A new screening method assesses the biocompatibility of nanoparticles (green) by visualizing their interactions with macrophages. [Laboratoire Bourquin/UNIFR and UNIGE]
A new screening method assesses the biocompatibility of nanoparticles (green) by visualizing their interactions with macrophages. [Laboratoire Bourquin/UNIFR and UNIGE]

Biomedical nanoparticles (NP) show great promise, but not all of them will make the grade. Some will be toxic. Some will have adverse interactions with macrophages. Some will induce harmful inflammatory reactions. Unfortunately, NP effects on the body are often unpredictable. In the absence of quick and reliable tests for NP safety and biocompatibility, NP development is stunted, and the clinical use of these virus-sized elements remains limited.

A new approach to NP testing has been developed by researchers from the Universities of Geneva (UNIGE) and Fribourg (UNIFR), Switzerland. They propose that NP candidates be tested for three attributes at once, accelerating and improving the reproducibility of the NP screening process. Ultimately, the new screening approach could fast-track NP applications such as contrast agents and drug-delivery vehicles.

Details of the new approach appeared February 2 in the journal Nanoscale, in an article entitled, “A Rapid Screening Method to Evaluate the Impact of Nanoparticles on Macrophages.” The new approach, the article indicated, could take less than a week to determine whether NP are compatible or not with the human body—an analysis that previously required several months of work.

“This assay is proposed as a standardized screening protocol to obtain a rapid overview of the impact of different types of NP on macrophages,” wrote the article’s authors. “Three essential questions are answered in parallel, in a single multiwell plate: Are the NP taken up by macrophages? Do the NP cause macrophage cell death? Do the NP induce inflammatory reactions?”

The study focused on macrophages because these cells are found on the front line of the immune system. They can, through their appetite for NP and their ability to trigger immune responses, predict the degree to which NP under investigation might be compatible with the human body.

The ideal medical NP should not be toxic (it should not kill the macrophages); it should not be entirely ingested by the macrophages (so that it retains its power to act); and it should limit the activation of the immune system (to avoid adverse side-effects).

Until now, evaluating the biocompatibility of nanomaterials was a laborious task that took several months and posed reproducibility problems, since not all the tests were performed on the same batch of particles. In the current study, the three essential elements of biocompatibility were assessed by means of flow cytometry.

“The macrophages are brought into contact with the NP for 24 hours, and are then passed in front of the laser beams,” explained Inès Mottas, the first author of the Nanoscale paper. “The fluorescence emitted by the macrophages makes it possible to count them and characterize their activation levels. Since the particles themselves are fluorescent, we can also measure the amount ingested by the macrophages.

“Our process means we can test the three elements simultaneously, and we only need a very small amount of particles,” continued Mottas. “We can obtain a comprehensive diagnosis of the NP submitted to us in 2 or 3 days.”

“Researchers can spend years developing a NP, without knowing what impact it will have on a living organism,” explained Carole Bourquin, professor in the medicine and science faculties at UNIGE and project leader. “So, there was a real need to design an effective screening method that could be implemented at the beginning of the development process. Indeed, if the NP aren't compatible, several years of research were simply thrown away.”

“When you begin to develop a new particle, it's very difficult to ensure that the recipe is exactly the same every time,” Mottas elaborated. “If we test different batches, the results may differ. Hence our idea of finding a way to test the three parameters simultaneously—and on the same sample—to establish the product's biocompatibility: its toxicity, its ability to activate the immune system, and the capacity of the macrophages to ingest them.”

The method devised in Geneva and Freiburg is already helping scientists to develop new particles. It focuses their work by enabling them to select the most promising particles quickly. “Due to high reproducibility,” the article’s authors added, “this method also allows quality control assessment for such aspects as immune-activating contaminants and batch-to-batch variability.”

Besides having a financial impact on the cost of research, this new approach also limits the use of animal testing. Furthermore, it is opening the door to the increasingly personalized treatment of certain pathologies. For example, by testing the NP on tumor cells isolated from a particular patient, it should theoretically be possible to identify the most effective treatment.

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