DNA triple-helix formation on nucleosome core particles. Effect of length of the oligopurine tract

We have used DNase I footprinting to examine the formation of intermolecular triplexes on DNA fragments which have been complexed with nucleosome core particles. We have prepared five DNA fragments, based on the 160-bp tyrT sequence, which contain different length oligopurine tracts (up to 25 bp) at two different positions along the fragment, and have examined their availability for triple-helix formation after reconstituting onto nucleosome core particles. These results are compared with the formation of shorter triplexes in the same regions. In general we find that increasing the length of the complex does not facilitate nucleosomal triplex formation and that the most important factor affecting triplex formation is the position of the target site within the nucleosome-bound fragment. In some instances we find that longer oligonucleotides inhibit triplex formation. Although successful triplex formation was achieved on the longest nucleosome-bound oligopurine tracts, this was accompanied by changes in cleavage pattern that suggest oligonucleotide-induced changes in nucleosome structure.

Autologous superficial femoral vein for aortic reconstruction in infected fields

Autogenous reconstruction is one option available for patients with aortic graft infection or mycotic aneurysms. We reviewed our recent institutional experience with all patients undergoing aortic reconstruction using autologous superficial femoral vein (SFV). Between February 1995 and November 1997, eight patients (five with prosthetic aortic graft infection and three with mycotic aneurysms, including one ruptured mycotic aneurysm) underwent single-stage aortic reconstruction using autologous SFV. Therapy for graft infection included graft excision and replacement with aortobifemoral or aortofemoral (with subsequent cross femoral) grafts fashioned from the SFV. The two patients undergoing elective repair of mycotic aneurysms were treated with extensive SFV patches, and the patient with a ruptured mycotic aneurysm underwent SFV tube grafting. Autogenous reconstruction of the aorta using the SFV in infected fields shows promise for salvage of life and limb during early experiences and short-term follow-up. Morbidity and mortality rates compare favorably with those from existing series, reconstruction is anatomic, and reinfection potential is low. Long-term follow-up and more extensive experience with this technique are needed to establish its role relative to other conventional methods.

Triple-helix formation at different positions on nucleosomal DNA

We have prepared a series of seven DNA fragments, based on the 160 base-pair tyrT sequence, which contain 12-14 base-pair oligopurine tracts at different positions, and have examined their availability for triple-helix formation after reconstituting onto nucleosome core particles. By using DNase I footprinting we find that in general, triplexes can only be formed at sites located toward the ends of nucleosomal DNA fragments. For the native fragment, bases 1-145 are in contact with the protein surface. Stable triplexes can be formed on these nucleosome-bound fragments for sites located before position 33 and beyond position 94. These are formed with both CT-containing oligonucleotides, generating parallel triplexes at pH 5.5, and GT-containing oligonucleotides forming antiparallel triplexes at pH 7.5. No antiparallel triplexes were formed at sites located between these positions. Parallel triplexes were also not formed at sites between positions 39-50 and 43-54 with oligonucleotide concentrations as high as 30 microM. However parallel triplex formation was evident at a site between positions 48 and 59, albeit with a reduced affinity compared to free DNA, suggesting that this oligopurine tract is less tightly associated with the nucleosome surface or that it has an altered translational position. The introduction of an oligopurine tract in the vicinity of the nucleosome dyad caused the fragment to adopt a different nucleosomal position, which could be targeted with parallel, but not antiparallel triplexes.

DNA triple-helix formation on nucleosome-bound poly(dA).poly(dT) tracts

We have used DNase I and hydroxyl-radical footprinting to examine the formation of intermolecular DNA triple helices on nucleosome-bound DNA fragments containing An.Tn tracts. We found that it is possible to form triplexes on these nucleosome-bound DNAs, but the stability of the complexes depends on the orientation of the A tract with respect to the protein surface. Hydroxyl-radical cleavage of these complexes suggests that the DNA fragments are still associated with the nucleosome. However, the phased cleavage pattern is lost in the vicinity of the triplex, suggesting that the DNA has locally moved away from the protein surface.

Unmet needs of remand prisoners

A needs assessment protocol which examines 11 problem areas was devised. This was administered to 277 prisoners on remand at Brixton Prison. We found high levels of unmet need for housing, treatment of substance abuse and neurotic symptoms. Twenty-nine per cent were transferred to hospital under the provisions of the Mental Health Act and about a third of those at liberty to do so complied with a discharge plan. Diversion and discharge planning can potentially meet the unmet needs of remand prisoners.

A paradox of cerebral hyperperfusion in the face of cerebral hypotension: the effect of perfusion pressure on cerebral blood flow and metabolism during normothermic cardiopulmonary bypass

BACKGROUND

The purpose of this study was to determine the impact of perfusion pressure on cerebral blood flow (CBF) and metabolism during normothermic cardiopulmonary bypass (CPB) and after weaning.

MATERIALS AND METHODS

Two groups of mongrel dogs were studied (Group A, CPB perfusion at 50 mm Hg, n = 6; and Group B, CPB perfusion at 100 mm Hg, n = 6). All animals underwent 2 h of normothermic bypass at cardiac indexes >2.1 L/min/m2 and were weaned from pump, maintained at pressures >75 mm Hg, and followed for an additional 2 h.

RESULTS

In both groups CBF increased over 85% from baseline, in proportion to the hemodilution during the initiation of CPB. Intracranial pressure increased moderately in both groups during CPB, compromising CBF at 1 h in Group A, but not in Group B. The Group A cerebral metabolic rate for oxygen (CMRO2), however, remained unchanged as the percentage of oxygen extraction increased to compensate for the decreased CBF. During recovery, temperature, mean arterial pressure, and cerebral perfusion pressure were not significantly different between the two groups. However, the CBF, percentage of oxygen extracted, and CMRO2 were significantly lower in Group A.

CONCLUSIONS

Normothermic CPB initiated with a crystalloid prime and performed at the lower end of a 50-70 mm Hg perfusion window resulted in a highly significant increase in CBF in order to compensate for hemodilution, while at the same time reduced the perfusion pressure available to supply the increased CBF. Together, these two events create a hemodynamic paradox of hyperperfusion in the face of hypotension. The reduction in CMRO2 in Group A is yet to be explained but seems to remain coupled to CBF and could represent a previously undescribed protective mechanism of hibernating cerebral tissue, similar to the phenomena of ischemic preconditioning in the heart, where cerebral tissue is stimulated to lower metabolism in response to inadequate CBF.

Intraoperative MIDCABG arteriography via the left radial artery: a comparison with Doppler ultrasound for assessment of graft patency

BACKGROUND

Minimally invasive direct coronary artery bypass grafting involving beating heart left internal mammary artery to left anterior descending coronary artery anastomoses are performed with increasing frequency. Controversy exists regarding the need for intraoperative assessment of graft patency.

METHODS

We designed a technique to perform arteriography of the left internal mammary artery by using left radial artery access and standard fluoroscopy to evaluate patency in the operating room. The last 50 of 87 minimally invasive direct coronary artery bypass grafting operations were evaluated by intraoperative arteriography and Doppler ultrasound. Angiograms were performed by the surgeon and involved cannulation and direct injection of contrast medium into the origin of the left internal mammary artery via the left radial artery.

RESULTS

Total procedure time was less than 15 minutes. No injuries to the left internal mammary artery were identified. Anastomotic occlusions were identified in 4 cases (8%), 2 of which involved sequential diagonal and left anterior descending anastomoses. These were corrected at the time of surgery with 2 cases requiring conversion to standard coronary artery bypass grafting. Qualitative assessment of grafts with Doppler ultrasound failed to definitively identify these occlusions. There were no deaths and no perioperative infarctions.

CONCLUSION

Intraoperative arteriography of the left internal mammary artery can be performed by the surgeon, and a significant number of anastomotic problems may be identified and corrected by using this technique. Therefore, a 100% early graft patency rate may be attainable.

ENT day surgery in England and Wales--an audit by the Royal College of Surgeons (Eng.) Comparative Audit Service

An audit of day surgery was carried out by the Royal College of Surgeons (Eng.) Comparative Audit service. Data from 121 respondents on over 3,962 day cases were analysed from both retrospective information and from prospective individual patient proformas. The day surgery rate is 31 per cent. The variability of facilities for day-surgery, the timing of lists, type of anaesthetic used and case-mix are discussed. Outcome and the reasons for admission to an overnight bed are analysed. The overall admission rate was found to be 2.8 per cent (range 0.6-19.5 per cent between consultants). Seventy per cent of ENT day-surgery was performed on morning lists which have a lower admission rate than afternoon lists. The main reasons for admission are vomiting 30 per cent, haemorrhage 20 per cent and inadequate recovery from anaesthetic 22 per cent. A more detailed analysis of reasons for admission were given for tonsillectomy, adenoidectomy, FESS, and grommets. Recommendations are given which might increase the scope of safe day-surgery and reduce admission rate.

Duodenal obstruction in thyroid storm

A 35-year-old, previously healthy woman, known to be thyrotoxic, was transferred from a community hospital for "acute abdomen." Abdominal pain, distention, and hyperemesis resolved with placement of nasogastric tube (NGT) and return of 2,600 mL of bilious fluid. Continued high NGT output made oral or NGT administration of antithyroid drugs impossible. We gave propylthiouracil (PTU) by retention enemas with therapeutic serum levels and sublingual saturated solution of potassium iodide (SSKI) with 70% absorption based on 24-hour free iodine urinary excretion. The patient's thyroxine (T4) and triiodothyronine (T3) radioimmunoassays were normal on hospital days 10 and 12, respectively. However, free T4 and T3 resin uptake did not normalize until hospital day 31. On hospital day 32, she tolerated removal of NGT without nausea and 4 days later was taking a regular diet. We conclude that our patient's gastrointestinal symptoms were a prominent feature of her thyrotoxicosis and that rectal PTU and sublingual SSKI are effective in administration of antithyroid drugs.

Nucleosome core particles inhibit DNA triple helix formation

We have used DNase I footprinting to examine the formation of DNA triple helices at target sites on DNA fragments that have been reconstituted with nucleosome core particles. We show that a 12 bp homopurine target site, located 45 bp from the end of the 160 bp tyrT(46A) fragment, cannot be targeted with either parallel (CT-containing) or antiparallel (GT-containing) triplex-forming oligonucleotides when reconstituted on to nucleosome core particles. Binding is not facilitated by the presence of a triplex-binding ligand. However, both parallel and antiparallel triplexes could be formed on a truncated DNA fragment in which the target site was located closer to the end of the DNA fragment. We suggest that intermolecular DNA triplexes can only be formed on those DNA regions that are less tightly associated with the protein core.

Minor groove binding ligands alter the rotational positioning of DNA fragments on nucleosome core particles

We have used hydroxyl radical and DNase I footprinting to examine the interaction of four AT-selective minor groove binding ligands (Hoechst 33258, distamycin, netropsin and berenil) with DNA fragments which have been reconstituted with nucleosome core particles. Hydroxyl radical footprints of reconstituted tyrT DNA show that all four ligands induce changes in the phased cleavage pattern, consistent with the suggestion that they cause the DNA to rotate by 180 degrees on the nucleosome surface. This observation was confirmed by a series of hydroxyl radical and DNase I footprinting experiments on a synthetic DNA fragment containing five different (A/T)4 sites spaced ten bases apart, in phase with the nucleosomal repeat. This fragment produces a phased cleavage pattern when bound to the nucleosome cores, with minima in the AT regions, suggesting that these regions are positioned with their narrow minor grooves facing towards the protein surface. In the presence of the minor groove binding ligands the hydroxyl radical cleavage maxima are shifted by about five base-pairs. It appears that the ligands have caused the DNA to rotate by about 180 degrees on the protein surface; those DNA regions which were facing out are turned in and vice versa. Regions to which the ligands are bound are turned away from the protein surface, thereby minimising electrostatic repulsion between the cationic charges on the ligand and protein. The absence of any observable footprints in the AT-regions suggests that these changes are induced at low levels of occupancy.

Treatment of diabetic gustatory sweating with topical glycopyrrolate cream

A 42-year-old insulin-dependent diabetic man presented with severe bilateral gustatory sweating associated with a deterioration in his glycaemic control. Conventional oral antimuscarinic medication was contraindicated because of his cardiac insufficiency. Topical 0.5% glycopyrrolate cream was tried and applied on alternate days to his face, which resulted in the complete cessation of his gustatory sweating without side-effects. Topical glycopyrrolate cream is an effective treatment of diabetic gustatory sweating without the adverse effects commonly found with oral anti-muscarinic medication.

Effect of a triplex-binding ligand on triple helix formation at a site within a natural DNA fragment

We have used DNase I footprinting to examine the effect of a triplex-binding ligand on the formation of parallel intermolecular DNA triple helices at a mixed sequence target site contained within a natural DNA fragment (tyrT). In the presence of 10 microM ligand (N-[2-(dimethylamino)ethyl]-2-(naphthyl)quinolin-4-ylamine), the binding of CTCTTTTTGCTT (12G) to the sequence GAGAAAAATGAA (generating a complex containing 8 x T x AT, 1 x G x TA and 3 x C+ x GC triplets) was enhanced 3-fold at pH 5.5. When the oligonucleotide CTCTTTTTTCTT (12T) was substituted for 12G (replacing G x TA with T x TA) there was a large reduction in affinity for the target sequence. However, this was stabilized by about 300-fold in the presence of the ligand, requiring a similar concentration to produce a footprint as 12G in the absence of the ligand. When the sequence of the target site was altered to GAGAAAAAAGAA, generating an uninterrupted run of purines [tyrT(46A)], the binding of 12T (generating a complex containing 9 x T x AT, and 3 x C+ x GC triplets) was enhanced 3-fold by 10 microM of the triplex-binding ligand. However, although the binding of 12G to this sequence generating a complex containing a G x AT triplet, was much weaker, this too was stabilized by about 30-fold by the ligand, requiring a similar concentration as the perfect matched oligonucleotide (12T) in the absence of the ligand. A secondary, less stable footprint was also observed in these fragments when using either 12T or 12G, which was evident only in the presence of the triplex-binding ligand. This site, which contained a number of triplet mismatches, appears to be realated to the formation of four or five central T x AT triplets. This reduction in the stringency of oligonucleotide binding by the triplex-binding ligand promotes the formation of complexes at non-targeted regions but may also have the potential for enabling recognition at sites that contain regions where there are no specific triplet matches.

Selective management of abdominal aortic aneurysms in a prospective measurement program

PURPOSE

The purpose of this study was to clarify the treatment of patients with small abdominal aortic aneurysms (AAAs) less than 5 cm in diameter and those believed to be unfit for operation with AAAs 5 cm diameter or greater.

METHODS

Four hundred ninety two patients with AAAs less than 5 cm when first seen were entered in a prospective measurement program by ultrasonography or computed tomography scan (exclusively after 1998) every 6 months. A decision regarding operative fitness was made when the AAA was 5 cm. Patients then underwent operation if fit or continued follow-up if their AAA was larger than 5 cm but they were unfit. A further group of 91 patients with aneurysms 5 cm or greater when first seen but unfit for repair were entered in the prospective measurement program.

RESULTS

In the group with AAAs less then 5 cm at entry, operation was performed in 201 patients as a result of increase in AAA size to 5 cm or greater (157), AAA expansion of more than 0.5 cm in 6 months (24), or for other reasons (20). Of those with AAAs smaller than 5 cm at entry, 291 have not undergone operation at a mean follow-up of 42 months. Expansion was significantly related to aneurysm size at entry and was highest in the 4.5 to 4.9 cm group at 0.7 cm/year. In the group of patients deemed unfit for operation with 5 cm AAAs [as a graduate of the less than 5 cm group at entry (85 patients) or first seen with AAA greater than 5 cm (91 patients)], 10 ruptures have occurred. Of these patients with ruptured AAAs, six had AAAs between 5.0 and 5.6 cm.

CONCLUSIONS

Because of the risk of rupture demonstrated in our series in AAAs 5 cm or slightly greater and the progressive increase in expansion to a mean of 0.7 cm/year in those AAAs between 4.5 and 4.9 cm at entry, recommendation for elective operation in patients with AAAs between 4.5 and 4.9 cm at entry, recommendation for elective operation in patients with AAAs between 4.5 and 5.0 cm should be strongly considered in a fit patient.

Epitope-labeled soluble human interleukin-5 (IL-5) receptors. Affinity cross-link labeling, IL-5 binding, and biological activity

The human receptor for the potent eosinophilopoietic cytokine interleukin-5 (IL-5) consists of two components: a 60-kDa ligand-binding alpha chain (IL-5 alpha R) and a 130-kDa beta chain (IL-5 beta R). Three ectodomain constructs of the alpha chain (alpha RED) bearing C-terminal epitope tags were engineered and expressed in baculovirus-infected Sf9 cells. Each recombinant alpha chain was secreted into the medium, maximum expression occurring 72 h post-infection. The various soluble alpha chains were shown by affinity cross-link labeling and competition with unlabeled IL-5 to bind recombinant human (rh) 125I-IL-5 specifically with an ED50 of 2-5 nM. The epitope tag provided a simple purification of the receptor from conditioned medium using immunoaffinity chromatography. The purified material had an apparent molecular mass of 43 kDa and was heterogeneously glycosylated. Sedimentation analysis revealed a 1:1 association of the purified epitope-tagged soluble receptor with its ligand, resulting in the formation of a 70-74-kDa complex. Circular dichroism analysis revealed that the soluble alpha chain existed with a significantly ordered structure consisting of 42% beta-sheet and 6% alpha-helix. Such analyses combined with fluorescence spectrometry suggested that ligand-receptor complex formation in solution resulted in minimal conformational changes, consistent with the suggestion that the membrane-associated form of the alpha chain itself has minimal signal transduction capability. Surface plasmon resonance studies of the interaction of the purified alpha RED with immobilized rhIL-5 revealed a specific, competable interaction with a dissociation constant of 9 nM. Preincubation of an IL-5-dependent cell line with the epitope-tagged alpha RED also dose-dependently neutralized rhIL-5-induced proliferation. These data demonstrate that biologically active epitope-tagged recombinant soluble IL-5 receptors are facile to produce in large quantities and may have therapeutic utility in the modulation of IL-5-dependent eosinophilia in man.

DNA sequence preferences of several AT-selective minor groove binding ligands

We have examined the interaction of distamycin, netropsin, Hoechst 33258 and berenil, which are AT-selective minor groove-binding ligands, with synthetic DNA fragments containing different arrangements of AT base pairs by DNase I footprinting. For fragments which contain multiple blocks of (A/T)4 quantitative DNase I footprinting reveals that AATT and AAAA are much better binding sites than TTAA and TATA. Hoechst 33258 shows that greatest discrimination between these sites with a 50-fold difference in affinity between AATT and TATA. Alone amongst these ligands, Hoechst 33258 binds to AATT better than AAAA. These differences in binding to the various AT-tracts are interpreted in terms of variations in DNA minor groove width and suggest that TpA steps within an AT-tract decrease the affinity of these ligands. The behaviour of each site also depends on the flanking sequences; adjacent pyrimidine-purine steps cause a decrease in affinity. The precise ranking order for the various binding sites is not the same for each ligand.

Bilateral sudden visual loss due to sphenoid mucocele in Albright's syndrome

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A single-step purification of biologically active recombinant human interleukin-5 from a baculovirus expression system

Recombinant human interleukin-5 (rhIL-5) was expressed in baculovirus-infected insect cells and purified to homogeneity from the culture medium in a single chromatographic step. Beginning with a cDNA encoding the full-length precursor form of human IL-5, including the authentic secretory leader sequence, recombinant baculovirus-infected insect cells expressed high levels of rhIL-5 (5-15 mg/liter culture) of which > 90% was processed to the mature form and secreted into the culture medium. After removing cells by centrifugation, rhIL-5 was purified by first adjusting the culture medium to the calculated pI value of mature IL-5 (pI 7.44) and then passing the conditioned medium through tandem linked anion- and cation-exchange columns. The resulting pass-through fraction contained the rhIL-5 and was devoid of contaminating proteins. An optional hydrophobic-interaction chromatography step effectively concentrated the pure homodimeric N-glycosylated rhIL-5 with a high overall yield (> 90%). N-terminal amino acid sequence determination indicated that cleavage of the human IL-5 leader sequence in insect cells occurred between Ala19 and Ile20. Recombinant human IL-5 prepared by this procedure bound to the high-affinity IL-5 receptor present on an eosinophilic leukemia cell line and elicited a proliferative response in the IL-5-dependent murine B-cell line BCL1. This rapid and simple procedure for the expression and purification of mature rhIL-5 should therefore enable studies requiring large amounts of this cytokine.

The extracellular domain of the epidermal growth factor receptor. Studies on the affinity and stoichiometry of binding, receptor dimerization and a binding-domain mutant

The binding of epidermal growth factor (EGF) or an EGF-like growth factor to the EGF receptor is the initial event which leads to receptor activation, and consequently the induction of cell growth. In order to study this binding interaction in detail, we produced the extracellular domain of the EGF receptor (EGFR) using the baculovirus expression system. Affinity-labeling and Western-blot analyses revealed that the baculovirus-infected insect cells secrete active EGFR extracellular domain relatively efficiently, however a significant amount of inactive EGFR extracellular domain is retained within the cells. The apparent dissociation constant (Kd) of the secreted EGFR extracellular domain for EGF and transforming growth factor alpha (TGF-alpha), as determined using an immobilized receptor binding assay, was approximately 200 nM. Interestingly, this Kd value is 30-40-fold lower than that of the full-length EGFR derived from detergent-solubilized A431 cell membranes. The stoichiometry of binding of the EGFR extracellular domain to EGF and TGF-alpha was examined by band-shift analysis on non-denaturing PAGE and was estimated to be 1:1. We have also shown, using sedimentation equilibrium analysis, that ligand binding induces significant dimerization of the EGFR extracellular domain. Finally, we carried out site-specific mutagenesis on the EGFR extracellular domain in order to define the ligand-binding region. We identified amino acid residues which are close to the binding site since they are common to the epitopes of several ligand-competitive monoclonal antibodies. However, these residues do not contribute directly to ligand binding since the affinity of the mutated EGFR extracellular domain for EGF and TGF-alpha was unaffected.

Complications in ENT--a nationwide audit carried out in November 1992

We report a prospective audit of complications following ENT surgery during November 1992 from 42 consultants across the United Kingdom. Complications were reported as codes, and results were analysed at the Royal College of Surgeons Comparative Audit Unit. A total of 174 complications were reported, giving an annualized complication rate per consultant of 5.7-7.0% (depending on whether only the most severe complication per patient is counted or all complications). This compares with an annual complication rate of 1.49% reported retrospectively for the year of 1991 by the same consultants.

Royal College of Surgeons comparative ENT audit 1990

The Royal College of Surgeons Comparative Audit Service was set up in 1990 so that surgeons could pool their audit data, to provide 'standards' with which to compare their own figures. A total of 405 consultant otolaryngologists were circularized in December 1991 inviting them to return data about their resources, workload, case-mix and complications, and about two specific audit topics-Myringoplasty and Carcinoma of the Larynx--for the calendar year 1990. A total of 65 consultants returned proformas with data on 52208 admissions and 31240 surgical procedures. The 'average' respondent admitted 829 patients in the year (19% of these day cases and 14% emergencies) and performed 744 surgical procedures with a mean complication rate of 1.39% using three theatre sessions per week. Cancelled theatre sessions per annum per consultant ranged from 0 to 71. The mean known success rate after myringoplasty was 65%, with hearing improvement in 53%. The 'average' ENT surgeon saw 3.5 new cases of invasive carcinoma of the larynx and treated 69% of these with radiotherapy alone, compared with 14% surgery alone. As well as allowing a profile to be drawn up of the 'average' respondent, this audit allowed individual consultants returning data to compare their own figures in detail with the pooled data, which were presented graphically at a meeting in April 1992.