Sinomenine, a natural dextrorotatory morphinan analog, is anti-inflammatory and neuroprotective through inhibition of microglial NADPH oxidase.
BACKGROUND
The mechanisms involved in the induction and regulation of inflammation resulting in dopaminergic (DA) neurotoxicity in Parkinson's disease (PD) are complex and incompletely understood. Microglia-mediated inflammation has recently been implicated as a critical mechanism responsible for progressive neurodegeneration.


METHODS
Mesencephalic neuron-glia cultures and reconstituted cultures were used to investigate the molecular mechanisms of sinomenine (SN)-mediated anti-inflammatory and neuroprotective effects in both the lipopolysaccharide (LPS)- and the 1-methyl-4-phenylpyridinium (MPP+)-mediated models of PD.


RESULTS
SN showed equivalent efficacy in protecting against DA neuron death in rat midbrain neuron-glial cultures at both micro- and sub-picomolar concentrations, but no protection was seen at nanomolar concentrations. The neuroprotective effect of SN was attributed to inhibition of microglial activation, since SN significantly decreased tumor necrosis factor-alpha (TNF-alpha, prostaglandin E2 (PGE2) and reactive oxygen species (ROS) production by microglia. In addition, from the therapeutic point of view, we focused on sub-picomolar concentration of SN for further mechanistic studies. We found that 10(-14) M of SN failed to protect DA neurons against MPP+-induced toxicity in the absence of microglia. More importantly, SN failed to show a protective effect in neuron-glia cultures from mice lacking functional NADPH oxidase (PHOX), a key enzyme for extracellular superoxide production in immune cells. Furthermore, we demonstrated that SN reduced LPS-induced extracellular ROS production through the inhibition of the PHOX cytosolic subunit p47phoxtranslocation to the cell membrane.


CONCLUSIONS
Our findings strongly suggest that the protective effects of SN are most likely mediated through the inhibition of microglial PHOX activity. These findings suggest a novel therapy to treat inflammation-mediated neurodegenerative diseases.
Qian
Li
L
Comprehensive Center for Inflammatory Disorders, University of North Carolina, Chapel Hill, North Carolina 27599, USA. qianl2@niehs.nih.gov
Xu
Zongli
Z
Zhang
Wei
W
Wilson
Belinda
B
Hong
Jau-Shyong
JS
Flood
Patrick M
PM
D000818:Animals; D000831:Animals, Newborn; D000893:Anti-Inflammatory Agents / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D018920:Coculture Techniques; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004660:Encephalitis / Q000188:drug therapy* / Q000201:enzymology / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects* / Q000201:enzymology; D009019:Morphinans / Q000819:agonists / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology; D018696:Neuroprotective Agents / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D010300:Parkinson Disease / Q000188:drug therapy / Q000201:enzymology / Q000503:physiopathology; D051381:Rats; D011916:Rats, Inbred F344; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000378:metabolism
D000893:Anti-Inflammatory Agents; D004791:Enzyme Inhibitors; D009019:Morphinans; D018696:Neuroprotective Agents; D014409:Tumor Necrosis Factor-alpha; C009271:sinomenine; D019255:NADPH Oxidases; D004298:Dopamine