Effect of hypothermia on interleukin-1 receptor antagonist pharmacodynamics in inflammatory-sensitized hypoxic-ischemic encephalopathy of term newborns

Abstract

Background: Hypothermia is increasingly tested in several neurological conditions, such as neonatal encephalopathy, stroke, traumatic brain injury, subarachnoid hemorrhage, spinal cord injury, and neurological outcomes of cardiac arrest. Current studies aim to increase benefits of hypothermia with new add-on therapies including immunomodulatory agents. Hypothermia has been shown to affect the metabolism of commonly used drugs, including those acting on neuroimmune pathways.

Objective: This study focuses on the effect of hypothermia on interleukin-1 receptor antagonist pharmacodynamics in a model of neonatal encephalopathy.

Methods: The effect of hypothermia on (i) the tissue concentration of the interleukin-1 receptor antagonist, (ii) the interleukin-1 inflammatory cascade, and (iii) the neuroprotective potential of interleukin-1 receptor antagonist has been assessed on our rat model of neonatal encephalopathy resulting from inflammation induced by bacterial compound plus hypoxia-ischemia.

Results: Hypothermia reduced the surface of core and penumbra lesions, as well as alleviated the brain weight loss induced by LPS+HI exposure. Hypothermia compared to normothermia significantly increased (range 50-65%) the concentration of the interleukin-1 receptor antagonist within the central nervous system. Despite this increase of intracerebral interleukin-1 receptor antagonist concentration, the intracerebral interleukin-1-induced tumor necrosis factor-alpha cascade was upregulated. In hypothermic condition, the known neuroprotective effect of interleukin-1 receptor antagonist was neutralized (50 mg/kg/12 h for 72 h) or even reversed (200 mg/kg/12 h for 72 h) as compared to normothermic condition.

Conclusion: Hypothermia interferes with the pharmacodynamic parameters of the interleukin-1 receptor antagonist, through a bioaccumulation of the drug within the central nervous system and a paradoxical upregulation of the interleukin-1 pathway. These effects seem to be at the origin of the loss of efficiency or even toxicity of the interleukin-1 receptor antagonist when combined with hypothermia. Such bioaccumulation could happen similarly with the use of other drugs combined to hypothermia in a clinical context.

Keywords: Cerebral palsy; HT; IL-1Ra; Inflammation; Neonatal encephalopathy.

Conflict of interest statement

Ethics approval

Our research protocol was approved by the Ethics Committee from the Research Institute of the McGill University Health Center (#2015-7691).

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1

Experimental design. The first hrIL-1Ra (50–200 mg/kg) or saline injection was administrated 30 min before the ip injection of LPS from Escherichia coli (50 μg/kg) in pups at P12. Four hours later, the right common carotid artery was ligated, and hypoxia was induced (8% O2 for 1.5 h). Rat pups were subjected or not to hrIL-1Ra (50–200 mg/kg q12 h from P12 to P14) and treated or not by HT (32.5 °C ± 0.5 °C for 4 h). Abbreviations: HI, hypoxia-ischemia; HT, hypothermia; hrIL-1Ra, human recombinant of interleukin-1 receptor antagonist; ip, intraperitoneally; LPS, lipopolysaccharide from Escherichia coli; P, postnatal day

Fig. 2

hrIL-1Ra titers within tissues of interest from pups exposed to LPS+HI+IL-1Ra±HT. hrIL-1Ra titers measured by ELISA at 24 h post-HI were increased within the plasma (a), right cerebral hemisphere (b), and CSF (c) in LPS+HI+HT+IL-1Ra (50 mg/kg) as compared to LPS+HI+IL-1Ra (50 mg/kg) condition. The concentrations of hrIL-1Ra were similar in both conditions at 4 h post-HI, as well as at 24 h post-HI within the liver (d). The number (n) of rats used was LPS+HI+IL-1Ra (n = 5–8 from 4 litters) and LPS+HI+HT+IL-1Ra (n = 5–8 from 4 litters). The bars indicate the mean ± SEM. *p ≤ 0.05, **p ≤ 0.01; independent T test. Abbreviations: CSF, cerebrospinal fluid; HI, hypoxia-ischemia; HT, hypothermia; hrIL-1Ra, human recombinant of interleukin-1 receptor antagonist; LPS, lipopolysaccharide from Escherichia coli

Fig. 3

IL-1β expression within tissues of interest from pups exposed to LPS+HI+IL-1Ra±HT. IL-1β concentration measured by ELISA at 4 h and 24 h post-HI within the plasma (a), right cerebral hemisphere (b), and liver (c) in LPS+HI+IL-1Ra (50 mg/kg) and LPS+HI+HT+IL-1Ra (50 mg/kg) conditions. HT increased the expression of IL-1β within the right hemisphere at 4 h post-HI (b). The number (n) of rats used was LPS+HI+IL-1Ra (n = 5–7 from 4 litters) and LPS+HI+HT+IL-1Ra (n = 4–8 from 4 litters). The bars indicate the mean ± SEM. *p ≤ 0.05; independent T test. Abbreviations: HI, hypoxia-ischemia; HT, hypothermia; hrIL-1Ra, human recombinant of interleukin-1 receptor antagonist; IL-1β, interleukin-1β; LPS, lipopolysaccharide from Escherichia coli

Fig. 4

TNF-α titers within tissues of interest from pups exposed to LPS+HI+IL-1Ra±HT. TNF-α concentrations measured by ELISA were increased at 24 h post-HI within the right cerebral hemisphere (a) and the liver (b) in LPS+HI+HT+IL-1Ra (50 mg/kg) as compared to LPS+HI+IL-1Ra (50 mg/kg) conditions. The TNF-α titers were similar in both conditions at 4 h post-HI. The number (n) of rats used was LPS+HI+IL-1Ra (n = 5–8 from 4 litters) and LPS+HI+HT+IL-1Ra (n = 6–8 from 4 litters). The bars indicate the mean ± SEM. *p ≤ 0.05; independent T test. Abbreviations: HI, hypoxia-ischemia; HT, hypothermia; hrIL-1Ra, human recombinant of interleukin-1 receptor antagonist; LPS, lipopolysaccharide from Escherichia coli; TNF-α, tumor necrosis-α

Fig. 5

Comparison of the extent of brain injuries between LPS+HI±HT±IL-1Ra conditions. Comparisons of the extent of core and penumbra injuries (within the neocortex, hippocampus, and caudate-putamen) between pups exposed to LPS+HI±HT±IL-1Ra (50–200 mg/kg) by H&E staining of the right forebrains at P20. HT reduced the surface of core and penumbra lesions (a–d), as well as alleviated the brain weight loss observed after LPS+HI exposure (e). The surface of core and penumbral lesions were similar in LPS+HI+HT+IL-1Ra (50 mg/kg) as compared to LPS+HI+HT condition (a–d). HT+hrIL-1Ra (200 mg/kg) increased the extent of penumbra injury as compared to the LPS+HI condition (b), as well as core and penumbral injuries as compared to LPS+HI+HT and LPS+HI+HT+IL-1Ra (50 mg/kg) (a–d). The number (n) of rats used was LPS+HI (n = 14–16 from 9 litters), LPS+HI+HT (n = 13–15 from 9 litters), LPS+HI+HT+IL-1Ra 50 mg/kg (n = 17–19 from 9 litters), and LPS+HI+HT+IL-1Ra 200 mg/kg (n = 6–7 from 3 litters). The bars indicate the mean ± SEM. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001; one-way ANOVA. Abbreviations: HI, hypoxia-ischemia; HT, hypothermia; hrIL-1Ra, human recombinant of interleukin-1 receptor antagonist; LPS, lipopolysaccharide from Escherichia coli

Fig. 6

Open field experiment at P20 in pups exposed to LPS+HI+HT±IL-1Ra (50 mg/kg). No difference was observed between the two conditions for the different open field parameters tested: the distance traveled (a), the mobile time (b), the time in the center (c), and the visited squares in the apparatus (d). The number (n) of rats used was LPS+HI+HT (n = 8–9 from 6 litters) and LPS+HI+HT+IL-1Ra 50 mg/kg (n = 6–7 from 5 litters). Independent T test. Abbreviations: HI, hypoxia-ischemia; HT, hypothermia; hrIL-1Ra, human recombinant of interleukin-1 receptor antagonist; LPS, lipopolysaccharide from Escherichia coli