Stable potassium isotope distribution in mouse organs and red blood cells: implication for biomarker development.

Potassium (K) is an essential electrolyte for cellular functions in living organisms, and disturbances in K+ homeostasis could lead to various chronic diseases (e.g. hypertension, cardiac disease, diabetes, and bone health). However, little is known about the natural distribution of stable K isotopes in mammals and its application to investigate the bodily homeostasis and/or as a biomarker for diseases. Here, we measured K isotopic compositions (δ41K, per mil deviation of 41K/39K from the NIST SRM 3141a standard) of brain, liver, kidney, and red blood cells (RBCs) from 10 mice (five females and five males) with three different genetic backgrounds. Our results reveal that different organs and RBCs have distinct K isotopic signatures. Specifically, the RBCs have heavy K isotopes enrichment with δ41K ranging from 0.67 to 0.08 ‰, while the brains show lighter K isotopic compositions with δ41K ranging from -1.13 to -0.09 ‰ compared to the livers (δ41K = -0.12 ± 0.58 ‰) and kidneys (δ41K = -0.24 ± 0.57 ‰). We found that the K isotopic and concentration variability is mostly controlled by the organs, with a minor effect of the genetic background and sex. Our study suggest that the K isotopic composition could be used as a biomarker for changes in K+ homeostasis and related diseases such as hypertension, cardiovascular, and neurodegenerative diseases.