Clinical use of doxorubicin is greatly limited by its severe cardiotoxic side effects.
L-carnitine is a vitamin-like substance which has been successfully used in many cardiomyopathies,
however, the intracellular mechanism(s) remain unclear. The objective of this study
was set to evaluate the protective effect of L-carnitine on doxorubicin-induced cardiomyocyte
apoptosis, and to explore its intracellular mechanism(s).
Primary cultured neonatal rat cardiomyocytes were treated with doxorubicin (1 µM)
with or without pretreatment with L-carnitine (1-30 mM). Lactate dehydrogenase assay,
terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling
staining, and flow cytometry measurement were used to assess cytotoxicity and apoptosis.
Fluorescent probes 2',7'-dichlorofluorescein diacetate and chemiluminescence assay
of superoxide production were used to detect the production of reactive oxygen species.
Western blotting was used to evaluate the quantity of cleaved caspase-3, cytosol cytochrome
c, and Bcl-x(L) expression.
L-carnitine inhibited doxorubicin-induced reactive oxygen species generation and NADPH
oxidase activation, reduced the quantity of cleaved caspase-3 and cytosol cytochrome
c, and increased Bcl-x(L) expression, resulting in protecting cardiomyocytes from
doxorubicin-induced apoptosis. In addition, L-carnitine was found to increase the
prostacyclin (PGI(2)) generation in cardiomyocytes. The siRNA transfection for PGI(2)
synthase significantly reduced L-carnitine-induced PGI(2) and L-carnitine's protective
effect. Furthermore, blockade the potential PGI(2) receptors, including PGI(2) receptors
(IP receptors), and peroxisome proliferator-activated receptors alpha and delta (PPARα
and PPARδ), revealed that the siRNA-mediated blockage of PPARα considerably reduced
the anti-apoptotic effect of L-carnitine.
These findings suggest that L-carnitine protects cardiomyocytes from doxorubicin-induced
apoptosis in part through PGI(2) and PPARα-signaling pathways, which may potentially
protect the heart from the severe toxicity of doxorubicin.
Copyright © 2009 Elsevier Ireland Ltd. All rights reserved.