Immunostimulant Antimutagenic And Anticancer Activity

Some studies have shown that orégano extracts or herbal mixtures with Origanum spp. possess in vitro antiviral activity or have immunostimulating effects both in vitro and in vivo. However, little knowledge has been attained so far on mechanisms of immunomodulating activity or underlying active compounds. It has been shown that ethanol extracts of O. vulgare inhibited intracellular propagation of ECHO9 Hill virus and also showed interferon inducing activity in vitro (Skwarek et al, 1994). Flavonoid luteoline, a constituent of Origani herba, has been considered as responsible for the induction of an interferon-like substance. A mixture of herbal preparation containing rosemary, sage, thyme and oregano (O. vulgare) showed radical scavenging activity and inhibition of the human immunodeficiency virus (HIV) infection at very low concentrations (Aruoma et al., 1996). It was suggested that the main active compounds of herbal preparations were carnosol, carnosic acid, carvacrol and thymol. Significant inhibitory effects of O. vulgare extracts against HIV-1 induced cytopathogenicity in MT-4 cells were also observed by Yamasaki et al. (1998). According to Krukowski et al. (1998), an increase in immunoglobulin (IgG) levels was observed in reared calves, fed with a conventional concentrate supplemented by a mineral-herbal mixture containing O. majorana.

A strong and dose-dependent capacity of inactivating dietary mutagen Trp-P-1 in the Salmonella typhimurium TA 98 assay was observed in O. vulgare water extracts, that exhibited significant antimutagenic effects in vitro (Ueda et al., 1991). Origanum majorana aqueous extracts were also able to suppress the mutagenicity of liver-specific carcinogen Trp-P-2 (Natake et al, 1989). When studying the mechanism of suppressing the mutagenicity of Trp-P-2 in O. vulgare, it was found that two flavonoids, galangin and quercetin acted as Trp-P-2 specific desmutagens, which neutralised this mutagen during or before mutating the bacteria (Salmonella typhimurium TA 98) (Kanazawa et al, 1995). The amounts of galangin and quercetin required for 50 per cent inhibition (IC50) against 20 ng of Trp-P-2 were 0.12 pg and 0.81 pg, respectively. It was also found that quercetin acted as a mutagen at high concentrations (>10 pg/plate), but was a desmutagen when applied at low (>0.1 <10 pg/plate) concentrations. Milic and Milic (1998) have found that isolated phenolic compounds from different spice plants, including O. vulgare, strongly inhibited pyrazine cation free radical formation in the Maillard reaction and the formation of mutagenic and carcinogenic amino-imida-zoazarene in creatinine containing model systems.

In a literature survey, referring to the anticancer activity of Origanum genus, different approaches, testing systems and cell lines have been used by different authors when assessing the carcinogenic potential of plants or their isolated compounds. However, there are no available data on practical/clinical use of oregano in cancer prevention. In 1966

an international project was performed with the aim of screening the native plants of former Yugoslavia for their potential agricultural use in the USA and Yugoslavia (Mayer et al, 1971). In the frame of this project 1466 samples of 754 plant species were analysed for chemical and antitumour activity. According to the results of the Cancer Chemotherapy National Service Center Screening Laboratories (Washington, DC) a high carvacrol (60—85 per cent) containing O. heracleoticum ( = O. vulgare spp. hirtum (Link) Ietswaart) was reported to show high antitumour activity. Lam and Zheng (1991) have found that essential oil of O. vulgare fed to mice, induced the activity of glutathione ^-transferase (GST) in various tissues. The GST enzyme system is involved in detoxification of chemical carcinogens and plays an important role in prevention of carcinogenesis, what would explain the anticancer potential of O. vulgare essential oil. This oil exhibited high levels of cytotoxicity (at dilutions of up to 1:10000) against four permanent eukary-otic cell lines including two derived from human cancers (epidermoid larynx carcinoma: Hep-2 and epitheloid cervix carcinoma: HeLa) (Sivropoulou etal., 1996). Other studies, that refer to in vitro cytotoxic and/or anti-proliferative effects of O. vulgare extracts or isolated compounds (carvacrol, thymol) include those of Bocharova et al. (1999) and He et al. (1997), who observed moderate suppressing activities of O. vulgare extracts (CE50 = 220 mg/ml) on human ovarian carcinoma cells (CaOv), or of isolated carvacrol and thymol (IC50 = 120 pmol/l) on Murine B 16(F10) melanoma cells — a tumour cell line with high metastatic potential.

Antitumour-promoting activity or in vitro cytotoxic effects towards different tumour cell lines were attributed also to O. majorana extracts or their constituents (Assaf et al, 1987; Okuyama et al, 1995; Hirobe et al, 1998). When studying cytotoxic activity of O. majorana water—alcoholic extracts and of isolated compounds (arbutin, methylar-butin and their aglycons — hydroquinone and hydroquinone monomethyl ether) towards cultured rat hepatoma cells (HTC line), a high dose-dependent HTC cytotoxi-city of hydroquinone was observed, whilst arbutin was not active (Assaf etal., 1987). At 300 pM hydroquinone caused 40 per cent cellular mortality after 24 h of incubation, but no cells remained viable after 72 h. It has been established that this well known antiseptic of the urinary tract was a more potent cytotoxic compound towards rat hepatoma cells than many classic antitumour agents like azauridin or colchicin, but less than valtrate, a monoterpenic ester of Valeriana spp.

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