Erythropoietin reduces lipopolysaccharide-induced cell damage and midkine secretion in U937 human histiocytic lymphoma cells

Introduction: Erythropoietin (EPO) is a haematopoietic stimulatory protein that is used to treat anaemia in patients on dialysis. In addition, EPO has been shown to have anti-inflammatory properties, which may be important as dialysis patients tend to exist within a chronic, low-grade inflammatory state, and tend to be more susceptible to infections. It has been suggested that EPO has direct immunomodulatory potency on monocytes/macrophages. Methods: In this study, we aimed to clarify the effects of EPO during the inflammatory processes in human mononuclear phagocytic cells by monitoring the secretion of the following cytokines; midkine, tumour necrosis factor alpha (TNF-alpha), and interleukin-6 (IL-6). For this purpose, U937 human histiocytic lymphoma cell lines were used. Time-dependent effects of varying doses of EPO (0.1 to 50 IU/ml) treatment during lipopolysaccharide (LPS)-mediated cytotoxicity was measured by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide test. LPS-stimulated midkine secretion was measured immunohistochemically and quantification of TNF-alpha, IL-6 and midkine secretion was achieved by ELISA. Results: EPO treatment prevented the direct toxic effects of LPS on the U937 cells. TNF-alpha, IL-6 and midkine secretions were found to increase in the U937 cells in response to LPS treatment. Interleukin-6 response was varied in a doseand time-dependent manner. Conclusions: Treatment with EPO significantly inhibits the LPS-induced secretion of midkine and TNF-alpha regardless of the dosage. The data presented here provide the first evidence to indicate that EPO treatment directly reverses some of the cytotoxic and secretory effects of LPS in mononuclear cells. Inhibition of midkine secretion might be responsible for the anti-inflammatory role of EPO.