Leo T. Burka

Lung-toxic furanoterpenoids produced by sweet potatoes (Ipomoea batatas) following microbial infection☆

Abstract The pulmonary toxicity of mold-damaged sweet potatoes has recently been ascribed to a “lung edema factor” which is produced in the roots in response to microbial infection. We now present data suggesting that this toxic principle comprises a group of at least four closely related compounds: 4-ipomeanol (1-(3-furyl)-4-hydroxy-1-pentanone), the isomeric 1-ipomeanol (1-(3-furyl)-1-hydroxy-4-pentanone). the corresponding diketone, ipomeanine (1-(3-furyl)-1,4-pentanedione), and the diol, 1,4-ipomeadiol (1-(3-furyl)-1,4-pentanediol). Isolation and purification of the compounds was accomplished using a combination of column chromatography, preparative gas chromatography, and high pressure liquid chromatography. Structures were initially determined from infrared, nuclear magnetic resonance, and mass spectra. Synthetic procedures for the compounds were devised in order to confirm the assigned structures and to provide an efficient source of the toxins for biological studies. All of these 1,4-dioxygenated-1-(3-furyl)-pentanes arc acutely toxic to the lungs of experimental animals, characteristically producing pulmonary edema and congestion, following a latent period of several hours after dosing. Mice receiving lethal doses of the toxins usually die within 24 h, and pathological findings are seen most often only in the lungs. However, mice initially surviving near-lethal doses of the toxins, particularly 1-ipomeanol and 1,4-ipomeadiol, may show evidence of nephrotoxicity within 1–3 days. The latter observation suggests that pathological responses other than lung damage should also be considered as possible features of moldy sweet potato toxicity.

Distribution, excretion, and binding of radioactivity in the rat after intraperitoneal administration of the lung-toxic furan, [14C]4-ipomeanol

Abstract 4-Ipomeanol [1-(3-furyl)-4-hydroxypentanone] is a poisonous metabolite produced in the mold-damaged sweet potato (Ipomoea batatas). In experimental animals the compound characteristically exhibits lung toxicity, producing prominent pulmonary edema and congestion. The distribution and excretion of radioactivity in rats after administration of [14C]4-ipomeanol has been studied. The toxin was given ip at doses of 2, 10, and 30 mg/kg. Approximately half of the administered radioactivity appeared in the urine within 2 hr, with only traces occurring in the feces and expired air. The greatest tissue concentration of radioactivity occurred in the lungs. Other organs showing significant concentrations were liver, kidney, and gastrointestinal tract. The maximal accumulation of activity occurred in the tissues within 0.5–1 h. The values declined over the next 1–2 hr, then reached a plateau representing residual activity. This residual activity is particularly high in lung, liver, and kidney, and represents the toxin or its metabolite(s) which has become tightly bound to tissue macromolecules. Binding occurs maximally in lung, and therefore may indicate that the binding phenomenon is involved in the toxic mechanism of 4-ipomeanol.

Mechanisms of hydroxylation by cytochrome P-450: Exchange of iron-oxygen intermediates with water

Abstract Highly-purified rat liver microsomal cytochrome P-450 converted cyclohexane to cyclohexanol in the presence of iodosobenzene. Oxygen from 18O-iodosobenzene was not incorporated into cyclohexanol but oxygen from H218O was readily incorporated. Cytochrome P-450 catalyzed the facile exchange of oxygen between iodosobenzene and water but neither cytochrome P-420 nor the apoenzyme did. Under these conditions cytochrome P-450 readily incorporated oxygen from 18O2 into cyclohexanol in the presence of NADPH-cytochrome P-450 reductase and NADPH. The results are interpreted in a mechanism in which cytochrome P-450 forms a common hydroxylating species in the presence of iodosobenzene or O2 plus NADPH.

Enzyme inhibition and the toxic action of moniliformin and other vinylogous α-ketoacids

Abstract The inhibition of two thiamine-requiring enzymes by the potent mycotoxin, moniliformin (1-hydroxycyclobutene-3,4-dione), was investigated. Rat brain transketolase and pyruvate dehydrogenase were inhibited 25 percent by 10 −9 M moniliformin. Studies carried out to determine if moniliformin causes enzyme inhibition by reaction with thiamine were negative. Varying the hydroxycyclobutenedione structure by substitution or ring expansion resulted in loss of toxicity and inhibition.

6-Oxodendrolasin, 6-hydroxydendrolasin, 9-oxofarnesol and 9-hydroxyfarnesol, stress metabolites of the sweet potato

Abstract Four sesquiterpene stress metabolites, 6-oxodendrolasin, 6-hydroxydendrolasin, 9-oxofarnesol, and 9-hydroxyfarnesol have been isolated from mercuric chloride-treated sweet potatoes. The metabolites have been synthesized and feeding studies have been carried out to determine the extent of incorporation of 14 C-labelled 6-oxodendrolasin and 9-hydroxyfarnesol into ipomeamarone.

Dithiocarbamate chelating agents for toxic heavy metals

Abstract Simple methods for the preparation of water soluble dithiocarbamates, several of which are newly synthesized, are presented along with some of their physical properties and a preliminary examination of their acute toxicity and their ability to offset acute mercuric chloride poisoning. Such compounds, although they do not possess great thermal stability, recommend themselves for wider application because of their ease of preparation and general effectiveness in binding those metal ions which form insoluble sulfides. Those compounds which possess an appreciable water solubility because of polar groups possess a rather slight degree of toxicity when administered intraperitoneally to mice. Some of these compounds are clearly effective as antidotes for acute mercury poisoning.

Development of tolerance to the pulmonary toxin, 4-ipomeanol

Abstract Tolerance to the pulmonary toxin, 4-ipomeanol, administered i.p. to mice, rats, or rabbits, or given i.v. to rats, was induced rapidly by i.p. pretreatments with small doses of 4-ipomeanol itself. Tolerance was inducible to a similar extent in male or female rats. In mice, the degree of tolerance was somewhat dependent upon the particular pretreatment regimen used. Ipomeanine, a lung-toxic furan that is closely related in structure to 4-ipomeanol, showed a cross-tolerance phenomenon with 4-ipomeanol in mice, but analogs of 4-ipomeanol that did not contain a furan ring, and which were not lung-toxic, did not induce tolerance. Pretreatments of mice with 4-ipomeanol produced tolerance to another type of lung toxin, α-naphthylthiourea (ANTU), but ANTU pretreatments did not produce tolerance to 4-ipomeanol. Secondary pretreatments with CCl4 or SKF-525A modified the degree of tolerance to 4-ipomeanol in 4-ipomeanol-pretreated animals, but CCl4 pretreatment alone did not alter the lethality of 4-ipomeanol. Pretreatments of mice with phenobarbital or 3-methylcholanthrene decreased the lethality of 4-ipomeanol. However, pretreatments of mice with tolerance-inducing doses of 4-ipomeanol did not alter the hexobarbital sleeping times or the zoxazolamine paralysis times in mice, suggesting that tolerance due to phenobarbital or 3-methylcholanthrene pretreatments was by a different mechanism than that resulting from 4-ipomeanol pretreatment. The amounts of 14CO2 appearing in the expired air were the same in control and tolerant rats administered [2-14C]ethanol. On the other hand, the amounts of radiolabeled 4-ipomeanol metabolites bound covalently to the lungs were markedly lower in 4-ipomeanol pretreated rats than in control rats; this observation is consistent with previous studies indicating that potentially lethal pulmonary damage by 4-ipomeanol is caused by an alkylating metabolite. Tolerance to 4-ipomeanol apparently results from an alteration in metabolism of the compound along toxifying and/or detoxifying pathways, but further studies are needed to determine the relative importance of changes in the 2 types of pathways. The tolerance phenomenon demonstrated with 4-ipomeanol may provide a useful model for investigating tolerance mechanisms generally applicable to other lung-toxic chemical and gases.

Phenolic chelating agents as antidotes for acute uranyl acetate intoxication in mice

Nine phenolic chelating agents were examined as antidotes for acute uranyl acetate intoxication. The ability of these compounds to promote survival was determined and the ability of two of them to remove uranium from the liver and kidney was compared with that of Na3 CaDTPA. The most effective compounds of this type in promoting survival were found to be Tiron and p‐aminosalicylic acid, but Tiron was much more effective in decreasing the uranium burden of the liver and kidneys. These compounds exhibit an antidotal action at higher uranium levels than the compounds reported in earlier studies. The compounds all seem to possess a very modest toxicity when administered ip.

Verrucosidin, a tremorgen from Penicillium verrucosum var cyclopium

The structure of a nitrogen-free fungal neurotoxin, verrucosidin, isolated from Penicillium verrucosum var cyclopium, has been established as (1) by chemical, spectroscopic, and X-ray crystallographic methods.

Biosynthesis of furanosesquiterpenoid stress metabolites in Ipomoea batatas: Isotopic oxygen incorporation into ipomeamarone

Abstract All three oxygen atoms in ipomeamarone, a major stress metabolise of the sweet potato, were found to originate from molecular oxygen and not from water or the sesquiterpene precursor, farnesol.