HDL Cholesterol Efflux and Serum Cholesterol Loading Capacity Alterations Associate to Macrophage Cholesterol Accumulation in FH Patients with Achilles Tendon Xanthoma

Achilles tendon xanthoma (ATX) formation involves macrophage cholesterol accumulation within the tendon, similar to that occurring in atheroma. Macrophage cholesterol homeostasis depends on serum lipoprotein functions, namely the high-density lipoprotein (HDL) capacity to promote cell cholesterol efflux (cholesterol efflux capacity, CEC) and the serum cholesterol loading capacity (CLC). We explored the HDL-CEC and serum CLC, comparing 16 FH patients with ATX to 29 FH patients without ATX. HDL-CEC through the main efflux mechanisms mediated by the transporters ATP binding cassette G1 (ABCG1) and A1 (ABCA1) and the aqueous diffusion (AD) process was determined by a cell-based radioisotopic technique and serum CLC fluorimetrically. Between the two groups, no significant differences were found in terms of plasma lipid profile. A trend toward reduction of cholesterol efflux via AD and a significant increase in ABCA1-mediated HDL-CEC (+18.6%) was observed in ATX compared to no ATX patients. In ATX-presenting patients, ABCG1-mediated HDL-CEC was lower (-11%) and serum CLC was higher (+14%) compared to patients without ATX. Considering all the patients together, ABCG1 HDL-CEC and serum CLC correlated with ATX thickness inversely (p = 0.013) and directly (p < 0.0001), respectively. In conclusion, lipoprotein dysfunctions seem to be involved in ATX physiopathology and progression in FH patients.