Glycyrrhizin protects rat heart against ischemia-reperfusion injury through blockade of HMGB1-dependent phospho-JNK/Bax pathway.
OBJECTIVE
Glycyrrhizin (GL) has been found to inhibit extracellular HMGB1 cytokine's activity, and protect spinal cord, liver and brain against I/R-induced injury in experimental animals. The purpose of this study was to investigate the protective effect of GL in rat myocardial I/R-induced injury and to elucidate the underlying mechanisms.


METHODS
Male adult Sprague-Dawley rats underwent a 30-min left coronary artery occlusion followed by a 24-h reperfusion. The rats were treated with glycyrrhizin or glycyrrhizin plus recombinant HMGB1 after 30 min of ischemia and before reperfusion. Serum HMGB1, TNF-α and IL-6 levels, and hemodynamic parameters were measured at the onset and different time points of reperfusion. At the end of the experiment, the heart was excised, and the infarct size and histological changes were examined. The levels of Bcl2, Bax and cytochrome c, as well as phospho-ERK1/2, phospho-JNK and phospho-P38 in the heart tissue were evaluated using Western blot analysis, and myocardial caspase-3 activity was measured colorimetrically using BD pharmingen caspase 3 assay kit.


RESULTS
Intravenous administration of GL (10 mg/kg) significantly reduced the infarct size, but did not change the hemodynamic parameters at different time points during reperfusion. GL significantly decreased the levels of serum HMGB1, TNF-α and IL-6. GL changed the distribution of Bax and cytochrome c expression between the mitochondrial and cytosolic fractions in the heart tissue, resulting in inhibition of myocardial apoptosis. Moreover, expression of phospho-JNK, but not ERK1/2 and P38 was decreased by GL in the heart tissue. All of the effects produced by GL treatment were reversed by co-administration with the recombinant HMGB1 (100 μg). Intravenous administration of SP600125, a selective phospho-JNK inhibitor (0.5 mg/kg), attenuated HMGB1-dependent Bax translocation and the subsequent apoptosis.


CONCLUSIONS
These results demonstrate that GL alleviates rat myocardial I/R-induced injury via directly inhibiting extracellular HMGB1 cytokine activity and blocking the phospho-JNK/Bax pathway.
Department of Cardiology, Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health, Qilu Hospital Shandong University, Ji-nan 250012, China.
Chang-lin
CL
Zhai
Mei-qi
MQ
Zhang
Yun
Y
Zhang
Hong-xia
HX
Xu
Jing-min
JM
Wang
Gui-peng
GP
An
Yuan-yuan
YY
Wang
Li
L
Li
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D015415:Biomarkers / Q000097:blood; D015153:Blotting, Western; D016207:Cytokines / Q000097:blood / Q000276:immunology; D019695:Glycyrrhizic Acid / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D024243:HMGB1 Protein / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008297:Male; D009203:Myocardial Infarction / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D015428:Myocardial Reperfusion Injury / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
D000893:Anti-Inflammatory Agents; C494828:Bax protein, rat; D015415:Biomarkers; D016207:Cytokines; D024243:HMGB1 Protein; C104200:Hbp1 protein, rat; D051028:bcl-2-Associated X Protein; D019695:Glycyrrhizic Acid; D048031:JNK Mitogen-Activated Protein Kinases