mycolactone and Skin-Ulcer

Skin ulcers are most commonly due to circulatory or metabolic disorders and are a major public health concern. In developed countries, chronic wounds affect more than 1 % of the population and their incidence is expected to follow those observed for diabetes and obesity. In tropical and subtropical countries, an additional issue is the occurrence of ulcers of infectious origins with diverse etiologies. While the severity of cutaneous Leishmaniasis correlates with protective immune responses, Buruli ulcers caused by Mycobacterium ulcerans develop in the absence of major inflammation. Based on these two examples, this review aims to demonstrate how studies on microorganism-provoked wounds can provide insight into the molecular mechanisms controlling skin integrity. We highlight the potential interest of a mouse model of non-inflammatory skin ulceration caused by intradermal injection of mycolactone, an original lipid toxin with ulcerative and immunosuppressive properties produced by M. ulcerans.

Topics: Animals; Humans; Immunity, Active; Leishmania; Macrolides; Mice; Mycobacterium ulcerans; Skin Ulcer

Buruli ulcer is a skin disease caused by infection with Mycobacterium ulcerans, which produces a potent toxin known as mycolactone, thus distinguishing itself from all other mycobacterial diseases. Mycolactone destroys cells in the subcutis, leading to the development of large ulcers with undermined edges. The genome sequence of M ulcerans has now been published and it transpires that two identical copies of a plasmid carry the genetic code for mycolactone. The mode of transmission of infection remains uncertain, although environmental sources of the organisms are now better understood. Considerable progress has been made in understanding the immune response to M ulcerans and there have been major advances in management of the disease with the introduction of rational antibiotic therapy. We summarise the current understanding of M ulcerans and its relations with human beings.

Topics: Adolescent; Animals; Anti-Bacterial Agents; Bacterial Toxins; Child; Child, Preschool; Humans; Macrolides; Mycobacterium Infections, Nontuberculous; Mycobacterium ulcerans; Skin Ulcer

Buruli ulcer is a chronic skin disease caused by Mycobacterium ulcerans, which produces a toxic lipid mycolactone. Despite the extensive necrosis and tissue damage, the lesions are painless. This absence of pain prevents patients from seeking early treatment and, as a result, many patients experience severe sequelae, including limb amputation. We have reported that mice inoculated with M. ulcerans show loss of pain sensation and nerve degeneration. However, the molecules responsible for the nerve damage have not been identified. In order to clarify whether mycolactone alone can induce nerve damage, mycolactone A/B was injected to footpads of BALB/c mice. A total of 100 microg of mycolactone induced footpad swelling, redness, and erosion. The von Frey sensory test showed hyperesthesia on day 7, recovery on day 21, and hypoesthesia on day 28. Histologically, the footpads showed epidermal erosion, moderate stromal edema, and moderate neutrophilic infiltration up to day 14, which gradually resolved. Nerve bundles showed intraneural hemorrhage, neutrophilic infiltration, and loss of Schwann cell nuclei on days 7 and 14. Ultrastructurally, vacuolar change of myelin started on day 14 and gradually subsided by day 42, but the density of myelinated fibers remained low. This study demonstrated that initial hyperesthesia is followed by sensory recovery and final hypoesthesia. Our present study suggests that mycolactone directly damages nerves and is responsible for the absence of pain characteristic of Buruli ulcer. Furthermore, mice injected with 200 microg of mycolactone showed pulmonary hemorrhage. This is the first study to demonstrate the systemic effects of mycolactone.

Topics: Analgesics; Animals; Bacterial Toxins; Buruli Ulcer; Female; Foot; Hemorrhage; Hyperesthesia; Hypesthesia; Lung; Macrolides; Mice; Mice, Inbred BALB C; Mycobacterium ulcerans; Necrosis; Nerve Tissue; Skin Ulcer; Time Factors

Mycobacterium ulcerans is the etiologic agent of Buruli ulcer (BU), an emerging tropical skin disease. Virulent M. ulcerans secretes mycolactone, a cytotoxic exotoxin with a key pathogenic role. M. ulcerans in biopsy specimens has been described as an extracellular bacillus. In vitro assays have suggested a mycolactone-induced inhibition of M. ulcerans uptake by macrophages in which its proliferation has not been demonstrated. Therefore, and uniquely for a mycobacterium, M. ulcerans has been classified as an extracellular pathogen. In specimens from patients and in mouse footpad lesions, extracellular bacilli were concentrated in central necrotic acellular areas; however, we found bacilli within macrophages in surrounding inflammatory infiltrates. We demonstrated that mycolactone-producing M. ulcerans isolates are efficiently phagocytosed by murine macrophages, indicating that the extracellular location of M. ulcerans is not a result of inhibition of phagocytosis. Additionally, we found that M. ulcerans multiplies inside cultured mouse macrophages when low multiplicities of infection are used to prevent early mycolactone-associated cytotoxicity. Following the proliferation phase within macrophages, M. ulcerans induces the lysis of the infected host cells, becoming extracellular. Our data show that M. ulcerans, like M. tuberculosis, is an intracellular parasite with phases of intramacrophage and extracellular multiplication. The occurrence of an intramacrophage phase is in accordance with the development of cell-mediated and delayed-type hypersensitivity responses in BU patients.

Topics: Animals; Bacterial Toxins; Cells, Cultured; Disease Models, Animal; Female; Foot; Histocytochemistry; Humans; Macrolides; Macrophages; Mice; Mice, Inbred BALB C; Microscopy, Electron, Transmission; Mycobacterium Infections, Nontuberculous; Mycobacterium ulcerans; Phagocytosis; Skin Diseases, Bacterial; Skin Ulcer

The role of biofilms in the pathogenesis of mycobacterial diseases remains largely unknown. Mycobacterium ulcerans, the etiological agent of Buruli ulcer, a disfiguring disease in humans, adopts a biofilm-like structure in vitro and in vivo, displaying an abundant extracellular matrix (ECM) that harbors vesicles. The composition and structure of the ECM differs from that of the classical matrix found in other bacterial biofilms. More than 80 proteins are present within this extracellular compartment and appear to be involved in stress responses, respiration, and intermediary metabolism. In addition to a large amount of carbohydrates and lipids, ECM is the reservoir of the polyketide toxin mycolactone, the sole virulence factor of M. ulcerans identified to date, and purified vesicles extracted from ECM are highly cytotoxic. ECM confers to the mycobacterium increased resistance to antimicrobial agents, and enhances colonization of insect vectors and mammalian hosts. The results of this study support a model whereby biofilm changes confer selective advantages to M. ulcerans in colonizing various ecological niches successfully, with repercussions for Buruli ulcer pathogenesis.

Topics: Animals; Bacterial Toxins; Biofilms; Carbohydrates; Ecology; Extracellular Matrix; Extracellular Matrix Proteins; Humans; Lipids; Macrolides; Mice; Mycobacterium Infections, Nontuberculous; Mycobacterium ulcerans; Skin Ulcer; Virulence Factors

Mycobacterium ulcerans is the causative agent of Buruli ulcer, a tropical ulcerative skin disease. One of the most intriguing aspects of this disease is the presence of extensive tissue damage in the absence of an acute inflammatory response. We recently purified and characterized a macrolide toxin, mycolactone, from M. ulcerans. Injection of this molecule into guinea pig skin reproduced cell death and lack of acute inflammatory response similar to that seen following the injection of viable bacteria. We also showed that mycolactone causes a cytopathic effect on mouse fibroblast L929 cells that is characterized by cytoskeletal rearrangements and growth arrest within 48 h. However, these results could not account for the extensive cell death which occurs in Buruli ulcer. The results presented here demonstrate that L929 and J774 mouse macrophage cells die via apoptosis after 3 to 5 days of exposure to mycolactone. Treatment of cells with a pan-caspase inhibitor can inhibit mycolactone-induced apoptosis. We demonstrate that injection of mycolactone into guinea pig skin results in cell death via apoptosis and that the extent of apoptosis increases as the lesion progresses. These results may help to explain why tissue damage in Buruli ulcer is not accompanied by an acute inflammatory response.

Topics: Animals; Apoptosis; Bacterial Toxins; Cell Line; DNA, Bacterial; Female; Guinea Pigs; In Situ Nick-End Labeling; Macrolides; Mice; Mycobacterium ulcerans; Skin Ulcer