The effects of insulin and liraglutide on osteoprotegerin and vascular calcification in vitro and in patients with type 2 diabetes Colin Davenport, Wan A Mahmood 1 , Hannah Forde, David T Ashley, Amar Agha, John McDermott 1 , Seamus Sreenan 1 , Christopher J Thompson, Frank McGrath 2 , Brendan McAdam 3 , Philip M Cummins 4 and Diarmuid Smith Department of Academic Endocrinology, Diabetes Day Centre, Beaumont Hospital, County Dublin, Dublin 9, Ireland, 1 Department of Diabetes and Endocrinology, Connolly Hospital, Blanchardstown, County Dublin, Dublin 9, Ireland, Departments of 2 Radiology and 3 Cardiology, Beaumont Hospital, County Dublin, Dublin 9, Ireland and 4 School of Biotechnology, Centre for Preventive Medicine, Dublin City University, County Dublin, Dublin 9, Ireland Correspondence should be addressed to C Davenport Email drcdavenport@gmail.com Abstract Objective: Vascular calcification (VC) is inhibited by the glycoprotein osteoprotegerin (OPG). It is unclear whether treatments for type 2 diabetes are capable of promoting or inhibiting VC. The present study examined the effects of insulin and liraglutide on i) the production of OPG and ii) the emergence of VC, both in vitro in human aortic smooth muscle cells (HASMCs) and in vivo in type 2 diabetes. Design/methods: HASMCs were exposed to insulin glargine or liraglutide, after which OPG production, alkaline phosphatase (ALP) activity and levels of Runx2, ALP and bone sialoprotein (BSP) mRNA were measured. A prospective, nonrandomised human subject study was also conducted, in which OPG levels and coronary artery calcification (CAC) were measured in a type 2 diabetes population before and 16 months after the commencement of either insulin or liraglutide treatment and in a control group that took oral hypoglycemics only. Results: Exposure to insulin glargine, but not liraglutide, was associated with significantly decreased OPG production (11 913G1409 pg/10 4 cells vs 282G13 pg/10 4 cells, control vs 10 nmol/l insulin, P!0.0001), increased ALP activity (0.82G0.06 IU/10 4 cells vs 2.40G0.16 IU/10 4 cells, control vs 10 nmol/l insulin, P!0.0001) and increased osteogenic gene expression by HASMCs. In the clinical study (nZ101), insulin treatment was associated with a significant reduction in OPG levels and, despite not achieving full statistical significance, a trend towards increased CAC in patients. Conclusion: Exogenous insulin down-regulated OPG in vitro and in vivo and promoted VC in vitro. Although neither insulin nor liraglutide significantly affected CAC in the present pilot study, these data support the establishment of randomised trials to investigate medications and VC in diabetes. European Journal of Endocrinology (2015) 173, 53–61 Introduction Vascular calcification (VC) has been shown to exert a number of adverse effects on the cardiovascular (CV) system, and it is particularly prevalent in patients with type 2 diabetes mellitus, who tend to develop VC to a greater degree and at an earlier age (1, 2, 3). At the cellular level, VC is the end product of a complex pathophysiological process in which cell populations such as vascular smooth muscle cells (VSMC) display osteoblastic activity similar to that seen in skeletal bone formation (1, 4). The glycoprotein osteoprotegerin (OPG), which is produced by VSMCs, has been identified as an inhibitor of this process (5, 6). Short-term clamp studies in human subjects have suggested that insulin decreases the production of OPG, while in rat models, glucagon-like European Journal of Endocrinology Clinical Study C Davenport and others Diabetes medication and vascular calcification 173 :1 53–61 www.eje-online.org Ñ 2015 European Society of Endocrinology DOI: 10.1530/EJE-14-1137 Printed in Great Britain Published by Bioscientifica Ltd. Downloaded from Bioscientifica.com at 06/10/2020 01:57:27AM via free access