Development of real-time bioradiographic system for functional and metabolic imaging in living brain tissue

Evaluation of cell viability and metabolic activity of a 3D cultured human epidermal model using a dynamic autoradiographic technique with a PET radiopharmaceutical

Quality control of tissues and organs for transplant is important to confirm their safety and effectiveness for regenerative medicine. However, quality evaluation is only carried out using a limited range of inspection criteria, because many of the available evaluation tests are invasive. In order to explore the potential of 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG)-bioradiography as a non-invasive test for estimation of the safety, soundness, and effectiveness of tissues for transplantation, [¹⁸F]FDG uptake and cell viability or metabolism were investigated using a reconstructed human epidermal model (RHEM). We developed an imaging system, and suitable bioradiographic image acquisition conditions and its effectiveness were investigated. [¹⁸F]FDG uptake increased in agreement with DNA content as a marker of cell numbers and for histological assessment during cell proliferation and keratinization. [¹⁸F]FDG uptake was significantly decreased in good agreement with the viability of tissues used with various hazardous chemical treatments. [¹⁸F]FDG uptake by the tissues was decreased by hypothermia treatment and increased by hypoxia treatment while maintaining cell viability in the tissue. Therefore, [¹⁸F]FDG-bioradiography can be useful to estimate cell viability or metabolism in this RHEM. This method might be utilized as a non-invasive test for quality evaluation of tissues for transplantation.

Increase of reactive oxygen species generation in cerebral cortex slices after the transiently enhanced metabolic activity

Under certain conditions such as hypoxia-reoxygenation, the generation of reactive oxygen species (ROS) increases following hypoxia caused by a decreased oxygen supply. As another hypoxic condition, an excess neural activity status including epileptic seizure induces a decrease in tissue oxygen partial pressure (pO₂) caused by enhanced oxygen utilization; however, whether ROS generation increases following the hypoxic status induced by transiently enhanced energy metabolism in brain tissue currently remains unknown. We herein investigated ROS-dependent chemiluminescence in cerebral cortex slices during the restoration of transiently enhanced energy metabolism induced by a high-potassium treatment with tissue pO₂ changes and redox balance. ROS generation in the tissue was enhanced after high-potassium-induced hypoxia, but not by the reversed order of the treatment: control-potassium then high-potassium treatment, high-potassium treatment alone, and control-potassium treatment alone. The high-potassium treatment induced a transient decrease in tissue pO₂ and a shift in the tissue redox balance towards reduction. The transient shift in the tissue redox balance towards reduction with enhanced metabolic activity and its recovery may correlate with ROS generation. This phenomenon may mimic ROS generation following the hypoxic status induced by transiently enhanced energy metabolism.

WITHDRAWN: Superoxide generation in different brain regions of rats during normoxia and hypoxia-reoxygenation

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.neures.2012.10.010. The duplicate article has therefore been withdrawn.

Superoxide generation in different brain regions of rats during normoxia and hypoxia-reoxygenation

The superoxide-dependent chemiluminescent intensity in different brain regions was examined in ex vivo tissue slices of rat brain during normoxia and hypoxia-reoxygenation with lucigenin. The chemiluminescent intensity increased during reoxygenation after hypoxic treatment. There was a higher level of chemiluminescent intensity in the hippocampus during normoxia, and a lower level in the white matter during normoxia and hypoxia-reoxygenation. A weak correlation was found between the chemiluminescent intensity and the glucose uptake rate during normoxia. Then we examined whether hypoxic strength correlates to superoxide generation. The chemiluminescent intensity increased in a hypoxic strength-dependent manner. The generation mechanism of superoxide was examined using carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, genipin, an inhibitor for uncoupling protein-2, alloprinol, a xanthine oxidase inhibitor, or apocynin, an NADPH oxidase inhibitor. The chemiluminescent signal was significantly inhibited by CCCP under normoxic condition and enhanced by genipin during normoxia and hypoxia-reoxygenation, but not by allopurinol or apocynin. These results suggest that superoxide generation is high in the hippocampus during normoxia and low in the white matter during normoxia and hypoxia-reoxygenation, superoxide generation in the hypoxia-reoxygenation brain correlates with the strength of hypoxia influenced by oxygen delivery, and mitochondrion is the major sites of intracellular superoxide generation.

Superoxide dismutase deficiency enhances superoxide levels in brain tissues during oxygenation and hypoxia-reoxygenation

To determine whether the mitochondria or cytoplasm produces superoxide during ischemia-reperfusion of the brain, we analyzed lucigenine-enhanced chemiluminescence emission in slices of brain tissue prepared from manganese-superoxide dismutase (Mn-SOD)-deficient (Sod2-deficient) and copper and zinc-superoxide dismutase (Cu,Zn-SOD)-deficient (Sod1-deficient) mice during oxygenation and hypoxia-reoxygenation. The steady-state level of chemiluminescence under oxygenated conditions was significantly enhanced by a lack of either Sod. We hypothesize that the enhanced chemiluminescence produced by Sod2 and Sod1 deficiency reflects in situ superoxide generation in the mitochondria and cytoplasm, respectively. Based on this hypothesis, the major site of intracellular superoxide generation was assumed to be the cytoplasm. However, mitochondria occupy less cellular space than the cytoplasm. In terms of volume, the superoxide concentration is assumed to be higher in mitochondria than in the cytoplasm. Mn-SOD activity was 18% of the Cu,Zn-SOD activity observed in the wild-type mouse brain. However, when mitochondrial SOD activity was expressed as per volume, it was assumed to be equal to that observed in the cytoplasm. This imbalance between superoxide and SOD activity is expected to cause mitochondrial oxidative damage. The chemiluminescence intensity increased significantly during reoxygenation and was enhanced by Sod2 deficiency but was not significantly affected by Sod1 deficiency. The superoxide concentration in the reoxygenated brain would be higher in the mitochondria than in the cytoplasm. The present study indicated that the major site of intracellular superoxide generation in the brain during oxygenation is the cytoplasm, whereas it is the mitochondria during reoxygenation.

Hydrogen-rich pure water prevents superoxide formation in brain slices of vitamin C-depleted SMP30/GNL knockout mice

Hydrogen is an established anti-oxidant that prevents acute oxidative stress. To clarify the mechanism of hydrogen's effect in the brain, we administered hydrogen-rich pure water (H(2)) to senescence marker protein-30 (SMP30)/gluconolactonase (GNL) knockout (KO) mice, which cannot synthesize vitamin C (VC), also a well-known anti-oxidant. These KO mice were divided into three groups; recipients of H(2), VC, or pure water (H(2)O), administered for 33 days. VC levels in H(2) and H(2)O groups were <6% of those in the VC group. Subsequently, superoxide formation during hypoxia-reoxygenation treatment of brain slices from these groups was estimated by a real-time biography imaging system, which models living brain tissues, with Lucigenin used as chemiluminescence probe for superoxide. A significant 27.2% less superoxide formed in the H(2) group subjected to ischemia-reperfusion than in the H(2)O group. Thus hydrogen-rich pure water acts as an anti-oxidant in the brain slices and prevents superoxide formation.

Age-related increase of superoxide generation in the brains of mammals and birds

Oxidative stress, an imbalance between endogenous levels of oxygen radicals and antioxidative defense, increases with aging. However, it is not clear which of these two factors is the more critical. To clarify the production of oxygen radicals increases with age, we examined oxygen radical-dependent chemiluminescent signals in ex vivo brain slices using a novel photonic imaging method. The chemiluminescent intensity was significantly decreased by the membrane permeable superoxide dismutase (SOD)/catalase mimic, but not by Cu,Zn-SOD. Inhibitors for complex I, III, and IV of the mitochondrial electron transport chain transiently enhanced the chemiluminescent signal. The superoxide-dependent chemiluminescent intensity in senescence accelerated mouse (SAM) brain tissues increases with age. Moreover, the slope of the age-dependent increase was steeper in SAMP10, a strain characterized by a short lifespan and atrophy in the frontal cerebral cortex, than the senescence-resistant strain SAMR1, which has a longer lifespan. An increase in chemiluminescence with age was also observed in C57/BL6 mice, Wistar rats, and pigeons, although levels of chemiluminescence were lower in the pigeons than murines. The rate of age-related increases of superoxide-dependent chemiluminescence was inversely related to the maximum lifespan of the animals. The activity of superoxide dismutase was unchanged during the aging process in the brain. This suggested that superoxide production itself may increase with age. We speculated that reactive oxygen may be a signal to determine the aging process.