Chronic Exposure to κ‐Opioids Enhances the Susceptibility of Immortalized Neurons (F‐11κ7) to Apoptosis‐Inducing Drugs by a Mechanism that May Involve Ceramide

Abstract

Chronic exposure of embryonic brain to opioids leads to microcephaly and developmental abnormalities. An immortalized mouse neuroblastoma X dorsal root ganglion hybrid cell line stably transfected to overexpress K-opioid receptors (F-1 lK 7) showed complete loss of K-receptor binding to [3H]U69,593after exposure to the K-agonist U69,593 for 24 h. U69,593 had no measurable effect on cell viability as determined by either cell viability or DNA fragmentation assays. However, when cell death (apoptosis) was induced by either staurosporine or the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002, cells pretreated with U69,593 for 24 h showed increased apoptosis compared with untreated cells. Thus, staurosporine (50 nM), wortmannin (4 1sM), and LY294002 (30 ‚uM) treatment for 24 h induced a 50% loss of cell viability and DNA fragmentation in 24 h. U69,593 pretreatment produced the same killing at lower concentrations, namely, 20 nM staurosporine, 2 p.M wortmannin, and 14 ‚uM LY294002, respectively. The effects of U69,593 were time-, dose-, and naloxone-reversible, suggesting that they are receptor-mediated. However, coaddition of U69,593 at the same time as staurosporine, wortmannin, or LY294002 did not enhance apoptosis. All three drugs that induced apoptosis were found to increase the level of ceramide, and pretreatment with U69,593 further increased the rate of formation of ceramide, a lipid that induces apoptosis in cells. We propose that chronic exposure to K-receptor agonists promotes increased vulnerability of neurons to apoptosis.

Regulation of nonphosphorylated and phosphorylated forms of neurofilament proteins in the prefrontal cortex of human opioid addicts

“…This opioid-induced reduction in the volume of the brain may also represent a form of neural injury. Recently, exposure of neuronal cultures from embryonic chick brain and specific cell lines to -and -opioid agonists increased their vulnerability to death by an apoptotic mechanism (Dawson et al, 1997;Goswami et al, 1998). In human lymphocytes, morphine has been shown to increase through a naloxone-sensitive mechanism, the expression of the protein Fas, a receptor that triggers cell apoptosis when it binds to its ligand FasL (Yin et al, 1999).…”

Multiple polyphosphoinositide pathways regulate apoptotic signalling in a dorsal root ganglion derived cell line

“…but co-addition of either ␦-or -opioids enhanced the effects of bradykinin by 2-fold in an F-11 cell line expressing ␦-receptors and high levels of transfected -opioid receptors. The enhancement was even greater when we pretreated with opioids for 24 hr, a manipulation previously shown to hyperactivate other signal transduction systems (Berry-Kravis et al, 1986;Dawson et al, 1997). Since the stimulation by opioids was blocked by preincubation with pertussis toxin, this strongly suggested the involvement of either G o or one of the G I or ␤␥ family of proteins in the opioid-mediated enhancement of the bradykinin effect (Georgoussi et al, 1993;Laugwitz et al, 1993), most likely the ␤␥ -subunits.…”

Cholestasis induced nephrotoxicity: The role of endogenous opioids

“…Induction of oxidative stress by opioid agonists is shown in several tissues such as the immune system, kidneys, epithelial cells and CNS (Payabvash et al 2006). Chronic exposure to exogenous opioid receptor agonists also increases vulnerability to apoptosis in the liver as well as neurons and certain tumor cell lines (Dawson et al 1997;Hatsukari et al 2003;Hatsukari et al 2007;Payabvash et al 2006). Morphine through the sustained activation of opioid receptors, can promote abnormal programmed cell death by enhancing the expression of pro-apoptotic FasL, Fas, and Bad proteins, and damping the expression of antiapoptotic Bcl-2 oncoprotein (Boronat et al 2001;Greeneltch et al 2005;Jaume et al 2004).…”