Carbon Isotope Incorporation Research Articles

Alterations of the chemical profile of cholesterol in cancer tissue as traced with ToF-SIMS.

Cancer has become one of the leading causes of death, with approximately ten million people worldwide dying from cancer each year. In most cases, cancer spreads to remote organs and develops a resistance to therapy. To reduce the deadly impact of cancer, novel targets for markers for early detection are necessary. Given the notable influence of rapid chemical turnover on isotope effects, the heightened turnover rate of cholesterol in cancer offers a promising way for investigation. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) offers a valuable tool of tracking cholesterol dynamics. Consequently, we employed ToF-SIMS to assess cholesterol alterations, aiming to uncover potential diagnostic vulnerabilities stemming from heightened cholesterol synthesis. Our study explored the chemical profile of cholesterol influenced by cancer cell metabolism using mammary glands from mice, both with and without cancer. Results revealed a significant increase in the fractional abundance of fragment cholesterol peaks (C27H45+) in cancerous tissues, indicating dysregulated cholesterol metabolism within cancer cells. This suggests potential structural weaknesses or incomplete synthesis. Further investigation into carbon isotope incorporation suggests that the isotopic patterns might be due to the integration of heavier carbon isotopes, although these patterns could be affected by other isotopic influences. Nevertheless, understanding isotope effect of cholesterol profiles have the potential to advance our understanding of cancer biology and improve diagnostic approaches.

Core-Labeling (Radio) Synthesis of Phenols.

We report a method that enables the fast incorporation of carbon isotopes into the ipso carbon of phenols. Our approach relies on the synthesis of a 1,5-dibromo-1,4-pentadiene precursor, which upon lithium-halogen exchange followed by treatment with carbonate esters results in a formal [5 + 1] cyclization to form the phenol product. Using this strategy, we have prepared 12 1-13C-labeled phenols, show proof-of-concept for the labeling of phenols with carbon-14, and demonstrate phenol synthesis directly from cyclotron-produced [11C]CO2.

Palladium-Catalyzed Carbon Isotope Exchange on Aliphatic and Benzoic Acid Chlorides.

An operationally simple protocol for a palladium-catalyzed 13CO and 14CO exchange with activated aliphatic and benzoic carbonyls is presented. Several 13C and 14C building blocks, natural product derivatives, and pharmaceuticals have been prepared to showcase the method for late-stage carbon isotope incorporation and its functional group compatibility.

The thermal dependence of carbon stable isotope incorporation and trophic discrimination in the domestic cricket, Acheta domesticus

Stable isotopes are valuable tools in physiological and ecological research, as they can be used to estimate diet, habitat use, and resource allocation. However, in most cases a priori knowledge of two key properties of stable isotopes is required, namely their rate of incorporation into the body (incorporation rate) and the change of isotope values between consumers and resources that arises during incorporation of the isotopes into the consumer’s tissues (trophic discrimination). Previous studies have quantified these properties across species and tissue types, but little is known about how they vary with temperature, a key driver of many biological rates and times. Here, we explored for the first time how temperature affects both carbon incorporation rate and trophic discrimination via growth rates, using the domestic cricket, Acheta domesticus. We raised crickets at 16 °C, 21 °C, and 26 °C and showed that temperature increased carbon isotope incorporation rate, which was driven by both an increased growth rate and catabolism at higher temperatures. Trophic discrimination of carbon isotopes decreased at higher temperatures, which we attributed to either lower activation energies needed to synthesize non-essential amino acids at higher temperatures or the increased utilization of available resources of consumers at higher temperatures. Our results demonstrate that temperature is a key driver of both carbon isotope incorporation rate and trophic discrimination, via mechanisms that likely persist across all ectotherms. Experiments to determine incorporation rates and trophic discrimination factors in ectotherms must include temperature as a major factor, and natural variation in temperature might have significant effects on these isotopic properties that then can affect inferences made from isotope values.

Oxygen and carbon isotope composition of modern planktic foraminifera and near-surface waters in the Fram Strait (Arctic Ocean) – a case study

Abstract. The upper 500 m of the water column and the sediment surface along an E–W transect in the Fram Strait were sampled for recent planktic foraminifera. The δ18O and δ13C values of the tests are compared to the stable isotope composition of the water samples taken from the same depths, and related to the characteristics of the water column. The polar species Neogloboquadrina pachyderma clearly dominates the species assemblage in the Fram Strait in the early summer, while the subpolar Turborotalita quinqueloba accounts only for 5–23%. In this area the average depth of calcification of N. pachyderma lies between 70–150 m water depth, T. quinqueloba shows a similar range with 50–120 m water depth. The δ18O values of N. pachyderma show an average vital effect of about −1.5‰ compared to calculated equilibrium calcite values. Except for the upper ∼75 m, the vertical profiles of δ13C of the net-sampled shells are nearly parallel to the values measured in the water column with an average offset of −1.6‰ and −3.6‰ for N. pachyderma and T. quinqueloba, respectively. The discrepancy found in the upper ~75 m might indicate an influence of the "carbonate ion effect" on the carbon isotope incorporation in the tests. Oxygen and carbon isotopes from the sediment surface yield higher values than those from the water column for both species. This may be because specimens from the water column reflect a modern snapshot only, while tests from surface sediments record environmental parameters from the past ~1000 years.

Stable isotope data (δ18O, δ13C) of the ammonite genus Simbirskites — implications for habitat reconstructions of extinct cephalopods

The accurate habitats of the extinct ammonites and belemnites are largely unknown. Most ammonites are thought to have had a pelagic lifestyle, while belemnites are often considered to have dwelled in deeper, colder waters. Stable isotope analysis (δ18O, δ13C) provides a useful method to reconstruct the habitats of these two groups of extinct cephalopods, but is at the same time limited by various unknowns, including the isotopic composition of the past seawater, ‘vital’ effects and diagenesis.In this paper, stable isotope data from 12 ammonite shells (Simbirskites spp.) from the upper Hauterivian of the Lower Saxony Basin (northwest Germany) are presented. Ontogenetic isotope profiles have been obtained from six of these shells in order to reconstruct habitat changes during their lifetime. These new ammonite data are combined with published stable isotope data from belemnites (Hibolithes jaculoides) and TEX86 palaeotemperature-estimates from the same section.The combination of isochronous ammonite and belemnite stable isotope data shows that the resulting values of both groups go along with each other. Calculated palaeotemperatures of the two groups differ by 5–10°C, with belemnites always showing the colder temperatures. All juvenile shells show an increase of the δ13Camm to more positive values throughout their ontogeny; they are stable in an adult shell-fragment. The incorporation of carbon isotopes in the ammonite shell therefore correlates with ontogeny and is influenced by metabolic effects, probably linked to the shell growth rate. The isotope profiles further suggest vertical habitat changes during the ontogeny of the ammonites, indicating that the δ13Camm values might record a combination of environmental and metabolic signals. Taking into account studies on oxygen isotope fractionation of recent aragonitic and calcitic mollusc shells, a similar pelagic habitat is proposed here for both, ammonites and belemnites.

Metabolic substrate use and the turnover of endogenous energy reserves in broad-tailed hummingbirds (Selasphorus platycercus)

We fed broad-tailed hummingbirds (Selasphorus platycercus) diets of contrasting carbon isotope composition and measured changes in the delta(13)C of expired breath through time. By measuring the delta(13)C in the breath of fed and fasted birds we were able to quantify the fraction of metabolism fueled by assimilated sugars and endogenous energy reserves. These measurements also allowed us to estimate the fractional turnover of carbon in the hummingbirds' energy reserves. When hummingbirds were feeding, they fueled their metabolism largely ( approximately 90%) with assimilated sugars. The rate of carbon isotope incorporation into the energy reserves of hummingbirds was higher when birds were gaining as opposed to losing body mass. The average residence time of a carbon atom in the hummingbirds' energy reserves ranged from 1 to 2 days.

Tracking the in vivo fate of recombinant polypeptides by isotopic labeling

We report a method to incorporate a stable isotope ( 13C) and a radioactive isotope ( 14C) into a recombinant polypeptide during Escherichia coli culture in M9 minimal medium supplemented with universally labeled 13C- or 14C-labeled glucose. We chose a thermally responsive elastin-like polypeptide (ELP) as a model polypeptide for this study because of its utility in various biotechnology applications such as drug delivery and tissue engineering. High cell densities were obtained by step-wise adaptation of E. coli to M9 medium in addition to supplementing the medium with trace elements that facilitated growth of E. coli. Furthermore, an optimal concentration of isopropyl-β- d-thiogalactopyranoside was determined for induction of ELP expression to achieve high yield (mg/L culture) of the ELP. The incorporation of carbon isotopes was stoichiometrically related to the ratio of labeled glucose to unlabeled glucose in the culture medium. The isotope-labeled variants retained the physicochemical properties of the unlabeled ELP, specifically its temperature dependent aggregation behavior. As an example of the utility of this method, the in vitro stability of 14C-labeled ELP in PBS and mouse serum was conveniently quantified by SDS–PAGE and autoradiography. In addition, the in vivo stability of the 14C-labeled ELP in plasma was determined along with its plasma pharmacokinetics.

Microscale δ18O and δ13C isotopic analysis of an ontogenetic series of the hadrosaurid dinosaur Edmontosaurus: implications for physiology and ecology

Stable isotope analysis of vertebrate biominerals, primarily in mammals, has been used to address questions of paleodiet, paleoclimate, trophic level, migration, foraging zone, and thermophysiology with varying degrees of success. Isotopes have been used less commonly to study physiology and ecology through ontogeny in dinosaurs, generally due to (1) the lack of modern analogs as a basis for comparison of observed fossil isotope values, and (2) difficulty in sampling very thin tooth enamel (a non-remodeled biomineral). By utilizing a relatively new technique in microsampling, this study addresses the following questions: Do microscale analyses of oxygen and carbon isotopes from mineralized tissues of hadrosaurid dinosaurs record temporal variation? If so, is the cause of the variation physiological or ecological? Isotope values from the carbonate component of enamel ( δ 18O ec and δ 13C e) were obtained by microsampling multiple teeth in a temporal series from the dental batteries of a juvenile, sub-adult, and adult Edmontosaurus from the Late Cretaceous Maastrichtian Hell Creek Formation of South Dakota. To establish isotope variability in an extant archosaur, consecutive teeth in a temporal series from an extant Alligator mississippiensis specimen were microsampled for isotopic analysis and compared to those of Edmontosaurus. To test for diagenesis, bulk samples from the phosphate component ( δ 18O p) of modern and fossil tooth enamel, bone, and dentine from Edmontosaurus, A. mississippiensis, and extant ratites were analyzed and compared. Edmontosaurus bone and dentine indicate a greater degree of alteration than does enamel, and while absolute δ 18O ec values may be altered, the pattern of seasonal cycles appears to be preserved and can provide detailed information on hadrosaur physiology (tooth mineralization times, rates, and seasons) and ecology (dietary information). δ 18O ec seasonal patterns are preserved in Edmontosaurus specimens, and are interpreted to correlate with annual δ 18O variation of local meteoric waters rather than thermophysiology, changes in drinking water sources, or migration. All teeth were mineralized in <0.65 year with no consistent season of mineralization. Mean tooth mineralization times are shorter in the juvenile and sub-adult than the adult. Enamel mineralization rates are estimated to be ∼38 mm/year in Edmontosaurus and ∼36 mm/year in Alligator (consistent with mineralization rates for modern ungulates), although the length of time for tooth formation is shorter in the archosaurs compared with mammals. Heavier than predicted δ 13C e values are hypothesized to result from (1) enrichment of δ 13C in ingested plant material due to higher atmospheric δ 13C ( δ 13C atm) in the Late Cretaceous; (2) taxon-specific δ 13C effects of ingested plants (primarily gymnosperms); (3) isotopic enrichment of ingested plant material ( δ 13C p) due to osmotic stress from proximity to the Western Cretaceous Interior Seaway, (4) taxon-specific δ 13C diet– δ 13C e fractionation factors for Edmontosaurus that vary from those observed in modern mammals, and/or (5) diagenesis. Microsampling provides a detailed perspective on the physiological (tooth mineralization times, rates, and seasons) and ecological (dietary) mechanisms of oxygen and carbon isotope incorporation in dinosaur biominerals that is not obtainable through bulk sampling alone.

Geochemistry of modern brachiopods: applications and implications for oceanography and paleoceanography

Modern Rhynchonellida, Terebratulida, Thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2–3940 m, from the equator to high latitudes covering the Atlantic, Pacific, Indian, Caribbean and Mediterranean Oceans/Seas. Well-preserved fibers of the secondary layer combined with Sr (450–1928 mg/kg), Mn (1–199 mg/kg) and Fe (1–610 mg/kg) contents confirm, with few exceptions, the excellent preservation of the modern brachiopod material. Evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations. It revealed that oxygen isotope incorporation into shell calcite (secondary layer) of modern articulated brachiopods, in most cases, occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions. Thecideida as a group (shallow water and low latitude) incorporate oxygen isotopes (−3.04‰ to +0.35‰) into shell calcite in equilibrium with their ambient water. A large majority of genera and species of the Terebratulida (shallow water and low-mid latitude) also incorporate oxygen (−2.30‰ to +3.48‰) into shell calcite in isotopic equilibrium with their surrounding water. In contrast, equilibrium incorporation of oxygen isotopes into shell calcite by the Rhynchonellida is uncertain, but a vital effect probably applies to the Craniida. The question of equilibrium/disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time. Isotope compositions range up to 4.5‰, 5.6‰ and 1.5‰ for δ 13C, and up to 5.5‰, 5.9‰ and 0.3‰ for δ 18O, for shallow-water low, mid, and high latitude brachiopods, respectively. Strontium isotopes of modern brachiopods, as expected, show no significant variation with location, latitude, water depth, temperature, salinity and general water conditions. Once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered, their isotopic/elemental values should be valuable diagenetic indicators and important oceanographic/chemostratigraphic proxies.

A diffusion-reaction model of carbon isotope fractionation in foraminifera

Abstract Fossil foraminiferal shells are utilized in paleoceanography to extract information about environmental conditions of the past ocean. Based on several assumptions, the ratio of 13 C and 12 C preserved in their shells is used to reconstruct, for example, the paleoproductivity or the oceanic pCO2. Metabolism of the living organism and the sea water chemistry, however, can influence the incorporation of carbon isotopes during calcification such that the signal of the shells differ from the signal of the sea water. These effects occur because the chemical microenvironment of the foraminifer (boundary layer thickness ∼500 μm) differs from the bulk sea water. Here, we present a numerical model that calculates the δ 13 C of the foraminiferal shell as a function of the sea water chemistry and the magnitude of vital effects. Concentration profiles of the chemical species of the carbonate system within the microenvironment of foraminifera are obtained by solving diffusion-reaction equations. The compounds of dissolved forms of carbon dioxide containing either the stable carbon isotope 13 C or 12 C are considered separately. Spherical symmetry of the foraminifer is assumed. The model outcome is compared to results from culture experiments with the planktonic foraminifer Orbulina universa. Model results indicate that the interaction between vital effects of the foraminifer and the sea water chemistry can account for changes in the δ 13 C of foraminiferal calcite of 0.3–0.4‰ when glacial and interglacial sea water conditions are compared. These effects occur even though the δ 13 C of the total dissolved inorganic carbon is kept constant. Thus, changes in sea water chemistry should be distinguished from events which changed the δ 13 C of the inorganic carbon of the sea water.