Reversal by ribo- and deoxyribonucleosides of dehydroepiandrosterone-induced inhibition of enzyme altered foci in the liver of rats subjected to the initiation--selection process of experimental carcinogenesis

The effect of dehydroepiandrosterone (DHEA) on the activity of NADPH-producing enzymes and the development of enzyme-altered foci has been investigated in the liver of female Wistar rats subjected to an initiating treatment (a necrogenic dose of diethylnitrosamine) followed, 15 days later, by a selection treatment [a 15-day feeding of a diet containing 0.03% 2-acetylaminofluorene (2-AAF), with a partial hepatectomy at the midpoint of this feeding]. At the end of the selection treatment all rat groups received, for 15 days, a basal diet containing, when indicated, 0.05% phenobarbital (PB) and/or 0.6% DHEA. The effect of DHEA on the activity of NADPH-producing enzymes was also studied in normal rats fed, for 15 days, a diet containing 0.6% DHEA and in their pair-fed controls. DHEA caused a 43-58% inhibition of glucose-6-phosphate dehydrogenase (G6PD) and, respectively, 338-420% and 21-24% increases in malic enzyme (ME) and isocitric dehydrogenase activities in all rat groups. This was coupled with a great fall in the production of ribulose-5-phosphate, while no change in NADP+/NADPH ratio occurred. Hepatocytes, isolated from DHEA-treated rats, exhibited a very low activity of hexose monophosphate shunt (HMS), which was not stimulated by methylene blue, an exogenous oxidizing agent that markedly stimulated HMS activity in control hepatocytes. DHEA caused a great fall in the percentage of liver occupied by gamma-glutamyltranspeptidase (GGT)-positive foci, in the rats subjected to the initiation-selection treatments. PB enhanced the development of these foci, an effect which was completely overcome by DHEA. In addition, focal cells no longer expressed a G6PD activity higher than that of surrounding liver in DHEA-treated rats, but exhibited a high histochemical reaction for ME. DHEA also caused a great fall in labelling index of GGT-positive foci. Starting at the end of 2-AAF feeding, a mixture of ribonucleosides (RNs) of adenine, cytosine, guanine and uracil and of deoxyribonucleosides (DRNs) of adenine, cytosine, guanine and thymine were injected i.p. every 8 h for 12 days to the rats subjected to the initiation-selection treatments plus PB. Rats were killed 3 days after the end of RN and DRN treatments. These treatments completely overcome the DHEA effect on the development of GGT-positive foci and DNA synthesis by the focal cells, without affecting G6PD activity of both whole liver and putative preneoplastic foci. Experiments with labeled nucleosides revealed that RNs and DRNs produced derivatives that were incorporated into liver DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Decreased stimulation by 12-O-tetradecanoylphorbol-13-acetate of superoxide radical production by polymorphonuclear leukocytes carrying the Mediterranean variant of glucose-6-phosphate dehydrogenase

Polymorphonuclear leukocytes (PMNs) from individuals carrying the Mediterranean variant of glucose-6-phosphate dehydrogenase (G6PD) exhibit a great decrease in this enzymatic activity and in hexose monophosphate shunt (HMS). 12-O-tetradecanoylphorbol-13-acetate (TPA) greatly stimulates HMS of normal PMNs, while it does not affect that of the deficient PMNs. Similarly, the stimulation of HMS by methylene blue is largely reduced in G6PD-deficient PMNs. These changes are paralleled by a 58% decrease in TPA-stimulated superoxide radical (O2-) formation by the deficient PMNs. G6PD activity is not detectable in the deficient PMNs incubated with dehydroepiandrosterone, and these cells show a near complete inhibition of O2- production. It thus seems that the low ability of G6PD-deficient PMNs in the production of O2- depends on the low NADPH generation by HMS in these cells. The decrease in TPA-stimulated O2- production suggests a reduced response of G6PD-deficient cells to promoting agents.

Benzo(a)pyrene metabolism by lymphocytes from normal individuals and individuals carrying the Mediterranean variant of glucose-6-phosphate dehydrogenase

In vitro growing human lymphocytes (HL) and fibroblasts, isolated from glucose-6-phosphate dehydrogenase (G6PD)-deficient subjects (Mediterranean variant), show a sharp decrease in this enzymatic activity and in NADPH:NADP+ ratio. These cells are less able than controls to hydroxylate benzo(a)pyrene (BaP) when tested in the absence of an exogenous NADPH-generating system. They exhibit great resistance to the toxic effect of BaP. G6PD-deficient fibroblasts are less prone than controls to in vitro transformation by BaP. To investigate whether this depends on a decreased production of active BaP metabolites and BaP:DNA adducts by G6PD-deficient cells, BaP metabolism was studied in G6PD-deficient HL cultured in vitro in the presence of mitogens and treated with BaP for 24 hr. HPLC profiles of organo- and water-soluble metabolites revealed that both types of benzo(a)anthracene (BaA)-induced HL produced: 4,5-, 7,8-, 9,10-diols, 1,3-, 3,6-quinones, 3-, 9-hydroxy and 2 peaks of more polar metabolites. There was a 25-76% decrease of organo- and water-soluble metabolites in the G6PD-deficient cells. When HL were incubated with 7,8-diol, the formation of metabolites mutagenic for Salmonella typhimurium (His-) was very low in G6PD-deficient cells. BaP:deoxyadenosine (dAde) and BaP:deoxyguanosine (dGua) adducts were identified after incubation of both types of HL with BaP. There was a 31-79% fall in adduct formation by G6PD-deficient cells. Our results indicate that G6PD-deficient human lymphocytes are less able to metabolize BaP than normal lymphocytes. We suggest that the NADPH pool is inadequate, in deficient cells, for active BaP metabolism.

The interference of leukocytes and platelets with measurement of clucose-6-phosphate dehydrogenase activity of erythrocytes with low activity variants of the enzyme

Complete removal of leukocytes and platelets from whole blood showed that the glucose-6-phosphage dehydrogenase (G6PD) activity in "pure" erythrocytes from G6PD deficient hemizygous Sardinian subjects is consistently lower than reported in the literature. Thus, although non of 27 hemizygous subjects showed undetectable erythrocyte G6PD activity, their levels ranged between 0.0015 and 0.008 IU/g Hb, as compared with a mean value of 4.5 IU/g Hb in normal subjects. Most of the biochemical peoperties that were formerly ascribed to erythrocyte G6PD appear to be those of the enzyme from contaminating leukocytes and (or) platelets.

Genetic variation in the quantitative levels of an NADP (H)-binding protein (FX) in human erythrocytes

FX is a red cell NADP(H)-binding protein that has been well defined biochemically and immunologically but whose function is still unknown. Preliminary data indicated that the levels of this protein are significantly increased in hemizygotes, heterozygotes, and homozygotes for the G6PD Mediterranean mutant, thus raising the question of whether or not the individual variation in FX levels is more or less directly influenced by X-linked genes. The present study, based on a large series of population and family data collected in Sardinia, confirms unequivocally the above mentioned interaction, but shows at the same time that the variances in FX levels "between sibships" are 2-3 times larger than those "within sibships," when the analysis is done separately for the G6PD-normal or the G6PD-deficient sibs. From the comparison of the interclass and intraclass correlation coefficients, it appears that about 60% of the total variation of FX is of genetic origin. Moreover, the FX levels of children, analyzed in a pairwise manner, were found to be more positively correlated with those of their fathers (r = 0.39) than with those of their maternal grandfathers (0.20). This latter finding obviously favors the conclusion that "autosomal" rather than "X-linked" genes are involved in the determination of the FX levels.

Characterization of glucose-6-phosphate dehydrogenase variants. II. G6PD Kephalonia, G6PD Attica, and G6PD "Seattle-like" found in Greece

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Characterization of glucose-6-phosphate dehydrogenase variants. I. Occurrence of a G6PD Seattle-like variant in Sardinia and its interaction with the G6PD Mediterranean variant

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