Kiyoyuki Yamada

Diarrhetic Shellfish Toxin, Dinophysistoxin‐1, Is a Potent Tumor Promoter on Mouse Skin

Dinophysistoxin‐1, 35‐methylokadaic acid, is a causative agent of diarrhetic shellfish poisoning. The biological activities and tumor‐promoting activity of dinophysistoxin‐1 were studied together with those of okadaic acid and 7‐O‐palmitoyl okadaic acid. Dinophysistoxin‐1 is a skin irritant and induces ornithine decarboxylase in mouse skin with the same potency as okadaic acid. 7‐O‐Palmitoyl okadaic acid induced a lower activity than the other compounds. Dinophysistoxin‐1 inhibited the specific [3H]okadaic acid binding to a participate fraction of mouse epidermis. The binding affinities of dinophysistoxin‐1 and okadaic acid to a particulate fraction were almost the same. Dinophysistoxin‐1 showed a tumor‐promoting activity as strong as that of okadaic acid in a two‐stage carcinogenesis experiment on mouse skin. The percentages of tumor‐bearing mice in the groups treated with 100 μg of 7,12‐dimethylbenz[α]anthracene (DMBA) followed by 5 μg of dinophysistoxin‐1, twice a week, and with DMBA followed by 5 μg of okadaic acid twice a week were 86.7% and 80.0% in week 30, respectively. The average number of tumors per mouse was 4.6 in the former group and 3.9 in the latter. Dinophysistoxin‐1 and okadaic acid act on cells through different pathways from the 12‐O‐tetradecanoylphorbol‐13‐acetate‐type tumor promoters.

Ptaquiloside, a novel norsesquiterpene glucoside from bracken, Pteridium aquilinum var. latiusculum

An unstable norsesquiterpene glucoside with a novel illudane skeleton, ptaquiloside (1) has been isolated from bracken fern, Pteridium aquilinum var. latiusculum and the planar structure has been established on the basis of spectral and chemical means.

The structure of aureothin, a nitro compound obtained from Streptomyces thioluteus

Abstract The structure of aureothin, the third nitro compound obtained from nature, has been elucidated as I. Several reactions of aureothin and its derivatives are described.

The structures of anisatin and neoanisatin: Toxic sesquiterpenes from Illicium Anisatum L.

Abstract Two toxic compounds, anisatin (I) and neoanisatin (XXV) were isolated from Illicium Anisatum L. Extensive studies on noranisatin (II), an oxidation product of I were carried out by chemical and spectral methods. Two dihydrocoumarins (XI, XII) were obtained by stepwise degradation of II, the structures of which were firmly established. On the basis of the structures of XI and XII together with spectral evidence of important derivatives such as VII, VIII, IX and XV, the structure of II was determined as IIk. Based on the structure of II, anisatin was represented as If, which contains a stable β-lactone. The structure of neoanisatin was established as XXVa by a variety of oxidation reactions: a common oxidation product VII was obtained from both natural products, I and XXV. Some of the reactions of special interest are illustrated.

Ptaquiloside, a potent carcinogen isolated from bracken fern pteridiumaquilinum var. latiusculum: structure elucidation based on chemical and spectral evidence, and reactions with amino acids, nucleosides, and nucleotides

Abstract The structure of ptaquiloside (1), a potent carcinogenic compound isolated from bracken fern, Pteridium aquilinum var. latiusculum has been elucidated on the basis of chemical and spectral evidence. The dienone 3 generated from 1 under alkaline conditions was shown to be a strong alkylating agent. For the purpose of obtaining the preliminary information on chemical modification of biopolymers such as proteins and DNA with the dienone 3, reactions of 3 with amino acids, nucleosides, and nucleotides have been carried out and the alkylated products have been characterized.

Specific binding of okadaic acid, a new tumor promoter in mouse skin.

The tumor promoteradaic acid binds specifically to a particulate as well as a cytosolic fraction of various mouse tissues, e.g., skin, brain, lung and colon. The K D value was 21.7 nM for receptors in the particulate fraction and 1.0 nM for those in the cytosolic fraction of mouse skin. The specific binding of [3H]okadaic acid to the particulate fraction of mouse skin was inhibited dose‐dependently byadaic acid, but notaidaic acid tetramethyl ether, an inactive compound, or by other tumor promoters, such as 12‐O‐tetradecanoylphorbol‐13‐acetate and teleocidin. The results suggest a new pathway of tumor promotion mediated through theadaic acid receptor(s).

Halicholactone and neohalicholactone, two novel fatty acid metabolites from the marine sponge halichondria okadai kadota

Halicholactone (1) and neohalicholactone (2), unusual fatty acid metabolites having a cyclopropane ring and a nine-membered lactone were isolated from the marine sponge Halichondria okadai Kadota. The planar structures of the new metabolites were elucidated on the basis of spectral and chemical means.

Anisatin, a potent GABA antagonist, isolated from Illicium anisatum

The neuropharmacological properties of anisatin were tested on the frog spinal cord and the crude synaptic membrane from rat brain. Anisatin (10(-5) M) reduced the amplitude of dorsal root potentials induced by stimulation of the adjacent dorsal root and presynaptic inhibition of the ventral root reflex. Anisatin shifted the dose-response curve for GABA-induced depolarization in the primary afferent terminal to the right and also reduced the maximum response to GABA. [3H]Muscimol binding to the crude synaptic membrane was not inhibited by anisatin. These results indicate that anisatin is a picrotoxin-like, non-competitive GABA-antagonist.

Production of antibodies and development of a radioimmunoassay for okadaic acid.

An okadaic acid immunogen, prepared by conjugation of okadaic acid to bovine albumin with carbodiimide, was used to immunize two rabbits. The rabbits responded by producing antibodies that neutralized okadaic acids stimulation of arachidonic acid metabolism and this neutralization increased during the course of immunization. The immune sera bound 3H-okadaic acid and this binding also increased with repeated immunization. After absorption of the rabbit IgG with a goat anti-rabbit IgG, binding was reduced greater than 99%. The binding of okadaic acid to the antibodies in one antiserum was inhibited by as little as 0.2 pmoles of unlabelled okadaic acid. The apparent association constant for binding with this antiserum was 4.17 x 10(9) M-1 (35 degrees C). Maitotoxin, teleocidin, 12-O-tetradecanoylphorbol-13-acetate, aplysiatoxin, palytoxin and brevetoxin B when tested at 29, 228, 168, 169, 3.7 and 112 pmole levels, respectively, did not inhibit binding. The serologic and biological activities of okadaic acid after incubation for 60 min in 0.01 N HCl at 35 degrees C or at 100 degrees C at pH 7.2 were unaffected.

Separation of carcinogenic fraction of bracken fern

Isolation of the carcinogen in the boiling water extract of bracken fern was conducted by following the active principle with a carcinogenicity bioassay. Fractionation of the bracken extract was carried out using adsorption on resin (Amberlite XAD-2 and TOYOPEARL HW-40 (c] and organic solvent extraction. A diet containing each of the fractions was given to 7 female Charles River Sprague-Dawley rats (CD rats) of 4 weeks old, except for the second fraction. All 7 rats given the last carcinogenic fraction developed mammary and intestinal tumors and 5 rats had urinary bladder tumors. Ptaquiloside (PT) which induced mammary cancer in female CD rats and rho-hydroxystyrene glycosides were isolated from this fraction.