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Signal pathway responsible for hepatocyte preconditioning by nitric oxide
Rita Carini1, Maria Grazia De Cesaris, Roberta Splendore
1Department of Medical Science, University "A Avogadro" of East Piedmont, Novara, Italy. carini@med.no.unipmn.it
Free Radical Biology & Medicine
|April 10, 2003
Summary
Nitric oxide (NO) preconditioning protects liver cells from injury by activating p38 MAPK. This pathway involves guanylate cyclase and cGMP-dependent kinase, reducing harmful sodium buildup during hypoxia.
Area of Science:
- Hepatology and Molecular Medicine
- Cellular Signaling and Injury Response
- Biochemistry and Pharmacology
Background:
- Nitric oxide (NO) is a key mediator in hepatic preconditioning, enhancing liver resistance to hypoxia/reperfusion injury.
- The precise molecular mechanisms underlying NO-mediated hepatoprotection remain incompletely understood.
- Investigating NO's role is crucial for developing therapeutic strategies against liver damage.
Purpose of the Study:
- To elucidate the signaling pathways through which the NO donor NOC-9 confers tolerance to hypoxic injury in hepatocytes.
- To determine the involvement of protein kinase C, soluble guanylate cyclase (sGC), cGMP-dependent kinase (cGK), and p38 mitogen-activated protein kinase (MAPK) in NOC-9-induced cytoprotection.
- To examine the effect of NO on intracellular sodium accumulation during hypoxic stress.
Main Methods:
- Isolated rat hepatocytes were preincubated with the NO donor NOC-9.
- Hepatocyte viability under hypoxic conditions was assessed.
- Specific inhibitors (ODQ for sGC, KT 5823 for cGK, SB203580 for p38 MAPK) and a cGMP analogue (8Br-cGMP) were used to probe signaling pathways.
- Western blot analysis was employed to detect the phosphorylation status of p38 MAPK.
- Intracellular sodium (Na+) levels were measured in hypoxic hepatocytes.
Main Results:
- NOC-9 preincubation significantly increased hepatocyte resistance to hypoxic injury.
- NOC-9-mediated protection was independent of protein kinase C but dependent on sGC and cGK activity.
- Activation of p38 MAPK phosphorylation was observed following NOC-9 or 8Br-cGMP treatment and was blocked by sGC/cGK inhibition.
- NO pretreatment reduced intracellular Na+ accumulation, an effect reversed by cGK and p38 MAPK inhibition.
- Inhibition of p38 MAPK abrogated NOC-9's protective effect against hypoxic injury.
Conclusions:
- Nitric oxide induces hepatic preconditioning through a signaling cascade involving soluble guanylate cyclase and cGMP-dependent kinase.
- Activation of p38 MAPK is a critical downstream effector in the NO-mediated cytoprotective pathway.
- This pathway contributes to enhanced hepatocyte tolerance by mitigating intracellular sodium overload during hypoxic stress.