Protection of N-methyl-N'-nitro-N-nitrosoguanidine-induced in vivo clastogenicity by aqueous garlic extract

Garlic (Allium sativum L.): A Brief Review of Its Antigenotoxic Effects

Traditional Medicine/Complementary and Alternative Medicine is a practice that incorporates medicine based on plants, animals, and minerals for diagnosing, treating, and preventing certain diseases, including chronic degenerative diseases such as obesity, diabetes, hypertension, atherosclerosis, and cancer. Different factors generate its continued acceptance, highlighting its diversity, easy access, low cost, and the presence of relatively few adverse effects and, importantly, a high possibility of discovering antigenotoxic agents. In this regard, it is known that the use of different antigenotoxic agents is an efficient alternative to preventing human cancer and that, in general, these can act by means of a combination of various mechanisms of action and against one or various mutagens and/or carcinogens. Therefore, it is relevant to confirm its usefulness, efficacy, and its spectrum of action through different assays. With this in mind, the present manuscript has as its objective the compilation of different investigations carried out with garlic that have demonstrated its genoprotective capacity, and that have been evaluated by means of five of the most outstanding tests (Ames test, sister chromatid exchange, chromosomal aberrations, micronucleus, and comet assay). Thus, we intend to provide information and bibliographic support to investigators in order for them to broaden their studies on the antigenotoxic spectrum of action of this perennial plant.

The inhibitory effects of garlic and Panax ginseng extract standardized with ginsenoside Rg3 on the genotoxicity, biochemical, and histological changes induced by ethylenediaminetetraacetic acid in male rats

Ethylenediaminetetraacetic acid (EDTA) is widely used in food and other industries to sequester metal ions and to prevent their disadvantageous effects. The objective of the current study was to evaluate the protective effect of Panax ginseng extract standardized with ginsenoside Rg3 (ginsenoside Rg3 content was 3.6% w/w, i.e., 36 microg/mg P. ginseng extract) and garlic against EDTA-induced biochemical, genotoxic, and histological changes in rats. Forty male rats were divided into eight treatment groups and treated for 7 days as follows: the control group, the group treated with EDTA (20 mg/kg b.w) and the groups treated with P. ginseng extract (20 mg/kg b.w), garlic (5 mg/kg b.w), P. ginseng plus garlic alone or in combination with EDTA. In vivo bone marrow micronucleus test and random amplified polymorphism DNA-PCR (RAPD-PCR) method were performed to assess the antigenotoxic effect of both protective agents. The results indicated that EDTA administration caused a significant decrease in the serum biochemical parameters and antioxidant enzymes activity. The administration also increased lipid peroxidation and the incidence of micronucleated polychromatic erythrocytes (MnPCEs), caused appearance of some changes in polymorphism band patterns, and induced different histopathological lesions in the livers, kidneys, and testis. Treatment with P. ginseng, garlic alone or plus EDTA significantly improved all the tested parameters. Moreover, P. ginseng extract was found to be more effective than garlic in restoring the parameters that were altered by EDTA.

Inhibition of carcinogen-induced DNA damage in rat liver and colon by garlic powders with varying alliin content

The present study was designed to investigate the protective efficiency of three garlic powders, obtained from bulbs grown in soils with different levels of sulfur fertilization, against DNA damage. Increasing fertilization of soil resulted in an increased alliin content of the powders. Garlic powders were administered to rats for 2 weeks (5% of the diet) and their antigenotoxic effects were examined in the liver and the colon using the comet assay. Consumption of the different garlic powders induced a 35-60% reduction in DNA damage induced by N-nitrosodimethylamine (NDMA) in rat liver. Increased alliin content of the garlic powder was associated strongly with a proportional decrease in NDMA induced DNA alteration. DNA damage induced by aflatoxin B1 in the liver or by 1,2-dimethylhydrazine in the colon were also decreased strongly by the three garlic powders but these decreases were not correlated to the alliin content of the garlic powders. Feeding garlic powders did not modify the genotoxic activity of the direct-acting carcinogen methylnitrosourea in the colon. Part of our results supports evidence that fertilization can have an impact on the protective capacity of garlic bulbs.

Combinatorial antigenotoxic and anticarcinogenic effects of tomato and garlic through modulation of xenobiotic-metabolizing enzymes during hamster buccal pouch carcinogenesis

OBJECTIVE

Combination chemoprevention by dietary agents is a promising approach toward cancer control. Many dietary agents are known to prevent experimental mutagenesis and carcinogenesis by modulating xenobiotic-metabolizing enzymes. The present study evaluated the combinatorial chemopreventive effects of tomato and garlic on hamster buccal pouch carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA).

METHODS

Hamsters were assigned to one of four groups. The right buccal pouches of animals in group 1 were painted with 0.5% DMBA three times a week. The right buccal pouches of animals in group 2 were painted with DMBA and received intragastric administration of a combined dose of tomato and garlic on days alternate to DMBA application. Animals in group 3 were given chemopreventive agents alone. Animals in group 4 served as controls. Levels of phase I and II enzymes and the frequency of bone marrow micronuclei were used as biomarkers of chemoprevention.

RESULTS

All the hamsters painted with DMBA alone developed buccal pouch carcinomas that exhibited increased activities of xenobiotic-metabolizing enzymes associated with increased frequencies of bone marrow micronuclei. In the liver, an increase in phase I enzymes was accompanied by compromised phase II detoxification activities. Combined administration of tomato and garlic effectively suppressed the incidence and mean tumor burden of hamster buccal pouch carcinomas. In addition, tomato and garlic combination significantly decreased phase I enzymes and increased phase II enzyme activities in the pouch and liver with a decreased incidence of bone marrow micronuclei.

CONCLUSION

From these results, we suggest that modulation of xenobiotic-metabolizing enzymes exerted by tomato and garlic combination plays a key role in mitigating the mutagenic and carcinogenic effects of DMBA.

Attenuation of N-methyl-N'-nitro-N-nitrosoguanidine induced genotoxicity and oxidative stress by tomato and garlic combination

The protective effect of pretreatment with tomato and garlic against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced genotoxicity and oxidative stress was investigated in male Swiss mice. In vivo bone marrow micronucleus test was performed to assess the antigenotoxic effect of tomato and garlic. Oxidative stress was monitored by estimating the extent of lipid peroxidation and the status of the glutathione redox cycle antioxidants. Increased frequency of bone marrow micronuclei with enhanced lipid peroxidation was associated with compromised antioxidant defenses in MNNG treated animals. Although pretreatment with tomato and garlic significantly reduced the frequencies of MNNG-induced bone marrow micronuclei, the combination of tomato and garlic exerted a greater protective effect. This was associated with modulation of lipid peroxidation as well as reduced glutathione (GSH) and the GSH-dependent enzymes glutathione peroxidase (GPx) and glutathione-S-transferase (GST). These findings suggest that a diet containing even low levels of different naturally occurring compounds is effective in exerting antigenotoxic effects by modulating oxidative stress.

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Herbal bioactivation: the good, the bad and the ugly

It has been well established that the formation of reactive metabolites of drugs is associated with drug toxicity. Similarly, there are accumulating data suggesting the role of the formation of reactive metabolites/intermediates through bioactivation in herbal toxicity and carcinogenicity. It has been hypothesized that the resultant reactive metabolites following herbal bioactivation covalently bind to cellular proteins and DNA, leading to toxicity via multiple mechanisms such as direct cytotoxicity, oncogene activation, and hypersensitivity reactions. This is exemplified by aristolochic acids present in Aristolochia spp, undergoing reduction of the nitro group by hepatic cytochrome P450 (CYP1A1/2) or peroxidases in extrahepatic tissues to reactive cyclic nitrenium ion. The latter was capable of reacting with DNA and proteins, resulting in activation of H-ras oncogene, gene mutation and finally carcinogenesis. Other examples are pulegone present in essential oils from many mint species; and teucrin A, a diterpenoid found in germander (Teuchrium chamaedrys) used as an adjuvant to slimming diets. Extensive pulegone metabolism generated p-cresol that was a glutathione depletory, and the furan ring of the diterpenoids in germander was oxidized by CYP3A4 to reactive epoxide which reacts with proteins such as CYP3A and epoxide hydrolase. On the other hand, some herbal/dietary constituents were shown to form reactive intermediates capable of irreversibly inhibiting various CYPs. The resultant metabolites lead to CYP inactivation by chemical modification of the heme, the apoprotein, or both as a result of covalent binding of modified heme to the apoprotein. Some examples include bergamottin, a furanocoumarin of grapefruit juice; capsaicin from chili peppers; glabridin, an isoflavan from licorice root; isothiocyanates found in all cruciferous vegetables; oleuropein rich in olive oil; dially sulfone found in garlic; and resveratrol, a constituent of red wine. CYPs have been known to metabolize more than 95% therapeutic drugs and activate a number of procarcinogens as well. Therefore, mechanism-based inhibition of CYPs may provide an explanation for some reported herb-drug interactions and chemopreventive activity of herbs. Due to the wide use and easy availability of herbal medicines, there is increasing concern about herbal toxicity. The safety and quality of herbal medicine should be ensured through greater research, pharmacovigilance, greater regulatory control and better communication between patients and health professionals.

Effects of allicin on both telomerase activity and apoptosis in gastric cancer SGC-7901 cells

AIM: To investigate the effects of allicin on both telomerase activity and apoptosis in gastric cancer SGC-7901 cells.

METHODS: The gastric cancer SGC-7901 adenocarcinoma cells were treated with allicin and the cell cycle, inhibitory rate, apoptosis, telomerase activity and morphologic changes were studied by MTT assay, flow cytometry (FCM), TRAP-PCR-ELISA assay, light microscope, electron microscope respectively. Results were compared with that of AZT (3’-Azido-3’-deoxythymidine).

RESULTS: SGC-7901 cells were suppressed after exposure to allicin of 0.016 mg/mL, 0.05 mg/mL, and 0.1 mg/mL for 48 h. Compared with the control, the difference was significant (P < 0.05). Allicin could induce apoptosis of the cells in a dose-dependent and non-linear manner and increase the proportion of cells in the G₂/M phase. Compared with the control, the difference was significant in terms of the percentage of cells in the G₂/M phase (P < 0.05). Allicin could inhibit telomerase activity in a time-dependent and dose-dependent pattern. After exposure to allicin at 0.016 mg/mL for 24 hours, SGC-7901 cells showed typical morphologic change.

CONCLUSION: Allicin can inhibit telomerase activity and induce apoptosis of gastric cancer SGC-7901 cells. Allicin may be more effective than AZT.

Inhibition of clastogenicity of benzo[a]pyrene and of its trans-7,8-dihydrodiol in mice in vivo by fruits, vegetables, and flavonoids

In the in vivo mouse bone marrow micronucleus assay, homogenates of spinach, artichoke, peaches, and blue grapes as well as commercial concentrates of these vegetables and fruits reduced induction of micronuclei by benzo[a]pyrene (BaP) by 43-50%. Concentrates of strawberries (31% reduction) and of cauliflower (20% reduction) were less potent. Inhibition of genotoxicity by spinach and peaches was not caused by any delay in maturation of micronucleated erythrocytes as shown by experiments with sampling times of 24, 48, and 72 h after dosing of BaP. Pre-treatment of the mice with spinach 48, 24, and 12h before application of BaP resulted in a 44% reduction of micronuclei while peaches generated only a marginal effect. A post-treatment procedure administering spinach or peaches 6h after dosing of BaP did not indicate any protective effects. When trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BaP-7,8-OH) was applied for induction of micronuclei spinach and peaches reduced the number of micronuclei by 55 and 48%, respectively. Pre-treatment of mice with spinach 96, 72, and 60 h before sacrifice caused a decline of hepatic 7-ethoxyresorufin-O-dealkylase (EROD) and of 7-pentoxyresorufin-O-dealkylase (PROD) activities by factors of 2.2 and 1.4, respectively. However, statistical significance was not reached. On the other hand, peaches had no influence on hepatic EROD or PROD activities. The flavonoids quercetin and its glucoside isoquercitrin, administered orally in doses of 0.03 mmol/kg body weight simultaneously with intraperitoneally given BaP, reduced the number of micronuclei in polychromatic erythrocytes of the bone marrow of mice by 73 and 33%. Ten-fold higher concentrations, however, reversed the effects with a particular strong increase observed with isoquercitrin (+109%; quercetin: +16%).

Interactions of herbs with cytochrome P450

A resurgence in the use of medical herbs in the Western world, and the co-use of modern and traditional therapies is becoming more common. Thus there is the potential for both pharmacokinetic and pharmacodynamic herb-drug interactions. For example, systems such as the cytochrome P450 (CYP) may be particularly vulnerable to modulation by the multiple active constituents of herbs, as it is well known that the CYPs are subject to induction and inhibition by exposure to a wide variety of xenobiotics. Using in vitro, in silico, and in vivo approaches, many herbs and natural compounds isolated from herbs have been identified as substrates, inhibitors, and/or inducers of various CYP enzymes. For example, St. John's wort is a potent inducer of CYP3A4, which is mediated by activating the orphan pregnane X receptor. It also contains ingredients that inhibit CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. Many other common medicinal herbs also exhibited inducing or inhibiting effects on the CYP system, with the latter being competitive, noncompetitive, or mechanism-based. It appears that the regulation of CYPs by herbal products complex, depending on the herb type, their administration dose and route, the target organ and species. Due to the difficulties in identifying the active constituents responsible for the modulation of CYP enzymes, prediction of herb-drug metabolic interactions is difficult. However, herb-CYP interactions may have important clinical and toxicological consequences. For example, induction of CYP3A4 by St. John's wort may partly provide an explanation for the enhanced plasma clearance of a number of drugs, such as cyclosporine and innadivir, which are known substrates of CYP3A4, although other mechanisms including modulation of gastric absorption and drug transporters cannot be ruled out. In contrast, many organosulfur compounds, such as diallyl sulfide from garlic, are potent inhibitors of CYP2E1; this may provide an explanation for garlic's chemoproventive effects, as many mutagens require activation by CYP2E1. Therefore, known or potential herb-CYP interactions exist, and further studies on their clinical and toxicological roles are warranted. Given that increasing numbers of people are exposed to a number of herbal preparations that contain many constituents with potential of CYP modulation, high-throughput screening assays should be developed to explore herb-CYP interactions.