(+)-Morphine Explained

(+)-Morphine also known as dextro-morphine is the "unnatural" enantiomer of the opioid drug (−)-morphine. Unlike "natural" levo-morphine, unnatural dextro-morphine is not present in Papaver somniferum and is the product of laboratory synthesis.

In contrast to natural morphine, the unnatural enantiomer has no affinity or efficacy for the mu opioid receptor and therefore has no analgesic effects. To the contrary, in rats, (+)-morphine acts as an antianalgesic and is approximately 71,000 times more potent as an antianalgesic than (−)-morphine is as an analgesic.^[1] (+)-Morphine derives its antianalgesic effects by being a selective-agonist of the Toll-like receptor 4 (TLR4), which due to not binding to opioid receptors allows it to effectively reverse the analgesic properties of (−)-morphine. TLR4 is involved in immune system responses, and activation of TLR4 induces glial activation and release of inflammatory mediators such as TNF-α and Interleukin-1.^{[2] [3]}

See also

• (+)-Naloxone
• Dextromethorphan

Notes and References

1. Wu HE, Thompson J, Sun HS, Terashvili M, Tseng LF . Antianalgesia: stereoselective action of dextro-morphine over levo-morphine on glia in the mouse spinal cord . The Journal of Pharmacology and Experimental Therapeutics . 314 . 3 . 1101–1108 . September 2005 . 15901793 . 10.1124/jpet.105.087130 . 7190985 .
2. Hutchinson MR, Zhang Y, Shridhar M, Evans JH, Buchanan MM, Zhao TX, Slivka PF, Coats BD, Rezvani N, Wieseler J, Hughes TS, Landgraf KE, Chan S, Fong S, Phipps S, Falke JJ, Leinwand LA, Maier SF, Yin H, Rice KC, Watkins LR . 6 . Evidence that opioids may have toll-like receptor 4 and MD-2 effects . Brain, Behavior, and Immunity . 24 . 1 . 83–95 . January 2010 . 19679181 . 2788078 . 10.1016/j.bbi.2009.08.004 .
3. Hutchinson MR, Lewis SS, Coats BD, Rezvani N, Zhang Y, Wieseler JL, Somogyi AA, Yin H, Maier SF, Rice KC, Watkins LR . 6 . Possible involvement of toll-like receptor 4/myeloid differentiation factor-2 activity of opioid inactive isomers causes spinal proinflammation and related behavioral consequences . Neuroscience . 167 . 3 . 880–893 . May 2010 . 20178837 . 2854318 . 10.1016/j.neuroscience.2010.02.011 .