Browsing by Subject "STABLE-ISOTOPE"

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  • Björnson, E.; Packard, C. J.; Adiels, M.; Andersson, L.; Matikainen, N.; Söderlund, S.; Kahri, J.; Hakkarainen, A.; Lundbom, N.; Lundbom, J.; Sihlbom, C.; Thorsell, A.; Zhou, H.; Taskinen, M. -R.; Boren, J. (2020)
    Background Renewed interest in triglyceride-rich lipoproteins as causative agents in cardiovascular disease mandates further exploration of the integrated metabolism of chylomicrons and very low-density lipoproteins (VLDL). Methods Novel tracer techniques and an integrated multi-compartmental model were used to determine the kinetics of apoB48- and apoB100-containing particles in the chylomicron and VLDL density intervals in 15 subjects with a wide range of plasma triglyceride levels. Results Following a fat-rich meal, apoB48 appeared in the chylomicron, VLDL1 and VLDL2 fractions in all subjects. Chylomicrons cleared rapidly from the circulation but apoB48-containing VLDL accumulated, and over the day were 3-fold higher in those with high versus low plasma triglyceride. ApoB48-containing particles were secreted directly into both the chylomicron and VLDL fractions at rates that were similar across the plasma triglyceride range studied. During fat absorption, whilst most triglyceride entered the circulation in chylomicrons, the majority of apoB48 particles were secreted into the VLDL density range. Conclusion The intestine secretes apoB48-containing particles not only as chylomicrons but also directly into the VLDL1 and VLDL2 density ranges both in the basal state and during dietary lipid absorption. Over the day, apoB48-containing particles appear to comprise about 20-25% of circulating VLDL and, especially in those with elevated triglycerides, form part of a slowly cleared 'remnant' particle population, thereby potentially increasing CHD risk. These findings provide a metabolic understanding of the potential consequences for increased CHD risk when slowed lipolysis leads to the accumulation of remnants, especially in individuals with hypertriglyceridemia.
  • Taskinen, Marja-Riitta; Björnson, Elias; Andersson, Linda; Kahri, Juhani; Porthan, Kimmo; Matikainen, Niina; Söderlund, Sanni; Pietiläinen, Kirsi; Hakkarainen, Antti; Lundbom, Nina; Nilsson, Ralf; Stahlman, Marcus; Adiels, Martin; Parini, Paolo; Packard, Chris; Boren, Jan (2020)
    BACKGROUND: Monoclonal antibodies to proprotein convertase subtilisin/kexin type 9 (PCSK9) significantly lower the levels of low-density lipoprotein and very-low-density lipoproteins (VLDL), but their effect on postprandial lipoprotein metabolism in dyslipidemic subjects is unclear. OBJECTIVE: This study aimed to investigate the effects of evolocumab on postprandial lipid responses, ectopic fat depots, whole-body cholesterol synthesis, hepatic lipogenesis, and fat oxidation in patients with type II diabetes. METHODS: The trial was a single-phase, nonrandomized study of 12-week treatment with evolocumab 140 mg subcutaneously every 2 weeks in 15 patients with type II diabetes on background statin therapy. Cardiometabolic responses to a high-fat mixed meal were assessed before and at the end of the intervention period. RESULTS: Evolocumab treatment reduced significantly postprandial rises in plasma total triglyceride (by 21%; P <.0001) and VLDL i triglyceride (by 15%; P = .018), but the increase in chylomicron triglyceride after the meal was not significantly perturbed (P = .053). There were reduced postprandial responses in plasma total apolipoprotein C-III (by 14%; P <.0001) and apolipoprotein B-48 concentration (by 17%; P = .0046) and in "remnant-like particles" cholesterol (by 29%; P <.0001) on the PCSK9 inhibitor. Treatment reduced the steady-state (ie, fasting and postprandial) concentrations of VLDL2 cholesterol by 50% (P <.0001) and VLDL2 triglyceride by 29% (P <.0001), in addition to the 78% reduction of low-density lipoprotein cholesterol (P <.001). The changes in apolipoprotein C-III associated significantly with reduction in postprandial responses of remnant-like particles cholesterol and triglyceride-rich lipoprotein cholesterol. Evolocumab therapy did not influence liver fat accumulation, hepatic de novo lipogenesis, or fasting beta-hydroxybutyrate but did increase total body cholesterol synthesis (P <.01). CONCLUSION: Evolocumab treatment improved postprandial responses of triglyceride-rich lipo-proteins and measures of cholesterol-enriched remnant particles in type II diabetic subjects. These results indicate that postprandial phenomena need to be taken into account in assessing the full range of actions of PCSK9 inhibitors in dyslipidemic individuals. (C) 2020 Published by Elsevier Inc. on behalf of National Lipid Association.
  • Björnson, E.; Packard, C. J.; Adiels, M.; Andersson, L.; Matikainen, Niina; Söderlund, S.; Kahri, J.; Sihlbom, C.; Thorsell, A.; Zhou, H.; Taskinen, M.-R.; Borén, J. (2019)
    Background Triglyceride-rich lipoproteins and their remnants have emerged as major risk factors for cardiovascular disease. New experimental approaches are required that permit simultaneous investigation of the dynamics of chylomicrons (CM) and apoB48 metabolism and of apoB100 in very low-density lipoproteins (VLDL). Methods Mass spectrometric techniques were used to determine the masses and tracer enrichments of apoB48 in the CM, VLDL1 and VLDL2 density intervals. An integrated non-steady-state multicompartmental model was constructed to describe the metabolism of apoB48- and apoB100-containing lipoproteins following a fat-rich meal, as well as during prolonged fasting. Results The kinetic model described the metabolism of apoB48 in CM, VLDL1 and VLDL2. It predicted a low level of basal apoB48 secretion and, during fat absorption, an increment in apoB48 release into not only CM but also directly into VLDL1 and VLDL2. ApoB48 particles with a long residence time were present in VLDL, and in subjects with high plasma triglycerides, these lipoproteins contributed to apoB48 measured during fasting conditions. Basal apoB48 secretion was about 50 mg day?1, and the increment during absorption was about 230 mg day?1. The fractional catabolic rates for apoB48 in VLDL1 and VLDL2 were substantially lower than for apoB48 in CM. Discussion This novel non-steady-state model integrates the metabolic properties of both apoB100 and apoB48 and the kinetics of triglyceride. The model is physiologically relevant and provides insight not only into apoB48 release in the basal and postabsorptive states but also into the contribution of the intestine to VLDL pool size and kinetics.
  • Marshall, John D.; Laudon, Hjalmar; Makela, Annikki; Peichl, Matthias; Hasselquist, Niles; Nasholm, Torgny (2021)
    Forests pass water and carbon through while converting portions to streamflow, soil organic matter, wood production, and other ecosystem services. The efficiencies of these transfers are but poorly quantified. New theory and new instruments have made it possible to use stable isotope composition to provide this quantification of efficiencies wherever there is a measurable difference between the branches of a branchpoint. We present a linked conceptual model that relies on isotopes of hydrogen, carbon, and oxygen to describe these branchpoints along the pathway from precipitation to soil and biomass carbon sequestration and illustrate how it can be tested and generalized. Plain Language Summary The way a forest works can be described in terms of carbon and water budgets, which describe the ways that carbon and water flow through the forest. The paths of such flows are frequently branched and the branches are often different in their stable isotope composition. This means that stable isotopes can be used to describe the branching events. We present isotopic methods of quantifying several such events, then link them in a chain that begins with the evaporation of water and ends with biomass production.
  • Calandra, Ivan; Labonne, Gaelle; Mathieu, Olivier; Henttonen, Heikki; Leveque, Jean; Milloux, Marie-Jeanne; Renvoise, Elodie; Montuire, Sophie; Navarro, Nicolas (2015)
    In the Arctic, food limitation is one of the driving factors behind small mammal population fluctuations. Active throughout the year, voles and lemmings (arvicoline rodents) are central prey in arctic food webs. Snow cover, however, makes the estimation of their winter diet challenging. We analyzed the isotopic composition of ever-growing incisors from species of voles and lemmings in northern Finland trapped in the spring and autumn. We found that resources appear to be reasonably partitioned and largely congruent with phylogeny. Our results reveal that winter resource use can be inferred from the tooth isotopic composition of rodents sampled in the spring, when trapping can be conducted, and that resources appear to be partitioned via competition under the snow.
  • Eloranta, Antti P.; Kahilainen, Kimmo K.; Amundsen, Per-Arne; Knudsen, Rune; Harrod, Chris; Jones, Roger I. (2015)
    Prey preference of top predators and energy flow across habitat boundaries are of fundamental importance for structure and function of aquatic and terrestrial ecosystems, as they may have strong effects on production, species diversity, and food-web stability. In lakes, littoral and pelagic food-web compartments are typically coupled and controlled by generalist fish top predators. However, the extent and determinants of such coupling remains a topical area of ecological research and is largely unknown in oligotrophic high-latitude lakes. We analyzed food-web structure and resource use by a generalist top predator, the Arctic charr Salvelinus alpinus (L.), in 17 oligotrophic subarctic lakes covering a marked gradient in size (0.5-1084 km(2)) and fish species richness (2-13 species). We expected top predators to shift from littoral to pelagic energy sources with increasing lake size, as the availability of pelagic prey resources and the competition for littoral prey are both likely to be higher in large lakes with multispecies fish communities. We also expected top predators to occupy a higher trophic position in lakes with greater fish species richness due to potential substitution of intermediate consumers (prey fish) and increased piscivory by top predators. Based on stable carbon and nitrogen isotope analyses, the mean reliance of Arctic charr on littoral energy sources showed a significant negative relationship with lake surface area, whereas the mean trophic position of Arctic charr, reflecting the lake food-chain length, increased with fish species richness. These results were supported by stomach contents data demonstrating a shift of Arctic charr from an invertebrate-dominated diet to piscivory on pelagic fish. Our study highlights that, because they determine the main energy source (littoral vs. pelagic) and the trophic position of generalist top predators, ecosystem size and fish diversity are particularly important factors influencing function and structure of food webs in high-latitude lakes.
  • Abaker, Wafa; Berninger, Frank; Saiz, Gustavo; Pumpanen, Jukka; Starr, Michael Robert (2018)
    Background: Over the last decades sub-Saharan Africa has experienced severe land degradation and food security challenges linked to loss of soil fertility and soil organic matter (SOM), recurrent drought and increasing population. Although primary production in drylands is strictly limited by water availability, nutrient deficiencies, particularly of nitrogen (N) and phosphorus (P), are also considered limiting factors for plant growth. It is known that SOM (often measured as soil organic carbon (SOC)) is a key indicator of soil fertility, therefore, management practices that increase SOM contents, such as increasing tree cover, can be expected to improve soil fertility. The objectives of this study were to investigate the effect of Acacia senegal (Senegalia senegal) trees on soil nitrogen, phosphorus and potassium (K) in relation to SOC, the potential of A. senegal for N-2 fixation, and to identify possible N and P ecosystem limitations. Methods: Soil nutrient (total N, P, K and available P and exchangeable K) concentrations and stocks were determined for the 0-10,10-20,20-30 and 30-50 cm layers of A. senegal plantations of varying age (ranging from 7 to 24-years-old) and adjacent grasslands (reference) at two sites in semi-arid areas of Sudan. At both sites, three plots were established in each grassland and plantation. The potential of A. senegal for N-2 fixation in relation to plantations age was assessed using delta N-15 isotopic abundances and nutrient limitations assessed using C:N:P stoichiometry. Results: Soil concentrations of all studied nutrients were relatively low but were significantly and directly correlated to SOC concentrations. SOC and nutrient concentrations were the highest in the topsoil (0-10 cm) and increased with plantations age. Acacia foliage delta N-15 values were >6%o and varied little with plantations age. Soil C:N and C:P ratios did not differ between grassland and plantations and only 0-10 cm layer N:P ratios showed significant differences between grassland and plantations. Discussion: The results indicated that soil fertility in the Sahel region is strongly related to SOM contents and therefore highlighting the importance of trees in the landscape. The higher mineral nutrient concentrations in the topsoil of the plantations may be an indication of 'nutrient uplift' by the deeper roots. The high foliar delta N-15 values indicated that N(2 )fixation was not an important contributor to soil N contents in the plantations. The accretion of soil N cannot be explained by deposition but may be related to inputs of excreted N brought into the area annually by grazing and browsing animals. The soil C:N:P stoichiometry indicated that the plantations may be limited by P and the grasslands limited by N.
  • Vehmaa, Anu; Katajisto, Tarja; Candolin, Ulrika (2018)
    To reconstruct changes in zooplankton communities in response to past anthropogenic perturbations, one possibility is to use the sedimentary records. We analyzed the sediments at a coastal site in the Northern Baltic Sea to relate changes in the zooplankton community to anthropogenic eutrophication and the invasion of a predatory cladoceran, Cercopagis pengoi. We sampled 30-cm laminated sediment cores and dated the sediment layers back to the 1950s. From each 1-cm layer, we measured eutrophication indicators (delta C-13, delta N-15, TC, TN, TP) and identified and counted zooplankton resting eggs (cladoceran, calanoid copepod, rotifer). In addition, we estimated the abundance of the cladoceran Bosmina (Eubosmina) maritima by counting subfossils (carapaces, headshields, and ephippia) and estimated the experienced stress as the relationship between sexual and asexual reproduction. Using redundancy and variance partitioning analyses, we found similar to 16% of the variation in the zooplankton community to be explained by eutrophication, and 24% of the variation in B. (E.) maritima abundance and reproduction mode to be explained by eutrophication and the introduction of the alien predator. Our results show a long-term shift from calanoid copepods and predatory cladocerans toward small-sized zooplankton species, like rotifers. Furthermore, the results indicate that the invasion of C. pengoi induced a short-term increase in sexual reproduction in B. (E.) maritima. The results indicate that anthropogenic eutrophication since the 1950s has altered the zooplankton community toward smaller species, while the invasion of the predatory cladoceran had only a transitory influence on the community during its expansion phase.
  • Lahtinen, Maria; Salmi, Anna-Kaisa (2019)
    A stable isotope investigation of a large Medieval population buried in Iin Hamina, northern Finland, has been used to reconstruct palaeodiet. Iin Hamina is situated approximately 30 km away from the modern city Oulu, in close proximity to the Bothnian Bay coast and the river Ii. The material used in this study is human skeletal material from an Iin Hamina cemetery dated as 15 to 17th centuries AD and animal bones excavated in Northern Ostrobothnia from pre-industrial contexts. Stable isotope analysis of well-preserved collagen indicate that both freshwater and marine fish was the dominant protein source for the people buried at the Iin Hamina cemetery.
  • Stoy, Paul C.; El-Madany, Tarek S.; Fisher, Joshua B.; Gentine, Pierre; Gerken, Tobias; Good, Stephen P.; Klosterhalfen, Anne; Liu, Shuguang; Miralles, Diego G.; Perez-Priego, Oscar; Rigden, Angela J.; Skaggs, Todd H.; Wohlfahrt, Georg; Anderson, Ray G.; Coenders-Gerrits, A. Miriam J.; Jung, Martin; Maes, Wouter H.; Mammarella, Ivan; Mauder, Matthias; Migliavacca, Mirco; Nelson, Jacob A.; Poyatos, Rafael; Reichstein, Markus; Scott, Russell L.; Wolf, Sebastian (2019)
    Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. It is difficult to partition ecosystem-scale evapotranspiration (ET) measurements into E and T, which makes it difficult to validate satellite data and land surface models. Here, we review current progress in partitioning E and T and provide a prospectus for how to improve theory and observations going forward. Recent advancements in analytical techniques create new opportunities for partitioning E and T at the ecosystem scale, but their assumptions have yet to be fully tested. For example, many approaches to partition E and T rely on the notion that plant canopy conductance and ecosystem water use efficiency exhibit optimal responses to atmospheric vapor pressure deficit (D). We use observations from 240 eddy covariance flux towers to demonstrate that optimal ecosystem response to D is a reasonable assumption, in agreement with recent studies, but more analysis is necessary to determine the conditions for which this assumption holds. Another critical assumption for many partitioning approaches is that ET can be approximated as T during ideal transpiring conditions, which has been challenged by observational studies. We demonstrate that T can exceed 95% of ET from certain ecosystems, but other ecosystems do not appear to reach this value, which suggests that this assumption is ecosystem-dependent with implications for partitioning. It is important to further improve approaches for partitioning E and T, yet few multi-method comparisons have been undertaken to date. Advances in our understanding of carbon-water coupling at the stomatal, leaf, and canopy level open new perspectives on how to quantify T via its strong coupling with photosynthesis. Photosynthesis can be constrained at the ecosystem and global scales with emerging data sources including solar-induced fluorescence, carbonyl sulfide flux measurements, thermography, and more. Such comparisons would improve our mechanistic understanding of ecosystem water fluxes and provide the observations necessary to validate remote sensing algorithms and land surface models to understand the changing global water cycle.
  • Etu-Sihvola, Heli; Bocherens, Hervé; Drucker, Dorothée; Junno, Aripekka; Mannermaa, Kristiina; Oinonen, Markku; Uusitalo, Joonas; Arppe, Laura (2019)
    Paleodietary research is a complex field, which requires large sets of background information. Owing to increasing interest and activity in the field, a substantial amount of archaeological isotope baseline data exist for Northern Europe, consisting mainly of animal bone collagen δ13C, δ15N, and δ34S values. However, the data are scattered into dozens of publications written in multiple languages and less-accessible formats, making the data laborious to use. This article presents the first compilation work of this data, the open access dIANA database (Dietary Isotopic baseline for the Ancient North; https://www.oasisnorth.org/diana.html), aimed to support (paleo)dietary research in the Baltic Sea area. The database work is complemented with new analyses of archaeological and (pre-)modern domestic and wild fauna from Finland and Russia broadening the selection of analysed species in the database. We present and discuss data examples, which on one hand show existing spatiotemporal isotope patterns related to diet and differences in the environmental carbon sources and on the other, also visualize the current status of baseline research and the need for further analyses in the circum-Baltic area.