Lipid peroxidation in hepatomas of different degrees of deviation

Lipid peroxidation rate in four different hepatomas is quite different and seems to be related to their degree of deviation, low deviation tumours displaying higher peroxidative ability. Moreover, the supernatant of the highly anaplastic Yoshida hepatoma is able to decrease the peroxidation rate in normal liver microsomes. This antioxidant ability is not dependent upon an increased level of glutathione. The concentration of reduced glutathione (GSH) declines strongly during incubation in conditions favouring lipid peroxidation. Unlike normal liver homogenates, this decline of GSH in hepatomas is not due to the transformation of GSH into oxidized glutathione (GSSG) but mostly to the increased activity of the γ-glutamyl-transpeptidase pathway.     

Phosphofructokinase isozymes of Morris hepatomas

The spin-lattice relaxation rate of solvent protons in suspensions of chloroplast thylakoid membranes undergoes a large transient depression following illumination in white light. This change appears to require the presence of chelatable paramagnetic ions; it is absent in chloroplasts exposed to 1 mm EDTA during the homogenization step of the isolation procedure, but reappears when 50 μm MnCl₂ is added to these suspensions. Conditions that inhibit light-induced R₁ changes are (i) anaerobiosis, (ii) inhibition of plastocyanin function byHg⁺²/CN, and (iii) the presence of superoxide dismutase. These observations suggest that chemical oxidation of nonfunctional Mn (II) by superoxide ion, which is generated under aerobic conditions by autooxidizable acceptors of Photosystem I, is responsible for the phenomenon. This interpretation was confirmed by experiments involving superoxide generation in the dark, using the NADPH-driven diaphorase activity of ferredoxin-NADP-reductase with benzylviologen as an autooxidizable acceptor.     

Protein kinase activity in Morris hepatomas

Rat liver protein kinase has been fractionated into five peaks of activity on isoelectrofocusing columns. The major liver peak, which was activated by cAMP, was decreased in two fast growing Morris hepatomas. The second major liver peak, independent of cAMP, was increased in the tumors.     

Cyclic AMP phosphodiesterase activity in three Morris hepatomas.

Rat liver cAMP phosphodiesterase has been fractionated into four peaks of activity with isoelectrofocusing column chromatography. The major two liver peaks (high Km enzymes) decreased with increasing growth rate while the minor two liver peaks (low Km enzymes) increased in one fast growing Morris hepatoma. There was also less total phosphodiesterase activity in the fast growing hepatoma.     

Pituitary growth hormone and somatotrophs in rats bearing chemically induced hepatomas.

Measurement of pituitary growth hormone (GH) content by polyacrylamide gel electrophoresis (PAGE) showed that rats bearing diethylnitrosamine (DENA) induced hepatomas contained significantly less GH than age-related controls. Light microscopy of these pituitaries revealed many apparently dying somatotrophs in tumour bearing rats. By electron microscopy the somatotrophs of DENA hepatoma rats were relatively inactive and some clearly dying, which could account for the reduced hormone content. However, electron microscopy of somatotrophs of rats with 2-acetyl-aminofluorene (2-AAF) hepatic tumour nodules revealed many very active cells with greatly increased content of free ribosomes and many granules poised for imminent release. Other somatotrophs of these rats showed lysosomal activity indicating reduced secretion after an active phase.     

Regulation of rat liver phosphofructokinase levels in Morris hepatomas.

The levels of the major liver phosphofructokinase isozyme (PFK-L₂) and the PFK regulatory factor were measured in adult and fetal liver as well as Morris hepatomas of different differentiation states. The results indicate that both the PFK-L₂ activity and the PFK regulatory factor levels in well and highly differentiated hepatomas are not statistically different from the amounts found in adult liver. In the poorly differentiated hepatomas and fetal liver, the levels of both PFK-L₂ and PFK regulatory factor are approximately 2 and 3 fold greater, respectively, than what was found in adult liver.     

Vitamin B6 metabolism in Morris hepatomas

The enzymes involved in the metabolism of vitamin B6 were measured in Morris hepatomas and livers of female Buffalo rats fed pyridoxine-sufficient and deficient diets. Pyridoxal phosphate levels in plasmas hepatomas, and livers were also determined. Nontumor-bearing animals were maintained as controls. Regardless of the B6 nutritional status, the concentration of pyridoxal phosphate was lower in the hepatomas than in the livers of the host animals. The apoenzyme levels of ornithine decarboxylase, a pyridoxal phosphate-dependent enzyme, were higher in the hepatomas from animals fed the B6-deficient diet. Liver pyridoxine kinase activity was higher in B6-sufficient animals. In contrast, tumor pyridoxine kinase activity was influenced by B6 intake and was significantly lower than that in host liver. Liver pyridoxine phosphate oxidase activity was not significantly affected by B6 intake or by the presence of tumor. In contrast, hepatomas had little or no pyridoxine phosphate oxidase activity. Pyridoxine phosphate phosphatase activity was elevated in tumors relative to livers. These data indicate that the metabolism of vitamin B6 is markedly different in the hepatomas than in host or control livers and suggest that the tumor is apparently incapable of the complete synthesis of co-enzymatically active pyridoxal phosphate from inactive precursor forms such as pyridoxine.     

Activity of chromatin-bound protease from rat liver and Morris hepatomas.

1. The activity of serine protease was studied in chromatin and in histone preparations from rat liver and Morris hepatomas, lines 5123 D and 7777. 2. Electrophoretic patterns of histones and the amounts of acid-soluble peptides released during incubation of chromatin and histones showed that there was no significant correlation between protease activity and tumour differentiation and its growth rate.     

Properties of guanylate cyclase in adult rat liver and several Morris hepatomas.

Guanylate cyclase (GTP pyrophyosphate-lyase (cyclizing), EC 4.6.1.2) activity was examined in preparations from normal rat liver and a series of Morris hepatomas. Homogenate gyanylate cyclase activites were 3.2, 1.6 and 1.2 nmol cyclic GMP formed per min/g tissue ihe non-substrate analogs of IMP were weak inhibitors of this enzyme, GMP and four of its analogs had Ki values ranging from 30 to 80 muM. The GMP analogs (8-azaGMP, 7-deaza-8-azaGMP, 2'-dGMP and beta-D-arabinosylGMP) and GMP were competitive inhibitors with respect to GTP.     

Serum lipoproteins of normal and cholesterol-fed rats

The density distribution of lipoproteins in rats fed chow or chow containing 1% cholesterol and 10% olive oil was studied. Lipoprotein fractions were prepared in the ultra-centrifuge between narrow density bands within the density range of 1.006-1.21 and were analyzed by chemical, electrophoretic, and immunological methods. In serum from normal rats there were three major lipoprotein fractions, with densities less than 1.006, 1.030-1.063, and 1.063-1.21. Almost no lipoprotein was found between d 1.006 and 1.030. Most of the low density lipoprotein appeared between a density of 1.04 and 1.05. In the density range 1.05-1.07, small amounts of both low density and high density lipoprotein were found. Feeding a diet high in cholesterol resulted in a marked increase in the concentration of lipoproteins of density less than 1.006, and a new lipoprotein fraction appeared between d 1.006 and 1.030; this fraction contained immunologically demonstrable low density and high density lipoproteins. In addition, there was a decrease in the high density lipoprotein fraction between d 1.070 and 1.21.     

The expressions of oncogenes and liver-specific genes in Morris hepatomas

The expression of three liver-specific genes and four oncogenes was studied in the Morris hepatomas 8994, 7288c, 7777, 5123tc, and 7800. Total RNA isolated from these tumors was probed with cDNA's for alpha-fetoprotein (AFP), albumin, tyrosine aminotransferase (TAT), and the oncogenes Ha-ras, Ki-ras, myc and src. When compared to mRNA's levels expressed in normal adult liver, we found AFP levels elevated in AFP-producing tumors, albumin and TAT mRNA levels depressed in all tumors, except TAT is elevated in 5123tc and the oncogenes with the exception of src elevated in all tumors. These results argue against a coordinated expression of these genes as a result of transformation, but suggest that oncogene expression is related to tumorigenesis or proliferation.     

Ornithine decarboxylase activity and DNA synthesis in Morris hepatomas 5123-C and 7800.

The activities of ornithine decarboxylase (ODC) and thymidine kinase (TK) and the rates of DNA synthesis were determined in hepatomas and livers of rats bearing Morris hepatoma 5123-C or 7800 and entrained to a schedule of 12 hours of light followed by 12 hours of darkness, with food (60% protein) available only during the first 2 hours of the dark period. ODC activity in hepatoma 5123-C displayed a diurnal oscillation, increasing 2-fold during the feeding period and then rapidly decaying to 20% of the peak level. The livers of rats bearing hepatoma 5123-C exhibited a similar oscillation of ODC activity, with peak values lower than in the hepatomas but higher than in the livers of control (non-tumor bearing) animals. TK activity and the rate of DNA synthesis in hepatoma 5123-C were low during most of the dark period but increased rapidly towards the end of the dark period. DNA synthesis reached a plateau at the dark-light interface and then rapidly declined, but TK activity remained high during the light period. Similar studies on hepatoma 7800 established that ODC activity in this hepatoma did not oscillate but remained at low levels throughout the day. Similarly, host livers of rats bearing hepatoma 7800 did not exhibit the diurnal oscillation of ODC activity characteristic of liver from control rats, but showed a slow increase in activity followed by a plateau and a slow decline to base-line levels. DNA synthesis in hepatoma 7800 was constant throughout the day, whereas TK activity may have increased during the dark period. In the livers of control rats and animals bearing hepatoma 5123-C or 7800, TK activity and rate of DNA synthesis were at low levels at all times studied and appeared not to oscillate.