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F A Dolbeare

Publications and source records attributed to F A Dolbeare.

11 recordsLinked to original sources
PubMed1995

Mutagenic activity and heterocyclic amine content of the human diet.

The mutagenic activity and the mass amount of heterocyclic amines responsible for the mutagenic activity have been measured in some cooked foods. Cooked meats are the predominant source of mutagenic activity in the diet with values ranging from 0 to 10,000 revertants per gram reported in the Ames/Salmonella test with strain TA98. Several heterocyclic amines are present and have been quantified using solid-phase extraction followed by HPLC. Frying at higher temperatures and for longer times produces the greatest mutagenic response, and concomitantly, the largest amounts of heterocyclic amines. Most of the mutagenic activity in fried meat samples can be accounted for by MeIQx(2-amino-3,8-dimethylimidazo[4,5-b]quinoxaline), DiMeIQx (2-amino-3,4,8-dimethylimidazo [4,5-f]quinoxaline) and IQ (2-amino-3-methylimidazo [4,5-f]quinoline), although other heterocyclic amines are present and PhIP (2-amino-3-methyl-6-phenylimidazo[4,5-b]pyridine) mutagenic activity becomes significant at higher temperatures. Non-meat products such as baked breads can also form significant mutagenic activity, particularly when overcooked. Commercially prepared hamburgers made from meat substitutes such as tofu, wheat gluten or tempeh and fried at 210 degrees C have up to 10% of the mutagenic activity of a fried beef patty cooked under the same conditions. When detected, amounts of heterocyclic amines in fried beef patties range from a total of 0.35 ng/g for commercial beef hamburgers to 142 ng/g for a beef patty cooked over a barbecue. Dietary intake is expected to have a large range, from less than one microgram per day to over 50 micrograms per day based on current knowledge of known heterocyclic amine chemicals and heterocyclic amine-containing foods.

Amines↗
PubMed1994

Effect of cooking time and temperature on the heterocyclic amine content of fried beef patties.

The mutagenic heterocyclic amines 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) were measured in ground-beef patties fried at 150, 190 and 230 degrees C for 2-10 min on each side. Heterocyclic amines were purified using solid-phase extraction and analysed by HPLC. Recovery-corrected amounts of each heterocyclic amine were determined by the method of standard addition based on spiked samples with recoveries ranging from 40 to 70%. Mutagenic activity measured by the Ames/Salmonella test was determined for each sample. The amounts of MeIQx, PhIP, DiMeIQx and IQ increased with time and temperature of cooking. 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 2-amino-9H-pyrido[2,3-b]indole (A alpha C) were not detected in any sample. The mutagenic activity response measured for the meat extracts (TA98 revertants) was similar to the mutagenic activity calculated from the mass of heterocyclic amines present. The rate of formation of PhIP in a model system containing creatinine and phenylalanine heated in 80% diethylene glycol was compared with PhIP formation during meat frying. The apparent heats of activation were 6.5 kcal/mol in the model system compared with 6.0 kcal/mol in the fried meat patties. The increase in PhIP and MeIQx formation fitted an exponential function over the range 0 to 11 min and from 150 to 230 degrees C. This report shows clearly that increases in cooking temperature and time can have a profound effect on the amounts of heterocyclic amines generated and subsequently consumed in the diet.

Animals↗
PubMed1994

Effect of microwave pretreatment on heterocyclic aromatic amine mutagens/carcinogens in fried beef patties.

To investigate a method to reduce the amount of mutagenic/carcinogenic heterocyclic aromatic amines formed during frying of ground beef, the mutagenic activity in Salmonella strain TA98 was assessed and the amount of known heterocyclic amines was determined by solid-phase extraction and HPLC. The beef patties received microwave treatment for various times before frying. Microwave pretreatment for 0, 1, 1.5, 2 or 3 min before frying at either 200 degrees C or 250 degrees C for 6 min per side reduced heterocyclic aromatic amine precursors (creatine, creatinine, amino acids, glucose), water, and fat up to 30%, in the patties and resulted in a decrease in mutagenic activity up to 95%. The sum of the four heterocyclic aromatic amines shown to be present--2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4,8-trimethylimidazo-[4,5-f]quinoxaline (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)--decreased three- to nine-fold compared with control, non-microwaved beef patties fried under identical conditions.

Amines↗
PubMed1994

Mutagenic activity of heterocyclic amines in cooked foods.

Mutagenic heterocyclic amines are generated in foods when they are cooked at temperatures over 150 degrees C. These compounds are present from 0.1 to 50 ppb, depending on the food and cooking conditions. These heterocyclic amines are not only present in cooked red meat, fish, and chicken, but are also present at lower levels in baked and fried foods derived from grain. Mutagenicity of fried beef hamburgers cooked at 230 degrees C is 800 +/- 37 TA98 revertants per gram cooked weight. We measured 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MelQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMelQx), and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) formation at this temperature and found 3.0 +/- 2.0, 1.0 +/- 0.18, and 0.06 +/- 0.03 ng/g, respectively. 2-amino-1-methyl-6-phenylimidaz[4,5-b]pyridine (PhIP) was found at a higher concentration of 9.6 ng/g. In our laboratory we have shown these heterocyclic amines are capable of producing both reverse and forward mutations in Salmonella bacteria and forward mutations in Chinese hamster ovary cells (CHO). We have also been able to show a statistically significant increase in mutations in the pancreas of the "mutamouse" following PhIP exposure. The pancreas also shows relatively high DNA binding compared to other organs in the mouse. The number and type of mutations depend on the repair capacity of the cells for both Salmonella and CHO. In Salmonella the mutations are primarily 2-base deletions when the cells lack uvrB repair, but mutations are more complex (larger deletions and insertions) but lower in frequency when repair is functional.(ABSTRACT TRUNCATED AT 250 WORDS)

Amines↗
PubMed1982

The analysis and interpretation of DNA distributions measured by flow cytometry.

A principal use of flow cytometers is for the measurement of fluorescence distributions of cells stained with DNA specific dyes. A large amount of effort has been and is being expended currently in the analysis of these distributions for the fractions of cells in the G1, S, and G2 + M phases. Several methods of analysis have been proposed and are being used; new methods continue to be introduced. Many, if not most, of these methods differ only in the mathematical function used to represent the phases of the cell cycle and represent attempts to fit exactly distributions with known phase fractions or unusual shapes. In this paper we show that these refinements probably are not necessary because of cell staining and sampling variability. This hypothesis was tested by measuring fluorescence distributions for Chinese hamster ovary and KHT mouse sarcoma cells stained with Hoechst-33258, chromomycin A3, propidium iodide, and acriflavine. Our results show that: a) single measurements can result in phase fraction estimates that are in error by as much as 40% for G2 + M phase and 15-20% for G1 and S phases; b) different dyes can yield phase fraction estimates that differ by as much as 40% due to differences in DNA specificity; c) the shapes of fluorescence distributions and their interpretation are very dependent on the dye being used and on its binding mechanism.

Acriflavine↗
PubMed1979

Naphthol AS-BI (7-bromo-3-hydroxy-2-naphtho-o-anisidine) phosphatase and naphthol AS-BI beta-D-glucuronidase in Chinese hamster ovary cells: biochemical and flow cytometric studies.

Conditions for the biochemical and flow cytometric assay of 7-bromo-3-hydroxy-2-naphtho-o-anisidine phosphatase and beta-D-glucuronidase activities in Chinese hamster ovary cells were studied. In the biochemical assay, the pH optimum for the phosphatase activity was pH 4.6 with a Km of 10(-5) M; the pH optimum for beta-D-glucuronidase activity was pH 5.0 with a Km of 2 x 10(-5) M. For intact cells the derived constants were 3 to 10 times higher. The rate of hydrolysis of both substrates was also examined by flow cytometry. Cellular fluorescence increased linearly for only about 15 min. Diffusion of the fluorescent product probably caused nonlinearity of the fluorescence increase and was demonstrated by mixing cells incubated with substrate with those that had not been incubated. After 15 min, cells that had not been exposed previously to product or substrate contained the fluorescent product. Cells fractionated into size classes by centrifugal elutriation also were analyzed by flow cytometry for beta-D-glucuronidase activity. The activity increased linearly with the increase in cell size corresponding to the progression from G1 through S and into G2-M phases of the cell cycle.

Animals↗
PubMed1977

Flow cytometric measurement of peptidases with use of 5-nitrosalicylaldehyde and 4-methoxy-beta-naphthylamine derivatives.

Enzyme activity can be measured in single cells or in cell suspensions by either static or flow microfluorometry when a fluorogenic substrate is used. We have used amino acid derivatives of arylamines as fluorogenic substrates for tagging cellular proteinases. The liberated aromatic amine, which can diffuse from the cell, is trapped as a fluorescent insoluble Schiff-base product with 5-nitrosalicylaldehyde, with the peak of fluorescence emission shifted from lambdaem 425 nm to lambdaem 530 and 595 nm. Although the reaction is faster at pH 4 than at higher pH's, the equilibrium during the assay of certain peptidase activities is such that the liberated aromatic amine is trapped in the cell at pH values as high as 7.5. 5-Nitrosalicylaldehyde causes almost no inhibition of substrate hydrolysis at 1 mmol/liter, a concentration exceeding that required for complete trapping of reaction product. The kinetics of enzymatic reactions with four synthetic substrates are demonstrated in intact Balb 3T3 cells and sonicated preparations in the presence of 5-nitrosalicylaldehyde. Hydrolytic rates for the substrate, CBZ-ala-arg-arg-4-methoxy-beta-naphthylamine, are given for single 3T3 cells by microfluorophotometry and for suspensions of 3T3 cells by flow cytometry. The clinical value of the method is demonstrated for differentiating mixed populations of leukocytes.

2-Naphthylamine↗