Restoring circadian synchrony in vitro facilitates physiological responses to environmental chemicals

Therapeutic nuclear magnetic resonance and intermittent hypoxia trigger time dependent on/off effects in circadian clocks and confirm a central role of superoxide in cellular magnetic field effects

Cellular magnetic field effects are assumed to base on coherent singlet-triplet interconversion of radical pairs that are sensitive to applied radiofrequency (RF) and weak magnetic fields (WEMFs), known as radical pair mechanism (RPM). As a leading model, the RPM explains how quantum effects can influence biochemical and cellular signalling. Consequently, radical pairs generate reactive oxygen species (ROS) that link the RPM to redox processes, such as the response to hypoxia and the circadian clock. Therapeutic nuclear magnetic resonance (tNMR) occupies a unique position in the RPM paradigm because of the used frequencies, which are far below the range of 0.1-100 MHz postulated for the RPM to occur. Nonetheless, tNMR was shown to induce RPM like effects, such as increased extracellular H2O2 levels and altered cellular bioenergetics. In this study we compared the impact of tNMR and intermittent hypoxia on the circadian clock, as well as the role of superoxide in tNMR induced ROS partitioning. We show that both, tNMR and intermittent hypoxia, exert on/off effects on cellular clocks that are dependent on the time of application (day versus night). In addition, our data provide further evidence that superoxide plays a central role in magnetic signal transduction. tNMR used in combination with scavengers, such as Vitamin C, led to strong ROS product redistributions. This discovery might represent the first indication of radical triads in biological systems.

Combined use of multiparametric high-content-screening and in vitro circadian reporter assays in neurotoxicity evaluation

Accumulating evidence indicates that chronic circadian rhythm disruption is associated with the development of neurodegenerative diseases induced by exposure to neurotoxic chemicals. Herein, we examined the relationship between cellular circadian rhythm disruption and cytotoxicity in neural cells. Moreover, we evaluated the potential application of an in vitro cellular circadian rhythm assay in determining circadian rhythm disruption as a sensitive and early marker of neurotoxicant-induced adverse effects. To explore these objectives, we established an in vitro cellular circadian rhythm assay using human glioblastoma (U87 MG) cells stably transfected with a circadian reporter vector (PER2-dLuc) and determined the lowest-observed-adverse-effect levels (LOAELs) of several common neurotoxicants. Additionally, we determined the LOAEL of each compound on multiple cytotoxicity endpoints (nuclear size [NC], mitochondrial membrane potential [MMP], calcium ions, or lipid peroxidation) using a multiparametric high-content screening (HCS) assay using transfected U87 MG cells treated with the same neurotoxicants for 24 and 72 h. Based on our findings, the LOAEL for cellular circadian rhythm disruption for most chemicals was slightly higher than that for most cytotoxicity indicators detected using HCS, and the LOAEL for MMP in the first 24 h was the closest to that for cellular circadian rhythm disruption. Dietary antioxidants (methylselenocysteine and N-acetyl-l-cysteine) prevented or restored neurotoxicant-induced cellular circadian rhythm disruption. Our results suggest that cellular circadian rhythm disruption is as sensitive as cytotoxicity indicators and occurs early as much as cytotoxic events during disease development. Moreover, the in vitro cellular circadian rhythm assay warrants further evaluation as an early screening tool for neurotoxicants.

Imeglimin profoundly affects the circadian clock in mouse embryonic fibroblasts

OBJECTIVE

Imeglimin is a novel antidiabetic drug structurally related to metformin. Metformin has been shown to modulate the circadian clock in rat fibroblasts. Accordingly, in the present study, we aimed to determine whether imeglimin can impact the circadian oscillator in mouse embryonic fibroblasts (MEFs).

METHODS

MEFs carrying a Bmal1-Emerald luciferase (Bmal1-ELuc) reporter were exposed to imeglimin (0.1 or 1 mM), metformin (0.1 or 1 mM), a nicotinamide phosphoribosyltransferase inhibitor FK866, and/or vehicle. Subsequently, Bmal1-ELuc expression and clock gene mRNA expression levels were measured at 10-min intervals for 55 h and 4-h intervals for 32 h, respectively.

RESULTS

Imeglimin significantly prolonged the period (from 26.3 to 30.0 h at 0.1 mM) and dose-dependently increased the amplitude (9.6-fold at 1 mM) of the Bmal1-ELuc expression rhythm; however, metformin exhibited minimal effects on these parameters. Moreover, imeglimin notably impacted the rhythmic mRNA expression of clock genes (Bmal1, Per1, and Cry1). The concurrent addition of FK866 partly inhibited the effects of imeglimin on both Bmal1-ELuc expression and clock gene mRNA expression.

CONCLUSION

Collectively, these results reveal that imeglimin profoundly affects the circadian clock in MEFs. Further studies are needed to evaluate whether imeglimin treatment could exert similar effects in vivo.

Microfluidic models of the neurovascular unit: a translational view

The vasculature of the brain consists of specialized endothelial cells that form a blood-brain barrier (BBB). This barrier, in conjunction with supporting cell types, forms the neurovascular unit (NVU). The NVU restricts the passage of certain substances from the bloodstream while selectively permitting essential nutrients and molecules to enter the brain. This protective role is crucial for optimal brain function, but presents a significant obstacle in treating neurological conditions, necessitating chemical modifications or advanced drug delivery methods for most drugs to cross the NVU. A deeper understanding of NVU in health and disease will aid in the identification of new therapeutic targets and drug delivery strategies for improved treatment of neurological disorders.To achieve this goal, we need models that reflect the human BBB and NVU in health and disease. Although animal models of the brain's vasculature have proven valuable, they are often of limited translational relevance due to interspecies differences or inability to faithfully mimic human disease conditions. For this reason, human in vitro models are essential to improve our understanding of the brain's vasculature under healthy and diseased conditions. This review delves into the advancements in in vitro modeling of the BBB and NVU, with a particular focus on microfluidic models. After providing a historical overview of the field, we shift our focus to recent developments, offering insights into the latest achievements and their associated constraints. We briefly examine the importance of chip materials and methods to facilitate fluid flow, emphasizing their critical roles in achieving the necessary throughput for the integration of microfluidic models into routine experimentation. Subsequently, we highlight the recent strides made in enhancing the biological complexity of microfluidic NVU models and propose recommendations for elevating the biological relevance of future iterations.Importantly, the NVU is an intricate structure and it is improbable that any model will fully encompass all its aspects. Fit-for-purpose models offer a valuable compromise between physiological relevance and ease-of-use and hold the future of NVU modeling: as simple as possible, as complex as needed.

Circadian regulation of liver metabolism: experimental approaches in human, rodent, and cellular models

Circadian rhythms are endogenous oscillations with approximately a 24-h period that allow organisms to anticipate the change between day and night. Disruptions that desynchronize or misalign circadian rhythms are associated with an increased risk of cardiometabolic disease. This review focuses on the liver circadian clock as relevant to the risk of developing metabolic diseases including nonalcoholic fatty liver disease (NAFLD), insulin resistance, and type 2 diabetes (T2D). Many liver functions exhibit rhythmicity. Approximately 40% of the hepatic transcriptome exhibits 24-h rhythms, along with rhythms in protein levels, posttranslational modification, and various metabolites. The liver circadian clock is critical for maintaining glucose and lipid homeostasis. Most of the attention in the metabolic field has been directed toward diet, exercise, and rather little to modifiable risks due to circadian misalignment or disruption. Therefore, the aim of this review is to systematically analyze the various approaches that study liver circadian pathways, targeting metabolic liver diseases, such as diabetes, nonalcoholic fatty liver disease, using human, rodent, and cell biology models.NEW & NOTEWORTHY Over the past decade, there has been an increased interest in understanding the intricate relationship between circadian rhythm and liver metabolism. In this review, we have systematically searched the literature to analyze the various experimental approaches utilizing human, rodent, and in vitro cellular approaches to dissect the link between liver circadian rhythms and metabolic disease.

Interaction between environmental pollutants and cancer drug efficacy: Bisphenol A, Bisphenol A diglycidyl ether and Perfluorooctanoic acid reduce vincristine cytotoxicity in acute lymphoblastic leukemia cells

Every day, we are exposed to many environmental pollutants that can enter our body through different routes and cause adverse effects on our health. Epidemiological studies suggest that these pollutants are responsible for approximately nine million deaths per year. Acute lymphoblastic leukemia (ALL) represents one of the major cancers affecting children, and although substantial progress has been made in its treatment, relapses are frequent after initial treatment and are now one of the leading causes of cancer-related death in pediatric patients. Currently, relatively little attention is paid to pollutant exposure during drug treatment and this is not taken into account for dose setting or regulatory purposes. In this work, we investigated how bisphenol A (BPA), its derivative bisphenol A diglycidyl ether (BADGE), and perfluorooctanoic acid (PFOA) alter vincristine treatment in ALL when administered before or together with the drug. We found that these three pollutants at nanomolar concentrations, lower than those established by current regulations, can reduce the cytotoxic effects of vincristine on ALL cells. Interestingly, we found that this is only achieved when exposure to pollutants occurs prior to administration of the chemotherapeutic drug. Moreover, we found that this effect could be mediated by activation of the PI3K/AKT pathway and stabilization of microtubules. This work strengthens the idea of starting to take into account exposure to pollutants to improve the efficacy of chemotherapy treatments.

Pharmacokinetic and Permeation Studies in Rat Brain of Natural Compounds Led to Investigate Eugenol as Direct Activator of Dopamine Release in PC12 Cells

Eugenol, cinnamaldehyde and D-limonene, the main components of natural essential oils, are endowed with antioxidant and anti-inflammatory properties which allow them to induce beneficial effects on intestinal, cardiac and neuronal levels. In order to characterize their pharmacokinetic profiles and aptitude to permeate in the central nervous system after intravenous and oral administration to rats, new analytical procedures, easily achievable with HPLC-UV techniques, were developed. The terminal half-lives of these compounds range from 12.4 ± 0.9 (D-limonene) and 23.1 ± 1.6 min (cinnamaldehyde); their oral bioavailability appears relatively poor, ranging from 4.25 ± 0.11% (eugenol) to 7.33 ± 0.37% (cinnamaldehyde). Eugenol evidences a marked aptitude to permeate in the cerebrospinal fluid (CSF) of rats following both intravenous and oral administrations, whereas cinnamaldehyde appears able to reach the CSF only after intravenous administration; limonene is totally unable to permeate in the CSF. Eugenol was therefore recruited for in vitro studies of viability and time-/dose-dependent dopamine release in neuronal differentiated PC12 cells (a recognized cellular model mimicking dopaminergic neurons), evidencing its ability to increase cell viability and to induce dopamine release according to a U-shaped time-course curve. Moreover, concentration-response data suggest that eugenol may induce beneficial effects against Parkinson's disease after oral administration.

The 4th dimension of in vitro systems - Time to level up

Various in vitro model systems have been established over the last decades to understand physiological processes, the causalities of diseases and the response of humans to environmental and industrial chemicals or therapeutic drugs. Common to all is a limited biological significance due to the impairment of functionality, for instance by the lack of physiological 3D tissue architecture or the loss of fundamental regulatory mechanisms including the circadian rhythm. The circadian rhythm is an adaption of living organisms to rhythmic environmental changes of the day-night cycle and coordinates behavior as well as various crucial physiological processes in a 24-hour pattern. Here, we discuss the impact of integrating circadian regulation in experimental approaches and toxicological assessments to improve the biological relevance of the obtained results. In particular, it is known for some time that an ongoing disruption of the circadian rhythmicity is associated with an increased risk for cardiovascular disease, metabolic dysfunction or cancer. In the context of health recovery, the importance of circadian control mechanism is recognized by chronopharmacological concepts to increase the efficiency of pharmacological treatment strategies. Despite the undeniable circadian dependency and the biological relevance of manifold cellular and molecular processes, the impact of circadian regulation is hardly considered in a wide range of biomedical and toxicological research areas. Reactivating the circadian regulation holds the promise to enhance the biological relevance and reliability of in vitro approaches. In the context of human health protection the implementation of a circadian regulation will subsequently generate advanced physiologically relevant in vitro approaches and allows an improved toxicological assessment of health risks. In addition, the establishment of circadian disruption as a novel toxicological endpoint will provide a better understanding of toxicological mode of actions of environmental and industrial chemicals or drugs and enlarge the knowledge of disease development.

Comprehensive multiplexed superfusion system enables physiological emulation in cell culture: exemplification by persistent circadian entrainment

Cells and tissues are routinely cultured in vitro for biological research with findings being extrapolated to their host organ and tissue function. However, most samples are cultured and studied in unphysiological environments, without temporal variation in the biochemical cues that are ubiquitous in vivo. The artificiality of these conditions undermines the predictive value of cell culture studies. We ascribe the prevalence of this suboptimal culture methodology to the lack of practical continuous flow systems that are economical and robust. Here, we design and implement an expandable multiplexed flow system for cell culture superfusion. By expanding on the concept of the planar peristaltic pump, we fabricated a highly compact and multiplexed pump head with up to 48 active pump lines. The pump is incorporated into a custom, open-top superfusion system configured for conventional multi-well culture plates. We then demonstrated the utility of the system for in vitro circadian entrainment using a daily cortisol pulse, generating a sustained circadian amplitude that is essential for physiological emulation and chrono-pharmacological studies. The multiplexed pump is complemented by a package of fluidic interconnection and management methods enabling user-friendly and scalable operation. Collectively, the suite of technologies provides a much-needed improvement in physiological emulation to support the predictive value of in vitro biomedical and biological research.

Tick-Tock Consider the Clock: The Influence of Circadian and External Cycles on Time of Day Variation in the Human Metabolome-A Review

The past decade has seen a large influx of work investigating time of day variation in different human biofluid and tissue metabolomes. The driver of this daily variation can be endogenous circadian rhythms driven by the central and/or peripheral clocks, or exogenous diurnal rhythms driven by behavioural and environmental cycles, which manifest as regular 24 h cycles of metabolite concentrations. This review, of all published studies to date, establishes the extent of daily variation with regard to the number and identity of 'rhythmic' metabolites observed in blood, saliva, urine, breath, and skeletal muscle. The probable sources driving such variation, in addition to what metabolite classes are most susceptible in adhering to or uncoupling from such cycles is described in addition to a compiled list of common rhythmic metabolites. The reviewed studies show that the metabolome undergoes significant time of day variation, primarily observed for amino acids and multiple lipid classes. Such 24 h rhythms, driven by various factors discussed herein, are an additional source of intra/inter-individual variation and are thus highly pertinent to all studies applying untargeted and targeted metabolomics platforms, particularly for the construction of biomarker panels. The potential implications are discussed alongside proposed minimum reporting criteria suggested to acknowledge time of day variation as a potential influence of results and to facilitate improved reproducibility.