Inhibition of Vinyl Carbamate-Induced Mutagenicity and Chromosomal Damage by a Garlic Component in Mice

Ethyl carbamate (EC) is formed during the fermentation process, and is found in alcoholic beverages and fermented foods including bread, cheese, yogurt, soya sauce and vinegar.  The amounts of EC found in various food items included the following: stone-fruit brandies (2000 ng/kg), table wines (10-15 ng/g), sake rice wine (130 ng/g), bread (7 ng/g) and soy sauce (18 ng/g).  The mean daily consumption of EC from various food items in adults has been estimated to be about 10 to 20 ng/kg of body weight.  First reported to produce tumors in the lungs of mice, EC was subsequently shown to initiate tumors in a variety of tissues including the skin, liver, mammary gland and lymphoid tissue.  However, the lung appears to be a susceptible target as lung tumors are found in 2 to 6 months after EC exposure, whereas tumor formation in other tissues occurs within a time period of at least a year. 

The carcinogenicity of EC is mediated by its alteration to VC and subsequently to VC epoxide, a byproduct that is believed to be responsible for modification of DNA and for producing mutations, events that are associated with the carcinogenic response.  Although similar tumors are evoked by EC and VC, VC is more carcinogenic than EC, producing lung tumors that are 20- to 50-fold greater in number than are induced by EC.

In this study, we have identified the mutations generated by VC in the lungs and small intestine of mice.  We have also carried out studies to determine the ability of VC to cause chromosomal damage in immature red blood cells.  In addition, we have performed studies to determine the potential of the garlic constituent DASO2 to inhibit the mutations and chromosomal damage caused by VC. 

Our results showed that spontaneous mutations were found in the lungs of untreated mice, but the total number of mutations or mutant frequency was minimal.  The mutant frequency in mice that received VC were 5-fold greater than that in untreated mice.  However, treatment of mice with DASO2 decreased the mutant frequencies induced by VC by about 70%.  In the small intestine, the spontaneous mutations found in untreated mice were similar to those in the lung, and were minimal.  Treatment of mice with VC produced a mutant frequency that was 3-fold higher than that in the untreated mice.  Hence, the mutagenic effects in the lung were more pronounced than in the small intestine of mice given the same dose of VC.  Mice that were treated with DASO2 prior to VC resulted in a decrease of 40% in the mutant frequency. These results showed that, although DASO2 decreased the production of mutations in both the lung and small intestine, the effects were more pronounced in the lung than in the small intestine.

We have identified the specific mutations in the lung and small intestine of mice that were untreated or were treated with DASO2, VC or DASO2 and VC.  The mutations detected in the lungs of mice that were untreated or treated with DASO2 were nearly identical, and comprised mainly of a single type.  On the other hand, three types of mutations were found in the lungs of mice that were treated with VC or with VC and DASO2. The type of mutations found in the small intestine of untreated mice or mice treated with DASO2 was similar to those observed in the lungs of mice subjected to the same treatment regimens.  A single type of mutation was commonly found, and this was identical to the one found in the lung.  As identified in the lung, the same three types of mutations were identified in the small intestine of mice given VC alone.  No differences were found in the distribution of the mutation types in the various groups of mice.

Studies were carried out to assess chromosomal damage in immature red blood cells from mice that were administered VC or DASO2 and VC.  The results showed that chromosomal damage was minimal in mice that were not given VC.  The chromosomal damage was pronounced in mice that received VC alone.  When the mice were given DASO2 and VC, the chromosomal damage was reduced.  Hence, treatment of mice with DASO2 prior to VC provided a protective effect against chromosomal damage caused by VC.

The results of this study affirmed that treatment of mice with DASO2 inhibited the formation of mutations and chromosomal damage produced by VC.

Reference: Hernandez LG and Forkert PG.  Inhibition of vinyl carbamate-induced mutagenicity and clastogenicity by the garlic constituent diallyl sulfone in F1 (Big Blue x A/J) transgenic mice.  Carcinogenesis doi:10.1093/carcin/bgm051, published March 8, 2007.