Emmanuelle Albalat

Isotopic Ag–Cu–Pb record of silver circulation through 16th–18th century Spain

Estimating global fluxes of precious metals is key to understanding early monetary systems. This work adds silver (Ag) to the metals (Pb and Cu) used so far to trace the provenance of coinage through variations in isotopic abundances. Silver, copper, and lead isotopes were measured in 91 coins from the East Mediterranean Antiquity and Roman world, medieval western Europe, 16th–18th century Spain, Mexico, and the Andes and show a great potential for provenance studies. Pre-1492 European silver can be distinguished from Mexican and Andean metal. European silver dominated Spanish coinage until Philip III, but had, 80 y later after the reign of Philip V, been flushed from the monetary mass and replaced by Mexican silver.

A simplified protocol for measurement of Ca isotopes in biological samples

We describe a chemical separation protocol of calcium from biological materials for isotopic measurement by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). The method was tested using elution profiles along with HCl and HNO3 acids only, on human urine, sheep serum and red blood cells (RBC), seawater and herbaceous plants. It allows the elimination of all interfering species (including K, Sr, Mg) and the remaining matrix (including Fe, P, Na and S) beyond required levels. In order to further test this protocol and better understand the Ca isotopic signatures of mammalian fluids and organs, we purified and analyzed a wide range of materials from sheep, i.e. serum, RBC, muscle, liver, kidneys, enamel, bone, urine and feces. The data show a wide range of variations, expressed as δ, over 1‰ per amu, with a precision of 0.1‰ or better, spanning most of the variability reported so far. Red blood cells appeared to be heavier than serum by 0.3‰ per amu. This isotopic difference between serum and red blood cells was not taken into account in previous studies and it provides further information on Ca isotopic cycling in organisms. The Ca isotopic compositions of organs are correlated with concentrations, bone and RBC representing the two end-members, bone being Ca rich and 44Ca-depleted and RBC Ca poor and 44Ca-enriched. The trend is compatible with a distillation process by which Ca is extruded from cells along with a kinetic fractionation process favoring lighter Ca isotopes.

Medical applications of Cu, Zn, and S isotope effects

This review examines recent applications of stable copper, zinc and sulfur isotopes to medical cases and notably cancer. The distribution of the natural stable isotopes of a particular element among coexisting molecular species varies as a function of the bond strength, the ionic charge, and the coordination, and it also changes with kinetics. Ab initio calculations show that compounds in which a metal binds to oxygen- (sulfate, phosphate, lactate) and nitrogen-bearing moieties (histidine) favor heavy isotopes, whereas bonds with sulfur (cysteine, methionine) favor light isotopes. Oxidized cations (e.g., Cu(ii)) and low coordination numbers are expected to favor heavy isotopes relative to their reduced counterparts (Cu(i)) and high coordination numbers. Here we discuss the first observations of Cu, Zn, and S isotopic variations, three elements closely related along multiple biological pathways, with emphasis on serum samples of healthy volunteers and of cancer patients. It was found that heavy isotopes of Zn and to an even greater extent Cu are enriched in erythrocytes relative to serum, while the difference is small for sulfur. Isotopic variations related to age and sex are relatively small. The 65Cu/63Cu ratio in the serum of patients with colon, breast, and liver cancer is conspicuously low relative to healthy subjects. The characteristic time over which Cu isotopes may change with disease progression (a few weeks) is consistent with both the turnover time of the element and albumin half-life. A parallel effect on sulfur isotopes is detected in a few un-medicated patients. Copper in liver tumor tissue is isotopically heavy. In contrast, Zn in breast cancer tumors is isotopically lighter than in healthy breast tissue. 66Zn/64Zn is very similar in the serum of cancer patients and in controls. Possible reasons for Cu isotope variations may be related to the cytosolic storage of Cu lactate (Warburg effect), release of intracellular copper from cysteine clusters (metallothionein), or the hepatocellular and biosynthetic dysfunction of the liver. We suggest that Cu isotope metallomics will help evaluate the homeostasis of this element during patient treatment, notably by chelates and blockers of Cu trafficking, and understand the many biochemical pathways in which this element is essential.

Hypoxia induces copper stable isotope fractionation in hepatocellular carcinoma, in a HIF-independent manner.

Hepatocellular carcinoma (HCC) is the most frequent type of primary liver cancer, with increasing incidence worldwide. The unrestrained proliferation of tumour cells leads to tumour hypoxia which in turn promotes cancer aggressiveness. While changes in the concentration of copper (Cu) have long been observed upon cancerization, we have recently reported that the isotopic composition of copper is also altered in several types of cancer. In particular, we showed that in hepatocellular carcinoma, tumour tissue contains heavier copper compared to the surrounding parenchyma. However, the reasons behind such isotopic signature remained elusive. Here we show that hypoxia causes heavy copper enrichment in several human cell lines. We also demonstrate that this effect of hypoxia is pH, HIF-1 and -2 independent. Our data identify a previously unrecognized cellular process associated with hypoxia, and suggests that in vivo tumour hypoxia determines copper isotope fractionation in HCC and other solid cancers.

Sulfur isotope analysis by MC-ICP-MS and application to small medical samples

We describe a technique of S isotope analysis in sulfate form with the first separation stage involving anion-exchange and the second stage of mass-spectrometric analysis by MC-ICP-MS using standard-sample-standard bracketing. Ammonium in 1 : 1 stoichiometric proportion with sulfate was used to improve transmission and stability and to avoid cone and membrane clogging by condensable species. The working resolution of ∼9000 allowed the main interferences, notably 32SH on 33S, to be resolved. The matrix effect caused by phosphorus present in biological samples is negligible for S/P ratios ≥10: our chemical protocol allows S/P ≥ 150 to be routinely achieved. Replicate measurements of S standard solutions give values of isotopic abundances within errors of accepted values and demonstrate a reproducibility of ±0.10‰ for δ34S and ±0.15‰ for δ33S (2s). The technique is adequate for quantities as small as 10 nanomoles. We investigated the δ34S of 110 samples of cancer patients and 10 samples of rheumatoid arthritis patients. We avoided the use of blood collection tubes with sulfate-containing heparin. Sulfur in serum is transported by albumin and fibrinogen. Most serum and plasma δ34S values fall within a narrow interval of ∼1‰ around a mean δ34SVCDT of ∼6.0‰. The δ34S values of total blood, serum, and plasma are very similar. Despite the short turnover time of albumin and fibrinogen, S is surprisingly well regulated. Subtle variations of 0.2–0.3‰ around the mean value can be assigned to sex and age, with sulfur in male and adult samples tending to be heavier than in their female and juvenile counterparts. This narrow range of variations across the spectrum of a large number of individuals not selected for controlled dietary habits seems paradoxical. In general, breast and prostate cancer and rheumatoid arthritis have very little effect on the average serum δ34S, but increase the scatter of values. We confirm that the serum of patients affected by liver cancer and other pathologies is depleted of albumin-born sulfur. While sulfur in the serum of patients with non-malignant liver pathologies tends to be isotopically light, the serum δ34S of medicated hepatocellular carcinoma patients tends to be at the high end of control values.

Correction: Sulfur isotope analysis by MC-ICP-MS and application to small medical samples

Correction for ‘Sulfur isotope analysis by MC-ICP-MS and application to small medical samples’ by Emmanuelle Albalat et al., J. Anal. At. Spectrom., 2016, DOI: 10.1039/c5ja00489f.