Evaluation of technetium pertechnetate as a radionuclide marker of pulmonary aspiration of gastric contents in rabbits

A Supramolecular Approach for Liver Radioembolization

Hepatic radioembolization therapies can suffer from discrepancies between diagnostic planning (scout-scan) and the therapeutic delivery itself, resulting in unwanted side-effects such as pulmonary shunting. We reasoned that a nanotechnology-based pre-targeting strategy could help overcome this shortcoming by directly linking pre-interventional diagnostics to the local delivery of therapy.

Methods: The host-guest interaction between adamantane and cyclodextrin was employed in an in vivo pre-targeting set-up. Adamantane (guest)-functionalized macro albumin aggregates (MAA-Ad; d = 18 μm) and (radiolabeled) Cy5 and β-cyclodextrin (host)-containing PIBMA polymers (^99mTc-Cy5_0.5CD₁₀PIBMA₃₉; MW ~ 18.8 kDa) functioned as the reactive pair. Following liver or lung embolization with (^99mTc)-MAA-Ad or (^99mTc)-MAA (control), the utility of the pre-targeting concept was evaluated after intravenous administration of ^99mTc-Cy5_0.5CD₁₀PIBMA₃₉.

Results: Interactions between MAA-Ad and Cy5_0.5CD₁₀PIBMA₃₉ could be monitored in solution using confocal microscopy and were quantified by radioisotope-based binding experiments. In vivo the accumulation of the MAA-Ad particles in the liver or lungs yielded an approximate ten-fold increase in accumulation of ^99mTc-Cy5_0.5CD₁₀PIBMA₃₉ in these organs (16.2 %ID/g and 10.5 %ID/g, respectively) compared to the control. Pre-targeting with MAA alone was shown to be only half as efficient. Uniquely, for the first time, this data demonstrates that the formation of supramolecular interactions between cyclodextrin and adamantane can be used to drive complex formation in the chemically challenging in vivo environment.

Conclusion: The in vivo distribution pattern of the cyclodextrin host could be guided by the pre-administration of the adamantane guest, thereby creating a direct link between the scout-scan (MAA-Ad) and delivery of therapy.

Biomarkers in the diagnosis of aspiration syndromes

Recognizing and managing the different types of aspiration events remain a challenging task due to the lack of distinguishing clinical or laboratory characteristics. Numerous biomarkers in serum, sputum and bronchoalveolar lavage have been studied, and their role in the recognition of aspiration remains controversial at this time. Recent animal investigations using an array of biomarkers based on distinct pathogenic features of each aspiration event have produced promising results; however, they have not been validated in humans. Newer markers are being introduced as diagnostic and prognostic tools in conditions such as community-acquired pneumonia and sepsis, but they have not been examined in aspiration. The present review summarizes the different biomarkers that have been studied in aspiration and those who might have a potential clinical use in the future.

A new pepsin assay to detect pulmonary aspiration of gastric contents among newly intubated patients

Aspiration of gastric contents by endotracheally intubated patients is associated with significant morbidity and mortality. Previous studies suggest that pepsin in tracheal aspirates may be a valuable marker of occult aspiration. We sought to show the sensitivity and specificity of a new, pepsin-specific assay in humans. A prospective, case-controlled study was conducted with subjects serving as their own controls. After planned endotracheal and nasogastric intubation for elective surgery, 20 participants had tracheal and gastric aspirates withdrawn. A blinded investigator tested samples for the presence of pepsin using the assay. Positive samples were then tested with pepstatin, a specific pepsin inhibitor, to ensure that positive results were due to pepsin. All tracheal aspirates tested negative and all gastric aspirates tested positive for pepsin. Pepstatin halted pepsin activity in all positive samples, ensuring that positive results were due to pepsin. A pepsin-specific assay is extremely reliable for detecting gastric contents in humans.

Detection of pulmonary aspiration of gastric contents in an animal model by assay of peptic activity in bronchoalveolar fluid

OBJECTIVE

To determine whether peptic activity in bronchoalveolar fluid, due to the presence of the gastric proteolytic enzyme pepsin, could serve as a biochemical marker for pulmonary aspiration of gastric contents.

DESIGN

Prospective, experimental trial.

SETTING

A university animal research laboratory.

SUBJECTS

Thirty-six New Zealand rabbits, weighing 2 to 4 kg.

INTERVENTIONS

New Zealand rabbits were anesthetized, intubated via tracheostomy, and mechanically ventilated. Pulmonary aspiration was induced by the intratracheal instillation of 2 mL/kg human gastric juice (pH 1.2 +/- 0.2; pepsin activity 0.02 +/- 0.006 microgram/mL; human gastric juice group, n = 24) or normal saline solution (pH 5.2 +/- 0.2; normal saline solution group; n = 12). Mechanical ventilation was continued. Bronchoalveolar lavage was performed at 15 mins (human gastric juice group, n = 8; normal saline solution group, n = 4), 30 mins (human gastric juice group, n = 8; normal saline solution group, n = 4), or 60 mins (human gastric juice group, n = 8; normal saline solution group, n = 4) postaspiration.

MEASUREMENTS AND MAIN RESULTS

Peak airway pressure and PaO2 values were measured at baseline and 15 and 30 mins after aspiration. The pH of retrieved bronchoalveolar lavage fluid was measured and pepsin activity in sample fluid was determined. Changes from baseline in peak airway pressure and PaO2 were significant in human gastric juice animals at 15 and 30 mins when compared with normal saline solution animals (PaO2 -4% vs. -44%, peak airway pressure 20% vs. 36% at 15 mins; PaO2 -16% vs. -79%, peak airway pressure 28% vs. 69% at 30 mins; normal saline solution group vs. human gastric juice group, p < .02). Bronchoalveolar lavage fluid pH was not significantly different between groups at any time postaspiration (6.6 +/- 0.7 vs. 6.0 +/- 0.4 at 15 mins; 7.4 +/- 0.9 vs. 6.5 +/- 0.4 at 30 mins; 7.2 +/- 0.5 vs. 6.4 +/- 0.4 at 60 mins, normal saline solution group vs. human gastric juice group, p = NS). No peptic activity was present in bronchoalveolar lavage fluid from normal saline solution animals at any time. In the human gastric juice group, peptic activity was detected in postaspiration bronchoalveolar lavage fluid in eight of eight animals at 15 mins, six of eight animals at 30 mins, and five of eight animals at 60 mins (normal saline solution group vs. human gastric juice group; p < .001 at 15 mins, p < .01 at 30 mins, p = NS at 60 mins). Peptic activity of bronchoalveolar lavage fluid varied; mean values were greater at 15 mins than at 30 or 60 mins (pepsin activity: 0.004 +/- 0.002 microgram/mL vs. 0.002 +/- 0.001 microgram/mL vs. 0.0006 +/- 0.0001 microgram/mL, respectively, p < .05).

CONCLUSIONS

The results of this study suggest that peptic activity in bronchoalveolar lavage fluid can be detected up to 60 mins after induced, experimental gastric juice aspiration and may prove a clinically useful biochemical marker for episodes of occult pulmonary aspiration of gastric contents.

A rabbit lung model for testing reaction to inhaled dental restorative particles

A study was designed to test the outcome of the deposition of particles of plastic composite dental restorative material in rabbit lungs. Grinding and polishing these restorations in situ produces some particles in the 0.5- to 10-microns size range that easily enter and remain in human lungs and are associated with industrial lung disease. Dental restorative plastic material was ground in the laboratory, suspended in saline solution, and injected transtracheally into four New Zealand white rabbits. Two control rabbits were similarly injected with saline solution transtracheally. Twenty-four hours later, the rabbits were injected with 1 mCi of 67Ga citrate intravenously and subsequently reanesthetized for scanning. Baseline scans were obtained in the six animals prior to the injection of the test particles. Positive gallium scans were obtained 72 h after the administration of particulate material in the four test rabbits. The gallium scans of the control rabbits remained no different from baseline. The study was repeated one month later. The animals were killed seven days after the last gallium scan. Light microscopy and transmission electron microscopy of the lungs of the test animals showed foci of chronic inflammation around particles of the restorative material. Particles were in vacuoles within alveolar macrophages and also free in interstitium. Control animals had normal histologic conditions. Silver amalgam and gold dental restorations have years of clinical use but the new plastic composite restorative materials are rapidly being introduced into human clinical dental practice. Normal use involves polymerization, grinding, and polishing of the material within the mouth. The chronic inflammation in the lungs of rabbits indicates a need to test dental restorative material for lung biocompatibility before further, extensive clinical use.