Precision-guided, Personalized Intrapleural Fibrinolytic Therapy for Empyema and Complicated Parapneumonic Pleural Effusions: The Case for the Fibrinolytic Potential

Abstract

Complicated pleural effusions and empyema with loculation and failed drainage are common clinical problems. In adults, intrapleural fibrinolytic therapy is commonly used with variable results and therapy remains empiric. Despite the intrapleural use of various plasminogen activators; fibrinolysins, for about sixty years, there is no clear consensus about which agent is most effective. Emerging evidence demonstrates that intrapleural administration of plasminogen activators is subject to rapid inhibition by plasminogen activator inhibitor-1 and that processing of fibrinolysins is importantly influenced by other factors including the levels and quality of pleural fluid DNA. Current therapy for loculation that accompanies pleural infections also includes surgery, which is invasive and for which patient selection can be problematic. Most of the clinical literature published to date has used flat dosing of intrapleural fibrinolytic therapy in all subjects but little is known about how that strategy influences the processing of the administered fibrinolysin or how this influences outcomes. We developed a new test of pleural fluids ex vivo, which is called the Fibrinolytic Potential or FP, in which a dose of a fibrinolysin is added to pleural fluids ex vivo after which the fibrinolytic activity is measured and normalized to baseline levels. Testing in preclinical and clinical empyema fluids reveals a wide range of responses, indicating that individual patients will likely respond differently to flat dosing of fibrinolysins. The test remains under development but is envisioned as a guide for dosing of these agents, representing a novel candidate approach to personalization of intrapleural fibrinolytic therapy.

Keywords: Intrapleural fibrinolytic therapy; plasminogen activators and personalized therapy.

Figure 1

No legend required.

Figure 2

Representative images and histology from rabbits with S. pneumoniae empyema (EMP) in rabbits are illustrated. EMP and pleural injury were induced by intrapleural injection of S. pneumoniae (1×108 cfu). (A) Chest ultrasonography at 1 week after induction of the model. Yellow arrows indicate pleural thickening, adhesions seen as rounded whitish structures; H=heart, D=diaphragm. (B) Postmortem gross visual evaluation of multiloculated empyema following S. pneumoniae-induced empyema in rabbits. (C) The pleural surface displays extensive fibrin (arrows) at the visceral parietal pleural surface, inflammation and subpleural pneumonitis. The visceral pleural surface is oriented at the bottom left portion (thicker arrow indicates lung parenchyma). Representative images shown are shown.

Figure 3

PAI-1: plasminogen activator inhibitor-1. Solid tabs indicate inhibition, arrows indicate cleavage or activation. The fugue indicates the key interactions responsible for plasminogen activation and inhibition in the pleural compartment.

Figure 4. Similarity in the Fibrinolytic Potential of humans and rabbits with empyema

A semi-logarithmic plot of changes in the fibrinolytic activity in pleural fluids of rabbits and humans with infectious pleural injury is illustrated. Low level baseline fibrinolytic activity (FA0) reflects inhibition of plasminogen activation that are characteristically observed in baseline empyema fluid samples. Supplementation of pleural fluid with exogenous plasminogen activator (4 nM uPA) inhibits PAI-1, activates accumulated plasminogen and results in a considerable (up to 3 orders of magnitude) increase in the level of the fibrinolytic activity (FAuPA). Notably, the Fibrinolytic Potential (FP= FAuPA – FAo; baseline) varies significantly among animals and among humans. While two chain uPA was used in this example, any fibrinolysin can be used in this assay.

Figure 5. The plot shows changes in the fluorescence emission with time reflecting formation and degradation of the FITC-fibrin in a well of a 96-well plate

An FITC-fibrin plate assay is described in detail elsewhere23,48. Briefly, thrombin, added at time indicated with arrow, induced polymerization of FITC-fibrinogen and a decrease in the fluorescence emission due to self-quenching of FITC groups in fibrin. Plasmin, added at the time point indicated by the arrow, digests FITC-fibrin and removes the quenching effect, resulting in an increase in the fluorescence emission to the original level. In the FPA, degradation of FITC-fibrin film at the bottom of wells of 96-well plates is used to detect fibrinolytic activity in samples of pleural fluids (Fig. 4) prior to (FA0) and after (FAuPA) supplementation with plasminogen activator.