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Implications of inducible nitric oxide synthase expression and enzyme activity
K D Kröncke1, C V Suschek, V Kolb-Bachofen
1Research Group Immunobiology in the Biomedical Research Centre, Heinrich-Heine-University, Düsseldorf, Germany. kroencke@uni-duesseldorf.de
Abstract:
We summarize here our current knowledge about inducible nitric oxide synthase (NOS) activity in human diseases and disorders. As basic research discovers more and more effects of low or high concentrations of NO toward molecular and cellular targets, successful therapies involving inhibition of NO synthesis or application of NO to treat human diseases are still lacking. This is in part due to the fact that the impact of NO on cell function or death are complex and often even appear to be contradictory. NO may be cytotoxic but may also protect cells from a toxic insult; it is apoptosis-inducing but also exhibits prominent anti-apoptotic activity. NO is an antioxidant but may also compromise the cellular redox state via oxidation of thiols like glutathione. NO may activate specific signal transduction pathways but is also reported to inhibit exactly these, and NO may activate or inhibit gene transcription. The situation may even be more complicated, because NO, depending on its concentration, may react with oxygen or the superoxide anion radical to yield reactive species with a much broader chemical reaction spectrum than NO itself. Thus, the action of NO during inflammatory reactions has to be considered in the context of timing and duration of its synthesis as well as stages and specific events in inflammation.
Insights
Inducible nitric oxide synthase (NOS) activity in human diseases remains complex. Despite numerous NO effects, effective therapies are limited due to its contradictory roles in cell function and disease.
Area of Science:
- Biomedical Science
- Molecular Biology
- Pathophysiology
Background:
- Inducible nitric oxide synthase (NOS) produces nitric oxide (NO), a molecule with diverse biological effects.
- Understanding NO's role in human diseases is crucial, yet therapeutic applications are limited.
- The complex and often contradictory actions of NO present significant challenges.
Purpose of the Study:
- To review current knowledge on inducible NOS activity in human diseases.
- To explore the multifaceted effects of nitric oxide (NO) on cellular processes.
- To discuss the challenges in developing NO-based therapies.
Main Methods:
- Literature review of inducible NOS (iNOS) and nitric oxide (NO) research.
- Analysis of NO's dual roles in cytotoxicity, apoptosis, and redox balance.
- Examination of NO's impact on signaling pathways and gene transcription.
Main Results:
- Nitric oxide (NO) exhibits paradoxical effects: it can be both protective and cytotoxic, pro-apoptotic and anti-apoptotic.
- NO's antioxidant properties are counterbalanced by its potential to oxidize cellular thiols.
- NO's signaling effects are concentration-dependent and can activate or inhibit pathways and transcription.
Conclusions:
- The complex, concentration-dependent, and context-specific actions of NO complicate therapeutic strategies.
- Further research is needed to elucidate the precise mechanisms of NO in various disease states.
- Timing, duration, and specific inflammatory events are critical factors in NO's biological impact.