Lack of effects of acemetacin on signalling pathways for leukocyte adherence may explain its gastrointestinal safety.

BACKGROUND AND PURPOSE: Acemetacin is a non-steroidal anti-inflammatory drug which is rapidly bioconverted to indomethacin, but produces significantly less gastric damage than indomethacin. This study was performed to investigate several possible mechanisms that could account for the gastrointestinal tolerability of acemetacin. EXPERIMENTAL APPROACH: The gastric and intestinal damaging effects of acemetacin and indomethacin were examined in the rat. Effects of the drugs on blood levels of leukotriene B(4) and thromboxane B(2), on leukocyte-endothelial adherence in post-capillary mesenteric venules, and on gastric expression of tumour necrosis factor-alpha (TNF-alpha) were determined. The two drugs were also compared for gastric toxicity in rats pretreated with inhibitors of COX-2 and NOS. KEY RESULTS: Acemetacin induced significantly less gastric and intestinal damage than indomethacin, despite markedly suppressing COX activity. Indomethacin, but not acemetacin, significantly increased leukocyte adherence within mesenteric venules, and gastric expression of TNF-alpha. Pretreatment with L-nitro-arginine methyl ester or lumiracoxib increased the severity of indomethacin-induced gastric damage, but this was not the case with acemetacin. CONCLUSIONS AND IMPLICATIONS: The increased gastric and intestinal tolerability of acemetacin may be related to the lack of induction of leukocyte-endothelial adherence. This may be attributable to the reduced ability of acemetacin to elevate leukotriene-B(4) synthesis and TNF-alpha expression, compared to indomethacin, despite the fact that acemetacin is rapidly bioconverted to indomethacin after its absorption.

Nitric oxide modulates eosinophil infiltration in antigen-induced airway inflammation in rats.

The influence of nitric oxide (NO) on eosinophil infiltration into the airways was investigated in rats actively sensitized with ovalbumin. The animals were treated chronically with the NO synthase inhibitor, N omega-Nitro-L-arginine methyl ester (L-NAME; 75 mumol rat-1 day-1), for 4 weeks. Bronchoalveolar lavage was performed at 6, 24, 48 and 72 h after intratracheal injection of ovalbumin. Intratracheal challenge of the sensitized rats with ovalbumin caused a significant increase in total leucocyte infiltration in bronchoalveolar lavage fluid both 24 and 48 h post-ovalbumin injection. Neutrophils and eosinophils peaked, respectively, at 24 h (29%) and 48 h (30%) in bronchoalveolar lavage fluid whereas the mononuclear cell did not differ significantly from the counts in non-sensitized rats at any time. At both 6 and 24 h post-ovalbumin injection, the chronic treatment of the animals with L-NAME affected neither the total nor the differential leucocyte content. However, at 48 h post-ovalbumin challenge, the total cell count was reduced by approximately 48% in the L-NAME-treated animals and this was associated with a marked inhibition (81%) of the eosinophil influx. Histological examination of the lungs from these animals (48 h post-ovalbumin challenge) also showed a prominent reduction (69.5%; P < 0.05) of the eosinophil infiltration in the respiratory segments. Our results demonstrate that NO plays a pivotal role in the eosinophil infiltration in airways of actively sensitized rats.

Pharmacological and immunohistochemical evidence for a functional nitric oxide synthase system in rat peritoneal eosinophils.

Eosinophil migration in vivo is markedly attenuated in rats treated chronically with the NO synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME). In this study, we investigated the existence of a NOS system in eosinophils. Our results demonstrated that rat peritoneal eosinophils strongly express both type II (30.2 +/- 11.6% of counted cells) and type III (24.7 +/- 7.4% of counted cells) NOS, as detected by immunohistochemistry using affinity purified mouse mAbs. Eosinophil migration in vitro was evaluated by using 48-well microchemotaxis chambers and the chemotactic agents used were N-formyl-methionyl-leucyl-phenylalanine (fMLP, 5 x 10(-8) M) and leukotriene B4 (LTB4, 10(-8) M). L-NAME (but not D-NAME) significantly inhibited the eosinophil migration induced by both fMLP (54% reduction for 1.0 mM; P < 0.05) and LTB4 (61% reduction for 1.0 mM; P < 0.05). In addition, the type II NOS inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine and the type I/II NOS inhibitor 1-(2-trifluoromethylphenyl) imidazole also markedly (P < 0. 05) attenuated fMLP- (52% and 38% reduction for 1.0 mM, respectively) and LTB4- (52% and 51% reduction for 1.0 mM, respectively) induced migration. The inhibition of eosinophil migration by L-NAME was mimicked by the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a] quinoxalin-1-one (0.01 and 0.1 mM) and reversed by either sodium nitroprusside (0.1 mM) or dibutyryl cyclic GMP (1 mM). We conclude that eosinophils do express NO synthase(s) and that nitric oxide plays an essential role in eosinophil locomotion by acting through a cyclic GMP transduction mechanism.