Hypoxia Inducible Factor Signaling Modulates Susceptibility to Mycobacterial Infection via a Nitric Oxide Dependent Mechanism

Tuberculosis is a current major world-health problem, exacerbated by the causative pathogen, Mycobacterium tuberculosis (Mtb), becoming increasingly resistant to conventional antibiotic treatment. Mtb is able to counteract the bactericidal mechanisms of leukocytes to survive intracellularly and develop a niche permissive for proliferation and dissemination. Understanding of the pathogenesis of mycobacterial infections such as tuberculosis (TB) remains limited, especially for early infection and for reactivation of latent infection. Signaling via hypoxia inducible factor α (HIF-α) transcription factors has previously been implicated in leukocyte activation and host defence. We have previously shown that hypoxic signaling via stabilization of Hif-1α prolongs the functionality of leukocytes in the innate immune response to injury. We sought to manipulate Hif-α signaling in a well-established Mycobacterium marinum (Mm) zebrafish model of TB to investigate effects on the host's ability to combat mycobacterial infection. Stabilization of host Hif-1α, both pharmacologically and genetically, at early stages of Mm infection was able to reduce the bacterial burden of infected larvae. Increasing Hif-1α signaling enhanced levels of reactive nitrogen species (RNS) in neutrophils prior to infection and was able to reduce larval mycobacterial burden. Conversely, decreasing Hif-2α signaling enhanced RNS levels and reduced bacterial burden, demonstrating that Hif-1α and Hif-2α have opposing effects on host susceptibility to mycobacterial infection. The antimicrobial effect of Hif-1α stabilization, and Hif-2α reduction, were demonstrated to be dependent on inducible nitric oxide synthase (iNOS) signaling at early stages of infection. Our findings indicate that induction of leukocyte iNOS by stabilizing Hif-1α, or reducing Hif-2α, aids the host during early stages of Mm infection. Stabilization of Hif-1α therefore represents a potential target for therapeutic intervention against tuberculosis

Guaiacol and 4‑Methylphenol as Specific Markers of Torrefied Malts.Fate of Volatile Phenols in Special Beers through Aging

Phenol-specific extracts of 12 Belgian special beers were analyzed by gas chromatography hyphenated to olfactometry (AEDA procedure) and mass spectrometry (single ion monitoring mode). As guaiacol and 4-methylphenol were revealed to be more concentrated in brown beers (>3.5 and >1.1 μg/L, respectively), they are proposed as specific markers of the utilization of dark malts. Analysis of five differently colored malts (5, 50, 500, 900, and 1500 °EBC) allowed confirmation of high levels of guaiacol (>180 μg/L; values given in wort, for 100% specialty malt) and 4-methylphenol (>7 μg/L) for chocolate and black malts only (versus respectively <3 μg/L and undetected in all other worts). Monitoring of beer aging highlighted major differences between phenols. Guaiacol and 4-methylphenol appeared even more concentrated in dark beers after 14 months of aging, reaching levels not far from their sensory thresholds. 4-Vinylphenols and 4-ethylphenols, on the contrary, proved to be gradually degraded in POF(+)-yeast-derived beers. Vanillin exhibited an interesting pattern: in beers initially containing <25 μg/L, the vanillin concentration increased over a 14 month aging period to levels exceeding its sensory threshold (up to 160 μg/L). Beers initially showing an above-threshold level of vanillin displayed a decrease during aging

Hop allylic alcohols are precursors of sulfur-containing odorants in fresh beer

Hop is known to bring methanesulfenic acid to wort, the precursor of an onion-like odorant in beer: dimethyltrisulfide. Recently, 2-mercapto-3-methylbutanol was also suspected to be responsible of some onion off-flavors in beer. In model media, 2-mercapto-3-methylbutanol, 3-mercapto-3-methylbutanol and 3-methyl-2-butene-1-thiol were shown to be synthesized from 3-methyl-2-buten-1-ol and hydrogen sulfide (radical anti-Markovnikov addition, electrophilic Markovnikov addition and nucleophilic substitution, respectively). The present work shows that these mechanisms also occur in pilot-scale beer productions by the presence of hydrogen sulfide excreted by yeast. 1.8 μg/L of 2-mercapto-3-methylbutanol was detected after fermentation of a wort spiked with 10 mg/L of 3-methyl-2-buten-1-ol. A strong onion-off-flavor was also detected in the fresh beer. Sensorial analyses were performed on purified 2-mercapto-3-methylbutanol (radical addition favored by adding hydrogen peroxide and catalytic traces of FeS). Its typical freshly-cut onion flavor revealed very different from the “onion soup” descriptor currently used to describe dimethyltrisulfide

Occurence of odorant polyfunctional thiols in the super alpha Tomahawk hop cultivar. Comparison with the thiol-rich Nelson Sauvin bitter variety

Tomahawk hop (Humulus lupulus) is a recently developed Super Alpha cultivar (14-18% α-acids w/w), already widely used by brewers to impart bitterness and a citrus-like aroma to beer. By comparison with two bitter varieties (Nelson Sauvin and Nugget) and two aromatic ones (Cascade and Saaz), the Tomahawk cultivar showed a very particular terpenoid profile, rich in both α- and β-selinenes (>600 mg/kg IST equiv in total), methyl geranate (>40 mg/kg IST equiv), and geraniol (>200 mg/kg). Tomahawk also proved to contain a wide variety of odorant polyfunctional thiols. The major β-sulfanyl acetate, 3-sulfanyl-2-ethylpropyl acetate, newly identified here, was found at similar levels in the famous Sauvignon-like Nelson Sauvin and Tomahawk varieties (15-44 μg/kg IST equiv). On the other hand, lower levels of total β-sulfanyl alcohols were measured in Tomahawk, although 3-sulfanylhexan-1-ol was found at a similar level and the 3-sulfanyl-4-methylpentan-1-ol previously claimed to be specific to the Nelson Sauvin variety was also evidenced in the Super Alpha cultivar (9-13 μg/kg IST equiv). As revealed by boiling and fermentation, Tomahawk hop also contains very interesting bound polyfunctional thiols that should be investigated for better use by brewers

How sotolon can impart a madeira off-flavor to aged beers

4,5-Dimethyl-3-hydroxy-2(5H)-furanone or sotolon is known to impart powerful Madeira-oxidized–curry–walnut notes to various alcoholic beverages. It has been much studied in oxidized Jura flor-sherry wines, aged Roussillon sweet wines, and old Port wines, in which it contributes to the characteristic “Madeira-oxidized” aroma of these beverages. No scientific paper describes how sotolon might be involved in the Madeira off-flavor found in aged beers. The specific extraction procedure applied here allowed us to quantify this lactone in 7 special beers, at levels sometimes well above its threshold (from 5 to 42 μg/L after 6, 12, 18, and 24 months of natural aging, while unquantifiable in fresh beer). Investigation of spiked beers led us to highlight the key role of pro-oxidants and acetaldehyde. Addition of ascorbic acid without sulfites should be avoided by brewers, as the former would intensify sotolon synthesis. Acetoin, a beer fermentation byproduct, also emerged as possible precursor in beer when combined with serine

Le houblonnage à cru des bières spéciales belges est bien plus qu'une simple dissolution des composés aromatiques du houblon

Le suivi de tanks de garde d’une production industrielle montre que les arômes du houblon se solubilisent dans la bière dès les deux premières semaines du processus de houblonnage à cru (cas du linalool, du myrcène et de l’acide 3-méthylbutanoïque). Par contre, trois semaines sont nécessaires pour la production de molécules odorantes issues de glycosides du houblon (4-vinylsyringol, citronellol, béta-damascénone). De nombreux arômes soufrés (thiols polyfonctionnels) aux odeurs de fruits exotiques sont également libérés. Le procédé de houblonnage à cru se révèle donc bien plus complexe qu’une simple solubilisation des huiles essentielles du houblon, surtout si la période de maturation est prolongée