ObjectivesThe purpose of this study was to determine whether apoptosis is a major mechanism of cell death in patients with sepsis. The activities of caspase-3 and the antiapoptotic protein, BCL-2, were investigated also.DesignA prospective study of 20 patients who died of sepsis and multiple organ d

Apoptotic cell death in patients with sepsis, shock, and multiple organ dysfunction

The complement system not only represents an effective innate immune mechanism of host defense to eradicate microbial pathogens, but it is also widely involved in many forms of acute and chronic inflammatory diseases including sepsis, acute lung injury, ischemia-reperfusion injury, and asthma, to give just a few examples. The complement-activated product, C5a, displays powerful biological activities that lead to inflammatory sequelae. C5a is a strong chemoattractant and is involved in the recruitment of inflammatory cells such as neutrophils, eosinophils, monocytes, and T lymphocytes, in activation of phagocytic cells and release of granule-based enzymes and generation of oxidants, all of which may contribute to innate immune functions or tissue damage. Accumulating data suggest that C5a provides a vital bridge between innate and adaptive immune functions, extending the roles of C5a in inflammation. Herein, we review human and animal data describing the cellular and molecular mechanisms of C5a in the development of inflammatory disorders, sepsis, acute lung injury, ischemia-reperfusion injury, and asthma.

Role of C5a in inflammatory responses

Sepsis induces lymphocyte apoptosis and prevention of lymphocyte death may improve the chances of surviving this disorder. We compared the efficacy of a selective caspase-3 inhibitor to a polycaspase inhibitor and to caspase-3-/- mice. Both inhibitors prevented lymphocyte apoptosis and improved survival. Caspase-3-/- mice shared a decreased, but not total, block of apoptosis. The polycaspase inhibitor caused a very substantial decrease in bacteremia. Caspase inhibitors did not benefit RAG-1-/- mice, which had a > tenfold increase in bacteremia compared to controls. Adoptive transfer of T cells that overexpressed the anti-apoptotic protein Bcl-2 increased survival. T cells stimulated with anti-CD3 and anti-CD28 produced increased interleukin 2 and interferon gamma by 6 h. Thus, caspase inhibitors enhance immunity by preventing lymphocyte apoptosis and lymphocytes act rapidly, within 24 h, to control infection.

Caspase inhibitors improve survival in sepsis: a critical role of the lymphocyte.

The balance between cell survival and death is under tight genetic control. A multiplicity of extracellular signals and intracellular mediators is involved in maintaining this balance. When the cell is exposed to physical, biochemical or biological injury, or deprived of necessary substances, it activates a series of stress-response genes. With minimal insults, the cell may recover. With greater insults, single cell death, or apoptosis, results; the cell dies and is recycled to its neighbours. If the insult overwhelms a large number of cells then necrosis ensues, with an accompanying inflammatory response. Dysregulation of the controlling mechanisms of this system results in disease. Deficient apoptosis is associated with cancer, auto-immunity and viral infections. Excessive apoptosis is associated with ischaemic heart disease, stroke, neurodegenerative disease, sepsis and multiple organ dysfunction syndrome. There are myriad therapeutic options unfolding as understanding is gained of apoptosis and its control.

https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2044.2000.01554.x

Apoptosis: mechanisms and clinical implications

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-α 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.

https://www.pnas.org/content/pnas/96/25/14541.full.pdf

Prevention of lymphocyte cell death in sepsis improves survival in mice.

Intraperitoneal injection of Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) induces thymic atrophy in mice The thymus weight, cell number, and viability began to decrease at 3 h, and reached their lowest level at 72 h The thymocyte death was associated with DNA fragmentation of approximately 200 base pairs in ladder form The kinetic study on histopathology revealed the process of thymocyte death and thymic atrophy Flow-cytometric analysis showed that CD4+CD8+ thymocytes decreased predominantly LPS caused thymocyte apoptosis, but only in LPS-responder mice, unlike Gram-negative bacteria that induced apoptosis in both LPS-responder (C3H/HeN) and LPS-nonresponder (C3H/HeJ) Gram-positive bacteria Streptococcus pneumoniae also caused apoptosis in LPS-nonresponder (C3H/HeJ) and LPS-responder mice (B6) The kinetics of serum TNF-alpha production after Gram-negative or Gram-positive bacteria injection was slightly different E coli induced serum TNF-alpha peak at 1 h in B6 mice, whereas S pneumoniae induced a peak at 6 h in C3H/HeJ and at 9 h in B6 mice Similarly, S pneumoniae induced thymocyte apoptosis around 9 to 12 h, which was 6 to 9 h later than that observed with E coli in B6 mice Anti-TNF-alpha Ab completely blocked the E coli-induced thymocyte apoptosis, but was only partially inhibitory on the S pneumoniae-induced thymocyte apoptosis Furthermore, thymocyte apoptosis induced by E coli was inhibited by cycloheximide or actinomycin D These data indicate that both Gram-negative and Gram-positive bacteria could induce thymus atrophy via apoptosis, and that TNF-alpha is a common denominator released and might be responsible for the thymocyte apoptosis

Shulhn-Der Wang

Papers

Sepsis-induced apoptosis of the thymocytes in mice.