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.

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.