R. S. Hotchkiss

Sepsis induces extensive lymphocyte apoptosis, a process which may be beneficial to host survival by down-regulating the inflammatory response or, alternatively, harmful by impairing host defenses. To determine the beneficial vs. adverse effects of lymphocyte apoptosis in sepsis, we blocked lymphocyte apoptosis either by N-benzyloxycarbonyl-Val-Ala-Asp(O-methyl) fluoromethyl ketone (z-VAD), a broad-spectrum caspase inhibitor, or by use of Bcl-2 Ig transgenic mice that selectively overexpress the antiapoptotic protein Bcl-2 in a lymphoid pattern. Both z-VAD and Bcl-2 prevented lymphocyte apoptosis and resulted in a marked improvement in survival. z-VAD did not decrease lymphocyte tumor necrosis factor-alpha production. Considered together, these two studies employing different methods of blocking lymphocyte apoptosis provide compelling evidence that immunodepression resulting from the loss of lymphocytes is a central pathogenic event in sepsis, and they challenge the current paradigm that regards sepsis as a disorder resulting from an uncontrolled inflammatory response. Caspase inhibitors may represent a treatment strategy in this highly lethal disorder.

Severe bloodstream-borne infection--i.e., sepsis--and the resulting multiorgan failure are now the most common cause of death in many intensive care units. One of the most fundamentally important and controversial issues concerning the pathophysiology of sepsis is the role of intracellular free calcium concentration ([Ca2+]i) in this disorder. Because of the critical role of calcium as an intracellular second messenger and as a potential cellular toxin, resolution of this issue is crucial. Using 19F NMR spectroscopy and the calcium indicator 5,5'-difluoro-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate we demonstrate in the intact perfused organ, the rat thoracic aorta, that [Ca2+]i in aortic smooth muscle is increased > 2-fold during sepsis. Furthermore, we determined that sodium dantrolene, a drug that decreases release of calcium from the sarcoplasmic reticulum and that is lifesaving in malignant hyperthermia (a disorder due to increased [Ca2+]i), is able to reduce the elevated [Ca2+]i in sepsis to control values when added in vitro or when given in vivo to the animal. These results suggest that an increase in [Ca2+]i is an early event in sepsis and that increased [Ca2+]i may be responsible for, or contribute to, cellular injury. Dantrolene may offer a therapeutic strategy in the treatment of sepsis.

Calcium functions as a critical intracellular second messenger and regulates many cellular processes such as muscle contractility, glycogen and protein turnover, hormone secretion, and vascular smooth muscle tone which are markedly abnormal during sepsis/endotoxemia. There also is increasing recognition of the role of calcium in the production of a variety of cytokines such as tumor necrosis factor alpha and interleukin-1 beta, which are important mediators of sepsis. Our hypothesis is that disturbances in cellular calcium regulation are responsible for or contribute to many of the metabolic manifestations of sepsis/endotoxemia and may be the driving force behind the development of multiorgan failure. In this article, we focus on a) new insights into calcium's regulation of the inflammatory cascade, b) the controversy concerning whether free cytosolic calcium concentration ([Ca2+]i) is increased in the disorder, and c) the potential therapeutic uses of calcium antagonists. An important message is that there are fundamental differences in the pathophysiology of the endotoxin model versus the cecal ligation and perforation (CLP) model of sepsis. Although calcium antagonists improve survival in the endotoxin model, they increase mortality in the CLP model of sepsis. Possible reasons for the differences in the effect of the drugs in the two different models and insight into the mechanisms of cell injury in endotoxin versus sepsis are presented.

BACKGROUND: In animal and human autopsy studies of sepsis, CD4+ splenocytes either undergo apoptosis or are polarized to the Th2 effector subtype. In mice, these changes occur within 24 hours of the onset of sepsis. Preventing the loss of CD4+ T cells and the Th2-polarization of CD4+ T cells provides a significant survival advantage in mouse models of sepsis. The molecular mechanism(s) for the phenotypic changes of splenic CD4+ T cells in sepsis are not well understood. STUDY DESIGN: CD4+ splenocytes were enriched by negative selection from disaggregated spleens of septic and sham-operated mice at 6 and 24 hours after surgery. Phenotypic analysis using cell surface markers (CD25, CD44, CD62L, CD69), cytokine secretion in response to CD3/CD28 coligation, and whole genome microarray gene expression profiles were obtained for these cells. RESULTS: Consistent with previous reports, sepsis induced a progressive decrease in the number of CD4+ splenocytes and a time-dependent alteration in CD4+ T-cell phenotype. At 6 hours, when no differences in cell number or surface marker expression were observed, significant alterations in RNA abundance were measured for 498 probe sets. Ontologic classification of these genes indicated changes in cellular physiology. Pathway analysis indicated that T-cell receptor signaling and mitogen-activated protein kinase signaling were significantly altered by sepsis. CONCLUSIONS: These data demonstrated a sepsis-specific transcriptional program that precedes sepsis-induced phenotypic changes in CD4+ splenocytes.