Effects of growth hormone (GH) replacement therapy on low-density lipoprotein apolipoprotein B100 kinetics in adult patients with GH deficiency: a stable isotope study

GH replacement therapy has been shown to improve the dyslipidemic condition in a substantial proportion of patients with adult GH deficiency. The mechanisms are not yet fully elucidated. Low-density lipoprotein (LDL) apolipoprotein B100 (apoB) formation and catabolism are important determinants of plasma cholesterol concentrations. This study examined the effect of GH replacement therapy on LDL apoB metabolism using a stable isotope turnover technique. LDL apoB kinetics was determined in 13 adult patients with GH deficiency before and after 3 months GH/placebo treatment in a randomized, double-blind, placebo-controlled study. LDL apoB (13)C-leucine enrichment was determined by isotope-ratio mass spectrometry. Plasma volume was assessed by standardized radionuclide dilution technique. GH replacement therapy significantly decreased LDL cholesterol, LDL apoB concentrations, and LDL apoB pool size compared with placebo. Compared with baseline, GH replacement therapy resulted in a significant increase in plasma volume and fractional catabolic rate, whereas LDL formation rate remained unchanged. LDL lipid content did not significantly change after GH and placebo. This study suggests that short-term GH replacement therapy decreases the LDL apoB pool by increasing removal of LDL particles without changing LDL composition or LDL apoB production rate. In addition, it is possible that the beneficial effects of GH on the cardiovascular system contribute to these findings.

Komatiites constrain molybdenum isotope composition of the Earth's mantle

In order to estimate the Mo isotope composition and Mo abundance in the Bulk Silicate Earth (BSE), a total of thirty komatiite samples from five localities on three continents were analyzed using an isotope dilution double spike technique. Calculated Mo concentrations of the emplaced komatiite lavas range from 25±325±3 to 66±22 ng/g66±22 ng/g, and the inferred Mo concentrations in the deep mantle sources of the komatiites range between 17±417±4 and 30±12 ng/g30±12 ng/g, with an average value of 23±7 ng/g23±7 ng/g (2SE). This average value represents our best estimate for the Mo concentration in the BSE; it is identical, within the uncertainty, to published previous estimates of 39±16 ng/g39±16 ng/g, but is at least a factor of 2 more precise. The Mo isotope compositions of the komatiite mantle sources overlap within uncertainty and range from View the MathML sourceδMo98=−0.04±0.28 to 0.11±0.10‰0.11±0.10‰, with an average of 0.04±0.06‰0.04±0.06‰ (2SE). This value is analytically indistinguishable from published Mo isotope compositions of ordinary and enstatite chondrites and represents the best estimate for the Mo isotope composition of the BSE. The inferred δ98Mo for the BSE is therefore lighter than the suggested average of the upper continental crust (0.3 to 0.4‰). Thus, from the mass balance standpoint, a reservoir with lighter Mo isotope composition should exist in the Earth's mantle; this reservoir can potentially be found in subducted oceanic crust. The similarity of δ98Mo between chondritic meteorites and estimates for the BSE from this study indicates that during the last major equilibration between Earth's core and mantle, i.e., the one that occurred during the giant impact that produced the Moon, chemical and isotopic equilibrium of Mo between Fe metal of the core and the silicate mantle was largely achieved.

Effects of growth hormone (GH) replacement therapy on very low density lipoprotein apolipoprotein B100 kinetics in patients with adult GH deficiency: a stable isotope study

Patients with adult GH deficiency are often dyslipidemic and may have an increased risk of cardiovascular disease. The secretion and clearance of very low density lipoprotein apolipoprotein B 100 (VLDL apoB) are important determinants of plasma lipid concentrations. This study examined the effect of GH replacement therapy on VLDL apoB metabolism using a stable isotope turnover technique. VLDL apoB kinetics were determined in 14 adult patients with GH deficiency before and after 3 months GH or placebo treatment in a randomized double blind, placebo-controlled study using a primed constant [1-(13)C]leucine infusion. VLDL apoB enrichment was determined by gas chromatography-mass spectrometry. GH replacement therapy increased plasma insulin-like growth factor I concentrations 2.9 +/- 0.5-fold (P < 0.001), fasting insulin concentrations 1.8 +/- 0.6-fold (P < 0.04), and hemoglobin A1C from 5.0 +/- 0.2% to 5.3 +/- 0.2% (mean +/- SEM; P < 0.001). It decreased fat mass by 3.4 +/- 1.3 kg (P < 0.05) and increased lean body mass by 3.5 +/- 0.8 kg (P < 0.01). The total cholesterol concentration (P < 0.02), the low density lipoprotein cholesterol concentration (P < 0.02), and the VLDL cholesterol/VLDL apoB ratio (P < 0.005) decreased. GH therapy did not significantly change the VLDL apoB pool size, but increased the VLDL apoB secretion rate from 9.2 +/- 2.0 to 25.9 +/- 10.3 mg/kg x day (P < 0.01) and the MCR from 11.5 +/- 2.7 to 20.3 +/- 3.2 mL/min (P < 0.03). No significant changes were observed in the placebo group. This study suggests that GH replacement therapy improves lipid profile by increasing the removal of VLDL apoB. Although GH therapy stimulates VLDL apoB secretion, this is offset by the increase in the VLDL apoB clearance rate, which we postulate is due to its effects in up-regulating low density lipoprotein receptors and modifying VLDL composition.

Bacterial decontamination of surgical wounds treated with Lavasept

In a prospective randomized controlled double-blind study in 50 acutely injured patients, bacterially contaminated type 2-4 soft tissue wounds were treated with moist dressings of 0.2% Lavasept (fractionated polyhexamethylenbiguanide and macrogolum 4000) solution (n=28) in comparison with Ringer solution (n=22). Standardized swabs were taken on days 0, 2, 8 and 15 and investigated for microorganisms. For a quantitative evaluation, the number of colony forming units (CFU) was determined by a serial dilution technique. The tissue compatibility and anti-inflammatory effect were rated on a scale of 0 (=bad) to 3 (=very good). The most frequently found microorganism was Staphylococcus aureus, which was isolated from 13 wounds. Use of Lavasept led to a faster and significant reduction in microorganisms on the wound surfaces. The number of CFU per wound remained constant or decreased, in contrast to the wounds treated with Ringer solution. This was true for both Gram-positive and Gram-negative bacteria. There was no evidence of impaired wound healing in either group. The anti-inflammatory effect and the tissue compatibility of Lavasept were rated significantly better than that of Ringer solution. It is concluded that Lavasept combines antiseptic action with good tissue compatibility.

The abundance and isotopic composition of Cd in iron meteorites

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility-controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of 113Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd-Pt-W isotope results from this study thus demonstrate that the relative magnitude of neutron capture-induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites.

The energy expenditure of 2 Holstein cow strains in an organic grazing system

Until recently, measurements of energy expenditure (EE; herein defined as heat production) in respiration chambers did not account for the extra energy requirements of grazing dairy cows on pasture. As energy is first limiting in most pasture-based milk production systems, its efficient use is important. Therefore, the aim of the present study was to compare EE, which can be affected by differences in body weight (BW), body composition, grazing behavior, physical activity, and milk production level, in 2 Holstein cow strains. Twelve Swiss Holstein-Friesian (HCH; 616 kg of BW) and 12 New Zealand Holstein-Friesian (HNZ; 570 kg of BW) cows in the third stage of lactation were paired according to their stage of lactation and kept in a rotational, full-time grazing system without concentrate supplementation. After adaption, the daily milk yield, grass intake using the alkane double-indicator technique, nutrient digestibility, physical activity, and grazing behavior recorded by an automatic jaw movement recorder were investigated over 7d. Using the (13)C bicarbonate dilution technique in combination with an automatic blood sampling system, EE based on measured carbon dioxide production was determined in 1 cow pair per day between 0800 to 1400 h. The HCH were heavier and had a lower body condition score compared with HNZ, but the difference in BW was smaller compared with former studies. Milk production, grass intake, and nutrient digestibility did not differ between the 2 cow strains, but HCH grazed for a longer time during the 6-h measurement period and performed more grazing mastication compared with the HNZ. No difference was found between the 2 cow strains with regard to EE (291 ± 15.6 kJ) per kilogram of metabolic BW, mainly due to a high between-animal variation in EE. As efficiency and energy use are important in sustainable, pasture-based, organic milk production systems, the determining factors for EE, such as methodology, genetics, physical activity, grazing behavior, and pasture quality, should be investigated and quantified in more detail in future studies.

Comparison of energy expenditure, eating pattern and physical activity of grazing and zero-grazing dairy cows at different time points during lactation

An experiment was conducted to determine the effect of grazing versus zero-grazing on energy expenditure (EE), feeding behaviour and physical activity in dairy cows at different stages of lactation. Fourteen Holstein cows were subjected to two treatments in a repeated crossover design with three experimental series (S1, S2, and S3) reflecting increased days in milk (DIM). At the beginning of each series, cows were on average at 38, 94 and 171 (standard deviation (SD) 10.8) DIM, respectively. Each series consisted of two periods containing a 7-d adaptation and a 7-d collection period each. Cows either grazed on pasture for 16–18.5 h per day or were kept in a freestall barn and had ad libitum access to herbage harvested from the same paddock. Herbage intake was estimated using the double alkane technique. On each day of the collection period, EE of one cow in the barn and of one cow on pasture was determined for 6 h by using the 13C bicarbonate dilution technique, with blood sample collection done either manually in the barn or using an automatic sampling system on pasture. Furthermore, during each collection period physical activity and feeding behaviour of cows were recorded over 3 d using pedometers and behaviour recorders. Milk yield decreased with increasing DIM (P<0.001) but was similar with both treatments. Herbage intake was lower (P<0.01) for grazing cows (16.8 kg dry matter (DM)/d) compared to zero-grazing cows (18.9 kg DM/d). The lowest (P<0.001) intake was observed in S1 and similar intakes were observed in S2 and S3. Within the 6-h measurement period, grazing cows expended 19% more (P<0.001) energy (319 versus 269 kJ/kg metabolic body size (BW0.75)) than zero-grazing cows and differences in EE did not change with increasing DIM. Grazing cows spent proportionally more (P<0.001) time walking and less time standing (P<0.001) and lying (P<0.05) than zero-grazing cows. The proportion of time spent eating was greater (P<0.001) and that of time spent ruminating was lower (P<0.05) for grazing cows compared to zero-grazing cows. In conclusion, lower feed intake along with the unchanged milk production indicates that grazing cows mobilized body reserves to cover additional energy requirements which were at least partly caused by more physical activity. However, changes in cows׳ behaviour between the considered time points during lactation were too small so that differences in EE remained similar between treatments with increasing DIM.

Optimized Demineralization Technique for the Measurement of Stable Isotope Ratios of Nonexchangeable H in Soil Organic Matter

To make use of the isotope ratio of nonexchangeable hydrogen (δ2Hn (nonexchangeable)) of bulk soil organic matter (SOM), the mineral matrix (containing structural water of clay minerals) must be separated from SOM and samples need to be analyzed after H isotope equilibration. We present a novel technique for demineralization of soil samples with HF and dilute HCl and recovery of the SOM fraction solubilized in the HF demineralization solution via solid-phase extraction. Compared with existing techniques, organic C (Corg) and organic N (Norg) recovery of demineralized SOM concentrates was significantly increased (Corg recovery using existing techniques vs new demineralization method: 58% vs 78%; Norg recovery: 60% vs 78%). Chemicals used for the demineralization treatment did not affect δ2Hn values as revealed by spiking with deuterated water. The new demineralization method minimized organic matter losses and thus artificial H isotope fractionation, opening up the opportunity to use δ2Hn analyses of SOM as a new tool in paleoclimatology or geospatial forensics.

Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador

Knowledge of the fate of deposited N in the possibly N-limited, highly biodiverse north Andean forests is important because of the possible effects of N inputs on plant performance and species composition. We analyzed concentrations and fluxes of NO3 −–N, NH4 +–N and dissolved organic N (DON) in rainfall, throughfall, litter leachate, mineral soil solutions (0.15–0.30 m depths) and stream water in a montane forest in Ecuador during four consecutive quarters and used the natural 15N abundance in NO3 − during the passage of rain water through the ecosystem and bulk δ15N values in soil to detect N transformations. Depletion of 15N in NO3 − and increased NO3 −–N fluxes during the passage through the canopy and the organic layer indicated nitrification in these compartments. During leaching from the organic layer to mineral soil and stream, NO3 − concentrations progressively decreased and were enriched in 15N but did not reach the δ15N values of solid phase organic matter (δ15N = 5.6–6.7‰). This suggested a combination of nitrification and denitrification in mineral soil. In the wettest quarter, the δ15N value of NO3 − in litter leachate was smaller (δ15N = −1.58‰) than in the other quarters (δ15N = −9.38 ± SE 0.46‰) probably because of reduced mineralization and associated fractionation against 15N. Nitrogen isotope fractionation of NO3 − between litter leachate and stream water was smaller in the wettest period than in the other periods probably because of a higher rate of denitrification and continuous dilution by isotopically lighter NO3 −–N from throughfall and nitrification in the organic layer during the wettest period. The stable N isotope composition of NO3 − gave valuable indications of N transformations during the passage of water through the forest ecosystem from rainfall to the stream.

A sublimation technique for high-precision measurements of d13CO2 and mixing ratios of CO2 and N2O from air trapped in ice cores

In order to provide high precision stable carbon isotope ratios (δ13CO2 or δ13C of CO2) from small bubbly, partially and fully clathrated ice core samples we developed a new method based on sublimation coupled to gas chromatography-isotope ratio mass spectrometry (GC-IRMS). In a first step the trapped air is quantitatively released from ~30 g of ice and CO2 together with N2O are separated from the bulk air components and stored in a miniature glass tube. In an off-line step, the extracted sample is introduced into a helium carrier flow using a minimised tube cracker device. Prior to measurement, N2O and organic sample contaminants are gas chromatographically separated from CO2. Pulses of a CO2/N2O mixture are admitted to the tube cracker and follow the path of the sample through the system. This allows an identical treatment and comparison of sample and standard peaks. The ability of the method to reproduce δ13C from bubble and clathrate ice is verified on different ice cores. We achieve reproducibilities for bubble ice between 0.05 ‰ and 0.07 ‰ and for clathrate ice between 0.05 ‰ and 0.09 ‰ (dependent on the ice core used). A comparison of our data with measurements on bubble ice from the same ice core but using a mechanical extraction device shows no significant systematic offset. In addition to δ13C, the CO2 and N2O mixing ratios can be volumetrically derived with a precision of 2 ppmv and 8 ppbv, respectively.

New online method for water isotope analysis of speleothem fluid inclusions using laser absorption spectroscopy (WS-CRDS)

A new online method to analyse water isotopes of speleothem fluid inclusions using a wavelength scanned cavity ring down spectroscopy (WS-CRDS) instrument is presented. This novel technique allows us simultaneously to measure hydrogen and oxygen isotopes for a released aliquot of water. To do so, we designed a new simple line that allows the online water extraction and isotope analysis of speleothem samples. The specificity of the method lies in the fact that fluid inclusions release is made on a standard water background, which mainly improves the δ D robustness. To saturate the line, a peristaltic pump continuously injects standard water into the line that is permanently heated to 140 °C and flushed with dry nitrogen gas. This permits instantaneous and complete vaporisation of the standard water, resulting in an artificial water background with well-known δ D and δ18O values. The speleothem sample is placed in a copper tube, attached to the line, and after system stabilisation it is crushed using a simple hydraulic device to liberate speleothem fluid inclusions water. The released water is carried by the nitrogen/standard water gas stream directly to a Picarro L1102-i for isotope determination. To test the accuracy and reproducibility of the line and to measure standard water during speleothem measurements, a syringe injection unit was added to the line. Peak evaluation is done similarly as in gas chromatography to obtain &delta D; and δ18O isotopic compositions of measured water aliquots. Precision is better than 1.5 ‰ for δ D and 0.4 ‰ for δ18O for water measurements for an extended range (−210 to 0 ‰ for δ D and −27 to 0 ‰ for δ18O) primarily dependent on the amount of water released from speleothem fluid inclusions and secondarily on the isotopic composition of the sample. The results show that WS-CRDS technology is suitable for speleothem fluid inclusion measurements and gives results that are comparable to the isotope ratio mass spectrometry (IRMS) technique.

On the interference of Kr during carbon isotope analysis of methane using continuous-flow combustion–isotope ratio mass spectrometry

Stable carbon isotope analysis of methane (delta C-13 of CH4) on atmospheric samples is one key method to constrain the current and past atmospheric CH4 budget. A frequently applied measurement technique is gas chromatography (GC) isotope ratio mass spectrometry (IRMS) coupled to a combustion-preconcentration unit. This report shows that the atmospheric trace gas krypton (Kr) can severely interfere during the mass spectrometric measurement, leading to significant biases in delta C-13 of CH4, if krypton is not sufficiently separated during the analysis. According to our experiments, the krypton interference is likely composed of two individual effects, with the lateral tailing of the doubly charged Kr-86 peak affecting the neighbouring m/z 44 and partially the m/z 45 Faraday cups. Additionally, a broad signal affecting m/z 45 and especially m/z 46 is assumed to result from scattered ions of singly charged krypton. The introduced bias in the measured isotope ratios is dependent on the chromatographic separation, the krypton-to-CH4 mixing ratio in the sample, the focusing of the mass spectrometer as well as the detector configuration and can amount to up to several per mil in delta C-13. Apart from technical solutions to avoid this interference, we present correction routines to a posteriori remove the bias.