B-type natriuretic peptide reverses vascular endothelial insulin resistance and ameliorates dysregulated redox signalling when administered alongside insulin in human atherosclerosis

Aim Atherosclerosis is a leading complication of type 2 diabetes. Physiologically, in endothelial cells, insulin stimulates activation of endothelial nitric oxide (NO) synthase (eNOS), producing the vasorelaxant, anti-inflammatory, and atheroprotective NO. Atherosclerosis patients exhibit vascular endothelial insulin resistance regardless of diabetic status. When these patients are given insulin, a pathological signalling cascade activates NADPH oxidase (NOX) and uncouples eNOS, resulting in excess production of superoxide and, consequently, vasoconstriction, inflammation, oxidative stress, and atherogenesis. Hence, diabetics on aggressive insulin therapy have poor cardiovascular outcomes. Dipeptidyl-peptidase-IV (DPPIV) inhibitors ameliorate this phenotype ex vivo but do not confer prognostic cardiovascular benefits clinically. B-type natriuretic peptide (BNP) is a DPPIV substrate that may modulate endothelial insulin and redox signalling. Methods Samples of plasma, intact internal mammary artery (IMA) and saphenous vein (SV) were collected from 128 adults undergoing coronary bypass surgery. Plasma BNP and insulin were measured by ELISA. Sequential rings of vessels were incubated in four conditions (control, insulin, BNP, insulin & BNP). Baseline, NOX-derived and LNAME-delta superoxide production were measured in IMAs through chemiluminescent luminometry. Endothelial function was quantified in SVs with vasomotor studies assessing endothelium-dependent relaxation with acetylcholine and bradykinin. Western blotting quantified relative activation of intracellular signalling molecules (AKT, ERK, eNOS, IRS1). Results In patients with low plasma BNP, increased endogenous insulin levels are significantly associated with increased IMA NOX-derived superoxide production (p=0.034). This effect is abolished in patients with BNP excess (p=0.50). Insulin significantly increases endothelium-dependent vasoconstriction (p=0.01) whilst BNP with insulin significantly reduces endothelium-dependent vasoconstriction (p=0.04). Insulin significantly increases IMA resting (p<0.0001) and NOX-derived (p=0.0005) superoxide production and uncouples eNOS NO production (p=0.027), whilst BNP combined with insulin restores these to normal levels. BNP with and without insulin recouples eNOS NO production (p=0.037). Insulin alone increases endothelial ERK (p=0.004) and IRS1 (p=0.03) phosphorylation but does not activate AKT or eNOS. Insulin with BNP increases AKT (P=0.004) and eNOS (p=0.03) phosphorylation and reduces IRS1 phosphorylation. A SNP responsible for increased nppb expression and plasma BNP (rs198983) is associated with increased NOX-derived superoxide (p<0.05) and increased major adverse cardiovascular events (p=0.03). Conclusion BNP resensitises the vascular endothelium to and ameliorates pathological redox signalling when co-administered with insulin. BNP may have a role as a future therapeutic in preventing and treating atherosclerosis with comorbid diabetes.