Recent Developments in the Identification of Novel Therapeutic Targets for the Treatment of Patients with Sepsis and Septic Shock

Altered plasma proteome during an early phase of peritonitis-induced sepsis

Sepsis is a systemic response to infection commonly found in critically ill patients and is associated with multi-organ failure and high mortality rate. Its pathophysiology and molecular mechanisms are complicated and remain poorly understood. In the present study, we performed a proteomics investigation to characterize early host responses to sepsis as determined by an altered plasma proteome in a porcine model of peritonitis-induced sepsis, which simulated several clinical characteristics of human sepsis syndrome. Haemodynamics, oxygen exchange, inflammatory responses, oxidative and nitrosative stress, and other laboratory parameters were closely monitored. Plasma samples were obtained from seven pigs before and 12 h after the induction of sepsis, and plasma proteins were resolved with two-dimensional gel electrophoresis (n=7 gels/group; before being compared with during sepsis). The resolved proteins were stained with the SYPRO Ruby fluorescence dye and subjected to quantitative and comparative analyses. From approx. 1500 protein spots visualized in each gel, levels of 36 protein spots were significantly altered in the plasma of animals with sepsis (sepsis/basal ratios or degrees of change ranged from 0.07 to 21.24). Q-TOF (quadrupole–time-of-flight) MS and MS/MS (tandem MS) identified 30 protein forms representing 22 unique proteins whose plasma levels were increased, whereas six forms of five unique proteins were significantly decreased during sepsis. The proteomic results could be related to the clinical features of this animal model, as most of these altered proteins have important roles in inflammatory responses and some of them play roles in oxidative and nitrosative stress. In conclusion, these findings may lead to a better understanding of the pathophysiology and molecular mechanisms underlying the sepsis syndrome.

Sepsis in 2003: are we still in the middle of nowhere?

PURPOSE OF REVIEW

Although enthusiasm of intensivists has been raised during the last 2-3 years due to several successful clinical trials, severe sepsis and septic shock still have an increasing incidence with more or less unchanged mortality. Within the last 12 months, the progress in sepsis research covering definitions, epidemiology, pathophysiology, diagnosis, standard and adjunctive therapy, as well as experimental approaches is encouraging. In this review, state-of-the-art publications of 2003 are presented to elucidate the possible impact on clinical routine.

RECENT FINDINGS

The rationale for using a new definition based on the PIRO system has been widely acknowledged, although it is not yet applicable in clinical practice. This includes genomic information for stratifying subgroups of patients, and a broader field of laboratory diagnostics due to clinical studies and basic research on the cellular mechanisms of inflammation and organ dysfunction. Early diagnosis is important for a fast implementation of specific therapies, and it has been confirmed that the time until the start of therapy has an impact on patient outcome. Thorough data analysis of successful trials with activated protein C has revealed encouraging details on long-term outcome and subgroup effects. Together with new findings on low-dose hydrocortisone, this stresses the relevance of adjunctive therapy in severe sepsis and septic shock.

SUMMARY

Scientific progress in areas of sepsis has been continuing throughout 2003, although the challenges are still enormous. The identification of more specific markers and new therapeutic approaches will hopefully improve the diagnosis, monitoring of therapy, and outcome in the septic patient.

High level expression of His-tagged colicin 5 in E. coli and characterization of its narrow-spectrum bactericidal activity and pore-forming action

Since antibiotics with a broad spectrum of activity would select for resistance among the normal flora, colicins having a narrow spectrum of activity can potentially be developed as novel antibiotics. Colicin-based bactericidal proteins with modified spectra of activity might also be developed by further gene fusion or gene modification. To achieve these goals, it is necessary to first build an efficient system to produce large amounts of colicin. In the presence of an immunity gene, we successfully constructed an expression vector pQE30-cfa-cfi producing high levels of His-tagged colicin 5 (60-80 mg/L). We found that the purified His-tagged colicin 5 possesses narrow-spectrum bactericidal activity against nonimmune Escherichia coli cells. It is highly toxic to sensitive E. coli cells at a low concentration of 0.01 microg/ml, while it is nontoxic to other tested gram-negative bacteria, gram-positive bacteria and yeast at a high concentration of 1000 microg/ml. His-tagged colicin 5 kills sensitive cells by permeabilizing their cell membranes. It is not hemolytic to rabbit erythrocytes and has no obvious cytotoxicity to other nucleated mammalian cells at a high concentration of 500 microg/ml. The His-tagged colicin 5 is similar to wild-type colicin 5 in spectrum and bactericidal activity against E. coli. It is a potential novel antibiotic particularly for treating human and animal infections caused by pathogenic E. coli. Besides producing high level of colicin 5, the highly efficient expression vector constructed here might also be a useful tool to develop colicin-based artificial bactericidal proteins.

Innate immune responses during infection

The innate immune system senses bacteria in the environment and defends against infection. Here we will discuss two types of sensor protein families. The plasma membrane receptors that comprise the Toll-like receptor (TLRs) family and the intracellular proteins termed NOD1 and NOD2. These proteins directly bind bacterial products such as lipopolysaccharides (LPS), peptidoglycan fragments, bacterial DNA, and receptor binding leads to intracellular signaling and gene expression. TLR signaling involves members of the MyD88 family of adaptor proteins. In contrast NOD1 or NOD2 utilize pathways that do not depend on the MyD88 family members.

Importance of hemostatic gene polymorphisms for susceptibility to and outcome of severe sepsis

Individuals vary considerably in their susceptibility to infection and in their ability to recover from apparently similar infectious processes. These differences can be partially explained by polymorphisms of the genes encoding proteins involved in mediating and controlling the innate immune response, the inflammatory cascade, coagulation, and fibrinolysis. It is evident from experimental studies that dysregulation of the coagulation system, which is characteristic of the pathophysiology of septic shock (a procoagulant and antifibrinolytic state), contributes to systemic inflammation and death in sepsis. Several genetic variations in proteins that increase coagulation or impair anticoagulation and fibrinolysis have been described. Thus, polymorphisms have been reported in prothrombin, fibrinogen, factor V, tissue factor, endothelial protein C receptor, and plasminogen activator inhibitor-1 genes. Some of them are associated with an increased risk of pulmonary emboli, acute myocardial infarction, stroke, and severe sepsis. Hence, the deletion polymorphism (4G) within the promoter region of the plasminogen activator inhibitor-1 gene leads to impaired fibrinolysis and influences the severity and outcome of meningococcal disease and the susceptibility to severe sepsis and multiple organ failure after trauma. The factor V Leiden mutation is associated with thrombotic events and has been reported to exacerbate purpura fulminans in meningococcal infection. Surprisingly, this genetic variant seems to provide a survival advantage in severe sepsis, underlying the extreme complexity of the interaction between inflammation and coagulation. The study of genetic polymorphisms might provide important insights into the pathogenesis of severe sepsis and could make it possible to identify individuals who are at risk of developing or dying of severe infections. As genetic associations are discovered, medical practice can become more preemptive, using the predictive ability of genetics to anticipate disease and recommend therapy.