Antibacterial effect of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1, 4-naphthoquinone-4-imine on Staphylococcus aureus

Antibacterial and antifungal activity of lawsone and novel naphthoquinone derivatives

INTRODUCTION

Naphthoquinone derivatives are under investigation as potential therapeutic agents. The antibacterial and antifungal activity of lawsone and of some novel naphthoquinone derivatives was assessed in vitro.

METHODS

The antimicrobial activity was determined using diffusion disk and the broth microdilution methods against seven bacteria and three Candida species, according to recommendations of the Clinical and Laboratory Standards Institute.

RESULTS

Two compounds (P05 et P06) presented a good antibacterial effectiveness against two gram-positive bacteria. No antifungal potency was observed against the three Candida albicans strains used in the test.

CONCLUSION

Our results prove that the introduction of substituents on ketone function position 4 decreased the antimicrobial properties of the synthetized compounds.

Aminonaphthoquinone induces oxidative stress inStaphylococcus aureus

The biological activity of 5-amino-8-hydroxy-1,4-naphthoquinone (ANQ) on Staphylococcus aureus was investigated in comparison with the unsubstituted 1,4-naphthoquinone (NQ). Complete inhibition of microbial growth was observed with ANQ and NQ at 50 and 10 µg/mL, respectively. The antibacterial effect of naphthoquinones decreased in the presence of sodium ascorbate, but the superoxide scavenger 4,5-dihydroxy-1,3-benzene-disulfonic acid (Tiron) was able to protect S. aureus only from the harmful effect of ANQ. Naphthoquinones blocked oxygen uptake and induced cyanide-insensitive oxygen consumption. When combining rotenone or salicylhydroxamic acid with ANQ or NQ, a slight decrease in respiratory activity was observed. Assays in the presence of naphthoquinones induced an increase of lipid peroxidation in S. aureus, as determined by thiobarbituric acid reactive substances. These results showed that 1,4-naphthoquinones effectively act as electron acceptors and induce an increase in reactive oxygen species that are toxic to S. aureus cells.

An unusual reduction on the quinonoid ring of 5-amino-8-hydroxy-1,4-naphthoquinone by Staphylococcus aureus

AIMS

The objective of this study was to investigate the interactions between 5-amino-8-hydroxy-1,4-naphthoquinone (ANQ) and Staphylococcus aureus.

METHODS AND RESULTS

The compound ANQ display antimicrobial activity against S. aureus. During incubation with 50 microg ml(-1) of ANQ, an unusual reduction reaction takes place and leads to the isolation of 2,3-dihydro-5-amino-8-hydroxy-1,4-naphthoquinone (ANQ-H(2)), fully characterized by means of (13)C-NMR and (1)H-NMR, plus infrared, UV-visible and mass spectroscopy. Oxygen uptake by S. aureus cells was inhibited by ANQ, but in a significantly minor extent by ANQ-H(2).

CONCLUSIONS

The ability of S. aureus to reduce the double bond at C2-C3 of the ANQ is a unusual behaviour for biological transformation of naphthoquinones.

SIGNIFICANCE AND IMPACT OF THE STUDY

This uncommon reaction may provide valuable understanding of the S. aureus regarding to the antimicrobial effect and the acquisition of resistance to naphthoquinones.

Use of 1,4-naphthoquinones for control ofErwinia carotovora

The antimicrobial effect of 5 naphthoquinones was tested against the phytopathogenic bacteria Erwinia carotovora. Disk diffusion tests and determination of minimal inhibitory concentrations (MIC) indicate that the compound naphthazarin (NTZ) has the best antibacterial activity among the naphthoquinones tested. Studies on the mode of action indicate the effect of NTZ was bactericidal at 10 µg/mL. When cultivation was done in the presence of sodium ascorbate, the restoration of E. carotovora growth was observed with 3 µg/mL NTZ, but not when a 10 µg/mL dose was used. The incubation of NTZ with bacterial suspension of E. carotovora resulted in important changes in the absorption spectra of this naphthoquinone, indicating that a redox reaction takes place. These results may suggest that NTZ induces an increase of reactive oxygen species that are toxic to the cell. The compound NTZ was also effective in preventing E. carotovora growth on potato tubers, inhibiting the soft rot development at a concentration of 2 mg/mL.Key words: antimicrobial, naphthazarin, phytopathogen, potato, 5,8-dihydroxy-1,4-naphthoquinone.

In vitro antimicrobial activity of a new series of 1,4-naphthoquinones

The antibacterial activity of a series of 1,4-naphthoquinones was demonstrated. Disk diffusion tests were carried out against several Gram-positive and Gram-negative bacteria. The compound 5-amino-8-hydroxy-1,4-naphthoquinone was the most effective, presenting inhibition zones measuring 20 mm against staphylococci, streptococci and bacilli at 50 microg/ml. Methicillin-resistant Staphylococcus aureus and several clinical isolates of this bacterium were also inhibited. Naphthazarin, 5-acetamido-8-hydroxy-1,4-naphthoquinone, and 2,3-diamino-1,4-naphthoquinone were the next most active compounds. The minimal inhibitory concentration of the active compounds was determined against S. aureus, ranging from 30 to 125 microg/ml. All compounds presented a minimal bactericidal concentration higher than 500 microg/ml, indicating that their effect was bacteriostatic. The EC50, defined as the drug concentration that produces 50% of maximal effect, was 8 microg/ml for 5-amino-8-hydroxy-1,4-naphthoquinone against S. aureus, S. intermedius, and S. epidermidis. These results indicate an effective in vitro activity of 5-amino-8-hydroxy-1,4-naphthoquinone and encourage further studies for its application in antibiotic therapy.

Effect of hydroxypropyl-beta-cyclodextrin on the solubility of an antibacterial isoxazolyl-naphthoquinone

The complexation of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I) with a highly soluble cyclodextrin, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was studied in aqueous media by solubility methods. I is an antibacterial and trypanocidal agent that is undergoing preclinical testing. Unfortunately, I exhibits low water solubility, and it is therefore difficult to prepare the solutions for biological tests. I inclusion took place with 1:1 stoichiometry. The stability constants of the I complexes calculated from the slope and the intercept of the phase solubility diagrams are larger in the less ionized form, whereas greater overall solubility is obtained in basic media.

Oxidative stress in Staphylococcus aureus associated to the cleavage of an isoxazolylnaphthoquinoneimine with antibacterial capacity

Staphylococcus aureus was inhibited by exposure to 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (Q1). This compound was cleavaged in the presence of bacteria and an efflux of isoxazolamine was detected whereas in the S. aureus membrane and cytoplasm was observed an absorption band similar to that of the bencenoid ring. Non-viable bacteria showed intact Q1 intracellularly and in the membrane. Antistaphylococcus effect was associated to Q1 interaction with the respiratory chain, the oxidative metabolites were stimulated; there was cellular injury simultaneous to reduction of antibiotic molecule and efflux of isoxazolamine. The bacteria treated with Q1 increased its oxygen consumption and superoxide anion generation. Superoxide dismutase (SOD) production was stimulated, but it was principally extracellular in S. aureus. Escherichia coli, a species resistant to the antibiotic, did not reduce Q1 and showed lower superoxide anion generation; besides, there was an increase of intracellular SOD with extracellular decrease.