Simultaneous recovery of dual pathways for ammonia metabolism do not improve further detoxification of ammonia in HepG2 cells

Evaluation of the blood ammonia level as a non-invasive predictor for the presence of esophageal varices and the risk of bleeding

BACKGROUND/AIMS

The development of esophageal varices (EV) and resultant bleeding are the most critical complications of portal hypertension. Upper gastrointestinal endoscopy is the gold standard for diagnosis of EV. To find a non-invasive method for diagnosis of EV and to predict the bleeding risk is appealing and would decrease the cost and discomfort of upper endoscopy. The aim of our study was to evaluate the blood ammonia level as a predictor of the presence of EV and of a high risk of bleeding.

MATERIALS AND METHODS

In this cross-sectional study, a total of 359 patients with cirrhosis were examined for the presence of EV by upper endoscopy. Abdominal ultrasonography, calculation of the Child-Pugh score, and measurement of blood ammonia were performed for each patient.

RESULTS

The blood ammonia level was significantly higher in patients with EV than in those without it (p<0.001), and in patients with a high risk of variceal bleeding than in those with a low risk (p=0.026).

CONCLUSION

An increased blood ammonia level and splenic vein diameter are predictors for the presence of EV and bleeding risk factors. The blood ammonia level may be clinically useful as it correlates with and is an independent predictor for both the endoscopic risk signs and risk factors of bleeding, and therefore, it could be used in patients with cirrhosis to decrease the number of screening endoscopies they are subjected to.

Optimizing combination of liver-enriched transcription factors and nuclear receptors simultaneously favors ammonia and drug metabolism in liver cells

The HepG2 cell line is widely used in studying liver diseases because of its immortalization, but its clinical application is limited by its low expression of the urea synthesis key enzymes and cytochromes P450 (CYPs). On the basis of our previous work, we investigated the transcriptional regulation of arginase 1 (Arg1) and ornithine transcarbamylase (OTC) in HepG2 cells. We also screened for the optimal combination of liver enrichment transcription factors (LETFs) and xenobiotic nuclear receptors that can promote the expression of key urea synthases and five major CYPs in HepG2 cells. Thus, recombinant HepG2 cells were established. Results showed that C/EBPβ, not C/EBPα, could upregulate expression of Arg1 and PGC1α and HNF4α cooperatively regulate the expression of OTC. The two optimal combinations C/EBPβ+HNF4α+HNF6+PXR and C/EBPβ+HNF4α+HNF6+CAR were selected. Compared with the control cells, the recombinant HepG2 cells modified by the two optimal combinations exhibited enhanced ammonia metabolism and CYP enzyme activity. Moreover, the HepG2/(C/EBPβ+HNF4α+HNF6+PXR) cells more strongly reduced ammonia than any other combination tested in this study. The present work indicated that optimizing the combination of transcription factors will simultaneously promote hepatocyte ammonia metabolism and drug metabolism. The recombinant HepG2 liver cell line constructed by the optimal combination provided an improved alternative means for bioartificial liver applications and drug toxicity testing.