Antimicrobial and cytotoxic effects of the Copaifera reticulata oleoresin and its main diterpene acids.

BACKGROUND

The oleoresin of Copaifera reticulata is a traditional Brazilian remedy used for the treatment of skin and urinary tract infections, respiratory diseases, rheumatism, ulcer and tumours; thus, playing an important role in the primary health care of the indigenous population.

OBJECTIVE

As most previous pharmacological tests used the crude oleoresin and only a few studies so far dealt with enriched fractions or pure chemically defined compounds, the aim of this study was to evaluate systematically the antimicrobial and cytotoxic properties of the Copaifera reticulata oleoresin and to assign traditional uses to specific secondary metabolites.

METHODS

The oleoresin as well as its neutral and acidic fractions were tested for their activity against six cancer cell lines, two clinically relevant bacterial strains, and two dermatophytes. Both fractions were analysed by GC-MS and UHPLC-ELSD, respectively. The antibacterial acidic phase was further fractionated by preparative chromatography to purify and characterize the compounds responsible for the observed pharmacological effect.

RESULTS

Whereas the use in anticancer treatment was not supported by our results, the crude oleoresin and its acidic fraction showed antibacterial activity against Enterococcus faecium (IC50 values of 4.2 and 4.8µg/mL, respectively) and methicillin-resistant Staphylococcus aureus (MRSA, IC50 values 5.3 and 7.2µg/mL, respectively). Purification of the acidic fraction resulted in the isolation of two dicarboxylic diterpene acids and the four main diterpene acids of the C. reticulata oleoresin, comprising three different diterpene scaffolds. Interestingly, the activity was not restricted to a particular diterpene-type but rather depended on the compounds' lipophilicity, with the most active constituent showing IC50 values of 1.6 (E. faecium) and 2.5µg/mL (MRSA), respectively. Furthermore, ent-polyalthic acid, the major diterpenoid, was significantly active against dermatophytes with IC50 values of 6.8µg/mL (Trichophyton rubrum) and 4.3µg/mL against (T. mentagrophytes).

CONCLUSIONS

The present study proved the antimicrobial effects of the C. reticulata oleoresin and its diterpenoid constituents, confirming its wide use in folk medicine for the treatment of skin and urinary tract infections. The inhibitory activity of copaiba diterpenoids against dermatophytic fungi as well as the gram-positive bacteria E. faecium and MRSA is being reported for the first time, providing potential lead structures for the treatment of these clinically relevant bacterial strains.