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Alteration of physiological activity of activated macrophages through L-arginine metabolism
Abstract:
Our aim in this study was to define the effect of L-arginine on macrophages (M phi) in relation to the decay of tumoricidal activity of activated M phi. We found that the activated M phi retained their cytotoxicity when cultured in L-arginine-deficient medium but not in conventional medium. Such a decline of tumoricidal activity was associated with increase of glucose consumption and concomitant lactate production, resulting in M phi death. Addition of glucose to the culture medium of activated M phi appeared to cause only a slight delay of the decrease of tumoricidal activity and M phi death. These events were also coincident with a decrease of electron transport activity in mitochondria. Cytological observation by electron microscopy clearly showed the structural alteration or destruction of mitochondria, which preceded the changes of other physiological and functional activities. These results demonstrate that the L-arginine-dependent cytolytic activity against tumor target cells also impairs M phi functions and ultimately induces M phi death, which is primarily mediated by the inhibition of mitochondrial activity.
Insights
L-arginine is crucial for activated macrophages (M phi) to kill tumor cells. Depleting L-arginine impairs M phi function, leading to cell death via mitochondrial damage.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Activated macrophages (M phi) possess tumoricidal activity.
- The metabolic requirements and limitations of M phi function are not fully understood.
Purpose of the Study:
- To investigate the role of L-arginine in maintaining the tumoricidal activity of activated M phi.
- To elucidate the mechanisms underlying the decay of M phi tumoricidal function.
Main Methods:
- Culturing activated M phi in L-arginine-deficient and conventional media.
- Measuring glucose consumption, lactate production, and M phi cytotoxicity.
- Assessing mitochondrial activity and structure via electron microscopy.
Main Results:
- Activated M phi retained cytotoxicity in L-arginine-deficient medium but lost it in conventional medium.
- Decline in tumoricidal activity correlated with increased glucose consumption, lactate production, and M phi death.
- Mitochondrial dysfunction, evidenced by decreased electron transport and structural damage, preceded functional decline.
Conclusions:
- L-arginine is essential for activated M phi to sustain tumoricidal activity.
- The loss of M phi tumoricidal function and subsequent cell death are linked to L-arginine depletion, impaired mitochondrial activity, and altered cellular metabolism.
- Mitochondrial inhibition is the primary mechanism leading to M phi death.