No Added Neuroprotective Effect of Remote Ischemic Postconditioning and Therapeutic Hypothermia After Mild Hypoxia-Ischemia in a Piglet Model

Abstract

Introduction: Hypoxic ischemic encephalopathy (HIE) is a major cause of death and disability in children worldwide. Apart from supportive care, the only established treatment for HIE is therapeutic hypothermia (TH). As TH is only partly neuroprotective, there is a need for additional therapies. Intermittent periods of limb ischemia, called remote ischemic postconditioning (RIPC), have been shown to be neuroprotective after HIE in rats and piglets. However, it is unknown whether RIPC adds to the effect of TH. We tested the neuroprotective effect of RIPC with TH compared to TH alone using magnetic resonance imaging and spectroscopy (MRI/MRS) in a piglet HIE model. Methods: Thirty-two male and female piglets were subjected to 45-min global hypoxia-ischemia (HI). Twenty-six animals were randomized to TH or RIPC plus TH; six animals received supportive care only. TH was induced through whole-body cooling. RIPC was induced 1 h after HI by four cycles of 5 min of ischemia and 5 min of reperfusion in both hind limbs. Primary outcome was Lac/NAA ratio at 24 h measured by MRS. Secondary outcomes were NAA/Cr, diffusion-weighted imaging (DWI), arterial spin labeling, aEGG score, and blood oxygen dependent (BOLD) signal measured by MRI/MRS at 6, 12, and 24 h after the hypoxic-ischemic insult. Results: All groups were subjected to a comparable but mild insult. No difference was found between the two intervention groups in Lac/NAA ratio, NAA/Cr ratio, DWI, arterial spin labeling, or BOLD signal. NAA/Cr ratio at 24 h was higher in the two intervention groups compared to supportive care only. There was no difference in aEEG score between the three groups. Andelius et al. Remote Postconditioning and Neonatal Encephalopathy Conclusion: Treatment with RIPC resulted in no additional neuroprotection when combined with TH. However, insult severity was mild and only evaluated at 24 h after HI with a short MRS echo time. In future studies more subtle neurological effects may be detected with increased MRS echo time and post mortem investigations, such as brain histology. Thus, the possible neuroprotective effect of RIPC needs further evaluation.

Hypothermia and heart rate variability in a healthy newborn piglet model

“…The study was based on a neonatal piglet model previously used by our group 18 , 19 , 34 . Six healthy, term, Danish Landrace piglets, male and female, under 12 h of age, and weights between 1500 and 2000 g were studied.…”

“…This can instead be done in an animal model where it is also possible to control for some of the previous mentioned factors related to HRV. Newborn piglets have previously been used to investigate various neonatal diseases, treatments, and physiological changes after birth [18][19][20] . Thus, the aim of this study was to investigate the effect of hypothermia on HRV in a controlled standardized setting in healthy, anesthetized, newborn piglets.…”

Remote ischemic postconditioning increased cerebral blood flow and oxygenation assessed by magnetic resonance imaging in newborn piglets after hypoxia-ischemia

“…Gunn et al ( 46 , 47 ) found that hypothermia suppressed hyperperfusion during the secondary phase of injury from 6 to 48 h after HI in fetal sheep, while improving cerebral blood flow to baseline levels from 72 h. This is similar to the apparent effects of RIPC shown in this study, as we found comparable cerebral blood flow between piglets treated with RIPC and sham animals at 72 h, while HI alone appeared to reduce these measures. We have previously found that RIPC had no additional effect to therapeutic hypothermia on ASL or BOLD values in piglets 24 h after mild HI ( 11 ). BOLD values may be used as markers of tissue oxygenation ( 28 , 29 ).…”

“…Especially as the incidence of HIE is higher in low-and middle-income countries where therapeutic hypothermia may be difficult to perform correctly and where deleterious effects of the treatment recently have been reported (4,5). The neuroprotective effects of remote ischemic postconditioning (RIPC) have been investigated in several HI animal models with conflicting results (6)(7)(8)(9)(10)(11)(12). We previously found that RIPC improved brain lactate/N-acetyl-aspartate (Lac/NAA) ratio in newborn piglets compared with untreated controls by magnetic resonance spectroscopy 72 h after HI (6).…”

No Differences in Cerebral Immunohistochemical Markers following Remote Ischemic Postconditioning in Newborn Piglets with Hypoxia–Ischemia

“…Several animal studies have investigated the neuroprotective effect of RIPC in neonatal HIE. 8 11 28 29 30 31 However, with conflicting findings showing effect and lack of effect, it is still uncertain whether RIPC may induce neuroprotection. 7 Therefore, we aimed to further investigate plausible effects of RIPC by cerebral immunohistochemical markers related to edema, apoptosis, and angiogenesis.…”