Chloroquine inhibits Rhodococcus equi replication in murine and foal alveolar macrophages by iron-starvation.

This study investigates how the drug Chloroquine (commonly used for malaria), limits the replication of the bacterium Rhodococcus equi in macrophages (a type of white blood cell) of mice and young horses by depriving these cells of iron.

Study Objective and Methodology

• The primary aim of this research was to assess Chloroquine’s ability to inhibit the multiplication of R. equi within both mouse and foal alveolar macrophages (a type of lung cell involved in defending the body against harmful particles and bacteria).
• The researchers also wished to determine if Chloroquine’s inhibitory action was related to iron-deprivation.
• The effects of Chloroquine on R. equi’s ability to survive outside cells and its toxicity to the specific type of mouse macrophages (J774A.1) was evaluated.
• R. equi survival in both mouse and foal macrophages under exposure to Chloroquine (at concentrations of 10 and 20μM), bovine saturated transferrin (a form of iron carrier), and bovine unsaturated transferrin was studied.
• To understand how Chloroquine works, the production of superoxide anion (a harmful by-product of oxygen metabolism), lysozyme activity (an enzyme that damages bacterial cell walls), and the expression levels of vapA and rhbC genes (both increase when deprived of iron) were examined.

Research Findings

• Chloroquine, at concentrations up to 20μM, did not affect R. equi’s ability to multiply outside of cells or the viability of mouse macrophages.
• R. equi survival within both mouse and foal macrophages significantly decreased upon exposure to Chloroquine.
• Treatment with bovine saturated transferrin did not counteract the effect of Chloroquine on R. equi survival, indicating the likely role of iron deprivation in the drug’s mechanism of action.
• Chloroquine exposure did not affect either the production of superoxide anion or lysozyme activity, however, the presence of the drug significantly increased the expression of vapA and rhbC genes, which supports the hypothesis of iron deprivation.

Conclusions

• The study findings reaffirm the theory that availability of iron within a cell is necessary for R. equi survival.
• They also support the initial hypothesis that Chloroquine inhibits R. equi’s replication within mouse and foal alveolar macrophages, by likely causing a state of iron deprivation.