Related Experiment Videos
Activation and effects of the food-derived heterocyclic amines in extrahepatic tissues
E Overvik1, H Hellmold, C Branting
1Department of Medical Nutrition, Karolinska Institute, Novum Research Center, Sweden.
Abstract:
Humans frequently inhale as well as ingest cooked-food mutagens, among which the heterocyclic amines are the quantitatively most important. An extensive systemic distribution of these mutagens implies that most tissues in the body are exposed. Tissues containing cytochrome P450 (CYP) may be particularly susceptible to DNA damage. Accordingly, animal experiments have shown that oral exposure to heterocyclic amines leads to tumor formation at multiple sites. CYP1A2, which has only been demonstrated in the liver, seems to be the isozyme most efficient in metabolically activating the heterocyclic amines. In extrahepatic tissues, however, other CYP forms are likely to be important. Using Salmonella mutagenicity as an endpoint, we have studied the metabolic activation of 2-amino-3-methylimidazo[4,5,f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5,f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by isolated lung microsomes from rats and mice. Our studies show that CYP2A3, an isozyme that has hitherto not been investigated with regard to its capacity to activate heterocyclic amines, catalyses a major part of the IQ activating reactions in the uninduced lung. The formation of mutagens during cooking of meat is highly temperature dependent and meat extracts heated at 200 degrees C show a strong mutagenic activity in the Ames Salmonella assay. These extracts caused mutations at the HPRT locus in normal human fibroblasts as well as a pronounced decrease in survival of the cells. Furthermore, the heated meat extracts caused a decreased proliferative activity in primary cultures of normal mouse colonic epithelial cells as measured by autoradiography.
Insights
Cooked food contains heterocyclic amines, which are mutagens that can damage DNA. The study identifies CYP2A3 as a key enzyme in the lung for activating these mutagens, highlighting potential risks from dietary exposure.
Area of Science:
- Biochemistry
- Toxicology
- Molecular Biology
Background:
- Heterocyclic amines (HCAs) are prevalent mutagens in cooked foods, posing systemic exposure risks.
- Cytochrome P450 (CYP) enzymes are implicated in HCA metabolism and potential DNA damage.
- While CYP1A2 is known for HCA activation in the liver, extrahepatic CYP forms are less understood.
Purpose of the Study:
- To investigate the metabolic activation of HCAs (IQ, MeIQx, PhIP) in extrahepatic tissues, specifically rat and mouse lungs.
- To identify the specific CYP isozymes involved in HCA activation in lung microsomes.
- To assess the mutagenic and cytotoxic effects of heated meat extracts on human and mouse cells.
Main Methods:
- Utilized Salmonella mutagenicity assays to study HCA activation by isolated lung microsomes.
- Employed isolated lung microsomes from rats and mice for enzymatic activation studies.
- Assessed mutagenicity in human fibroblasts (HPRT locus) and cellular proliferation in mouse colonic epithelial cells exposed to heated meat extracts.
Main Results:
- CYP2A3 was identified as a significant catalyst for IQ activation in uninduced rat and mouse lungs.
- Heated meat extracts (200°C) demonstrated strong mutagenic activity in the Ames Salmonella assay.
- Heated meat extracts induced mutations in human fibroblasts and reduced the survival and proliferation of mouse colonic cells.
Conclusions:
- CYP2A3 plays a crucial role in activating IQ in the lung, an extrahepatic tissue.
- Dietary exposure to HCAs from cooked meat poses a mutagenic and cytotoxic risk to various cell types.
- Further research into extrahepatic CYP enzymes is warranted for a comprehensive understanding of HCA toxicity.