The maximal and current accuracy of rigorous protein-ligand binding free energy calculations

Computational techniques can speed up the identification of hits and accelerate the development of candidate molecules for drug discovery. Among techniques for predicting relative binding affinities, the most consistently accurate is free energy perturbation (FEP), a class of rigorous physics-based methods. However, uncertainty remains about how accurate FEP is and can ever be. Here, we present what we believe to be the largest publicly available dataset of proteins and congeneric series of small molecules, and assess the accuracy of the leading FEP workflow. To ascertain the limit of achievable accuracy, we also survey the reproducibility of experimental relative affinity measurements. We find a wide variability in experimental accuracy and a correspondence between binding and functional assays. When careful preparation of protein and ligand structures is undertaken, FEP can achieve accuracy comparable to experimental reproducibility. Throughout, we highlight reliable protocols that can help maximize the accuracy of FEP in prospective studies.

Enhancing Water Sampling in Free Energy Calculations with Grand Canonical Monte Carlo

The prediction of protein-ligand binding affinities using free energy perturbation (FEP) is becoming increasingly routine in structure-based drug discovery. Most FEP packages use molecular dynamics (MD) to sample the configurations of proteins and ligands, as MD is well-suited to capturing coupled motion. However, MD can be prohibitively inefficient at sampling water molecules that are buried within binding sites, which has severely limited the domain of applicability of FEP and its prospective usage in drug discovery. In this paper, we present an advancement of FEP that augments MD with grand canonical Monte Carlo (GCMC), an enhanced sampling method, to overcome the problem of sampling water. We accomplished this without degrading computational performance. On both old and newly assembled data sets of protein-ligand complexes, we show that the use of GCMC in FEP is essential for accurate and robust predictions for ligand perturbations that disrupt buried water.

Ligand Binding Free Energies with Adaptive Water Networks: Two-Dimensional Grand Canonical Alchemical Perturbations

Computational methods to calculate ligand binding affinities are increasing in popularity, due to improvements in simulation algorithms, computational resources, and easy-to-use software. However, issues can arise in relative ligand binding free energy simulations if the ligands considered have different active site water networks, as simulations are typically performed with a predetermined number of water molecules (fixed N ensembles) in preassigned locations. If an alchemical perturbation is attempted where the change should result in a different active site water network, the water molecules may not be able to adapt appropriately within the time scales of the simulations—particularly if the active site is occluded. By combining the grand canonical ensemble (μVT) to sample active site water molecules, with conventional alchemical free energy methods, the water network is able to dynamically adapt to the changing ligand. We refer to this approach as grand canonical alchemical perturbation (GCAP). In this work we demonstrate GCAP for two systems; Scytalone Dehydratase (SD) and Adenosine A_2A receptor. For both systems, GCAP is shown to perform well at reproducing experimental binding affinities. Calculating the relative binding affinities with a naïve, conventional attempt to solvate the active site illustrates how poor results can be if proper consideration of water molecules in occluded pockets is neglected. GCAP results are shown to be consistent with time-consuming double decoupling simulations. In addition, by obtaining the free energy surface for ligand perturbations, as a function of both the free energy coupling parameter and water chemical potential, it is possible to directly deconvolute the binding energetics in terms of protein–ligand direct interactions and protein binding site hydration.

Binding Modes of Ligands Using Enhanced Sampling (BLUES): Rapid Decorrelation of Ligand Binding Modes via Nonequilibrium Candidate Monte Carlo

Accurately predicting protein-ligand binding affinities and binding modes is a major goal in computational chemistry, but even the prediction of ligand binding modes in proteins poses major challenges. Here, we focus on solving the binding mode prediction problem for rigid fragments. That is, we focus on computing the dominant placement, conformation, and orientations of a relatively rigid, fragment-like ligand in a receptor, and the populations of the multiple binding modes which may be relevant. This problem is important in its own right, but is even more timely given the recent success of alchemical free energy calculations. Alchemical calculations are increasingly used to predict binding free energies of ligands to receptors. However, the accuracy of these calculations is dependent on proper sampling of the relevant ligand binding modes. Unfortunately, ligand binding modes may often be uncertain, hard to predict, and/or slow to interconvert on simulation time scales, so proper sampling with current techniques can require prohibitively long simulations. We need new methods which dramatically improve sampling of ligand binding modes. Here, we develop and apply a nonequilibrium candidate Monte Carlo (NCMC) method to improve sampling of ligand binding modes. In this technique, the ligand is rotated and subsequently allowed to relax in its new position through alchemical perturbation before accepting or rejecting the rotation and relaxation as a nonequilibrium Monte Carlo move. When applied to a T4 lysozyme model binding system, this NCMC method shows over 2 orders of magnitude improvement in binding mode sampling efficiency compared to a brute force molecular dynamics simulation. This is a first step toward applying this methodology to pharmaceutically relevant binding of fragments and, eventually, drug-like molecules. We are making this approach available via our new Binding modes of ligands using enhanced sampling (BLUES) package which is freely available on GitHub.

Biomolecular Simulations under Realistic Macroscopic Salt Conditions

Biomolecular simulations are typically performed in an aqueous environment where the number of ions remains fixed for the duration of the simulation, generally with either a minimally neutralizing ion environment or a number of salt pairs intended to match the macroscopic salt concentration. In contrast, real biomolecules experience local ion environments where the salt concentration is dynamic and may differ from bulk. The degree of salt concentration variability and average deviation from the macroscopic concentration remains, as yet, unknown. Here, we describe the theory and implementation of a Monte Carlo osmostat that can be added to explicit solvent molecular dynamics or Monte Carlo simulations to sample from a semigrand canonical ensemble in which the number of salt pairs fluctuates dynamically during the simulation. The osmostat reproduces the correct equilibrium statistics for a simulation volume that can exchange ions with a large reservoir at a defined macroscopic salt concentration. To achieve useful Monte Carlo acceptance rates, the method makes use of nonequilibrium candidate Monte Carlo (NCMC) moves in which monovalent ions and water molecules are alchemically transmuted using short nonequilibrium trajectories, with a modified Metropolis-Hastings criterion ensuring correct equilibrium statistics for an ( Δμ, N, p, T) ensemble to achieve a ∼1046× boost in acceptance rates. We demonstrate how typical protein (DHFR and the tyrosine kinase Src) and nucleic acid (Drew-Dickerson B-DNA dodecamer) systems exhibit salt concentration distributions that significantly differ from fixed-salt bulk simulations and display fluctuations that are on the same order of magnitude as the average.

Large-scale analysis of water stability in bromodomain binding pockets with grand canonical Monte Carlo

Conserved water molecules are of interest in drug design, as displacement of such waters can lead to higher affinity ligands and in some cases, contribute towards selectivity. Bromodomains, small protein domains involved in the epigenetic regulation of gene transcription, display a network of four conserved water molecules in their binding pockets and have recently been the focus of intense medicinal chemistry efforts. Understanding why certain bromodomains have displaceable water molecules and others do not is extremely challenging, and it remains unclear which water molecules in a given bromodomain can be targeted for displacement. Here we estimate the stability of the conserved water molecules in 35 bromodomains via binding free energy calculations using all-atom grand canonical Monte Carlo simulations. Encouraging quantitative agreement to the available experimental evidence is found. We thus discuss the expected ease of water displacement in different bromodomains and the implications for ligand selectivity.

Replica-Exchange and Standard State Binding Free Energies with Grand Canonical Monte Carlo

The ability of grand canonical Monte Carlo (GCMC) to create and annihilate molecules in a given region greatly aids the identification of water sites and water binding free energies in protein cavities. However, acceptance rates without the application of biased moves can be low, resulting in large variations in the observed water occupancies. Here, we show that replica-exchange of the chemical potential significantly reduces the variance of the GCMC data. This improvement comes at a negligible increase in computational expense when simulations comprise of runs at different chemical potentials. Replica-exchange GCMC is also found to substantially increase the precision of water binding free energies as calculated with grand canonical integration, which has allowed us to address a missing standard state correction.

Waterdock 2.0: Water placement prediction for Holo-structures with a pymol plugin

Water is often found to mediate interactions between a ligand and a protein. It can play a significant role in orientating the ligand within a binding pocket and contribute to the free energy of binding. It would thus be extremely useful to be able to accurately predict the position and orientation of water molecules within a binding pocket. Recently, we developed the WaterDock protocol that was able to predict 97% of the water molecules in a test set. However, this approach generated false positives at a rate of over 20% in most cases and whilst this might be acceptable for some applications, in high throughput scenarios this is not desirable. Here we tackle this problem via the inclusion of knowledge regarding the solvation structure of ligand functional groups. We call this new protocol WaterDock2 and demonstrate that this protocol maintains a similar true positive rate to the original implementation but is capable of reducing the false-positive rate by over 50%. To improve the usability of the method, we have also developed a plugin for the popular graphics program PyMOL. The plugin also contains an implementation of the original WaterDock.

Water Sites, Networks, And Free Energies with Grand Canonical Monte Carlo

Water molecules play integral roles in the formation of many protein-ligand complexes, and recent computational efforts have been focused on predicting the thermodynamic properties of individual waters and how they may be exploited in rational drug design. However, when water molecules form highly coupled hydrogen-bonding networks, there is, as yet, no method that can rigorously calculate the free energy to bind the entire network or assess the degree of cooperativity between waters. In this work, we report theoretical and methodological developments to the grand canonical Monte Carlo simulation technique. Central to our results is a rigorous equation that can be used to calculate efficiently the binding free energies of water networks of arbitrary size and complexity. Using a single set of simulations, our methods can locate waters, estimate their binding affinities, capture the cooperativity of the water network, and evaluate the hydration free energy of entire protein binding sites. Our techniques have been applied to multiple test systems and compare favorably to thermodynamic integration simulations and experimental data. The implications of these methods in drug design are discussed.

One Size Does Not Fit All: The Limits of Structure-Based Models in Drug Discovery

A major goal in computational chemistry has been to discover the set of rules that can accurately predict the binding affinity of any protein-drug complex, using only a single snapshot of its three-dimensional structure. Despite the continual development of structure-based models, predictive accuracy remains low, and the fundamental factors that inhibit the inference of all-encompassing rules have yet to be fully explored. Using statistical learning theory and information theory, here we prove that even the very best generalized structure-based model is inherently limited in its accuracy, and protein-specific models are always likely to be better. Our results refute the prevailing assumption that large data sets and advanced machine learning techniques will yield accurate, universally applicable models. We anticipate that the results will aid the development of more robust virtual screening strategies and scoring function error estimations.

Oseltamivir-resistant 2009 H1N1 influenza pneumonia during therapy in a renal transplant recipient

The emergence of oseltamivir-resistant 2009 H1N1 influenza virus (conferred by the H275Y substitution in NA) during therapy or prophylaxis in immunocompromised patients is a serious concern. The optimal therapy for immunosuppressed patients with oseltamivir-resistant 2009 H1N1 influenza virus is unknown and few options exist. We report a 10-yr-old recipient of kidney transplant who was hospitalized with oseltamivir-resistant 2009 H1N1 influenza pneumonia complicated by severe respiratory failure, ARDS, and renal failure requiring institution of ECMO and CRRT. On presentation, treatment with oseltamivir (second course) and broad-spectrum antibiotics was initiated. Immunosuppressive agents were stopped on hospital day (d) 2. On hospital d 7, given his critical status, immunocompromised state, and difficulty in obtaining intravenous zanamivir, after obtaining ethical approval and parental consent, he was treated with intravenous peramivir (through an Emergency Investigational New Drug Application) for two wk. He tolerated the regimen well and his clinical status improved gradually. Several factors may have contributed to virus clearance and survival including recovery of the immune system, aggressive critical care support, and administration of peramivir. Ongoing surveillance is essential to monitor how oseltamivir-resistant H275Y mutant viruses may evolve in the future.

Rapid and accurate prediction and scoring of water molecules in protein binding sites

Water plays a critical role in ligand-protein interactions. However, it is still challenging to predict accurately not only where water molecules prefer to bind, but also which of those water molecules might be displaceable. The latter is often seen as a route to optimizing affinity of potential drug candidates. Using a protocol we call WaterDock, we show that the freely available AutoDock Vina tool can be used to predict accurately the binding sites of water molecules. WaterDock was validated using data from X-ray crystallography, neutron diffraction and molecular dynamics simulations and correctly predicted 97% of the water molecules in the test set. In addition, we combined data-mining, heuristic and machine learning techniques to develop probabilistic water molecule classifiers. When applied to WaterDock predictions in the Astex Diverse Set of protein ligand complexes, we could identify whether a water molecule was conserved or displaced to an accuracy of 75%. A second model predicted whether water molecules were displaced by polar groups or by non-polar groups to an accuracy of 80%. These results should prove useful for anyone wishing to undertake rational design of new compounds where the displacement of water molecules is being considered as a route to improved affinity.

S5-5: A Phase III, Randomized, Double-Blind, Placebo-Controlled Registration Trial To Evaluate the Efficacy and Safety of Pertuzumab + Trastuzumab + Docetaxel vs. Placebo + Trastuzumab + Docetaxel in Patients with Previously Untreated HER2−Positive Metastatic Breast Cancer (CLEOPATRA)

Background: Pertuzumab (P) is a fully humanized investigational monoclonal antibody that binds to human epidermal growth factor receptor 2 (HER2), preventing dimerization of HER2 with other HER family members and inducing antibody-dependent cell-mediated cytotoxicity. Its mechanisms of action are complementary to those of the anti-HER2 antibody trastuzumab (H) and the two antibodies combined have superior activity compared with either antibody alone in preclinical and clinical studies. In patients with advanced disease, P in combination with H has been shown to be active in patients whose disease has progressed while on H therapy (Baselga et al. J Clin Oncol 2010). Furthermore, P has been shown to improve the activity of H and docetaxel (T) in a randomized neoadjuvant study (Gianni et al. SABCS 2010, S3-2). No increase in overall toxicity and, in particular, no increase in cardiac events was observed with the addition of P to H and HT regimens.

Methods: In this double-blind Phase III study patients with centrally confirmed HER2−positive metastatic or locally recurrent, unresectable breast cancer were randomized to receive either placebo+H+T or P+H+T. Patients could have received one prior hormonal treatment for metastatic breast cancer and/or prior systemic neoadjuvant or adjuvant therapy including prior H and T. Patients had to have a baseline left ventricular ejection fraction ≥50% and no history of declines to <50% during or after prior H therapy.

Study medication was as follows: P 840 mg loading dose followed by 420 mg q3w; H 8 mg/kg loading dose followed by 6 mg/kg q3w; T 75 mg/m2 q3w (with subsequent dose escalation to 100 mg/m2 if 75 mg/m2 was well tolerated). Patients were recommended to receive at least 6 cycles of T. In the case of chemotherapy discontinuation due to cumulative toxicity, antibody therapy was continued until disease progression, unacceptable toxicity, or withdrawal of consent.

Patients were stratified according to region and prior treatment status (adjuvant therapy or de novo metastatic breast cancer).

The primary endpoint for the study was progression-free survival (PFS) as determined by independent review. The primary analysis was planned to take place when approximately 381 independently confirmed PFS events had occurred. This would provide 80% power to detect a 33% improvement in PFS (HR=0.75) at the two-sided significance level of 5%. Secondary endpoints included overall survival, investigator-determined PFS, overall response rate, duration of response, safety, and quality of life.

Patient safety was monitored throughout the study by an independent data monitoring committee and a cardiac review committee.

This study is registered at ClinicalTrials.gov: NCT00567190.

Results: 808 patients were recruited between February 2008 and July 2010. The required number of PFS events for analysis of the primary endpoint has been reached and independent assessment PFS is currently being performed. Results of the primary analysis of efficacy and safety will be presented.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S5-5.

Purpura fulminans caused by community-associated methicillin-resistant Staphylococcus aureus

Sepsis-induced purpura fulminans is a rare but life-threatening condition characterized by rapidly progressive hemorrhagic infarction of the skin due to dermal vascular thrombosis resulting in tissue loss and severe scarring. Although most commonly related to meningococcal or invasive group A streptococcal disease, it may also be caused by several other bacterial or viral pathogens including Pneumococcus and Varicella. Purpura fulminans associated with Staphylococcus aureus sepsis is rare but has been reported in adults. However, the syndrome is very unusual in children, and to our knowledge, only 2 cases of staphylococcal purpura fulminans have been reported in children, both due to methicillin-susceptible S aureus in the United Kingdom. We report the first well-described case of purpura fulminans due to community-associated methicillin-resistant S aureus in a child.

Inhaled nitric oxide induced NOS inhibition and rebound pulmonary hypertension: a role for superoxide and peroxynitrite in the intact lamb

Previous in vivo studies indicate that inhaled nitric oxide (NO) decreases nitric oxide synthase (NOS) activity and that this decrease is associated with significant increases in pulmonary vascular resistance (PVR) upon the acute withdrawal of inhaled NO (rebound pulmonary hypertension). In vitro studies suggest that superoxide and peroxynitrite production during inhaled NO therapy may mediate these effects, but in vivo data are lacking. The objective of this study was to determine the role of superoxide in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy in vivo. In control lambs, 24 h of inhaled NO (40 ppm) decreased NOS activity by 40% (P<0.05) and increased endothelin-1 levels by 64% (P<0.05). Withdrawal of NO resulted in an acute increase in PVR (60.7%, P<0.05). Associated with these changes, superoxide and peroxynitrite levels increased more than twofold (P<0.05) following 24 h of inhaled NO therapy. However, in lambs treated with polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) during inhaled NO therapy, there was no change in NOS activity, no increase in superoxide or peroxynitrite levels, and no increase in PVR upon the withdrawal of inhaled NO. In addition, endothelial NOS nitration was 18-fold higher (P<0.05) in control lambs than in PEG-SOD-treated lambs following 24 h of inhaled NO. These data suggest that superoxide and peroxynitrite participate in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy. Reactive oxygen species scavenging may be a useful therapeutic strategy to ameliorate alterations in endogenous NO signaling during inhaled NO therapy.

Tezosentan, a combined parenteral endothelin receptor antagonist, produces pulmonary vasodilation in lambs with acute and chronic pulmonary hypertension

OBJECTIVE

To investigate the hemodynamic effects of tezosentan in the intact lamb both at rest and during acute and chronic pulmonary hypertension.

DESIGN

Prospective, randomized experimental study.

SETTING

University-based research laboratory.

SUBJECTS

Lambs with and without pulmonary hypertension.

INTERVENTIONS

Six newborn lambs were instrumented to measure vascular pressures and left pulmonary blood flow. The hemodynamic effects of tezosentan (0.5, 1.0, 5.0 mg/kg, intravenously) were studied at rest and during U46619-induced pulmonary hypertension. Following in utero placement of an aortopulmonary vascular graft, nine additional lambs with increased pulmonary blood flow and chronic pulmonary hypertension (shunt) were also studied at 1 wk (n = 5) and 8 wks (n = 4) of age.

MEASUREMENTS AND MAIN RESULTS

At rest, tezosentan had no significant effect on any of the variables. During acute U46619-induced pulmonary hypertension, tezosentan caused a dose-dependent decrease in pulmonary arterial pressure (from 5.9% +/- 4.7 to 16.0% +/- 10.7; p < .05) and pulmonary vascular resistance (from 6.2% +/- 8.0 to 21% +/- 8.8; p < .05). Mean systemic arterial pressure was unchanged. In 1- and 8-wk-old shunt lambs with increased pulmonary blood flow, tezosentan (1 mg/kg) produced potent nonselective pulmonary vasodilation.

CONCLUSIONS

Tezosentan, a combined endothelin receptor antagonist optimized for parenteral use, induces potent selective pulmonary vasodilation during acute U46619-induced pulmonary hypertension and potent nonselective vasodilation in chronic pulmonary hypertension secondary to increased pulmonary blood flow. In general, the hemodynamic effects of bolus doses of tezosentan occurred within 60 secs of administration and lasted approximately 5-10 mins. The hemodynamic profile of intravenous tezosentan may make it a useful adjunct therapy for acute pulmonary hypertensive disorders and warrants further study.

Endothelial alterations during inhaled NO in lambs with pulmonary hypertension: implications for rebound hypertension

Clinically significant increases in pulmonary vascular resistance (PVR) have been noted upon acute withdrawal of inhaled nitric oxide (iNO). Previous studies in the normal pulmonary circulation demonstrate that iNO increases endothelin-1 (ET-1) levels and decreases endogenous nitric oxide synthase (NOS) activity, implicating an endothelial etiology for the increase in resistance upon iNO withdrawal. However, the effect of iNO on endogenous endothelial function in the clinically relevant pulmonary hypertensive circulation is unknown. The objective of this study was to determine the effects of iNO on endogenous NO-cGMP and ET-1 signaling in lambs with preexisting pulmonary hypertension secondary to increased pulmonary blood flow. Eight fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt lambs). After delivery (4 wk), the shunt lambs were mechanically ventilated with iNO (40 ppm) for 24 h. After 24 h of inhaled NO, plasma ET-1 levels increased by 34.8% independently of changes in protein levels (P < 0.05). Contrary to findings in normal lambs, total NOS activity did not decrease during iNO. In fact, Western blot analysis demonstrated that tissue endothelial NOS protein levels decreased by 43% such that NOS activity relative to protein levels actually increased during iNO (P < 0.05). In addition, the beta-subunit of soluble guanylate cyclase decreased by 70%, whereas phosphodiesterase 5 levels were unchanged (P < 0.05). Withdrawal of iNO was associated with an acute increase in PVR, which exceeded baseline PVR by 45%, and a decrease in cGMP concentrations to levels that were below baseline. These data suggest that the endothelial response to iNO and the potential mechanisms of rebound pulmonary hypertension are dependent upon the underlying pulmonary vasculature.

Modification of radiation-induced acute oral mucositis in the rat

PURPOSE

A new non-toxic drug (compound A) consisting of curcumin, alpha-tocopherol and sunflower oil was developed and its efficacy tested in the treatment of radiation-induced oral mucositis in the rat.

MATERIAL AND METHODS

Mature (12 weeks old, 200-225 g) female Sprague-Dawley rats were used. While under general anaesthesia, the tongues of the animals were slightly extended outside and a region of the underside of the tongue was irradiated in-situ with single doses of 2.27 MeV beta-rays from a 5-mm diameter 90Sr/90Y plaque. The dose-rate of the source was about 10 Gy min(-1) at the surface of the mucus membrane. Irradiations and subsequent assessment of the lesion were carried out under general anaesthesia maintained by a 1.5% halothane/oxygen mixture. Six groups of animals were irradiated with single doses of 13.5, 15.0, 16.5 or 18Gy. One subgroup (radiation only) received no further treatment, while the other five groups received 0.5 ml day(-1) of either compound A, sunflower oil, alpha-tocopherol, curcumin or water containing 10% ethanol by oral gavage until the end of experiments. Mucosal ulceration (erosion of mucosal epithelium) was considered as an end-point. From the day after irradiation until any acute radiation-induced oral mucosal lesion had healed, the tongues of the animals were assessed daily for the presence of radiation-induced mucositis (mucosal ulceration). Quantal data for the incidence of radiation-induced mucositis were analysed using logit analysis and a dose-modification factor was obtained.

RESULTS

There was a modest increase in ED50, the dose expected to cause mucositis in 50% of the animals after both alpha-tocopherol and sunflower oil were administered. This resulted in dose-modification factors of 1.05. While curcumin treatment resulted in a dose-modification factor of 1.09. Compound A significantly reduced the incidence of radiation-induced mucositis with a statistically significant dose-modification factor of 1.2 +/- 0.1.

CONCLUSIONS

Curcumin and other components of compound A appeared to be effective in the prevention of radiation-induced oral mucositis. However, the overall effect observed with the combination drug (compound A) appeared greater than additive.

Long-term survival in a phase III, randomised study of topotecan versus paclitaxel in advanced epithelial ovarian carcinoma

BACKGROUND

We have continued to monitor the survival of patients randomised in a previously reported multicentre phase III study of topotecan versus paclitaxel in patients with advanced epithelial ovarian cancer who had failed one prior platinum-based regimen.

PATIENTS AND METHODS

Patients with bidimensionally measurable disease were randomised to topotecan (1.5 mg/m(2)/day for 5 days) or paclitaxel (175 mg/m(2)/day as a 3-h infusion) every 21 days. Patients were eligible for treatment with the alternate therapy at third line. The European Organisation for Research and Treatment of Cancer Quality of Life (EORTC QOL)-C30 questionnaire was also used to measure eight symptoms at baseline and during each course (pain, anorexia, diarrhoea, fatigue, nausea and vomiting, dyspnea, constipation and insomnia).

RESULTS

A total of 226 patients were evaluable for response. Demographic characteristics were similar in both treatment groups, as were results of the EORTC QOL-30 questionnaire. For the topotecan group, median time to progression was 18.9 weeks (range <1 to 92.6+ weeks; 25% censored), and, for paclitaxel, 14.7 weeks (range <1 to 137.3+ weeks; 12.3% censored); P = 0.076. At 4 years post-randomisation, median survival in the topotecan group was 63.0 weeks (range <1 to 238.4+ weeks; 20.5% censored) and, for paclitaxel, 53.0 weeks (range <1 to 226.3+ weeks; 12.3% censored); P = 0.44.

CONCLUSION

Topotecan continues to demonstrate comparable efficacy and survival to paclitaxel with manageable and non-cumulative haematological toxicity. Non-haematological toxicity was generally mild for both groups. The long-term survival rate indicates substantial therapeutic benefit for this group of patients receiving topotecan at relapse of ovarian cancer.

Emergence of smooth muscle cell endothelin B-mediated vasoconstriction in lambs with experimental congenital heart disease and increased pulmonary blood flow

BACKGROUND

Endothelin-1 (ET-1) has been implicated in the pathophysiology of pulmonary hypertension. In 1-month-old lambs with increased pulmonary blood flow, we have demonstrated early alterations in the ET-1 cascade. The objective of this study was to investigate the role of potential later alterations of the ET cascade in the pathophysiology of pulmonary hypertension secondary to increased pulmonary blood flow.

METHODS AND RESULTS

Eighteen fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt) and were studied 8 weeks after spontaneous delivery. Compared with age-matched control lambs, lung tissue ET-1 levels were increased in shunt lambs (317.2+/-113.8 versus 209.8+/-61.8 pg/g, P<0.05). In shunt lambs (n=9), exogenous ET-1 induced potent pulmonary vasoconstriction, which was blocked by the ETA receptor antagonist PD 156707 (n=3). This pulmonary vasoconstriction was mimicked by exogenous Ala1,3,11,15 ET-1 (4 Ala ET-1), the ETB receptor agonist, and was blocked by the ETB receptor antagonist BQ 788 (n=3). However, in control lambs (n=7), ET-1 and 4 Ala ET-1 did not change pulmonary vascular tone. In contrast to 4-week-old shunt lambs, immunohistochemistry revealed the emergence of ETB receptors on smooth muscle cells in the vasculature of 8-week-old shunt lambs.

CONCLUSIONS

Over time, increased pulmonary blood flow and/or pressure results in the emergence of ETB-mediated vasoconstriction, which coincides with the emergence of ETB receptors on smooth muscle cells. These data suggest an important role for ETB receptors in the pathophysiology of pulmonary hypertension in this animal model of increased pulmonary blood flow.

Topotecan in combination with carboplatin: phase I trial evaluation of two treatment schedules

BACKGROUND

Topotecan and cisplatin combinations have shown schedule-dependent toxicity, which may in part be due to cisplatin nephrotoxicity. As carboplatin is less nephrotoxic and increasingly replacing cisplatin in clinical practice, the aim of this study was to define the optimal sequence and dose for topotecan in combination with carboplatin.

PATIENTS AND METHODS

Two parallel phase I trials, with pharmacokinetic studies, were conducted administering carboplatin on day 1 with topotecan on days 1-5 (schedule A) or days 8-12 (schedule B). repeated every 3 weeks.

RESULTS

Twenty-one patients were treated over two dose levels, carboplatin AUC 4 [glomerular filtration rate (GFR) calculated from 51Cr-EDTA clearance] with topotecan 0.5 or 0.75 mg/m2. At the first dose level, six patients were evaluable for each schedule. With schedule A, from 34 cycles, there were two dose reductions and 10 treatment delays due to myelosuppression. With schedule B from 25 cycles, there was one reduction and 10 delays. At dose level 2, both patients in schedule A had dose-limiting neutropenia. In contrast, there was no dose-limiting toxicity with schedule B in six patients, although the majority of cycles were delayed.

CONCLUSION

The combination of topotecan and carboplatin using these 3-weekly schedules lead to significant myelotoxicity with attendant dose reductions and delays; the optimal scheduling of these agents remains to be defined.

Evidence for humoral effects on the radiation response of rat foot skin

The influence of perturbation of the physiologic state of the whole body on the outcome of radiation exposure has been examined in a rat foot model. Irradiation was carried out using 60Co gamma-rays. Moist desquamation was used as an endpoint. Rats were given a priming dose of 2 Gy, 4 Gy or 7 Gy to their whole body except their hind feet (partial body priming dose). After a variable time period both hind feet of these animals were irradiated with graded doses of 60Co gamma-rays. The incidence of moist desquamation in the irradiated feet of these animals was compared with the incidence of moist desquamation in animals that had not received the initial partial body priming dose. It was noticed that the incidence of moist desquamation in the rat foot skin of animals that received 7 Gy partial body priming dose 4 h prior to irradiation of their hind feet was significantly less than moist desquamation in control animals. The ED(50) value of 22.53+/-0.16 Gy for moist desquamation of the foot skin of control animals was significantly lower (p<0.01) than the value of 25.25+/-0.29 Gy obtained for animals that received a partial body priming dose of 7 Gy 4 h prior to irradiation of their hind feet. It was concluded that the response of rat foot skin to radiation was not purely the result of epidermal stem cell kill and that it can be modified by alterations in the overall physiological state of the animal's body brought about by a priming dose to the whole of the animal's body except the hind feet.

Oral topotecan as single-agent second-line chemotherapy in patients with advanced ovarian cancer

PURPOSE

To evaluate oral topotecan as single-agent, second-line therapy in patients with ovarian cancer previously treated with a platinum-based regimen.

PATIENTS AND METHODS

Patients (N = 116) received oral topotecan 2.3 mg/m2 daily for 5 days every 21 days. Eligibility criteria included histologic diagnosis of International Federation of Gynecology and Obstetrics stage III or IV epithelial ovarian cancer, bidimensionally measurable disease, prior platinum-containing chemotherapy, age > or = 18 years, performance status < or = 2, and life expectancy > or = 12 weeks.

RESULTS

Overall response rate was 21.6% (25 of 116 patients). Median duration of response was 25.0 weeks; median time to response was 8.4 weeks. Median time to progression was 14.1 weeks; median survival was 62.2 weeks. Grade 4 neutropenia was experienced by 50.4% of patients in 13.4% of courses administered. Grade 4 thrombocytopenia was experienced by 22.1% of patients in 5.1% of courses. Grade 3 or 4 anemia was experienced by 29.2% of patients in 8.5% of courses. Most frequent nonhematologic toxicities were predominantly (> 90%) grade 1 or 2 and included nausea, alopecia, diarrhea, and vomiting.

CONCLUSION

Second-line oral topotecan administered at 2.3 mg/m2 for 5 days every 21 days demonstrated activity in patients with progressive or recurrent ovarian cancer after first-line platinum-based chemotherapy. This activity was comparable to that seen in previous studies with intravenous topotecan. Grade 4 neutropenia was less frequent with oral topotecan than previously reported for intravenous topotecan. Oral topotecan is an active, tolerable, and convenient formulation of an established agent for the second-line treatment of advanced epithelial ovarian cancer and may also facilitate exploring prolonged treatment schedules.

Stabilization of disease as an indicator of clinical benefit associated with chemotherapy in non-small cell lung cancer patients

In Phase II oncology studies, response rate has traditionally been used to assess activity. However stabilization of disease (SD) may also provide patient benefit. To assess the value of SD (stabilization of measurable disease for at least 8 weeks) as a predictor of survival following chemotherapy in patients with non-small cell lung cancer (NSCLC), we have analyzed data from 198 NSCLC patients receiving topotecan i.v. or orally as first-line therapy either as single agent or in combination. Proportional hazards (Cox) regression models showed that responders [complete response (CR) + partial response (PR), 1.5% and 11.6% respectively] had an estimated risk of death that was 9.8% (95% CI: 4.2% to 22.7%) of that for progressive disease (PD) (60.1% of the patient population). Similarly, patients with SD (26.8% of the patient population) showed a potential benefit with a risk of death that was 27.7% of the one of patients with PD (95% CI: 17.8% to 43.1%). In conclusion SD may be a useful indicator of patient benefit from chemotherapy for NSCLC.

Phase II trial of topotecan administered as a 21-day continuous infusion in previously untreated patients with stage IIIB and IV non-small-cell lung cancer

Topotecan (9-dimethylaminoethyl-10-hydroxycamptothecin) is a topoisomerase I inhibitor. Twenty-six patients with stage IIIB or IV non-small-cell lung cancer (NSCLC) who had received no prior chemotherapy were treated in a multicenter study with topotecan 0.6 mg/m2/day for 21 days by continuous intravenous infusion every 28 days; this starting dose was decreased to 0.5 mg/m2/day in the last 23 patients because of myelosuppression. There was one partial response, for a response rate of 4% (95% confidence interval, 0.1%-19.6%). Median survival was 9 months. One-year survival was 39%. Of the 58 lung cancer symptoms at baseline, 40% were resolved by the end of best response (all in the partial response patient, 62% in stable disease patients, 26% in progressive disease patients). Catheter-related infections complicated 19% of courses. Red-cell transfusions were given in 50% of courses. Toxicity included grade 4 neutropenia (4%), grade 3-4 anemia (19%), grade 4 thrombocytopenia (8%), and catheter-related infections (19% courses). Although the major objective response rate was only 4%, patients treated with topotecan given as a 21-day continuous intravenous infusion experienced a decrease in cancer-related symptoms and a 1-year survival of 39%.

Comparison of oral chloral hydrate with intramuscular ketamine, meperidine, and promethazine for pediatric sedation--preliminary report

Fifteen consecutive pediatric patients ranging from 3 to 5 years old were selected to receive one of three sedative/hypnotic techniques. Group 1 received oral chloral hydrate 50 mg/kg, and groups 2 and 3 received intramuscular ketamine 2 mg/kg and 3 mg/kg, respectively. In addition to ketamine, patients in groups 2 and 3 received transmucosal intramuscular injections of meperidine and promethazine into the masseter muscle. Sedation for the satisfactory completion of restorative dentistry was obtained for over 40 min on average in the chloral hydrate group, but completion of dental surgery longer than 40 min was achieved in groups 2 and 3 only by intravenous supplements of ketamine.

A comparison of cardiac rate-pressure product and pressure-rate quotient with Holter monitoring in patients with hypertension and cardiovascular disease: a follow-up report

OBJECTIVES

The purpose of this study was to evaluate patients with hypertension or cardiovascular disease, or both, for myocardial ischemia and cardiac arrhythmias while undergoing minor oral surgery.

STUDY DESIGN

Sixteen patients were studied with noninvasive monitoring including heart rate, systolic, diastolic, and mean arterial blood pressure to calculate rate-pressure product (systolic blood pressure multiplied by heart rate) and pressure-rate quotient (mean arterial pressure divided by heart rate). These calculated measures were compared with the incidence of cardiac arrhythmias and ST segment depression recorded on a continuous Holter monitoring system.

RESULTS

Nine of 16 (56%) developed supraventricular or ventricular ectopy during dental extractions or minor preprosthetic surgery performed with local anesthesia 2% xylocaine with 1/100,000 epinephrine dilution. Three of the nine patients who experienced these arrhythmias had coincident abnormal rate pressure product and pressure-rate quotient values. None of these patients exhibited ST-T wave changes suggestive of myocardial ischemia. Atrial or ventricular ectopy suggests that myocardial irritability was more likely to occur than ischemia as measured by Holter monitoring and compared with abnormal rate pressure product and pressure-rate quotient values recorded.

Modulation of the cell kinetics of pig skin by the topical application of evening primrose oil or Lioxasol

The daily topical application of two compounds, a cream containing 10% evening primrose oil (EPO) and Lioxasol (a compound used clinically to treat radiation burns), resulted in increased cell proliferative activity in the skin of female Large White pigs. The effect was most pronounced in the case of the EPO based cream, and was comparable in magnitude with that observed in a previous study on pig skin using orally administered EPO. There was an increase in the size of the rete pegs in the epidermis by 6 weeks after the start of application of the EPO cream. However, this did not translate into an increase in the total thickness of the viable epidermis (excluding the stratum corneum) due to a reduction in the density of rete pegs, from 2 weeks after treatment. Lioxasol had no overall effect on the size of the rete pegs. The labelling index (LI) of cells in the basal layer of the epidermis of pigs receiving a daily topical application of EPO increased progressively with time from the start of application. The LI was maximal (17.9 +/- 2.4%) at the end of the observation period (8 weeks) at which time it was a factor of approximately 2 higher than in the basal layer prior to treatment. A considerably less marked increase in the LI of the basal layer was seen after the application of Lioxasol. The overall increase was approximately 20%, relative to the LI in the untreated epidermis. Labelled cell nuclei were also counted in the papillary dermis. After the application of the EPO cream, no significant increase in the number of labelled cells was observed until week 8, at which time values were approximately twice those in untreated skin. In Lioxasol treated skin the effect on the numbers of labelled cells in the papillary dermis was more immediate, with a approximately 60% increase at 2 weeks. This enhanced level of labelling was maintained until the end of the observation period of 10 weeks. Studies on the cell kinetics of the skin using the alcohol component of the Lioxasol preparation suggested that alcohol rather than Lioxasol was the most significant ingredient. It was concluded that the EPO cream merited further evaluation as a potential modulator of skin response to ionizing radiation.

Inhaled nitric oxide reduces the utilization of extracorporeal membrane oxygenation in persistent pulmonary hypertension of the newborn

OBJECTIVE

To determine if the use of inhaled nitric oxide therapy reduces the need for extracorporeal membrane oxygenation (ECMO) in persistent pulmonary hypertension of the newborn.

DESIGN

A matched cohort study with retrospective data extraction.

SETTING

Pediatric and neonatal intensive care units at a medical school-affiliated children's hospital serving as a regional referral center for respiratory failure.

PATIENTS

Records of all neonates transferred for rescue therapy for persistent pulmonary hypertension during the study period were analyzed, with inclusion in the study based on defined gas exchange parameters, and with exclusion from the study based on the presence of congenital heart disease, diaphragmatic hernia, or lethal chromosomal abnormality. Assignment to cohorts was based on availability of inhaled nitric oxide therapy: group 1 patients were admitted when inhaled nitric oxide was unavailable; group 2 patients were admitted when inhaled nitric oxide was available.

INTERVENTIONS

Standard criteria (alveolar-arterial oxygen tension gradient of > 600 torr [> 80 kPa], or oxygenation index of > 40) were used to trigger initial evaluation for ECMO when these criteria were met for 2 hrs, and ECMO was initiated if these criteria continued to be met for 12 hrs, or if cardiovascular instability occurred. Ventilator management in all patients was directed to improve arterial oxygenation, such that ECMO criteria were no longer met. Patients in group 2 only were treated with inhaled nitric oxide after meeting ECMO evaluation criteria, and they continued to receive inhaled nitric oxide if a quantifiable improvement in gas exchange occurred.

MEASUREMENTS AND MAIN RESULTS

Fifty patients qualified for inclusion in the analysis (29 patients in group 1, and 21 patients in group 2). In group 1, 21 (72%) patients met ECMO criteria, and 16 (76%) patients required ECMO therapy. In group 2, 16 (76%) patients met ECMO criteria, 15 patients received inhaled nitric oxide therapy, and only four (25%) patients required ECMO therapy (p = .003 compared with group 1). Treatment with inhaled nitric oxide resulted in an initial increase in PaO2, without adverse effects, in all of the treated patients. The reduction in ECMO utilization in group 2 was achieved with a higher rate of complication-free survival (survival without oxygen, requirement at 28 days, p = .018; survival without intracranial hemorrhage, p = .048), and a lower hospital cost per survivor (p = .021), compared with group 1 patients.

CONCLUSION

In neonates with persistent pulmonary hypertension, therapy with inhaled nitric oxide reliably and safely improves oxygenation, thereby resulting in a decreased need for ECMO therapy, improved patient outcome, and lower hospital costs.

Comparative assessment of single-dose and fractionated boron neutron capture therapy

The effects of fractionating boron neutron capture therapy (BNCT) were evaluated in the intracerebral rat 9L gliosarcoma and rat spinal cord models using the Brookhaven Medical Research Reactor (BMRR) thermal neutron beam. The amino acid analog p-boronophenylalanine (BPA) was administered prior to each exposure to the thermal neutron beam. The total physical absorbed dose to the tumor during BNCT using BPA was 91% high-linear energy transfer (LET) radiation. Two tumor doses of 5.1 Gy spaced 48 h apart (n = 14) or three tumor doses of 5.2 Gy, each separated by 48 h (n = 10), produced 43 and 70% long-term (> 1 year) survivors, respectively [corrected]. The outcome of neither the two nor the three fractions of radiation was statistically different from that of the corresponding single-fraction group. In the rat spinal cord, the ED50 for radiation myelopathy (as indicated by limb paralysis within 7 months) after exposure to the thermal beam alone was 13.6 +/- 0.4 Gy. Dividing the beam-only irradiation into two or four consecutive daily fractions increased the ED50 to 14.7 +/- 0.2 Gy and 15.5 +/- 0.4 Gy, respectively. Thermal neutron irradiation in the presence of BPA resulted in an ED50 for myelopathy of 13.8 +/- 0.6 Gy after a single fraction and 14.9 +/- 0.9 Gy after two fractions. An increase in the number of fractions to four resulted in an ED50 of 14.3 +/- 0.6 Gy. The total physical absorbed dose to the blood in the vasculature of the spinal cord during BNCT using BPA was 80% high-LET radiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid determination of drugs in biofluids by capillary electrophoresis. Measurement of antipyrine in saliva for pharmacokinetic studies

A micellar electrokinetic capillary chromatography method was developed that permitted the resolution of antipyrine from endogenous compounds and its quantitation in neat saliva in as little as 1 min. Final conditions were: SpectraPhoresis 1000, 30(23) cm x 50 microns silica capillary, 50 mM sodium phosphate pH 9.6, 50 mM SDS, 10 s hydrodynamic load, detection scanning 200-300 nm or 260 nm, run 25 kV. To overcome the effects of Joule heating the capillary was cooled to 15 degrees C. Sensitivity was < 10 microM and linearity extended to 350 microM. Comparison with an HPLC assay demonstrated that hydrodynamic injection gave a loading bias unless samples and standards were of equal viscosity. For 75 samples from five subjects the correlation of CE vs. HPLC was then r = 0.99.

Trophic effects of essential fatty acids on pig skin

The daily oral administration of 3 ml of two oils (So-5407 and So-1129) containing essential fatty acids (EFAs) for 16 weeks resulted in a transient increase in cell proliferative activity in the skin of female Large White pigs. The So-5407 oil contained 7% gamma-linolenic acid (GLA) whereas So-1129 was an oil of similar composition, but with no GLA. Hyperplasia of the epidermis was observed after the administration of both oils, and this was characterized by an increase in the size of the rete pegs. The maximum effect occurred at 4 weeks after the start of oil administration, at which time the number of viable cell layers had increased by a factor of approximately 1.5, and mean epidermal thickness (excluding the stratum corneum) was approximately 40% greater than that of the epidermis prior to oil administration. There was a marked increase in the labelling index (LI) of the basal cell layer of the epidermis in pigs receiving So-5407. Maximum LIs were quantified at 4 weeks after the start of administration and were 18.8 +/- 1.3% and 13.1 +/- 1.7% for pigs receiving So-5407 and So-1129, respectively. After this time the LI declined progressively and had returned to values within normal limits (P > 0.1) by 8 weeks after the start of administration of both oils. A similar pattern of change in the LI was seen in the follicular epithelium, although the peak values at 4 weeks after the start of oil administration of 12.2 +/- 1.8% and 10.8 +/- 0.9 for the groups receiving So-5407 and So-1129, respectively, were lower than in the epidermis. Labelled cells were also counted in the papillary dermis and maximum values were again seen at 4 weeks after the start of oil administration. Of the two oils, So-1129 had the greatest effect, with the number of labelled cells in the papillary dermis being a factor of three to four-fold higher than in skin prior to oil administration, between 2 and 12 weeks after the start of administration.

Amelioration of both early and late radiation-induced damage to pig skin by essential fatty acids

PURPOSE

To evaluate the possible role of essential fatty acids, specifically gamma-linolenic and eicosapentaenoic acid, in the amelioration of early and late radiation damage to the skin.

METHODS AND MATERIALS

Skin sites on the flank of 22-25 kg female large white pigs were irradiated with either single or fractionated doses (20 F/28 days) of beta-rays from 22.5 mm diameter 90Sr/90Y plaques at a dose rate of approximately 3 Gy/min. Essential fatty acids were administered orally in the form of two 'active' oils, So-1100 and So-5407, which contained gamma-linolenic acid and a mixture of that oil with eicosapentaenoic acid, respectively. Oils (1.5-6.0 ml) were given daily for 4 weeks prior, both 4 weeks prior and 10-16 weeks after, or in the case of one single dose study, just for 10 weeks after irradiation. Control animals received a 'placebo' oil, So-1129, containing no gamma linolenic acid or eicosapentaenoic acid over similar time scales before and after irradiation. Acute and late skin reactions were assessed visually and the dose-related incidence of a specific reaction used to compare the effects of different treatment schedules.

RESULTS

A reduction in the severity of both the early and late radiation reactions in the skin was only observed when 'active' oils were given over the time course of the expression of radiation damage. Prior treatment with oils did not modify the radiation reaction. A 3.0 ml daily dose of either So-1100 or So-5407 given prior to, but also after irradiation with single and fractionated doses of beta-rays produced the most significant modification to the radiation reactions, effects consistent with dose modification factors between 1.06-1.24 for the acute reactions of bright red erythema and/or moist desquamation, and of 1.14-1.35 for the late reactions of dusky/mauve erythema and dermal necrosis. There was the strong suggestion of an effect produced by the 'placebo' oil, So-1129, after higher daily doses of oil.

CONCLUSIONS

Essential fatty acids can modulate normal tissue reactions when given over the time when radiation damage is normally expressed. Dose modification factors suggest that a > or = 10% higher dose is required to produce the same level of normal tissue injury. Clinical application of selected essential fatty acids at appropriate doses may lead to a significant increase in the therapeutic gain in patients treated for cancer by radiotherapy.

The modulation of radiation-induced damage to pig skin by essential fatty acids

The ability of essential fatty acids (EFAs) to modulate radiation-induced normal tissue injury was assessed in pig skin. Female Large White pigs (approximately 25 Kg) received 3 ml/day orally of either an 'active' oil [So-1100, containing 9% gamma-linolenic acid (GLA)] or a 'placebo' oil (So-1129) for just 4 weeks before or for 4 weeks before and for 16 weeks after irradiation; localised irradiation of skin was with single doses of beta-rays from 22.5 mm diameter 90Sr/90Y plaques. The severity of the acute reaction, assessed in terms of erythema or moist desquamation, was significantly less in those pigs that received So-1100 both before and after irradiation, as compared with those receiving that oil only prior to irradiation and the 'placebo' groups. Dose modification factors (DMFs) of between 1.13-1.24 were obtained. A similar reduction in the severity of acute skin injury was seen in pigs receiving So-1100 for only 10 weeks after irradiation. Late skin damage, assessed in terms of late erythema or dermal necrosis, was also reduced with So-1100, with DMFs of 1.14-1.51. No such modification was observed if So-1100 was only administered for 4 weeks prior to irradiation. No adverse side-effects were apparent as a result of EFA administration. So-1100 may represent a safe and valuable method of increasing the therapeutic gain in radiotherapy.

Optimized separation of purine bases and nucleosides in human cord plasma by capillary zone electrophoresis

An optimized separation of the main purine compounds of human serum by capillary zone electrophoresis is presented. Separations were performed in an uncoated silica capillary (44 cm x 75 microns I.D., 37 cm to window) on a SpectraPhoresis 1000 system with UV detection. The separation of adenine (Ade), adenosine (Ado), guanine (Gua), guanosine (Guo), hypoxanthine (Hyp), inosine (Ino), xanthine (Xan) and uric acid (UA) was optimized with respect to pH, temperature, applied potential and hydrodynamic injection time. Optimum conditions were 20 mM borate buffer (pH 9.4), 37 degrees C, 20 kV and 9 s load and detection at 260 nm. Linearity extended from 1 to 125 microM. The sensitivity of the method was 0.5 microM, which is adequate for measuring Ade, Gua, Hyp and UA in plasma samples. Plasma samples from newborns were precipitated with an equal volume of perchloric acid (7%, v/v), the supernatant was adjusted to neutral pH with potassium carbonate and, before injection, the sample was alkalized with sodium hydroxide. The method presented here allows the determination of Ade, Guo, Hyp and UA. The levels of the determined purines were compared in samples from control newborns, preterm babies and newborns with asphyxia or acidic serum pH values.

Separation and tryptic digest mapping of normal and variant haemoglobins by capillary electrophoresis

Characterization of haemoglobin (Hb) through whole protein separations and tryptic digest mapping allows the identification of structural Hb variants which result in haemoglobinopathies. Tryptic digest mapping by conventional two-dimensional paper chromatograph-electrophoresis provides high resolution but requires 48 h, while gradient elution reversed-phase high-performance liquid chromatography (HPLC) is faster (1.5 h), there is decreased resolution. CE analysis provides a fast separation with high resolution. We have used CE to optimise the tryptic digestion of globin purified from normal human haemoglobin A and to analyze tryptic digests from normal Hb. The separations were optimised and peak identification performed using UV scanning detection. In the optimised tryptic digest separation up to 28 peaks could be resolved in < 20 min. These peaks were identified as far as possible and a high-resolution map of the digest was constructed. The optimised analytical conditions were used to observe the separation pattern obtained from normal adult haemoglobin (HbA), common variant haemoglobins and some rarer haemoglobin variants.

Plasma and 24 h-urinary catecholamine concentrations in normal and patient populations

Using a single HPLC-ECD methodology, plasma catecholamine data were compiled from 545 patients and 144 healthy subjects, and 24 h urinary free catecholamine data from 106 patients. From these data, normal reference ranges were derived for the clinical investigation of suspected phaeochromocytomas, specifically to address the question as to when a result is normal and when further investigation may be required. We have shown that noradrenaline and adrenaline concentrations in plasma and urine are not normally distributed, and basal plasma noradrenaline is significantly lower in normal volunteers than in hospital patients. We have also demonstrated that a reference range which does not take account of these factors will give a significant number of false-positive results. Age and sex did not appear to be significant variables for either plasma or urinary catecholamines. In the investigation of phaeochromocytoma, 95% confidence limits may be used as a warning to repeat sampling and 99% confidence limits as rendering the diagnosis extremely probable. In patients with phaeochromocytomas, urinary catecholamines had a 99.5% specificity and 100% sensitivity in the diagnosis, and thus provide for a rapid and efficient diagnostic screen.

The use of venous catheterization in the diagnosis and localization of bilateral phaeochromocytomas

OBJECTIVE

The purpose was to assess the value of venous catheter sampling as a method for the location of phaeochromocytomas, particularly when imaging techniques have been equivocal or ambiguous.

DESIGN

Venous catheter sampling was carried out in cases of suspected phaeochromocytoma, and compared with samples obtained from other patients without phaeochromocytomas undergoing adrenal venous catheterization.

PATIENTS

Three patients had phaeochromocytomas (subsequently confirmed by histology); five patients had no clinical or biochemical evidence of phaeochromocytoma but were being investigated for other conditions.

MEASUREMENTS

Catecholamine and cortisol assays were performed on plasma samples from the adrenal veins and elsewhere, and the noradrenaline to adrenaline (NA:AD) ratio was calculated. RESULTS In patients without phaeochromocytomas the NA:AD ratio was less than 1 in nine adrenal vein samples; in four adrenal vein samples with NA:AD ratio of greater than 1, the presence of a phaeochromocytoma was subsequently confirmed. An extra-adrenal tumour was also located by comparison of central and peripheral venous catecholamine concentrations.

CONCLUSIONS

Venous catheterization with measurements of catecholamines, and determination of NA:AD ratios, allows for the rapid and confident diagnosis and localization of unilateral, bilateral, and extra-adrenal phaeochromocytomas.