Inhibition of histidine decarboxylase and tumour promoter-induced arachidonic acid release by lecanoric acid analogues

Schistosomicidal effect of divaricatic acid from Canoparmelia texana (Lichen): In vitro evaluation and ultrastructural analysis against adult worms of Schistosoma mansoni

In this study we evaluated the in vitro effect of divaricatic acid against coupled worms of Schistosoma mansoni. The schistosomicidal effect was evaluated through the bioassay of motility and mortality, cellular viability of the worms and ultrastructural analysis through Scanning Electron Microscopy. To evaluate the cytotoxicity of divaricatic acid, a cell viability assay was performed with human peripheral blood mononuclear cells. Divaricatic acid proved effect against S. mansoni after 3 hours of exposure. At the end of 24 h the concentrations of 100 - 200 μM presented lethality to the worms. Motility changes were observed at sublethal concentrations. The IC₅₀ obtained by the cell viability assay for S. mansoni was 100.6 μM (96.24 - 105.2 μM). Extensive damage to the worm's tegument was observed such as peeling, erosion, bubbles, edema, damage and loss of tubercles and spines, fissures and tissue ruptures. No cytotoxicity was observed in human peripheral blood mononuclear cells. This report provides data showing the schistosomicidal effect of divaricatic acid on S. mansoni, causing death, motile changes and ultrastructural damage to worms. In addition, divaricatic acid was shown to be non-toxic to human peripheral blood mononuclear cells at concentrations effective on S. mansoni.

Laboratory assessment of divaricatic acid against Biomphalaria glabrata and Schistosoma mansoni cercariae

In this study, the molluscicidal and antiparasitic activities of divaricatic acid was evaluated, targeting the mollusc Biomphalaria glabrata and cercariae of the helminth Schistosoma mansoni. In addition, the environmental toxicity of divaricatic acid was assessed by bioassay using the microcrustacean Artemia salina. Divaricatic acid showed high toxicity against both adult snails (5μg/mL) and embryos (20μg/mL after 6h of exposure). Similar activity was observed in Schistosoma mansoni cercariae after only a short exposure time (10μg/mL after 30min of exposure). The divaricatic acid did not show toxicity in the acute test using Artemia salina at concentrations equal to or below 200μg/mL. The divaricatic acid proved to be a promising substance for the elimination of the snail Biomphalaria glabrata, an intermediate host of schistosomiasis, as well as the cercariae of the pathogen, while being non-toxic to the Artemia salina at the same concentrations. This is the first experimental observation of the molluscicidal and cercaricide activity of divaricatic acid.

Thapsigargin, a histamine secretagogue, is a non-12-O-tetradecanoylphorbol-13-acetate (TPA) type tumor promoter in two-stage mouse skin carcinogenesis

Thapsigargin, a hexaoxygenated tetraacylated sesquiterpene lactone, induced irritation of mouse ear and histidine decarboxylase (HDC) activity in mouse skin, but it did not induce ornithine decarboxylase in mouse skin or adhesion of human promyelocytic leukemia (HL-60) cells. Although thapsigargin did not give consistent positive results in a short-term screening system for tumor promoters, it was tested in a two-stage carcinogenesis experiment on mouse skin. The potency of thapsigargin to induce HDC in mouse skin was used to determine the dose in this experiment. Application of 10 micrograms (17 nmol) thapsigargin induced HDC activity of 139 pmol CO2/mg protein per 60 min. Tumors were found in the skin of 53.5% of the mice treated with DMBA plus 5 micrograms (8.5 nmol) thapsigargin in week 22, in none of those treated with thapsigargin alone by week 30. One tumor appeared in 1 of 15 mice treated with DMBA alone in week 21. Thapsigargin cannot bind to the phorbol ester receptor in the particulate fraction of mouse skin and so is classified as a non-12-O-tetradecanoylphorbol-13-acetate (TPA) type tumor promoter. It is a new tumor promoter differing in many respects from the well-defined TPA type tumor promoters. Several naturally occurring analogues of thapsigargin, such as thapsigargicin and thapsitranstagin, might also be new non-TPA type tumor promoters, because thapsigargicin and thapsitranstagin induced irritation of mouse ear and HDC activity in mouse skin.

Inhibition of tumor promotion by a lecanoric acid analogue

3',5'-Dichloro-2,4'-dihydroxybenzanilide, an inhibitor of histidine decarboxylase, inhibited skin tumor promotion induced by 12-O-tetradecanoylphorbol-13-acetate in mice.