Influence of circadian regulatory systems on in vitro test methods

Human health risk assessment of chemicals, pesticides or medical devices with consumer contact is conducted on the basis of validated test methods. In recent years, alternative methods to animal testing have gained importance for toxicological assessment strategies at national and international level. Continuous improvement of appropriate alternative methods is required to continue this process. In this context, the reflection of physiological properties of humans and animals is of crucial relevance. This includes, among others, the inner clock or circadian rhythm, which regulates such vital processes as body temperature, cardiovascular activity and metabolic activity.

The Impact of the circadian rhythm (day-night rhythm) on sensitivity and specificity of cell culture-based test systems

The Bf3R focuses on the impact of the circadian rhythm (day-night rhythm) on the sensitivity and specificity of cell culture-based test systems. In mammals, the circadian rhythm is triggered by the switch of light and darkness and maintains the synchrony of each cell of an organism via neuronal and endocrine signaling pathways. The disruption of this synchrony not only has a massive impact on the metabolism, but can also promote the development of diseases such as cancer. At a cellular and molecular level, the circadian rhythm is characterized by an oscillating expression of so-called CLOCK genes. These CLOCK genes in turn control the expression of ≈ 10% of all human genes and thus determine the temporal activity of all cells. In cell culture-based assay systems, the rhythmic expression of CLOCK genes can be stimulated to establish a synchronous circadian rhythm.

The Bf3R employs such synchronized cells into suitable test systems and aims to answer the following central questions:

1. Is it possible to increase the sensitivity and specificity of cellular reactions in non-animal test systems by an intact and synchronous circadian rhythm?

2. Is the sensitivity and specificity of non-animal test systems dependent on the daytime?

3. Do chemicals influence the integrity of the circadian rhythm and thus promote the development of diseases?

Oscillating expression of CLOCK genes

The CLOCK genes PER2 and BMAL1 are anticyclically expressed during the day and night, respectively. As transcription factors, both control the temporal activity of physiological processes.

Further reading:

Ndikung, J.; Storm, D.; Violet, N.; Kramer, A.; Schönfelder, G.; Ertych, N.; Oelgeschlager, M. Restoring circadian synchrony in vitro facilitates physiological responses to environmental chemicals. Environment International 2020;134:105265. https://www.sciencedirect.com/science/article/pii/S0160412019321865

The 4th dimension of in vitro systems - Time to level up. Mihelakis M, Ndikung J, Oelgeschläger M, Ertych N. Environ Int. 2022 Jun;164:107256. doi: 10.1016/j.envint.2022.107256.
https://www.sciencedirect.com/science/article/pii/S0160412022001829?via%3Dihub