Apolipoprotein A1 (Apo A-I) is the main protein of "good" HDL cholesterol. It supports the transport of excess cholesterol from the vessels to the liver, where it is broken down and excreted. Thus, Apo A-I plays a central role in protecting the vessels from calcification.
High Apo A-I levels are associated with a lower risk of cardiovascular diseases. Low levels, on the other hand, may indicate an increased risk of arteriosclerosis, especially if "bad" LDL cholesterol is also elevated.