Distinctive calcium isotopic composition of mice organs and fluids: implications for biological research.

The stable calcium (Ca) isotopes offer a minimally invasive method for assessing Ca balance in the body, providing a new avenue for research and clinical applications. In this study, we measured the Ca isotopic composition of soft tissues (brain, muscle, liver, and kidney), mineralized tissue (bone), and blood (plasma) from 10 mice (5 females and 5 males) with three different genetic backgrounds and same age (3 months old). The results reveal a distinctive Ca isotopic composition in different body compartments of mice, primally controlled by each compartment's unique Ca metabolism and genetic background, independent of sex. The bones are enriched in the lighter Ca isotopes (δ44/40Cabone = - 0.10 ± 0.55 ‰) compared to blood and other soft tissues, reflecting the preferential incorporation of lighter Ca isotopes through bone formation, while heavier Ca isotopes remain preferentially in blood. The brain and muscle are enriched in lighter Ca isotopes (δ44/40Cabrain = - 0.10 ± 0.53 ‰; δ44/40Camuscle = 0.19 ± 0.41 ‰) relative to blood and other soft tissues, making the brain the isotopically lightest soft tissues of the mouse body. In contrast, the kidney is enriched in heavier isotopes (δ44/40Cakidney = 0.86 ± 0.31 ‰) reflecting filtration and reabsorption by the kidney. This study provides important insight into the Ca isotopic composition of various body compartments and fluids.

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 their application to investigate bodily homeostasis and/or as biomarkers 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 suggests 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.

Chromite-induced magnesium isotope fractionation during mafic magma differentiation.

To better understand the mechanism of Mg isotopic variation in magma systems, here we report high precision Mg isotopic data of 17 bulk rock samples including dunite, clinopyroxenite, hornblendite and gabbro and 10 pairs of dunite-hosted olivine and chromite separates from the well-characterized Alaskan-type Xiadong intrusion in NW China, which formed by continuous and high degree of lithological differentiation from mafic magmas. Chromite separates have highly variable δ26Mg values from -0.10‰ to 0.40‰, and are consistently heavier than coexisting olivine separates (-0.39‰ to -0.15‰). Both mineral δ26Mg values and the degrees of inter-mineral fractionation are well correlated with geochemical indicators of magma differentiation, indicating that these inter-sample and inter-mineral Mg isotope fractionations are caused by magma evolution. The δ26Mg values range from -0.20‰ to -0.02‰ in the dunite, -0.43‰ in the clinopyroxenite, -0.43‰ to -0.28‰ in the hornblendite, 0.18‰ in the chromite-bearing hornblendite, and -0.56‰ to -0.16‰ in the gabbro. The Mg isotopic variations in different types of rocks are closely related to fractional crystallization and accumulation of different proportions of oxides vs. silicates. Chromite crystallization and accumulation is the most important factor in controlling Mg isotope fractionation during the formation of the Xiadong intrusion. Compared to basaltic and granitic magmas, differentiation of the Alaskan-type intrusions occurs at a relatively high oxygen fugacity, which favors chromite crystallization and consequently significant Mg isotope fractionations at both mineral and whole-rock scales. Therefore, Mg isotope systematics can be used to trace the degree of magma differentiation and related-mineralization.

Extremely large fractionation of Li isotopes in a chromitite-bearing mantle sequence.

We report Li isotopic compositions of olivine from the mantle sequence of the Luobusa ophiolite, southern Tibet. The olivine in the Luobusa ophiolite has Li concentrations from ~0.1 to 0.9 ppm and a broad range of δ(7)Li (+14 to -20‰). An inverse correlation of Li concentration and δ(7)Li in olivine from harzburgite suggests recent diffusive ingress of Li into the rock. Olivine from dunite enveloping podiform chromitites shows positive δ(7)Li values higher than those of MORB, whereas olivine from the chromitite has negative δ(7)Li values. Such variations are difficult to reconcile by diffusive fractionation and are thought to record the nature of the magma sources. Our results clearly indicate that the Luobusa chromitites formed from magmas with light Li isotopic compositions and that the dunites are products of melt-rock interaction. The isotopically light magmas originated by partial melting of a subducted slab after high degrees of dehydration and then penetrated the overlying mantle wedge. This study provides evidence for Li isotope heterogeneity in the mantle that resulted from subduction of a recycled oceanic component.

Abnormal lithium isotope composition from the ancient lithospheric mantle beneath the North China Craton.

Lithium elemental and isotopic compositions of olivines in peridotite xenoliths from Hebi in the North China Craton provide direct evidence for the highly variable δ(7)Li in Archean lithospheric mantle. The δ(7)Li in the cores of olivines from the Hebi high-Mg# peridotites (Fo > 91) show extreme variation from -27 to +21, in marked deviation from the δ(7)Li range of fresh MORB (+1.6 to +5.6) although the Li abundances of the olivines are within the range of normal mantle (1-2 ppm). The Li abundances and δ(7)Li characteristics of the Hebi olivines could not have been produced by recent diffusive-driven isotopic fractionation of Li and therefore the δ(7)Li in the cores of these olivines record the isotopic signature of the subcontinental lithospheric mantle. Our data demonstrate that abnormal δ(7)Li may be preserved in the ancient lithospheric mantle as observed in our study from the central North China Craton, which suggest that the subcontinental lithospheric mantle has experienced modification of fluid/melt derived from recycled oceanic crust.