An In Vivo Study of a Rat Fluid-Percussion-Induced Traumatic Brain Injury Model with [11C]PBR28 and [18F]flumazenil PET Imaging

Abstract

Traumatic brain injury (TBI) modelled by lateral fluid percussion-induction (LFPI) in rats is a widely used experimental rodent model to explore and understand the underlying cellular and molecular alterations in the brain caused by TBI in humans. Current improvements in imaging with positron emission tomography (PET) have made it possible to map certain features of TBI-induced cellular and molecular changes equally in humans and animals. The PET imaging technique is an apt supplement to nanotheranostic-based treatment alternatives that are emerging to tackle TBI. The present study aims to investigate whether the two radioligands, [11C]PBR28 and [18F]flumazenil, are able to accurately quantify in vivo molecular-cellular changes in a rodent TBI-model for two different biochemical targets of the processes. In addition, it serves to observe any palpable variations associated with primary and secondary injury sites, and in the affected versus the contralateral hemispheres. As [11C]PBR28 is a radioligand of the 18 kD translocator protein, the up-regulation of which is coupled to the level of neuroinflammation in the brain, and [18F]flumazenil is a radioligand for GABAA-benzodiazepine receptors, whose level mirrors interneuronal activity and eventually cell death, the use of the two radioligands may reveal two critical features of TBI. An up-regulation in the [11C]PBR28 uptake triggered by the LFP in the injured (right) hemisphere was noted on day 14, while the uptake of [18F]flumazenil was down-regulated on day 14. When comparing the left (contralateral) and right (LFPI) hemispheres, the differences between the two in neuroinflammation were obvious. Our results demonstrate a potential way to measure the molecular alterations in a rodent-based TBI model using PET imaging with [11C]PBR28 and [18F]flumazenil. These radioligands are promising options that can be eventually used in exploring the complex in vivo pharmacokinetics and delivery mechanisms of nanoparticles in TBI treatment.

Automated Synthesis of [18F]Flumazenil Application in GABAA Receptor Neuroimaging Availability for Rat Model of Anxiety

“…The purification of crude [ 18 F]flumazenil was previously carried out using acetonitrile and water as the mobile phase [ 31 , 45 , 46 , 47 ]. However, acetonitrile is flammable, volatile, toxic, and must be removed during the purification process.…”

“…To further characterize the nature of GABA A receptor uptake, the effects of pre-treatment with 200 µg diazepam (BZR agonist) were studied in ex vivo autoradiography, and pre-treatment with 0.01–10 mg/kg diazepam for NanoPET/CT in vivo imaging. Pre-saturation studies have shown a high displaceable component for diazepam administration in the frontal cortex, cortex, amygdala, and hippocampus contrasted to [ 18 F]flumazenil, indicating that the structural modification of [ 18 F]flumazenil results will show in high affinity for GABA A /cBZRs (central benzodiazepine receptors) [ 23 , 30 , 31 ].…”

“…Preparation of [ 11 C]-flumazenil, a confirmed benzene diazo salt-specific antagonist, began in 1981, and the compound is widely used in clinical practice since 2008 [ 26 , 27 , 28 , 29 ]. [ 18 F]flumazenil, with an identical structure to [ 11 C]flumazenil, was shown to have pharmacokinetic, peripheral metabolism, and PET imaging characteristics similar to [ 11 C]flumazenil in a cynomolgus monkey [ 30 , 31 ]. [ 18 F]flumazenil PET has evolved to be one of the most useful radiopharmaceuticals for the PET imaging of GABA A receptors, with potential as a clinical tool for analyzing localization of the epileptogenic zone in pre-surgical evaluations of drug-resistant temporal lobe epilepsy (TLE), with excellent sensitivity and anatomical resolution [ 25 , 32 , 33 ].…”

Identification of Hepatic Metabolites of [¹⁸F]Flumazenil and Evaluation of its Application in Neuroimaging

“…including the benzodiazepine binding site. Upon receiving a signal from GABA, a chloride channel is opened that allows the entry of Cl-into the nerve cells, thereby reducing the intracellular potential of GABAA (type A) receptors [5,11,12]. GABA is the major inhibitory neurotransmitter in the central nervous system (CNS), and its receptors are widely distributed throughout the mammalian host.…”

“…Previous pre-clinical studies have suggested that an increased synaptic GABA concentration enhances the affinity of GABAA receptors for benzodiazepine ligands [16,17]. Flumazenil antagonizes the benzodiazepine binding site of the GABA/benzodiazepine receptor complex (BZR) in the CNS, thereby preventing chloride channel opening and inhibiting neuronal hyperpolarization [11,18]. Intravenous flumazenil treatment is used to recover from anesthesia and reduce the hypnotic and sedative effects of benzodiazepines via competitive inhibition at the benzodiazepine binding site on the GABAA receptor.…”