Morphology of cardiac muscle in septic shock. Observations with a porcine septic shock model

The morphology of cardiac muscle was investigated in a porcine model of septic shock, created by intermitted application of Escherichia coli-endotoxin. The earliest lesions, found after 18 h of septic shock, were endothelial cell swelling, marked leucostasis and slight ischaemic alterations of the muscle fibres. At the end point of the experiments, after 48 h, some fibrin thrombi were found associated with more pronounced ischaemic alterations of cardiac muscle cells and some necrotic fibres. Comparing these findings with the severe endothelial and muscle fibre lesions found in skeletal muscle, the endothelial cells of the heart microvasculature, are clearly more resistant to the attack of the endotoxins and mediators liberated in septic shock.     

Treatment of LD100 Escherichia coli septic shock with netilmicin and methylprednisolone in baboons

Treatment efficacy with netilmicin sulphate/methylprednisolone sodium succinate in a severe septic shock baboon model, using an LD₁₀₀ of liveEscherichia coli, was evaluated. All the animals treated with both netilmicin and methylprednisolone were premanent ( 7 days) survivors, whereas none of the untreated baboons lived more than 24 hours. These results indicate that, in a baboon model, netilmicin is an effective alternative to gentamicin (with methylprednisolone) in the treatment of severe septic shock.     

Skeletal muscle oedema and muscle fibre necrosis during septic shock. Observations with a porcine septic shock model

In domestic pigs, intermitted application of Escherichia coli-endotoxin was used to create an animal model for a prolonged hypo- and hyperdynamic septic shock-like state and to investigate mechanisms of multiple organ failure. Here, we describe the changes in skeletal muscle after 18 h (2 animals) and 48 h (6 animals) of septic shock. Two pigs for each observation period that received physiologic saline solutions instead of endotoxin served as controls. The earliest lesions were endothelial cell damage with endomysial oedema and swelling of mitochondria in muscle fibres. With increasing degree of endothelial cell damage, pericytes showed degenerative changes with cytoplasmic fragmentation and karyolysis. After 48 h of shock, endomysial oedema was increased with fibrinogen present. Muscle fibre diameters were increased and swollen mitochondria and segmental necrosis of muscle fibres were frequently observed. However, phagocytic reaction or regenerative changes were not detected. In this respect, skeletal muscle lesions in septic shock differ from ischemic damage, which is characterized by early phagocytosis. Tumour necrosis factor alpha (TNF) was increased greatly and significantly in the serum of the pigs that received endotoxin. The lesions described may be the result of both direct damage to muscle fibres by the endotoxin and/or the increased levels of TNF and indirect damage because of the increased diffusion distance, due to the endomysial oedema. The loss of blood proteins into the endomysium may also play a role in generating hypoproteinemia in patients with septic shock.     

Role of T cells in a murine model of Escherichia coli sepsis

To study the role of T cells in gram-negative sepsis, we developed a mouse model in which i.v. injection of Escherichia coli results in severe systemic illness, with high mortality rates after day 5. A large proportion of both CD4(+) and CD8(+) T cells are activated within 1 day after infection, as evidenced by up-regulation of CD69 and down-regulation of CD62L. Even more surprisingly, T cell-deficient mice exhibit markedly decreased disease severity compared to WT mice, indicating a pathogenic role of T cells. Mice lacking IFN-gamma also show diminished disease, and exhibit reduced T cell activation. Therefore, the pathogenic role of T cells may be mediated by IFN-gamma. Both T cell- and IFN-gamma-deficient mice have reduced serum IL-6 levels compared to WT mice, suggesting that T cells may stimulate innate immune responses, resulting in enhancement of disease. These data indicate an important role for T cells in a mouse model of E. coli sepsis, and reveal an unexpected early and pathogenic T cell response to this bacterial infection.     

Prevention of lethality and suppression of proinflammatory cytokines in experimental septic shock by microencapsulated CNI-1493.

CNI-1493, a newly developed, water-soluble tetravalent guanylhydrazone, is a powerful inhibitor of tumor necrosis factor (TNF) and interleukin-1 (IL-1) synthesis. Microencapsulation of drugs into microcapsules that target macrophages has improved the effectiveness of both TNF and IL-1 neutralizing antibodies in experimental models of septic shock. It is the purpose of this study to determine if microencapsulation of CNI-1493 will improve cytokine inhibition. CNI-1493 was microencapsulated using albumin into 1 microm spheres. Comparable amounts of CNI-1493 in solution and in microencapsulated form were added to 1 ml aliquots of whole blood along with 100 ng of endotoxin. TNF and IL-1 were measured by ELISA. Microencapsulated CNI-1493 was also given to rats with endotoxic shock (15 mg/kg Escherichia coli endotoxin) and rats with peritonitis induced by peritoneally injecting 10(10) CFU E. coli. Equivalent amounts of encapsulated and solution CN I-493 were given intravenously. Endotoxin 15 mg/kg was also given to rats 6 and 24 h after a dose of encapsulated CNI-1493 to determine the duration of action of encapsulated drug. The microencapsulated CNI-1493 produced significantly greater inhibition of TNF and IL-1 at all doses in the whole blood model. There was significantly improved survival and cytokine inhibition in the endotoxic shock model as well as the peritonitis model in rats treated with microencapsulated CNI-1493. There was also 83% survival in rats given endotoxin 24 h after a dose of encapsulated CNI-1493. From these data, we conclude that CNI-1493 is a potent inhibitor of cytokine production and is greatly potentiated by microencapsulation, which transports the drug to macrophages.     

Push-pull sorbent-based pheresis treatment in an experimental canine endotoxemia model: preliminary report.

The Biologic-DTPF System (DTPF), an extracorporeal blood treatment device with potential to treat sepsis, was tested in a preliminary study using a canine endotoxemia model. Six dogs were used and they formed four treatment groups, as control group (n=1) and three groups based on the type of sorbent present in the plasma filter (PF) system: sham treatment with no sorbent (n=1), charcoal as sorbent (n=2), and charcoal/silica as sorbent ("silica" group, n=2). Cardiodynamic data were recorded before treatment and every 30 minutes, and blood samples were collected to determine blood chemistry and to detect the levels of endotoxin and selected plasma cytokines: interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF). The dogs were given Escherichia coli endotoxin (2 mg/kg) as an intravenous drip (extended over a period of 30 minutes). Thirty minutes after the end of infusion all animals except the control were treated with the DTPF system for four hours. To determine the effect of treatment, data collected at one hour from the initiation of treatment until the end of treatment were compared between control and treated dogs. The endotoxin levels in the control dog were higher (P < 0.05) than other groups. The control dog had lower levels of TNF than other groups. The control dog had similar levels of IL-1 (P > 0.05) and higher levels (P < 0.05) at 4 hours into treatment compared to other groups. The control dog had similar levels of IL-6 as other groups (P > 0.05). In the control dog, the mean arterial pressure (MAP) fell and then remained low but stable at 1-4 hours. The charcoal group had lower MAP than the control dog at 1-4 hours (P < 0.05). The silica group had higher MAP levels similar to the control dog. After treatment, the control dog had higher (P < 0.05) values of hematocrit, hemoglobin, calcium, potassium, and albumin compared to the treated groups. As expected for a system removing plasma during sepsis, the DTPF System had some adverse effects on the physiologic status of the dogs, especially when loaded with charcoal sorbent only. The findings of the present study suggest that the filters are capable of eliminating endotoxin and there is some evidence of cytokine removal. Although the charcoal dogs did poorly, addition of silica to the sorbent offset any negative effects. Further work is underway to improve the efficiency of the system, primarily to enhance the capacity of the sorbents for cytokines. A more realistic canine sepsis model with mortality after several days (the Escherichia coli- infected intraperitoneal clot) will also be considered in future studies.     

Presence and expression of aerobactin genes in virulent avian strains of Escherichia coli.

Virulent and nonvirulent isolates of avian Escherichia coli were tested for the presence of aerobactin genes by colony hybridization with a specific gene probe constructed from plasmid pABN1 (A. Bindereif and J. B. Neilands, J. Bacteriol. 153:1111-1113, 1983). Positive hybridization with the gene probe was highly correlated with virulence, as measured by the 50% lethal dose of the strains for chicks. Evidence for the expression of aerobactin genes in the virulent strains was obtained by demonstrating their susceptibility to cloacin DF13, which binds to the same receptor that binds aerobactin, and their ability to produce aerobactin, as revealed by cross-feeding the E. coli mutant WO987 (aroB fepA iuc iut+), which is unable to synthesize but capable of taking up aerobactin. We suggest that the production of aerobactin is involved in the virulence of avian septicemic E. coli.     

L-alpha-phosphatidylcholine-induced stimulation of PGI2 production in canine gallbladders following hypovolemic shock and Escherichia coli sepsis

In vitro production of PGI2 in canine gallbladders subjected to hypovolemic shock and Escherichia coli sepsis was studied to determine whether a precursor above arachidonic acid in the cyclooxyenase cascade might be operative in the production of prostacyclin, which, in turn, may play a role in the pathogenesis of acute acalculous cholecystitis (AC). L-alpha-phosphatidylcholine (LaP), an arachidonic acid precursor, was used as the test agent. LaP did not stimulate PGI2 production from either gallbladder surface in the hypovelimic animals or the mucosa of the septic shock group. However, it did stimulate PGI2 production from the SS serosa compared with controls, 1375 +/- 432 versus 633 +/- 198 pg/cm2/min (P less than .05). In conclusion, lack of stimulation of PGI2 in the hypovolemic model suggests that PGI2 does not play a role in AC. Alternatively, it may play a role in preventing this disease process in septic shock. This study demonstrates the use of precursors of arachidonic acid and the cyclooxygenase pathway as active participants in the production of PGI2, although it is unclear whether the prostacyclin produced helps prevent AC in septic shock.     

Interleukin-2 and granulocyte-macrophage colony-stimulating factor stimulate growth of a virulent strain of Escherichia coli.

The effect of human recombinant interleukin-2 (IL-2) and human recombinant granulocyte-macrophage colony-stimulating factor on the growth of a virulent strain of Escherichia coli in tissue culture medium and in untreated, normal mouse serum was investigated. Both of these cytokines enhanced the growth of the microorganism two- to threefold in tissue culture medium with or without additional fetal calf serum and in untreated mouse serum. IL-4 did not have any effect on the growth of this microbe under the conditions tested. That the enhancement of growth seen with recombinant IL-2 was due to the active cytokine was shown by the following data: (i) addition of an antibody to IL-2 abrogated the growth-promoting effect; (ii) the excipient buffer, which contained everything except the active cytokine, was inactive in modifying bacterial growth; and (iii) heat-inactivated recombinant IL-2 did not promote enhanced microbial growth. The enhancement of growth with IL-2 was significant with concentrations as low as 1 U/ml. Growth of an avirulent strain of E. coli was not stimulated by IL-2. Moreover, addition of IL-2 to growth virulent E. coli in tissue culture medium led to rapid removal of the cytokine from the medium. Collectively, these data suggest that cytokines may act as growth factors for some virulent bacteria.     

Role of platelets in the pathogenesis of canine endotoxin shock.

Endotoxin-platelet interactions are thought to be of major importance in the response of dogs and other species to bacterial endotoxin; the mechanisms postulated are: (i) the release of vasoactive substances, (ii) the formation of occlusive platelet aggregates, and (iii) induction of intravascular coagulation. The role of platelets in canine endotoxin shock was examined in animals with thrombocytopenia induced by estrogen pretreatment (less than 10,000 platelets/mm3) and in controls. After intravenously administered endotoxin, the hemodynamic responses, mortality, and gross necropsy findings were similar in both groups. These data indicate that endotoxin-platelet interactions are not determinative in the pathogenesis of canine endotoxin shock.     

Protective role of interleukin 6 in the lipopolysaccharide-galactosamine septic shock model.

C57BL/6J mice given low doses of lipopolysaccharide (LPS) (100 ng per mouse) plus D-galactosamine (8 mg per mouse) die within 24 h following LPS administration. We used this septic shock model to confirm the role of tumor necrosis factor in mortality using a monoclonal antibody to tumor necrosis factor to prevent lethality. Furthermore, we demonstrated that interleukin 6, rather than playing a lethal role, protected mice against death in this septic shock model. Antibody to interleukin 6 did not affect the fatal outcome in this low-LPS-dose model. However, pretreatment with antibody to tumor necrosis factor did protect the mice against death, in a dose-dependent manner. Moreover, mortality was enhanced by pretreatment with antibody to interleukin 6 when tumor necrosis factor was partly limited by anti-tumor necrosis factor treatment. Mortality was significantly reduced by pretreatment with both recombinant interleukin 6 and low doses of antibody to tumor necrosis factor; in the absence of the low dose of antibody to tumor necrosis factor, interleukin 6 alone did not confer any protection. These data demonstrate in vivo antagonistic activities of tumor necrosis factor and interleukin 6 and show that interleukin 6 can play a protective role against death from septic shock.     

Role of granulocytes and monocytes in experimental Escherichia coli endocarditis.

The role of granulocytes and monocytes during the induction and course of Escherichia coli endocarditis was investigated in rabbits by selectively depleting monocytes from the circulation with the drug VP16-213 and granulocytes and monocytes with nitrogen mustard. For induction, the number of E. coli needed to infect the vegetations in 50% of the rabbits was significantly lower in rabbits with combined granulocytopenia and monocytopenia than in those with selective monocytopenia or in control rabbits, whereas the number of E. coli needed to infect 50% of the rabbits did not differ between the latter two. During the course of the endocarditis in endocardial vegetations, the numbers of CFU per gram of vegetation were significantly higher in the rabbits with combined granulocytopenia and monocytopenia than in the monocytopenic and control rabbits but did not differ between the latter two. The numbers of granulocytes in the circulation and the numbers of CFU per gram of vegetation showed a significant negative correlation that was not measurably influenced by the duration of the disease but was dependent on the number of E. coli injected for the induction of endocarditis. Granulocytes were found to be most effective at the lowest numbers of bacteria injected. In the circulation, too, the numbers of CFU per milliliter were significantly higher in rabbits with combined granulocytopenia and monocytopenia than in those with selective monocytopenia and control rabbits, and there was a significant negative correlation between the numbers of granulocytes and CFU per milliliter of blood. From these findings we conclude that granulocytes play a protective role during the induction and course of E. coli endocarditis in rabbits, whereas no role is demonstrable for monocytes.     

Lethal endotoxic shock using alpha-galactosylceramide sensitization as a new experimental model of septic shock

The effect of alpha-galactosylceramide (alpha-GalCer) on lipopolysaccharide (LPS)-mediated lethality was examined. Administration of LPS killed all mice pretreated with alpha-GalCer, but not untreated control mice. The lethal shock in alpha-GalCer-sensitized mice was accompanied by severe pulmonary lesions with marked infiltration of inflammatory cells and massive cell death. On the other hand, hepatic lesions were focal and mild. A number of cells in pulmonary and hepatic lesions underwent apoptotic cell death. alpha-GalCer sensitization was ineffective for the development of the systemic lethal shock in Valpha14-positive natural killer T cell-deficient mice. Sensitization with alpha-GalCer led to the circulation of a high level of interferon (IFN)-gamma and further augmented the production of tumor necrosis factor (TNF)-alpha in response to LPS. The lethal shock was abolished by the administration of anti-IFN-gamma or TNF-alpha antibody. Further, the lethal shock did not occur in TNF-alpha-deficient mice. Taken together, alpha-GalCer sensitization rendered mice very susceptible to LPS-mediated lethal shock, and IFN-gamma and TNF-alpha were found to play a critical role in the preparation and execution of the systemic lethal shock, respectively. The LPS-mediated lethal shock using alpha-GalCer sensitization might be useful for researchers employing experimental models of sepsis and septic shock.     

Role of nitric oxide in thermoregulation during septic shock: involvement of vasopressin

We tested the hypothesis that the nitric oxide (NO) pathway in the central nervous system (CNS) plays a role in hypothermia, as well as in the febrile response during experimental septic shock, by regulating vasopressin (AVP) release. Experiments were performed on male Wistar rats treated with N ^G-nitro-l-arginine methyl ester (l-NAME), a non-selective NO synthase (NOS) inhibitor, injected intracerebroventricularly (250 µg/1 l) 30 min before lipopolysaccharide (LPS) 1.5 mg/kg i.v. injection. One hour after LPS administration we observed a significant drop in body temperature (hypothermic response), followed by a temperature increase after the second hour (febrile response), which remained until the end of the experiment. Increased plasmatic AVP levels were concomitantly observed during hypothermia, nearly returning to basal levels during the febrile phase. When l-NAME was administered with LPS, plasmatic AVP concentrations remained high throughout the experiment, hypothermia was accentuated and the febrile response was abolished. Additionally, pre-treatment with -mercapto-,-cyclopentamethylenepropionyl¹, O-Et-Tyr², Val⁴, Arg⁸-vasopressin, an AVP V1 receptor blocker (10 µg/kg) administered i.v., reduced hypothermia and exacerbated the febrile response to endotoxin. In conclusion, our data indicate that the central NO pathway plays an inhibitory role in AVP release during experimental septic shock, which seems to be critical for the thermoregulation during this pathophysiological state.     

Role of the kallikrein-kininogen-kinin system in the inflammatory reaction and septic shock

Kinins, which are vasodilatory, permeability-increasing, pain-producing polypeptides, are formed from inactive precursors: kininogens. Their actions make kinins a particularly powerful potential pro-inflammatory factor. However the absence of specific antagonists has so far made it impossible to ascribe them a definite role in inflammation. Two studies of experimental endotoxemia in burns patients, septicemia and septic shock have demonstrated the following facts: activation occurs of specific ( pKK ) and non-specific (plasminogen-plasmin system) kininogenases , K-HMW and K-LMW levels are significantly decreased. Kininogen consumption corresponds to increased BDK production. This would therefore appear to be one of the humoral factors responsible for haemodynamic changes. Though measurement of kininogen levels is still a painstaking process, the development of chromogenic substrates has made pKK and KK measurement simple and fast. Once they have been validated physico-pathologically in a large number of patients, such assays should take their place among the diagnostic weapons of clinical biology at the disposal of clinicians.     

Effect of fangchinoline in murine models of multiple organ dysfunction syndrome and septic shock

OBJECTIVE AND DESIGN: To study the effect of the alkaloid fangchinoline on zymosan-induced multiple organ dysfunction syndrome (MODS) and Escherichia coli (E. coli)-induced septic shock. MATERIAL: Male ICR mice were used. Macrophages were isolated from peritoneal cavity for in vitro study. Treatment: Fangchinoline was administered i.p. at a dose of 1 or 5 mg/kg into the mice. METHODS: MODS was induced by intraperitoneal (i.p.) injection of zymosan at a dose 1.0 or 0.8/g b.w. E. coli-induced septic shock was provoked by i.p. inoculation of 5 x 10(8) bacterial cells into mice. TNF-alpha in serum and supernatants from peritoneal macrophages was detected by the use of L-929 cell cytotoxic assay. Alternative pathway (AP) complement activity was determined by hemolytic assay. RESULTS: Fangchinoline increased the survival rate in lethal MODS and septic shock. The alkaloid prevented the loss of body weight and liver enlargement in MODS and suppressed serum tumor necrosis factor-alpha (TNF-alpha) accumulation in MODS and septic shock. CONCLUSIONS: The result suggest that fangchinoline due mainly to its ability to downregulate TNF-alpha production might have protective effect in murine models of zymosan-induced MODS and E. coli-induced septic shock.     

A morphologic study of live Escherichia coli organism shock in baboons.

This study was designed to examine the response of the baboon during a 24 hr period following live Escherichia coli organism infusion. Experiments were performed on 10 young adult adolescent baboons. Eight of the baboons received a mean concentration of 1.5 × 10¹⁰ organisms/kg infused during a 30 to 360 min period. Two control baboons received anesthesia and 0.9% sodium chloride solution during the 24 hr period. Heart, lung, liver, and kidney were evaluated with both light and electron microscopy and the morphologic data were interrelated with the physiologic data. The acute lung lesion seen in 2 to 6 hr studies was not found in this prolonged shock model. Both the liver and kidney exhibited dysfunction; these pathophysiologic alterations were accompanied by morphologic changes. Sinusoidal fibrin thrombi and hepatocyte damage were observed in the liver, and were associated with increases in LDH, FLDH, and hypoglycemia. Glomerular fibrin thrombi and tubular epithelial changes of cytoplasmic vacuolization and brush border loss were present in the kidney, and an increase in BUN levels was noted. Our data would indicate that the live E. coli infusion baboon model shows pathologic and physiologic derangements quite similar to those reported in the patient in septic shock.