Takao Hirata

Translocation of protein kinase C-α, δ and ϵ isoforms in ischemic rat heart

To explore the spatial and temporal localization of PKC isoforms during ischemia, we quantified PKC isoforms in the subcellular fractions in perfused rat heart by immunoblotting using specific antibodies against PKC isoforms. PKCs-alpha and epsilon translocated from the 100000 x g supernatant (S, cytosolic) fraction to the 1000 x g pellet (PI, nucleus-myofibril) and the 1000-100000 x g pellet (P2, membrane) fractions during 5-40 min of ischemia. PKC-delta redistributed from the P2 to the S fraction. A 50-kDa fragment of PKC-alpha appeared during ischemia possibly through calpain action. Immunohistochemical observations showed the different localizations of PKC-alpha, delta, and epsilon in the myocytes. The PKC assay displayed high basal levels of Ca(2+)-independent PKC, the activation of Ca(2+)-dependent PKC in the P1 and P2 fractions, and the activation of Ca(2+)-independent PKC in the P1 fraction after 20 min of ischemia. These observations show that ischemia induces different patterns of translocation of the three PKC isoforms, suggesting differences in their roles.

Nuclear translocation of PKCζ during ischemia and its inhibition by wortmannin, an inhibitor of phosphatidylinositol 3-kinase

Protein kinase Cζ (PKCζ), a member of the atypical PKC subgroup, is insensitive to Ca2+, diacylglycerol, and phorbol esters, but is activated by phospholipids such as phosphatidylinositol‐3,4,5‐triphosphate, a product of phosphatidylinositol 3‐kinase (PI3‐kinase). Here we show that PKCζ translocates from the cytosol to the 1000×g pellet (nuclear‐myofibrillar) fraction during ischemia for 40 min in Langendorff‐perfused rat hearts. In addition, immunohistochemical observation shows that ischemia induces the translocation of PKCζ to the nucleus. The nuclear translocation during ischemia is inhibited in a dose‐dependent manner by wortmannin (10−9–10−7 M), an inhibitor of PI3‐kinase.

The temporal profile of genomic responses and protein synthesis in ischemic tolerance of the rat brain induced by repeated hyperbaric oxygen

Repeated hyperbaric oxygen (HBO) exposure prior to ischemia has been reported to provide neuroprotection against ischemic brain injury. The present study examined the time course of neuroprotection of HBO (3.5 atmosphere absolute, 100% oxygen, 1 h for 5 consecutive days) and the changes of gene/protein expression in rats. First, at 6 h, 12 h, 24 h, and 72 h after HBO sessions, rats were subjected to forebrain ischemia (8 min). Histopathological examination of hippocampal CA1 neurons was done 7 days after ischemia. Second, temporal genomic responses and protein expression were examined at the same time points after HBO sessions without subjecting animals to ischemia. HBO significantly reduced loss of hippocampal CA1 neurons that normally follows transient forebrain ischemia when the last HBO session was 6 h, 12 h, or 24 h before ischemia (survived neurons 55%, 75%, and 53%, respectively), whereas if there was a 72-h delay before the ischemic insult, HBO was not protective (survived neurons only 6%). Statistical analysis on microarray data showed significant upregulation in 60 probe sets including 7 annotated genes (p75NTR, C/EBPdelta, CD74, Edg2, Trip10, Nrp1, and Igf2), whose time course expressions corresponded to HBO-induced neuroprotection. The protein levels of p75NTR, C/EBPdelta, and CD74 were significantly increased (maximum fold changes 2.9, 2.0, and 7.9, respectively). The results suggest that HBO-induced neuroprotection against ischemic injury has time window, protective at 6 h, 12 h and 24 h but not protective at 72 h. Although the precise interaction is to be determined, the genes/proteins relevant to neurotrophin and inflammatory-immune system may be involved in HBO-induced neuroprotection.

Repeated preconditioning with hyperbaric oxygen induces neuroprotection against forebrain ischemia via suppression of p38 mitogen activated protein kinase

We previously reported in rats that preconditioning with hyperbaric oxygen (HBO; 100% O(2) 3.5-atomsphere absolute (ATA), 1 h/day for 5 days) provided neuroprotection against transient (8 min) forebrain ischemia possibly through protein synthesis relevant to neurotrophin receptor and inflammatory-immune system. A recent report suggested that HBO-induced neuroprotection is relevant to brain derived neurotrophic factor and its downstream event involving suppression of p38 mitogen activated protein kinase (p38) activation. In the present study, we first performed a dose comparison (1, 2, and 3.5 ATA) of HBO-induced neuroprotection and then investigated pharmacological modification by 10 mg/kg anisomycin (a protein synthesis inhibitor and potent activator for p38) and 200 microg/kg SB203580 (a p38 inhibitor), which were given intraperitoneally 60 and 30 min before every 3.5 ATA-HBO treatment, respectively. Most prominent protective effect on hippocampal CA1 neurons was observed with 3.5 ATA-HBO (survived neurons: 69% [62-73%] vs. untreated: 3.9% [2-8%], 1 ATA: 8.8% [0-26%], 2 ATA-HBO: 46% [22-62%] (median [range]) (7 days after ischemia). Anisomycin abolished a neuroprotective effect (survived neuron: 1.2% [0-7%]). SB203580, when given between administration of anisomycin and HBO treatment, resumed a neuroprotective effect (survived neuron: 52% [37-62%]). The level of phosphorylated p38 at 10-min reperfusion was significantly decreased in 3.5 ATA-HBO group (32% [12-53%] of sham). Single pretreatment with 100 and 200 microg/kg of SB203580 exerted a similar neuroprotective effect (39% [25-51%] and 59% [50-72%]) to 2 and 3.5 ATA-HBO preconditioning, respectively. It is concluded that suppression of p38 phosphorylation plays a key role in HBO-induced neuroprotection and that pretreatment with a p38 inhibitor (SB203580) can provide similar neuroprotection.

Neutrophil elastase inhibitor attenuates hippocampal neuronal damage after transient forebrain ischemia in rats

Inflammatory responses have been known to contribute to the development of neuronal damage after brain ischemia in experimental animals. Also, neutrophil elastase activity in the plasma has been elevated in the patients with acute cerebral infarction. In order to clarify whether neutrophil elastase distributes into the brain parenchyma and exacerbates neuronal damage following ischemia, we examined the effects of specific neutrophil elastase inhibitor, ONO-5046, on hippocampal CA1 neuronal death in relation to neutrophil elastase activity in the plasma and its distribution in the brain and to caspase-3/7 activity. ONO-5046 (5 and 10 mg/kg) or saline (control group) was administrated after 8 min of forebrain ischemia in rats. Ratio of surviving neurons (median, [range]) in hippocampal CA1 seven days after ischemia was significantly higher in the ONO-5046 5 mg/kg (31% [12-57%]), and 10 mg/kg groups (69% [39-76%]) than in the control group (3.2% [0-10%]). Plasma neutrophil elastase activity in the ONO-5046 10 mg/kg group was significantly lower than in the control group (14 [11-25] vs. 41 [35-68] nmol/ml). Neutrophil elastase distributed in the extracellular space in the hippocampal CA1 neuronal layer in the control group, while, in the ONO-5046 10 mg/kg group, trace of neutrophil elastase was detected only in the endothelium. Caspase-3/7 activity was elevated after ischemia over 8 h in the control group, while, in the ONO-5046 10 mg/kg group, no elevation was observed. The results suggest that neutrophil elastase may contribute to neuronal death in hippocampal CA1 following forebrain ischemia and that neutrophil elastase inhibitor attenuates neuronal death.

Target-controlled infusion of propofol for a patient with myotonic dystrophy.

We present a patient with myotonic dystrophy (MD) who was anesthetized with propofol using a target-controlled technique for electrophysiologic examination and cardiac catheter ablation. The patient became apneic unexpectedly at the same time when he fell asleep, with effect-site propofol concentration of 1.6 µg ml−1. We had to insert a laryngeal mask airway (LMA), and mechanical ventilation was performed. The patient opened his eyes on verbal command at an effect-site concentration of 1.2 µg ml−1 after the procedure. This concentration (1.2 µg ml−1) was slightly lower than our institutional average for adult male patients (1.5 ± 0.2 µg ml−1). However, the time from the end of anesthesia to the patients awakening was about 10 min. We considered that emergence from anesthesia was not delayed in this case. Careful titration of propofol by target-controlled infusion (TCI) enabled to evaluate the patients sensitivity to propofol. We conclude that TCI of propofol was a useful anesthetic technique in the MD patient. Respiratory depression might occur in MD patients at low propofol concentrations. Precise control and titration over target propofol concentration is important in anesthetic management for MD patients.

The nerve root entry zone is highly vulnerable to intrathecal tetracaine in rabbits.

It has been speculated that the nerve root entry zone in the spinal cord, known as the Obersteiner-Redlich zone, may be more sensitive to large concentrations of local anesthetics administered intrathecally. However, there has been no morphological evidence for this. In the present study, we examined morphological changes of nerve fibers at the nerve root entry zone after administration of intrathecal tetracaine in rabbits. Rabbits were assigned to 4 groups (n = 6 in each) and received intrathecal 0.3 mL saline (control), or 1%, 2%, or 4% tetracaine. Neurological and histopathological assessments were performed 1 wk after the administration. Tetracaine 1% selectively injured the myelin sheaths made by oligodendrocytes at the nerve root entry zones of both ventral and dorsal roots, although neurological dysfunction could not be detected. With tetracaine 2% and 4%, histopathological damage extended to the dorsal funiculus, distal part of roots, and cauda equina and neurological dysfunction became apparent. These results demonstrate that the myelin sheaths made by oligodendrocytes at the nerve root entry zone are highly vulnerable to large concentrations of tetracaine given intrathecally.