The temperature dependence and involvement of mitochondria permeability transition and caspase activation in damage to organotypic hippocampal slices following in vitro ischemia

An insulin based model to explain changes and interactions in human breath-holding

Until now oxygen was thought to be the leading factor of hypoxic conditions. Whereas now it appears that insulin is the key regulator of hypoxic conditions. Insulin seems to regulate the redox state of the organism and to determine the breakpoint of human breath-holding. This new hypoxia-insulin hypotheses might have major clinical relevance. Besides the clinical relevance, this hypothesis could explain, for the first time, why the training of the diaphragm, among other factors, results in an increase in breath-holding performance. Elite freedivers/apnea divers are able to reach static breath-holding times to over 6 min. Untrained persons exhibit an unpleasant feeling after more or less a minute. Breath-holding is stopped at the breakpoint. The partial oxygen pressure as well as the carbon dioxide pressure failed to directly influence the breakpoint in earlier studies. The factors that contribute to the breakpoint are still under debate. Under hypoxic conditions the organism needs more glucose, because it changes from the oxygen consuming pentose phosphate (36 ATP/glucose molecule) to the anaerobic glycolytic pathway (2ATP/glucose molecule). Hence insulin, as it promotes the absorption of glucose, is set in the center of interest regarding hypoxic conditions. This paper provides an insulin based model that could explain the changes and interactions in human breath-holding. The correlation between hypoxia and reactive oxygen species (ROS) and their influence on the sympathetic nerve system and hypoxia-inducible factor 1 alpha (HIF-1α) is dealt with. It reviews as well the direct interrelation of HIF-1α and insulin. The depression of insulin secretion through the vagus nerve activation via inspiration is discussed. Furthermore the paper describes the action of insulin on the carotid bodies and the diaphragm and therefore a possible role in respiration pattern. Freedivers that go over the breakpoint of breath-holding could exhibit seizures and thus the effect of insulin, blood glucose levels and corticosteroids in hippocampal seizures is highlighted.

Minor Changes in Core Temperature Prior to Cardiac Arrest Influence Outcomes: An Experimental Study

AIM

To investigate whether slight variations in core temperature prior to cardiac arrest (CA) influence short-term outcomes and mitochondrial functions.

METHODS AND MATERIALS

Three groups of New Zealand White rabbits (n = 12/group) were submitted to 15 minutes of CA at 38°C (T-38 group), 39°C (T-39), or 40°C (T 40) and 120 minutes of reperfusion. A Sham-operated group (n = 6) underwent only surgery. Restoration of spontaneous circulation (ROSC), survival, hemodynamics, and pupillary reactivity were recorded. Animals surviving to the end of the observation period were euthanized to assess fresh brain and heart mitochondrial functions (permeability transition and oxidative phosphorylation). Markers of brain and heart damages were also measured.

RESULTS

The duration of asphyxia required to induce CA was significantly lower in the T-40 group when compared to the T-38 group (P < .05). The rate of ROSC was >80% in all groups (P = nonsignificant [ns]). Survival significantly differed among the T-38, T-39, and T-40 groups: 10 (83%) of 12, 7 (58%) of 12, and 4 (33%) of 12, respectively (log-rank test, P = .027). At the end of the protocol, none of the animals in the T-40 group had pupillary reflexes compared to 8 (67%) of 12 in the T-38 group (P < .05). Troponin and protein S100B were significantly higher in the T-40 versus T-38 group (P < .05). Cardiac arrest significantly impaired both inner mitochondrial membrane integrity and oxidative phosphorylation in all groups. Brain mitochondria disorders were significantly more severe in the T-40 group compared to the T-38 group (P < .05).

CONCLUSION

Small changes in body temperature prior to asphyxial CA significantly influence brain mitochondrial functions and short-term outcomes in rabbits.

Hypothermia protects human neurons

BACKGROUND AND AIMS

Hypothermia provides neuroprotection after cardiac arrest, hypoxic-ischemic encephalopathy, and in animal models of ischemic stroke. However, as drug development for stroke has been beset by translational failure, we sought additional evidence that hypothermia protects human neurons against ischemic injury.

METHODS

Human embryonic stem cells were cultured and differentiated to provide a source of neurons expressing β III tubulin, microtubule-associated protein 2, and the Neuronal Nuclei antigen. Oxygen deprivation, oxygen-glucose deprivation, and H2 O2 -induced oxidative stress were used to induce relevant injury.

RESULTS

Hypothermia to 33°C protected these human neurons against H2 O2 -induced oxidative stress reducing lactate dehydrogenase release and Terminal deoxynucleotidyl transferase dUTP nick end labeling-staining by 53% (P ≤ 0·0001; 95% confidence interval 34·8-71·04) and 42% (P ≤ 0·0001; 95% confidence interval 27·5-56·6), respectively, after 24 h in culture. Hypothermia provided similar protection against oxygen-glucose deprivation (42%, P ≤ 0·001, 95% confidence interval 18·3-71·3 and 26%, P ≤ 0·001; 95% confidence interval 12·4-52·2, respectively) but provided no protection against oxygen deprivation alone. Protection (21%) persisted against H2 O2 -induced oxidative stress even when hypothermia was initiated six-hours after onset of injury (P ≤ 0·05; 95% confidence interval 0·57-43·1).

CONCLUSION

We conclude that hypothermia protects stem cell-derived human neurons against insults relevant to stroke over a clinically relevant time frame. Protection against H2 O2 -induced injury and combined oxygen and glucose deprivation but not against oxygen deprivation alone suggests an interaction in which protection benefits from reduction in available glucose under some but not all circumstances.

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.

Potassium-induced structural changes of the endoplasmic reticulum in pyramidal neurons in murine organotypic hippocampal slices

The endoplasmic reticulum (ER) structure is of central importance for the regulation of cellular anabolism, stress response, and signal transduction. Generally continuous, the ER can temporarily undergo dramatic structural rearrangements resulting in a fragmented appearance. In this study we assess the dynamic nature of ER fission in pyramidal neurons in organotypic hippocampal slice cultures stimulated by depolarizing concentration of potassium (50 mM). The slices were obtained from transgenic mice expressing fluorescent ER-targeted DsRed2 protein. We employed live tissue confocal microscopy imaging with fluorescence recovery after photobleaching (FRAP) to monitor the extent of structural rearrangements of the ER. In control slices, the ER structure was continuous. Potassium stimulation resulted in extensive fragmentation (fission), whereas return to basal potassium levels (2.5 mM) led to ER fusion and normalization of ER structure. This ER fission/fusion could be repeated several times in the same neuron, demonstrating the reversibility of the process. Blockade of the N-methyl-D-aspartate receptor (NMDAR) with the antagonist D-AP5 or removal of extracellular Ca(2+) prevented depolarization-induced ER fission. ER fission is sensitive to temperature, and decreasing temperature from 35°C to 30°C augments fission, implying that the altering of ER continuity may be a protective response against damage. We conclude that events that generate membrane depolarisation in brain tissue lead to the release of endogenous glutamate that may regulate neuronal ER continuity. The rapid and reversible NMDAR-mediated changes in ER structure reflect an adaptive, innate property of the ER for synaptic activation as well as response to tissue stress, injury, and disease.

Neuroprotective effects of FK506 against excitotoxicity in organotypic hippocampal slice culture

FK506 has been originally classified as an immunosuppressant and is known to exhibit neurotrophic actions in vitro and protective effects on some neurological conditions. We investigated the neuroprotective effects of FK506 on kainic acid (KA)-induced neuronal death in organotypic hippocampal slice cultures (OHSCs). After an 18 h KA (5 microM) treatment, significantly neuronal death was detected in the CA3 region using propidium iodide staining. However, neuronal death was significantly prevented at 24 and 48 h after treatment with 0.1 microM FK506. Using cresyl violet staining, we also observed that an increased number of CA3 neurons survived in the 0.1 microM FK506 group compared to the KA only group. Based on the results of the Western blot analysis, the expressions of 5-lipoxygenase and caspase-3 were reduced 24h after 0.1 microM FK506 treatment. The levels of superoxide dismutase (SOD) and phospho-Akt expression were increased by treatment with 0.1 microM FK506. These results suggest that FK506 may have a positive role in protecting neurons against cell death in the KA injury model of OHSCs.

Rho kinase inhibition protects CA1 cells in organotypic hippocampal slices during in vitro ischemia

The actin cytoskeleton is a dynamic superstructure that regulates multiple cellular functions and that has been implicated in cell death regulation. We investigated whether modulating the neuronal actin cytoskeleton polymerization by Rho-GTPase kinase (ROCK) inhibition influences cell death in hippocampal neuronal cultures and in murine organotypic hippocampal slice cultures subjected to in vitro ischemia (IVI). During IVI, spines on vehicle treated hippocampal neurons collapsed and large dendritic actin aggregates were formed. Following ROCK inhibition by Y27632, the actin aggregates were markedly smaller while large filopodia extended from the dendritic trunk. Y27632 also provided strong neuroprotection of hippocampal pyramidal CA1 neurons, which was of similar magnitude as protection by NMDA receptor blockade. Likewise, treatment with the F-actin depolymerizing agent latrunculin during IVI diminished actin aggregation and mitigated cell death following IVI. We propose that ROCK inhibition protects neurons against ischemic damage by disrupting actin polymerization thereby mitigating NMDA receptor induced toxicity and releasing ATP bound to actin for cellular energy use. We conclude that ROCK inhibitors abrogate multiple detrimental processes and could therefore be useful in stroke therapy.

Mitochondrial targeting of cyclosporin A enables selective inhibition of cyclophilin-D and enhanced cytoprotection after glucose and oxygen deprivation

CsA (cyclosporin A) is a hydrophobic undecapeptide that inhibits CyPs (cyclophilins), a family of PPIases (peptidylprolyl cis-trans isomerases). In some experimental models, CsA offers partial protection against lethal cell injury brought about by transient ischaemia; this is believed to reflect inhibition of CyP-D, a mitochondrial isoform that facilitates formation of the permeability transition pore in the mitochondrial inner membrane. To evaluate this further, we have targeted CsA to mitochondria so that it becomes selective for CyP-D in cells. This was achieved by conjugating the inhibitor to the lipophilic triphenylphosphonium cation, enabling its accumulation in mitochondria due to the inner membrane potential. In a cell-free system and in B50 neuroblastoma cells the novel reagent (but not CsA itself) preferentially inhibited CyP-D over extramitochondrial CyP-A. In hippocampal neurons, mitochondrial targeting markedly enhanced the capacity of CsA to prevent cell necrosis brought about by oxygen and glucose deprivation, but largely abolished its capacity to inhibit glutamate-induced cell death. It is concluded that CyP-D has a major pathogenic role in 'energy failure', but not in glutamate excitotoxicity, where cytoprotection primarily reflects CsA interaction with extramitochondrial CyPs and calcineurin. Moreover, the therapeutic potential of CsA against ischaemia/reperfusion injuries not involving glutamate may be improved by mitochondrial targeting.

Multimodal Strategies for Resuscitating Injured Cells

Our cells and tissues are challenged constantly by exposure to extreme conditions that cause acute and chronic stress. Wounding at the cellular level is a common event, and results from cell exposure to supra-physiologic forces, or is the consequence of action by reactive chemical agents. An individual cellular wound results from either the alteration of protein or DNA structure, or the disruption of molecular assemblies, the most important of which is the cell's membranes. Tissue healing at the macroscopic level is a complex and coordinated process involving many different cell types while, in contrast, the wounds of individual cells heal primarily via biomolecular interactions. Like tissue wound healing, cellular wound healing involves the upregulation or acceleration of processes that are constitutively expressed in routine physiologic repair of cellular structures In addition, recent advances have been made in the identification of pharmaceutical strategies to aid the cellular repair response. Many of these strategies offer promise for augmenting the already present cellular repair mechanisms.