Search for compounds that inhibit the genotoxic and carcinogenic effects of heterocyclic aromatic amines

Over the last 30 years approximately 160 reports have been published on die tary compounds that protect from the mutagenic and carcinogenic effects of heterocyclic aromatic amines (HAAs). In the first section of this review, t he current state of knowledge is briefly summarized. Based on the evaluatio n of the available data, various protective mechanisms are described, and t he use of different methodologies for the detection of protective effects i s critically discussed. In most antimutagenicity studies (>70 %) bacterial indicators (predominantly Salmonella strain TA98) were used, and about 600 individual compounds and complex mixtures have been identified that attenua te the effects of HAAs. The most frequently used in vivo method to detect p rotective effects are adduct measurements; anticarcinogenic dietary factors were identified by aberrant crypt foci assays and liver foci tests with ra ts. The mechanisms of protection include inactivation of HAAs and their met abolites by direct binding, inhibition of enzymes involved in the metabolic activation of the amines, induction of detoxifying enzymes, and interactio n with DNA repair processes. The detection spectrum of conventional in vitr o mutagenicity assays with metabolically incompetent indicator cells is lim ited. These procedures reflect only simple mechanisms such as direct bindin g of the HAAs to pyrroles and fibers. It has been shown that these compound s are also effective in rodents. More complex mechanisms, namely, interacti ons with metabolic activation reactions are not adequately represented in i n vitro assays with exogenous enzyme homogenates, and false-negative as wel l as false-positive results may be obtained. More appropriate approaches fo r the detection of protective effects are recently developed test systems w ith metabolically competent cells such as the human Hep G2 line or primary hepatocytes. SCGE tests and DNA adduct measurements with laboratory rodents enable the detection of antigenotoxic effects in different organs, includi ng those that are targets for tumor induction by the amines. Medium term as says based on aberrant crypt foci in colon and liver foci tests have been u sed to prove that certain compounds that prevented DNA damage by HAAs also reduced their carcinogenic effects. These experiments are costly and time c onsuming and, due to the weak induction capacity of the amines, only pronou nced anticarcinogenic effects can be detected. Over the years, a large bulk of data on HAA protective compounds has accumulated, but only for a few (e .g., fibers, pyrroles, constituents of teas, and lactic acid bacteria) is t here sufficient evidence to support the assumption that they are protective in humans as well.