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Effect of phosphate esters, nucleotides and nucleosides on 5'-nucleotidase of cultured mouse macrophages
Abstract:
Mouse peritoneal macrophages elicited by intraperitoneal injection of sodium caseinate exhibit low levels of ecto-5'-nucleotidase (E. C. 3.1.3.5) activity in contrast to macrophages obtained by peritoneal lavage. When elicited cells were cultured under standard conditions in the presence of serum, a 2.5-fold increase in 5'-nucleotidase activity was observed over a period of 48 hours. Addition of adenosine monophosphate to the culture medium led to an augmented (5-fold) increase in the specific activity (per unit cell protein) as well as an absolute increase (per culture plate) of 5'-nucleotidase. Other adenosine-containing compounds also had stimulatory effects. The levels of this enzyme thus appear to be regulated by the extracellular levels of adenosine nucleotides. The product of the enzymatic reaction--adenosine--when added to the medium exhibited a toxic effect on these cells--as did adenosine monophosphate. However, the former substance did not augment the increase in enzyme activity during culture. The toxic effect could be suppressed when the cells were cultured in the presence of uridine 5'-monophosphate. The latter substance also depressed the stimulation of enzyme activity due to AMP.
Insights
Mouse macrophages show low ecto-5'-nucleotidase activity, but culturing with adenosine nucleotides increases it. Extracellular adenosine can be toxic, but uridine monophosphate offers protection and reduces enzyme stimulation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Ecto-5'-nucleotidase (5'-NT) activity varies in mouse macrophages.
- Elicited macrophages have lower 5'-NT than lavaged macrophages.
Purpose of the Study:
- Investigate regulation of 5'-NT activity in elicited macrophages.
- Determine the effect of extracellular nucleotides on 5'-NT levels.
- Assess the impact of reaction products and other compounds on enzyme activity and cell viability.
Main Methods:
- Culturing elicited mouse peritoneal macrophages.
- Measuring ecto-5'-nucleotidase activity.
- Assessing cell viability in response to various compounds.
Main Results:
- Culturing increased 5'-NT activity 2.5-fold.
- Adenosine monophosphate (AMP) augmented this increase 5-fold.
- Extracellular adenosine and AMP showed toxicity, suppressible by uridine 5'-monophosphate (UMP).
Conclusions:
- Ecto-5'-nucleotidase levels are regulated by extracellular adenosine nucleotides.
- Adenosine and AMP can be toxic to macrophages.
- Uridine monophosphate can mitigate toxicity and modulate enzyme activity stimulation.