The Equine Antimicrobial Peptide eCATH1 Is Effective against the Facultative Intracellular Pathogen Rhodococcus equi in Mice

Abstract

f Rhodococcus equi, the causal agent of rhodococcosis, is a major pathogen of foals and is also responsible for severe infections in immunocompromised humans. Of great concern, strains resistant to currently used antibiotics have emerged. As the number of drugs that are efficient in vivo is limited because of the intracellular localization of the bacterium inside macrophages, new active but cell-permeant drugs will be needed in the near future. In the present study, we evaluated, by in vitro and ex vivo experiments, the ability of the alpha-helical equine antimicrobial peptide eCATH1 to kill intracellular bacterial cells. Moreover, the therapeutic potential of the peptide was assessed in experimental rhodococcosis induced in mice, while the in vivo toxicity was evaluated by behavioral and histopathological analysis. The study revealed that eCATH1 significantly reduced the number of bacteria inside macrophages. Furthermore, the bactericidal potential of the peptide was maintained in vivo at doses that appeared to have no visible deleterious effects for the mice even after 7 days of treatment. Indeed, daily subcutaneous injections of 1 mg/kg body weight of eCATH1 led to a significant reduction of the bacterial load in organs comparable to that obtained after treatment with 10 mg/kg body weight of rifampin. Interestingly, the combination of the peptide with rifampin showed a synergistic interaction in both ex vivo and in vivo experiments. These results emphasize the therapeutic potential that eCATH1 represents in the treatment of rhodococcosis.

Killing of Trypanozoon Parasites by the Equine Cathelicidin eCATH1

“…The synthetic eCATH1, which is an ␣-helical equine antimicrobial peptide composed of 26 amino acid residues, has been shown to have the most potent antimicrobial activity against bacteria (16). Previous work in our laboratory revealed that eCATH1 was not cytotoxic against mammalian cells at bacteriolytic concentrations (18), that it maintained its potent activity even at physiological salt concentrations (18), and that it effectively killed intracellular bacterial cells in an in vivo model of Rhodococcus equi-infected mice (19), supporting the idea that eCATH1 is a strong candidate for possible use as a therapeutic in animals.…”

“…However, treatment with the peptide was insufficient to completely cure an acute infection, and treated mice succumbed to late-stage parasitemia 24 h after the end of the treatment, suggesting that the concentration of eCATH1 was not sufficient to eradicate the parasites. It has previously been shown that the antimicrobial activity of eCATH1 is slightly diminished under physiological salt conditions (18) but is still potent against a model of Rhodococcus equi-infected mice (19). Thus, it would be interesting to test whether a higher dose of eCATH1 and/or a prolonged treatment would clear the infection.…”

“…brucei, and T. evansi. Furthermore, it has previously been reported that eCATH1 is capable of killing bacteria inside macrophages (19) and, thus, may have the potential to gain access to intracellular parasites. There is, hence, considerable potential to broaden this approach to diseases caused by related trypanosomatids, such as T. cruzi or Leishmania infections, which represent a challenge as they are primarily intracellular in mammals and as AMP-based drugs need to gain access to intracellular compartments to kill parasites at concentrations that are parasiticidal.…”

Porcine β-Defensin 2 Attenuates Inflammation and Mucosal Lesions in Dextran Sodium Sulfate–Induced Colitis

“…We referenced the previous studies to determine the induction method of the colitis model (34)(35)(36) and a rough dose range of peptide first (36)(37)(38)(39)(40)(41)(42). We found that providing drinking water containing DSS induces colitis was one of the well-established experimental models for studying IBD (43).…”

In vitroeffectiveness of the antimicrobial peptide eCATH1 against antibiotic-resistant bacterial pathogens of horses

“…and R. equi (Skerlavaj et al ., ; Schlusselhuber et al ., ). Moreover, a recent study demonstrated its intracellular antirhodococcal properties in mice (Schlusselhuber et al ., ). In the present study, the investigation of the in vitro activity of eCATH1 was extended to a large panel of clinically relevant equine Gram‐negative and Gram‐positive bacterial isolates mostly resistant to conventional antibiotics.…”