Extracorporeal endotoxin removal in a canine model of septic shock

Efficacy of hemofiltration with PEPA membrane for IL-6 removal in a rat sepsis model

Recently, intensive care physicians have focused on continuous hemodiafiltration with a cytokine-adsorbing hemofilter in the treatment of sepsis. We aimed to establish extracorporeal circulation in a rat sepsis model to evaluate the cytokine removal properties of mini-modules using two types of membrane materials. Rats were divided into polyester polymer alloy (PEPA) and cellulose triacetate (CTA) groups as membrane materials of mini-modules. One hour after 0.1 mg/kg of lipopolysaccharide administration, continuous hemofiltration (CHF) was started in each group. Plasma interleukin-6 (IL-6), an important mediator of sepsis, was measured over time during hemofiltration. The peak IL-6 concentration in PEPA group was approximately 13,000 pg/mL, in comparison to approximately 31,000 pg/mL in CTA group. IL-6 clearance in PEPA group was much more than CTA group. Since IL-6 was not detected in the filtrate in PEPA group, it was considered that IL-6 was adsorbed to the membrane. In conclusion, our results suggest that CHF with PEPA hemofilter can be suitable for removing IL-6 from the blood stream efficiently.

Coupled plasma filtration adsorption

BACKGROUND

Severe sepsis and septic shock are perhaps the major cause of morbidity and mortality in Intensive Care. Their pathogenesis is only partly understood. Circulating peptides and lipid-derived substances (so-called mediators), however, appear to participate in the development of organ dysfunction. It might be possible to treat plasma in such a way that the injurious effect of mediators can be attenuated.

INVESTIGATIONS

Several ex vivo studies have shown that it is technically possible to adsorb mediators by means of specially developed sorbents. The application of these sorbents to the treatment of plasma in animals with experimental sepsis has shown that several markers of inflammation can be attenuated and that animal survival can be increased. We have recently transferred such technology to the treatment of human septic shock using a technique called Coupled Plasma Filtration Adsorption (CPFA). CPFA was found to attenuate the hypotension of septic shock and to dramatically alter the immuno-paralytic toxicity of septic plasma. Monocytes of patients treated with CPFA underwent a major improvement in their ability to respond to endotoxin.

CONCLUSIONS

CPFA represents a promising new approach to blood purification in sepsis. The findings associated with its application to humans highlight the importance of continuing to investigate blood purification as a possible approach to the treatment of septic shock, the potential usefulness of the humoral theory of sepsis, and the dominant state of immunosuppression associated with established septic shock.

Endotoxin and cytokine removal in sepsis

Sepsis, the leading cause of mortality in intensive care units, is a complex series of interrelated effects caused by the overproduction of multiple mediators and their unrestrained biological activity. Both proinflammatory and antiinflammatory mediators participate in the high complexity of sepsis and explain the failure of specific therapies to improve survival. Continuous extracorporeal therapies have been proposed as therapeutic options and as tools for blood purification in sepsis. Along these lines and in order to achieve higher clearances and mass removal rates, we studied the effects of plasmafiltration coupled with adsorption and provided in vitro and in vivo evidence that adsoprtion of multiple cytokines, activated complement components, and lipid mediators such as the platelet-activating factor occurs. We also showed that such treatment may lead to improved survival in a rabbit model of sepsis and to improved hemodynamics, reduced norepinephrine dose, and restoration of near-to-normal responsiveness of blood leukocytes to endotoxin in humans. It is anticipated that treatment of plasma, as a modular device to conventional hemofiltration, may pave the way to innovative approaches in the extracorporeal treatment of septic patients.

Adsorption in sepsis

The pathophysiology of sepsis offers a highly complicated scenario. In sepsis, endotoxin or other gram-positive-derived products induce a complex and dynamic cellular response, giving rise to several mediators known to be relevant in the pathogenesis of septic shock such as specific mediators, substances responsible for up- or down-regulation of cytokine receptors and cytokine antagonists, inactivators of translational or transductional pathways, and precursor molecules. In this review, we delve into some new concepts stemming up from the use of sorbents in continuous plasma filtration. Nonspecific simultaneous removal of several mediators of the inflammatory cascade have led to improved outcomes in animal models of septic shock and to improved hemodynamics in a pilot clinical study. It seems of great importance to explore all possible treatment techniques that may have a direct impact on circulating mediators of sepsis and that also may interfere with the imbalance between proinflammatory and anti-inflammatory substances in the critically ill patient with multiple organ failure. In this view, the application of sorbents appears to open new and interesting therapeutic options. The search for innovative treatments specifically targeted to the special needs of the critically ill patients seems therefore more important than the attempt to adjust concepts and technologies that are normally applied to patients with chronic renal failure.

Antiendotoxin strategies

Endotoxin is a potent stimulator of the inflammatory response and is believed to initiate the pathology in Gram-negative sepsis. Agents are being developed that bind and neutralize or block the effects of endotoxin, with the goal of improving outcome in the treatment of sepsis. Strategies discussed in this article include anti-LPS antibodies, LPS binding proteins and lipoproteins, polymyxin B conjugates, lipid A analogues, and extracorporeal techniques for endotoxin removal.

Extracorporeal endotoxin removal by polymyxin B immobilized fiber cartridge: designing and antiendotoxin efficacy in the clinical application

We have developed an extracorporeal hemoadsorption cartridge, the PMX cartridge, to eliminate endotoxin from peripheral blood circulation. As an adsorbent, a polymyxin B covalently immobilized fiber (PMX-F) was developed. After the optimization of the condition of immobilization, fixed polymyxin B maintained its ability to adsorb endotoxin and its bactericidal activity. PMX-F could detoxify many kinds of endotoxin in vitro. Fixed polymyxin B was estimated to interact with the lipid A portion of endotoxin. Utilization of fibrous adsorbents enabled us to design the PMX cartridge with a large surface area and low blood pressure drop in the blood flow compartment and to apply it safely to the direct hemoperfusion procedure. In Japan, the PMX cartridge is now being clinically applied as one of the therapeutical interventions for sepsis, septic shock, and septic multiple organ failure. In multicenter clinical studies, the blood endotoxin level has been significantly decreased. Accompanied with elimination of endotoxin, hemodynamic abnormalities such as low blood pressure and low systemic vascular resistance were significantly improved. In more recent multicenter studies, the average number of failed organs; severity of illness score, such as Goris score; and vasopressor dosage were significantly decreased. The PMX cartridge is expected to be effective in the intervention for the treatment of septic shock. Endotoxin may be one of the therapeutical targets for the treatment of sepsis.

Extracorporeal adsorbent-based strategies in sepsis

Gram-negative bacterial sepsis remains a challenging diagnostic and therapeutic dilemma to the practicing clinician. Bacterial-derived products (eg, gram-negative bacterial lipopolysaccharide or endotoxin) and host inflammatory mediators (eg, tumor necrosis factor-alpha and interleukin-1) are believed to play a pivotal role in the pathogenesis of sepsis and septic shock. Despite the many advances in the treatment of sepsis, mortality rates in septic patients remain high. Indeed, numerous clinical trials using biologically engineered immunotherapies targeting specific inflammatory mediators have proven unsuccessful. This lack of success has led to a renewed interest in blood purification techniques using extracorporeal therapies. During sepsis, circulating bacterial-derived products as well as inflammatory mediators can be reduced and/or eliminated by various extracorporeal adjunctive therapies such as plasma exchange, continuous renal replacement, and adsorbent-based therapies. Adsorbents have commonly been used orally for gastrointestinal removal of toxins or drugs. However, their potential use in sepsis has received little attention. The incorporation of adsorbents in hemoperfusion columns has allowed their use for the removal of toxic compounds from the circulatory system. Adsorbents developed for use in sepsis can bind toxins in a nonselective (eg, charcoal), selective (eg, polymyxin B-immobilized polystyrene-derivative fiber), or specific (eg, antibody-coated microsphere-based detoxification system) way. However, despite an explosive development in the experimental use of these promising therapies, randomized clinical trials are currently lacking. In summary, a multi-disciplinary complex therapeutic approach remains a prerequisite to the successful treatment of sepsis.