Selective inhibition by dexamethasone of induction of NO synthase, but not of induction of l‐arginine transport, in activated murine macrophage J774 cells

Abstract

1 Effects of dexamethasone on induction of nitric oxide (NO) synathase and L-arginine transport by lipopolysaccharide (LPS) were examined in a murine cultured macrophage cell line J774. Metabolism of L-arginine to L-citrulline and subsequent changes in intracellular amino acids pools were correlated with changes in nitrite production. 3 Induction of NO synthase by LPS (1 jig ml-', 24 h) alone was accompanied by a marked increase in arginine utilisation leading to decreased intracellular arginine levels and elevated intracellular and extracellular L-citrulline levels. These changes were further enhanced in the presence of interferon-y (IFN-y, 100 units ml-', 24h).4 Dexamethasone (1 jaM) abolished the increases in both nitrite and citrulline production induced by LPS alone but only partially reversed the combined effects of LPS and IFN-y. In contrast, treatment of cells with dexamethasone (10 jtM) had no effect on the LPS-mediated induction of arginine transport or the decrease in intracellular arginine concentration. 5 We conclude that induction of arginine transporter activity in LPS-stimulated J774 cells involves de novo synthesis of carrier proteins, which increases transport of exogenous arginine during enhanced NO production. Moreover, the intracellular signalling pathways mediating induction of arginine transport and of NO synthase by LPS in activated macrophages diverge, since only the latter is sensitive to dexamethasone.

Selective Targeting of Nitric Oxide Synthase Inhibitors to System y+ in Activated Macrophages

“…Activation of murine macrophage J774 cells with lipopolysaccharide (LPS) results in a cycloheximide-dependent induction of NO synthase and arginine transport via system y + (1)(2)(3).…”

“…In activated macrophages generation of NO by inducible NO synthase (iNOS) is critically dependent on extracellular arginine (2,4,5), despite reports that activated cells contain high intracellular arginine levels (1,6). N G -derivatized analogues of L-arginine are potent inhibitors of iNOS, and their rank order of potency has been attributed to different NOS isoforms and/or their differential rates of cellular uptake (7,8).…”

“…Uptake was expressed in units of pmol μg protein -1 min -1 . Nitric oxide production was monitored by measuring nitrite accumulation in the culture medium using the Griess reaction (1)(2)(3)11).…”

Induction of L‐arginine transport and nitric oxide synthase in vascular smooth muscle cells: synergistic actions of pro‐inflammatory cytokines and bacterial lipopolysaccharide

“…Nitrite accumulation in the culture medium was determined calorimetrically by a diazotization reaction using the standard Griess reagent (Green et al, 1982), as described previously (Bogle et al, 1992a;Baydoun et al, 1993a).…”

“…In this regard we have shown previously that LPS induces a timeand dose-dependent stimulation of iNOS and L-arginine transporter activity in cultured J774 macrophages thereby providing a possible mechanism for sustaining substrate supply during periods of enhanced NO synthesis (Bogle et al, 1992a;Baydoun et al, 1993a). In this study we have further investigated this phenomenon and examined the effects of LPS in combination with other pro-inflammatory mediators, including the cytokines interferon-y (IFN-y), tumour necrosis factor-(TNF-a) and interleukin-la (IL-la) on L-arginine transport in correlation with the expression of iNOS in rat aortic smooth muscle cells in culture.…”