Effects of age on mortality and antibiotic efficacy in cecal ligation and puncture

Severity of burn injury and sepsis determines the cytokine responses of bone marrow progenitor-derived macrophages

BACKGROUND

Although thermal injury and sepsis result in enhanced monocytopoiesis, the functional characteristics of macrophages that develop in the microenvironment of burn and sepsis are unknown. Here we compare cytokine responses of bone marrow progenitor-derived macrophages (BMO) and peritoneal macrophages (PMO) after graded levels of thermal injury and sepsis.

METHODS

Mice were randomly divided into sham (S), burn (B), and burn sepsis (BS) groups. The mild injury group received either a 7-second dorsal scald burn alone or in combination with 1,000 colony forming units (CFU) Pseudomonas aeruginosa at the wound site. The severe injury group was subjected to a 10-second burn with or without inoculation of 5,000 CFU P. aeruginosa. ER-MP12+ progenitors were separated from bone marrow cells 72 hour after injury. Macrophage colony stimulating factor (M-CSF) and Granulocyte-macrophage colony stimulating factor (GM-CSF) responsive clonogenic potentials, and lipopolysaccharide (LPS)-stimulated cytokine production were determined.

RESULTS

In mild injury and sepsis, GM-CSF and M-CSF responsive clonal growth of ER-MP12+ progenitors was enhanced in the B and BS groups compared with the S group. M-CSF responsive colony growth in severe sepsis was significantly higher than that in all the other groups. LPS-stimulated tumor necrosis factor-alpha and Interleukin-6 levels were higher in the B and BS groups compared with the S group. Severe injury and sepsis attenuated this response significantly. The cytokine responses of PMO from both injury groups were similar to that of BMO.

CONCLUSION

Severity of burn injury and the magnitude of sepsis influence the cytokine responses of BMO and PMO in a similar manner suggesting the microenvironment of burn injury and sepsis profoundly influence the functional phenotype of BMO.

Liver cytokine production and ICAM-1 expression following bone fracture, tissue trauma, and hemorrhage in middle-aged mice

Although studies have indicated that hemorrhagic shock and resuscitation produces hepatic damage by mechanisms involving adhesion molecules in endothelial cells and hepatocytes, it is not known if there is any difference in the extent of hepatic damage following bone fracture, soft tissue trauma, and hemorrhage (Fx-TH) between young and middle-aged animals. To study this, young (6-8 wk) and middle-aged (approximately 12 mo) C3H/HeN male mice were subjected to a right lower leg fracture, soft tissue trauma, (i.e., midline laparotomy), and hemorrhage (blood withdrawal to decrease the blood pressure to 35 +/- 5 mmHg for 90 min) followed by resuscitation with four times the shed blood volume in the form of lactated Ringer solution. Mice were euthanized 24 h later, and liver tissues were harvested. Total bilirubin levels in the hepatocyte extract increased markedly following Fx-TH in both groups of mice; however, the increase in middle-aged mice was significantly higher compared with young mice. TNF-alpha and IL-6 levels in the hepatocyte extract following Fx-TH increased significantly in middle-aged mice but remained unchanged in young mice. IL-10 levels significantly decreased in middle-aged mice following Fx-TH but remained unchanged in young mice. Kupffer cells from middle-aged mice produced significantly higher IL-6 and IL-10 levels compared with young mice. Protein levels and mRNA expression of ICAM-1 in hepatocytes were also significantly higher in middle-aged mice compared with young mice following Fx-TH. These results collectively suggest that the extent of hepatic damage following Fx-TH is dependent on the age of the subject.

Endotoxin-induced myocardial dysfunction in senescent rats

Introduction

Aging is associated with a decline in cardiac contractility and altered immune function. The aim of this study was to determine whether aging alters endotoxin-induced myocardial dysfunction.

Methods

Senescent (24 month) and young adult (3 month) male Wistar rats were treated with intravenous lipopolysaccharide (LPS) (0.5 mg/kg (senescent and young rats) or 5 mg/kg (young rats only)), or saline (senescent and young control groups). Twelve hours after injection, cardiac contractility (isolated perfused hearts), myofilament Ca²⁺ sensitivity (skinned fibers), left ventricular nitric oxide end-oxidation products (NOx and NO₂) and markers of oxidative stress (thiobarbituric acid reactive species (TBARS) and antioxidant enzymes) were investigated.

Results

LPS (0.5 mg/kg) administration resulted in decreased contractility in senescent rats (left ventricular developed pressure (LVDP), 25 ± 4 vs 53 ± 4 mmHg/g heart weight in control; P < 0.05) of amplitude similar to that in young rats with LPS 5 mg/kg (LVDP, 48 ± 7 vs 100 ± 7 mmHg/g heart weight in control; P < 0.05). In contrast to young LPS rats (0.5 and 5 mg/kg LPS), myofilament Ca²⁺ sensitivity was unaltered in senescent LPS hearts. Myocardial NOx and NO₂ were increased in a similar fashion by LPS in young (both LPS doses) and senescent rats. TBARS and antioxidant enzyme activities were unaltered by sepsis whatever the age of animals.

Conclusion

Low dose of LPS induced a severe myocardial dysfunction in senescent rats. Ca²⁺ myofilament responsiveness, which is typically reduced in myocardium of young adult septic rats, however, was unaltered in senescent rats. If these results are confirmed in in vivo conditions, they may provide a cellular explanation for the divergent reports on ventricular diastolic function in septic shock. In addition, Ca²⁺-sensitizing agents may not be as effective in aged subjects as in younger subjects.

Age-dependent lipopolysaccharide-induced iNOS expression and multiorgan failure in rats: effects of melatonin treatment

Senescence amplifies the sensitivity to endotoxemia, which correlates with increased nitric oxide (NO) levels and mortality. Melatonin displays antioxidant and anti-inflammatory effects, but its levels decrease with age. Lipopolysaccharide (LPS) (10 mg/kg) was injected to 3- and 18-month-old rats 6 h before they were killed, and melatonin (60 mg/kg) was injected before and/or after LPS. Inducible nitric oxide synthase (iNOS) expression and activity, nitrite content, lipoperoxidation (LPO) levels, and serum markers of liver, renal, and metabolic dysfunction, were measured in liver and lung of these animals. An age-dependent increase in iNOS activity, NO content, and LPO levels was observed, and these changes were augmented further by LPS. Melatonin decreased the expression and activity of iNOS, reducing NO and LPO levels to basal values in both septic LPS-treated groups. Liver, kidney, and metabolic dysfunctions were also significantly higher in aged that in young rats and further increased by LPS. Melatonin treatment counteracted these alterations in young and aged septic rats. Melatonin reduced LPS-dependent iNOS expression and multiorgan failure in a similar extent in young and aged rats. Because aged rats showed higher organ and metabolic impairment than young animals in response to LPS, the results also suggest an increased efficacy of the anti-septic properties of melatonin in the aged animals.

Increasing anastomosis safety and preventing abdominal adhesion formation by the use of polypeptides in the rat

BACKGROUND AND AIMS

Postoperative adhesions can potentially be reduced using different anti-adhesive agents, though these drugs tend to compromise healing of an intestinal anastomosis. No method that significantly increases anastomosis safety is known at present. The aim of the study was to develop a concept of preventing postoperative adhesions using differently charged bioactive polypeptides, also considering healing and safety of an intestinal anastomosis.

METHODS

An ileocolic anastomosis was performed under both "clean" and "septic" conditions in the rat. The treatment group received intraperitoneal poly-L-lysine and poly-L-glutamate, while controls received sodium chloride. Abdominal adhesions, anastomosis leakage and burst pressure were analysed after 1, 3, 5 and 7 days in the clean anastomosis model and after 7 days in the septic model.

RESULTS

A significant decrease (p<0.01) in the amount of adhesions was seen in animals treated with polypeptides after 1, 3 and 5 days, while no difference was seen after 7 days. The anastomosis demonstrated a significantly higher burst pressure as evaluated at days 1 and 3 (p<0.05 and p<0.01, respectively) in the polypeptide-treated animals, while no difference was seen between the groups at day 5 or 7.

CONCLUSION

The use of differently charged polypeptides administered intraperitoneally after surgery resulted in a significant decrease in the extent of postoperative adhesions. Furthermore, an increase in intestinal anastomosis safety, based on improved burst pressure during the first 3 days, i.e. the critical period during the healing process, was noted. No adverse effects were seen in surgery during septic conditions.

Age-dependent responses to hepatic ischemia/reperfusion injury

The current study explored the concept that adult and pediatric populations differ in their response to major injury. Male C57BL/6 mice of a "young adult" (8-12 weeks) or "mature adult" (12-13 months) age were subjected to partial hepatic ischemia and reperfusion. Mature adult mice displayed significantly more liver injury than young adult mice as assessed histologically and by serum levels of alanine aminotransferase. Interestingly, there was far less neutrophil accumulation in the livers of mature adult mice. However, liver-recruited neutrophils from mature adult mice had a higher activation state than those from young adult mice. Activation of the inflammatory transcription factor, NF-kappaB, was suppressed in whole livers from mature adult mice. In isolated liver cells, Kupffer cells showed no difference in NF-kappaB activation, but hepatocytes from mature adult mice had delayed NF-kappaB activation in response to TNF. Furthermore, isolated hepatocytes from young adult mice produced abundant amounts of the chemokine, macrophage inflammatory protein-2, whereas hepatocytes from mature adult mice produced little, if any macrophage inflammatory protein-2. Mature adult mice had much lower hepatic expression of the cytoprotective protein, heat shock protein 70, than did young adult mice. In contrast, serum heat shock protein 70 levels, which has been linked to subsequent tissue injury, were higher in mature adult mice than in young adult mice. These data suggest that there are multiple alterations at the cellular and molecular levels that contribute to enhanced postischemic liver injury in mature adult mice.

Differential effect of imipenem treatment on injury caused by cecal ligation and puncture in wild-type and NK cell-deficient beta(2)-microgloblin knockout mice

Our previous studies showed that beta(2)-microglobulin knockout mice treated with anti-asialoGM1 (beta2MKO/alphaAsGM1 mice) are resistant to injury caused by cecal ligation and puncture (CLP). However, CLP-induced injury is complex. Potential mechanisms of injury include systemic infection, cecal ischemia, and translocation of bacterial toxins such as endotoxin and superantigens. Currently, it is unclear which of these mechanisms of injury contributes to mortality in wild-type mice and whether beta2MKO/alphaAsGM1 mice are resistant to any particular mechanisms of injury. In the present study, we hypothesized that systemic infection is the major cause of injury after CLP in wild-type mice and that beta2MKO/alphaAsGM1 mice are resistant to infection-induced injury. To test this hypothesis, wild-type and beta2MKO/alphaAsGM1 mice were treated with the broad-spectrum antibiotic imipenem immediately after CLP to decrease the impact of systemic infection in our model. Treatment of wild-type and beta2MKO/alphaAsGM1 mice with imipenem decreased bacterial counts by at least two orders of magnitude. However, all wild-type mice, whether treated with saline or imipenem, died by 42 h after CLP and had significant hypothermia, metabolic acidosis, and high plasma concentrations of the cytokines interleukin-6, macrophage inflammatory protein-2, and keratinocyte-derived chemokine. beta2MKO/alphaAsGM1 mice showed 40% long-term survival, which was increased to 90% by imipenem treatment. beta2MKO/alphaAsGM1 mice had less hypothermia, decreased metabolic acidosis, and lower cytokine concentrations at 18 h after CLP compared with wild-type mice. These results suggest that infection is not the major cause of mortality for wild-type mice in our model of CLP. Other mechanisms of injury such as cecal ischemia or translocation of microbial toxins may be more important. beta2MKO/alphaAsGM1 mice appear resistant to these early, non-infection-related causes of CLP-induced injury but showed delayed mortality associated with bacterial dissemination, which was ablated by treatment with imipenem.

The effect of age on the development and outcome of adult sepsis

OBJECTIVE

Sepsis is an increasingly common and lethal medical condition that occurs in people of all ages. The influence of age on sepsis risk and outcome is incompletely understood. We sought to determine the independent effect of age on the incidence, severity, and outcome of adult sepsis.

DESIGN

Longitudinal observational study using national hospital discharge data.

SETTING

Approximately 500 geographically separated nonfederal acute care hospitals in the United States.

PATIENTS

Patients were 10,422,301 adult sepsis patients hospitalized over 24 yrs, from 1979 to 2002.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Incident sepsis cases were age adjusted and characterized by demographics, sources and types of infection, comorbid medical conditions, and hospital discharge status. Elderly patients (> or = 65 yrs of age) accounted for 12% of the U.S. population and 64.9% of sepsis cases, yielding a relative risk of 13.1 compared with younger patients (95% confidence interval, 12.6-13.6). Elderly patients were more likely to have Gram-negative infections, particularly in association with pneumonia (relative risk, 1.66; 95% confidence interval, 1.63-1.69) and to have comorbid medical conditions (relative risk, 1.99; 95% confidence interval, 1.92-2.06). Case-fatality rates increased linearly by age; age was an independent predictor of mortality in an adjusted multivariable regression (odds ratio, 2.26; 95% confidence interval, 2.17-2.36). Elderly sepsis patients died earlier during hospitalization, and elderly survivors were more likely to be discharged to a nonacute health care facility.

CONCLUSIONS

The incidence of sepsis is disproportionately increased in elderly adults, and age is an independent predictor of mortality. Compared with younger sepsis patients, elderly nonsurvivors of sepsis die earlier during hospitalization and elderly survivors more frequently require skilled nursing or rehabilitative care after hospitalization. These findings have implications for patient care and health care resource prioritization and provide insights for expanded scientific investigations and potential patient interventions.

RODENT MODELS OF INTRA-ABDOMINAL INFECTION

The first question to ask when deciding which model to use for the preclinical testing of a therapeutic agent should be: What exactly is it that the chosen model is attempting to model? Therefore, in the context of intra-abdominal models of infection, the question becomes, is the goal to mimic diffuse peritonitis, intra-abdominal abscesses, septic shock, or a multiple organ dysfunction-type syndrome. Having decided on the clinical situation to model, it becomes important to ensure that the model is as congruent with the clinical situation as feasible, especially when the goal is the preclinical testing of possible therapeutic agents. Consequently, different types of rodent intra-abdominal infection models will be reviewed, focusing on their rationales as well as their strengths and weaknesses as models of clinical disease.

Differential effect of imipenem treatment on wild-type and NK cell-deficient CD8 knockout mice during acute intra-abdominal injury

CD8 knockout mice depleted of natural killer (NK) cells by treatment with anti-asialoGM1 (CD8KO/alphaAsGM1 mice) are resistant to injury caused by cecal ligation and puncture (CLP). However, CLP-induced injury is complex. Potential sources of injury include bacterial dissemination, cecal ischemia, and translocation of bacterial toxins. We treated wild-type and CD8KO/alphaAsGM1 mice with imipenem after CLP to decrease bacterial dissemination. Additional mice were subjected to cecal ligation without puncture of the cecal wall or cecal ligation and removal of cecal contents. Imipenem treatment decreased bacterial counts by at least two orders of magnitude. However, all wild-type mice, whether treated with saline or imipenem, died by 42 h after CLP and exhibited significant hypothermia, metabolic acidosis, and high plasma cytokine concentrations. Wild-type mice subjected to cecal ligation without puncture also died, despite very low bacterial counts in blood, but wild-type mice subjected to cecal ligation and washout of cecal contents survived. In CD8KO/alphaAsGM1 mice subjected to CLP, imipenem treatment increased survival from 50% to 100%. After cecal ligation without puncture, long-term survival was 80-90% in CD8KO/alphaAsGM1 mice. Hypothermia, metabolic acidosis, and cytokine production were attenuated in CD8KO/alphaAsGM1 mice compared with wild-type controls. These results indicate that bacterial dissemination is not a major source of injury in wild-type mice after CLP, but the presence of gut flora in the cecal lumen is required for induction of systemic inflammation after cecal injury. CD8KO/alphaAsGM1 mice are resistant to the systemic manifestations of cecal injury.

IL-10 Plasma Levels are Elevated After LPS Injection in Splenectomized A/J Mice1

BACKGROUND

Splenectomy is clinically indicated in certain cases of hypersplenism and splenic trauma. However, it is associated with serious complications, in particular, reduced clearance of encapsulated organisms and a high incidence of sepsis, which has been coined overwhelming post-splenectomy sepsis (OPSS). In addition to the role of the spleen in the clearance of microorganisms, this organ may be involved in regulation of the inflammatory response. We investigated the effect of splenectomy on the inflammatory process induced by LPS in a murine model that resembles, in part, the pathophysiological aspects of sepsis.

MATERIALS AND METHODS

Male mice (8-weeks-old) from different inbred strains were randomized into three groups: splenectomized (SPX), sham operated (SHAM), and non-operated controls (NoOp). After 9 days of recovery, mice were injected with LPS (15 mg/kg) and cytokine plasma levels were measured by ELISA at 1.5 or 6 h after injection. Peritoneal macrophages (PMphi) were isolated from the three groups, and cytokine production was evaluated after incubation with LPS in culture conditions.

RESULTS

IL-10 plasma levels were elevated in SPX A/J mice (6.7 +/- 0.4 mug/ml) after injection of LPS (15 mg/kg) compared to NoOp A/J mice (4.2 +/- 0.2 mug/ml, P < 0.05). Similar elevation in IL-10 plasma levels was detected in SPX DBA/2J mice as compared to NoOp DBA/2J mice, but not in C57BL/6J and BALB/cJ mice. In contrast, SPX AKR mice displayed lower IL-10 levels than NoOp mice. PMphis from SPX A/J mice produced elevated levels of IL-10 compared to PMphis from SHAM or NoOp A/J mice, mimicking the in vivo observations.

CONCLUSION

Our data suggest that the spleen plays an important role in modulating the inflammatory process induced by LPS, extending beyond passive clearance of encapsulated organisms. In addition, the contribution of the spleen to the inflammatory process may be influenced by the genetic background.

Iron dysregulation combined with aging prevents sepsis-induced apoptosis

BACKGROUND

Sepsis, iron loading, and aging cause independent increases in gut epithelial and splenic apoptosis. It is unknown how their combination will affect apoptosis and systemic cytokine levels.

MATERIALS AND METHODS

Hfe-/- mice (a murine homologue of hemochromatosis) abnormally accumulate iron in their tissues. Aged (24-26 months) or mature (16-18 months) Hfe-/- mice and wild type (WT) littermates were subjected to cecal ligation and puncture (CLP) or sham laparotomy. Intestine, spleen, and blood were harvested 24 h later and assessed for apoptosis and cytokine levels.

RESULTS

Gut epithelial and splenic apoptosis were low in both aged septic and sham Hfe-/- mice, regardless of the amount of iron in their diet. Mature septic WT mice had increased apoptosis compared to age-matched sham WT mice. Mature septic Hfe-/- mice had similar levels of intestinal cell death to age-matched septic WT mice but higher levels of splenic apoptosis. Apoptosis was significantly lower in septic aged Hfe-/- mice than septic mature Hfe-/- animals. Interleukin-6 was elevated in septic aged Hfe-/- mice compared to sham mice.

CONCLUSIONS

Although sepsis, chronic iron dysregulation, and aging each increase gut and splenic apoptosis, their combination yields cell death levels similar to sham animals despite the fact that aged Hfe-/- mice are able to mount an inflammatory response following CLP and mature Hfe-/- mice have elevated sepsis-induced apoptosis. Combining sepsis with two risk factors that ordinarily increase cell death and increase mortality in CLP yields an apoptotic response that could not have been predicted based upon each element in isolation.

An exaggerated inflammatory response after CLP correlates with a negative outcome

BACKGROUND

Sepsis is the leading cause of morbidity and mortality in the surgical intensive care unit. We postulate that the variable clinical profile of septic patients is the product of multiple factors, including initiating insult, environment, and genetic make-up. This hypothesis was tested by changing the severity of the insult and the genetic background in an experimental murine model of sepsis.

MATERIALS AND METHODS

Eight-week-old, male A/J and C57BL/6J (B6) mice underwent cecal ligation and puncture (CLP). The cecum was ligated just below the ileocecal valve (>1-cm ligation) or 1 cm from the end of the cecum (1-cm ligation) and single punctured using a 16- or 25-gauge needle (CLP16 or CLP25) or double punctured with a 25-gauge needle (CLP25 x 2). Cytokines were measured in plasma samples by ELISA at different time points after CLP.

RESULTS

Elevated TNF-alpha and IL-6 plasma levels were observed in A/J as compared to B6 mice at 10 and 20 h after CLP16 (1-cm ligation). In contrast, IL-10 levels were decreased in A/J versus B6 mice at 6 h but increased at 10 h. After CLP25 and CLP25 x 2 (1-cm ligation), TNF-alpha was significantly increased at 10 h, but there was no difference in IL-10 and IL-6. CLP with >1-cm ligation resulted in increased cytokine expression after CLP25, CLP25 x 2, and CLP16 versus 1-cm ligation. Mortality after CLP16 was significantly higher in B6 mice with >1-cm versus 1-cm ligation. A/J mortality did not differ between the two procedures.

CONCLUSION

Mortality rate and cytokine profiles after CLP vary depending on the insult severity and the genetic make-up.

Genetic determinants influencing the response to injury, inflammation, and sepsis

The genetic background has recently been recognized as an important element in the response to injury, contributing to the variability in the clinical outcome of critically ill patients. The traditional approach to studying the genetic contribution requires the availability of families with multiple members who have experienced similar disease conditions, a situation that is nearly impossible to find in the case of trauma. Association studies looking at unrelated individuals across populations require large economic and labor-intensive efforts. Thus, a candidate gene approach has been the sole methodology used to correlate genetic variability with clinical outcome. However, this approach cannot provide a comprehensive description of a multigenic condition. Animal models are an alternative for studying the genetic contributions to variability in the response to injury. A murine model is ideal because a large set of inbred strains are available; congenic, consomic, transgenic, and recombinant strains can also be used. Employing this paradigm, we have demonstrated that the response to several stressors, such as injection of E. coli lipopolysaccharide (LPS) and polymicrobial sepsis induced by cecal ligation and puncture (CLP), is modified by the genetic background. The inflammatory response in mice has also been shown to be affected by sex, age, and other, nongenetic components such as diet. We have exploited the differences in response among various inbred mouse strains to map loci contributing to the inflammatory response. Fine mapping strategies allow the refinement of sets of candidate genes, which can be identified by positional cloning. Detection of genetic variation affecting the inflammatory response in murine models provides a basis for determining whether polymorphisms in orthologous human genes correlate with particular clinical outcomes from injury. Thus, discovery of these genes could impact patient care by acting as markers of a specific predisposition in humans.

Age disproportionately increases sepsis-induced apoptosis in the spleen and gut epithelium

Both aging and sepsis independently increase splenic and gut epithelial apoptosis. Sepsis-induced apoptosis in either cell type is also associated with increased mortality in young mice. We sought to determine whether age alters sepsis-induced splenic and gut epithelial cell death. Young (2 months) and aged (22 months) male ND4 mice were subjected to either single-puncture cecal ligation and puncture (CLP) with a 23-gauge needle or sham laparotomy. Apoptosis was assessed 24 hours later in the spleen and gut epithelium by active caspase 3 and hematoxylin and eosin staining. Aged septic mice had increased splenic apoptosis compared with either young septic animals or aged sham animals (15 vs. 7 vs. 5 apoptotic cells/high-powered field, P < 0.05). Similarly, aged septic animals had an elevation in gut epithelial cell death compared with either young septic or aged sham mice (33 vs. 16 vs. 6 apoptotic cells/100 contiguous crypts, P < 0.05). Elevated intestinal cell death was not associated with changes in either gut proliferation or cell division. To verify that the increase in splenic apoptosis seen in septic aged animals was not strain specific, double-puncture CLP with a 25-gauge needle or sham laparotomy was performed on young (4 months) or aged (24 months) C57BL/6 male mice. Similar to results seen in outbred animals, aged septic animals in this inbred strain had increased splenic apoptosis compared with either young septic animals or aged sham animals (23 vs. 7 vs. 4 apoptotic cells/ high powered field, P < 0.05). These results indicate that although infection and aging each independently cause an increase in splenic and gut epithelial apoptosis, their combination leads to a disproportionate increase in cell death in these rapidly dividing cell populations,and potentially plays a role in the marked increase in mortality seen with aging in sepsis.

Concept of PIRO as a new conceptual framework to understand sepsis

OBJECTIVE

To define and introduce the PIRO model for categorizing sepsis in infants and children.

DESIGN

A summary of the literature published during the 5 yrs since this concept has been formulated, along with a consensus opinion of experts in the field of sepsis and septic shock.

RESULTS

The imprecision and intrinsic heterogeneity of the patient population defined as septic has prompted the introduction of a new sepsis classification system known as PIRO. PIRO stands for predisposition, infection, response, and organ dysfunction. It is hoped that by defining the septic process through a detailed analysis of each of its component parts, the development of sepsis will be better understood. This may contribute to improved therapeutic interventions for sepsis in the future.

CONCLUSIONS

The PIRO model is a conceptual framework for understanding sepsis that has many favorable attributes. The PIRO model should be directly tested in both the research laboratory and in clinical trial designs to determine the practical value and clinical relevance of this new classification scheme for sepsis.

Age and caloric restriction diets are confounding factors that modify the response to lipopolysaccharide by peritoneal macrophages in C57BL/6 mice

Aging is the result of several detrimental changes that lead to a decrease in homeostasis, an increase in the incidence of degenerative diseases, and death. A caloric-restricted diet (CR), which consists of a significant reduction in calorie intake (40%) without malnutrition, has been shown to delay the onset of age-related diseases and pathologies and to extend life span. The aims of this study were to assess the effects of aging and CR on lipopolysaccharide (LPS)-dependant cytokine production by peritoneal macrophages (PMphis). Resident naïve PMphis were isolated from 2- to 24-month-old male C57BL/6 mice and were stimulated with Escherichia coli LPS (100 ng/mL) for 1 to 5 h in culture conditions. A linear decrease in the production of LPS-induced tumor necrosis factor alpha (TNF-alpha) and interleukin (IL) 10 was observed with age. LPS-induced IL-6 and IL-1beta levels were also reduced with age, but in a nonlinear fashion. Expression of CD14, the major receptor for LPS, on the PMphi surface was also observed to decline with age. Moreover, TNF-alpha production by PMphis was reduced in mice undergoing the two different CR diets of limited daily feeding and intermittent fasting, as compared with ad libitum-fed mice. The results of this study add the new variables age and diet to the paradigm proposing that the response to LPS is modulated by multiple components, including genetic background and sex.

Arterial baroreflex function determines the survival time in lipopolysaccharide-induced shock in rats

Lipopolysaccharide (LPS) mimics many of the effects of septic shock. LPS-induced death has been attributed to systemic hypotension, hyporeactiveness to vasoconstrictors, metabolic acidosis, and organ damage. However, there is no research directed to the involvement of the baroreflex sensitivity (BRS) in LPS-induced death. The purpose of this study was to evaluate the effect of BRS on the survival time after lethal LPS challenge. Four groups of rats were used. Each rat received an equivalent dose of intravenous LPS (50 mg/kg). It was found that the anesthetized sinoaortic-denervated (SAD) rats (representative of the lowest BRS, BRS = 0.022 +/- 0.015 ms/mmHg) survived the shortest time (36 +/- 11.1 min). The conscious SAD rats (BRS = 0.198 +/- 0.035 ms/mmHg) and the anesthetized sham-operated rats (BRS = 0.304 +/- 0.072 ms/mmHg) were alive a relatively long time (101 +/- 11.5 min and 110 +/- 12.4 min, respectively). The conscious sham-operated rats (BRS = 0.943 +/- 0.097 ms/mmHg) survived the longest time (148 +/- 6.5 min). These results demonstrated that arterial baroreflex function determined the survival time in the LPS-induced lethal shock.

High-dose exogenous iron following cecal ligation and puncture increases mortality rate in mice and is associated with an increase in gut epithelial and splenic apoptosis

OBJECTIVES

Despite having dysregulated iron metabolism, critically ill patients may receive exogenous iron for the treatment of anemia. Iron is associated with increased tissue apoptosis and may facilitate bacterial growth. We hypothesized that exogenous iron administration given after the onset of sepsis would lead to increased mortality rate. To discriminate between elevated cell death and bacterial overgrowth as potential mediators of mortality, we examined gut epithelial and lymphocyte apoptosis and systemic bacterial counts in animals given iron supplementation after the onset of sepsis.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal laboratory in a university medical center.

SUBJECTS

Male C57BL/6 mice, 6-10 wks old.

INTERVENTIONS

C57BL/6 mice were subjected to cecal ligation and puncture (CLP), a well-accepted model of intra-abdominal sepsis, followed by daily subcutaneous injections of either 1 mL of iron dextran (5 mg/mL) or 0.9% NaCl for a total of five doses. Animals (n = 78) were followed for survival for 8 days. Separate cohorts (n = 76) were killed 24 or 48 hrs after cecal ligation and puncture or sham laparotomy and were assayed for gut epithelial and splenic apoptosis as well as for quantitative blood cultures.

MEASUREMENTS AND MAIN RESULTS

Eight-day survival was 7% in animals that received iron and 26% in mice that received 0.9% NaCl (p < .005). Iron supplementation after cecal ligation and puncture increased apoptosis by both active caspase 3 and hematoxylin and eosin staining in both the intestinal epithelium and spleen at 24 hrs (p < .05). Iron supplementation after sham laparotomy did not cause mortality or elevated apoptosis. Quantitative blood cultures revealed no detectable differences between septic animals that received iron and those that received 0.9% NaCl.

CONCLUSIONS

High-dose iron supplementation with iron dextran after the onset of sepsis significantly increases mortality rate in this animal model. Iron-induced mortality may be mediated by an increase in gut epithelial and splenic apoptosis, whereas severity of bacteremia does not appear to play a causative role.

Antibiotics Improve Survival in Sepsis Independent of Injury Severity but do not Change Mortality in Mice with Markedly Elevated Interleukin 6 Levels

Genetically identical mice have a heterogeneous response to antibiotic therapy in sepsis, with only a subset deriving therapeutic benefit. We sought to determine whether the severity of a septic insult correlates with the survival benefit conferred by antibiotics. We also sought to determine whether antibiotics given 12 h after injury alter survival in animals predicted to die based upon high interleukin (IL)-6 levels drawn 6 h earlier. Adult male ND4 mice (n = 363) were subjected to double-puncture cecal ligation and puncture (CLP) with a 19-, 21-, or 23-gauge needle. Animals were randomized to receive imipenem or 0.9% NaCl every 12 h after CLP for 5 days. Ten-day survival was 16%, 26%, and 52%, respectively, for untreated animals. Antibiotics decreased the absolute risk of death 17% to 23% regardless of injury severity. In a separate cohort, mice (n = 37) were subjected to single or double-puncture CLP with a 21-gauge needle. IL-6 levels were assayed 6 h postoperatively and mice were followed for survival. Levels greater than 14,000 pg/mL were identified as predicting a 100% mortality (7/7 animals dead). A third set of mice (n = 94) then underwent double-puncture CLP with either 21-, 23-, or 25-gauge needle and had IL-6 levels measured in a similar fashion. Animals were randomized to receive imipenem or 0.9% NaCl beginning 12 h postoperatively (6 h after IL-6 levels were drawn) and continued for 5 days or until death. Although antibiotics decreased mortality overall, all animals with IL-6 levels greater than 14,000 pg/mL (n = 13) died, regardless of whether they received antibiotics or the gauge of needle used. These results indicate that antibiotics improve outcome in murine sepsis, regardless of injury severity. Furthermore, there is a threshold IL-6 level that can be identified 6 h after sepsis above which animals are destined to die, and antibiotic treatment does not alter their outcome.

Humane Endpoints in Shock Research

In biomedical research using animal models, the phrase "humane endpoints" refers to predetermined criteria used to judge when the research animals should be humanely euthanized. The intended goal of humane endpoints is to minimize the distress or suffering of research animals; however, if applied incorrectly, this well-intended concept could lead to premature decisions and inaccurate data, resulting in a waste of animal life. A concensus on specific endpoints for shock and inflammation research is not available but several biochemical, physical and behavioral parameters have been suggested for other research models. In addition, the authors have found, in the studies presented here, that increasing body weight, decreased body temperature, and inability to ambulate are important parameters in a model of cecal ligation and puncture. However, it is clear that the applicability of these endpoints may change with the model of disease, intensity of insults, experimental treatments and other factors. Consequently, humane endpoints should be assigned cautiously and preferably after preliminary studies to prevent aberrant research results. In order to accomplish this, investigators must become aware of certain concepts including: when to implement endpoints, what endpoints to consider, and how to establish the endpoints for their studies. Equipped with the basic principles of humane endpoints, investigators can make informed decisions that meet current standards of animal care while still achieving the scientific goals of their research studies.