Off-pump coronary artery bypass surgery is associated with fewer gene expression changes in the human myocardium in comparison with on-pump surgery

Abstract

Off-pump coronary artery bypass surgery reduces the myocardial injury associated with on pump surgery with cardiopulmonary bypass (CPB) and ischemic-cardioplegic arrest (CA). We sought to find a mechanistic explanation for this by comparing the transcriptomic changes in the myocardium of patients undergoing on- and off-pump surgery. Transcriptomic analyses were performed on left ventricular biopsies obtained from patients prior to (pre-op) and after completion of all coronary anastomoses (post-op). Microarray results were validated with real-time polymerase chain reaction. In on-pump group, 68 genes were upregulated in post-op vs. pre-op biopsies (P < 0.01, >or=2-fold). They included inflammatory genes CCL3 and CCL4, apoptotic gene GADD45B and prostaglandin synthesis gene PTGS2 (COX-2). In the off-pump group, 17 genes were upregulated in post-op vs. pre-op biopsies (P < 0.01, >or=2-fold), all shared with on-pump patients. To uncover the genes implicated in CPB and ischemic-CA response, we compared the postoperative gene profiles of the two groups. Thirty-eight genes were upregulated in the on-pump vs. off-pump patients (P < 0.01, >or=2-fold). On-pump surgery induces injury-related response, as demonstrated by the upregulation of apoptosis and remodeling markers, whereas off-pump surgery ameliorates that by mainly upregulating a cytoprotective genetic program. Blood levels of the identified cytokines and chemokines followed the same pattern obtained by transcriptomics, suggesting that the myocardium is a likely source for these proteomic changes. In conclusion, off-pump surgery is associated with fewer alterations in gene expression connected with inflammation, apoptosis, and remodeling seen after on-pump surgery with CPB and ischemic-CA.

Fig. 1.

A: Venn diagram of the significantly regulated genes >2-fold of on-pump post- vs. preoperative and off-pump post- vs. preoperative comparisons groups. B: Venn diagram of the significantly regulated genes >2-fold of on-pump post- vs. preoperative and on-pump postoperative vs. off-pump postoperative comparisons groups. C: bar chart of Gene Ontology (GO) annotations for the category “biologic process.” The chart shows the number of transcripts in the categories separately for on-pump and off-pump comparison.

Fig. 2.

Biological association network of the significantly regulated genes >2-fold in on-pump post- vs. preoperative comparison created using Pathway Studio Software.

Fig. 3.

Confirmation of the results from the microarray analysis of changed genes pre- and postoperatively in on- and off-pump surgery. Changes in mRNA expression of CCL3 (MIP1α), CCL4 (MIP1β), CCL2 (MCP1), IL-8, PTGS2 (COX2), and SNF1LK was verified in all 10 patients by quantitative real-time RT-PCR. Results are shown as means (± SE) fold-change. *P < 0.05; ***P < 0.001; ns, not significant.

Fig. 4.

Time course of plasma levels of IL6, IL8, MCP1, MCP2, MIP1α, and MIP1β. Dots connected by solid line represent the time course for median protein concentration in plasma samples (in pg/ml). For MCP1, MCP2, MIP1α, and MIP1β, significantly enhanced protein expression was confirmed after 4 h of on-pump surgery, whereas no changes were observed following off-pump surgery. For IL-6 and IL-8, significantly enhanced protein expression was confirmed after 4 h of on-pump and off-pump surgeries. Results are shown as means (± SE). *P < 0.05 vs. preoperative, **P < 0.01 vs. preoperative.