Biological fractionation of lithium isotopes by cellular Na+/H+ exchangers unravels fundamental transport mechanisms

Lithium Levels in Umbilical Cord Blood from Two Cities in China: Indicating Unidentified Sources of Human Exposure

As lithium demand continues to grow, increasing environmental lithium concentrations pose potential health risks to sensitive populations, particularly pregnant women and fetuses. However, data on fetal lithium exposure and umbilical cord blood lithium concentrations in nonpolluted regions remain scarce. To address this gap, we monitored lithium concentrations in maternal and umbilical cord blood in Beijing and Changsha, and analyzed exposure sources using a one-compartment model. Significant regional differences were observed: in 2019 and 2021, the mean (±SD) of lithium concentrations in umbilical cord blood in Beijing were 13.05 ± 7.34 and 11.23 ± 2.56 μg/L, respectively, while in Changsha, a significantly lower level of 0.61 ± 0.64 μg/L was found. Model estimates indicated that umbilical cord blood lithium in Changsha primarily originated from cereal, vegetables, and drinking water. However, most of the lithium in Beijing's cord blood came from unidentified sources, likely anthropogenic. This study highlights significant regional differences in umbilical cord blood lithium exposure and underscores the existence of unidentified exposure sources in Beijing except natural resource. As lithium usage increases in the future, ongoing monitoring and evaluation of potential health risks to fetuses will be critical.

Effects of lithium isotopes on sodium/lithium co-transport and calcium efflux through the sodium/calcium/lithium exchanger in mitochondria

The effects of lithium (Li) isotopes and their impact on biological processes have recently gained increased attention due to the significance of Li as a pharmacological agent and the potential that Li isotopic effects in neuroscience contexts may constitute a new example of quantum effects in biology. Previous studies have shown that the two Li isotopes, which differ in mass and nuclear spin, have unusual different effects in vivo and in vitro and, although some molecular targets for Li isotope fractionation have been proposed, it is not known whether those result in observable downstream neurophysiological effects. In this work we studied fluxes of Li+, sodium (Na+) and calcium (Ca2+) ions in the mitochondrial sodium/calcium/lithium exchanger (NCLX), the only transporter known with recognized specificity for Li+. We studied the effect of Li+ isotopes on Ca2+ efflux from heart mitochondria in comparison to natural Li+ and Na+ using Ca2+-induced fluorescence and investigated a possible Li isotope fractionation in mitochondria using inductively coupled plasma mass spectrometry (ICP-MS). Our fluorescence data indicate that Ca2+ efflux increases with higher concentrations of either Li+ or Na+. We found that the simultaneous presence of Li+ and Na+ increases Ca2+ efflux compared to Ca2+ efflux caused by the same concentration of Li+ alone. However, no differentiation in the Ca2+ efflux between the two Li+ isotopes was observed, either for Li+ alone or in mixtures of Li+ and Na+. Our ICP-MS data demonstrate that there is selectivity between Na+ and Li+ (greater Na+ than Li+ uptake) and, most interestingly, between the Li+ isotopes (greater 6Li+ than 7Li+ uptake) by the inner mitochondrial membrane. In summary, we observed no Li+ isotope differentiation for Ca2+ efflux in mitochondria via NCLX but found a Li+ isotope fractionation during Li+ uptake by mitochondria with NCLX active or blocked. Our results suggest that the transport of Li+ via NCLX is not the main pathway for Li+ isotope fractionation and that this differentiation does not affect Ca2+ efflux in mitochondria. Therefore, explaining the puzzling effects of Li+ isotopes observed in other contexts will require further investigation to identify the molecular targets for Li+ isotope differentiation.

Assessing dead time effects when attempting isotope ratio quantification by time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a quasi-non-destructive technique capable of analyzing the outer monolayers of a solid sample and detecting all elements of the periodic table and their isotopes. Its ability to analyze the outer monolayers resides in sputtering the sample surface with a low-dose primary ion gun, which, in turn, imposes the use of a detector capable of counting a single ion at a time. Consequently, the detector saturates when more than one ion arrives at the same time hindering the use of TOF-SIMS for quantification purposes such as isotope ratio estimation. Even though a simple Poisson-based correction is usually implemented in TOF-SIMS acquisition software to compensate the detector saturation effects, this correction is only valid up to a certain extent and can be unnoticed by the inexperienced user. This tutorial describes a methodology based on different practices reported in the literature for dealing with the detector saturation effects and assessing the validity limits of Poisson-based correction when attempting to use TOF-SIMS data for quantification purposes. As a practical example, a dried lithium hydroxide solution was analyzed by TOF-SIMS with the aim of estimating the 6Li/7Li isotope ratio. The approach presented here can be used by new TOF-SIMS users on their own data for understanding the effects of detector saturation, determine the validity limits of Poisson-based correction, and take into account important considerations when treating the data for quantification purposes.