Hypothermia is not therapeutic in a neonatal piglet model of inflammation-sensitized hypoxia–ischemia

Abstract

Background Perinatal inflammation combined with hypoxia–ischemia (HI) exacerbates injury in the developing brain. Therapeutic hypothermia (HT) is standard care for neonatal encephalopathy; however, its benefit in inflammation-sensitized HI (IS-HI) is unknown. Methods Twelve newborn piglets received a 2 µg/kg bolus and 1 µg/kg/h infusion over 52 h of Escherichia coli lipopolysaccharide (LPS). HI was induced 4 h after LPS bolus. After HI, piglets were randomized to HT (33.5 °C 1–25 h after HI, n = 6) or normothermia (NT, n = 6). Amplitude-integrated electroencephalogram (aEEG) was recorded and magnetic resonance spectroscopy (MRS) was acquired at 24 and 48 h. At 48 h, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive brain cell death, microglial activation/proliferation, astrogliosis, and cleaved caspase-3 (CC3) were quantified. Hematology and plasma cytokines were serially measured. Results Two HT piglets died. aEEG recovery, thalamic and white matter MRS lactate/N-acetylaspartate, and TUNEL-positive cell death were similar between groups. HT increased microglial activation in the caudate, but had no other effect on glial activation/proliferation. HT reduced CC3 overall. HT suppressed platelet count and attenuated leukocytosis. Cytokine profile was unchanged by HT. Conclusions We did not observe protection with HT in this piglet IS-HI model based on aEEG, MRS, and immunohistochemistry. Immunosuppressive effects of HT and countering neuroinflammation by LPS may contribute to the observed lack of HT efficacy. Other immunomodulatory strategies may be more effective in IS-HI. Impact Acute infection/inflammation is known to exacerbate perinatal brain injury and can worsen the outcomes in neonatal encephalopathy. Therapeutic HT is the current standard of care for all infants with NE, but the benefit in infants with coinfection/inflammation is unknown. In a piglet model of inflammation (LPS)-sensitized HI, we observed no evidence of neuroprotection with cooling for 24 h, based on our primary outcome measures: aEEG, MRS Lac/NAA, and histological brain cell death. Additional neuroprotective agents, with beneficial immunomodulatory effects, require exploration in IS-HI models.

Evaluating Neuroprotective Effects of Uridine, Erythropoietin, and Therapeutic Hypothermia in a Ferret Model of Inflammation-Sensitized Hypoxic-Ischemic Encephalopathy

“…Part of the lack of complete neuroprotection by TH may be due to heterogeneous etiologies of injury in the clinical setting, including HIE complicated by infection or chronic placental insufficiency [38,39]. In particular, TH has not been neuroprotective in preclinical models of HI sensitized with LPS [13,40,41]. The lack of significant neuroprotection conferred by TH in our ferret model is therefore not unexpected due to the use of LPS for inflammatory presensitization, though TH animals did demonstrate improved behavioral outcomes in some tests compared to other HIH-exposed animals.…”

“…Examining the mechanisms of Epo neuroprotection in this model are beyond the scope of this manuscript but will form the basis of future work. By comparison, although we have not studied response to these therapies without the presensitizing effect of LPS in the model, it is likely that the inclusion of LPS is the primary reason for a lack of neuroprotective effect of TH [13,40,41]. However, as more definitive evidence is accumulating regarding the lack of TH neuroprotection in lower income settings [5], perhaps due to more protracted or chronic perinatal insults, the model as used here may be particularly useful for examining therapies for use in scenarios where TH is not beneficial.…”

Rise and Fall of Therapeutic Hypothermia in Low-Resource Settings: Lessons from the HELIX Trial

“…Meanwhile, some researchers proposed infection was the main cause of encephalopathy in African settings. More recent data from Africa [13,21] and South Asia suggest that the incidence of coexistent sepsis in Africa and South Asia is not higher than high-income countries [14] and coexistent sepsis cannot explain lack of hypothermic neuroprotection in LMIC.…”

Neurological Outcome Following Newborn Encephalopathy With and Without Perinatal Infection: A Systematic Review

“…Several animal studies have found that endotoxin-induced inflammation prior to hypoxia-ischemia severely exacerbates brain injury in newborns ( 24 – 31 ). In addition to the possible aggravation of brain damage, both animal ( 32 – 37 ) and clinical studies ( 38 – 41 ) have suggested that infections may affect both the efficacy and safety of therapeutic hypothermia.…”