Molecular Imaging Study Of Neuroinflammation In Hepatic Encephalopathy Of Chronic Liver Failure

Part I Comparison Study of [18F]DPA-714 and [11C]PK11195 in Vivo Imaging of Neuroinflammation in Chronic Hepatic Encephalopathy RatsPurpose:Neuroinflammation has been considered to be the pathogenesis of hepatic encephalopathy (HE), and the translocator protein (TSPO) is an important target in vivo molecular imaging of neuroinflammation. [11C]PK11195 is a useful TSPO radiotracer in positron emission tomography (PET) imaging of neuroinflammation. The new generation TSPO radiotracer [18F]DPA-714 has been proposed as a promising radiotracer for in vivo PET studies.In this study, we used the bile duct ligation (BDL) and fed hyperammonemic diet (HD) rats to simulate a chronic HE in cirrhosis, and directly compared the two radiotracers [11C]PK11195 and [18F]DPA-714 in vivo imaging of neuroinflammation in chronic HE.Methods:In 16 male Sprague-Dawley (SD) rats,10 rats underwent BDL operations and were fed by ammonia water daily during the 2 weeks after operation until their sacrifice, the other rats underwent Sham operations. Before Micro-PET imaging, rotarod, beam walking test, and motor activity were examined to estimate the neurological features. One day before Micro-PET imaging, the canthus blood plasma was extracted to measure venous blood ammonia values.[11C]PK11195 Micro-PET scan was acquired with dynamic scan for 30 minutes and static scan at 1 hour after tracer injection for 2 days. The third day, [18F]DPA-714 imaging was obtained with dynamic scan for one hour and static scan at 2 hours after tracer injection. The average percentage injected dose per gram (%ID/g) values of whole brain and regional brain regions were calculated in each rat. The blood was acquired from carotid artery at the second day after Micro-PET scan to measure the biochemical indexes, such as liver function and inflammatory factors. The liver and brain were obtained and pathological analysis was performed. Independent-samples t test was performed for quantitative data between BDL+HD group and Sham group.Results:One and 3 rats died in Sham and BDL+HD groups, respectively. The rats of BDL+HD group had poor mental situations, decreased body weights (t=3.417, P=0.008), impaired neurological features and hepatic dysfunction (all P<0.05). Besides, the venous blood ammonia values and inflammatory factors of BDL+HD group were significantly higher than Sham group (all P<0.05). The brain tissue showed significant microglia activation in BDL+HD group by immunohistochemical staining. The Micro-PET imaging showed no significant differences in whole brain and regional brain average %ID/g values of [11C]PK11195 Micro-PET imaging (all P>0.05). While in [18F]DPA-714 Micro-PET imaging, BDL+HD group rats showed higher whole brain average %ID/g than Sham group at 900 s,1500 s,2100 s,2700 s, and 3300 s time points of dynamic scan (P were 0.044,0.007,0.021,0.002, and 0.003, respectively), and at the time points of 2700 s and 3300 s, brain regions including bilateral basal ganglia, cingulate cortex, hippocampus, somatosensory cortex, thalamus, midbrain, cerebellum, pons, and medulla showed significant difference between two groups (all P<0.05).Conclusion:[18F]DPA-714, as a new TSPO radiotracer, is suitable for in vivo imaging of neuroinflammation of chronic HE. Bilateral basal ganglia, hippocampus, cerebellum, thalamus, and midbrain showed significant difference between BDL+HD group and Sham group. The 50 min time point after [18F]DPA-714 injection is suitable for further research of neuroinflammation of chronic HE.Part II Molecular Imaging Study in the Effectiveness of Ibuprofen to Treat Neuroinflammation of Chronic Hepatic Encephalopathy RatsPurpose:Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, was considered to be useful for treating neuroinflammation. In this study, IBU was injected intraperitoneally to treat neuroinflammation of chronic HE rat models, and Micro-PET with [18]DPA-714 radiotracer was used to estimate the effectiveness of ibuprofen to treat neuroinflammation of chronic HE.Methods:Six groups were included:Sham+ normal saline (NS), Sham+IBU, BDL+NS, BDL+HD+NS, BDL+IBU, and BDL+HD+IBU, including 40 male SD rats (n=6 for Sham+NS and Sham+IBU groups, n=7 for other groups). BDL surgery, HD, and sham operation were same as the Part I. Treatment with IBU was started 10 days after surgery and was maintained during all the duration of the experiments, until sacrifice of the rats. IBU in sterile saline was injected intraperitoneally,30 mg/kg per day in 0.5 ml/100 g body weight, normal saline was injected intraperitoneally in 0.5 ml/100 g body weight. Before Micro-PET imaging, rotarod, beam walking test, and motor activity were examined to estimate the neurological features. One day before Micro-PET imaging, the canthus blood was extracted to measure venous blood ammonia values. [18F]DPA-714 Micro-PET imaging of each rat was acquired 10 min static scan at 50 min after imaging agent injection. The average %ID/g values of whole brain and regional brain were calculated in each rat. The blood was acquired from carotid artery at the second day after Micro-PET scan to measure the biochemical indexes, such as liver function and inflammatory factors. The liver and brain were obtained and pathological analysis was performed. One-way ANOVA was performed for quantitative data statistical analysis among each group. Least-significant difference (LSD) test and Dunnett’s T3 test were performed in pairwise comparison.Results:Sham+NS group, BDL+HD+NS group, and BDL+IBU group had one rat died, respectively, and 2 rats were died in BDL+HD+IBU group. All BDL rats had hepatic dysfunction. The venous blood ammonia values of Sham, BDL, and BDL+HD groups showed progressive increasement (F=30.640, P<0.001). The neurological features of IBU groups showed better than NS group, and similar with Sham groups (all P<0.05). The neurological features of each group rats were consistent with serum inflammatory factors values and the brain tissue immunohistochemical staining results of each group rats. The Micro-PET imaging showed, the whole brain average %ID/g values of IBU groups had a significant decrease than NS groups, and similar with Sham groups (F=8.047,.P<0.001). The regional brain including bilateral basal ganglia, cingulate cortex, motor cortex, somatosensory cortex, auditory and visual cortex, hippocampus, hypothalamus, midbrain, and cerebellum grey matter had significant difference among each group (all P<0.01). And these brain regions average %ID/g values of IBU groups were lower than NS groups, and similar with Sham groups.Conclusion:IBU could restore the motor function and improve the mental situations and [18F]DPA-714 is a useful tracer for in vivo evaluating the effectiveness of ibuprofen to treat neuroinflammation in chronic HE rats.