Anti-inflammatory effect ofViscum albumagglutinin-I (VAA-I): induction of apoptosis in activated neutrophils and inhibition of lipopolysaccharide-induced neutrophilic inflammationin vivo

Abstract

SUMMARY Viscum album agglutinin‐I (VAA‐I) is a plant lectin which possesses antitumoral properties. This lectin is also known for its immunostimulatory effects when used at low concentrations (1–100 ng/ml). We have demonstrated recently that VAA‐I is a potent inducer of human neutrophil apoptosis in vitro when used at higher concentrations. The role of VAA‐I on activated neutrophils has not so far been investigated and its potential proinflammatory properties in vivo are poorly documented. Herein, we demonstrated that VAA‐I (1000 ng/ml) induces apoptosis in lipopolysaccharide (LPS)‐treated human neutrophils in vitro as well as in murine neutrophils isolated from lipopolysaccharide (LPS)‐induced neutrophil influx. Using this model, we found that administration of VAA‐I (100 or 1000 ng/ml) did not induce an inflammatory response. However, when used at 1 or 10 ng/ml, VAA‐I was found to significantly induce a transitory inflammatory response, based on an increased leucocyte infiltration (>98% neutrophils). Also, we found that VAA‐I inhibits LPS‐induced neutrophil influx when administered simultaneously with LPS. In such conditions, some characteristic apoptotic neutrophils were observed in the pouch. Unlike LPS, which increased the production of some cytokines, VAA‐I (1 or 10 ng/ml) did not increase the production of tumour necrosis factor (TNF)‐α, interleukin (IL)‐1Ra, IL‐1α, IL‐β, IL‐8, IL‐10 or IL‐12 (p70) in human neutrophils. We conclude that VAA‐I possesses the ability to induce apoptosis of preactivated neutrophils at a concentration that does not induce a proinflammatory response. Moreover, we conclude that VAA‐I can inhibit a LPS‐induced proinflammatory response in vivo. These data may provide new clinical perspectives in future mistletoe therapy and favour its potential utilization based on anti‐inflammatory activity that at first appears contradictory with its use as immunostimulant.

The intriguing normal acute inflammatory response in mice lacking vimentin

“…This was expected not only because of the importance of vimentin in the cell architecture and a variety of cell functions and responses, but also because we have demonstrated recently that vimentin is an important target cleaved by caspases in spontaneous or agent-induced neutrophil apoptosis [12,[14][15][16][17][18]. In addition, some vimentin-cleaved fragments have been found to be pro-apoptotic themselves [29].…”

“…In contrast to our results, a slightly increased proportion of incoming neutrophils in vim -/-mice, when compared with resident macrophages, has been reported in a mild peritonitis murine model (supplementary information, figure S2c in [9]). However, in contrast to the severe LPS-induced air pouch model that we have used in which neutrophil influx occurred after few hours, the cells used in the peritonitis model to evaluate the inflammatory state were harvested after 25 h. At this period of time, the leucocyte influx is no longer observable in most of the agent-induced air pouch, including LPS [18] and IL-21 [25]. This indicates that, unlike neutrophils (this report), macrophage functions can be altered in vim -/-mice when compared with vim +/+ macrophages, because in this model resident macrophages may be the primary target of an inflammatory agent.…”

“…To investigate the role of vimentin during an inflammatory response, we used the murine air pouch model [18,25]. In this model, when LPS is administered into the pouch, more than~85% of the infiltrated cells are neutrophils, the rest being almost exclusively monocytic cells [25].…”

“…Furthermore, the presence of vimentin on the cell surface of apoptotic neutrophils may be involved in the recognition process of apoptotic neutrophils by phagocytes for the resolution of inflammation, although this remains to be demonstrated. Using the murine air pouch model, we have also demonstrated that vimentin was cleaved when neutrophils harvested from lipopolysaccharide (LPS)-induced air pouches were incubated in vitro with the potent pro-apoptotic plant lectin Viscum album agglutinin-I [18]. Given the importance of vimentin in general immunology [9,[19][20][21][22][23], inflammation and biology of neutrophils [10][11][12][13][14]17], and the fact that a generation of mice totally devoid of vimentin could develop and reproduce normally [3], we decided to investigate the role of vimentin during an inflammatory response in vivo and on neutrophil cell functions in vitro, two situations which have been curiously not or poorly investigated.…”

Preparation, characterization, and safety evaluation of poly(lactide-co-glycolide) nanoparticles for protein delivery into macrophages

“…45,[48][49][50] At day 6, 1 mL of water or various concentrations of NPs or free BSA was injected into the air pouch. After 6 hours, mice were sacrificed by CO 2 asphyxiation, the pouches were washed three times (once with 1 mL and then twice with 2 mL of Hank's Balanced Salt Solution containing 10 mM EDTA), and the exudates were centrifuged.…”