Unprecedented Antimicrobial and Cytotoxic Polyketides from Cultures of Diaporthe africana sp. nov

Four unprecedented polyketides named isoprenylisobenzofuran B (2), isoprenylisobenzofuran C₁/C₂ (3), diaporisoindole F₁/F₂ (4), and isochromophilonol A₁/A₂ (7) were isolated from ethyl acetate extracts of the newly described endophytic fungus Diaporthe africana. Additionally, the previously reported cyclic depsipeptide eucalactam B (1) was also identified, along with the known compounds diaporisoindole A/B (5), tenellone B (6) and beauvericin (8). The taxonomic identification of the fungus was accomplished using a polyphasic approach combining multi-gene phylogenetic analysis and microscopic morphological characters. The structures 1-8 were determined by a detailed analysis of their spectral data, namely high-resolution electrospray ionization mass spectrometry (HR-ESIMS), 1D/2D nuclear magnetic resonance (NMR) spectroscopy, as well as electronic circular dichroism (ECD) spectra. In addition, chemical methods such as Marfey's analysis were also employed to determine the stereochemistry in compound 1. All the compounds obtained were evaluated for antimicrobial and in vitro cytotoxic properties. Compounds 3-8 were active against certain fungi and Gram-positive bacteria with MIC values of 8.3 to 66.6 µg/mL. In addition, 3-5 displayed cytotoxic effects (22.0 ≤ IC₅₀ ≤ 59.2 µM) against KB3.1 and L929 cell lines, whereas compounds 6-8 inhibited the growth of seven mammalian cancer cell lines with IC₅₀ ranging from 17.7 to 49.5 µM (6), 0.9 to 12.9 µM (7) and 1.9 to 4.3 µM (8).

Antibacterial and antishigellosis activity of Xylopia staudtii (engl. & diels), Annonaceae

ETHNOPHARMACOLOGICAL RELEVANCE

Xylopia staudtii is a medicinal plant which fruits are traditionally used in western Cameroon as a spice in the preparation of soups known for their abdominal cramp relieving properties. Often identified as Xylopia africana, its bark is used in the treatment of dysentery in Mont Cameroun localities. This plant could therefore contain active ingredients against intestinal pathogens, including Shigella spp, which are responsible of the deathly dysenteric diarrhoea.

AIM OF THE STUDY

This study aims to assess the efficacy of the hydroethanolic extract from Xylopia staudtii bark in immunodepressed mice infected with Shigella flexneri.

MATERIALS AND METHODS

Qualitative detection of compounds in the crude extract was done using UPLC-DAD-(HR) ESI-MS analysis in an attempt to link the activity to the chemical composition. The MIC and the MBC of the extract was determined using broth dilution method. Shigellosis was induced by intraperitoneal administration of Shigella flexneri to immunodepressed mice pretreated with streptomycin. These infected mice were then treated with the extract (100, 200 and 400 mg/kg), and reference substances (ciprofloxacin and saline). During the 9 days of treatment, animal morphology, fecal pathology and deaths were recorded. At the end of the treatment period, blood and organs were collected from any surviving animals for hematological, biochemical and histopathological analyses.

RESULTS

The extract was found to be significantly active, with a bactericidal effect against Shigella and a bacteriostatic effect against Escherichia coli. It was able to reduce and stop the faecal pathology caused by the infection in mice, as well as the rate of deaths which was brought to zero (0) in animal treated at 400 mg/kg. The bacteria load in faeces was reduced by 100% in animal treated at 400 mg/kg. Xylopia staudtii extract elicited anti-inflammatory properties by reducing MPO activity and Lcn2 intestinal level. It also prevents damages in the intestinal tissue and the shortening of colon which characterise Shigella infection. The serum level of ASAT, ALAT, bilirubin, urea and creatinine in animals treated with the extract was similar to those of normal animal used in the study. These activities of the plant may be due at least in part to the presence of ent-kauran type diterpens such as kaurenoic acid identified in the extract.

CONCLUSION

These findings support the usage of Xylopia staudtii as an antimicrobial against bacillary dysentery, making this plant a potential candidate for the formulation of an improved standardized traditional medicine.