Lucy Trombley

Comparative Clearance of Quartz and Cristobalite from the Lung

The two silicon dioxide polymorphs, quartz and cristobalite, are known to have different toxicities. The clearance kinetics and biological response of two sources of quartz and one source of pure cristobalite were compared. Models were also developed to show the accumulation of cristobalite in the lungs of Fischer 344 rats as the result of short-term exposures at three different concentrations. The amount of cristobalite cleared from the lung was considerably less than that of the two quartz materials, with little or no clearance after the initial 30 days post exposure. As an indicator of the cellular biological response to the aerosols, total and differential cell counts were measured on bronchoalveolar lavage specimens. Cristobalite showed an early and sustained response with an elevated macrophage, neutrophil, and lymphocyte count through 180 days post exposure. The two quartz materials were not identical in their biological behavior even though they had identical crystal structure and similar trace element analysis. One quartz sample (MIN5) showed an increase in cell response (macrophage, neutrophils, and lymphocytes) approximately 30% that of cristobalite, whereas the other quartz material was not significantly different from control values. In addition, lung hydroxyproline content was greater in the cristobalite-exposed animals.

Cerebrovascular response to continuous cold perfusion and hypothermic circulatory arrest

OBJECTIVE Clinical and laboratory studies have documented changes in cerebrovascular resistance after hypothermic circulatory arrest, both with and without adjunctive cerebral perfusion modalities. This study was designed to clarify whether these changes are due to cerebral edema, resistance vessel abnormalities, or alterations in the cerebral microcirculation. METHODS Four mature swine underwent hypothermic circulatory arrest for 60 minutes, and 7 mature swine underwent cold cerebral perfusion for 60 minutes to simulate antegrade selective perfusion. All were rewarmed and weaned from cardiopulmonary bypass. Pial vascular diameter and reactivity were measured in vivo through a cranial window and ex vivo in an organ chamber; cerebral microvascular endothelium was studied in culture for release of vasoactive mediators. Cerebral water content was recorded. RESULTS Cold perfusion caused pial arteriole and venule constriction, whereas hypothermic circulatory arrest alone caused pial arteriole and venule dilatation. Cold perfusion caused a temporal loss of endothelium-dependent vasodilatation, most notably to bradykinin. Hypothermic circulatory arrest caused a loss of nitric oxide-mediated endothelium-dependent vasodilatation. Endothelium-independent vasoreactivity remained intact in both groups. Endothelial cells from the cold group had a vasoconstrictive secretory phenotype, whereas endothelial cells from the hypothermic circulatory arrest group had a vasodilatory phenotype. Cerebral water content was the same in both groups. CONCLUSION The increase in cerebrovascular resistance observed after cold cerebral perfusion is caused by resistance vessel constriction and may be promoted by an altered microcirculation. Hypothermic circulatory arrest alone is associated with endothelium-dependent vasoparesis. Both could contribute to cerebral injury in the early hours after operation.

Intrathoracic Distribution and Transport of Aerosolized Silica in the Rat

Short-term exposure of rats to aerosols of the silicon dioxide, cristobalite, leads to pulmonary inflammation persisting several months. Clearance of particles occurs during the first two weeks after cessation of exposure, after which there is little additional clearance in the whole lung. In the present studies, quantitation of silica in lung compartments at selected times following exposure indicated movement of particles between the alveolar space and the lung tissue per se, with increased alveolar silica content associated with decreased silica content in the tissue compartment. Further, changes in the silica content in the alveolar compartment were generally associated with fluctuations in the alveolar macrophage population. Silica accumulated linearly in the mediastinal lymph nodes and thymus for several months after cessation of exposure, while negligible amounts were found in kidney, spleen, liver, and blood. A compartmental model was used to describe the distribution and translocation kinetics of the inhaled silica in the lung and extrapulmonary tissues.

A novel model of blunt thoracic aortic injury: a mechanism confirmed?

BACKGROUND There is no consensus on the mechanism of traumatic injury to the thoracic aorta and no reproducible animal model. Advances in injury scene analysis suggest that lateral and oblique force vectors cause aortic injury. We hypothesized that the spectrum of aortic injury could be reproduced in an animal model by application of an obliquely directed load to the pressurized aorta. METHODS Graded air impulses of 80, 100, 110, and 120 pounds per square inch (PSI) were delivered to the descending thoracic aorta of 19 swine with a novel pneumatic device. Aortic isthmus strain was recorded with microminiature probes. Gross and microscopic injury was recorded with digital photography. RESULTS The spectrum of human aortic injury was reproduced in this model. Deep injuries to the aortic media were common. The majority of injuries occurred within the region of the isthmus. Impulse pressure of 120 PSI caused transections, whereas lower impulse pressure resulted in less severe injuries. Aortic isthmus strain was greater in the animals exposed to 120 PSI than those receiving lower PSI (19.6 +/- 4.9% vs. 8.7 +/- 2.5%, p = 0.067). CONCLUSIONS Direct loading of the pressurized descending thoracic aorta causes isthmus injury secondary to aortic wall strain. Deep medial lesions are common and could propagate soon after injury to form pseudoaneurysms. A critical load is required to cause complete uncontained transection with exsanguination, which may have relevance to injury scene death.

V(D)J Recombinase-Mediated Processing of Coding Junctions at Cryptic Recombination Signal Sequences in Peripheral T Cells during Human Development

V(D)J recombinase mediates rearrangements at immune loci and cryptic recombination signal sequences (cRSS), resulting in a variety of genomic rearrangements in normal lymphocytes and leukemic cells from children and adults. The frequency at which these rearrangements occur and their potential pathologic consequences are developmentally dependent. To gain insight into V(D)J recombinase-mediated events during human development, we investigated 265 coding junctions associated with cRSS sites at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in peripheral T cells from 111 children during the late stages of fetal development through early adolescence. We observed a number of specific V(D)J recombinase processing features that were both age and gender dependent. In particular, TdT-mediated nucleotide insertions varied depending on age and gender, including percentage of coding junctions containing N-nucleotide inserts, predominance of GC nucleotides, and presence of inverted repeats (Pr-nucleotides) at processed coding ends. In addition, the extent of exonucleolytic processing of coding ends was inversely related to age. We also observed a coding-partner-dependent difference in exonucleolytic processing and an age-specific difference in the subtypes of V(D)J-mediated events. We investigated these age- and gender-specific differences with recombination signal information content analysis of the cRSS sites in the human HPRT locus to gain insight into the mechanisms mediating these developmentally specific V(D)J recombinase-mediated rearrangements in humans.

HPRT mutations in vivo in human CD 34+ hematopoietic stem cells

The HPRT mutations in T lymphocytes are widely utilized as biomarkers of environmental exposure and effect. The HPRT gene detects a wide variety of mutation types, many of which are similar at the molecular level to those found in oncogenes in cancers. However, it remains to be determined whether the assay for mutations in T lymphocytes is reflective of mutagenic events in tissues or cells which have high frequencies of malignancy in humans. We now demonstrate that the HPRT gene can be utilized to detect mutations in myeloid stem cells, which are frequent progenitor cells of leukemias. This myeloid stem cell assay shows an age related increase in mutation at HPRT and also detects increases in mutant frequency (M-MF) in patients who have undergone chemotherapy. The myeloid mutants are confirmed to have mutations in the HPRT gene by DNA sequence analysis. Increases in M-MF are seen as expected in the clonally unstable myeloid stem cells of patients with myelodysplastic syndromes; however, unexpectedly these patients also have elevated T-lymphocyte mutant frequencies (T-MF). A good correlation is shown between M-MFs and T-MFs in the same patients. Thus, it appears that the T-lymphocyte assay, which is technically much less demanding than the myeloid assay, appears to faithfully represent the frequency of mutagenic events in the myeloid lineage.