Inhibition of 36CI− influx and [35S]TBPS binding in the rat brain by leumedins: A novel class of anti-inflammatory agents

The leumedins, a series of N‐(fluorenyl‐9‐methoxycarbonyl) amino acids, are putative anti‐inflammatory agents that have been shown to inhibit leukocyte recruitment into inflammed tissue. While the exact mechanism of action of these agents is unknown, there are some reports suggesting that leumedins selectively block transmembrane ion flux in neutrophils. In order to examine the possibility that the leumedins may interact with chloride transport mechanisms, we evaluated representative leumedins for their ability to interact with the GABA/benzodiazepine chloride ionophore in rat brain. NPC 17923, at micromolar concentrations, was found to compete for 2 nM [35S]TBPS binding (IC50 = 16 μM) and inhibit 36CI— influx (IC50 = 133 μM) in rat brain. Saturation studies indicated that NPC 17923 inhibited [35S]TBPS binding in a noncompetitive fashion. Other less potent leumedins also inhibited [35S]TBPS binding in a concentration‐dependent fashion. The leumedins had no significant activity at other GABA/benzodiazepine recognition sites labeled by [3H]muscimol, [3H]flunitrazepam, or [3H]RO15‐4513. The two most potent leumedins effectively attenuated 36CI— influx into rat brain, while all of the leumedins examined blocked 36CI— influx into guinea pig neutrophils at moderate micromolar concentrations. The present data offer the first demonstration that the leumedins can block chloride flux at the rat brain GABA/benzodiazepine chloride ionophore and in guinea pig neutrophils at similar concentrations required to produce anti‐inflammatory actions on human neutrophils. These results show that while the leumedins can block chloride flux in both neurons and neutrophils, the relative low affinity of the leumedins to produce this effect suggests an apparent nonselective interaction at a number of different chloride transporters similar to that found with the disulfonic stilbene derivative chloride channel blockers. © 1995 Wiley‐Liss, Inc.