Therapeutic hypothermia effect on asphyxial cardiac arrest-induced renal ischemia/reperfusion injury via change of Nrf2/HO-1 levels

Abstract

The present study aimed to investigate the renoprotective effect of therapeutic hypothermia (TH) on renal ischemia-reperfusion injury (RI/RI) induced by asphyxial cardiac arrest (CA) in rats. A total of 48 male rats were randomly divided into five groups: i) Sham (n=6); ii) Normothermia + CA (Normo.) (n=14); iii) Normo. and 2 h of TH after return of spontaneous circulation (ROSC) (n=12); iv) Normo. and 4 h of TH after ROSC (n=9); and v) Normo. and 6 h of TH after ROSC (n=7). All rats except the Sham group underwent asphyxia CA and were sacrificed 1 day after ROSC. The survival rate increased from 42.8% in the Normo. group to 50, 66.6 and 85.7% in the groups with 2, 4 and 6 h of TH after CA, respectively. TH attenuated the histopathological changes of the renal tissues following ROSC and the levels of blood urea nitrogen, serum creatinine and malondialdehyde in renal tissues. On immunohistochemistry, the relative optical density of nuclear erythroid-related factor-2 (Nrf2) and heme oxygenase (HO-1) expression in renal tissues increased in the Normo. group compared with that in the Sham group and exhibited further significant increases at 6 h of TH after ROSC. In conclusion, TH attenuated renal injury and increased the expression of Nrf2 and HO-1 in a TH treatment time-dependent manner.

Keywords: cardiac arrest; cardiopulmonary resuscitation; heme oxygenase 1; nuclear erythroid-2-related factor 2; therapeutic hypothermia.

Figure 1

Schematic diagram and survival rate. (A) Schematic representation of the asphyxial CA model in rats and measurements obtained during the animal stabilization period (baseline), induction of CA, CA, CPR time, ROSC, TH duration and time-point of sacrifice. (B) The survival rate of the experimental rats was compared using Kaplan-Meier analysis (P<0.05). The Normo. group had a survival rate of 42.8% and it increased significantly at 2 h (50%), 4 h (66.6%) and 6 h (85.7%) of TH after CPR. Groups: Normo., Normothermia + CA; Hypo., TH after ROSC following CA. CPR, cardiopulmonary resuscitation; CA, cardiac arrest; TH, therapeutic hypothermia; ROSC, return of spontaneous circulation.

Figure 2

Serum BUN, Cr and MDA. Serum BUN, serum Cr and MDA content of the renal tissues increased significantly in the Normo. group compared to the sham group. The level of (A) BUN, (B) serum Cr and (C) MDA decreased insignificantly after 2 and 4 h of TH and increased significantly after 6 h of TH. The level of BUN, Cr and MDA data are presented as median and interquartile range. ^#P<0.05 compared with the Sham group; ^*P<0.05 compared with the Normo. group. Groups: Normo., Normothermia + CA; Hypo., TH after return of spontaneous circulation following CA. BUN, blood urea nitrogen; Cr, creatinine; MDA, malondialdehyde; TH, therapeutic hypothermia; CA, cardiac arrest; pro., protein.

Figure 3

Histology of renal tissues in the different groups. H&E staining of (A) the sham group indicated no tubular injury. (B) In the Normo. group, obvious tubular injury was present (arrow). Renal tubules exhibited severe dilatation and loss of brush borders with necrosis. (C-E) TH ameliorated tubular injury (arrows); (C) 2 h, (D) 4 h and (E) 6 h of TH (magnification, x400). (F) Tubular injury score in the different groups. Glomerular tubular injury data are expressed as the median with interquartile range. ^#P<0.05 compared with the Sham group; ^*P<0.05 compared with the Normo. group. Groups: Normo., Normothermia + CA; Hypo., TH after return of spontaneous circulation following CA. TH, therapeutic hypothermia; CA, cardiac arrest.

Figure 4

PAS staining. PAS staining of (A) the Sham group indicated no glomerular damage. (B) Glomerular capillary dilation (arrow) and the glomerular diameter increased significantly in the Normo. group. (C-E) Glomerular capillary dilatation was ameliorated after TH (arrows); (C) 2 h, (D) 4 h and (E) 6 h of TH (magnification, x1,000). (F) Renal glomerular damage score in the different groups. Renal glomerular damage score data are expressed as the median with interquartile range. ^#P<0.05 compared with the Sham group; ^*P<0.05 compared with the Normo. group. Groups: Normo., Normothermia + CA; Hypo., TH after return of spontaneous circulation following CA. TH, therapeutic hypothermia; CA, cardiac arrest; PAS, periodic acid Schiff.

Figure 5

IHC analysis of Nrf2 expression in renal tissues. Representative IHC staining images for Nrf2 in the kidney tissues of (A) the Sham group, (B) Normo. group, (C) 2 h TH group, (D) 4 h TH group and (E) 6 h TH group (positive staining indicated by arrows; magnification, x400). It was revealed that TH increased the expression of Nrf2 in the renal cortex. (F) The ROD% of Nrf2 expression was significantly increased at 6 h of TH. ROD% of Nrf2 data are expressed as the median with interquartile range. ^*P<0.05 compared with the Normo. group. Groups: Normo., Normothermia + CA; Hypo., TH after return of spontaneous circulation following CA. TH, therapeutic hypothermia; CA, cardiac arrest; Nrf2, nuclear erythroid-related factor-2; IHC, immunohistochemical; ROD, relative optical density.

Figure 6

IHC analysis of HO-1 expression in renal cortical tissues. Representative IHC staining images for HO-1 in the kidney tissues of (A) the Sham group, (B) Normo. group, (C) 2 h TH group, (D) 4 h TH group and (E) 6 h TH group (positive staining indicated by arrows; magnification, x400). It was indicated that TH increased HO-1 expression in the renal cortical tissues. (F) The ROD% of HO-1 staining was elevated in the Normo. vs. Sham group and increased significantly at 6 h of TH in comparison with the Normo. group. ROD% of HO-1 data are expressed as the median with interquartile range. ^*P<0.05 compared with the Normo. group. Groups: Normo., Normothermia + CA; Hypo., TH after return of spontaneous circulation following CA. TH, therapeutic hypothermia; CA, cardiac arrest; IHC, immunohistochemical; ROD, relative optical density; HO-1, heme oxygenase.