Abstract
The effective treatment of pain is typically limited by a decrease in the pain-relieving action of morphine that follows its chronic administration (tolerance). Therefore, restoring opioid efficacy is of great clinical importance. In a murine model of opioid antinociceptive tolerance, repeated administration of morphine significantly stimulated the enzymatic activities of spinal cord serine palmitoyltransferase, ceramide synthase, and acid sphingomyelinase (enzymes involved in the de novo and sphingomyelinase pathways of ceramide biosynthesis, respectively) and led to peroxynitrite-derive nitroxidative stress and neuroimmune activation [activation of spinal glial cells and increase formation of tumor necrosis factor-α, interleukin (IL)-1β, and IL-6]. Inhibition of ceramide biosynthesis with various pharmacological inhibitors significantly attenuated the increase in spinal ceramide production, nitroxidative stress, and neuroimmune activation. These events culminated in a significant inhibition of the development of morphine antinociceptive tolerance at doses devoid of behavioral side effects. Our findings implicate ceramide as a key upstream signaling molecule in the development of morphine antinociceptive tolerance and provide the rationale for development of inhibitors of ceramide biosynthesis as adjuncts to opiates for the management of chronic pain.
Footnotes
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This work was supported by the Saint Louis University Seed Fund; the National Institutes of Health [Grant RO1-HL077328]; COFIN 2005 [Grant 2005057404004]; Istituto di Ricovero e Cura a Carattere Scientifico Centro Neurolesi “Bonino-Pulejo” grant; and the University of Florence (Florence, Italy).
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M.M.N. and S.C. contributed equally to this work.
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doi:10.1124/jpet.108.146290.
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ABBREVIATIONS: TNF, tumor necrosis factor; IL, interleukin; SMase, sphingomyelinase; FB1, fumonisin B1; D609, tricyclodecan-9-xanthogenate; SPT, serine palmitoyl transferase; PBS, phosphate-buffered saline; GFAP, glial fibrillary acidic protein; RT, room temperature; NF, nuclear factor; MnSOD, manganese superoxide dismutase; %MPE, percentage maximal possible antinociceptive effect; CS, ceramide synthase; ASMase, acid sphingomyelinase; NT, 3-nitrotyrosine; Mor, morphine.
- Received September 17, 2008.
- Accepted November 24, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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