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H G Mandel

Publications and source records attributed to H G Mandel.

At least 37 records · Page 2Linked to original sources
PubMed1989

Urinary O6-methylguanine excretion in the rat after O6-methylguanine but not N-methylnitrosourea administration.

Urinary makers that permit monitoring the exposure of rats to methylating carcinogens could be of considerable value. Because of the association of the formation and retention of O6-methylguanine (m6Gua) with carcinogenesis, the urinary recovery of this compound would be of particular interest. Urine of rats receiving 200 muCi 3H-methyl nitrosourea (MNU) was therefore subjected to HPLC analysis to detect labeled m6Gua. Following the intraperitoneal injection of 3H-MNU (16 or 80 mg/kg), 3H-m6Gua could not be detected in the urine, although its presence was demonstrated in liver DNA under such conditions. Rats were also administered 3H-MNU followed by pretreatment with unlabeled m6Gua to block the repair enzyme, m6G-DNA-transmethylase, which might have obscured an excision mechanism. This procedure permitted the recovery of about half of the administered dose of m6Gua in the urine, but none of this compound contained tritium. We conclude that m6Gua, though formed in the DNA from MNU, is not excised and excreted as such in the urine. Thus m6Gua could not be used to serve as a suitable urinary marker for exposure to methylating carcinogens.

Animals↗
PubMed1988

DNA-directed actions of 3-deazaguanine: effects on DNA integrity and DNA elongation/ligation.

The cytotoxic action of the guanine analogue, 3-deazaguanine, was shown previously to be closely associated with deazaguanine-induced inhibition of DNA synthesis and incorporation of deazaguanine into DNA. The DNA-directed effects of the compound have been further investigated by studying the effect of deazaguanine on DNA integrity, and on the ability of pulse-labeled L1210 cells to synthesize full length DNA. Deazaguanine caused DNA single strand breaks in newly synthesized DNA but not in preformed DNA. The amount of DNA single strand breaks correlated with both deazaguanine exposure and with the amount of deazaguanine incorporated into the DNA. When cells were allowed to recover in drug-free medium for 12 or 24 h after drug exposure little effect on either the amount of DNA single strand breaks or cell viability relative to controls was observed. Deazaguanine also inhibited the ability of L1210 cells to synthesize full length DNA after pulse labeling of DNA. This effect was temporally related to the inhibition by deazaguanine of total DNA synthesis.

Animals↗
PubMed1987

Metabolic basis for the protective effect of the antioxidant ethoxyquin on aflatoxin B1 hepatocarcinogenesis in the rat.

The effect of dietary administration of 0.5% ethoxyquin (EQ) on the in vivo induction of enzymes and effect on aflatoxin B1 (AFB1)-DNA binding in liver and the consequent in vitro metabolism of AFB1 by male Fischer F344 rat liver-derived fractions have been examined. EQ increased microsomal cytochrome P-450s, in particular those isozymes classed as phenobarbital inducible, and the in vitro rate of metabolism of AFB1. The formation of the presumed detoxified metabolites, aflatoxins M1 and Q1, was enhanced to a greater extent than was the formation of the active metabolite, aflatoxin B1-8,9 epoxide (assessed by the level of aflatoxin B1-8,9-dihydrodiol). Prolonged feeding with EQ was accompanied eventually by a reduction in the initially elevated cytochrome P-450 content, but this was not reflected in any significant decrease in the rate of AFB1 metabolism in vitro. EQ increased the glutathione S-transferase activity of the liver cytosol fractions as assessed with the model substrate 1-chloro-2,4-dinitrobenzene. The capacity of these fractions specifically to catalyze the conjugation of AFB1 with glutathione was induced to a far greater extent than was the conjugation of 1-chloro-2,4-dinitrobenzene. gamma-Glutamyl transpeptidase was induced in the periportal areas of the liver lobule. Reduced in vivo binding of [3H]AFB1 to DNA of liver and kidney was found to result from EQ treatment. It is concluded that the reduced hepatocarcinogenesis which results from feeding EQ simultaneously with AFB1 is due to the reduction in DNA-adduct formation which in turn is due at least in part to increased detoxifying metabolism in the microsomal, cytosolic, and plasma membrane compartments of the liver cells.

Aflatoxin B1↗
PubMed1986

Increased aortic DNA synthesis precedes renal hypertension in rats. An obligatory step?

The rate of DNA synthesis was determined in rats with developing and established two-kidney, one clip renal hypertension. Rate of DNA synthesis was measured as [3H]thymidine incorporation into DNA per hour. After stenosis of the renal artery, blood pressure increased over a 2-week period. Five days after clipping, there was an increase in the rate of aortic DNA synthesis before an increase in blood pressure was detected, whereas there was no DNA effect in sham-operated animals. This difference in [3H]thymidine incorporation into aortic DNA could not be accounted for by alterations in thymidine pool sizes. The increase in DNA synthesis was still present 3 weeks after renal artery stenosis, although by that time blood pressure had plateaued. The role of DNA synthesis in the development of renal hypertension was investigated by determining whether inhibition of DNA synthesis with cytosine arabinoside could prevent the increase in blood pressure. Treatment of clipped rats with cytosine arabinoside for 5 days delayed the increase in blood pressure for more than 4 days, as compared with the effect of saline treatment in clipped rats. Although the possibility remains that some effect of cytosine arabinoside other than its effect on DNA synthesis could have influenced blood pressure, there were no differences in body weight, food intake, water intake, or urine output between cytosine arabinoside-treated and saline-treated rats with renal artery clips, and cytosine arabinoside treatment had no effect on blood pressure or body weight in normal rats. These results suggest that an increase in DNA synthesis may be an obligatory step in the genesis of renal hypertension.

Animals↗
PubMed1986

Correlation of biochemical effects and incorporation of 3-deazaguanine into nucleic acids to cytotoxicity in L1210 cells.

3-Deazaguanine, a tumor-inhibitory purine antimetabolite, is cytotoxic to L1210 leukemic cells in culture. The log percentage of viability correlated strongly (r2 = 0.986) with the product of the concentration of 3-deazaguanine, or [3-deazaguanine], and period of exposure (t) when [3-deazaguanine] was between 3 and 50 microM, and t was 12 or 24 h. We wished to relate this cytotoxicity to biochemical effects mediated by 3-deazaguanine. 3-Deazaguanine inhibited both DNA and protein synthesis, and both log DNA synthesis and log protein synthesis correlated inversely with [3-deazaguanine] X t and directly with cell viability (P less than 0.001). L1210 cells accumulated 3-deazaguanine 5'-triphosphate to a level of 1.5 nmol/10(6) cells. 3-Deazaguanine treatment had no effect on intracellular cytidine 5'-triphosphate levels, but reduced adenosine 5'-triphosphate and uridine 5'-triphosphate levels by 40% relative to control and guanosine 5'-triphosphate levels by 85% relative to control at a [3-deazaguanine] X t value at which 3-deazaguanine 5'-triphosphate accumulation was near maximal. Incorporation of 2-14C-labeled 3-deazaguanine into DNA and RNA, separated by Cs2SO4 density gradient centrifugation, was demonstrated. Incorporation into DNA was linear versus [3-deazaguanine] X t and correlated inversely with cell viability (P less than 0.001). These data suggest that 3-deazaguanine is anabolized and incorporated into DNA, and that this incorporation is related to decreased DNA synthesis and cell death. The decrease in protein synthesis and diminution of guanosine 5'-triphosphate levels following drug treatment may also contribute to the growth-inhibitory actions of 3-deazaguanine.

Animals↗
PubMed1985

Dissimilar actions of 6-mercaptopurine and 6-thioguanine in Chinese hamster ovary cells.

The actions of 6-thioguanine (TG) and 6-mercaptopurine (MP) were compared in Chinese hamster ovary (CHO) cells. Several differences were noted between these two agents. TG caused a greater maximal loss of clonogenicity, leaving about one log fewer survivors than did MP, although the cells killed by MP appeared to succumb much more rapidly than those killed by TG. MP-treated populations experienced a G1 or G1/S arrest which was quickly reversed upon drug removal, while TG-treated cells were arrested in late S/G2, after some delay. Although TG induced a gross chromosome deformation [unilateral chromatid damage, as described earlier in Maybaum and Mandel, Cancer Res. 43, 3852 (1983)] MP caused little or no such deformation. Addition of 4-amino-5-imidazolecarboxamide (AIC) to MP treatments antagonized MP-induced loss of clonogenicity, while AIC caused a dose-dependent potentiation of TG-induced loss of clonogenicity. The interaction between TG and AIC does not seem to represent an increase in either purine starvation or incorporation of TG into DNA, suggesting that a third mechanism is involved. We suggest that this additional mechanism may possibly be related to the induction of differentiation by TG that has been reported in other systems.

Aminoimidazole Carboxamide↗
PubMed1983

Funding more NIH research grants.

Because of the prospect of a serious decline in the nation's biomedical research capacity owing to diminished federal appropriations, temporary measures should be initiated promptly by the National Institutes of Health to preserve the stability of resources and diversity of research required for future productivity. It is recommended that the available funds be distributed in such a way as to permit some support for 50 percent of competing grant applications approved by the National Institutes of Health study sections. Measures proposed for consideration are a sliding scale for funding, a greater across-the-board reduction, a limit on support for an individual laboratory, and a review of indirect costs.

National Institutes of Health (U.S.)↗
PubMed1983

Unilateral chromatid damage: a new basis for 6-thioguanine cytotoxicity.

Using the technique of premature chromosome condensation, which permits the visual inspection of interphase chromatin, we have shown previously that 28 hr after exposure to 6-thioguanine (TG) specific and drastic morphological changes in the chromosomes of Chinese hamster ovary fibroblasts in the G2 phase of the cell cycle become evident. In this paper, we demonstrate that this damage is a dose-related effect, appearing as sharp curling or "kinking" at lower TG concentrations and as unilateral chromatid damage and gross chromosome disruption at higher TG concentrations. With the use of a scoring system for quantitating the severity of this specific damage, the threshold concentrations for the appearance of unilateral chromatid damage and for loss of colony-forming ability were shown to be identical. Since the appearance of unilateral chromatid damage paralleled the appearance of TG-induced cytotoxicity in terms of time and dose, and since the severe disruption of G2 prematurely condensed chromosomes is consistent with TG-induced G2 arrest seen in this and other systems, we conclude that unilateral chromatid damage is centrally involved in the delayed cytotoxicity of TG in Chinese hamster ovary cells.

Animals↗
PubMed1982

Glial DNA synthesis and cell proliferation in the lesioned frontal cortex of the rat.

Proliferation of rat neurological cells was quantified following a lesion of the frontal cortex, with the rate of incorporation of intraventricularly administered [3H]thymidine ([3H]TdR) into cortical DNA serving as an index of glial proliferation. Incorporation of [3H]uridine into the corresponding RNA fractions did not serve this purpose. The intraventricular route of administration of thymidine greatly reduced the amount of [3H]TdR needed to label DNA relative to systemic injection. The rate of incorporation of [3H]TdR into DNA was linear for 75 min post-injection. Significantly more [3H]TdR was incorporated into DNA of the lesioned frontal cortex than that of the contralateral control cortex, during the first 4 days post-trauma. The majority of the acid-insoluble radioactivity (from [3H]TdR) was localized in the nuclear subcellular fraction of the cortex. Experiments indicated that the enhanced incorporation of [3H]TdR was not the result of altered metabolism or pool sizes of TdR in the lesioned cortex. Histological analysis indicated that there was a significant increase in the number of glial cells in the lesioned cortex by day 4 post-lesion, which corresponded to the increase in DNA synthetic activity. It was concluded that mechanical trauma to the frontal cortex of the rat results in an increase in the number of glial cells at and near the lesion which is accompanied by an increase in incorporation of [3H]TdR into cortical DNA. This method of measuring posttraumatic DNA synthesis has several advantages over autoradiography.

Animals↗
PubMed1982

Inhibition of initiation of translation in L1210 cells by 8-azaguanine.

The inhibition of protein synthesis by 8-azaguanine (azaG) in L1210 cells in culture was investigated. AzaG selectively inhibited protein synthesis at concentrations where viability was decreased significantly. AzaG altered the polyribosome sedimentation profile, increasing the numbers of monosomes and smaller polysomes and decreasing the number of larger polysomes. The reversal by cycloheximide of the alterations in the polysome profile suggested that azaG inhibited the initiation of translation. This was confirmed by the demonstration of inhibition of the formation of the 43S and 80S initiation complexes.

Animals↗
PubMed1982

Crisis in NIH funding.

Explore the source record for details and available documents.

National Institutes of Health (U.S.)↗
PubMed1982

Purine analogs revisited: interference in protein formation.

We have examined in L1210 cells in vitro the effects of three guanine analogs (8-azaguanine, 3-deazaguanine, and 6-thioguanine) on protein biosynthesis and have compared this action with respect to effects on macromolecular synthesis and mechanisms of tumor growth inhibition and cell viability. The major site of action of azaG was the inhibition of protein synthesis. TG seemed to inhibit RNA synthesis more than DNA and protein synthesis. In contrast, DG inhibited both protein and DNA synthesis but not RNA synthesis. Whereas the LD50 and ID50 for macromolecular synthesis for DG and also for azaG were quite similar, for TG the LD50 was one-tenth that of the ID50 for macromolecular synthesis. Since azaG, DG, and TG had different effects on protein and RNA synthesis, the effects of the analogs on the process of translation were examined. DG and azaG, but not TG, altered the polyribosome sedimentation profile, increasing the numbers of monosomes and smaller polysomes and decreasing the number of larger polysomes. This shift in the polysome profile was reversed by low concentrations of cycloheximide, suggesting that DG and azaG inhibited the initiation of translation. This was examined directly by the incorporation of 35S-met-tRNA into the initiation complexes. DG and azaG inhibited the formation of the 43S and 80S initiation complexes and this inhibition correlated closely with the inhibition of total protein synthesis. It is likely that the inhibition of tumor growth by azaG is due to the inhibition of initiation of translation, perhaps through actions on mRNA. The mechanism of growth inhibition for DG is not yet known but may similarly involve actions at this level.

Animals↗
PubMed1982

Trauma-induced glial proliferation: possible involvement of the immune system.

Rat neurologlial cells proliferate following trauma to the frontal cortex. Since previous reports have indicated that activated T-lymphocytes secrete a factor which can induce the proliferation of glial cells in vitro, we investigated the effects of immunosuppression on the trauma-induced proliferation of glial cells in the rat. Animals were treated with either methotrexate (2.5 and 10 mg/kg/day), hydrocortisone (100 mg/kg/day), or saline for five days prior to lesioning of the cortex. Immunocompetence was estimated by measuring sheep red blood cell hemagglutination titers at the time of killing. On the last day of drug treatment, rats were mechanically lesioned on the frontal cortex, and the incorporation of intraventricularly injected 3H-thymidine (3H-TdR) into cortical DNA, a measure of glial cell proliferation, was determined two days after lesioning. Intraperitoneal treatment with methotrexate before the lesioning depressed 3H-TdR incorporation into brain DNA, and reduced hemagglutination titers and thymus and spleen weight. However, intramuscular hydrocortisone pretreatment, which had immunosuppressive actions similar to methotrexate, had a much smaller effect on 3H-TdR incorporation into brain DNA following trauma. Methotrexate given acutely after lesioning did not depress thymidine utilization in the lesioned rat cortex, apparently because of poor penetration of the folate analog into the brain. Thus, we conclude that inhibition of glial cell proliferation resulting from methotrexate pretreatment had been produced indirectly, probably by its severe immunosuppressive effects.

Animals↗
PubMed1982

3-Deazaguanine: inhibition of initiation of translation in L1210 cells.

In L1210 cells in culture, 3-deazaguanine (DG), a relatively new purine analog, was found to inhibit DNA and protein synthesis but not total RNA synthesis. The effect of the drug on protein synthesis was therefore further examined. Polyadenylic acid-containing RNA synthesis was not decreased by DG treatment, suggesting that the inhibiton of protein synthesis was a function of an alteration in the process of translation. DG altered the polyribosome sedimentation profile in a dose-dependent manner, increasing the numbers of monosomes and smaller polysomes and decreasing the number of larger polysomes. The nascent polypeptides in DG-treated cells were labeled with [3H]leucine, and the increased number of monosomes was not associated with a proportionate amount of [3H]leucine when compared to the polysomes. This indicated that the monosomes had not been derived directly from the breakdown of active polysomes. The shift in the polysome profile was reversed by cycloheximide, suggesting that DG profile inhibited the initiation of translation. This was confirmed by the demonstration of the inhibition of DG of the formation of the 43S preinitiation complex. The inhibition of the initiation of protein synthesis by DG may contribute to the antitumor actions of this new purine analog.

Animals↗
PubMed1982

Effects of DNA synthesis inhibitors on post-traumatic glial cell proliferation.

This study attempts to inhibit post-traumatic glial cell scarring in rats lesioned in the frontal cortex, by treatment with several antiproliferative drugs. [3H]Thymidine ([3H]TdR) incorporation into DNA served as the biochemical index of glial cell proliferation and histological observations confirmed the biochemical effects. Cytosine arabinoside (ara-C), given i.p. at a total daily dosage of 15 to 100 mg/kg, was found to inhibit the incorporation of [3H]TdR into cortical DNA and also inhibited the proliferation of glial cells after cortical trauma. Treatment using ara-C induced marked histological changes in glial cells near the lesion, indicating that the inhibition by the drug of DNA synthesis correlated with cytotoxicity to proliferating glial cells. Experiments using [3H]ara-C confirmed that this drug entered lesioned brain tissue, although at levels considerably lower than those found in the periphery. Cyclophosphamide also reduced [3H]TdR incorporation into both lesioned and control cortices; however, this effect, unlike that of ara-C, was not proportionately greater in the lesioned cortex. Vincristine, but not vinblastine, also inhibited [3H]TdR incorporation into the lesioned cortex, possibly reflecting differences in the neuronal uptake of the vinca alkaloids. We propose that ara-C can inhibit the proliferation of glial cells after neural trauma and that judicious use of this agent may lessen scarring in the injured central nervous system, possibly enhancing the regenerative capacity of the brain.

Animals↗
PubMed1981

The target cell determinants of the antitumor actions of 5-FU: does FU incorporation into RNA play a role?

Sufficient evidence has accumulated to permit the conclusion that there are at least two major determinants for the effectiveness of 5-FU against tumors. These are the formation of fluorodeoxyuridylate (FdUMP) and the incorporation of 5-FU into RNA. Either or both of these determinants can be of critical significance in the tumor-inhibitory actions of 5-FU and the sensitivity of normal tissues of this drug, depending on the biological system and the experimental conditions. The critical role for FdUMP and inhibition of DNA synthesis as a cell target determinant is supported by the recognition of "thymineless death;" the time-course correlation of levels of this metabolite (and/or or susceptibility of thymidylate synthetase) with tumor sensitivity to 5-FU and with cytotoxicity to specific organs and tissues; and the reversibility of the actions of 5-Fu by thymidine in vitro. A role for 5-FU incorporated in RNA (FU-RNA) is based on various toxic consequences of the incorporation of the analog, including the inhibition of ribosomal maturation; the occasionally reported lack of rescue from growth inhibition with thymidine, which prevents the 5-FU induced inhibition of DNA synthesis, apparently with increased FU-RNA formation; the activity of uridine as a partial rescue agent, and various studies revealing correlations of FU-RNA with enhanced therapeutic response.

Animals↗