The complex pathophysiology of WMD enables multiple targets at different time points of the diseaseprocess. For instance, in the early phase therapies are mainly concentrated on reduction of excitotoxic, oxidative and apoptotic mediators of injury. The development of therapies to reduce brain injury secondary to WMD is important because of the severity of disability that may result.
HIF-1α an important factor in the regulation of hypoxia, and has been proved to be involved in hypoxic-ischemic preconditioning in multiple species of tissues as a transcription factor. Physiologically, HIF-1α is hydroxylated by prolyl-4-hydroxylases (PHDs) in the oxygen-dependent degradation domain of proline. After that,HIF-1α becomes ubiquitin ligase complex, which is degraded by proteasome. HIF-1α is degraded by this mechanism. Under normoxic conditions, HIF-1α protein has a very short half-life (less than 5 min under posthypoxic conditions in cell culture), and decreases in oxygen concentration cause its stability to increase almost immediately, as reduction of PHD activity leadind to degradation of proteasome.[22] HIF-1α targets a wide variety of genes,including genes involved in energy metabolism,angiogenesis,cell proliferation,and survival.among others,[23]and also plays a role in hypoxic preconditioning in many organs by increasing the expression of HIF-1α ,[24, 25]especially in the brain, the role of HIF-1α is well recognized. Prass et al.[26] showed that hypoxia-induced HIF-1α DNA connectivity increased, leading to cerebral ischemic tolerance. Hypoxic stimulation up-regulates the expression of HIF-1α and EPO protein, produces reactive oxygen species, and plays an obvious neuroprotective role.[27] Recently, a number of microRNAs induced during hypoxia have been identified.One of these microRNAs, miR-210 is strongly induced by HIF-1α and has pleiotropic effects.[28] Fasanaro et al. reported that the expression level of miR-210 in endothelial cells was up-regulated in hypoxic environment, while promoting angiogenesis to a certain extent.[29] It is also closely related to hypoxic-ischemic diseases of the brain. Most studies have shown a direct link between the expression of miR-210 and hypoxia .[30–34] In particular,at the binding site of HIF-1α on its promoter,the expression of miR-210 was significantly up-regulated between normal and transformed cells.[33] Some studies have shown that miR-210 plays an important role in cell survival during hypoxia as a highly up-regulated microRNA.,[28, 29]Under normoxic conditions, the presence of miR-210 is not effective, but when hypoxia occurs,the increase of miR-210 expression will reduce the effect of hypoxic environment on cell metabolism to a minimum.[35] miR-210 is a stable target of HIF-1α,that is activated under hypoxic environment, which induces the up-regulation of the expression of miR-210 .[17]Hypoxia can promote the expression of HIF-1α increasing at 4 hours, peaking at 8 hours and decreasing at 24 hours,and apoptosis increases significantly at 24 hours after hypoxia,accompanied by down-regulation of HIF-1α expression, that suggesting HIF-1α may play a protective role in regulating apoptosis.[36] Animal experiments and cell culture data showed that the level of miR-210 increased immediately after hypoxic injury, and then decreased for several days. Along with ischemia and hypoxia, the level of HIF-1α also changed continuously. Therefore, the increase of miR-210 level after HI injury was regulated by HIF-1α and related to the time of injury.[28, 37] Kelly [38]recently discovered the loop of miR-210 regulating HIF-1α and identified a new HIF-1α regulatory factor, glycerol-3-phosphate dehydrogenase 1-like (GPD1L). The induction of miR-210 by HIF-1α reduced the expression of GPD1L protein, thereby increasing the stability of HIF-1α. In conclusion, HIF-1α protein increased significantly in a certain period of time, peaked at 24 hours, and then gradually decreased to baseline level with the extension of time after HI injury in neonate rats. The protective effect was enhanced and then weakened. If intervention treatment was given after HI,HIF-1α degradation was inhibited to protect brain tissue,and the expression of miR-210 is related to the level of HIF-1α protein, that will bring new ideas for the follow-up treatment of neonatal brain damage.Our data suggest that the expression levels of HIF-1α protein and miR-210 in brain tissue increased after LPS combined with HI injury(p༜0.05), which is consistent with the above study.
Xenon is an NMDA receptor antagonist that has been precluded from the widespread clinical use as a general anesthetic due to its relatively high cost.[14, 15, 39] Xenon has well documented neuroprotective properties that were reported in models of premature brain injury,[7, 10, 11, 39]as shown in our previous papers.[19]In this study, we investigated the acute neuroprotective outcomes of xenon in an in vivo model of premature brain injury. In accordance with previous reports, we opted to use a 3-hour xenon treatment interval.[21, 40] The present results indicate that xenon has the greatest neuroprotective effect in the range of 37.5–50 vol%, which is consistent with previous studies that 50% xenon can provide sufficient neuroprotective effect .[41–43] On the contrary, others have shown that xenon at 75% volume concentration has the greatest neuroprotective effect and does not affect oxygenation[41]. However, in addition to neuroprotective effect, xenon at this concentration may have adverse side effects .[43] We choose a mixture of 50% xenon, 30% oxygen and 20% nitrogen to intervene,the mixture has 2.8 × the density but almost the same viscosity as air .[44]In our study, following LPS and HI insult, we observed the expression of miR-210and HIF-1α elevated,and our results revealed that the administration of 50% xenon balanced with 30% oxygen and 20% nitrogen for 3 hours after injury resulted in a significant increase of miR-210 and HIF-1α(p < 0.05). These results suggest that xenon can alleviate white matter damage by activating HIF-1α expression, and the stable expression of HIF-1α can regulate the expression of microRNA-210, which plays a neuroprotective role by inhibiting neuronal apoptosis through related pathways. The available time-window for treatment effectiveness and administration is an important aspect to consider in potential treatments for premature brain injury. Therefore, we investigated the effectiveness of xenon when administered immediately or delayed for 2 or 5 hours following LPS and HI-induced injury. The level of microRNA-210 did not increase significantly, but the level of HIF-1α protein did not decrease significantly.Maintaining and stabilizing the level of HIF-1α protein still served to protect brain tissue. In addition, results revealed that the delay in xenon administration for 5 hours resulted in a significant increase of HIF-1α ( p > 0.05), which may suggest that xenon still exerts its neuroprotective effects for up to 5 hours after injury,and the regulation between HIF-1α and microRNA-210 is related to the time of injury,and may suggest that xenon still exerts its neuroprotective effects for up to 5 hours after injury,the sooner the beter.
In summary, we showed that xenon is an efficient neuroprotective agent against premature brain injury in a rodent model of WMD. Our results indicated that xenon treatment up-regulated the expression of miR-210 and HIF-1α and improved neurological outcome after WMD. The therapeutic time-window of xenon extends for up to 5 hours. Our findings are in agreement with the previously demonstrated neuroprotective effects of xenon in HI injury.[7, 19] The duration of xenon treatment was relatively short (3 hours) which might suggest that the extension of treatment time might result in better neuroprotection and a longer therapeutic time window. Our findings support the idea that xenon could provide a first-line treatment for white matter injury in premature infants. The development of xenon-closed circuit delivery system and advances in gas extraction technology will potentially lead to enhanced procedures of xenon dosing with reduced cost.[45] Further, xenon is a non-flammable gas that can be easily administered at the bedside. In conclusion, the present study revealed a novel effect of xenon in protection against premature brain injury. Future experimental studies and clinical trials would be valuable in providing further insights into xenon neuroprotective efficacy.