Haematoporphyrin diacetate: a probe to distinguish malignant from normal tissue by selective fluorescence.

Haematoporphyrin diacetate has been synthesized and purified. Following introduction into mice bearing squamous-cell carcinomas it was found to produce a fluorescence of the tumour tissue which was much stronger than that of the surrounding normal tissue. Haematoporphyrin diacetate was also shown to be the major active component of the impure compound known as haematoporphyrin derivative which has been widely used in tumour fluorescence studies.

Antithyroid and antiperoxidase activity of tropolone and 3-hydroxy-4-pyrone.

Tropolone (TR) and 3-hydroxy-4-pyrone were investigated for antithyroid activity following the finding that the 2-hydroxy-oxo pyridine, 3-hydroxy-4(1H)-pyridone (DHP, I), is goitrogenic. Both compounds inhibited the thyroidal uptake of radioiodine in rats and resembled the thioamide drugs in inhibiting the organic binding of iodine by the thyroid gland rather than the trapping of iodide, but were weaker binding inhibitors than 6-methyl-2-thiouracil (MeTU). Both compounds also inhibited the iodination of bovine serum albumin and thyroglobulin, catalyzed by thyroidperoxidase (TPO), lactoperoxidase (LPO), chloroperoxidase (CPO) and horseradish peroxidase (HPO) in vitro. The inhibitory effect of TR but not that of 3-hydroxy-4-pyrone was antagonized by ferrous ions. When fed to mice at levels of intake expected to produce goitre both compounds were toxic and caused severe liver damage. Thyroid enlargement was not observed in any of these feeiding experiments, but the thyroids of mice fed 0.1% TR showed moderate hyperplasia. It was concluded that both compounds are weakly goitrogenic. Hyperactivity was observed in the mice fed TR which may be associated with inhibition of catechol methyl transferase (COMT).

The goitrogen 3-hydroxy-4(1H)-pyridone, a ruminal metabolite from Leucaena leucocephala: effects in mice and rats.

Mice fed a diet containing 1% (w/w) 3-hydroxy-4(1H)-pyridone (DHP) developed goitre even with a diet high in iodine whereas mimosine (0.5% w/w) did not produce goitre even with a low-iodine diet. Thyroid enlargement was apparent (measured morphometrically) by the 7th week and was advanced by the 11th week. Histologically the goitre was hyperplastic in type. No marked histological changes were found in other organs of mice fed DHP or any organs of mice fed mimosine, except for some atrophy of hair follicles. A single intragastric dose of DHP inhibited the uptake of 125I by the thyroid in the rat but an equivalent dose of mimosine did not. Evidence is presented that the inhibition occurs at the iodine binding step, as with methyl thiouracil, rather than at the iodide trapping step, as with thiocyanate. Chronic treatment of mice with DHP, as with 6-methyl thiouracil, increased the avidity of the thyroid in taking up 125I. The major conjugated form of DHP in mammals, DHP-3-O-glucuronide, was almost as effective a goitrogen as the unconjugated compound when given by mouth but considerably less active than the free form in the blood stream. It was concluded that DHP is a potent antithyroid compound of the thiouracil type with low general toxicity, since mammals can tolerate a level of intake sufficient to produce goitre in spite of iodine supplementation.

Comparative toxicities of mimosine and some chemically related compounds to mouse bone marrow cells in liquid culture.

Mimosine, a plant amino acid which is toxic in mammals, was shown to be a potent inhibitor of incorporation of [3H]thymidine in mouse bone marrow cells in liquid culture (is greater than 70% inhibition at a concentration of 2 x 10(-4) M). To determine the parts of the molecule responsible for the inhibitory mechanism the effects of 13 chemically related compounds were examined in this system. The structural features necessary for inhibitory activity of the 4(1H)-pyridones were (1) the 3-hydroxyl-4-oxo function of the pyridone ring together with (2) an alpha-alanine or a 2-aminoethyl side chain. Compounds based on several other hydroxy heterocyclic functions were either weakly active or inactive. 3-Hydroxy-4(1H)-pyridone, the goitrogen to which mimosine is converted in ruminants, was only slightly inhibitory. These results are compared with published information on the effects of some of these compounds on other types of mammalian cells in vitro. The mouse bone marrow system in which inhibition of incorporation of [3H]thymidine is used as an index of cytotoxicity was shown to be sensitive and reproducible, and could be useful for structure-activity investigations of other cytotoxic compounds.

Effects on the liver in the rat of ingestion of Indigofera spicata, a legume containing an inhibitor of arginine metabolism.

The non-protein amino acid indospicine, which occurs in the free state in high concentration in the tropical pasture legume Indigofera spicata, causes toxic liver lesions in ruminants. Indospicine is a specific antagonist of arginine and an inhibitor of protein synthesis. The liver lesion was studied in rats at four dose levels by feeding diets containing 96, 48, 24 and 15 per cent. of the seed. The too higher levels caused death of most animals in 2-6 wk. Females were more susceptible than males. The rats fed the 24 per cent. seed diet developed a nodular cirrhosis by 6 wk and survived up to 18 wk. The rats fed the 15 per cent. seed diet developed cirrhosis at 16 wk and survived up to 28 wk. Prior to the onset of cirrhosis the liver showed a characteristic lesion consisting of hepatomegaly, periportal fatty change, portal cellularity due to proliferation of ovoid and cuboidal duct cells, gross enlargement of the hepatocyte cytoplasm nuclei and nucleoli in spite of brisk mitotic activity, and focal centrilobular necrosis. The lesion was interpreted as a restricted hepatic response to a growth stimulus, possibly the mobilisation of tissue amino acids. Improvement occurred in the rats fed the two lower dosage levels after nodular cirrhosis developed, producing a new parenchyma. An attempt is made to relate the lesions to the biochemical derangement induced by a specific amino acid antagonist.

Primary epithelial tumour in the right atrium of the heart and inferior vena cava in NZR/gd inbred rats; pathology of 18 cases.

In NZR/Gd inbred albino rats, tumours occurred in the right atrium or inferior vena cava of approximately 20 per cent. of untreated animals, of both sexes, over the age of 1 yr. The tumours were centred in the wall of the right atrium in 15 cases, and in the inferior vena cava in another three cases; they appeared to be primary in these sites. The tumours were slowly growing, but eventually malignant. Light- and electron-microscopic study showed the tumours were composed of epithelial alveoli imbedded in a collagenous connective tissue containing spindle cells and thin-walled blood capillaries. The epithelium varied from flat to low columnar, and often secreted mucoid material into the lumina, or sometimes into surrounding tissue. This tumour, for which the name atrio-caval epithelial mesothelioma is suggested, very closely resembles a rare epithelial tumour of the right atrium previously described in humans under a variety of names. An underlying embryological anomaly had been postulated in these tumours in humans, and the occurrence of pathologically similar lesions in high incidence in hearts of NZR/Gd inbred rats should help test the hypothesis of genetic and developmental causes in the genesis of this rare cardiac neoplasm.