Author(s): Murakami A, Takahashi D, Koshimizu K, Ohigashi H, Murakami A, Takahashi D, Koshimizu K, Ohigashi H
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Abstract In contrast to chemopreventive strategies using individual agents, a combination of specified compounds may be effectual to achieve desirable results with higher efficacy and lower toxicity. In the present in vitro study, we examined combinations of agents and assessed which concentrations were appropriate to yield notable synergism. L-N(G)-Monomethyl-L-arginine (L-NMMA), a synthetic inducible nitric oxide synthase (iNOS) inhibitor, and zerumbone, a natural sesquiterpene that suppresses iNOS de novo synthesis, were combined at various concentrations, with the aim to diminish combined lipopolysaccharide- and interferon-gamma-induced nitric oxide generation in a murine macrophage line, RAW264.7. Although the combinatorial effects (CEs) were antagonistic or additive at higher concentrations, significant synergism was obtained at lower concentrations where each agent alone did not cause significant inhibition. Similarly, the CEs were synergistic when (-)-epigallocatechin gallate (EGCG) and genistein were combined at lower concentrations, whereas those of two iNOS inhibitors, L-NMMA and L-N(G)-aminoethyl-L-ornithine, were either additive or antagonistic at all concentrations tested, suggesting that a combination of given agents with different action mechanisms is a prerequisite for synergistic effects. For suppression of phorbol ester-induced superoxide anion radical (O(2)*(-)) generation in differentiated HL-60 cells, the CEs of 1'-acetoxycahvicol acetate (ACA), a phenyl propanoid that suppresses O(2)*(-) generation, and O(2)*(-) dismutase were also synergistic, though only at lower concentrations. The CEs of ACA/EGCG were antagonistic or additive, even at low concentrations, suggesting that the signal transduction pathways triggered by these agents are antagonistic. The present findings suggest that individual food phytochemicals have complex interactions that can be antagonistic, additive, and/or synergistic in biological systems, depending upon certain environmental factors including concentrations. Further, these results support and emphasize the concept that combinations of different types of chemicals at low concentrations are one of the essential areas of study for chemopreventive strategies. Copyright 2002 Elsevier Science B.V.
This article was published in Mutat Res
and referenced in Journal of Environmental & Analytical Toxicology