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Hyperforin is a modulator of inducible nitric oxide synthase and phagocytosis in microglia and macrophages
Birgit Kraus1, Horst Wolff, Erich F Elstner
1Institute of Pharmaceutical Biology, University of Regensburg, Universitätsstrasse 31, Regensburg, Germany. birgit1.kraus@chemie.uni-regensburg.de
Abstract:
Upon activation, microglia, the immunocompetent cells in the brain, get highly phagocytic and release pro-inflammatory mediators like nitric oxide (NO). Excessive NO production is pivotal in neurodegenerative disorders, and there is evidence that abnormalities in NO production and inflammatory responses may at least support a range of neuropsychiatric disorders, including depression. Although extracts of St. John's wort (Hypericum perforatum L.) have been used for centuries in traditional medicine, notably for the treatment of depression, there is still considerable lack in scientific knowledge about the impact on microglia. We used N11 and BV2 mouse microglia, as well as RAW 264.7 macrophages to investigate the effects of St. John's wort extract and constituents thereof on NO production Moreover, flow cytometry and fluorescence microscopy were employed to analyze the influence on phagocytosis, transcription factor activation states, and cell motility. We found that extracts of St. John's wort efficiently suppress lipopolysaccharide-induced NO release and identified hyperforin as the responsible compound, being effective at concentrations between 0.25 and 0.75 microM. The reduced NO production was mediated by diminished inducible nitric oxide synthase expression on the mRNA and protein level. In addition, at similar concentrations, hyperforin reduced zymosan phygocytosis to 20-40% and putatively acted by downregulating the CD206 macrophage mannose receptor and modulation of cell motility. We found that the observed effects correlate with a suppression of the activated state of Nf-kappaB and phospho-CREB, while c-JUN, STAT1, and HIF-1alpha activity and cyclooxygenase-2 expression remained unaffected by hyperforin. These results reveal that hyperforin influences pro-inflammatory and immunological responses of microglia that are involved in the progression of neuropathologic disorders.
Insights
St. John's wort extract, specifically hyperforin, suppresses nitric oxide (NO) production and phagocytosis in microglia. This finding offers insights into the anti-inflammatory effects of St. John's wort on brain immune cells.
Area of Science:
- Neuroimmunology
- Pharmacology
- Cell Biology
Background:
- Microglia play a crucial role in brain immunity, releasing nitric oxide (NO) and exhibiting phagocytic activity.
- Dysregulated NO production and neuroinflammation are implicated in neurodegenerative and neuropsychiatric disorders like depression.
- St. John's wort (Hypericum perforatum L.) is traditionally used for depression, but its impact on microglia remains under-researched.
Purpose of the Study:
- To investigate the effects of St. John's wort extract and its constituents on microglial NO production and phagocytosis.
- To identify the specific compound in St. John's wort responsible for these effects.
- To elucidate the molecular mechanisms underlying these actions on microglia.
Main Methods:
- Utilized N11, BV2 mouse microglia, and RAW 264.7 macrophage cell lines.
- Assessed NO production, phagocytosis, cell motility, and transcription factor activation (Nf-kappaB, CREB, c-JUN, STAT1, HIF-1alpha) using flow cytometry and fluorescence microscopy.
- Analyzed inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression at mRNA and protein levels.
Main Results:
- St. John's wort extract significantly suppressed lipopolysaccharide-induced NO release.
- Hyperforin was identified as the active compound, reducing NO production at 0.25-0.75 microM by downregulating iNOS expression.
- Hyperforin also reduced zymosan phagocytosis and modulated cell motility, potentially via CD206 downregulation.
- Hyperforin suppressed Nf-kappaB and phospho-CREB activation but did not affect c-JUN, STAT1, or HIF-1alpha.
Conclusions:
- Hyperforin, a constituent of St. John's wort, exerts anti-inflammatory effects on microglia by inhibiting NO production and phagocytosis.
- These findings suggest a potential mechanism for the traditional use of St. John's wort in treating depression and other neuropathologies.
- Hyperforin's modulation of microglial inflammatory responses warrants further investigation for therapeutic applications in neurological disorders.
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