Experimental empyema. Time course and pathogenesis of pleural fluid acidosis and low pleural fluid glucose

HDAC Inhibitor Abrogates LTA-Induced PAI-1 Expression in Pleural Mesothelial Cells and Attenuates Experimental Pleural Fibrosis

Lipoteichoic acid (LTA) stimulates pleural mesothelial cell (PMC) to overproduce plasminogen activator inhibitor-1 (PAI-1), and thus may promote pleural fibrosis in Gram-positive bacteria (GPB) parapneumonic effusion (PPE). Histone deacetylase inhibitor (HDACi) was found to possess anti-fibrotic properties. However, the effects of HDACi on pleural fibrosis remain unclear. The effusion PAI-1 was measured among 64 patients with GPB PPE. Pleural fibrosis was measured as radiographical residual pleural thickening (RPT) and opacity at a 12-month follow-up. The LTA-stimulated human PMCs and intrapleural doxycycline-injected rats were pretreated with or without the pan-HDACi, m-carboxycinnamic acid bis-hydroxamide (CBHA), then PAI-1 and collagen expression and activated signalings in PMCs, and morphologic pleural changes in rats were measured. Effusion PAI-1 levels were significantly higher in GPB PPE patients with RPT > 10 mm (n = 26) than those without (n = 38), and had positive correlation with pleural fibrosis shadowing. CBHA significantly reduced LTA-induced PAI-1 and collagen expression via inhibition of JNK, and decreased PAI-1 promoter activity and mRNA levels in PMCs. Furthermore, in doxycycline-treated rats, CBHA substantially repressed PAI-1 and collagen synthesis in pleural mesothelium and minimized pleural fibrosis. Conclusively, CBHA abrogates LTA-induced PAI-1 and collagen expression in PMCs and attenuates experimental pleural fibrosis. PAI-1 inhibition by HDACi may confer potential therapy for pleural fibrosis.

Relationship of pleural fluid pH and glucose: a multi-centre study of 2,971 cases

Background

Pleural fluid pH and glucose levels are both recommended in the workup of pleural effusions. Whether their levels correlate and predict each other or contribute independent knowledge is unclear. We aimed to investigate the pH/glucose relationship, assess their concordance and ascertain whether performing both tests provides additional information to performing either test alone.

Methods

The pH and glucose measurements from 2,971 pleural fluid samples, from three centers in Spain, UK and Australia, were categorized into Cancer (n=1,045), Infection (n=544), Tuberculosis (n=249) and Others (n=1,133) groups. The relationship between pH and glucose values and their concordance at clinically relevant cutoffs (pH 7.2 and glucose 3.3 mmol/L) were assessed.

Results

The mean pH of the cohort was 7.38 (SD 0.22) and median glucose 5.99 (range, 0.00-29.36) mmol/L. A regression model of the relationship between glucose (log-transformed) and pH with a restricted cubic spline showed linear (P<0.01) and nonlinear effects (P<0.01). The relationship was strong with a narrow confidence interval but the prediction interval was wide. Most (91.9%) samples were concordant using pH and glucose levels at cutoffs of 7.20 and 3.30 mmol/L respectively. Using pH alone, without glucose, captured 95.0% of the infection-related effusions with either pH or glucose below cutoff and glucose alone identified 91.7%.

Conclusions

Pleural fluid pH and glucose have a strong non-linear relationship but, in most situations, the level of one cannot accurately predict the other. Concordance rates were high and either test is sufficient in the majority of cases.

Induction of pleural empyema in rats by thoracentesis with intrapleural pressure monitoring

Our objective was to evaluate experimental induction of empyema in rats by intrapleural inoculation of Staphylococcus aureus by means of thoracentesis with pleural pressure monitoring. Forty female albino Wistar rats, anesthetized with droperidol and fentanyl, underwent intrapleural inoculation of a 0.2-ml solution. Group I ( N=25) received 10(10) colony-forming units/ml of Staphylococcus aureus cultivated in brain-heart infusion agar (BHI); group II (N = 15), the control group, received sterile BHI agar. Rats were inoculated after right hemithorax thoracentesis with a needle connected to an oscilloscope for pressure monitoring to confirm that the needle was inside the pleural space. Animals were killed after 3 (groups Ia and IIa) to 5 (groups Ib and IIb) days with sodium pentobarbital. The macroscopic changes, amount of pleural fluid, and anatomopathological aspects of pleura and lungs were recorded, as well as death causes and bacteriological findings of pleural fluid for animals that died before the time established for euthanasia. In group I, three animals died of thoracentesis complications, and five others died in the first 24 h due to septicemia; blood and spleen cultures isolated the bacteria previously inoculated. In group II, there was one death of unknown cause. Of the 17 rats inoculated with bacteria, nine (group Ia) were killed on the 3rd day; all had bacteria in pleural fluid (volume 0.5-3.8 ml). The other eight rats (group Ib) were killed on the 5th day; three (39.5%) had pleural fluid with bacteria (0.5-1.5 ml), and five (60.5%) had no pleural fluid. Rats from group II killed on the 3rd (group IIa) and 5th (group IIb) days had no pleural fluid. Pathologic examination revealed inflammatory infiltrate (93.75%) and fibrin (18.75%) in pleura, and inflammatory interstitial infiltrate (12.5%) in the right lung in group I; no changes were observed in 93.3% of the lungs in group II. Macroscopic examination revealed only turbid and bloody pleural fluid (class I) without pleural adhesions. Pleural inflammatory infiltrate was found in rats that received the bacteria but had no fluid at necropsy (class 0). One control rat, although with no clinical signs of disease or pleural fluid, had signs of pleural and pulmonary infection at necropsy. We conclude that empyema may be induced in rats by the inoculation of Staphylococcus aureus by means of thoracentesis with pleural pressure monitoring. The highest amount of pleural fluid was observed 3 days after bacterial inoculation.

Pharmacokinetics and therapeutic efficacy of gentamicin in an experimental pleural empyema rabbit model

The pharmacokinetics and therapeutic efficacy of gentamicin were investigated in an experimental pleural empyema rabbit model. Pleural effusion was induced by the intrapleural administration of turpentine, and empyema was induced by direct inoculation of the effusion with Klebsiella pneumoniae. Pleural empyema compared with effusion was characterized by lower pH, oxygen tension (PaO2), and glucose levels and higher leukocyte count, lactic acid concentration, and PaCO2. After a single administration, gentamicin was first detectable in the pleural fluid at 60 min, whereas peak levels in empyema were observed at 180 min. Gentamicin persisted in the empyema longer than in blood. Animals treated with gentamicin only had 60% bacterial cure on day 7; those treated with gentamicin in an oxygen chamber had 100% cure on day 5 (P = 0.004). Low oxygen tension diminished the antibacterial efficacy of gentamicin in this model. An increase in oxygen tension improved the therapeutic results without alteration of the pharmacokinetics of gentamicin.

Bacillus Calmette-Guérin-stimulated neutrophils release chemotaxins for monocytes in rabbit pleural spaces and in vitro

Neutrophils are often seen first at sites of granulomatous inflammation but their contribution to monocyte recruitment and granuloma formation is unknown. We tested the hypothesis that neutrophils release chemotaxins which attract monocytes. We found that rapid accumulations of fluid and influxes of neutrophils followed by monocytes occurred in bacillus Calmette--Guérin (BCG)-sensitized rabbits given BCG intrapleurally but did not occur in nitrogen mustard-treated (neutropenic) BCG-sensitized rabbits given BCG intrapleurally--unless the rabbits were also given intrapleural injections of neutrophils. We also found monocyte chemotaxins in pleural spaces of control and neutrophil-reconstituted neutropenic but not in neutropenic rabbits given BCG intrapleurally. Moreover, pleural fluid monocyte chemotaxins had molecular weights (12,000-15,000 and 1,000) that were similar to molecular weights of monocyte chemotaxins present in supernatants from mixtures of neutrophils and BCG in vitro. In addition, intrapleural injection of neutrophils and BCG or supernatants from in vitro mixtures of neutrophils and BCG (but not neutrophils or BCG alone) increased the numbers of monocytes and 3H cell pellet activity in pleural fluids from untreated neutropenic rabbits or neutropenic rabbits previously injected intravenously with 3[H]methyl thymidine-labeled monocytes. Furthermore, fewer BCG were recovered from pleural fluids of BCG-sensitized control compared to neutropenic rabbits given BCG, and at autopsy 10 d after instillation of BCG, control but not neutropenic rabbits had well-defined granulomas without adhesions on their pleural surfaces. Our results suggest that BCG stimulates neutrophils to release chemotaxins that recruit monocytes, and that these responses might contribute to granuloma formation in tuberculous pleurisy.