Cardiovascular and metabolic effects of whole or fractionated gram-negative bacterial endotoxin in the unanesthetized Rhesus monkey

A host-directed macrocyclic peptide therapeutic for MDR gram negative bacterial infections

The emergence of infections by carbapenem resistant Enterobacteriaceae (CRE) pathogens has created an urgent public health threat, as carbapenems are among the drugs of last resort for infections caused by a growing fraction of multi-drug resistant (MDR) bacteria. There is global consensus that new preventive and therapeutic strategies are urgently needed to combat the growing problem of MDR bacterial infections. Here, we report on the efficacy of a novel macrocyclic peptide, minimized theta-defensin (MTD)-12813 in CRE sepsis. MTD12813 is a theta-defensin inspired cyclic peptide that is highly effective against CRE pathogens K. pneumoniae and E. coli in vivo. In mouse septicemia models, single dose administration of MTD12813 significantly enhanced survival by promoting rapid host-mediated bacterial clearance and by modulating pathologic cytokine responses, restoring immune homeostasis, and preventing lethal septic shock. The peptide lacks direct antibacterial activity in the presence of mouse serum or in peritoneal fluid, further evidence for its indirect antibacterial mode of action. MTD12813 is highly stable in biological matrices, resistant to bacterial proteases, and nontoxic to mice at dose levels 100 times the therapeutic dose level, properties which support further development of the peptide as a first in class anti-infective therapeutic.

Differential susceptibility of rhesus monkeys to high doses of endotoxin

We investigated susceptibility of rhesus monkeys ( Macaca mulatta) to Escherichia coli endotoxin (ETX) in two ways. We infused 8 monkeys (group A) with various doses of ETX (1.0-7.5 mg/kg) to assess the effect of dose on shock severity; and we infused 6 monkeys (group B) with 1.0 mg ETX/kg to test biological variability to ETX challenge. Controls were 7 saline-infused monkeys. Systolic pressure, heart rate (HR), temperature, plasma ETX and inflammatory markers — tumor necrosis factor-α (TNF), interleukin-1 (IL-1) and IL-6 — were quantified before and at 1.5, 2.5, 6 and 26 h after infusion. The highest plasma concentrations of ETX (at 1.5 h) — < 8% that infused — correlated well with the infused doses. ETX elicited hypotension and increases in HR in all monkeys. Fever did not occur. The degree of hypotension and increase in HR and death did not correlate with ETX dose (or plasma ETX concentrations). The response of inflammatory cytokines to ETX was greater in nonsurvivors than in survivors. The observed low mortality rate (4/14) suggests that rhesus monkeys are rather resistant to high endotoxin concentrations similar to baboons but unlike humans or chimpanzees. The lack of correlation between ETX dose and shock severity suggests that there is a critical ETX concentration in each animal that leads to controllable or uncontrollable cytokine elevation in plasma, with reversible or irreversible shock, and resulting survival or death.

Splanchnic ischaemia and its role in multiple organ failure

Multiple organ failure remains the leading cause of death in the intensive care unit. Increasing numbers of investigators have focused their attention on the role of gastrointestinal tract in the pathogenesis of this syndrome. Their data indicate that inadequate gut perfusion leads to a measurable imbalance between oxygen delivery and the needs of the tissues, i.e., ischaemia. Gut ischaemia of sufficient duration impairs gastrointestinal tract barrier function, facilitating the passage of enteric bacterial endotoxin into the circulation. It has been hypothesized that production of tumor necrosis factor alpha, and other biologic mediators by endotoxin-stimulated macrophages, triggers a generalized and uncontrolled inflammatory response that ultimately leads to multiple organ failure. Preliminary evidence suggests that survival can be improved significantly if gut ischaemia is promptly identified and aggressively treated by administration of fluids and inotropic drugs, using gastric intramucosal pH as the therapeutic endpoint. Future studies are needed to determine whether additional treatment modalities can improve outcome once the inflammatory response has fully developed.

Multiple Organ Failure Syndrome—Part I: Epidemiology, Prognosis, and Pathophysiology

The multiple organ failure syndrome (MOFS) is the leading cause of death in intensive care units. Although sepsis is an important cause of MOFS, it is clear that MOFS can occur in the absence of infection. The pathophysiology of MOFS is complex and multifactorial and includes derangements in oxygen delivery and consumption, the release of inflammatory and vasoactive mediators capable of inflicting tissue damage, and alterations in the barrier function of the intestinal mucosa. Although advances have been made in our understanding of MOFS, treatment remains nonspecific and largely supportive. Early and aggressive restoration of tissue perfusion, adequate treatment of infection, timely nutritional support, and support of individual failed organs remain the mainstay of therapy. Therapeutic agents directed against the various mediators associated with the pathophysiology of MOFS may prove useful in the future.

Respiratory failure, mechanisms of abnormal gas exchange, and oxygen delivery

Patients with respiratory failure may have abnormal gas exchange based on a number of mechanisms. Each of these mechanisms may indicate a different underlying pathology and thus suggest different therapeutic interventions. In addition, the ability to monitor changes in physiologic function can be complicated but is achievable when proper protocols are followed. It should be clear that an adequate understanding of the underlying physiology is crucial to the successful management of these very difficult patients.

Interaction of leukocytes and endotoxin with the plasmin and kinin systems

Leukocytes can generate a substance that, when added to some partially purified human kininogen, is capable of forming kinins. The addition of endotoxin or polystyrene latex particles to the incubated leukocytes doubled the amount of kinin generated. Certain preparations of kininogen, however, failed to allow kinin formation by the leukocytes. No evidence could be found that an activator of prekallikrein or a kallikrein was present in the granulocyte preparations. However, the addition of highly purified plasminogen to inactive kininogen preparations restored their ability to generate kinins in the presence of leukocytes. All the kininogen preparations that allowed kinin formation when incubated with leukocytes contained plasminogen. These data suggest that a plasminogen activator is present on the leukocyte surface. This activator activates plasminogen to form plasmin which in turn acts on kininogen to release a kinin and thus provides a mechanism for the formation of kinins in inflammatory exudates and during endotoxemia.