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Parietin

| NFPA-H = | NFPA-F = | NFPA-R = | NFPA-S =

Parietin, or physcion, is the predominant cortical pigment of lichens in the genus Caloplaca, a secondary product of the lichen Xanthoria parietina, and a pigment found in the roots of curled dock (Rumex crispus). It has an orange-yellow color and absorbs blue light.

Parietin has also been shown to protect lichens against UV-B light, at high altitudes in alpine regions. The UV-B light stimulates production of parietin, protecting the lichens from damage. Lichens in arctic regions such as Svalbard retain this capability though they do not encounter damaging levels of UV-B, a capability that could help protect the lichens in case of ozone layer thinning.

It has also shown antifungal activity against barley powdery mildew and cucumber powdery mildew, more efficiently in the latter case than treatments with fenarimol and polyoxin B.

It reacts with KOH to form a deep, reddish-magenta compound.

Effect on human cancer cells

Also found in rhubarb, the orange compound appears to have potential to suppress 6-phosphogluconate dehydrogenase, or 6PGD. 6PGD is the third enzyme of the pentose phosphate pathway, or PPP, an oxidative process fueling growth in a still-relatively-unknown way. But it appears that arresting the chemical machinery at its third step could be promising for oncology. The parietin, identified from an FDA database of 2,000 known suppressors of 6PGD, killed half the human leukemia cells over two days in the laboratory. The pigment also slowed the growth of other human cancer cells in mouse models, according to the study. A more-potent derivative of the parietin called S3 may even cut the growth of lung cancer cells implanted in mice by two-thirds, over the course of 11 days. The compound also appears to be non-toxic to healthy cells.

References

References

  1. (1979-11-01). "Toxicity and mutagenicity of molds of the Aspergillus glaucus group. Identification of physcion and three related anthraquinones as main toxic constituents from Aspergillus chevalieri". Journal of Agricultural and Food Chemistry.
  2. Gauslaa Yngvar, Margrete Ustvedt Elin. (2003). "Is parietin a UV-B or a blue-light screening pigment in the lichen Xanthoria parietina?". Photochem. Photobiol. Sci..
  3. Nybakken Line. (2004). "The lichens Xanthoria elegans and Cetraria islandica maintain a high protection against UV-B radiation in Arctic habitats". Oecologia.
  4. Asbjorn Solhaug Knut. (2003). "UV-induction of sun-screening pigments in lichens". New Phytologist.
  5. Gyung Ja Choi. (December 2004). "Effects of chrysophanol, parietin, and nepodin of ''Rumex crispus'' on barley and cucumber powdery mildews". Crop Protection.
  6. (2015-10-22). "Cancer Growth Could be Slowed by Little-known Pigment in Rhubarb".
  7. (2015-10-21). "Orange lichens are source for potential anticancer drug".
  8. (2015-04-09). "Antiproliferative, Antibacterial and Antifungal Activity of the Lichen Xanthoria parietina and Its Secondary Metabolite Parietin". International Journal of Molecular Sciences.
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