In this study, blood endotoxin, HMGB1, and urinary 8-OHdG levels in patients with ARDS were significantly higher than those in healthy controls and PMX-F treatment markedly improved oxygenation and blood pressure, blood endotoxin, blood HMGB1, and urinary 8-OHdG levels. Uriu et al.22 reported that improvement of hyperdynamic circulation was directly related to endotoxin removal and that endotoxin plays an important role in the development of septic shock. Tsushima et al.11 reported that in patients with ARDS, PMX-F treatment improved circulatory disturbance and oxygenation despite the underlying disease and that mortality improved remarkably compared with that before the induction of PMX-F treatment.
HMGB1 mediates the induction of delayed endotoxin lethality and acute lung injury.23 The pathophysiology of ARDS involves resident lung cells, including epithelial cells, as well as neutrophils, monocytes/macrophages, and platelets.24 HMGB1 is released by activated macrophages as a late-phase mediator during prolonged inflammation.25 Vascular smooth muscle cells positive for HMGB1 were shown to express CRP and matrix metalloproteinase (MMP)-9.25 MMPs play an important role in pathogenic pulmonary processes, and MMP-9 is essential for remodeling of the basement membrane in various pulmonary inflammatory diseases including ARDS.26 HMGB1 binds LPS in a concentration-dependent manner, and this binding was shown to be inhibited by polymyxin B.27 A mixture of HMGB1 and LPS vs. HMGB1 or LPS alone, results in a higher increase in tumor necrosis factor-alpha production in peripheral blood monocytes.27 Thus, we propose that HMGB1 plays an important role in ARDS with endotoxemia. Recently, HMGB1 levels were shown to be higher in bronchoalveolar lavage (BAL) fluid obtained from the site of infection in patients with pneumonia than in lavage fluid from healthy control subjects, suggesting that HMGB1 release may occur predominantly at the site of infection.28 However, little is known about HMGB1 levels in BAL fluid from patients with ARDS. Measuring HMGB1 has been quite challenging because no ELISA was available until recently.20,21 Earlier studies used blotting methods for measuring HMGB1.29 Gaini et al.30 reported that median HMGB1 levels measured by ELISA were 1.54 ng/ml in non-infected patients, 2.41 ng/ml in infected patients without sepsis, 2.24 ng/ml in patients with sepsis, and 2.18 ng/ml in patients with severe sepsis. In this study, blood HMGB1 levels in patients with ARDS were extremely high (mean: 26.5 ng/ml) based on the same ELISA system. Our data may be due, in part, to disease severity or to the time of blood sampling (because HMGB1 is a “late-onset” cytokine). Recently, Sakamoto et al.31 reported that HMGB1 levels improved significantly after successful PMX-F treatment and that the circulation dynamics of patients with septic shock can be improved by reducing HMGB1 levels.
Oxidant-mediated tissue injury is probably important in the pathogenesis of ARDS.32 Oxidants are generated as a result of the inflammatory response by phagocytic cells such as mononuclear cells.33 Levels of reactive species correlate with both the disease outcome and the severity of the injury to the alveolar epithelium in acute lung injury.33 The most frequently detected and studied oxidized nucleoside in nuclear and mitochondrial DNA lesions is 8-OHdG. On DNA repair, 8-OHdG is excreted into the urine.34 Recently, investigators have reported the importance of urinary 8-OHdG in both adult and pediatric medicine.35,36 In this study, urinary 8-OHdG levels were significantly higher in patients with ARDS than in healthy volunteers. Oxidative stress is induced by administration of LPS. We first showed that urinary 8-OHdG levels in patients with ARDS correlated with blood endotoxin levels. Li et al.37 reported that the degrees of inflammation and oxidative stress were positively related to LPS. It may be important to study correlation between urinary 8-OHdG and other known oxidative stress markers including plasma malondialdehyde, plasma F2 isoprostanes, and plasma thiobarbituric acid reactant substances in patients with ARDS. Some investigators reported that trace elements and vitamins that support antioxidant functions are safe and may be associated with a reduction in mortality in critically ill patients.38 Nathens et al.39 reported that the early antioxidant supplementation with alpha-tocopherol and ascorbic acid reduces the incidence of organ failure in critically ill patients including patients with ARDS. In contrast, oxidative stress is increased in critically ill patients according to antioxidant vitamin intake, independent of disease severity.40 In this study, PMX-F treatment significantly inhibited urinary 8-OHdG levels in patients with ARDS.
In this study, we could not compare between patients with ARDS with PMX-F treatment and those who did not receive PMX-F treatment. Patients with ARDS were severe, therefore, randomized study was ethically difficult. However, it would be needed to compare patients with ARDS treated with PMX-F treatment or not in future. Sakamoto et al.41 reported the effectiveness of continuous hemodiafiltration (CHDF) after PMX-F treatment of septic shock patients with endotoxemia. Nakada et al.42 reported that cytokine-oriented critical care using CHDF may be an effective strategy for the treatment of septic shock. It may be needed to compare patients with ARDS with endotoxemia treated with PMX-F and those treated with CHDF or those treated with both combinations.
In summary, we showed that blood HMGB1 and urinary 8-OHdG levels are increased in patients with ARDS and that PMX-F treatment is effective in decreasing these levels.
The authors thank Mr. Hisataka Shoji, Mr. Yoshihiro Nakamura, and Mr. Misao Hachiya, Toray Medical Co., Ltd., Tokyo, Japan, for their helpful suggestions. The authors also thank Mr. Yoshinobu Takahashi, Shinmatsudo Central General Hospital, Chiba, Japan, for his technical assistance.
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