1). It is known that UDCA not only improves cholestasis but also serum IgM concentrations.4, 6 The combination therapy of bezafibrate

and UDCA further reduced the IgM concentration from 306 ± 60 (UDCA alone) to 232 ± 41 mg/dL (UDCA + bezafibrate), consistent with the findings reported by Iwasaki et al.16 Furthermore, our results showed that the combination therapy significantly reduced serum total cholesterol, LDL cholesterol, and triglyceride concentrations compared with UDCA alone. The mechanisms of the anticholestatic effect of bezafibrate remain unclear. Because MDR3 is a target gene of PPARα17 and bezafibrate is a ligand of PPARα, β/δ, and γ,18 stimulation of biliary phospholipid secretion due to the up-regulation of MDR3 has generally been believed to be the main mechanism of the action. In fact, our experiment using HepaRG cells showed significantly PARP inhibitor elevated expression of MDR3 mRNA following the addition of bezafibrate (Fig. 5B). However, MDR3 is activated by both bezafibrate as well as UDCA.7 Furthermore, recent reports have demonstrated that the expression of MDR3 was already markedly up-regulated

in PBC patients30 and it was not significantly affected by bezafibrate treatment.31 Therefore, the anticholestatic effect of bezafibrate may be caused by mechanisms independent of phospholipid secretion. Other possible anticholestatic mechanisms of bezafibrate by way of PPARα activation include MK-1775 in vivo Histidine ammonia-lyase down-regulation of NTCP,17 CYP7A1,32, 33 and CYP27A1.33 NTCP transports basolateral (sinusoidal) bile acids into hepatocytes, whereas CYP7A1 and CYP27A1 are key enzymes in the classic and alternative bile acid biosynthetic pathways, respectively. Coordinate down-regulation of these three proteins leads to a decrease in hepatic

bile acid concentration and may protect hepatocytes against cytotoxic bile acids. In addition, the reduction of hepatic bile acid levels attenuates the activity of FXR. It is known that deactivation of FXR up-regulates MRP4,34 one of the important basolateral transporters for the efflux of bile acids from hepatocytes to the sinusoid in cholestasis. The transcription of MRP4 is positively controlled by the constitutive androstane receptor (CAR; NR1I3)35 and a CAR responsive element is embedded within an FXR responsive element in the human MRP4 promoter. Therefore, activated FXR competes with CAR for binding to this overlapping binding site, which down-regulates MRP4.36 The most striking results among our serum biomarker analyses are the elevation of 4β-HC, as well as the reduction of C4 during treatment with bezafibrate. Serum 4β-HC concentration is considered a biomarker of CYP3A4/5 activity,37 whereas C4 is a marker of CYP7A1 activity or de novo bile acid synthesis.