Parietin is the predominant
cortical pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...
of
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.[Caloplaca
''Caloplaca'' is a lichen genus comprising a number of distinct species. Members of the genus are commonly called firedot lichen, jewel lichen.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, gold lichens, "ora ...]
'', a secondary product of the lichen ''
Xanthoria parietina
''Xanthoria parietina'' is a foliose lichen in the family Teloschistaceae. It has wide distribution, and many common names such as common orange lichen, yellow scale, maritime sunburst lichen and shore lichen. It can be found near the shore on ro ...
'', and a pigment found in the roots of
Curled Dock
''Rumex crispus'', the curly dock, curled dock or yellow dock, is a perennial flowering plant in the family Polygonaceae, native to Europe and Western Asia.
Description
The plant produces an inflorescence or flower stalk that grows to high. I ...
(''Rumex crispus''). It has an orangy-yellow color and absorbs blue light.
It is also known as physcion.
It 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 and the parietin protects the lichens from damage. Lichens in arctic regions such as Svarlbard 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 anti-fungal activity against
barley powdery mildew and
cucumber powdery mildew, more efficiently in the latter case than treatments with
fenarimol
Fenarimol, sold under the tradenames Bloc, Rimidin and Rubigan, is a fungicide which acts against rusts, blackspot and mildew fungi. It is used on ornamental plants, trees, lawns, tomatoes, peppers, eggplants, cucumbers and melons. It is mainly ...
and
polyoxin B.
It reacts with
KOH to form a deep, reddish-magenta compound.
Effect on human cancer cells
Also found in
rhubarb
Rhubarb is the fleshy, edible stalks ( petioles) of species and hybrids (culinary rhubarb) of ''Rheum'' in the family Polygonaceae, which are cooked and used for food. The whole plant – a herbaceous perennial growing from short, thick rhizo ...
, the orange compound appears to have potential to suppress
6-phosphogluconate dehydrogenase
6-Phosphogluconate dehydrogenase (6PGD) is an enzyme in the pentose phosphate pathway. It forms ribulose 5-phosphate from 6-phosphogluconate:
:6-phospho-D-gluconate + NAD(P)+ \rightleftharpoons D-Ribulose 5-phosphate + CO2 + NAD(P)H + H+
It i ...
, or 6PGD. 6PGD is the third enzyme of the
pentose phosphate pathway
The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt and the HMP Shunt) is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-pho ...
, 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
''Caloplaca coralloides'' chemistry*
*
{{Anthraquinone
Anthraquinone dyes
Antifungals
Dihydroxyanthraquinones
Phenol ethers
Lichen products