Calcitriol Accelerates Vascular Calcification Irrespective of Vitamin K Status in a Rat Model of Chronic Kidney Disease with Hyperphosphatemia and Secondary Hyperparathyroidism.

Patients with chronic kidney disease (CKD) have a markedly increased risk for developing cardiovascular disease. Nontraditional risk factors, such as increased phosphate retention, increased serum fibroblast growth factor 23 (FGF-23), and deficiencies in vitamins D and K metabolism, likely play key roles in the development of vascular calcification during CKD progression. Calcitriol [1,25-(OH)2-D3] is a key transcriptional regulator of matrix Gla protein, a vitamin K-dependent protein that inhibits vascular calcification. We hypothesized that calcitriol treatment would inhibit the development of vascular calcification and this inhibition would be dependent on vitamin K status in a rat model of CKD. Rats were treated with dietary adenine (0.25%) to induce CKD, with either 0, 20, or 80 ng/kg of calcitriol with low or high dietary vitamin K1 (0.2 or 100 mg/kg) for 7 weeks. Calcitriol at both lower (20 ng/kg) and moderate (80 ng/kg) doses increased the severity of vascular calcification, and contrary to our hypothesis this was not significantly improved by high dietary vitamin K1. Calcitriol had a dose-dependent effect on: 1) lowering serum parathyroid hormone, 2) increasing serum calcium, and 3) increasing serum FGF-23. Calcitriol treatment significantly increased aortic expression of the calcification genes Runx2 and Pit-1 These data also implicate impaired vitamin D catabolism in CKD, which may contribute to the development of calcitriol toxicity and increased vascular calcification. The present findings demonstrate that in an adenine-induced rat model of CKD calcitriol treatment at doses as low as 20 ng/kg can increase the severity of vascular calcification regardless of vitamin K status.