Pharmacological properties of specioside from the stem bark of Tabebuia aurea

Cytotoxic and antileishmanial triterpenes of Tabebuia aurea (Silva Manso) leaves

The bioactivity-guided fractionation of the total ethanolic extract of the leaves of Tabebuia aurea revealed the cytotoxic and antileishmanial potency of the ethyl acetate fraction, in which its phytochemical investigation resulted in the isolation of five triterpenes; identified as oleanolic acid (1), ursolic acid (2), pomolic acid (3), tormentic acid (4), 3β,6β,19α-trihydroxy-urs-12-en-28-oic acid (5) in addition to one triterpenoid glucoside, spathodic acid 28-O-β-D-glucopyranoside (6). Whereas compound 1 showed cytotoxic activity against three different cell lines; A549, MCF-7 and HepG2 with IC₅₀ values of 31.7 ± 1.2, 27.4 ± 1.8 and 28.8 ± 1.1 μg/mL, respectively (etoposide as a positive control: 28.1 ± 4.2, 22.5 ± 4.5, and 20.4 ± 0.8 μg/mL, respectively), while compounds 1 and 2 showed antileishmanial activity with IC₅₀ values of 10.2 ± 0.9 μg/mL and 5.1 ± 0.4 μg/mL, respectively (miltefosine: 7.7 ± 2.1 μg/mL).

Synergistic Effect of Polyphenol-Rich Complex of Plant and Green Propolis Extracts with Antibiotics against Respiratory Infections Causing Bacteria

Bacterial infections are a prevalent complication after primary viral respiratory infections and are associated with high morbidity and mortality. Antibiotics are widely used against bacterial respiratory pathogens; however, the rise in antibiotic-resistant strains urges us to search for new antimicrobial compounds, including ones that act synergistically with antibiotics. In this study, the minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations of a polyphenol-rich complex of green propolis, Tabebuia avellanedae bark, and Olea europaea leaf extracts against Staphylococcus aureus, Haemophilus influenzae, and Klebsiella pneumoniae were determined, followed by an analysis of the synergistic effect with clarithromycin, azithromycin, and amoxiclav (875/125 mg amoxicillin/clavulanic acid). A combination of extracts showed activity against all three bacterial strains, with MIC values ranging from 0.78 to 12.5 mg/mL and MBC values from 1.56 to 12.5 mg/mL. The extracts showed synergistic activity with azithromycin and clarithromycin against S. aureus, with clarithromycin against K. pneumoniae, and with all three tested antibiotics against H. influenzae. Synergy with clarithromycin was additionally evaluated in a time-kill assay where the synergistic effects against S. aureus and K. pneumoniae were seen within the first 6 h of incubation. The results show the potential of polyphenol-rich extracts in enhancing the efficacy of antibiotic therapy and indicate their potential to be used in the management of respiratory infections.

New derivatives of the iridoid specioside from fungal biotransformation

Iridoids are widely found from species of Bignoniaceae family and exhibit several biological activities, such as anti-inflammatory, antimicrobial, antioxidant, and antitumor. Specioside is an iridoid found from Tabebuia species, mainly in Tabebuia aurea. Thus, here fungus-mediated biotransformation of the iridoid specioside was investigated by seven fungi. The fungus-mediated biotransformation reactions resulted in a total of nineteen different analogs by fungus Aspergillus niger, Aspergillus flavus, Aspergillus japonicus, Aspergillus terreus, Aspergillus niveus, Penicillium crustosum, and Thermoascus aurantiacus. Non-glycosylated specioside was the main metabolite observed. The other analogs were yielded from ester hydrolysis, hydroxylation, methylation, and hydrogenation reactions. The non-glycosylated specioside and coumaric acid were yielded by all fungi-mediated biotransformation. Thus, fungus applied in this study showed the ability to perform hydroxylation and glycosidic, as well as ester hydrolysis reactions from glycosylated iridoid. KEY POINTS: • The biotransformation of specioside by seven fungi yielded nineteen analogs. • The non-glycosylated specioside was the main analog obtained. • Ester hydrolysis, hydroxylation, methylation, and hydrogenation reactions were observe.