Medes (France)

In the past decade, there has been a surge in interest in space exploration studies, particularly due to the prospect of exploring distant planets such as Mars. However, long-duration space missions may pose cognitive challenges resulting from spaceflight-induced perceptual and motor changes, prolonged cephalic fluid shifts, and high cognitive load. One method for monitoring cognitive activity is functional near-infrared spectroscopy (fNIRS), a technique not yet tested under prolonged microgravity conditions beyond parabolic flight periods. Since fNIRS relies on cerebral oxygenation levels, should we adjust it for the fluid shift? To address this, the study explores the impact of simulated microgravity on cerebral oxygenation measures using fNIRS during a cognitive task, employing head-down tilt at different inclination levels and the Toulouse N-back Task (assessing memory and mental calculation) with varying difficulty levels. Eighteen subjects participated in the experiment. The results indicated that increasing difficulty levels of the cognitive task led to decreased accuracy, longer response times, and higher perceived difficulty scores. The inclination levels did not affect task performance. Increased difficulty was also concomitant with increasing HbO and decreasing HbR concentrations unaffected by the head-down tilt angle variations. These promising findings suggest that fNIRS measures could be used under microgravity conditions to measure cognitive load without correction for fluid shift.

After over 50 years of use, lithium-salts remain the first-line therapy for the management of bipolar disorder. Throughout this period, the potential for lithium salts has been extensively studied and numerous data favor its use in the treatment of neurodegenerative disorders such as Alzheimer's disease (AD). We reviewed existing evidence gathered from clinical case reports and studies on the effect of lithium on neuropsychological symptoms of AD and as a disease-modifying treatment acting on cognitive symptoms. The review summarizes the molecular pathways, involving GSK-3β inhibition and neuroprotection, through which lithium is proposed to exert its effect. Limitations to its current use in AD are discussed and future perspectives as a potential treatment option for AD are considered in regard to ongoing clinical trials using different forms of lithium.

Dear Editor, We congratulate Ojeda-Fernández et al1 on their study of the association between metformin use and lower risks of hospitalization and mortality in COVID-19 patients with diabetes. The study, one of the largest yet published, emphasizes the consistency of the association between metformin use and improved COVID-19 outcomes after hospital admission and in the medium term. However, we believe the published data on this topic should be interpreted with caution. In Table 1, we present an up-to-date summary of studies on the relationship between metformin use and COVID-19 that (i) were published in peer-reviewed medical journals and (ii) included more than 100 patients overall and more than 50 metformin users in particular. Duplicate studies and studies published in languages other than English, French or Italian were excluded. Overall, almost all the studies found that the short- and/or medium-term survival outcomes for metformin users were generally favourable. Ojeda-Fernández et al attributed the favourable association between metformin use and survival to a confounding effect of the indication; metformin is used early in the care trajectory for type 2 diabetes and is discontinued in long-term diabetes with cardiorenal comorbidities, whereas insulin is usually started later—typically when metformin is no longer indicated. Only few studies reported on the duration of diabetes in metformin users and non-users; this lack of data prevents meaningful conclusions from being drawn. However, 15 studies reported the proportion of participants who were being treated with insulin. Of these, 14 estimated the relative risk in the metformin group versus the non-metformin group. We performed a meta-regression analysis of the 14 datasets in order to determine whether or not the proportion of insulin-treated patients could account for the observed between-study heterogeneity. The analysis revealed a significant, inverse association between relative risk reduction and the proportion of insulin-treated patients (P = 0.0247). However, inclusion of the proportion of insulin-treated patients only reduced the I2 value very slightly (from 69.3% to 68.83%)—meaning there was still a substantial amount of residual between-study variance. In conclusion, although the findings by Ojeda-Fernández et al reinforce the conclusion that metformin is associated with a lower rate of mortality in type 2 diabetes patients with COVID-19, the assessment of this association is still strewn with pitfalls. Therefore, more studies are needed. Design and data collection: Abdallah Al-Salameh and Jean-Daniel Lalau. Analysis: Abdallah Al-Salameh, Nicolas Wiernsperger, Bertrand Cariou and Jean-Daniel Lalau. Writing manuscript: Abdallah Al-Salameh, Nicolas Wiernsperger, Bertrand Cariou and Jean-Daniel Lalau. This study did not receive any specific funding from agencies or organizations in the public, commercial, or not-for-profit sectors. Abdallah Al-Salameh reports personal fees from AstraZeneca, Lilly, and Novo Nordisk, none of which related to the subject discussed in this manuscript. Nicolas Wiernsperger declares no conflicts of interest that could be perceived as prejudicing the impartiality of the research reported. Bertrand Cariou reports grants and personal fees from Amgen, personal fees from AstraZeneca, personal fees from Akcea, personal fees from Genfit, personal fees from Gilead, personal fees from Eli Lilly, personal fees from Novo Nordisk, personal fees from MSD, grants and personal fees from Sanofi, and grants and personal fees from Regeneron. Jean-Daniel Lalau reports personal fees from AstraZeneca, Brothier, Lilly, MSD, Novo Nordisk, Pfizer, and Sanofi. The peer review history for this article is available at https://publons.com/publon/10.1111/dom.14746. Data sharing not applicable to this article as no datasets were generated The peer review history for this article is available at https://publons.com/publon/10.1111/dom.14746. Data sharing not applicable to this article as no datasets were generated

Future long-duration human spaceflight calls for developments to limit biocontamination of the surface habitats. The MATISS experiment tests surface treatments in the ISS’s atmosphere. Four sample holders were mounted with glass lamella with hydrophobic coatings, and exposed in the Columbus module for ~6 months. About 7800 particles were detected by tile scanning optical microscopy (×3 and ×30 magnification) indicating a relatively clean environment (a few particles per mm2), but leading to a significant coverage-rate (>2% in 20 years). Varied shapes were displayed in the coarse (50–1500 µm2) and fine (0.5–50 µm2) area fractions, consistent with scale dices (tissue or skin) and microbial cells, respectively. The 200–900 µm2 fraction of the coarse particles was systematically higher on FDTS and SiOCH than on Parylene, while the opposite was observed for the <10 µm2 fraction of the fine particles. This trend suggests two biocontamination sources and a surface deposition impacted by hydrophobic coatings.

This study was performed to determine the effects of 28 d of head-down tilt (HDT) (simulated weightlessness) on cardiovascular responses to orthostatic stress induced by lower body negative pressure (LBNP) (before, during, and after HDT) and +60 degrees head-up tilt (before and after HDT) in 12 subjects. Half of them underwent countermeasures (CM) of regular muscular exercise (isometric and isokinetic training) and LBNP sessions (-30 mm Hg) as generally performed during spaceflight; the other six were a control group (C). The countermeasure effect on the orthostatic responses to LBNP and tilt test was assessed by studying the changes after HDT in the two groups. Essentially, blood pressure was better maintained in group CM in the tilt test after HDT (MBP at the end of the tilt vs. baseline value: +16% (CM); -19% (C)). LBNP and muscular exercise may have contributed to this improvement. One of the probable contributing factors is the relative conservation of plasma volume, at the end of HDT, in group CM (-2.2%), compared to group C (-11.2%). Transcranial Doppler (TCD) recordings of middle cerebral artery (MCA) velocities permitted indirect evaluation of cerebral blood flow changes during the orthostatic tests. MCA velocities decreased significantly although slightly (-7 to -12%) during LBNP sessions without changes along the HDT showing that the cerebral circulation was well preserved in each group. On the other hand, subjects undergoing presyncopal symptoms presented a drop in MCA velocities, suggesting a decrease in cerebral blood flow.