Holotomography Reveals Protein Concentration Changes in Cardiac Spheroids under Ischemic Stress

Multicellular spheroids better recapitulate native cardiac tissue than two-dimensional systems, preserving cell–cell and cell–matrix interactions and relevant signalling. However, analytical tools for extracting quantitative data from these complex models remain limited. Here, we present an optimised holotomography (HT) workflow for fixed spheroids, enabling label-free quantification of protein concentration and dry mass across conditions. Using a hypoxia-reperfusion injury model to mimic myocardial infarction, HT measurements reveal a statistically significant reduction in the protein concentration of cardioids, reflecting impaired structural integrity and declining viability, subtle changes often missed by conventional approaches. These findings establish HT as a robust, scalable method for quantitative analysis of 3D cardiac models, with direct relevance for disease modelling and preclinical research.