Pharmacological TNAP inhibition efficiently inhibits arterial media calcification in a warfarin rat model but deserves careful consideration of potential physiological bone formation/mineralization impairment.

Abstract Arterial media calcification is frequently seen in elderly and patients with chronic kidney disease (CKD), diabetes and osteoporosis. Pyrophosphate is a well-known calcification inhibitor that binds to nascent hydroxyapatite crystals and prevents further incorporation of inorganic phosphate into these crystals. However, the enzyme tissue-nonspecific alkaline phosphatase (TNAP), which is expressed in calcified arteries, degrades extracellular pyrophosphate into phosphate ions, by which pyrophosphate loses its ability to block vascular calcification. Here, we aimed to evaluate whether pharmacological TNAP inhibition is able to prevent the development of arterial calcification in a rat model of warfarin-induced vascular calcification. To investigate the effect of the pharmacological TNAP inhibitor SBI-425 on vascular calcification and bone metabolism, a 0.30% warfarin rat model was used. Warfarin exposure resulted in distinct calcification in the aorta and peripheral arteries. Daily administration of the TNAP inhibitor SBI-425 (10 mg/kg/day) for 7 weeks significantly reduced vascular calcification as indicated by a significant decrease in calcium content in the aorta (vehicle 3.84 ± 0.64 mg calcium/g wet tissue vs TNAP inhibitor 0.70 ± 0.23 mg calcium/g wet tissue) and peripheral arteries and a distinct reduction in area % calcification on Von Kossa stained aortic sections as compared to vehicle. Administration of SBI-425 resulted in decreased bone formation rate and mineral apposition rate, and increased osteoid maturation time and this without significant changes in osteoclast- and eroded perimeter. Administration of TNAP inhibitor SBI-425 significantly reduced the calcification in the aorta and peripheral arteries of a rat model of warfarin-induced vascular calcification. However, suppression of TNAP activity should be limited in order to maintain adequate physiological bone mineralization.