Chyng-Yann Shiue

Background. [¹⁸F]FEPPA is a potent TSPO imaging agent that has been found to be a potential tracer for imaging neuroinflammation. In order to fulfill the demand of this tracer for preclinical and clinical studies, we have developed a one-pot automated synthesis with simplified HPLC purification of this tracer, which was then used for PET imaging of neuroinflammation in fine particulate matter- (PM2.5-) exposed rats. Results. Using this automated synthesis method, the RCY of the [¹⁸F]FEPPA was [ ] ([ ], EOB) in a synthesis time of [ ] min from EOB. The radiochemical purity and molar activities were greater than 99% and [ ] GBq/ μmol (EOS, [ ]), respectively. The quality of the [¹⁸F]FEPPA synthesized by this method met the U.S. Pharmacopoeia (USP) criteria. The stability test showed that the [¹⁸F]FEPPA was stable at [ ]°C for up to 4 hr after the end of synthesis (EOS). Moreover, microPET imaging showed that increased tracer activity of [¹⁸F]FEPPA in the brain of PM2.5-exposed rats ([ ]) were higher than that of normal controls ([ ]) and regional-specific. Conclusions. Using the improved semipreparative HPLC purification, [¹⁸F]FEPPA has been produced in high quantity, high quality, and high reproducibility and, for the first time, used for PET imaging the effects of PM2.5 in the rat brain. It is ready to be used for imaging inflammation in various clinical or preclinical studies, especially for nearby PET centers without cyclotrons.

Bezafibrate, a pan-peroxisome proliferator-activated receptor (PPAR) agonist, reportedly attenuated tau pathology in a transgenic mouse model of primary tauopathy. Since tau pathology is a neuropathological hallmark of Alzheimer’s disease (AD), bezafibrate may be a potential drug for the treatment of AD. However, no study has investigated its effects in AD models. Thus, we aimed to evaluate whether bezafibrate has neuroprotective effects in a sporadic AD model induced by streptozotocin (STZ) intracerebroventricular (ICV) injection. Rats were administered STZ-ICV (3 mg/kg) followed by bezafibrate (50 mg/kg/day, intraperitoneal) for 4 weeks. Behavior tests and positron emission tomography (PET) were performed to evaluate longitudinal changes in cognitive function, tau pathology, and cerebral glucose metabolism. Immunofluorescence staining was performed to assess neuronal survival and microglial accumulation. STZ-ICV administration induced significant cognitive impairment and substantial neuronal loss, tau pathology, glucose hypometabolism, and microgliosis in the cortex and hippocampus, while bezafibrate effectively attenuated these abnormalities. This study demonstrated that bezafibrate has long-lasting neuroprotective effects in a sporadic AD model. Our data indicate that the neuroprotective effects of bezafibrate might be associated with its ability to ameliorate tau pathology, brain glucose hypometabolism, and neuroinflammation. These findings suggest that bezafibrate is a potential multi-target drug candidate for the treatment of AD.

Intra-striatal transplantation of fetal ventral mesencephalic (VM) tissue has a therapeutic effect on patients with Parkinson’s disease (PD). Sertoli cells (SCs) possess immune-modulatory properties that benefit transplantation. We hypothesized that co-graft of SCs with VM tissue can attenuate rejection. Hemi-parkinsonian rats were generated by injecting 6-hydroxydopamine into the right medial forebrain bundle of Sprague Dawley (SD) rats. The rats were then intrastriatally transplanted with VM tissue from rats or pigs (rVM or pVM), with/without a co-graft of SCs (rVM+SCs or pVM+SCs). Recovery of dopaminergic function and survival of the grafts were evaluated using the apomorphine-induced rotation test and small animal-positron emission tomography (PET) coupled with [¹⁸F] DOPA or [¹⁸F] FE-PE2I, respectively. Immunohistochemistry (IHC) examination was used to determine the survival of the grafted dopaminergic neurons in the striatum and to investigate immune-modulatory effects of SCs. The results showed that the rVM+SCs and pVM+SCs groups had significantly improved drug-induced rotational behavior compared with the VM alone groups. PET revealed a significant increase in specific uptake ratios (SURs) of [¹⁸F] DOPA and [¹⁸F] FE-PE2I in the grafted striatum of the rVM+SCs and pVM+SCs groups as compared to that of the rVM and pVM groups. SC and VM tissue co-graft led to better dopaminergic (DA) cell survival. The co-grafted groups exhibited lower populations of T-cells and activated microglia compared to the groups without SCs. Our results suggest that co-graft of SCs benefit both xeno- and allo-transplantation of VM tissue in a PD rat model. Use of SCs enhanced the survival of the grafted dopaminergic neurons and improved functional recovery. The enhancement may in part be attributable to the immune-modulatory properties of SCs. In addition, [¹⁸F]DOPA and [¹⁸F]FE-PE2I coupled with PET may provide a feasible method for in vivo evaluation of the functional integrity of the grafted DA cell in parkinsonian rats.

Background: Methamphetamine (METH)-associated alterations in the striatal dopamine (DA) system or dopamine transport (DAT) have been identified in clinical and preclinical studies with positron emission tomography (PET) imaging but have not been well correlated with in vivo serotonin transporter (SERT) availability due to the lack of appropriate imaging agents to assess SERTs. N,N-dimethyl-2-(2-amino-4-[¹⁸F]-fluorophenylthio) benzylamine (4-[¹⁸F]-ADAM) has been developed by our group and validated for its high affinity and selectivity for SERTs, allowing the in vivo examination of SERT density, location, and binding function. The aims of this study were to investigate the potential of SERT imaging using 4-[¹⁸F]-ADAM PET to estimate the long-lasting effects of METH-induced serotonergic neurotoxicity, and further determine whether a correlative relationship exists between SERT availability/activity and tyrosine hydroxylase (TH) activity in various brain regions due to the long-lasting consequences of METH treatment. Results: Male rats received four administrations of METH (5 or 10 mg/kg, s.c.) or saline (1 ml/kg, s.c.) at 1-h intervals. At 30 days post-administration, in vivo SERT availability and activity were measured by 4-[¹⁸F]ADAM PET imaging. In contrast to the controls, the uptake of 4-[¹⁸F]ADAM in METH-treated mice was significantly reduced in a dose-dependent manner in the midbrain, followed by the hypothalamus, thalamus, striatum, hippocampus, and frontal cortex. The regional effects of METH on TH activity were assessed by quantitative immunohistochemistry and presented as integrated optical density (IOD). A significant decrease in TH immunostaining and IOD ratios was seen in the caudate, putamen, nucleus accumbens, substantia nigra pars compacta, and substantia nigra pars reticulata in the METH-treated rats compared to controls. Conclusion: The present results suggested that the long-lasting response to METH decreased the uptake of 4-[¹⁸F]-ADAM and varied regionally along with TH immunoreactivity. In addition, 4-[¹⁸F]ADAM PET could be used to detect serotonergic neuron loss and to evaluate the severity of serotonergic neurotoxicity of METH.

[¹⁸F]T807 is a potent tau protein imaging agent. In order to fulfill the demand from preclinical and clinical studies, we developed an automated one-pot two-step synthesis of this potent tau imaging agent and studied its stability, and dosimetry in mice and monkeys. We also conducted a preliminary study of this imaging agent in humans. Using this one-pot two-step method, the radiochemical yield (RCY) of [¹⁸F]T807 was 20.5 ± 6.1% (n = 15) at the end of bombardment (EOB) in a synthesis time of 70±5 min. The chemical and radiochemical purities were >90% and the specific activities were 151 ± 52 GBq/μmol. The quality of [¹⁸F]T807 synthesized by this method met the U.S. Pharmacopoeia (USP) criteria. The stability test showed that the [¹⁸F]T807 injection was stable at room temperature for up to 4 h after the end of synthesis (EOS). The estimated effective dose of the [¹⁸F]T807 injection extrapolated from monkeys was 19 μSv/MBq (n = 2), while the estimated effective doses of the [¹⁸F]T807 injection extrapolated from fasted and non-fasted mice were 123 ± 27 (n = 3) and 94 ± 19 (n = 4) μSv/MBq, respectively. This one-pot two-step automated method produced the [¹⁸F]T807 injection with high reproducibility and high quality. PET imaging and radiation dosimetry evaluation in mice and Formosan rock monkeys suggested that the [¹⁸F]T807 injection synthesized by this method is suitable for use in human PET imaging studies. Thus, this method could fulfill the demand for the [¹⁸F]T807 injection in both preclinical and clinical studies of tauopathies, especially for nearby study sites without cyclotrons.

Serotonin (5-HT) plays a crucial role in modulating the afferent fiber discharge rate in the inferior colliculus, auditory cortex, and other nuclei of the ascending auditory system. Resveratrol, a natural polyphenol phytoalexin, can inhibit serotonin transporters (SERT) to increase synaptic 5-HT levels. In this study, we investigated the effects of resveratrol on noise-induced damage in the serotonergic system. Male Sprague-Dawley rats were anaesthetized and exposed to an 8-kHz tone at 116 dB for 3.5 h. Resveratrol (30 mg/kg, intraperitoneal injection [IP]) and citalopram (20 mg/kg, IP), a specific SERT inhibitor used as a positive control, were administered once a day for four consecutive days, with the first treatment occurring 2 days before noise exposure. Auditory brainstem response testing and positron emission tomography (PET) with N,N-dimethyl-2-(2-amino-4-[¹⁸F]fluorophenylthio)benzylamine (4-[¹⁸F]-ADAM, a specific radioligand for SERT) were used to evaluate functionality of the auditory system and integrity of the serotonergic system, respectively, before and after noise exposure. Finally, immunohistochemistry was performed 1 day after the last PET scan. Our results indicate that noise-induced serotonergic fiber loss occurred in multiple brain regions including the midbrain, thalamus, hypothalamus, striatum, auditory cortex, and frontal cortex. This noise-induced damage to the serotonergic system was ameliorated in response to treatment with resveratrol and citalopram. However, noise exposure increased the hearing threshold in the rats regardless of drug treatment status. We conclude that resveratrol has protective effects against noise-induced loss of SERT.

Suicide is an important issue in the military service, since it can influence military morale and create dangerous situations for other personnel. The serotonin transporter (SERT) has been suggested to be involved in the pathophysiology of depression and suicidal behaviours. The aims of this study were to examine whether the brain SERT availability differs between military conscripts with depression and control subjects, and whether suicidal ideation is correlated with SERT availability. We used N,N-dimethyl-2-(2-amino-4-[(18)F]-fluorophenylthio)benzylamine (4-[(18)F]-ADAM) as a radioligand for positron emission tomography (PET) imaging. All participants completed the Hamilton Depression Rating Scale and Beck Scale for Suicide Ideation (BSS) prior to PET imaging. The effect of major depression and BSS scores had an interaction on SERT availability. After adjusting for the BSS score, subjects with depression had lower SERT availability than control subjects (F1,17 = 23.85, P < 0.001). A positive correlation between SERT availability and BSS scores was observed in the depression group (F1,8 = 30.67, P = 0.001). The status of depression and intensity of suicidal ideation exert opposite effects on SERT availability. The extent of suicidal ideation may moderate the reduction effect in SERT binding observed in major depression in male military conscripts.