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Mycolactone is a diffusible lipid toxin produced by Mycobacterium ulcerans, the causative agent of Buruli ulcer disease. Altough bacterially derived mycolactone has been shown to traffic from cutaneous foci of infection to the bloodstream, the mechanisms underpinning its access to systemic circulation and import by host cells remain largely unknown. Using biophysical and cell-based approaches, we demonstrate that mycolactone specific association to serum albumin and lipoproteins is necessary for its solubilization and is a major mechanism to regulate its bioavailability. We also demonstrate that Scavenger Receptor (SR)-B1 contributes to the cellular uptake of mycolactone. Overall, we suggest a new mechanism of transport and cell entry, challenging the dogma that the toxin enters host cells via passive diffusion. [ABSTRACT FROM AUTHOR]

Mycobacterium ulcerans, the causative agent of Buruli ulcer (BU) disease, is unique amongst human pathogens in its capacity to produce a lipid toxin called mycolactone. While previous studies have demonstrated that bacterially-released mycolactone diffuses beyond infection foci, the spatiotemporal distribution of mycolactone remained largely unknown. Here, we used the zebrafish model to provide the first global kinetic analysis of mycolactone's diffusion in vivo, and multicellular co-culture systems to address the critical question of the toxin's access to the brain. Zebrafish larvae were injected with a fluorescent-derivative of mycolactone to visualize the in vivo diffusion of the toxin from the peripheral circulation. A rapid, body-wide distribution of mycolactone was observed, with selective accumulation in tissues near the injection site and brain, together with an important excretion through the gastro-intestinal tract. Our conclusion that mycolactone reached the central nervous system was reinforced by an in cellulo model of human blood brain barrier and a mouse model of M. ulcerans-infection. Here we show that mycolactone has a broad but heterogenous profile of distribution in vivo. Our investigations in vitro and in vivo support the view that a fraction of bacterially-produced mycolactone gains access to the central nervous system. The relative persistence of mycolactone in the bloodstream suggests that assays of circulating mycolactone are relevant for BU disease monitoring and treatment optimization. Author summary: Mycolactone is the major virulence factor of Mycobacterium ulcerans, the human pathogen causing Buruli ulcer (BU) disease. While it is now established that mycolactone is able to diffuse from infected tissues to exert immunomodulatory and analgesic effects at the systemic level, the in vivo spatiotemporal distribution of mycolactone remained largely unknown. Here, using the zebrafish larva, we describe the spatiotemporal distribution of a fluorescent derivative of mycolactone in vivo. We show that fluorescent mycolactone quickly diffuses from the blood circulation into various organs, and accumulates in muscles and brain. Mycolactone's diffusion into the central nervous system was further confirmed in the mouse model of M. ulcerans infection. We reported previously that mycolactone suppresses the production of inflammatory mediators by primary microglia at nanomolar concentrations in vitro [1]. In the present study, we provide evidence suggesting that bacterially-produced mycolactone is able to reach the brain. While additional in vivo investigations will be required, we can speculate that the amount of mycolactone reaching the brain in the context of M. ulcerans infection is sufficient to modulate inflammation and pain transmission. [ABSTRACT FROM AUTHOR]

γ-Trifluoromethylated allenamides were obtained in good to excellent yields through a base-induced isomerization from the corresponding protected trifluoromethylated propargylic amines. This method, which simply required the treatment of the starting propargylic amines with sodium hydroxide in THF, was found to be fairly general and tolerates various alkyl and aryl substituents and a range of protecting groups on the nitrogen atom. The reactivity of the γ-trifluoromethylated allenamides was explored and they were found to be excellent substrates for radical- and gold(I)-catalyzed cyclizations yielding fluoroalkylated nitrogen heterocycles. [ABSTRACT FROM AUTHOR]

The article focuses findings of a study on mycolactone for therapeutic use against inflammatory disorders. It states that bacterial production of mycolactone in human skin causes a combination of ulcerative, analgesic, and anti-inflammatory effects, and mentions that the minimal structure retaining immunosuppressive activity was a truncated version of mycolactone. It infers translational potential of mycolactone core-derived structures as prospective immunosuppressants.

Buruli ulcer, classified as a neglected tropical disease by the World Health Organization, is caused by a mycobacterium which secretes a macrolidic exotoxin called mycolactone A/B. In this article, several synthetic strategies for the preparation of this toxin are discussed, highlighting the importance of total synthesis for the exploration of biological mechanism underpinning relevant human diseases.

A modular total synthesis of mycolactone A/B, the exotoxin produced by Mycobacterium ulcerans, has been achieved through the orchestration of several Pd-catalyzed key steps. While this route leads to a mixture of the natural product and its C12 epimer (4 : 1 ratio), this was inconsequential from the biological activity standpoint. Compared to the previously reported routes, this synthetic blueprint allows the late-stage modification of the toxin, as exemplified by the preparation of [22,22,22- 2 H 3 ]-mycolactone A/B.

Mycolactone, an immunosuppressive macrolide released by the human pathogen Mycobacterium ulcerans, was previously shown to impair Sec61-dependent protein translocation, but the underlying molecular mechanism was not identified. In this study, we show that mycolactone directly targets the α subunit of the Sec61 translocon to block the production of secreted and integral membrane proteins with high potency. We identify a single-amino acid mutation conferring resistance to mycolactone, which localizes its interaction site near the lumenal plug of Sec61α. Quantitative proteomics reveals that during T cell activation, mycolactone-mediated Sec61 blockade affects a selective subset of secretory proteins including key signal-transmitting receptors and adhesion molecules. Expression of mutant Sec61α in mycolactone-treated T cells rescued their homing potential and effector functions. Furthermore, when expressed in macrophages, the mycolactone-resistant mutant restored IFN-γ receptor-mediated antimicrobial responses. Thus, our data provide definitive genetic evidence that Sec61 is the host receptor mediating the diverse immunomodulatory effects of mycolactone and identify Sec61 as a novel regulator of immune cell functions., (© 2016 Baron et al.)