Exploring with [18F]UCB-H the in vivo cariations in SV2A expression through the kainic acid rat model of temporal lobe epilepsy

Purpose The main purpose of this study was to understand how the positron emission tomography (PET) measure of the synaptic vesicle 2A (SV2A) protein varies in vivo during the development of temporal lobe epilepsy (TLE) in the kainic acid rat model. Procedures Twenty Sprague Dawley male rats were administered with multiple systemic doses of saline (control group, n = 5) or kainic acid (5 mg/kg/injection, epileptic group, n = 15). Both groups were scanned at the four phases of TLE (early, latent, transition, and chronic phase) with the [F-18]UCB-H PET radiotracer and T2-structural magnetic resonance imaging. At the end of the scans (3 months post-status epilepticus), rats were monitored for 7 days with electroencephalography for the detection of spontaneous electrographic seizures. Finally, the immunofluorescence staining for SV2A expression was performed. Results Control rats presented a significant increase in [F-18]UCB-H binding at the last two scans, compared with the first ones (p < 0.001). This increase existed but was lower in epileptic animals, producing significant group differences in all the phases of the disease (p < 0.028). Furthermore, the quantification of the SV2A expression in vivo with the [F-18]UCB-H radiotracer or ex vivo with immunofluorescence led to equivalent results, with a positive correlation between both. Conclusions Even if further studies in humans are required, the ability to detect a progressive decrease in SV2A expression during the development of temporal lobe epilepsy supports the use of [F-18]UCB-H as a useful tool to differentiate, in vivo, between healthy and epileptic animals along with the development of the epileptic disease

[18F]UCB-H BINDING QUANTIFICATION IN RAT BRAIN: FROM MODELLING TO SUV

Introduction Image quantification in Positron Emission Tomography (PET) is usually achieved through the invasive and sometimes infeasible arterial blood sampling [1, 2]. Alternative methods have been proposed, but a validation of their results is necessary [3, 4]. In the scope of improving the use of [18F]UCB-H, a specific biomarker for the Synaptic Vesicle protein 2A (SV2A) [5, 6, 7, 8], we have compared the distribution volume (VT) obtained through full kinetic modelling using a Population Based Input Function (PBIF) [9], and the Standardized Uptake Value (SUV). Methods Twelve Sprague Dawley male rats were pre-treated with vehicle (saline), 1 or 10 mg/kg of SV2A ligand (Keppra®, IP). Thirty minutes later, [18F]UCB-H was injected (IV) and a 90 min microPET dynamic acquisition was started followed by a T2 structural MRI. Primary image analysis was focused in examining tracer measurement stability through 10 min time windows. Subsequently, we calculated the correlation between VT (90 minutes) and SUV values over consecutive 20-minute time frames searching for the optimal frame to perform a static acquisition [10]. Finally, we did a supplementary test-retest static acquisition, from 60 to 80 minutes, in order to test group differences in SUV. Results/Discussion Evaluation of ten minutes time windows showed more stability in VT than in SUV measures, for all the groups. This change in signal seems to decrease in late time frames. We found also a strong correlation (R2>0.6) between dynamic VT and twenty minutes frame SUV, especially between 20 min and 60 min. From this, we can infer that an optimal frame to perform a static acquisition with [18F]UCB-H would be between 50 and 80 minutes. Using a static acquisition from 60 to 80 minutes, the SUV highlighted statistically significant differences between the group injected with vehicle and the other groups (p<0.01), but not between groups pre-treated with 1mg/kg and 10mg/kg of Keppra®. Conclusions Our work shows that a strong correlation between the SUV and the VT parameter based on a PBIF does exist. This opens the way to a possible simplification for SV2A in vivo imaging with [18F]UCB-H. Despite the fact that SUV is affected by many factors [11] and that it can overestimate results relative to VT [10], it is able to detect important differences in SV2A expression. Based on these results, SUV could become an interesting and easy to obtain parameter to study group differences in the context of several diseases. References 1. Acton PD et al. Radiologic Clinics of North America. 2004; 42(6):1055. 2. Kinahan PE & Fletcher JW. Seminars in Ultrasound, CT and MRI 2010; 31(6): 496. 3. Heurling K et al. Brain Res. 2017; 1670:220. 4. Tomasi G et al. Molecular Imaging and Biology. 2012; 14(2):131. 5. Bretin F et al. EJNMMI res. 2013; 3(1):35. 6. Warnock GI et al. J Nucl Med. 2014; 55(8):1336. 7. Bretin F et al. Molecular Imaging and Biology. 2015; 17(4):557. 8. Salmon E et al. Alzheimer's & Dementia. 2017; 13(7):781. 9. Becker G et al. Molecular Pharmaceutics. 2017; 14(8):2719. 10. Lockhart SN et al. PLoS One. 2016; 11(6):e0158460. 11. Boellaard R. J Nucl Med. 2009; 50(Suppl 1):11S-20S. Acknowledgement This work was funded by University of Liège, F.R.S.-FNRS, Walloon Region and UCB Pharma. Alain Plenevaux is research director from F.R.S.-FNRS.SV2A Projec

Associative memory and its cerebral correlates in Alzheimer’s disease: Evidence for distinct deficits of relational and conjunctive memory

This study investigated the impact of Alzheimer's disease (AD) on conjunctive and relational binding in episodic memory. Mild AD patients and controls had to remember item-color associations by imagining color either as a contextual association (relational memory) or as a feature of the item to be encoded (conjunctive memory). Patients' performance in each condition was correlated with cerebral metabolism measured by FDG-PET. The results showed that AD patients had an impaired capacity to remember item-color associations, with deficits in both relational and conjunctive memory. However, performance in the two kinds of associative memory varied independently across patients. Partial least square analyses revealed that poor conjunctive memory was related to hypometabolism in an anterior temporal-posterior fusiform brain network, whereas relational memory correlated with metabolism in regions of the default mode network. These findings support the hypothesis of distinct neural systems specialized in different types of associative memory and point to heterogeneous profiles of memory alteration in Alzheimer's disease as a function of damage to the respective neural networks

EPILEPSY AND THE SV2A PROTEIN: new insights about the disease.

Around two million of people worldwide are affected by neurodegenerative diseases, such as Alzheimer, Parkinson or Epilepsy. Despite the social and the economic impact of these diseases, their causes still remain unclear. In the case of the epilepsy, for example, around 25% of the patients suffer drug-resistant epilepsy, for which there is no medicament able to mitigate the epileptic crises or the associated symptomatology, such as cognitive problems and mood disorders. In 1974, UCB Pharma synthetized a new antiepileptic drug with a high therapeutic index: the Levetiracetam. The target of this medicament is the Synaptic Vesicle Protein 2A (SV2A) whose specific role in the pathology is still unknown. The main goal of my thesis is to better understand the relationship between this protein and the epilepsy. On the one hand, the production and phenotyping of conditional knockout mice for the SV2A protein allowed us to discover a possible implication of this protein in the spatial memory and anxiety process, an important part of the epileptic symptomatology. On the other hand, the synthesis of the radiotracer [18F]UCB-H, with a high affinity for the SV2A protein, enabled the in vivo evaluation (with the mPET technique) of a rat model of the temporal lobe epilepsy through the disease process. Results showed a strong correlation between the severity of the epilepsy (EEG technique) and the SV2A levels in different brain regions, highlighting the importance of this protein in the development of the disease. In summary, although further studies in humans are necessary, this protein emerges as an important key in clinical diagnosis and medical research, being implicated in all the aspects of the epileptic disease

Quantification of [18F]UCB-H Binding in the Rat Brain: From Kinetic Modelling to Standardised Uptake Value

Purpose: [18F]UCB-H is a specific positron emission tomography (PET) biomarker for the Synaptic Vesicle protein 2A (SV2A), the binding site of the antiepileptic drug levetiracetam. With a view to optimising acquisition time and simplifying data analysis with this radiotracer, we compared two parameters: the distribution volume (Vt) obtained from Logan graphical analysis using a Population-Based Input Function, and the Standardised Uptake Value (SUV). Procedures: Twelve Sprague Dawley male rats, pre-treated with three different doses of levetiracetam were employed to develop the methodology. Three additional kainic acid (KA) treated rats (temporal lobe epilepsy model) were also used to test the procedure. Image analyses focused on: (i) length of the dynamic acquisition (90 versus 60 min); (ii) correlations between Vt and SUV over 20-min consecutive time-frames; (iii) and (iv) evaluation of differences between groups using the Vt and the SUV; and (v) preliminary evaluation of the methodology in the KA epilepsy model. Results: A large correlation between the Vt issued from 60 to 90-min acquisitions was observed. Further analyses highlighted a large correlation (r 9 0.8) between the Vt and the SUV. Equivalent differences between groups were detected for both parameters, especially in the 20–40 and 40– 60-min time-frames. The same results were also obtained with the epilepsy model. Conclusions: Our results enable the acquisition setting to be changed from a 90-min dynamic to a 20-min static PET acquisition. According to a better image quality, the 20–40-min time-frame appears optimal. Due to its equivalence to the Vt, the SUV parameter can be considered in order to quantify [18F]UCB-H uptake in the rat brain. This work, therefore, establishes a starting point for the simplification of SV2A in vivo quantification with [18F]UCB-H, and represents a step forward to the clinical application of this PET radiotracer.SV2A projec

EPILEPSY AND THE SV2A PROTEIN: new insights about the disease.

Around two million of people worldwide are affected by neurodegenerative diseases, such as Alzheimer, Parkinson or Epilepsy. Despite the social and the economic impact of these diseases, their causes still remain unclear. In the case of the epilepsy, for example, around 25% of the patients suffer drug-resistant epilepsy, for which there is no medicament able to mitigate the epileptic crises or the associated symptomatology, such as cognitive problems and mood disorders. In 1974, UCB Pharma synthetized a new antiepileptic drug with a high therapeutic index: the Levetiracetam. The target of this medicament is the Synaptic Vesicle Protein 2A (SV2A) whose specific role in the pathology is still unknown. The main goal of my thesis is to better understand the relationship between this protein and the epilepsy. On the one hand, the production and phenotyping of conditional knockout mice for the SV2A protein allowed us to discover a possible implication of this protein in the spatial memory and anxiety process, an important part of the epileptic symptomatology. On the other hand, the synthesis of the radiotracer [18F]UCB-H, with a high affinity for the SV2A protein, enabled the in vivo evaluation (with the mPET technique) of a rat model of the temporal lobe epilepsy through the disease process. Results showed a strong correlation between the severity of the epilepsy (EEG technique) and the SV2A levels in different brain regions, highlighting the importance of this protein in the development of the disease. In summary, although further studies in humans are necessary, this protein emerges as an important key in clinical diagnosis and medical research, being implicated in all the aspects of the epileptic disease.SV2A projec

THE SV2A PROTEIN: IMAGING SYNAPTIC DENSITY DURING THE PROGRESSION OF THE TEMPORAL LOBE EPILEPSY IN THE KASE RAT MODEL

Introduction The temporal lobe epilepsy (TLE) is the most common epileptic disorder. New antiepileptic drugs target the Synaptic Vesicle protein 2A (SV2A) (1). Nevertheless, the prevailing literature addressing the relation between this protein and the epilepsy is limited (2, 3). This study provides insights on the role of the SV2A protein during the four stages of TLE (4, 5), throughout its in vivo study with the [18F]UCB-H radiotracer (6). Methods Twenty-four male Sprague-Dawley were subjected to multiple injections (7) of i) Saline (Sham), or ii) 5mg/kg of Kainic Acid (KA). The rats not reacting to KA (NKA) were also scanned. In each TLE stages, a [18F]UCB-H dynamic scan was performed, followed by a T2-structural MRI. EEG recordings were performed to determine the number of crises. Data processing was done with PMOD 3.6. Results were expressed as SUV and statistically analyzed with the SPSS and the SPM. Results During the acute phase, statistically significant differences were found between Sham and KA in striatum, cerebellum, and medulla. In the latent phase, these SUV differences were detected between the NKA and KA in the same regions along with hippocampus and thalamus. When the spontaneous crises started, these group differences became statistically significant in all the regions but the cortex. During the chronic phase, all the regions showed statistically significant differences between groups. Furthermore, the voxel-wise analysis highlighted statistically significant differences in voxels at the level of amygdala and hippocampus. Conclusions These results show that [18F]UCB-H is able to detect early modifications in SV2A expression (3 days after the TLE model creation), in particular in regions implicated in the epileptic process. This radiotracer can potentially be used as a suitable biomarker for the early detection of the epileptic disease, being able to distinguish between stages in this neurodegenerative disease.SV2A projec

18F-FPRGD2 PET/CT imaging of integrin αvβ3 in renal carcinomas: Correlation with histopathology

This study aimed to correlate 18F-FB-mini-PEG-E[c(RGDyK)](2) (18F-FPRGD2) uptake to integrin αvβ3 expression and angiogene-sis in renal tumors.Methods: 18F-FPRGD2 PET/CT was performed on 27 patients before surgical resection (median 4 d) of a renal mass. The 18F-FPRGD2 uptake was compared with integrin αvβ3, CD31, CD105, and Ki-67 using immunohistochemistry; with pla-cental growth factor and vascular endothelial growth factor recep-tors 1 and 2 using reverse transcription polymerase chain reaction; and with vascular endothelial growth factor A isoforms using enzyme-linked immunosorbent assay. Results: Overall, 18F-FPRGD2 uptake significantly correlated (P, 0.0001) with integrin αvβ3 expression in renal masses. However, it correlated only with integrin αvβ3-positive vessels in the group of papillary carcinomas whereas it correlated with integrin αvβ3 expression by tumor cells in the clear cell carcinoma group. Conclusion: 18F-FPRGD2 up-take reflects the expression of integrin αvβ3 in renal tumors but represents angiogenesis only when tumor cells do not express the integrin