Cell type-specific induction of O6-alkylguanine-DNA alkyltransferase mRNA expression in rat liver during regeneration, inflammation and preneoplasia.

PURPOSE AND METHODS: To investigate the potential role of an aberrant cellular DNA repair in target cells during malignant transformation we studied cell type-specific mRNA expression of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (O6-AGT) in normal and regenerating rat liver, chronic hepatitis and preneoplastic liver lesions by in situ hybridization and semiautomatic image analysis. RESULTS: O6-AGT mRNA expression was found to be four to five times higher in hepatocytes than in nonparenchymal cells. A 1.9-fold increase in O6-AGT mRNA was observed after partial hepatectomy. Intraperitoneal injection of diethylnitrosamine led to a 1.3-fold and 2.6-fold rise in periportal and perivenous hepatocytes, respectively. Ethylnitrosourea produced an enhancement of mRNA levels up to 1.6-fold in hepatocytes without regional differences. In megalocytic hepatocytes of Long-Evans Cinnamon rats with chronic hepatitis, a 4.4-fold mRNA induction was found. In small preneoplastic lesions induced after chronic diethylnitrosamine-exposure, O6-AGT mRNA expression was identical to that of adjacent normal tissue. Intermediate and large lesions revealed 1.5- to 1.6-fold higher mRNA levels. CONCLUSIONS: These results suggest an induction of O6-AGT mRNA expression in hepatocellular target tissue under conditions of increased carcinogen sensitivity . The O6-AGT expression in early preneoplastic lesions did not differ from normal surrounding liver tissue, thus excluding the possibility that progression of preneoplasia in rat liver is associated with a deficient mRNA expression of this DNA repair protein. On the contrary, enhanced O6-AGT mRNA expression in more advanced foci and early neoplastic nodules may confer a selective advantage upon early malignant hepatocytes with regard to further tumor progression.

Amplification, rearrangements, and enhanced expression of c-myc in chemically induced rat liver tumors in vivo and in vitro.

c-myc expression, amplification, and rearrangement were studied in neoplastic hepatic nodules of rats after diethylnitrosamine treatment, in hepatocellular carcinomas induced by N-methyl-N-nitrosourea, and in tumorigenic liver cell lines derived from rat hepatocytes transformed by diethylnitrosamine in vivo. Steady-state levels of c-myc transcripts, as measured by Northern blot hybridization, were slightly increased in neoplastic hepatic nodules and showed high levels in some hepatocellular carcinomas and some tumorigenic liver cell lines. DNA of the samples was analyzed after restriction nuclease treatment by Southern blot hybridization, using different probes specific for the three exons of the c-myc gene. The results suggest rearrangements of the complete gene and/or amplification in some cases. Rearrangements include the 5'-part of the first exon and a stretch upstream c-myc supposed to contain control elements of c-myc expression. Aberrations of this kind are most pronounced in advanced metastasizing hepatocellular carcinomas and highly tumorigenic, metastasizing liver cell lines. Heterogenicity of genomic alterations and c-myc transcript levels were found among different samples of the same hepatocellular carcinoma indicating subclonal diversification.

Correlations between ploidy and initiation probability determined by DNA cytophotometry in individual altered hepatic foci.

Single cell DNA cytophotometry of ATPase-deficient putative preneoplastic foci in rat liver, induced by a single dose of N-methyl-N-nitrosourea (25 mg/kg or 50 mg/kg) and subsequent phenobarbital feeding (0.05% in the diet), revealed three different types: the majority of foci consisted of an almost exclusive diploid cell population, others showed a preferential tetraploid pattern and a few large foci contained a mixture of di-, tetra- and octoploid hepatocytes. The results of this selective measurement of individual preneoplastic foci in Feulgen-stained 20-microns-thick cryostat sections indicate that not only diploid hepatocytes are a target for the transforming action of a carcinogen, but also tetraploid cells, and that both initiated cell types are capable of expanding as a homogeneous clone. However, clonal homogeneity appears to be lost when foci enlarge. A few preneoplastic foci, heterogeneous with respect to DNA content and endowed with an increased proliferative potential, may represent cell populations at high risk of further development into malignancy.

Clozapine induced increase of human plasma norepinephrine.

Four psychotic patients and 5 controls were treated with clozapine (200--400 mg/day during 30 days, patients, respectively 100 mg/day during 7 days, controls) and plasma norepinephrine (NE) concentration was measured. In the morning, shortly after end of sleep, plasma NE concentration was significantly increased under clozapine treatment in both populations. The effects of clozapine were explained with a direct pharmacological action of the drug on NE receptors.

Stress at birth: plasma noradrenaline concentrations of women in labour and in cord blood.

Radioenzymatically measured plasma noradrenaline concentrations, present at birth in umbilical veins of 19 healthy, 17 acutely asphyxiated, and 9 chronically distressed newborn infants were found to be elevated above maternal values proportional to the degree of distress and to plasma H ion concentrations.