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Biomedical subjects

M A Turner

Publications and source records attributed to M A Turner.

At least 37 records · Page 2Linked to original sources
PubMed2000

Primary sclerosing cholangitis: evaluation with MR cholangiography-a case-control study.

PURPOSE: To determine the accuracy of magnetic resonance (MR) cholangiography for detection of primary sclerosing cholangitis (PSC) and localization of PSC in the biliary tract. MATERIALS AND METHODS: In a prospective case-control study involving 102 patients, the MR cholangiograms obtained in 34 patients with PSC established with endoscopic retrograde cholangiopancreatography (ERCP) were compared with the MR cholangiograms obtained in 68 age-matched control patients with hepatobiliary diseases other than PSC. Two abdominal radiologists conducted an independent, blinded random review of the MR cholangiograms to assess for the presence or absence of PSC and determine the location of PSC in the biliary tract, and then compared the findings with those at ERCP. RESULTS: MR cholangiography was found to be accurate in detecting PSC and in defining the extent of disease. In the detection of PSC, the sensitivities were 88% and 85%; specificities, 97% and 92%; positive predictive values, 94% and 85%; and negative predictive values, 94% and 93% for readers 1 and 2, respectively. Interobserver agreement was excellent (kappa = 0.79). In the localization of extrahepatic PSC, the sensitivities were 83% and 89%; and specificities, 83% and 83% for readers 1 and 2, respectively. Interobserver agreement was good (kappa = 0.62). In the localization of intrahepatic PSC, the sensitivity was 87% for both readers; interobserver agreement was good (kappa = 0.71). CONCLUSION: MR cholangiography enables accurate detection and localization of PSC.

Adult↗
PubMed2000

Structure and function of S-adenosylhomocysteine hydrolase.

In mammals, S-adenosylhomocysteine hydrolase (AdoHcyase) is the only known enzyme to catalyze the breakdown of S-adenosylhomocysteine (AdoHcy) to homocysteine and adenosine. AdoHcy is the product of all adenosylmethionine (AdoMet)-dependent biological transmethylations. These reactions have a wide range of products, and are common in all facets of biometabolism. As a product inhibitor, elevated levels of AdoHcy suppress AdoMet-dependent transmethylations. Thus, AdoHcyase is a regulator of biological transmethylation in general. The three-dimensional structure of AdoHcyase complexed with reduced nicotinamide adenine dinucleotide phosphate (NADH) and the inhibitor (1'R, 2'S, 3'R)-9-(2',3'-dihyroxycyclopenten-1-yl)adenine (DHCeA) was solved by a combination of the crystallographic direct methods program, SnB, to determine the selenium atom substructure and by treating the multiwavelength anomalous diffraction data as a special case of multiple isomorphous replacement. The enzyme architecture resembles that observed for NAD-dependent dehydrogenases, with the catalytic domain and the cofactor-binding domain each containing a modified Rossmann fold. The two domains form a deep active site cleft containing the cofactor and bound inhibitor molecule. A comparison of the inhibitor complex of the human enzyme and the structure of the rat enzyme, solved without inhibitor, suggests that a 17 degrees rigid body movement of the catalytic domain occurs upon inhibitor/substrate binding.

Adenosylhomocysteinase↗
PubMed1999

Crystal structure of an inactive duck delta II crystallin mutant with bound argininosuccinate.

Delta-crystallin, the major soluble protein component of avian and reptilian eye lenses, is highly homologous to the urea cycle enzyme, argininosuccinate lyase (ASL). In duck lenses, there are two highly homologous delta crystallins, delta I and delta II, that are 94% identical in amino acid sequence. While delta II crystallin has been shown to exhibit ASL activity in vitro, delta I is enzymatically inactive. The X-ray structure of a His to Asn mutant of duck delta II crystallin (H162N) with bound argininosuccinate has been determined to 2.3 A resolution using the molecular replacement technique. The overall fold of the protein is similar to other members of the superfamily to which this protein belongs, with the active site located in a cleft formed by three different monomers in the tetramer. The active site of the H162N mutant structure reveals that the side chain of Glu 296 has a different orientation relative to the homologous residue in the H91N mutant structure [Abu-Abed et al. (1997) Biochemistry 36, 14012-14022]. This shift results in the loss of the hydrogen bond between His 162 and Glu 296 seen in the H91N and turkey delta I crystallin structures; this H-bond is believed to be crucial for the catalytic mechanism of ASL/delta II crystallin. Argininosuccinate was found to be bound to residues in each of the three monomers that form the active site. The fumarate moiety is oriented toward active site residues His 162 and Glu 296 and other residues that are part of two of the three highly conserved regions of amino acid sequence in the superfamily, while the arginine moiety of the substrate is oriented toward residues which belong to either domain 1 or domain 2. The analysis of the structure reveals that significant conformational changes occur on substrate binding. The comparison of this structure with the inactive turkey delta I crystallin reveals that the conformation of domain 1 is crucial for substrate affinity and that the delta I protein is almost certainly inactive because it can no longer bind the substrate.

Amino Acid Sequence↗
PubMed1999

Benign diseases of the biliary tract: evaluation with MR cholangiography.

MR cholangiography (MRC) is a noninvasive, rapid means of evaluating the biliary tract that, in many instances, may replace invasive procedures such as diagnostic endoscopic retrograde cholangiography and percutaneous transhepatic cholangiography. This article describes and illustrates the MRC features of benign diseases of the biliary tract such as choledocholithiasis; intrahepatic bile duct calculi; congenital anomalies, including aberrant bile ducts and choledochal cysts; postsurgical strictures; and strictures related to chronic pancreatitis.

Biliary Tract↗
PubMed1999

Treatment of forensic patients: an expanding role for public psychiatric hospitals.

This article explores the increased role of state-operated public psychiatric hospitals in treating forensic patients. Patients with a forensic legal status have a mental illness and are involved with the criminal justice system. Using data from Missouri's forensic system, the article compares the characteristics of voluntary hospital patients with those of the largest hospitalized group of forensic patients--those found not guilty by reason of insanity (NGRI). Overall, NGRI patients tended to be higher functioning, less likely to have committed assaultive acts, and more likely to have substance abuse and personality disorder diagnoses. The article explores the treatment needs of forensic patients who reside in public psychiatric hospitals and discusses the effect of the strong presence of forensic patients in public psychiatric hospitals on social work practice, including clinical work with forensic patients, social work administration, and social work advocacy.

Criminal Law↗
PubMed1999

Anion efflux from cytotrophoblast cells derived from normal term human placenta is stimulated by hyposmotic challenge and extracellular A23187 but not by membrane-soluble cAMP.

The regulation of placental anion transport influences fetal accretion and placental homeostasis. We investigated whether efflux of 125I- or 36Cl- from multinucleated cytotrophoblast cells derived from human term placenta is regulated by one of three stimuli: (a) the calcium ionophore A23187, (b) a 'cocktail' of agents designed to raise intracellular levels of cAMP, (c) a hyposmotic solution. After loading with the appropriate isotope for 2 h and thorough washing, cells were exposed to sequential aliquots of buffer applied and removed each minute. Following an equilibration period of 5 min one of the stimuli was applied at room temperature At the end of the experiment the cells were lysed to give a lysate count which was used to express the count obtained from each aliquot as percentage efflux of that possible for that minute. The cAMP 'cocktail' and A23187 were applied for 5 min; the hyposmotic solution was applied for 10 min. The results for 125I- at 7 min showed that the mean efflux in the presence of hyposmotic shock was greater than control (5.7 +/- 1.0% min-1 versus 2.2 +/- 0.1% min-1, respectively; mean +/- S.E.M., n = 4 placentas). Similarly mean efflux at 6 min in the presence of A23187 was also significantly greater than control (6.5 +/- 1.9% min-1 versus 2.6 +/- 1.0% min-1, respectively, n = 3 placentas). The mean efflux in the presence of the cAMP cocktail was not different from control at any time point. The results were qualitatively the same if 36Cl- was used in the place of 125I- and when the experiment was performed with 36Cl- in a HCO3- buffer gassed with CO2. Mean 125I- efflux at 6 min in response to hyposmotic challenge was 33% less (P < 0.01) in the presence of 1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 37% less (P < 0.005) in the presence of 10 microM tamoxifen but no different if the hyposmotic solution was nominally calcium free. We conclude that there are differential effects of second messengers on anion efflux from the differentiated cytotrophoblast cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1999

Orthotopic liver transplantation: evaluation with MR cholangiography.

PURPOSE: To determine the accuracy of magnetic resonance (MR) cholangiography for demonstration of the biliary tract and detection of biliary complications in patients who have undergone orthotopic liver transplantation. MATERIALS AND METHODS: Breath-hold half-Fourier rapid acquisition with relaxation enhancement MR cholangiography was performed in 25 patients who had undergone orthotopic liver transplantation. MR cholangiograms were prospectively and independently interpreted by two radiologists for depiction of the biliary tract and ductal anastomosis and for complications (eg, biliary dilatation, stricture, stones). MR cholangiographic findings were correlated with findings from direct cholangiography (n = 24) and surgery (n = 1). RESULTS: MR cholangiography completely demonstrated first-order intrahepatic bile ducts in 23 (92%) patients, the donor extrahepatic bile duct in 25 (100%), the recipient extrahepatic bile duct in 17 of 18 (94%), and the anastomosis in 24 (96%). The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of MR cholangiography for detection of biliary dilatation and stricture were each 100%. Complete interobserver agreement occurred in the detection of biliary dilatation and stricture. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of MR cholangiography for detection of stones were 100% for one radiologist and 86%, 100%, 96%, 100%, and 95%, respectively, for the other. Both radiologists agreed on the diagnosis of bile duct stones in six of seven cases (kappa = 0.90). CONCLUSION: MR cholangiography enables accurate depiction of the biliary tract and detection of biliary complications in patients with an orthotopic liver transplant.

Adolescent↗
PubMed1999

Generating novel ideas: fluency performance in high-functioning and learning disabled individuals with autism.

Tasks of fluency tap the ability to generate multiple responses spontaneously following a single cue or instruction. The present study compared the fluency performance of subjects with autism and clinical control subjects at two different levels of ability (high-functioning subjects with a verbal IQ of 76 or greater, and globally learning disabled subjects with a verbal IQ of 74 or below). A battery of tasks was employed to assess subjects' word fluency (for letters and semantic categories), ideational fluency (for uses of objects and interpretations of meaningless line drawings), and design fluency (for abstract meaningless designs). Subjects with autism showed reduced fluency for both the word and ideational fluency tasks, generating significantly fewer responses than the clinical control subjects. Results were particularly striking for the ideational fluency tasks. On these tasks, autistic subjects produced very low response totals, with the performance of the high-functioning subjects with autism equivalent to that of the learning disabled subjects with autism and significantly inferior to that of the learning disabled control individuals. In contrast, the results of the design fluency paradigm paint a different picture. This paradigm revealed no significant difference in the quantity of designs generated by the subjects with autism and the control subjects but a clear qualitative difference, with the autistic group producing significantly higher rates of disallowed and perseverative responses. Whilst the results of the word and ideational fluency tasks are suggested to support the hypothesis that individuals with autism are impaired in the generation of novel responses and behaviour, the results of the design fluency task are equally consistent with an impairment in the regulation of behaviour through inhibition and/or monitoring. The implications of these findings for the study of executive function abilities in autism are discussed.

Adolescent↗
PubMed1999

Advances in continuous, noninvasive hemodynamic surveillance. Impedance cardiography.

In the current climate of shrinking health care reimbursement and increasing importance of patient centered care, impedance cardiography is one method of enhancing quality of patient care and appropriate use of resources. Hemodynamic and thoracic fluid status data may be obtained quickly, accurately, and without risk, providing a global clinical perspective. Patients benefit from the ability to immediately obtain real time hemodynamic data, particularly those patients who otherwise may not be afforded a high level of monitoring or those needing hemodynamic monitoring when assessment and treatment are delayed because of inaccessibility of critical care beds or in the cardiac catheterization laboratory. Application of a technology assessment model to impedance cardiography illustrates the utility of this method of hemodynamic monitoring. Careful review and critique of the literature differentiates the available impedance technologies, supports use in areas not traditionally associated with hemodynamic monitoring, such as the home and emergency department, and validates the use of impedance cardiography in place of, or as an indication for, pulmonary artery catheterization.

Cardiac Output↗
PubMed1999

Magnetic resonance pancreatography (MRP).

Magnetic resonance pancreatography (MRP) is a technique that permits accurate evaluation of the pancreatic duct without instrumentation, contrast material administration, or ionizing radiation. Because MRP is entirely noninvasive, MRP avoids complications associated with endoscopic retrograde pancreatography (ERP) such as pancreatitis and perforation. MRP allows for the noninvasive evaluation of patients with acute and chronic pancreatitis, variant anatomy of the pancreatic duct, pancreatic duct trauma, and pancreatic neoplasia. MRP yields diagnostic information in the setting of a failed or incomplete ERP. When MRP is performed in conjunction with conventional abdominal MR, the result is a comprehensive examination of the pancreatic duct as well as the pancreas and other solid organs of the abdomen.

Acute Disease↗
PubMed1999

Recurrent acute pancreatitis caused by a gastric duplication communicating with an aberrant pancreas.

A 24-year-old female patient who had suffered from recurrent bouts of acute pancreatitis for over 3 years was found on endoscopic retrograde cholangiopancreatography to have an aberrant pancreatic duct that terminated in a cyst. An aberrant lobe of pancreas had been discovered at exploratory laparotomy 3 years previously and was left untreated. Excision of the aberrant lobe of pancreas and accompanying gastric duplication cyst was curative. This case illustrates the importance of obtaining endoscopic retrograde cholangiopancreatography in all young individuals with recurrent pancreatitis to detect this rare, but curable, cause of pancreatitis.

Acute Disease↗
PubMed1998

Bioaccumulation of radionuclides in fertilized Canadian Shield lake basins.

Radionuclide tracers of heavy metals (59Fe, 60Co, 65Zn, 75Se, 85Sr, 134Cs and 203Hg) representing potential contamination from nuclear power plants, industry and agriculture were added to separate basins of Lake 226, Experimental Lakes Area, northwestern Ontario. The two basins were part of a eutrophication experiment and differed in their trophic status; the north basin (L226N) was eutrophic whereas the south basin (L226S) was mesotrophic. Our objective was to determine the uptake of the radionuclides by biota and the effect of lake trophic status on their bioaccumulation. The trophic status of the lakes did not appear to have a marked effect on the accumulation of radionuclides by the biota. This may have been because of a mid-summer leakage of nutrients between the basins which enhanced primary production in L226S, because there is a time lag between primary production and the availability of the radionuclides to the fishes or because trophic status does not affect the uptake of at least some of these radionuclides. However, there was a tendency for faster uptake of the radionuclides in L226N by fish than L226S, but the differences were not significant. Concentrations in the biota generally decreased in the order: fathead minnow > pearl dace > tadpoles > slimy sculpin > leeches. Concentrations in biota generally decreased in the order. 65Zn > 203Hg > 75Se > 134Cs > 60Co > 85Sr = 59Fe. Cobalt-60 concentrations in tadpoles were greater than in the other biota. Radionuclide concentrations in the tissues of lake whitefish indicated that uptake was predominantly from food. Radionuclide concentrations were usually higher in the posterior gut, liver and kidney than in other tissues, whereas body burdens were generally high in the muscle for 75Se, 134Cs and 203Hg; kidney and gut for 60Co; and bone for 65Zn and 75Se. Mercury-203 burdens were also high in the bone and gut.

Agriculture↗
PubMed1998

Intragenic complementation at the argininosuccinate lyase locus: reconstruction of the active site.

Intragenic complementation has been observed at the argininosuccinate lyase (ASL) locus and the ASL alleles in the ASL-deficient cell strains of two complementation phenotypes have been identified. The frequent complementers, strains that participate in the majority of the complementation events, were found to be either homozygous or heterozygous for the Q286R allele, while the high-activity complementers, those strains in which complementation is associated with a high restoration of activity, were found to be either homozygous or heterozygous for the D87G allele. Direct proof of the intragenic complementation observed at the ASL locus has been obtained with the co-expression of the D87G and Q286R alleles in COS cells. A significant increase in the ASL activity was observed when the two alleles were co-expressed relative to the expression of each mutant allele alone. The increase in activity was comparable to that observed previously in the fibroblast complementation studies. The structure determinations of ASL and the homologous eye lens protein, duck delta II crystallin, have revealed that the active site of ASL is made up of residues from three different monomers. The structural mapping of the Q286 and D87 residues shows that both are located near the active site but that, in any one active site, each is contributed by a different monomer. The molecular symmetry of the ASL protein is such that when mutant monomers combine randomly, one active site will contain both mutations and at least one active site will contain no mutations at all. It is these 'native' active sites in the hybrid Q286R/D87G proteins that give rise to the partial recovery of enzymatic activity observed during intragenic complementation.

Animals↗
PubMed1998

Structure determination of selenomethionyl S-adenosylhomocysteine hydrolase using data at a single wavelength.

S-Adenosylhomocysteine (AdoHcy) hydrolase regulates all adenosylmethionine-(AdoMet) dependent transmethylations by hydrolyzing the potent feedback inhibitor AdoHcy to homocysteine and adenosine. The crystallographic structure determination of a selenomethionyl-incorporated AdoHcy hydrolase inhibitor complex was accomplished using single wavelength anomalous diffraction data and the direct methods program, Snb v2.0, which produced the positions of all 30 crystallographically distinct selenium atoms. The mode of enzyme-cofactor binding is unique, requiring interactions from two protein monomers. An unusual dual role for a catalytic water molecule in the active site is revealed in the complex with the adenosine analog 2'-hydroxy, 3'-ketocyclopent-4'-enyladenine.

Adenosylhomocysteinase↗
PubMed1998

Half-Fourier RARE MR cholangiopancreatography: experience in 300 subjects.

PURPOSE: To determine prospectively the clinical applications and diagnostic accuracy of half-Fourier rapid acquisition with relaxation enhancement (RARE) magnetic resonance (MR) cholangiopancreatography (MRCP) in a large patient population. MATERIALS AND METHODS: Breath-hold, heavily T2-weighted half-Fourier RARE MRCP was performed in 265 patients with suspected pancreaticobiliary disease and in 35 control patients without symptoms or signs referrable to the biliary tract or pancreatic duct. MRCP findings were correlated with those at direct cholangiography, pathologic examination, cross-sectional imaging, and clinical follow-up. RESULTS: Diagnostic MRCP examinations were obtained in 299 (99.7%) subjects. MRCP yielded an accuracy of 100% in determining the presence of pancreaticobiliary disease, the presence and level of biliary obstruction, and obstruction due to bile duct calculi. The accuracy of MRCP and MR imaging in determining the presence and level of malignant obstruction was 98.2%. MRCP obviated endoscopic retrograde cholangiopancreatography (ERCP) by excluding choledocholithiasis in patients with acute pancreatitis (n = 13) and nonspecific abdominal pain (n = 82). In patients with sclerosing cholangitis and acquired immunodeficiency syndrome cholangiopathy, MRCP depicted the biliary tract as clearly as did ERCP (n = 9). After failed ERCP, MRCP delineated the pancreaticobiliary tract and helped determine therapeutic options (n = 27). CONCLUSION: Half-Fourier RARE MRCP enables accurate evaluation of pancreaticobiliary disease and obviates ERCP in some patients.

Adolescent↗
PubMed1998

Adjustable laparoscopic gastric band for the treatment of morbid obesity: radiologic evaluation.

OBJECTIVE: This article describes the radiographic appearance of a recently developed laparoscopically placed adjustable gastric band for the treatment of morbid obesity. The optimal technique for contrast evaluation of the device, complications associated with its use, and the technique for stoma adjustments are also discussed. SUBJECTS AND METHODS: Between May and December 1996, 23 patients at our institution underwent laparoscopic placement of adjustable silicone gastric bands for treatment of morbid obesity. All patients underwent a barium upper gastrointestinal series before surgery, 1 day after band placement, at variable intervals when each patient returned for band adjustment, and at 1 year. RESULTS: Unlike the case in other gastric weight loss procedures, the optimal patient position for contrast evaluation of gastric bands was anteroposterior or slightly right posterior oblique. Twenty-one of 23 patients had no complications shown on the postoperative upper gastrointestinal series. Stoma size was approximately 3-8 mm, and most patients showed delayed esophageal emptying without obstruction. Two patients had herniation of the stomach through the gastric band with pouch enlargement, resulting in obstruction and the need for additional surgery. We saw no leaks or band erosions. Nineteen stoma adjustments were performed in 13 patients. One patient had an inverted port that could not be accessed for adjustment. CONCLUSION: As adjustable gastric bands become more widely used, radiologists need to be familiar with the radiographic appearance of the devices, the complications associated with their use, and the optimal patient positioning for contrast evaluation. Radiologists may also be involved with band adjustment to decrease or increase the stoma size and therefore need to understand the technique and potential difficulties of adjusting the stoma.

Adult↗
PubMed1998

Magnetic resonance cholangiopancreatography: a new technique for evaluating the biliary tract and pancreatic duct.

Magnetic resonance cholangiopancreatography (MRCP) represents a new development in MR technology that provides a noninvasive accurate means of evaluating the biliary tree and pancreatic duct. Recent technical refinements that allow for imaging of the entire biliary tree and pancreatic duct in 18 seconds make this examination easily performed even in critically ill patients. The clinical applications of MRCP are illustrated in a variety of scenarios that include choledocholithiasis, malignant obstruction, incomplete/failed endoscopic retrograde cholangiopancreatographies (ERCPs), postsurgical alterations of the biliary tract and gastrointestinal tract such as biliary-enteric anastomoses, intrahepatic bile duct pathology such as sclerosing cholangitis and AIDS cholangiopathy, chronic pancreatitis, congenital anomalies of the biliary tract and pancreatic duct, and gallbladder pathology.

Bile Duct Diseases↗