title: Tyrosine and tyramine increase endogenous ganglionic morphine and dopamine levels in vitro and in vivo: cyp2d6 and tyrosine hydroxylase modulation demonstrates a dopamine coupling.
abstract: BACKGROUND
  The ability of animals to make morphine has been in question for the last 30 years. Studies have demonstrated that animals do contain morphine precursors and metabolites, as well as the ability to use some morphine precursors to make morphine.
  
  
  METHODS
  The present study uses excised ganglia from the marine invertebrate Mytilus edulis as well as whole animals. Morphine and dopamine levels were determined by high performance liquid chromatography coupled to electrochemical detection and radioimmunoassay. Tissues and whole animals were also exposed to morphine precursors and exposed to the CYP2D6 inhibitor quinidine and the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). Additionally, via RT-PCR, a cDNA fragment of the CYP2D6 enzyme in the ganglia of M. edulis was identified.
  
  
  RESULTS
  Pedal ganglia incubated with either tyramine or tyrosine, or whole animals receiving injections, exhibited a statistically significant concentration- and time-dependent increase in their endogenous morphine and dopamine levels (2.51 +/- 0.76 ng/g for tyrosine and 2.39 +/- 0.64 ng/g for tyramine compared to approximately 1.0 ng/g morphine wet weight). Incubation with quinidine and/or AMPT diminished ganglionic morphine and dopamine synthesis at various steps in the synthesis process. We also demonstrated that CYP2D6 mediates the tyramine to dopamine step in this process, as did tyrosine hydroxylase in the step from tyrosine to L-DOPA. Furthermore, via RT-PCR, we identified a cDNA fragment of the CYP2D6 enzyme in the ganglia, which exhibits 94% sequence identity with its human counterpart. Evidence that tyrosine and tyramine were, in part, being converted to dopamine then morphine, and that this process can be inhibited by altering either or both CYP2D6 or tyrosine hydroxylase, is also provided.
  
  
  CONCLUSIONS
  It appears that animals have the ability to make morphine. This process also appears to be dynamic in that the inhibition of one pathway allows the other to continue with morphine synthesis. Moreover, dopamine and morphine synthesis were coupled.
authors.affiliation: Neuroscience Research Institute, State University of New York, College at Old Westbury, New York 11568, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhu
authors.forename: Kirk J
authors.initials: KJ
authors.lastname: Mantione
authors.forename: Lihua
authors.initials: L
authors.lastname: Shen
authors.forename: Patrick
authors.initials: P
authors.lastname: Cadet
authors.forename: Tobias
authors.initials: T
authors.lastname: Esch
authors.forename: Yannick
authors.initials: Y
authors.lastname: Goumon
authors.forename: Enrica
authors.initials: E
authors.lastname: Bianchi
authors.forename: Dario
authors.initials: D
authors.lastname: Sonetti
authors.forename: George B
authors.initials: GB
authors.lastname: Stefano
mesh_terms: D000818:Animals; D001483:Base Sequence; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D018076:DNA, Complementary / Q000235:genetics; D004298:Dopamine / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017952:Ganglia, Invertebrate / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008969:Molecular Sequence Data; D009020:Morphine / Q000378:metabolism*; D049880:Mytilus edulis / Q000033:anatomy & histology; D011802:Quinidine / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D014439:Tyramine / Q000494:pharmacology*; D014443:Tyrosine / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D015854:Up-Regulation; D019805:alpha-Methyltyrosine / Q000494:pharmacology
chemical_list: D065690:Cytochrome P-450 CYP2D6 Inhibitors; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D014443:Tyrosine; D019805:alpha-Methyltyrosine; D009020:Morphine; D019389:Cytochrome P-450 CYP2D6; D014446:Tyrosine 3-Monooxygenase; D011802:Quinidine; D004298:Dopamine; D014439:Tyramine