Natriuretic peptides reverse vascular insulin resistance and supress insulin-induced mechanisms of atherogenesis

Aim Patients with atherosclerosis and type 2 diabetes (T2DM) on aggressive insulin therapy have poor coronary artery disease (CAD) outcomes. CAD patients with and without T2DM exhibit vascular endothelial insulin resistance (VIR). When exposed to insulin, dysregulated vascular signalling increases vascular inflammation and oxidative stress via activation of NADPH oxidases (NOX) and uncoupling of endothelial nitric oxide synthase (eNOS). DPPIV inhibitors ameliorate this effect ex vivo but do not confer prognostic benefits. Natriuretic peptides (NPs; ANP and BNP) are DPPIV substrates that may modulate vascular insulin and redox signalling. Methods Blood (n=881), internal mammary artery (IMA) and saphenous vein (SV) (n=738) were collected from adults undergoing coronary bypass. Patients with heart failure and on DPPIV/Neprilysin inhibitors were excluded. Vessel rings were incubated in 4 conditions (control, insulin, NP, insulin & NP). Subsequently resting, NOX-derived and LNAME-delta superoxide were measured in IMAs via chemiluminescence. Endothelial function was quantified in SVs via vasomotor studies. Western blotting quantified activation of signalling molecules (AKT, ERK, eNOS, IRS1, RAC1, p47-Phox). RNA was extracted from IMAs and sequenced. Plasma NT-proBNP was measured by ELISA. DNA was extracted from whole blood and genotyped. Patients were followed up for 10 years. Results Insulin increases IMA resting and NOX-derived superoxide and uncouples eNOS(A-C). BNP combined with insulin reduces resting and NOX-derived superoxide and uncouples eNOS(A-C). These results are replicated with ANP. Insulin impairs endothelium-dependent vasorelaxation whilst BNP with insulin improves endothelium-dependent vasorelaxation(D). Insulin alone increases vascu[CA1] lar ERK and IRS1 phosphorylation and RAC1/p47-Phox activation and membrane translocation(E-F) but does not activate AKT or eNOS. BNP with insulin restores AKT and eNOS phosphorylation and reduces IRS1 phosphorylation and RAC1/p47-Phox activation and translocation(E-F). Insulin reduces BH4 (eNOS cofactor) and increases BH2 whilst BNP with insulin increases BH4 and doesn’t increase BH2. Increased IMA NP receptor 1 (NPR1) expression is associated with reduced oxidative stress and improved endothelial function. In patients with high and low IMA NPR1 expression, top differentially expressed genes related to insulin signaling pathways. In pre-diabetics and T2DM, both increased plasma NT-proBNP(G-H) and SNP rs198389 (increases NPPB expression) were associated with reduced major adverse cardiovascular event rates. This effect was greater in patients on insulin. No effect was seen in non-diabetics. Conclusion We demonstrate for the first time that NPs directly sensitise human vessels to insulin, switching the effects of exogenous insulin from pro-oxidant to anti-oxidant. NPs could be used to transform the pro-atherogenic profile of insulin therapy in T2DM and enhance management of CAD.