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Biomedical subjects

M C Archer

Publications and source records attributed to M C Archer.

At least 73 records · Page 4Linked to original sources
PubMed1988

Alkylation of individual genes in rat liver by the carcinogen N-nitrosodimethylamine.

A method for quantifying alkylated bases in defined gene sequences of rat liver following carcinogen treatment is described. After restriction, the genomic DNA is heated to 65 degrees at pH 8.0 to cause depurination of 7-alkylguanine and 3-alkyladenine residues. Reaction with spermidine then generates strand breaks. After gel electrophoresis and Southern transfer, sequences of interest are visualized using specific probes. The presence of strand breaks in restriction fragments reduces their intensity compared to unmethylated fragments. The method was applied to show that the transcriptionally active albumin gene is damaged by the hepatocarcinogen N-nitrosodimethylamine to a much greater extent than the untranscribed IgE gene in rat liver.

Albumins↗
PubMed1988

Streptozotocin toxicity to cultured pancreatic islets of the Syrian hamster.

Pancreatic islets of the Syrian golden hamster were maintained in culture for extended periods of time. Toxicity of streptozotocin in these cultures was evaluated by measurement of insulin secretion. Exposure of islets to 1 or 2 mM streptozotocin immediately following isolation resulted in a permanent and dose-related inhibition of insulin secretion. This was accompanied by islet disruption as observed by phase-contrast microscopy. Culture of islets for 24 hours before streptozotocin exposure afforded protection from toxicity. For example, exposure of freshly isolated islets to 2 mM streptozotocin resulted in complete destruction of beta cells, whereas islets similarly exposed after a 24 hr culture period continued to secrete insulin for many months. Islets maintained in culture for one week before exposure to 0.1-0.5 mM streptozotocin, however, became more sensitive than freshly isolated islets. Repeated weekly exposure of cultured islets to a "non-toxic" concentration (0.1 mM) resulted in sustained suppression of insulin secretion after 11 weeks.

Animals↗
PubMed1988

Interaction of alpha-acetoxy-N-nitrosopyrrolidine with DNA assessed by loss of restriction endonuclease recognition sites and formation of apurinic/apyrimidinic sites.

alpha-Acetoxy-N-nitrosopyrrolidine (AcO-NPYR), in the presence of esterase, was reacted with the plasmid pBR322. The AcO-NPYR-treated plasmid was nicked by reaction with spermidine, suggesting the presence of apurinic sites. The treated plasmid also blocked the action of the restriction endonuclease BglI and, to a lesser extent, DraI. The recognition sequences of these restriction enzymes suggest that AcO-NPYR interacts preferentially with guanine and/or cytosine bases in DNA.

Apurinic Acid↗
PubMed1988

Alterations in pancreatic islet function produced by carcinogenic nitrosamines in the Syrian hamster.

Exposure of hamsters to 5 daily doses of 20 mg/kg N-nitrosobis(2-oxopropyl)amine (BOP) or 76 mg/kg N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP), resulted in reduced insulin secretion in freshly isolated pancreatic islets. These treatments also reduced plasma insulin and glucose levels, and were hepatotoxic. The inhibition of insulin secretion, however, was transient. Islets isolated from treated hamsters that were then placed in culture secreted elevated levels of insulin for many months. When cultured islets were directly exposed to the nitrosamines for 3 days, there was also a transient reduction of insulin secretion that was subsequently normalized after removal of the nitrosamine from the medium. These results show that BOP and HPOP modify beta-cell function both directly, and possibly indirectly, via damage to the liver. Furthermore, the lack of immediate inhibition of insulin secretion when islets were incubated in the presence of BOP or HPOP as well as glucose, suggests that the nitrosamines do not bind to the glucose receptor.

Animals↗
PubMed1987

Micronucleus formation induced in rat liver and esophagus by nitrosamines.

The rat hepatocarcinogen nitrosodimethylamine and the esophageal carcinogens nitrosomethylbenzylamine and nitrosomethylamylamine were shown to produce chromosomal damage, as manifested by micronucleus formation, in their target tissues. There was cross-reactivity in the two tissues, however, at high dose levels. Nitrosodiethylamine, which produces tumors in both the liver and esophagus in the rat, also produced micronuclei in both tissues.

Animals↗
PubMed1987

Activation of the human c-Ha-ras-1 proto-oncogene by in-vitro reaction with N-nitrosomethyl(acetoxymethyl)amine.

Reaction of N-nitrosomethyl(acetoxymethyl)amine in vitro in the presence of esterase with a plasmid containing the human c-Ha-ras-1 gene has been shown to generate a transforming oncogene when the methylated DNA is transfected into NIH 3T3 cells. Our results show that an activated nitrosamine can mutate a normal cellular proto-oncogene, a reaction that may be the necessary first step in the multistage process of tumour induction.

Animals↗
PubMed1987

Absence of urinary N-nitrosodimethylamine in fasting humans following alcohol consumption.

Fasted volunteers consumed 350 mg nitrate in beet juice; 1 h later, they consumed a volume of 10% alcohol in carbonated water sufficient to raise blood alcohol concentrations to at least 80 mg/100 ml. This alcohol concentration was then maintained over a 6-h period. During this period, and during the subsequent 12 h, no N-nitrosodimethylamine (NDMA) or any other volatile nitrosamine was excreted in the urine of the volunteers (detection limit, 0.01 mumol). Therefore, less than 0.5 mumol NDMA is likely to be present in the stomach of a fasting human at any time.

Adult↗
PubMed1986

Analysis of the immunoadjuvant octadecyl tyrosine hydrochloride.

A simple, rapid, high performance liquid chromatographic (HPLC) method for the analysis of the immunoadjuvant octadecyl tyrosine hydrochloride is described. The HPLC procedure can be applied to the direct determination of amino acid reactants present as contaminants in the adjuvant (tyrosine, ethyl tyrosine) and from this information the content of octadecanol reactant can be estimated. Further, these same determinations provide a means of monitoring immunoadjuvant stability in any vaccine preparation.

Adjuvants, Immunologic↗
PubMed1986

Alcohol consumption does not lead to urinary excretion of N-nitrosodimethylamine in the fasting human.

To test the hypothesis that N-nitrosodimethylamine (NDMA) and possibly other nitrosamines are synthesized naturally in the gastrointestinal tract, the urinary excretion of nitrosamines has been measured in people whose first pass clearance and metabolism of nitrosamines had been inhibited by administration of ethanol. Five fasted volunteers consumed 350 mg of nitrate in beet juice followed, 1 h later, by a volume of 10% alcohol in carbonated water sufficient to raise their blood alcohol concentrations to 50-80 mg/100 ml. This alcohol concentration was then maintained over a 6 h period. No NDMA or any other volatile nitrosamines were excreted in urine during this 6 h period or during the subsequent 12 h (detection limit = 0.01 mumol). These results suggest that less than 0.5 mumol NDMA, formed by endogenous nitrosation in the fasting human, is likely to be present in the stomach at any time.

Adult↗
PubMed1986

Cellular toxicity of pancreatic carcinogens.

Azaserine (CAS: 115-02-6), streptozocin (CAS: 18883-66-4; streptozotocin), and N-nitrosobis(2-oxopropyl)amine [(BOP) CAS: 60599-38-4] produce different types of pancreatic tumors in rodents. We have investigated the toxic effects of these compounds on pancreatic tissues from Wistar rats and Syrian hamsters. Inhibition of protein synthesis was used as a measure of toxicity. Pancreatic islets and acinar cells from rat and hamster were labeled with [3H]leucine for 60 minutes in vitro in the presence of the various carcinogens. Azaserine, which produces acinar cell tumors in the rat, inhibited synthesis by all tissues; rat acinar cells, however, were most sensitive. Glutamine, but not serine, provided some protection against azaserine toxicity. Streptozocin inhibited synthesis by islets of both species and acinar cells from hamster; islets were the most sensitive. BOP and N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine, which induce ductal tumors in the hamster, had no effect on any of the tissues examined. These results indicate that the specificities of the cellular toxicities of the pancreatic carcinogens parallel, to some degree, their tumorigenic effects.

Animals↗
PubMed1985

Monolayer culture of pancreatic islets from the Syrian hamster.

Pancreatic islets of Langerhans of the Syrian hamster were maintained in culture for as long as 43 wk. Islets were prepared by collagenase/hyaluronidase digestion of minced pancreas. The islets quickly attached to the plastic culture flasks and lost their spherical form as they flattened out to form circular monolayers. Few fibroblastoid cells were observed. As outward migration continued, the islets became vacuolated with the ultimate formation of monolayer rings. Throughout the culture period the beta cells continued to synthesize and secrete insulin. Furthermore, the cells maintained a responsiveness to glucose stimulation with increased rates of hormone secretion in the presence of elevated concentrations of the sugar. These studies demonstrate the suitability of Syrian hamster islets for studies involving long-term culture.

Animals↗
PubMed1985

Mechanism of DNA methylation by N-nitroso(2-oxopropyl)propylamine.

Using an in vitro assay system for measuring 7-methylguanine formation in DNA, it was demonstrated that N-nitroso(2-oxopropyl)propylamine (NOPPA) is converted into a methylating agent by a microsomal, cytochrome P-450 dependent mixed function oxidase from rat liver. Formation of propionaldehyde, but not formaldehyde, in this assay system, indicated that a single alpha-oxidation reaction on the propyl side chain of NOPPA leads to the formation of a methylating agent. A mechanism for this reaction is proposed.

Animals↗
PubMed1985

Formation of O6-methylguanine in rat liver DNA by nitrosamines does not predict initiation of preneoplastic foci.

Nitrosodimethylamine (NDMA) at 26 mumol/kg, and nitrosomethylbenzylamine (NMBzA) at 33.5 mumol/kg were equally potent in producing 7-methylguanine and O6-methylguanine in rat liver DNA. These doses were used to compare the abilities of the two nitrosamines to initiate production of putative preneoplastic foci in rat liver. Whereas NMBzA resulted in no increase above the background level of foci (0.9 +/- 0.1 foci/cm2), NDMA produced 7.5 +/- 0.6 foci/cm2. Co-administration of NDMA and NMBzA produced no more foci than NDMA alone, even though the combined effect of the two nitrosamines on DNA methylation was additive. The results suggest that methylation of hepatic DNA by nitrosamines does not predict initiation of preneoplastic foci.

Animals↗
PubMed1984

Studies on the metabolic activation of beta-keto nitrosamines: mechanisms of DNA methylation by N-(2-oxopropyl)-N-nitrosourea and N-nitroso-N-acetoxymethyl-N-2-oxopropylamine.

At pH 7.35, N-(2-oxopropyl)-N-nitrosourea (OPNU) reacted with calf thymus DNA to yield O6-methylguanine, 7-methylguanine and 3-methyladenine. Kinetic measurements of the base catalyzed decomposition of OPNU and the extent of methylation of DNA by OPNU suggested that methylnitrosourea is not formed as an intermediate product. Diazoacetone, acetic acid and methanol were identified as products of decomposition of OPNU at pH 7.35. Reaction of OPNU with N-methylmaleimide yielded the product resulting from 1,3-dipolar cycloaddition of diazomethane. Hydrolysis of N-nitroso-N-acetoxymethyl-N-2-oxopropylamine (NAMOPA) in the presence of hog liver esterase also produced diazoacetone, acetic acid and methanol. Enzymatic hydrolysis of NAMOPA in the presence of DNA produced O6-methylguanine, 7-methylguanine and 3-methyladenine. These results suggest that OPNU undergoes base-catalyzed decomposition and NAMOPA undergoes enzymatic hydrolysis to yield the same intermediate, 2-oxopropyldiazotate. This diazotate then reacts either by protonation followed by loss of water to form diazoacetone, or by internal nucleophilic attack by the diazotate oxygen on the carbonyl carbon to form an oxadiazoline intermediate which then collapses to form acetate and the methylating agent diazomethane. These reaction schemes are used to suggest the mechanism by which N-nitroso-2-oxopropylpropylamine methylates hepatic DNA in vivo.

Alkylating Agents↗
PubMed1984

Oxidation of ammonia and hydroxylamine to nitrate in the rat and in vitro.

We have demonstrated that ammonia is oxidized to nitrate in the rat. Male Sprague-Dawley rats gavaged with 1000 mumol N-15-ammonium chloride each day for 5 days were found to excrete low, but significant amounts of excess N-15-nitrate in their urines on the five days of treatment and on the five subsequent days. We recovered a total of 0.28 +/- 0.03 mumol excess N-15-nitrate (mean +/- SE) per rat, which indicates that ammonia is converted to nitrate in a yield of approximately 0.0080%. The oxidation of N-15-labeled glycine and L-glutamic acid to N-15-nitrate could not be detected. N-15-Hydroxylamine was oxidized in the rat to N-15-nitrate in a yield of 4.7%, which shows that hydroxylamine is a possible intermediate in the ammonia oxidation process. Injection of rats with Arochlor 1254, an inducer of several isozymes of cytochrome P-450, did not significantly affect the rate of endogeneous nitrate synthesis. Carbon tetrachloride, which causes hepatic lipid peroxidation, produced a small but significant increase in nitrate synthesis. We confirmed the observation that a bacterial endotoxin can greatly stimulate nitrate synthesis, and we showed that concurrent treatment with superoxide dismutase does not modify the effect of the endotoxin. An in vitro chemical model system was used to demonstrate that oxidation of ammonia to nitrate by the hydroxyl radical at physiological pH is chemically feasible. Our results are consistent with the hypothesis that ammonia is oxidized to nitrate in vivo by a non-enzymatic process which involves active oxygen species such as the hydroxyl radical. We estimate that a 215 g rat produces 3.0 mumol of nitrate per day via ammonia oxidation.

Ammonia↗
PubMed1984

Formation of O6-methylguanine in regenerating rat liver by N-nitrosomethylbenzylamine is not sufficient for initiation of preneoplastic foci.

The DNA methylating activities of N-nitrosodimethylamine (NDMA), an initiator of hepatic gamma-glutamyltranspeptidase-positive foci, and N-nitrosomethylbenzylamine (NMBzA), which does not initiate, were studied in regenerating rat liver. Equimolar doses of 14C-labelled NDMA and NMBzA (33.5 mumol/kg) were administered to male Sprague-Dawley rats 18 h after partial hepatectomy. NDMA and NMBzA both produced 7-methylguanine and O6-methylguanine. The results suggest that although the formation of O6-methylguanine may be necessary it is not sufficient for initiation of preneoplastic foci.

Animals↗