Amiodarone accumulates two cholesterol precursors in myocardium: A controlled clinical study

BACKGROUND

Amiodarone is an effective antiarrhythmic drug, which interferes with cholesterol synthesis. In the human body, it inhibits two enzymes in the cholesterol-synthesis pathway, followed by increases especially in serum desmosterol and zymostenol concentrations and a decrease in that of serum lathosterol.

OBJECTIVES

We explored whether desmosterol and zymostenol accumulate also in myocardial tissue during amiodarone treatment.

METHODS

Thirty-three patients admitted for cardiac transplantation volunteered for the study. Ten patients were on amiodarone treatment (AD group) and 23 were not (control group). The groups were matched as regards demographic and clinical variables. Myocardial samples were obtained from the removed hearts from 31 patients. Cholesterol, non-cholesterol sterols and squalene were quantified by means of gas-liquid chromatography.

RESULTS

In serum and myocardium, desmosterol was 19- and 18-fold higher and zymostenol 4- and 2-fold higher in the AD group versus the control group (p < 0.001 for all). In contrast, myocardial cholesterol, squalene and lathosterol levels were lower in the AD group than in the control group (p < 0.05 for all). Levels of phytosterols and cholestanol were similar in the serum and myocardium in the two groups. Levels of myocardial and serum desmosterol, zymostenol, lathosterol and phytosterols correlated with each other in both groups (p < 0.05 for all).

CONCLUSION

Amiodarone treatment caused the accumulation of desmosterol and zymostenol in myocardium. In particular, myocardial desmosterol concentrations were substantially elevated, which may play a part in some of the therapeutic and adverse effects of amiodarone treatment.

Amiodarone Alters Cholesterol Biosynthesis through Tissue-Dependent Inhibition of Emopamil Binding Protein and Dehydrocholesterol Reductase 24

Amiodarone is prescribed for the treatment and prevention of irregular heartbeats. Although effective in clinical practice, the long-term use of amiodarone has many unwanted side effects, including cardiac, pulmonary, hepatic, and neurological toxicities. Our objective was to elucidate effects of amiodarone exposure on the cholesterol metabolism in cultured neuronal and non-neuronal cells and in individuals taking amiodarone. We observed that amiodarone increases distinct cholesterol precursors in different cell types in a dose-dependent manner. In liver and kidney cell lines, amiodarone causes increase in desmosterol levels, and in primary cortical neurons and astrocytes, amiodarone increases zymosterol, zymostenol, and 8-dehydrocholesterol (8-DHC). We conclude that amiodarone inhibits two enzymes in the pathway, emopamil binding protein (EBP) and dehydrocholesterol reductase 24 (DHCR24). Cortical neurons and astrocytes are more sensitive to amiodarone than liver and kidney cell lines. We confirmed the inhibition of EBP enzyme by analyzing the sterol intermediates in EBP-deficient Neuro2a cells versus amiodarone-treated control Neuro2a cells. To determine if the cell culture experiments have clinical relevance, we analyzed serum samples from amiodarone users. We found that in patient serum samples containing detectable amount of amiodarone there are elevated levels of the sterol precursors zymosterol, 8-DHC, and desmosterol. This study illustrates the need for close monitoring of blood biochemistry during prolonged amiodarone use to minimize the risk of side effects.

Ligand-dependent transcriptional induction of lethal autophagy: A new perspective for cancer treatment

Dendrogenin A (DDA) is a mammalian metabolite that displays anticancer and chemopreventive properties in mice. At the cancer cell level, DDA induces differentiation and death. We investigated herein the nature of DDA cytoxicity in cancer cells. We showed that DDA triggers biochemical and cellular features of macroautophagy/autophagy and that autophagy is cytotoxic. DDA induces both the accumulation of pro-lysosomal sterols and stimulates the expression of regulators of autophagy such as NR4A, LC3 and TFEB through binding to the liver X receptor (LXR), a ligand-dependent transcription factor consisting of 2 isoforms, NR1H2 and NR1H3. These effects are not observed with canonical LXR agonists such as the oxysterol 22(R)-hydroxycholesterol or the synthetic molecules T0901317 and GW3965. DDA effects were measured on melanoma and acute myeloid leukemia cells including patient-derived leukemia cells in vitro and in vivo. Importantly the induction of lethal autophagy kills cells independently of their cytogenetic subgroups and does not differentiate bulk cancer cells from cancer cell progenitors. Together these data show that DDA drives LXR to induce the expression of autophagic genes leading to cancer cells death. This opens up new perspectives for cancer treatment.