Tumor necrosis factor-alpha inhibition reduces CXCL-8 levels but fails to prevent fibrin generation and does not improve outcome in a rabbit model of endotoxic shock

Recent advances in the pathogenetic mechanisms of sepsis-associated acute kidney injury

Sepsis is a serious medical condition that can lead to multi-organ failure and shock, and it is associated with increased mortality. Acute kidney injury (AKI) is a frequent complication of sepsis in critically ill patients, and often requires renal replacement therapy. The pathophysiology of AKI in sepsis has not yet been fully defined. In the past, classic theories were mainly focused on systemic hemodynamic derangements, underscoring the key role of whole kidney hypoperfusion due to reduced renal blood flow. However, a growing body of experimental and clinical evidence now shows that, at least in the early phase of sepsis-associated AKI, renal blood flow is normal, or even increased. This could suggest a dissociation between renal blood flow and kidney function. In addition, the scant data available from kidney biopsies in human studies do not support diffuse acute tubular necrosis as the predominant lesion. Instead, increasing importance is now attributed to kidney damage resulting from a complex interaction between immunologic mechanisms, inflammatory cascade activation, and deranged coagulation pathways, leading to microvascular dysfunction, endothelial damage, leukocyte/platelet activation with the formation of micro-thrombi, epithelial tubular cell injury and dysfunction. Moreover, the same processes, through maladaptive responses leading to fibrosis acting from the very beginning, may set the stage for progression to chronic kidney disease in survivors from sepsis-associated AKI episodes. The aim of this narrative review is to summarize and discuss the latest evidence on the pathophysiological mechanisms involved in septic AKI, based on the most recent data from the literature.

Effects of polymyxin B-immobilized fiber using a rat cecal ligation and perforation model

We evaluated the efficacy of polymyxin B-immobilized fiber (PMX-F) on organ dysfunction using a rat cecal ligation and perforation (CLP) model. Fifteen-week-old Sprague-Dawley rats (n = 21) were divided into three groups. For a PMX group, n = 7, peritonitis was induced by CLP. After 24 hours from CLP, endotoxin adsorption was performed for 1 hour with a PMX-F column. A sham group, n = 7, external circulation was performed with nonimmobilized fiber column. A control group, n = 7, were sacrificed 25 hours after CLP (no hemoperfusion performed). The changes in interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-alpha and plasminogen activator inhibitor (PAI)-1 were measured. The lungs, liver, and kidneys were stained with hematoxylin and eosin and anti-PAI-1 antibodies. Terminal uridine-triphosphate nick-end labeling assay was performed to evaluate apoptosis. The PMX group showed a tendency to decrease in blood levels of IL-6 and PAI-1 compared with the sham group. Anti-PAI-1 antibody staining was seen in the lungs of the control and sham groups. The PMX group showed significantly decreased apoptotic cells in renal tubule cells compared with sham and control groups. We conclude that PMX-F may have inhibited PAI-1 expression in the lungs and decreased apoptosis of renal tubule cells.

Pathophysiology of septic acute kidney injury: what do we really know?

Septic acute kidney injury accounts for close to 50% of all cases of acute kidney injury in the intensive care unit and, in its various forms, affects between 15% and 20% of intensive care unit patients. However, there is little we really know about its pathophysiology. Although hemodynamic factors might play a role in the loss of glomerular filtration rate, they may not act through the induction of renal ischemia. Septic acute renal failure may, at least in patients with a hyperdynamic circulation, represent a unique form of acute renal failure: hyperemic acute renal failure. Measurements of renal blood flow in septic humans are now needed to resolve this pivotal pathophysiological question. Whatever may happen to renal blood flow during septic acute kidney injury in humans, the evidence available suggests that urinalysis fails to provide useful diagnostic or prognostic information in this setting. In addition, nonhemodynamic mechanisms of cell injury are likely to be at work. These mechanisms are likely due to a combination of immunologic, toxic, and inflammatory factors that may affect the microvasculature and the tubular cells. Among these mechanisms, apoptosis may turn out to be important. It is possible that, as evidence accumulates, the paradigms currently used to explain acute renal failure in sepsis will shift from ischemia and vasoconstriction to hyperemia and vasodilation and from acute tubular necrosis to acute tubular apoptosis or simply tubular cell dysfunction or exfoliation. If this were to happen, our therapeutic approaches would also be profoundly altered.

NEUTRALIZATION OF TUMOR NECROSIS FACTOR IN PRECLINICAL MODELS OF SEPSIS

Tumor necrosis factor (TNFalpha), a cardinal early mediator of the innate host inflammatory response, has been an attractive target for therapeutic intervention in human sepsis. However, pooled data from 12 completed randomized controlled trials show only a very modest impact on mortality in a highly heterogeneous population of patients. To gain insight into the preclinical in vivo biology of TNFalpha that might aid in better identifying appropriate patient populations for therapeutic intervention, we undertook a systematic review of published reports of preclinical studies assessing the consequences of neutralization of TNFalpha in models of acute infection or inflammation. We identified 143 reports incorporating 484 unique experimental comparisons in seven different animal species. The effects of neutralization of TNFalpha in these were quite variable. Neutralization of TNFalpha was beneficial in endotoxemia, or after systemic challenge with gram-negative organisms, Staphylococcus aureus, or Group B streptococci. On the other hand, neutralization was detrimental in infections caused by Streptococcus pneumoniae, Candida spp., or intracellular pathogens such as Listeria and Mycobacterium tuberculosis, and in models of pneumonia. Treatment was more efficacious when delivered before infectious challenge, and the therapeutic signal increased as the baseline mortality in the placebo group increased. Evidence of neutralization of TNFalpha bioactivity, and of attenuation of inflammation, was typically accompanied by evidence of impairment of antimicrobial defenses. Multiple specific and nonspecific therapeutic strategies were identified. We conclude that the beneficial effects of TNF in systemic inflammation occur at the cost of impaired antimicrobial defenses, and that a better understanding of the consequences of neutralization of TNFalpha in vivo could aid in better defining optimal patient populations for therapeutic intervention.

The pathogenesis of septic acute renal failure

PURPOSE OF REVIEW

Acute renal failure is a serious condition that affects as many as 20% of ICU patients. The most common causes of acute renal failure in the ICU patient are severe sepsis and septic shock. The mortality of acute renal failure in septic critically ill patients remains high despite our increasing ability to support vital organs. This is partly the result of our poor understanding of the pathogenesis of sepsis-induced renal dysfunction. Accordingly, a review of our current understanding of the pathogenesis of septic acute renal failure is timely and relevant.

RECENT FINDINGS

Throughout the past half century, acute renal failure of acute illness has essentially been considered a hemodynamic disease caused by kidney ischemia, a view derived by findings in animal models. Unfortunately most such models are greatly deficient in that they do not reproduce the high cardiac output, low systemic vascular resistance state typically seen during human sepsis. Furthermore, most models inducing so-called acute tubular necrosis are based on ischemia-reperfusion (renal artery clamping), an event with little relevance to human sepsis. Recent research highlights a new possible and emerging concept for the pathogenesis of septic acute renal failure: acute apoptosis. This concepts fits well with the typical paucity of histologic changes seen in so-called acute tubular necrosis and with growing evidence of a role for apoptosis in organ injury during sepsis and inflammation in general. Furthermore, the authors present evidence that some potential treatments recently shown to affect the mortality of critically ill patients, (activated protein C, intensive insulin treatment, and low-volume mechanical ventilation) might have antiapoptotic activity.

SUMMARY

This review suggests that, on the evidence available, septic acute renal failure is more likely to be an immune or toxic state rather than simply a hemodynamic condition. The authors speculate that future insights into its pathogenesis might lead to a paradigm shift away from the concept of acute tubular necrosis, which has never been convincingly shown in sepsis, to that of acute tubular apoptosis.