Skullcapflavone II, a novel NQO1 inhibitor, alleviates aristolochic acid I-induced liver and kidney injury in mice.

Aristolochic acid I (AAI) is a well established nephrotoxin and human carcinogen. Cytosolic NAD(P)H quinone oxidoreductase 1 (NQO1) plays an important role in the nitro reduction of aristolochic acids, leading to production of aristoloactam and AA-DNA adduct. Application of a potent NQO1 inhibitor dicoumarol is limited by its life-threatening side effect as an anticoagulant and the subsequent hemorrhagic complications. As traditional medicines containing AAI remain available in the market, novel NQO1 inhibitors are urgently needed to attenuate the toxicity of AAI exposure. In this study, we employed comprehensive 2D NQO1 biochromatography to screen candidate compounds that could bind with NQO1 protein. Four compounds, i.e., skullcapflavone II (SFII), oroxylin A, wogonin and tectochrysin were screened out from Scutellaria baicalensis. Among them, SFII was the most promising NQO1 inhibitor with a binding affinity (KD = 4.198 µmol/L) and inhibitory activity (IC50 = 2.87 µmol/L). In human normal liver cell line (L02) and human renal proximal tubular epithelial cell line (HK-2), SFII significantly alleviated AAI-induced DNA damage and apoptosis. In adult mice, oral administration of SFII dose-dependently ameliorated AAI-induced renal fibrosis and dysfunction. In infant mice, oral administration of SFII suppressed AAI-induced hepatocellular carcinoma initiation. Moreover, administration of SFII did not affect the coagulation function in short term in adult mice. In conclusion, SFII has been identified as a novel NQO1 inhibitor that might impede the risk of AAI to kidney and liver without obvious side effect.

4-phenylbutyric acid promotes hepatocellular carcinoma via initiating cancer stem cells through activation of PPAR-α.

BACKGROUND AND AIMS: 4-phenylbutyric acid (4-PBA) is a low molecular weight fatty acid that is used in clinical practice to treat inherited urea cycle disorders. In previous reports, it acted as a chemical chaperone inhibiting endoplasmic reticulum (ER) stress and unfolded protein response signaling. A few studies have suggested its function against hepatic fibrosis in mice models. However, its role in hepatocarcinogenesis remained unknown. METHODS: 4-PBA was administered alone or in combination with diethylnitrosamine to investigate its long-term effect on liver tumorigenesis. The role of 4-PBA in oncogene-induced hepatocellular carcinoma (HCC) mice model using sleeping beauty system co-expressed with hMet and ß-catenin point mutation (S45Y) was also observed. RNA-seq and PCR array were used to screen the pathways and genes involved. In vitro and in vivo studies were conducted to explore the effect of 4-PBA on liver and validate the underlying mechanism. RESULTS: 4-PBA alone didn't cause liver tumor in long term. However, it promoted liver tumorigenesis in HCC mice models via initiation of liver cancer stem cells (LCSCs) through Wnt5b-Fzd5 mediating ß-catenin signaling. Peroxisome proliferator-activated receptors (PPAR)-α induced by 4-PBA was responsible for the activation of ß-catenin signaling. Thus, intervention of PPAR-α reversed 4-PBA-induced initiation of LCSCs and HCC development in vivo. Further study revealed that 4-PBA could not only upregulate the expression of PPAR-α transcriptionally but also enhance its stabilization via protecting it from proteolysis. Moreover, high PPAR-α expression predicted poor prognosis in HCC patients. CONCLUSIONS: 4-PBA could upregulate PPAR-α to initiate LCSCs by activating ß-catenin signaling pathway, promoting HCC at early stage. Therefore, more discretion should be taken to monitor the potential tumor-promoting effect of 4-PBA under HCC-inducing environment.