Proceedings of The Physiological Society

Physiology 2015 (Cardiff, UK) (2015) Proc Physiol Soc 34, PC136

Poster Communications

Examining the effects of vitamin D receptor activators (VDRAs) on vascular smooth muscle cell (VSMC) calcification using intact vessels from chronic kidney disease (CKD) patients

J. L. Laycock1, B. Caplin2, R. Fish2, B. Lindsey2, D. Wheeler2, D. Long1, C. Shanahan3, R. Shroff4

1. Institute of Child Health, University College London, London, -- Please select State/province--, United Kingdom. 2. Royal Free Hospital, London, United Kingdom. 3. Kings College London, London, United Kingdom. 4. Great Ormond Street Hospital, London, United Kingdom.

CKD patients are at high risk of cardiovascular disease, abnormal mineral metabolism predisposes patients to vascular calcification. This is a highly regulated, cell mediated process that predominantly involves VSMCs. CKD patients are often deficient in vitamin D and are prescribed VDRAs to prevent secondary hyperparathyroidism. The effect of VDRAs on calcification is not fully understood. This study used intact arteries from children and adults with CKD as a clinically relevant model. The inferior epigastric artery that is routinely removed and discarded at the time of renal transplant was harvested for ex vivo studies. Informed written consent was obtained from all participants. Arteries were dissected into vessel rings, cultured in normal or raised P&Ca media to mimic CKD and treated with physiological doses (x10-8M) of VDRAs (calcitriol or alfacalcidol). Vessel rings were homogenised and their calcium load and activity of osteogenic marker alkaline phosphatase (ALP) measured by colorimetric assay. All data refers to fold change to vehicle + SE in raised P&Ca media. In pediatric patients calcitriol increased calcium load in predialysis vessels by 3.20+0.89 (n=11) and to a greater extent in dialysis vessels by 6.12+1.5 (n=10). Alfacalcidol increased calcium load in predialysis vessels by 2.86+0.45 (n=5) and more so in dialysis vessels by 3.89+0.71 (n=6). In addition ALP activity in dialysis vessels was increased with calcitriol by 2.05+0.2 (n=7), whereas alfacalcidol had no effect 0.97+0.02 (n=3). In contrast, calcitriol had no effect on calcium load in any of the CKD adult vessels 1.15+0.26 (n=10). VSMCs explanted from non-renal control and dialysis patients were treated with x10-9, x10-8 and x10-7M calcitriol and gene expression analysed by qPCR. Dose dependent responses were observed with x10-7M calcitriol eliciting the greatest response, the vitamin D receptor increased 1.4+0.1 in control (n=3) and 2.5+0.5 in dialysis (n=3). Expression of the vitamin D inactivating 24 hydroxylase enzyme was also increased a greater extent in dialysis VSMCs, from 0.051+0.025 to 18.4+8.7 per 1000 18S (n=3) compared to 0.004 to 6.3 per 1000 18S in control VSMCs (n=3). The major finding of this study was alfacalcidol and to a greater extent calcitriol increased calcification in pediatric CKD vessels particularly in dialysis. In these vessels calcitriol also increased ALP activity. Calcitriol did not affect calcification in vessels from adult CKD patients. Dialysis VSMCs were more responsive than controls to calcitriol regulated gene expression and may have an exaggerated response to VDRAs. The effect of VDRAs on vascular calcification, particularly in pediatric patients, needs to be further investigated in order to be taken into consideration when prescribing VDRAs to CKD patients.

Where applicable, experiments conform with Society ethical requirements