Neuropathic pain is a maladaptive immune response to peripheral nerve injury that causes a chronic painful condition refractory to most analgesics. Nitric oxide (NO), which is produced by nitric oxide synthases (NOSs), has been implicated as a key factor in the pathogenesis of neuropathic pain. beta-Carbolines are a large group of natural and synthetic indole alkaloids, some of which block activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB), a predominant transcriptional regulator of NOS expression. Here, we characterize the inhibitory effects of a novel 6-chloro-8-(glycinyl)-amino-beta-carboline (8-Gly carb) on NO formation and NF-kappaB activation in macrophages. 8-Gly carb was significantly more potent than the NOS inhibitor NG-nitro-L-arginine methyl ester in inhibiting constitutive and inducible NO formation in primary rat macrophages. 8-Gly carb interfered with NF-kappaB-mediated gene expression in differentiated THP1-XBlue cells, a human NF-kappaB reporter macrophage cell line, but only at concentrations severalfold higher than needed to significantly inhibit NO production. 8-Gly carb also had no effect on tumor necrosis factor alpha (TNFalpha)-induced phosphorylation of the p38 mitogen-activated protein kinase in differentiated THP1 cells, and did not inhibit lipopolysaccharide- or TNFalpha-stimulated expression of TNFalpha and interleukin-1beta. These data demonstrate that relative to other carbolines and pharmacologic inhibitors of NOS, 8-Gly carb exhibits a unique pharmacological profile by inhibiting constitutive and inducible NO formation independent of NF-kappaB activation and cytokine expression. Thus, this novel carboline derivative holds promise as a parent compound, leading to therapeutic agents that prevent the development of neuropathic pain mediated by macrophage-derived NO without interfering with cytokine expression required for neural recovery following peripheral nerve injury. CI - Copyright (c) 2015 by The American Society for Pharmacology and Experimental Therapeutics.