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. 2008 Sep-Oct;14(9-10):590-8.
doi: 10.2119/2007-00050.Yuan.

Protective effects of epigallocatechin gallate on colon preneoplastic lesions induced by 2-amino-3-methylimidazo[4,5-f ] quinoline in mice

Jun-Hua Yuan  1 , Yan-Qing Li, Xiao-Yun Yang
Affiliations

Protective effects of epigallocatechin gallate on colon preneoplastic lesions induced by 2-amino-3-methylimidazo[4,5-f ] quinoline in mice

Jun-Hua Yuan et al. Mol Med. 2008 Sep-Oct.

Abstract

Epigallocatechin gallate (EGCG), a key active ingredient in green tea, has multiple anticarcinogenic effects. The aim of the present study was to investigate if EGCG could prevent the formation of colon aberrant crypt foci (ACF) induced by 2-amino-3-methylimidazo[4,5-f ]quinoline (IQ) and to explore possible mechanisms for resultant effects. Sixty male BALB/cA nude, immunodeficient mice were divided into six groups including a normal unexposed control, mice induced with IQ alone, three groups treated with varying doses of EGCG post-IQ induction, and a EGCG-treated control population. Six weeks later, the mice were killed, and tissues subjected to hematoxylin-eosin (H&E) and 0.2% methylene blue staining to observe histopathological alterations of colon mucus and the formation of ACF, respectively. Protein expression of NF-E2-related factor 2 (Nrf2) was assessed via immunohistochemistry (IHC) and Western analysis, and mRNA levels of Nrf2 and uridine 5'-diphosphate-glucuronosyltransferase (UGT)1A10 were determined in colon tissues. Our results demonstrate that, compared with IQ-induced controls, the degree of atypical hyperplasia decreased and the number of total ACF and total AC also decreased significantly (P < 0.05 and P < 0.01, respectively) in mice belonging to all EGCG dosing groups. At the same time, the protein levels of Nrf2 detected by IHC and Western blotting increased (both P < 0.01 compared with IQ group), and the mRNA levels of Nrf2 and UGT1A10 increased (both P < 0.01 compared with IQ group). In conclusion, EGCG had preventive effects on preneoplastic lesions induced by IQ. Our observations suggest that this effect may be the result of activation of the Nrf2-UGT1A10 signaling pathway.

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Figures

Figure 1
Figure 1
Experimental treatment of nude mice in six groups. The total experiment lasted for 6 wks. Group 1 was defined as the normal control. At the first and last 2 wks, the mice were given a basal diet. From the beginning of the third wk, the mice were treated with 0.2 mL corn oil every 2 d by oral gavage for 2 wks. Group 2 was the model group and mice were treated with IQ (50 mg/kg) dissolved in 0.2 mL corn oil for 2 wks. Groups 3–5 were treated with different doses of EGCG before and during the 2-wk treatment with the same dose of IQ as group 2. Doses of EGCG were 5, 10, and 20 mg/kg dissolved in 0.2 mL sterilized pure water every d. The group 6 EGCG control was treated with medium doses of EGCG (10 mg/kg) in the preceding 4 wks.
Figure 2
Figure 2
Body weight time course of mice in all six groups. formula image, normal control; formula image, IQ; ▵, low dose (EGCG + IQ); formula image, middle dose (EGCG + IQ); formula image, high dose (EGCG + IQ); ♦, EGCG.
Figure 3
Figure 3
Comparison of the body weights of mice at the end of the experiment. Data presented as mean ± SD.
Figure 4
Figure 4
Colon tissues histology from five groups following H&E staining (1, original magnification 200×; 2–6, original magnification 400×).
Figure 5
Figure 5
Observations of ACF by 0.2% methylene blue staining (1–5, original magnification 200×; 6, original magnification 100×).
Figure 6
Figure 6
Immunohistochemical staining for Nrf2 in colon tissues. (A) Representative observations of Nrf2 staining in six groups (original magnification 400×). (B) The mean optical density values of Nrf2 in colon tissues. Data presented as mean ± SD.
Figure 7
Figure 7
Representative Western blotting for Nrf2 protein expression in the colon tissues of mice in six groups. (A) The bands of Nrf2 are represented by different gray scales in six groups. (B) Specific bands were quantified by scanning densitometry and normalized to the signal of β-actin. Data presented as mean ± SD.
Figure 8
Figure 8
Nrf2 and UGT1A10 mRNA expressions in the colon tissues of mice in all six groups. (A) The electrophoretic bands of Nrf2 and UGT1A10 are represented on agarose gel by different gray scales. (B) Specific bands were quantified by scanning densitometry and normalized to the signal of β-actin. Data presented as mean ± SD.
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