summer months were defined as March to August while fall/winter months were defined as September to February and were compared through 2-tailed t-tests (SciPy library v.1.10.1 and Pinguoin library on Python v.3.8.8). Average daylight hours and temperature in New Haven, CT were obtained online (www.wunderground.com) and compared to VT with Spearman's correlations.

RESULTS

There were no significant differences observed between the TSPO levels of spring/summer and fall/winter months in the brain (t = 0.52, p = 0.61). Additional analysis on all individual brain regions also indicated non-significance. Likewise, no significant correlations were found between TSPO levels in the whole brain and brain regions against daylight hours (ρ= 0.05, p = 0.74), temperature (ρ = 0.04, p = 0.81), or month (ρ = 0.08, p = 0.60). Controlling TSPO gene polymorphisms and other variables had no significant effect on the outcome.

CONCLUSION

To the best of our knowledge, this is the first human study to investigate seasonal changes in TSPO expression. Our results can be interpreted as the lack of seasonal variability in the neuroimmune system, but important limitations include high interindividual variability, test-retest variability, specificity of the tracer, and a limited sample size. Limitations notwithstanding, our results conclude that TSPO levels in the brain are not impacted by light and temperature changes in different seasons.

Effects of intermittent fasting on quality of life tolerance of chemotherapy in patients with gynecological cancers: study protocol of a randomized-controlled multi-center trial

Fatigue is a very common side effect during intravenous chemotherapy. Unfortunately, only few effective therapeutic options are available, mostly based on daily activity. In our pilot trial we were able to demonstrate that intermittent fasting can reduce fatigue in healthy people, thus we aimed to assess the effects of the fasting dietary on quality of life during chemotherapy in patients with gynecological cancer, especially on the domain of fatigue. The IFAST trial is designed as a prospective, randomized-controlled, multi-center trial. Participation will be offered to women with gynecological cancers (breast cancer, ovarian cancer including peritoneal and fallopian tube cancers, endometrial cancer and cervical cancer) who are planned to receive intravenous chemotherapy for at least three months. Eligible patients will be randomized 1:1, stratified by tumor type and study center. Primary endpoint is the difference in mean change in fatigue, assessed with the Functional Assessment of Chronic Illness Therapy-Fatigue Scale (FACIT- FS©). Exploratory secondary endpoints will include general Quality of Life impairment, tolerance of chemotherapy, immunological changes, peripheral cell damage in blood cells, as well as tumor response to chemotherapy. There is new evidence that prolonged fasting periods of 46-96 hours during chemotherapy can positively influence the quality of life during chemotherapy. However, these fasting regiments are not feasible for many patients. Intermittent fasting could be a feasible (manageable) option for many patients to actively improve their quality of life and tolerance to chemotherapy and possibly even enhance the effectiveness of chemotherapy.

Trial Registration

https://drks.de, identifier DRKS00031429.

Allergy-related outcomes and sleep-related disorders in adults: a cross-sectional study based on NHANES 2005-2006

Background

Epidemiological evidence between the sleep disorders and allergy-related outcomes is limited.

Objectives

The purpose of the present study was to estimate the relationship between sleep disorders and allergy-related outcomes in adults.

Methods

We built logistic regression models to examine the associations between sleep disorders and allergy-related outcomes in adult participants using the 2005–2006 NHANES database. Allergy-related outcomes included sIgE levels, asthma, hay fever, sneezing, wheezing, and eczema. Sleep disorders included sleep latency, sleep length, sleep problems, OSA symptoms, and daytime sleepiness. A t-test was used for between-group comparisons.

Results

Participants with OSA symptoms had 2.72 × higher odds of experiencing hay fever and 1.54 × higher odds of having eczema compared to Non-OSA symptoms participants. Participants with insufficient sleep (≤ 6 h/night) had 1.27 × higher odds of developing allergic sensitisation compared to participants with adequate sleep (7–8 h/night). Sneezing was positively associated with sleep problems (OR: 1.706; 95% CI 1.386, 2.099), OSA symptoms (OR: 1.297; 95% CI 1.049, 1.605), and daytime sleepiness (OR: 1.569; 95% CI 1.205, 2.04).

Conclusion

Our findings suggest a positive association between allergy-related outcomes and sleep disorders. In particular, OSA symptoms, daytime sleepiness, and sleep problems are strongly associated with allergic conditions.

Graphical Abstract

The Inter-Rater and Intra-Rater Reliability of the Actual Aquatic Skills Test (AAST) for Assessing Young Children's Motor Competence in the Water

As children’s actual aquatic skills are important for the prevention of drowning as well as their engagement in lifelong aquatic physical activity, researchers and practitioners should be able to assess this vital concept accurately and reliably. Therefore, this study aimed to investigate the inter-rater and intra-rater reliability of the Actual Aquatic Skills Test (AAST), consisting of 17 different test items for the assessment of young children’s motor competence in the water. Six raters received a training and evaluation session on scoring the AAST, after which five of them assessed four test videos (of various children (n = 38) performing the test items) twice, with one to two weeks in between (i.e., test and re-test). Inter-rater and intra-rater reliability were determined per test video and for the different AAST test items across videos using Gwet’s Agreement Coefficient 2 (Gwet’s AC2). The Gwet’s AC2 for inter-rater reliability at the test varied from 0.414 to 1.000, indicating a moderate to perfect agreement between raters. For intra-rater reliability, it ranged from 0.628 to 1.000, demonstrating a good to perfect agreement between test and re-test scoring. In conclusion, the AAST is a promising tool to reliably assess young children’s actual aquatic skills in an indoor swimming pool.

Have (R)-[11C]PK11195 challengers fulfilled the promise? A scoping review of clinical TSPO PET studies

PURPOSE

The prototypical TSPO radiotracer (R)-[11C]PK11195 has been used in humans for more than thirty years to visualize neuroinflammation in several pathologies. Alternative radiotracers have been developed to improve signal-to-noise ratio and started to be tested clinically in 2008. Here we examined the scientific value of these "(R)-[11C]PK11195 challengers" in clinical research to determine if they could supersede (R)-[11C]PK11195.

METHODS

A systematic MEDLINE (PubMed) search was performed (up to end of year 2020) to extract publications reporting TSPO PET in patients with identified pathologies, excluding studies in healthy subjects and methodological studies.

RESULTS

Of the 288 publications selected, 152 used 13 challengers, and 142 used (R)-[11C]PK11195. Over the last 20 years, the number of (R)-[11C]PK11195 studies remained stable (6 ± 3 per year), but was surpassed by the total number of challenger studies for the last 6 years. In total, 3914 patients underwent a TSPO PET scan, and 47% (1851 patients) received (R)-[11C]PK11195. The 2 main challengers were [11C]PBR28 (24%-938 patients) and [18F]FEPPA (11%-429 patients). Only one-in-ten patients (11%-447) underwent 2 TSPO scans, among whom 40 (1%) were scanned with 2 different TSPO radiotracers.

CONCLUSIONS

Generally, challengers confirmed disease-specific initial (R)-[11C]PK11195 findings. However, while their better signal-to-noise ratio seems particularly useful in diseases with moderate and widespread neuroinflammation, most challengers present an allelic-dependent (Ala147Thr polymorphism) TSPO binding and genetic stratification is hindering their clinical implementation. As new challengers, insensitive to TSPO human polymorphism, are about to enter clinical evaluation, we propose this systematic review to be regularly updated (living review).

Applicability, potential and limitations of TSPO PET imaging as a clinical immunopsychiatry biomarker

PURPOSE

TSPO PET imaging may hold promise as a single-step diagnostic work-up for clinical immunopsychiatry. This review paper on the clinical applicability of TSPO PET for primary psychiatric disorders discusses if and why TSPO PET imaging might become the first clinical immunopsychiatry biomarker and the investment prerequisites and scientific advancements needed to accommodate this transition from bench to bedside.

METHODS

We conducted a systematic search of the literature to identify clinical studies of TSPO PET imaging in patients with primary psychiatric disorders. We included both original case-control studies as well as longitudinal cohort studies of patients with a primary psychiatric diagnosis.

RESULTS

Thirty-one original studies met our inclusion criteria. In the field of immunopsychiatry, TSPO PET has until now mostly been studied in schizophrenia and related psychotic disorders, and to a lesser extent in mood disorders and neurodevelopmental disorders. Quantitative TSPO PET appears most promising as a predictive biomarker for the transdiagnostic identification of subgroups or disease stages that could benefit from immunological treatments, or as a prognostic biomarker forecasting patients' illness course. Current scanning protocols are still too unreliable, impractical and invasive for clinical use in symptomatic psychiatric patients.

CONCLUSION

TSPO PET imaging in its present form does not yet offer a sufficiently attractive cost-benefit ratio to become a clinical immunopsychiatry biomarker. Its translation to psychiatric clinical practice will depend on the prioritising of longitudinal research and the establishment of a uniform protocol rendering clinically meaningful TSPO uptake quantification at the shortest possible scan duration without arterial cannulation.

Sleep, Fatigue, and Depressive Symptoms among Female Nurses with Allergic Rhinitis

Allergic rhinitis (AR) is a common chronic disease that negatively affects physical and mental health. The purpose of this study was to determine the effects of allergic rhinitis on sleep, fatigue, and depressive symptoms among Korean female nurses. This was a cross-sectional study conducted using data from the Korea Nurses' Health Study (KNHS), and a total of 8645 female nurses was selected for the final analysis. The demographic characteristics, Body Mass Index, alcohol consumption, shift work, comorbidities (atopic dermatitis and asthma), self-rated health, sleep disturbance (Jenkins Sleep Questionnaire), fatigue (Chalder Fatigue Scale), and depressive symptoms (Perceived Health Questionnaire-9) were collected. The data were analyzed using chi-square tests, t-tests, and hierarchical multiple regression analyses. Participants with allergic rhinitis had significantly greater sleep disturbance, fatigue, and depressive symptoms than those without allergic rhinitis, and allergic rhinitis was a significant factor influencing sleep disturbance and fatigue among the participants after controlling for confounding variables. Therefore, it is imperative to develop effective interventions to manage allergic rhinitis symptoms and improve sleep and fatigue in affected nurses.

Rationale and Design of a Panel Study Investigating Six Health Effects of Airborne Pollen: The EPOCHAL Study

Background: While airborne pollen is widely recognized as a seasonal cause of sneezing and itchy eyes, its effects on pulmonary function, cardiovascular health, sleep quality, and cognitive performance are less well-established. It is likely that the public health impact of pollen may increase in the future due to a higher population prevalence of pollen sensitization as well as earlier, longer, and more intense pollen seasons, trends attributed to climate change. The effects of pollen on health outcomes have previously been studied through cross-sectional design or at two time points, namely preceding and within the period of pollen exposure. We are not aware of any observational study in adults that has analyzed the dose-response relationship between daily ambient pollen concentration and cardiovascular, pulmonary, cognitive, sleep, or quality of life outcomes. Many studies have relied on self-reported pollen allergy status rather than objectively confirming pollen sensitization. In addition, many studies lacked statistical power due to small sample sizes or were highly restrictive with their inclusion criteria, making the findings less transferable to the “real world.”

Methods: The EPOCHAL study is an observational panel study which aims to relate ambient pollen concentration to six specific health domains: (1) pulmonary function and inflammation; (2) cardiovascular outcomes (blood pressure and heart rate variability); (3) cognitive performance; (4) sleep; (5) health-related quality of life (HRQoL); and (6) allergic rhinitis symptom severity. Our goal is to enroll 400 individuals with diverse allergen sensitization profiles. The six health domains will be assessed while ambient exposure to pollen of different plants naturally varies. Health data will be collected through six home nurse visits (at approximately weekly intervals) as well as 10 days of independent tracking of blood pressure, sleep, cognitive performance, HRQoL, and symptom severity by participants. Through repeated health assessments, we aim to uncover and characterize dose-response relationships between exposure to different species of pollen and numerous acute health effects, considering (non-)linearity, thresholds, plateaus and slopes.

Conclusion: A gain of knowledge in pollen-health outcome relationships is critical to inform future public health policies and will ultimately lead toward better symptom forecasts and improved personalized prevention and treatment.

Objective and Subjective Sleep in Rheumatoid Arthritis and Severe Seasonal Allergy: Preliminary Assessments of the Role of Sickness, Central and Peripheral Inflammation

INTRODUCTION

Disturbed sleep in inflammatory disorders such as allergy and rheumatoid arthritis (RA) is common and may be directly or indirectly related to disease processes, but has not been well characterized in these patient groups, especially not with objective methods.

AIM

The present study aimed to characterize objective and subjective sleep in patients with allergy or RA using sleep diaries, one-channel EEG and actigraphy. It also aimed to investigate if sleep measures were associated with central immune activation, assessed using translocator protein (TSPO) positron emission tomography, as well as cytokine markers of peripheral inflammation and disease-specific symptoms or general symptoms of sickness.

METHODS

In total, 18 patients with seasonal pollen allergy, 18 patients with RA and 26 healthy controls were included in the study. Allergy patients and matched controls were assessed twice, in and out of pollen season, and RA patients and controls were assessed once. Sleep was recorded for approximately 1 week at each occasion.

RESULTS

Patients with allergy had increased levels of slow-wave sleep during pollen season. In contrast, patients with RA had less SWS compared to healthy controls, while no differences were observed in sleep duration or subjective sleep quality. Across groups, neither proinflammatory cytokines, grey matter TSPO levels nor general sickness symptoms were associated with objective or subjective measures of sleep. Rhinitis, but not conjunctivitis, was correlated to worse subjective sleep and more slow wave sleep in allergy. Functional status, but not disease activity, predicted lower subjective sleep in RA.

CONCLUSION

This study tentatively indicates that both patients with allergy and RA display sleep alterations but does not support inflammation as an independent predictor of the sleep disturbance across these patient groups.

Longitudinal Changes in Sleep: Associations with Shifts in Circulating Cytokines and Emotional Distress in a Cancer Survivor Population

BACKGROUND

Sleep disturbances are associated with numerous mood disorders. Similarly, anxiety and depression are associated with modulation of the psychoneuroimmune (PNI) axis. This study hypothesized that changes in both monitored and self-reported measures of sleep would relate to changes in circulating cytokine levels in an emotionally distressed population of cervical cancer survivors.

METHODS

Biospecimens, patient-reported outcome (PRO) measures, and actigraphy were collected from cervical cancer survivors enrolled in a biobehavioral clinical trial. Longitudinal changes over a 4-month period were examined. Sleep time measured by actigraphy and PRO were analyzed for correlative changes with emotional distress and serum cytokines (n = 71).

RESULTS

Longitudinal change in the actigraph measure of sleep time was inversely associated with changes in depression and anxiety (test for linear trend, p = 0.02 and p = 0.05 respectively), as well as acute-phase response/pro-inflammatory cytokines (test for linear trend, p = 0.003, interleukin (IL)-2; 0.022, IL-1β; 0.0002, IL-6; and 0.049, tumor necrosis factor α). Conversely, changes in self-reported sleep problems were related to an increase in depression and anxiety (p = 0.001 and p = 0.01 respectively), the T helper 2 (Th2) cytokine IL-5 (p = 0.027), and the counter-regulatory cytokine IL-10 (0.016).

CONCLUSION

This study showed that an increase in sleep time or decrease in sleep problems corresponded with a reduction in self-reported emotional distress and attenuation of pro-inflammatory, Th2, and counter-regulatory cytokines. Our results support sleep measurement as a meaningful biobehavioral variable in cancer survivorship. This study also indicates that sleep investigators should be aware that choice of methodology might influence concordance with different classes of immune parameters.

Sick for science: experimental endotoxemia as a translational tool to develop and test new therapies for inflammation-associated depression

Depression is one of the global leading causes of disability, but treatments remain limited and classical antidepressants were found to be ineffective in a substantial proportion of patients. Thus, novel effective therapies for the treatment of depression are urgently needed. Given the emerging role of inflammation in the etiology and pathophysiology of affective disorders, we herein illustrate how experimental endotoxemia, a translational model of systemic inflammation, could be used as a tool to develop and test new therapeutic options against depression. Our concept is based on the striking overlap of inflammatory, neural, and affective characteristics in patients with inflammation-associated depression and in endotoxin-challenged healthy subjects. Experimental administration of endotoxin in healthy volunteers is safe, well-tolerated, and without known long-term health risks. It offers a highly standardized translational approach to characterize potential targets of therapies against inflammation-associated depression, as well as to identify characteristics of patients that would benefit from these interventions, and, therefore, could contribute to improve personalization of treatment and to increase the overall rate of responders.

Presence of Allergies and Their Impact on Sleep in Children Who Stutter

Purpose

Population-based research has identified insomnia or trouble sleeping, sleepiness during the day, and fatigue during the day as frequent coexisting conditions in children who stutter (CWS). Considering that allergies are well known to disturb sleep, the purpose of this study was to explore if there is an association between the presence of allergies and sleep issues among CWS, as well as if allergies are frequent in CWS.

Method

Data from the 2012 National Health Interview Survey were used. Children used in this sample were those whose caregivers answered definitively whether or not the child stuttered within the past 12 months. Additionally, caregivers identified the presence of allergies and/or asthma and the presence of insomnia or trouble sleeping in the sample child.

Results

The sample included 200 CWS and 9,951 children who do not stutter (CWNS). The odds of insomnia/trouble sleeping were greater in CWS who present with allergies and/or asthma, with the exception of food allergy, compared to CWS who do not present with with allergies and/or asthma. Additionally, the odds of insomnia/trouble sleeping were greater in CWS without any allergy, asthma, and coexisting disability ( OR = 7.48, p < .001) as compared to CWNS without any allergy, asthma, and coexisting disability. The presence of either any allergy or an asthma attack was higher among CWS (46.4%) compared to CWNS (29.5%), p < .001. Specifically, CWS were found to be at greater odds of presenting with any kind of respiratory allergy ( OR = 1.72, p = .034), food allergy ( OR = 2.32, p = .002), and skin allergy ( OR = 1.84, p = .009) than CWNS.

Conclusions

CWS were found to be at greater odds of allergies and asthma, conditions that also impair sleep. Interestingly, insomnia/trouble sleeping was prevalent among CWS, even when allergies, asthma, and coexisting disabilities were not present. The possible implications of these findings are discussed.

In-vivo imaging of neuroinflammation in veterans with Gulf War illness

Gulf War Illness (GWI) is a chronic disorder affecting approximately 30% of the veterans who served in the 1991 Gulf War. It is characterised by a constellation of symptoms including musculoskeletal pain, cognitive problems and fatigue. The cause of GWI is not definitively known but exposure to neurotoxicants, the prophylactic use of pyridostigmine bromide (PB) pills, and/or stressors during deployment have all been suspected to play some pathogenic role. Recent animal models of GWI have suggested that neuroinflammatory mechanisms may be implicated, including a dysregulated activation of microglia and astrocytes. However, neuroinflammation has not previously been directly observed in veterans with GWI. To measure GWI-related neuroinflammation in GW veterans, we conducted a Positron Emission Tomography (PET) study using [¹¹C]PBR28, which binds to the 18 kDa translocator protein (TSPO), a protein upregulated in activated microglia/macrophages and astrocytes. Veterans with GWI (n = 15) and healthy controls (HC, n = 33, including a subgroup of healthy GW veterans, HC_VET, n = 8), were examined using integrated [¹¹C]PBR28 PET/MRI. Standardized uptake values normalized by occipital cortex signal (SUVR) were compared across groups and against clinical variables and circulating inflammatory cytokines (TNF-α, IL-6 and IL-1β). SUVR were validated against volume of distribution ratio (n = 13). Whether compared to the whole HC group, or only the HC_VET subgroup, veterans with GWI demonstrated widespread cortical elevations in [¹¹C]PBR28 PET signal, in areas including precuneus, prefrontal, primary motor and somatosensory cortices. There were no significant group differences in the plasma levels of the inflammatory cytokines evaluated. There were also no significant correlations between [¹¹C]PBR28 PET signal and clinical variables or circulating inflammatory cytokines. Our study provides the first direct evidence of brain upregulation of the neuroinflammatory marker TSPO in veterans with GWI and supports the exploration of neuroinflammation as a therapeutic target for this disorder.

Academic achievement of adolescents with asthma or atopic disease

Background

Over a fifth of children and adolescents suffer with asthma or atopic disease. It is unclear whether asthma impacts academic performance in children and adolescents, and little is known about the association of eczema, food allergy or hayfever and academic performance.

Objective

To examine whether asthma, eczema, food allergy or hayfever impacts on adolescent academic performance and to assess the role of unmeasured confounding.

Methods

This study used the Childhood and Adolescent Twin Study of Sweden cohort born 1992‐1998. At age 9‐12 years, parents reported on their child's ever or current asthma, eczema, food allergy and hayfever status (n = 10 963). At age 15, linked national patient and medication register information was used to create current and ever asthma definitions including severe and uncontrolled asthma for the same children. Academic outcomes in Grade 9 (age 15‐16 years) included: eligibility for high school (Grades 10‐12), and total mark of the best 16 subject units, retrieved from the Grade 9 academic register. Whole cohort analyses adjusted for known covariates were performed, and co‐twin control analyses to assess unmeasured confounders.

Results

There were no associations found for asthma or food allergy at 9‐12 years and academic outcomes in adolescence. In addition, at age 15, there were no statistically significant associations with current, ever, severe or uncontrolled asthma and academic outcomes. Eczema and hayfever at age 9‐12 years were found to be positively associated with academic outcomes; however, co‐twin control analyses did not support these findings, suggesting the main analyses may be subject to unmeasured confounding.

Conclusion and clinical relevance

Having asthma or an atopic disease during childhood or adolescence does not negatively impact on academic performance. This information can be used by clinicians when talking with children and parents about the implications of living with asthma or atopic disease.

Accuracy and reliability of [11C]PBR28 specific binding estimated without the use of a reference region

[¹¹C]PBR28 is a positron emission tomography radioligand used to examine the expression of the 18 kDa translocator protein (TSPO). TSPO is located in glial cells and can function as a marker for immune activation. Since TSPO is expressed throughout the brain, no true reference region exists. For this reason, an arterial input function is required for accurate quantification of [¹¹C]PBR28 binding and the most common outcome measure is the total distribution volume (V_T). Notably, V_T reflects both specific binding and non-displaceable binding. Therefore, estimates of specific binding, such as binding potential (e.g. BP_ND) and specific distribution volume (V_S) should theoretically be more sensitive to underlying differences in TSPO expression. It is unknown, however, if unbiased and accurate estimates of these outcome measures are obtainable for [¹¹C]PBR28. The Simultaneous Estimation (SIME) method uses time-activity-curves from multiple brain regions with the aim to obtain a brain-wide estimate of the non-displaceable distribution volume (V_ND), which can subsequently be used to improve the estimation of BP_ND and V_S. In this study we evaluated the accuracy of SIME-derived V_ND, and the reliability of resulting estimates of specific binding for [¹¹C]PBR28, using a combination of simulation experiments and in vivo studies in healthy humans. The simulation experiments, based on data from 54 unique [¹¹C]PBR28 examinations, showed that V_ND values estimated using SIME were both precise and accurate. Data from a pharmacological competition challenge (n = 5) showed that SIME provided V_ND values that were on average 19% lower than those obtained using the Lassen plot, but similar to values obtained using the Likelihood-Estimation of Occupancy technique. Test-retest data (n = 11) showed that SIME-derived V_S values exhibited good reliability and precision, while larger variability was observed in SIME-derived BP_ND values. The results support the use of SIME for quantifying specific binding of [¹¹C]PBR28, and suggest that V_S can be used in complement to the conventional outcome measure V_T. Additional studies in patient cohorts are warranted.