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Biomedical subjects

M D Burke

Publications and source records attributed to M D Burke.

At least 91 records · Page 5Linked to original sources
PubMed1989

The first six years' experience with the Pathology Residents' In-Service Examination, 1983-1988.

Data derived from the 1983-1988 administrations of the American Society of Clinical Pathology Residents In-Service Examination (PRISE) are presented. Data indicate an increase in participation by U.S. and Canadian pathology residency training programs (from 55% in 1983 to approximately 90% in 1988). Demographic data reflect an increase in the proportion of foreign medical graduates (from 24.8% in 1983 to 32.8% in 1988) in U.S. training programs with concomitant decrease in proportion of U.S. medical graduates (from 74.8% to 61.5%, respectively). Canadian residents comprise approximately 5% of the test population. Response surveys from residents and program directors indicate a high degree of satisfaction with the PRISE. In 1988 40.6% of all program directors thought that the PRISE satisfied their objectives very well, and 56% thought that objectives were met satisfactorily. For residents the corresponding rates were 21.2% and 70.7%. Trends in resident group performance in each subspecialty area of pathology, and the implications for residency training are discussed.

Adult↗
PubMed1988

The influence of culture medium composition on drug metabolising enzyme activities of the human liver derived Hep G2 cell line.

When grown in the standard Dulbecco's medium the human liver derived Hep G2 hepatoma cell line shows only 10-20% of the cytochrome P-450-dependent mixed function oxidase (MFO) activity of freshly isolated human adult hepatocytes. However, the MFO activities and, to a lesser extent, the activities of UDP-glucuronyltransferase and glutathione-S-transferase can be increased by altering the composition of the growth medium. Modified Earle's medium was more effective in this respect than Williams' E medium and increased the O-dealkylations of ethoxyresorufin, benzyloxyresorufin and pentoxyresorufin 50-, 30- and 10-fold, respectively.

Carcinoma, Hepatocellular↗
PubMed1988

Mixed function oxidase and UDP-glucuronyltransferase activities in the human Hep G2 hepatoma cell line.

In cultured human hepatoma cells phenolphthalein glucuronidation was increased 3-fold by 2 mM phenobarbitone (PB) in the culture medium but not by 25 microM benz(a)anthracene (BA), while 1-naphthol glucuronidation was not increased by either PB or BA. Ethoxyresorufin O-deethylation (EROD) was increased 15-fold by BA but not by PB, while the O-dealkylations of pentoxyresorufin (PROD) and benzyloxyresorufin (BROD) were increased by either PB or BA. The BROD activity increased by BA was sensitive to inhibition by alpha-naphthoflavone whereas that induced by PB was not. This suggests induction of different cytochrome P-450 isoenzymes. Control Hep G2 cells had similar glucuronide conjugation and cytochrome reductase activities to freshly isolated human adult hepatocytes, but had lower O-dealkylation and elevated microsomal epoxide hydrolase activities.

Carcinoma, Hepatocellular↗
PubMed1988

Alteration of physicians' orders by nonphysicians.

We prospectively evaluated the accuracy with which clerical and laboratory staff carried out physicians' written orders for thyroid function testing in 181 patients at two institutions. In 54% of the patients studied, support staff were found to have added or deleted one or more tests from the original written orders. When the ordering physicians were asked to identify the clinical indications for the tests they had ordered, 37% of their orders either lacked an appropriate test or included an unnecessary test request. In contrast, after clerical and laboratory staff had changed orders, only 25% of patients had inappropriate tests performed or necessary tests omitted. Clerical staff using computer-based ordering menus significantly improved the appropriateness of physicians' orders compared with clerks who lacked such guidance. Laboratory technologists who used informal, knowledge-based rules also tended to improve the appropriateness of physicians' orders. We conclude that a substantial proportion of physicians' orders for diagnostic tests may be modified during the test requisitioning process. The use of testing regimens by ward clerks and laboratory technologists may explain their ability to improve on physicians' orders.

Clinical Laboratory Information Systems↗
PubMed1988

Evidence that the catalytic differences of two structurally homologous forms of cytochrome P-450 relate to their heme environment.

Cytochromes P-450 PB3a and PB3b, which appear to be equivalent to forms b and e described by Ryan et al. [Ryan, D.E., Thomas, P.E., & Levin, W. (1982) Arch. Biochem. Biophys. 216, 272-288], have been shown to share 97% sequence homology [Suwa, Y., Mizukami, Y., Sogawa, K., & Fujii-Kuriyama, Y. (1985) J. Biol. Chem. 260, 7980-7984] yet exhibit an intriguing difference in enzymatic activity. Studies to establish the basis for this difference, including a development of the technique of surface-enhanced resonance Raman spectroscopy (SERRS), are reported. Studies on substrate binding, metabolism, and redox properties, as well as SERRS, indicate a significant difference in the heme environment of these two proteins. No significant difference in the interaction of the two proteins with P-450 reductase could be established. However, this interaction appeared sensitive to changes in ionic strength, suggesting ionic interactions are important in the functional coupling of these electron-transport components. A marked variation in the ratio of PB3a to PB3b activity in the metabolism of different substrates, which included a series of structurally similar resorufin analogues, provided further evidence that reductase coupling was not a critical factor. Therefore, the few amino acid differences observed between these proteins indicate sites that may be important in influencing the heme environment of these cytochrome P-450's.

Animals↗
PubMed1988

Dehydrogenase enzyme histochemistry on freeze-dried or fixed resin-embedded tissue.

A method has been developed for the histochemical demonstration of a variety of dehydrogenases in freeze-dried or fixed resin-embedded tissue. Seven dehydrogenases were studied. Lactate dehydrogenase, NADH dehydrogenase and NADPH tetrazolium reductase were all demonstrable in sections of paraformaldehyde-fixed resin-embedded tissue. Freeze-dried specimens were embedded, without fixation, in glycol methacrylate resin or LR Gold resin at either 4 degrees C or -20 degrees C. All the dehydrogenases except succinate dehydrogenase retained their activity in freeze-dried, resin-embedded tissue. Enzyme activity was maximally preserved by embedding the freeze-dried tissue specimens in glycol methacrylate resin at -20 degrees C. The dehydrogenases were accurately localized without any diffusion when the tissue sections were incubated in aqueous media. Addition of a colloid stabilizer to the incubating medium was not required. Freeze-drying combined with low-temperature resin embedding permits accurate enzyme localization without diffusion, maintenance of enzyme activity and excellent tissue morphology.

Animals↗
PubMed1988

Analytical versus clinical sensitivity and specificity in pregnancy testing.

A typical urine pregnancy test with the enzyme-linked immunoassay for human chorionic gonadotropin (Tandem Icon human chorionic gonadotropin) was performed as was a qualitative serum radioimmunoassay for human chorionic gonadotropin when the positive cutoff for the latter was set at 30 IU/L. There was 99.5% concordance between the two methods when performed on 871 simultaneous urine and serum specimens. Although the serum radioimmunoassay can detect levels of human chorionic gonadotropin as low as 10 IU/L, in this study the majority of patients with serum levels between 10 and 30 IU/L were not pregnant on clinical follow-up. Of nine patients with adequate clinical follow-up, a negative urine pregnancy test result, and a serum human chorionic gonadotropin level between 10 and 30 IU/L, only one proved to be pregnant. The Tandem Icon human chorionic gonadotropin urine test is sufficient for routine pregnancy testing and to rule out the need for immediate intervention in cases of ectopic pregnancy.

Chorionic Gonadotropin↗
PubMed1988

The immunocytochemical localisation and distribution of cytochrome P-450 in normal human hepatic and extrahepatic tissues with a monoclonal antibody to human cytochrome P-450.

1. The localisation and distribution of cytochrome P-450 in human tissues has been studied by immunocytochemistry using a monoclonal antibody to a major form of human hepatic cytochrome P-450, P-450hA7, which is closely related to cytochromes P-450 HLp and P-450NF. 2. Strong immunoreactivity was identified in hepatocytes, columnar absorptive epithelial cells of the small intestine, polymorphonuclear leucocytes and their precursors in the bone marrow, and in mast cells. 3. Weak immunoreactivity was present in the proximal tubules of the kidney, pancreatic acini, gall bladder epithelium, squamous epithelium and sebaceous glands of the skin, interstitial cells of the testis and luteal cells of the ovary. 4. Immunoreactivity could not be demonstrated in the adrenal gland, placenta, colonic epithelium and alveolar type II cells and Clara cells of the lung.

Adult↗
PubMed1988

Enzyme histochemical demonstration of NADH dehydrogenase on resin-embedded tissue.

We describe a method for enzyme histochemical demonstration of NADH dehydrogenase in cold (4 degrees C)-processed resin-embedded tissue. The effects on NADH dehydrogenase activity of processing tissue through a variety of dehydrating agents and embedding in three different acrylic resins were evaluated. The optimal procedure to maintain NADH dehydrogenase activity used a short (3-hr) fixation in 1% paraformaldehyde solution, followed by dehydration in acetone and embedding in glycol methacrylate resin. Embedding of tissue in resin combined preservation and accurate localization of NADH dehydrogenase activity with good tissue morphology. Blocks of the resin-embedded tissue could be stored at room temperature for at least 6 months without loss of NADH dehydrogenase activity.

Animals↗
PubMed1988

Effects of induction on the metabolism and cytochrome P-450 binding of harman and other beta-carbolines.

1. The metabolism of harman by liver microsomes from non-induced, phenobarbitone (PB)-induced and 3-methylcholanthrene (MC)-induced mice was investigated. Initial reaction rates for harman disappearance were measured and showed a 4-fold induction by PB and a 10.6-fold induction by MC. 2. The major metabolite formed with each microsomal preparation was identified as 6-hydroxyharman. 3. Microsomal cytochrome P-450 binding was measured for harman and other beta-carbolines and both Type I and Type II binding spectra were observed, being dependent upon the mode of induction.

Alkaloids↗
PubMed1987

Monoclonal antibodies against human cytochrome P-450 recognizing different pregnenolone 16 alpha-carbonitrile-inducible rat cytochromes P-450.

Six murine monoclonal antibodies against human hepatic cytochrome P-450 have been raised, using human liver microsomes (microsomal fractions) or semi-purified human cytochrome P-450 as immunogen. All six antibodies recognized the same highly purified of human liver cytochrome P-450 of molecular mass 53 kDa and gave rise to a single band at 53 kDa on immunoblots of human liver microsomes from 11 individuals. The antibodies also recognized proteins at 52 kDa and 54 kDa on immunoblots of control and induced male-rat liver microsomes, showing four different banding patterns. Antibodies HL4 and HP16 recognized a 52 kDa protein that was only weakly expressed in untreated rats and which was strongly induced by pregnenolone 16 alpha-carbonitrile (PCN) but not by phenobarbitone (PB), 3-methylcholanthrene (3MC), isosafrole (ISF), Aroclor 1254 (ARO), clofibrate or imidazole. HP10 and HL5 recognized a constitutive 52 kDa protein that was weakly induced by PCN but not by the other agents and was suppressed by 3MC and ARO. HP3 recognized a 54 kDa protein that was undetectable in control rats but was strongly induced by PB, PCN, ISF and ARO. HL3 appeared to recognize a combination of the proteins recognized by the other antibodies plus a 54 kDa protein that was weakly expressed in control rats. The constitutive proteins recognized were male-specific.

Animals↗
PubMed1987

The effects of cigarette smoke compared to 3-methylcholanthrene and phenobarbitone on alkoxyresorufin metabolism by lung and liver microsomes from rats.

The rates of metabolism of phenoxazone and a homologous series of its ethers (alkoxyresorufins) by liver and lung microsomes of rats exposed to cigarette smoke were compared with the metabolism in rats pretreated with 3-methylcholanthrene (3MC) or phenobarbitone (PB). The rate of resorufin production was dependent on the length of the ether side chain. Liver and lung microsomes from control rats differed in their activity profiles (rate of resorufin production plotted against side-chain length), showing highest activity with ethoxy- and benzyloxyresorufin respectively. 3MC and PB selectively induced hepatic microsomal resorufin production with only certain of the substrates and the two agents differed in their selectivity, inducing most greatly with ethoxy- and benzyloxyresorufin respectively. Pulmonary microsomal resorufin production was induced by 3MC with a substrate selectivity similar to that shown for liver, but PB suppressed pulmonary metabolism with all the substrates. A single, short exposure to cigarette smoke induced ethoxyresorufin O-deethylase activity transiently in liver and lung microsomes. Three consecutive daily short exposures to cigarette smoke caused a weak 3MC-like induction of liver microsomal alkoxyresorufin metabolism, but the effect on lung microsomes was like weak 3MC and PB inductions combined. It is concluded that cigarette smoke induces selected cytochrome P-450-linked alkoxyresorufin O-dealkylase activities to a similar extent in both lung and liver and that the effects of cigarette smoke are characteristic of both 3MC-type and non-3MC-type inducers.

Animals↗
PubMed1987

Human adult hepatocytes in primary monolayer culture. Maintenance of mixed function oxidase and conjugation pathways of drug metabolism.

The stabilities of several drug oxidation and conjugation pathways in human adult hepatocytes have been investigated during 72 hr culture. Cytochrome P-450-dependent mixed function oxidase was measured by the O-dealkylations of ethoxyresorufin (EROD), pentoxyresorufin (PROD) and benzyloxyresorufin (BROD), which are probes for different isozymes of cytochrome P-450 in the rat. EROD declined to 64% of initial fresh cell values after 72 hr in culture, whereas PROD increased to 162% and BROD remained relatively constant. Addition of phenobarbitone to the culture medium selectively increased PROD to a greater extent than EROD and did not affect BROD. NADPH-cytochrome c reductase and NADH-cytochrome b5 reductase were markedly labile during culture, declining to 32% and 22% of fresh cell values respectively. Epoxide hydrolase (EH) showed a large transient increase (2-5-fold) in enzyme activity 24 hr after culture, declining to fresh cell values by 48 hr. UDP-glucuronyltransferase (GT) activity towards phenolphthalein and 1-naphthol also increased (2-3-fold) during the 72 hr of culture, the greater and more rapid increase being observed with phenolphthalein glucuronidation. Sulphotransferase activity declined rapidly within 24 hr of culture, whereas reduced glutathione (GSH) levels and GSH conjugation were maintained at fresh cell values for 72 hr.

Adult↗