D2O and HDS in the coma of 67P/Churyumov-Gerasimenko

The European Rosetta mission has been following comet 67P/Churyumov-Gerasimenko for 2 years, studying the nucleus and coma in great detail. For most of these 2 years the Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA) has analysed the volatile part of the coma. With its high mass resolution and sensitivity it was able to not only detect deuterated water HDO, but also doubly deuterated water, D₂O and deuterated hydrogen sulfide HDS. The ratios for [HDO]/[H₂O], [D₂O]/[HDO] and [HDS]/[H₂S] derived from our measurements are (1.05 ± 0.14) × 10^-3, (1.80 ± 0.9) × 10^-2 and (1.2 ± 0.3) × 10^-3, respectively. These results yield a very high ratio of 17 for [D₂O]/[HDO] relative to [HDO]/[H₂O]. Statistically one would expect just 1/4. Such a high value can be explained by cometary water coming unprocessed from the presolar cloud, where water is formed on grains, leading to high deuterium fractionation. The high [HDS]/[H₂S] ratio is compatible with upper limits determined in low-mass star-forming regions and also points to a direct correlation of cometary H₂S with presolar grain surface chemistry.This article is part of the themed issue 'Cometary science after Rosetta'.

Photochemistry of forbidden oxygen lines in the inner coma of 67P/Churyumov-Gerasimenko

Observations of the green and red-doublet emission lines have previously been realized for several comets. We present here a chemistry-emission coupled model to study the production and loss mechanisms of the O(¹S) and O(¹D) states, which are responsible for the emission lines of interest for comet 67P/Churyumov-Gerasimenko. The recent discovery of O₂ in significant abundance relative to water 3.80 ± 0.85% within the coma of 67P has been taken into consideration for the first time in such models. We evaluate the effect of the presence of O₂ on the green to red-doublet emission intensity ratio, which is traditionally used to assess the CO₂ abundance within cometary atmospheres. Model simulations, solving the continuity equation with transport, show that not taking O₂ into account leads to an underestimation of the CO₂ abundance within 67P, with a relative error of about 25%. This strongly suggests that the green to red-doublet emission intensity ratio alone is not a proper tool for determining the CO₂ abundance, as previously suggested. Indeed, there is no compelling reason why O₂ would not be a common cometary volatile, making revision of earlier assessments regarding the CO₂ abundance in cometary atmospheres necessary. The large uncertainties of the CO₂ photodissociation cross section imply that more studies are required in order to better constrain the O(¹S) and O(¹D) production through this mechanism. Space weather phenomena, such as powerful solar flares, could be used as tools for doing so, providing additional information on a good estimation of the O₂ abundance within cometary atmospheres.

Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature

Molecular nitrogen (N2) is thought to have been the most abundant form of nitrogen in the protosolar nebula. It is the main N-bearing molecule in the atmospheres of Pluto and Triton and probably the main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered the most primitive bodies in the solar system, N2 has not been detected. Here we report the direct in situ measurement of N2 in the Jupiter family comet 67P/Churyumov-Gerasimenko, made by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis mass spectrometer aboard the Rosetta spacecraft. A N2/CO ratio of (5.70 ± 0.66) × 10(-3) (2σ standard deviation of the sampled mean) corresponds to depletion by a factor of ~25.4 ± 8.9 as compared to the protosolar value. This depletion suggests that cometary grains formed at low-temperature conditions below ~30 kelvin.

Cometary science. Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.

Performance evaluation of a miniature laser ablation time-of-flight mass spectrometer designed for in situ investigations in planetary space research

Key performance features of a miniature laser ablation time-of-flight mass spectrometer designed for in situ investigations of the chemical composition of planetary surfaces are presented. This mass spectrometer is well suited for elemental and isotopic analysis of raw solid materials with high sensitivity and high spatial resolution. In this study, ultraviolet laser radiation with irradiances suitable for ablation (< 1 GW/cm(2)) is used to achieve stable ion formation and low sample consumption. In comparison to our previous laser ablation studies at infrared wavelengths, several improvements to the experimental setup have been made, which allow accurate control over the experimental conditions and good reproducibility of measurements. Current performance evaluations indicate significant improvements to several instrumental figures of merit. Calibration of the mass scale is performed within a mass accuracy (Δm/m) in the range of 100 ppm, and a typical mass resolution (m/Δm) ~600 is achieved at the lead mass peaks. At lower laser irradiances, the mass resolution is better, about (m/Δm) ~900 for lead, and limited by the laser pulse duration of 3 ns. The effective dynamic range of the instrument was enhanced from about 6 decades determined in previous study up to more than 8 decades at present. Current studies show high sensitivity in detection of both metallic and non-metallic elements. Their abundance down to tens of ppb can be measured together with their isotopic patterns. Due to strict control of the experimental parameters, e.g. laser characteristics, ion-optical parameters and sample position, by computer control, measurements can be performed with high reproducibility.

Optimization of mass spectrometers using the adaptive particle swarm algorithm

Optimization of mass spectrometers using the adaptive particle swarm algorithm (APSA) is described along with implementations for ion optical simulations and various time-of-flight (TOF) instruments. The need for in situ self optimization is addressed through discussion of the reflectron TOF mass spectrometer (RTOF) on the European Space Agency mission Rosetta. In addition, a tool for optimization of laboratory mass spectrometers is presented and tested on two different instruments. After the application of APSA optimization, a substantial increase in performance for mass spectrometers that have manually been tuned for several weeks or months is demonstrated.

Impact of radiation therapy on the oncolytic adenovirus dl520: implications on the treatment of glioblastoma

BACKGROUND AND PURPOSE

Viral oncolytic therapy is emerging as a new form of anticancer therapy and has shown promising preclinical results, especially in combination with radio- and chemotherapy. We recently reported that nuclear localization of the human transcription factor YB-1 in multidrug-resistant cells facilitates E1-independent adenoviral replication. The aim of this study was to evaluate the combined treatment of the conditionally-replicating adenovirus dl520 and radiotherapy in glioma cell lines in vitro and in human tumor xenografts. Furthermore, the dependency of YB-1 on dl520 replication was verified by shRNA directed down regulation of YB-1.

METHODS AND MATERIAL

Localization of YB-1 was determined by immunostaining. Glioma cell lines LN-18, U373 and U87 were infected with dl520. Induction of cytopathic effect (CPE), viral replication, viral yield and viral release were determined after viral infection, radiation therapy and the combination of both treatment modalities. The capacity of treatments alone or combined to induce tumor growth inhibition of subcutaneous U373 tumors was tested also in nude mice.

RESULTS

Quantitative real-time PCR demonstrated that the shRNA-mediated down regulation of YB-1 is leading to a dramatic decrease in adenoviral replication of dl520. Immunostaining analysis showed that the YB-1 protein was predominantly located in the cytoplasm in the perinuclear space and less abundant in the nucleus. After irradiation we found an increase of nuclear YB-1. The addition of radiotherapy increased the oncolytic effect of dl520 with enhanced viral replication, viral yield and viral release. The oncolytic activity of dl520 plus radiation inhibited the growth of subcutaneous U373 tumors in a xenograft mouse model.

CONCLUSIONS

Radiation mediated increase of nuclear YB-1 in glioma cells enhanced the oncolytic potential of adenovirus dl520.

Outcome and cost analysis of sacral nerve stimulation for faecal incontinence

BACKGROUND

Sacral nerve stimulation (SNS) may be successful in treating incapacitating faecal incontinence. The technique is expensive, and no cost analysis is currently available. The aim of this study was to assess clinical outcome and analyse cost-effectiveness.

METHODS

Thirty-six consecutive patients underwent a two-stage SNS procedure. Outcome parameters and real costs were assessed prospectively.

RESULTS

SNS was tested successfully in 33 of 36 patients, and 31 patients were stimulated permanently. In the first stage, eight of 36 patients reported minor complications (pain, infection or electrode dislocation), resulting in a cost of euro 4053 (range euro 2838-7273) per patient. For the second stage (permanent stimulation), eight of 33 patients had an infection, pain or loss of effectiveness, resulting in a cost of euro 11,292 (range euro 7406-20,274) per patient. Estimated costs for further follow-up were euro 997 per year. The 5-year cumulative cost for SNS was euro 22,150 per patient, compared with euro 33,996 for colostomy, euro 31,590 for dynamic graciloplasty and euro 3234 for conservative treatment.

CONCLUSION

SNS is a highly cost-effective treatment for faecal incontinence. Options for further reduction of SNS costs include strict patient selection, treatment in an outpatient setting and using cheaper devices.

Novel three-pronged strategy to enhance cancer cell killing in glioblastoma cell lines: histone deacetylase inhibitor, chemotherapy, and oncolytic adenovirus dl520

Resistance to radiation and chemotherapy remains an obstacle to the treatment of brain tumors. We have demonstrated that the replication-deficient adenovirus d1520, which lacks the E1A 13S protein, replicates efficiently and exhibits oncolytic potential in multidrug-resistant cells with nuclear localization of the human transcription factor YB-1. However, besides others, key factors regarding oncolytic virotherapy are limited tumor transduction rate and low replication efficiency. The objective of this study was to determine whether the chemotherapeutic agent irinotecan, by enhancing nuclear localization of YB-1, and the histone deacetylase inhibitor trichostatin A, by upregulating coxsackievirus-adenovirus receptor (CAR) expression, could augment replication of and cell lysis by adenovirus dl520 in glioblastomas in vitro. We found that trichostatin A upregulated CAR expression and that irinotecan caused increased nuclear localization of YB-1 in both glioblastoma cell lines. Irinotecan alone, and trichostatin A alone, enhanced replication of and cell lysis by dl520. Importantly, when combining both agents, the replication efficiency (maximum, 27-fold) and induction of cytopathic effect (maximum, 3.8-fold) of dl520 were further augmented significantly. These results support the hypothesis that the enhanced oncolytic effect of dl520, after incubation with chemotherapeutic agents, is mediated by an increased accumulation of YB-1 in the nucleus (due to irinotecan) and by upregulation of CAR (due to trichostatin A). Thus, therapy combining virotherapy, chemotherapy, and histone deacetylase inhibitor treatment is a novel approach to enhance the oncolytic efficacy of dl520.

Inhibition of the multidrug-resistant phenotype by targeting YB-1 with a conditionally oncolytic adenovirus: implications for combinatorial treatment regimen with chemotherapeutic agents

Bearing in mind the limited success of available treatment modalities for the therapy of multidrug-resistant tumor cells, alternative and complementary strategies need to be developed. It is known that the transcriptional activation of genes, such as MDR1 and MRP1, which play a major role in the development of a multidrug-resistant phenotype in tumor cells, involves the Y-box protein YB-1. Thus, YB-1 is a promising target for new therapeutic approaches to defeat multidrug resistance. In addition, it has been reported previously that YB-1 is an important factor in adenoviral replication because it activates transcription from the adenoviral E2-late promoter. Here, we report that an oncolytic adenovirus, named Xvir03, expressing the viral proteins E1B55k and E4orf6, leads to nuclear translocation of YB-1 and in consequence to viral replication and cell lysis in vitro and in vivo. Moreover, we show that Xvir03 down-regulates the expression of MDR1 and MRP1, indicating that recruiting YB-1 to the adenoviral E2-late promoter for viral replication is responsible for this effect. Thus, nuclear translocation of YB-1 by Xvir03 leads to resensitization of tumor cells to cytotoxic drugs. These data reveal a link between chemotherapy and virotherapy based on the cellular transcription factor YB-1 and provide the basis for formulating a model for a novel combined therapy regimen named Mutually Synergistic Therapy.