Brain p3-Alcß peptide restores neuronal viability impaired by Alzheimer's amyloid ß-peptide.

We propose a new therapeutic strategy for Alzheimer's disease (AD). Brain peptide p3-Alcß37 is generated from the neuronal protein alcadein ß through cleavage of γ-secretase, similar to the generation of amyloid ß (Aß) derived from Aß-protein precursor/APP. Neurotoxicity by Aß oligomers (Aßo) is the prime cause prior to the loss of brain function in AD. We found that p3-Alcß37 and its shorter peptide p3-Alcß9-19 enhanced the mitochondrial activity of neurons and protected neurons against Aßo-induced toxicity. This is due to the suppression of the Aßo-mediated excessive Ca2+ influx into neurons by p3-Alcß. Successful transfer of p3-Alcß9-19 into the brain following peripheral administration improved the mitochondrial viability in the brain of AD mice model, in which the mitochondrial activity is attenuated by increasing the neurotoxic human Aß42 burden, as revealed through brain PET imaging to monitor mitochondrial function. Because mitochondrial dysfunction is common in the brain of AD patients alongside increased Aß and reduced p3-Alcß37 levels, the administration of p3-Alcß9-19 may be a promising treatment for restoring, protecting, and promoting brain functions in patients with AD.

Early distribution of18 F-labeled AAV9 vectors in the cerebrospinal fluid after intracerebroventricular or intracisternal magna infusion in non-human primates.

BACKGROUND: The delivery of adeno-associated virus (AAV) vectors via the cerebrospinal fluid (CSF) has emerged as a valuable method for widespread transduction in the central nervous system. Although infusion into the cerebral ventricles is a common protocol in preclinical studies of small animals, the cisterna magna has been recognized as an alternative target for clinical studies because it can be reached in a less invasive manner using an intrathecal catheter via the subarachnoid space from a lumbar puncture. METHODS: We evaluated the early distribution of fluorine-18-labeled AAV9 vectors infused into the lateral ventricle or cisterna magna of four non-human primates using positron emission tomography. The expression of the green fluorescent protein was immunohistochemically determined. RESULTS: In both approaches, the labeled vectors diffused into the broad arachnoid space around the brain stem and cervical spinal cord within 30 min. Both infusion routes efficiently transduced neurons in the cervical spinal cord. CONCLUSIONS: For gene therapy that primarily targets the cervical spinal cord and brainstem, such as amyotrophic lateral sclerosis, cisterna magna infusion would be a feasible and effective administration method.

In vivo alterations of mitochondrial activity and amyloidosis in early-stage senescence-accelerated mice: a positron emission tomography study.

PURPOSE: While marked reductions in neural activity and mitochondrial function have been reported in Alzheimer's disease (AD), the degree of mitochondrial activity in mild cognitive impairment (MCI) or early-stage AD remains unexplored. Here, we used positron emission tomography (PET) to examine the direct relationship between mitochondrial activity (18F-BCPP-EF) and ß-amyloid (Aß) deposition (11C-PiB) in the same brains of senescence-accelerated mouse prone 10 (SAMP10) mice, an Aß-developing neuroinflammatory animal model showing accelerated senescence with deterioration in cognitive functioning similar to that in MCI. METHODS: Five- to 25-week-old SAMP10 and control SAMR1 mice, were used in the experiments. PET was used to measure the binding levels (standard uptake value ratios; SUVRs) of [18F]2-tert-butyl-4-chloro-5-2H-pyridazin-3-one (18F-BCPP-EF) for mitochondrial complex 1 availability, and 11C-PiB for Aß deposition, in the same animals, and immunohistochemistry for ATPB (an ATP synthase on the mitochondrial inner membrane) was also performed, to determine changes in mitochondrial activity in relation to amyloid burden during the early stage of cognitive impairment. RESULTS: The SUVR of 18F-BCPP-EF was significantly lower and that of 11C-PiB was higher in the 15-week-old SAMP10 mice than in the control and 5-week-old SAMP10 mice. The two parameters were found to negatively correlate with each other. The immunohistochemical analysis demonstrated temporal upregulation of ATPB levels at 15-week-old, but decreased at 25 week-old SAMP10 mice. CONCLUSION: The present results provide in vivo evidence of a decrease in mitochondrial energy production and elevated amyloidosis at an early stage in SAMP10 mice. The inverse correlation between these two phenomena suggests a concurrent change in neuronal energy failure by Aß-induced elevation of neuroinflammatory responses. Comparison of PET data with histological findings suggests that temporal increase of ATPB level may not be neurofunctionally implicated during neuropathological processes, including Aß pathology, in an animal model of early-phase AD spectrum disorder.

Head-to-head comparison of (R)-[11C]verapamil and [18F]MC225 in non-human primates, tracers for measuring P-glycoprotein function.

PURPOSE: P-glycoprotein (P-gp) function is altered in several brain disorders; thus, it is of interest to monitor the P-gp function in vivo using PET. (R)-[11C]verapamil is considered the gold standard tracer to measure the P-gp function; however, it presents some drawbacks that limit its use. New P-gp tracers have been developed with improved properties, such as [18F]MC225. This study compares the characteristics of (R)-[11C]verapamil and [18F]MC225 in the same subjects. METHODS: Three non-human primates underwent 4 PET scans: 2 with (R)-[11C]verapamil and 2 with [18F]MC225, at baseline and after P-gp inhibition. The 30-min PET data were analyzed using 1-Tissue Compartment Model (1-TCM) and metabolite-corrected plasma as input function. Tracer kinetic parameters at baseline and after inhibition were compared. Regional differences and simplified methods to quantify the P-gp function were also assessed. RESULTS: At baseline, [18F]MC225 VT values were higher, and k2 values were lower than those of (R)-[11C]verapamil, whereas K1 values were not significantly different. After inhibition, VT values of the 2 tracers were similar; however, (R)-[11C]verapamil K1 and k2 values were higher than those of [18F]MC225. Significant regional differences between tracers were found at baseline, which disappeared after inhibition. The positive slope of the SUV-TAC was positively correlated to the K1 and VT of both tracers. CONCLUSION: [18F]MC225 and (R)-[11C]verapamil show comparable sensitivity to measure the P-gp function in non-human primates. Moreover, this study highlights the 30-min VT as the best parameter to measure decreases in the P-gp function with both tracers. [18F]MC225 may become the first radiofluorinated tracer able to measure decreases and increases in the P-gp function due to its higher baseline VT.

Pharmacokinetic Modeling of (R)-[11C]verapamil to Measure the P-Glycoprotein Function in Nonhuman Primates.

(R)-[11C]verapamil is a radiotracer widely used for the evaluation of the P-glycoprotein (P-gp) function at the blood-brain barrier (BBB). Several studies have evaluated the pharmacokinetics of (R)-[11C]verapamil in rats and humans under different conditions. However, to the best of our knowledge, the pharmacokinetics of (R)-[11C]verapamil have not yet been evaluated in nonhuman primates. Our study aims to establish (R)-[11C]verapamil as a reference P-gp tracer for comparison of a newly developed P-gp positron emission tomography (PET) tracer in a species close to humans. Therefore, the study assesses the kinetics of (R)-[11C]verapamil and evaluates the effect of scan duration and P-gp inhibition on estimated pharmacokinetic parameters. Three nonhuman primates underwent two dynamic 91 min PET scans with arterial blood sampling, one at baseline and another after inhibition of the P-gp function. The (R)-[11C]verapamil data were analyzed using 1-tissue compartment model (1-TCM) and 2-tissue compartment model fits using plasma-corrected for polar radio-metabolites or non-corrected for radio-metabolites as an input function and with various scan durations (10, 20, 30, 60, and 91 min). The preferred model was chosen according to the Akaike information criterion and the standard errors (SE %) of the estimated parameters. 1-TCM was selected as the model of choice to analyze the (R)-[11C]verapamil data at baseline and after inhibition and for all scan durations tested. The volume of distribution (VT) and the efflux constant k2 estimations were affected by the evaluated scan durations, whereas the influx constant K1 estimations remained relatively constant. After P-gp inhibition (tariquidar, 8 mg/kg), in a 91 min scan duration, the whole-brain VT increased significantly up to 208% (p < 0.001) and K1 up to 159% (p < 0.001) compared with baseline scans. The k2 values decreased significantly after P-gp inhibition in all the scan durations except for the 91 min scans. This study suggests the use of K1, calculated with 1-TCM and using short PET scans (10 to 30 min), as a suitable parameter to measure the P-gp function at the BBB of nonhuman primates.

Synthesis and evaluation of N-isopropyl-p-[11C]methylamphetamine as a novel cerebral blood flow tracer for positron emission tomography.

INTRODUCTION: Increases in fasting plasma glucose (PG) levels lead to a decrease in 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) uptake in the normal brain, especially in the precuneus, resulting in an Alzheimer's disease (AD)-like uptake pattern. Therefore, patients with higher PG levels, such as those with diabetes, can be erroneously diagnosed with AD when positron emission tomography (PET) imaging is done using [18F]FDG, due to reduced uptake of [18F]FDG in the precuneus. To help avoid an erroneous diagnosis of AD due to differences in glucose metabolism, evaluating cerebral blood flow (CBF) in the brain is useful. However, current techniques such as single photon emission computed tomography (SPECT) and [15O]H2O PET have limitations regarding early diagnosis of AD because the images they produce are of low resolution. Here, we developed a novel CBF PET tracer that may be more useful than [18F]FDG for diagnosis of AD. METHODS: We synthesized and evaluated N-isopropyl-p-[11C]methylamphetamine ([11C]4) as a carbon-11-labeled analogue of the standard CBF SPECT tracer N-isopropyl-p-[123I]iodoamphetamine. Fundamental biological evaluations such as biodistribution, peripheral metabolism in mice, and brain kinetics of [11C]4 in non-human primates with PET with successive measurement of [15O]H2O were performed. RESULTS: [11C]4 was synthesized by methylation of the corresponding tributyltin precursor (2) with [11C]MeI in a palladium-promoted Stille cross-coupling reaction. The brain uptake of [11C]4 in mice peaked at 5-15 min after injection and then promptly decreased. Most radioactivity in the brain was detected in the unchanged form, although in the periphery, [11C]4 was rapidly metabolized to hydrophilic components. Acetazolamide (AZM) treatment significantly increased the brain uptake of [11C]4 without affecting the blood levels of radioactivity in mice. Preliminary kinetics analysis showed that the K1 of [11C]4 reflected regional CBF in a vehicle-treated monkey, but that the K1 did not reflect CBF in higher flow regions after AZM loading. CONCLUSION: [11C]4 is a potential novel CBF PET tracer. Further validation studies are needed before [11C]4 can be used in humans.

Pharmacokinetic Modeling of [18F]MC225 for Quantification of the P-Glycoprotein Function at the Blood-Brain Barrier in Non-Human Primates with PET.

[18F]MC225 has been developed as a weak substrate of P-glycoprotein (P-gp) aimed to measure changes in the P-gp function at the blood-brain barrier with positron emission tomography. This study evaluates [18F]MC225 kinetics in non-human primates and investigates the effect of both scan duration and P-gp inhibition. Three rhesus monkeys underwent two 91-min dynamic scans with blood sampling at baseline and after P-gp inhibition (8 mg/kg tariquidar). Data were analyzed using the 1-tissue compartment model (1-TCM) and 2-tissue compartment model (2-TCM) fits using metabolite-corrected plasma as the input function and for various scan durations (10, 20, 30, 60, and 91 min). The preferred model was chosen according to the Akaike information criterion and the standard errors (%) of the estimated parameters. For the 91-min scan duration, the influx constant K1 increased by 40.7% and the volume of distribution (VT) by 30.4% after P-gp inhibition, while the efflux constant k2 did not change significantly. Similar changes were found for all evaluated scan durations. K1 did not depend on scan duration (10 min-K1 = 0.2191 vs 91 min-K1 = 0.2258), while VT and k2 did. A scan duration of 10 min seems sufficient to properly evaluate the P-gp function using K1 obtained with 1-TCM. For the 91-min scan, VT and K1 can be estimated with a 2-TCM, and both parameters can be used to assess P-gp function.

Upregulation of cannabinoid receptor type 2, but not TSPO, in senescence-accelerated neuroinflammation in mice: a positron emission tomography study.

BACKGROUND: Microglial cells are activated in response to changes in brain homeostasis during aging, dementia, and stroke. Type 2 endocannabinoid receptors (CB2) and translocator protein 18 kD (TSPO) are considered to reflect distinct aspects of microglia-related neuroinflammatory responses in the brain. CB2 activation is considered to relate to the neuroprotective responses that may occur predominantly in the early stage of brain disorders such as Alzheimer's disease, while an increase in TSPO expression tends to occur later during neuroinflammation, in a proinflammatory fashion. However, this information was deduced from studies with different animal samples under different experimental settings. In this study, we aimed to examine the early microglial status in the inflammation occurring in the brains of senescence-accelerated mouse prone 10 (SAMP10) mice, using positron emission tomography (PET) with CB2 and TSPO tracers, together with immunohistochemistry. METHODS: Five- and 15-week-old SAMP10 mice that undergo neurodegeneration after 7 months of age were used. The binding levels of the TSPO tracer (R)-[11C]PK11195 and CB2 tracer [11C]NE40 were measured using PET in combination with immunohistochemistry for CB2 and TSPO. To our knowledge, this is the first study to report PET data for CB2 and TSPO at the early stage of cognitive impairment in an animal model. RESULTS: The standard uptake value ratios (SUVRs) of [11C]NE40 binding were significantly higher than those of (R)-[11C]PK11195 binding in the cerebral cortical region at 15 weeks of age. At 5 weeks of age, the [11C]NE40 SUVR tended to be higher than the (R)-[11C]PK11195 SUVR. The (R)-[11C]PK11195 SUVR did not significantly differ between 5- and 15-week-old mice. Consistently, immunostaining analysis confirmed the upregulation of CB2, but not TSPO. CONCLUSIONS: The use of the CB2 tracer [11C]NE40 and/or an immunohistochemical approach allows evaluation of the role of microglia in acute neuroinflammatory processes in the early stage of neurodegeneration. The present results provide in vivo evidence of different responses of two types of microglia to senescence-accelerated neuroinflammation, implying the perturbation of microglial balance by aging. Specific treatment for CB2-positive microglia might help ameliorate senescence-related neuroinflammation and the following neurodegeneration.

Sensitive and early detection of mitochondrial dysfunction in the liver of NASH model mice by PET imaging with 18F-BCPP-BF.

BACKGROUND: Nonalcoholic fatty liver disease is a common disorder that progresses from simple fatty liver (steatosis) to nonalcoholic steatohepatitis (NASH). It is thought that mitochondrial dysfunction plays a critical role in the progression of NASH. In this study, we developed a non-invasive method for early diagnosis and staging of NASH that directly measures mitochondrial complex-I (MC-I) activity in the liver of NASH model mice by positron emission tomography (PET) imaging using the novel tracer 2-tert-butyl-4-chloro-5-[6-(4-[18F]fluorobutoxy)-pyridin-3-ylmethoxy]-2H-pyridazin-3-one (18F-BCPP-BF). Liver uptake of 18F-BCPP-BF in NASH and age-matched control mice was measured as a standard uptake value over a period of 1 to 12 weeks. Histopathological evaluation of the liver tissue was performed by haematoxylin and eosin staining, and fibrosis was assessed by Masson's trichrome staining. RESULTS: Significant mitochondrial dysfunction was detected as early as 1 week after commencing the diet, and MC-I activity in the liver measured by PET was reduced by > 50% relative to that in age-matched control mice after 6 weeks. Liver uptake of 18F-BCPP-BF was low throughout the 12-week experimental period. Histopathological examination revealed that steatosis, inflammation, and ballooning progressed from 1 to 6 weeks, with fibrosis observed from 6 to 12 weeks. CONCLUSIONS: PET scans and histopathological analysis revealed that mitochondrial dysfunction in the liver contributed to the progression of NASH. PET imaging with 18F-BCPP-BF is a useful tool for detecting NASH at early stages and for monitoring therapeutic response.

Evaluation of D-isomers of 4-borono-2-18F-fluoro-phenylalanine and O-11C-methyl-tyrosine as brain tumor imaging agents: a comparative PET study with their L-isomers in rat brain glioma.

BACKGROUND: The potential of the D-isomerization of 4-borono-2-18F-fluoro-phenylalanine (18F-FBPA) to improve its target tumor to non-target normal brain tissue ratio (TBR) was evaluated in rat brain glioma and compared with those of L- and D-11C-methyl-tyrosine (11C-CMT). The L- or D-isomer of 18F-FBPA was injected into rats through the tail vein, and their whole body kinetics and distributions were assessed using the tissue dissection method up to 90 min after the injection. The kinetics of L- and D-18F-FBPA or L- and D-11C-CMT in the C-6 glioma-inoculated rat brain were measured for 90 or 60 min, respectively, using high-resolution animal PET, and their TBRs were assessed. RESULTS: Tissue dissection analyses showed that D-18F-FBPA uptake was significantly lower than that of L-18F-FBPA in the brain and abdominal organs, except for the kidney and bladder, reflecting the faster elimination rate of D-18F-FBPA than L-18F-FBPA from the blood to the urinary tract. PET imaging using 18F-FBPA revealed that although the brain uptake of D-18F-FBPA was significantly lower than that of L-18F-FBPA, the TBR of the D-isomer improved to 6.93 from 1.45 for the L-isomer. Similar results were obtained with PET imaging using 11C-CMT with a smaller improvement in TBR to 1.75 for D-11C-CMT from 1.33 for L-11C-CMT. CONCLUSIONS: The present results indicate that D-18F-FBPA is a better brain tumor imaging agent with higher TBR than its original L-isomer and previously reported tyrosine-based PET imaging agents. This improved TBR of D-18F-FBPA without any pre-treatments, such as tentative blood-brain barrier disruption using hyperosmotic agents or sonication, suggests that the D-isomerization of BPA results in the more selective accumulation of 10B in tumor cells that is more effective and less toxic than conventional L-BPA.

Effect of Oxygen Affinity of Liposome-Encapsulated Hemoglobin on Cerebral Ischemia and Reperfusion as Detected by Positron Emission Tomography in Nonhuman Primates.

We tested a hypothesis that liposome-encapsulated hemoglobin (LEH) with high oxygen (O2 ) affinity (h-LEH, P50 O2 = 10 mm Hg) may work better than LEH with low O2 affinity (l-LEH, P50 O2 = 40 mm Hg) in cerebral ischemia and reperfusion injury using positron emission tomography (PET) in primates undergoing middle cerebral artery (MCA) occlusion and reperfusion. Cerebral blood flow (CBF), O2 extract fraction (OEF), and cerebral metabolic rate of O2 (CMRO2 ) were successively determined by PET before ischemia, at 2 h of ischemia, immediately after reperfusion, and 3 h after reperfusion. Five minutes after MCA occlusion, 10 mL/kg of h-LEH (n = 6) was intravenously infused and compared with the results from previous data of monkeys treated with l-LEH (n = 6), empty liposome (n = 4), or saline (n = 8) as control. After the series of PET studies, the integrated area of cerebral infarction was determined histologically in 12 coronal brain slices. There was no significant difference in CBF, OEF, or CMRO2 up to 2 h of ischemia. A high CBF with a low OEF tended to be suppressed after reperfusion in LEH-treated monkeys. Three hours after reperfusion, the area of mild CMRO2 reduction (down to -30%) decreased (P < 0.05) and the area of mild CMRO2 increase (up to 30%) expanded in LEH-treated monkeys (P < 0.05) regardless of O2 affinity with no difference in the area of moderate-to-severe reduction (<-30%) or increase (<+30%) in CMRO2 compared to animals treated with empty liposome or saline. Distribution of CMRO2 reduction and histological damages showed that LEH mainly protected the cerebral cortex rather than basal ganglia where neuronal dendritic processes were severely lost. There was little difference between the animals treated with l-LEH or h-LEH both at 10 mL/kg or between treatment with empty liposome or saline. In conclusion, LEH was effective regardless of O2 affinity in preserving CMRO2 and in reducing the area of histological damage in the cerebral cortex, but not in basal ganglia, shortly after occlusion/reperfusion of MCA in monkey.

Effect of MPTP on Serotonergic Neuronal Systems and Mitochondrial Complex I Activity in the Living Brain: A PET Study on Conscious Rhesus Monkeys.

The objective of the present PET study was to compare the effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on serotonergic neuronal systems and mitochondrial complex I (MC-I) activity with that of dopamine in conscious rhesus monkeys (Macaca mulatta). Methods: A Parkinson disease monkey model was prepared by repeated administration of MPTP. For the PET measurements, normal and MPTP-treated conscious monkeys received an intravenous injection of 11C-DASB for serotonin transporter, 18F-MPPF for serotonin 1A receptor, 11C-PE2I for dopamine transporter, 11C-6MemTyr for dopamine synthesis, 11C-raclopride for dopamine D2 receptor, or 18F-BCPP-EF for MC-I. Serotonin and dopamine parameters were calculated using time-activity curves in the cerebellum as the input function. The total distribution volume of 18F-BCPP-EF was assessed using Logan plot graphical analysis with metabolite-corrected plasma as the input function. Results: MPTP-induced diffuse reductions in MC-I activity were observed throughout the brain, except the cerebellum. Significant reductions in the presynaptic dopamine parameters-dopamine transporter and dopamine synthesis-were detected in the striatum and substantia nigra pars compacta of MPTP-treated monkeys, whereas no significant differences in postsynaptic dopamine D2 receptor binding were observed. Serotonin transporter binding was reduced by MPTP not only in striatal regions but also in extrastriatal regions. In contrast, serotonin 1A receptor binding was unaffected by MPTP anywhere in the brain. In the cortex, the reduction of serotonin transporter binding correlated with that of MC-I. Conclusion: The results obtained by multiparametric PET measurements in a Parkinson disease monkey model demonstrated that chronic MPTP treatment induced reductions not only in the dopaminergic system in the nigrostriatal pathway but also in serotonin transporter in the cortical and subcortical regions. These results suggest that the neurotoxicity of MPTP is not exclusive to the nigrostriatal pathway, as predicted from MC-I damage in the extrastriatal regions of the brain.

In vivo TSPO and cannabinoid receptor type 2 availability early in post-stroke neuroinflammation in rats: a positron emission tomography study.

BACKGROUND: Upregulated levels of 18-kDa translocator proteins (TSPO) and type 2 endocannabinoid receptors (CB2) are considered to reflect different aspects of microglia-related neuroinflammatory responses in the brain. Relative to the increase in the TSPO expression that occurs slightly later during neuroinflammation in a proinflammatory fashion, CB2 activation is considered to relate to the neuroprotective responses that occurs predominantly at an early stage of brain disorders. These findings, however, were deduced from studies with different animal samples under different experimental settings. Here, we aimed to examined the differences in TSPO binding and CB2 availability at an early stage of stroke in the same animal using positron emission tomography (PET). METHODS: We used a total of eight Sprague-Dawley rats that underwent photothrombotic stroke surgery. The binding levels of a TSPO tracer [11C](R)PK11195 and a CB2 tracer [11C]NE40 were measured at 24 h after the surgery in the same animal using PET in combination with immunohistochemistry for CB2 and several other markers. A morphological inspection was also performed with X-ray computed tomography for small animals. RESULTS: The levels of [11C]NE40 binding potential (BPND) were significantly higher in the cerebral cortical region on the lesion side than those on the non-lesion side, whereas no difference was found in the levels of [11C](R)PK11195 BPND between hemispheres. The tracer influx index (R1) data were all reduced on the lesion side irrespective of tracers. This increase in [11C]NE40 BPND was concomitant with an elevation in CB2 expression mainly within the microglia in the peri-infarct area, as shown by immunohistochemical examinations with Iba-1, CD11b/c+, and NG2+ staining. CONCLUSIONS: The present results provide in vivo evidence of different responses of microglia occurring in the acute state of stroke. The use of the CB2 tracer [11C]NE40 allows us to evaluate the roles played by the neuroprotective aspect of microglia in acute neuroinflammatory processes.

Reduction of dopamine D2/3 receptor binding in the striatum after a single administration of esketamine, but not R-ketamine: a PET study in conscious monkeys.

R-ketamine appears to be a potent, long-lasting and safer antidepressant, relative to esketamine (S-ketamine), since it might be free of psychotomimetic side effects. Using [11C]raclopride and positron emission tomography (PET), we investigated whether esketamine and R-ketamine can affect dopamine D2/3 receptor binding in the conscious monkey brain. A single infusion of esketamine (0.5 mg/kg), but not R-ketamine (0.5 mg/kg), caused a reduction of binding availability of dopamine D2/3 receptor in the monkey striatum. This study suggests that unlike to R-ketamine, esketamine can cause dopamine release in the striatum, and that its release might be associated with psychotomimetic effects of esketamine.

Effects of acetaminophen on mitochondrial complex I activity in the rat liver and kidney: a PET study with 18F-BCPP-BF.

BACKGROUND: In the present study, 2-tert-butyl-4-chloro-5-[6-(4-18F-fluorobutoxy)-pyridin-3-ylmethoxy]-2H-pyridazin-3-one (18F-BCPP-BF), a PET probe for mitochondrial complex I (MC-I), was used to validate whether MC-I is a useful biomarker for detecting acetaminophen-induced dysfunctions in the liver and kidney. The kinetic and distribution of 18F-BCPP-BF were assessed in rats using high-resolution animal PET in vivo. The binding specificity of 18F-BCPP-BF to MC-I in the liver and kidney was confirmed by the pre-administration of rotenone, a specific MC-I inhibitor. The effects of acetaminophen on MC-I activity were assessed 2 and 24 h after the administration of vehicle or acetaminophen at a dose of 100 or 300 mg/kg. Biochemical parameters in plasma and urine were assessed 2, 6, and 24 h after the administration of vehicle or acetaminophen. RESULTS: The uptake of 18F-BCPP-BF by the liver and kidney was significantly inhibited by the pre-administration of rotenone. Two and more hours after the administration of acetaminophen, the uptake of 18F-BCPP-BF was dose-dependently reduced in the liver, even at 100 mg/kg, and in the kidney at 300 mg/kg, whereas biological parameters started to be affected 6 h or later at doses of 300 mg/kg. CONCLUSIONS: The present study demonstrated that 18F-BCPP-BF has potential as a PET probe for the quantitative imaging of hepatic and renal dysfunction as impaired MC-I activity in the early phase of the treatment for an overdose of acetaminophen in the living body with PET.

PET Imaging of Mitochondrial Complex I with 18F-BCPP-EF in the Brains of MPTP-Treated Monkeys.

UNLABELLED: (18)F-BCPP-EF was applied to assess mitochondrial complex I (MC-I) activity in the brains of Parkinson disease model monkeys prepared by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and also presynaptic dopamine parameters. METHODS: (11)C-ß-CFT for the dopamine transporter; (11)C-3,4-dihydroxy-phenyl-L-alanine (ß-(11)C-L-DOPA), L-6-(18)F-fluorodopa ((18)F-FDOPA), or 6-(11)C-methyl-m-tyrosine ((11)C-6MemTyr) for dopamine synthesis; or 2-tert-butyl-4-chrolo-5-{6-[2-(2-(18)F-fluoroethoxy)-ethoxy]-pyridin-3-ylmethoxy}-2H-pyridazin-3-one ((18)F-BCPP-EF) for MC-I was intravenously injected into normal and MPTP monkeys in order to analyze their uptake in the striatum. RESULTS: Significant reductions in presynaptic dopamine parameters and MC-I activity were detected in the striatum of MPTP monkeys. Correlations were observed between MC-I activity and dopamine transporter as well as between MC-I activity and dopamine synthesis in the striatum. The order of detectability of impaired MC-I activity was (11)C-6MemTyr >> ß-(11)C-L-DOPA > (18)F-FDOPA. CONCLUSION: (18)F-BCPP-EF has potential as a PET probe for the quantitative imaging of MC-I damage in the living brains of Parkinson disease model monkeys using PET.

Evaluation of 6-11C-Methyl-m-Tyrosine as a PET Probe for Presynaptic Dopaminergic Activity: A Comparison PET Study with ß-11C-l-DOPA and 18F-FDOPA in Parkinson Disease Monkeys.

UNLABELLED: We recently developed a novel PET probe, 6-(11)C-methyl-m-tyrosine ((11)C-6MemTyr), for quantitative imaging of presynaptic dopamine synthesis in the living brain. In the present study, (11)C-6MemTyr was compared with ß-(11)C-l-DOPA and 6-(18)F-fluoro-l-dopa ((18)F-FDOPA) in the brains of normal and Parkinson disease (PD) model monkeys (Macaca fascicularis). METHODS: PD model monkeys were prepared by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and (11)C-ß-CFT was applied to assess neuronal damage as dopamine transporter (DAT) availability. (11)C-6MemTyr, ß-(11)C-l-DOPA, or (18)F-FDOPA was injected with and without carbidopa, a specific inhibitor of peripheral aromatic L-amino acid decarboxylase. In normal and PD monkeys, the dopamine synthesis rates calculated using PET probes were analyzed by the correlation plot with DAT availability in the striatum. RESULTS: In normal monkeys, whole-brain uptake of ß-(11)C-l-DOPA and (18)F-FDOPA were significantly increased by carbidopa at the clinical dose of 5 mg/kg by mouth. In contrast, (11)C-6MemTyr was not affected by carbidopa at this dose, and the metabolic constant value of (11)C-6MemTyr in the striatum was significantly higher than those of the other 2 PET probes. Significant reduction of the presynaptic DAT availability in the striatum was detected in MPTP monkeys, and correlation analyses demonstrated that (11)C-6MemTyr could detect dopaminergic damage in the striatum with much more sensitivity than the other PET probes. CONCLUSION: (11)C-6MemTyr is a potential PET probe for quantitative imaging of presynaptic dopamine activity in the living brain with PET.

Comparing α7 nicotinic acetylcholine receptor binding, amyloid-ß deposition, and mitochondria complex-I function in living brain: A PET study in aged monkeys.

This study was aimed to assess the correlations among α7 nicotinic acetylcholine receptor (α7-nAChR) binding, amyloid-ß (Aß) deposition, and mitochondrial complex I (MC-I) activity in the brain of aged monkeys (Macaca mulatta). Positron emission tomography (PET) measurements with [(11) C](R)-MeQAA, [(11) C]PIB, and [(18) F]BCPP-EF were conducted in monkeys in a conscious condition. [(11) C](R)-MeQAA binding was analyzed by a simplified reference tissue model to calculate nondisplaceable binding potential (BPND), [(11) C]PIB uptake was calculated by standard uptake value ratio (SUVR), and [(18) F]BCPP-EF binding was determined by Logan graphical analysis to calculate total distribution volume (VT) with arterial blood sampling. Higher brain uptake was determined in the thalamus, hippocampus, striatum, and cortical regions for [(11) C](R)-MeQAA, while being lower in the cerebellum. Significant age-related reduction of [(11) C](R)-MeQAA binding to α7-nAChR was determined only in the occipital cortex. The plot of Vt of [(18) F]BCPP-EF against BPND of [(11) C](R)-MeQAA indicated a significant negative correlation in the hippocampus and cortical regions in aged animals. Plotting of SUVR of [(11) C]PIB against BPND of [(11) C](R)-MeQAA showed a positive correlation. The in vivo binding of [(11) C](R)-MeQAA could reflect the upregulation of α7-nAChR induced by neurodegenerative damage determined by Aß deposition as well as impaired MC-I activity in living brain.

Synthesis of 6-[(11)C]methyl-m-tyrosine ([(11)C]6MemTyr) for dopamine synthesis imaging in living brain using PET.

A novel PET probe, 6-[(11)C]methyl-m-tyrosine ([(11)C]6MemTyr), was developed for quantitative imaging of presynaptic dopamine (DA) synthesis in the living brain using positron emission tomography (PET). This probe was evaluated by comparison with conventional 6-[(18)F]fluoro-l-dopa ([(18)F]FDOPA). [(11)C]6MemTyr was labeled using rapid Pd(0)-mediated C-[(11)C]methylation with [(11)C]methyl iodide. The synthesis time was only 35min, and its radiochemical yield was 76%, with radiochemical purity of >99%. PET measurements indicated that [(11)C]6MemTyr could image presynaptic DA synthesis in the striatum of living monkey brain, providing much higher contrast between the striatum and the cerebellum than that with [(18)F]FDOPA.

Comparing amyloid-ß deposition, neuroinflammation, glucose metabolism, and mitochondrial complex I activity in brain: a PET study in aged monkeys.

PURPOSE: The aim of the present study was to compare amyloid-ß (Aß) deposition, translocator protein (TSPO) activity, regional cerebral metabolic rate of glucose (rCMRglc), and mitochondrial complex I (MC-I) activity in the brain of aged monkeys. METHODS: PET scans with (11)C-PIB (Aß), (18)F-BCPP-EF (MC-I), (11)C-DPA-713 (TSPO), and (18)F-FDG (rCMRglc) were performed in aged monkeys (Macaca mulatta) in the conscious state and under isoflurane anaesthesia. (11)C-PIB binding to Aß and (11)C-DPA-713 binding to TSPO were evaluated in terms of standard uptake values (SUV). The total volume of distribution (V T) of (18)F-BCPP-EF and rCMRglc with (18)F-FDG were calculated using arterial blood sampling. RESULTS: Isoflurane did not affect MC-I activity measured in terms of (18)F-BCPP-EF uptake in living brain. There was a significant negative correlation between (18)F-BCPP-EF binding (V T) and (11)C-PIB uptake (SUVR), and there was a significant positive correlation between (11)C-DPA-713 uptake (SUV) and (11)C-PIB uptake. In contrast, there was no significant correlation between rCMRglc ratio and (11)C-PIB uptake. CONCLUSION: (18)F-BCPP-EF could be a potential PET probe for quantitative imaging of impaired MC-I activity that is correlated with Aß deposition in the living brain.