Long-term treatment with acylated analogues of apelin-13 amide ameliorates diabetes and improves lipid profile of high-fat fed mice.

Previous studies have shown that modified apelin analogues exhibited enzyme resistance in plasma and improved circulating half-life compared to apelin-13. This study investigated the antidiabetic effects of chronic administration of stable long acting fatty acid modified apelin analogues, namely, (Lys8GluPAL)apelin-13 amide and pGlu(Lys8GluPAL)apelin-13 amide, in high-fat fed obese-diabetic mice. Male NIH Swiss mice (groups n = 8) were maintained either on a high-fat diet (45% fat) from 8 to 28 weeks old, or control mice were fed a normal diet (10% fat). When diet induced obesity-diabetes was established after high-fat feeding, mice were injected i.p. once daily with apelin analogues, liraglutide (25 nmol/kg) or saline (controls). Administration of (Lys8GluPAL)apelin-13 amide and pGlu(Lys8GluPAL)apelin-13 amide for 28 days significantly reduced food intake and decreased body weight. Non-fasting glucose was reduced (p<0.01 to p<0.001) and plasma insulin concentrations increased (p<0.01 to p<0.001). This was accompanied by enhanced insulin responses (p<0.01 to p<0.001) and significant reductions in glucose excursion after oral (p<0.01) or i.p. (p<0.01) glucose challenges and feeding. Apelin analogues also significantly improved HbA1c (p<0.01), enhanced insulin sensitivity (p<0.01), reduced triglycerides (p<0.001), increased HDL-cholesterol (p<0.01) and decreased LDL-cholesterol (p<0.01), compared to high-fat fed saline treated control mice. Cholesterol levels were decreased (p<0.01) by pGlu(Lys8GluPAL)apelin-13 amide and both apelin treated groups showed improved bone mineral content, reduced fat deposits and increased plasma GLP-1. Daily treatment with liraglutide mirrored many of these changes (not on bone or adipose tissue), but unlike apelin analogues increased plasma amylase. Consumption of O2, production of CO2, respiratory exchange ratio and energy expenditure were improved by apelin analogues. These results indicate that long-term treatment with acylated analogues (Lys8GluPAL)apelin-13 amide and particularly pGlu(Lys8GluPAL)apelin-13 amide resulted in similar or enhanced therapeutic responses to liraglutide in high-fat fed mice. Fatty acid derived apelin analogues represent a new and exciting development in the treatment of obesity-diabetes.The Department for the Economy, Northern Ireland (https://www.nidirect.gov.uk/articles/department-economy-studentships, formerly DEL-NI) provided a PhD studentship to CH and FOH to perform this work. Invest-NI Proof of Concept funding (https://www.investni.com/support-for-business/proof-of-concept.html, PoC518) was secured by FOH and PRF

Sustained glucagon receptor antagonism in insulin deficient high fat fed mice

This work was supported by an Invest Northern Ireland Proof-of-Concept grant (PoC106), a Department for the Economy, Northern Ireland PhD studentship and Ulster University Selective Research FundingPeer reviewedPublisher PD

Apelin as a potential treatment for chronic kidney disease

Chronic kidney disease (CKD) is a global health emergency. It affects ~10% of the global population, and cardiovascular disease is its commonest endpoint. Current standard of care treatment involves using blockers of the renin-angiotensin0aldosterone system (RAAS) and sodium-glucose co-transporter 2 inhibitors which reduce blood pressure and proteinuria and slow CKD progression. However, despite these agents many patients with CKD still progress to kidney failure and the requirement for dialysis or a kidney transplant. Newer treatments are urgently needed, and something that could also offer both cardiovascular and renal protection would be particularly attractive. The apelin system, comprising the apelin receptor and its two endogenous ligands, apelin and elabela, is a very appealing therapeutic target for CKD. Apelin is a vasodilator and the most potent inotrope discovered to date. Clinical studies demonstrate that it lowers blood pressure and increases cardiac output in healthy humans and in those with heart failure. In pre-clinical studies, apelin regulates kidney blood flow and promotes aquaresis. The aims of this thesis were to define the actions of the apelin system in human kidneys and explore its potential therapeutic benefit in clinical CKD. Firstly, I have shown that the apelin system is expressed throughout the nephron in healthy human kidneys. Additionally, as estimated glomerular filtration rate (eGFR) declines, plasma apelin concentration increases. Apelin concentration is associated with arterial stiffness and endothelial function, both validated surrogate measures of cardiovascular risk. Moreover, plasma apelin independently associates with eGFR decline. These data highlight the important relationship between the apelin system and the kidney and justify studies of apelin receptor agonism in CKD. This thesis presents data from the first human studies examining the cardiovascular and renal responses to pyroglutamated apelin-13 ([Pyr1]apelin-13, the most abundant apelin isoform in human plasma) in health and CKD. Endothelial dysfunction is a feature of CKD and a measure of increased cardiovascular risk. I have demonstrated that apelin enhances endothelial function in CKD. Intra-arterial infusion of [Pyr1]apelin-13 led to a ~30% increase in forearm blood flow and was associated with an increase in tissue plasminogen activator (an endogenous fibrinolytic released by the endothelium). Using renal clearance studies, I measured systemic and renal haemodynamic and tubular responses to apelin and placebo in healthy humans and in patients with CKD receiving standard of care treatment. Acute infusion of [Pyr1]apelin-13 led to a fall in blood pressure and systemic vascular resistance and an increase in cardiac output in both health and CKD. In both health and CKD, [Pyr1]apelin increased renal blood flow; GFR fell in patients with CKD only. In those with CKD, I also observed a fall in filtration fraction and proteinuria. Finally, [Pyr1]apelin-13 promoted natriuresis and free water clearance in health and CKD. In summary, the work presented here shows that the apelin system offers exciting therapeutic potential in CKD. Acute apelin infusion has beneficial cardiovascular and renal effects which, if maintained longer-term would be expected to translate to cardiorenal protection. The development of oral apelin analogues, and subsequent clinical trials, is now justified for patients with kidney disease