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I R Rowland

Publications and source records attributed to I R Rowland.

At least 55 records · Page 3Linked to original sources
PubMed1991

Inhibition of dinitropyrene mutagenicity in vitro and in vivo using Salmonella typhimurium and the intrasanguinous host-mediated assay.

Dinitropyrenes (DNP), present in polluted air, are potent direct-acting mutagens in Salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of rat-liver S9 or microsomes. This has now been confirmed using mouse hepatic fractions. Since most in vitro test systems do not adequately simulate conditions encountered in the intact animal, we have investigated dinitropyrene mutagenicity to Salmonella in the host-mediated assay. 1,8-Dinitropyrene (1,8-DNP) given p.o. to BALB/c mice induced a weak mutagenic effect in S. typhimurium TA98 recovered from the liver 1 h after i.v. administration (optimum time). Over the entire dose range tested no toxicity to bacterial cells was detected. Mutation induction in vivo was dose-related with maximum response at 1 mg DNP/kg body weight. This optimum dose, however, was non-mutagenic to strains TA98/1,8-DNP6 (O-transacetylase-deficient) or TA98NR/1,8-DNP6 (nitroreductase- and O-transacetylase-deficient). 1,3-Dinitropyrene and 1,6-dinitropyrene were weakly mutagenic to TA98 at doses similar to 1,8-DNP. Studies with [14C]1,8-DNP showed that 1 h after oral dosing (1 mg/kg), over 100 ng of 1,8-DNP equivalents were present in the liver (= 0.73% dose). However, only about 5.5 ng were present in the bacterial pellet, suggesting that hepatic components in vivo, as in vitro, bind to DNP, thus interfering with its interaction with Salmonella.

Administration, Oral↗
PubMed1991

Influence of dietary protein and gut microflora on endogenous synthesis of nitrate induced by bacterial endotoxin in the rat.

Germ-free (GF) rats were maintained on a diet marginally adequate in protein, with and without a supplement of NH4Cl. Their urinary excretion of total nitrogen, nitrate, urea and creatinine was measured before and for 4 days after injection of Escherichia coli endotoxin (lipopolysaccharide; LPS). Although more nitrogen was excreted by rats on the diet supplemented with NH4Cl, nitrate excretion was increased to a similar extent in rats on both diets. This suggests that oxidation of ammonia released by deamination of amino acids is an unlikely pathway of nitrate synthesis. In a second experiment, nitrate excretion before and after injection of LPS was measured in GF and conventional (CV) rats given high- or low-protein diets. Urinary 3-methylhistidine (3MH) was measured as an index of breakdown of tissue protein. In both environments, nitrate excretion was significantly greater, before and after LPS administration, by rats on the high-protein diet than by their counterparts on the low-protein diet, and was generally greater by GF than by CV rats. Since only small, non-significant rises in urinary 3MH were observed after LPS treatment, it was concluded that the bulk of the nitrogen required for nitrate synthesis in response to endotoxin is derived from dietary protein rather than from nitrogenous products of tissue breakdown.

Administration, Oral↗
PubMed1991

Endogenous N-nitrosation in man assessed by measurement of apparent total N-nitroso compounds in faeces.

The faecal concentration of substances responding to the chemical test for N-nitroso compounds (apparent total N-nitroso compounds, ATNC) was investigated in human subjects consuming their normal free-choice diet. Concentrations ranged from 40 to 590 micrograms (N-NO)/kg faeces. To ascertain the likely relative contributions of endogenous ATNC formation and preformed, dietary ATNC, the subjects consumed a diet low in nitrate and ATNC for 8 days. At the end of this period, ATNC had decreased substantially with concentrations ranging from below the 40 micrograms (N-NO)/kg detection limit up to 143 micrograms (N-NO)/kg, mean 82 micrograms (N-NO)/kg. On supplementing this diet with 300 mg nitrate/day, faecal ATNC levels increased markedly. On the third day of this regime, values were in the range 73-714 micrograms (N-NO)/kg with a mean of 307 micrograms (N-NO)/kg. The results, together with the known limited occurrence of ATNC in the majority of foodstuffs so far tested, generally non-detectable or less than 100 micrograms (N-NO)/kg, suggest that endogenous formation via species derived from dietary nitrate is likely to be an important source of ATNC in human faeces.

Adult↗
PubMed1990

Dietary fat modifies the in vivo mutagenicity of some food-borne carcinogens.

Female BALB/c mice were fed a low fat diet (1% safflower oil, by weight) or one supplemented with 25% (by weight) of beef fat or olive oil. The abilities of these diets to modify the in vitro and in vivo hepatic conversion of the dietary carcinogens aflatoxin B1, 2-amino-3, 4-dimethylimidazo[4,5-f]quinoline (MeIQ) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) to bacterial mutagens was evaluated. Dietary olive oil appeared to increase the metabolism of both MeIQ and Trp-P-2 to bacterial mutagens in vivo using the intrasanguineous host-mediated assay. Feeding mice either of the high-fat diets increased hepatic conversion of these two compounds to bacterial mutagens in vitro. Dietary fat had no effect on the metabolism of aflatoxin B1. Subsequent experiments suggested that the in vivo effects of dietary olive oil on MeIQ and Trp-P-2 mutagenesis were due to the induction of hepatic enzyme activities rather than to increased rates of uptake of the carcinogen from the gut-lumen.

Aflatoxin B1↗
PubMed1990

Effects of Escherichia coli lipopolysaccharide on nitrate synthesis and on nitrosation of proline in rats.

Male Ola:SD rats were fed purified diets containing 5 or 20% lactalbumin as the protein source, with or without concomitant administration of Escherichia coli lipopolysaccharide (50-250 micrograms/kg, ip), and changes in 24-hr urinary nitrate excretion, plasma urea, plasma-nitrate pool size and 24-hr urinary nitrosoproline excretion were measured. Urinary nitrate and urinary 14C-nitrosoproline excretion (after oral [14C]proline administration) were significantly greater for rats receiving the high-protein diet compared with those on the low-protein diet. The co-administration of lipopolysaccharide increased nitrate excretion in both diet groups (although the increase was greatest (relatively) in the animals fed 5% lactalbumin), but did not significantly alter urinary nitrosoproline excretion by either group. Plasma urea concentrations and plasma-nitrate pool size were increased by a high-protein diet and/or lipopolysaccharide administration. These findings suggest that treatments which alter the availability of nitrate in vivo are not necessarily associated with increased nitrosation of proline.

Animals↗
PubMed1990

Distribution and excretion of 1,8-dinitro[14C]pyrene in the mouse.

The disposition of the environmental pollutant and potent mutagen and carcinogen, 1,8-dinitropyrene (DNP) in female BALB/c mice was investigated. In the first 48 h after oral administration of 1,8-dinitro[4,5,9,10-14C]pyrene ([14C]DNP), 42% of the dose was eliminated in the faeces and 12% in the urine. Faeces was the major pathway of excretion with 45% of the dose being eliminated by this route in 9 days. Distribution of DNP in various tissues (blood, liver, spleen, lungs, kidneys, stomach, small and large intestine) was studied over 9 days. There was a linear increase in the concentration of radioactive material in the blood, liver and kidneys up to 6 h after [14C]DNP administration, representing 0.27, 2.9 and 0.21% of the radioactive dose, respectively. The corresponding figures after 24 h decreased to 0.1, 1.6 and 0.12%, respectively. In comparison, radioactivity present in the spleen and lungs was low and did not significantly change with time. In studies with ligated sections of the gastrointestinal tract, DNP absorption was from the small and large intestine and there was none from the stomach. The rate of absorption of DNP from the small intestine was greater than that from the large intestine, although overall uptake of the compound was poor (more than 80% of the original dose was recovered from the ligated small intestine after 120 min). The data from these studies suggest that although absorption of orally administered DNP is slow, the compound or its metabolites persist in the body for long periods and the liver should be considered as the major target organ.

Administration, Oral↗
PubMed1990

Activation and detoxification of 1,8-dinitropyrene by mammalian hepatic fractions in the Salmonella mutagenicity assay.

1,8-Dinitropyrene (DNP) is a potent, direct-acting mutagen to Salmonella typhimurium TA98 due to activation by bacterial metabolism. We have studied the effects of uninduced and Aroclor-induced rodent liver post-mitochondrial supernatant (S9), microsomes or cytosolic preparations on its activity. With the plate incorporation protocol, the reported S9-mediated inhibition of mutagenicity was confirmed and shown to be greater after induction when equivalent levels of protein were plated. Cytosol increased mutagenicity considerably whereas the inhibitory effect of S9 could be attributed to the microsomal fraction. The activating and detoxifying capacities of the various hepatic fractions derived from male Sprague-Dawley rats and female BALB/c mice were similar. In the absence of hepatic preparations, DNP mutagenicity was much lower in TA98/1,8DNP6 (deficient in transacetylase) than in TA98, although mutagenic activity could be still increased in the former strain by addition of uninduced cytosol. When DNP was pre-incubated in a liquid assay with S9 before addition of TA98, inhibition occurred and was time dependent. Thus the overall detoxifying effect of S9 is independent of bacterial metabolism. Furthermore, inhibition occurred under conditions where cytosol and microsomal components of S9 were kept together, indicating that the detoxifying effect of the microsomes predominates. The data therefore suggest that the microsomal-mediated detoxification by S9 may be due to the presence of an inhibitory component, enzymatic or otherwise, whose concentration is increased after Aroclor-induction. Nitro-reductase activities detected in TA98 and TA98/1,8-DNP6 were 10-fold higher than those in the mammalian fractions, although the activities in the latter increased to the bacterial enzyme levels after incubation of induced S9 or microsomes, but not cytosol, with an NADPH-generating system.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Cytochemical localization of mercury in Saccharomyces cerevisiae treated with mercuric chloride.

We describe a cytochemical method for localizing mercury at the electron microscopic level in the yeast Saccharomyces cerevisiae. After addition of a lethal concentration of mercuric chloride to growing yeast cells, mercury was associated with the cell wall and cytoplasmic membrane. Little or no mercury was present in the cytoplasm. Electron probe X-ray microanalysis (EPMA) confirmed that the cytochemical reaction, visualized as mercury-silver complexes, was localized in dense bodies consisting of a core of mercury sulfide polymers surrounded by a shell of silver atoms.

Electron Probe Microanalysis↗
PubMed1989

Developmental changes in hepatic activation of dietary mutagens by mice.

Metabolic activation of the food mutagens 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and aflatoxin B1 by female BALB/c mice of different ages (2-24 weeks) was investigated in vivo and in vitro using Salmonella typhimurium TA98 as the indicator organism. The in vivo activation of the three mutagens was investigated in 4- and 24-week-old mice using an intrasanguineous host-mediated assay. All three compounds showed reduced levels of activation with the older hosts. Hepatic S9 fractions from female mice of varying ages between 2 and 24 weeks were used in the in vitro mutagenicity assay. To achieve optimal activation to bacterial mutagens, 5% S9 was required for aflatoxin B1 and Trp-P-2 and 10% S9 for MeIQ; age of donor generally had little effect on the profile of these protein activation curves. Under these optimal conditions MeIQ and Trp-P-2 both exhibited, as before, age-dependent decreases in activation over a wide range of mutagen concentrations, however the in vitro activation of aflatoxin showed no consistent change with age. Spectrophotometric measurements of S9 cytochrome P-450 content showed a decrease in concentration with increasing age, but this was not sufficient to account for changes observed in hepatic mutagen activation. However, changes in the activities of certain cytochrome P-450 isoenzymes and cytosolic GSH-transferases, which in turn result in changes in the activation and detoxification capacity of the liver, would appear to explain age-dependent changes in the activity of mutagens in vivo.

Aflatoxin B1↗
PubMed1989

Effect of dietary fibre on the mutagenicity and distribution of 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ).

Female BALB/c mice were fed either a fibre-free diet or one supplemented with 30% wheat-bran for 5 weeks. The ability of these mice to convert MeIQ to a bacterial mutagen in vivo was determined using intrasanguinous host-mediated bacterial mutation assays. Less mutagenic activity was detected in the livers of mice fed the bran-supplemented diet compared with those fed the fibre-free diet. Subsequent experiments demonstrated that the effect of brain was not due to modifications in hepatic metabolism, but to changes in uptake of MeIQ from the gastrointestinal tract.

Administration, Oral↗
PubMed1989

Modified mutagen activation in hepatic fractions from rats fed dietary rutin--interaction between gut flora and host metabolism.

Male Sprague-Dawley rats were fed a purified diet or one supplemented with the glycosidic plant flavonoid (+)rutin for 14 days. Rutin treatment significantly increased caecal bacterial beta-glucosidase activity (responsible for the conversion of rutin to the flavonoid quercetin) and there was an associated increase in the capacity of hepatic fractions (S-9) to activate the food pyrolysis products IQ, MeIQ and MeIQx to bacterial mutagens in vitro. Hepatic conversion of aflatoxin B1 to a mutagen was unaltered while in vitro activation of quercetin was significantly lower in tissue fractions from the rutin-fed rats compared with those from controls. Rutin treatment was without effect, however, on a number of hepatic cytochrome P-450-dependent mixed-function oxidase activities. The results suggest that products of bacterial metabolism of rutin formed in the hindgut may influence the activity of hepatic enzymes involved in the activation of certain classes of mutagen.

Animals↗
PubMed1989

Modification of in vivo heterocyclic amine genotoxicity by dietary flavonoids.

Female BALB/c mice were fed diets containing equimolar amounts of quercetin or its glycoside, rutin, for 5 weeks. These mice were used either in host-mediated bacterial mutation assays or as sources of hepatic microsomes. In host-mediated bacterial mutation assays using radiolabelled mutagens, the heterocyclic amines 2-amino-3,5-dimethyl[4,5-f]imidazoquinoline (MeIQ) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) induced greater numbers of revertants in mice fed either of the flavonoid diets compared with control. Experiments using hepatic microsomes revealed that although feeding mice either flavonoid produced slight changes in some parameters of hepatic xenobiotic metabolism (mixed function oxidase and glutathione transferase activities), microsomes from quercetin-fed mice were more potent activators of both MeIQ and Trp-P-2 compared with microsomes from control or rutin-fed mice. This difference in microsomal ability may be due to the different biological availability of the two flavonoids within the gastrointestinal tract.

Animals↗
PubMed1989

The influence of incubation pH on the activity of rat and human gut flora enzymes.

The activities of three bacterial biotransformation enzymes (beta-glucuronidase, beta-glucosidase, nitrate reductase) were determined in suspensions of rat caecal contents or human faeces over the pH range 6-8. All three enzymes were influenced by pH, as exemplified by beta-glucosidase activity which diminished as pH increased. In other instances the rat and human flora showed distinct profiles, with nitrate reductase activity undetectable in human faeces below pH 6.6, whereas the rat caecal flora displayed optimal reduction of nitrate around neutrality. The most pronounced host-species difference was found with beta-glucuronidase, which showed maximal activity at pH 6.0 in human faecal bacteria, while the rat caecal flora expressed greatest activity at pH 8.0. All three enzyme activities were associated with that fraction of rat caecal or human faecal material sedimented by centrifugation at 5000 g for 15 min, with little or no metabolism occurring in the 11,000 g supernatant fluid. The results demonstrate that pH has a pronounced effect on the enzymic activity of bacterial preparations from rat and human sources.

Animals↗
PubMed1988

Protein-related differences in the excretion of nitrosoproline and nitrate by the rat--possible modification of de novo nitrate synthesis.

Male Ola:SD rats were fed purified diets containing 5 or 20% lactalbumin as the source of protein, and the daily urinary excretion of nitrate and nitrosoproline was measured. Animals fed the high-protein diet consistently excreted more nitrate and nitrosoproline than littermates fed the low-protein ration, despite a similar, negligible amount of nitrate in both diets. Furthermore, whereas nitrite administration enhanced nitrosoproline excretion in both diet groups, nitrate administration increased nitrosamine output in the low-protein animals but did not affect nitrosation by rats given the 20% lactalbumin ration. Animals fed the 5% lactalbumin diet produced a smaller volume of urine than did the 20% diet group but other measurements of renal function were comparable for both treatments. The results suggest differences in endogenous nitrosation between rats fed diets high or marginal in protein, possibly reflecting decreased nitrate synthesis in the low-protein group.

Animals↗
PubMed1988

An investigation of the endogenous formation of apparent total N-nitroso compounds in conventional microflora and germ-free rats.

The endogenous formation of apparent total N-nitroso compounds (ATNC) has been investigated in germ-free (GF) and conventional (CV) microflora rats as a function of the drinking-water nitrate concentration. ATNC levels were below the 40 micrograms (N-NO)/kg detection limit in the blood, liver, kidney, spleen and small intestine of all CV and GF rats. For the CV rats ATNC were detected in concentrations of up to 370 micrograms (N-NO)/kg in the large intestine and up to 50 micrograms (N-NO)/kg in the stomach and there was a significant positive correlation between ATNC formation and the drinking-water nitrate level. Comparison of these results with those from GF rats showed that the ATNC in the stomach and large intestine of the CV animals were formed by microbial action, most probably involving bacterial nitrate-reductase activity.

Animals↗
PubMed1988

Distribution of radiolabelled [2-14C]IQ and MeIQx in the mouse.

The kinetics of distribution of radiolabelled [2-14C]IQ (2-amino-3-methylimidazo[4,5-f]quinoline) and [2-14C]MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline) following the oral administration to BALB/c mice of single doses were studied. Both compounds were taken up into the blood-stream and other tissues rapidly after administration and approximately 20-25% of the radioactive dose of IQ or MeIQx was excreted in urine over 6 h, reflecting the rapid absorption of the mutagens. Significantly greater levels of MeIQx than IQ were isolated from the lungs and blood of treated mice. In studies of the uptake of IQ from closed sections of the gut, little IQ was absorbed from the stomach. Although there was some evidence that it could be absorbed from the large intestine, the primary site of IQ absorption was the small intestine.

Administration, Oral↗