Hawley H. Seiler Resident Award. Transcriptional profile of brain injury in hypothermic circulatory arrest and cardiopulmonary bypass

Abstract

Background: Little is known about the molecular mechanisms of neurologic complications after hypothermic circulatory arrest (HCA) with cardiopulmonary bypass (CPB). Canine genome sequencing allows profiling of genomic changes after HCA and CPB alone. We hypothesize that gene regulation will increase with increased severity of injury.

Methods: Dogs underwent 2-hour HCA at 18 degrees C (n = 10), 1-hour HCA (n = 8), or 2-hour CPB at 32 degrees C alone (n = 8). In each group, half were sacrificed at 8 hours and half at 24 hours after treatment. After neurologic scoring, brains were harvested for genomic analysis. Hippocampal RNA isolates were analyzed using canine oligonucleotide expression arrays containing 42,028 probes.

Results: Consistent with prior work, dogs that underwent 2-hour HCA experienced severe neurologic injury. One hour of HCA caused intermediate clinical damage. Cardiopulmonary bypass alone yielded normal clinical scores. Cardiopulmonary bypass, 1-hour HCA, and 2-hour HCA groups historically demonstrated increasing degrees of histopathologic damage (previously published). Exploratory analysis revealed differences in significantly regulated genes (false discovery rate < 10%, absolute fold change > or = 1.2), with increases in differential gene expression with injury severity. At 8 hours and 24 hours after insult, 2-hour HCA dogs had 502 and 1,057 genes regulated, respectively; 1-hour HCA dogs had 179 and 56 genes regulated; and CPB alone dogs had 5 and 0 genes regulated.

Conclusions: Our genomic profile of canine brains after HCA and CPB revealed 1-hour and 2-hour HCA induced markedly increased gene regulation, in contrast to the minimal effect of CPB alone. This adds to the body of neurologic literature supporting the safety of CPB alone and the minimal effect of CPB on a normal brain, while illuminating genomic results of both.

Fig 1

Mean neurologic scores based on University of Pittsburg Canine Neurological Score (0–480) 24 hours after 2-hour hypothermic circulatory arrest (2H HCA), 1-hour hypothermic circulatory arrest (1H HCA), or cardiopulmonary bypass (CPB) alone. Higher score indicates worse neurologic function. Error bars are one standard deviation. *p < 0.05 by Tukey-Kramer method after one-way analysis of variance (ANOVA).

Fig 2

Venn diagram demonstrating the number of genes significantly regulated within each treatment group and the number of coregulated gene in the three groups at 8 (A) and 24 (B) hours. (CPB = cardiopulmonary bypass; 1h HCA = 1 hour of hypothermic circulatory arrest; 2h HCA = 2 hours of hypothermic circulatory arrest.)

Fig 3

Volcano plots of mRNA expression in the hippocampus of dogs 8 hours after 2-hour hypothermic circulatory arrest (2h HCA; A), 1-hour hypothermic circulatory arrest (1h HCA; B), or cardiopulmonary bypass (CPB; C). Symbols indicate biologic process gene ontology term: filled circle = apoptosis; filled triangle = inflammatory response; star = apoptosis and inflammatory response; cross = other/no annotation. Genes in black meet our statistical criteria: false discovery rate < 0.10 and absolute fold change ≥ 1.2.

Fig 4

Volcano plots of mRNA expression in the hippocampus of dogs 24 hours after 2-hour hypothermic circulatory arrest (2h HCA; A), 1-hour hypothermic circulatory arrest (1h HCA; B), or cardiopulmonary bypass (CPB; C). Symbols indicate biologic process gene ontology terms: filled circle = apoptosis; filled triangle = inflammatory response; star = apoptosis and inflammatory response; cross = other/no gene ontology annotation. Genes in black meet our statistical criteria: false discovery rate < 0.10 and absolute fold change ≥1.2.

Fig 5

Summary plot of the temporal pattern of gene expression in each treatment group with notable overlapping gene ontology categories regulated at each time. (CPB = cardiopulmonary bypass; 1H HCA = 1 hour of hypothermic circulatory arrest; 2H HCA = 2 hours of hypothermic circulatory arrest.)