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Autoxidation, peroxides and malaria

January 18, 2017 - 17:50 -- Pierre Lutgen

Oxidative stress as cause for the death of parasites was a major field of research some 30 years ago.

Complex adaptations are necessary for the survival of the malaria parasite. There is a tenuous balance between the requirements for successful replication for the parasite and maintenance of an intact host erythrocyte. This is most evident in the oxidant damage which may be done to the host cell by the parasite, damage which may come close to destroying the erythrocyte before the parasite is able to mature. G6PD deficient erythrocytes for example are particularly oxidant sensitive and bad hosts for the parasite. In the discovery of antimalarial drugs, we may unwittingly have exploited the same principle discovered by natural selection- that malaria infected red cells are selectively damaged by oxidants.

                                                    Plasmodium is killed by an oxidative burst.

The defense mechanisms of the erythrocyte correlate closely with the severity of infection. In whole blood from Plasmodium falciparum infected humans, increase of intracellular hydrogen peroxide and spontaneous generation of ROS was found to be elevated 7-fold compared to blood from normal controls. It is known since more than 30 years that erythrocytes parasitized with malaria are highly susceptible to damage by an oxidative stress.

      A Wozencraft, S Croft, G Sayers. Oxygen radical release by adherent cell populations during the initial stages of lethal rodent malarial infection. Immunology 1985

      Ockenhouse CF, Schulman S, Shear HL, Induction of crisis forms in the human malaria parasite Plasmodium falciparum by activated, monocyte derived macrophages. 19984, J Immunol 133, 1601.

      Allison AC, Eugui EM. The role of cell-mediated immune responses in resistance to malaria, with special reference to oxidant stress. Annu Rev Immunol. 1983;1:361-92.

Deleterious properties of thalassaemia and glucose-6-phosphate dehydrogenase deficiency (G6PD−) provide protection against malaria. The red cells of adult carriers are refractory to parasite development because of oxidant sensitivity.

       M. Friedman. Oxidant damage mediates variant red cell resistance to malaria. Nature 280, 245 - 247 (19 July 1979); doi:10.1038/280245a0

A transient hemolysis accompanies the damage to parasites. This hemolysis can be provoked by strong oxidants like alloxan or hydrogen peroxide, followed by a sharp decrease in parasitemia. The predisposition to hemolysis of infected erythrocytes suggests that these cells are already under oxidative stress.

       IA Clark and NH Hunt. Evidence for reactive oxygen intermediates causing hemolysis and parasite death in malaria. Infection and Immunity. 1983 39-1, 1-6.

Hemoglobin can generate superoxide O₂¯.

       H Misra, I Fridovich, The generation of superoxide radical during the autoxidation of hemoglobin. J Biol Chem, 1972 247-21 6960-2

Glucose also produces peroxides and hydrogen peroxide. The production of reactive oxygen species is increased in hyperglycaemia.

       Zhimin Tao, Ryan A. Raffel, Abdul-Kader Souid and Jerry Goodisma, Kinetic Studies on Enzyme-Catalyzed Reactions: Oxidation of Glucose, Decomposition of Hydrogen Peroxide and their Combination. Biophys J. 2009 Apr 8; 96(7): 2977–2988. doi: 10.1016/j.bpj.2008.11.071

       T Tzanov, s Costa, G Gübitz, Hydrogen peroxide generation with immobilized glucose oxidase for textile bleaching J Biotechn 2002, 93, 87-4

       Bonnefont-Rousselot D, Glucose and reactive oxygen species. Curr Opinion Clin Nutr Metab Care, 2002 5(5). 561-8

       Ksiazek K, Wisniewska J, The role of glucose and reactive oxygen species in diabetes mellitus. Przegl Lek, 2001, 58(10), 915-8.

Toxoplasma gondii are susceptible to the hydrogen peroxide produced by glucose and glucose oxidase.

       H Murray, Z Cohn. Macrophage oxygen-dependent antimicrobial activity. Susceptibility of Toxoplaasma gondii. J Exp Med , 1979, 150, 938-949

Glucose produces peroxides not only in animals but also in plants. Soluble sugars and glucose in particular are not only sources of carbon and energy, but also of oxidative stress,  by glucose auto-oxidation. In Artemisia annua sugars function in artemisinin biosynthesis.

       PR Arsenault, DR Vail, KK Wobbe, PJ Weathers, Effect of sugars on artemisin production in Artemisia annua. Molecules, 2010, 15(4), 2302-2318.

       I Couée, C Sulmon, A El Amrani: Ilvolvement of soluble sugars in reactive oxygen species balance and responses to oxidative stress in plants. J Exper Botany, 2006, 57, 449-459

In freshly prepared coffees, as reported in the literature, hydrogen peroxide forms slowly as the beverage becomes oxygenated. Aqueous extracts of both green and black teas undergo extensive autoxidation under physiological conditions. This may also explain why freshly prepared Artemisia annua infusions are microbicidal and why freshly prepared infusions are more efficient against malaria.

      Rinkus S, Taylor RT. Analysis of hydrogen peroxide in freshly prepared coffees. Food Chem Toxicol. 1990 May;28(5):323-31.

      Roginsky V, Alegria AE, Oxidation of tea extracts and tea catechins by molecular oxygen. J Agric Food Chem 2005, 53(11) 4529-35

In 2000 we had analysed the concentration of different sugars in 5 Artemisia samples from different origins. The content for glucose was 150, for sucrose 150 and for fructose 200 µM/L on the average, but the concentrations were varying widely from one sample to the other. It was the lowest in Artemisia afra (D Evers, personal communication).

                                          Macrophages, natural killer cells and phagocytes.

The killing of Plasmodium by macrophages results from the release of ROS and H₂O₂ by macrophages. These cells bind to the surface of parasitized erythrocytes and are activated to release superoxide (O2-). Hydrogen peroxide is one of the most important weapons in macrophage antimicrobial mechanisms.

       C Nathan, R Root, Hydrogen peroxide release from mouse peritoneal macrophages. J Exp Medic 1977, 146, 1648-1662

When suitably triggered, by Trypanosoma cruzi for example, or by streptococcal preparations. macrophages release enough H₂O₂ to kill the parasites

       C Nathan, N Nogueira, Z Cohn, Activation of macrophages in vivo and in vitro. Peroxide release and killing of Trypanosoma cruzi: J Exp Med, 1979, 149, 1056-1068

       H Saito, H Tomioka. Enhanced hydrogen peroxide release from macrophages stimulated with streptococcal preparation. Infection and Immunity, 1979,26-2, 779-782

Phagocytosis-associated oxidative mechanisms mediate the destruction of the malaria parasite. The magnitude of the oxidative response corresponds to the number of parasites present.

       Ockenhouse CF, Shear HL. Oxidative killing of intraerythrocytic malaria parasite Plasmodium yoelii by activated macrophages.

                                        Dogma or hype: the harmful effects of lipid peroxidation?

Many studies have found a lack of effect of antioxidant supplementation in regard to health promotion in humans. Moreover, this supplementation has been linked to increased incidence of a number of diseases. An excellent review paper was published in Germany, with the title « Extending life span by increasing oxidative stress”.

       Ristow M, Schmeisser S. Extending life span by increasing oxidative stress. Free Radic Biol Med. 2011 Jul 15;51(2):327-36. doi: 10.1016/j.freeradbiomed.2011.05.010.

Even worse, a supply of strong antioxidants like vitamin C or aspirin may open the battle field for the parasite invasion.

       I Ottestad I, Vogt G, Retterstøl K, Myhrstad MC, Haugen JE, Nilsson A, Ravn-Haren G, Nordvi B, Brønner KW, Andersen LF, Holven KB, Ulven SM. Oxidised fish oil does not influence established markers of oxidative stress in healthy human subjects: a randomised controlled trial. Br J Nutr. 2012 Jul;108(2):315-26. doi: 10.1017/S0007114511005484.

       Benjamin B. Albert, David Cameron-Smith, Paul L. Hofman and Wayne S. Cutfield. Oxidation of Marine Omega-3 Supplements and Human Health. Biomed Res Int. 2013; 2013: 464921. doi: 10.1155/2013/4649

       Elmira Arab-Tehrany, Muriel Jacquot, Claire Gaiani, Muhammad Imran, Stephane Desobry, Michel Linder. Beneficial effects and oxidative stability of omega-3 long-chain polyunsaturated fatty acids. Trends in food science & technology 2012 v.25 no.1 pp. 24-33 21

These recent papers raise many questions. Lipid peroxidation and radical concentration is indeed much higher in malaria infected patients than in controls. It is a defense mechanism of the human host.

        P Kamble, A Bargale, Comparative study of free radical activity in plasmodium falciparum and Plasmodium vivax patients. International Journal of Pharma and Bio Sciences

Marine omega-3 rich oils are some of the world’s most popular supplements. These oils are highly prone to oxidation to lipid peroxides and other secondary oxidation products. Oxidized oils may have altered biological activity making them ineffective or harmful. Though there is also evidence that some beneficial effects of marine oils could be mediated through lipid peroxides. To date, human clinical trials have not reported the oxidative status of the trial oil. This makes it impossible to understand the importance of oxidation to efficacy or harm. Oxidation of trial oils may be responsible for the conflicting omega-3 trial literature, including the prevention of cardiovascular disease. The paper of Ottestad et al. confirms that the health effects of intake of oxidised fish oil have not previously been investigated in human subjects. In a double-blinded randomised controlled study, healthy subjects (aged 18-50 years, n 54) were assigned into one of three groups receiving capsules containing either 8 g/d of fish oil, oxidised fish oil or a control diet for 7 weeks. No significant changes between the different groups were observed with regard to in vivo lipid peroxidation, α-tocopherol activity,inflammation or liver function tests. This would indicate that intake of oxidised fish oil may not have unfavourable short-term effects in healthy human subjects.

Most toxicology studies with respect to oxidized oils have been conducted in animals utilizing dosages or levels of oxidation that are unrealistic in the human diet.

The Peroxide Value is a measure of how much peroxide is present in oil. When polyunsaturated fatty acids oxidize, the first compounds created are peroxides, so this is a measure of primary oxidation. The method is fairly robust and is not limited to unsaturated fatty acids. Another oxidative stress marker is malondialdehyde.

Scopoletin is a dye that can be used to detect the release of reactive oxygen species during the oxidative burst. Scopoletin is fluorescent under UV light. It is probably the strongest antioxidant present in Artemisia plants, only slightly inferior to α-tocopherol.

       Anuj Malik, Radical scavenging by scopoletin, J Chem Pharm Res 2011, 3(3):659-665

                                              Not only Artemisia annua contains peroxides.

By increasing the oxidative stress with xenobiotics a concentration of peroxides may be reached which destroys the erythrocyte and the parasite. Oxidative stress is also one of the mechanisms provoked by artemisinin and derivatives.

For other Artemisia plants, despite the fact that some have strong antimalarial properties, this mechanism could not be invoked because it was believed that they did not contain artemisinin. But an analysis of the volatile components of four Ethiopian Artemisia species shows that Artemisia afra contains 29.10 % of 6,7-epoxi linalool in the essential oil, and the 3 other none.

       Nibret E, Wink M. Volatile components of four Ethiopian Artemisia species extracts and their in vitro antitrypanosomal and cytotoxic activities. Phytomedicine. 2010 Apr;17(5):369-74. doi: 10.1016/j.phymed.2009.07.016.

Artemisia afra also contains 1-desoxy-1alpha-peroxy-rupicolin A-8-O-acetate which has an antiplasmodial activity of 8 microg/ml in vitro. The high concentrations of 6,7-epoxi-linaool in Artemisia afra and epoxy-ocimene in Artemisia absinthium are probably the major reason of antimalarial properties of these plants known since several thousand years.

         Kraft C, Jenett-Siems K, Siems K, Jakupovic J, Mavi S, Bienzle U, Eich E. In vitro antiplasmodial evaluation of medicinal plants from Zimbabwe. Phytother Res. 2003 Feb;17(2):123-8.

Artemisia absinthium contains another peroxide: epoxy ocimene. This is well documented in the literature. The best review can be found in a document of The European Medicines Agency. The report gives the concentrations of epoxy-ocimene in different regions with the highest value of 65% found in France

        Assessment report on Artemisia absinthium L Herba EMEA/HMPC/234444/2008

Several papers report similar values.

        Asta Judzentiene, Jurga Budiene, Renata Gircyte. Toxic Activity and Chemical Composition of LithuanianWormwood (Artemisia absinthium L.) Essential Oils. Rec. Nat. Prod. 6:2 (2012) 180-183

        Chialva F.; Liddle P.A.P.; Doglia G., 1983: Chemo taxonomy of wormwood Artemisia absinthium 1. composition of the essential oil of several chemotypes. Zeitschrift fuer Lebensmittel-Untersuchung und -Forschung 176(5): 363-366

        Juteau F, Jerkovic I, Masotti V, Milos M, Mastelic J 2003. Composition and antimicrobial activity of the essential oil of Artemisia absinthium from Croatia and France. Planta Med 69: 158-161.

        Anne Orav, Ain Raal, Elmar Arakb, Mati Müürisep, and Tiiu Kailas. Composition of the essential oil of Artemisia absinthium L. of different geographical origin. Proc. Estonian Acad. Sci. Chem., 2006, 55, 3, 155–165

Artemisia pallens contains a 3,4-epoxy derivative of davanone. Davanone and hydroxydavanone are strong antimalarials with an IC50 of 0,5 microgr/ml. They can easily be oxidated by photosensitization.

        Meryl A Abrahams. Bio-assay guides fractionation of Artemisia afra for in vitro antimalarial activity against Plasmodium falciparum. PhD Thesis Cape Town University, 1966.

        C Catalan, M Cuenca, W Herz. Sesquiterpene ketones related to davanone from Artemisia pallens. Phytochemistry, Vol. 29. No. R, pp. 2702-m2703, 1990

        AF Thomas, R Dubini, The oxidation of davanone, Isolation of davana ethers and sesquiterpenes of Artemisia pallens. Helv Chim Acta, 1974. 57 223.

Artemisia alba Turra is rich in highly oxygenated sesquiterpenes including hydroxydavanone.

        M Todorova, A Trendafilova, L Simmons, Highly oxygenated sesquiterpenes in Artemisia alba Turra. Phytochemistry, 2015, 110, 140-149.

A more extensive study screening 357 Brazilian plants from 30 families for the presence of peroxides finds that an overwhelming number of 214 plants of the Asteraceae family contain peroxides. This is probably the explanation of the antimalarial properties of this family.

        Eloir Pedro Schenkel; Gerhard Rücker; Detlef Manns; Miriam B. FalkenbergIII; Nelson I. Matzenbacher; Marcos SobralI; Lilian A. Mentz; Sérgio A.L. Bordignon; Berta M. Heinzmann. Investigação de plantas brasileiras quanto à presença de peróxidos. Rev. Bras. Cienc. Farm. vol.38 no.2 São Paulo June 2002. doi.org/10.1590/S1516-93322002000200008

It is interesting to find other plants with a well known antimalarial efficacy which contain similar peroxides. This is the case for example for Carica papaya. In an analysis of monoterpenols in 17 fruits, 6,7-epoxy-linalool is only found in this particular fruit.

        Ilc T, Parage C, Boachon B, Navrot N and Werck-Reichhart D (2016). Monoterpenol Oxidative Metabolism: Role in Plant Adaptation and Potential Applications. Front. Plant Sci. 7:509.doi: 10.3389/fpls.2016.00509

        P Winterhalter, D Katzenberger, P Schreier. 6,7-epoxy-linaool and related oxygenated perpenoids from Carica papaya. Phytochemistry 1986, 25-6, 1347-50.

Other antimalarial plants like Cymbopogon citratus also contain 6,7-epoxyde-linalool

        Sforcin JM, Amaral JT, Fernandes A Jr, Sousa JP, Bastos JK.Lemongrass effects on IL-1beta and IL-6 production by macrophages. Nat Prod Res. 2009;23(12):1151-9. doi: 10.1080/14786410902800681.

One of the first peroxides studied by the Chinese in 1972 in Program 523 was yingzhaosu isolated from the roots of Yingzhao, Artabotrys uncinatus a traditional Chinese herbal medicine for treatment of malaria.

        T.Liang. Isolation of Yingzhaosu- , Acta Chim. Sin. 37, 215 (1979),

The hypothesis that peroxides of Artemisia afra and Artemisia absinthium play a key role is substantiated by the fact that the pharmaceutical industry desperately tries to develop a synthetic peroxide.

        W. Jefford, Charles. Synthetic Peroxides as Potent Antimalarials. News and Views. Current Topics in Medicinal Chemistry, Volume 12, Number 5, March 2012, pp. 373-399(27)

Hydrogen peroxide is well present in plants and animals. At a first glance this beneficial role of peroxides and hydrogen peroxide in living organisms appears to be in contradiction with the antioxidant theories. One could even say, the antioxidant hype and business. Naturally occurring hydro- and endoperoxides represent a large group of compounds which are shown to possess antimalarial, antibacterial and many other activities.

       VM Dembitsky. Astonishing diversity of natural peroxides as potential therapeutic agents. Molecular and Genetic Medicine, 2015 9.1 1000163

                                              Auto-oxidation of essential oils and fatty acids

The USDA evaluated the effect of freeze, oven, shade, and sun drying on the leaf concentration of artemisinin, dihydroartemisinic acid, artemisinic acid and on the leaf antioxidant capacity.

        Ferreira JF, Luthria DL. Drying affects artemisinin, dihydroartemisinic acid, artemisinic acid, and the antioxidant capacity of Artemisia annua L. leaves. Agric Food Chem. 2010 Feb 10;58(3):1691-8. doi: 10.1021/jf903222j.

Freeze-dried samples had the lowest artemisinin concentrations as compared to the other drying methods. A significant decrease (82% average) in dihydroartemisinic acid was observed for all drying procedures, with a simultaneous, significant increase in artemisinin. The average bioconversion was 43% for oven- and shade-dried plants and 94% for sun-dried plants, reiterating the hypothesis that dihydroartemisinic acid, not artemisinic acid, is the main biosynthetic precursor of artemisinin and suggesting that sun drying improves this bioconversion. Similar results had been found in Tasmania. Artemisinin increased in the plants 21 days after harvest, either in the sun or the shade, more than in oven dried samples.

        J.C. Laughlin. Post-harvest Drying Treatment Effects on Amtimalarial Constituents of Artemiasia annua L.. ISHS Acta Horticulturae 576: International Conference on Medicinal and Aromatic Plants. Possibilities and Limitations of Medicinal and Aromatic Plant Production in the 21st Century

In 1992 it had already been reported that dihydroartemisinic acid could be converted into artemisinin simply by exposure to air.

        Kim, N.C. and Kim, S.U. (1992) Biosynthesis of artemisinin from 11,12-dihydroarteannuic acid. J. Korean Agric. Chem. Soc., 35, 106–109

        Sy, LK, Brown, GD, Haynes, R. A novel endoperoxide and related sesquiterpenes from Artemisia annua which are possibly derived from allylic hydroperoxides. Tetrahedron, 1998, v. 54 n. 17, p. 4345-4356 DOI: http://dx.doi.org/10.1016/S0040-4020(98)00148-3

        Ngo Koon Sin, Synthesis, isolation and autoxidation of sesquiterpenes, Thesis University of Hongkong June 1999.

In the Netherlands at Wageningen, the accumulation and concentrations of the artemisinin in green and dead leaves of Artemisia annua was analyzed. Concentrations of the total of artemisinin plus its precursors were higher in green leaves than in dead leaves in the younger crop stages, but higher in dead leaves than in green leaves at the final harvests. The molar quantity of dihydroartemisinic acid, the last enzymatically produced precursor, was higher than that of artemisinin in green leaves, but only 19 - 27% of that of artemisinin in dead leaves. Dead leaves were very important for the final artemisinin yield. The authors suggest to study the conversion of dihydroartemisinic acid into artemisinin during post-harvest handling.

         Lommen WJ, Elzinga S, Verstappen FW, Bouwmeester HJ. Artemisinin and sesquiterpene precursors in dead and green leaves of Artemisia annua L. crops. Planta Med. 2007 Aug;73(10):1133-9.

It is likely that most artemisinin found in dried plant material is formed by auto-oxidation after the death of the plant, by air-drying in sunlight“. An important reason to dry our plants in sunshine.

         E Ravina. The Evolution of Drug Discovery. Wiley VCH Verlag WeinheimSBN: 978-3-527-32669-3 528 pages March 2011

Oxygen can exist in two electronic states. Stable ground-state (triplet oxygen ³O₂) has two unpaired electrons with parallel spins. In excited-state oxygen (singlet oxygen, ¹O₂) the two electron spins are antiparallel. In this excited singlet state molecular oxygen lies 22 kcal/mol above the ground state. Singlet oxygen is formed by irradiation of gaseous oxygen with ultraviolet or high intensity visible light. The singlet oxygen reacts with organic compounds in the same way as hydrogen peroxide or aromatic endoperoxides. With several of our academic partners we had found in 2009 that the addition of Artemisia annua infusion to contaminated water efficiently killed all bacteria, under ambient light. But in a joint work with the University of Bangui it was found that in dark conditions the addition of the Artemisia annua extract in water contaminated with E. coli, S. aureus or S. paratyphi caused a significant increase in the bacteria abundance in monospecific culture condition. Molecules contained in the extract of A. annua are potentially implicated in the physical and chemical changes of the medium enabling the growth of the bacteria. This implies that under ambient light some oxidated reactive species were formed which are absent under dark conditions.

         Olga B. Mobili, Moïse Nola, Joseph Mabingui. Assessment of the effect of Artemisia annua leave extract infusion pH under dark conditions on Staphylococcus aureus, Salmonella paratyphi and Escherichia coli. J Appl Biosc. 2013 62, 4595-4609

                                        Autoxidation of Artemisia annua compounds

Arachidonic acid, a polyunsaturated fatty acid is easily peroxidized, generating free radicals, which in turn can lead to superoxide production.

It is evident from a study published already in 1992 that oxidized fatty acids are more effective in inducing parasiticidal effects of P. falciparum. It is also likely that the effect of the parent nonoxidized fatty acid is related to fatty acid oxidation by the parasite or RBC, because antioxidants such as BHT and vitamin E markedly reduce the antimalarial activity of the fatty acids. Lipid hydroperoxides (mainly mono- and dihydroxy derivatives) are major products of autooxidation, although a variety of other compounds. Whether some or all of these products are effective at inducing degeneration of the parasite remains to be determined. Fatty acid hydroperoxides may act by oxidizing reduced glutathione and thereby making the parasite more susceptible to oxidative stress.

          L M Kumaratilake, B S Robinson, A Ferrante, A Poulos. AntImalarial properties of n-3 and n-6 Polyunsaturated Faty Acids : In vitro effects on Plasmodium falciparum and in vivo effects on P.berghei.J. Clin. Invest. Volume 89, March 1992, 961-967

Arachidonic acid is present in eggs, meat, fish oil, and not in plants or vegetables. But it is well present in Artemisia plants. A phytochemical analysis of five Artemisia species in Turkey shows that saturated fatty acids in these plants represent on the average 40 % of the total and the unsaturated fatty acids 60 %, including those with antimalarial activities like linoleic acid, arachidonic acid and linolenic acid.

          Kursat, M.; Emre, I.; Yılmaz, O.; Cıvelek, S.; Demır, E.; Turkoglu, I. Phytochemical contents of five Artemisia species. Notulae Scientia Biologicae 2015 Vol.7 No.4 pp.495-499 ref.47

The real surprise is that based on the total fatty acid content. Artemisia armeniaca contains 6.47% arachidonic acid, A incana 7.79%, A tournefortiana 2.61%, A hausknechtii 7.44% A scoparia 3.17%. This is ten times higher than in meat, eggs or fish oil. And it is possibly related to the prophylactic and therapeutic properties of all Artemisia plants. More important even is the presence of eicosadieonic acid 20:2 n-6 EDA in these Artemisia plants. 10 % on the average in the five plants. EDA is also generating prostaglandins.

Huang YS Huang WC Chuang LT. Eicosadienoic acid differentially modulates production of pro-inflammatory modulators in murine macrophages. Mol Cell Biochem, 2011 358 85-94.

The findings of Kursat op.cit, have been confirmed by a study from Taskkent. The hydrocarbon extract of Artemisia annua contains 17,2 mass% for the sum of 20.0. 22.0 amd 24.0 PUFAs. An extraordinary finding considering that they are absent in other plants.

           N T Ul’chenko, Z A Khushbaktova, N P Bekker A L Glushenkova. Lipids from flowers and leaves of Artemisia annua and their biological activity. Chemistry of Natural Compounds. 2005, 41, 3.

Another paper finds that Artemisia annua contains 1.06 % of arachidonate.

           AA Malik, J Ahmad, M Ali. Volatiles of Artemisia annua as influenced by soil application of organic residues. Res J Medicinal Plants, 2012, 6 (6) 433-440.

The unsaturated fatty acid 20:3 n-6 kills the roundworm Caenorhabditis elegans by producing a range of epoxy and hydroxy metabolites.

           M Deline, K Keller, JL Watts Epoxides rerived from dietary di-homo-gamma-linolenic acid induce germ cell death in C.elegans. Scientific reports 2015, 5:15417.

Arachidonic acid promotes an oxidative burst in leukocytes and plays a role in lymphocyte activation and function. Some of the peroxides formed have a very complex structure with a bicyclic endoperoxide moiety and a cyclic peroxide function in the same molecule.

           C Pompéia, M Cury-Boaventura, R Curi. Arachidonic acid triggers an oxidative burst in leukocytes: Bras J.Medical Biolog Res 2003, 36, 1549-1560.

           E Jordan, The role of arachidonic acid metabolites in lymphocyte activation and function. Current topics in membranes and transport. 1990, 35, 333-347

           Huyyong Yin, J Marrow, N Porter. Identification of a novel class of endoperoxides from arichidonate autoxidation, J Biol Chem, 2004, 279 3766-3776.

Arachidonic acid is oxygenated in the rat liver by CYP 3A4.

           Orellana M, Valdes E, Capdevila, gil L. Nutritionally triggered alterations in arachidonic acid by rat liver microsomal cytochrome P450. Arch Biochem Biophys 1989, 274, 251-258

Compounds rich in allylic hydrogen atoms make up most probable targets for autoxidation considering that hydrogen atom abstraction is giving rise to resonance -stabilized radicals. Oxidative changes and deterioration reactions in essential oils, which may lead to both sensory as well as pharmacologically relevant alterations, have scarcely been systematically addressed. The identification of oxidation products resulting from oxidative events appears to be a valuable future objective.

           C Turek, F Stintzing, Stability of Essential Oils: a Review. Comprehensive Reviews In Food Science and Food Safety, 2013, 12-1, 40-53

Several autoxidation products of eicosapentaenoic acid (EPA, 20:5 n-3) have been identified in vitro and in vivo. Based on the free radical mechanism of arachidonic acid autoxidation regioisomeric hydroperoxydes can be generated.

           Yin H, Brooks JD, Gao L, Porter NA, Morrow JD. Identification of novel autoxidation products of the omega-3 fatty acid eicosapentaenoic acid in vitro and in vivo J Biol Chem. 2007 Oct 12;282(41):29890-901.

Arachidonic acid may also be converted into the hydroxyperoxy-HPETE-acid and attack Plasmodium like other peroxides do.

           Y Kimura, H Okuda, Effects of coffee tannins on arachidonate metabolism. Journal of Natural products, 1987, 50, 392-399.

           H Yin, J Morrow, N Porter, Identification of a novel class of endoperoxides from arachidonate autoxidation. J Biol Chem, 2004, 279, 30, 3766-3776.

Limonene is easily oxidized into limonene hydroperoxide and it probably this molecule which is responsible for therapeutic and disinfectant properties. This would also explain the biological action of limonene, its hydroperoxide being water soluble and bioavailable. Autoxidation of alpha-pinene also proceeds with much higher yields of highly oxidized products than previously reported.

          T Berndt, S Richters, T Jokinen, M Ehn, Hydroxyl radical-induced formation of highly oxidized organic compounds. Nature communications, 2 Dec 2016.

Beta-caryphyllene epoxide can be easily synthesized from beta-caryophyllene by autoxidation. It is the main constituent of essential oil obtained from various plants. It has antimicrobial and antitermite properties.

           Ashitani I, Kusumoto N, Takahashi K. Antitermite activity of beta-caryphyllene epoxide and episulfide. Z.Naturforsch C 2013, 68, 301-6.

Malarial infection has the ability to activate the immune system which causes the release of reactive oxygen species (ROS). Traditionally, ROS have been thought of as useless by-products of respiratory metabolism and believed to be generally deleterious to biological systems. However, growing evidence indicates that in many instances, ROS generation is not a useless or harmful process but, rather, an essential element for certain biological responses. Plasmodium however, has a number of mechanisms to minimize the cellular effects of ROS. These defense mechanisms include the production of antioxidants. Coevolution of the malaria parasite and its human host have resulted in a complex network of interactions. Plasmodium depends on an adequate antioxidant defense system. To this end, it even imports reducing proteins from its host.

            Koncarevic S, Rohrbach P, Deponte M, Krohne G, Prieto JH, Yates J 3rd, Rahlfs S, Becker K. The malarial parasite Plasmodium falciparum imports the human protein peroxiredoxin 2 for peroxide detoxification. Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13323-8. doi: 10.1073/pnas.0905387106