Silybin is widely used as a hepatoprotective agent in various
liver disease therapies and has been previously identified as a
CYP3A inhibitor. However, little is known about the effect of
silybin on
CYP3A and the regulatory mechanism during high-fat-diet (HFD)-induced liver
inflammation. In our study, we found that
silybin restored
CYP3A expression and activity that were decreased by HFD and
conditioned medium (CM) from
palmitate-treated Kupffer cells. Moreover,
silybin suppressed liver
inflammation in HFD-fed mice and inhibited nuclear factor κ-B translocation into the nucleus through elevation of
SIRT2 expression and promotion of p65 deacetylation. This effect was confirmed by overexpression of
SIRT2, which suppressed p65 nuclear translocation and restored
CYP3A transcription affected by CM. The hepatic NAD+ concentration markedly decreased in HFD-fed mice and CM-treated hepatocytes/HepG2 cells but increased after
silybin treatment. Supplementing
nicotinamide mononucleotide as an NAD+ donor inhibited p65 acetylation, decreased p65 nuclear translocation, and restored
cyp3a transcription in both HepG2 cells and mouse hepatocytes. These results suggest that
silybin regulates metabolic
enzymes during liver
inflammation by a mechanism related to the increase in NAD+ and
SIRT2 levels. In addition,
silybin enhanced the intracellular NAD+ concentration by decreasing poly-
ADP ribosyl polymerase-1 expression. In summary,
silybin increased NAD+ concentration, promoted
SIRT2 expression, and lowered p65 acetylation both in vivo and in vitro, which supported the recovery of
CYP3A expression. These findings indicate that the
NAD+/
SIRT2 pathway plays an important role in
CYP3A regulation during
nonalcoholic fatty liver disease. SIGNIFICANCE STATEMENT: This research revealed the differential regulation of
CYP3A by
silybin under physiological and
fatty liver pathological conditions. In the treatment of
nonalcoholic fatty liver disease,
silybin restored, not inhibited,
CYP3A expression and activity through the
NAD+/
sirtuin 2 pathway in accordance with its anti-inflammatory effect.