Simultaneous measurement of cytosolic and mitochondrial Ca(2+) during ischemia in mice whole-brain slice preparation and its application to drug evaluation

We developed a conventional imaging method to measure Ca(2+) concentration in cytosol (using FuraRed as an indicator) and mitochondria (using Rhod-2 as an indicator), simultaneously, by alternative excitation with specific wave length. After confirming the availability of the method in Hela cells, we applied it to mouse whole-brain slice -preparation, which was exposed to oxygen- and glucose-deprived artificial cerebrospinal fluid (ischemic ACSF) for 12 min. The fluorescence (>570 nm) at the cerebral cortex and hippocampus due to FuraRed (excited by 480 ± 10 nm) decreased (indicating the increase in cytosolic Ca(2+)-concentration), while the fluorescence due to Rhod-2 (excited by 560 ± 10 nm) increased (indicating the increase in mitochondrial Ca(2+) concentration) during exposure to ischemic conditions. We found the characteristic protective effects of cyclosporine A (10(-6) M), a known blocker for mitochondrial permeability transition, and SEA0400 (10(-6) M), a blocker for Na(+)/Ca(2+) exchanger, on the abnormal Ca(2+) increase in cytosol. We confirmed that the present method will be useful for future pathological and pharmacological studies on ischemia-induced brain damage.

Cyclophilin-D inhibition in neuroprotection: dawn of a new era of mitochondrial medicine

Traumatic brain injury and ischemia can result in marked neuronal degeneration and residual impairment of cerebral function. However, no effective pharmacological treatment directed at tissues of the central nervous system (CNS) for acute intervention has been developed. The detailed pathophysiological cascade leading to -neurodegeneration in these conditions has not been elucidated, but cellular calcium overload and mitochondrial dysfunction have been implicated in a wide range of animal models involving degeneration of the CNS. In particular, activation of the calcium-induced mitochondrial permeability transition (mPT) is considered to be a major cause of cell death inferred by the broad and potent neuroprotective effects of -pharmacological inhibitors of mPT, especially modulators of cyclophilin activity and, more specifically, genetic inactivation of the mitochondrial cyclophilin, cyclophilin D. Reviewed are evidence and challenges that could bring on the dawning of mitochondrial medicine aimed at safeguarding energy supply following acute injury to the CNS.

Mitochondrial respiration in human viable platelets--methodology and influence of gender, age and storage

Studying whole cell preparations with intact mitochondria and respiratory complexes has a clear benefit compared to isolated or disrupted mitochondria due to the dynamic interplay between mitochondria and other cellular compartments. Platelet mitochondria have a potential to serve as a source of human viable mitochondria when studying mitochondrial physiology and pathogenic mechanisms, as well as for the diagnostics of mitochondrial diseases. The objective of the present study was to perform a detailed evaluation of platelet mitochondrial respiration using high-resolution respirometry. Further, we aimed to explore the limits of sample size and the impact of storage as well as to establish a wide range of reference data from different pediatric and adult cohorts. Our results indicate that platelet mitochondria are well suited for ex-vivo analysis with the need for minute sample amounts and excellent reproducibility and stability.

[Anesthesia management during coronary artery aneurysmectomy and tricuspid valvulectomy]

A 54-year-old man with infective tricuspid endocarditis and an infective right coronary artery aneurysm was scheduled for simultaneous coronary artery aneurysmectomy and tricuspid valvulectomy. However, the tricuspid valve replacement and annuloplasty procedures could not be performed because vegetation was noted on all his tricuspid leaflets. Moreover, the infective right coronary artery aneurysm was located proximal to the annulus of the tricuspid valve. Complications of tricuspid valvulectomy include tricuspid regurgitation, right ventricular capacity load and right ventricular pressure load. In the present case, after the patient was weaned from cardiopulmonary bypass (CPB), transesophageal echocardiography (TEE) revealed severe tricuspid regurgitation and shifting of the interventricular septum toward the left ventricle at the telediastolic stage. We managed this condition on the basis of the TEE findings with fluid therapy and a nitroglycerin vasoactive agonist, and adjusted the ventilator setting to reduce pulmonary vascular resistance. In the present case of infective tricuspid endocarditis with infective right coronary artery aneurysm, the selection of the appropriate surgical method was important. Moreover, respiratory management which did not increase pulmonary vascular resistance and adequate fluid management based on TEE findings after weaning from CPB were equally important during anesthesia for tricuspid valvulectomy.

[Current status of intraoperative motor evoked potential monitoring: a questionnaire study]

BACKGROUND

Intraoperative motor evoked potential (MEP) monitoring has been used for the purpose of preventing neural complications in surgical treatments. There is little information about the current status of intraoperative MEP monitoring in Japan.

METHODS

The survey targeted anesthesia departments mainly of university hospitals throughout the country.

RESULTS

Answers were obtained from 60 institutions (a response rate of 68%). Intraoperative MEP has been monitored in 58 institutions. Intraoperative MEP monitoring in 35 institutions did not exceed 50 times per year. Especially during thoracoabdominal aortic aneurysm repair, frequency of MEP monitoring in 51 institutions was limited to 10 times per year. A few anesthesiologists were concerned with evaluation of MEP in craniotomy and spine surgery. In contrast, anesthesiologists in 15 institutions were responsible for evaluation of MEP during thoracoabdominal aortic aneurysm repair. Warning criteria of MEP and therapeutic strategies in case of critical MEP change differed by institution. Fifty four responders expected a guideline for clinical use of intraoperative MEP monitoring.

CONCLUSIONS

A clinical practice guideline for intraoperative MEP monitoring based on the information from previous investigations and a planned multicenter clinical study is necessary to enhance its utility.

Evaluation of the protective effects of cyclosporin a and FK506 on abnormal cytosolic and mitochondrial Ca²⁺ dynamics during ischemia and exposure to high glutamate concentration in mouse brain slice preparations

We examined the protective effects of the immunosuppressants cyclosporin A (CsA) and FK506 on abnormal cytosolic Ca²⁺ ([Ca²⁺]c) and mitochondrial Ca²⁺ concentration ([Ca²⁺]m) dynamics induced by ischemia or high L-glutamate concentration in mouse brain slice preparations. We used fura-4F and rhod-2 as indicators for [Ca²⁺]c and [Ca²⁺]m, respectively, in their acetoxymethylester form. Slice preparations loaded with either of these two indicators were exposed to ischemic artificial cerebrospinal fluid (oxygen- and glucose-deprived medium) for 12 min or to aerobic medium with high L-glutamate concentration (isotonic 20 mM L-glutamate) for 5 min. CsA (1 - 10 μM) showed significant protective effects on the maximum increase in ischemia-induced [Ca²⁺]c and [Ca²⁺]m. FK506 (10 μM) showed significant protective effects on the [Ca²⁺]m increase, but not on the ischemia-induced [Ca²⁺]c increase. Both immunosuppressants showed almost equal protective effects on the [Ca²⁺]c and [Ca²⁺]m increases induced by high L-glutamate concentration. These results suggest that the protective effects of CsA and FK506 on Ca²⁺ overloading may be dependent upon the common pharmacological sites of actions relating to their effects as immunosuppressants. The small, but significant depressant effects of these drugs could give us important clues for rescuing critical brain damage induced by Ca²⁺ overloading.

Int6 silencing causes induction of angiogenic factors in neuronal cells via accumulation of hypoxia-inducible factor 2α and decreases brain damage in rats

We have previously shown that when siRNA against Int6 (siRNA-Int6) was used, hypoxia-inducible factor 2α (HIF2α) activity was stabilized even under normoxic conditions, and the expression of several angiogenic factors was increased. In neuronal tissues, the mechanism underlying angiogenesis remains largely unknown. In the current study, we investigate the role of the tumor suppressor Int6/eIF3e in the regulation of the expression of angiogenic factors in neuronal cells. In addition, we test whether siRNA-Int6 reduces cold-induced brain damage in rats. We used human neuroblastoma SHSY5Y cells transfected with either siRNA-Int6, or a negative control siRNA. Real-time PCR and supersensitive multiplex assay were used to detect gene and protein expression of several angiogenic factors after transfection. For the animal studies, Wistar rats were subjected to brain damage by cold injury, and 50 μg siRNA-Int6, 100 μg siRNA-Int6, or negative control was administrated. At day 7 post-treatment, brain sections were stained and image analysis system was used to determine the damaged area. Our experiments using SHSY5Y cells revealed a significant effect of siRNA-Int6 on the expression of HIF2α but not HIF1α, both at 8 and 24h after transfection. The siRNA-Int6 led to significant up-regulation of angiogenic factors, including vascular endothelial growth factor and platelet-derived growth factor-B, both at the mRNA and protein levels. Furthermore, our animal studies revealed significantly reduced area of cold-induced damage in rats receiving siRNA-Int6, compared to negative controls. Our findings indicate that Int6 act as a hypoxia-independent master switch of angiogenesis in neuronal cells, and that inhibition of Int6 by siRNA may be an effective therapeutic strategy in treating ischemic diseases such as brain ischemia and injury.

[Organ protective effects of volatile anesthetics and perioperative outcomes]

Anesthetic agents, especially, volatile anesthetics are considered to exert organ toxicity such as nephrotoxicity and hepatotoxicity; however, recent aggressive researches explored the beneficial effects of volatile anesthetics as an organ protectant. Ischemic preconditioning is a phenomenon in which single or multiple brief periods of ischemia have been shown to protect the myocardium and brain against prolonged ischemic insult. General anesthesia showed the protection against both ischemic myocardial and brain reperfusion injuries. This phenomenon is called anesthetic preconditioning. Regarding the organ protection, anesthetic preconditioning is one of the useful ways to diverse the organ protective effects not only to heart but also brain. Nowadays, ischemic postconditioning, consisting of repeated brief cycles of ischemia-reperfusion performed immediately after reperfusion following a prolonged ischemic insult, dramatically reduces infarct size in experimental models and such clinical studies are reported. Both preconditioning and postconditioning share the same signal transduction pathway and inhibit the mitochondrial permeability transition (MPT) that leads to either apoptosis or necrosis of myocardium and neuronal cell. Both phenomena look very promising, but we still lack the real evidence for human reserach in terms of the clinical outcome and further analysis is necessary. Neurotoxicities of anesthetic agents are very crucial problems for the patient and they are considered to be due to the activation of IP3 receptor in ER after exposure to volatile anesthetics. Massive release of Ca2+ from ER induces Ca2+ overload leading to mitochondria permeability transition (MPT) and induces apoptosis in the brain or aggravates the neurodegenerative disease. Susceptible mechanisms and beneficial treatment for the toxicity of general anesthesia is considered as a critical subject to discuss and challenge to solve for our future.

Cyclophilin D-sensitive mitochondrial permeability transition in adult human brain and liver mitochondria

The mitochondrial permeability transition (mPT) is considered to be a major cause of cell death under a variety of pathophysiological conditions of the central nervous system (CNS) and other organs. Pharmacological inhibition or genetic knockout of the matrix protein cyclophilin D (CypD) prevents mPT and cell degeneration in several models of brain injury. If these findings in animal models are translatable to human disease, pharmacological inhibition of mPT offers a promising therapeutic target. The objective of this study was to validate the presence of a CypD-sensitive mPT in adult human brain and liver mitochondria. In order to perform functional characterization of human mitochondria, fresh tissue samples were obtained during hemorrhage or tumor surgery and mitochondria were rapidly isolated. Mitochondrial calcium retention capacity, a quantitative assay for mPT, was significantly increased by the CypD inhibitor cyclosporin A in both human brain and liver mitochondria, whereas thiol-reactive compounds and oxidants sensitized mitochondria to calcium-induced mPT. Brain mitochondria underwent swelling upon calcium overload, which was reversible upon calcium removal. To further explore mPT of human mitochondria, liver mitochondria were demonstrated to exhibit several classical features of the mPT phenomenon, such as calcium-induced loss of membrane potential and respiratory coupling, as well as release of the pro-apoptotic protein cytochrome c. We concluded that adult viable human brain and liver mitochondria possess an active CypD-sensitive mPT. Our findings support the rationale of CypD and mPT inhibition as pharmacological targets in acute and chronic neurodegeneration.

Effects of different types of anesthetic agents on cellular protein kinase C-γ dynamics in mouse brain

BACKGROUND/AIMS

Although protein kinase C-γ (PKC-γ) is a target for the effects of volatile anesthetics, the molecular mechanisms of the kinase function during their action remain unclear. We examined the effects of different types of anesthetics on PKC-γ knockout mice. Furthermore, we investigated the dynamics of the kinase in brain cells obtained from mice anesthetized with these anesthetics.

METHODS

We measured the required times for loss of righting reflex (rtfLORR) after administration of isoflurane, sevoflurane, or propofol on PKC-γ knockout mice and compared the times with those of wild-type mice. We also used immunoblotting to investigate the intracellular distribution of PKC-γ and phosphorylated PKC-γ (p-PKC-γ) in brain cell fractions obtained from wild-type mice during the loss of righting reflex induced by these anesthetics.

RESULTS

Isoflurane (2.6%) and sevoflurane (3.4%) used at twice the minimum alveolar concentration significantly prolonged the rtfLORRs in PKC-γ knockout mice compared to those in wild-type mice. On the other hand, no significant difference was observed between knockout and wild-type mice treated with propofol (200 mg/kg). Examination of the cellular fractions isolated from volatile anesthetic-treated mouse brains showed that PKC-γ was significantly decreased in the synaptic membrane fraction (P2), whereas p-PKC-γ was significantly increased in P2. There was no significant change in the supernatant fraction (S). In propofol-treated mice, PKC-γ and p-PKC-γ showed no significant changes in P2 or S.

CONCLUSION

Our results provide new evidence to support the possibility of the involvement of PKC-γ in the actions of volatile anesthetics.

Increased levels of 8-hydroxydeoxyguanosine in the vitreous of patients with diabetic retinopathy

We determined the intravitreous level of 8-hydroxydeoxyguanosine (8-OHdG) in diabetic retinopathy (DR) and analyzed the relation between oxidative stress and DR. Vitreous 8-OHdG concentration increased significantly in 18 patients (20 eyes) with DR compared with controls with macular disease. This result suggests that increased oxidative stress is involved in DR.

Increased potassium conductance of brain mitochondria induces resistance to permeability transition by enhancing matrix volume

Modulation of K(+) conductance of the inner mitochondrial membrane has been proposed to mediate preconditioning in ischemia-reperfusion injury. The mechanism is not entirely understood, but it has been linked to a decreased activation of mitochondrial permeability transition (mPT). In the present study K(+) channel activity was mimicked by picomolar concentrations of valinomycin. Isolated brain mitochondria were exposed to continuous infusions of calcium. Monitoring of extramitochondrial Ca(2+) and mitochondrial respiration provided a quantitative assay for mPT sensitivity by determining calcium retention capacity (CRC). Valinomycin and cyclophilin D inhibition separately and additively increased CRC. Comparable degrees of respiratory uncoupling induced by increased K(+) or H(+) conductance had opposite effects on mPT sensitivity. Protonophores dose-dependently decreased CRC, demonstrating that so-called mild uncoupling was not beneficial per se. The putative mitoK(ATP) channel opener diazoxide did not mimic the effect of valinomycin. An alkaline matrix pH was required for mitochondria to retain calcium, but increased K(+) conductance did not result in augmented DeltapH. The beneficial effect of valinomycin on CRC was not mediated by H(2)O(2)-induced protein kinase Cepsilon activation. Rather, increased K(+) conductance reduced H(2)O(2) generation during calcium infusion. Lowering the osmolarity of the buffer induced an increase in mitochondrial volume and improved CRC similar to valinomycin without inducing uncoupling or otherwise affecting respiration. We propose that increased potassium conductance in brain mitochondria may cause a direct physiological effect on matrix volume inducing resistance to pathological calcium challenges.

Evaluation of putative inhibitors of mitochondrial permeability transition for brain disorders--specificity vs. toxicity

Inhibition of mitochondrial permeability transition (mPT) has emerged as a promising approach for neuroprotection and development of well-tolerated mPT inhibitors with favorable blood-brain barrier penetration is highly warranted. In a recent study, 28 clinically available drugs with a common heterocyclic structure were identified as mPT inhibitors e.g. trifluoperazine, promethazine and nortriptyline. In addition, neuroprotection by structurally unrelated drugs e.g. neurosteroids, 4-hydroxy-tamoxifen and trimetazidine has been attributed to direct inhibition of mPT. The regulation of mPT is complex and highly dependent on the prevailing experimental conditions. Several features of mPT, such as swelling, depolarization or NADH oxidation, can also occur independently of the mPT phenomenon. Here, in isolated rodent brain-derived and human liver mitochondria, we re-evaluate drugs promoted as potent mPT inhibitors. We address the definition of an mPT inhibitor and present strategies to reliably detect mPT inhibition in vitro. Surprisingly, none of the 12 compounds tested displayed convincing mPT inhibition or effects comparable to cyclophilin D inhibition by the non-immunosuppressive cyclophilin inhibitor D-MeAla(3)-EtVal(4)-Cyclosporin (Debio 025). Propofol and 2-aminoethoxydiphenyl borate (2-APB) inhibited swelling in de-energized mitochondria but did not increase calcium retention capacity (CRC). Progesterone, trifluoperazine, allopregnanolone and 4-hydroxy-tamoxifen dose-dependently reduced CRC and respiratory control and were thus toxic rather than beneficial to mitochondrial function. Interestingly, topiramate increased CRC at high concentrations likely by a mechanism separate from direct mPT inhibition. We conclude that a clinically relevant mPT inhibitor should have a mitochondrial target and increase mitochondrial calcium retention at concentrations which can be translated to human use.

[Pulmonary schwannoma with hypervascularity; report of a case]

A 54-year-old female was admitted to our hospital with a mass shadow in the right pulmonary hilum. The chest computed tomography (CT) scan revealed a well-circumscribed mass in the lower lobe of the right lung. Bronchoscopic examination showed a submucosal tumor in the right basal bronchus which bled easily, and the angiogram showed a tumor with hypervascularity. The tumor was suspected to be a sclerosing hemangioma or malignant tumor. A right basal segmentectomy was performed, and the pathological diagnosis was that of schwannoma. During the 8 year follow-up period, she exhibited no evidence of recurrence.

Probing the molecular mechanisms of neuronal degeneration: importance of mitochondrial dysfunction and calcineurin activation

Cerebral injury is a critical aspect of the management of patients in intensive care. Pathological conditions induced by cerebral ischemia, hypoxia, head trauma, and seizure activity can result in marked residual impairment of cerebral function. We have investigated the potential mechanisms leading to neuronal cell death in pathological conditions, with the aim of discovering therapeutic targets and methods to minimize neuronal damage resulting from insults directed at the central nervous system (CNS). Over the years, deeper understanding of the mechanisms of neuronal cell death has indeed evolved, enabling clinical critical care management to salvage neurons that are at the brink of degeneration and to support recovery of brain function. However, no substantial breakthrough has been achieved in the quest to develop effective pharmacological neuroprotective therapy directed at tissues of the CNS. The current situation is unacceptable, and preservation of function and protection of the brain from terminal impairment will be a vital medical issue in the twenty-first century. To achieve this goal, it is critical to clarify the key mechanisms leading to neuronal cell death. Here, we discuss the importance of the calcineurin/immunophilin signal transduction pathway and mitochondrial involvement in the detrimental chain of events leading to neuronal degeneration.

Calcium-induced generation of reactive oxygen species in brain mitochondria is mediated by permeability transition

Mitochondrial uptake of calcium in excitotoxicity is associated with subsequent increase in reactive oxygen species (ROS) generation and delayed cellular calcium deregulation in ischemic and neurodegenerative insults. The mechanisms linking mitochondrial calcium uptake and ROS production remain unknown but activation of the mitochondrial permeability transition (mPT) may be one such mechanism. In the present study, calcium increased ROS generation in isolated rodent brain and human liver mitochondria undergoing mPT despite an associated loss of membrane potential, NADH and respiration. Unspecific permeabilization of the inner mitochondrial membrane by alamethicin likewise increased ROS independently of calcium, and the ROS increase was further potentiated if NAD(H) was added to the system. Importantly, calcium per se did not induce a ROS increase unless mPT was triggered. Twenty-one cyclosporin A analogs were evaluated for inhibition of calcium-induced ROS and their efficacy clearly paralleled their potency of inhibiting mPT-mediated mitochondrial swelling. We conclude that while intact respiring mitochondria possess powerful antioxidant capability, mPT induces a dysregulated oxidative state with loss of GSH- and NADPH-dependent ROS detoxification. We propose that mPT is a significant cause of pathological ROS generation in excitotoxic cell death.

Spinal cord mitochondria display lower calcium retention capacity compared with brain mitochondria without inherent differences in sensitivity to cyclophilin D inhibition

The mitochondrial permeability transition (mPT) is a potential pathogenic mechanism in neurodegeneration. Varying sensitivity to calcium-induced mPT has been demonstrated for regions within the CNS possibly correlating with vulnerability following insults. The spinal cord is selectively vulnerable in e.g. amyotrophic lateral sclerosis and increased mPT sensitivity of mitochondria derived from the spinal cord has previously been demonstrated. In this study, we introduce whole-body hypothermia prior to removal of CNS tissue to minimize the effects of differential tissue extraction prior to isolation of spinal cord and cortical brain mitochondria. Spinal cord mitochondria were able to retain considerably less calcium when administered as continuous infusion, which was not related to a general increased sensitivity of the mPT to calcium, its desensitization to calcium by the cyclophilin D inhibitor cyclosporin-A, or to differences in respiratory parameters. Spinal cord mitochondria maintained a higher concentration of extramitochondrial calcium during infusion than brain mitochondria possibly related to an increased set-point concentration for calcium uptake. A hampered transport and retention capacity of calcium may translate into an increased susceptibility of the spinal cord to neurodegenerative processes involving calcium-mediated damage.