Mammalian morphine: de novo formation of morphine in human cells

Morphine, the major alkaloid of opium of Papaver somniferum, is one of the strongest analgesic compounds known. "Endogenous morphine" has been long isolated and authenticated by mass spectrometry in trace amounts from animal and human specific tissue or fluids. The most widely accepted explanation presently is that morphine detected in human and animal tissue is of exogenous sources (e.g. dietary origin).

The biosynthetic experiments were performed with human neurobalstoma cells (SH-SY5Y) and human pancreas carcinoma (DAN-G) cells. The application experiments were done in the presence of isotopically labeled potential precursors such as (18)O(2) and [ring-(13)C(6)]-L-tyrosine. Benzylisoquinoline alkaloids present in mammalian cells were identified by GC-MS/MS.

Growth of the SH-SY5Y cells in the presence of (18)O2 led to [(18)O(2)]-labeled morphine and [(18)O(2)]-labeled reticuline, each had a molecular mass four mass units higher than if grown in (16)O(2), indicating the presence of two atoms of (18)O per molecule. DAN-G cells cultured in an (18)O(2) atmosphere produced (S)-[ (18)O(2)]-norlaudanosoline and (S)-[ (18)O(2)]-reticuline, each labeled with (18)O atoms at only two of the four possible positions. Feeding of [ring-(13)C(6)]-tyramine, (S)-[1-(13)C, N-(13)CH(3)]-reticuline and [N-CD(3)]-thebaine to SH-SY5Y cells led each to the labeling of morphine, as established by GC-MS/MS.

Taken together, morphine, reticuline and norlaudanosoline are unequivocally biosynthesized by cultured human cells. The precursors of morphine in the human cell lines were conclusively shown to be oxygen, tyramine, reticuline and thebaine.