Membrane Active Immunomodulator As a Novel Therapy for an Infectious Bacterial Disease, Buruli Ulcer

Mycobacterium ulcerans causes the necrotizing skin disease Buruli ulcer (BU), characterized by the formation of subcutaneous lesions and immunosuppression thought to be mediated by the virulence factor mycolactone. Since early BU lesions are typically painless, patients often seek standard oral antibiotic therapy at the advanced stages when the treatment is less effective. Given that currently there is no curative topical treatment for BU, our objective was to evaluate a plasma membrane fluidizer, diethyl azelate (DEA), as a potential novel topical therapy for BU.

We evaluated the effects of DEA against bacterial extracts and live strains of M. ulcerans ATCC 35840 (mycolactone positive; M+) and ATCC 19423 (mycolactone negative; M-) by measuring cytokine levels in cultured cells and tissue extracts using multiplexed immunoassays and numbers of skin lesions as the endpoints.

In vitro, DEA counteracted immunosuppression induced by extract from the M+ strain in the 3-D human skin model (EpiDerm) and in human dendritic cells. In vivo, topical DEA reduced immunosuppressive activities of M+ and M- strains at all stages of BU, including advanced ulcers. DEA also diminished lesion formation and ulceration, accelerated healing of skin lesions and preserved normal immune responsiveness to pathogen-associated molecular pattern receptor agonists in blood of infected animals.

The efficacy of DEA in BU models is linked to overcoming the immunosuppressive activity of virulence factors produced by M. ulcerans. Thanks to its pluripotent activity, DEA is a promising novel treatment for BU and possibly other pathogenic mycobacteria.