Beyond Correlation: Establishing Causality in Protein Corona Formation for Nanomedicine.

In contemporary studies on the role of the protein corona in specific biological applications, identifying correlation is widely used to draw conclusions from observations and statistical methods, yet it merely identifies associations without establishing a direct influence between variables. This over reliance on observation can lead to spurious connections where co-occurrence does not imply causation. In contrast, a causality-focused approach asserts the direct impact of one variable on another, offering a more robust framework for inference and the drawing of scientific conclusions. This approach allows researchers to better predict how changes in a nanoparticle's physicochemical properties or biological conditions will affect protein corona composition and decoration, in turn affecting their safety and therapeutic/diagnostic efficacies. As a proof of concept, we explore the concept of "actual causality" (introduced by Halpern and Pearl) to mathematically prove how spiking small molecules, including metabolites, lipids, vitamins, and nutrients, into plasma can induce diverse protein corona patterns on identical nanoparticles. This approach significantly enhances the depth of plasma proteome profiling. Our findings reveal that among the various spiked small molecules, phosphatidylcholine was the actual cause of the observed increase in the proteomic depth of the plasma sample. By considering the concept of causality in the field of protein coronas, the nanomedicine community can substantially improve the ability to design safer and more efficient nanoparticles for both diagnostic and therapeutic purposes.