Bile Acid Aspiration in Suspected Ventilator-Associated Pneumonia

doi:10.1378/chest.08-2668

Chest

Volume 136, Issue 1, July 2009, Pages 118-124

https://doi.org/10.1378/chest.08-2668 Get rights and content

Aims

The aims of this study were to measure the levels of bile acids in patients with suspected ventilator-associated pneumonia (VAP) and provide a possible pathway for neutrophilic inflammation to explain its proinflammatory effect on the airway.

Methods

Bile acid levels were measured by spectrophotometric enzymatic assay, and liquid chromatography mass spectrometry was used to quantify the major bile acids. Alveolar cells were grown on modified air-liquid interface culture inserts, and bile acids were then employed to stimulate the cells. Reverse transcriptase polymerase chain reaction and Western blots were used to determine the involved gene expression and protein levels.

Results

The mean (± SE) concentration of total bile acids in tracheal aspirates was 6.2 ± 2.1 and 1.1 ± 0.4 μmol/L/g sputum, respectively, for patients with and without VAP (p < 0.05). The interleukin (IL)-8 level was significantly higher in the VAP group (p < 0.05). The major bile acid, chenodeoxycholic acid, stimulated alveolar epithelial cells to increase IL-8 production at both the messenger RNA and protein level through p38 and c-Jun N-terminal kinase (JNK) activation. The selective p38 and JNK inhibitors, as well as dexamethasone, successfully inhibited IL-8 production.

Conclusion

These data suggest that early intervention to prevent bile acid aspiration may reduce the intensity of neutrophilic inflammation in intubated and mechanically ventilated patients in the ICU.

Section snippets

Study Setting and Population

This prospective observational study was conducted between June 2006 and October 2006 in one ICU in a university-affiliated medical center. The education program used in this ICU to reduce the incidence of VAP was adopted according to the policy reported by Zack et al.¹⁵ We analyzed the levels and influence of bile acids in patients with suspected VAP. All consecutive patients who had received mechanical ventilation in our ICU for at least 4 days were enrolled in the study if they had suspected

Bile Acids and IL-8 in the Airway

Airway secretions were collected from intubated and mechanically ventilated patients with or without suspected VAP. Table 1 shows the characteristics of these patients and the organisms on culture. The concentrations of total bile acids and IL-8 were significantly higher in the suspected VAP group than those without suspected VAP. Figure 1, A, shows the levels of total bile acids in the airway secretions. For further analysis of bile acids in the airways, liquid chromatography-electrospray

Discussion

Aspiration has been considered to be an important risk factor for the development of VAP.19, 20, 21 Placing mechanically ventilated patients in a semirecumbent position is strongly recommended in education programs to prevent VAP15, 22; on the contrary, one well-conducted study²³ demonstrated that difference in treatment position angle (28° vs 10°) did not reduce the incidence of VAP. Another view is that aspiration may introduce bacterial pathogens into the respiratory tract. Several studies²⁰

Conclusions

The bile acid levels in the airway are significantly higher in intubated and mechanically ventilated patients with suspected VAP than in those without VAP. The consequence of alveolar epithelial cells exposure to bile acids may be enhanced neutrophilic inflammation through the activation of MAP kinase and subsequent IL-8 production.

Acknowledgment

We thank Dr. Chen for his valuable assistance in the analysis of bile acid components.

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Cited by (38)

Aspiration of conjugated bile acids predicts adverse lung transplant outcomes and correlates with airway lipid and cytokine dysregulation
2021, Journal of Heart and Lung Transplantation
Citation Excerpt :
This study has shown particular relevance for TCDCA. The unconjugated form of this primary bile acid, CDCA, has been previously implicated in cellular damage, permeability and increased reactive oxygen species.17-19 The conjugation with taurine adds a sulfonic acid functional group to the molecule, increasing its acidity and solubility.
Duodeno-gastroesophageal reflux aspiration is associated with chronic lung allograft dysfunction (CLAD). Reflux aspirate can contain bile acids (BA), functional molecules in the gastro-intestinal tract with emulsifying properties. We sought to determine and quantify the various BA species in airways of the lung transplant recipients to better understand the various effects of aspirated BA that contribute to post-transplantation outcomes.
Bronchial washings (BW) were prospectively collected from lung transplant recipients and subsequently assayed by liquid chromatography-mass spectrometry for 13 BA and 25 lipid families. Patients were monitored for CLAD, rejection, inflammation and airway infections.
Detectable BA were present in 45/50 patients (90%) at 3 months after transplant. Elevated BA and predominance of conjugated species were independent predictors of CLAD (hazard ratio 7.9; 95% confidence interval 2.7-23.6; p < 0.001 and 7.3; 2.4-22; p < 0.001, respectively) and mortality (hazard ratio 4.4; 1.5-12.7; p = 0.007 and 4.8; 1.4-15.8; p = 0.01, respectively). High BA associated with increased positive bacterial cultures (60% vs 25%, p = 0.02). Primary conjugated species independently correlated with the rate of bacterial cultures during the first-year post-transplant (Beta coefficient: 0.77; 0.28-1.26; p = 0.003) and changes in airway lipidome and cytokines.
Higher BA levels and predominance of conjugated BA are independent predictors of chronic lung allograft dysfunction, mortality and bacterial infections. Primary conjugated BA are related to distinct changes in airway lipidome and inflammatory cytokines. This elucidates novel evidence into the mechanism following BA aspiration and proposes novel markers for prediction of adverse post-transplant outcomes.
The profibrotic effects of chronic microaspiration of bile acids on lungs of rats at different stages
2020, International Immunopharmacology
Citation Excerpt :
Thereby, presumably, non-acid components, e.g. bile acids, may be active players in the formation of pulmonary fibrosis. Studies reported that the major components of bile acids (DCA and CDCA) have all been detected in airways of patients with GERD-associated lung diseases [14,15]. Our previous study revealed that microaspiration of bile acids could promote the development of pulmonary fibrosis in vivo [9].
This study aimed to explore the profibrotic effects of chronic microaspiration of two major bile acids, including chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA), on lungs of rats at different stages, as well as the underlying mechanisms in vivo. A rat model was induced by weekly intratracheal instillation of DCA and CDCA. Our results showed that chronic microaspiration of bile acids resulted in alveolar structure disorder, and inflammatory cells infiltration in the pulmonary interstitium at the early stage. Subsequently, numerous fibroblasts were proliferated, and collagen deposition was profoundly increased over the interstitium of the airways and vessels. Compared with control group, the expression of α-smooth muscle actin, type I collagen, hydroxyproline, transforming growth factor-β1 (TGF-β1), and matrix metalloproteinase-9 in the lung tissues were remarkably elevated at the 2nd week, reached the highest level at the 6th week, and maintained high at the 8th week in both DCA- and CDCA-treated groups (P < 0.05). Furthermore, chronic microaspiration of bile acids led to higher levels of glutathione and malondialdehyde, while lower level of superoxide dismutase in lung tissues compared with controls (P < 0.05), thereby resulting in the oxidant/antioxidant enzyme imbalance in the formation of fibrosis. In addition, we also found a consistent growth in the expression of farnesoid X receptor (FXR) in both DCA- and CDCA-treated groups. Our findings suggested that chronic microaspiration of bile acids could initiate the process of pulmonary fibrosis from the early phase and promote its progression in a time-dependent manner, which likely involved the TGF-β1, oxidative stress, and FXR-related pathways.
The effect of gastric juice on interleukin-8 production by cystic fibrosis primary bronchial epithelial cells
2013, Journal of Cystic Fibrosis
Citation Excerpt :
In LTx patients, clear correlations between levels of bile acids and IL-8 in BALF have been found [9,10]. Wu et al. demonstrated that exposure of airway epithelial cells in vitro to chenodeoxycholic acid, a major component of bile acids, is capable to induce an increase in IL-8 production [26]. Pepsin itself is inactive at pH 6.5, however, it remains stable to pH 8.0 and can be reactivated when pH is reduced.
CF patients are often treated with proton pump inhibitors (PPIs) to reduce acidic gastro-esophageal reflux (GER) and bronchial aspiration of duodeno-gastric contents is common in CF. We have previously demonstrated that gastric juice (GJ) from patients “on” PPI can induce interleukin-8 (IL-8) production by bronchial epithelial cells in culture. We hypothesized that such effect would be more pronounced in CF patients known to have high inflammatory susceptibility. We aimed to evaluate the effect of GJ on IL-8 production by primary bronchial epithelial cells (PBEC), derived from a CF patient and a healthy subject.
PBEC obtained from one donor (normal PBEC) and one receptor (CF-PBEC) for lung transplantation were stimulated with GJ from patients “off” and “on” PPI. IL-8 levels were measured in the supernatant.
GJ from patients “on” PPI provoked a significant higher IL-8 production compared to GJ from patients “off” PPI, both in normal PBEC [462 (200–1468) vs. 11 (4–28) pg/ml, p = 0.0001] as in CF-PBEC [1468 (841–2449) vs. 85 (26–131) pg/ml, p < 0.0001]. Exposure of the cells to GJ “off” PPI and “on” PPI provoked significantly higher IL-8 production in the CF-PBEC compared to the normal PBEC [“off” PPI 85 (26–131) vs. 11 (4–28) pg/ml, p = 0.01; “on” PPI 1468 (841–2449) vs. 462 (200–1468) pg/ml, p = 0.01]. Filtration (0.20 μm) of the GJ “on” PPI, to eliminate large particles and bacterial sub-products, resulted in a significant decrease of IL-8 production.
Patients with CF, treated with PPIs, have GJ with high pH and high endotoxin levels. These patients often have GER and bronchial aspiration. The aspirated material (GJ “on” PPI) has a significantly enhanced inflammatory effect on CF bronchial epithelial cells in culture. As chronic PPI treatment in CF may result in a paradoxically increased inflammatory effect in the airways, alternative anti-reflux therapies should be considered in CF.
Are the enzymatic methods currently being used to measure bronchoalveolar lavage bile salt levels fit for purpose?
2013, Journal of Heart and Lung Transplantation
Microaspiration after gastroesophageal reflux has been implicated in the chronic loss of allograft function in lung transplant patients. Bronchoalveolar lavage fluid (BALF) assessment for pepsin and bile salts is a common method to document reflux and aspiration. Clinically used methods for bile salt analysis include tandem mass spectrometry and diagnostic enzymatic kits designed to measure bile salts in serum. In clinical research, the enzymatic kits have been commonly used for BALF assays in lung transplant recipients, with reports of detection limits of 0.2 μmol/liter, and the levels used to inform clinical decisions. This study assessed the sensitivity of detection by 2 enzymatic assay kits compared with tandem mass spectrometry.
These 2 kits were used to measure (1) the absorbance changes for 0 to 50 μmol/liter bile salts, (2) levels in gastric juice (10–10,010 μmol/liter), and (3) bile salt levels of 40 BALF samples that were also measured using tandem mass spectrometry (0.01–1.19 μmol/liter). Measurements of pH/impedance were done in 14 of 15 patients.
Neither kit had detection limits as low as claimed in previous BALF studies. The kits could be made more sensitive with a longer incubation time, (5 μmol/liter). All patients had detectable lavage bile acids using mass spectroscopy, 71% had pathologic distal gastroesophageal reflux, and 43% had pathologic proximal reflux.
The enzymatic kits are not sensitive enough for use in situations where bile salt levels are much below 5 μmol/liter, which is the case in BALF. In addition, reports in the literature of levels significantly below 5 μmol/liter need reassessing. Tandem mass spectrometry with a lower limit of detection of 0.01 μmol/liter should be the method of choice.
Aspiration Pneumonia
2024, Seminars in Respiratory and Critical Care Medicine
Bile acid-induced lung injury: Update of reverse translational biology
2022, American Journal of Physiology - Lung Cellular and Molecular Physiology

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This work was supported by research grants from Taipei Veterans General Hospital (V96C1-065).

The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).

^*: These authors made equal contributions to this study.

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Chest

Original ResearchCritical Care MedicineBile Acid Aspiration in Suspected Ventilator-Associated Pneumonia

Aims

Methods

Results

Conclusion

Section snippets

Study Setting and Population

Bile Acids and IL-8 in the Airway

Discussion

Conclusions

Acknowledgment

Am J Transplant

J Thorac Cardiovasc Surg

Chest

Chest

Chest

Lancet

Chest

Lancet

J Hosp Infect

Gastroenterology

Chest

Respir Med

Pulm Pharmacol Ther

Tracheobronchial aspiration of gastric contents in critically ill tube-fed patients: frequency, outcomes, and risk factors

Crit Care Med

Raised bile acid concentrations in SIDS lungs at necropsy

Arch Dis Child

Bile acid pneumonia: a “new” form of neonatal respiratory distress syndrome?

Pediatrics

Original Research
Critical Care Medicine
Bile Acid Aspiration in Suspected Ventilator-Associated Pneumonia