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Biomedical subjects

E D Brown

Publications and source records attributed to E D Brown.

At least 37 records · Page 2Linked to original sources
PubMed1995

High concentrations of the carcinogen 2-amino-1-methyl-6-phenylimidazo- [4,5-b]pyridine (PhIP) occur in chicken but are dependent on the cooking method.

Heterocyclic aromatic amines (HAAs) are mutagenic and carcinogenic compounds found in meats cooked at high temperatures. Although chicken is consumed in large quantities in the United States, there is little information on its HAA content. The objective of this study was to measure the five predominant HAAs (IQ, MeIQ, MeIQx, DiMeIQx, and PhIP) in chicken cooked by various methods to different degrees of doneness. Chicken breasts were panfried, oven-broiled, or grilled/barbecued. Whole chickens were roasted or stewed. Skinless, boneless chicken breasts were cooked to three degrees of doneness: just until done, well done, or very well done. High levels of PhIP (ranging from 12 to 480 ng/g cooked meat) were found in chicken breasts when panfried, oven-broiled, and grilled/barbecued but not in while roasted or stewed chicken. PhIP concentration increased in skinless, boneless chicken breast with longer cooking time, higher internal temperature, and greater degree of surface browning. PhIP concentration was also high in chicken breasts cooked with skin and bones. MeIQx and DiMeIQx levels increased with the degree of doneness, whereas IQ and MeIQ were not detectable in any of these chicken samples. Certain cooking methods produce PhIP, a known colon and breast carcinogen in rodents and possibly a human carcinogen, at substantially higher levels in chicken than has been reported previously in red meat.

Animals↗
PubMed1995

Urinary malondialdehyde-equivalents during ingestion of meat cooked at high or low temperatures.

Excretion of malondialdehyde (MDA)-generating substances in the urine has been suggested as an indicator of in vivo lipid peroxidation. However, MDA in the urine also reflects the amount of lipid peroxidation products consumed in the diet. We determined MDA as the thiobarbituric acid (TBA)-MDA complex in urine of 19 healthy adults (10 male and 9 female) fed large quantities (3.6-4.1 g/kg body weight) of ground beef cooked at a low or a high temperature. Subjects ate a controlled diet with no alcohol or nutritional supplements. For 7 d they consumed ground beef cooked at 100 degrees C for 20 min (low-temperature meat) followed by 7 d with meat fried at 250 degrees C for 22 min (high-temperature meat). Prior to the study, subjects consumed their normal free choice diet with moderate amounts of meat. The concentration of MDA in urine at baseline was 2.1 +/- 0.3 mumol TBA-MDA equivalents/day (mean +/- SEM). After 7 d of low-temperature meat, urinary TBA-MDA equivalents increased to 23.1 +/- 1.4 mumol/d. Urinary TBA-MDA equivalents were consistently lower (6.9-8.0 mumol/d) 1, 2, 3, and 7 d after subjects changed to high-temperature meat. After 7 d of treatment, 97% of the MDA-equivalents in the meat was recovered in 24-h urine samples. The low temperature meat had 3-4 times more MDA than did the high-temperature meat. These data indicate that the amount of meat eaten and the cooking procedures used can dramatically alter urinary MDA. Dietary sources of MDA must be controlled if urinary MDA is to be used as an indicator of oxidative stress.

Adult↗
PubMed1995

Heterocyclic amine content in fast-food meat products.

Heterocyclic aromatic amines are sometimes formed during the cooking of muscle meats, and their mutagenic and carcinogenic effects are of potential concern in the aetiology of human cancer. In a large survey of the heterocyclic amine content of foods, fried or charbroiled hamburgers, fried chicken, chicken breast sandwiches, fish sandwiches and breakfast sausages were purchased from fast-food restaurants. At least three different chains were visited per product and samples from five stores from each chain were pooled. The solid-phase extraction and HPLC method was used to analyse pooled samples for heterocyclic amine content and mutagenic activity with the Ames/Salmonella assay. Samples were analysed in a blind study which also contained quality control samples of two types, one high and one low in heterocyclic amine content and mutagenic activity. Results from the fast-food products showed undetectable levels of heterocyclic amines in 10 of 17 samples and only low levels [< or = 1 ng/g total of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx)] in the remaining samples. Compared with literature values based primarily on laboratory and home cooking conditions, fast-food meat products appear to contribute only a small percentage of the estimated daily dietary intake of heterocyclic amines.

Amines↗
PubMed1995

Lower levels of urinary 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx) in humans with higher CYP1A2 activity.

Heterocyclic aromatics amines (HAAs), such as 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), are metabolically activated by cytochrome P4501A2 (CYP1A2) and N-acetyltransferase (NAT2). We examined the relationship between CYP1A2 and NAT2 activity and the excretion of total unconjugated MeIQx in 66 healthy subjects. The subjects ate a control diet for 7 days containing lean ground beef cooked at low temperature. On day 8, they were tested for CYP1A2 and NAT2 activity by caffeine phenotyping. On the evening of day 8, subjects consumed lean ground beef cooked at high temperature containing 9.0 ng of MeIQx/g of meat. The subjects ate 3.1-4.0 g meat/kg body wt. Twelve-hour urine samples were collected and MeIQx was measured by gas chromatography-mass spectrometry. Using linear regression analyses, we found that higher CYP1A2 activity was associated with lower levels of total unconjugated MeIQx in the urine (P = 0.008) when adjusted for amount of meat eaten, while NAT2 activity showed no relationship with the latter. This suggest that a greater percentage of MeIQx is converted to metabolites such as the N-hydroxy derivative when CYP1A2 activity is higher. This finding supports the concept that inter-individual variation is CYP1A2 activity may be relevant for cancers associated with exposure to HAAs.

Adult↗
PubMed1995

MurA (MurZ), the enzyme that catalyzes the first committed step in peptidoglycan biosynthesis, is essential in Escherichia coli.

The Escherichia coli gene murZ was recently shown to encode UDP-N-acetylglucosamine enolpyruvyl transferase, which catalyzes the first committed step of peptidoglycan biosynthesis (J. L. Marquardt, D. A. Siegele, R. Kolter, and C. T. Walsh, J. Bacteriol. 174:5748-5752, 1992). The map position of murZ (69.3 min) differed from that determined for murA (90 min), a gene which had been previously proposed to encode the same activity (P.S. Venkateswaran and H. C. Wu, J. Bacteriol. 110:935-944, 1972). Here we describe the construction of a chromosomal deletion of murZ and a plasmid containing murZ under arabinose control. Growth of cells containing the murZ deletion was dependent on the expression of murZ from the plasmid. We conclude that murZ is an essential gene and encodes the sole UDP-N-acetylglucosamine enolpyruvyl transferase of E. coli. To simplify the nomenclature, we recommend that murA be used to designate the gene at 69.3 min that encodes this activity and that the designation murZ be abandoned.

Alkyl and Aryl Transferases↗
PubMed1995

Anatomic changes in the pelvis after uncomplicated vaginal delivery: evaluation with serial MR imaging.

PURPOSE: To demonstrate the normal involution process of the post-partum pelvis with serial magnetic resonance (MR) imaging. MATERIALS AND METHODS: MR imaging was performed in 14 women after uncomplicated vaginal delivery. Six women underwent serial MR examinations at less than 30 hours and at 1 week, 2 weeks, 6 weeks, and 6 months after delivery; eight women were examined only within 30 hours of delivery. The dimensions and signal intensity of the uterus and cervix and the appearance of other pelvic structures were evaluated. RESULTS: The mean length of the uterine corpus was 13.8 cm within 30 hours of delivery and 5.0 cm at 6 months. The mean length of the cervix was 5.6 cm within 30 hours of delivery and 2.9 cm at 6 months. The junctional zone was not visible before 2 weeks; however, it was visible in all cases at 6 months. The outer cervical stroma had high signal intensity less than 30 hours after delivery and intermediate signal intensity thereafter. The inner cervical stroma was visible as a low-signal-intensity stripe on all images. CONCLUSION: Knowledge of the normal MR appearance of the involuting postpartum pelvis provides a baseline for interpretation of MR images obtained during this period.

Adult↗
PubMed1995

Magnetic resonance imaging of the spleen and pancreas.

MRI of the spleen and pancreas requires specialized sequences which diminish artifacts in the upper abdomen. High temporal resolution sequences (e.g., spoiled gradient echo) acquired immediately after intravenous Gd-DTPA administration are necessary for imaging both the spleen and pancreas. In evaluating the spleen, early post Gd-DTPA images are essential as many focal disease processes (e.g., lymphomatous deposits or metastases) equilibrate rapidly (< 2 min) with splenic parenchyma. Complete pancreatic examination also requires the use of T1-weighted fat suppressed spin echo. T2-weighted images provide complementary information in a number of settings, in particular in the evaluation of islet cell tumors. Pancreatic ductal carcinoma is low signal on T1-weighted images and enhances in a diminished fashion on immediate post Gd-DTPA images. These tumors are well differentiated from focal chronic pancreatitis and islet celltumors based on their appearances on combined T1, T2-weighted and immediate post Gd-DTPA enhanced images.

Contrast Media↗
PubMed1995

Magnetic resonance imaging of the adrenal gland and kidney.

MR is able to detect and characterize the majority of disease entities which affect the adrenal glands and kidneys. In the evaluation of the adrenal glands in-phase and out-of-phase T1-weighted imaging may be the most effective noninvasive method to distinguish benign adenomas from malignant masses. T2-weighted images are sensitive and relatively specific for the investigation of pheochromocytoma. Although MRI is excellent at evaluating the kidneys, the lower cost and good image quality of CT render it the primary diagnostic tool for renal imaging. The major current applications for MRI of the kidneys include evaluation of patients with allergy to iodinated contrast, renal failure, and the characterization of complicated renal lesions. Evaluation of venous thrombus in the context of renal cancer is likely also a useful role for MRI.

Adrenal Gland Diseases↗
PubMed1994

Pan-fried meat containing high levels of heterocyclic aromatic amines but low levels of polycyclic aromatic hydrocarbons induces cytochrome P4501A2 activity in humans.

Heterocyclic aromatic amines (HAAs) are formed when meat juices are pyrolyzed. In humans HAAs are activated in vivo by cytochrome P4501A2 (CYP1A2) and N-acetyltransferase (NAT2) to mutagens or carcinogens. While activity of NAT2 is noninducible, exposure to cigarettes, polycyclic aromatic hydrocarbons, and cruciferous vegetables has been shown to induce CYP1A2 activity in humans. To date, it is unknown if pan-fried meat, which is consumed at high levels in the United States, is capable of inducing CYP1A2. In order to address this issue, we measured CYP1A2 and NAT2 activities in 66 healthy nonsmokers (33 males and 33 females) in a controlled metabolic feeding study. The study was designed to minimize the influence of known inducers of CYP1A2. Subjects consumed meat pan-fried at a low temperature (100 degrees C) for 7 days followed by 7 days of meat pan-fried at a high temperature (250 degrees C). The low temperature-cooked meat had undetectable levels of HAAs while the high temperature-cooked meat contained high amounts of HAAs [9.0 ng/g of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2.1 ng/g of 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), and 32.8 ng/g of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)]. In contrast, total polycyclic aromatic hydrocarbon content was similar in both meat samples (10.7 ng/g in low temperature-cooked meat and 10.1 ng/g in high temperature-cooked meat). At the end of each period, subjects were tested for CYP1A2 and NAT2 enzyme activity by caffeine metabolism phenotyping. NAT2 activity remained unchanged throughout the study while CYP1A2 activity increased in 47 of 65 (72%) of the subjects after consuming high temperature-cooked meat (P < 0.0002), suggesting induction by some compound(s) formed during high temperature cooking. If HAAs are shown to be human carcinogens in epidemiological studies, then meat cooked at high temperatures may pose an increased cancer risk because it contains both inducers of CYP1A2 and procarcinogens MeIQx, DiMeIQx, and PhIP known to be activated by this enzyme.

Carcinogens↗
PubMed1994

Detection and characterization of a phospholactoyl-enzyme adduct in the reaction catalyzed by UDP-N-acetylglucosamine enolpyruvoyl transferase, MurZ.

The MurZ enzyme catalyzes enolpyruvoyl transfer from phosphoenolpyruvate to the 3-OH of UDP-N-acetylglucosamine (UDP-GlcNAc) in Escherichia coli peptidoglycan biosynthesis. The kinetic mechanism of MurZ has been shown to involve the generation of a non-covalently bound tetrahedral phospholactoyl-UDP-GlcNAc intermediate [Marquardt, J.L., et al. (1993) J. Am. Chem. Soc. 115, 10398-10399]. In the work described here, MurZ overproduced in E. coli copurified with 1 equiv of bound PEP. Enzyme free of bound PEP was prepared by incubation of purified MurZ with UDP-GlcNAc followed by removal of small molecules. Addition of either [14C]PEP or [32P]PEP to PEP-free enzyme led to stoichiometric labeling. The MurZ-PEP complex was stable to 6.7 M urea, and digestion of the [32P]PEP-labeled protein followed by SDS-PAGE generated a labeled peptide of molecular weight 5000. Solution NMR of MurZ incubated with [2-13C]PEP suggested a tetrahedral phospholactoyl enzyme adduct attached via C-2 to an enzyme nucleophile. The kon for generation of the phospholactoyl enzyme in the absence of UDP-GlcNAc was 0.24 microM-1 s-1, too slow to represent the binding order of the kinetically preferred pathway since the lower limit of the second-order binding constant for PEP (kcat/Km) is 15 microM-1 s-1. Rapid chemical quench analysis under single-turnover conditions using [32P]PEP in the presence of UDP-GlcNAc demonstrated that the covalent enzyme-phospholactoyl adduct appeared and decayed on a time scale consistent with catalysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkyl and Aryl Transferases↗
PubMed1994

Kinetics, stoichiometry, and identification of the reactive thiolate in the inactivation of UDP-GlcNAc enolpyruvoyl transferase by the antibiotic fosfomycin.

Fosfomycin [(1R,2S)-1,2-epoxypropylphosphonic acid] has been shown to exert its antibiotic effect through the inhibition of UDP-GlcNAc enolpyruvoyl transferase [Kahan, F. M., et al. (1974) Ann. N.Y. Acad. Sci. 235, 364], the enzyme responsible for catalyzing the first committed step in bacterial cell wall biosynthesis. Time-dependent inactivation of MurZ by fosfomycin was found to be greatly accelerated by the presence of cosubstrate UDP-GlcNAc but could also be speeded appreciably by the unreactive substrate analog 3-deoxy-UDP-GlcNAc. These results argue against a reaction-based participation of the cosubstrate and suggest that UDP-GlcNAc has a role in influencing active site conformation critical to the inactivation event. A study of the influence of UDP-GlcNAc and fosfomycin on the kinetics of inactivation allowed the determination of dissociation constants for fosfomycin (KF = 8.6 microM) and UDP-GlcNAc (KS = 14 microM), in addition to a limiting inactivation rate constant (k(inact) = 7.4 min-1) at saturating UDP-GlcNAc and fosfomycin concentrations. Mass spectrometry of inactivated MurZ demonstrated an increase in molecular weight of 138, consistent with the covalent addition of a molar equivalent of fosfomycin (136 kDa). Titration of MurZ with fosfomycin revealed a stoichiometry of 1 molecule of inhibitor per active site when assessed using either enzyme activity or mass spectrometry as an index of modification. Peptide mapping of tryptic digests of fosfomycin-inactivated MurZ revealed modification of a unique 41-mer, the sequence of which revealed that Cys115 was the site of attachment of fosfomycin.

Alkyl and Aryl Transferases↗
PubMed1994

Expression of recombinant human casein kinase II and recombinant heat shock protein 90 in Escherichia coli and characterization of their interactions.

To assess the interaction of human casein kinase II (CKII) with the heat shock protein 90 (HSP90) class of chaperone proteins, human CKII alpha and beta subunits and beta S2A mutant were expressed and purified separately or from a tandem coexpression construct in Escherichia coli. Recombinant human HSP90 beta and recombinant yeast HSP90 as His6 constructs were also expressed in and purified from E. coli. The rhCKII S2A mutant removed the regulatory beta subunit autophosphorylation site but had no effect on catalytic efficiency with peptide or protein substrates. As a CKII substrate, recombinant hHSP90 beta displayed a Km of 9.8 microM and a kcat of 4.1 min-1 and was phosphorylated to 1.5 mol/mol, whereas ryHSP90, lacking the known serine CKII sites of hHSP90, was phosphorylated at a 19-fold lower kcat/Km ratio to levels of 0.8 mol/mol. The endoplasmic reticulum HSP90 family member Grp94 was phosphorylated to 1.4 mol/mol but, in contrast, HSC70 and FKBP25 chaperones were phosphorylated to < 0.01 mol/mol. Neither phospho nor dephospho forms of hHSP90 showed significant activation of CKII toward the peptide substrate RRREEETEEE in contrast to a previous report that activation was observed at high molar ratios of chaperone to kinase.

Amino Acid Sequence↗
PubMed1994

Rhythmicity of egg production by Heligmosomoides polygyrus in wild wood mice, Apodemus sylvaticus.

The rhythmicity of egg production by Heligmosomoides polygyrus (Nematoda) in wild caught wood mice (Apodemus sylvaticus) was studied. Faecal production followed a 24 h cycle, with peaks at 0400 h and troughs at 1300-1900 h. The patterns in eggs per gram of faeces (EPG) and total eggs were similar to each other, though the former was more accentuated. Both of these followed a 24 h cycle, with peaks coinciding with troughs in faecal production and vice versa. Faecal weight was inversely correlated with EPG, but was not significantly correlated with total eggs. The pattern in EPG presumably reflected the effect of faecal production on the total eggs excreted in each 3 h period. The observed cycle in total eggs probably describes the pattern of egg production by the worm, although other factors, such as the host's intestinal rhythms, may contribute to this cycle.

Animals↗
PubMed1994

Hypervascular malignant liver lesions: comparison of various MR imaging pulse sequences and dynamic CT.

PURPOSE: To compare the appearance of hypervascular liver lesions on gadolinium-enhanced fast low-angle shot (FLASH) imaging with T2-weighted fat-suppressed spin-echo imaging, dynamic nonequilibrium-phase FLASH imaging, and dynamic nonequilibrium-phase iodine-enhanced computed tomography (CT) and to characterize the appearance of lesions on serial postgadolinium FLASH images. MATERIALS AND METHODS: Twenty-nine patients with hypervascular malignant liver lesions were examined with dynamic contrast-enhanced CT and magnetic resonance (MR) imaging within a 1-month interval. MR sequences included T2-weighted fat-suppression, precontrast FLASH, and postgadolinium FLASH at 1 second (sinusoid phase), 45 seconds (nonequilibrium phase), and 10 minutes. RESULTS: More than five lesions were detected in 12 patients with CT, 15 patients with T2-weighted fat-suppression imaging, 16 with sinusoid-phase FLASH imaging, and 11 with nonequilibrium-phase FLASH imaging. In six patients, a statistically significant (P = .03) increase in the number of lesions detected, by category, was observed on sinusoid-phase FLASH images compared with CT images. CONCLUSION: Sinusoid-phase FLASH imaging is superior to nonequilibrium-phase imaging with MR or CT for the demonstration of hypervascular malignant lesions.

Adolescent↗
PubMed1994

Hepatic hemangiomas: a multi-institutional study of appearance on T2-weighted and serial gadolinium-enhanced gradient-echo MR images.

PURPOSE: To define the appearance of hepatic hemangiomas on T2-weighted and serial gadolinium-enhanced gradient-echo magnetic resonance (MR) images. MATERIALS AND METHODS: In four university hospitals, with 1.0- or 1.5-T MR imaging, T2-weighted and T1-weighted gradient-echo images were obtained in 66 adult patients before and at 1, 45, and 90 seconds and 10 minutes after injection of a gadolinium chelate. Hemangiomas were categorized as small (< 1.5-cm-diameter), medium (1.5-5.0-cm), and large (> 5.0-cm) tumors. RESULTS: In all, 154 hemangiomas were depicted (81 small, 56 medium, and 17 large tumors). All 154 lesions were hyperintense on T2-weighted images. Three patterns of contrast enhancement were observed: (a) uniform enhancement at 1 second (35 of 81 small lesions and no medium or large lesions), (b) peripheral nodular enhancement progressing centripetally to uniform enhancement (75 of all 154 lesions), and (c) peripheral nodular enhancement with persistent hypointensity centrally (44 of all 154 lesions, including 16 of 17 large lesions). CONCLUSION: Three patterns of enhancement of hemangiomas were observed. High signal intensity on T2-weighted images provided complementary information.

Adult↗
PubMed1994

Low-cost, office-based, screening colonoscopy.

OBJECTIVES: Performing full colonoscopy at regular intervals and removing lesions at an early stage might significantly lower the incidence and mortality of colorectal cancer. Such a program must be inexpensive, safe, and time-efficient. METHODS: Screening colonoscopy was performed on 639 patients. For a normal examination, the physician's time is limited to giving the medication for conscious sedation, performing the colonoscopy, and completing a written report form. The total charge for a normal screening colonoscopy is $150. RESULTS: Adenomatous and/or hyperplastic polyps were detected in 218 patients (34.1%). One hundred sixty adenomatous and 134 hyperplastic polyps were removed. Forty-eight percent (48.1%) of the adenomatous and 21.6% of the hyperplastic polyps were above the sigmoid colon. Six adenocarcinomas were detected in five patients. One patient had a delayed bleeding episode requiring no transfusion or therapeutic intervention, and one patient had a "post-polypectomy syndrome" requiring no therapeutic intervention. The average physician time in the endoscopy room for normal examinations was 18 min. CONCLUSIONS: Screening colonoscopy can be safely performed in an office facility. Physician time with the patient should be limited to allow a low cost that compares favorably with screening costs for other malignancies. Long-term studies to assess the capability of screening colonoscopy to lower mortality from colorectal cancer should continue.

Adenocarcinoma↗
PubMed1994

Contrast-enhanced magnetic resonance imaging of the abdomen.

The use of intravenous gadolinium chelates in imaging of the abdomen is helpful in the detection and characterization of disease entities. It is well recognized that magnetic resonance (MR) imaging is more sensitive to the presence or absence of gadolinium chelates than computed tomography is to iodine. By exploiting this strength of gadolinium and MR sequences that reduce artifacts, the usefulness of abdominal MR examinations can be maximized. As a nonspecific extracellular contrast agent, the enhancement of gadolinium chelates reflect blood delivery (capillary phase imaging), capillary permeability (interstitial enhancement), and venous drainage (late interstitial/washout enhancement). In general terms, MR evaluation of abdominal organs is benefited by imaging in both capillary and interstitial phases of enhancement since these separate phases reflect different physiological aspects of disease processes. In this review, optimized investigation using intravenous gadolinium chelates is described for diseases of the kidney, gastrointestinal tract, liver, gallbladder, pancreas, spleen, and adrenal glands. The use of newer intravenous and oral contrast agents, particularly relating to the investigation of bowel and liver diseases, is also discussed.

Abdomen↗