Flavin Monooxygenase-Generated N-Hydroxypipecolic Acid Is a Critical Element of Plant Systemic Immunity.

Following a previous microbial inoculation, plants can induce broad-spectrum immunity to pathogen infection, a phenomenon known as systemic acquired resistance (SAR). SAR establishment in Arabidopsis thaliana is regulated by the Lys catabolite pipecolic acid (Pip) and flavin-dependent-monooxygenase1 (FMO1). Here, we show that elevated Pip is sufficient to induce an FMO1-dependent transcriptional reprogramming of leaves that is reminiscent of SAR. In planta and in vitro analyses demonstrate that FMO1 functions as a pipecolate N-hydroxylase, catalyzing the biochemical conversion of Pip to N-hydroxypipecolic acid (NHP). NHP systemically accumulates in plants after microbial attack. When exogenously applied, it overrides the defect of NHP-deficient fmo1 in acquired resistance and acts as a potent inducer of plant immunity to bacterial and oomycete infection. Our work has identified a pathogen-inducible L-Lys catabolic pathway in plants that generates the N-hydroxylated amino acid NHP as a critical regulator of systemic acquired resistance to pathogen infection.

SA and NHP glucosyltransferase UGT76B1 affects plant defense in both SID2- and NPR1-dependent and independent manner.

KEY MESSAGE: The small-molecule glucosyltransferase loss-of-function mutant ugt76b1 exhibits both SID2- or NPR1-dependent and independent facets of enhanced plant immunity, whereupon FMO1 is required for the SID2 and NPR1 independence. The small-molecule glucosyltransferase UGT76B1 inactivates salicylic acid (SA), isoleucic acid (ILA), and N-hydroxypipecolic acid (NHP). ugt76b1 loss-of-function plants manifest an enhanced defense status. Thus, we were interested how UGT76B1 genetically integrates in defense pathways and whether all impacts depend on SA and NHP. We study the integration of UGT76B1 by transcriptome analyses of ugt76b1. The comparison of transcripts altered by the loss of UGT76B1 with public transcriptome data reveals both SA-responsive, ISOCHORISMATE SYNTHASE 1/SALICYLIC ACID INDUCTION DEFICIENT 2 (ICS1/SID2)- and NON EXPRESSOR OF PR GENES 1 (NPR1)-dependent, consistent with the role of UGT76B1 in glucosylating SA, and SA-non-responsive, SID2/NPR1-independent genes. We also discovered that UGT76B1 impacts on a group of genes showing non-SA-responsiveness and regulation by infections independent from SID2/NPR1. Enhanced resistance of ugt76b1 against Pseudomonas syringae is partially independent from SID2 and NPR1. In contrast, the ugt76b1-activated resistance is completely dependent on FMO1 encoding the NHP-synthesizing FLAVIN-DEPENDENT MONOOXYGENASE 1). Moreover, FMO1 ranks top among the ugt76b1-induced SID2- and NPR1-independent pathogen responsive genes, suggesting that FMO1 determines the SID2- and NPR1-independent effect of ugt76b1. Furthermore, the genetic study revealed that FMO1, ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), SID2, and NPR1 are required for the SA-JA crosstalk and senescence development of ugt76b1, indicating that EDS1 and FMO1 have a similar effect like stress-induced SA biosynthesis (SID2) or the key SA signaling regulator NPR1. Thus, UGT76B1 influences both SID2/NPR1-dependent and independent plant immunity, and the SID2/NPR1 independence is relying on FMO1 and its product NHP, another substrate of UGT76B1.

Epigenetic regulation of N-hydroxypipecolic acid biosynthesis by the AIPP3-PHD2-CPL2 complex.

N-Hydroxypipecolic acid (NHP) is a signaling molecule crucial for systemic acquired resistance (SAR), a systemic immune response in plants that provides long-lasting and broad-spectrum protection against secondary pathogen infections. To identify negative regulators of NHP biosynthesis, we performed a forward genetic screen to search for mutants with elevated expression of the NHP biosynthesis gene FLAVIN-DEPENDENT MONOOXYGENASE 1 (FMO1). Analysis of two constitutive expression of FMO1 (cef) and one induced expression of FMO1 (ief) mutants revealed that the AIPP3-PHD2-CPL2 protein complex, which is involved in the recognition of the histone modification H3K27me3 and transcriptional repression, contributes to the negative regulation of FMO1 expression and NHP biosynthesis. Our study suggests that epigenetic regulation plays a crucial role in controlling FMO1 expression and NHP levels in plants.

Flavin-containing monooxygenase 3 (FMO3): genetic variants and their consequences for drug metabolism and disease.

The review focuses on genetic variants of human flavin-containing monooxygenase 3 (FMO3) and their impact on enzyme activity, drug metabolism and disease.The majority of FMO-mediated metabolism in adult human liver is catalyzed by FMO3. Some drugs are metabolized in human liver predominantly by FMO3, but most drug substrates of FMO3 are metabolized also by other enzymes, particularly cytochromes P-450, and the FMO3-catalyzed reaction is not the major route of metabolism.Rare variants that severely affect production or activity of FMO3 cause the disorder trimethylaminuria and impair metabolism of drug substrates of FMO3. More common variants, particularly p.[(Glu158Lys);(Glu308Gly)], can moderately affect activity of FMO3 in vitro and reduce metabolism of drug substrates in vivo, in some cases increasing drug efficacy or toxicity.Common variants of FMO3 have been associated with a number of disorders, but additional studies are needed to confirm or refute such associations.Elevated plasma concentrations of trimethylamine N-oxide, a product of an FMO3-catalyzed reaction, have been implicated in certain diseases, particularly cardiovascular disease. However, the evidence is often contradictory and additional work is required to establish whether trimethylamine N-oxide is a cause, effect or biomarker of the disease.Genetic variants of other FMOs are also briefly discussed.

FMO1 gene expression independently predicts favorable recurrence-free survival of classical papillary thyroid cancer.

Aim: To examine the expression profile of FMO1 in papillary thyroid cancer (PTC) and its prognostic value in recurrence-free survival (RFS). Methods: A retrospective analysis was performed using data from the Cancer Genome Atlas and Human Protein Atlas. Results: The most frequent variants of PTC had decreased FMO1 expression compared with their respective adjacent normal tissues. However, even under the best cut-off model, high FMO1 expression was only significantly associated with better RFS in classical PTC (p < 0.001), but not in other two variants. High FMO1 expression independently predicted favorable RFS (hazard ratio: 0.202; 95% CI: 0.084-0.487; p < 0.001) in classical PTC. Conclusion: High FMO1 expression might serve as a biomarker that independently predicts favorable RFS in classical PTC patients.

FMO1 Promotes Nonalcoholic Fatty Liver Disease Progression by Regulating PPARα Activation and Inducing Ferroptosis.

BACKGROUND: The function of flavin containing dimethylaniline monooxygenase 1 (FMO1), which is known to play a part in lipid metabolism, remains unclear in the development of nonalcoholic fatty liver disease (NAFLD). This research has the objective of examining the contributions of FMO1 in the progression of NAFLD and the associated mechanisms, particularly the peroxisome proliferator activated receptor alpha (PPARα) and ferroptosis pathways. METHODS: An in vitro NAFLD model was established by treating L02 cells with free fatty acids (FFAs). The FMO1 and ferroptosis levels were examined in the cellular NAFLD model. FMO1 was knocked down using short-interfering RNA transfection. The effects of FMO1 knockdown on lipid accumulation, PPARα expression, and ferroptosis were examined in the cellular NAFLD model. Additionally, the effects of FMO1 and/or PPARα overexpression on lipid metabolism and ferroptosis were analyzed. Furthermore, L02 cells were pre-treated with GW7647 (PPARα agonist) or RSL3 (ferroptosis activator) and stimulated with FFAs. RESULTS: The levels of FMO1 and ferroptosis were upregulated in the in vitro NAFLD model. FMO1 knockdown suppressed the FFA-induced accumulation of lipids in hepatocytes, downregulation of PPARα expression, and upregulation of ferroptosis. In contrast, FMO1 overexpression dysregulated lipid metabolism and downregulated PPARα levels. Meanwhile, PPARα overexpression mitigated the FMO1 overexpression-induced upregulation of ferroptosis and lipid accumulation. Treatment with RSL3 suppressed the effects of PPARα overexpression on lipid accumulation and FMO1 expression. CONCLUSIONS: FMO1 upregulates ferroptosis by suppressing PPARα in NAFLD, which leads to the dysregulation of lipid metabolism.

Upregulation of Taurine Biosynthesis and Bile Acid Conjugation with Taurine through FXR in a Mouse Model with Human-like Bile Acid Composition.

Taurine, the end product in the sulfur-containing amino acid pathway, is conjugated with bile acids (BAs) in the liver. The rate-limiting enzymes in both taurine synthesis and BA conjugation may be regulated by a nucleus receptor, FXR, that promotes BA homeostasis. However, it is controversial because BAs act as natural FXR agonists or antagonists in humans and mice, respectively, due to the species differences in BA synthesis. The present study evaluated the influences of different BA compositions on both pathways in the liver by comparing Cyp2a12-/-/Cyp2c70-/- mice with a human-like BA composition (DKO) and wild-type (WT) mice. The DKO liver contains abundant natural FXR agonistic BAs, and the taurine-conjugated BA proportion and the taurine concentration were significantly increased, while the total BA concentration was significantly decreased compared to those in the WT liver with natural FXR antagonistic BAs. The mRNA expression levels of the enzymes Bacs and Baat in BA aminations and Cdo and Fmo1 in the taurine synthesis, as well as Fxr and its target gene, Shp, were significantly higher in the DKO liver than in the WT liver. The present study, using a model with a human-like BA composition in the liver, confirmed, for the first time in mice, that both the taurine synthesis and BA amidation pathways are upregulated by FXR activation.

Liver Genes Expression Induced by Tamoxifen Loaded Solid Lipid Nanoparticles in Wistar Female Rats.

The objective of this study was to investigate the effect of free tamoxifen and tamoxifen-loaded solid lipid nanoparticles (SLN) on cytochrome P450 (CYP3A2) and flavin-containing monooxygenase1 (FMO1) genes expression in the liver of female Wistar rats. Thirty female Wistar rats aged 7-8 weeks, were divided into six groups of six rats each. The first, second, third, and fourth groups were ovariectomized and received tamoxifen (2 mg/kg of body weight dissolved in 1 ml olive oil), tamoxifen-loaded SLN (2 mg/kg of body weight dispersed in 1 ml olive oil), SLN (10 mg/kg of body weight dispersed in 1 ml olive oil), and 1 ml olive oil, respectively. The fifth group comprised untreated ovariectomized control group and the sixth group served as unovariectomized healthy group. The treatments were given orally to the animals on 21 consecutive days using gastric intubations. At the end of the study, the rats were scarified and studied for some serum biochemical profile and two liver genes expression. The group treated with tamoxifen-loaded SLN showed significantly increased gene expression of CYP3A2 in comparison with the control, healthy, and group treated with free tamoxifen. The gene expression of FMO1 in the group that received tamoxifen-loaded SLN was significantly lower than that in the group treated with free tamoxifen. In addition, the group treated with free tamoxifen showed significantly increased gene expression of FMO1 as compared to the control and healthy groups. Encapsulation of tamoxifen inside solid lipid nanoparticles increased the gene expression of CYP3A2 and decreased the gene expression of FMO1.

Benzydamine N-oxygenation as an index for flavin-containing monooxygenase activity and benzydamine N-demethylation by cytochrome P450 enzymes in liver microsomes from rats, dogs, monkeys, and humans.

Benzydamine is an anti-inflammatory drug that undergoes flavin-containing monooxygenase (FMO)-dependent metabolism to benzydamine N-oxide; however, benzydamine N-demethylation is also catalyzed by liver microsomes. In this study, benzydamine N-oxygenation and N-demethylation mediated by liver microsomes from rats, dogs, monkeys, and humans were characterized comprehensively. Values of the maximum velocity/Michaelis constant ratio for benzydamine N-oxygenation by liver microsomes from dogs and rats were higher than those from monkeys and humans, despite roughly similar rates of N-demethylation in the four species. Benzydamine N-oxygenation by liver microsomes was extensively suppressed by preheating liver microsomes at 45 °C for 5 min or at 37 °C for 5-10 min without NADPH, and benzydamine N-demethylation was strongly inhibited by 1-aminbobenztriazole. Liver microsomal benzydamine N-oxygenation was inhibited by dimethyl sulfoxide and methimazole, whereas N-demethylation was inhibited by quinidine. High benzydamine N-oxygenation activities of recombinant human FMO1 and FMO3 and human kidney microsomes were observed at pH 8.4, whereas N-demethylation by cytochrome P450 2D6 was faster at pH 7.4. These results suggest that benzydamine N-oxygenation and N-demethylation are mediated by FMO1/3 and P450s, respectively, and that the contribution of FMO to metabolic eliminations of new drug candidates might be underestimated under certain experimental conditions suitable for P450 enzymes.

Drug oxygenation activities mediated by liver microsomal flavin-containing monooxygenases 1 and 3 in humans, monkeys, rats, and minipigs.

Liver microsomal flavin-containing monooxygenases (FMO, EC 1.14.13.8) 1 and 3 were functionally characterized in terms of expression levels and molecular catalytic capacities in human, cynomolgus monkey, rat, and minipig livers. Liver microsomal FMO3 in humans and monkeys and FMO1 and FMO3 in rats and minipigs could be determined immunochemically with commercially available anti-human FMO3 peptide antibodies or rat FMO1 peptide antibodies. With respect to FMO-dependent N-oxygenation of benzydamine and tozasertib and S-oxygenation of methimazole and sulindac sulfide activities, rat and minipig liver microsomes had high maximum velocity values (Vmax) and high catalytic efficiency (Vmax/Km, Michaelis constant) compared with those for human or monkey liver microsomes. Apparent Km values for recombinantly expressed rat FMO3-mediated N- and S-oxygenations were approximately 10-100-fold those of rat FMO1, although these enzymes had similar Vmax values. The mean catalytic efficiencies (Vmax/Km, 1.4 and 0.4 min(-1)µM(-1), respectively) of recombinant human and monkey FMO3 were higher than those of FMO1, whereas Vmax/Km values for rat and minipig FMO3 were low compared with those of FMO1. Minipig liver microsomal FMO1 efficiently catalyzed N- and S-oxygenation reactions; in addition, the minipig liver microsomal FMO1 concentration was higher than the levels in rats, humans, and monkeys. These results suggest that liver microsomal FMO1 could contribute to the relatively high FMO-mediated drug N- and S-oxygenation activities in rat and minipig liver microsomes and that lower expression of FMO1 in human and monkey livers could be a determinant factor for species differences in liver drug N- and S-oxygenation activities between experimental animals and humans.

Characterization of Targeted Mouse Embryonic Stem Cell Chromosomes : Karyotyping and Fluorescence In Situ Hybridization of Metaphase Spreads.

The manipulation of genes in mouse embryonic stem (ES) cells can result in chromosome abnormalities. This chapter describes methods for karyotyping of the manipulated ES cell line before injection into blastocysts and the use of fluorescence in situ hybridization to confirm the deletion of a targeted gene. The method is illustrated by describing how an ES cell line targeted for the deletion of Fmo genes was characterized.