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The author focuses on the use of imaging modality to detect apoptotic cell death in septic patients. He relates the study "Imaging Lymphoid Cell Death In Vivo During Polymicrobial Sepsis," by L. Zou and colleagues in the November 2015 issue. He notes that the authors of the study develop a novel noninvasive method to monitor apoptotic cell death in sepsis, but the annexin-V imaging has a number of issues limiting its usage in septic patients.

Some labile cell types whose numbers are normally controlled through programmed cell death are subject to markedly increased destruction during some severe infections. Lymphocytes, in particular, undergo massive and apparently unregulated apoptosis in human patients and laboratory animals with sepsis, potentially playing a major role in the severe immunosuppression that characterizes the terminal phase of fatal illness. Extensive lymphocyte apoptosis has also occurred in humans and animals infected with several exotic agents, including Bacillus anthracis, the cause of anthrax; Yersinia pestis, the cause of plague; and Ebola virus. Prevention of lymphocyte apoptosis, through either genetic modification of the host or treatment with specific inhibitors, markedly improves survival in murine sepsis models. These findings suggest that interventions aimed at reducing the extent of immune cell apoptosis could improve outcomes for a variety of severe human infections, including those caused by emerging pathogens and bioterrorism agents. [ABSTRACT FROM AUTHOR]

Sepsis is the leading cause of death in surgical intensive care units and is a major cause of morbidity and mortality in neonatal and medical intensive care units. The Centers for Disease Control and Prevention estimates that, in the United States alone, ∼500,000 people develop sepsis and 175,000 people die each year. Sepsis is a growing problem; its incidence has tripled from 1972 to 1992. Recently, apoptosis has been identified as an important mechanism of cell death in animal models of sepsis and endotoxemia. During sepsis, there is extensive apoptotic death of lymphocytes and gastrointestinal epithelial cells. The extensive apoptotic death of lymphocytes is likely an important cause of the profound immunosuppression that is a hallmark of patients with sepsis. The apoptosis of gastrointestinal epithelial cells may compromise the integrity of the bowel wall, resulting in translocation of bacteria or endotoxins into the systemic circulation. The potential importance of apoptosis in the pathophysiology of sepsis is illustrated by results from animal models that demonstrate that blocking lymphocyte apoptosis improves survival in sepsis. A variety of strategies to inhibit apoptosis may ultimately provide an effective therapy for this highly lethal disorder. [ABSTRACT FROM AUTHOR]

Lymphocytes help determine whether gut epithelial cells proliferate or differentiate but are not known to affect whether they live or die. Here, we report that lymphocytes play a controlling role in mediating gut epithelial apoptosis in sepsis but not under basal conditions. Gut epithelial apoptosis is similar in unmanipulated Rag-1-/- and wild-type (WT) mice. However, Rag-1-/- animals have a 5-fold augmentation in gut epithelial apoptosis following cecal ligation and puncture (CLP) compared to septic WT mice. Reconstitution of lymphocytes in Rag-1-/- mice via adoptive transfer decreases intestinal apoptosis to levels seen in WT animals. Subset analysis indicates that CD4+ but not CD8+, γδ, or B cells are responsible for the antiapoptotic effect of lymphocytes on the gut epithelium. Gut-specific overexpression of Bcl-2 in transgenic mice decreases mortality following CLP. This survival benefit is lymphocyte dependent since gut-specific overexpression of Bcl-2 fails to alter survival when the transgene is overexpressed in Rag-1-/- mice. Further, adoptively transferring lymphocytes to Rag-1-/- mice that simultaneously overexpress gut-specific Bcl-2 results in improved mortality following sepsis. Thus, sepsis unmasks CD4+ lymphocyte control of gut apoptosis that is not present under homeostatic conditions, which acts as a key determinant of both cellular survival and host mortality. [ABSTRACT FROM AUTHOR]

Abstract: Cell penetrating peptides (CPPs) have been used to deliver the anti-apoptotic Bcl-xL-derived BH4 peptide to prevent injury-induced apoptosis both in vitro and in vivo. Here we demonstrate that the nuclear localization sequence (NLS) from the SV40 large T antigen has favorable properties for BH4 domain delivery to lymphocytes compared to sequences based on the HIV-1 TAT sequence. While both TAT-BH4 and NLS-BH4 protected primary human mononuclear cells from radiation-induced apoptotic cell death, TAT-BH4 caused persistent membrane damage and even cell death at the highest concentrations tested (5–10μM) and correlated with in vivo toxicity as intravenous administration of TAT-BH4 caused rapid death. The NLS-BH4 peptide has significantly attenuated toxicity compared to TAT-BH4 and we established a dosing regimen of NLS-BH4 that conferred a significant survival advantage in a post-exposure treatment model of LD90 total body irradiation. [Copyright &y& Elsevier]

Background: Clinical signs and symptoms of sepsis are nonspecific and often indistinguishable from those of nonseptic critical illness. This ambiguity frequently delays the diagnosis of sepsis until culture results can confirm the presence or absence of an infectious organism. Lymphocyte phenotyping can be conducted rapidly and may provide information on the presence of infection before culture results are available. In this study, we hypothesized that lymphocyte phenotype can distinguish between septic and nonseptic critical illness. Study Design: C57Bl/6 mice were subjected to either P aeruginosa pneumonia or lipopolysaccharide-induced acute lung injury (ALI). Animals were sacrificed 24 hours postinjury and splenic lymphocytes were harvested. Additionally, 13 patients in a surgical ICU were enrolled in the study. Whole blood was obtained and lymphocytes were isolated by density gradient centrifugation. Lymphocyte phenotype was identified through flow cytometry after labeling lymphocytes for CD3, CD4, CD8, CD20, CD40, CD69, and CD86 with fluorochrome-conjugated antibodies. Results: CD69 expression on B cells and CD8+ splenocytes from septic mice was significantly increased compared with acute lung injury mice (p < 0.001 and p < 0.05, respectively). Similarly, CD4+ and CD8+ lymphocytes from septic patients had a two- to threefold increase in the expression of CD69 compared with nonseptic critically ill patients (p < 0.05). Conclusions: These data indicated that CD69 expression on lymphocytes may be useful in distinguishing between septic and nonseptic critical illness. Continued investigation into the expression of CD69 during sepsis is warranted. [Copyright &y& Elsevier]

Lymphocyte apoptosis is a hallmark of sepsis and contributes to disease mortality. In other acute injuries, such as myocardial and cerebral ischemia/ reperfusion, apoptosis plays a significant role in disease-associated morbidity and mortality. We previously showed that constitutive activation of the potent antiapoptotic Akt/protein kinase B signaling pathway in lymphocytes both reduces sepsis-induced lymphocyte apoptosis and confers a significant survival advantage compared to wild-type littermates. Here, we demonstrate a therapeutic approach to acutely augment Akt activity in a wild-type animal. A cell-permeable peptide conjugated to the Akt-binding domain of the endogenous Akt coactivator, Tcl-1, prolongs Akt activity, activates extracellular regulated kinase (ERK) signaling and protects lymphocytes from numerous apoptotic stimuli both in vitro and in vivo. Molecular approaches to activate the antiapoptotic Akt and ERK signaling pathways may provide a novel tool to study these signaling pathways, as well as a new antiapoptotic strategy for the treatment of sepsis and other acute injuries. [ABSTRACT FROM AUTHOR]

Abstract: The risk of terrorist attacks utilizing either nuclear or radiological weapons has raised concerns about the current lack of effective radioprotectants. Here it is demonstrated that the BH4 peptide domain of the anti-apoptotic protein Bcl-xL can be delivered to cells by covalent attachment to the TAT peptide transduction domain (TAT-BH4) and provide protection in vitro and in vivo from radiation-induced apoptotic cell death. Isolated human lymphocytes treated with TAT-BH4 were protected against apoptosis following exposure to 15Gy radiation. In mice exposed to 5Gy radiation, TAT-BH4 treatment protected splenocytes and thymocytes from radiation-induced apoptotic cell death. Most importantly, in vivo radiation protection was observed in mice whether TAT-BH4 treatment was given prior to or after irradiation. Thus, by targeting steps within the apoptosis signaling pathway it is possible to develop post-exposure treatments to protect radio-sensitive tissues. [Copyright &y& Elsevier]

Lymphocyte apoptosis plays a central role in the pathophysiology of sepsis. Lymphocyte apoptosis was examined in mice with defective death receptor pathways due to transgenic expression of a dominant negative mutant of Fas-associated death domain (FADD-DN) or Bid-/- and in mice with defective mitochondrial-mediated pathways due to loss of Bim-/-, Puma-/-, or Noxa-/-. FADD-DN transgenic and Bid-/- mice had significant albeit incomplete protection, and this protection was associated with increased survival. Surprisingly, splenic B cells were also protected in FADD-DN mice although transgene expression was confined to T cells, providing evidence for an indirect protective mechanism. Bim-/- provided virtually complete protection against lymphocyte apoptosis whereas Puma-/- and Noxa-/- mice had modest or no protection, respectively. Bim-/- mice had improved survival, and adoptive transfer of splenocytes from Bim-/- mice into Rag 1-/- mice demonstrated that this was a lymphocyte intrinsic effect. The improved survival was associated with decreased interleukin (IL) -10 and IL-6 cytokines. Collectively, these data indicate that numerous death stimuli are generated during sepsis, and it therefore appears unlikely that blocking a single "trigger" can inhibit apoptosis. If siRNA becomes practical therapeutically, proapoptotic proteins would be potential targets. [ABSTRACT FROM AUTHOR]

Abstract: The anti-apoptotic Bcl-2 protein has the remarkable ability to prevent cell death from several noxious stimuli. Intriguingly, Bcl-2 overexpression in one cell type has been reported to protect against cell death in neighboring non-Bcl-2 overexpressing cell types. The mechanism of this “trans” protection has been speculated to be secondary to the release of a cytoprotective factor by Bcl-2 overexpressing cells. We employed a series of adoptive transfer experiments in which lymphocytes that overexpress Bcl-2 were administered to either wild type mice or mice lacking mature T and B cells (Rag-1−/−) to detect the presence or absence of the putative protective factor. We were unable to demonstrate “trans” protection. However, adoptive transfer of apoptotic or necrotic cells exacerbated the degree of apoptotic death in neighboring non-Bcl-2 overexpressing cells (p ⩽0.05). Therefore, this data suggests that dying cells emit signals triggering cell death in neighboring non-Bcl-2 overexpressing cells, i.e., a “trans” destructive effect. [Copyright &y& Elsevier]