Abstract
A Microfluidics Heart–Kidney Model
A multi-organ in vitro platform was designed and developed, to investigate the dynamic interplay between the heart and the kidneys.1 The relationship between these organs is complex and multifactorial, with dysfunction in one organ often leading to problems in the other. Although organ-on-chip models of the heart and the kidneys exist and have been used to study the organs separately, the interaction between them has been challenging to replicate. To address this gap, and uncover the mechanisms governing heart–kidney interactions, Gabbin et al. developed an in vitro human cell-based microfluidic cardiorenal unit. To create their model, they used cardiac microtissues and kidney organoids derived from human induced pluripotent stem cells, and placed them into separate, but communicating, chambers of a commercially available perfusion chip. They found that cardiac and renal tissue morphology, structure and function was maintained after 72 hours of on-chip dynamic culture. While the system requires further development, it shows potential as a platform for disease modelling and therapeutic discovery, since it is both reproducible and physiologically relevant.
1. Gabbin B, Meraviglia V, Angenent ML, et al. Heart and kidney organoids maintain organ-specific function in a microfluidic system. Mater Today Bio 2023; 23: 100818.
An In Vitro Intestinal Absorption Model
An in vitro system has been described that simulates the gastrointestinal (GI) solubility and intestinal permeation of drugs, during the process of stomach to duodenum transfer.1 To accurately simulate biorelevant drug concentrations during transit through the GI tract in vitro, dynamic GI transfer models must replicate the dynamics of gastric emptying and duodenal emptying, as well as the appropriate gastric and duodenal secretions. The Diamod® is an automated computer-controlled dynamic GI transfer model, with interconnected permeation consisting of two reactor vessels. The first vessel simulates the stomach; the second vessel consists of an inner donor compartment, which simulates the duodenal lumen. The latter vessel is mounted within an outer acceptor compartment, which simulates the blood stream and contains a sink solution to accept the test compound that permeates from the inner donor compartment.
The team’s aim was to evaluate Diamod’s in vivo predictive power, by studying the influence of water intake on the GI behaviour of itraconazole, and the influence of food on the GI dissolution and permeation of indinavir sulphate. These compounds were selected because in vivo clinical data show that transfer from the stomach to the duodenum influenced their duodenal solubility, and that the plasma concentrations of the drugs were strongly influenced by solubility–permeability interactions. Therefore, it was essential to employ an in vitro tool that could simultaneously replicate GI solubility and intestinal permeation, while also encompassing the transition from the stomach to the duodenum. Diamod was found to accurately predict the effects of water intake on the GI behaviour of itraconazole (e.g. water decreased itraconazole’s duodenal solute concentrations). It also correctly simulated how food intake had a negative effect on indinavir sulphate, which was mediated by increased stomach pH, entrapment of the drug in colloidal structures and the slower gastric emptying. The authors concluded that “the Diamod® is a useful in vitro model to mechanistically study the gastrointestinal performance of drugs”.1
1. Moens F, Vandevijver G, De Blaiser A, et al. The Dynamic Intestinal Absorption Model (Diamod®), an in vitro tool to study the interconnected kinetics of gastrointestinal solubility, supersaturation, precipitation, and intestinal permeation processes of oral drugs. Int J Pharm X 2023; 5: 100177.
An In Vitro Model of Human Fetal Spinal Cord Development
A novel methodology for the development of an in vitro model capable of amplifying human fetal spinal cord cells has been described in Neural Regeneration Research.1
During spinal cord development, roof plate secretion of bone morphogenetic proteins (BMPs) directs the cellular fate of sensory neurons, but the underlying biology is poorly understood. Research on the role of the type-II bone morphogenic protein receptor (BMPRII), which is expressed by neural precursor cells during embryogenesis, has mostly relied on animal models. However, due to significant species differences between rodents and humans, including variations in central nervous system structure, findings from murine models cannot be assumed to directly apply to human spinal cord development. Thus Weible et al.1 set out to reproduce early human neurodevelopmental processes in vitro through organotypic neurosphere formation. They isolated and characterised BMPRII+ human neural precursor cells from human fetal spinal cords, and found that leukaemia inhibitory factor (LIF) and high-density reaggregate cultures promoted the organotypic reorganisation of neurospheres.
The authors note that the techniques used to isolate and expand BMPRII+ human precursor cells — which did not involve genetic immortalisation or other manipulations that could affect physiological phenotype — could provide a reliable and straightforward means of gaining a better understanding of developmental neurobiology. In addition, this human cell-based in vitro model offers a unique tool for conducting research on spinal cord injuries and testing potential drug therapies.
1. Weible II MW, Lovelace MD, Mundell HD, et al. BMPRII+ neural precursor cells isolated and characterized from organotypic neurospheres: An in vitro model of human fetal spinal cord development. Neural Regen Res 2024; 19: 447–457.
Drosophila Used for Study on Neuromuscular Effects of COVID-19
SARS-CoV-2, the virus responsible for COVID-19, gains access to host cells by interacting with the angiotensin-converting enzyme 2 (ACE2) receptor. Even though SARS-CoV-2 mainly targets the respiratory system, a large percentage of COVID-19 patients present with neuromuscular issues. A better understanding of how the SARS-CoV-2 virus affects the neuromuscular system is required — for example, whether it occurs through direct damage, via ACE2 inactivation as a result of the infection, or as a result of the generation of ACE2 autoantibodies. To investigate this further, Herrera and Cauchi employed Drosophila as a model.1 Specifically, their aim was to explore whether the reduction of ACE2 expression alone would be enough to induce neuromuscular abnormalities. The results revealed that, when the ACE2 orthologues Ance or Ance3 are moderately silenced, it leads to reduced survival in the presence of thermal stress only when accompanied by increased physical activity-induced neuromuscular fatigue. Severe knockdown of Ance or Ance3 in muscle tissue significantly decreased adult viability and led to noticeable motor deficits (e.g. decreased mobility and impaired flight capability). Targeted knockdown of Ance and Ance3 in neurons caused wing abnormalities and age-dependent declines in motor function in adult flies, respectively. Interestingly, RNA sequencing analysis revealed several genes with differential splicing patterns that are essential for synaptic function following the depletion of Ance or Ance3. These results support the hypothesis that the loss of a renin-angiotensin system-independent function of ACE2 contributes to the neuromuscular issues associated with SARS-CoV-2 infection.
1. Herrera P and Cauchi RJ. Functional characterisation of the ACE2 orthologues in Drosophila provides insights into the neuromuscular complications of COVID-19. Biochim Biophys Acta Mol Basis Dis 2023; 1869: 166818.
A Research Model Developed with Ex Vivo Placental Tissues
Reproductive failure in ruminants is frequently linked to transmissible agents (e.g. Toxoplasma gondii and Neospora caninum), but the underlying mechanisms remain poorly understood. In vivo models offer valuable insights into abortion pathogenesis, but they are costly and raise ethical concerns. Unfortunately, existing in vitro models fall short of replicating the intricate placental structure found in live animals. To address these limitations, Horcajo et al.1 developed an ex vivo model based on ovine placental tissue and took advantage of ongoing experiments on healthy pregnant ewes to create a tissue biobank. To explore the possibility of using cryopreserved placental explants, they compared fresh and thawed tissue explants, assessing several indicators of tissue architecture, viability and functionality. Their results suggest that placental explants cryopreserved in ethylene glycol by using slow freezing rates, maintain not only their structure and function, but also their receptivity to T. gondii and N. caninum infection. According to the authors, this approach could be used to study other reproductive pathogens and be adapted to other related species. Furthermore, as this approach could be employed with other target tissues (e.g. intestine), it has potential to reduce the number of experimental animals used in future research.
1. Horcajo P, Ortega-Mora LM, Benavides J, et al. Ovine placental explants: A new ex vivo model to study host‒pathogen interactions in reproductive pathogens. Theriogenology 2023; 212: 157‒171.
A Human-based Study from the FRAME Lab
A study on the expression of myostatin has recently been published by researchers in the FRAME laboratory. Myostatin is mainly expressed and secreted in skeletal muscle, and is a member of the TGF-β family. It functions as a negative regulator of skeletal muscle growth, appearing to be upregulated in obese individuals and associated with insulin resistance. However, as these factors are also connected with the ageing process, Wilhelmsen et al.1 aimed to define the influence of excess adiposity, insulin resistance and ageing on the expression of myostatin mRNA in human skeletal muscle. To achieve this goal and carry out a human-focused study, they relied on volunteers to provide blood and tissue samples, which were used for in vitro assays and to generate primary muscle cultures. The team found that, while mRNA expression of myostatin is upregulated in the skeletal muscle of aged adults with excess adiposity and insulin resistance, it is not correlated with older age.
They attempted to explore possible causative factors by using in vitro models of human primary myotubes, observing that the obesity-mediated upregulation of myostatin mRNA could not be replicated by exposing the cultures to the subcutaneous adipose tissue secretome of obese individuals, or by increasing the availability of fatty acids (which induces insulin resistance). The authors summarise that “in the absence of excessive adiposity, ageing alone was not associated with a change in myostatin gene expression in human skeletal muscle” and that “factors intrinsic to skeletal muscle may be responsible for the obesity-mediated upregulation of myostatin”.1
1. Wilhelmsen A, Stephens FB, Bennett AJ, et al. Skeletal muscle myostatin mRNA expression is upregulated in aged human adults with excess adiposity but is not associated with insulin resistance and ageing. Geroscience 2023 Oct 6. DOI: 10.1007/s11357-023-00956-6.