Doxorubicin enhances oxysterol levels resulting in a LXR-mediated upregulation of cardiac cholesterol transporters
The anthracycline-mediated cardiotoxicity is still not completely understood. To examine the impact of cholesterol metabolism and transport in this context, cholesterol and oxysterol levels as well as the expression of the cholesterol transporters ABCA1 and ABCG1 were analyzed in doxorubicin-treated HL-1 murine cardiomyocytes as well as in mouse model for acute doxorubicin-induced cardiotoxicity. Doxorubicin-treated HL-1 cells exhibited enhanced cholesterol (153 ± 20% of control), oxysterol (24 S-hydroxycholesterol: 206 ± 29% of control) and cholesterol precursor levels (lathosterol: 122 ± 12% of control; desmosterol: 188 ± 10% of control) indicating enhanced cholesterol synthesis. Moreover, abca1 and abcg1 were upregulated on mRNA, protein and functional level caused by a doxorubicin-mediated activation of the nuclear receptor LXR. In addition, the oxysterols not only induced the abca1 and abcg1 in HL-1 cells but also enhanced the expression of endothelin-1 and transforming growth factor-β, which have already been identified as important factors in doxorubicin-induced cardiotoxicity. These in vitro findings were verified in a murine model for acute doxorubicin-induced cardiotoxicity, demonstrating elevated cardiac (2.1 ± 0.2 vs. 3.6 ± 1.0 ng/mg) and systemic cholesterol levels (105.0 ± 8.4 vs. 130.0 ± 4.3 mg/dl), respectively, as well as enhanced oxysterol levels such as cardiac 24 S-hydroxycholesterol (2.1 ± 0.2 vs. 3.6 ± 1.0 ng/mg). In line with these findings cardiac mRNA expression of abca1 (303% of control) and abcg1 (161% of control) was induced.
Taken together, our data demonstrate enhanced cholesterol and oxysterol levels by doxorubicin, resulting in a LXR-dependent upregulation of abca1 and abcg1. In this context, the cytotoxic effects of oxysterols and their impact on cardiac gene expression should be considered as an important factor in doxorubicin-induced cardiotoxicity.