Low-Iron Diet and Chelation Therapy Rescue Severe Atherosclerosis Associated with High Circulating Iron Levels

In 1981 Sullivan proposed the "iron hypothesis", which states that iron is detrimental for the cardiovascular system, promoting atherosclerosis progression. Iron levels are increased in hereditary hemochromatosis as well as in iron-loading anemias, such as thalassemia, sickle cell disease and the myelodysplastic syndromes. In the latter iron levels may be further increased due to red blood transfusions. To date it is unclear whether iron overload in these disorders promotes atherosclerosis. Conflicting evidence is provided by epidemiological data and studies in disease models.

To study susceptibility to atherosclerosis we analyzed ApoE-null mice crossbred with a mouse model of hereditary hemochromatosis type IV, due to a point mutation in the iron exporter ferroportin that prevents hepcidin binding (Altamura et al., Cell Metabolism 2014). We show that at 6 and 12 months of age hemochromatotic ApoE-null mice show a strong increase in lesion size and numbers compared to ApoE-null mice. The atherosclerotic phenotype positively correlates with increased levels of serum iron and transferrin saturation, as well as with iron deposition in the vascular smooth muscle cells, which cause vascular oxidative stress and vessel stiffness. High circulating iron levels promote circulating LDL oxidation, vascular endothelium activation and permeabilization, nitric oxide consumption and inflammation (increased MCP1 and VEGF). In hemochromatotic ApoE-null mice atherosclerotic plaques show reduced collagen deposition and elevated macrophage numbers as well as lipid content and calcification, suggesting enhanced plaque vulnerability and accelerated disease progression. Consistently, these mice develop compensatory left ventricular hypertrophy, associated with increased left ventricle diastolic volume and area.

To reduce iron levels we maintained hemochromatotic ApoE-null mice either on a low iron diet (iron content: <10 ppm) or on iron chelation therapy (Deferiprone 8 ml/kg daily). Both, prolonged maintenance on a low iron diet or iron chelator treatment rescued the severe atherosclerotic phenotype in 6 and 10 month-old mice. Importantly, these treatments significantly lowered serum iron levels and transferrin saturation as well as arterial iron deposition. As a consequence, endothelial activation and pro-inflammatory molecule production are strongly reduced, limiting atherosclerosis progression in these mice.

Taken together our data suggest that high circulating iron levels strongly enhance the severity of atherosclerosis, thus indicating that systemic iron overload is a risk factor for cardiovascular disease. Furthermore our results demonstrate the beneficial effects of dietary iron limitation and iron chelation in counteracting iron-induced atherosclerosis progression. These observations have potential implications for pathological conditions associated with elevated systemic iron levels and highlight the importance of maintaining low systemic iron levels in these patients.