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Mechanisms involved in the chemoprevention of flavonoids
M H Siess1, A M Le Bon, M C Canivenc-Lavier
1Unité de Toxicologie Nutritionnelle, Institut National de la Recherche Agronomique, Dijon, France. siess@dijon.inra.fr
Abstract:
Flavonoids, widespread in edible plants, have been studied extensively for their anticarcinogenic properties. However, only few studies have been done with these constituents being administered by the dietary route. In our research, the effects of feeding rats with flavone, flavanone, tangeretin, and quercetin were investigated on two steps of aflatoxin B1 (AFB1)-induced hepatocarcinogenesis (initiation and promotion). Nonpolar flavonoids such as flavone, flavanone and tangeretin administered through the initiation period, decreased the number of -gamma-glutamyl transpeptidase-preneoplastic foci. In the same conditions of administration, quercetin, a polyhydroxylated flavonoid, showed no protective effect. Moreover, feeding rats with flavanone during the phenobarbital-induced promotion step significantly reduced the areas of placental glutathione S-transferase preneoplastic foci. Quercetin, flavone, and tangeretin, administered in the same conditions, caused no significant effect. Therefore flavanone act as an anti-initiator as well as an anti-promotor. Several mechanisms were involved in the anti-initiating effects of flavone, flavanone, and tangeretin: enhancement of enzymes involved in the detoxication of AFB1 (glutathione S-transferase, UDP-glucuronyl transferase), increase of the formation of AFB1-glutathione conjugates and inhibition of the binding of AFB1 to DNA. Although the relevance of these data to the human situation remains to be demonstrated, they confirm that several flavonoids administered by the dietary route possess promising chemoprotective effects.
Insights
Dietary flavonoids like flavanone show promise in cancer prevention. This study found flavanone reduced preneoplastic foci in rats, acting as both an anti-initiator and anti-promoter against aflatoxin B1-induced liver cancer.
Area of Science:
- Biochemistry
- Toxicology
- Cancer Research
Background:
- Flavonoids are plant compounds with studied anticarcinogenic properties.
- Few studies have investigated dietary administration of flavonoids for cancer chemoprevention.
- Aflatoxin B1 (AFB1) is a known hepatocarcinogen.
Purpose of the Study:
- To investigate the effects of dietary flavone, flavanone, tangeretin, and quercetin on AFB1-induced hepatocarcinogenesis in rats.
- To determine the efficacy of these flavonoids during the initiation and promotion stages of liver cancer.
Main Methods:
- Rats were fed diets containing specific flavonoids (flavone, flavanone, tangeretin, quercetin).
- Hepatocarcinogenesis was induced by AFB1.
- The study assessed the impact of flavonoids on preneoplastic foci during initiation and promotion phases.
Main Results:
- Nonpolar flavonoids (flavone, flavanone, tangeretin) reduced preneoplastic foci during AFB1 initiation.
- Flavanone significantly reduced preneoplastic foci during the promotion stage.
- Quercetin showed no protective effect in either stage.
- Flavanone demonstrated both anti-initiating and anti-promoting effects.
Conclusions:
- Flavanone exhibits significant chemoprotective effects against AFB1-induced hepatocarcinogenesis in rats.
- Mechanisms include enhanced detoxification enzymes, increased AFB1-glutathione conjugates, and inhibited AFB1-DNA binding.
- Dietary flavonoids hold potential for cancer chemoprevention, warranting further human studies.