Dear editor
We read with interest the article “Cortical spreading depression produces a neuroprotective effect activating mitochondrial uncoupling protein-5″ published in Neuropsychiatr Dis Treat by Viggiano et al.1 The authors showed that cerebral spreading depression (CSD) triggered uncoupling protein-5 (UCP-5),1 which had been reported to exert a long-term effect upon neuron protection.2 The result is another piece in CSD literature on modifying gene expressions to provide neuroprotection to subsequent ischemic episodes.3,4
An unmentioned but additional factor for neuroprotection in CSD could be acidosis.
Acidosis is a known consequence of CSD.5 In the literature, brief acidosis in ischemic conditions when oxygen supply is low has been shown to be cytoprotective and neuroprotective,6–10 a result related sometimes to the concept of the “pH paradox.”9,11,12 Acidosis had been reported to reduce stroke infarct size with CO2 applied for a short time after reperfusion6 as well as during ischemic stroke.10 Brief acidosis applied after birth asphyxia7 was reported to successfully suppress brain alkalosis, which led to seizures. Hence, brief and relatively mild acidosis induced under the condition of CSD may be one of the neuroprotective factors for CSD. The role of acidosis in neuroprotection by CSD warrants further investigation.
Interestingly, CSD-induced acidosis could be one explanation of impaired cerebral vascular reactivity13–16 after CSD. It has been reported that once tissue reaches a certain low pH threshold, blood flow increase would be insignificant in response to even stronger CO2 challenge.10
Footnotes
Disclosure
The authors report no conflicts of interest in this communication.
References
- 1.Viggiano E, Monda V, Messina A, et al. Cortical spreading depression produces a neuroprotective effect activating mitochondrial uncoupling protein-5. Neuropsychiatr Dis Treat. 2016;12:1705–1710. doi: 10.2147/NDT.S107074. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Nakase T, Yoshida Y, Nagata K. Amplified expression of uncoupling proteins in human brain ischemic lesions. Neuropathology. 2007;27(5):442–447. doi: 10.1111/j.1440-1789.2007.00815.x. [DOI] [PubMed] [Google Scholar]
- 3.Passaro D, Rana G, Piscopo M, Viggiano E, De Luca B, Fucci L. Epigenetic chromatin modifications in the cortical spreading depression. Brain Res. 2010;1329:1–9. doi: 10.1016/j.brainres.2010.03.001. [DOI] [PubMed] [Google Scholar]
- 4.Taga K, Patel PM, Drummond JC, Cole DJ, Kelly PJ. Transient neuronal depolarization induces tolerance to subsequent forebrain ischemia in rats. Anesthesiology. 1997;87(4):918–925. doi: 10.1097/00000542-199710000-00027. [DOI] [PubMed] [Google Scholar]
- 5.Mutch WA, Hansen AJ. Extracellular pH changes during spreading depression and cerebral ischemia: mechanisms of brain pH regulation. J Cereb Blood Flow Metab. 1984;4(1):17–27. doi: 10.1038/jcbfm.1984.3. [DOI] [PubMed] [Google Scholar]
- 6.Fan YY, Shen Z, He P, et al. A novel neuroprotective strategy for ischemic stroke: transient mild acidosis treatment by CO2 inhalation at reperfusion. J Cereb Blood Flow Metab. 2014;34(2):275–283. doi: 10.1038/jcbfm.2013.193. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Helmy MM, Tolner EA, Vanhatalo S, Voipio J, Kaila K. Brain alkalosis causes birth asphyxia seizures, suggesting therapeutic strategy. Ann Neurol. 2011;69(3):493–500. doi: 10.1002/ana.22223. [DOI] [PubMed] [Google Scholar]
- 8.Khacho M, Tarabay M, Patten D, et al. Acidosis overrides oxygen deprivation to maintain mitochondrial function and cell survival. Nat Commun. 2014;5:3550. doi: 10.1038/ncomms4550. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Laffey JG. Protective effects of acidosis. Anaesthesia. 2001;56(10):1013–1014. doi: 10.1046/j.1365-2044.2001.02279-18.x. [DOI] [PubMed] [Google Scholar]
- 10.Simon RP, Niro M, Gwinn R. Brain acidosis induced by hypercarbic ventilation attenuates focal ischemic injury. J Pharmacol Exp Ther. 1993;267(3):1428–1431. [PubMed] [Google Scholar]
- 11.Laffey JG, Kavanagh BP. Carbon dioxide and the critically ill – too little of a good thing? Lancet. 1999;354(9186):1283–1286. doi: 10.1016/S0140-6736(99)02388-0. [DOI] [PubMed] [Google Scholar]
- 12.Swenson ER. Therapeutic hypercapnic acidosis: pushing the envelope. Am J Respir Crit Care Med. 2004;169(1):8–9. doi: 10.1164/rccm.2310008. [DOI] [PubMed] [Google Scholar]
- 13.Lauritzen M. Long-lasting reduction of cortical blood flow of the brain after spreading depression with preserved autoregulation and impaired CO2 response. J Cereb Blood Flow Metab. 1984;4(4):546–554. doi: 10.1038/jcbfm.1984.79. [DOI] [PubMed] [Google Scholar]
- 14.Wahl M, Lauritzen M, Schilling L. Change of cerebrovascular reactivity after cortical spreading depression in cats and rats. Brain Res. 1987;411(1):72–80. doi: 10.1016/0006-8993(87)90682-2. [DOI] [PubMed] [Google Scholar]
- 15.Scheckenbach KE, Dreier JP, Dirnagl U, Lindauer U. Impaired cerebrovascular reactivity after cortical spreading depression in rats: restoration by nitric oxide or cGMP. Exp Neurol. 2006;202(2):449–455. doi: 10.1016/j.expneurol.2006.07.007. [DOI] [PubMed] [Google Scholar]
- 16.Guiou M, Sheth S, Nemoto M, et al. Cortical spreading depression produces long-term disruption of activity-related changes in cerebral blood volume and neurovascular coupling. J Biomed Opt. 2005;10(1):11004. doi: 10.1117/1.1852556. [DOI] [PubMed] [Google Scholar]