Studies on Mold Dextranases

Nine strains capable of producing dextranase were isolated from soil. Among them, a strain belonging to the genus Aspergillus was chosen as the best producer of the enzyme. The mold produced greater amounts of dextranase than those found in some strains in the genus Penicillium, when grown aerobically at 28°C for 5 to 6 days in medium containing 1% dextran, 1% NaNO₃ or polypeptone, 0.2% yeast extracts, 0.4% K₂HPO₄ and small amounts of inorganic salts, pH 8.5. From the comparative taxonomic experiments, the mold used here was identified to be a strain belonging to Aspergillus carneus.     

Survival of human normal thyroid cells after X-ray irradiation

Normal thyroid cells from 25 individuals treated surgically for malignant or benign thyroid tumour were cultured in vitro and radiation induced cytotoxicity was studied. The mean lethal dose (Do), quasi-threshold (Dq), and extrapolation number (n) of survival curves of actively dividing thyroid cells assayed by colony formation were estimated to be 92.9 +/- 2.8 cGy (rad), 58.1 +/- 6.9 cGy and 2.0 +/- 0.1, respectively (average for 25 individuals +/- standard error). These results suggest that proliferating human thyroid cells are more sensitive to X-rays than most other nonhaematologic mammalian cells in similar assays. Cell survival was not significantly affected by sex, age, disease or exposure to atomic bomb radiation of the cell donor. However, the number of samples currently available is too small for definite conclusions in this regard.     

Treatment of murine SCC VII tumors with localized hyperthermia and temperature-sensitive liposomes containing cisplatin

The release of cisplatin (CDDP) encapsulated in temperature-sensitive unilamellar liposomes to murine SCC VII carcinoma by localized hyperthermia and the effects of the treatment on tumor growth were studied. A transition temperature of the temperature-sensitive liposomes containing cisplatin (LIP-CDDP) was 41 degrees C. Twenty-four hours after injection of LIP-CDDP, the heated tumors (42 degrees C, 60 min) contained 3.3 times more CDDP than the unheated tumors receiving free CDDP. Although the uptake of liposome-associated CDDP by liver was approximately threefold greater at 1.5 h after injection than uptake of free CDDP, it decreased about 50% over a 24-h period. No difference in uptake of the two forms of CDDP by kidney was observed. The combination of LIP-CDDP and localized heating at 42 or 43 degrees C was more effective relative to the amount of CDDP in delaying tumor growth than that of free CDDP and hyperthermia. Treatment with LIP-CDDP plus local heating resulted in a dose-modifying factor of 5.3 when compared with free CDDP and no hyperthermia. The dose-modifying factor was 2.8 when treatment with LIP-CDDP and heat was compared with treatment with free CDDP and heat. Thus CDDP could be released selectively from the temperature-sensitive liposomes by heat and resulted in both a greater uptake of the drug and a delay in tumor growth.     

Effects of a beta 3-adrenoceptor agonist, BRL 26830A, on insulin and glucagon release in mice.

The beta 3-adrenoceptor agonist, BRL 26830A, which is not inhibited by either beta 1 or beta 2-selective antagonists, has been shown to possess anti-obesity and anti-diabetic actions. However, the effects of this agent on insulin and glucagon release have not yet been substantiated. Therefore, we tested the hypothesis that BRL 26830A promotes insulin and glucagon secretion via beta 3 receptors on pancreatic islet B and A cells. In ICR mice fasted for 48 h, BRL 26830A significantly stimulated insulin secretion from 5 min after administration, markedly decreased blood glucose levels from 30 min after administration, and significantly increased glucagon secretion from 30 min after administration. The administration of a non-selective beta-receptor antagonist, at a dose of 50 mg/kg, 30 min prior to BRL 26830A injection completely abolished the effects induced by BRL 26830A. However, the administration of a beta 1-selective antagonist at doses of 50 or 100 mg/kg did not produce any significant effects. On the action of BRL 26830A, whereas the administration of a beta 2-selective antagonist at 50 mg/kg, a near maximal effective dose, partially abolished the effects of BRL 26830A. BRL 26830A had no effect on insulin, glucagon, or glucose levels in streptozocin (STZ) diabetic mice fasted for 48 h. These results suggest that, in mice, BRL 26830A may promote insulin secretion mainly via beta 3 receptors and partially via beta 2 receptors on pancreatic-islet B cells, and that glucagon may be secreted as the result of hypoglycemia induced by this agent.     

Evidence for the formation of strand-break precursors in hydroxy-attacked thymidine 5'-monophosphate by the spin trapping method

A method combining spin trapping, ESR, and HPLC was employed to obtain evidence for the formation of sugar radicals in OH-attacked TMP with special emphasis on the detection of strand-break precursors of DNA. OH radicals were produced by irradiating an N2O-saturated aqueous solution with X-rays. When an N2O-saturated aqueous solution containing TMP and a spin trapping reagent, MNP, was irradiated with X-rays, it was estimated on the basis of theoretical calculations using rate constants that 94% of the TMP radicals were induced by OH radicals. Since several spin adducts between TMP radicals and MNP, as well as the byproducts of the spin trapping reagent itself, were produced, reverse-phase HPLC was used to separate them. The presence of six spin adducts was confirmed by ESR examination. Further examination of these spin adducts by UV absorbance spectrophotometry showed the presence of a chromophore at 260 nm in three adducts. Since a gradual increase in the release of unaltered base from these adducts was observed when they were allowed to stand for 0-22 h at room temperature, they could be regarded as the spin adducts of sugar radicals and MNP. ESR spectra from the spin adducts were consistent with hydrogen abstraction radicals at the C1', C4', and C5' positions of the sugar moiety. These radicals appeared to be precursors of AP sites and strand breaks. In addition to these spin adducts, ESR spectra that were consistent with the spin adducts of base radicals (the C5 and C6 radicals) and MNP were observed.     

Induction of DNA double-strand breaks in Chinese hamster V79 cells by 2-chlorodeoxyadenosine

2-Chlorodeoxyadenosine was found to induce DNA double-strand breaks as well as cell death in log-phase Chinese hamster V79 cells. The induction of DNA double-strand breaks, measured by a neutral elution technique, was observed after a 2-h incubation of the cells in the presence of 5 microM of 2-chlorodeoxyadenosine, but these breaks were almost rejoined by a subsequent 1-h incubation, even though this drug was present in the medium during incubation. This repair was prevented by the addition of nicotinamide, which is known to inhibit poly(ADP-ribose) synthesis that is strongly associated with the DNA ligation, but not prevented by the addition of 9-beta-D-arabinofuranosyladenine (araA), which is known to inhibit DNA polymerization. These results suggest that the repair of CdA-induced double-strand breaks is achieved by ligation alone without DNA polymerization. When 35 microM of cycloheximide and 1.3 mM of dibutyryl cAMP were added to the medium, it was found that the induction of double-strand breaks by 2-chlorodeoxyadenosine was suppressed, while the cytotoxicity of 2-chlorodeoxyadenosine measured by colony-forming ability was not interfered with. These results suggest that the induction of DNA double-strand breaks is not associated with the cytotoxicity of this drug.     

Sensitivity to radiation of human normal, hyperthyroid, and neoplastic thyroid epithelial cells in primary culture

Samples of thyroid tissue removed surgically from 63 patients were cultured in vitro and exposed to X irradiation to investigate the radiosensitivities of various types of thyroid epithelial cells. A total of 76 samples were obtained, including neoplastic cells from patients with papillary carcinoma (PC) or follicular adenoma (FA), cells from hyperthyroidism (HY) patients, and normal cells from the surgical margins of PC and FA patients. Culturing of the cells was performed in a manner which has been shown to yield a predominance of epithelial cells. Results of colony formation assays indicated that cells from HY and FA patients were the least radiosensitive: when adjusted to the overall geometric mean plating efficiency of 5.5%, the average mean lethal dose Do was 97.6 cGy for HY cells and 96.7 and 94.3 cGy, respectively for neoplastic and normal cells from FA patients. Cells from PC patients were more radiosensitive, normal cells having an adjusted average Do of 85.0 cGy and PC cells a significantly (P = 0.05) lower average Do of 74.4 cGy. After allowing for this variation by cell type, in vitro radiosensitivity was not significantly related to age at surgery (P = 0.82) or sex (P = 0.10). These results suggest that malignant thyroid cells may be especially radiosensitive.     

FEULGEN NUCLEAL REACTION : I. QUANTITATIVE EXTRACTION OF FUCHSIN FROM FEULGEN-STAINED NUCLEOPROTEIN

A new extraction method for the quantitative determination of the fuchsin contained in a Feulgen-stained nucleoprotein sample has been introduced. The method is based on the following facts: (1) Treatment of a Feulgen-stained nucleoprotein sample with hot acid or alkali brings about a splitting of the linkage between fuchsin-SO₂ and the hydrolyzed nucleic acid moiety of nucleoprotein through aldehyde groups. (2) It also effectuates the formation of fuchsin from the liberated fuchsin-SO₂. (3) The fuchsin is made colorless by the treatment, but is restored to its original pink colored state when the pH of the acidic or alkaline medium is adjusted to 4.6. (4) The fuchsin, either pink colored or decolorized by alkali, can be extracted from an aqueous phase by amyl alcohol. A linear relationship was found to exist between the amount of fuchsin extracted by the FEM from a Feulgen-stained nucleoprotein sample and its DNA content. This relationship holds over a wide range of DNA concentration. From experiments utilizing this method, knowledge may be gained about the mechanism of the Feulgen reaction in situ which can lead to an improvement of the reaction in the field of cytochemistry.