Histamine, dithiaden and human polymorphonuclear leukocytes in vitro

Abstract

IntroductionH 1 -antihistamines, recently defined as inverse agonists or neutral antagonists, exert an antiinflammatory effect, which might result both from receptor interaction and non-receptormediated activities. It has been suggested that the physicochemical nature of H 1 -antihistamines, namely lipophilic molecules which carry a positive charge, allows them to associate with cell membranes and competitively inhibit the binding of second messengers, e. g. Ca 2+ , thereby reducing the activity of calcium-dependent enzymes [1]. In this study, we compared the effect of the H 1 -antihistamine Dithiaden ® (Dit) with histamine (His) on reactive oxygen metabolite (ROM) generation by human polymorphonuclear leukocytes (PMNL) under different mechanisms of stimulation. Materials and methodsThe oxidative burst of PMNL was measured in whole human blood by the luminol-enhanced chemiluminescence (CL) method in luminometer Immunotech LM-01T (Immunotech, Czech Republic [2]). Luminolenhanced CL of isolated PMNL was recorded in Lumi-aggregometer model 500 Harveston, USA [3,4]). Samples were treated with the appropriate stimuli in the final contentrations: N-formylmethionyl-leucyl-phenylalanine (fMLP) 0.1 mmol/L, calcium ionophore A23187 0.5 mmol/L, phorbol-12-myristate-13 acetate (PMA) 0.01 mmol/L, or opsonised zymosan (OZ) 0.1 g/L. Statistical significance of differences between the means was established by Student's ttest and p values below 0.05 were considered significant. Figure 1 demonstrates the effect of His and Dit on CL of whole blood stimulated with OZ. His showed a dose-dependent inhibitory effect on the CL at concentrations above 10 mmol/L. In contrast, Dit significantly decreased CL at concentrations from 10 nmol/L. In isolated PMNL, His decreased CL in the rank order of stimuli: fMLP > A23187 > OZ and had no effect on CL stimulated with PMA. Dit dose-dependently decreased CL in the rank order of stimuli PMA > OZ > A23187 and increased CL induced with fMLP only at a concentration of 10 mmol/L. Figure 2 (panel A) shows the effect of Dit and His on CL of PMNL stimulated with OZ. Dit but not His at a concentration of 10 mmol/L decreased OZ-stimulated CL. Simultaneous administration of Dit and His did not affect the inhibitory effect of Dit. In contrast, Dit (10 mmol/L) increased CL of isolated PMNL stimulated with fMLP ( Fig. 2, panel B). His in equimolar concentration significantly decreased fMLP-stimulated CL and, when applied simultaneously with Dit, it abolished the effect of the latter. Results and discussionIt seems likely that His does not play a regulatory role in aggregation of leukocytes and the inhibitory effect of Dit might be nonspecific [5]. In OZ-stimulated PMNL (both whole blood and isolated cells), His and Dit worked synergistically by a dose-dependent inhibition of CL, with Dit being much more potent. However, in fMLP-stimulated PMNL, His antagonised the potentiation of CL by Dit. The difference in the effect of His and Dit on CL stimulated with OZ and fMLP may be due to the different mechanisms of...