Lipoxygenase-derived eicosanoids are involved in the inhibitory effect of Crotalus durissus terrificus venom or crotoxin on rat macrophage phagocytosis

Crotalus durissus terrificus snake venom and its major toxin, crotoxin or type II PLA2 subunit of this toxin, induce an inhibitory effect on spreading and phagocytosis in 2h incubated macrophages. The involvement of arachidonate-derived mediators on the inhibitory action of the venom or toxins on rat peritoneal macrophage phagocytosis was presently investigated. Peritoneal cells harvested from naive rats and incubated with the venom or toxins or harvested from the peritoneal cavity of rats pre-treated with the toxins were used. Zileuton, a 5-lipoxygenase inhibitor but not indomethacin, a cyclooxygenase inhibitor, given in vivo and in vitro abolished the inhibitory effect of venom or toxins on phagocytosis. Resident peritoneal macrophages incubated with the venom or toxins showed increased levels of prostaglandin E2 and lipoxin A4, with no change in leukotriene B4. These results suggest that lipoxygenase-derived eicosanoids are involved in the inhibitory effect of C.d. terrificus venom, crotoxin or PLA2 on macrophage phagocytosis.

Role of insulin on PGE2 generation during LPS-induced lung inflammation in rats

Alterations in arachidonic acid (AA) metabolism have been reported to occur in diabetes mellitus. The present study was carried out to verify if these alterations are due to the relative lack of insulin or to high levels of blood glucose. Male Wistar rats were rendered diabetic by alloxan injection (42 mg/kg, i.v.), 10 or 30 days before the experiments. Some diabetic rats received a single dose (4 IU, s.c.) of NPH insulin 2 h before an intratracheal instillation of lipopolysaccharide (LPS, 750 microg) or saline. Six hours after LPS challenge, the following parameters were analysed: blood glucose levels, total and differential leukocyte counts in bronchoalveolar lavage (BAL) fluid; linoleic acid and AA content in blood neutrophils (HPLC), and levels of prostaglandin (PG)E(2) in BAL (ELISA). Relative to controls, a reduced number of neutrophils (18%) and decreased amounts of PGE(2) (40%) were observed in the BAL fluid of diabetic rats in response to LPS. A single dose of insulin was not able to reduce blood sugar levels to normal values, but instead resulted in the normalization of both leukocyte migration to the lungs and levels of PGE(2). Accordingly, these abnormalities might be primarily linked to a continuing insulin deficiency rather than to secondary hyperglycaemia occurring in the diabetic rat. In conclusion, data presented suggest that insulin might regulate neutrophil migration and generation of PGE(2) during the course of acute lung injury induced by LPS.

Evidence that arachidonic acid derived from neutrophils and prostaglandin E2 are associated with the induction of acute lung inflammation by lipopolysaccharide of Escherichia coli

OBJECTIVE

The involvement of arachidonic acid (AA) and PGE2 during the E. coli lipopolysaccharide (LPS)-induced acute lung injury was investigated.

MATERIAL

Adult male Wistar rats were used. For in vitro studies, rat neutrophils, bronchoalveolar lavage (BAL) fluid, and lug vascular endothelium were used, as described below.

TREATMENT

Rats were given an intratracheal injection of LPS (750 microg).

METHODS

Total and differential cell counts in BAL fluid; enzyme-linked immunoassay (ELISA) analyses of TNF-alpha, IL-1beta, LTB4 and PGE2 in BAL, and immunohistochemical detection of ICAM-1 on lung vascular endothelium were performed six h after LPS challenge. Fatty acid composition of blood neutrophils and plasma was analyzed by HPLC.

RESULTS

Rats instilled with LPS presented a sixty three-fold increase in the number of neutrophils in BAL (from 0.5 x 10(6) to 31.5 x 10(6) cells), accompanied by increased levels of TNF-alpha and IL-1beta (p < 0.001), and a three-fold increase in ICAM-1 expression on vascular endothelium. The content of AA in blood neutrophils was reduced by 50%, whereas the level of PGE2 in BAL was increased by 3.5 fold, without changes in the levels of LTB4.

CONCLUSIONS

These findings suggest that AA and PGE2 are associated with LPS challenge.