Polyethylene glycol solution as an oral contrast agent for MRI of the small bowel in a patient population.

AIM: To assess the efficacy of polyethylene glycol solution as an oral contrast agent in a patient population. MATERIAL AND METHODS: Patients were fasted from 12.00 am. Administration of the oral contrast medium commenced 15 min before imaging and comprised one sachet of Norgine (Klean-prep, Middlesex, UK) reconstituted in 1 l water of which the patient took between 500-750 ml. Norgine is a balanced mixture of polyethylene glycol and electrolytes, which when added to water produces a clear colourless, iso-osmotic solution. RESULTS: In total 38 candidates were identified retrospectively covering a 2-year period. Visualization of the jejunum, ileal loops and ileocaecal region was excellent or sufficient in 87, 95 and 89%, respectively. The time taken to obtain complete visualization of the small bowel, from the jejunum to the ileocecal region varied from 15-240 min with an average time of 65 min and 73.7% of patients necessitating delayed imaging. CONCLUSIONS: Polyethylene glycol was demonstrated to be an excellent oral contrast medium in distending the small bowel. However, small bowel transit times were significantly delayed and problematic necessitating repeated imaging within the patient population. As result of theses findings longer examination time should be expected within a patient population and this should be borne in mind when scheduling patients.

Spontaneous ureterocolic fistula secondary to calculous pyohydroureteronephrosis.

We report a case of ureterocolic fistula secondary to urolithiasis in a 70-year-old female imaged with both CT and an antegrade nephrostogram. The ureterocolic fistula was managed with insertion of an antegrade ureteral stent.

SAPHO syndrome presenting as septic arthritis in the hip.

We report the case of a young female presenting to our care with right hip pain. Initially treated as a septic arthritis, there was no response to antibiotic treatment. Further clinical and radiological investigation showed signs of SAPHO syndrome. This is a syndrome characterised by the variable presentation of synovitis, acne, pustulosis, hyperostosis and osteitis. The patient subsequently settled on conservative management and made a full recovery.

Magnetic resonance venography in assessing venous patency after multiple venous catheters.

BACKGROUND/PURPOSE: Venous thrombosis is a well-recognised complication of central venous catheters (CVC). The aim of the study was to assess the value of magnetic resonance venography (MRV) in assessing venous patency in children with suspected venous thrombosis. METHODS: Contrast studies through the CVC (linogram) and Doppler ultrasonography were the initial investigations performed in children with suspected CVC-related thrombosis. Two-dimensional gated inflow and phase contrast MRV also was performed to assess the extent of venous thrombosis and to locate patent veins for replacement CVC. When the MRV identified a suitable patent vein, the CVC was reinserted by direct venous cut down or the percutaneous method under a general anaesthetic. RESULTS: A total of 25 children (median age, 5 years; range, 2 months to 17 years) who had multiple CVC insertions (median, 3; range, 1-9), underwent MRV for suspected venous thrombosis. Of 10 patients in whom the catheter was completely occluded, MRV identified extensive thrombosis of the central veins in 6. In 7 other children the linogram showed adherent thrombus at the tip of the CVC only. In 5 of these 7 children MRV showed extensive thrombosis of the vein in which the catheters were placed. Doppler ultrasonography diagnosed thrombotic occlusion of the neck veins in 7 children. The MRV studies showed more extensive thrombosis in 4 of these 7 patients. Additionally, MRV showed thrombosis of the intrathoracic veins in 11 patients who had patent neck veins on ultrasound scan. MRV identified a patent vein for reinsertion of CVC in 22 of 25 children. At operation, venous patency was confirmed in 20 patients (91%). CONCLUSION: MRV in children with suspected CVC-related thrombosis is more accurate than Doppler ultrasonography, and contrast studies for defining the extent of venous thrombosis. MRV correctly shows venous anatomy and patency for reinsertion of CVC.

Pseudoaneurysm of the uterine artery after abdominal hysterectomy: radiologic diagnosis and management.

Uterine artery pseudoaneurysm is a rare but serious complication of pelvic surgery. Radiology has an important role in its diagnosis and primary management. We believe that this complication and its management are of importance to those assessing for complications following pelvic surgery.

Effect of phosphorothioate substitutions on DNA cleavage by Escherichia coli DNA topoisomerase I.

To evaluate the structural influence of the DNA phosphate backbone on the activity of Escherichia coli DNA topoisomerase I, modified forms of oligonucleotide dA(7) were synthesized with a chiral phosphorothioate replacing the non-bridging oxygens at each position along the backbone. A deoxy-iodo-uracil replaced the 5'-base to crosslink the oligonucleotides by ultraviolet (UV) and assess binding affinity. At the scissile phosphate there was little effect on the cleavage rate. At the +1 phosphate, the rectus phosphorus (Rp)-thio-substitution reduced the rate of cleavage by a factor of 10. At the +3 and -2 positions from the scissile bond, the Rp-isomer was cleaved at a faster rate than the sinister phosphorus (Sp)-isomer. The results demonstrate the importance of backbone contacts between DNA substrate and E. coli topoisomerase I.

Extracranial vascular malformation: value of antenatal and postnatal MRI in management.

We report a case where fetal MRI using a low-field-strength magnet (0.5 T) accurately confirmed a large extracranial vascular malformation, which was suspected on antenatal US. Fetal MRI enabled better counselling of the parents and allowed suitable plans to be made regarding method of delivery and early management of the neonate. To our knowledge this is the first case of an extracranial vascular malformation imaged using fetal MRI.

Cystic retroperitoneal lymphangioma: treatment by image-guided percutaneous catheter drainage and sclerotherapy.

Retroperitoneal cystic lymphangiomas are extremely rare and the majority are symptomatic during childhood. Although benign, they can compress and infiltrate vital structures. Surgery is curative but is associated with a high complication rate. An alternative treatment strategy is image-guided percutaneous catheter drainage of the lymphangioma followed by sclerotherapy. Resolution of a large retroperitoneal cystic lymphangioma in a 4-year-old child treated by this technique is reported. To our knowledge, this technique has not been previously described in this condition and we believe that it offers significant advantages over surgery.

Delayed presentation of pseudoaneurysm complicating closed humeral fracture: MR diagnosis.

Vascular injuries resulting from closed fractures of the humerus are rare. We describe two patients who developed unsuspected pseudoaneurysms following closed humeral fracture. Both patients presented with a mass, suspicious for malignancy. In each case, diagnosis was made by magnetic resonance imaging.

A pictorial review of atlanto-axial rotatory fixation: key points for the radiologist.

Atlanto-axial rotatory fixation (AARF) is a rare condition which occurs more commonly in children than in adults. The terminology can be confusing and the condition is also known as 'atlanto-axial rotatory subluxation' and 'atlanto-axial rotary dislocation'. Rotatory fixation is the preferred term, however, as in most cases the fixation occurs within the normal range of rotation of the joint. By definition, therefore, the joint is neither subluxed nor dislocated. AARF is a cause of acquired torticollis. Diagnosis can be difficult and is often delayed. The radiologist plays a key role in confirming the diagnosis. The classification system proposed by Fielding in 1977 is most frequently used and will be discussed in detail. Given that this classification system was devised in the days before computed tomography (CT), as well as the fact that combined atlanto-axial and atlanto-occipital rotatory subluxation (AORF) is omitted from the classification, we propose a modification to the classification of this rare but significant disorder. The radiological findings in six cases of AARF will be illustrated, including a case with associated atlanto-occipital subluxation. The pertinent literature is reviewed and a more comprehensive classification system proposed. The imaging approach to diagnosis and the orthopaedic approach to management will be discussed.

Site-directed mutagenesis of conserved aspartates, glutamates and arginines in the active site region of Escherichia coli DNA topoisomerase I.

To catalyze relaxation of supercoiled DNA, DNA topoisomerases form a covalent enzyme-DNA intermediate via nucleophilic attack of a tyrosine hydroxyl group on the DNA phosphodiester backbone bond during the step of DNA cleavage. Strand passage then takes place to change the linking number. This is followed by DNA religation during which the displaced DNA hydroxyl group attacks the phosphotyrosine linkage to reform the DNA phosphodiester bond. Mg(II) is required for the relaxation activity of type IA and type II DNA topoisomerases. A number of conserved amino acids with acidic and basic side chains are present near Tyr-319 in the active site of the crystal structure of the 67-kDa N-terminal fragment of Escherichia coli DNA topoisomerase I. Their roles in enzyme catalysis were investigated by site-directed mutation to alanine. Mutation of Arg-136 abolished all the enzyme relaxation activity even though DNA cleavage activity was retained. The Glu-9, Asp-111, Asp-113, Glu-115, and Arg-321 mutants had partial loss of relaxation activity in vitro. All the mutants failed to complement chromosomal topA mutation in E. coli AS17 at 42 degreesC, possibly accounting for the conservation of these residues in evolution.

Effect of Mg(II) binding on the structure and activity of Escherichia coli DNA topoisomerase I.

Escherichia coli DNA topoisomerase I requires Mg(II) as a cofactor for the relaxation of negatively supercoiled DNA. Mg(II) binding to the enzyme was shown by fluorescence spectroscopy to affect the tertiary structure of the enzyme. Addition of 2 mM MgCl2 resulted in a 30% decrease in the maximum emission of tryptophan fluorescence of the enzyme. These Mg(II)-induced changes in fluorescence properties were reversible by the addition of EDTA and not obtained with other divalent cations. After incubation with Mg(II) and dialysis, inductively coupled plasma (ICP) analysis showed that each enzyme molecule could form a complex with 1-2 Mg(II) bound to each enzyme molecule. Such Mg(II).enzyme complexes were found to be active in the relaxation of negatively supercoiled DNA in the absence of additional Mg(II). Results from ICP analysis after equilibrium dialysis and relaxation assays with limiting Mg(II) concentrations indicated that both Mg(II) binding sites had to be occupied for the enzyme to catalyze relaxation of negatively supercoiled DNA.

Site selectivity of daunomycin.

We have reexamined the binding properties of the antitumor drug daunomycin using double-helical oligonucleotides 16 base pairs long that were designed to contain preferred binding sites for the drug. The preferred sites are contained in a six base pair core which is flanked on the 5' and 3' ends by tracts of adenines. The flanking sequences, which augment helix stability and reduce and effects, were chosen because daunomycin is known to bind poorly to poly(dA).poly(dT). Four major sequences were examined in the six base pair core: CGTACG, TAGCTG, TCATCC, and (TA)3 and compared with calf thymus DNA. A randomly generated 16 bp sequence containing no A tracts and a sequence containing only tracts of As and Ts were also used. Fluorometric, absorption, calorimetric, and stopped-flow techniques were used to examine the binding. The affinity of the drug for oligomers containing known binding sites was comparable to or enhanced relative to that for calf thymus bulk DNA. Association constants ranged from 1.0 x 10(8) to 3.0 x 10(7) M-1. The strongest core binding site found was CGTACG, but its affinity is only 2-fold larger than that of other core sequences. Appreciable binding to the flanking A tracts was observed. An oligonucleotide which incorporates the CGTACG sequence in a short hairpin helix binds an order of magnitude more weakly. Complex lifetimes measured by stopped flow generally increase with equilibrium stability; the kinetics confirm the existence of a set of weaker sites. The exothermic binding enthalpy for daunomycin with the CGTACG core sequence is more than twice as large as for the TATATA sequence. Binding to dA20.dT20 is endothermic, and a less exothermic component can be detected in the calorimetric binding curve of the oligomers containing flanking A tracts.

Binding affinity and site selectivity of daunomycin analogues.

We have tested a series of daunomycin analogues for binding affinity to a group of oligonucleotides that contain binding sites specific for daunomycin and that were previously screened for relative binding affinity for daunomycin. The series of drugs differed from daunomycin in the sugar moiety, including substitution of a hydroxyl group for the charged amino group and replacement of the 2'-OH by an iodo substituent. Data were analyzed by Scatchard plots and association constants were estimated from the gamma-intercept at saturating levels of oligonucleotide. Because of the solubility problems associated with these compounds, Scatchard plots could not be extended to high levels of binding. A second method of analysis of the fluorescence data confirmed the semiquantitative association constants obtained from the intercepts of the Scatchard plots. The association constants were in the range of 10(5)-10(7) M-1. When compared with daunomycin, the compounds with hydroxyl substituted for the amino group in the sugar ring generally bound less well to the oligonucleotides, by factors of up to several hundred. Much of the binding lost upon removal of the charged amino group was restored, however, with compounds containing an iodo substituent on the sugar ring. Changing the iodo-substituted sugar from the natural L-form to the D-form diminished binding by 6-50-fold, depending on sequence. This result implies a stereospecific interaction of the natural sugar with the DNA chain. A positively cooperative curve was observed in the Scatchard plot for the D-form sugar.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of conformations of benzo[a]pyrene diol epoxide-DNA adducts derived from stereoisomers of different tumorigenicities on base sequence.

The conformations of covalent adducts derived from the binding of the highly tumorigenic stereoisomer (+)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyren e [(+)-anti-BPDE] and its nontumorigenic (-)-anti-BPDE isomer with poly[(dG).(dC)], poly[(dG-dC).(dG-dC)], poly[(dT-dC).(dG-dA)], and poly[(dA-dC).(dG-dT)] were investigated by employing UV absorbance and linear dichroism methods. The degrees of orientation of the BPDE residues (bound covalently to N2 of deoxyguanosine), relative to the DNA bases, are most pronounced in the alternating and nonalternating (dG).(dC) polymers and decrease in polymers with neighboring dA.dT base pairs. The tumorigenic (+)-anti-BPDE isomer gives rise predominantly to external (solvent-exposed) site II adducts, while the (-)-enantiomer gives rise predominantly to site I adducts with significant carcinogen-nucleoside interactions. In the mixed (dA-dC).(dG-dT) and (dT-dC).(dG-dA) copolymers, the (+)-anti-BPDE isomer also binds predominantly to N2 of deoxyguanosine, but the adducts are weakly oriented with respect to the DNA bases. The incidence of site II adducts is considerably reduced as compared to the (dG).(dC) and (dG-dC).(dG-dC) polymers, and there is a greater proportion of site I adducts; the presence of a significant proportion of unordered adduct forms is also suggested from the diffuseness and broadness of the absorption spectra in the dA.dT base pair containing polymers. The preference of formation of site II adducts in dG-rich sequences in the case of the biologically highly active (+)-anti-BPDE isomer is discussed in terms of the known binding and mutation spectra.

Linear dichroism properties and orientations of different ultraviolet transition moments of benzo[a]pyrene derivatives bound noncovalently and covalently to DNA.

Linear dichroism and absorption methods are used to study the orientations of transition moments of absorption bands of polycyclic aromatic epoxide derivatives which overlap with those of the DNA band in the 240-300 nm region. Both the short and long axes of the pyrene residues of 1-oxiranylpyrene (1-OP) and the (+) and (-) enantiomers of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) noncovalently bound to double-stranded native DNA are oriented approximately perpendicular to the axis of the DNA helix, consistent with intercalative modes of binding. The covalent binding of these three epoxide derivatives to DNA is accompanied by reorientations of both the short and long axes of the pyrene residues. Covalent adducts derived from the highly mutagenic (+)-anti-BPDE are characterized by tilts of the short axis within 35 degrees or less, and of the long axis by more than 60-80 degrees, with respect to the planes of the DNA bases. In the adducts derived from the binding of the less mutagenic (-)-anti-BPDE and 1-OP epoxide derivatives to DNA, the long axes of the pyrenyl rings are predominantly oriented within 25 degrees of the planes of the DNA bases; however, in the case of the (-) enantiomer of BPDE, there is significant heterogeneity of conformations. In the case of the 1-OP covalent DNA adducts, the short axis of the pyrene ring system is tilted away from the planes of the DNA bases, and the pyrene ring system is not intercalated between DNA base-pairs as in the noncovalent complexes. The stereochemical properties of the saturated 7,8,9,10-ring in BPDE, or the lack of the 7 and 8 carbon atoms in 1-OP, do not seem to affect noncovalent intercalative complex formation which, most likely, is influenced mainly by the flat pyrenyl residues. These structural features, however, strongly influence the conformations of the covalent adducts, which in turn may be responsible for the differences in the mutagenic activities of these molecules.

Conformations of complexes derived from the interactions of two stereoisomeric bay-region 5-methylchrysene diol epoxides with DNA.

The reaction mechanisms of two isomeric bay-region diol epoxides of 5-methylchrysene (trans-1,2-dihydroxy-anti-3,4-epoxy-1,2,3,4-tetrahydro-5-methylchrysene (DE-I) and trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydro-5-methylchrysene (DE-II) with double-stranded DNA in aqueous solutions were studied utilizing kinetic flow dichroism and fluorescence techniques. As in the case of the previously studied benzo(a)pyrene-7,8-diol-9,10-oxide isomers (BaPDE), both DE-I and DE-II rapidly form intercalation-type complexes (association constants K = 2700 and 1500 M-1 respectively in a neutral 5mM phosphate solution). The physically bound diol epoxide molecules react on time scales of minutes to form predominantly tetraols; a greater fraction (6 +/- 1%) of DE-I than of DE-II (2-3%) molecules react with the DNA to form covalent products. The DE-II isomer is characterized by a greater reactivity than DE-I, and the rates of reaction are markedly accelerated in the presence of DNA in both cases. The linear dichroism spectra of the covalent adducts reveal that the conformations of both types of adducts are similar, with the long axes of the phenanthrenyl chromophores tilted, on the average, at angles of 38-52 degrees with respect to the average orientations of the transition moments (at 260 nm) of the DNA bases. The conformations of the covalently bound DE-I and DE-II molecules resemble those observed in the case of the highly tumorigenic (+) enantiomer of anti-BaPDE.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of stability of 7 beta,8 alpha-dihyroxy-9 alpha epoxybenzo(a)pyrene by complex formation with serum albumin.

The biologically active and chemically unstable metabolite of benzo(a)pyrene, 7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-epoxybenzo(a)pyrene (BPDE), binds to human serum albumin in aqueous solutions with an association constant of 2.6 X 10(5)M-1. At pH 7.2, 24 degrees C and in 5mM sodium cacodylate buffer solution, this binding increases the lifetime of the diol epoxide by a factor of nearly 3. It is suggested that the formation of such physical complexes with proteins having hydrophobic interiors or with lipids may provide a mechanism by which highly reactive metabolites are transported from the site of metabolic synthesis to biological target molecules (e.g., DNA), in a reactive aqueous environment.