thapsigargin and thapsigargicin

The sesquiterpene lactones isolated from Geigeria were found to be incapable of inducing rat peritoneal mast cell degranulation at levels of 0.3-1.6 mM. The sulphydryl reagent, N-ethylmaleimide, too was unable to trigger mast cell secretion. Instead, it was observed that these compounds inhibited the release of histamine induced by Compound 48/80. Pretreatment of the lactones and N-ethylmaleimide with the amino acid, L-cysteine, reduced their inhibition ability of histamine release to a considerable extent, but not completely. Geigerin(V), which lacks an alpha-methylene group and the chemically prepared cysteine-adduct of dihydrogriesenin(I), were also capable of inhibiting mast cell secretion by Compound 48/80, but to a lesser extent.

Topics: Alkylation; Animals; Cysteine; Ethylmaleimide; Histamine Release; Lactones; Male; Mast Cells; p-Methoxy-N-methylphenethylamine; Plant Extracts; Rats; Rats, Inbred Strains; Sesquiterpenes; Sesquiterpenes, Guaiane; Thapsigargin

The effect of thapsigargicin and thapsigargin, extracted from the roots of Thapsia garganica L., on isolated photosynthetic membranes (thylakoids) and intact chloroplasts from spinach leaves (Spinacia oleracea L.) was investigated. Both sesquiterpene lactone tetraesters impair membranes and organelles in an identical, chlorophyll-dependent manner. In thylakoids these compounds primarily act as inhibitors of photophosphorylation. At lower sesquiterpene lactone tetraester/chlorophyll ratios, cyclic and non-cyclic photophosphorylation, ADP-stimulated electron transport and the photosynthetic control ratio progressively decreased with increasing concentrations of thapsigargicin and thapsigargin, whereas the state 4 electron flow, the coupling efficiency of photophosphorylation, the light-induced proton gradient, and the H+ flux across the membranes remained nearly unaffected. Half-maximal inhibition of photophosphorylation was obtained with 4-5 X 10(-7) moles sesquiterpene lactone tetraesters per mg chlorophyll. At higher sesquiterpene lactone tetraester/chlorophyll ratios, uncoupling of photophosphorylation from electron transport occurred. This was evident from stimulation of the state 4 electron flow, decline in the ADP/2e- ratio, increase in proton permeability and decrease in delta pH, whereas the uncoupled electron transport was only little impaired. In intact chloroplasts inhibition of HCO-3, 3-phosphoglycerate and oxaloacetate reduction by thapsigargicin and thapsigargin was not caused by inactivation of the photochemical reactions of the thylakoid membranes but were rather due to alterations in the permeability properties of the chloroplast envelope. This was concluded from similarities in the kinetics of these reactions. It is suggested that the highly lipid soluble sesquiterpene lactone tetraesters effectively disrupt the lipid-protein associations of biomembranes.

Topics: Adenosine Triphosphate; Chlorophyll; Chloroplasts; Electron Transport; Hydrogen; Kinetics; Lactones; Light; Photophosphorylation; Plant Extracts; Plants; Sesquiterpenes; Thapsigargin

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.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Carcinogens; Dose-Response Relationship, Drug; Enzyme Induction; Female; Histamine Release; Histidine Decarboxylase; Irritants; Lactones; Mice; Mice, Inbred Strains; Ornithine Decarboxylase; Plant Extracts; Sesquiterpenes; Skin Neoplasms; Tetradecanoylphorbol Acetate; Thapsigargin; Tritium

The ability of thapsigargin and thapsigargicin to activate mast cells and leukocytes has been investigated. The thapsigargin-induced histamine release from rat peritoneal mast cells was found to be dependent on the concentration of thapsigargin, the purity of the mast cell preparations, and the number of mast cells in suspension. Thapsigargin induced histamine release from human basophil leukocytes. Thapsigargin induced beta-glucuronidase and lysozyme release from human neutrophil leukocytes. Thapsigargin caused a release of histamine from mesentery, lung, and heart mast cells of the rat, but only to a minor extent from the corresponding guinea-pig cells. Thapsigargicin induced histamine release from mesentery, lung, and heart mast cells of the rat at concentrations from 0.1 microM but provoked only a release from the corresponding guinea-pig cells in the concentration-range 0.16 to 1.6 microM. Thapsigargin increased the cytoplasmic free calcium level in intact human blood platelets at concentrations from 3.0 nM.

Topics: Adult; Animals; Blood Platelets; Calcium; Glucuronidase; Guinea Pigs; Histamine Release; Humans; In Vitro Techniques; Lactones; Leukocytes; Mast Cells; Muramidase; Plant Extracts; Plants, Medicinal; Potassium; Rats; Rats, Inbred Strains; Sesquiterpenes; Thapsigargin