The ecological role of essential oils and their possible therapeutic activities. Marco Valussi!

Transcription

1 The ecological role of essential oils and their possible therapeutic activities Marco Valussi!

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3 Why do plants produce SM? The received view : coevolutionary arms-race! vs.! The screening hypothesis

4 Plant Coevolutionary armsrace Detox 1 Detox 2 Detox 4 Sm 1 Sm 2 Sm 3 Animal Used by animal for other purposes

5 ! Problems of the coevolutionary arms-race (CAR) model They could be exaptations! Too many similar compounds in a plant, most weakly active! It is a rare event for a molecule to be pharmacologically active

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7 ! Problems of the CAR model It is improbabile for a molecule with low biological activity to be part of the chemicals arms race! No organism can retain a molecule which causes a loss without immediate advantages! Then why have so many molecules with low biomolecular activity been maintained?

8 ! The Screening Hypothesis Firn R.D. and Jones C.G (2003). Natural products a simple model to explain chemical diversity. Natural Products Reports, 20, ! Evolution would favor organisms that could generate and retain chemical diversity at low cost. Since the greater the chemical diversity the greater the chance of producing the rare chemical with potent bioactivity, the organisms better able to produce and retain it will have an increased likelihood of better fitness.

9 ! The Screening Hypothesis The metabolic traits that would help increase generation and retention of chemical diversity:! enzymes with a broad substrate tolerance! reactions giving branched and shared pathways! matrix pathways

10 E2 E3 M2 M3 M4 E1 M1 E2 Promiscuous enzymes E3 E1 M2 M3 M4

11 Reactions giving multiple products E4 M2 E4 M1 M3 E4 M4

12 M1 M2 M3 M3+ M1+ M2+ M4 M5 Matrix metabolic pathways M6 M6+ M4+ M5+

13 ! The opportunistic theory of terpenoid production Owen, S.M. and Penuelas, J. (2005) Opportunistic emissions of volatile isoprenoids. Trends Plant Sci. 10, ! Volatile isoprenoids synthesis occurred as a fortuitous accident of essential isoprenoid synthesis.

14 No effects Biological effects Fortuitous emission Etc. Carotenoids Mevalonate and MPE C5 C10 C15 Cn Essential isoprenoids! (high mw) Non essential, volatile! isoprenoids chlorophyll side chains

15 Why are SM useful to humans? Chance or what?

16 Signalling GIT physiology Human target Detoxification Adaptive advantage SMs Coincidence Signalling Xenohormesis Nonhuman target Evolutionary continuity

17 SH Many weak SMs Network pharmacology, coincidental synergy Plants Metabolic machinery CAR Single potent SM Classical pharmacology, adaptation, heuristic

18 Are complex mixtures interesting? And if so, why?

19 The classical position MAPs are just vessels for diluted "drugs".! By "reverse pharmacology" it would then be possible to identify the real active single compound and isolate it.! The traditional uses are just that, traditional uses that cannot be confirmed.

20 A new position MAPs influence physiology and pathology through a mixtures of different compounds and possibly via different modes of action! Complex mixtures can facilitate synergy, and the SH supports this view.! The SH however does not imply that plants produce SMs in order to facilitate synergy

21 Many weak SMs Pharmacody namic Inhibition of many steps Membrane action Synergy Pharmacoki netics Enzymatic action Analogies Polypharmacy Network pharmacology

22 Network pharmacology Network pharmacology: multiple, low-dose, weak ligands can disrupt a network like a single strong ligand.! SH proposes that SMs are in general low potency and low affinity molecules, hence candidates for network pharmacology agents.

23 Synergy in essential oils as antimicrobials

24 Synergy in EOs Dearth of data in support of synergy in EOs, mainly in vitro studies.! Predictions are complex: minor and major components, their stereochemistry.! Cases of antagonism (EO less active than fractions or molecules)

25 Thymus vulgaris CT thymol The interactions (FICi) between seven of its compounds (thymol, carvacrol, linalol, p-cymene, borneol, alpha-terpinene, gamma-terpinene) tested at 1:1 were:! 1% antagonistic! 21% synergistic! 42% additive! 36% indifferent.! Most of the synergistic mixtures were synergistic in all different rations, according to the isobole method

26 Two intracellular! steps Cinnamaldehyde Eugenol Carvacrol Eugenol/! cinnamaldehyde Pharmacokinetics p-cymene Thymol Carvacrol Geraniol Anti efflux Antibiotic Carvacrol Two membrane! steps AcrA Intracellular! protein ATP production Antibiotic Antibiotic Enzyme Protein synthesis

27 Synergy Individual potency does not determine the potential of the combination.! Synergy more likely with a strongly active molecule and a weak one: carvacrol+ cymene; eugenol + menthol! Additivity more likely with two equally active molecules: carvacrol + thymol! The chemical features which make a molecule more antibacterial make it less easy to partition in the membrane! The lack of them make it easier to infiltrate the membrane and enlarge it, facilitating the passage of the more active molecule

28 Interesting synergistic EOs

29 EO Molecule 1 Molecule 2 Examples Cinnamomum zeylanicum cortex et fol Ocimum basilicum CT linalool; CT estragole Origanum marjorama CT linalool cinnamaldhe yde eugenol E. coli eugenol linalool E. coli, L. monocytogenes, E. aerogenes carvacrol linalool Origanum vulgare carvacrol p-cymene E. coli, B. cereus, E. faecalis thymol/ carvacrol thymol p-cymene carvacrol Satureja spp. thymol carvacrol E. coli, B. cereus, E. faecalis P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium Thymbra spicata carvacrol p-cymene E. coli, B. cereus, E. faecalis Thymus serpyllum thymol carvacrol P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium Thymus spp. thymol p-cymene

30 Thymus spp. CT borneol Thymus spp. CT linalool Thymus spp. CT thymol/carvacrol Thymus vulgaris CT carvacrol Thymus vulgaris CT limonene Thymus vulgaris CT thymol EO Molecule 1 Molecule 2 Examples thymol carvacrol P. aeruginosa, E. aerogene,s E. coli, L. monocytogenes, Salmonella thyphimurium thymol linalool P. aeruginosa, L. monocytogenes linalool p-cymene C. tropicalis thymol carvacrol P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium carvacrol p-cymene E. coli, B. cereus, E. faecalis thymol/ carvacrol linalool linalool p-cymene C. tropicalis thymol carvacrol P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium Thymus x citriodorus carvacrol p-cymene E. coli, B. cereus, E. faecalis Thymus zygis CT thymol thymol thymol p-cymene carvacrol Trachyspermum ammi thymol carvacrol P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium P. aeruginosa, E. aerogenes, E. coli, L. monocytogenes, Salmonella thyphimurium

31 Conclusions

32 ! Strong coevolutionary hypothesis Strong heuristic tool: an unknown EO could act via network pharmacology, being in a way designed by evolutionary forces, and being possibly better than any isolated compound

33 ! Weak coevolutionary hypothesis Synergy is present in EOsbecause of their rich chemical diversity, but this can t be used as a heuristic tool.! It can be used as an explanation when confronted by an EO which is superior or shows different activities and effectiveness than any isolated molecule

34 ! Concluding remarks It is difficult to give an answer to the main question, but! experimental data on synergy, network pharmacology, and the complexity of biological systems, point towards the plausibility of a synergistic mechanism in EOs! To maintain that the activities of medicinal plants must be always reduced to the activity of a single molecule is bad science! The way forward: delve deeper in the field, invest in more clinical trials

35 Thank you for your attention.