Differential Fmo3 gene expression in various liver injury models involving hepatic oxidative stress in mice

Abstract

Flavin-containing monooxygenase-3 (FMO3) catalyzes metabolic reactions similar to cytochrome P450 monooxygenase however, most metabolites of FMO3 are considered non-toxic. Recent findings in our laboratory demonstrated Fmo3gene induction following toxic acetaminophen (APAP) treatment in mice.The goal of this study was to evaluate Fmo3gene expression in diverseother mouse models of hepatic oxidative stress and injury. Fmo3 gene regulation by Nrf2 was also investigated using Nrf2 knockout (Nrf2 KO) mice. In our studies, male C57BL/6J mice were treated with toxic dosesof hepatotoxicants or underwent bile duct ligation (BDL, 10d). Hepatotoxicants included APAP (400 mg/kg, 24 to 72h), alpha-naphthylisothiocyanate (ANIT; 50 mg/kg, 2 to 48h), carbontetrachloride (CCl4;10 or 30 μL/kg, 24 and 48h) and allyl alcohol (AlOH; 30 or 60 mg/kg, 6 and 24h). Because oxidative stress activates nuclear factor (erythroid-derived 2)-like 2 (Nrf2), additional studies investigated Fmo3 gene regulation by Nrf2 using Nrf2 knockout (Nrf2 KO) mice. At appropriate time-points, blood and liver samples were collected for assessment of plasma alanine aminotransferase (ALT) activity, plasma and hepatic bile acid levels, as well as liver Fmo3 mRNA and protein expression. Fmo3 mRNA expression increased significantly by 43-fold at 12h after ANIT treatment,and this increase translates to a 4-fold change in protein levels. BDL also increased Fmo3 mRNA expression by 1899-fold, but with no change in protein levels. Treatment of mice with CCl4decreased liver Fmo3gene expression, whileno change in expression was detected with AlOH treatment. Nrf2 KO mice are more susceptible to APAP (400 mg/kg, 72h) treatment compared to their wild-type (WT) counterparts, which is evidenced by greater plasma ALT activity. Fmo3 mRNA and protein expression increased in Nrf2 KO mice after APAP treatment. Collectively, not all hepatotoxicantsthat produce oxidative stress alter Fmo3gene expression. Along with APAP, toxic ANIT treatment in mice markedly increasedFmo3 gene expression. While BDL increased Fmo3 mRNA expression, protein level did not change. The discrepancy with Fmo3 induction in cholestatic models, ANIT and BDL, is not entirely clear. Results from Nrf2 KO mice with APAP suggest that the transcriptional regulation of Fmo3 during liver injury may not involve Nrf2.

Ginseng alleviates cyclophosphamide-induced hepatotoxicity via reversing disordered homeostasis of glutathione and bile acid

“…Bile acids are the main endogenous ingredients in bile, which are synthesized and secreted by hepatcyctes into the bile canaliculus. Oxidative stress could disturb the homeostasis of bile acids, whereas, disordered homeostasis of bile acids could aggravate the oxidative stress of liver 37 38 40 46 . Besides, unbalanced composition of bile acids can directly induce the hepatotoxicity via several pathways, including proinflammatory and cytotoxicity 47 .…”

Oxidative stress-responsive transcription factor NRF2 is not indispensable for the human hepatic Flavin-containing monooxygenase-3 (FMO3) gene expression in HepG2 cells

“…A gene array analysis performed in our laboratory also identified increased Fmo3 gene expression after APAP treatment (O'Connor et al, 2014). We have also demonstrated enhanced Fmo3 gene expression after treatment with other hepatotoxicants such as alpha-naphthyl isothiocyanate and after bile duct ligation (Rudraiah et al, 2014b, Rudraiah et al, 2014a). Given that all three of these latter treatments results in oxidative stress, the goal of the present study was to determine whether FMO3 regulation under oxidative stress conditions might involve NRF2-KEAP1 regulatory pathway activation, which is known to mediate many oxidative-stress induced changes in gene expression.…”

“…Additionally, we also showed that toxic alpha-naphthyl isothiocyanate (ANIT) treatment and bile duct ligation (BDL) induced Fmo3 gene expression (Rudraiah et al, 2014a). Most hepatotoxicants that induce Fmo3 also induce oxidative stress.…”

From hepatoprotection models to new therapeutic modalities for treating liver diseases: a personal perspective

“…This observation is in agreement with a recent finding by Leiser et al , who demonstrated that FMO enzymes increase the lifespan and enhance proteostasis in nematodes undergoing a hypoxic response, which is another form of stress/cytotoxicity 31 . It is intriguing that FMO3, once considered to be non-inducible by xenobiotic treatment, has been shown not only to be inducible by our group and others 12, 13, 32, 33 but also to protect against APAP-induced cytotoxicity in hepatocytes 13 . This highlights the evolving nature of our understanding about FMO3 function, which calls for more mechanistic studies to delineate FMO3’s role in protecting against APAP hepatotoxicity.…”