Validation of image-derived input function using a long axial field of view PET/CT scanner for two different tracers

BACKGROUND

Accurate image-derived input function (IDIF) from highly sensitive large axial field of view (LAFOV) PET/CT scanners could avoid the need of invasive blood sampling for kinetic modelling. The aim is to validate the use of IDIF for two kinds of tracers, 3 different IDIF locations and 9 different reconstruction settings.

METHODS

Eight [18F]FDG and 10 [18F]DPA-714 scans were acquired respectively during 70 and 60 min on the Vision Quadra PET/CT system. PET images were reconstructed using various reconstruction settings. IDIFs were taken from ascending aorta (AA), descending aorta (DA), and left ventricular cavity (LV). The calibration factor (CF) extracted from the comparison between the IDIFs and the manual blood samples as reference was used for IDIFs accuracy and precision assessment. To illustrate the effect of various calibrated-IDIFs on Patlak linearization for [18F]FDG and Logan linearization for [18F]DPA-714, the same target time-activity curves were applied for each calibrated-IDIF.

RESULTS

For [18F]FDG, the accuracy and precision of the IDIFs were high (mean CF ≥ 0.82, SD ≤ 0.06). Compared to the striatum influx (Ki) extracted using calibrated AA IDIF with the updated European Association of Nuclear Medicine Research Ltd. standard reconstruction (EARL2), Ki mean differences were < 2% using the other calibrated IDIFs. For [18F]DPA714, high accuracy of the IDIFs was observed (mean CF ≥ 0.86) except using absolute scatter correction, DA and LV (respectively mean CF = 0.68, 0.47 and 0.44). However, the precision of the AA IDIFs was low (SD ≥ 0.10). Compared to the distribution volume (VT) in a frontal region obtained using calibrated continuous arterial sampler input function as reference, VT mean differences were small using calibrated AA IDIFs (for example VT mean difference = -5.3% using EARL2), but higher using calibrated DA and LV IDIFs (respectively + 12.5% and + 19.1%).

CONCLUSIONS

For [18F]FDG, IDIF do not need calibration against manual blood samples. For [18F]DPA-714, AA IDIF can replace continuous arterial sampling for simplified kinetic quantification but only with calibration against arterial blood samples. The accuracy and precision of IDIF from LAFOV PET/CT system depend on tracer, reconstruction settings and IDIF VOI locations, warranting careful optimization.

Performance of a [18F]Flortaucipir PET Visual Read Method Across the Alzheimer Disease Continuum and in Dementia With Lewy Bodies

BACKGROUND AND OBJECTIVES

Recently, the US Food and Drug Administration approved the tau-binding radiotracer [18F]flortaucipir and an accompanying visual read method to support the diagnostic process in cognitively impaired patients assessed for Alzheimer disease (AD). Studies evaluating this visual read method are limited. In this study, we evaluated the performance of the visual read method in participants along the AD continuum and dementia with Lewy bodies (DLB) by determining its reliability, accordance with semiquantitative analyses, and associations with clinically relevant variables.

METHODS

We included participants who underwent tau-PET at Amsterdam University Medical Center. A subset underwent follow-up tau-PET. Two trained nuclear medicine physicians visually assessed all scans. Inter-reader agreement was calculated using Cohen κ. To examine the concordance of visual read tau positivity with semiquantification, we defined standardized uptake value ratio (SUVr) positivity using different threshold approaches. To evaluate the prognostic value of tau-PET visual read, we performed linear mixed models with longitudinal Mini-Mental State Examination (MMSE).

RESULTS

We included 263 participants (mean age 68.5 years, 45.6% female), including 147 cognitively unimpaired (CU) participants, 97 amyloid-positive participants with mild cognitive impairment or AD dementia (AD), and 19 participants with DLB. The visual read inter-reader agreement was excellent (κ = 0.95, CI 0.91-0.99). None of the amyloid-negative CU participants (0/92 [0%]) and 1 amyloid-negative participant with DLB (1/12 [8.3%]) were tau-positive. Among amyloid-positive participants, 13 CU participants (13/52 [25.0%]), 85 with AD (85/97 [87.6%]), and 3 with DLB (3/7 [42.9%]) were tau-positive. Two-year follow-up visual read status was identical to baseline. Tau-PET visual read corresponded strongly to SUVr status, with up to 90.4% concordance. Visual read tau positivity was associated with a decline on the MMSE in CU participants (β = -0.52, CI -0.74 to -0.30, p < 0.001) and participants with AD (β = -0.30, CI -0.58 to -0.02, p = 0.04).

DISCUSSION

The excellent inter-reader agreement, strong correspondence with SUVr, and longitudinal stability indicate that the visual read method is reliable and robust, supporting clinical application. Furthermore, visual read tau positivity was associated with prospective cognitive decline, highlighting its additional prognostic potential. Future studies in unselected cohorts are needed for a better generalizability to the clinical population.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that [18F]flortaucipir visual read accurately distinguishes patients with low tau-tracer binding from those with high tau-tracer binding and is associated with amyloid positivity and cognitive decline.

Head-to-head comparison of relative cerebral blood flow derived from dynamic [18F]florbetapir and [18F]flortaucipir PET in subjects with subjective cognitive decline

BACKGROUND

Dynamic PET imaging studies provide accurate estimates of specific binding, but also measure the relative tracer delivery (R1), which is a proxy for relative cerebral blood flow (rCBF). Recently, studies suggested that R1 obtained from different tracers could be used interchangeably and is irrespective of target tissue. However, the similarities or differences of R1 obtained from different PET tracers still require validation. Therefore, the goal of the current study was to compare R1 estimates, derived from dynamic [18F]florbetapir (amyloid) and [18F]flortaucipir (tau) PET, in the same subjects with subjective cognitive decline (SCD).

RESULTS

Voxel-wise analysis presented a small cluster (1.6% of the whole brain) with higher R1 values for [18F]flortaucipir compared to [18F]florbetapir in the Aβ-negative group. These voxels were part of the hippocampus and the left middle occipital gyrus. In part of the thalamus, midbrain and cerebellum, voxels (2.5% of the whole brain) with higher R1 values for [18F]florbetapir were observed. In the Aβ-positive group, a cluster (0.2% of the whole brain) of higher R1 values was observed in part of the hippocampus, right parahippocampal gyrus and in the left sagittal stratum for [18F]flortaucipir compared to [18F]florbetapir. Furthermore, in part of the thalamus, left amygdala, midbrain and right parahippocampal gyrus voxels (0.4% of the whole brain) with higher R1 values for [18F]florbetapir were observed. Despite these differences, [18F]florbetapir R1 had high correspondence with [18F]flortaucipir R1 across all regions of interest (ROIs) and subjects (Aβ-:r2 = 0.79, slope = 0.85, ICC = 0.76; Aβ+: r2 = 0.87, slope = 0.93, ICC = 0.77).

CONCLUSION

[18F]flortaucipir and [18F]florbetapir showed similar R1 estimates in cortical regions. This finding, put together with previous studies, indicates that R1 could be considered a surrogate for relative cerebral blood flow (rCBF) in the cortex and may be used interchangeably, but with caution, regardless of the choice of these two tracers.

Tau protein spreads through functionally connected neurons in Alzheimer's disease: a combined MEG/PET study

Recent studies on Alzheimer's disease (AD) suggest that tau proteins spread through the brain following neuronal connections. Several mechanisms could be involved in this process: spreading between brain regions that interact strongly (functional connectivity); through the pattern of anatomical connections (structural connectivity); or simple diffusion. Using magnetoencephalography (MEG), we investigated which spreading pathways influence tau protein spreading by modelling the tau propagation process using an epidemic spreading model. We compared the modelled tau depositions with 18F-flortaucipir PET binding potentials at several stages of the AD continuum. In this cross-sectional study, we analysed source-reconstructed MEG data and dynamic 100-min 18F-flortaucipir PET from 57 subjects positive for amyloid-β pathology [preclinical AD (n = 16), mild cognitive impairment (MCI) due to AD (n = 16) and AD dementia (n = 25)]. Cognitively healthy subjects without amyloid-β pathology were included as controls (n = 25). Tau propagation was modelled as an epidemic process (susceptible-infected model) on MEG-based functional networks [in alpha (8-13 Hz) and beta (13-30 Hz) bands], a structural or diffusion network, starting from the middle and inferior temporal lobe. The group-level network of the control group was used as input for the model to predict tau deposition in three stages of the AD continuum. To assess performance, model output was compared to the group-specific tau deposition patterns as measured with 18F-flortaucipir PET. We repeated the analysis by using networks of the preceding disease stage and/or using regions with most observed tau deposition during the preceding stage as seeds. In the preclinical AD stage, the functional networks predicted most of the modelled tau-PET binding potential, with best correlations between model and tau-PET [corrected amplitude envelope correlation (AEC-c) alpha C = 0.584; AEC-c beta C = 0.569], followed by the structural network (C = 0.451) and simple diffusion (C = 0.451). Prediction accuracy declined for the MCI and AD dementia stages, although the correlation between modelled tau and tau-PET binding remained highest for the functional networks (C = 0.384; C = 0.376). Replacing the control-network with the network from the preceding disease stage and/or alternative seeds improved prediction accuracy in MCI but not in the dementia stage. These results suggest that in addition to structural connections, functional connections play an important role in tau spread, and highlight that neuronal dynamics play a key role in promoting this pathological process. Aberrant neuronal communication patterns should be taken into account when identifying targets for future therapy. Our results also suggest that this process is more important in earlier disease stages (preclinical AD/MCI); possibly, in later stages, other processes may be influential.

Tau pathology as determinant of changes in atrophy and cerebral blood flow: a multi-modal longitudinal imaging study

PURPOSE

Tau pathology is associated with concurrent atrophy and decreased cerebral blood flow (CBF) in Alzheimer's disease (AD), but less is known about their temporal relationships. Our aim was therefore to investigate the association of concurrent and longitudinal tau PET with longitudinal changes in atrophy and relative CBF.

METHODS

We included 61 individuals from the Amsterdam Dementia Cohort (mean age 65.1 ± 7.5 years, 44% female, 57% amyloid-β positive [Aβ +], 26 cognitively impaired [CI]) who underwent dynamic [18F]flortaucipir PET and structural MRI at baseline and 25 ± 5 months follow-up. In addition, we included 86 individuals (68 CI) who only underwent baseline dynamic [18F]flortaucipir PET and MRI scans to increase power in our statistical models. We obtained [18F]flortaucipir PET binding potential (BPND) and R1 values reflecting tau load and relative CBF, respectively, and computed cortical thickness from the structural MRI scans using FreeSurfer. We assessed the regional associations between i) baseline and ii) annual change in tau PET BPND in Braak I, III/IV, and V/VI regions and cortical thickness or R1 in cortical gray matter regions (spanning the whole brain) over time using linear mixed models with random intercepts adjusted for age, sex, time between baseline and follow-up assessments, and baseline BPND in case of analyses with annual change as determinant. All analyses were performed in Aβ-  cognitively normal (CN) individuals and Aβ+  (CN and CI) individuals separately.

RESULTS

In Aβ+ individuals, greater baseline Braak III/IV and V/VI tau PET binding was associated with faster cortical thinning in primarily frontotemporal regions. Annual changes in tau PET were not associated with cortical thinning over time in either Aβ+ or Aβ-  individuals. Baseline tau PET was not associated with longitudinal changes in relative CBF, but increases in Braak III/IV tau PET over time were associated with increases in parietal relative CBF over time in Aβ + individuals.

CONCLUSION

We showed that higher tau load was related to accelerated cortical thinning, but not to decreases in relative CBF. Moreover, tau PET load at baseline was a stronger predictor of cortical thinning than change of tau PET signal.

Neurobiological basis and risk factors of persistent fatigue and concentration problems after COVID-19: study protocol for a prospective case-control study (VeCosCO)

INTRODUCTION

The risk factors for persistent fatigue and cognitive complaints after infection with SARS-CoV-2 and the underlying pathophysiology are largely unknown. Both clinical factors and cognitive-behavioural factors have been suggested to play a role in the perpetuation of complaints. A neurobiological aetiology, such as neuroinflammation, could be the underlying pathophysiological mechanism for persisting complaints.To unravel factors associated with persisting complaints, VeCosCO will compare individuals with and without persistent fatigue and cognitive complaints >3 months after infection with SARS-CoV-2. The study consists of two work packages. The first work package aims to (1) investigate the relation between persisting complaints and neuropsychological functioning; (2) determine risk factors and at-risk phenotypes for the development of persistent fatigue and cognitive complaints, including the presence of postexertional malaise and (3) describe consequences of persistent complaints on quality of life, healthcare consumption and physical functioning. The second work package aims to (1) determine the presence of neuroinflammation with [¹⁸F]DPA-714 whole-body positron emission tomography (PET) scans in patients with persisting complaints and (2) explore the relationship between (neuro)inflammation and brain structure and functioning measured with MRI.

METHODS AND ANALYSIS

This is a prospective case-control study in participants with and without persistent fatigue and cognitive complaints, >3 months after laboratory-confirmed SARS-CoV-2 infection. Participants will be mainly included from existing COVID-19 cohorts in the Netherlands covering the full spectrum of COVID-19 acute disease severity. Primary outcomes are neuropsychological functioning, postexertional malaise, neuroinflammation measured using [¹⁸F]DPA-714 PET, and brain functioning and structure using (f)MRI.

ETHICS AND DISSEMINATION

Work package 1 (NL79575.018.21) and 2 (NL77033.029.21) were approved by the medical ethical review board of the Amsterdam University Medical Centers (The Netherlands). Informed consent is required prior to participation in the study. Results of this study will be submitted for publication in peer-reviewed journals and shared with the key population.

A Head-to-Head Comparison Between Plasma pTau181 and Tau PET Along the Alzheimer's Disease Continuum

Both plasma tau phosphorylated at threonine-181 (pTau181) and tau PET show potential for detecting Alzheimer's disease (AD) pathology and predicting clinical progression. In this study, we performed a head-to-head comparison between plasma pTau181 and tau PET along the AD continuum. Methods: We included participants from the Amsterdam Dementia Cohort who underwent ¹⁸F-flortaucipir (tau) PET and had a plasma sample biobanked within 12 mo from tau PET. Fifty subjective cognitive decline (SCD) participants (31 Aβ-negative and 19 Aβ-positive) and 60 Aβ-positive participants with mild cognitive impairment (MCI) or dementia due to AD were included. A subset had 2-y longitudinal plasma pTau181 and tau PET available (n = 40). Longitudinal neuropsychological test data covering 3.2 ± 2.7 y from both before and after tau PET were available. Plasma pTau181 and tau PET were compared in their accuracies in discriminating between cognitive stage (MCI/AD vs. SCD) and preclinical Aβ status (SCD Aβ-positive vs. SCD Aβ-negative), their associations with cross-sectional and longitudinal neuropsychological test performance, and their longitudinal changes over time. Results: When discriminating between preclinical Aβ status, the area under the curve (AUC) for plasma pTau181 (0.83) and tau PET (entorhinal, 0.87; temporal, 0.85; neocortical, 0.67) were equally high (all DeLong P > 0.05), but tau PET outperformed plasma pTau181 in discriminating MCI/AD from SCD (AUC for plasma pTau181: 0.74; AUCs for tau PET: entorhinal, 0.89; temporal, 0.92; neocortical, 0.89) (all P < 0.01). Overall, tau PET showed stronger associations with cognitive decline and was associated with a wider variety of cognitive tests than plasma pTau181 (plasma pTau181, -0.02 > β < -0.12; tau PET, -0.01 > β < -0.22). Both plasma pTau181 and tau PET increased more steeply over time in MCI/AD than in SCD (P < 0.05), but only tau PET annual changes were associated with cognitive decline. Conclusion: Our results suggest that plasma pTau181 and tau PET perform equally well in identifying Aβ pathology but that tau PET better monitors disease stage and clinical progression.

Precision estimates of relative and absolute cerebral blood flow in Alzheimer's disease and cognitively normal individuals

Alzheimer's disease is characterized by regional reductions in cerebral blood flow (CBF). Although the gold standard for measuring CBF is [¹⁵O]H₂O PET, proxies of relative CBF, derived from the early distribution phase of amyloid and tau tracers, have gained attention. The present study assessed precision of [¹⁵O]H₂O derived relative and absolute CBF, and compared precision of these measures with that of (relative) CBF proxies. Dynamic [¹⁵O]H₂O, [¹⁸F]florbetapir and [¹⁸F]flortaucipir PET test-retest (TrT) datasets with eleven, nine and fourteen subjects, respectively, were included. Analyses were performed using an arterial input model and/or a simplified reference tissue model, depending on the data available. Relative CBF values (i.e. K₁/K₁' and/or R₁) were obtained using cerebellar cortex as reference tissue and TrT repeatability (i.e. precision) was calculated and compared between tracers, parameters and clinical groups. Relative CBF had significantly better TrT repeatability than absolute CBF derived from [¹⁵O]H₂O (r = -0.53), while best TrT repeatability was observed for [¹⁸F]florbetapir and [¹⁸F]flortaucipir R₁ (r = -0.23, r = -0.33). Furthermore, only R₁ showed, better TrT repeatability for cognitively normal individuals. High precision of CBF proxies could be due to a compensatory effect of the extraction fraction, although changes in extraction fraction could also bias these proxies, but not the gold standard.

Longitudinal Tau PET Using 18F-Flortaucipir: The Effect of Relative Cerebral Blood Flow on Quantitative and Semiquantitative Parameters

Semiquantitative PET measures such as SUV ratio (SUVr) have several advantages over quantitative measures, such as practical applicability and relative computational simplicity. However, SUVr may potentially be affected by changes in blood flow, whereas quantitative measures such as nondisplaceable binding potential (BP_ND) are not. For ¹⁸F-flortaucipir PET, the sensitivity of SUVr for changes in blood flow is currently unknown. Therefore, we compared semiquantitative (SUVr) and quantitative (BP_ND) parameters of longitudinal ¹⁸F-flortaucipir PET scans and assessed their vulnerability to changes in blood flow. Methods: Subjects with subjective cognitive decline (n = 38) and Alzheimer disease patients (n = 24) underwent baseline and 2-y follow-up dynamic ¹⁸F-flortaucipir PET scans. BP_ND and relative tracer delivery were estimated using receptor parametric mapping, and SUVr at 80-100 min was calculated. Regional SUVrs were compared with corresponding distribution volume ratio (BP_ND + 1) using paired t tests. Additionally, simulations were performed to model effects of larger flow changes in different binding categories. Results: Results in subjective cognitive decline and Alzheimer disease showed only minor differences between SUVr and BP_ND changes over time. Relative tracer delivery changes were small in all groups. Simulations illustrated a variable bias for SUVr depending on the amount of binding. Conclusion: SUVr provided an accurate estimate of changes in specific binding for ¹⁸F-flortaucipir over a 2-y follow-up during which changes in flow were small. Notwithstanding, simulations showed that large(r) flow changes may affect ¹⁸F-flortaucipir SUVr. Given that it is currently unknown to what order of magnitude pharmacotherapeutic interventions may induce changes in cerebral blood flow, caution may be warranted when changes in flow are potentially large(r), as in clinical trials.

Cerebral blood flow, amyloid burden, and cognition in cognitively normal individuals

PURPOSE

The role of cerebral blood flow (CBF) in the early stages of Alzheimer's disease is complex and largely unknown. We investigated cross-sectional and longitudinal associations between CBF, amyloid burden, and cognition, in cognitively normal individuals with subjective cognitive decline (SCD).

METHODS

We included 187 cognitively normal individuals with SCD from the SCIENCe project (65 ± 8 years, 39% F, MMSE 29 ± 1). Each underwent a dynamic (0-70 min) [18F]florbetapir PET and T1-weighted MRI scan, enabling calculation of mean binding potential (BPND; specific amyloid binding) and R1 (measure of relative (r)CBF). Eighty-three individuals underwent a second [18F]florbetapir PET (2.6 ± 0.7 years). Participants annually underwent neuropsychological assessment (follow-up time 3.8 ± 3.1 years; number of observations n = 774).

RESULTS

A low baseline R1 was associated with steeper decline on tests addressing memory, attention, and global cognition (range betas 0.01 to 0.27, p < 0.05). High BPND was associated with steeper decline on tests covering all domains (range betas - 0.004 to - 0.70, p < 0.05). When both predictors were simultaneously added to the model, associations remained essentially unchanged. Additionally, we found longitudinal associations between R1 and BPND. High baseline BPND predicted decline over time in R1 (all regions, range betasBP×time - 0.09 to - 0.14, p < 0.05). Vice versa, low baseline R1 predicted increase in BPND in frontal, temporal, and composite ROIs over time (range betasR1×time - 0.03 to - 0.08, p < 0.05).

CONCLUSION

Our results suggest that amyloid accumulation and decrease in rCBF are two parallel disease processes without a fixed order, both providing unique predictive information for cognitive decline and each process enhancing the other longitudinally.

Longitudinal change in ATN biomarkers in cognitively normal individuals

BACKGROUND

Biomarkers for amyloid, tau, and neurodegeneration (ATN) have predictive value for clinical progression, but it is not clear how individuals move through these stages. We examined changes in ATN profiles over time, and investigated determinants of change in A status, in a sample of cognitively normal individuals presenting with subjective cognitive decline (SCD).

METHODS

We included 92 individuals with SCD from the SCIENCe project with [¹⁸F]florbetapir PET (A) available at two time points (65 ± 8y, 42% female, MMSE 29 ± 1, follow-up 2.5 ± 0.7y). We additionally used [¹⁸F]flortaucipir PET for T and medial temporal atrophy score on MRI for N. Thirty-nine individuals had complete biomarker data at baseline and follow-up, enabling the construction of ATN profiles at two time points. All underwent extensive neuropsychological assessments (follow-up time 4.9 ± 2.8y, median number of visits n = 4). We investigated changes in biomarker status and ATN profiles over time. We assessed which factors predisposed for a change from A- to A+ using logistic regression. We additionally used linear mixed models to assess change from A- to A+, compared to the group that remained A- at follow-up, as predictor for cognitive decline.

RESULTS

At baseline, 62% had normal AD biomarkers (A-T-N- n = 24), 5% had non-AD pathologic change (A-T-N+ n = 2,) and 33% fell within the Alzheimer's continuum (A+T-N- n = 9, A+T+N- n = 3, A+T+N+ n = 1). Seventeen subjects (44%) changed to another ATN profile over time. Only 6/17 followed the Alzheimer's disease sequence of A → T → N, while 11/17 followed a different order (e.g., reverted back to negative biomarker status). APOE ε4 carriership inferred an increased risk of changing from A- to A+ (OR 5.2 (95% CI 1.2-22.8)). Individuals who changed from A- to A+, showed subtly steeper decline on Stroop I (β - 0.03 (SE 0.01)) and Stroop III (- 0.03 (0.01)), compared to individuals who remained A-.

CONCLUSION

We observed considerable variability in the order of ATN biomarkers becoming abnormal. Individuals who became A+ at follow-up showed subtle decline on tests for attention and executive functioning, confirming clinical relevance of amyloid positivity.

[18F]Flortaucipir PET Across Various MAPT Mutations in Presymptomatic and Symptomatic Carriers

OBJECTIVE

To assess the [18F]flortaucipir binding distribution across MAPT mutations in presymptomatic and symptomatic carriers.

METHODS

We compared regional [18F]flortaucipir binding potential (BPND) derived from a 130-minute dynamic [18F]flortaucipir PET scan in 9 (pre)symptomatic MAPT mutation carriers (4 with P301L [1 symptomatic], 2 with R406W [1 symptomatic], 1 presymptomatic L315R, 1 presymptomatic S320F, and 1 symptomatic G272V carrier) with 30 cognitively normal controls and 52 patients with Alzheimer disease.

RESULTS

[18F]Flortaucipir BPND images showed overall highest binding in the symptomatic carriers. This was most pronounced in the symptomatic R406W carrier in whom tau binding exceeded the normal control range in the anterior cingulate cortex, insula, amygdala, temporal, parietal, and frontal lobe. Elevated medial temporal lobe BPND was observed in a presymptomatic R406W carrier. The single symptomatic carrier and 1 of the 3 presymptomatic P301L carriers showed elevated [18F]flortaucipir BPND in the insula, parietal, and frontal lobe compared to controls. The symptomatic G272V carrier exhibited a widespread elevated cortical BPND, with at neuropathologic examination a combination of 3R pathology and encephalitis. The L315R presymptomatic mutation carrier showed higher frontal BPND compared to controls. The BPND values of the S320F presymptomatic mutation carrier fell within the range of controls.

CONCLUSION

Presymptomatic MAPT mutation carriers already showed subtle elevated tau binding, whereas symptomatic MAPT mutation carriers showed a more marked increase in [18F]flortaucipir BPND. Tau deposition was most pronounced in R406W MAPT (pre)symptomatic mutation carriers, which is associated with both 3R and 4R tau accumulation. Thus, [18F]flortaucipir may serve as an early biomarker for MAPT mutation carriers in mutations that cause 3R/4R tauopathies.

Effect of Shortening the Scan Duration on Quantitative Accuracy of [18F]Flortaucipir Studies

PURPOSE

Dynamic positron emission tomography (PET) protocols allow for accurate quantification of [18F]flortaucipir-specific binding. However, dynamic acquisitions can be challenging given the long required scan duration of 130 min. The current study assessed the effect of shorter scan protocols for [18F]flortaucipir on its quantitative accuracy.

PROCEDURES

Two study cohorts with Alzheimer's disease (AD) patients and healthy controls (HC) were included. All subjects underwent a 130-min dynamic [18F]flortaucipir PET scan consisting of two parts (0-60/80-130 min) post-injection. Arterial sampling was acquired during scanning of the first cohort only. For the second cohort, a second PET scan was acquired within 1-4 weeks of the first PET scan to assess test-retest repeatability (TRT). Three alternative time intervals were explored for the second part of the scan: 80-120, 80-110 and 80-100 min. Furthermore, the first part of the scan was also varied: 0-50, 0-40 and 0-30 min time intervals were assessed. The gap in the reference TACs was interpolated using four different interpolation methods: population-based input function 2T4k_VB (POP-IP_2T4k_VB), cubic, linear and exponential. Regional binding potential (BPND) and relative tracer delivery (R1) values estimated using simplified reference tissue model (SRTM) and/or receptor parametric mapping (RPM). The different scan protocols were compared to the respective values estimated using the original scan acquisition. In addition, TRT of the RPM BPND and R1 values estimated using the optimal shortest scan duration was also assessed.

RESULTS

RPM BPND and R1 obtained using 0-30/80-100 min scan and POP-IP_2T4k_VB reference region interpolation had an excellent correlation with the respective parametric values estimated using the original scan duration (r2 > 0.95). The TRT of RPM BPND and R1 using the shortest scan duration was - 1 ± 5 % and - 1 ± 6 % respectively.

CONCLUSIONS

This study demonstrated that [18F]flortaucipir PET scan can be acquired with sufficient quantitative accuracy using only 50 min of dual-time-window scanning time.

Heterogeneous distribution of tau pathology in the behavioural variant of Alzheimer's disease

OBJECTIVE

The clinical phenotype of the rare behavioural variant of Alzheimer's disease (bvAD) is insufficiently understood. Given the strong clinico-anatomical correlations of tau pathology in AD, we investigated the distribution of tau deposits in bvAD, in-vivo and ex-vivo, using positron emission tomography (PET) and postmortem examination.

METHODS

For the tau PET study, seven amyloid-β positive bvAD patients underwent [18F]flortaucipir or [18F]RO948 PET. We converted tau PET uptake values into standardised (W-)scores, adjusting for age, sex and mini mental state examination in a 'typical' memory-predominant AD (n=205) group. W-scores were computed within entorhinal, temporoparietal, medial and lateral prefrontal, insular and whole-brain regions-of-interest, frontal-to-entorhinal and frontal-to-parietal ratios and within intrinsic functional connectivity network templates. For the postmortem study, the percentage of AT8 (tau)-positive area in hippocampus CA1, temporal, parietal, frontal and insular cortices were compared between autopsy-confirmed patients with bvAD (n=8) and typical AD (tAD;n=7).

RESULTS

Individual regional W-scores ≥1.96 (corresponding to p<0.05) were observed in three cases, that is, case #5: medial prefrontal cortex (W=2.13) and anterior default mode network (W=3.79), case #2: lateral prefrontal cortex (W=2.79) and salience network (W=2.77), and case #7: frontal-to-entorhinal ratio (W=2.04). The remaining four cases fell within the normal distributions of the tAD group. Postmortem AT8 staining indicated no group-level regional differences in phosphorylated tau levels between bvAD and tAD (all p>0.05).

CONCLUSIONS

Both in-vivo and ex-vivo, patients with bvAD showed heterogeneous distributions of tau pathology. Since key regions involved in behavioural regulation were not consistently disproportionally affected by tau pathology, other factors are more likely driving the clinical phenotype in bvAD.

Test-retest repeatability of [18F]Flortaucipir PET in Alzheimer's disease and cognitively normal individuals

The aim of this study was to investigate the test-retest (TRT) repeatability of various parametric quantification methods for [18F]Flortaucipir positron emission tomography (PET). We included eight subjects with dementia or mild cognitive impairment due to Alzheimer's disease and six cognitively normal subjects. All underwent two 130-min dynamic [18F]Flortaucipir PET scans within 3 ± 1 weeks. Data were analyzed using reference region models receptor parametric mapping (RPM), simplified reference tissue method 2 (SRTM2) and reference logan (RLogan), as well as standardized uptake value ratios (SUVr, time intervals 40-60, 80-100 and 110-130 min post-injection) with cerebellar gray matter as reference region. We obtained distribution volume ratio or SUVr, first for all brain regions and then in three tau-specific regions-of-interest (ROIs). TRT repeatability (%) was defined as |retest-test|/(average (test + retest)) × 100. For all methods and across ROIs, TRT repeatability ranged from (median (IQR)) 0.84% (0.68-2.15) to 6.84% (2.99-11.50). TRT repeatability was good for all reference methods used, although semi-quantitative models (i.e. SUVr) performed marginally worse than quantitative models, for instance TRT repeatability of RPM: 1.98% (0.78-3.58) vs. SUVr80-100: 3.05% (1.28-5.52), p < 0.001. Furthermore, for SUVr80-100 and SUVr110-130, with higher average SUVr, more variation was observed. In conclusion, while TRT repeatability was good for all models used, quantitative methods performed slightly better than semi-quantitative methods.

Isocaloric low protein diet in a mouse model for vanishing white matter does not impact ISR deregulation in brain, but reveals ISR deregulation in liver

Objective: Vanishing white matter (VWM) is a genetic brain white matter disorder caused by mutations in eIF2B. eIF2B is central in the integrated stress response (ISR), during which its activity is inhibited by various cellular stresses. VWM is a chronic progressive disease with episodes of rapid neurological deterioration provoked by stresses. VWM patients and VWM mouse models show ISR deregulation in brain, correlating with chronic disease development. ISR inhibition ameliorates the chronic disease in VWM mice. The subacute deteriorations have not been modeled yet. We hypothesized that ISR activation could worsen disease progression in mice and model the episodic neurological deterioration.Method: We chose to activate the ISR by subjecting wild-type (wt) and VWM mice to an isocaloric low protein diet. This model would allow us to investigate the contribution of ISR activation in subacute decline in VWM.Results: We found that the low protein diet did not significantly affect amino acid levels nor ISR levels in wt and VWM mouse brain. Our study serendipitously led to the discovery of increased levels of glycine, asparagine and Fgf21 mRNA in VWM mouse brain irrespective of the dietary protein content. Strikingly, the ISR was not activated by the low protein diet in the liver of VWM in contrast to wt mice, due to a modest ISR deregulation in this organ.Discussion: A model for subacute neurological deterioration in VWM was not established. Possibly, ISR deregulation in VWM results in reduced ISR responsiveness.

Tau PET and relative cerebral blood flow in dementia with Lewy bodies: A PET study

PURPOSE

Alpha-synuclein often co-occurs with Alzheimer's disease (AD) pathology in Dementia with Lewy Bodies (DLB). From a dynamic [18F]flortaucipir PET scan we derived measures of both tau binding and relative cerebral blood flow (rCBF). We tested whether regional tau binding or rCBF differed between DLB patients and AD patients and controls and examined their association with clinical characteristics of DLB.

METHODS

Eighteen patients with probable DLB, 65 AD patients and 50 controls underwent a dynamic 130-minute [18F]flortaucipir PET scan. DLB patients with positive biomarkers for AD based on cerebrospinal fluid or amyloid PET were considered as DLB with AD pathology (DLB-AD+). Receptor parametric mapping (cerebellar gray matter reference region) was used to extract regional binding potential (BPND) and R1, reflecting (AD-specific) tau pathology and rCBF, respectively. First, we performed regional comparisons of [18F]flortaucipir BPND and R1 between diagnostic groups. In DLB patients only, we performed regression analyses between regional [18F]flortaucipir BPND, R1 and performance on ten neuropsychological tests.

RESULTS

Regional [18F]flortaucipir BPND in DLB was comparable with tau binding in controls (p > 0.05). Subtle higher tau binding was observed in DLB-AD+ compared to DLB-AD- in the medial temporal and parietal lobe (both p < 0.05). Occipital and lateral parietal R1 was lower in DLB compared to AD and controls (all p < 0.01). Lower frontal R1 was associated with impaired performance on digit span forward (standardized beta, stβ = 0.72) and category fluency (stβ = 0.69) tests. Lower parietal R1 was related to lower delayed (stβ = 0.50) and immediate (stβ = 0.48) recall, VOSP number location (stβ = 0.70) and fragmented letters (stβ = 0.59) scores. Lower occipital R1 was associated to worse performance on VOSP fragmented letters (stβ = 0.61), all p < 0.05.

CONCLUSION

The amount of tau binding in DLB was minimal and did not differ from controls. However, there were DLB-specific occipital and lateral parietal relative cerebral blood flow reductions compared to both controls and AD patients. Regional rCBF, but not tau binding, was related to cognitive impairment. This indicates that assessment of rCBF may give more insight into disease mechanisms in DLB than tau PET.

Long-term follow-up of distal radius fractures, an evaluation of the current guideline: the relation between malunion, osteoarthritis and functional outcome

BACKGROUND

Last decades there is an increased tendency of performing surgery on displaced distal radius fractures. However, it is unclear whether this affects the development of osteoarthritis. This study aims to determine the relation between anatomical position, radiological osteoarthritis and functional outcome of the elderly wrist, 10-15 years after a distal radius fracture.

PATIENTS AND METHODS

173 patients between the age of 50 and 70 at time of trauma were included in this retrospective cohort study with a 10-15-year follow-up. Based on the reassessed initial X-rays, the patients were placed into 4 groups (1: anatomical, 2a: acceptable, 2b: current operative indication but treated conservative, 2c: operative indication and operated). Functional outcome was measured, questionnaires were answered, and new bilateral X-rays of the wrist were obtained. Factors influencing osteoarthritis, the difference in osteoarthritis between the groups and the difference between the fractured and non-fractured wrists were studied.

RESULTS

Group 2b showed a significantly higher degree of osteoarthritis in comparison with the contralateral wrist. In the other groups, this difference was not observed. We found no significant difference in OA and functional outcomes between the groups. The degree of osteoarthritis of the non-fractured wrist appeared to be highly associated with osteoarthritis of the fractured wrist.

CONCLUSION

The results of this study showed that the degree of radiocarpal osteoarthritis is higher in conservatively treated patients that should have been operated on according to current guidelines in comparison with patients without an indication for surgery. This might suggest that our current guidelines can be effective in prevention of posttraumatic osteoarthritis. However, the effect on the functional outcome is very limited. Since the degree of radiocarpal osteoarthritis of the non-fractured wrist appeared to be highly associated with the degree of osteoarthritis of the fractured wrist, future studies should always assess osteoarthritis of both wrists in order to study the real posttraumatic effect of a fracture.

Tau pathology and relative cerebral blood flow are independently associated with cognition in Alzheimer's disease

Purpose

We aimed to investigate associations between tau pathology and relative cerebral blood flow (rCBF), and their relationship with cognition in Alzheimer’s disease (AD), by using a single dynamic [¹⁸F]flortaucipir positron emission tomography (PET) scan.

Methods

Seventy-one subjects with AD (66 ± 8 years, mini-mental state examination (MMSE) 23 ± 4) underwent a dynamic 130-min [¹⁸F]flortaucipir PET scan. Cognitive assessment consisted of composite scores of four cognitive domains. For tau pathology and rCBF, receptor parametric mapping (cerebellar gray matter reference region) was used to create uncorrected and partial volume-corrected parametric images of non-displaceable binding potential (BP_ND) and R₁, respectively. (Voxel-wise) linear regressions were used to investigate associations between BP_ND and/or R₁ and cognition_.

Results

Higher [¹⁸F]flortaucipir BP_ND was associated with lower R₁ in the lateral temporal, parietal and occipital regions. Higher medial temporal BP_ND was associated with worse memory, and higher lateral temporal BP_ND with worse executive functioning and language. Higher parietal BP_ND was associated with worse executive functioning, language and attention, and higher occipital BP_ND with lower cognitive scores across all domains. Higher frontal BP_ND was associated with worse executive function and attention. For [¹⁸F]flortaucipir R₁, lower values in the lateral temporal and parietal ROIs were associated with worse executive functioning, language and attention, and lower occipital R₁ with lower language and attention scores. When [¹⁸F]flortaucipir BP_ND and R₁ were modelled simultaneously, associations between lower R₁ in the lateral temporal ROI  and worse attention remained, as well as for lower parietal R₁ and worse executive functioning and attention.

Conclusion

Tau pathology was associated with locally reduced rCBF. Tau pathology and low rCBF were both independently associated with worse cognitive performance. For tau pathology, these associations spanned widespread neocortex, while for rCBF, independent associations were restricted to lateral temporal and parietal regions and the executive functioning and attention domains. These findings indicate that each biomarker may independently contribute to cognitive impairment in AD.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04831-w) contains supplementary material, which is available to authorized users.

Regional [18F]flortaucipir PET is more closely associated with disease severity than CSF p-tau in Alzheimer's disease

Purpose

In vivo Alzheimer’s disease (AD) biomarkers for tau pathology are cerebrospinal fluid (CSF) phosphorylated tau (p-tau) and [¹⁸F]flortaucipir positron emission tomography (PET). Our aim was to assess associations between CSF p-tau with [¹⁸F]flortaucipir PET and the associations of both tau biomarkers with cognition and atrophy.

Methods

We included 78 amyloid positive cognitively impaired patients (clinical diagnoses mild cognitive impairment (MCI, n = 8) and AD dementia (n = 45) and 25 cognitively normal subjects with subjective cognitive decline (SCD) (40% amyloid-positive)). Dynamic 130 min [¹⁸F]flortaucipir PET scans were acquired to generate binding potential (BP_ND) images using receptor parametric mapping and standardized uptake values ratios of 80–100 min (SUVr_80-100min) post injection. We obtained regional BP_ND and SUVr from entorhinal, limbic, and neocortical regions-of-interest (ROIs), closely aligning to the neuropathological tau staging schemes. Cognition was assessed using MMSE and composite scores of four cognitive domains, and atrophy was measured using gray matter volume covering the major brain lobes. First, we used linear regressions to investigate associations between CSF p-tau (independent variable) and tau PET (dependent variable). Second, we used linear regressions to investigate associations between CSF p-tau, tau PET (separate independent variables, model 1), and cognition (dependent variable). We then assessed the independent effects of CSF p-tau and tau PET on cognition by simultaneously adding the other tau biomarker as a predictor (model 2). Finally, we performed the same procedure for model 1 and 2, but replaced cognition with atrophy. Models were adjusted for age, sex, time lag between assessments, education (cognition only), and total intracranial volume (atrophy only).

Results

Higher [¹⁸F]flortaucipir BP_ND was associated with higher CSF p-tau (range of standardized betas (sβ) across ROIs, 0.43–0.46; all p < 0.01). [¹⁸F]flortaucipir BP_ND was more strongly associated with cognition and atrophy than CSF p-tau. When [¹⁸F]flortaucipir BP_ND and CSF p-tau were entered simultaneously, [¹⁸F]flortaucipir BP_ND (range sβ = − 0.20 to – 0.57, all p < 0.05) was strongly associated with multiple cognitive domains and atrophy regions. SUVr showed comparable results to BP_ND.

Conclusion

Regional [¹⁸F]flortaucipir BP_ND correlated stronger with cognition and neurodegeneration than CSF p-tau, suggesting that tau PET more accurately reflects disease severity in AD.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04758-2) contains supplementary material, which is available to authorized users.

Hippocampal [18F]flortaucipir BPND corrected for possible spill-in of the choroid plexus retains strong clinico-pathological relationships

BACKGROUND

Off-target [¹⁸F]flortaucipir (tau) PET binding in the choroid plexus causes spill-in into the nearby hippocampus, which may influence the correlation between [¹⁸F]flortaucipir binding and measures of cognition. Previously, we showed that partial volume correction (combination of Van Cittert iterative deconvolution and HYPR denoising; PVC HDH) and manually eroding the hippocampus resulted in a significant decrease of the choroid plexus spill-in. In this study, we compared three different approaches for the quantification of hippocampal [¹⁸F]flortaucipir signal using a semi-automated technique, and assessed correlations with cognitive performance across methods.

METHODS

Dynamic 130 min [¹⁸F]flortaucipir PET scans were performed in 109 subjects (45 cognitively normal subjects (CN) and 64 mild cognitive impairment/Alzheimer's disease (AD) dementia patients. We extracted hippocampal binding potential (BP_ND) using receptor parametric mapping with cerebellar grey matter as reference region. PVC HDH was performed. Based on our previous study in which we manually eroded 40% ± 10% of voxels of the hippocampus, three hippocampal volumes-of-interest (VOIs) were generated: a non-optimized 100% hippocampal VOI [100%], and combining HDH with eroding a percentage of the highest hippocampus BP_ND voxels (i.e. lowering spill-in) resulting in optimized 50%[50%HDH] and 40%[40%HDH] hippocampal VOIs. Cognitive performance was assessed with the Mini-Mental State Examination (MMSE) and Rey auditory verbal learning delayed recall. We performed receiver operating characteristic analyses to investigate which method could best discriminate MCI/AD from controls. Subsequently, we performed linear regressions to investigate associations between the hippocampal [¹⁸F]flortaucipir BP_ND VOIs and MMSE/delayed recall adjusted for age, sex and education.

RESULTS

We found higher hippocampal [¹⁸F]flortaucipir BP_ND in MCI/AD patients (BP_ND100%=0.27±0.15) compared to CN (BP_ND100%= 0.07±0.13) and all methods showed comparable discriminative effects (AUC_100%=0.85[CI=0.78-0.93]; AUC_50%HDH=0.84[CI=0.74-0.92]; AUC_40%HDH=0.83[CI=0.74-0.92]). Across groups, higher [¹⁸F]flortaucipir BP_ND was related to lower scores on MMSE (standardized β_100%=-0.38[CI=-0.57-0.20]; β_50%HDH= -0.37[CI=-0.54-0.19]; β_40%HDH=-0.35[CI=-0.53-0.17], all p<0.001) and delayed recall (standardized β_100%=-0.64[CI=-0.79-0.49]; β_50%HDH= -0.61[CI=-0.76-0.46]; β_40%HDH=-0.59[CI=-0.75-0.44]; all p<0.001), with comparable effect sizes for all hippocampal VOIs.

CONCLUSIONS

Hippocampal tau load measured with [¹⁸F]flortaucipir PET is strongly associated with cognitive function. Both discrimination between diagnostic groups and associations between hippocampal [¹⁸F]flortaucipir BP_ND and memory were comparable for all methods. The non-optimized 100% hippocampal VOI may be sufficient for clinical interpretation. However, proper correction for choroid plexus spillover and may be required in case of smaller effect sizes between subject groups or for longitudinal studies.

Associations between quantitative [18F]flortaucipir tau PET and atrophy across the Alzheimer's disease spectrum

Background

Neuropathological studies have linked tau aggregates to neuronal loss. To describe the spatial distribution of neurofibrillary tangle pathology in post-mortem tissue, Braak staging has been used. The aim of this study was to examine in vivo associations between tau pathology, quantified with [¹⁸F]flortaucipir PET in regions corresponding to Braak stages, and atrophy across the Alzheimer’s disease (AD) spectrum.

Methods

We included 100 subjects, including 58 amyloid-β positive patients with mild cognitive impairment (MCI, n = 6) or AD dementia (n = 52) and 42 controls with subjective cognitive decline (36% amyloid-β positive). All subjects underwent a dynamic [¹⁸F]flortaucipir PET to generate non-displaceable binding potential (BP_ND) maps. We extracted average [¹⁸F]flortaucipir BP_ND entorhinal, Braak III–IV (limbic) and Braak V–VI (neocortical) regions of interest (ROIs). T1-weighted MRI was used to assess gray matter (GM) volumes. We performed linear regression analyses using [¹⁸F]flortaucipir BP_ND ROIs as independent and GM density (ROI or voxelwise) as dependent variable.

Results

In MCI/AD subjects (age [mean ± SD] 65 ± 8 years, MMSE 23 ± 4), [¹⁸F]flortaucipir BP_ND was higher than in controls (age 65 ± 8, MMSE 29 ± 1) across all ROIs (entorhinal 0.06 ± 0.21 vs 0.46 ± 0.25 p < 0.001, Braak III–IV 0.11 ± 0.10 vs 0.46 ± 0.26, p < 0.001, Braak V–VI 0.07 ± 0.07 vs 0.38 ± 0.29, p < 0.001). In MCI/AD, greater [¹⁸F]flortaucipir BP_ND in entorhinal cortex was associated with lower GM density in medial temporal lobe (β − 0.40, p < 0.001). Greater [¹⁸F]flortaucipir BP_ND in ROI Braak III–IV and Braak V–VI was associated with smaller GM density in lateral and inferior temporal, parietal, occipital, and frontal lobes (range standardized βs − 0.30 to − 0.55, p < 0.01), but not in medial temporal lobe (β − 0.22, p 0.07). [¹⁸F]Flortaucipir BP_ND in ROI Braak I–II was not associated with GM density loss anywhere. When quantifying [¹⁸F]flortaucipir BP_ND across brain lobes, we observed both local and distant associations with GM atrophy. In controls, there were no significant associations between [¹⁸F]flortaucipir BP_ND and GM density (standardized βs ranging from − 0.24 to 0.02, all p > 0.05).

Conclusions

In MCI/AD patients, [¹⁸F]flortaucipir binding in entorhinal, limbic, and neocortical regions was associated with cortical atrophy.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0510-3) contains supplementary material, which is available to authorized users.

Optical properties and fabrication of dielectric metasurfaces based on amorphous silicon nanodisk arrays

Dielectric metasurfaces based on amorphous silicon (a-Si) nanodisks are interesting for nanophotonic applications due to the high refractive index and mature/low temperature fabrication of a-Si. The investigated metasurfaces consist of a-Si nanodisk arrays embedded in a transparent film. The diameter-dependent optical properties of the nanodisk Mie resonators have been investigated by finite-difference time-domain (FDTD) simulations and spectrally-resolved reflectivity and transmission measurements. Well-ordered substrate-free a-Si nanodisk arrays were fabricated and characterized with regard to their broadband anti-reflection properties when placed on a crystalline silicon (c-Si) surface, and reflectivity/ transmission properties when embedded in a polydimethylsiloxane (PDMS) film. Our results confirm broadband anti-reflection when placed on silicon, while the optical characteristics of the nanodisks embedded in PDMS are shown to be potentially useful for color/NIR filter applications as well as for coloring on the micro/nanoscale.

Refractive index sensing in the visible/NIR spectrum using silicon nanopillar arrays

Si nanopillar (NP) arrays are investigated as refractive index sensors in the visible/NIR wavelength range, suitable for Si photodetector responsivity. The NP arrays are fabricated by nanoimprint lithography and dry etching, and coated with thin dielectric layers. The reflectivity peaks obtained by finite-difference time-domain (FDTD) simulations show a linear shift with coating layer thickness. At 730 nm wavelength, sensitivities of ~0.3 and ~0.9 nm/nm of SiO₂ and Si₃N₄, respectively, are obtained; and the optical thicknesses of the deposited surface coatings are determined by comparing the experimental and simulated data. The results show that NP arrays can be used for sensing surface bio-layers. The proposed method could be useful to determine the optical thickness of surface coatings, conformal and non-conformal, in NP-based optical devices.

High energy excitations measured by neutron spectroscopy in FePS(3)

The quasi-two-dimensional antiferromagnet FePS(3) has been investigated using inelastic neutron spectroscopy with the time-of-flight spectrometer HET at the ISIS spallation neutron source. In the paramagnetic regime, two clearly resolved, high energy excitations were observed in the low scattering angle detector banks at 195(5) meV and 430(10) meV. The absence of these transitions from the high angle detector banks indicates that they are likely to be due to the crystal fields and magnetic in origin. The two transitions most probably represent electronic transitions in the Fe(2+) ion among the low lying crystal field and spin-orbit split levels raised from the ground state. It has not yet been determined why the energies are greater than those observed in a comparable Raman experiment.

Discovery of a novel carboxylesterase through functional screening of a pre-enriched environmental library

AIMS

The aim of this study was to demonstrate the application of environmental sample pre-enrichment to access novel carboxylesterases from environmental genomes, along with subsequent heterologous expression and characterization of the discovered enzyme(s).

METHODS AND RESULTS

A positive recombinant clone (UVCL29), conferring an esterase phenotype was identified from a shotgun gene library. The complete sequence of the 3.0 kb DNA insert from the pUVCL29 recombinant plasmid was obtained using primer-walking strategies. Nucleotide sequence analysis revealed a complete 945 bp open reading frame (ORF1). Translational analysis of the ORF1 showed a protein of 314 amino acids (named EstAM) with a predicted molecular weight of 34 kDa. EstAM's primary structure showed a classical (-G-D-S-A-G-) motif, corresponding with the generally conserved (G-x-S-x-G) esterase signature motif. Identity searches indicated that EstAM has high sequence similarity with esterases from family IV. EstAM was successfully expressed in Escherichia coli in a biologically active form. Partial purification was achieved using a one-step Pro-PurTM IMAC column. Biochemical characterization revealed that EstAM has a temperature optimum of 40 degrees C.

CONCLUSION

Based on its substrate profile, EstAM was classified as a carboxylesterase because of its preference for short p-nitrophenyl ester substrates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is a demonstration of the successful application of environmental sample pre-enrichment technology in accessing novel esterases from a mining environment.