The Effects of Polyhexamethylene Biguanide (PHMB) and TLR Agonists Alone or as Polyplex Nanoparticles against Promastigotes and Amastigotes.

Dogs are the main reservoir for manifesting from a subclinical to a fatal disease. Limited treatments are available, although new antiparasitics and immunomodulators are pursued. Polyhexamethylene biguanide (PHMB) has a broad antimicrobial spectrum, including antiparasitic activity. Here, we evaluated the potential for Toll-like receptor agonists (TLRa) and PHMB alone, and as polyplex nanoparticles containing PHMB and TLR4 or TLR9 agonists, to selectively kill . Susceptibility of promastigotes to PHMB, miltefosine, and allopurinol was performed, and the half-maximum inhibitory concentrations (IC) were determined. Then, DH-82 cells were infected and treated with PHMB alone or combined with TLR4a (MPLA-SM) or TLR9a (CpG ODNs) and allopurinol alone. The IC values of promastigotes were PHMB (1.495 µM), miltefosine (9.455 µM), and allopurinol (0.124 µM). After infection, treated DH-82 cells displayed a lower percentage ( 0.0316), intensity ( 0.0002), and index of infection ( 0.0022) when compared to non-treated cells. PHMB induced lower percentage of infection alone ( 0.043), in combination with TLR9a ( 0.043), and with TLR4a ( 0.0213). Supernatants were collected and used to measure TNF-α and IL-6 levels. Increased TNF-α was observed after PHMB TLR4a, relative to uninfected and infected untreated macrophages ( 0.043). PHMB combined with TLR4a shows promise as a potential anti- drug combination, as well as inducer of proinflammatory response, as demonstrated by decreased infection and increased TNF-α production.