Induction of metallothionein synthesis in cultured cells by substances released from endotoxin-activated macrophages
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Abstract:
The involvement of macrophages in the induction of metallothionein (MT) synthesis by bacterial endotoxin was studied in vitro. Rat peritoneal macrophages were incubated with endotoxin. The incubation medium from endotoxin-activated macrophages accelerated MT synthesis by human hepatic Chang cells. However, the incubation medium from non-activated macrophages did not. Endotoxin added to the culture medium of Chang cells was ineffective in inducing MT synthesis. The contents of zinc, copper and cadmium, which are primary inducers of MT, in the incubation medium of macrophages in the presence of endotoxin were not different from those in the absence of endotoxin. These results suggest that MT synthesis is induced by endotoxin-treated macrophages.
Insights
Bacterial endotoxins stimulate macrophages to produce factors that induce metallothionein (MT) synthesis in other cells. This study shows endotoxin-activated macrophages, not endotoxin itself, are key to initiating this metallothionein response.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Metallothionein (MT) is a crucial protein involved in heavy metal detoxification and cellular defense.
- Bacterial endotoxins are potent immune stimulants with complex cellular effects.
- The role of macrophages in mediating endotoxin-induced MT synthesis requires clarification.
Purpose of the Study:
- To investigate the role of macrophages in mediating bacterial endotoxin-induced metallothionein (MT) synthesis.
- To determine if endotoxin-activated macrophages release factors that induce MT synthesis in other cell types.
Main Methods:
- In vitro incubation of rat peritoneal macrophages with bacterial endotoxin.
- Collection and application of conditioned media from activated and non-activated macrophages to human hepatic Chang cells.
- Analysis of MT synthesis induction in Chang cells.
- Measurement of zinc, copper, and cadmium levels in the incubation media.
Main Results:
- Incubation medium from endotoxin-activated macrophages significantly accelerated MT synthesis in human hepatic Chang cells.
- Incubation medium from non-activated macrophages did not induce MT synthesis.
- Direct addition of endotoxin to Chang cells did not induce MT synthesis.
- No significant differences in zinc, copper, or cadmium levels were observed between media with or without endotoxin-activated macrophages.
Conclusions:
- Endotoxin-treated macrophages play a critical role in inducing metallothionein synthesis.
- Macrophages release soluble factors that mediate the endotoxin-induced MT synthesis.
- The induction mechanism does not appear to involve changes in extracellular heavy metal concentrations.