Interaction of Various Piper methysticum Cultivars with CNS Receptors in vitro

Abstract

Methanolic leaf and root extracts of the Hawaiian kava (Piper methysticum Forst.) cultivars, Mahakea, Nene, Purple Moi and PNG, were tested on binding affinities to CNS receptors including GABA_A (GABA and benzodiazepine binding site), dopamine D₂, opioid (μ and δ), serotonin (5-HT₆ and 5-HT₇) and histamine (H₁ and H₂). HPLC analysis was carried out in order to determine the amount of the main kavalactones kavain, 7,8-dihydrokavain, methysticin, 7,8-dihydromethysticin, yangonin and 5,6-demethoxyyangonin. The most potent binding inhibition was observed for leaf extracts to GABA_A receptors (GABA binding site) with IC₅₀ values of approximately 3 μg/ml, whereas root extracts were less active with IC₅₀ values ranging from 5 μg/ml (Nene) to 87 μg/ml (Mahakea). Since the leaf extracts generally contained lower amounts of the kavalactones than the root extracts, there might exist additional substances responsible for these activities. Leaf extracts also inhibited binding to dopamine D₂, opioid (μ and δ) and histamine (H₁ and H₂) receptors more potently than the corresponding root extracts with IC₅₀ values ranging from 1 to 100 μg/ml vs. ≥ 100 μg/l, respectively. Significant differences in the potential of binding inhibition were also observed between cultivars. Binding to serotonin (5-HT₆ and 5-HT₇) and benzodiazepine receptors was only weakly inhibited by both root and leaf extracts of all four cultivars. In conclusion, our investigation indicates that the GABA_A, dopamine D₂, opioid (μ and δ) and histamine (H₁ and H₂) receptors might be involved in the pharmacological action of kava extracts. Since the cultivars contained similar amounts of kavalactones, while their pharmacological activities differed markedly, other constituents may play a role in the observed activities. Additionally, leaves generally exhibited more potent binding inhibition than roots, therefore leaf of P. methysticum might be an interesting subject for further pharmacological studies.

Abbreviations

BHK:baby hamster kidney

CHO:Chinese hamster ovary

CNS:central nervous system

DMY:5,6-demethoxyyangonin

DHM:7,8-dihydromethysticin

DHK:7,8-dihydrokavain

GABA:γ-aminobutyric acid

³H-LSD:³ H-lysergic acid diethylamide

HPLC:high performance liquid chromatography

IC₅₀:50 % inhibitory concentration

SFV:Semliki Forest Virus

Key words

Piper methysticum - Piperaceae - leaf extracts - root extracts - styryl pyrones - cultivars - CNS recombinant receptors

References

• 1 Lebot V, Merlin M, Lindstrom L. Kava: the Pacific elexir. Healing Arts Press 1997
• 2 Singh Y N. Kava: an overview.  J. Herbal Gram. 1997;  39 33-55
• 3 Hölzl J, Juretzek W, Schneider G, Stahl-Bispuk E. Piper. In: Hänsel R, Keller K, Rimpler H, Schneider G, editors Hager's Handbuch der pharmazeutischen Praxis. Springer-Verlag 1994 Vol. 6: 191-220
• 4 Smith R M. Kava lactones in Piper methysticum from Fiji: compositions of extracts from roots, stems and leaves.  Phytochemistry. 1983;  22 1055-6
• 5 Mayer H J, Kretzschmar R. Kawapyrone: Eine neuartige Substanzgruppe zentraler Muskelrelaxantien vom Typ des Mephenesins.  Klinische Wochenschrift. 1966;  4 902-3
• 6 Gleitz J, Beile A, Peters T. Kavain inhibits veratridine activated voltage dependent Na(+)-channels in synaptosomes prepared from rat cerebral cortex.  Neuropharmacology. 1995;  34 1133-8
• 7 Gleitz J, Beile A, Wilkens P, Ameri A, Peters T. Antithrombotic action of the kavapyrone kavain prepared from Piper methysticum on human platelets.  Planta Medica. 1997;  63 27-30
• 8 Taylor C P, Meldrum B S. Na⁺ channels as targets for neuro-protective drugs.  J. Trends in Pharmacological Sciences. 1995;  16 309-16
• 9 Bloom F E. Neurotransmission and the central nervous system. In: Hardman JG, Limbird LE, editors The pharmacological basis of therapeutics. MacGraw-Hill Health Professions Division 1996 9th edition: pp. 267-93
• 10 Jussofie A, Schmitz A, Hiemke C. Kavapyrone-enriched extract from Piper methysticum as modulator of the GABA binding site in different regions of rat brain.  Psychopharmacology. 1994;  116 469-74
• 11 Davis L P, Drew C A, Duffield P, Johnston A R, Jamieson D D. Kava pyrones and resin: studies on GABA_A, GABA_B and benzodiazepine sites in rodent brain.  Pharmacology and Toxicology. 1992;  71 120-6
• 12 Boonen G, Häberlein H. Influence of genuine kavapyrone enantiomers on the GABA_A binding site.  Planta Medica. 1998;  64 504-6
• 13 Kretzschmar R. Pharmakologische Untersuchungen zur zentralnervösen Wirkung und zum Wirkungsmechanismus der Kava-Droge (Piper methysticum Forst) und ihrer kristallinen Inhaltsstoffe. In: Rietbrock N, editor Phytopharmaka in Forschung und klinischer Anwendung. Loew 1995: 29-38
• 14 Ross S, de Freese L, Melzer M, Kolhmann R. Kava-lactone determination by a new RP-HPLC separation enabling high performance of sample analysis in aqueous solutions. Proceeding of the 46^th Annual Congress of the Society for Medicinal Plant Research (GA). Vienna; 1998: 31, August - 4, September: Poster E21
• 15 Simmen U, Burkard W, Berger K, Schaffner W, Lundstrom K. Extracts and constituents of Hypericum perforatum inhibit the binding of various ligands to recombinant receptors expressed with the Semliki Forest virus system.  Journal of Receptor and Transduction Research. 1999;  19 59-74
• 16 Lundstrom K, Mills A, Buell G, Allet E, Adami N, Lijiestrom P. High-level expression of the human neurokinin-1 receptor in mammalian cell lines using the Semliki Forest virus expression system.  European Biochemistry. 1994;  224 197-21
• 17 Smith P K, Krohn R I, Hermanson G T, Mallia A K, Gertner F H, Provenzano M D, Fujimoto E K, Goeke N M, Olson B J, Klenk D C. Measurement of protein using bicinchoninic acid.  Analytical Biochemistry. 1985;  150 76-85
• 18 Mansour A, Chalmers D T, Fox C A, Meador-Woodruff J H, Watson S J. Biochemical anatomy: insights into the cell biology and pharmacology of neurotransmitter systems in the brain. In: Schatzberg AF, Nemeroff CB, editors The American Psychiatric Press Textbook of Psychopharmacology. The American Psychiatric Press Inc. 1995: pp. 45-63
• 19 Cavadas C, Araujo I, Cotrim M D, Amaral T, Cunha A P, Macedo T, Ribeiro C F. In vitro study on the interaction of Valeriana officialis L. extracts and their amino acids on GABA_A receptor in rat brain.  Arzneim. Forsch.-Drug Res. 1995;  45 753-5
• 20 Nichols M. Understanding Kava. J. Health Supplement Retailer July 1996: 44