Flavoglaucin, a toxic metabolite from Eurotium (Aspergillus) chevalieri, has been found to induce a drastic swelling, to uncouple the oxidative phosphorylation, and to depress state 3 respiration in isolated rat liver mitochondria. It has been recently suggested that flavoglaucin depresses mitochondrial respiration by directly interacting with respiratory chain at complex III region in mitochondria. In the present study, it was confirmed that flavoglaucin indeed inhibited the reaction of the complex III at cytochromes bc1, segment, accumulating a reduced form of cytochrome b, in the succinate oxidation system.
The effects of averufin on both succinate-and NAD-linked respiratory chain were compared using rat liver mitochondria and electron transport particles (ETP). Averufin was found to exert a strong inhibition on both systems, showing somewhat stronger inhibition on the NAD- than on succinate-linked respiratory chains. Neither succinate nor NADH-dehydrogenase activity was affected by averufin. Both succinate- and HADH-cyto-chrome c reductases were markedly inhibited by averufin. These results in combination with our previous finding (no inhibition on cytochrome c oxidase by averufin) imply that the complex III of the respiratory chain is the site of action by averufin. A result was obtained which suggested that averufin interfered with membrane transport system of the inner membrane against organic anions in TCA cycle, in addition to the inhibitory effect on the respiratory chain.
A simple and improved enzyme-linked immunosorbent assay, one step ELISA, for quantitation of ochratoxin A and T-2 toxin was developed by the utilization of horseradish peroxidase (HRP) labelled anti-toxin monoclonal antibody on 96 well immunomicroplate. One step ELISA is not only handy method but also considerably improved one with respect to the sensitivity for the toxins compared with indirect (or two step) ELISA. The detection limits for ochratoxin A and T-2 toxin were ca. 50 pg and 5 pg/assay, respectively.
The 50% lethal doses (LD50, mg/kg) of nivalenol (NIV), one of the trichothecene mycotoxins produced by Fusarium species, in 6-week-old male ddY mice were determined as 38.9 (po), 7.4 (ip), 7.16 (sc) and 7.3 (iv). The minimum effective doses (μg/spot) for dermal toxicity in 6-week-old male Sprague-Dawley rats were 0.02 (T-2 toxin, T-2), 1.0 (NIV) and 2.0 (deoxynivalenol, DON). The relative cytotoxicity of 50% survival concentration (μg/ml) in the H4-II-E (Reuber rat hepatoma cell), 3Y-1 (Fischer rat embryofibroblast), Rous sarcoma virus-transformed 3Y-1 and Kagura-1 (aflatoxin B1-induced rat hepatoma cell) was 50-300 times on T-2 and 2-6 times on NIV in comparison to DON as 1.
In order to clarify environmental factors that contribute to invasion of Aspergillus flavus, one of the aflatoxin-producing fungi, into the maize kernels, the distribution of A. flavus as the potential inoculum in soil and atomosphere of maize fields and drying or storage facilities was examined in 8 provinces of Thailand during dry season (January-February, 1986). A. flavus was isolated from almost all of the soil samples. Although the numbers were quite different among the positive samples, it was concluded that the soil from middlemen's drying facilities and farmer's barn was, in general, more heavily contaminated than those from the fields. No A. flavus spore was trapped in 90 L of air samples from the 21 fields examined. On the contrary, A. flavus spores were trapped in almost all of the middlemen's drying facilities, although their numbers were smaller than those detected on the same locations in rainy season.
The distribution and aflatoxin productivity of atypical sclerotigenic strains of Aspergillus flavus isolated from soils in Thailand were investigated. Out of the 27 soil samples from 8 provinces, 9 samples were detectable for the strains. Among these 9 samples, 7 were collected from the maize fields in two northern provinces: Chiang Rai and Chiang Mai. All of 11 isolates of the strains tested produced aflatoxins, while half of 24 isolates of the typical strains produced them.
Maize ears were inoculated with spores of Aspergillus flavus in the field. The inoculations were carried out by two methods either with physical damage or without physical damage during the developing period of maize kernels. Only from the physically damaged group, high amounts of aflatoxins were detected. The fungal infection developed quickly along with the production of aflatoxins, although the amounts of aflatoxins in the maize kernels decreased about 5 weeks after the inoculation.
The amounts of aflatoxins in maize collected from various points ranging from field to silo during the rainy season of 1984 and 1985 were measured. In 1985, the aflatoxin contamination at fields and farm storages was infequent and low in levels. However, maize samples collected from either middleman's storages or silos in 1984 and 1985 were highly contaminated with aflatoxins. The highest amounts of aflatoxin B1 detected from samples were 1310 and 767 ppb in 1984 and 1985, respectively. These results clearly showed that most of the aflatoxin contamination on the maize occurred after harvest, especially during the period of storage at the middleman's place.
A survey for the occurrence of deoxynivalenol (DON), nivalenol (NIV) and zearalenone (ZEN) in cereals harvested in various parts of the world was carried out using a new method, which is rapid and sensitive for detecting Fusarium mycotoxins. A total of 183 samples from 9 countries were analyzed, and they were found to be frequently contaminated with DON, NIV and ZEN. This is the first report to demonstrate a worldwide multicontamination of Fusarium mycotoxins in cereals; of NIV together with DON and ZEN.
The production of nivalenol (NIV) and fusarenon-X (FX) by Fusarium sp. strain Fn 2 B on three cereal substrates (polished rice, wheat and corn) was examined. The highest productions of both NIV and FX were observed on polished rice. The maximal yields of NIV and FX on polished rice were 8, 532 mg/kg after 28 days at 25°C and 1, 992 mg/kg after 14 days at 25°C, respectively, and their amounts were markedly decreased at lower temperature.
In Japan, epidemic occurrence of a destructive blight of pine trees has been reported as very serious problems on forest pathology. In the course of pathological studies on the causal agent, it was found that cut branch of Japanese red pine was wilted with culture filtrate of Botrytis cinerea isolated from the pine tree. This fungus was frequently used for cultivation of a pine wood nematode, Bursaphelenchus xylophilus, because the nematode is mycophagous. The phytotoxicity of culture filtrate was proven by a cytotoxic test using pine tissue culture, and abscisic acid and unidentified cytotoxic compounds were chemically isolated from the toxic fraction. The lethal effect of abscisic acid to the cultured pine cells was not observed at the level below 500 ppm, but the growth inhibition occurred above 125 ppm. Although the wilting effect of abscisic acid to seedlings of the Japanese red pine was not confirmed, their water consumption was strongly inhibited.