Harmful Effects of the Azathioprine Metabolite 6-Mercaptopurine in Vascular Cells: Induction of Mineralization

Abstract

Vascular mineralization contributes to the high cardiovascular morbidity and mortality in patients who suffer from chronic kidney disease and in individuals who have undergone solid organ transplantation. The immunosuppressive regimen used to treat these patients appears to have an impact on vascular alterations. The effect of 6-mercaptopurine (6-MP) on vascular calcification has not yet been determined. This study investigates the effect of 6-MP on vascular mineralization by the induction of trans-differentiation of rat vascular smooth muscle cells in vitro. 6-MP not only induces the expression of osteo-chondrocyte-like transcription factors and proteins but also activates alkaline phosphatase enzyme activity and produces calcium deposition in in vitro and ex vivo models. These processes are dependent on 6-MP-induced production of reactive oxygen species, intracellular activation of mitogen-activated kinases and phosphorylation of the transcription factor Cbfa1. Furthermore, the metabolic products of 6-MP, 6-thioguanine nucleotides and 6-methyl-thio-inosine monophosphate have major impacts on cellular calcification. These data provide evidence for a possible harmful effect of the immunosuppressive drug 6-MP in vascular diseases, such as arteriosclerosis.

Long-Term Treatment of Azathioprine in Rats Induces Vessel Mineralization

“…Extracellular calcium content of different vascular beds was determined as previously published [ 10 , 18 ].…”

“…Several indications exist that AZA treatment has an impact on the cardiovascular risk and pathophysiology of the vessel wall [ 8 , 9 ]. In a previous study, we found an induction of mVC and oxidative stress upon treatment with the cleavage product of AZA, 6-mercaptopurine (6-MP), using an in vitro model with rat VSMCs [ 10 ]. Extensive research in the field of VSMC calcification revealed the involvement of several mechanisms including osteogenic, senescence and inflammatory signaling.…”

Research Models for Studying Vascular Calcification

“…Currently, aortic rings from rats and mice are commonly used for studying vessel calcification under various conditions. The stimulation time varies from 3-14 days [6,24,25,28,59,[62][63][64][65]. Although the utilization of aortic rings comes closer to the physiologic setting, a multitude of influencing factors is still lost.…”

Epidemiology, risk factors and management of cardiovascular diseases in IBD

“…8 Using in vitro and ex vivo models, a study published in 2014 demonstrated that 6-mercaptopurine can induce phenotypic transformation of vascular smooth muscle cells, which would predispose patients to arteriosclerosis, potentially increasing the risk of cardiovascular events. 72 Anti-TNF agents do not seem to modify cardiovascular risk in observational studies in IBD; whether this finding represents a true inability to modify cardiovascular risk with treatment of systemic inflammation, or simply an inability to account for confounding by disease severity remains unclear. For instance, a comparable risk of CHD was seen in patients treated with anti-TNF agents (IRR 0.60, 95% CI 0.25-1.44) and in patients not on anti-TNF agents (IRR 1.24, 95% CI 1.16-1.32), using patients without IBD as a reference.…”