Melatonin reduces brain injury following inflammation‐amplified hypoxia–ischemia in a translational newborn piglet study of neonatal encephalopathy

Abstract There is a need to develop therapies for neonatal encephalopathy (NE) in low‐ and middle‐income countries (LMICs) where the burden of disease is greatest and therapeutic hypothermia (HT) is not effective. We aimed to assess the efficacy of melatonin following inflammation‐amplified hypoxia–ischaemia (IA‐HI) in the newborn piglet. The IA‐HI model accounts for the contribution of infection/inflammation in this setting and HT is not cytoprotective. We hypothesised that intravenous melatonin (5% ethanol, at 20 mg/kg over 2 h at 1 h after HI + 10 mg/kg/12 h between 24 and 60 h) is safe and associated with: (i) reduction in magnetic resonance spectroscopy lactate/ N ‐acetylaspartate (MRS Lac/sNAA); (ii) preservation of phosphorus MRS phosphocreatine/phosphate exchange pool (PCr/Epp); (iii) improved aEEG/EEG recovery and (iv) cytoprotection on immunohistochemistry. Male and female piglets underwent IA‐HI by carotid artery occlusion and reduction in FiO 2 to 6% at 4 h into Escherichia coli lipopolysaccharide sensitisation (2 μg/kg bolus + 1 μg/kg/h over 12 h). At 1 h after IA‐HI, piglets were randomised to HI‐saline ( n = 12) or melatonin ( n = 11). There were no differences in insult severity between groups. Target melatonin levels (15–30 mg/L) were achieved within 3 h and blood ethanol levels were <0.25 g/L. At 60 h, compared to HI‐saline, melatonin was associated with a reduction of 0.197 log 10 units (95% CrI [−0.366, −0.028], Pr (sup) 98.8%) in basal‐ganglia and thalamic Lac/NAA, and 0.257 (95% CrI [−0.676, 0.164], Pr (sup) 89.3%) in white matter Lac/NAA. PCr/Epp was higher in melatonin versus HI‐saline (Pr (sup) 97.6%). Melatonin was associated with earlier aEEG/EEG recovery from 19 to 24 h (Pr (sup) 95.4%). Compared to HI‐saline, melatonin was associated with increased NeuN+ cell density (Pr (sup) 99.3%) across five of eight regions and reduction in TUNEL‐positive cell death (Pr (sup) 89.7%). This study supports the translation of melatonin to early‐phase clinical trials. Melatonin is protective following IA‐HI where HT is not effective. These data guide the design of future dose‐escalation studies in the next phase of the translational pipeline.