The Protective Effects Of Histone Acetyltransferase Inhabitor Garcinol In Mice With Endotoxin-induced Acute Liver Injury And The Potential Mechanisms

Objective: Acetylation is an important post-translational modifcation.Acetylation regulates the function of histiones and multipleinflammation-related transcription factors, which is one of the importantmechanisms to control the transcription of inflammatory genes. Acetylationmodification is a reversible process, the acetylaton and deacetylation iscatalysed by histone acetyl transferases (HATs) and histone deacetylases(HDACs), respectively. Recently, the regulatory effects of HDACsinhibitors on inflammatory responses were studies in detail, whereas therewere few literatures about the potential inflammation-regulating effects ofHATs inhibitors. Garcinol was recently indentified as a potent HATsinhibitor. In this study, acute liver injury was induced by the administrationof lipopolysaccharide/D-galactosamine (LPS/D-Gal) in mice, and then thepotential pharmacological effects of garcinol on hepatic lesions andpotential mechanisms were evaluated.Methods：Acute liver injury was induced in BALB/c mice withintraperitoneal injection of LPS (10μg/kg) combined with D-Gal (700 mg/kg). To evaluate the potential pharmacological effects of garcinol,vehicle or various doses of garcinol (2.5mg/kg,5mg/kg or10mg/kg, i.p.)were administered0.5h prior to LPS/D-Gal challenge. The mice weresacrifced at1.5h after LPS/D-Gal challenge and blood samples wereharvested for measuring TNF-α and IL-6levels. Another set of animalswere sacrifced at6h after LPS/D-Gal challenge. The blood samples andliver tissue were harvested for determining plasma aminotransferases (ASTand ALT) levers, hepatic malondialdehyde (MDA) content andcaspase-3,-8,-9activities. The levels of p65, acetylated p65, p53, acetylatedp53, cleaved caspase3, Bax and Bcl–2in liver tissue were determined byWestern blot. In addition, the formalin-fxed specimens were stained withhematoxylin&eosin routinely for morphological evaluation. Hepaticapoptosis was accessed using erminal deoxynucleotidyltransferase-mediated nucleotide nick-end labeling (TUNEL) assay andcleaved caspase-3was analysised by immunohistochemistryResults：These experimental data suggested that HATs inhibitorgarcinol might provide protective benefts in LPS/D-Gal-induced liverinjury. Garcinol did not suppress the expression of pro-infammatorycytokines but it signifcantly suppressed hepatocytes apoptosis. Briefly,(1)The elevation of aminotransferases induced by LPS/D-Gal wassignifcantly suppressed by garcinol (2.5mg/kg～10mg/kg) in adose-dependent manner. These were accomplished with reduced hepatic MDA content and improved histological alterations;(2) Garcinolsignificantly reduced the acetylation of NF-κB p65(Lys310) induced byLPS/D-Gal but garcinol had no obvious effects on the plasma level ofTNF-α and IL-6;(3) Garcinol signifcantly attenuated LPS/D-Gal-inducedhepatic apoptosis as evidenced by reduced number of TUNEL-positivecells in liver sections, markedly suppressed level of cleaved caspase-3anddecreased activities of caspase-3,-8,-9in liver tissues;(4) Garcinol alsoobviously inhibited the acetylation of p53(Lys379) and significantlyreduced the expression of Bax induced by LPS/D-Gal, but it did not alterthe level of Bcl-2.Conclusion：Our experimental data indicated the HATs inhibitorgarcinol protected against LPS/D-Gal-induced liver damage in mice.Garcinol did not inhibit the expression of pro-infammatory cytokines, butit signifcantly suppressed hepatocytes apoptosis by inhibiting theacetyltion of p53, which might reduce its activity, decrease the expressionof Bax and suppress apoptosis. According to the reported literatures andour experimental data, we proposed that the acetylation modification mighttarget multiple proteins and exert diverse regulatory effects in inflammatoryresponse. The complicated modulatory effects of acetylation on the totaloutcome of inflammation and the underlying mechanisms remain furtherinvestigation. In addition, HATs inhibitor attenuated fulminant hepatitis viainhibiting apoptosis, which might provide potential value for the treatment of severe hepatisis. However, these benefical effects of HATs inhibitor alsorequire more experimental studies to determine the detailed mechanismsand the therapeutic significance.