L-Asparagine synthetase in serum as a marker for neoplasia.

L-Asparagine synthetase appears in serum approximately 7 days after the s.c. implantation of 1 X 10(5) cells of Leukemia 5178Y/AR (resistant to L-asparaginase) and increases in activity as the neoplasm grows and metastasizes. The principal source of the enzyme is the primary tumor. After intravranial inoculation of tumor, the rate of leakage of the enzyme is more pronounced than when the subcutaneous, intramuscular, or intraperitoneal routes are used. 1-(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea (NSC 79037), a nitro-sourea effective in the palliation of L5178Y/AR, temporarily halts the influx of enzyme into the blood stream, as does surgical excision of the s.c. tumor nodules. Treatment of mice with L-asparaginase within 24 hr of inoculation of the tumor markedly augments both tumor growth and the rate of penetration of L-asparagine synthetase into the circulation. Several other L-asparagine synthetase into the circulation. Several other L-asparaginase-resistant tumors also were found to spill L-asparagine synthetase into the serum, but the correlation between this phenomenon and the specific activity of the enzyme in homogenates of the tumor was imperfect.

In vitro evaluation of MR hypointensity in Aspergillus colonies.

PURPOSE: To demonstrate that paramagnetic elements in fungal colonies can cause hypointensity in MR images. METHODS: Aspergillus fumigatus grown in vitro was imaged with CT and MR at the time of initial inoculation and 5 days later. CT and MR images, T2 values, scanning electron microscopy, energy-dispersive analysis, and furnace atomic absorption spectrometry were performed. RESULTS: After 5 days of growth, MR images of A fumigatus revealed curvilinear hypointensities on T2-weighted images corresponding to the fungal growth. Gradient-echo images revealed two distinct components of hypointensity with different calculated T2 values. Phase-angle-difference images revealed a phase shift characteristic of magnetic-susceptibility paramagnetic effects, which corresponded to the hypointense regions on gradient-echo images. Energy-dispersive analysis and furnace atomic absorption spectrometry confirmed the presence of paramagnetic elements. CONCLUSION: It was shown that in vitro A fumigatus concentrates metal elements contained within the nutrient broth. These focal collections of calculated T2 values are caused at least partly by magnetic susceptibility effects.

The mutagenicity of dialkyl nitrosamines in the Salmonella plate assay.

N-nitrosodimethylamine (DMN) is not mutagenic in the standard Salmonella plate incorporation assay (Ames test) in the presence of an in vitro metabolic activation system (S-9) derived from rat liver. When the S-9 was derived from Aroclor- or phenobarbital-induced mouse or hamster liver or from uninduced hamster liver, mutagenic activity was observed. Increasing the amount of S-9 above the usual maximum level of 50 microliter per plate increased the mutagenic response. Similarly, the mutagenicity of N-nitrosodiethylamine (DEN) and N-nitrosodi(n-butyl)amine (DBN) was greater in the presence of hamster liver S-9 than when mouse or rat liver was used. Data are also presented indicating that the ability of rat liver S-9 to mediate the mutagenic activity of DMN in the "preincubation" assay is due to the fact that the various components are present in this assay at several times the concentrations attained in the standard plate incorporation assay.