Speckle contrast of interfering fluorescence X-rays

With the development of X-ray free-electron lasers (XFELs), producing pulses of femtosecond durations comparable with the coherence times of X-ray fluorescence, it has become possible to observe intensity-intensity correlations due to the interference of emission from independent atoms. This has been used to compare durations of X-ray pulses and to measure the size of a focusedX-ray beam, for example. Here it is shown that it is also possible to observe the interference of fluorescence photons through the measurement of the speckle contrast of angle-resolved fluorescence patterns. Speckle contrast is often used as a measure of the degree of coherence of the incident beam or the fluctuations of the illuminated sample as determined from X-ray diffraction patterns formed by elastic scattering, rather than from fluorescence patterns as addressed here. Commonly used approaches to estimate speckle contrast were found to suffer when applied to XFEL-generated fluorescence patterns due to low photon counts and a significant variation of the excitation pulse energy from shot to shot. A new method to reliably estimate speckle contrast under such conditions, using a weighting scheme, is introduced. The method is demonstrated by comparing the speckle contrast of fluorescence observed with pulses of 3 fs to 15 fs duration.

Femtosecond quantification of void evolution during rapid material failure

Understanding high-velocity impact, and the subsequent high strain rate material deformation and potential catastrophic failure, is of critical importance across a range of scientific and engineering disciplines that include astrophysics, materials science, and aerospace engineering. The deformation and failure mechanisms are not thoroughly understood, given the challenges of experimentally quantifying material evolution at extremely short time scales. Here, copper foils are rapidly strained via picosecond laser ablation and probed in situ with femtosecond x-ray free electron (XFEL) pulses. Small-angle x-ray scattering (SAXS) monitors the void distribution evolution, while wide-angle scattering (WAXS) simultaneously determines the strain evolution. The ability to quantifiably characterize the nanoscale during high strain rate failure with ultrafast SAXS, complementing WAXS, represents a broadening in the range of science that can be performed with XFEL. It is shown that ultimate failure occurs via void nucleation, growth, and coalescence, and the data agree well with molecular dynamics simulations.

Erratum: Delayed Onset of Nonthermal Melting in Single-Crystal Silicon Pumped with Hard X Rays [Phys. Rev. Lett. 120, 265701 (2018)]

This corrects the article DOI: 10.1103/PhysRevLett.120.265701.

Blastulation of a zygote to a hatched blastocyst without any clear cell division: an observational finding in a time-lapse system after in vitro fertilization

PURPOSE

To describe an interesting not previously described morphokinetic finding.

METHODS

Retrospective case report of a couple undergoing controlled ovarian stimulation (COS) followed by in vitro fertilization and blastocyst transfer.

RESULTS

We identified a unique finding of blastulation of a fertilized human zygote after conventional in vitro fertilization. The fertilized zygote did not show any clear cytokinesis until approximately 107 h post insemination, when it started dividing into a blastocyst. By 113 h post insemination, inner cell mass and trophectoderm cells could be clearly distinguished and the blastocyst was completely hatched by 136 h post insemination.

CONCLUSION

Time-lapse systems offer more detailed observations of embryonic development. Here, we report an atypical development of an embryo that was not described previously. We hope to become an insightful discussion among peers and incentive the publication of such findings in the future.

A deep UV trigger for ground-state ring-opening dynamics of 1,3-cyclohexadiene

We explore the photo-induced kinetics of 1,3-cyclohexadiene upon excitation at 200 nm to the 3p state by ultrafast time-resolved, gas-phase x-ray scattering using the Linac Coherent Light Source. Analysis of the scattering anisotropy reveals that the excitation leads to the 3px and 3py Rydberg electronic states, which relax to the ground state with a time constant of 208 ± 11 fs. In contrast to the well-studied 266 nm excitation, at 200 nm the majority of the molecules (76 ± 3%) relax to vibrationally hot cyclohexadiene in the ground electronic state. A subsequent reaction on the ground electronic state surface leads from the hot cyclohexadiene to 1,3,5-hexatriene, with rates for the forward and backward reactions of 174 ± 13 and 355 ± 45 ps, respectively. The scattering pattern of the final hexatriene product reveals a thermal distribution of rotamers about the carbon-carbon single bonds.

Erratum: Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses. Corrigendum

[This corrects the article DOI: 10.1107/S2052252517003591.].

Delayed Onset of Nonthermal Melting in Single-Crystal Silicon Pumped with Hard X Rays

In this work, we monitor the onset of nonthermal melting in single-crystal silicon by implementing an x-ray pump-x-ray probe scheme. Using the ultrashort pulses provided by the Linac Coherent Light Source (SLAC) and a custom-built split-and-delay line for hard x rays, we achieve the temporal resolution needed to detect the onset of the transition. Our data show no loss of long-range order up to 150±40  fs from photoabsorption, which we interpret as the time needed for the electronic system to equilibrate at or above the critical nonthermal melting temperature. Once such equilibration is reached, the loss of long-range atomic order proceeds inertially and is completed within 315±40  fs from photoabsorption.

Retinal isomerization in bacteriorhodopsin captured by a femtosecond x-ray laser

Ultrafast isomerization of retinal is the primary step in photoresponsive biological functions including vision in humans and ion transport across bacterial membranes. We used an x-ray laser to study the subpicosecond structural dynamics of retinal isomerization in the light-driven proton pump bacteriorhodopsin. A series of structural snapshots with near-atomic spatial resolution and temporal resolution in the femtosecond regime show how the excited all-trans retinal samples conformational states within the protein binding pocket before passing through a twisted geometry and emerging in the 13-cis conformation. Our findings suggest ultrafast collective motions of aspartic acid residues and functional water molecules in the proximity of the retinal Schiff base as a key facet of this stereoselective and efficient photochemical reaction.

Enzyme intermediates captured "on the fly" by mix-and-inject serial crystallography

BACKGROUND

Ever since the first atomic structure of an enzyme was solved, the discovery of the mechanism and dynamics of reactions catalyzed by biomolecules has been the key goal for the understanding of the molecular processes that drive life on earth. Despite a large number of successful methods for trapping reaction intermediates, the direct observation of an ongoing reaction has been possible only in rare and exceptional cases.

RESULTS

Here, we demonstrate a general method for capturing enzyme catalysis "in action" by mix-and-inject serial crystallography (MISC). Specifically, we follow the catalytic reaction of the Mycobacterium tuberculosis β-lactamase with the third-generation antibiotic ceftriaxone by time-resolved serial femtosecond crystallography. The results reveal, in near atomic detail, antibiotic cleavage and inactivation from 30 ms to 2 s.

CONCLUSIONS

MISC is a versatile and generally applicable method to investigate reactions of biological macromolecules, some of which are of immense biological significance and might be, in addition, important targets for structure-based drug design. With megahertz X-ray pulse rates expected at the Linac Coherent Light Source II and the European X-ray free-electron laser, multiple, finely spaced time delays can be collected rapidly, allowing a comprehensive description of biomolecular reactions in terms of structure and kinetics from the same set of X-ray data.

Stimulated X-Ray Emission Spectroscopy in Transition Metal Complexes

We report the observation and analysis of the gain curve of amplified Kα x-ray emission from solutions of Mn(II) and Mn(VII) complexes using an x-ray free electron laser to create the 1s core-hole population inversion. We find spectra at amplification levels extending over 4 orders of magnitude until saturation. We observe bandwidths below the Mn 1s core-hole lifetime broadening in the onset of the stimulated emission. In the exponential amplification regime the resolution corrected spectral width of ∼1.7  eV FWHM is constant over 3 orders of magnitude, pointing to the buildup of transform limited pulses of ∼1  fs duration. Driving the amplification into saturation leads to broadening and a shift of the line. Importantly, the chemical sensitivity of the stimulated x-ray emission to the Mn oxidation state is preserved at power densities of ∼10^{20}  W/cm^{2} for the incoming x-ray pulses. Differences in signal sensitivity and spectral information compared to conventional (spontaneous) x-ray emission spectroscopy are discussed. Our findings build a baseline for nonlinear x-ray spectroscopy for a wide range of transition metal complexes in inorganic chemistry, catalysis, and materials science.

Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses

This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of ∼40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from ∼35 to ∼300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 × 10¹² photons per µm² per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.

OnDA: online data analysis and feedback for serial X-ray imaging

This article describes a free and open-source data analysis utility designed for fast online feedback during serial X-ray diffraction and scattering experiments: OnDA (online data analysis). Three complete real-time monitors for common types of serial X-ray imaging experiments are presented. These monitors are capable of providing the essential information required for quick decision making in the face of extreme rates of data collection. In addition, a set of modules, functions and algorithms that allow developers to modify the provided monitors or develop new ones are provided. The emphasis here is on simple, modular and scalable code that is based on open-source libraries and protocols. OnDA monitors have already proven to be invaluable tools in several experiments, especially for scoring and monitoring of diffraction data during serial crystallography experiments at both free-electron laser and synchrotron facilities. It is felt that in the future the kind of fast feedback that OnDA monitors provide will help researchers to deal with the expected very high throughput data flow at next-generation facilities such as the European X-ray free-electron laser.

Protein structure determination by single-wavelength anomalous diffraction phasing of X-ray free-electron laser data

Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) offers unprecedented possibilities for macromolecular structure determination of systems that are prone to radiation damage. However, phasing XFEL data de novo is complicated by the inherent inaccuracy of SFX data, and only a few successful examples, mostly based on exceedingly strong anomalous or isomorphous difference signals, have been reported. Here, it is shown that SFX data from thaumatin microcrystals can be successfully phased using only the weak anomalous scattering from the endogenous S atoms. Moreover, a step-by-step investigation is presented of the particular problems of SAD phasing of SFX data, analysing data from a derivative with a strong anomalous signal as well as the weak signal from endogenous S atoms.

Effects of self-seeding and crystal post-selection on the quality of Monte Carlo-integrated SFX data

Serial femtosecond crystallography (SFX) is an emerging method for data collection at free-electron lasers (FELs) in which single diffraction snapshots are taken from a large number of crystals. The partial intensities collected in this way are then combined in a scheme called Monte Carlo integration, which provides the full diffraction intensities. However, apart from having to perform this merging, the Monte Carlo integration must also average out all variations in crystal quality, crystal size, X-ray beam properties and other factors, necessitating data collection from thousands of crystals. Because the pulses provided by FELs running in the typical self-amplified spontaneous emission (SASE) mode of operation have very irregular, spiky spectra that vary strongly from pulse to pulse, it has been suggested that this is an important source of variation contributing to inaccuracies in the intensities, and that, by using monochromatic pulses produced through a process called self-seeding, fewer images might be needed for Monte Carlo integration to converge, resulting in more accurate data. This paper reports the results of two experiments performed at the Linac Coherent Light Source in which data collected in both SASE and self-seeded mode were compared. Importantly, no improvement attributable to the use of self-seeding was detected. In addition, other possible sources of variation that affect SFX data quality were investigated, such as crystal-to-crystal variations reflected in the unit-cell parameters; however, these factors were found to have no influence on data quality either. Possibly, there is another source of variation as yet undetected that affects SFX data quality much more than any of the factors investigated here.

De novo phasing of protein crystallography data from a free-electron laser

Free-electron lasers (FELs) are pushing back the limits of possibility in protein crystallography. Using the high-intensity, femtosecond duration pulses afforded by FELs allow data collection from micrometer-sized crystals while outrunning radiation damage. Moreover, FELs may be used for pump-probe experiments with unprecedented time resolution. However, the intricacies of FEL data collection pose specific challenges: as every FEL pulse destroys the sample, data are mostly collected from a stream of microcrystals and averaged to remove the variations in crystal size and quality as well as shot-to-shot variations in beam parameters. This technique is called serial femtosecond crystallography (SFX). In SFX, several tens of thousands of images typically need to be averaged to obtain reasonably accurate structure factor amplitudes. We previously showed that SFX yields structure factor amplitudes accurate enough to detect the weak anomalous signal of endogenous sulfur atoms. Now we show that SFX can be used to collect data accurate enough for de-novo phasing of a protein structure[1]. Using a model system (gadolinium-derivatized lysozyme) we collected ~60,000 diffraction images and obtained structure factor amplitudes that allowed phasing by single-wavelength anomalous diffraction. This first demonstration of de novo phasing from FEL data leads us to anticipate that FEL-based crystallography will become an important tool for the structure determination of proteins that are extremely radiation sensitive or that are difficult to crystallize, such as membrane proteins.

W/SiC x-ray multilayers optimized for use above 100 keV

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100-200 keV. Grazing-incidence x-ray reflectance at E = 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range E approximately 150-170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E = 120-180 keV. We describe our experimental investigation in detail compare the new W/SiC multilayers with both W/Si and W/B4C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope.

Role of brain natriuretic peptide in risk stratification of patients with congestive heart failure

OBJECTIVES

Using a prospective study design, we assessed the value of brain natriuretic peptide (BNP) to identify patients with heart failure who have an increased risk of deterioration of their functional status. Furthermore, we examined the relationship between BNP and various clinical characteristics incorporated into an established survival model used for risk stratification.

BACKGROUND

Prediction of the clinical course is a crucial part of the decision-making process about the adequate treatment strategy for patients with advanced congestive heart failure (CHF). Although laborious, multivariable indexes have been established for risk stratification, simple plasma BNP measurements may be as useful as prognostic indicators.

METHODS

In 78 patients referred to our heart failure clinic, plasma BNP levels were compared with the results of a multivariable prognostic model. To assess the prognostic power of BNP, the clinical course of this cohort was monitored for a median follow-up period of 398 days.

RESULTS

At study entry, plasma BNP and the heart failure survival score (HFSS) showed a significant correlation (r = -0.706). During follow-up, Kaplan-Meier estimates of freedom from clinical events differed significantly for patients above and below the 75th percentile concentrations of plasma BNP (p < 0.0001). Changes in plasma BNP were significantly related to changes in limitations of physical activity, as demonstrated by logistic regression analysis (chi-square statistic = 24.9, p < 0.0001). Proportional hazards analysis confirmed BNP as a powerful predictor of functional status deterioration (p < 0.0001). This prognostic information was as powerful as that derived from the multivariable HFSS.

CONCLUSIONS

Measurement of plasma BNP concentrations might provide a useful and cost-effective screening tool that helps reduce the need and frequency for more expensive cardiac tests.

Pathogenetic mechanisms of cardiac allograft vasculopathy--impact of nitric oxide

In the cytokine-enriched environment of the chronically rejecting allograft, nitric oxide (NO) is predominantly produced by the inducible isoform of NOS synthase (NOS2) expressed by recipient-derived infiltrating immune cells as well as donor-derived vascular smooth muscle cells and endothelial cells. Early and persistent upregulation of NOS2 in allografts with cardiac allograft vasculopathy and downregulation of NOS2 coinciding with immunosuppressive attenuation of cardiac allograft vasculopathy have suggested NO as a regulator of cardiac allograft vasculopathy, the hallmark of chronic rejection. Pathogenetically, the development of cardiac allograft vasculopathy can be divided into an early phase, characterized by endothelial dysfunction, and a later phase, characterized by structural changes of vessel wall morphology. Several lines of evidence have shown that NO might play an essential role in both phases. Endothelial dysfunction due to immune-mediated injury of endothelial cells has been suggested as an early response-to-injury event in the pathogenesis of cardiac allograft vasculopathy. Functional studies in human transplant recipients have documented endothelial dysfunction of coronary artery vessels. Administration of L-arginine, the precursor of NO, improved endothelial function of both epicardial coronary arteries and coronary microvasculature indicating a protective effect of NO. To assess the impact of NO on the development of late structural changes, the severity of cardiac allograft vasculopathy was assessed in mice with targeted deletion of NOS2. A significant increase of vascular occlusion in NOS2-knockout mice demonstrated an antiarteriosclerotic effect of NOS2. In part, this effect could be explained by reduced neointimal smooth muscle cell accumulation after alloimmune injury. Taken together, NO plays an important role in maintaining vessel integrity after transplantation. Disruptions in NO pathways seem to play a key role in the progression from endothelial dysfunction to structural changes.

KARMEN time anomaly: search for a neutral particle of mass 33.9 MeV in pion decay

We have searched for the pion decay pi(+)-->&mgr;+X, where X is a neutral particle of mass 33.905 MeV. This process was suggested by the KARMEN Collaboration to explain an anomaly in their observed time distribution of neutrino induced reactions. Having measured the muon momentum spectrum of charged pions decaying in flight, we find no evidence for this process and place an upper limit on the branching fraction eta</=6.0x10(-10) of such a decay at a 95% confidence level.

Attenuated cardiac allograft vasculopathy in mice with targeted deletion of the transcription factor STAT4

BACKGROUND

To study transcription factor signaling pathways that mediate cardiac allograft vasculopathy, we used mice with targeted gene deletion of signal transducer and activator of transcription (STAT)4 and STAT6 as recipients in our mouse cardiac transplant model of chronic rejection.

METHODS AND RESULTS

At day 55 after transplantation, cardiac grafts placed into STAT4 -/- (n=10) had reduced frequency (24+/-2%) and severity (9+/-4%) of vascular occlusion compared with wild-type controls (n=7, frequency 70+/-12% [P<0.001], severity 25+/-6% [P<0.05]). This decrease was associated with reduced intragraft expression ((32)P RT-PCR and immunohistochemistry) of the Th1 signature cytokines interferon-gamma (P<0.001) and interleukin (IL)-2 (P<0.001). Furthermore, cardiac grafts in STAT4 -/- had fewer infiltrating CD45(+) mononuclear cells (99+/-27 cells/mm(3) compared with 551+/-168 cells/mm(3) in wild-type controls [P<0.05]) and reduced expression of P-selectin (P<0.001) and E-selectin (P<0.01) ligand, recently shown to regulate Th1 cell recruitment. In contrast, in grafts placed into STAT6 -/- (n=11), the development of cardiac allograft vasculopathy (frequency 62+/-8%, severity 28+/-6%) and Th2 cytokine profiles (IL-4, IL-10) were comparable to those in wild-type controls.

CONCLUSIONS

Hence, we show that immune responses mediated by STAT4, but not STAT6, contribute to the development of cardiac allograft vasculopathy. We speculate that when present, STAT4-mediated signaling pathways may promote cardiac allograft vasculopathy by directing Th1-specific lymphocyte recruitment, activation, and effector functions.

Alloimmune-mediated apoptosis: comparison in mouse models of acute and chronic cardiac rejection

BACKGROUND

The purpose of the present study was (1) to compare apoptotic activity in models of acute and chronic rejection and (2) to study the cellular distribution of parenchymal versus inflammatory cell apoptosis.

METHODS

Heterotopic cardiac mouse transplantation (CBA into C57BL/6) was used to produce allografts undergoing acute (day 7, untreated recipients, n=6) or chronic (day 55, anti-CD4/8 for 28 days, n=6) rejection. As references, we used 55-day isograft controls (n=5) and native hearts (n=6). To assess apoptotic activity, we quantified DNA laddering (32P incorporation), DNA fragmentation (antinucleosome ELISA), and caspase-1 transcript levels (32P-reverse transcriptase-polymerase chain reaction). To localize apoptosis, we performed terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.

RESULTS

DNA laddering and nucleosome levels were increased in allografts undergoing acute or chronic rejection when compared with both controls. Both parameters were twofold higher in acutely compared with chronically rejecting hearts. Caspase-1 transcript levels were increased in acutely (P<0.0001) and chronically rejecting hearts (P=0.004). Acutely rejecting grafts had more terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive nuclei (53+/-3 nuclei/high-powered field) than chronically rejecting grafts (9+/-1 nuclei/high-powered field, P<0.0001), but the distribution between graft-infiltrating inflammatory cells and myocytes was similar. Vascular cells undergoing apoptosis were infrequent in both forms.

CONCLUSION

Using four separate indices, apoptotic activity is more pronounced in cardiac allografts undergoing acute compared with chronic rejection. This reflects, in part, the degree of alloimmune response. However, we speculate that the contributions of apoptosis to various forms of rejection are multifactorial. The long-term outcome to the graft may depend upon the magnitude, timing, and target of programmed cell death.

Attenuated acute cardiac rejection in NOS2 -/- recipients correlates with reduced apoptosis

BACKGROUND

The mechanisms through which NOS2-mediated pathways regulate graft failure in acute cardiac rejection are ill defined. To determine whether apoptosis promoted by NOS2 may contribute, we used a heterotopic transplant model to study mouse cardiac allografts placed in recipients with targeted gene deletion of NOS2.

METHODS AND RESULTS

Using 5 different indexes of apoptosis, we showed that mouse cardiac allografts placed in NOS2 -/- recipients (n=7) had reduced apoptotic activity compared with those in NOS2 +/+ controls (n=8). There were significantly fewer TUNEL-positive nuclei per high-powered field (P<0.01), less DNA fragmentation (antinucleosome ELISA; P<0.05), lower corrected transcript levels for caspase-1 and -3 (32P reverse transcriptase-polymerase chain reaction; P<0.01), and reduced caspase-3 activity (cleavage of DEVD-pNA [P<0.001] and poly [ADP-ribose] polymerase) in grafts from NOS2 -/- recipients. This concordant reduction in apoptotic indexes paralleled the improved histological outcome of grafts transplanted into NOS2 -/- recipients (assessed as rejection scores; P=0.012). To identify pathways controlled by NOS2, we compared intragraft transcript levels of potential triggers and regulators. Whereas Fas ligand/Fas and tumor necrosis factor (TNF)-alpha/TNF receptor-1 levels were not altered by NOS2 deficiency, transcript levels for p53 were significantly lower in grafts from NOS2 -/- recipients, coinciding with a significant increase in the antiapoptotic Bcl-2/Bax balance and decrease in Bcl-Xl levels.

CONCLUSIONS

Using NOS2 knockout mice, we demonstrated that NOS2-mediated pathways can promote acute rejection, at least in part, by inducing apoptotic cell death. When NOS2 is present, p53 might control NOS2-mediated apoptosis by stimulating Bax and repressing Bcl-2 and Bcl-Xl expression, which may activate the cell death program in the rejecting heart.

NOS2 mediates opposing effects in models of acute and chronic cardiac rejection: insights from NOS2-knockout mice

To compare regulatory effects of NOS2 in acute and chronic cardiac allograft rejection, we used NOS2 knockout mice as recipients in a cardiac transplant model. To study acute and chronic rejection separately but within the same genetic strain combination, we compared allografts placed into recipients without or with immunosuppression (anti-CD4/8 for 28 days). NOS2 mRNA and protein expression were compared using 32P-RT-PCR and immunohistochemistry. In our acute rejection model, NOS2 was predominately localized to graft-infiltrating immune cells. At day 7, grafts in NOS2-deficient recipients (n = 7) showed reduced inflammatory infiltrates and myocyte damage resulting in significantly lower rejection scores (1.6 +/- 0.4) compared to wild-type controls (n = 18; 2.8 +/- 0.2, P = 0.002). In contrast, in our chronic rejection model, additional NOS2 expression was localized to graft-parenchymal cells. At day 55, grafts in NOS2-deficient recipients (n = 12) showed more parenchymal infiltration and parenchymal destruction (rejection score 3.8 +/- 0.1) than wild-type controls (n = 15; 1.6 +/- 0.2, P < 0.0001). This was associated with a significant decrease in ventricular contractility (palpation score 0.3 +/- 0.1 compared to 2.3 +/- 0.3 in wild-type, P < 0.0001). Hence, NOS2 promotes acute but prevents chronic rejection. These opposing effects during acute and chronic cardiac allograft rejection are dependent on the temporal and spatial expression pattern of NOS2 during both forms of rejection.

Immune sources of transforming growth factor-beta1 reduce transplant arteriosclerosis: insight derived from a knockout mouse model

Activated CD4-positive T cells are essential in the early stages of arteriosclerotic lesion development after cardiac transplantation. Besides its parenchymal effects, transforming growth factor-beta1 (TGF-beta1) mediates immunosuppressive effects on proliferation and activation of CD4 cells. This study was designed to assess immune contributions of TGF-beta1 to arteriosclerosis by comparing the effect of TGF-beta1-deficient and -competent infiltrating inflammatory cells on the development of intimal thickening in a heterotopic mouse transplant model (CBA to C57B6). Transplant arteriosclerosis was evaluated in cardiac grafts placed into knockout recipients heterozygous for TGF-beta1 (n=7) and was compared with those placed into wild-type recipients (n=11). At 55 days, allografts in TGF-beta1-deficient recipients had increased concentric intimal thickening. Computer-assisted analysis of all elastin-positive vessels (n=173) showed significantly increased luminal occlusion (67.8+/-5.6%) in grafts from TGF-beta1-deficient recipients compared with wild-type recipients (47.4+/-4.1%, P=0.003). To determine whether TGF-beta1 deficiency altered CD4 activation patterns, we studied intragraft cytokine expression. Using 32P-reverse-transcriptase polymerase chain reaction assays, we show that TGF-beta1-deficient recipients had an increased expression of the transcription factor STAT 4, interferon gamma, and interleukin-2 (Th1-type response) and unaltered or reduced expression of the transcription factor STAT 6, interleukin-4, and interleukin-10 (Th2-type response). Hence, when present, immune sources of TGF-beta1 attenuate transplant arteriosclerosis. This effect is associated with attenuation of Th1 forces.

Exacerbated transplant arteriosclerosis in inducible nitric oxide-deficient mice

BACKGROUND

Inducible NO synthase (NOS2, or iNOS) is upregulated in grafts with transplant arteriosclerosis. However, the functional role of NOS2 in the pathogenesis of transplant arteriosclerosis remains unclear. NOS2 may regulate lesion development by modulating the early alloimmune response and/or late myointimal thickening.

METHODS AND RESULTS

To determine whether NOS2-mediated pathways protect against or promote transplant arteriosclerosis, we used NOS2-deficient mice as recipients in our vascularized chronic cardiac rejection model. The severity of vascular thickening in 55-day grafts placed into NOS2 -/- recipients (n=13) was compared with that in wild-type recipients (n=15). Computer-assisted analysis of all elastin-stained vessels (n=283) showed significantly increased luminal occlusion (77.11+/-9.4% versus 40.8+/-13.6%, P<.0001) and intima/media ratios in allografts from NOS2 -/- recipients (1.9+/-1.3 versus 0.4+/-0.3, P=.0002). To elucidate potential mechanisms, we studied NOS2 effects on T-cell differentiation (Th1/Th2) and neointimal smooth muscle cell accumulation. Normalized mRNA levels for Th1- (signal transducer and activator of transcription [STAT] 4, interleukin [IL]-2, interferon-gamma) and Th2- (STAT 6, IL-4, and IL-5) associated factors were comparable in both groups. In contrast, quantitative analysis of the alpha-actin-positive area showed a significant increase in the contribution of smooth muscle cells within the neointima in allografts from NOS2 -/- recipients (28.2+/-2.0%) compared with wild-type controls (13.2+/-2.3%; P<.0001).

CONCLUSIONS

NOS2 plays a protective role in the development of transplant arteriosclerosis, suppressing neointimal smooth muscle cell accumulation.

Reduced transplant arteriosclerosis in murine cardiac allografts placed in interferon-gamma knockout recipients

To investigate the functional role of interferon (IFN)-gamma in transplant arteriosclerosis, BALB/c hearts were transplanted in immunosuppressed C57BL/6J recipients with (n = 10) or without (n = 10) targeted IFN-gamma gene deletion. In 55-day heart allografts, IFN-gamma deficiency resulted in a significant decrease in vascular thickening. The severity of intimal thickening measured as the percentage of luminal occlusion (mean +/- SEM) in all elastin stained vessels (n = 410) decreased from 37+/-5% in wild-type recipients to 18+/-5% in IFN-gamma -/- recipients (P < 0.005). In the few diseased vessels in grafts from IFN-gamma -/- recipients, the neointima was more cellular with a 90% increase in the nuclear density. This finding correlated with a 50% reduction in fibrosis estimated by alpha-smooth muscle actin cell accumulation in the neointima. The reduction in severity and altered composition of vascular thickening in grafts from IFN-gamma -/- recipients shows that IFN-gamma contributes to arteriosclerotic development following transplantation.

[Heart transplantation--state of the art today]

In spite of pharmacological progress, end stage congestive heart failure is still associated with a decrease in quality and expectation of life. Heart transplantation remains the last therapeutic option for these patients. While the one year survival rate has increased over the last few years up to 84%, a major problem remains the significant lack of donors. Therefore, the criteria for the selection of candidates for cardiac transplantation have to be kept quite tight: Evidence of poor outcome without transplantation is associated with ejection fractions below 20 to 25%, cardiac indices less than 2.01/min/m2, left ventricular filling pressure above 20 mm Hg and a enddiastolic diameter of > 80 mm. There are, however, also quite important functional parameters indicating the need for heart transplantation, e.g. the maximal oxygene uptake being less than 10 ml/kg/min or below 50% of the age-appropriate value. Elevated pulmonary vascular resistance above 4 to 5 Wood units without a significant decrease during application of prostaglandin derivatives or inhalation of NO represents a contraindication for orthotopic heart transplantation; alternatively, a heterotopic transplantation can be considered. Since there is a significant shortage of suitable donor organs, the donor criteria have been broadened, e. g. the accepted donor age was increased to 60 years. Based on these extended criteria, a careful donor evaluation including cardiac history, cardiac examination, ECG and echocardiogram has to be performed. Coronary angiography in older donors is suggested, but in many cases not possible due to circumstances. Further precondition for a good graft function is a sophisticated donor management until the time of explantation. Hypovolemia and hypocalemia, hypothermia, hypoxia and rapid lost of circulating triiodothyronine (T3) have to be detected and balanced. The cardioplegic solution used might not only have an impact on the immediate postoperative performance of the graft, but also on the long term outcome, particularly with regard to graft vessel disease. There are generally two types of solutions: Those with intracellular and those with extracellular electrolyte concentrations. In addition, the potassium concentration might be of some importance. Potassium seems to damage endothelial cells and trigger subsequent immunological reactions. Therefore, high potassium concentrations in the cardioplegic solution might correlate with the incidence of graft vessel disease during the long term follow-up. The surgical technique for orthotopic heart transplantation developed at the beginning of the sixties by Lower and Shumway has been used unchanged for the last 30 years. The only alteration recently introduced is the separate direct anastomosis of the pulmonary and systemic veins in order to improve the atrial function. Until recently the commonly employed immunosuppressive strategy after heart transplantation consisted of the standard drugs cyclosporin, azathioprin and prednisolon. Some transplant-units use additionally induction therapy with antibody preparations. Many centers, however, abolished this regimen due to significant short and long term side effects. Promising new, more specific antibodies (which are chimerized or humanised) could revive the induction concept. The most thoroughly tested novel immunosuppressive agent is tacrolimus (FK506). It has been demonstrated to be 10 to 100 times more potent than cyclosporin A in in vitro and in vivo models. It binds to a different binding protein (FK-binding-protein) than cyclosporin (cyclophilin), but has a similar mechanism of action inhibiting the expression of T-cell-activator genes for certain cytokines. First non-randomised studies after heart transplantation performed at the University of Pittsburgh revealed that significantly more tacrolimus than cyclosporin patients were free of rejection. In order to confirm these observations, we performed a prospective randomised controlled clin

Isolated defect of adenosine-mediated coronary vasodilation: functional evidence for a new microangiopathic entity

OBJECTIVES

The present study describes an isolated defect of the coronary vasodilation in response to adenosine in five patients examined for clinically suspected coronary microangiopathy.

BACKGROUND

Coronary microangiopathies can be defined functionally as dysregulation of the microcirculatory vasomotion.

METHODS

The five patients were compared with 24 control subjects. Coronary flow velocity was measured with an intracoronary Doppler guide wire (0.018 in. [0.046 cm], 12 MHz) at rest and during intracoronary administration of adenosine (80 micrograms/min and 160 micrograms/min over 3 min each), papaverine (10-mg bolus) and acetylcholine (30 micrograms/min over 5 min). Diameters of the epicardial coronary arteries were measured by quantitative coronary angiography.

RESULTS

All subjects (patients and control) exhibited angiographically normal epicardial coronary arteries and normal and comparable endothelium-independent and -dependent vasomotion, as assessed with papaverine (mean [+/-SD]-relative coronary flow reserve 2.62 +/- 0.66 vs. 2.97 +/- 0.88, p = 0.32) and acetylcholine (volumetric coronary flow reserve 2.61 +/- 0.27 vs. 2.91 +/- 0.67, p = 0.58), respectively. Affected patients were identified by an isolated complete defect of the adenosine-mediated vasodilation compared with control subjects (relative coronary flow reserve in response to 80 micrograms/min of adenosine 1.08 +/- 0.17 vs. 2.45 +/- 0.74 [p < 0.001] and 160 micrograms/min of adenosine 1.03 +/- 0.15 vs. 2.89 +/- 0.65 [p < 0.001]).

CONCLUSIONS

These findings are consistent with functional evidence for a new entity of a coronary microangiopathy affecting a subtype of the endothelium-independent vasomotion.

Time-dependent decrease of presynaptic inotropic supersensitivity: physiological evidence of sympathetic reinnervation after heart transplantation

BACKGROUND

Sympathetic cardiac denervation of the transplanted human heart causes a loss of the presynaptic neuronal uptake1-mechanism with consecutive supersensitivity to uptake1-dependent catecholamines. A return of neuronal function (reinnervation) should result in a decrease of supersensitivity to catecholamines subjected to this uptake system and thus may alter the inotropic regulation.

METHODS

Inotropic dose-response curves were compared in 12 patients who were studied 3 to 15 months after transplantation (early) and 17 patients who were studied 23 to 156 months after transplantation (late) with isoproterenol (uptake1-independent) and epinephrine (uptake1-dependent). The inotropic response to increasing doses of isoproterenol (5 to 20 ng/kg per min) and epinephrine (10 to 40 ng/kg per min) was assessed with echocardiography as increase of the systolic pressure/dimension ratio (delta P/D) and of the rate-corrected velocity of circumferential fiber shortening (delta Vcfc).

RESULTS

Inotropic dose/response curves to isoproterenol were identical in the early and late recipients (during 20 ng/kg per min. isoproterenol: delta P/D 2.07 +/- 1.36 vs 2.18 +/- 1.42 mm Hg/mm; delta Vcfc 1.55 +/- 0.33 vs 1.40 +/- 0.38 square root of min-1 x %/ms), indicating an unchanged inotropic effect mediated by the postsynaptic beta-receptor/effector system. However, the inotropic response to epinephrine in early recipients was significantly attenuated in the late recipients (during 40 ng/kg per min. epinephrine: delta P/D 3.35 +/- 2.06 vs 1.51 +/- 0.68 mm Hg/mm, p < 0.01; delta Vcfc 1.80 +/- 0.42 vs 1.05 +/- 0.35 square root of min-1 x %/ms, p < 0.001).

CONCLUSIONS

These findings provide evidence for an at least partial restoration of the neuronal catecholamine uptake and are consistent with a time-dependent sympathetic reinnervation after heart transplantation. Restoration of neuronal uptake seems to be of functional importance, because it profoundly alters the inotropic effect of circulating endogenous catecholamines in long-term survivors after heart transplantation.

Parasympathetic denervation supersensitivity of the transplanted human ventricle in vivo

Sympathetic inotropic supersensitivity after transplantation-associated denervation of the cardiac autonomic nervous system has been described in humans previously. Potential changes of the parasympathetic regulation of the human ventricular contractility have not been investigated yet. We studied the antiadrenergic, negative inotropic effect of carbachol (3.6 micrograms/kg) during continuous beta-adrenergic stimulation (with isoproterenol, 20 ng.kg-1.min-1) in seven heart transplant recipients and seven healthy controls. Changes in ventricular contractility were calculated as increase of the systolic pressure-to-dimension ratio (delta P/D) and the rate-corrected velocity of circumferential fiber shortening (delta Vcfc), using M-mode echocardiography. In the control group, the isoproterenol-induced increase in contractility was attenuated only insignificantly by carbachol [delta P/D from 1.53 +/- 0.53 to 0.81 +/- 0.55 mmHg/mm, delta Vcfc from 0.77 +/- 0.20 to 0.63 +/- 0.22% x square root of beats/min (bpm)/ms]. In contrast, the transplant group exhibited a significant reduction of the isoproterenol-induced increase in contractility [delta P/D from 1.27 +/- 0.71 to -0.81 +/- 0.51 mmHg/mm (P < 0.01), delta Vcfc from 1.04 +/- 0.84 to 0.04 +/- 0.43% x square root of bpm/ms (P < 0.01)]. These data are consistent with parasympathetic indirect negative inotropic supersensitivity of the transplanted human heart in vivo.

Supersensitivity mismatch of adenosine in the transplanted human heart: chrono- and dromotropy versus inotropy

Supersensitive negative chronotropic and dromotropic effects have been described for adenosine after human heart transplantation. The present study investigated a potential antiadrenergic negative inotropic effect of adenosine in heart transplant recipients compared to normal subjects. Sinus cycle length, PR interval, blood pressure, and inotropic response in vivo were compared in seven orthotopic heart transplant recipients and seven healthy volunteers (controls). Fractional shortening, velocity of circumferential fiber shortening, and systolic pressure/dimension ratio were calculated using M-mode echocardiography. Baseline ventricular contractility was normal in both groups. Although adenosine induced a significant exaggeration of the negative chronotropic and dromotropic effect in the transplant group, the positive inotropic effect of 20 ng/kg x min isoproterenol (FS 53.2 +/- 8.8 vs 51.0 +/- 4.6%, P/D 5.8 +/- 1.9 vs 6.0 +/- 0.8 mm Hg/mm, Vcf 0.21 +/- 0.04 vs 0.20 +/- 0.02%/ms for heart recipients vs controls) was not reduced by the additional administration of 150 micrograms/kg adenosine (FS 52.2 +/- 8.6 vs 51.7 +/- 5.6%, P/D 5.5 +/- 1.5 vs 5.4 +/- 0.8 mm Hg/mm, Vcf 0.24 +/- 0.07 vs 0.21 +/- 0.02%/ms for transplant recipients vs controls). In contrast to a chronotropic and dromotropic supersensitivity, adenosine does not attenuate the catecholamine-induced increase in contractility in the human ventricle in vivo after heart transplantation.

Antiadrenergic effect of carbachol but not of adenosine on contractility in the intact human ventricle in vivo

OBJECTIVES

The purpose of this study was to investigate the antiadrenergic effects of adenosine and carbachol on beta-adrenoceptor-stimulated human ventricular contractility in vivo. In addition, the antiadrenergic effects of adenosine and carbachol were compared in vitro.

BACKGROUND

Adenosine is reported to exhibit an antiadrenergic negative inotropic response in the beta-adrenergic-stimulated ventricular myocardium in vitro. The effect of adenosine is similar to the antiadrenergic effect of m-cholinoceptor stimulation in vitro.

METHODS

The inotropic response in vivo was assessed in seven healthy volunteers by M-mode echocardiography and simultaneous blood pressure monitoring. It was calculated as the increase in the rate-corrected velocity of circumferential fiber shortening and in the systolic pressure/dimension ratio. All volunteers received pretreatment with 450 mg of dipyridamole/day for 48 h. In addition, the effects of adenosine and carbachol in the presence of 0.03 mumol/liter of isoproterenol on cumulative concentration-response curves of isolated, electrically driven human ventricular muscle strips were compared in vitro (n = 13).

RESULTS

The positive inotropic response to continuous infusion of 20 ng/kg per min of isoproterenol (increase of rate-corrected velocity of circumferential fiber shortening [10.2 +/- 2.1% x square root of beats/min per ms] and increase of systolic pressure/dimension ratio 1.09 +/- 0.3 mm Hg/mm) was significantly (p < 0.01) reduced by 3.6 micrograms/kg body weight of intravenous carbachol (4.2 +/- 1.2% x square root of beats/min per ms, 0.21 +/- 0.18 mm Hg/mm) but not by 50 micrograms/kg of intravenous adenosine (8.2 +/- 3.1% x square root of beats/min per ms, 1.35 +/- 0.42 mm Hg/mm), although adenosine induced a significant negative dromotropic effect. In vitro comparison of force of contraction with cumulative concentration-response curves in the presence of 0.03 mumol/liter of isoproterenol demonstrated an EC50 value (concentration producing half-maximal effect) for adenosine 466 times higher than that for carbachol (65.3 vs. 0.14 mumol/liter, p < 0.001).

CONCLUSIONS

In contrast to carbachol, adenosine does not attenuate the catecholamine-induced increase in contractility in the human ventricle in vivo. These differences between the A1-adenosine receptor- and m-cholinoceptor-mediated effects could be due to fewer A1-adenosine receptors or a less efficient receptor-effector coupling, or both.