Cardiovascular T2-star (T2*) magnetic resonance for the early diagnosis of myocardial iron overload

AIMS

To develop and validate a non-invasive method for measuring myocardial iron in order to allow diagnosis and treatment before overt cardiomyopathy and failure develops.

METHODS AND RESULTS

We have developed a new magnetic resonance T2-star (T2*) technique for the measurement of tissue iron, with validation to chemical estimation of iron in patients undergoing liver biopsy. To assess the clinical value of this technique, we subsequently correlated myocardial iron measured by this T2* technique with ventricular function in 106 patients with thalassaemia major. There was a significant, curvilinear, inverse correlation between iron concentration by biopsy and liver T2* (r=0.93, P<0.0001). Inter-study cardiac reproducibility was 5.0%. As myocardial iron increased, there was a progressive decline in ejection fraction (r=0.61, P<0.001). All patients with ventricular dysfunction had a myocardial T2* of <20 ms. There was no significant correlation between myocardial T2* and the conventional parameters of iron status, serum ferritin and liver iron. Multivariate analysis of clinical parameters to predict the requirement for cardiac medication identified myocardial T2* as the most significant variable (odds ratio 0.79, P<0.002).

CONCLUSIONS

Myocardial iron deposition can be reproducibly quantified using myocardial T2* and this is the most significant variable for predicting the need for ventricular dysfunction treatment. Myocardial iron content cannot be predicted from serum ferritin or liver iron, and conventional assessments of cardiac function can only detect those with advanced disease. Early intensification of iron chelation therapy, guided by this technique, should reduce mortality from this reversible cardiomyopathy.

Nitroxyl radical addition to pentafulvenones forming cyclopentadienyl radicals: a test for cyclopentadienyl radical destabilization

Photochemical Wolff rearrangements in alkane solvents of the 6-diazo-2,4-cyclohexadienones 4 and 13-15 give pentafulvenone (1), 2,3-benzopentafulvenone (2), dibenzopentafulvenone (3), and 2,4-di-tert-butylpentafulvenone (16), as identified by conventional UV and IR spectroscopy. Reactions of these fulvenyl ketenes with tetramethylpiperidinyloxyl (TEMPO) proceed by addition of TEMPO to the carbonyl carbon forming delocalized radicals for 1 and 2 which add one or more further TEMPO molecules, while the initial radical products formed from 3 and 16 dimerize. The rate constants of these reactions compared to hydration rate constants for the same compounds show the benzannulated derivatives 2 and 3 fit a previous correlation k(2)(TEMPO) vs k((H(2)O), whereas for 1 and 16 there is evidence for inhibition of reactions with radicals. The deviations are consistent with an absence of aromatic stabilization of the cyclopentadienyl radicals from 1 and 16 that is compensated in the benzannulated derivatives.

Identification of alkylidene hydrazides as glucagon receptor antagonists

High throughput screening of our small molecule combinatorial library identified a class of benzoylnaphthalenehydrazones with modest affinity for the human glucagon receptor. Optimization of this initial hit through a series of targeted libraries and traditional medicinal chemistry led to ligands with nanomolar affinities. Pharmacological evaluation demonstrated that these ligands were competitive glucagon receptor antagonists. Intravenous administration of a representative benzoylnaphthalenehydrazone into rats attenuated glucagon-stimulated glucose levels.

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Does the presence of ultrasound really affect computed tomographic scan use? A prospective randomized trial of ultrasound in trauma

OBJECTIVE

There is a paucity of evidence demonstrating that emergency department (ED) ultrasound changes clinical practice in trauma patients. We hypothesized that the presence of ultrasound would affect clinical decision making as evidenced through abdominal computed tomographic (CT) scan use in blunt multiple trauma patients.

METHODS

This study used a prospective randomized format in an urban county ED with Level II trauma center status (ED census, 72,000 patients per year). Participants were patients with multiple blunt injuries meeting trauma center triage criteria. Patients were randomized to receive either abdominal ultrasound or no ultrasound (control) during initial ED resuscitation. The primary outcome variable was use of abdominal CT scan in patients with and without ultrasound.

RESULTS

Two hundred eight patients were enrolled. The mean age was 40 +/- 18 years, and 62% were men. Mechanism of injury was motor vehicle crash, 56%; automobile versus pedestrian, 18%; motorcycle crash, 16%; falls, 10%; and other, 10%. One hundred four ultrasound and 104 control patients were analyzed. There were no apparent differences between ultrasound and control groups in demographics, injury type, or Injury Severity Score. Fifty-four of 104 (52%) of the control group received abdominal CT scans versus 37 of 104 (36%) abdominal CT scans for the ultrasound group; mean difference in proportions was 15.9 (p < 0.01; 95% confidence interval, 2.6-29.1).

CONCLUSION

In this trial, the routine use of abdominal ultrasound in the evaluation of patients with multiple blunt injuries resulted in significantly fewer abdominal CT scans being obtained. A larger trial is needed to more clearly define the clinical and financial impact of ultrasound in the management of blunt abdominal trauma.

Pion Interferometry of square root of (s(NN)) =130 GeV Au + Au collisions at RHIC

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].

Implications of the "contrast blush" finding on computed tomographic scan of the spleen in trauma

BACKGROUND

The "contrast blush" (CB) computed tomographic (CT) scan finding has often been used clinically as an indicator for therapeutic splenic intervention (SI) (splenectomy, splenorrhaphy, or angiographic embolization). We sought to examine the prognostic significance of this finding.

METHODS

The records and CT scans of 324 trauma patients from two Level I trauma centers who had blunt splenic injury and a CT scan of the abdomen within 24 hours of admission were reviewed and screened for CB.

RESULTS

CB was identified in 11% of patients, and its incidence was significantly related to the grade of injury: grade I/II, 3.2%; grade III, 11.8%; and grade IV/V, 26.3% (p < 0.001). SI was also related to the grade: grade I/II, 7.7%; grade III, 37.6%; and grade IV/V, 69.7% (p < 0.001). The chance of having SI was greater in those with CB (75.0%) when compared with those without CB (25.0%) (p < 0.001; odds ratio, 9.2). A multivariate logistic regression analysis revealed that SI correlated independently with splenic grade, emergency department hypotension, and age, but did not demonstrate a correlation with CB.

CONCLUSION

CB is not an absolute indication for an operative or angiographic intervention. Factors such as patient age, grade of injury, and presence of hypotension need to be considered in the clinical management of these patients.

Monochromatic aberrations of the human eye in a large population

From both a fundamental and a clinical point of view, it is necessary to know the distribution of the eye's aberrations in the normal population and to be able to describe them as efficiently as possible. We used a modified Hartmann-Shack wave-front sensor to measure the monochromatic wave aberration of both eyes for 109 normal human subjects across a 5.7-mm pupil. We analyzed the distribution of the eye's aberrations in the population and found that most Zernike modes are relatively uncorrelated with each other across the population. A principal components analysis was applied to our wave-aberration measurements with the resulting principal components providing only a slightly more compact description of the population data than Zernike modes. This indicates that Zernike modes are efficient basis functions for describing the eye's wave aberration. Even though there appears to be a random variation in the eye's aberrations from subject to subject, many aberrations in the left eye were found to be significantly correlated with their counterparts in the right eye.

A novel method for the isolation of motile bacteria using gradient culture systems

Isolation of motile bacteria from stream water samples was achieved by using Lutrol F127 (poloxamer 407) as a gelling agent in culture media. This block copolymer has the property of repeatedly liquefying and solidifying at low and high temperatures, respectively. The ability of motile bacteria to move through liquid-state Lutrol F127 towards a higher nutrient concentration was exploited. After establishment of the nutrient gradient and inoculation, the system was cooled to liquefy the medium and kept liquid to allow motile bacteria to move. Raising the temperature allowed solidification and prevented further movement. Colonies could be easily removed. The proportion of motile isolates (determined by microscopic observation) increased from 42% in the indigenous population to 100% after isolation using the gradient system.

Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Elliptic flow in Au+Au collisions at square root(S)NN = 130 GeV

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at square root(S)NN = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

The representation of blood flow in endourologic surgical simulations

An image-based approach has been developed to represent bleeding in a simulator for transurethral resection of prostate (TURP). While previous attempts have simulated bleeding over tissue surfaces or in blood vessels, our approach focused on the macroscopic visualization of bleeding in a fluid environment. TURP is an ideal procedure for simulation-based training because of the dynamic environment and the variety of flow patterns it presents. The first step in the development of the simulator was the generation of blood flow movies which consisted of capturing videos of bleeding vessels in vitro, processing them to separate the actual blood from the background anatomy and organizing the movies into a parametric database. During the running of the simulation, resection of prostate tissue systematically triggers bleeding events and the playback of a blood flow movie. The blood flow movie is texture mapped onto a virtual surface that is positioned oriented, morphed, composited and looped into the virtual scene.

The effects of ropivacaine hydrochloride on platelet function: an assessment using the platelet function analyser (PFA-100)

Amide local anaesthetics impair blood clotting in a concentration-dependent manner by inhibition of platelet function and enhanced fibrinolysis. We hypothesised that the presence of ropivacaine in the epidural space could decrease the efficacy of an epidural blood patch, as this technique requires that the injected blood can clot in order to be effective. Ropivacaine is an aminoamide local anaesthetic used increasingly for epidural analgesia during labour. The concentration of local anaesthetic in blood achieved in the epidural space during the performance of an epidural blood patch is likely to be the greatest which occurs (intentionally) in any clinical setting. This study was undertaken to investigate whether concentrations of ropivacaine in blood, which could occur: (i) clinically in the epidural space and (ii) in plasma during an epidural infusion of ropivacaine, alter platelet function. A platelet function analyser (Dade PFA-100, Miami) was employed to assess the effects of ropivacaine-treated blood on platelet function. The greater concentrations of ropivacaine studied (3.75 and 1.88 mg x ml(-1)), which correspond to those which could occur in the epidural space, produced significant inhibition of platelet aggregation. We conclude that the presence of ropivacaine in the epidural space may decrease the efficacy of an early or prophylactic epidural blood patch.

Prognostic indicators in venous ulcers

BACKGROUND

Venous ulcers can be difficult to heal, and prognostic factors for healing have not been fully elucidated.

OBJECTIVE

The objective of this study was to analyze the results of a large multicenter venous ulcer trial to retrospectively establish prognostic factors for venous ulcer healing.

METHODS

This study examined data from a previously published prospective randomized placebo-controlled trial of an oral medication versus placebo treatment for venous ulcers. Local leg ulcer care involved the use of a moisture-retentive dressing and sustained graduated compression with a paste bandage and a self-adherent wrap. The oral medication or placebo was administered on a daily basis with the same dressings and bandage system in both groups for 12 weeks. A total of 165 patients completed the full 12-week treatment period; 83 received ifetroban, 82 received placebo.

RESULTS

There was no statistically significant difference in outcome between the two groups. The study showed that consistent local ulcer treatment with a clearly defined system of care was associated with an unexpectedly high percentage (55%) of long-standing large venous ulcers (mean duration, 27 months; mean area, 15.9 cm(2)) being healed in both groups. Baseline ulcer area and duration of leg ulcer were found to be important in predicting outcome. Ulcers of short duration were found to be most likely to heal. Percent healing and ulcer area at week 3 were good predictors of 100% healing. Ulcers that had at least 40% healing by week 3 predicted more than 70% of the outcomes correctly.

CONCLUSION

From this large study it was determined that baseline ulcer area and ulcer duration are significant predictors of 100% healing and time to heal. Percent healing and ulcer area at week 3 are good predictors of complete ulcer healing. Ulcers that are large, long-standing, and slow to heal after 3 weeks of optimal therapy are unlikely to heal rapidly, and might benefit from alternative therapies.

The effect of dehydroepiandrosterone on Zucker rats selected for fat food preference

When allowed to select between macronutrients in a 1-h-a-day meal paradigm, Zucker rats consume 20-80% of their total caloric intake as fat. If they receive an intraperitoneal injection of DHEA 2 h before such a test meal, they consume fewer total calories. The magnitude of this effect on each macronutrient depends upon the animal's initial preference for fat; the higher the initial fat preference, the more profound is the decrease in caloric intake and the more pronounced the effect on fat consumption. Doses as low as 25 mg DHEA/kg body weight are effective. Lean Zucker rats that prefer to consume a high-fat diet have higher epinephrine and dopamine levels in select regions of the hypothalamus known to control food intake. Administration of DHEA to such animals 2 h before decapitation reduces the content of norepinephrine and these monoamines to levels that mimic the values found in the low-fat-preferring animals. It is hypothesized that exogenous DHEA causes the acute release of norepinephrine, epinephrine, and dopamine in select regions of the hypothalamus, and this release causes a decrease in food intake, particularly fat.

Nucleic acid-based fluorescent probes in microbial ecology: application of flow cytometry

Microorganisms in natural environments have often been treated as 'black box' systems. Researchers have measured the inputs and outputs of the box, and have made bulk measurements on cell behaviour. However, unravelling the details of the diversity and interactions that exist within these microbial populations has proven exceptionally difficult. The information gained from the black box approach has been invaluable, and has allowed models of global foodwebs to be generated and tested. However, there is still little information about the interactions of individual microbial cells within natural populations. Such studies are essential to fully understand the integrated functioning of ecosystems. To achieve this goal, researchers need to be able to identify individual cells within a population, enumerate them, estimate both viability and activity, and monitor changes in response to relevant parameters. Due to the diversity, heterogeneity and numbers of cells that make up these populations, these measurements require automation and speed. At present, the use of flow cytometry in conjunction with nucleic acid probes provides an excellent method with which to pursue such studies.

Visual Benefit of Correcting Higher Order Aberrations of the Eye

There is currently considerable debate concerning the visual impact of correcting the higher order aberrations of the eye. We describe new measurements of a large population of human eyes and compute the visual benefit of correcting higher order aberrations. We also describe the increase in contrast sensitivity when higher order aberrations are corrected with an adaptive optics system. All these results suggest that many, though not all, observers with normal vision would receive worthwhile improvements in spatial vision from customized vision correction, at least over a range of viewing distances and particularly when the pupils are large. Keratoconic patients or patients suffering from spherical aberration as a result of laser refractive surgery as it is presently performed would especially benefit. These results encourage the development of methods to correct higher order aberrations.

Credentialling Australian critical care nurses: the pilot study

In October 1998, the Australian College of Critical Care Nurses (ACCCN) launched a model to credential specialist level critical care nurses. This model was 'road tested' during a pilot study, when experienced critical care nurses were invited to apply to become the first Australian credentialled critical care nurses. The pilot study was designed to ensure all individuals taking part in the process were surveyed regarding adequacy of the credentialling package and the credentialling process. Applicants were required to provide evidence of practise at the specialist level, as described in the Competency Standards for Specialist Level Critical Care Nurses. Evidence was presented via curriculum vitae, professional journal and supported by three peer reviewers and two referees. Each application was sent to a three-person assessor panel, which assessed the evidence in the application against the Competency Standards for Specialist Level Critical Care Nurses. A total of six applications from five states and one territory were received by April 1999. Five of the applicants were assessed to have met the Competency Standards and were awarded the credential, Australia Credentialled Critical Care Nurse (ACCN), which they will hold for a period of 3 years. Feedback from assessors, applicants, peer reviewers and referees involved in the pilot study has resulted in the further refinement of the credentialling package and processes. Australian critical care nurses will now have the opportunity to seek to be credentialled four times per year.

Universal precautions--do Irish anaesthetists comply?

BACKGROUND

Anaesthetists are at high risk from blood-borne pathogens. Universal Precautions (UP) include the routine use of appropriate barrier precautions and techniques to reduce the likelihood of exposure to blood, body fluids and tissues that may contain pathogens. The compliance of Irish anaesthetists with these precautions has not been studied.

AIM

To study the attitudes of Irish anaesthetists to Universal Precautions.

METHOD

A postal questionnaire was sent to 210 anaesthetists currently practising in Ireland. The questionnaire was based on a model used in Australia and New Zealand.

RESULTS

There was a 50% response rate to the survey. Only 15% of respondents had taken a risk history from a patient in the preceding four weeks. Resheathing of needles was commonplace. The effectiveness of hepatitis B immunisation was rarely checked and only 66% of respondents believe implementation of Universal Precautions to be practical.

CONCLUSION

Irish anaesthetists comply poorly with Universal Precautions.

Changes in viability and macromolecular content of long-term batch cultures of Salmonella typhimurium measured by flow cytometry

Exposure of many Gram-negative bacteria to prolonged starvation induces alternative programmes of gene expression, along with a transition into a dormant condition sometimes referred to as a viable non-culturable (VBNC) state. Knowledge of how pathogenic species respond to nutrient limitation is therefore important for their detection and dissemination. This study used flow cytometry, coupled with fluorescent dyes for viability and macromolecular content, to study the responses of the pathogen Salmonella typhimurium to prolonged batch culture. Statistical analysis of the flow cytometric data, together with total and culturable cell counts, failed to demonstrate a VBNC state in this pathogen, contrary to reports from other workers. Analysis of rRNA and protein content identified a small proportion of cells in 110 day-old cultures that represented an active sub-population. This observation may provide an explanation for the long-term survival properties of this organism during prolonged exposure to nutrient limitation, as well as the high degree of heterogeneity observed in labelled cells.

Determination of non-transferrin-bound iron in genetic hemochromatosis using a new HPLC-based method

BACKGROUND/AIMS

Non-transferrin-bound iron may play a major pathogenic role in iron overload diseases due to its high hepatic uptake and potential damaging effect. The aim of this study was to evaluate the relevance of measuring serum non-transferrin-bound iron levels in genetic hemochromatosis using a new high performance liquid chromatography-based method.

METHODS

This method includes a presaturation step of transferrin with cobalt(II) in order to avoid secondary deplacement of non-transferrin-bound iron toward transferrin during the assay. Six genetic hemochromatotic patients were followed serially during venesection treatment.

RESULTS/CONCLUSIONS

The results indicate: (i) that this new method permits detection of non-transferrin-bound iron when transferrin is not fully saturated, (ii) that non-transferrin-bound iron levels persist almost until the completion of treatment, (iii) that non-transferrin-bound iron levels are well correlated with transferrin saturation for a given patient, and (iv) that despite some individual variations, a transferrin saturation value lower than 35% usually corresponds to the disappearance of non-transferrin-bound iron.

Survival and filamentation of Salmonella enterica serovar enteritidis PT4 and Salmonella enterica serovar typhimurium DT104 at low water activity

In this study we investigated the long-term survival of and morphological changes in Salmonella strains at low water activity (a(w)). Salmonella enterica serovar Enteritidis PT4 and Salmonella enterica serovar Typhimurium DT104 survived at low a(w) for long periods, but minimum humectant concentrations of 8% NaCl (a(w), 0. 95), 96% sucrose (a(w), 0.94), and 32% glycerol (a(w), 0.92) were bactericidal under most conditions. Salmonella rpoS mutants were usually more sensitive to bactericidal levels of NaCl, sucrose, and glycerol. At a lethal a(w), incubation at 37 degrees C resulted in more rapid loss of viability than incubation at 21 degrees C. At a(w) values of 0.93 to 0.98, strains of S. enterica serovar Enteritidis and S. enterica serovar Typhimurium formed filaments, some of which were at least 200 microm long. Filamentation was independent of rpoS expression. When the preparations were returned to high-a(w) conditions, the filaments formed septa, and division was complete within approximately 2 to 3 h. The variable survival of Salmonella strains at low a(w) highlights the importance of strain choice when researchers produce modelling data to simulate worst-case scenarios or conduct risk assessments based on laboratory data. The continued increase in Salmonella biomass at low a(w) (without a concomitant increase in microbial count) would not have been detected by traditional microbiological enumeration tests if the tests had been performed immediately after low-a(w) storage. If Salmonella strains form filaments in food products that have low a(w) values (0.92 to 0.98), there are significant implications for public health and for designing methods for microbiological monitoring.

Design of potent dicyclic (1-5/4-10) gonadotropin releasing hormone (GnRH) antagonists

In three earlier papers, the structures and biological potencies of numerous mono- and dicyclic antagonists of GnRH were reported. Among these, two families, each containing two to four members were identified that had very high antagonist potencies in an antiovulatory assay (within a factor of 2 of those of the most potent linear analogues) and high affinities (K(i) < 0.5 nM) for the rat GnRH receptor (rGnRHR). The most favored cycles bridged the side chains of residues (4-10),(1,2) (5-8),(2) (4-10/5-8),(2) (1-3),(3) and (1-3/4-10).(3) Our goal was to identify a consensus model of bioactive conformations of GnRH antagonists, yet these biocompatible constraints did not sufficiently restrain the spatial location of the N-terminal tripeptide with respect to the C-terminal heptapeptide, due largely to the rotational freedom about the bonds connecting these regions. Examination of models derived from NMR studies of cyclo(4-10) analogues suggested a large number of possible cyclic constraints such as cyclo (0-8), (1-8), or (2-8). All analogues tested with these substitutions were inactive as antiovulatory agents at 1 mg/rat (5-9) and had low affinity for rGnRHR. On the other hand, bridging positions 3 and 8 with a [DAsp(3)] to [Dbu(8)] (12, K(i) = 13 nM) or [Orn(8)] (13, K(i) = 14 nM) in the parent compound cyclo(3-8)[Ac-DNal(1),DCpa(2),DXaa(3), Arg(5),DNal(6),Xbb(8),DAla(10)]GnRH yielded analogues that blocked ovulation at 250 microgram/rat. Analogue 14 (K(i) = 2.3 nM), with a [DAsp(3), Lys(8)] bridge, was fully active at 50 microgram/rat. Loss of potency (>20-fold) was observed with the substitution of [DAsp(3)] in 14 by [DGlu(3)] in 15 (K(i) = 23 nM). Dicyclic analogues possessing the (4-10) cycle and selected (1-6), (2-6), and (2-8) cycles led to analogues that were inactive at doses of 500 microgram/rat or larger. Two analogues with (1-8/4-10) cycles (16, K(i) = 1.1 nM) or (3-8/4-10) cycles (22, K(i) = 17 nM) showed full antiovulatory potency at 250 microgram/rat. None of these substitutions yielded analogues potent enough (>80% inhibition of ovulation at 5 microgram/rat or less and K(i) < 0.5 nM) to be candidates for structural analysis by NMR. On the other hand, four dicyclic (1, 1'-5/4-10) analogues met this criterion: dicyclo(1, 1'-5/4-10)[Ac-Asp(1)(Gly),DCpa(2),DTrp(3),Asp(4),Dbu(5 ), DNal(6), Dpr(10)]GnRH (32, K(i) = 0.22 nM), dicyclo(1, 1'-5/4-10)[Ac-Asp(1)(Gly),DCpa(2),DNal(3),Asp(4),Dbu(5 ), DNal(6), Dpr(10)]GnRH (34, K(i) = 0.38 nM), dicyclo(1, 1'-5/4-10)[Ac-Asp(1)(betaAla),DCpa(2), DTrp(3),Asp(4),Dbu(5),DNal(6), Dpr(10)]GnRH (40, K(i) = 0.15 nM), and dicyclo(1, 1'-5/4-10)[Ac-Glu(1)(Gly), DCpa(2),DTrp(3),Asp(4),Dbu(5),DNal(6), Dpr(10)]GnRH (41, K(i) = 0.24 nM). Since they differed slightly in terms of the (1,1'-5) bridge length (21 and 22 atoms) and bridgehead configuration, we may hypothesize that they assume similar bioactive conformations that satisfy a very discriminating receptor, since many other closely related analogues were significantly less potent.

Design of monocyclic (1-3) and dicyclic (1-3/4-10) gonadotropin releasing hormone (GnRH) antagonists

Careful analysis of the NMR structures of cyclo(4-10)[Ac-Delta(3)Pro(1),DFpa(2),DTrp(3),Asp(4),DNal (6), Dpr(10)]GnRH, dicyclo(4-10/5-8)[Ac-DNal(1),DCpa(2),DTrp(3), Asp(4), Glu(5),DArg(6),Lys(8),Dpr(10)]GnRH, and dicyclo(4-10/5, 5'-8)[Ac-DNal(1),DCpa(2),DPal(3),Asp(4), Glu(5)(Gly),DArg(6),Dbu(8), Dpr(10)]GnRH showed that, in the N-terminal tripeptide, a type II beta-turn around residues 1 and 2 was probable along with a gamma-turn around DTrp(3)/DPal(3). This suggested the possibility of constraining the N-terminus by the introduction of a cyclo(1-3) scaffold. Optimization of ring size and composition led to the discovery of cyclo(1-3)[Ac-DAsp(1),DCpa(2),DLys(3),DNal(6), DAla(10)]GnRH (5, K(i) = 0.82 nM), cyclo(1,1'-3)[Ac-DAsp(1)(Gly), DCpa(2),DOrn(3),DNal(6),DAla(10)]GnRH (13, K(i) = 0.34 nM), cyclo(1, 1'-3)[Ac-DAsp(1)(Gly),DCpa(2),DLys(3),DNal(6),DA la(10)]GnRH (20, K(i) = 0.14 nM), and cyclo(1,1'-3)[Ac-DAsp(1)(betaAla), DCpa(2), DOrn(3),DNal(6),DAla(10)]GnRH (21, K(i) = 0.17 nM), which inhibited ovulation significantly at doses equal to or lower than 25 microgram/rat. These results were particularly unexpected in view of the critical role(s) originally ascribed to the side chains of residues 1 and 3.(1) Other closely related analogues, such as those where the [DAsp(1)(betaAla), DOrn(3)] cycle of 21 was changed to [DOrn(1)(betaAla), DAsp(3)] of cyclo(1,1'-3)[Ac-DOrn(1)(betaAla), DCpa(2),DAsp(3),DNal(6),DAla(10)]GnRH (22, K(i) = 2.2 nM) or where the size of the cycle was conserved and [DAsp(1)(betaAla), DOrn(3)] was replaced by [DGlu(1)(Gly), DOrn(3)] as in cyclo(1, 1'-3)[Ac-DGlu(1)(Gly),DCpa(2),DOrn(3),DNal(6),DA la(10)]GnRH (23, K(i) = 4.2 nM), were approximately 100 and 25 times less potent in vivo, respectively. Analogues with ring sizes of 18 ¿cyclo(1, 1'-3)[Ac-DGlu(1)(Gly),DCpa(2),DLys(3),DNal(6),DA la(10)]GnRH (24)¿ and 19 ¿cyclo(1,1'-3)[Ac-DGlu(1)(betaAla),DCpa(2),DLys( 3),DNal(6), DAla(10)]GnRH (25)¿ atoms were also less potent than 21 with slightly higher K(i) values (1.5 and 2.2 nM, respectively). These results suggested that the N-terminal tripeptide was likely to assume a folded conformation favoring the close proximity of the side chains of residues 1 and 3. The dicyclic analogue dicyclo(1-3/4-10)[Ac-DAsp(1),DCpa(2),DLys(3),Asp (4),DNal(6), Dpr(10)]GnRH (26) was fully active at 500 microgram, with a K(i) value of 1 nM. The in vivo potency of 26 was at least 10-fold less than that of monocyclic cyclo(1-3)[Ac-DAsp(1),DCpa(2),DLys(3),DNal(6), DAla(10)]GnRH (5); this suggested the existence of unfavorable interactions between the now optimized and constrained (1-3) and (4-10) cyclic moieties that must interact as originally hypothesized. Tricyclo(1-3/4-10/5-8)[Ac-DGlu(1),DCpa(2), DLys(3),Asp(4),Glu(5), DNal(6),Lys(8),Dpr(10)] GnRH (27) was inactive at 500 microgram/rat with a corresponding low affinity (K(i) = 4.6 nM) when compared to those of the most potent analogues (K(i) < 0.5 nM).