Dependence of cross-bridge kinetics on myosin light chain isoforms in rabbit and rat skeletal muscle fibres

Cross-bridge kinetics underlying stretch-induced force transients was studied in fibres with different myosin light chain (MLC) isoforms from skeletal muscles of rabbit and rat. The force transients were induced by stepwise stretches (< 0.3% of fibre length) applied on maximally Ca²⁺-activated skinned fibres. Fast fibre types IIB, IID (or IIX) and IIA and the slow fibre type I containing the myosin heavy chain isoforms MHC-IIb, MHC-IId (or MHC-IIx), MHC-IIa and MHC-I, respectively, were investigated. The MLC isoform content varied within fibre types. Fast fibre types contained the fast regulatory MLC isoform MLC2f and different proportions of the fast alkali MLC isoforms MLC1f and MLC3f. Type I fibres contained the slow regulatory MLC isoform MLC2s and the slow alkali MLC isoform MLC1s. Slow MLC isoforms were also present in several type IIA fibres. The kinetics of force transients differed by a factor of about 30 between fibre types (order from fastest to slowest kinetics: IIB > IID > IIA ≫ I). The kinetics of the force transients was not dependent on the relative content of MLC1f and MLC3f. Type IIA fibres containing fast and slow MLC isoforms were about 1.2 times slower than type IIA fibres containing only fast MLC isoforms. We conclude that while the cross-bridge kinetics is mainly determined by the MHC isoforms present, it is affected by fast and slow MLC isoforms but not by the relative content of MLC1f and MLC3f. Thus, the physiological role of fast and slow MLC isoforms in type IIA fibres is a fine-tuning of the cross-bridge kinetics.     

Monte Carlo study of photon fields from a flattening filter-free clinical accelerator

In conventional clinical linear accelerators, the flattening filter scatters and absorbs a large fraction of primary photons. Increasing the beam-on time, which also increases the out-of-field exposure to patients, compensates for the reduction in photon fluence. In recent years, intensity modulated radiation therapy has been introduced, yielding better dose distributions than conventional three-dimensional conformal therapy. The drawback of this method is the further increase in beam-on time. An accelerator with the flattening filter removed, which would increase photon fluence greatly, could deliver considerably higher dose rates. The objective of the present study is to investigate the dosimetric properties of 6 and 18 MV photon beams from an accelerator without a flattening filter. The dosimetric data were generated using the Monte Carlo programs BEAMnrc and DOSXYZnrc. The accelerator model was based on the Varian Clinac 2100 design. We compared depth doses, dose rates, lateral profiles, doses outside collimation, total and collimator scatter factors for an accelerator with and without a flatteneing filter. The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose.     

Influenza virus NS vectors expressing the mycobacterium tuberculosis ESAT-6 protein induce CD4+ Th1 immune response and protect animals against tuberculosis challenge

Infection with Mycobacterium tuberculosis remains a major cause of morbidity and mortality all over the world. Since the effectiveness of the only available tuberculosis vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is suboptimal, there is a strong demand to develop new tuberculosis vaccines. As tuberculosis is an airborne disease, the intranasal route of vaccination might be preferable. Live influenza virus vaccines might be considered as potential vectors for mucosal immunization against various viral or bacterial pathogens, including M. tuberculosis. We generated several subtypes of attenuated recombinant influenza A viruses expressing the 6-kDa early secretory antigenic target protein (ESAT-6) of M. tuberculosis from the NS1 reading frame. We were able to demonstrate the potency of influenza virus NS vectors to induce an M. tuberculosis-specific Th1 immune response in mice. Moreover, intranasal immunization of mice and guinea pigs with such vectors induced protection against mycobacterial challenge, similar to that induced by BCG vaccination.     

Development of new radiopharmaceuticals for imaging monoamine oxidase B

Introduction

Imaging monoamine oxidase B (MAO-B) in the central nervous system with PET is an important goal for psychiatric studies. We here report an improved and automated radiosynthesis of N-(6-[¹⁸F]-fluorohexyl)-N-methylpropargylamine ([¹⁸F]FHMP; [¹⁸F]-1), as well as the radiosynthesis of two new promising candidates for imaging cerebral MAO-B, namely, carbon-11-labeled 3-(4-[¹¹C]-methoxyphenyl)-6-methyl-2H-1-benzopyran-2-one ([¹¹C]-2) and N-((1H-pyrrol-2-yl)methyl)-N-[¹¹C]-methyl-1-phenylmethanamine ([¹¹C]-3).

Methods

Fluorine-18-labeled 1 was prepared via a tosyloxy precursor in 29%±5% uncorrected radiochemical yield, relative to [¹⁸F]-fluoride. Both carbon-11-labeled compounds were prepared with [¹¹C]CH₃I using the “LOOP” method in 11% and 18% uncorrected radiochemical yields, respectively, relative to starting [¹¹C]CO₂. All radiotracers had specific activities >37 GBq/μmol and were >98% radiochemically pure at end of synthesis (<40 min). All radiotracers were evaluated by ex vivo biodistribution studies in conscious rodents.

Results

A major radioactive metabolite in the rodent brain was observed following administration of [¹⁸F]-1. While [¹¹C]-2 had moderate brain penetration and good clearance from normal brain tissue, distribution of radioactivity in brain was indicative of free and nonspecific binding. Good brain uptake was observed with [¹¹C]-3 (0.8%–1.4% injected dose per gram at 5 min postinjection), binding appeared to be reversible and distribution conformed with regional distribution of MAO-B in the rat brain. Preinjection of 3 or l-deprenyl showed a modest reduction (up to 25%) of brain activity.

Conclusion

Carbon-11-labeled 3 was found to have the most favorable properties of the radiotracers evaluated; however, the signal-to-noise ratio was too low to warrant further in vivo imaging studies. Alternative radiotracers for imaging MAO-B are under development.     

Basal cell carcinoma of the prostate: a case report

A 69-year-old man presented with gross hematuria and irritative urinary symptoms. He underwent transurethral resection of his prostate. The prostate chips revealed 70% poorly differentiated carcinoma with neuroendocrine features, initially read as small cell carcinoma, later as basal cell carcinoma. PSA at this time was 0.3. He received 4 cycles of etoposide and cisplatin. After which, rebiopsy of the prostate showed tumor consistent with poorly differentiated basal cell carcinoma. Given progression on chemotherapy, decision was made to proceed with radical prostatectomy. Metastatic workup was negative. Gross extraprostatic invasion was noted but lymph nodes were free of metastatic disease.     

Design, spectrum measurements and simulations for a 238Pu alpha-particle irradiator for bystander effect and genomic instability experiments.

Design, spectrum measurements and simulations for an alpha-particle irradiator for bystander effect and genomic instability experiments are presented. Measured alpha-particle energy spectra were used to confirm the characteristics of the source of the irradiator specified by the manufacturer of the source. The spectra were measured in vacuum with a high-resolution spectrometer and simulated with an AASI Monte Carlo code. As a next step, we simulated alpha-particle energy spectra at the target plane of the irradiator for three different source-to-target distances. In these simulations, helium was used as the medium between the source and the exit window of the irradiator; its pressure and temperature corresponded to those of the ambient air. Mean energies and full-widths at half-maximum (FWHM) were calculated for the three different helium gas tracks.     

Effect of acute versus chronic theophylline administration on acute restraint stress-induced increase of pentylenetetrazol seizure threshold in mice

Various stressful paradigms were found to induce anticonvulsant effects in different seizure models. Methylxanthines, such as theophylline might contribute to the reduction of restraint-induced stress. Therefore, in this study the influence of acute restraint stress on pentylenetetrazol (PTZ) seizure thresholds as well as the effect of acute and chronic theophylline pretreatment on stress-induced modulation of the seizure threshold were assessed in mice. The onset of the three consecutive seizure phases: myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hind limb extension (THE) was delayed after exposure to a 2 h restraint stress by 34%, 23% and 24%, respectively. In nonstressed mice, acute theophylline injection (100 mg/kg, i.p.) decreased the threshold only for THE. However, in stressed animals, the pretreatment with the methylxanthine significantly enhanced the dose of the convulsant producing the same seizure phase. In nonstressed mice, long-term theophylline treatment (50 mg/kg, twice daily for 14 days) increased PTZ threshold for all three seizure phases. In contrast, in chronically treated with theophylline mice exposed to restraint stress, significant decrease in the PTZ threshold for all seizure phases compared to control stressed animals have been observed. These results suggest that, depending on the treatment regimen (acute versus chronic), theophylline specifically and differentially modulates the anticonvulsant effect of restraint stress in mice.