A Rhein-Based Derivative Targets Staphylococcus aureus

Abstract

The rise in antibiotic-resistant bacteria highlights the need for novel antimicrobial agents. This study presents the design and synthesis of a series of rhein (RH)-derived compounds with improved antimicrobial properties. The lead compound, RH17, exhibited a potent antibacterial activity against Staphylococcus aureus (S. aureus) isolates, with minimum inhibitory concentrations (MICs) ranging from 8 to 16 μg/mL. RH17 disrupted bacterial membrane stability, hindered metabolic processes, and led to an increase in reactive oxygen species (ROS) production. These mechanisms were confirmed through bacterial growth inhibition assays, membrane function assessments, and ROS detection. Notably, RH17 outperformed the parent compound RH and demonstrated bactericidal effects in S. aureus. The findings suggest that RH17 is a promising candidate for further development as an antimicrobial agent against Gram-positive pathogens, addressing the urgent need for new therapies.

Keywords: Gram-positive pathogen; anthraquinone derivatives; membrane target; rhein.

Figure 1

The synthesis of RH derivatives (RH1–17). Reagents and conditions: (a) DCM (0.01 mM DMF), oxalyl chloride, N₂, reflux, overnight; (b) anhydrous THF, corresponding amines, r.t., 12–24 h; (c) DCM, TEA, Boc-NH-PEG1-OH, r.t., 3 h; (d) Dioxane, HCl, r.t., 5 h.

Figure 2

The antibacterial potency of RH17. (A) Antimicrobial activity of RH17 against S. aureus ATCC 29213. (B,C) Effect of varying concentrations of RH17 on growth curves of S. aureus isolates. The presented data are depicted as means ± standard deviation (SD). (B) S. aureus ATCC 29213; (C) MRSA T144. (D) Time-kill curve of S. aureus ATCC 29213 at different concentrations of RH17. (E–H) The antibiofilm activity of RH17 and RH. (E,F) RH17 and RH treatment inhibited biofilm formation on S. aureus ATCC 29213 after 24 h. (E) RH17; (F) RH. (G,H) RH17 and RH eradicated 24 h pre-formed S. aureus ATCC 29213 biofilms. (G) RH17; (H) RH.

Figure 3

The antibacterial mechanism of RH17. (A) The fluidity of the membrane was decreased for S. aureus ATCC 29213 after treatment with RH17 for 1 h. Benzyl alcohol (BZ) at 50 mM was used as the positive control. (B) There were no effects on the membrane permeability for S. aureus ATCC 29213 after treatment with RH17 for 1 h. Nisin at 200 μg/mL was used as the positive control. (C) The effect of RH17 on the time-kill curves of S. aureus ATCC 29213 arrested by cold temperature (0 °C in an ice-water bath) showed no significant impact. Daptomycin (DAP) was used as the positive control, which demonstrated strong bactericidal activity under the same conditions. (D) The effect of RH17 on S. aureus ATCC 29213 after 1 h treatment showed a reduction in intracellular ATP levels. (E) The effect of RH17 on S. aureus ATCC 29213 showed a decrease in fluorescence intensity. Nisin at 200 μg/mL was used as the positive control. (F) The effect of RH17 on S. aureus ATCC 29213 after 1 h treatment resulted in increased ROS production. ROS UP at 500 μg/mL was used as the positive control. A p-value of “n.s.” means not significant, suggesting no meaningful difference between groups.