Chyng-Yann Shiue

Characterization of 4-[ 18F]-ADAM as an imaging agent for SERT in non-human primate brain using PET: A dynamic study

INTRODUCTIONnSerotonin transporter (SERT) has been associated with many psychiatric diseases. This study investigated the biodistribution of a serotonin transporter imaging agent, N,N-dimethyl-2-(2-amino-4-(18)F-fluorophenylthio)benzylamine (4-[(18)F]-ADAM), in nonhuman primate brain using positron emission tomography (PET).nnnMETHODSnSix and four Macaca cyclopis monkeys were used to determine the transit time (i.e., time necessary to reach biodistribution equilibrium) and the reproducibility of 4-[(18)F]-ADAM biodistribution in the brain, respectively. The sensitivity and specificity of 4-[(18)F]-ADAM binding to SERT were evaluated in one monkey challenged with different doses of fluoxetine and one monkey treated with 3,4-methylendioxymethamphetamine (MDMA). Dynamic PET imaging was performed for 3 h after 4-[(18)F]-ADAM intravenous bolus injection. The specific uptake ratios (SURs) in the midbrain (MB), thalamus (TH), striatum (ST) and frontal cortex (FC) were calculated.nnnRESULTSnThe distribution of 4-[(18)F]-ADAM reached equilibrium 120-150 min after injection. The mean SURs were 2.49 ± 0.13 in MB, 1.59 ± 0.17 in TH, 1.35 ± 0.06 in ST and 0.34 ± 0.03 in FC, and the minimum variability was shown 120-150 min after 4-[(18)F]-ADAM injection. Using SURs and intraclass coefficient of correlation, the test/retest variability was under 8% and above 0.8, respectively, in SERT-rich areas. Challenge with fluoxetin (0.75-2 mg) dose-dependently inhibited the SURs in various brain regions. 4-[(18)F]-ADAM binding was markedly reduced in the brain of an MDMA-treated monkey compared to that in brains of normal controls.nnnCONCLUSIONn4-[(18)F]-ADAM appears to be a highly selective radioligand for imaging SERT in monkey brain.

Investigating the effects of noise-induced hearing loss on serotonin transporters in rat brain using 4-[18F]-ADAM/small animal PET.

The serotonin transporter (SERT) is an important marker of the status of serotonergic neurons. The main function of SERT is to regulate the serotonin concentration in the synapse. Recent studies have shown that SERT is expressed in the central auditory pathway and may play a role in the auditory process. However, little is known about the effects of noise on the cerebral serotonin system. In this study, we explored the status of brain SERT in a rat model of noise-induced hearing loss using 4-[(18)F]-ADAM (a SERT imaging agent) and small animal positron emission tomography (PET) imaging. Male Sprague Dawley rats were exposed to an 8 kHz noise at 118 dB sound pressure level for 3.5h. An auditory brainstem response test and 4-[(18)F]-ADAM/small animal PET were performed at different time points after noise exposure. The specific uptake ratios (SURs) for 4-[(18)F]-ADAM were calculated from the PET imaging data in six brain regions. Immunohistochemistry and surface preparation of the cochleae were performed 30 days after noise exposure. Our data clearly showed that the hearing and cochlear outer hair cells of the rats were lost after noise exposure. In the PET study, the SURs of SERT were markedly reduced by 35%-58% in various brain regions one day after noise exposure. The decrement remained on days 8 and 15 and was approximately 26%-48% on day 29. The distribution and intensity of SERT immunostaining in the brain paralleled the PET imaging data. These results suggest that noise-induced hearing loss involves a reduction in SERT expression in various regions of the rat brain and that changes in SERT are detectable by 4-[(18)F]-ADAM/small animal PET in vivo.

PET imaging of serotonin transporters with 4-[18F]-ADAM in a Parkinsonian rat model.

This study was undertaken to address the effects of fetal mesencephalic tissue transplantation on the serotonin system in a rat model of Parkinsons disease (PD) while also investigating the usefulness of 4-[18F]-ADAM (a serotonin transporter imaging agent) coupled with micro-PET for imaging serotonin transporters (SERTs). A PD model was induced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle of the nigrostriatal pathway, while cell transplantation was performed via intrastriatal injection of mesencephalic brain tissue dissected from embryonic (E14) rats. The 4-[18F]-ADAM/micro-PET scanning was performed following both 6-OHDA lesioning and transplantation. Immunohistochemistry (IHC) studies were also performed following the final PET scan, and the results were compared to show a 17–43% decrease in the specific uptake ratio (SUR) and a 23–52% decrease in serotonin transporter immunoreactivity (SERT-ir) within various brain regions on the lesioned side. The number of methamphetamine-induced rotations also decreased significantly at the 4th week postgraft. In addition, striatal SUR and the SERT-ir levels were restored to 77% and 83% 5 weeks postgraft. These results suggest that Parkinsons disease also affects the serotonergic system, while both the dopaminergic and serotonergic systems can be partially restored in a rat model of PD after E14 mesencephalic tissue transplantation. In addition, we have also determined that 4-[18F]-ADAM/micro-PET can be used to detect serotonergic neuron loss, monitor the progress of Parkinsons disease, and oversee the effectiveness of therapy.

Suicidal ideation modulates the reduction in serotonin transporter availability in male military conscripts with major depression: A 4-[18F]-ADAM PET study

Objectives. 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. Methods.We used N,N-dimethyl-2-(2-amino-4-[18F]-fluorophenylthio)benzylamine (4-[18F]-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. Results. 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. Conclusions. The extent of suicidal ideation may moderate the reduction effect in SERT binding observed in major depression in male military conscripts.

Evaluation of brain SERT occupancy by resveratrol against MDMA-induced neurobiological and behavioral changes in rats: A 4-[18F]-ADAM/small-animal PET study

The misuse of 3,4-methylenedioxymethamphetamine (MDMA) has drawn a growing concern worldwide for its psychophysiological impacts on humans. MDMA abusers are often accompanied by long-term serotonergic neurotoxicity, which is associated with reduced density of cerebral serotonin transporters (SERT) and depressive disorders. Resveratrol (RSV) is a natural polyphenolic phytoalexin that has been known for its antidepressant and neuroprotective effects. However, biological targets of RSV as well as its neuroprotective effects against MDMA remained largely unknown. In this study, we examined binding potency of RSV and MDMA to SERT using small-animal positron emission tomography (PET) with the SERT radioligand, N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM) and investigated the protection of RSV against the acute and long-term adverse effects of MDMA. We found that RSV exhibit binding potentials to SERT in vivo in a dose-dependent manner with variation among brain regions. When the MDMA-treated rats (10mg/kg, s.c.) were co-injected with RSV (20mg/kg, i.p.) twice daily for 4 consecutive days, MDMA-induced acute elevation in plasma corticosterone was significantly reduced. Further, 4-[(18)F]-ADAM PET imaging revealed that RSV protected against the MDMA-induced decrease in SERT availability in the midbrain and the thalamus 2 weeks following the co-treatment. The PET data were comparable to the observation from the forced swim test that RSV sufficiently ameliorated the depressive-like behaviors of the MDMA-treated rats. Together, these findings suggest that RSV is a potential antidepressant and may confer protection against neurobiological and behavioral changes induced by MDMA.

PET Imaging of Serotonin Transporters with 4-[18F]-ADAM in a Parkinsonian Rat Model with Porcine Neural Xenografts:

Parkinsons disease (PD) is a neurodegenerative disease characterized by a loss of dopaminergic neurons in the nigrostriatal pathway. Apart from effective strategies to halt the underlying neuronal degeneration, cell replacement now offers novel prospects for PD therapy. Porcine embryonic neural tissue has been considered an alternative source to human fetal grafts in neurodegenerative disorders because its use avoids major practical and ethical issues. This study was undertaken to evaluate the effects of embryonic day 27 (E27) porcine mesencephalic tissue transplantation in a PD rat model using animal positron emission tomography (PET) coupled with 4-[18F]-ADAM, a serotonin transporter (SERT) imaging agent. The parkinsonian rat was induced by injecting 6-hydroxydopamine into the medial forebrain bundle (MFB) of the right nigrostriatal pathway. The apomorphine-induced rotation behavioral test and 4-[18F]-ADAM/animal PET scanning were carried out following 6-OHDA lesioning. At the second week following 6-OHDA lesioning, the parkinsonian rat rotates substantially on apomorphine-induced contralateral turning. In addition, the mean striatal-specific uptake ratio (SUR) of 4-[18F]-ADAM decreased by 44%. After transplantation, the number of drug-induced rotations decreased markedly, and the mean SUR of 4-[18F]-ADAM and the level of SERT immunoreactivity (SERT-ir) in striatum were partially restored. The mean SUR level was restored to 71% compared to that for the contralateral intact side, which together with the abundant survival of tyrosine hydroxylase (TH) neurons accounted for functional recovery at the fourth week postgraft. In regard to the extent of donor-derived cells, we found the neurons of the xenografts from E27 transgenic pigs harboring red fluorescent protein (RFP) localized with TH-ir cells and SERT-ir in the grafted area. Thus, transplanted E27 porcine mesencephalic tissue may restore dopaminergic and serotonergic systems in the parkinsonian rat. The 4-[18F]-ADAM/animal PET can be used to detect serotonergic neuron loss in PD and monitor the efficacy of therapy.

KA-bridged transplantation of mesencephalic tissue and olfactory ensheathing cells in a Parkinsonian rat model

The pathology of Parkinsons disease (PD) results mainly from nigrostriatal pathway damage. Unfortunately, commonly used PD therapies do not repair the disconnected circuitry. It has been reported that using kainic acid (KA, an excitatory amino acid) in bridging transplantation may be useful to generate an artificial tract and reconstruct the nigrostriatal pathway in 6‐hydroxydopamine (6‐OHDA) lesioned rats. In this study, we used KA bridging and a co‐graft of rat olfactory ensheathing cells (OECs) and rat E14 embryonic ventral mesencephalic (VM) tissue to restore the nigrostriatal pathway of the PD model rats. The methamphetamine‐induced rotational behaviour, 4‐[18F]–ADAM (a selectively serotonin transporter radioligand)/micro‐PET imaging, and immunohistochemistry were used to assess the effects of the transplantation. At 9 weeks post‐grafting in PD model rats, the results showed that the PD rats undergoing VM tissue and OECs co‐grafts (VM–OECs) exhibited better motor recovery compared to the rats receiving VM tissue transplantation only. The striatal uptake of 4‐[18F]–ADAM and tyrosine hydroxylase immunoreactivity (TH‐ir) of the grafted area in the VM–OECs group were also more improved than those of the VM alone group. These results suggested that OECs may enhance the survival of the grafted VM tissue and facilitate the recovery of motor function after VM transplantation. Moreover, OECs possibly promote the elongation of dopaminergic and serotonergic axon in the bridging graft. Copyright

Fully automated one-pot two-step synthesis of 4-[18F]-ADAM, a potent serotonin transporter imaging agent

INTRODUCTIONnN,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM, 2) is a potent serotonin transporter (SERT) imaging agent. In order to fulfill the demand of clinical studies, we have developed a fully automated one-pot two-step synthesis of this potent SERT imaging agent.nnnMETHODSnThe 4-[(18)F]-ADAM (2) was synthesized using a commercially available GE TRACERlab FN module. Briefly, the precursor, N,N-dimethyl-2-(2,4-dinitrophenylthio) benzylamine (1) in DMSO was reacted with K[(18)F]/K2.2.2 in a glassy carbon reaction vessel at 120°C for 7.5min followed by reduction of the intermediate with NaBH4/Cu(OAc)2 in EtOH in the same vessel at 80°C for 20min. The reaction mixture was then purified with high-performance liquid chromatography (HPLC) and solid phase extraction (SPE) to give (2). The quality of (2) synthesized by this method was verified by HPLC and TLC as compared to its authentic sample synthesized by two-pot two-step method.nnnRESULTSnUsing this automated one-pot two-step method, the radiochemical yield (RCY) of (2) was 2.5±0.8% (n=12, EOS) in a synthesis time of 100±6min from EOB with a specific activity of 4.4±1.9Ci/μmol (n=12, EOS). Radioligand (2) was stable over 4h at room temperature.nnnCONCLUSIONSnThis fully automated one-pot two-step synthetic method using a commercially available GE TRACERlab FN module could simplify the synthesis of 4-[(18)F]-ADAM (2) and fulfill its demand for both animal and human studies, especially for study sites without a cyclotron.