[Assessment of myocardial function and perfusion by MRI two days and four months after acute myocardial infarction revascularised by primary angioplasty]

The extent of gadolinium enhancement assessed by cardiac MRI is an accepted marker of myocardial necrosis. The correlation between late enhancement and other parameters of infarct size after myocardial infarction have previously been described. However, the prognostic value of the extent of late enhancement in terms of myocardial recovery remains controversial especially in revascularised infarcts analysed by early MRI. In order to clarify this question the authors compared the results of MRI at two days and four months after myocardial infarction benefiting from early revascularisation. Between July 2002 and November 2004, the authors included patients with myocardial infarction treated by primary angioplasty and examined by MRI (Siemens Symphony 1.5 T) at two days and three to five months after myocardial infarction. The left ventricular ejection fraction, volume, mass and wall thickness were measured. Perfusion at first passage (PP) and late enhancement were analysed after injection of 20 cc of gadolinium. An eight segment short axis model was used for PP and analysis of late enhancement. Each segment was assessed for transmural or subendocardial hypoperfusion for PP assessment and the wall thickness with late enhancement (1-25%, 26-50%, 51-75%, and 76-100%) was measured to calculate the percentage of myocardial mass showing late enhancement. Thirty-nine patients (thirty three men) were included. The average age was 59 +/- 10 years. TIMI III flow was obtained in all but one (TIMI II) patient. Cardiac MRI was performed 2.1 +/- 1.5 days and 4.6 +/- 1.7 months after myocardial infarction. The ejection fraction increased from 48.7 +/- 12.6% to 54.2 +/- 11.1%, p<0.05, and was related to infarct size (p<0.01). Forty-eight per cent of dysfunctional segments at the initial MRI improved their contractility and the extent of transmural late enhancement was inversely correlated with wall thickening at initial (p<0.01) and four month MRI (p<0.01). The PP improved significantly (regression from 9.5 +/- 8.2% to 2.8 +/- 4.1% of segments with abnormal myocardial perfusion, p<0.01). The late enhancement with respect to total myocardial mass decreased from 20.0 +/- 10.7% to 13.0 +/- 8.1%, p<0.01). Despite restoring TIMI III flow, early myocardial reperfusion is incomplete and improves in the medium term. The authors also observed a reduction in late enhancement at four months, indicating that the results immediately after myocardial infarction may overestimate the infarct size and that this sign does not represent necrotic tissue alone but also viable myocardium with a potential for recovery.

Using X-ray absorption spectra to monitor specific radiation damage to anomalously scattering atoms in macromolecular crystallography

Radiation damage in macromolecular crystals is not suppressed even at 90 K. This is particularly true for covalent bonds involving an anomalous scatterer (such as bromine) at the 'peak wavelength'. It is shown that a series of absorption spectra recorded on a brominated RNA faithfully monitor the extent of cleavage. The continuous spectral changes during irradiation preserve an 'isosbestic point', each spectrum being a linear combination of 'zero' and 'infinite' dose spectra. This easily yields a good estimate of the partial occupancy of bromine at any intermediate dose. The considerable effect on the near-edge features in the spectra of the crystal orientation versus the beam polarization has also been examined and found to be in good agreement with a previous study. Any significant influence of the (C-Br bond/beam polarization) angle on the cleavage kinetics of bromine was also searched for, but was not detected. These results will be useful for standard SAD/MAD experiments and for the emerging 'radiation-damage-induced phasing' method exploiting both the anomalous signal of an anomalous scatterer and the 'isomorphous' signal resulting from its cleavage.

La neuropathie motrice pure, une complication rare de la radiothérapie: trois observations et une revue de la littérature

BACKGROUND

Early or late neurological symptoms with lesions of peripheral or central nervous system can originated from radiotherapy.

METHODS

We report three cases of pure motor neuropathy in patients, which were treated by X-ray treatment several years ago.

RESULTS

Three patients (35-65 years old) have been presenting a pure motor neuropathy between 8.5 and 21 years after radiotherapy for Hodgkin disease (two cases) or testicular seminoma (one case). In each case, a proximodistal weakness with proximal predominance was observed and confirmed by the electromyographic findings. After a gradual worsening, we observed a clinical stability in patients treated by anticoagulant (one case) or pentoxifylline (two cases).

CONCLUSION

Pure motor neuropathy is a rare and late complication of the radiotherapy. A treatment with anticoagulant or pentoxifylline, with or without tocopherol, has been suggested.

New aspects of the alpha-helix to beta-sheet transition in stretched hard alpha-keratin fibers

The putative transformation of alpha-helices into beta-sheets has been studied for more than 50 years in the case of hard alpha-keratin. In a previous study of stretched keratin fibers, we specified the conditions for beta-sheet appearance within horsehair: the formation of beta-sheets requires at least 30% relative humidity. However, this phenomenon was observed in the whole tissue. Then there was no clear chemical identification of the beta-sheets (keratin or matrix proteins) and the exact location of the beta-sheets across the fiber could not be specified. In this study, using wide-angle x-ray scattering and high spatial resolution infrared microspectroscopy, we could determine and characterize the structural elements across hair sections stretched in water, which provides new information about the aforementioned transition. Our results show that the process can be split into three steps: 1), unraveling of the alpha-helical coiled-coil domains, which starts at roughly 5% macroscopic strain; 2), further transformation of the unraveled coiled-coils into beta-sheet structures, which occurs above roughly 20% macroscopic strain; and 3), spatial expanding of the beta-structured zones from the sample center to its periphery.

Phasing in the presence of severe site-specific radiation damage through dose-dependent modelling of heavy atoms

The case of a brominated RNA crystal structure determination in which standard three-wavelength MAD phasing was unsuccessful because of fast X-ray-induced debromination was reinvestigated [Ennifar et al. (2002), Acta Cryst. D58, 1262-1268]. It was found that if the data are kept unmerged and if a dose-stamp is associated with each reflection measurement, dose-dependent occupancies can be refined for the Br atoms. Such a parametrization has been implemented in the macromolecular phasing program SHARP. Refining such dose-dependent occupancies on an unmerged data set gave a dramatic improvement, even for SAD phases from only the first wavelength (peak), and resulted in a good electron-density map after solvent flattening. The adverse effect of radiation damage has been turned into a beneficial one. The crucial difference is made by the use of unmerged data: phasing power is generated through the intensity differences of symmetry-related reflections recorded at different doses, i.e. corresponding to different states of the X-ray-induced debromination. This approach should prove useful in all situations of experimental phasing where site-specific radiation damage occurs unavoidably and undesirably and not only in cases in which radiation damage is purposely being created in order to demonstrate its potential usefulness.

Imaging capabilities of synchrotron infrared microspectroscopy

It has become increasingly clear that synchrotron infrared micro-spectroscopy is an extremely valuable analysis tool when determining the chemical composition of biological and biomedical samples, at the diffraction-limited spatial resolution. Highly resolved infrared micro-spectroscopy, together with the high signal-to-noise level of the recorded spectra, is essential in generating chemical and statistical (multivariate) images. This is illustrated in the case of individual cell and hair section studies. Unprecedented chemical images of lipid distribution and secondary structure relative concentration have been achieved using the synchrotron source. A comparison with a Focal plane Array imaging system, on the same hair section, shows that, despite the fast imaging processing and improved quality achieved with the focal plane array detectors, spectral quality is markedly superior in the case of the synchrotron source. It is clear that the two approaches could be very complementary if combined on the same sample area, in a synchrotron facility.

Monitoring of umbilical cord blood lead levels and sources assessment among the Inuit

Analyses completed on samples collected between 1993 and 1996 showed that about 7% of 475 Inuit newborns from northern Quebec (Canada) had a cord blood lead concentration equal to or greater than 0.48 micromol/l, an intervention level adopted by many governmental agencies. A comparison between the cord blood lead isotope ratios of Inuit and southern Quebec newborns showed that lead sources for these populations were different. Our investigation suggests that lead shots used for game hunting were an important source of lead exposure in the Inuit population. A cohort study conducted in three Inuit communities shows a significant decrease of cord blood lead concentrations after a public health intervention to reduce the use of lead shot. Lead shot ammunition can be a major and preventable source of human exposure to lead.

Microbeam synchrotron imaging of hairs from ancient Egyptian mummies

Developments in microfocus synchrotron techniques have led to new results regarding the long-term alteration of archaeological samples of biological origin. Here, ancient hair samples from two Egyptian mummies have been analyzed using a conjunction of structural and elemental synchrotron methods. In this favored context of conservation, structural analysis revealed a remarkable preservation of keratin supramolecular organization at any observed length scale. Bulk keratin structure has therefore not been modified significantly over 2000 years. However, infrared spectroscopy indicated a partial disorganization of keratins close to the hair surface through polypeptide bond breakage. Elemental mapping showed a strongly heterogeneous distribution which can be related to mummification and cosmetic treatments.

Biological and biomedical applications of synchrotron infrared microspectroscopy

The high brightness of synchrotron light,which is about three orders of magnitudegreater than a thermal source, has beenexploited in biological and biomedicalapplications of infrared microspectroscopy. The potential of this analytical tool isdocumented in this article in the study ofhuman tissue (hair and skin) and individualcells: biochemical and bio-structuralchanges based on corresponding functionalgroups have been identified and imaged withunprecedented spatial resolution. Thistechnique also provides a new tool foranalysis of biochemical kinetics of samplesduring disease and treatment. In the future, the combination ofinfrared microspectroscopy with othersynchrotron-based microscopic techniques,such as X-ray microscopy, at the samesample location is discussed.