Modulation of cytokine responses in sepsis

Beneficial pleiotropic actions of melatonin in an experimental model of septic shock in mice: regulation of pro-/anti-inflammatory cytokine network, protection against oxidative damage and anti-apoptotic effects

Septic shock, the most severe problem of sepsis, is a lethal condition caused by the interaction of a pathogen-induced long chain of sequential intracellular events in immune cells, epithelium, endothelium, and the neuroendocrine system. The lethal effects of septic shock are associated with the production and release of numerous pro-inflammatory biochemical mediators including cytokines, nitric oxide and toxic oxygen and nitrogen radicals, together with development of massive apoptosis. As melatonin has remarkable properties as a cytokine modulator, antioxidant and anti-apoptotic agent, the present study was designed to evaluate the possible protective effect of melatonin against LPS-induced septic shock in Swiss mice. We observed that intraperitoneally (i.p.) administered-melatonin (10 mg/kg) 30 min prior, and 1 hr after i.p. LPS injection (0.75 mg/animal) markedly protected mice from the LPS lethal effects with 90% survival rates for melatonin and 20% for LPS-injected mice after 72 hr. The melatonin effect was mediated by modulating the release of pro-/anti-inflammatory cytokine levels, protection from oxidative damage and counteracting apoptotic cell death. Melatonin was able to partially counteract the increase in LPS-induced pro-inflammatory cytokine levels such as tumor necrosis factor-alpha, IL-12 and interferon-gamma at the local site of injection, while it increased the production of the anti-inflammatory cytokine IL-10 both locally and systemically. Furthermore, melatonin inhibited the LPS-induced nitrite/nitrate and lipid peroxidation levels in brain and liver and counteracted the sepsis-associated apoptotic process in spleen. In conclusion, we have demonstrated that melatonin improves the survival of mice with septic shock via its pleiotropic functions as an immunomodulator, antioxidant and anti-apoptotic mediator.

Smoke inhalation enhances early alveolar leukocyte responsiveness to endotoxin

BACKGROUND

Pulmonary dysfunction after smoke inhalation and thermal injury is associated with excessive morbidity and mortality. The purpose of this study was to evaluate alveolar leukocyte function after thermal injury and smoke inhalation.

METHODS

Twenty-one patients with thermal injury only (n = 8); thermal injury and smoke inhalation injury (n = 8); and nonburned controls (n = 5) were assessed by means of bronchoscopically directed lavage (bronchoalveolar lavage [BAL]) on the first and fourth days postinjury. BAL-isolated pulmonary leukocytes were assessed for number, composition, viability, and production of tumor necrosis factor (TNF)alpha, interleukin (IL)-8, and IL-6 in response to 100 ng/mL of lipopolysaccharide (LPS) (mean +/- SEM; significance at p < 0.05).

RESULTS

Six of eight Smoke patients had gross evidence of lung injury. On day 1, Smoke and Burn BAL isolates yielded greater cell counts than Control (10.6 vs. 4.5 vs. 2.4 x 10(6)/mL). Smoke macrophages on day 1 produced more TNFalpha (1.2 vs. 0.2 ng/mL), IL-6 (8.0 vs. 1.9 ng/mL), and IL-8 (85 vs. 32 ng/mL) after LPS stimulation compared with respective unstimulated (0 ng/mL of LPS) day-1 Smoke cells. LPS-stimulated Burn cells on day 1 produced more IL-8 (150 vs. 62 ng/mL) but not TNFalpha (0.4 vs. 0.25 ng/mL) or IL-6 (1.8 vs. 0.69 ng/mL), when compared with respective unstimulated Burn cells. By day 4, LPS-stimulated Smoke and Burn cells produced significantly more TNFalpha (Smoke, 0.41 vs. 0.16 ng/mL; Burn, 0.87 vs. 0.51 ng/mL) and IL-6 (Smoke, 2.5 vs. 0.47 ng/mL; Burn, 4.1 vs. 1.47 ng/mL), but not IL-8 (Smoke, 51.1 vs. 51.1 ng/mL; Burn, 54.4 vs. 55.6 ng/mL), compared with respective unstimulated day-4 cells.

CONCLUSION

Smoke inhalation induces a massive influx of alveolar leukocytes that are primed for an early, enhanced LPS-activated cytokine response compared with alveolar leukocytes isolated after burn injury alone or normal controls.

Transgenic mice expressing rabbit C-reactive protein are resistant to endotoxemia

C-reactive protein (CRP), the prototypic acute-phase reactant in humans, is synthesized in liver in response to a wide variety of inflammatory stimuli. We have generated a line of transgenic mice that express rabbit CRP from the rat phosphoenolpyruvate carboxykinase (PEPCK) promoter in response to gluconeogenic signals. Here we show that transgenic mice expressing high levels of CRP were partially protected from a lethal challenge of bacterial lipopolysaccharide compared with littermates in which CRP expression had been suppressed. Similar protection was observed with challenges from platelet-activating factor (PAF) and the combination of tumor necrosis factor alpha (TNF-alpha) plus interleukin 1beta, but not with TNF-alpha alone. We further demonstrate that although PAF was able to bind CRP, the mechanism by which CRP provides protection probably does not involve sequestration of PAF. The biologically inactive precursor of PAF, lyso-PAF, also bound CRP but did not render the transgenic mice sensitive to PAF when CRP-expressing animals were simultaneously challenged with PAF and an excess of lyso-PAF. These results suggest that CRP functions in vivo by modulating host defense systems.