Validation of a genetic risk score for atrial fibrillation: A prospective multicenter cohort study.

BACKGROUND: Atrial fibrillation (AF) is the most commonly encountered arrhythmia and is associated with an elevated risk of stroke. Improving the identification of patients with the highest risk for AF to enable appropriate surveillance and treatment, if necessary, is critical to reducing AF-associated morbidity and mortality. Multiple common single nucleotide polymorphisms (SNPs) are unequivocally associated with the lifetime risk of AF. In the current study we aimed to prospectively validate an AF genetic risk score (GRS) in previously undiagnosed patients at risk for AF. METHODS AND FINDINGS: Individuals 40 years of age or older with 1 clinical risk factor for AF, presenting with symptoms of AF, or with a first diagnosis of AF, were enrolled for genetic testing and ambulatory cardiac rhythm monitoring with an adhesive patch monitor or a long-term Holter monitor (mean wear time 10 days 21 hours and 13 days 18 hours, respectively). An AF event was the first diagnosis of AF by ECG, patch monitor, or long-term Holter monitor. The AF GRS was determined for each participant based on the weighted contribution of 12 genetic risk loci. Of 904 participants, 85 manifested AF. Their mean age was 66.2 (SD 11.8) years; 38% of participants were male. Participants in the highest quintile of AF GRS were more likely (odds ratio 3.11; 95% CI 1.27-7.58; p = 0.01) to have had an AF event than participants in the lowest quintile after adjusting for age, sex, smoking status, BMI, hypertension, diabetes mellitus, heart failure, and prior myocardial infarction. Study limitations included an ethnically homogenous population, a restricted rhythm monitoring period, and the evolving discovery of SNPs associated with AF. CONCLUSIONS: Prospective assessment of a GRS for AF identified participants with elevated risk of AF beyond established clinical criteria. Accordingly, a GRS for AF could be incorporated into overall risk assessment to better identify patients at the highest risk of developing AF, although further testing in larger populations is needed to confirm these findings. TRIAL REGISTRATION: ClinicalTrials.gov NCT01970969.

A novel promoter element containing multiple overlapping xenobiotic and hypoxia response elements mediates induction of cytochrome P4502S1 by both dioxin and hypoxia.

Cytochrome P4502S1 (CYP2S1) is expressed at high levels in epithelial tissues and is inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) via the aryl hydrocarbon receptor (AHR). Transcriptional initiation of mouse Cyp2s1 was found to occur at three regions, approximately 198, 102, and 22 nucleotides from the translational initiation codon. Approximately 400 nucleotides upstream of its translational initiation codon, mouse Cyp2s1 contains three overlapping xenobiotic-responsive element (XRE) sequences, which make a major contribution toward dioxin inducibility. Each XRE sequence in this trimeric XRE can bind the AHR/aryl hydrocarbon receptor nuclear translocator (ARNT) dimer in a dioxin-dependent fashion in vitro and can mediate dioxin-dependent transcription. Cyp2s1 is also markedly inducible by hypoxia. Induction is dependent on hypoxiainducible factor-1 (HIF-1) and is mediated in large part by three overlapping hypoxia response elements (HREs) embedded within the trimeric XRE segment. Although each HRE within this segment can bind HIF-1alpha/ARNT in vitro, the most 3' HRE contributes the most toward hypoxia inducibility. AHR/ARNT and HIF-1alpha/ARNT dimers bind to the region containing the trimeric XRE segment of the endogenous Cyp2s1 gene in vivo in a dioxin-dependent fashion and hypoxia-dependent fashion, respectively. These observations identify a novel regulatory cassette that mediates changes in Cyp2s1 expression.

CYP2S1: a short review.

A new member of the cytochrome P450 superfamily, CYP2S1, has recently been identified in human and mouse. In this paper, we review the data currently available for CYP2S1. The human CYP2S1 gene is located in chromosome 19q13.2 within a cluster including CYP2 family members CYP2A6, CYP2A13, CYP2B6, and CYP2F1. These genes also show the highest homology to the human CYP2S1. The gene has recently been found to harbor genetic polymorphism. CYP2S1 is inducible by dioxin, the induction being mediated by the Aryl Hydrocarbon Receptor (AHR) and Aryl Hydrocarbon Nuclear Translocator (ARNT) in a manner typical for CYP1 family members. In line with this, CYP2S1 has been shown to be inducible by coal tar, an abundant source of PAHs, and it was recently reported to metabolize naphthalene. This points to the involvement of CYP2S1 in the metabolism of toxic and carcinogenic compounds, similar to other dioxin-inducible CYPs. CYP2S1 is expressed in epithelial cells of a wide variety of extrahepatic tissues. The highest expression levels have been observed in the epithelial tissues frequently exposed to xenobiotics, e.g., the respiratory, gastrointestinal, and urinary tracts, and in the skin. The observed ubiquitous tissue distribution, as well as the expression of CYP2S1 throughout embryogenesis suggest that CYP2S1 is likely to metabolize important endogenous substrates; thus far, retinoic acid has been identified. In conclusion, CYP2S1 exhibits many features of interest for human health and thus warrants further investigation.

Identification of aldehyde oxidase 1 and aldehyde oxidase homologue 1 as dioxin-inducible genes.

Aldehyde oxidases are a family of highly related molybdo-flavoenzymes acting upon a variety of compounds of industrial and medical importance. We have identified aldehyde oxidase 1 (AOX1) as a 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) inducible gene in the mouse hepatoma cell line Hepa-1. AOX1 mRNA levels were not increased by dioxin in mutant derivatives of the Hepa-1 cell line lacking either functional aryl hydrocarbon receptor (AHR) or aryl hydrocarbon receptor nuclear translocator (ARNT) proteins, thus demonstrating that transcriptional induction of AOX1 in response to dioxin occurs through the AHR pathway. Dioxin induction of AOX1 mRNA was also observed in mouse liver. In addition, levels of AOX1 protein as well as those of aldehyde oxidase homologue 1 (AOH1), a recently identified homolog of AOX1, were elevated in mouse liver in response to dioxin. Employing an aldehyde oxidase specific substrate, AOX1/AOH1 activity was shown to be induced by dioxin in mouse liver. This activity was inhibited by a known inhibitor of aldehyde oxidases, and eliminated by including tungstate in the mouse diet, which is known to lead to inactivation of molybdoflavoenzymes, thus confirming that the enzymatic activity was attributable to AOX1/AOH1. Our observations thus identify two additional xenobiotic metabolizing enzymes induced by dioxin.

Mitogen-inducible gene 6 (MIG-6), adipophilin and tuftelin are inducible by hypoxia.

Adaptation to hypoxia is essential for tumor progression. Transcriptional activation of hypoxia-regulated genes is mediated by hypoxia-inducible factor 1 (HIF-1), a heterodimer of HIF-1alpha and ARNT (Ah receptor nuclear translocator; HIF-1beta). Using representational difference analysis, we identified three novel hypoxia-inducible genes: MIG-6 (gene 33), adipophilin and tuftelin. The mRNAs for these genes were inducible by 1% O(2) in the human HepG2 and MCF-7 cell lines. Hypoxic induction of the MIG-6 and tuftelin proteins was also observed. Induction was ARNT-dependent. Induction also occurred in livers of mice treated with CoCl(2), which mimics hypoxia. The potential roles of these genes in adaptation to hypoxia and in tumorigenesis will be of considerable interest.

Identification of a novel dioxin-inducible cytochrome P450.

Representational difference analysis was used to isolate cDNAs corresponding to 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin)-inducible genes from mouse Hepa-1 cells. One cDNA encoded a novel cytochrome P450. The human homolog was also isolated and later proved to be human CYP2S1. The induction of mouse CYP2S1 mRNA by dioxin represents a primary response and required the aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator proteins. The induction of CYP2S1 also occurred in mouse liver and lung, with the highest expression found in lung. CYP2S1 was also inducible in a human lung epithelial cell line. The dioxin-inducibility of CY2S1 is exceptional, because all previously well-characterized cases of the induction of cytochromes P450 by dioxin involve members of the CYP1 family.