Estudo fitoquímico, atividades antioxidante, antimicrobiana e citotóxica da espécie Cassia bakeriana Craib

Abstract

The species Cassia bakeriana Craib. is popularly known as pink cassia and belongs to the genus Cassia and family Leguminoseae. The present study had several goals: determine the macromolecular composition of the wood and bark of C. bakeriana; determine the content of phenolics and proanthocyanidins, as well as the antioxidant activity of extracts (wood, bark and leaves); evaluate the antimicrobial activity of various extracts of bark and leaves; characterize and determine the antimicrobial activity of essential oils (wood, bark and leaves); phytochemical study of the dichloromethane extract of the bark and the determination of the cytotoxic potential of the samples with the higher antioxidant and antimicrobial activities. The percentages of extractives, acid insoluble lignin (Klason), acid-soluble lignin, holocellulose, α-cellulose, hemicellulose and ashes, in wood were: 13.04, 21.0, 0.76, 67.4, 35.35, 32.06 and 2.08, respectively. The values found in bark: 53.88, 15.06, 0.6, 27.41, 20.32, 7.1 and 4.87. The contents of total phenols by Folin-Ciocalteau method and proanthocyanidins by vanillin in sulphuric acid indicated a positive correlation with the increasing polarity of the extracts of bark and leaves, with higher levels in the bark extracts. The extracts in ethanol, dichloromethane, ethyl acetate and methanol of leaves and bark of C. bakeriana showed good antioxidant activity by DPPH free radical scavenging method with CE50 values below 50 μg mL-1, and special attention to methanol extract of leaves with CE50 of 8.67 μg mL-1. The same extracts that showed good antioxidant activity, showed low toxicity to Vero cells (cytotoxic concentration ˃512 mg mL-1). The components of the essential oils from wood, bark and leaves of C. bakeriana were identified by GC-MS and tested for antimicrobial activity against aerobic and anaerobic oral microorganisms by broth microdilution method. Although these extracts did not showed high concentration of terpenes, the oils from leaves and bark showed significant antimicrobial activity with MIC\'s ranging between 62.5 and 125 μg mL-1, for most of the bacteria used in tests. According to the MIC\'s and selectivity index, the oil from the leaves showed promising antimicrobial activity and low cytotoxicity to Vero cells. The chloroform extract obtained from the bark in soxhlet extractor and the dichloromethane extract obtained by liquid-liquid partition also showed activity against oral microorganisms with MIC\'s below μg mL-1. Both extracts showed higher antimicrobial activity against anaerobes. The dichloromethane extract of the bark was subjected to biofractioning directed by antimicrobial activity, using phytochemicals methods, as well as HPLC coupled to mass spectrometry with electrospray ionization technique. The 1,8-dihydroxy-anthraquinone-3-carboxylic acid (rhein) was isolated from the dichloromethane fraction of the bark and identified spectroscopic methods as 1H-NMR, HSQC, COSY, FTIR and mass spectrometry. The compound rhein showed strong antimicrobial activity against oral anaerobic microorganisms.