Age-related increase in coronary microvascular contractile response to endothelin-1 in patients undergoing cardioplegic arrest and cardiopulmonary bypass

Purpose: Aging decreases coronary blood flow and maximal flow reserve, rendering myocardium more susceptible to ischemic insult following cardioplegia/cardiopulmonary bypass (CP/CPB). Endothelin-1 is a potent vasoconstrictor implicated in low coronary reflow phenomenon following CP/CPB-induced ischemia/reperfusion. Human studies investigating endothelin-1 signaling in the aging heart before and after CP/CPB are lacking.

Methods: Human atrial tissue and arterial blood samples were examined from patients undergoing cardiac surgery before and after CP/CPB. Patients were divided into younger (age < 65) and older (age ≥65) groups. Immediately following harvest, coronary microvessels ( < 200μm in diameter) were dissected from atrial samples (N = 20), and ex vivo contractile response to endothelin-1 was assessed using video microscopy. Receptor protein expression and perivascular localization were measured using immunoblotting and immunofluorescence photomicroscopy, respectively. Enzyme-linked immunosorbent assay was used to quantify plasma concentration of endothelin-1. Atrial samples were analyzed using RNA deep-sequencing.

Results: Older patients had significantly increased ex vivo coronary microvascular contractile response to endothelin-1 both pre-CP/CPB (p = 0.021) and post-CP/CPB (p = 0.021) compared to younger counterparts (Figure). Differential tissue expression of endothelinA receptor (ETAR) and endothelinB receptor (ETBR) was not associated with age. Perivascular localization of ETAR, the receptor that mediates the dominant vasoconstrictor effect of endothelin-1, trended to an increase in pre-CP/CPB (p = 0.076) and post-CP/CPB (p = 0.164) myocardium of older patients. Plasma endothelin-1 trended to an increase both pre-CP/CPB (p = 0.232) and post-CP/CPB (p = 0.251) in older patients. RNA deep-sequencing showed significant pre-CP/CPB upregulation of genes encoding proteins that mediate endothelin-induced vascular smooth muscle contraction through calcium signaling (CACNG8, DGKB, PLCZ1, GNB1L, CAMK4, GPR68, MYL6, GPR171, CBARP), and downregulation of ARHGAP28, whose encoding protein opposes vasoconstriction (Table). Advanced age was associated with post-CP/CPB upregulation of genes encoding proteins that mediate endothelin-induced vasoconstriction through calcium signaling (AL 132640.1, CACNA1A, GPR35, and TPM3P6). RNA deep-sequencing also showed post-CP/CPB downregulation of ECE1, PRKCE, ITPKC, and PLCL2 in older patients. There was no significant change in expression of genes encoding endothelin-1 (EDN1), ETAR (EDNRA), ETBR (EDNRB), nitric oxide synthase (NOS1), or prostacyclin synthase (PTGIS) with advanced age.

Conclusion: Older patients have increased expression of pro-vasoconstrictive genes associated with increased perivascular localization of putative vasoconstrictive ETAR and circulating endothelin-1. This translates to phenotypic effect of increased coronary microvascular contractile response after CP/CPB. Older patients undergoing CP/CPB are at increased risk for myocardial hypoperfusion resulting from increased endothelin-induced vasospasm postoperatively.

Identify the source of the funding for this research project: National Institute of Health/National Institute of General Medical Sciences (NIH/NIGMS) T32GM065085-18 (D.B.); F32HL160063 (S.A.S.); 1R01HL127072-01A1, 1R01HL136347-01, and R01HL136347-04S1 (J.F.); R01HL46716 and R01HL128831 (F.W.S.).