A rapid high-precision analytical method for triple oxygen isotope analysis of CO2 gas using tunable infrared laser direct absorption spectroscopy

RATIONALE

The simultaneous analysis of the three stable isotopes of oxygen-triple oxygen isotope analysis-has become an important analytical technique in natural sciences. Determination of the abundance of the rare ¹⁷ O isotope in CO₂ gas using magnetic sector isotope ratio mass spectrometry is complicated by the isobaric interference of ¹⁷ O by ¹³ C (¹³ C¹⁶ O¹⁶ O and ¹² C¹⁶ O¹⁷ O, both have mass 45 amu). A number of analytical techniques have been used to measure the ¹⁷ O/¹⁶ O ratio of CO₂ gas. They either are time consuming and technically challenging or have limited precision. A rapid and precise alternative to the available analytical methods is desirable.

METHODS

We present the results of triple oxygen isotope analyses using an Aerodyne tunable infrared laser direct absorption spectroscopy (TILDAS) CO₂ analyzer configured for ¹⁶ O, ¹⁷ O, and ¹⁸ O combined with a custom gas inlet system. We evaluate the sensitivity of our results to a number of parameters. CO₂ samples with a wide range of δ¹⁸ O values (from -9.28‰ to 39.56‰) were measured and compared to results using the well-established fluorination-gas source mass spectrometry method.

RESULTS

The TILDAS system has a precision (standard error, 2σ) of better than ±0.03‰ for δ¹⁸ O and ±10 per meg for Δ'¹⁷ O values, equivalent to the precision of previous analytical methods. Samples as small as 3 μmol CO₂ (equivalent to 300 μg CaCO₃ ) can be analyzed with a total analysis time of ~30 min.

CONCLUSIONS

We have successfully developed an analytical technique for the simultaneous determination of the δ¹⁷ O and δ¹⁸ O values of CO₂ gas. The precision is equal to or better than that of existing techniques, with no additional chemical treatments required. Analysis time is rapid, and the system is easily automated so that large numbers of samples can be analyzed with minimal effort.

Long-term oral delivery of encapsulated rapamycin is not detrimental to immunity in old mice (178.11)

Recently, encapsulated rapamycin (e-rapa) was shown to extend lifespan in mice when given at an old age (Harrison Nature 2009), so it has been suggested that this mTOR inhibitor may be efficacious in slowing the aging process. However, use of rapa in the elderly might further compromise immune competence. Therefore, we sought to test the effects of e-rapa on immunity in older individuals by looking at T cell and B cell responses. Because rapa has been shown to be protective against some bacteria and viruses, effects on humoral immunity to a viable microbe were tested. Adult (4 months) and old (20 months) mice on e-rapa or control diets were challenged with the periodontal bacteria Aggregatibacter actinomycetemcomitans; e-rapa did not negatively impact the antibody titers seen in either age group. E-rapa effects on responses to a protein antigen, TAChRα, were also tested. No significant e-rapa effect was seen on antibody titers following primary or boost immunizations. Moreover, pilot data show that T cell proliferation to p146-162, the immunodominant epitope of TAChRα, was not significantly affected by the encapsulated drug. Since TAChR is the autoantigen in Myasthenia Gravis, we also immunized TAChRα transgenic mice (JI 169:6570) and showed that tolerance was maintained and the levels of TREGS were unaffected by e-rapa treatment. To-date, our data suggest that encapsulated rapamycin will not negatively impact immune regulation in old individuals.

Stable isotope-labeled excipients for drug product identification and counterfeit detection

PURPOSE

Counterfeit drug products have become a major problem worldwide and a number of techniques to detect counterfeit products or reduce the potential for counterfeiting have been investigated. This study examined the use of stable isotope-labeled excipients in solid dosage forms as a method to identify drug products and to detect counterfeits.

METHODS

(2)H- and (13)C-glucose were used as model excipients and incorporated in wet granulated formulations at a variety of different isotopic ratios. The ratios of (2)H/(1)H and (13)C/(12)C in each product were then determined by isotope ratio mass spectrometry.

RESULTS

Results demonstrated the ability to detect the isotope-labeled glucose in both granules and tablets.

CONCLUSIONS

It was possible to use the isotope ratios to differentiate between specific batches of granules, demonstrating the potential of this technique for in-product, batch-specific identification.

Treg and rapamycin effects on humoral immunity in young and old mice (84.12)

Recently, the mTOR inhibitor rapamycin was shown to extend lifespan in mice even when administered at 20 months of age (Harrison et al. Nature 2009). Although studies have shown that it enhances vaccine efficacy and immune memory, others demonstrated an increase in Tregs and a depression of T cell proliferation. Thus, to assess the effect of rapamycin on humoral immunity, young and old mice were fed a rapamycin or control diet and then immunized 3 times with the protein antigen Omp34 from Aggregatibacter actinomycetemcomitans (Aa), a periodontal pathogen. As expected, rapamycin impaired antibody responses to Omp34 in young mice. In older mice, the humoral response was low and not enhanced by the drug. Serum cytokines were also measured and treatment with rapamycin had no effects. In order to address the role of Tregs, mice in each group were given 3 injections of αCD25 (functionally inactivates Tregs) or an isotype control antibody prior to each immunization. However, this treatment did not reverse the effects seen in antibody titers or cytokine levels, suggesting that Tregs alone do not account for the effects seen. After the last immunization, mice were challenged with viable Aa and protection was assessed. Rapamycin had no effect on protection, but surprisingly, antibody production to Aa in older mice was higher in those fed rapamycin. In younger mice, drug treatment had no effect. In conclusion, rapamycin’s effects on immunity should be assessed in old and young mice.

Translocation of Inhaled Ultrafine Particles to the Brain

Ultrafine particles (UFP, particles <100 nm) are ubiquitous in ambient urban and indoor air from multiple sources and may contribute to adverse respiratory and cardiovascular effects of particulate matter (PM). Depending on their particle size, inhaled UFP are efficiently deposited in nasal, tracheobronchial, and alveolar regions due to diffusion. Our previous rat studies have shown that UFP can translocate to interstitial sites in the respiratory tract as well as to extrapulmonary organs such as liver within 4 to 24 h postexposure. There were also indications that the olfactory bulb of the brain was targeted. Our objective in this follow-up study, therefore, was to determine whether translocation of inhaled ultrafine solid particles to regions of the brain takes place, hypothesizing that UFP depositing on the olfactory mucosa of the nasal region will translocate along the olfactory nerve into the olfactory bulb. This should result in significant increases in that region on the days following the exposure as opposed to other areas of the central nervous system (CNS). We generated ultrafine elemental (13)C particles (CMD = 36 nm; GSD = 1.66) from [(13)C] graphite rods by electric spark discharge in an argon atmosphere at a concentration of 160 microg/m(3). Rats were exposed for 6 h, and lungs, cerebrum, cerebellum and olfactory bulbs were removed 1, 3, 5, and 7 days after exposure. (13)C concentrations were determined by isotope ratio mass spectroscopy and compared to background (13)C levels of sham-exposed controls (day 0). The background corrected pulmonary (13)C added as ultrafine (13)C particles on day 1 postexposure was 1.34 microg/lung. Lung (13)C concentration decreased from 1.39 microg/g (day 1) to 0.59 microg/g by 7 days postexposure. There was a significant and persistent increase in added (13)C in the olfactory bulb of 0.35 microg/g on day 1, which increased to 0.43 microg/g by day 7. Day 1 (13)C concentrations of cerebrum and cerebellum were also significantly increased but the increase was inconsistent, significant only on one additional day of the postexposure period, possibly reflecting translocation across the blood-brain barrier in certain brain regions. The increases in olfactory bulbs are consistent with earlier studies in nonhuman primates and rodents that demonstrated that intranasally instilled solid UFP translocate along axons of the olfactory nerve into the CNS. We conclude from our study that the CNS can be targeted by airborne solid ultrafine particles and that the most likely mechanism is from deposits on the olfactory mucosa of the nasopharyngeal region of the respiratory tract and subsequent translocation via the olfactory nerve. Depending on particle size, >50% of inhaled UFP can be depositing in the nasopharyngeal region during nasal breathing. Preliminary estimates from the present results show that approximately 20% of the UFP deposited on the olfactory mucosa of the rat can be translocated to the olfactory bulb. Such neuronal translocation constitutes an additional not generally recognized clearance pathway for inhaled solid UFP, whose significance for humans, however, still needs to be established. It could provide a portal of entry into the CNS for solid UFP, circumventing the tight blood-brain barrier. Whether this translocation of inhaled UFP can cause CNS effects needs to be determined in future studies.

Tree-ring isotope records of tropical cyclone activity

The destruction wrought by North Atlantic hurricanes in 2004 and 2005 dramatically emphasizes the need for better understanding of tropical cyclone activity apart from the records provided by meteorological data and historical documentation. We present a 220-year record of oxygen isotope values of alpha-cellulose in longleaf pine tree rings that preserves anomalously low isotope values in the latewood portion of the ring in years corresponding with known 19th and 20th century landfalling/near-coastal tropical storms and hurricanes. Our results suggest the potential for a tree-ring oxygen isotope proxy record of tropical cyclone occurrence extending back many centuries based on remnant pine wood from protected areas in the southeastern U.S.

Extrapulmonary translocation of ultrafine carbon particles following whole-body inhalation exposure of rats

Studies with intravenously injected ultrafine particles have shown that the liver is the major organ of their uptake from the blood circulation. Measuring translocation of inhaled ultrafine particles to extrapulmonary organs via the blood compartment is hampered by methodological difficulties (i.e., label may come off, partial solubilization) and analytical limitations (measurement of very small amounts). The objective of our pilot study was to determine whether ultrafine elemental carbon particles translocate to the liver and other extrapulmonary organs following inhalation as singlet particles by rats. We generated ultrafine (13)C particles as an aerosol with count median diameters (CMDs) of 20-29 nm (GSD 1.7) using electric spark discharge of (13)C graphite electrodes in argon. Nine Fischer 344 rats were exposed to these particles for 6 h. in whole-body inhalation chambers at concentrations of 180 and 80 microg/m(3); 3 animals each were killed at 0.5, 18, and 24 h postexposure. Six unexposed rats served as controls. Lung lobes, liver, heart, brain, olfactory bulb, and kidney were excised, homogenized, and freeze-dried for analysis of the added (13)C by isotope ratio mass spectrometry. Organic (13)C was not detected in the (13)C particles. The (13)C retained in the lung at 0.5 h postexposure was about 70% less than predicted by rat deposition models for ultrafine particles, and did not change significantly during the 24-h postexposure period. Normalized to exposure concentration, the added (13)C per gram of lung on average in the postexposure period was approximately 9 ng/g organ/microg/m(3). Significant amounts of (13)C had accumulated in the liver by 0.5 h postinhalation only at the high exposure concentration, whereas by 18 and 24 h postexposure the (13)C amount of the livers of all exposed rats was about fivefold greater than the (13)C burden retained in the lung. No significant increase in (13)C was detected in the other organs which were examined. These results demonstrate effective translocation of ultrafine elemental carbon particles to the liver by 1 d after inhalation exposure. Translocation pathways include direct input into the blood compartment from ultrafine carbon particles deposited throughout the respiratory tract. However, since predictive particle deposition models indicate that respiratory tract deposits alone may not fully account for the hepatic (13)C burden, input from ultrafine particles present in the GI tract needs to be considered as well. Such translocation to blood and extrapulmonary tissues may well be different between ultrafine carbon and other insoluble (metal) ultrafine particles.