Acidic conditions exacerbate interferon-gamma-induced intestinal epithelial hyperpermeability: role of peroxynitrous acid.

OBJECTIVE: Nitric oxide (NO*) derived from exogenous donors has been shown to increase the permeability of cultured intestinal epithelial monolayers, an effect that is augmented by mildly acidic conditions. Because interferon-gamma (IFN-gamma) also increases intestinal epithelial permeability, at least partly by an NO*-dependent mechanism, we sought to determine whether IFN-gamma-induced hyperpermeability is increased under acidic conditions. METHODS: Human intestinal epithelial (Caco-2BBe) cells were grown as monolayers on permeable supports in bicameral chambers. Permeability was assessed by measuring transepithelial electrical resistance (TER) or the transepithelial passage of fluorescein disulfonic acid. Inducible nitric oxide synthase (iNOS) messenger RNA expression was determined by northern blot analysis. Concentrations of nitrite and nitrate (NO2-/NO3-), stable oxidation products of NO*, were determined using the Greiss reaction. Cellular adenosine triphosphate (ATP) levels were determined using the luciferin/luciferase method. MEASUREMENTS AND MAIN RESULTS: Incubation of Caco-2BBe monolayers with INF-gamma (1000 units/mL) at an extracellular pH (pHo) of 7.4 increased permeability to fluorescein disulfonic acid and decreased TER. However, incubation of monolayers with IFN-gamma under mildly acidic conditions (i.e., pHo 7.0-6.6) accelerated the decrease in TER and augmented the increase in permeability induced by the cytokine. IFN-gamma-induced iNOS messenger RNA expression and NO2-/NO3- accumulation in medium were unaffected by acidic conditions. At pHo 7.4, incubation of Caco-2BBe monolayers with IFN-gamma (1000 units/mL) for 72 hrs had no effect on intracellular ATP content compared with monolayers simultaneously incubated under the same conditions but in the absence of the cytokine. However, when the cells were incubated for 72 hrs with the same concentration of IFN-gamma under mildly acidic conditions (i.e., pHo 7.0 or 6.6), ATP levels were significantly decreased. At pHo 7.0, IFN-gamma-induced increases in permeability were ameliorated by addition of the following agents: 2-phenyl-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (a NO* scavenger), N(G)-monomethyl-L-arginine (a iNOS inhibitor), dimethyl sulfoxide (a hydroxyl radical scavenger), and ascorbate (a peroxynitrous acid scavenger). CONCLUSION: Mild acidosis augments IFN-gamma-induced intestinal epithelial hyperpermeability and ATP depletion, possibly by fostering the formation of peroxynitrous acid and/or hydroxyl radical.

Effect of human hemoglobin on systemic and regional hemodynamics in a porcine model of endotoxemic shock.

OBJECTIVE: Excessive release of nitric oxide has been implicated as being an important factor contributing to systemic arterial hypotension in septic shock. Hemoglobin is an effective nitric oxide scavenger. The purpose of this study was to test the hypothesis that treatment with cross-linked human hemoglobin can ameliorate systemic arterial hypotension and improve organ perfusion in a porcine model of normodynamic endotoxemic shock. DESIGN: Prospective, randomized, controlled trial. SETTING: Laboratory at a university medical center. SUBJECTS: Fourteen, male, random-bred swine. INTERVENTIONS: All animals were challenged with Escherichia coli lipopolysaccharide (400 microg/kg) infused from t = 0 to 90 mins. Pigs in group 1 (n = 7) were infused with cross-linked human hemoglobin (150 mg/kg) at t = 30 mins. Pigs in group 2 (n = 7) were infused at t = 30 mins with 150 mg/kg of dextran (average molecular weight 70,000 daltons) as a 5% (weight per volume) solution. MEASUREMENTS AND MAIN RESULTS: After infusion of endotoxin, mean arterial pressure decreased significantly (p < .05) but baseline cardiac index was maintained in both groups. In hemoglobin-treated pigs (group 1), mean arterial pressure was higher than in controls (group 2) from t = 60 to 120 mins (p < .05). There were no significant differences between the two groups in systemic vascular resistance index, renal blood flow, mesenteric blood flow, systemic oxygen delivery, or systemic oxygen extraction. Ileal mucosal blood flow was lower (p < .07) in group 1 than in group 2. Mean pulmonary arterial pressure increased relative to baseline in both groups, but was significantly greater in group 1 as compared with group 2. Compared with controls, infusion of hemoglobin significantly exacerbated endotoxin-induced arterial hypoxemia (p < .05). CONCLUSIONS: Treatment with hemoglobin improved mean arterial pressure in endotoxemic swine without significantly impairing blood flow to the renal or mesenteric vascular beds. Infusion of hemoglobin, however, significantly exacerbated endotoxin-induced pulmonary hypertension and arterial hypoxemia. Additional pharmacologic strategies may be necessary to ameliorate the potential adverse pulmonary effects of administering hemoglobin solutions to patients with sepsis.

Treatment of severe pneumonia in hospitalized patients: results of a multicenter, randomized, double-blind trial comparing intravenous ciprofloxacin with imipenem-cilastatin. The Severe Pneumonia Study Group.

Intravenously administered ciprofloxacin was compared with imipenem for the treatment of severe pneumonia. In this prospective, randomized, double-blind, multicenter trial, which included an intent-to-treat analysis, a total of 405 patients with severe pneumonia were enrolled. The mean APACHE II score was 17.6, 79% of the patients required mechanical ventilation, and 78% had nosocomial pneumonia. A subgroup of 205 patients (98 ciprofloxacin-treated patients and 107 imipenem-treated patients) were evaluable for the major efficacy endpoints. Patients were randomized to receive intravenous treatment with either ciprofloxacin (400 mg every 8 h) or imipenem (1,000 mg every 8 h), and doses were adjusted for renal function. The primary and secondary efficacy endpoints were bacteriological and clinical responses at 3 to 7 days after completion of therapy. Ciprofloxacin-treated patients had a higher bacteriological eradication rate than did imipenem-treated patients (69 versus 59%; 95% confidence interval of -0.6%, 26.2%; P = 0.069) and also a significantly higher clinical response rate (69 versus 56%; 95% confidence interval of 3.5%, 28.5%; P = 0.021). The greatest difference between ciprofloxacin and imipenem was in eradication of members of the family Enterobacteriaceae (93 versus 65%; P = 0.009). Stepwise logistic regression analysis demonstrated the following factors to be associated with bacteriological eradication: absence of Pseudomonas aeruginosa (P < 0.01), higher weight (P < 0.01), a low APACHE II score (P = 0.03), and treatment with ciprofloxacin (P = 0.04). When P. aeruginosa was recovered from initial respiratory tract cultures, failure to achieve bacteriological eradication and development of resistance during therapy were common in both treatment groups (67 and 33% for ciprofloxacin and 59 and 53% for imipenem, respectively). Seizures were observed more frequently with imipenem than with ciprofloxacin (6 versus 1%; P = 0.028). These results demonstrate that in patients with severe pneumonia, monotherapy with ciprofloxacin is at least equivalent to monotherapy with imipenem in terms of bacteriological eradication and clinical response. For both treatment groups, the presence of P. aeruginosa had a negative impact on treatment success. Seizures were more common with imipenem than with ciprofloxacin. Monotherapy for severe pneumonia is a safe and effective initial strategy but may need to be modified if P. aeruginosa is suspected or recovered from patients.

A novel leukotriene B4-receptor antagonist in endotoxin shock: a prospective, controlled trial in a porcine model.

OBJECTIVE: To evaluate the hypothesis that treatment with LY255283, a novel leukotriene B4-receptor antagonist, is beneficial in an animal model of the adult respiratory distress syndrome induced by endotoxin. DESIGN: Prospective, randomized, controlled trial. SETTING: Laboratory at a large university medical center. SUBJECTS: Twenty-five, immature, random-bred swine. INTERVENTIONS: Four groups of pigs were studied: the LPS group of animals (n = 6) were infused with Escherichia coli lipopolysaccharide (strain 0111:B4, 250 micrograms/kg) from 0 to 60 mins; the LPS + 255283 group of animals (n = 6) were infused with lipopolysaccharide as above, but were also treated with LY255283 (30 mg/kg, then 10 mg/kg/hr), beginning at -15 mins; the 255283 group of animals (n = 6) were infused with the same dose of LY255283, but were not challenged with lipopolysaccharide; and the RL control group of subjects (n = 7) received only the lactated Ringer's solution vehicle. Beginning at 30 mins, all groups were infused with dextran-70 solution as needed to maintain cardiac output at 90% to 110% of baseline value. MEASUREMENTS AND MAIN RESULTS: Treatment with LY255283 significantly (p < .05) ameliorated lipopolysaccharide-induced systemic arterial hypotension, pulmonary arterial hypertension, and arterial hypoxemia. Treatment with this drug also abrogated lipopolysaccharide-induced increases in pulmonary extravascular water content and bronchoalveolar lavage fluid protein concentration. CONCLUSIONS: These data suggest that leukotriene B4 may be an important mediator of acute lung injury in this porcine model of septic shock and acute lung injury. Further studies to assess the specificity of LY255283 as a leukotriene B4 antagonist are necessary in order to exclude the possibility that the beneficial effects of this compound are due to pharmacologic actions other than the blockade of LTB4 receptors.

Antibiotic therapy of intra-abdominal sepsis in the elderly: experience with ticarcillin and clavulanic acid.

Age is a major factor in determining the outcome for older patients with intra-abdominal sepsis. Poor outcome in these patients may be related to a number of physiologic and immunologic changes associated with aging. The treatment of intra-abdominal sepsis can itself pose special risks for the elderly. Standard regimens containing aminoglycosides have a substantial risk of nephrotoxicity, which is magnified in elderly patients. Alternatives to standard aminoglycoside-containing regimens, therefore, are desirable. Most intra-abdominal infections involve multiple pathogens, usually both aerobic and anaerobic. The polymicrobial nature of intra-abdominal sepsis mandates antimicrobial chemotherapy effective against a broad range of organisms. In the past several years, a host of new antibiotics have been introduced that used alone or in combination with other drugs has the potential of safely avoiding aminoglycosides in many patients with intra-abdominal sepsis. One such agent, ticarcillin with clavulanate potassium, is active against a wide spectrum of aerobic and anaerobic pathogens. In a prospective, randomized, open label trial, ticarcillin and clavulanate was compared with gentamicin and clindamycin. Although the sample size was too small to allow meaningful statistical comparisons of efficacy and safety, both regimens were effective and well tolerated. In general, prolonged administration of aminoglycosides is rarely indicated for the treatment of intra-abdominal sepsis in the elderly, although initial empiric use of aminoglycosides may sometimes be warranted.