Copper transporters are responsible for copper isotopic fractionation in eukaryotic cells

STEAP Proteins: Roles in disease biology and potential for therapeutic intervention

Iron and copper are essential metal ions, and maintaining their metabolic balance is critical for organismal health. The Six-Transmembrane Epithelial Antigen of the Prostate (STEAP) protein family, comprising STEAP1, STEAP2, STEAP3, and STEAP4, plays a vital role in cellular metal homeostasis. These proteins are located on the cell membrane and are characterized by six transmembrane domains. With the exception of STEAP1, the STEAP proteins function as metal oxidoreductases due to their F420H2:NADP+ oxidoreductase (FNO)-like domain. However, STEAP1 contributes to metal metabolism through its heme group and interaction with other STEAP proteins. Beyond metal metabolism, STEAP proteins are involved in critical cellular processes, including the regulation of the cell cycle, proliferation, differentiation, and apoptosis. Notably, STEAP proteins are recognized as potential biomarkers and therapeutic targets in human cancers, particularly prostate cancer. This review outlines the structural features and functional roles of STEAP proteins in various diseases, including cancers, insulin resistance, non-alcoholic fatty liver disease (NAFLD), and benign prostatic hyperplasia, with a focus on their potential for therapeutic intervention.

Unveiling the hidden impact of long-term metal-rich volcanic pollution on male reproductive functions using isotope metallomics

Volcanic eruptions release particles in a range of sizes that can chronically affect the health of communities within tens of kilometers of the volcano. Many years after an eruption, resuspension of volcanic ash can exacerbate the health impact of primary eruptive events. So far, our global understanding of the health effects triggered by chronic exposure to volcanic particles at the whole-body scale is limited. Recently, it has been shown that mice chronically exposed to metal-rich volcanic ash deposits present metallome deregulations associated with pathophysiological changes. These deregulations preferentially impact the reproductive functions, questioning about the impact of ash on fertility. This work aims to further assess the mechanisms driving the ash-related fertility disorders and develop predictive biomarkers. For that, elemental concentrations and Cu-Zn-Fe isotope measurements coupled to metabolomic, proteomic and transcriptomic analyses were measured in blood, liver and two organs of the male reproductive system (testis, seminal vesicle). The samples were collected on wild-type and mice exposed over two months to volcanic ash. Mice exposed to ash are characterized by (i) significant metallomic deregulations, (ii) higher oxidative stress correlating with isotopic variations of redox-sensitive elements and (iii) testicular and hepatic alterations, marked by gains in organ mass, hepatic lipid accumulation and circulating bile acids overload, all of which might exacerbate testicular defects. Together, these results demonstrate that prolonged exposure to metal-rich ash is a threat for male reproduction and that investigating redox-sensitive isotopes might help identifying early signs of oxidative stress-related testicular injuries, with future implications for hepato-testicular disease prevention.

Advancing Biomarker Research: In Situ Cu Isotope Analysis in Liver Tumors by LA-MC-ICP-MS

Stable metal isotopes have received increasing attention as medical biomarkers due to their potential to detect changes in metal metabolism related to diseases. In particular, copper stable isotopes are a powerful tool to identify isotopic variation between tumors and healthy tissue, suggesting application in cancer diagnosis. However, potential mechanisms causing isotope fractionation, such as redox- or bond-forming reactions and interactions of metals during transmembrane import and export, are less well understood. Here, we established an in situ method using laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) to advance our understanding of the underlying processes responsible for isotope fractionation between normal and diseased tissues. Gelatin-based bracketing standards and quality control reference materials, crucial for laser ablation analysis, were developed to allow correction for instrumentally induced isotope fractionation during LA-MC-ICP-MS analysis. Using such matrix-matched standards, the method achieved intermediate precisions for delta values of better than 0.15 ‰ (2 s) for inorganic reference materials and of better than 0.17 ‰ (2 s) for biological reference materials. The developed routine was tested on rabbit VX2 liver tumor samples, a model system resembling human hepatocellular carcinoma (HCC) used to study liver cancer. In situ Cu isotope compositions between healthy (δ NIST 976 65/63 ( Cu ) = -1.5 ‰ to 0.2 ‰) and tumorous (δ NIST 976 65/63 ( Cu ) = 0.0 ‰ to 1.3 ‰) liver tissue show distinct differences in their isotope ratios. The observed isotopic dichotomy is consistent with previous solution-based MC-ICP-MS work, showing enrichment of heavy 65Cu in cancer biopsies relative to healthy tissue.

Copper and zinc isotope fractionation during phototrophic biofilm growth

Copper (Cu) and zinc (Zn) are two trace metals that exhibit both limiting and toxic effects on aquatic microorganisms. However, in contrast to good knowledge of these metal interactions with individual microbial cultures, the biofilm, complex natural consortium of microorganisms, remains poorly understood with respect to its control on Cu and Zn in the aquatic environments. Towards constraining the magnitude and mechanisms of Cu and Zn isotope fractionation in the presence of phototrophic biofilms composed of different proportion of diatoms, green algae and cyanobacteria, we studied long-term growth in a rotating annular bioreactor and quantified the uptake of metals and their isotope fractionation at environmentally-relevant Cu and Zn concentrations. An enrichment of the biofilm in heavy Cu isotope at the beginning of growth suggests the dominance of adsorption processes, followed by intracellular uptake leading to progressive enrichment in light isotope and an excretion of heavy isotope, likely linked to Cu(II) reduction. In the case of Zn, we evidenced only weak isotope fractionation which implies the presence of heavier isotope adsorption (notably in the case of cyanobacteria-dominated biofilm) followed by intracellular incorporation of lighter isotopes. The microbial community plays important role in overall magnitude and even direction of fractionation, suggesting sizable complexity of the processes controlling metal isotope fractionation during phototrophic biofilm growth. However, Cu and Zn isotopes during long-term metal accumulation in riverine biofilm can be used for monitoring the source of environmental pollution in aquatic systems, provided that variations within different sources exceed the natural isotopic fractionation between the biofilm and aqueous solution.

Copper and zinc isotope systematics in different bivalve mollusk species from the French coastline: Implications for biomonitoring

Zinc (Zn) and copper (Cu) stable isotopic compositions have been analyzed in various species of bivalve mollusks worldwide, but no comprehensive systematic interspecies comparison exists. Thus, we assessed isotope differences between species harvested in emblematic French coastal ecosystems to unveil biologically driven Cu and Zn isotope fractionation patterns. Inter-species isotopic variability of Cu is larger than Zn, with organisms that regulate internal concentrations displaying preferential bioaccumulation of heavy isotopes. The degree of internal isotope fractionation decreases from mussels > clams > oysters, affecting Cu more than Zn. The less pronounced Zn inter-specie variability helps preserve source information more reliably. Spatial analysis of a single oyster species denotes thus an important isotope variability of environmental Zn sources, including natural, anthropogenic and dietary components. Overall, results highlight the importance of considering systematic offset in Cu and Zn isotope values when comparing data from different bivalve species.

Copper isotope ratios in serum do not track cancerous tumor evolution, but organ failure

Relative to healthy controls, lighter copper isotopic compositions have been observed in the serum of breast cancer and end-stage liver disease patients, raising the possibility that Cu isotope ratios could be used as a tracer for disease progression. Here, we assess the potential of natural Cu isotopic variations (expressed as δ65Cu) as diagnostic tools for cancer progression and/or liver failure by performing a first-order analysis of Cu isotopic cycling in the human body. Using a box model, we simulate the kinetics of Cu mass transfer throughout significant reservoirs in the body, allowing isotopic fractionation to occur during Cu uptake/release from these reservoirs. With this model, we determine under which conditions the serum δ65Cu values would reflect perturbation related to cancer growth and/or liver failure at a level resolvable with modern mass spectrometry. We find that tumor growth alone is unable to explain the light isotopic signature observed in serum. Instead, we find that metabolic changes to the liver function resulting in a ∼1‰ isotope fractionation during Cu uptake from the blood into the liver can readily explain the long-term serum isotopic shift of ∼0.2‰ observed in cancer patients. A similar fractionation (∼1.3‰) during Cu uptake into the liver also readily explains the -1.2‰ shift observed in the serum of cirrhosis patients with ascites, suggesting a potentially common driver of isotopic fractionation in both cases. Using this model, we then test hypotheses put forward by previous studies and begin to probe the mechanisms behind the measured isotopic compositions.

Diet, cellular, and systemic homeostasis control the cycling of potassium stable isotopes in endothermic vertebrates

The naturally occurring stable isotopes of potassium (41K/39K, expressed as δ41K) have the potential to make significant contributions to vertebrate and human biology. The utility of K stable isotopes is, however, conditioned by the understanding of the dietary and biological factors controlling natural variability of δ41K. This paper reports a systematic study of K isotopes in extant terrestrial endothermic vertebrates. δ41K has been measured in 158 samples of tissues, biofluids, and excreta from 40 individuals of four vertebrate species (rat, guinea pig, pig and quail) reared in two controlled feeding experiments. We show that biological processing of K by endothermic vertebrates produces remarkable intra-organism δ41K variations of ca. 1.6‰. Dietary δ41K is the primary control of interindividual variability and δ41K of bodily K is +0.5-0.6‰ higher than diet. Such a trophic isotope effect is expected to propagate throughout trophic chains, opening promising use for reconstructing dietary behaviors in vertebrate ecosystems. In individuals, cellular δ41K is related to the intensity of K cycling and effectors of K homeostasis, including plasma membrane permeability and electrical potential. Renal and intestinal transepithelial transports also control fractionation of K isotopes. Using a box-modeling approach, we establish a first model of K isotope homeostasis. We predict a strong sensitivity of δ41K to variations of intracellular and renal K cycling in normal and pathological contexts. Thus, K isotopes constitute a promising tool for the study of K dyshomeostasis.

Rescue effect of curcumin against copper toxicity

Turmeric has long been used not only as an indispensable part of Asian cuisine but as a medicinal herb for dressing wounds, bites, burns, treating eye infections and acne. Curcuminoids are the active substances and their synthetic derivatives (i.e. diacetylcurcumin (DAC) and metal-curcumin complexes) possess an incredibly wide range of medicinal properties that encompass chelation capacity for multiple heavy metals, antioxidant activity, anti-inflammatory properties, cytotoxicity against cancerous cells, antiviral and antibacterial effects, antihypertensive and insulin sensitizing role, and regulatory role on apoptosis. The aforementioned properties have put curcumin on spotlight as a potential treatment for ailments such as, hepatic diseases, neurodegenerative diseases, metabolic syndrome, dyslipidemia, cardiovascular disease, auto-immune diseases, malignancies and conditions associated with metal overload. Copper is essential for major biological functions, however, an excess causes chronic ailments including neurodegenerative disorders. The fascinating approach of curcumin could alleviate such effect by forming a complex. Thus, this review aims to present available data on the effect of copper-curcumin interaction in various in vitro, ex-vivo in vivo, and clinical studies.

Translocation of elements and fractionation of Mg, Cu, Zn, and Cd stable isotopes in a penny bun mushroom (Boletus edulis) from western Czech Republic

Boletus edulis mushroom behaved as an accumulating biosystem with respect to Ag, Rb, Zn, and K. The mushroom was not an efficient accumulator of toxic As, Pb, and Cr, but Se and Cd displayed much higher concentrations in the mushroom than in the substrate samples. Other elements were bioexclusive. Different elements had different within-mushroom mobilities. The highest mobilities were displayed by Zn and Ag, and the lowest by Ti. The mushroom's fruiting body preferentially took up lighter Mg, Cu, and Cd isotopes (Δ26MgFB-soil =  -0.75‰; Δ65CuFB-soil =  -0.96‰; Δ114CdFB-soil =  -0.63‰), and the heavier 66Zn isotope (Δ66ZnFB-soil = 0.92‰). Positive within-mushroom Zn isotope fractionation resulted in accumulation of the heavier 66Zn (Δ66Zncap-stipe = 0.12‰) in the mushroom's upper parts. Cadmium displayed virtually no within-mushroom isotope fractionation. Different parts of the fruiting body fractionated Mg and Cu isotopes differently. The middle part of the stipe (3-6 cm) was strongly depleted in the heavier 26 Mg with respect to the 0-3 cm (Δ26Mgstipe(3-6)-stipe(0-3) =  -0.73‰) and 6-9 cm (Δ26Mgstipe(6-9)-stipe(3-6) = 0.28‰) sections. The same stipe part was strongly enriched in the heavier 65Cu with respect to the 0-3 cm (Δ65Custipe(3-6)-stipe(0-3) = 0.63‰) and 6-9 cm (Δ65Custipe(6-9)-stipe(3-6) =  -0.42‰) sections. An overall tendency for the upper mushroom's parts to accumulate heavier isotopes was noted for Mg (Δ26Mgcap-stipe = 0.20‰), Zn (Δ66Zncap-stipe = 0.12‰), and Cd (Δ114Cdcap-stipe = 0.04‰), whereas Cu showed the opposite trend (Δ65Cucap-stipe =  -0.08‰).

Isotopic composition of serum zinc and copper in healthy children and children with autism spectrum disorder in North America

To better understand zinc and copper regulation and their involvement in various biochemical pathways as it relates to autism spectrum disorder (ASD), isotopic composition of serum zinc and copper were evaluated in both healthy children and children with ASD in North America. No significant difference in isotopic composition of serum zinc or copper with respect to healthy controls and ASD children were identified. However, the isotopic composition of serum copper in boys was found to be enriched in ⁶⁵Cu in comparison to previously published healthy adult copper isotopic composition. Furthermore, in both boys and girls, the average isotopic composition of serum zinc is heavier than previously published healthy adult isotopic zinc composition. There was also a negative association between total zinc concentrations in serum and the zinc isotopic composition of serum in boys. Finally, children with heavier isotopic composition of copper also showed a high degree of variability in their zinc isotopic composition. While numerous studies have measured the isotopic composition of serum zinc and copper in adults, this is one of the first studies which measured the isotopic composition of serum copper and zinc in children, specifically those diagnosed with ASD. The results of this study showed that age and gender specific normal ranges of isotopic composition must be established to effectively use isotopic composition analysis in studying various diseases including ASD.

Natural copper isotopic abnormity in maternal serum at early pregnancy associated to risk of spontaneous preterm birth

Spontaneous preterm birth (SPB) has drawn public attention due to its increasing incidence and adverse effects on fetal growth. Effect of copper (Cu) imbalance in maternal bodies on the risk of SPB remains a subject of debate, and the related mechanisms are still unraveled. Here we applied natural stable copper isotopes to explore the underlying association and mechanism of copper imbalance with SPB using a nested case-control study. We collected maternal sera at the early pregnancy stage and then measured their copper isotopic ratio (⁶⁵Cu/⁶³Cu, expressed as δ⁶⁵Cu) as well as physiological and biochemical indexes from women with and without delivering SPB. We found that SPB cases had no significant difference in serum copper level from their controls, but their serum copper was significantly isotopically heavier than the controls (δ⁶⁵Cu value = 0.15 ± 0.34 ‰ versus -0.15 ± 0.17 ‰, P = 0.0149). Compared with the controls with lower δ⁶⁵Cu values, the crude odds ratio (OR) associated with SPB risk increased to 4.00 (95 % confidence interval (CI): 1.37-11.70) and the adjusted OR reached up to 11.35 (95 % CI: 1.35-95.60). Furthermore, via the copper isotopic fractionation, we revealed that dietary intake and blood ceruloplasmin may play more important roles than blood lipids and mother-to-child transmission in the copper imbalance associated with SPB. Further studies will be needed to understand the mechanisms of isotope fractionation related to reproductive health.

Metallome deregulation and health-related impacts due to long-term exposure to recent volcanic ash deposits: New chemical and isotopic insights

Volcanic ash exposure can lead to significant health risks. Damage to the respiratory and pulmonary systems are the most evident toxic side effects although the causes of these symptoms remain unclear. Conversely, the effects on other organs remain largely under-explored, limiting our understanding of the long-term volcanic ash-related risk at the whole-body scale. The metallome i.e. metal concentrations and isotopic compositions within the body, is suspected to be affected by volcanic ash exposure, having thus the potential for capturing some specificities of ash toxicity. However, the means by and extent to which the metallome is affected at the entire body scale and how the consequent chemical and isotopic deregulations correlate with pathophysiological dysfunctions are currently poorly understood. Here, we adopt a transdisciplinary approach combining high precision chemical analyses (major and trace element concentrations) and CuZn isotope measurements in seven organs and two biological fluids of isogenic mice (C57BL/6) exposed to eruption products from La Soufrière de Guadeloupe (Eastern Carribean), in tandem with biological parameters including physiological and morphological data. Based on principal component analysis, we show that after one month of exposure to volcanic ash deposits, the mice metallome; originally organ-specific and isotopically-typified, is highly disrupted as shown for example by heavy metal accumulation in testis (e.g., Fe, Zn) and Cu, Zn isotopic divergence in liver, intestine and blood. These metallomic variations are correlated with early testicular defects and might reflect the warning signs of premature (entero)hepatic impairments that may seriously affect fertility and favor the emergence of liver diseases after prolonged exposure. Monitoring the temporal evolution of the Cu and Zn isotope compositions seems to be a promising technique to identify the main biological processes and vital functions that are vulnerable to environmental volcanogenic pollutants although this will require further validation on human subjects.

Copper isotope composition of hemocyanin

BACKGROUND

Copper is a metal that plays a central role in biology, for example, as co-factor in various redox enzymes. Its stable isotopic composition is being used as tracer of its transport in living organisms and as a biomarker for diseases affecting its homeostasis. While the application of copper stable isotopes to biological studies is a growing field, there are presently no biological standards that are systematically analyzed in the different laboratories, as it is the case for geological samples (e.g., by using widely available basalt samples). It is therefore paramount for the community to establish such standard. Copper also binds oxygen in the respiratory protein, hemocyanin, in the hemolymph of mollusks and arthropods and is thus critical to respiration for these species.

METHODS

Here, the Cu isotope composition of hemocyanin of different modern species of mollusks and arthropods (Megathura crenulate Keyhole limpet, Limulus polyphemus Horseshoe crab and Concholepas concholepas Chilean abalone), as well as theoretical constraints on the origin of these isotopic fractionations through ab initio calculations are reported.

RESULTS

The isotopic fractionation factors for Cu(I) and Cu(II), both in hemocyanin and in seawater, predict an enrichment in the lighter isotope of Cu in the hemocyanin by over 1 permil compared to seawater. The hemocyanin of Chilean abalone and Horseshoe crab have Cu isotope compositions (δ65Cu = +0.63 ± 0.04‰ and +0.61 ± 0.04‰, respectively, with δ65Cu the permil deviation of the 65Cu/63Cu ratio from the NIST SRM 976 standard), similar to that of the octopus reported in literature (+0.62‰), that are undistinguishable from seawater, suggesting quantitative Cu absorption for these organisms. Conversely, the Keyhole limpet is enriched in the lighter isotope of Cu, which is in line with the ab initio calculation and therefore Cu isotopic fractionation during incorporation of Cu into the hemocyanin.

CONCLUSIONS

Because these hemocyanin standard samples are widely available, they could serve in the future as inter-laboratory standards to verify the accuracy of the Cu isotopic measurements on biological matrices.

Stable Isotope Fractionation of Metals and Metalloids in Plants: A Review

This work critically reviews stable isotope fractionation of essential (B, Mg, K, Ca, Fe, Ni, Cu, Zn, Mo), beneficial (Si), and non-essential (Cd, Tl) metals and metalloids in plants. The review (i) provides basic principles and methodologies for non-traditional isotope analyses, (ii) compiles isotope fractionation for uptake and translocation for each element and connects them to physiological processes, and (iii) interlinks knowledge from different elements to identify common and contrasting drivers of isotope fractionation. Different biological and physico-chemical processes drive isotope fractionation in plants. During uptake, Ca and Mg fractionate through root apoplast adsorption, Si through diffusion during membrane passage, Fe and Cu through reduction prior to membrane transport in strategy I plants, and Zn, Cu, and Cd through membrane transport. During translocation and utilization, isotopes fractionate through precipitation into insoluble forms, such as phytoliths (Si) or oxalate (Ca), structural binding to cell walls (Ca), and membrane transport and binding to soluble organic ligands (Zn, Cd). These processes can lead to similar (Cu, Fe) and opposing (Ca vs. Mg, Zn vs. Cd) isotope fractionation patterns of chemically similar elements in plants. Isotope fractionation in plants is influenced by biotic factors, such as phenological stages and plant genetics, as well as abiotic factors. Different nutrient supply induced shifts in isotope fractionation patterns for Mg, Cu, and Zn, suggesting that isotope process tracing can be used as a tool to detect and quantify different uptake pathways in response to abiotic stresses. However, the interpretation of isotope fractionation in plants is challenging because many isotope fractionation factors associated with specific processes are unknown and experiments are often exploratory. To overcome these limitations, fundamental geochemical research should expand the database of isotope fractionation factors and disentangle kinetic and equilibrium fractionation. In addition, plant growth studies should further shift toward hypothesis-driven experiments, for example, by integrating contrasting nutrient supplies, using established model plants, genetic approaches, and by combining isotope analyses with complementary speciation techniques. To fully exploit the potential of isotope process tracing in plants, the interdisciplinary expertise of plant and isotope geochemical scientists is required.

Nrf2 signaling pathway in trace metal carcinogenesis: A cross-talk between oxidative stress and angiogenesis

A large number of people worldwide are affected by chronic metal exposure, which is known to be associated with different type of malignancies. The mechanisms of metal carcinogenicity are complex in nature, and excessive reactive oxygen species (ROS) generation induced by chronic metal exposure, among the other factors, has been proposed as one of the major mechanisms involved in that process. In tumor cells, ROS buildup may lead to cell death through intrinsic and extrinsic signaling pathways. Furthermore, ROS-mediated redox signaling has a crucial role in angiogenesis, which is recognized as an essential step in tumor progression. There are several redox-modulating pathways and among them, the nuclear factor erythroid2-related factor2 (Nrf2), as a sensor of oxidative or electrophilic stress, has introduced as a master regulator of cellular response against environmental stresses. Activation of Nrf2 signaling induces expression of wide variety of antioxidant and detoxification enzymes genes. Thus, this transcription factor has recently received much attention as a target for cancer chemoprevention. But meanwhile, constitutive Nrf2 activation in cancerous cells may promote cancer progression and resistance to chemotherapy. The current review describes the major underlying mechanisms involved in carcinogenesis of trace metals: copper, silver, and cadmium, with a special focus on the Nrf2 signaling pathway as a crossroad between oxidative stress and angiogenesis.

Identification of two-dimensional copper signatures in human blood for bladder cancer with machine learning

Currently, almost all available cancer biomarkers are based on concentrations of compounds, often suffering from low sensitivity, poor specificity, and false positive or negative results. The stable isotopic composition of elements provides a different dimension from the concentration and has been widely used as a tracer in geochemistry. In health research, stable isotopic analysis has also shown potential as a new diagnostic/prognostic tool, which is still in the nascent stage. Here we discovered that bladder cancer (BCa) could induce a significant variation in the ratio of natural copper isotopes (⁶⁵Cu/⁶³Cu) in the blood of patients relative to benign and healthy controls. Such inherent copper isotopic signatures permitted new insights into molecular mechanisms of copper imbalance underlying the carcinogenic process. More importantly, to enhance the diagnostic capability, a machine learning model was developed to classify BCa and non-BCa subjects based on two-dimensional copper signatures (copper isotopic composition and concentration in plasma and red blood cells) with a high sensitivity, high true negative rate, and low false positive rate. Our results demonstrated the promise of blood copper signatures combined with machine learning as a versatile tool for cancer research and potential clinical application.

The blood Cu concentration and isotopic composition enable new insights into Cu imbalance and diagnosis of bladder cancer with machine learning.

Stable Cu Isotope Ratios Show Changes in Cu Uptake and Transport Mechanisms in Vitis vinifera Due to High Cu Exposure

Even though copper (Cu) is an essential plant nutrient, it can become toxic under certain conditions. Toxic effects do not only depend on soil Cu content, but also on environmental and physiological factors, that are not well understood. In this study, the mechanisms of Cu bioavailability and the homeostasis of Vitis vinifera L. cv. Tannat were investigated under controlled conditions, using stable Cu isotope analysis. We measured Cu concentrations and δ⁶⁵Cu isotope ratios in soils, soil solutions, roots, and leaves of grapevine plants grown on six different vineyard soils, in a 16-week greenhouse experiment. The mobility of Cu in the soil solutions was controlled by the solubility of soil organic matter. No direct relationship between Cu contents in soils or soil solutions and Cu contents in roots could be established, indicating a partly homeostatic control of Cu uptake. Isotope fractionation between soil solutions and roots shifted from light to heavy with increasing Cu exposure, in line with a shift from active to passive uptake. Passive uptake appears to exceed active uptake for soil solution concentrations higher than 270 μg L^-1. Isotope fractionation between roots and leaves was increasingly negative with increasing root Cu contents, even though the leaf Cu contents did not differ significantly. Our results suggest that Cu isotope analysis is a sensitive tool to monitor differences in Cu uptake and translocation pathways even before differences in tissue contents can be observed.

Regulatory Roles of Six-Transmembrane Epithelial Antigen of the Prostate Family Members in the Occurrence and Development of Malignant Tumors

The human six-transmembrane epithelial antigen of the prostate (STEAP) proteins, which include STEAP1-4 and atypical STEAP1B, contain six transmembrane domains and are located in the cell membrane. STEAPs are considered archaeal metal oxidoreductases, based on their heme groups and F420H2:NADP+ oxidoreductase (FNO)-like structures, and play an important role in cell metal metabolism. Interestingly, STEAPs not only participate in biological processes, such as molecular transport, cell cycling, immune response, and intracellular and extracellular activities, but also are closely related to the occurrence and development of several diseases, especially malignant tumors. Up to now, the expression patterns of STEAPs have been found to be diverse in different types of tumors, with controversial participation in different aspects of malignancy, such as cell proliferation, migration, invasion, apoptosis, and therapeutic resistance. It is clinically important to explore the potential roles of STEAPs as new immunotherapeutic targets for the treatment of different malignant tumors. Therefore, this review focuses on the molecular mechanism and function of STEAPs in the occurrence and development of different cancers in order to understand the role of STEAPs in cancer and provide a new theoretical basis for the treatment of diverse cancers.

Biodynamics and adverse effects of CuO nanoparticles and CuCl2 in the oligochaete T. tubifex: Cu form influence biodynamics in water, but not sediment

The use of copper oxide (CuO) NPs results in the release of these particles into the aquatic environment. Here, the particles settle out and accumulate in the sediment. However, little is known about the biodynamics of sediment-associated NPs in benthic organisms. We compared the toxicity and biodynamics of CuO NPs (7 nm) and dissolved Cu (CuCl₂) in the sediment-dwelling oligochaete, Tubifex tubifex, to gain insights into the relative importance of metal form (CuCl₂ vs CuO NPs) and exposure route (water vs sediment). Isotopically enriched ⁶⁵Cu was used as a tracer to distinguish background from newly accumulated ⁶⁵Cu in worms. For each exposure route, we conducted three experiments: one uptake, one elimination, and one longer-term net accumulation experiment to parameterize uptake and elimination of ⁶⁵CuCl₂ and ⁶⁵CuO NPs in T. tubifex. ⁶⁵Cu accumulation was detected for both ⁶⁵CuCl₂ and ⁶⁵CuO NPs regardless of whether T. tubifex were exposed in sediment- or water-only setups. Water exposures to ⁶⁵CuCl₂ resulted in tail trauma whereas limited effects were seen for sediment exposures or exposures to ⁶⁵CuO NPs via either exposure route. Uptake rate constants and accumulation of ⁶⁵Cu in T. tubifex were higher following ⁶⁵CuCl₂ exposure than ⁶⁵CuO NPs, in water, but not in sediment. Thus, the relative importance of exposure route and Cu form for uptake dynamics is not straightforward suggesting that findings on bioaccumulation and toxicity in water exposures cannot be directly extrapolated to sediment.

Changes of Cadmium Storage Forms and Isotope Ratios in Rice During Grain Filling

Rice poses a major source of the toxic contaminant cadmium (Cd) for humans. Here, we elucidated the role of Cd storage forms (i.e., the chemical Cd speciation) on the dynamics of Cd within rice. In a pot trial, we grew rice on a Cd-contaminated soil in upland conditions and sampled roots and shoots parts at flowering and maturity. Cd concentrations, isotope ratios, Cd speciation (X-ray absorption spectroscopy), and micronutrient concentrations were analyzed. During grain filling, Cd and preferentially light Cd isotopes were strongly retained in roots where the Cd storage form did not change (Cd bound to thiols, Cd-S = 100%). In the same period, no net change of Cd mass occurred in roots and shoots, and the shoots became enriched in heavy isotopes (Δ114/110Cd maturity-flowering = 0.14 ± 0.04‰). These results are consistent with a sequestration of Cd in root vacuoles that includes strong binding of Cd to thiol containing ligands that favor light isotopes, with a small fraction of Cd strongly enriched in heavy isotopes being transferred to shoots during grain filling. The Cd speciation in the shoots changed from predominantly Cd-S (72%) to Cd bound to O ligands (Cd-O, 80%) during grain filling. Cd-O may represent Cd binding to organic acids in vacuoles and/or binding to cell walls in the apoplast. Despite this change of ligands, which was attributed to plant senescence, Cd was largely immobile in the shoots since only 0.77% of Cd in the shoots were transferred into the grains. Thus, both storage forms (Cd-S and Cd-O) contributed to the retention of Cd in the straw. Cd was mainly bound to S in nodes I and grains (Cd-S > 84%), and these organs were strongly enriched in heavy isotopes compared to straw (Δ114/110Cd grains/nodes- straw = 0.66-0.72‰) and flag leaves (Δ114/110Cd grains/nodes-flag leaves = 0.49-0.52‰). Hence, xylem to phloem transfer in the node favors heavy isotopes, and the Cd-S form may persist during the transfer of Cd from node to grain. This study highlights the importance of Cd storage forms during its journey to grain and potentially into the food chain.

Differences in Copper Isotope Fractionation Between Mussels (Regulators) and Oysters (Hyperaccumulators): Insights from a Ten-Year Biomonitoring Study

Copper (Cu) isotope compositions in bivalve mollusks used in marine-monitoring networks is a promising tool to monitor anthropogenic Cu contamination in coastal and marine ecosystems. To test this new biomonitoring tool, we investigated Cu isotope variations of two bivalves-the oyster Crassostrea gigas and the mussel Mytilus edulis-over 10 years (2009-2018) in a French coastal site contaminated by diffuse Cu anthropogenic sources. Each species displayed temporal concentration profiles consistent with their bioaccumulation mechanisms, that is, the Cu-regulating mussels with almost constant Cu concentrations and the Cu-hyperaccumulating oysters with variable concentrations that track Cu bioavailability trends at the sampling site. The temporal isotope profiles were analogous for both bivalve species, and an overall shift toward positive δ⁶⁵Cu values with the increase of Cu bioavailabilities was associated with anthropogenic Cu inputs. Interestingly, mussels showed wider amplitudes in the isotope variations than oysters, suggesting that each species incorporates Cu isotopes in their tissues at different rates, depending on their bioaccumulation mechanisms and physiological features. This study is the first to demonstrate the potential of Cu isotopes in bivalves to infer Cu bioavailability changes related to anthropogenic inputs of this metal into the marine environment.

Cu isotope ratios are meaningful in ovarian cancer diagnosis

BACKGROUND

Ovarian cancer diagnosis is currently based on imaging and circulating CA-125 concentrations with well-known limits to sensitivity and specificity. New biomarkers are required to complement CA-125 testing to increase effectiveness. Increases in sensitivity of isotopic separation via multi collector inductively coupled plasma-mass spectrometry have recently allowed highly accurate measurement of copper (Cu) isotopic variations. Studies in breast cancer patients have revealed changes of serum copper isotopic composition demonstrating the potential for development as a cancer biomarker. Evaluating ⁶⁵Cu/⁶³Cu ratios (δ⁶⁵Cu) in serum samples from cancer patients has revealed a strong correlation with cancer development. In this study blood samples from forty-four ovarian cancer patients, and 13 ovarian biopsies were investigated.

RESULTS

Here we demonstrate that changes in Cu isotopes also occurs in ovarian cancer patients. Copper composition determined by multiple collector inductively coupled plasma mass spectrometry revealed that the copper isotopic ratio δ⁶⁵Cu in the plasma of 44 ovarian cancer patient cohort was significantly lower than in a group of 48 healthy donors, and indicated that serum was enriched for ⁶³Cu. Further analysis revealed that the isotopic composition of tumour biopsies was enriched for ⁶⁵Cu compared with adjacent healthy ovarian tissues.

CONCLUSIONS

We propose that these changes are due to increase lactate and Cu transporter activities in the tumour. These observations demonstrate that, combined with existing strategies, δ⁶⁵Cu could be developed for use in ovarian cancer early detection.

Isotope metallomics approaches for medical research

Metallomics is a rapidly evolving field of bio-metal research that integrates techniques and perspectives from other "-omics" sciences (e.g. genomics, proteomics) and from research vocations further afield. Perhaps the most esoteric of this latter category has been the recent coupling of biomedicine with element and isotope geochemistry, commonly referred to as isotope metallomics. Over the course of less than two decades, isotope metallomics has produced numerous benchmark studies highlighting the use of stable metal isotope distribution in developing disease diagnostics-e.g. cancer, neurodegeneration, osteoporosis-as well as their utility in deciphering the underlying mechanisms of such diseases. These pioneering works indicate an enormous wealth of potential and provide a call to action for researchers to combine and leverage expertise and resources to create a clear and meaningful path forward. Doing so with efficacy and impact will require not only building on existing research, but also broadening collaborative networks, bolstering and deepening cross-disciplinary channels, and establishing unified and realizable objectives. The aim of this review is to briefly summarize the field and its underpinnings, provide a directory of the state of the art, outline the most encouraging paths forward, including their limitations, outlook and speculative upcoming breakthroughs, and finally to offer a vision of how to cultivate isotope metallomics for an impactful future.

Body distribution of stable copper isotopes during the progression of cholestatic liver disease induced by common bile duct ligation in mice

Patients with chronic liver disease from different aetiologies show a light serum Cu isotopic composition compared to the reference population, with the enrichment in the 63Cu isotope correlating with the severity of the disease. However, the mechanisms underlying Cu isotope fractionation at the onset and during progression of the disease are still unclear. In this work, a common bile duct ligation (CBDL) murine model was used to investigate the effect of cholestasis-induced liver disease on the Cu isotopic composition. Wild type male and female mice underwent surgical ligation of the common bile duct and were sacrificed 2, 4 and 6 weeks, and 4, 6 and 8 weeks after the surgical intervention, respectively. The age- and gender-matched control mice underwent sham surgery. Disease progression was evaluated using serum bilirubin levels, hepatic pro-inflammatory chemokine levels and Metavir fibrosis score. CBDL-operated mice show an overall body enrichment in the light isotope 63Cu. The Cu isotopic composition of organs, bone and serum becomes gradually lighter compared to the sham-operated mice with increasing severity of the disease. The light Cu isotopic composition of the CBDL-operated mice might result from an altered Cu intake and/or excretion. As the intestinal uptake of dietary Cu is largely mediated by transporters of Cu(i), mRNA and protein expression levels of two major metal transporters (CTR1 and DMT1) and Cu reductases (STEAP proteins and duodenal cytochrome B) were examined in the duodenal tissues as potential factors inducing Cu isotope fractionation. However, no significant differences in protein expression levels were observed between the CBDL- and sham-operated mice.

Elemental and Isotopic Variations of Copper and Zinc Associated with the Diel Activity of Phototrophic Biofilm

The response in metal concentrations and isotopic composition to variations in photosynthetic activity of aquatic micro-organisms is crucially important for understanding the environmental controls on metal fluxes and isotope excursions. Here we studied the impacts of two successive diel cycles on physicochemical parameters, Cu and Zn concentrations, and isotopic composition in solution in the presence of mature phototrophic biofilm in a rotating annular bioreactor. The diel cycles induced fluctuations in temperature, pH, and dissolved oxygen concentration following the variation in the photosynthesis activity of the biofilm. Diel variations in metal concentrations were primarily related to the pH variation, with an increase in metal concentration in solution related to a pH decrease. For both metals, δ(⁶⁶Zn) and δ(⁶⁵Cu) in solution exhibited complex but reproducible diel cycles. Diel variations in photosynthetic activity led to alternatively positive and negative isotope fractionation, producing the sorption of light Zn (Δ(⁶⁶Zn_{sorbed-solution}) = -0.1 ± 0.06‰) and heavy Cu isotopes (Δ(⁶⁵Cu_{sorbed-solution}) = +0.17 ± 0.06‰) during the day at high pH and the excretion of lighter Zn isotopes (-0.4‰ < Δ(⁶⁶Zn_{excreted-biofilm}) < +0.14‰) and heavy Cu isotopes (Δ(⁶⁵Cu_{excreted-biofilm}) = +0.7 ± 0.3‰) during the night at lower pH. We interpreted Zn and Cu diel cycles as a combination of a desorption of exopolymeric substance-metal complexes and a small active efflux during the night with adsorption and incorporation via an active uptake during the day. The hysteresis of metal concentration in solution over the diel cycle suggested the more important role of uptake compared to desorption and efflux from the biofilm. The phototrophic biofilm presents a non-negligible highly labile metal pool with important potential for contrasting isotopic fractionation at the diel scale.

High-precision isotopic analysis of serum and whole blood Cu, Fe and Zn to assess possible homeostasis alterations due to bariatric surgery

Bariatric surgery is an effective procedure to achieve weight loss in obese patients. However, homeostasis of essential metals may be disrupted as the main absorption site is bypassed. In this study, we determined Cu, Fe and Zn isotopic compositions in paired serum and whole blood samples of patients who underwent Roux-en-Y gastric bypass (RYGB) surgery for evaluation of longitudinal changes and their potential relation to mineral element concentrations and relevant clinical parameters used for monitoring the patient's condition. Samples from eight patients were collected pre-surgery and at 3, 6 and 12 months post-surgery. Multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) was used for high-precision isotope ratio measurements. Alterations in metal homeostasis related to bariatric surgery were reflected in the serum and whole blood Cu, Fe and Zn isotopic compositions. The serum and whole blood Cu became isotopically lighter (lower δ⁶⁵Cu values) after bariatric surgery, reaching statistical significance at 6 months post-surgery (p < 0.05). The difference between the serum and the whole blood Zn isotopic composition increased after surgery, reaching significance from 6 months post-surgery onwards (p < 0.05). Those changes in Cu, Fe and Zn isotopic compositions were not accompanied by similar changes in their respective concentrations, making isotopic analysis more sensitive to physiological changes than elemental content. Furthermore, the Zn isotopic composition correlates with blood glycaemic and lipid parameters, while the Fe isotopic composition correlates with glycaemic parameters. Graphical Abstract.

Selenium and iodine in diabetes mellitus with a focus on the interplay and speciation of the elements

Diabetes mellitus is a chronic metabolic disease caused by insulin deficiency (type I) or dysfunction (type II). Diabetes is a threatening public health concern. It is considered as one of the priority non-communicable diseases, due to its high and increasing incidence, the associated healthcare costs, and threatening medical complications. Two trace elements selenium (Se) and iodine (I) were intensively discussed in the context of diabetic pathology and, possibly, etiology. It seems there is a multilayer involvement of these essential nutrients in glucose tolerance, energy metabolism, insulin signaling and resistance, which are mainly related to the antioxidant selenoenzymes and the thyroid hormones. Other factors might be related to (auto)immunity, protection against endoplasmic reticulum stress, and leptin signaling. The aim of the current review is to evaluate the current understanding of the role of selenium and iodine in diabetes with a focus on the biochemical interplay between the elements, their possible role as biomarkers, and their chemical speciation. Possible impacts from novel analytical techniques related to trace element speciation and isotopic analysis are outlined.

Copper Isotope Compositions of Superoxide Dismutase and Metallothionein from Post-Mortem Human Frontal Cortex

The natural copper isotopic compositions of superoxide dismutase and metallothionein from six post-mortem human frontal cortices were determined using a combination of size exclusion protein liquid chromatography, followed by anion exchange chromatography and multiple collector inductively-coupled plasma mass spectrometry. Superoxide dismutase was enriched in the heavier 65Cu relative to the metallothionein fraction in all specimen pairs. The isotopic compositions were independent of copper content. This finding provides evidence that nitrogen ligands in protein copper binding sites will be enriched in heavy metal isotopes, and sulphur ligands will preferentially incorporate lighter isotopes in vivo. This in turn has implications for understanding isotopic distributions within different components in the body and the dominant ligands in different tissues. Differences in Cu isotope distributions between the two proteins were seen between Alzheimer’s disease and healthy control samples, when normalised for sex.

Antibiotic treatment affects the expression levels of copper transporters and the isotopic composition of copper in the colon of mice

Copper is a critical enzyme cofactor in the body but also a potent cellular toxin when intracellularly unbound. Thus, there is a delicate balance of intracellular copper, maintained by a series of complex interactions between the metal and specific copper transport and binding proteins. The gastrointestinal (GI) tract is the primary site of copper entry into the body and there has been considerable progress in understanding the intricacies of copper metabolism in this region. The GI tract is also host to diverse bacterial populations, and their role in copper metabolism is not well understood. In this study, we compared the isotopic fractionation of copper in the GI tract of mice with intestinal microbiota significantly depleted by antibiotic treatment to that in mice not receiving such treatment. We demonstrated variability in copper isotopic composition along the length of the gut. A significant difference, ∼1.0‰, in copper isotope abundances was measured in the proximal colon of antibiotic-treated mice. The changes in copper isotopic composition in the colon are accompanied by changes in copper transporters. Both CTR1, a copper importer, and ATP7A, a copper transporter across membranes, were significantly down-regulated in the colon of antibiotic-treated mice. This study demonstrated that isotope abundance measurements of metals can be used as an indicator of changes in metabolic processes in vivo. These measurements revealed a host-microbial interaction in the GI tract involved in the regulation of copper transport.

Isotopic variations of copper at the protein fraction level in neuronal human cells exposed in vitro to uranium

Accurate isotope ratio determination was downscaled to the level of metal-containing protein fractions obtained from cell line lysates.

Impact of uranium uptake on isotopic fractionation and endogenous element homeostasis in human neuron-like cells

The impact of natural uranium (U) on differentiated human neuron-like cells exposed to 1, 10, 125, and 250 µM of U for seven days was assessed. In particular, the effect of the U uptake on the homeostatic modulation of several endogenous elements (Mg, P, Mn, Fe, Zn, and Cu), the U isotopic fractionation upon its incorporation by the cells and the evolution of the intracellular Cu and Zn isotopic signatures were studied. The intracellular accumulation of U was accompanied by a preferential uptake of ²³⁵U for cells exposed to 1 and 10 µM of U, whereas no significant isotopic fractionation was observed between the extra- and the intracellular media for higher exposure U concentrations. The U uptake was also found to modulate the homeostasis of Cu, Fe, and Mn for cells exposed to 125 and 250 µM of U, but the intracellular Cu isotopic signature was not modified. The intracellular Zn isotopic signature was not modified either. The activation of the non-specific U uptake pathway might be related to this homeostatic modulation. All together, these results show that isotopic and quantitative analyses of toxic and endogenous elements are powerful tools to help deciphering the toxicity mechanisms of heavy metals.

Stable Isotope Composition of Metal Elements in Biological Samples as Tracers for Element Metabolism

Stable isotope composition varies due to different reactivity or mobility among the isotopes. Various pioneering studies revealed that isotope fractionation is common for many elements, and it is now widely recognized that the stable isotope compositions of biometals can be used as new tracers for element metabolism. In this review, we summarize the recently published isotope compositions of iron (Fe), copper (Cu), zinc (Zn), and calcium (Ca) in various biological samples, including tissues from plants, animals, and humans. Discussions were carried out with respect to age, sex, organ, and the presence or absence of particular diseases for animals and humans. For Fe and Cu isotopes, changes in oxidation states generate large isotopic fractionation through the metabolism of those elements. Isotope composition of Zn greatly fractionates among tissues even without changes in oxidation state. Isotopic composition of Ca is a powerful tracer for the metabolism of Ca in bones. The review results suggest that the stable isotope compositions of the biometals can be used as effective markers for diagnostics of various kinds of diseases related to metabolic disorders.

Computational modelling of the redistribution of copper isotopes by proteins in the liver

The copper isotopic composition of blood serum as the mass balance of the copper isotopic composition of serum proteins.