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Stimulation of the nitric oxide synthase pathway in human hepatocytes by cytokines and endotoxin
A K Nussler1, M Di Silvio, T R Billiar
1Department of Surgery, University of Pittsburgh School of Medicine, Pennsylvania 15261.
Abstract:
Nitric oxide (NO) is a short-lived biologic mediator that is shown to be induced in various cell types and to cause many metabolic changes in target cells. Inhibition of tumor cell growth and antimicrobial activity has been attributed to the stimulation of the inducible type of the NO synthase (NOS). However, there is limited evidence for the existence of such inducible NOS in a human cell type. We show here the induction of NO biosynthesis in freshly isolated human hepatocytes (HC) after stimulation with interleukin 1, tumor necrosis factor (TNF), IFN-gamma, and endotoxin. Increased levels of nitrite (NO2-) and nitrate (NO3-) in culture supernatants were associated with NADPH-dependent NOS activity in the cell lysates. The production of NO2- and NO3- was inhibited by NG-monomethyl L-arginine and was associated with an increase in cyclic guanylate monophosphate release. The data presented here provide evidence for the existence of typical inducible NO biosynthesis in a human cell type.
Insights
Researchers demonstrate inducible nitric oxide (NO) biosynthesis in human hepatocytes. This finding provides evidence for NO synthase induction in a key human cell type, impacting cellular metabolism and immune responses.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Nitric oxide (NO) is a critical mediator involved in various cellular processes.
- Inducible nitric oxide synthase (iNOS) stimulation is linked to anti-tumor and antimicrobial effects.
- Evidence for inducible NOS in human cells, particularly hepatocytes, is limited.
Purpose of the Study:
- To investigate the induction of NO biosynthesis in human hepatocytes (HC).
- To determine if human hepatocytes express inducible nitric oxide synthase (iNOS).
Main Methods:
- Primary human hepatocytes were stimulated with cytokines (interleukin-1, tumor necrosis factor, IFN-gamma) and endotoxin.
- Nitrite (NO2-) and nitrate (NO3-) levels in culture supernatants were measured.
- NADPH-dependent nitric oxide synthase (NOS) activity in cell lysates was assessed.
- Inhibition studies were performed using NG-monomethyl L-arginine.
- Cyclic guanylate monophosphate (cGMP) release was measured.
Main Results:
- Human hepatocytes exhibited NO biosynthesis upon stimulation with interleukin-1, tumor necrosis factor, IFN-gamma, and endotoxin.
- Increased nitrite and nitrate levels correlated with NADPH-dependent NOS activity.
- NO production was inhibited by NG-monomethyl L-arginine.
- An increase in cyclic guanylate monophosphate release was observed.
Conclusions:
- The study provides clear evidence for inducible NO biosynthesis in human hepatocytes.
- Human hepatocytes possess a functional inducible nitric oxide synthase (iNOS) system.
- This finding has significant implications for understanding NO's role in human liver physiology and disease.