Semiquantitation of intrahepatic MDR3 mRNA levels by reverse transcription/competitive polymerase chain reaction

Background/Aims: Knockout mice lacking mdr2, the murine analogue of human MDR3 P-glycoprotein, develop chronic non-suppurative cholangitis. Recently, a deficiency in MDR3 messenger RNA (mRNA) has been reported in a subtype of progressive familial intrahepatic cholestasis. Thus, reduced MDR3 gene expression could be involved in human cholestatic liver diseases. Methods: We developed a sensitive and specific reverse transcription/competitive polymerase chain reaction for the semiquantitation of intrahepatic MDR3 mRNA levels. Using this method we determined the MDR3 mRNA levels in 52 liver specimens from primary biliary cirrhosis (n=11), chronic hepatitis B (n-5), chronic hepatitis C (n=14), non-cholestatic cirrhosis (n=9) and controls (n=13). Results: MDR3 mRNA was detected in all specimens with some variation in mRNA levels. No significant differences in the mean MDR3 mRNA levels were present between the groups studied, including normal controls. Conclusions: We found no evidence for deficient or severely reduced intrahepatic MDR3 mRNA in primary biliary cirrhosis, nor were mRNA levels altered significantly by virus-induced inflammation or by cirrhosis. The reverse transcription/competitive polymerase chain reaction assay described here should be a useful tool in the semiquantitative study of MDR3 mRNA levels in small tissue specimens.