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Biomedical subjects

S Weinhouse

Publications and source records attributed to S Weinhouse.

At least 19 recordsLinked to original sources
PubMed1986

The role of diet and nutrition in cancer.

Experimental and epidemiologic studies in recent years are pointing to diet as an important contributor to the cancer death toll which in the US this year will reach nearly one half million. Obesity, high fat intake, low fiber content and a dearth of vitamin A- and C-containing fruits and vegetables have been identified as risk factors; but these are not independent variables. The complex network of metabolic mechanisms involved are still obscure and association is not necessarily causation. Experts may agree on the data, but differ on whether we know enough to recommend dietary changes to the public. The Society in its continued efforts toward cancer prevention, has taken the stand that the available evidence, although inferential, is sufficiently solid to share with the public, and its guidelines are compatible with currently acceptable good nutritional practice. This conference should be a landmark of progress in the Society's continuing surveillance of this active field of investigation.

Carcinogens↗
PubMed1979

Formation of carbonyl chloride in carbon tetrachloride metabolism by rat liver in vitro.

In order to identify intermediates of CCl4 metabolism, whole, suitably fortified rat liver homogenates were incubated with 14CCl4 in the presence and absence of "pools" of unlabeled suspected intermediates. In the presence of NADH or NADPH, incorporation of radioactivity was rapid and substantial in CO2, lipid, protein, and the acid-soluble fraction. It was not influenced by the presence of large pools of unlabeled chloroform or formate, thus excluding these substances as obligatory intermediates. However, when incubated with L-cysteine, radioactivity incorporation in the acid-soluble fraction was almost doubled, and about one-third of the radioactivity of this fraction was identified as 2-oxothiazolidine 4-carboxylic acid. This substance is formed chemically by condensation of cysteine with carbonyl chloride and has been identified previously by others as a product of chloroform metabolism by liver microsomes in the presence of L-cysteine. Based on current knowledge of CCl4 metabolism, the following aerobic pathway is envisioned: microsomal cleavage to Cl- and .CCl3 and oxidation of the latter to the unstable intermediate, Cl3COH, which loses HCl to yield COCl2. COCl2 is likely to be the major source of CO2 from CCl4 but is probably not the intermediate that binds to lipid and protein. The addition of glutathione had no effect on CCl4 metabolism in rat liver homogenate, suggesting that glutathione S-transferases, which catalyze other dehalogenation reactions, do not play a role in CCl4 metabolism.

Aerobiosis↗
PubMed1977

Metabolism of [3H]-methylcholanthrene in the perfused rat liver.

The metabolism of [3H]-3-methylcholanthrene (3-MC) was studied in the isolated, perfused rat liver. Following addition of 250 mug to the perfusion fluid, 3-MC disappeared rapidly. After 2 hr, approximately 34% of the radioactivity was excreted in the bile, 6% remained in the perfusate, and 60% was found in the liver. Of the liver radioactivity, 80% was unchanged 3-MC, 11% was conjugated metabolites, 4% was free hydroxymetabolites, and 4% was nonextractable, presumably bound to macromolecules. Of the perfusate radioactivity, 82% was conjugated metabolites, 3% was free hydroxymetabolites, and 15% was unchanged 3-MG. A similar distribution was observed in intact, bile-cannulated rats, but biliary excretion was about one-fourth as high with double the i.v.-injected dose. Biliary excretion in perfused livers rose rapidly during the first 30 to 40 min, then decreased steadily. It was nearly twice as high in male as in female rat livers. Pretreatment of rats with 3-MC more than doubled the biliary excretion rate over the first 20 to 30 min in livers of both sexes and raised that of the female to that of the male rat liver. Neither retinol acetate nor 7,8-benzoflavone had any appreciable effect on biliary excretion of 3-MC metabolites. 2-Diethylaminoethyl-2,2-diphenylvalerate, a well-known microsomal oxygenase inhibitor, lowered excretion by 80 to 90% and lengthened the lag period, and dibutyryl-3',5'-cyclic adenosine monophosphate markedly increased the rate of excretion of 3-MC metabolites. Fractionation of bile by chromatography on Sephadex LH-20 revealed six well-defined peaks of radioactivity. In contrast, bile of intact rats given 3-MC gave a pattern on Sephadex chromatography consisting of only three peaks. Preliminary data suggest that these consist of conjugates of dihydroxymetabolites as well as more highly hydroxylate derivatives. The data obtained indicate that the perfused liver is an appropriate experimental model for studies on the hepatobiliary metabolism of carcinogens.

Animals↗
PubMed1977

Urea synthesis in Novikoff and Morris hepatomas.

The rates of urea synthesis in rat liver and in a series of rat liver neoplasms with widely different growth rates and degree of differentiation were investigated using tissue slices incubated in a Krebs-Ringer bicarbonate buffer. Urea synthesis did not occur in fast-growing, poorly differentiated Novikoff and Morris 3924A hepatomas, but it did occur in slow-growing, well- and highly differentiated hepatomas; however, there was no correlation with growth rate or degree of differentiation. Urea synthesis was comparable with normal liver, at about 32 mumoles/hr/g tissue, in the slow-growing Morris hepatomas 21, 28A, 47C, and 44; but it was very low in two other slow-growing, highly differentiated hepatomas, 9618A and 20. The well-differentiated Morris hepatoma 5123C had intermediate levels of urea synthesis. This pattern of urea synthesis closely paralleled the previously reported activity of carbamyl phosphate synthetase in these tumors. The rate of urea synthesis was normal in livers of Buffalo rats bearing fast- or slow-growing hepatomas in low urea synthesis rates, but it was markedly lowered in the livers of rats bearing large, slow-growing tumors with high urea synthesis rates. Urea synthesis in liver declined as the tumors increased in size. The total rate of urea synthesis in liver and tumor, as well as the concentrations of urea in the serum and urine of tumor-bearing animals, remained remarkably constant throughout the period of tumor growth, suggesting the existence of a homeostatic mechanism that controls the urea cycle activity in accordance with the synthetic activity of the tumor. In parabiotic animals, carbamyl phosphate synthetase activity and urea synthesis were lowered in the host livers of partners bearing tumors with high carbamyl phosphate synthetase- and urea-synthetic activity, but there was no significant effect on urea cycle activity in the normal partners. This result discounts the likelihood of a circulating humoral factor that controls hepatic urea cycle activity.

Animals↗
PubMed1975

Carcinofetal alterations in glycogen phosphorylase isozymes in rat hepatomas.

As part of a continuing study on the loss or retention of enzymes involved in specific hepatic functions in a series of rat liver neoplasms ranging widely in growth rate and degree of differentiation, isozyme patterns of glycogen phosphorylase in rat hepatomas were compared with those in rat tissues during development. A third phosphorylase isozyme, distinguishable kinetically, immunologically, electrophoretically, and by isoelectric focusing from liver and muscle types is commonly present in various rat hepatomas including Novikoff, Morris, and Yoshida hepatomas with various degrees of retention of liver type according to their degree of differentiation. This isozyme is also the sole type in the placenta and early embryo, and in liver and muscle is replaced with the organ specific liver and muscle types during development. In other organs, the replacement is only partial, and, especially in adult rat brain, this type is retained. Thus, this isozyme seems to be a prototype whose appearance in hepatomas is one of many examples of carcinofetal alterations in isozymes.

Animals↗
PubMed1975

Stimulation of tumor-cell respiration by inhibitors of pyruvate kinase.

In a model system consisting of highly coupled rat liver mitochondria respiring in the presence of substrate, pyruvate kinase, phosphoenolpyruvate, ATP, hexokinase and glucose, the increase in the mitochondrial concentration results in a progressive decrease in the activity of pyruvate kinase. These results are in accord with a role of pyruvate kinase as a determinant of glycolytic activity by competing with mitochondrial oxidative phosphorylation for the available ADP. The addition of adequate amounts of the amino acids, cysteine, alanine and phenylalanine, known as inhibitors of pyruvate kinase, to living Ehrlich ascites tumor cell suspensions results in a stimulation of the respiratory rate and in a decrease of the glycolytic rate of the cells. Concomitant with these changes, there is an accumulation of intracellular phosphoenolpyruvate and ADP, and a decrease in pyruvate and ATP. These results provide additional evidence for paying attention to pyruvate kinase as another key enzyme whose properties and activities may be major determinants for the control of glycolysis and the Crabtree and Pasteur effects of tumor cells.

Amino Acids↗
PubMed1975

Carbamyl phosphate synthetases in rat liver neoplasms.

Isozymes of carbamyl phosphate synthetase (CPS), CPS I, a mitochondrial enzyme found exclusively in liver and involved in urea synthesis, and of CPS II, a soluble cytoplasmic enzyme widely distributed in animal tissues, were assayed in rat liver and in a series of rat liver neoplasms ranging widely in growth rate and degree of differentiation. CPS I was absent from fast-growing, poorly differentiated hepatomas, such as the Novikoff hepatoma and Morris hepatomas 3924A and 9098F, but was present in slow-growing, well- and highly differentiated Morris hepatomas. However, there was no close correlation between the growth rate or degree of differentiation and the CPS I activity. Activity was very high, at levels comparable with normal liver at about 9 UNITS/G, IN SLOW-GROWING, HEPATOMAS 21, 47C, and 28A but was very low in other slow-growing highly differentiated hepatomas 9618A, 66, and 16. CPS II activity was present in normal liver and all hepatomas examined, but with very low activity, of the order of 1% or less of that of CPS I activity, with maximal values at 5 to 70 milliunits/g. Again, there was no clear correlation with growth rate; the activity was lowest in fast-growing, poorly differentiated hepatomas. A striking observation was a marked lowering of CPS I activity in livers of rats bearing large, slow-growing tumors that have high CPS I activity. As the tumors grew larger and the liver CPS I decreased, a relatively constant total CPS I activity was maintained, suggesting the existence of a homeostatic mechanism. The effect was not observed in rats bearing either fast-growing hepatomas or slow-growing hepatomas with low CPS I activity and was not due to some specific nutritional effects of the tumor on the host.

Animals↗