Protective effect of the dimer of 16,16-diMePGB1 against KCN-induced mitochondrial failure in hepatocytes

Kallikrein activates prothrombin

Kallikrein is a multitalented enzyme in hemostasis and inflammation. Normally, kallikrein is formed in intrinsic hemostasis and activates factor XII. A total of 10 microL of 0 to 100 microg/mL human plasma kallikrein in 6% human albumin-PBS were incubated with 90 microL 111.1 microg/mL prothrombin in 6% human albumin in absence and presence of 23 mM Ca(++). After 0 to 64 minutes (37 degrees C), 100 microL of 2.5 M arginine, pH 9, were added. Fifty microliters of 0.72 mM HD-CHG-Ala-Arg-pNA in 1.36 M arginine were added and increase in absorbance at 405 nm was determined. Within 8 minutes (37 degrees C), 1 microg/mL kallikrein, ie, 2.5% of the normal plasmatic prekallikrein concentration, generates approximately 3 mIU/mL thrombin in absence and 27 mIU/mL thrombin in presence of Ca(++). Kallikrein can directly activate prothrombin; there is a shortcut in the intrinsic hemostasis system that generates catalytic amounts of thrombin without following the known intrinsic clotting pathway.

Mediator Responses in Surgical Infections

BACKGROUND

Surgical infections, and sepsis in particular, are characterized by extensive release of mediators. Our laboratories have been interested in understanding how these substances contribute to morbidity and mortality during various stages of surgical infections in order to develop new and more effective therapeutics and treatment strategies.

METHODS

In a series of in vitro studies, human plasma was exposed to lipopolysaccharide (LPS), and whole blood was treated with peptidoglycan from Staphylococcus aureus. The activity of peptidoglycan also was studied in the rat, and LPS infusion was tested in dog and pig models. In a clinical study, the relation of serum LPS to multiple organ dysfunction and failure was studied in patients in the surgical intensive care unit.

RESULTS

Exposure of plasma to LPS led to formation of bradykinin, activation of the plasma kallikrein-kinin system, and reduction of kallikrein inhibitor capacity. The coagulation, fibrinolysis, and complement cascades were activated. Peptidoglycan caused rapid release of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 from macrophages and activation of the genes encoding pro-inflammatory and anti-inflammatory cytokines. In the rat, peptidoglycan induced cytokine release, caused liver and kidney dysfunction, and induced matrix metalloproteinase-9 (MMP-9) activity in the liver and lung. In the dog and pig, LPS caused substantial activation of plasma proteases. Clinically, a finding of LPS in the plasma was associated with multiple organ dysfunction and failure. These patients also revealed substantial activation of the plasma cascade systems, as well as systemic cytokine release.

CONCLUSION

On the basis of these observations, we developed a monitoring system to recognize early signs of infection.

Endotoxin pretreatment in vivo increases the mitochondrial respiratory capacity in rat hepatocytes

Administration of sublethal doses of endotoxin produces tolerance to subsequent oxidative stress in diverse animal models. Although endotoxin induces antioxidant enzymes, particularly manganous superoxide dismutase (Mn-SOD), the phenomenon of tolerance remains incompletely understood. Previously I determined that endotoxin treatment in rats increased lung mitochondrial respiration-dependent (i.e., independent of Mn-SOD) scavenging of superoxide anion. Because nonenzymatic scavenging of superoxide anion correlates with the mitochondrial membrane energy gradient, I hypothesized that endotoxin increases the mitochondrial transmembrane potential. Endotoxin treatment (500 micrograms/kg intraperitoneally 48 h earlier) increased the hepatocyte mitochondrial transmembrane potential as determined by two separate methods: the intramitochondrial sequestration of triphenylmethylphosphonium (electrical potential or delta psi) and the fluorescence intensity of the hepatocyte mitochondria when stained with rhodamine-123 and examined by confocal microscopy. These findings suggest that endotoxin treatment increased the total mitochondrial membrane potential per hepatocyte. In parallel, endotoxin treatment increased the fluorescence intensity of hepatocyte mitochondria after staining with 10-N-nonyl-acridine orange, a dye that binds to the mitochondrial inner membrane independently of the transmembrane potential. This suggests that an increase in mitochondrial inner membrane mass is responsible for the net increase in inner membrane potential per cell following endotoxin pretreatment. These findings complement previous studies in which endotoxin treatment increased the mitochondrial-specific antioxidant Mn-SOD and support the more recent finding that endotoxin treatment also increased nonenzymatic scavenging of superoxide by lung mitochondria. Taken, together, these observations suggest that mitochondrial biogenesis, and the subsequent increase in both enzymatic and nonenzymatic scavenging of superoxide anion, is a central feature of endotoxin-mediated tolerance to oxidative stress.

Continuous monitoring of mitochondrial membrane potential in hepatocyte cell suspensions

We report a simple fluorometric method for the continuous monitoring of mitochondrial membrane potential and cell viability in suspensions of hepatocytes exposed in vitro to cytotoxic agents. Suspensions of freshly isolated hepatocytes (10(6) cells/mL) preloaded with rhodamine 123 (Rh 123, 100 mumol/L) are transferred to a thermostatically controlled mixed cuvette to which the desired cytotoxic agent is added. Rh 123 is a cationic fluorophore that is actively accumulated by cells in direct proportion to the mitochondrial membrane potential. Cell viability was estimated by monitoring propidium iodide (PI) fluorescence. Exposure of cell suspensions to the mitochondrial uncoupling agent FCCP caused an immediate and titratable increase in Rh 123 fluorescence. Subsequent treatment with digitonin did not change Rh 123 fluorescence, suggeseting that Rh 123 equilibrates rapidly across the intact cell membrane. Likewise, treatment of hepatocyte suspensions with inhibitors of mitochondrial respiration (rotenone, cyanide, or menadione) caused an immediate increase in Rh 123 fluorescence. This was accompanied by a progressive increase in PI fluorescence, suggesting a causal relationship between mitochondrial depolarization and cell injury. In contrast, 1,4-benzoquinone caused a time-dependent and linear increase in PI fluorescence that paralleled changes in Rh 123 fluorescence. Comparing the time courses for changes in PI and Rh 123 fluorescence suggests that for benzoquinone, the depolarization of the mitochondria is a consequence rather than a cause of the cell injury. This modified procedure provides a simple and specific technique for continuously monitoring mitochondrial membrane potential and cell viability in suspensions of freshly isolated hepatocytes. The advantage is that there is no need to separate cells from the incubation medium, making it possible to record real-time changes in mitochondrial membrane potential and cell viability throughout the in vitro exposure period.

Loss of mitochondrial membrane potential is not essential to hepatocyte killing by allyl alcohol

Allyl alcohol-induced LDH leakage from isolated rat hepatocytes was preceded by a decrease in rhodmine 123 retention, signifying a loss of mitochondrial membrane potential. Addition of dithiothreitol (DTT) prevented the drop in membrane potential and completely prevented cell killing by allyl alcohol. In contrast, cyclosporin A and trifluoperazine delayed the loss of membrane potential without affecting cytolethality. The results indicate that a drop in mitochondrial membrane potential is not essential for allyl alcohol lethality. The mitochondrial dysfunction produced by allyl alcohol appears to be the consequence of an earlier event in the toxicity that is reversible by DTT.

Mitochondrial dysfunction during anoxia and acute cell injury

Mitochondrial function is closely linked to the maintenance of mitochondrial integrity. During short-term anoxia, ion-transport systems in the inner membrane are inhibited to protect against loss of the promotive force and associated osmotic imbalance that can cause irreversible loss of mitochondrial integrity and function. In two models of chemically induced mitochondrial failure, a prostaglandin B1 derivative, di-calciphor, protected against mitochondrial failure and prevented cell death. Characteristics were similar to those observed in mitochondria during short-term anoxia. Thus, the results indicate that di-calciphor may represent a new type of mitochondrial protectant that inhibits ion transport and thus slows the loss of osmotic stability and delays mitochondrial dysfunction under traumatic and toxicologic conditions.

Tri-Calciphor (16,16-dimethyl-15-dehydroprostaglandin B1 trimer)-mediated mitochondrial Ca2+ movements: modulation by phosphate

The trimeric derivative of 16,16-dimethyl-15-dehydroprostaglandin B1 (termed tri-Calciphor), which protects tissues against ischemic damage, induced Ca2+ efflux and swelling in mitochondria in the absence of phosphate, Mg2+ and ATP. When glutamate/malate rather than succinate was the substrate, higher tri-Calciphor concentrations were required for the ionophoretic activity. Ca2+ efflux and mitochondrial swelling induced by tri-Calciphor were completely inhibited by ATP, phosphate and Mg2+ added together, and partially inhibited with phosphate plus either ATP or Mg2+. Between 0 and 7 microM added Ca2+ and in the presence of phosphate, ATP and Mg2+, tri-Calciphor stimulated the uptake of Ca2+ by mitochondria and increased the efficiency of buffering of extramitochondrial Ca2+. Thus, depending on the assay conditions, two different effects involving Ca2+ movements and mitochondria are observed with tri-Calciphor.