Elevated Carbon Monoxide in the Exhaled Breath of Mice during a Systemic Bacterial Infection

Abstract

Blood is the specimen of choice for most laboratory tests for diagnosis and disease monitoring. Sampling exhaled breath is a noninvasive alternative to phlebotomy and has the potential for real-time monitoring at the bedside. Improved instrumentation has advanced breath analysis for several gaseous compounds from humans. However, application to small animal models of diseases and physiology has been limited. To extend breath analysis to mice, we crafted a means for collecting nose-only breath samples from groups and individual animals who were awake. Samples were subjected to gas chromatography and mass spectrometry procedures developed for highly sensitive analysis of trace volatile organic compounds (VOCs) in the atmosphere. We evaluated the system with experimental systemic infections of severe combined immunodeficiency Mus musculus with the bacterium Borrelia hermsii. Infected mice developed bacterial densities of ∼107 per ml of blood by day 4 or 5 and in comparison to uninfected controls had hepatosplenomegaly and elevations of both inflammatory and anti-inflammatory cytokines. While 12 samples from individual infected mice on days 4 and 5 and 6 samples from uninfected mice did not significantly differ for 72 different VOCs, carbon monoxide (CO) was elevated in samples from infected mice, with a mean (95% confidence limits) effect size of 4.2 (2.8–5.6), when differences in CO2 in the breath were taken into account. Normalized CO values declined to the uninfected range after one day of treatment with the antibiotic ceftriaxone. Strongly correlated with CO in the breath were levels of heme oxygenase-1 protein in serum and HMOX1 transcripts in whole blood. These results (i) provide further evidence of the informativeness of CO concentration in the exhaled breath during systemic infection and inflammation, and (ii) encourage evaluation of this noninvasive analytic approach in other various other rodent models of infection and for utility in clinical management.

Chromosome Sequence of Borrelia miyamotoi, an Uncultivable Tick-Borne Agent of Human Infection

“…To obtain cells for DNA, we infected severe-combined immunodeficient mice (C.BKa- Igh b /IcrCrl) as described (9). When bacterial densities in the blood reached ~10 7  cells/ml, the mice were terminally exsanguinated under anesthesia.…”

Elevated Carbon Monoxide to Carbon Dioxide Ratio in the Exhaled Breath of Mice Treated With a Single Dose of Lipopolysaccharide

“…Plasma samples were subjected to bead-based immunoassays at Myriad RBM (Austin, Texas) for the 59 analytes of the RodentMAP version 2.0 panel. Quantitative reverse transcription polymerase chain reaction for the mouse heme oxygenase-1 gene ( HMOX1 ) and β-actin transcripts was carried out as described on total RNA extracted from whole blood [ 7 ]. Standards were clones of the targets in a plasmid vector.…”

“…Breath samples from individual lightly restrained, unanesthetized mice were obtained with a nose-only multiport collection chamber and attached high-efficiency particular air filter and electropolished stainless steel canister as described previously [ 7 , 11 , 12 ]. Mice were first accommodated over 4 days of training to restraint without distress or interference with respiratory effort.…”

“…To this end, we applied the analytical capabilities of atmospheric chemistry for detection and quantitation of volatile organic chemicals in the breath to an infection experimental model in mice [ 7 ]. With only approximately 0.05% the mass of an adult human, mice pose a technical challenge for breath analysis.…”

Assessment of exhaled carbon monoxide in exacerbations of chronic obstructive pulmonary disease

“…In some animal models, systemic bacterial infection was also associated with an increased CO concentration in exhaled breath (3).…”