The opioid antagonist, β-funaltrexamine, inhibits chemokine expression in human astroglial cells

Abstract

Emerging evidence indicates that neuroinflammatory responses in astroglia, including chemokine expression, are altered by opioids. Astroglial chemokines, such as CXCL10, are instrumental in response to many neuropathological insults. Opioid mediated disruption of astroglial CXCL10 expression may be detrimental in opioid abusers or patients receiving acute opioid therapy. We have characterized the in vitro effects of opioids on CXCL10 protein expression in human astroglial (A172) cells. The proinflammatory cytokine, tumor necrosis factor (TNF)α induced CXCL10 expression in A172 cells. Using MG-132, helenalin and SN50 [inhibitors of the transcription factor, nuclear factor (NF)-κB], we determined that NF-κB activation is instrumental in TNFα induced CXCL10 expression in A172 astroglia. Morphine exposure during the 24 h TNFα stimulation period did not alter CXCL10 expression. However, fentanyl, a more potent mu opioid receptor (MOR) agonist, inhibited TNFα induced CXCL10 expression. Interestingly, neither the nonselective opioid receptor antagonist, naltrexone nor β-funaltrexamine (β-FNA), a highly selective MOR antagonist, blocked fentanyl mediated inhibition of TNFα induced CXCL10 expression. Rather, β-FNA dose dependently inhibited TNFα induced CXCL10 expression with a greater potency than that observed for fentanyl. Immunoblot analysis indicated that morphine, fentanyl and β-FNA each reduced TNFα induced nuclear translocation of NF-κB p65. These data show that β-FNA and fentanyl inhibit TNFα induced CXCL10 expression via a MOR independent mechanism. Data also suggest that inhibition of TNFα induced CXCL10 expression by fentanyl and β-FNA is not directly related to a reduction in NF-κB p65 nuclear translocation. Further investigation is necessary in order to fully elucidate the mechanism through which these two opioid compounds inhibit CXCL10 expression. Understanding the mechanism by which chemokine expression is suppressed, particularly by the opioid antagonist, β-FNA, may provide insights into the development of safe and effective treatments for neuroinflammation.

TNF Alpha Production in Morphine-Treated Human Neural Cells Is NF-κB-Dependent

“…It has been shown that NF-κB activation is instrumental in TNFα-induced CXCL10 expression in A172 astroglia and that morphine addition did not alter CXCL10 expression. However, the addition of BFA inhibited TNFα-induced CXCL10 expression in these cells, which correlate with our results (Davis et al 2007). On the other hand, morphine can trigger phosphorylation of p38MAPK and its targets including MKK4 and Ask-1 leading to a cascade of biochemical events that impact TNFα expression.…”

β-Funaltrexamine Inhibits Inducible Nitric-oxide Synthase Expression in Human Astroglial Cells

“…We recently found that translocation of the p65 subunit of the transcription factor NF-κB into the nucleus is inhibited by β-FNA (Davis et al 2007). Thus, it may be that β-FNA inhibits iNOS induction through modulation of NF-κB expression or function; however, further investigation is needed.…”

“…To assess the effects of β-FNA on iNOS expression, β-FNA (0.05-33 μM; Sigma, St. Louis, MO) was added to cell cultures at the time of cytokine stimulation. Cell viability was monitored using the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium (MTT) assay as previously described (Davis et al 2007). …”

Exploring the Neuroimmunopharmacology of Opioids: An Integrative Review of Mechanisms of Central Immune Signaling and Their Implications for Opioid Analgesia

“…These examples of nonstereoselectivity clearly preclude the role of classic opioid receptors in these responses and thus raise the question of the validity of the classic opioid receptor involvement in other studies in which (Ϫ)-naloxone was employed in isolation. It is noteworthy that this question is not restricted to (Ϫ)-naloxone; the selective opioid receptor antagonist ␤-funaltrexamine possesses properties similar to those of (ϩ)-naloxone, raising the question of the opioid receptor requirement for these actions (Davis et al, 2007(Davis et al, , 2008. The clear nonclassic actions of morphine were also demonstrated by Li et al (2010Li et al ( , 2009) who reported neuronal apoptosis was dependent on TLR2 expression via glycogen synthase kinase 3␤-and ␤ arrestin-sensitive mechanisms.…”