Interleukin-1β transfer across the blood-brain barrier in the ovine fetus

Abstract

Pro-inflammatory cytokines contribute to hypoxic-ischemic brain injury. Blood-brain barrier (BBB) dysfunction represents an important component of hypoxic-ischemic brain injury in the fetus. Hypoxic-ischemic injury could accentuate systemic cytokine transfer across the fetal BBB. There has been considerable conjecture suggesting that systemic cytokines could cross the BBB during the perinatal period. Nonetheless, evidence to support this contention is sparse. We hypothesized that ischemia-reperfusion increases the transfer of systemic interleukin-1β (IL-1β) across the BBB in the fetus. Ovine fetuses at 127 days of gestation were studied 4 hours after 30 minutes of bilateral carotid artery occlusion and compared with a nonischemic group. Recombinant ovine IL-1β protein was expressed from an IL-1β pGEX-2 T vector in E. coli BL-21 cells and purified. The BBB function was quantified in 12 brain regions using a blood-to-brain transfer constant with intravenous (125)I-radiolabeled IL-1β ((125)I-IL-1β). Interleukin-1β crossed the intact BBB in nonischemic fetuses. Blood-to-brain transport of (125)I-IL-1β was higher (P<0.05) across brain regions in fetuses exposed to ischemia-reperfusion than nonischemic fetuses. We conclude that systemic IL-1β crosses the intact fetal BBB, and that ischemia-reperfusion increases transfer of this cytokine across the fetal BBB. Therefore, altered BBB function after hypoxia-ischemia facilitates entry of systemic cytokines into the brain of the fetus.

Figure 1

Western immunoblot showing the interleukin-1β (IL-1β) ovine protein before and after the additional purification by size-exclusion chromatographic column described in Materials and methods.

Figure 2

Representative fetal arterial plasma radioactivity profile of ¹²⁵I-radiolabeled IL-1β (¹²⁵I-IL-1β) in dpm/μL plotted against study time in minutes. ^99mTc-red blood cell (RBC) is shown by the black square. ¹²⁵I-IL-1β was given intravenously to the fetus at study time zero. IL-1β, interleukin-1β.

Figure 3

Changes in electrocorticogram (ECoG) and carotid blood flow during the study. ECoG (A) and carotid blood flow (B) values for the nonischemic (open circles, n=6) and ischemic–reperfusion (closed circle, n=6) plotted against study time in hours. The study design is reproduced on the x axis. The box indicating ‘BBBP' shows the time of the blood–brain barrier permeability study. ECoG (A) Power spectral densities, PSD-ECoG plotted as the difference from the individually averaged baseline ECoG values. Values are shown as median±s.e.m. for ECoG and mean±s.e.m. for carotid arterial blood flow, *P<0.05 ischemia versus baseline within the ischemic group.

Figure 4

Blood-to-brain transfer constants (K_i) in the nonischemic (open bars, n=6) and ischemic–reperfusion (closed bars, n=6), groups plotted for the brain regions on the x axis. Values are mean±s.e.m. *P<0.05 versus nonischemic group.