Dihydromethidine (DHM) labeled with 18F at the para position of the benzene ring has been developed as a positron emission tomography (PET) radiotracer for non-invasive imaging of reactive oxygen species (ROS).

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Objective:Oxidative stress plays an important role in the onset of many neuronal and peripheral disorders. We examined the feasibility of obtaining semiquantitative fluorescent images of reactive oxygen species (ROS) generation in mouse brain and kidney utilizing a planar laser scanner and dihydroethidium (DHE).Methods:To investigate ROS generation in brain, sodium nitroprusside was injected into the striatum. Dihydroethidium was injected into the tail vein. After DHE injection, tissue slices were analyzed utilizing a planar laser scanner. For kidney study, cis-diamminedichloroplatinum [II] (cisplatin) was intraperitoneally administrated into mice.Results:Clear and semiquantitative fluorescent images of ROS generation in the mouse brain and kidney were obtained. Furthermore, the fluorescence intensity was stable and not affected by fading. Sodium nitroprusside induced approximately 6 times the fluorescence accumulation in the brain. Cisplatin caused renal injury in all mice, and in comparison with control mice, more than 10 times fluorescence accumulation was observed in the renal medulla with tubular necrosis and vacuolization.Conclusions:We successfully obtained ex vivo semiquantitative fluorescent images of ROS generation utilizing a planar laser scanner and DHE. This simple method is useful for ROS detection in several ROS-related animal models and would be applicable to a variety of biochemical processes.

Purpose Our study aimed to elucidate the intracellular processes associated with quinolinic acid (QA)-induced brain injury by acquiring semiquantitative fluorescent images of reactive oxygen species (ROS) generation and positron emission tomography (PET) images of mitochondrial complex I (MC-I) activity. Methods Ex vivo fluorescent imaging with dihydroethidium (DHE) and PET scans with 18F-BCPP-EF were conducted at 3 h and 24 h after QA injection into the rat striatum. Immunohistochemical studies were performed 24 h after QA injection into the rat brain using monoclonal antibodies against neuronal nuclei (NeuN) and CD11b. Results A strong DHE-derived fluorescent signal was detected in a focal area within the QA-injected striatum 3 h after QA injection, and increased fluorescent signal spread throughout the striatum and parts of the cerebral cortex after 24 h. By contrast, 18F-BCPP-EF uptake in the QA-injected rat brain was unchanged after 3 h and markedly decreased after 24 h, not only in the striatum but also in the cerebral hemisphere. The fluorescent signal in the striatum 24 h after QA injection colocalised with microglial marker expression. Conclusions We successfully obtained functional images of focal ROS generation during the early period of excitotoxic injury, and microglial ROS generation and mitochondrial dysfunction were observed during the progression of the inflammatory response. Both ex vivo DHE imaging and in vivo 18F-BCPP-EF-PET were sufficiently sensitive to detect the respective processes of QA-induced brain damage. Our study contributes to the functional imaging of multiple events during the pathological process.

BackgroundNonalcoholic 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.ResultsSignificant 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.ConclusionsPET 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.