Il se confirme qu’il y a deux espèces d’artemisia annua. L’une riche en acide artemisinique qui ne se transforme pas en artemisinine dans la plante; l’autre riche en acide dihydroartemisinique, précurseur de l’artemisinine.
Il se confirme également que l’artemisinine ne se transforme pas par métabolisme naturel en dihydroartemisinine. Cette transformation peut uniquement se faire par procédé chimique pour produire l’artesunate ou l’artemether
Or are there two chemotypes of artemisia annua ?
Artemisinin was initially called arteannuin and sold under this name as qinghoasu.
Arteannuin-B without endoperoxide bridge is a precursor or competitor to artemisinin.
Arteannuin-B was detected by Efferth in Chinese samples but not in Anamed samples (T Efferth et al Phytomedicine, 18, 2011, 959-969). He finds also that it is as cytotoxic against cancer cells as artemisinin.
It is very difficult to detect any arteannuin-B in Brazilian artemisia annua from Campinas, at least by HPLC-ELSD. Very often the arteannuin-B peak overlaps with the peaks of degradation products of artemisinin (CA Peng et al., J of Chromatography, 1133, 2006, 254-8).
D Fulzele et al. ( Phytotherapy Research , 5, 1991, 149-153) find that plants from Europe produced the highest level of artemisin and those from Lucknow produced the highest level of arteannuin-B
L.Olofsonet al., ( BMC Plant biology, 11, 2011, 45) state that the conversion of dihydroartemisinic acid to artemisinin is believed to be a non enzymatic spontaneous reaction. In a similar way artemisinic acid is converted to arteannuin-B . The genetic variation within A. annua appears to be high. One chemotype shows high content of dihydroartemisinic acid and artemisinin, while the second chemotype shows high content of artemisinic acid and arteannuin-B.
This is confirmed by GD Brown (Molecules, 2010, 15, 7603-98) and by P Weathers (Phytochem Rev 19 Feb 2010).
Artemisinic acid even appears to inhibit the transformation of dihydroartemisinic acid into artemisinin, by inhibition of the CYP transcription. (PR Arsenault et al., Plant Pysiol 154 oct 2010).
Chenfei Ma et al., (J of Chromatography A 1186, 2008, 412-19) also studied two chemotypes and find that in one of the samples at the flowering stage artemisinin had no significant increase , but arteannuin-B increased significantly. High arteannuin-B creates a bottle-neck in the production of artemisinin.
It is possible however that a decoction of the artemisia annua herb might lead to an in vivo transformation of certain precursors into artemisinin
Artemisinin has an EC50 of 10ng/ml against plasmodium compared to 1000 for arteannuin-B (Nguyen Tien Ban 1999 http://www.proseanet.org).
Against human and plant pathogenic fungi only arteannuin B shows activity whereas artemisinin shows none ( HQ Tang et al., Planta Medic 66, 2000. 391-393)
J Ferreira (J Agric Food Chem 58, 2010, 1691-98) also finds d that during the drying process of artemisia annua herb only dihydtroartemisinic acid is transformed into artemisinin, artemisinic acid stays stable in the leaves. The same author also claims that the two different chemotypes of artemisia annua are very different in their polyphenol composition ( Molecules. 2010. 15)
In light of this the biosynthesis of artemisinic acid by many research groups for the production of artemisinin appears to be a mistake.
Research at Basel ( Molecules, 2010 November) has firmly confirmed this: dihydroartemisinic acid is a late-stage precursor to artemisinin and the closely related metabolite artemisinic acic is not. They have also found that some derivates from artemisinic acid, the arteannuin-B precursor, have shown 10-20 times more in vitro antimalarial activities against plasmodium falciparum than artemisinin.
A similar concept is developed by TE Wallart et al., ( Planta Med 66. 2000, 57-62
And by HJ Woerdenbag et al., (Flavour and Fragrance Journal 8, 1993, 131-137) distinguishing between a Chinese and a Vietnamese chemotype. The former containing 4.0% essential oil but only 0.17 artemisinin, the latter 1.0%.
The Chinese ( W Wu et al., Planta Med, 77, 2011, 1048-53 ) have recently detected considerable differences in artemisinic acid and dihydroartemisinic acid between two chemotypes within the species Artemisia annua.
Huge differences were also found in the work of L. Al-Soweimel , Worcester, 2009, between the content in artemisinin and arteannuin between strains from Yugoslavia and China. They relate this to differences in the precursors artemisinic acid and dihydroartemisinic acid
Étiquettes : artesunate produit chimique