Jacques Vanderstraeten

Kidney function during exercise in healthy and diseased humans: An update

SummaryExercise induces profound changes in renal haemodynamics and protein excretion. The rate of ultrafiltration across the glomerular capillary is determined by the imbalance between the transcapillary hydraulic and colloid osmotic pressure gradients. Despite a major reduction in the renal plasma flow, the filtration fraction can double with maximal exercise, preserving the transfer of metabolites or substances through the glomerulus.Tubular processes and excretion rates are modified by exercise. Despite large increases in plasma lactate during strenuous exercise, renal excretion plays a limited role in lactate metabolism. Apparently, the mechanism of transcellular transport of lactate is saturated during severe exercise. Urea reabsorption is enhanced during prolonged exercise, and this process may act to limit the dehydration of an individual. As uric acid transport is also carrier-mediated, it appears that there is no saturation of the carrier system during prolonged exercise.Postexercise proteinuria is directly related to the intensity of exercise rather than to its duration. This excretion of excess proteins is a transient state with a half-time decay of about 1 hour. The increased clearance of plasma proteins suggests an increased glomerular permeability and a partial inhibition of tubular reabsorption. Studies suggest that exercise decreases the glomerular electrostatic barrier and facilitates transfer of macromolecules. Postexercise proteinuria appears to be age-dependent.Nephropathy is a common observation in the diabetic patient. In young and adult diabetic patients, exhaustive physical exercise does not provoke an enhanced dysfunction of the kidney to what is already found in healthy individuals. Heart and kidney transplant patients have a lesser postexercise proteinuria as compared with healthy individuals.

Gene and Protein Expression following Exposure to Radiofrequency Fields from Mobile Phones

Background Since 1999, several articles have been published on genome-wide and/or proteome-wide response after exposure to radiofrequency (RF) fields whose signal and intensities were similar to or typical of those of currently used mobile telephones. These studies were performed using powerful high-throughput screening techniques (HTSTs) of transcriptomics and/or proteomics, which allow for the simultaneous screening of the expression of thousands of genes or proteins. Objectives We reviewed these HTST-based studies and compared the results with currently accepted concepts about the effects of RF fields on gene expression. In this article we also discuss these last in light of the recent concept of microwave-assisted chemistry. Discussion To date, the results of HTST-based studies of transcriptomics and/or proteomics after exposure to RF fields relevant to human exposure are still inconclusive, as most of the positive reports are flawed by methodologic imperfections or shortcomings. In addition, when positive findings were reported, no precise response pattern could be identified in a reproducible way. In particular, results from HTST studies tend to exclude the role of a cell stressor for exposure to RF fields at nonthermal intensities. However, on the basis of lessons from microwave-assisted chemistry, we can assume that RF fields might affect heat-sensitive gene or protein expression to an extent larger than would be predicted from temperature change only. But in all likelihood, this would concern intensities higher than those relevant to usual human exposure. Conclusions The precise role of transcriptomics and proteomics in the screening of bioeffects from exposure to RF fields from mobile phones is still uncertain in view of the lack of positively identified phenotypic change and the lack of theoretical, as well as experimental, arguments for specific gene and/or protein response patterns after this kind of exposure.

Health effects of extremely low-frequency magnetic fields: reconsidering the melatonin hypothesis in the light of current data on magnetoreception

The so‐called ‘Melatonin Hypothesis’ proposed that decreased nocturnal production of melatonin (MLT) might explain the increased risk of breast cancer that has been formerly attributed to extremely low‐frequency (ELF) magnetic fields (MF) of weak intensity. Although the risk of ELF MF upon breast cancer was later dismissed, repeated reports were published of partial inhibition of MLT secretion in rats under long‐term (≥ 4 weeks) exposure to weak ELF MF. Since 2004, however, this topic has not been experimentally studied any more. In the present study, we propose to go back to the MLT hypothesis and apply it to childhood leukemia, for which an increased risk has been robustly associated with residential exposure to ELF MF. Contrary to the original hypothesis, however, we do not consider decreased MLT levels, but disruption of circadian rhythmicity per se as the effector mechanism. Indeed, the role of the circadian timing system in the development of childhood leukemia has been well established. Motivation for going back to the MLT hypothesis comes from recent data that suggest magnetosensory disruption by ELF MF in mammals, and magnetosensitivity in humans, together with current evidence for an influence on circadian rhythmicity from disruption of non‐photic sensory stimuli of various natures. We thus suggest further study on circadian rhythmicity in humans (children if possible) under long‐term exposure to weak ELF MF. Copyright

Does magnetoreception mediate biological effects of power-frequency magnetic fields?

The question of possible biological effects of power-frequency magnetic fields (PF-MF) remains controversial, notably because no valid mechanism of interaction could be proposed so far for intensities relevant to human and animal exposure (e.g. such as near high-tension power lines). In rodents, however, a few consistent effects of weak PF-MF have been reported. These are, notably, influence on spatial memory and partial inhibition of melatonin secretion under long-lasting exposure. Recent developments in study of magnetoreception in mammals justify reviving the hypothesis previously proposed of the intervention of the magnetic sense in melatonin disruption by PF-MF. We revisit this hypothesis and revise and extend it with respect to current knowledge and, particularly, with respect to reported effects on spatial memory. Proposals are made for experimental testing of the hypothesis. We argue that these tests may provide further insight into mechanisms of biological interactions of PF-MF and also, into mechanisms of magnetoreception per se.

Low-Light Dependence of the Magnetic Field Effect on Cryptochromes: Possible Relevance to Plant Ecology.

Various responses to static magnetic fields (MF) have been reported in plants, and it has been suggested that the geomagnetic field influences plant physiology. Accordingly, diverse mechanisms have been proposed to mediate MF effects in plants. The currently most probable sensor candidates are cryptochromes (Cry) which are sensitive to submillitesla MF. Here, we propose a quantitative approach of the MF effect on Cry depending on light intensity, and try to link it to a possible functional role for magnetic sensitivity in plants. Based on a theoretical evaluation and on a review of relevant data on Arabidopsis thaliana Cry 1, we point out that the MF effect on the signaling state of Cry, as well as the possible consequences of that effect on certain phenotypes (growth in particular) show parallel dependences on light intensity, being most prominent at low light levels. Based on these findings, we propose that Cry magnetosensitivity in plants could represent an ecological adaptation which regulates the amount of Cry signaling state under low light conditions. That hypothesis would preferentially be tested by studying sensitive and specific endpoints, such as the expression of clock proteins that are downregulated by Cry, but under light intensities lower than those used so far. Finally, we highlight that the low-light dependence of the MF effect described here could also apply to light-dependent functions of animal Cry, in particular magnetoreception which, from the present evaluation, would be based on the magnetic sensitivity of the photoreduction reaction, like in plants.

Could magnetic fields affect the circadian clock function of cryptochromes? Testing the basic premise of the cryptochrome hypothesis (ELF magnetic fields)

AbstractIt has been suggested that weak 50/60 Hz [extremely low frequency (ELF)] magnetic fields (MF) could affect circadian biorhythms by disrupting the clock function of cryptochromes (the “cryptochrome hypothesis,” currently under study). That hypothesis is based on the premise that weak (Earth strength) static magnetic fields affect the redox balance of cryptochromes, thus possibly their signaling state as well. An appropriate method for testing this postulate could be real time or short-term study of the circadian clock function of retinal cryptochromes under exposure to the static field intensities that elicit the largest redox changes (maximal “low field” and “high field” effects, respectively) compared to zero field. Positive results might encourage further study of the cryptochrome hypothesis itself. However, they would indicate the need for performing a similar study, this time comparing the effects of only slight intensity changes (low field range) in order to explore the possible role of the proximity of metal structures and furniture as a confounder under the cryptochrome hypothesis.

Effect of exposure to extremely low frequency magnetic fields on melatonin levels in calves is seasonally dependent

The question of health effects of extremely low frequency (50/60 Hz) magnetic fields (ELFMF) has been widely discussed, but the mechanisms of interaction of these fields with biological systems for intensities relevant to human and animal exposure are still under question. The melatonin (MLT) hypothesis suggests that exposure to ELFMF might decrease MLT production thereby promoting cancerogenesis. So far, most studies of MLT secretion under exposure to ELFMF reported negative or inconsistent results. Here, we measured salivary MLT in 1–2 months old cattle calves exposed to 50 Hz-MF in the hundreds of nT-range. We found an inhibitory effect of the ELFMF upon MLT secretion in winter (in accordance with the MLT hypothesis). In contrast, in summer, MLT concentration was increased by ELFMF exposure (contrary to the MLT hypothesis). The inhibitory effect in winter was much stronger than the positive effect in summer. We hypothesize that this season-dependent effect upon MLT synthesis might by mediated by an effect of ELFMF upon the serotonin metabolism and conclude that future tests of ELFMF effects should also measure serotonin levels and consider association with the seasonal effects (photoperiod or temperature) during the exposure.

Corrigendum: Low-Light Dependence of the Magnetic Field Effect on Cryptochromes: Possible Relevance to Plant Ecology

[This corrects the article DOI: 10.3389/fpls.2018.00121.].

The reproducing kernel method applied to time dependent thermalization-II

Abstract The formalism of the reproducing kernel method is used to evaluate exponents of bounded operators. Reproducing kernels are built with interpolating properties that do take into account any approximate knowledge of the spectrum. The explicit solution of linear evolution equations is reduced to the solution of a few static problems.