A Novel Biomarker for Cellular Toxicity and Phospholipid Accumulation by Cationic Amphiphilic Drugs

Drug-induced phospholipidosis (DIPL) is a phospholipid-hyperaccumulated state in cells, tissues and organs after treatment with cationic amphiphilic drugs (CADs). The biological meaning of phospholipidosis remains unknown. Although a hypothesis has been proposed that DIPL is a biological defense from CADs, experimental data supporting the hypothesis are poor. In this study, we compared CAD toxicity with RAW264 cells with/without egg phosphatidylcholine (egg PC) treatment to identify the role of phospholipids in DIPL. The 50% inhibitory concentrations of chlorpromazine, imipramine and propranolol were significantly increased by egg PC, in accordance with the hypothesis. Then, DIPL biomarkers, bis(monoacylglycero) phosphate (BMP) and the ratio of phosphatidylinositols (PIs) were measured to study the changes of these biomarkers by the relief of CAD toxicity with egg PC. BMP 22:6_22:6 was not increased by imipramine treatment alone due to imipramine toxicity. Co-treatmentof egg PC with imipramine did not decrease BMP 22:6_22:6, which was inconsistent with the relief of toxicity. Conversely, the ratio of PIs increased by imipramine treatment alone, whereas it decreased by co-treatment with egg PC. These results suggest that the ratio of PIs reflects cellular phospholipid accumulation concurrent with CAD toxicity and that it is useful as a DIPL biomarker with high specificity.