Angiotensin-(1-7) and angiotensin-(1-9): assessment as therapeutic targets in acute vascular injury and remodelling

Heart disease is commonly caused by the buildup of fat or plaques in blood vessels that deliver blood to the heart, causing them to become blocked. To unblock blood vessels doctors use two approaches, in one a balloon is inserted into the blockage and inflated to clear it and in another a piece of vein is removed from the patients leg and implanted into the heart to bypass the blockage. Both approaches are effective to treat the patients, however damage to the blood vessel by the inflated balloon or to the vein used to bypass the blockage by the high blood pressure in the heart cause these treatments to fail, by triggering overgrowth of the blood vessels causing them to become blocked again. Currently, there is a need for new treatments to prevent this failure. We have identified a new potential therapeutic target that may be able to prevent this overgrowth. The body produces specific hormones which travel via the bloodstream and engage with receptors which contribute to the normal function of blood vessels, the heart and kidney. The main hormone from this system, angiotensin II, can become overactive and contribute to the development of cardiovascular diseases, including the adverse vascular overgrowth which blocks blood vessels. We have identified an alternative hormone in this pathway which can block the growth of the cells in blood vessels and potentially prevent the vessels from becoming blocked. Here, we will investigate this hormone more fully to understand how it functions and to test whether it has therapeutic benefit in animal models of vessel blockage. This will help us understand the function better and highlight whether it is a suitable molecular to develop into a therapeutic drug in the future.

The renin angiotensin system (RAS) is key to cardiovascular diseases, including cardiac and vascular remodelling. Pathophysiological effects via angiotensin (Ang) II are established, while Ang-(1-7), which signals via Mas, antagonises Ang II via the counter-regulatory RAS axis. We recently published Ang-(1-9) as an active peptide at the angiotensin type 2 receptor (AT2R), inhibiting cardiomyocyte hypertrophy and cardiac fibrosis. This highlighted Ang-(1-9) as a new counter-regulatory RAS axis member. Here we have assessed the effects of Ang-(1-9) in human endothelial cells (EC) and smooth muscle cells (SMC). Ang-(1-7) and Ang-(1-9) prevent SMC migration and proliferation via Mas or the AT2R, respectively without affecting EC growth and movement. SMC migration and proliferation are central to neointima development which leads to occlusion of arteries that have undergone percutaneous intervention via a balloon catheter leading to restenosis, or failure of vein grafts following coronary artery bypass procedures. As proof of concept we delivered Ang-(1-7) and Ang-(1-9) into wire injured carotid arteries in mice and observed that Ang-(1-9) was more efficient than Ang-(1-7) at inhibiting neointimal hyperplasia and furthermore that in vivo each peptide acted via its specific receptor. Since Ang-(1-7) and Ang-(1-9) demonstrate favourable attributes in the setting of acute vascular injury, here we will intensely investigate our initial findings in relevant in vitro, ex vivo and in vivo models of vein graft failure. The findings will enhance counter-regulatory RAS axis understanding by investigations into the mechanisms of action of these peptides and highlight therapeutic targets in vascular remodeling which can be further developed in the future.

The beneficiaries are far ranging. First, the cardiovascular research community, both basic and clinical will benefit from increased knowledge regarding the counter-regulatory axis of the renin angiotensin system. The work will further our basic knowledge of proving the mechanisms of action of both angiotensin-(1-7) and angiotensin-(1-9) and provide further evidence for direct differential role for angiotensin-(1-9). This will highlight an additional therapeutic role for angiotensin-(1-9) and will therefore be of interest to explore further in future research. This may well be through a direct translational route partnered with clinical researchers in the NHS as new discoveries with therapeutic value in cardiovascular disease may have a major role in helping reduce the current substantial morbidity and mortality in patients. In wider research the anti-migratory aspects and any anti-proliferative effects which will be explored in this proposal could be expected to impact on other areas of disease research where a remodelling phenotype underpins the pathology, including cancer, inflammatory disorders, fibrotic remodelling disorders in other tissues such as the kidney, or wound healing.

The PDRA working on the grant will gain broad skills directly related to many areas of modern research including molecular, biochemical and in vivo skills. Their attendance and presentation at conferences will directly benefit their core skills in presentation, communication and collaboration. Working within a individual project within a research group will foster their skills in both independent and team working. Since the PDRA will be expected to design experiments and plan their work (in liaison with the PI and other co-Inv) they will develop time management and leadership skills. In liaison with the PI the PDRA will also be expected to be mindful of designing and delivering the project within a defined budget and timescale, clearly developing their project management and financial control skills.

Second, there are already commercial enterprises exploring the utility of both ACE2 and angiotensin-(1-7) as clinical therapeutic interventions in cardiovascular disease (e.g Tarix Pharmaceuticals) and companies such as these are driving clinical development in this area. Therefore, with further proof of independent effects for angiotensin-(1-9) companies may be interested in the medium term in exploration of it as an alternative therapeutic intervention.

In the long term then the research has the potential to lead to studies which directly impacts patient's lives. This could be envisaged to be on two levels. As a therapeutic modality angiotensin-(1-9) could be rapidly developed for clinical trials as has been achieved for angiotensin-(1-7) as it is an endogenous peptide and proof of concept exists for safe infusion of angiotensin-(1-7) in patients. Furthermore, it could be that levels of angiotensin peptides such as angiotensin-(1-7) and angiotensin-(1-9) could be biomarkers which change in cardiovascular disease patients based on severity of disease or upon other interventions. Therefore, the NHS and commercial companies may be interested in low cost, minimal intervention tests to measure new informative biomarkers. Such areas may be of interest to both large pharmaceutical companies and small to medium size biotechnology companies. In both these areas angiotensin-(1-9) could be envisaged to have wider societal and economic benefits to reduce cardiovascular disease burden. Education of patients could be envisaged to be realistically achievable since current interventions in clinical cardiovascular disease from hypertension through to heart failure involves pharmacological manipulation of the renin angiotensin system, highlighting that angiotensin-(1-9) would fit into a biological system which is tangible to patients knowledge and understanding since currrent interventions target it.