Caffeine treatment started before injury reduces hypoxic–ischemic white-matter damage in neonatal rats by regulating phenotypic microglia polarization

BACKGROUND: Reducing neuroinflammatory damage is an effective strategy for treating white-matter damage (WMD) in premature infants. Caffeine can ameliorate hypoxia–ischemia-induced brain WMD; however, its neuroprotective effect and mechanism against hypoxic–ischemic WMD remain unclear. METHODS: We used 3-day-old Sprague–Dawley rats to establish a model of cerebral hypoxia–ischemia-induced brain WMD after unilateral common carotid artery ligation and hypoxia exposure (8% O(2) + 92% N(2)) for 2.5 h. Mechanism experiments were conducted to detect M1/M2 polarization and activation of microglia and NLRP3 inflammasome. RESULTS: Caffeine inhibited NLRP3 inflammasome activation, reduced microglial Iba-1 activation, inhibited microglia M1 polarization, and promoted microglia M2 polarization by downregulating CD86 and iNOS protein expression, inhibiting the transcription of the proinflammatory TNF-α and IL-1β, upregulating CD206 and Arg-1 expression, and promoting the transcription of the anti-inflammatory factors IL-10 and TGF-β. Importantly, we found that these caffeine-mediated effects could be reversed after inhibiting A2aR activity. CONCLUSIONS: Caffeine improved long-term cognitive function in neonatal rats with hypoxic–ischemic WMD via A2aR-mediated inhibition of NLRP3 inflammasome activation, reduction of microglial activation, regulation of the phenotypic polarization of microglia and the release of inflammatory factors, and improvement of myelination development. IMPACT: The direct protective effect of caffeine on hypoxic–ischemic white-matter damage (WMD) and its mechanism remains unclear. This study elucidated this mechanism using neonatal rats as an animal model of hypoxia–ischemia-induced cerebral WMD. The findings demonstrated caffeine as a promising therapeutic tool against immature WMD to protect neonatal cognitive function. We found that caffeine pretreatment reduced WMD in immature brains via regulation of microglial activation and polarization by adenosine A2a receptor, thereby, providing a scientific basis for future clinical application of caffeine.