Therapeutic Distant Organ Effects of Regional Hypothermia during Mesenteric Ischemia-Reperfusion Injury

Background: Mesenteric ischemia/reperfusion injury (IRI) occurs in various clinical settings including shock, sepsis, and aortic surgery. Therapeutic hypothermia is cytoprotective in various IRI models, however, little is known regarding the effects of regional hypothermia on distant organ dysfunction during mesenteric IRI. We investigated the structural, functional, and transcriptional changes in the lung during mesenteric IRI in rats, and hypothesized that regional gut hypothermia during SMAO protects the lung and preferentially modulates the IRI-activated transcriptome in the rat lung.
Methods: Sprague-Dawley rats (n >5) underwent 60 minutes SMAO or sham laparotomy, with (IRI-H) or without (IRI) regional hypothermia. Hypothermia was induced by placing the small intestine in moistened gauze between two cold compresses and maintained at a temperature of 15-20°C during ischemia. At 6 or 24 hours, the animals were sacrificed and lung tissue was collected for histological analysis and assessment of pulmonary microvascular permeability. For microarray analysis, total RNA from lung (n=4/group) was isolated 6 or 24 hours after sham or SMAO +/- regional hypothermia. Gene expression profiling was conducted using Illumina's Sentrix RatRef-12 v1 Expression BeadChip (>22,000 probes) and analyzed by BeadStudio_1.5 and Significance Analysis of Microarrays (SAM)_2.0. Genes with fold change (FC)>1.5 and false discovery rate (FDR) <5% were considered significantly affected by IRI.
Results: At 24 hours following SMAO, rat lungs demonstrated increased neutrophil infiltration and alveolar hemorrhage compared to sham controls and IRI-H, and BAL protein concentration was increased in IRI-treated rats compared to sham (665±29 vs.145±24, p<.05) and IRI-H (665±29 vs. 85±58, p<.05). Wet:dry ratios were also increased in IRI compared to sham (1.17±.01 vs. 1.21±.01, p<05) and IRI-H (1.21±.0 vs. 1.13±.001, P<.05). Lung gene expression profiling identified 411 lung genes with increased expression during mesenteric IRI (at 6 h) compared with sham, of which 154 genes were increased in IRI-H (Fig 1). At 24 hours, only 42 genes demonstrated sustained increased expression during IRI compared to sham, of which 30 were increased in IRI-H. Hierarchical cluster analysis of the most significantly affected genes identified discordant expression patterns between IRI and IRI-H (Fig. 1). Detailed analysis of select differentially expressed lung genes between IRI and IRI-H revealed upregulation of several genes related to leukocyte activation and trafficking that were suppressed by hypothermia.

Conclusions: Using an established model of rodent SMAO, we identified deleterious lung structural and functional changes during IRI that were mitigated by regional intraischemic hypothermia (IH). Furthermore, IH preferentially modulates the IRI-activated lung transcriptome by down-regulation of select pro-inflammatory genes and leukocyte chemoattractants. This study identifies potential novel diagnostic and therapeutic targets that mediate distant organ protective effects of regional hypothermia during mesenteric IRI.