Felodipine-induced inhibition of polymorphonuclear leukocyte functions

Effects of renal cytoprotective agents on erythrocyte membrane stability

To elucidate potential mechanisms of ischemic renal injury, investigators often use drugs that interfere with specific pathological pathways and study their protective efficacy in in vitro models of ischemia, such as isolated renal proximal tubules subjected to hypoxia. However, the protective effects of certain drugs may depend on non-specific membrane-stabilizing properties. We have studied the effects of several drugs on membrane integrity using osmotic lysis of erythrocytes as a model system. Freshly isolated rabbit erythrocytes were subjected to a hypotonic shock, and the protective effects of various calcium channel blockers, phospholipase inhibitors, free fatty acids, the NO-synthase inhibitor L-NAME, the amino acid glycine and its receptor-analogue strychnine, and two chloride channel blockers were examined. Most agents protected erythrocytes against hypotonic hemolysis when added to the medium in the same concentration range as used in suspensions of hypoxic proximal tubules. Only the protective agents that proposedly act via a blockade of chloride influx (glycine, strychnine and the chloride channel blockers), did not attenuate hypotonic hemolysis. The erythrocyte hemolysis assay may provide an easy and rapid method to screen for non-specific membrane-stabilizing effects of potentially cytoprotective agents.

Effects of calcium blockers on the cytosolic calcium, H2O2 production and elastase release in human neutrophils

Activated neutrophils are assumed to be one plausible cause of tissue injury in the ischaemic and reperfused myocardium. We studied the inhibitory effects of the calcium antagonists felodipine, nimodipine and verapamil on human neutrophil activation in order to elucidate the mechanisms underlying their myocardioprotective effects and to determine whether calcium antagonists with different chemical structures vary in their effect on neutrophil activation. Neutrophils were stimulated with formyl-Met-Leu-Phe (0.1 microM) or by phorbol myristate acetate (0.16 microM), and the rise in cytosolic calcium and the H2O2 production were determined. For felodipine, the inhibitory effect on granulocyte elastase release was also studied. The calcium antagonists reduced formyl-Met-Leu-Phe and phorbol myristate acetate-induced neutrophil activation in a concentration-dependent manner, the order of potency being: felodipine > nimodipine > verapamil. For felodipine, the IC50 (concentration causing 50% reduction) values were 3 x 10(-6) and 2 x 10(-6) M for the formyl-Met-Leu-Phe-induced cytosolic calcium increase and H2O2 production, respectively. The IC50-value for the phorbol myristate acetate-induced cytosolic calcium increase was 6 x 10(-6) and for H2O2 production 4 x 10(-6) M. For formyl-Met-Leu-Phe-induced granulocyte elastase release, the IC50-value was 5 x 10(-6) M. The inhibitory effect of felodipine on the phorbol myristate acetate-induced granulocyte elastase release did not exceed 50%. Nimodipine was a less potent inhibitor than felodipine for both formyl-Met-Leu-Phe- and phorbol myristate acetate-induced cell activities. Verapamil was even less potent than the other two agents. The present study demonstrates that felodipine potentially suppresses neutrophil activation at micromolar concentrations. However, this observation should not be directly extrapolated to explain the tissue protection by the compounds without evidence of profound local accumulation.

The antiinflammatory activity of topically applied novel calcium-channel antagonists

The antiinflammatory activities of two novel calcium-channel antagonists, AGN 190742 and AGN 190744, were evaluated in murine models of cutaneous inflammation. These 2(5H)-furanone ring compounds block both depolarization-dependent Ca2+ entry and receptor-mediated responses in GH3 cells. Topical application of AGN 190742 or AGN 190744 inhibits neutrophil infiltration and epidermal hyperplasia induced by repeated treatment of mouse skin with phorbol ester. AGN 190744 also is active in an arachidonic acid model of acute inflammation. These data suggest that topical application of calcium-channel antagonists can inhibit cutaneous inflammatory responses and that AGN 190742 and/or AGN 190744 may serve as useful pharmacological probes for examining these responses in vivo.