Accelerated capacity of glutamate uptake via blood elements as a possible tool of rapid remote conditioning mediated tissue protection.

Recently, the function of blood cells in remote ischemic conditioning (RIC) mediated neuroprotection was undoubtedly confirmed. In the present paper, we have focused on the role of blood elements in glutamate homeostasis. The blood of remote conditioned (tolerant) animals was incubated ex vivo with 100 µM glutamate, and the quantitative and qualitative changes of excitatory amino acid transporters (EAAT 1, 2, and 3) were determined. We confirmed RIC mediated accelerated sequestration of extracellular glutamate via EAATs and altered distribution of that amino acid between plasma and cell elements compared to non-tolerant counterparts. The activity of EAATs was elevated in erythrocytes and monocytes, while the density of transporters was not affected. Quantitative changes of EAAT1 density were detected solely in platelets where the forced scavenging was independent of EAATs inhibition. Surprisingly, the trafficking of immunovisualised EAAT2 and 3 raised at tolerant erythrocytes and monocytes. We have found that protein synthesis underlined this process. On the other hand, depletion of protein synthesis did not significantly affect the scavenging capacity of those cell populations. Our work has demonstrated that the elevated blood scavenging of glutamate overdose could be one of the potential mechanisms underlying RIC mediated tissue protection.

Brain to blood efflux as a mechanism underlying the neuroprotection mediated by rapid remote preconditioning in brain ischemia.

Glutamate represents the main excitatory neurotransmitter in the mammalian brain; however, its excessive elevation in the extracellular space is cytotoxic and can result in neuronal death. The ischemia initiated brain damage reflects changes in glutamate concentration in peripheral blood. This paper investigated the role of the brain in blood efflux of the glutamate in an improved tolerance of the brain tissue to ischemic conditions. In the rat model of focal brain ischemia, the neuroprotection was initiated by rapid remote ischemic preconditioning (rRIPC). Our results confirmed a strong neuroprotective effect of rRIPC. We observed reduced infarction by about 78% related to improved neuronal survival by about 70% in the ischemic core. The level of tissue glutamate in core and penumbra dropped significantly and decreased to control value also in the core region of the contralateral hemisphere. Despite significant improvement of blood-brain barrier integrity (by about 76%), the additional gain of glutamate content in the peripheral blood was caused by rRIPC. Based on our results, we can assume that neuroprotection mediated by rapid remote ischemic preconditioning could lie in the regulated, whole-brain release of glutamate from nerve tissue to the blood, which preserves neurons from the exposure to glutamate toxicity and results in reduced infarction.

Rapid remote conditioning mediates modulation of blood cell paracrine activity and leads to the production of a secretome with neuroprotective features.

The indirect use of the protective potential of stem cells in the form of cell secretomes has become an attractive strategy in regenerative medicine. In the present work, we studied the paracrine activity of blood cells that could be modulated towards a neuroprotective nature using in vivo remote conditioning (i.e. tolerant blood cells). The increased neuronal survival mediated by the tolerant secretome was clearly confirmed in vitro in a model of glutamate toxicity in a primary culture of rat cortical neurons and in vivo in a pre- and post-treatment of rats that were subjected to transient occlusion of the middle cerebral artery. Bioinformatic-based analysis of the protein profile revealed higher amounts of proteins released by the tolerant blood cells; 29 proteins were recognised as secreted. More than half of these secreted proteins were involved in the biological processes of the response to the stimulus (GO:0050896) and the response to chemicals (GO:0042221). The protective phenotype was most likely mediated by the synergistic effect of multiple identified proteins, including unique to the tolerant secretome (ceruloplasmin, D-3-phosphoglycerate dehydrogenase) and was promoted by the co-participation of several reaction pathways. The most probably of these pathways were post-translation protein modification, MAP2K and MAPK activation and platelet activation. Taken together, our results demonstrate that properly stimulated blood cells could serve as a source for cell-free-based therapies of regenerative medicine.

Response of distant regions affected by diaschisis commissuralis in one of the most common models of transient focal ischemia in rats.

Stroke induces widespread changes in the brain. In this paper, we monitored some markers of early (2 h) and delayed events (1, 3 and 7 days of reperfusion) initiated by middle cerebral artery occlusion in core/penumbra counterparts of the non-ischemic hemisphere (i.e. contra-core and contra-penumbra). Our results showed that a profound transient drop (2 h and 3 days) of protein synthesis was measured in the contra-core, while the contra-penumbra exhibited translation over-activity at the same time. Glutamate release was detected only in the contra-core, with a peak on the first day. Degenerating neurons became visible in the striatum (day 1), followed by cortex (day 3), earlier in contra-penumbra and later in contra-core. Moreover, the loss of NADPH diaphorase-positive neurons in the non-ischemic hemisphere was detected, with the greatest drop at the first day. Total microglia also started to fall, the earliest in the contra-penumbra region of the striatum (day 1), followed by the contra-core of the striatum and both cortex regions at the seventh day. In conclusion, transient focal ischemia affects remote regions of the brain and initiates processes involved in neuronal degeneration in an order which corresponds to the tissue sensitivity to ischemia, namely earlier in the contra-penumbra, and afterwards in the contra-core. The mechanism of secondary damage would influence the progressive neuronal loss of more distant brain regions.

Neuroprotection mediated by remote preconditioning is associated with a decrease in systemic oxidative stress and changes in brain and blood glutamate concentration.

It has been shown that ischemia of remote organs can generate resistance to ischemic conditions within sensitive brain tissues. However, only limited information about its mechanism is available. In the present paper, we used hind-limb ischemia by tourniquet to generate early remote ischemic tolerance in rats. The main objective was to investigate the role of glutamate in the process of neuroprotection and discover parameters that are affected in the blood of ischemia-affected animals. Our results showed that pretreatment with a hind-limb tourniquet caused a decrease in neurodegeneration by about 30%. However, we did not observe neurological deficit recovery. When compared to ischemia, glutamate concentration decreased in all observed brain regions (cortex, CA1 and dentate gyrus of hippocampus), regardless of their sensitivity to blood restrictions. In contrast to this, the blood levels raised significantly from 26% to 29% during the first four days of postischemic reperfusion. Pretreatment of animals reduced systemic oxidative stress-as represented by lymphocytic DNA damage-by about 80%, while changes in blood antioxidant enzymes (catalase, superoxide dismutase) were not detected. With these data we can further hypothesize that hind-limb-tourniquet preconditioning could accelerate brain-to-blood efflux of glutamate which could positively impact neuronal survival of ischemia-affected brain regions. Moreover, remote preconditioning improved systemic oxidative stress and did not seem to be affected by enzymatic antioxidant defenses in the blood.

A Single Dose of Atorvastatin Applied Acutely after Spinal Cord Injury Suppresses Inflammation, Apoptosis, and Promotes Axon Outgrowth, Which Might Be Essential for Favorable Functional Outcome.

The aim of our study was to limit the inflammatory response after a spinal cord injury (SCI) using Atorvastatin (ATR), a potent inhibitor of cholesterol biosynthesis. Adult Wistar rats were divided into five experimental groups: one control group, two Th9 compression (40 g/15 min) groups, and two Th9 compression + ATR (5 mg/kg, i.p.) groups. The animals survived one day and six weeks. ATR applied in a single dose immediately post-SCI strongly reduced IL-1ß release at 4 and 24 h and considerably reduced the activation of resident cells at one day post-injury. Acute ATR treatment effectively prevented the excessive infiltration of destructive M1 macrophages cranially, at the lesion site, and caudally (by 66%, 62%, and 52%, respectively) one day post-injury, whereas the infiltration of beneficial M2 macrophages was less affected (by 27%, 41%, and 16%). In addition, at the same time point, ATR visibly decreased caspase-3 cleavage in neurons, astrocytes, and oligodendrocytes. Six weeks post-SCI, ATR increased the expression of neurofilaments in the dorsolateral columns and Gap43-positive fibers in the lateral columns around the epicenter, and from day 30 to 42, significantly improved the motor activity of the hindlimbs. We suggest that early modulation of the inflammatory response via effects on the M1/M2 macrophages and the inhibition of caspase-3 expression could be crucial for the functional outcome.