Spatiotemporal analysis of mycolactone distribution in vivo reveals partial diffusion in the central nervous system

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.