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Effect of L-arginine on the retention of macrophage tumoricidal activity
Abstract:
It has been reported that the tumoricidal activity of macrophages (M phi) depends on L-arginine and that L-arginine metabolites such as reactive nitrogen intermediates alter M phi physical capacities. The aim of this report is to investigate the dose-related effect of L-arginine on the expression and retention of M phi tumoricidal activity. Cytotoxicity of M phi activated by IFN-gamma plus LPS was detected in the presence of about 0.1 mM or more of L-arginine. This paralleled the NO2- production in the presence, but not in the absence, of L-arginine. On the other hand, activated M phi were destined to die and lost their tumoricidal activity with time in the presence of 0.3 mM or more L-arginine. They retained, however, considerable activity in the absence or presence of 0.15 mM L-arginine. This retention of M phi cytotoxicity was longer when M phi were preactivated by 100 ng/ml than 10 ng/ml of LPS in combination with IFN-gamma. Addition of indomethacin, an inhibitor of prostaglandin production, did not prevent the decay of M phi cytotoxicity but rather facilitated it even in the absence of L-arginine. Regardless of indomethacin, consecutive stimulation with LPS or LPS plus IFN-gamma during culture was effective in maintaining the tumoricidal activity at a high level. In addition, we found that M phi which had lost tumoricidal activity during culture in L-arginine deficient medium could be reactivated by LPS to attack tumor target cells.
Insights
L-arginine is crucial for macrophage tumoricidal activity, but high doses cause rapid cell death. Optimizing L-arginine levels and using stimuli like LPS can maintain macrophage anti-tumor functions.
Area of Science:
- Immunology
- Cell Biology
Background:
- Macrophages (M phi) exhibit tumoricidal activity dependent on L-arginine.
- L-arginine metabolites, including reactive nitrogen intermediates, influence M phi function.
Purpose of the Study:
- To investigate the dose-dependent effects of L-arginine on macrophage tumoricidal activity.
- To understand how L-arginine concentration impacts the expression and duration of M phi anti-tumor functions.
Main Methods:
- Assessing M phi cytotoxicity against tumor cells.
- Measuring nitric oxide (NO2-) production in M phi cultures.
- Evaluating the impact of L-arginine concentrations (0.15 mM, 0.3 mM, etc.) on M phi activity.
- Investigating the role of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) in M phi activation and maintenance.
- Examining the effect of indomethacin, a prostaglandin inhibitor.
Main Results:
- Macrophage tumoricidal activity was observed at L-arginine concentrations of 0.1 mM or higher, correlating with NO2- production.
- High L-arginine levels (≥0.3 mM) led to decreased M phi activity and cell death over time.
- Lower L-arginine concentrations (0.15 mM or absence) promoted retention of M phi cytotoxicity.
- Pre-activation with higher LPS doses (100 ng/ml vs. 10 ng/ml) enhanced M phi cytotoxicity retention.
- Indomethacin did not prevent M phi cytotoxicity decay and could accelerate it.
- Repeated stimulation with LPS or LPS plus IFN-gamma maintained high M phi tumoricidal activity.
- LPS could reactivate M phi that had lost activity in L-arginine-deficient medium.
Conclusions:
- L-arginine concentration critically modulates macrophage tumoricidal activity, with a narrow optimal range.
- Macrophage survival and sustained anti-tumor function depend on careful management of L-arginine levels and appropriate stimulation protocols.
- Strategies involving L-arginine level modulation and intermittent LPS stimulation show promise for enhancing macrophage-based cancer immunotherapy.