Archive for mai 2013

Prophylaxie contre le paludisme avec le Neem

mai 25, 2013

The Makerere University at Kampala has been able to demonstrate over the recent years that the regular consumption of Artemisia annua tea may lead to a strong preventive effect against malaria. ( PE Ogwang et al., Trop J Pharmac Res, 2012,13:3, 445-453; PE Ogwang et al., Brit J Pharmac Res 201, 1 :4, 124.132). This research effort sponsored by government of Uganda and Carnegie corporation USA, has led to the development of drug called Artavol® which is now available in pharmacies in Uganda. This product contains ingredients from three medicinal herbs.

In fact major research efforts are now devoted to the study the prophylactic effect of other plants or herbs. For example in India ( B Prakash et al., JEthnopharmacology, 146, 2013, 768.772) or Burkina Faso (RS Yerbanga et al., J Etnopharmacology 140, 2012, 255-260). In all these papers Neem (Azadirachta indica) is often the most active constituent.

The flavonoid quercetin is one of the major constituents of Neem and interferes with the cytochrome P-450 reductase ( MM Iwu et al ; Pharmacol Res Commun. 18:1, 1986, 81-91). Quercetin is a common and strong antioxidant usually present in glycolisated forms, such as quercitrin or rutin. The latter releases quercitin to perform its anti-inflammatory effect (M Comalada, Eur J Immunol 2005, 35:2, 584-92). It has a protective effect against chloroquine hepatotoxic effects ( SK Mishra et al. Hindawi Publishing Corporation, Malaria Research and Treatment, 2010, ID141734) A study from Luxembourg showed that Neem leaf extract induced apoptosis in leukemia cancer cells and that the important constituent quercetine probably played a key role ( M Schumacher et al., Genes Nutr 211, 6:2, 149-160).

Quercetin also is a strong inhibitor of the growth of the intraerythrocytic malaria parasite with an IC50 of 15 µM. (A Lehane, BMC Research Notes, 2008, 1:26). This was confirmed by a more recent study (D Ganesh et al., Parasitol Res 2012, 11:6, 2289). Among 8 flavonoids the quercetin analogue rutin was the most active antiplasmodial substance. In a study from Indonesia the extract of neem leaves had an IC50 of 3,8 µg/ml on Plasmodium falciparum.(Y Hanifah et al., Conf Proc Syla Kuala, 2011).

But the prophylactic effect of Neem extracts like the effect of Artemisia extracts is only effective progressively and in the long term. In a study by M Barlow-Benschop in Tanzania on 152 patients showed a decrease of malaria episodes from 57% at 3 months to 81% after 6 months of treatment. The treatment probably triggers an increase of the monocyte and/or T-cell count.

Very surprising and interesting results are delivered by a study from Nigeria ( C Mghemena et al., J Amer Sc. 2010, 6:8, 503-506). The authors investigated the effect of methanol, ethanol and aqueous extracts of neem and lemon grass against plasmodium development. After treatment with these 6 different extracts the albino mice were left for eight days and then infected with P.berghei. The aqueous extract of Neem had by far the highest suppression (76.1%) 8 days after infection.

This rather short range prophylaxis could be interesting for travelers. Neem tea has no side effects unlike other chemical prophylactic drugs.

Pierre Lutgen & Patrick Ogwang Engeu

Publicités

Malaria prophylaxis with Neem

mai 24, 2013

The Makerere University at Kampala has been able to demonstrate over the recent years that the regular consumption of Artemisia annua tea may lead to a strong preventive effect against malaria. ( PE Ogwang et al., Trop J Pharmac Res, 2012,13:3, 445-453; PE Ogwang et al., Brit J Pharmac Res 201, 1 :4, 124.132). This research effort sponsored by government of Uganda and Carnegie corporation USA, has led to the development of drug called Artavol® which is now available in pharmacies in Uganda. This product contains ingredients from three medicinal herbs.

In fact major research efforts are now devoted to the study the prophylactic effect of other plants or herbs. For example in India ( B Prakash et al., JEthnopharmacology, 146, 2013, 768.772) or Burkina Faso (RS Yerbanga et al., J Etnopharmacology 140, 2012, 255-260). In all these papers Neem (Azadirachta indica) is often the most active constituent.

The flavonoid quercetin is one of the major constituents of Neem and interferes with the cytochrome P-450 reductase ( MM Iwu et al ; Pharmacol Res Commun. 18:1, 1986, 81-91). Quercetin is a common and strong antioxidant usually present in glycolisated forms, such as quercitrin or rutin. The latter releases quercitin to perform its anti-inflammatory effect (M Comalada, Eur J Immunol 2005, 35:2, 584-92). It has a protective effect against chloroquine hepatotoxic effects ( SK Mishra et al. Hindawi Publishing Corporation, Malaria Research and Treatment, 2010, ID141734) A study from Luxembourg showed that Neem leaf extract induced apoptosis in leukemia cancer cells and that the important constituent quercetine probably played a key role ( M Schumacher et al., Genes Nutr 211, 6:2, 149-160).

Quercetin also is a strong inhibitor of the growth of the intraerythrocytic malaria parasite with an IC50 of 15 µM. (A Lehane, BMC Research Notes, 2008, 1:26). This was confirmed by a more recent study (D Ganesh et al., Parasitol Res 2012, 11:6, 2289). Among 8 flavonoids the quercetin analogue rutin was the most active antiplasmodial substance. In a study from Indonesia the extract of neem leaves had an IC50 of 3,8 µg/ml on Plasmodium falciparum.(Y Hanifah et al., Conf Proc Syla Kuala, 2011).

But the prophylactic effect of Neem extracts like the effect of Artemisia extracts is only effective progressively and in the long term. In a study by M Barlow-Benschop in Tanzania on 152 patients showed a decrease of malaria episodes from 57% at 3 months to 81% after 6 months of treatment. The treatment probably triggers an increase of the monocyte and/or T-cell count.

Very surprising and interesting results are delivered by a study from Nigeria ( C Mghemena et al., J Amer Sc. 2010, 6:8, 503-506). The authors investigated the effect of methanol, ethanol and aqueous extracts of neem and lemon grass against plasmodium development. After treatment with these 6 different extracts the albino mice were left for eight days and then infected with P.berghei. The aqueous extract of Neem had by far the highest suppression (76.1%) 8 days after infection.

This rather short range prophylaxis could be interesting for travelers. Neem tea has no side effects unlike other chemical prophylactic drugs.

Pierre Lutgen & Patrick Ogwang Engeu

Is artemisinic acid a precursor of artemisinin?

mai 4, 2013

Two competing chemotypes

Already twenty years ago the possibility of two chemotypes for Artemisia annua had been suggested ( HJ Woerdenbag et al., Flavour and Fragrance Journal 8, 1993, 131-137) distinguishing between a Chinese and a Vietnamese chemotype, the former containing 0.17 artemisinin, the latter 1.0%.
D Fulzele et al. ( Phytotherapy Research , 5, 1991, 149-153) found that plants from Europe produced the highest level of artemisin and those from Lucknow produced the highest level of arteannuin-B.
L Maes, F Van Nieuwerburgh from Gent University et al., ( J of Chromatography A 1118, 2006, 180.187) studied the influence of different enzymes on the production of arteannuin B and artemisinin in the two chemotypes , those from the National Botanical Garden at Meise poor in artemisinin and rich in B-arteannuin and those from Pedro de Magalhaes, Brazil rich in artemisinin and poor in B-arteannuin. 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).

Huge differences were also found in the work of L. Al-Soweimel , (BS thesis, Worcester, 2009) concerning the content in artemisinin and arteannuin-B between strains from Yugoslavia and China. They relate this to differences in the precursors artemisinic acid and dihydroartemisinic acid. The author finds surprisingly high concentrations of artemisinic acid in both chemotypes. The Chinese ( W Wu et al., Planta Med, 77, 2011, 1048-53 ) have recently confirmed considerable differences in artemisinic acid and dihydroartemisinic acid between two chemotypes within the species Artemisia annua. The two chemotypes use the two different pathways employed in plants for the production of isoprenoids, the one localized in the plastid, the other in the cytosol.
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.
L.Olofson et 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 DHAA and artemisinin, while the second chemotype shows high content of artemisinic acid and arteannuin-B. Based on results obtained by Jorge Ferreira (personal communication) the plant keeps a healthy reservoir of the precursor DHAA even while the precursor is transformed into artemisinin. Sun and oxygen are sufficient for this transformation, no enzyme is required. 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. A similar concept had been developed by TE Wallart et al., ( Planta Med 66. 2000, 57-62).

It is possible however that a decoction of the artemisia annua herb might lead to an in vivo transformation of certain precursors into artemisinin.
Very few investigations have been devoted to a comparison between artemisinin and artemisinic acid. Several studied the phytotoxicity. It was found ( L.Stiles et al., Journal of Chemical Ecology, April 1994, 20:4, 969-978) that both molecules induced almost the same effect at a concentration of 5 µM for artemisisin versus 10 µM for artemisinic acid. Similar studies were made on seeds (GD Baghi et al., Phytochemistry, 45:6, 1997, 1131-33). 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 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 complicated process.
Artemisinic acid is a dead end product which cannot be converted into artemisinin. That does not mean that it is useless: although having less efficacy than artemisinin, it has a variety of pharmacological activity, such as antimalarial, antipyretic, antibacterial, antitumor (J Kong et al., RSC Adv, 01 Feb 2013). Recently it has been shown that it is a regulator of adipocyte differentiation, that it reduces IL-6 secretion, thus influencing insulin resistance and the inflammatory state characterizing obesity (J Lee et al., J Cell Biochem, 2012, 113:7. 2488-99) 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 derivatives from artemisinic acid, the arteannuin-B precursor, have shown in vitro higher antimalarial activities against Plasmodium falciparum than artemisinin. The discovery of novel derivatives of artemisinic acid will begin a new era in natural drug formulation pathway. (Pooja Singh, 01/2011; Proceedings of: 80th annual Symposium of biological chemists).

lutgenp@gms.lu