Mohamed Ali Bahri

Pharmacokinetic Characterization of [18F]UCB-H PET Radiopharmaceutical in the Rat Brain

The synaptic vesicle glycoprotein 2A (SV2A), a protein essential to the proper nervous system function, is found in presynaptic vesicles. Thus, SV2A targeting, using dedicated radiotracers combined with positron emission tomography (PET), allows the assessment of synaptic density in the living brain. The first-in-class fluorinated SV2A specific radioligand, [18F]UCB-H, is now available at high activity through an efficient radiosynthesis compliant with current good manufacturing practices (cGMP). We report here a noninvasive method to quantify [18F]UCB-H binding in rat brain with microPET. Validation study in rats confirmed the need of high enantiomeric purity to target SV2A in vivo. We demonstrated the reliability of a population-based input function to quantify SV2A in preclinical microPET setting. Finally, we investigated the in vivo metabolism of [18F]UCB-H and confirmed the negligible amount of radiometabolites in the rat brain. Hence, the in vivo quantification of SV2A using [18F]UCB-H microPET seems a promising tool for the assessment of the synaptic density in the rat brain, and opens the way for longitudinal follow-up in neurodegenerative disease rodent models.

Measuring brain synaptic vesicle protein 2A with positron emission tomography and [18F]UCB-H.

Brain distribution of synaptic vesicle protein 2A was measured with fluorine‐18 UCB‐H ([18F]UCB‐H) and positron emission tomography (PET).

Regiospecific radiolabelling of Nanofitin on Ni magnetic beads with [18F]FBEM and in vivo PET studies

INTRODUCTIONnNanofitins are low molecular weight, single chain and cysteine-free protein scaffolds able to selectively bind a defined biological target. They derive from Sac7d bacterial protein family and are highly stable over a wide range of pH (0-13) and temperature (Tm ~80°C). Their extreme stability, low cost of production and high tolerability for chemical coupling make Nanofitins a very interesting alternative to antibodies and their fragments. Here, a hexahistidine tagged model Nanofitin (H4) directed against hen egg white lysozyme was radiolabelled and injected in mice to provide a baseline biodistribution and pharmacokinetic profiles to support future Nanofitin development programs.nnnMETHODnA single cysteine residue has been genetically inserted in a model Nanofitin and its regioselective radiolabelling has been performed with 4-[18F]fluorobenzamido-N-ethylamino-maleimide ([18F]FBEM). The synthesis of [18F]FBEM has been completely implemented on a radiosynthesis unit (FastLab) including HPLC purification and formulation. Coupling with the [18F]FBEM has been achieved on a solid support (Ni magnetic beads) allowing rapid purification at room temperature without organic solvent. PET-MRI studies on C57BL/6 mice were conducted after injection of [18F]FBEM-Cys-H4 in order to access the biodistribution of this Nanofitin model.nnnRESULTSnRadiochemical yield (decay corrected) of 54±7% (n=4) was obtained after optimization for coupling the [18F]FBEM to Nanofitin. Pharmacokinetics results of [18F]FBEM-Cys-H4 revealed a fast clearance through the liver and the kidneys.nnnCONCLUSIONnAn efficient new method on Ni magnetic beads was developed to radiolabelled his-tagged biomolecules with [18F]FBEM. This procedure was applied on a Nanofitin model Cys-H4 and biodistribution kinetic studies were achieved to evaluate the potential use of Nanofitin for diagnostic imaging. Fast clearance indicates that Nanofitins represent very interesting tools for diagnostic imaging.

BCI performance and brain metabolism profile in severely brain-injured patients without response to command at bedside

Detection and interpretation of signs of “covert command following” in patients with disorders of consciousness (DOC) remains a challenge for clinicians. In this study, we used a tactile P3-based BCI in 12 patients without behavioral command following, attempting to establish “covert command following.” These results were then confronted to cerebral metabolism preservation as measured with glucose PET (FDG-PET). One patient showed “covert command following” (i.e., above-threshold BCI performance) during the active tactile paradigm. This patient also showed a higher cerebral glucose metabolism within the language network (presumably required for command following) when compared with the other patients without “covert command-following” but having a cerebral glucose metabolism indicative of minimally conscious state. Our results suggest that the P3-based BCI might probe “covert command following” in patients without behavioral response to command and therefore could be a valuable addition in the clinical assessment of patients with DOC.

A Heartbeat Away From Consciousness: Heart Rate Variability Entropy can discriminate disorders of consciousness and is correlated with resting-state fMRI brain connectivity of the Central Autonomic Network

Background: Disorders of consciousness are challenging to diagnose, with inconsistent behavioral responses, motor and cognitive disabilities, leading to approximately 40% misdiagnoses. Heart rate variability (HRV) reflects the complexity of the heart-brain two-way dynamic interactions. HRV entropy analysis quantifies the unpredictability and complexity of the heart rate beats intervals. We here investigate the complexity index (CI), a score of HRV complexity by aggregating the non-linear multi-scale entropies over a range of time scales, and its discriminative power in chronic patients with unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS), and its relation to brain functional connectivity. Methods: We investigated the CI in short (CIs) and long (CIl) time scales in 14 UWS and 16 MCS sedated. CI for MCS and UWS groups were compared using a Mann-Whitney exact test. Spearmans correlation tests were conducted between the Coma Recovery Scale-revised (CRS-R) and both CI. Discriminative power of both CI was assessed with One-R machine learning model. Correlation between CI and brain connectivity (detected with functional magnetic resonance imagery using seed-based and hypothesis-free intrinsic connectivity) was investigated using a linear regression in a subgroup of 10 UWS and 11 MCS patients with sufficient image quality. Results: Higher CIs and CIl values were observed in MCS compared to UWS. Positive correlations were found between CRS-R and both CI. The One-R classifier selected CIl as the best discriminator between UWS and MCS with 90% accuracy, 7% false positive and 13% false negative rates after a 10-fold cross-validation test. Positive correlations were observed between both CI and the recovery of functional connectivity of brain areas belonging to the central autonomic networks (CAN). Conclusion: CI of MCS compared to UWS patients has high discriminative power and low false negative rate at one third of the estimated human assessors misdiagnosis, providing an easy, inexpensive and non-invasive diagnostic tool. CI reflects functional connectivity changes in the CAN, suggesting that CI can provide an indirect way to screen and monitor connectivity changes in this neural system. Future studies should assess the extent of CIs predictive power in a larger cohort of patients and prognostic power in acute patients.

Comparative assessment of 6-[18F]fluoro-L-m-tyrosine and 6-[18F]fluoro-L-dopa to evaluate dopaminergic presynaptic integrity in a Parkinson’s disease rat model.

Because of the progressive loss of nigro‐striatal dopaminergic terminals in Parkinsons disease (PD), in vivo quantitative imaging of dopamine (DA) containing neurons in animal models of PD is of critical importance in the preclinical evaluation of highly awaited disease‐modifying therapies. Among existing methods, the high sensitivity of positron emission tomography (PET) is attractive to achieve that goal. The aim of this study was to perform a quantitative comparison of brain images obtained in 6‐hydroxydopamine (6‐OHDA) lesioned rats using two dopaminergic PET radiotracers, namely [18F]fluoro‐3,4‐dihydroxyphenyl‐L‐alanine ([18F]FDOPA) and 6‐[18F]fluoro‐L‐m‐tyrosine ([18F]FMT). Because the imaging signal is theoretically less contaminated by metabolites, we hypothesized that the latter would show stronger relationship with behavioural and post‐mortem measures of striatal dopaminergic deficiency. We used a within‐subject design to measure striatal [18F]FMT and [18F]FDOPA uptake in eight partially lesioned, eight fully lesioned and ten sham‐treated rats. Animals were pretreated with an L‐aromatic amino acid decarboxylase inhibitor. A catechol‐O‐methyl transferase inhibitor was also given before [18F]FDOPA PET. Quantitative estimates of striatal uptake were computed using conventional graphical Patlak method. Striatal dopaminergic deficiencies were measured with apomorphine‐induced rotations and post‐mortem striatal DA content. We observed a strong relationship between [18F]FMT and [18F]FDOPA estimates of decreased uptake in the denervated striatum using the tissue‐derived uptake rate constant Kc. However, only [18F]FMT Kc succeeded to discriminate between the partial and the full 6‐OHDA lesion and correlated well with the post‐mortem striatal DA content. This study indicates that the [18F]FMT could be more sensitive, with respect of [18F]FDOPA, to investigate DA terminals loss in 6‐OHDA rats, and open the way to in vivo L‐aromatic amino acid decarboxylase activity targeting in future investigations on progressive PD models.