In Vivo Expression of Cyclooxygenase-1 in Activated Microglia and Macrophages During Neuroinflammation Visualized by PET with ¹¹C-Ketoprofen Methyl Ester

Abstract

Cyclooxygenase (COX)-1 and -2 are prostanoid-synthesizing enzymes that play important roles in the regulation of neuroinflammation and in the development of neurodegenerative disorders. However, the specific functions of these isoforms are still unclear. We recently developed 11 C-labeled ketoprofen methyl ester as a PET probe that targets the COXs for imaging neuroinflammation, though its responsible isoform is yet to be determined. In the present study, we performed ex vivo and in vivo imaging studies with 11 C-ketoprofen methyl ester and determined the contributions of the COX isoforms during the neuroinflammatory process. Methods: To identify the COX isoform responsible for 11 C-ketoprofen methyl ester in the brain, we examined the ex vivo autoradiography of 11 C-ketoprofen methyl ester using COX-deficient mice. Time-dependent changes in accumulation of 11 C-ketoprofen methyl ester during the neuroinflammatory process were evaluated by PET in rats with hemispheric neuroinflammation induced by intrastriatal injection of lipopolysaccharide or quinolinic acid. In both rat models, cell-type specificity of COX isoform expression during neuroinflammation was identified immunohistochemically. Results: Ex vivo autoradiographic analysis of COX-deficient mice revealed a significant reduction of 11 C-ketoprofen methyl ester accumulation only in COX-1-deficient mice, not COX-2-deficient mice. PET of rats after intrastriatal injection of lipopolysaccharide showed a significant increase in accumulation of 11 C-ketoprofen methyl ester in the inflamed area. This increase was evident at the early phase of 6 h, peaked at day 1, and then returned to basal levels by day 7. In addition, immunohistochemical analysis revealed that the population of activated microglia and macrophages was elevated at the early phase with COX-1 expression but not COX-2. A significant increase in 11 C-ketoprofen methyl ester accumulation was also observed at day 1 after intrastriatal injection of quinolinic acid, with increased COX-1-expressing activated microglia and macrophages. Conclusion: We have identified 11 C-ketoprofen methyl ester as a COX-1-selective PET probe, and using this, we have also demonstrated a time-dependent expression of COX-1 in activated microglia and macrophages during the neuroinflammatory process in the living brain. Thus, COX-1 may play a crucial role in the pathology of neuroinflammation and might be a critical target for the diagnosis and therapy of neurodegenerative disorders.

Detection of Cyclooxygenase-1 in Activated Microglia During Amyloid Plaque Progression: PET Studies in Alzheimer’s Disease Model Mice

“…Importantly, expression of COX-1 was observed in activated microglia, which were tightly surrounded and enclosed by amyloid plaques. We previously reported that the expression level of COX-1 was constitutive and was not changed even in the lipopolysaccharideinduced inflamed area of the brain with activated microglia (8). Considering these results from our study, (S)-11 C-KTP-Me could detect the increased numbers of activated microglia that is closely associated with development of Ab plaques in AD progression.…”

“…11 C-KTP-Me is promptly and almost completely hydrolyzed to acid form, 11 C-KTP, in rat brain within 5 min after the intravenous injection and can be used with PET to visualize time-dependent changes in COX-1 in activated microglia during neuroinflammatory processes (7,8). This finding provided evidence that COX-1 plays a critical role in microglial activation during acute neuroinflammation in vivo.…”

“…4A). To identify the cellular origin of (S)-11 C-KTP-Me accumulation in APP-Tg mice, we performed triple immunostaining for COX-1 or COX-2 with microglial markers Iba-1 or CD11b and Ab [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . Ab plaques were age-dependently increased in size and number, and COX-1 immunopositive microglia were also found in association with areas of abundant Ab (Fig.…”

Molecular Mechanisms of Reward and Aversion

“…There exist two genetically distinct isoforms of the cyclooxygenases: COX1 and COX2. COX1 is in general a constitutive enzyme, but has been demonstrated to be upregulated during certain inflammatory conditions (Schwab et al, 2000;Shukuri et al, 2011;Anrather et al, 2011;Matousek et al, 2010). The COX2 gene on the other hand has several transcriptional regulatory sites in its promoter and can be induced by various pro-inflammatory cytokines.…”

Pd0–Mediated Rapid C–[11C]Methylation and C–[18F]Fluoromethylation: Revolutionary Advanced Methods for General Incorporation of Short–Lived Positron–Emitting 11C and 18F Radionuclides in an Organic Framework

“…A metabolite analysis in the rat brain revealed that the intravenously administrated methyl ester was initially taken up in the brain and then underwent hydrolysis to form a pharmacologically active form of the corresponding acids. Hence, we succeeded in the general 11 C-labeling of 2-arenylpropionic acids and their methyl esters as PET probes of NSAIDs to construct a potentially useful PET-probe library for the in vivo imaging of inflammation involved in the COX expression (Shukuri et al, 2011). The above racemic NSADs are readily separated by a chiral column to give an optically pure compound.…”