Biological activities of Turkish Oregano

Pharmacological activities of the essential oils of O.onites and O.minutiflorum were tested. Both the oils reduced the tonus of rat stomach fundus. They also reduced the carbachol-induced contractions on isolated rat ileum and inhibited the spontaneous activity of sheep ureter. They exhibited analgesic activity in hot-plate test on mice as well. Acute toxicity of the oils were determined on albino mice. Acute toxicity tests resulted in sedation and anaestesia followed by respiratory failure and death. LD50 values for the oils were found as 1.6 mL/kg for O. onites and as 2.4 mL/kg for O. minutiflorum (Cingi etal, 1992).

Origanum onites oil was shown to have hypotensive activity at 0.5 mL i.v. on rats, while origanum water showed hypertensive activity. The following positive pharmacological effects were observed with origanum water on rats: bile flow, barbiturate sleeping time, isolated ileum and aorta experiments. origanum water inhibited gastrointestinal contractions and showed choleretic effect. Acute and chronic toxicity of origanum water were tested on mice and rats. LD50 was found to be more than 21.9 mL/kg i.p. on mice indicating the safe use of origanum water (Aydin etal, 1997, 1997a,b,c).

Pure carvacrol ex origanum oil (99.3 per cent purity) was also tested on rat ileum and was found to possess strong antispasmodic activity. The oil of O. onites and carvacrol (1 mg/kg i.p.) were shown to have analgesic activity in tail-flick test on mice (Aydin etal, 1996).

Carvacrol was tested for lung tumours induced by DMBA on rats in vivo and was found to have strong antitumour activity at 0.1 mg . kg-1 i.p. Evidences for anti-angiogenic effects of carvacrol were observed suggesting a possible link with calcium metabolism (Zeytinoglu etal., 1998).

Additional evidence for its antitumour activity was obtained when carvacrol was tested on CO25 myoblast cells bearing a mutant human N-ras oncogene during the transformation and differentiation processes. It was found to inhibit DNA synthesis while there was no change in protein synthesis. These findings suggested that the antitumour effect of carvacrol was not due to cytotoxicity but possibly due to prevention of the prenylation of several proteins including ras (Zeytinoglu etal., 2000).

Carvacrol containing oils of O. onites, Satureja hortensis and Thymus serpyllum completely inhibited the growth of the following yeast causing food spoilage: Candida tropicalis, Hansenula anomala, Kloeckera apiculata, Pichia membranea, Rhodotorula glutinis and Saccharomyces cerevisiae (Kivanc and Akgul, 1989).

Table 4.3 Some biological activities of carvacrol tested at TBAM (Baser, 1998)

Insecticidal activity

Plant growth inhibition Antileishmanial activity Bactericidal activity

Fungicidal activity

Mast cell degranulation activity

Against common grain insects (100% mortality at 10% concentration)

Lemna test at 50 ppm. 100% inhibition and bleaching effect

Leishmania major promastigotes in vitro IC50 3.125 pg/ml Agar well diffusion protocol, 100 pg/ml. (Bacillus cereus 100% inh., Pseudomonas aeruginosa 90% inh., Shigella boydii 80% inh.) Agar tube dilution method, 200 pg/ml against human, animal and plant pathogens (Candida albicans 100%, Aspergillus niger 100%, Microsporum canis, Fusarium solani). Origanum onites oil was used in this pharmacological test. The test revealed antihistaminic activity of the oil

Several oregano spices including O. onites and O. vulgare subsp. hirtum inhibited the following food-borne bacteria: Bacillus cereus, Escherichia coli, Enterobacter aerogenes, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella aureus, S. thypi (Akgul and Kivanc, 1998).

O. onites exhibited complete inhibition of the following food-borne fungi: Aspergillus flavus, Aspergillus niger, Geotrichum candidum, Mucor sp., Penicillium roquefortii and some other Penicillium sp. The combined use of oregano and table salt (Sodium chloride) showed a synergistic antifungal effect (Akgul and Kivanc, 1998a).

The essential oils of O. onites and O. vulgare subsp. hirtum were found to be effective against all the molds and bacteria tested except for P. aeruginosa. The other microorganisms tested were Bacillus subtilis, Staphylococcus aureus, E. coli, A. niger, Aspergillus candidus, P. chrysogenum, Fusarium sp. (Dortunc and Cevikbas, 1992).

The oil of O. minutiflorum as well as carvacrol and thymol resulted in complete inhibition of the following fungi: Fusarium moniliforme, Rhizoctonia solani, Sclerotinia sclerotiorum, Phytophthora capsici (Muller-Riebau et al, 1995).

Carvacrol and thymol at 100—400 ppm completely inhibited the growth of most food-borne bacteria. Carvacrol showed the highest antibacterial activity. The combination of carvacrol, cuminaldehyde, sodium chloride and ascorbic acid showed the greater inhibitory effect against all the bacteria tested including P. aeruginosa (Kivanc and Akgul, 1998).

Carvacrol (500 mg) at 28 °C completely inhibited the growth and toxin production of A. flavus and Aspergillus parasiticus. Aflatoxin production was inhibited to a greater degree than that for the growth. A. flavus was more sensitive to carvacrol than A. parasiticus (Akgul et al, 1991).

Some other biological activities of carvacrol and O. onites oil tested at TBAM are summarized in Table 4.3 (Baser, 1998).

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