Water compartmentalization, cell viability and morphology changes monitored under stress by 1H-NMR relaxometry and phase contrast optical microscopy

The quasi-continuous distributions of spin-lattice (T1) and spin-spin (T2) relaxation times of a population of cells kept under stress conditions for about 400 h has been obtained by 1H-NMR relaxometry. The comparison with the results obtained from the analysis of cell viability and morphological variations by phase contrast optical microscopy and performed with acquisition times, duration and conditions matching those of the relaxometry experiments allowed us to identify three main phases of the processes related to the exchanges of water and remodeling of cellular compartments: between 0 and 40 h the intra- and extra-cellular compartments are characterized by a T2 of ~250 ms and of ~2 s respectively and the cell population halflife has been experimentally evaluated to be ~45 h; after 40 and until 100 h cells NMR parameter changes suggest that the confined water is increasing according to the progressive fragmentation of the cells membrane; over 100 h almost all cells are non-viable and the constancy of the main NMR parameters reflects the reaching of the final equilibrium of the system. In conclusion our observations validated the use of NMR as a non-destructive, noninvasive powerful technique for monitoring the progression of cellular processes involving compartments water exchange and reorganization.