Attenuation of Tumor Necrosis Factor-induced Endothelial Cell Cytotoxicity and Neutrophil Chemiluminescence

Abstract

Our laboratory has previously shown that the administration of tumor necrosis factor (TNF), a cytokine produced by activated mononuclear cells, to guinea pigs produces a syndrome similar to gram-negative sepsis or ARDS. Pentoxifylline (PTX), a methylxanthine, protects against TNF-induced and sepsis-induced acute lung injury in vivo. We now report on in vitro cellular studies of PMN-mediated cellular injury and its attenuation. We studied TNF-induced bovine pulmonary artery endothelial cell (EC) cytotoxicity both with and without PMN. A 51Cr release assay was used to measure EC damage. Further, we investigated PMN function in response to TNF by measuring chemiluminescence. Agents that attenuate EC damage and PMN activation were evaluated in the above assays. Results revealed that TNF causes EC injury (p less than 0.05) and PMN increase TNF-induced EC injury. Furthermore, PTX, aminophylline (AMPH), caffeine, and forskolin attenuate TNF-induced EC cytotoxicity only in the presence of PMN (p less than 0.05). Of interest, dibutyryl cAMP (DBcAMP) protects EC from TNF-induced injury both with and without PMN. Agents that may increase cAMP levels in PMN (PTX, DBcAMP, forskolin, isobutyl methylxanthine, and terbutaline) significantly attenuate TNF-induced PMN chemiluminescence (p less than 0.05). We conclude that TNF causes EC damage and PMN increase this damage. Furthermore, PTX, AMPH, caffeine, and forskolin can attenuate TNF-induced EC injury in the presence of PMN, whereas DBcAMP attenuates TNF-induced EC injury with and without PMN. In addition, agents that may increase intracellular cAMP levels in PMN can attenuate TNF-induced PMN chemiluminescence. Thus, these agents likely attenuate TNF-induced PMN-mediated EC injury through their inhibitory effects on PMN.

Tumor necrosis factor-alpha-induced inhibition of phosphatidylcholine synthesis by human type II pneumocytes is partially mediated by prostaglandins.

“…Beneficial effects of PTXF have been reported in experimental models of septic shock and ARDS (11). This substance decreased the production of TNFa by activated macrophages (20) and has proven capable of blocking some effects of TNFa on the endothelium (21). Our results show clearly that PTXF can also block the inhibitory effect of TNFa on the synthesis of PC.…”

Pentoxifylline does not protect against hyperoxic lung injury in rats

“…These agents act as potent activators of circulating neutrophils, inducing increased endothelial adhesion, degranulation and oxidative burst, as well as decreased chemotaxis [18,19]. Evidence suggests that pentoxifylline protects against endotoxin-induced lung injury by counteracting these effects of TNF upon neutrophils [9][10][11][12]20].…”

“…It has been postulated that pentoxifylline inhibits the effect of tumour necrosis factor (TNF) on neutrophils [8][9][10], and/or inhibits monocyte synthesis of TNF in response to endotoxin [11]. Pentoxifylline exerts its effects on neutrophils at the cell surface through a mechanism that has yet to be characterized.…”

Caffeine potentiates the lethality of tumour necrosis factor in cancer cells

“…These events lead to a series of pathophysiological situations which may be detrimental or even lethal to the host if the production of TNF persists for a long time (Fiers, 1991). It is of interest that caffeine and other methylxanthines reportedly suppress production of TNF (Dezube etal., 1990) and various aspects of the TNFmediated immune system cell functions (Zheng et al, 1990;Dezube et al, 1990;Fiers, 1991). Therefore, it could be predicted that methylxanthines, while enhancing the cytotoxicity of TNF, may also reduce its undesired side effects.…”