Toward Circular Recycling of Polyurethanes: Depolymerization and Recovery of Isocyanates

We report a depolymerization strategy to nearly quantitatively regenerate isocyanates from thermoplastic and thermoset polyurethanes (PUs) and then resynthesize PUs using the recovered isocyanates. To date, chemical/advanced recycling of PUs has focused primarily on the recovery of polyols and diamines under comparatively harsh conditions (e.g., high pressure and temperature), and the recovery of isocyanates has been difficult. Our approach leverages an organoboron Lewis acid to depolymerize PUs directly to isocyanates under mild conditions (e.g., ∼80 °C in toluene) without the need for phosgene or other harsh reagents, and we show that both laboratory-synthesized and commercially sourced PUs can be depolymerized. Furthermore, we demonstrate the utility of the recovered isocyanate in the production of second-generation PUs with thermal properties and molecular weights similar to those of the virgin PUs. Overall, this route uniquely provides an opportunity for circularity in PU materials and can add significant value to end-of-life PU products.

Female sex and systolic blood pressure are independently associated with coronary microvascular dysfunction in asymptomatic adults with type 2 diabetes

Introduction

Coronary microvascular dysfunction is frequently reported in people with type 2 diabetes (T2D), is associated with reduced exercise capacity, and is a prognostic marker. Identifying modifiable risk factors associated with microvascular dysfunction may facilitate early intervention to improve outcomes in these patients.

Purpose

To identify independent determinants of myocardial perfusion reserve (MPR) in asymptomatic adults with T2D and no prevalent cardiovascular disease.

Methods

Prospective cross-sectional study. People with and without T2D and no signs, symptoms or evidence of cardiovascular disease underwent comprehensive phenotyping with echocardiography, coronary artery calcium scoring, and multiparametric cardiac MRI including adenosine stress and rest perfusion with automated pixel-wise myocardial blood flow (MBF) mapping. Participants with regional perfusion defects indicating obstructive coronary disease or silent myocardial infarct on late-gadolinium enhancement were excluded from analysis. Univariable and multivariable linear regression was performed to identify independent determinants of MPR.

Results

Two-hundred people with T2D (diabetes duration 11±8 years) were compared with 39 sex- and ethnicity-matched non-diabetic controls (Table 1). People with T2D had higher body mass index (BMI) and ambulatory 24-hour systolic blood pressure (SBP). There was evidence of concentric left ventricular (LV) remodelling (higher LV mass/volume), extracellular matrix expansion (higher ECV fraction), and both systolic and diastolic dysfunction (lower global longitudinal systolic strain and E/A ratio, respectively) in those with T2D. Resting MBF was similar between groups, but stress MBF tended to be lower in T2D compared to controls with significantly reduced MPR in T2Ds (2.87±0.86 vs 3.18±0.82, p=0.043). In univariable analysis, MPR correlated with sex, 24-hour SBP, and E/e' ratio. In a multivariable model adjusting for clinical (age, sex, smoking status, BMI, ambulatory SBP, diabetes duration, HbA1c, low-density lipoprotein, albuminuria) and imaging variables (E/e' ratio, LV mass/volume, global longitudinal strain, myocardial ECV, coronary calcium score) known to affect coronary perfusion, female sex (β=−0.227, p=0.013) and 24-hour SBP (β=−0.275, p=0.001) were the only variables independently associated with MPR.

Conclusion

Female sex is associated with coronary microvascular dysfunction in asymptomatic people with T2D but not LV mass or myocardial extracellular volume. Systolic BP is the only modifiable independent determinant of MPR and may be an early target for intervention to prevent heart failure development in these patients.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): National Institute for Health Research (NIHR) United Kingdom through a Research Professorship award (RP-2017-08-ST2-007).British Heart Foundation through a Clinical Research Training Fellowship award (FS/16/47/32190).

Epicardial adipose tissue volume and density is associated with cardiac dysfunction in asymptomatic people with type 2 diabetes

Background

Type 2 diabetes (T2D) is associated with several perturbations of cardiac structure and function, which are precursors to the development of heart failure. Excess accumulation of epicardial adipose tissue (EAT) may contribute to cardiac dysfunction in individuals with T2D. Lipid-laden adipocytes have a lower computed tomography (CT) attenuation and can be readily identified using cardiac CT. Using a multimodality cardiac imaging approach, we aimed to assess the association of total and low attenuation EAT volume with early markers of cardiac dysfunction in people with T2D.

Methods

Prospective case-control study, in which participants with and without T2D and no known cardiovascular disease, underwent comprehensive cardiovascular phenotyping including multiparametric cardiac magnetic resonance imaging (MRI), echocardiography and non-contrast cardiac CT. EAT volume was measured from CT scans using a deep learning method and volumes indexed to body surface area. Total EAT was defined according to CT adipose tissue attenuation range of −30 to −190 Hounsfield Units (HU) and low attenuation EAT as −90 to −190 HU. Left ventricular (LV) volumes, function and strain measurements were derived from cardiac MRI images and diastolic function also assessed using echocardiography. Markers of early cardiac dysfunction in those with T2D were assessed for associations with EAT in T2D participants using multivariable linear regression analyses.

Results

Two hundred and fifty-four participants were included: demographic, anthropometric and imaging variables are displayed in Table 1. Subjects with T2D had increased LV concentric remodelling (higher LV mass/volume ratio), diastolic dysfunction (lower circumferential peak early diastolic strain rate (PEDSR) and average E/e') and reduced systolic function (global longitudinal strain, GLS) compared with controls. Total and low attenuation indexed EAT volumes were 1.6-fold and 2-fold higher, respectively, in participants with T2D compared to controls (Figure 1). After adjustment for age, gender, ethnicity, insulin resistance, systolic blood pressure and waist/hip ratio, total and low attenuation indexed EAT volume were independently associated with LV mass/volume ratio (total indexed EAT volume: β=0.002, p=0.02, low attenuation indexed EAT volume: β=0.004, p=0.01) and LV GLS (total indexed EAT volume: β=−0.02, p<0.01, low attenuation indexed EAT volume: β=−0.04, p=0.02) in subjects with T2D, but not indices of diastolic dysfunction.

Conclusion

Total and low attenuation EAT volumes are higher in individuals with T2D, and excess EAT accumulation is independently associated with early markers of cardiac dysfunction. Further studies into the underlying mechanisms of this interaction may facilitate the development of interventions targeted at EAT, which could mitigate against the development of heart failure in people with T2D.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): United Kingdom National Institute for Health Research

Inter-field strength agreement of left atrial assessment at 1.5T and 3T

Background

The agreement of left atrial (LA) volumetric and strain parameters between 1.5 and 3-tesla cardiovascular magnetic resonance (CMR) is not known. We aimed to investigate inter-field strength agreement of LA measurements in healthy volunteers scanned at both field strengths on the same day.

Methods

22 healthy volunteers were prospectively recruited and randomized to undergo scanning at either 1.5T or 3T first, immediately crossing over to the other field strength and scanned by the same radiographer. Steady-state free precession cines were analyzed blinded using Medis Suite. LA volumes and LA emptying fraction (LAEF) were calculated using the biplane area length method. LA strain (LAS) was assessed on 4- and 2-chamber and average values were calculated for LA reservoir, conduit, and booster pump function. Data were compared with paired t-tests and agreement was assessed by Bland-Altman plots and intra-class correlation coefficients (ICC).

Results

The median age was 32.5 (IQR 27.5, 42.5) and 45% were male. Key results are shown in the table and figure. There were no significant differences in the LA volumetric or strain mean values between 1.5T and 3T, although Bland-Altman analysis demonstrated a slightly positive bias at 1.5T for LAVmax, LAEF and LAS parameters. The inter-field strength agreement was excellent for LA volumes, reservoir and conduit strain (ICC >0.85, p<0.001), whilst LAEF showed good agreement (ICC=0.77, p=0.001). LAS at booster pump showed poor agreement, with the lowest ICC. The limits of agreement on Bland-Altman analysis were comparable for LAEF and LAS at reservoir.

Conclusion

There was excellent inter-field strength agreement for LA volumes, reservoir and conduit strain, suggesting that measurements can be used interchangeably between field strengths. Booster pump LAS had poor agreement, which is likely due to the fact that this measurement is less reproducible than volumes and reservoir/conduit LAS.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): National Institute for Health Research (NIHR)

Inter-field strength agreement of cardiovascular magnetic resonance cine-derived strain and strain rate measures: a randomised study

Background

Left ventricular (LV) strain and strain rate measurements can be derived from routinely acquired cardiovascular magnetic resonance (CMR) cine images by feature tracking techniques. However, the inter-field strength agreement of strain measurements derived from these techniques is not known. We hypothesised that there would be excellent inter-field strength agreement (between 1.5 and 3 Tesla [T]) for the measurement of global strain and strain rate derived from cine imaging.

Methods

Prospective, randomised cross-over observational study. Healthy volunteers each underwent CMR scans at 1.5T and 3T within 30 minutes on the same day in a randomised order. Retrospectively ECG gated, short and long-axis balanced steady state free precession cine images were obtained using standardised acquisition parameters at both field strengths. Two software packages were used to derive LV global longitudinal, circumferential and long and short axis radial systolic strain, peak systolic, early diastolic and late diastolic strain rates. All strain values are expressed as positive numbers.

Results

Twenty-two subjects (mean age 36±12 years; 45% male) were studied. No differences in heart rate and blood pressure measurements during scanning were observed between field strengths. The abstract figure shows an example of strain analysis and Bland-Altman plots for global longitudinal and circumferential strain. Minimal bias was seen in all strain and strain rate measurements between field strengths using the first software package. Strain and strain rate values derived from long axis images (longitudinal and long axis radial) showed poor to fair agreement (intraclass correlation co-efficient (ICC) range 0.39–0.71), whereas measures derived from short axis images (circumferential and short axis radial) showed good to excellent agreement between field strengths (ICC range 0.78–0.91). Similar results were observed with the second software package, though the differences in agreement between long and short axis derived measures were less pronounced.

Conclusion

Longitudinal strain and strain rate measures derived from CMR feature tracking have poor inter-field strength agreement between 1.5T and 3T. By contrast, agreement of circumferential and short axis radial strain and strain rate measurements at 1.5T and 3T is good. These results need to be considered when assessing strain at different field strengths.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): United Kingdom National Institute for Health Research

Impaired myocardial calcium handling in people with type 2 diabetes: an in vivo manganese-enhanced magnetic resonance imaging study

Background

There is a high prevalence of subclinical cardiac dysfunction in people with type 2 diabetes (T2D) which is associated with subsequent development of heart failure. Dysregulated myocardial calcium handling has been demonstrated in animal models of T2D and may be a key mechanism driving the development of heart failure. Manganese-enhanced cardiac magnetic resonance imaging (MEMRI) provides a unique method to assess in vivo myocardial calcium handling.

Purpose

To determine whether myocardial calcium handling is perturbed in people with T2D with no history of cardiovascular disease. We hypothesised that myocardial manganese uptake would be reduced in people with T2D compared with healthy volunteers.

Methods

Cross-sectional case-control study, adults with (n=20) and without (n=9) T2D underwent both gadolinium-enhanced MRI and MEMRI. Standard gadolinium-enhanced MRI was used to assess cardiac structure, function and tissue characteristics. MEMRI scans were performed within two weeks of the initial scan. Native T1 maps were obtained in the mid-short axis slice position using a Modified Look-Locker Inversion recovery sequence. An intravenous infusion of manganese dipyridoxyl diphosphate (5 μmol/kg (0.1 mL/kg) at 1 mL/min) was administered and T1 maps at the same location were repetitively acquired every 2.5 min for 30 min. Regions of interest were drawn in the inferoseptal segment and blood pool for all T1 maps from 0 to 30 min by a single observer. The primary outcome was the rate of manganese uptake which was assessed by Patlak modelling as a measure of myocardial calcium handling. Manganese uptake constants were compared using analysis of co-variance, with age, sex and body mass index as co-variates.

Results

Subjects with T2D were older (62±7 vs. 57±5 years, p=0.046) but body mass index (29.0±4.5 vs. 26.2±3.4 kg/m2, p=0.106), systolic (135±16 vs. 134±17 mmHg, p=0.809) and diastolic (81±10 vs. 83±9 mmHg, p=0.736) blood pressures were similar. Compared to control subjects, participants with T2D had normal systolic function but more concentric left ventricular remodelling (mass/volume ratio 0.90±0.14 vs. 0.71±0.06 g/mL, p<0.001) and reduced peak early diastolic strain rate (0.64±0.17 vs. 0.91±0.26 s–1, p=0.002). Myocardial manganese uptake was substantially reduced in people with T2D compared with controls (6.51±1.46 vs. 8.45±2.52 ml/100 g of tissue/min, p=0.003) (Figure 1).

Conclusions

For the first time, we have demonstrated in vivo that despite no history of cardiovascular disease and normal systolic function, patients with T2D have marked impairment of myocardial calcium handling. This has potential major implications for the pathogenesis, diagnosis and treatment of diabetic cardiomyopathy.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): British Heart Foundation and National Institute for Health Research

Test-retest reproducibility of echocardiography and CMR in the same patients for assessing left atrial function

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia

Background

 Cardiovascular magnetic resonance (CMR) has been shown to give higher left atrial (LA) volumes than trans-thoracic echocardiography (TTE) but the agreement and test-retest reproducibility of LA functional measure have not been directly compared in the same patient cohort.

Methods

 People with type 2 diabetes mellitus (T2D) without cardiovascular disease underwent TTE and CMR on the same day on two separate occasions with a mean period of 11± 4 days. TTE images were analysed using TomTec-ARENA (v2.4, 2D-CPA), where Medis Suite (v3.1, medical imaging system) was used for CMR images. The analysis included LA strain, corresponding to LA reservoir, conduit, and booster pump (contraction function), LA volumes, and LA emptying fraction (LAEF), which was calculated using area length method. Strain and volume were assessed on 4- and 2-chamber long-axis and average values were calculated for both modalities.

Results

 10 participants with T2D (mean age 65.6 ± 7.3 years, 50% male) were studied. CMR LA volumes were significantly higher and LAEF significantly lower compared to TTE (P < 0.01 for all), whilst reservoir strain on CMR was lower compared to TTE (29.2 ± 6.5 vs 33.8 ± 3.7, p = 0.04).  The inter-modality agreement was moderate for LA volumes and contraction strain (ICC ≥0.55) and poor for LAEF, strain at reservoir and conduit. Overall, the test-retest reproducibility of CMR was higher than for TTE, but the overall limits of agreement were not too dissimilar on Bland-Altman analysis (Table & Figure). TTE reproducibility was good for LA volumes and strain at conduit (CoV 18-24%, ICC ∼0.80) and moderate for LAEF, strain at reservoir and contraction. CMR showed excellent test-retest reproducibility for LA volumes, EF and strain at reservoir (CoV 7-20%, ICC ≥0.83).

Conclusion

 The test-retest reproducibility of CMR is slightly better than TTE for LA assessment using volumes and strain. LA volumes have superior reproducibility compared to functional LA parameters. Abstract Table: Test-retest reproducibility  Abstract Figure: Bland-Altman plot

Cardiac magnetic resonance strain and mechanical dispersion assessment in patients with chronic total coronary artery occlusion

Background

Chronic total occlusions (CTO) are a frequent angiographic finding. Viability of CTO-subtended myocardium is dependent on the presence of an adequate collateral circulation. At rest, collateral supply may be sufficient to avert ischaemia and maintain normal systolic function. However, it remains unclear whether CTO-subtended myocardium may be considered truly normal, or whether subtle functional abnormalities may be present at rest.

Purpose

To determine whether, in the absence of infarction and hibernation, CTO-subtended myocardium remains functionally normal or whether abnormalities of strain and/or mechanical dispersion may be present at rest.

Methods

In a retrospective, single centre, observational study, we studied patients with ≥1 angiographically-diagnosed CTO referred for clinical stress perfusion cardiovascular magnetic resonance (CMR), and compared healthy volunteers (HVs) with a normal stress CMR scan. CMR imaging comprised functional and scar assessment with qualitative [visual] evaluation of infarction and segmental wall motion. Patients with infarction and/or wall motion score index (WMSI) ≥1 were excluded from further analysis. In remaining CTO subjects and HVs, segmental peak systolic longitudinal strain and circumferential strain were analysed (in 3 long-axis planes and 3 short-axis planes, respectively) and mechanical dispersion for both orientations was computed. Image analysis was performed using Medis (QStrain) software blinded to all clinical information.

Results

From a total of 389 patients with ≥1 angiographically-diagnosed CTO, 68 had normal WMSI and no infarction (63.0±11.7 years, 79.4% male, LVEF 62.6±4.5%). Fifty HVs (61.1±7.0 years, 74.0% males, LVEF 61.1±5.3%) were also studied. The majority of CTO patients had concomitant coronary artery disease in at least one non-CTO vessel (n=37, 54.4%). GLS was lower in CTO patients than HVs (−21.8%±1.5% versus −24.0±1.1%; p<0.0001; Figure 1). By contrast, GCS was greater in CTO patients (−32.7±2.5% versus −28.8±2.1%; p<0.0001). Mechanical dispersion was increased in CTO patients (Figure 2), both longitudinally (90.3±14.6 ms in CTO patients versus 68.6±11.1 ms in HVs; p<0.0001) and circumferentially (66.7±9.1 ms versus 55.3±6.6 ms, respectively; p=0.02).

Conclusion

Subclinical changes in left ventricular dynamics are present at rest in CTO patients with fully viable myocardium and no evidence of resting regional wall abnormality. Further study is warranted to evaluate the potential association between mechanical dispersion and arrhythmic events in CTO.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): NIHR Clinician Scientist Award (CS-2018-18-ST2-007 to J.R.A.) and Research Professorship award (RP-2017-08-ST2-007 to G.P.M.). Figure 1. Strain analysis. CTO vs HVFigure 2. Mechanical dispersion. CTO vs HV

Prognostic value of pulmonary transit time by cardiac magnetic resonance in patients with heart failure with preserved ejection fraction

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): National Institute for Health Research Leicester Cardiovascular Biomedical Research Centre

Background

Quantifying pulmonary transit time (PTT) from cardiac magnetic resonance (CMR) first pass perfusion imaging is a novel technique for the evaluation of haemodynamic congestion in heart failure. Previous studies have demonstrated that PTT is prolonged in patients with heart failure with reduced ejection fraction (HFrEF) and that it provides independent prognostic information in this patient group. However, the potential diagnostic and prognostic roles of PTT assessment in patients with heart failure with preserved ejection fraction (HFpEF) remain to be established.

Aim

To compare PTT in healthy controls and in patients with HFpEF, and to determine the prognostic value of PTT in HFpEF.

Methods

In a prospective, observational study, HFpEF and age-matched control subjects underwent multi-parametric CMR at 3-Tesla, comprising quantitative left ventricular volumetric assessment using a standard steady-state free precession (SSFP) pulse sequence, and first-pass perfusion imaging at rest using a T1-weighted segmented inversion recovery gradient echo sequence (following injection of 0.04mmol/kg of contrast). PTT was calculated as the time interval between the peaks of signal intensity curves in the right and left ventricular blood pools (defined on the basal slice of the rest perfusion images). The primary endpoint was the composite of death or hospitalisation with heart failure.

Results

88 HFpEF patients (age 73 ± 9 years, 51% male, EF 56.4 ± 5.6%) and 40 controls (age 73 ± 5 years, 43% male, EF 58.5 ± 4.7%) were studied. PTT was comparable in HFpEF patients (7.7 ± 3.8s) and in healthy controls (7.5 ± 1.8, p = 0.69). Normalised to cardiac cycle lengths, PTT remained comparable in HFpEF patients and healthy controls (8.5 ± 4.0 cardiac cycles versus 7.8 ± 1.6 cardiac cycles, respectively, p = 0.19). In the HFpEF group, during median follow-up of 3.4 years, there were 38 events (25 hospitalisations with heart failure, 13 deaths); a significant relationship between survival and PTT was not demonstrated (HR 1.06 [0.99,1.14] for a one-unit increase, p = 0.098).

Conclusion

In HFpEF, PTT is not prolonged compared with PTT in healthy subjects. Unlike in HFrEF, PTT does not appear to be diagnostically or prognostically significant in HFpEF.

Figure 1: Graph showing signal intensity curves in the right (red) and left (green) ventricular blood pools

Figure 2: Kaplan-Meier plot showing comparable rates of the composite endpoint in patients with PTT greater/less than median PTT (8 cardiac cycles)

GH replacement in patients with non-functioning pituitary adenoma (NFA) treated solely by surgery is not associated with increased risk of tumour recurrence

BACKGROUND

Subjects with non-functioning pituitary adenomas (NFAs) frequently develop GH deficiency due to tumour expansion or as a consequence of tumour therapy. The safety of GH replacement (GHR) in these individuals remains unclear.

OBJECTIVE

To assess the effect of GHR on tumour recurrence in patients with NFAs solely treated by surgical removal.

PATIENTS AND METHODS

The study involved all patients with NFA who presented to the Department of Endocrinology in Oxford between January 1989 and July 2005 and were treated solely by surgical removal of the tumour. Patients with follow up < 1 year were excluded. Recurrence was diagnosed on the basis of radiological appearances (detectable tumour after gross total removal or regrowth of pre-existing residue) on regular imaging surveillance.

RESULTS

One hundred and thirty patients were included in the study, and were followed up for a mean period of 6.8 +/- 4.2 years (median 5.7, range 1.2-17.6). Twenty-three patients received GHR [16 male, 7 female, mean age at tumour diagnosis 53.7 +/- 14.6 years (range 20-80)]. The mean duration of GHR was 4.6 +/- 2.5 years (median 5.3, range 0.4-8.7). One hundred and seven subjects did not receive GH therapy [61 male, 46 female, mean age at tumour diagnosis 56.2 +/- 14.0 years (range 20-87)]. Tumour regrowth occurred in 38 non-GH treated subjects (36%) and 8 GHR subjects (35%). Regrowth was detected at a mean of 4.8 +/- 2.8 years (range 1-11 years) in the non-GH treated group, and at 6.5 +/- 2.3 years in the GHR group. In the GHR group, recurrence occurred after a mean of 2.9 +/- 2.2 years (range 0.4-5.9 years) following commencement of GH treatment. The Cox regression analysis showed that after adjusting for sex, age at tumour diagnosis, cavernous sinus invasion at diagnosis and type of tumour removal (partial or complete based on postoperative scan), GH treatment was not a significant independent predictor of recurrence (P = 0.09; hazard ratio = 0.51; 95% CI, 0.24-1.12).

CONCLUSION

GH replacement in patients with NFA treated by surgery alone is not associated with an increased risk of tumour recurrence.

Distribution of hydrogen in the near surface of Mars: evidence for subsurface ice deposits

Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15% of the layer by weight.

Telomerase inhibitors for the treatment of cancer: the current perspective

Telomerase is a holoenzyme responsible for the maintenance of telomeres, the protein-nucleic acid complexes at the ends of eukaryotic chromosomes that serve to maintain chromosomal stability and integrity. Telomerase activity is essential for the sustained proliferation of most immortal cells, including cancer cells. Since the discovery that telomerase activity is detected in 85-90% of all human tumours and tumour-derived cell lines but not in most normal somatic cells, telomerase has become the focus of much attention as a novel and potentially highly-specific target for the development of new anticancer chemotherapeutics. Herein we review the current perspective for the development of telomerase inhibitors as cancer chemotherapeutics. These include antisense strategies, reverse transcriptase inhibitors and compounds capable of interacting with high-order telomeric DNA tetraplex ("G-quadruplex") structures, so as to prevent enzyme access to the necessary linear telomere substrate. Critical appraisal of each individual approach is provided together with highlighted areas of likely future development.

Design, docking, and evaluation of multiple libraries against multiple targets

We present a general approach to the design, docking, and virtual screening of multiple combinatorial libraries against a family of proteins. The method consists of three main stages: docking the scaffold, selecting the best substituents at each site of diversity, and comparing the resultant molecules within and between the libraries. The core "divide-and-conquer" algorithm for side-chain selection, developed from an earlier version (Sun et al., J Comp Aided Mol Design 1998;12:597-604), provides a way to explore large lists of substituents with linear rather than combinatorial time dependence. We have applied our method to three combinatorial libraries and three serine proteases: trypsin, chymotrypsin, and elastase. We show that the scaffold docking procedure, in conjunction with a novel vector-based orientation filter, reproduces crystallographic binding modes. In addition, the free-energy-based scoring procedure (Zou et al., J Am Chem Soc 1999;121:8033-8043) is able to reproduce experimental binding data for P1 mutants of macromolecular protease inhibitors. Finally, we show that our method discriminates between a peptide library and virtual libraries built on benzodiazepine and tetrahydroisoquinolinone scaffolds. Implications of the docking results for library design are explored.

Chemical modification of a variant of human MIP-1alpha; implications for dimer structure

A sequence variant of human MIP-1alpha, in which Asp26 has been replaced by Al alpha, has been chemically modified by the addition of 13C-labeled methyl groups at each of the lysine residues and the N-terminus. The sites of methylation have been verified by a combination of MALDI-TOF mass spectrometric experiments and tryptic digestion followed by N-terminal mapping. The effect of the modification on the structure and activity of the protein have been determined by analytical ultra-centrifugation, 13C NMR spectroscopy and receptor binding studies. The results of these experiments suggest that huMIP-alpha D26A (BB10010), when present as a dimer, adopts a globular structure, like MCP-3, rather than the elongated or cylindrical structure determined for dimers of huMIP-1beta and RANTES.

The elemental composition of asteroid 433 eros: results of the NEAR-shoemaker X-ray spectrometer

We report major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000. Low aluminum abundances for all regions argue against global differentiation of Eros. Magnesium/silicon, aluminum/silicon, calcium/silicon, and iron/silicon ratios are best interpreted as a relatively primitive, chondritic composition. Marked depletions in sulfur and possible aluminum and calcium depletions, relative to ordinary chondrites, may represent signatures of limited partial melting or impact volatilization.

Internal mammary artery perfusing Leriche's syndrome in association with significant coronary arteriosclerosis: four case reports and review of literature

Four cases of collateral perfusion of a lower extremity by way of an internal mammary artery in the presence of Leriche's syndrome are described. Angiographic documentation preceding coronary artery bypass grafting prevented an acutely ischemic leg in two of the cases.

Internal mammary artery perfusing the Leriche's syndrome

Two cases of collateral perfusion of a lower extremity, by way of an internal mammary artery, in the presence of Leriche's syndrome are described. The importance of recognizing this condition prior to coronary artery bypass grafting is emphasized.

Structural equilibria in RNA as revealed by 19F NMR

We have incorporated 5-fluorouridine into several sites within a 19-mer RNA modelled on the translational operator of the MS2 bacteriophage. The 19F NMR spectra demonstrate the different chemical shifts of helical and loop fluorouridines of the hairpin secondary structure. Addition of salt gives rise to a species in which the loop fluorouridine gains the chemical shift of its helical counterparts, due to the formation of the alternative bi-molecular duplex form. This is supported by UV thermal melting behaviour which becomes highly dependent on the RNA concentration. Distinct 19F NMR signals for duplex and hairpin forms allow the duplex-hairpin equilibrium constant to be determined under a range of conditions, enabling thermodynamic characterisation and its salt dependence to be determined. Mg2+ also promotes duplex formation, but more strongly than Na+, such that at 25 degrees C, 10 mM MgCl2 has a comparable duplex-promoting effect to 300 mM NaCl. A similar effect is observed with Sr2+, but not Ca2+ or Ba2+. Additional hairpin species are observed in the presence of Na+ as well as Mg2+, Ca2+, Sr2+ and Ba2+ ions. The overall, ensemble average, hairpin conformation is therefore salt-dependent. Electrostatic considerations are thus involved in the balance between different hairpin conformers as well as the duplex-hairpin equilibrium. The data presented here demonstrate that 19F NMR is a powerful tool for the study of conformational heterogeneity in RNA, which is particularly important for probing the effects of metal ions on RNA structure. The thermodynamic characterisation of duplex-hairpin equilibria will also be valuable in the development of theoretical models of nucleic acid structure.

The H(2)(18)O solvent-induced isotope shift in (19)F NMR

The H(2)(16)O/H(2)(18)O solvent-induced isotope shifts ((18)O SIIS) of the (19)F NMR signals of a number of fluorine compounds have been measured. These isotope shifts are observed to be upfield, downfield, or zero, depending on the specific compound and the precise solution conditions. At 25 degrees C and with an (18)O enrichment of 86%, the (18)O SIIS of several fluorinated amino acids were in the range of 0.0014-0.0018 ppm downfield. 5-Fluorouridine displays a significantly wider range of (18)O SIIS values. A 5-fluorouridine-labeled 16-mer RNA also displayed observable (18)O SIIS values, but the characteristics of these were significantly modified from those of free 5-fluorouridine. The experimental observations are consistent with the (18)O SIIS being composed of upfield and downfield components, with the relative contributions of these determining the size and direction of the overall isotope shift. This is discussed in terms of a combination of van der Waals interactions between the fluorine atom and the solvent, electrical and hydrogen bonding effects, and the perturbations to these due to (18)O substitution in the solvent water. This isotope effect promises to be a highly useful tool in a range of (19)F NMR studies.

Leriche's syndrome with total perfusion of the left lower extremity by way of the left internal mammary artery

A case of collateral perfusion of a lower extremity by way of an internal mammary artery in the presence of Leriche's syndrome is described. The importance of recognizing this condition before coronary artery bypass grafting is emphasized.

Evaluation of home blood pressure monitors in children and adolescents

OBJECTIVE

This study was designed to adapt commercially available home blood pressure monitors for use in children ages 4 to 18 years and to compare the recordings obtained from the adapted devices to those obtained using a standard mercury sphygmomanometer.

METHODS

Sequential same-arm blood pressures were measured by trained observers in 106 children, ages 4 to 18 years, using a calibrated mercury-gravity manometer (reference device) as the standard method, and 3 test devices (an aneroid manometer and two semiautomated oscillometric devices). For each patient, mid-arm circumference was measured and appropriate blood pressure cuff size was selected. Systolic and diastolic pressures were measured by trained observers using the reference device and the aneroid manometer in accordance with criteria established by the Second Task Force on Blood Pressure Control in Children. Other than variation in cuff size, all manufacturers' recommendations were followed for each test device.

RESULTS

Outcome was assessed using criteria established by the British Hypertension Society (BHS) and the Association for the Advancement of Medical Instrumentation (AAMI). The aneroid manometer consistently received a grade of A using BHS criteria and also passed using AAMI criteria. Neither of the two semiautomated monitors achieved a passing grade, although the Labtron monitor performed slightly better than the Marshall 85 monitor.

CONCLUSIONS

Home blood pressure monitors must be validated for use in children prior to widespread use. Given appropriate training and verification of observer accuracy, the aneroid manometer can be recommended for home use in children ages 4 to 18 years.

Permeation of human ovarian tissue with cryoprotective agents in preparation for cryopreservation

The recent improvements in the treatment of cancer by chemo- and radiotherapy have led to a significant increase in the survival rates of patients with malignant disease, but at the expense of distressing side effects. One major problem, especially for younger patients, is that aggressive therapy destroys a significant proportion of the follicular population, which can result in either temporary or permanent infertility. Freeze-banking pieces of ovarian cortex prior to treatment is one strategy for preserving fecundity. When the patient is in remission, fertility could, theoretically, be restored by autografting the thawed tissue at the orthotopic site or by growing isolated follicles to maturity in vitro. Recent studies have found good follicular survival in frozen-thawed human ovarian tissue but to optimize the process an effective cryopreservation method needs to be developed. An essential part of such a technique is to permeate the tissue with a cryoprotectant to minimize ice formation and the extent of this equilibration is an important determinant of post-thaw cellular survival. In the current study, we have investigated the diffusion of four cryoprotective agents into human tissue at both 4 degrees C and 37 degrees C. We have also studied the effect of adding different concentrations of the non penetrating cryoprotective agent, sucrose, to the freezing media using the release of lactate dehydrogenase as a measure of its protective effect. At 4 degrees C propylene glycol and glycerol penetrated the tissue significantly slower than either ethylene glycol or dimethyl sulphoxide. At the higher temperature of 37 degrees C all four cryoprotectants penetrated at a faster rate, however concern about enhanced toxicity prevents the use of these conditions in practice. Thus, the results suggest that the best method of preparing tissue for freezing is exposure for 30 min to 1.5 M solutions of ethylene glycol or dimethyl sulphoxide at 4 degrees C; this achieved a mean tissue concentration that was almost 80% that of the bathing solution. We also report that the addition of low concentrations of sucrose to the freezing medium does not have a significant protective effect against freezing injury.

Capturing the structure of a catalytic RNA intermediate: the hammerhead ribozyme

The crystal structure of an unmodified hammerhead RNA in the absence of divalent metal ions has been solved, and it was shown that this ribozyme can cleave itself in the crystal when divalent metal ions are added. This biologically active RNA fold is the same as that found previously for two modified hammerhead ribozymes. Addition of divalent cations at low pH makes it possible to capture the uncleaved RNA in metal-bound form. A conformational intermediate, having an additional Mg(II) bound to the cleavage-site phosphate, was captured by freeze-trapping the RNA at an active pH prior to cleavage. The most significant conformational changes were limited to the active site of the ribozyme, and the changed conformation requires only small additional movements to reach a proposed transition-state.

Antibiotic interactions with the hammerhead ribozyme:tetracyclines as a new class of hammerhead inhibitor

A screening of a range of common laboratory antibiotics for inhibition of the hammerhead ribozyme has shown that in addition to certain aminoglycosides (most notably neomycin B) the tetracyclines are also effective inhibitors, with chlorotetracycline being more effective than tetracycline. Inhibition by chlorotetracycline is not as strong as that by neomycin B but is more complicated, with at least two binding sites apparent. As with hammerhead inhibition by neomycin B, chlorotetracycline inhibition can be overcome by raising the concentration of the Mg2+ ion cofactor. We find that around six Mg2+ ions will displace neomycin B, compared with twelve for chlorotetracycline. Inhibition observed in the presence of mixtures of neomycin B and chlorotetracycline is consistent with separate binding sites on the hammerhead for these two classes of antibiotic. Under certain conditions of the mixing order and low concentration of chlorotetracycline, enhancement of single-turnover hammerhead cleavage by up to 20% is observed, with higher concentrations of antibiotic being inhibitory. We have also found that the presence of 2.5% (v/v) DMSO causes a 30% enhancement of the single-turnover cleavage. These results thus extend the range of known inhibitors of hammerhead cleavage, and also demonstrate how the cleavage can be accelerated.

The roles of the conserved pyrimidine bases in hammerhead ribozyme catalysis: evidence for a magnesium ion-binding site

We report details of the synthesis and characterization of oligoribonucleotides containing 4-thiouridine or 2-pyrimidinone ribonucleoside (4HC). We have used these probes to examine the roles of the conserved pyrimidines in the central core of the hammerhead ribozyme. The effects on catalysis of singly-substituted hammerhead ribozyme and substrate strands were quantified in multiple-turnover reactions. Various effects were observed on kcat. and Km, with up to a 7-fold decrease and a 3-fold increase respectively. For substitutions with 4HC at positions 3 or 17, catalytic activity in single turnover reactions can be increased up to 8-fold equivalent to 40% of wild-type activity, by increasing the concentration of the Mg2+ cofactor, implying that these substitutions had a deleterious effect on Mg2+ binding. Calculations of the change in the apparent free energy of binding for variants at positions 3, 4 or 17 are each consistent with deletion of a single hydrogen-bond to an uncharged group in the ribozyme. The cytidine 5' to the scissile phosphate had not previously been thought to play a direct role in catalysis, however, removal of the exocyclic amino group decreased kcat. 4-fold. Recently, the crystal structures of a hammerhead ribozyme bound to either a non-cleavable 2'-deoxy substrate strand or a ribo-substrate strand have been reported. The kinetic properties of the variants described here are consistent with several key interactions seen in the crystals, in particular they provide experimental support for the assignment of the proposed catalytically active magnesium ion-binding site.

Effects of substitution of Thr63 by alanine on the structure and function of Lactobacillus casei dihydrofolate reductase

A mutant of Lactobacillus casei dihydrofolate reductase has been constructed in which Thr63, a residue which interacts with the 2'-phosphate group of the bound coenzyme, is replaced by alanine. This substitution does not affect kcat, but produces an 800-fold increase in the Km for NADPH, which reflects dissociation of NADPH from the enzyme-NADPH-tetrahydrofolate complex, and a 625-fold increase (corresponding to 3.8 kcal/mol) in the dissociation constant for the enzyme-NADPH complex. The difference in magnitude of these effects indicates a small effect of the substitution on the negative cooperativity between NADPH and tetrahydrofolate. Stopped-flow studies of the kinetics of NADPH binding show that the weaker binding arises predominantly from a decrease in the association rate constant. NMR spectroscopy was used to compare the structures of the mutant and wild-type enzymes in solution, in their complexes with methotrexate and with methotrexate and NADPH. This showed that only minimal structural changes result from the mutation; a total of 47 residues were monitored from their resolved 1H resonances, and of these nine in the binary complex and six in the ternary differed in chemical shift between mutant and wild-type enzyme. These affected residues are confined to the immediate vicinity of residue 63. There is a substantial difference in the 31P chemical shift of the 2'-phosphate of the bound coenzyme, reflecting the loss of the interaction with the side chain of Thr63. The only changes in nuclear Overhauser effects (NOEs) observed were decreases in the intensity of NOEs between protons of the adenine ring of the bound coenzyme and the nearby residues Leu62 and Ile102, showing that the substitution of Thr63 does cause a change in the position or orientation of the adenine ring in its binding site.

A general purification procedure for chemically synthesized oligoribonucleotides

A general procedure for the purification of chemically synthesized oligoribonucleotides is reported. Purification based on the use of a single reverse-phase HPLC column with buffer systems of differing ion-pairing capacity is described. These methods have been applied to the preparation of a series of RNAs which range in size from 10 to 46 nucleotides. The yields obtained are high, up to 53% (based on isolated product compared to those obtained from final trityl assay). The purity of the isolated material is 96-99%. Thus with this general procedure, milligram quantities of extremely pure RNA can be efficiently obtained.

NMR studies of multiple conformations in complexes of Lactobacillus casei dihydrofolate reductase with analogues of pyrimethamine

1H and 19F NMR signals from bound ligands have been assigned in one- and two-dimensional NMR spectra of complexes of Lactobacillus casei dihydrofolate reductase with various pyrimethamine analogues (including pyrimethamine [1, 2,4-diamino-5-(4'-chlorophenyl)-6-ethylpyrimidine], fluoropyrimethamine [2, 2,4-diamino-5-(4'-fluorophenyl)-6-ethylpyrimidine], fluoronitropyrimethamine [3, 2,4-diamino-5-(4'-fluoro-3'-nitrophenyl) -6-ethylpyrimidine], and methylbenzoprim [4, 2,4-diamino-5-[4'- (methylbenzylamino)-3'-nitrophenyl]-6-ethylpyrimidine]). The signals were identified mainly by correlating signals from bound and free ligands by using 2D exchange experiments. Analogues (such as 1 and 2) with symmetrically substituted phenyl rings give rise to 1H signals from four nonequivalent aromatic protons, clearly indicating the presence of hindered rotation about the pyrimidine-phenyl bond. Analogues containing asymmetrically substituted aromatic rings (such as 3 and 4) exist as mixtures of two rotational isomers (an enantiomeric pair) because of this hindered rotation and the NMR spectra revealed that both isomers (forms A and B) bind to the enzyme with comparable, though unequal, binding energies. In this case two complete sets of bound proton signals were observed. The phenyl ring protons in each of the two forms experience essentially the same protein environment (same shielding) as that experienced by the corresponding protons in bound pyrimethamine: this confirms that forms A and B correspond to two rotational isomers resulting from approximately 180 degrees rotation about the pyrimidine-phenyl bond, with the 2,4-diaminopyrimidine ring being bound similarly in both forms. The relative orientations of the two forms have been determined from NOE through-space connections between protons on the ligand and protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The 1H-NMR assignments of the aromatic resonances in complexes of Lactobacillus casei dihydrofolate reductase and the origins of their chemical shifts

All the aromatic proton resonances in the 500-MHz NMR spectra of Lactobacillus casei dihydrofolate reductase have been assigned for several of its complexes with inhibitors. For the complexes with methotrexate and trimethoprim this was achieved by using a combination of NMR techniques in conjunction with a selectively deuterated protein designed to simplify the spectra such that nuclear Overhauser effect (NOE) connections could be detected with greater ease and certainty. By correlating these NOE data with crystal structure data on related complexes it was possible to assign all the aromatic resonances and to extend these assignments to spectra of other complexes of dihydrofolate reductase. The conformation-dependent chemical shifts observed for many of the resonances could be explained qualitatively, but not quantitatively, in terms of ring-current shifts. The discrepancies between calculated ring-current shifts and the observed conformation-dependent shifts could not in general be accounted for satisfactorily in terms of carbonyl-group anisotropic shielding contributions calculated using presently available models. In the case of the H delta 1, delta 2 protons of Phe30 some of the discrepancy probably results from a difference in the conformation of the Phe ring between the solution and crystal states.

Twenty-four-hour variations in ornithine decarboxylase and acid phosphatase in mice

Polyamines are essential for cell growth and differentiation. Ornithine decarboxylase (ODC) is the rate-limiting enzyme in polyamine biosynthesis. Acid phosphatases (AP) are lysosomal enzymes that are important in normal intracellular metabolism. Twenty-four-hour variations in these enzymes may be important in understanding the temporal responses of different tissues to various stimuli. The purpose of this study was to examine a variety of tissues for fluctuations in the levels of ODC and AP over a 24-hr period. Significant circadian variations in the amount of ODC activity were observed in all tissues examined. Activity of AP varied with time of day in the liver, kidney, and heart. The highest and lowest measurements of ODC activity were as follows: liver, 81.5 +/- 7.0, 47.9 +/- 4.4; colon, 11.7 +/- 1.2, 3.1 +/- 0.7; stomach 3.1 +/- 0.4, 0.9 +/- 0.1; kidney, 420.9 +/- 0.9, 67.5 +/- 0.8; and heart, 4.7 +/- 1.0, 2.5 +/- 0.2. The highest and lowest measurements of AP activity were as follows: liver 3.8 +/- 0.1, 2.8 +/- 0.1; kidney, 3.4 +/- 0.1, 1.9 +/- 0.1; and heart, 2.6 +/- 0.1, 2.0 +/- 0.1. These findings suggest that rhythmic fluctuations in polyamine biosynthesis and lysosomal enzymes may influence other metabolic pathways differentially throughout 24 hr.

Dihydrofolate reductase: control of the mode of substrate binding by aspartate 26

The complex of Lactobacillus casei dihydrofolate reductase with the substrate folate and the coenzyme NADP+ has been shown to exist in solution as a mixture of three slowly interconverting conformations whose proportions are pH-dependent and which differ in the orientation of the pteridine ring of the substrate in the binding site. The Asp26----Asn mutant of L. casei dihydrofolate reductase has been prepared by oligonucleotide-directed mutagenesis and studied by one- and two-dimensional 1H-NMR spectroscopy. NMR studies of the mutant enzyme--folate--NADP+ complex show that this exists to greater than 90% in a single conformation over the pH* range 5-7.1. The single conformation observed corresponds to conformation I (the 'methotrexate-like' conformation) of the wild-type enzyme--folate--NADP+ complex. These observations demonstrate that Asp26 is the ionizable group controlling the pH-dependence of the conformational equilibrium seen in the wild-type enzyme.

The stereochemical course of phosphoryl transfer catalyzed by herpes simplex virus type I-induced thymidine kinase

Herpes simplex virus type I (HSV-I)-induced thymidine kinase has been shown to catalyze phosphoryl transfer from adenosine 5'-[gamma-(S)-16O,17O,18O]triphosphate to thymidine with inversion of configuration at phosphorus. The simplest interpretation of this result is that phosphoryl transfer occurs by a single in-line group transfer between ATP and thymidine within the ternary enzyme complex.

Improved transmission electron microscopy (TEM) of cultured cells through a "floating sheet" method

Cultured cells provide isolated systems for both biochemical and morphological studies. Previous methods of processing cell culture specimens for electron microscopy (EM) have been limited to sectioning either a monolayer or centrifuged cell suspensions which are not morphologically intact. In our improved method, N-butylglycidyl ether is added to cell cultures (2-5 min with agitation) following in situ fixation (3.0% glutaraldehyde in 0.1 M Pipes, pH 7.2, for 20 min, osmium tetraoxide 4% for 20 min). A thin pliable "sheet" of cells floats free from the plastic culture device and can be manipulated (centrifuged or folded) to obtain a vast number of morphologically intact cells for examination. We have examined several cell types (vascular smooth muscle, lung, liver, and endothelial cells) grown in two types of plastic culture flasks (Nunc and Falcon). This new method provides excellent EM morphology, maximizes the number of cells examined, and allows determination of cell orientation since a remnant of the dissolved flask remains loosely bound to the bottom of the cells.

The use of structured scenarios in genetic counselling

Nineteen women at risk of bearing a child with either Duchenne muscular dystrophy or a neural tube defect participated in a structured scenario study. Eight scenarios were created to allow the women to "try out" possible reproductive outcomes. Our findings suggest that the use of scenarios may be helpful in reproductive counselling, particularly for those women who have difficulty discussing emotional issues.

Computed Tomographic Analysis of Meteorite Inclusions

The discovery of isotopic anomalies in the calcium- and aluminum-rich inclusions of the Allende meteorite has improved our knowledge of the origin of the solar system. Inability to find more inclusions without destroying the meteorite has hampered further study. By using a fourth-generation computed tomographic scanner with modifications to the software only, the interior of heterogeneous materials such as Allende can be nondestructively probed. The regions of material with high and low atomic numbers are displayed quickly. The object can then be cut to obtain for analysis just the areas of interest.

Cosmic-Ray Record in Solar System Matter

The energetic nuclei in cosmic rays interact with meteoroids, the moon, planets, and other solar system matter. The nuclides and heavy nuclei tracks produced by the cosmic-ray particles in these targets contain a wealth of information about the history of the objects and temporal and spatial variations in the particle fluxes. Most lunar samples and meny meteorites have complex histories of cosmicray exposure from erosion, gardening, fragmentation, orbital changes, and other processes. There appear to be variations in the past fluxes of solar particles, and possibly also galactic cosmic rays, on time scales of 10(4) to 10(7) years.

Alpha Particles in Solar Cosmic Rays over the Last 80,000 Years

Present-day (1967 to 1969) fluxes of alpha particles from solar cosmic rays, determined from satellite measurements, were used to calculate the production rates of cobalt-57, cobalt-58, and nickel-59 in lunar surface samples. Comparisons with the activities of nickel-59 (half-life, 8 x 10(4) years) measured in lunar samples indicate that the long-term and present-day fluxes of solar alpha particles are comparable within a factor of approximately 4.