Distribution of cytochrome P450 2C, 2E1, 3A4, and 3A5 in human colon mucosa

Abstract

Background: Despite the fact that the alimentary tract is part of the body's first line of defense against orally ingested xenobiotica, little is known about the distribution and expression of cytochrome P450 (CYP) enzymes in human colon. Therefore, expression and protein levels of four representative CYPs (CYP2C(8), CYP2E1, CYP3A4, and CYP3A5) were determined in human colon mucosa biopsies obtained from ascending, descending and sigmoid colon.

Methods: Expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 mRNA in colon mucosa was determined by RT-PCR. Protein concentration of CYPs was determined using Western blot methods.

Results: Extensive interindividual variability was found for the expression of most of the genes. However, expression of CYP2C mRNA levels were significantly higher in the ascending colon than in the sigmoid colon. In contrast, mRNA levels of CYP2E1 and CYP3A5 were significantly lower in the ascending colon in comparison to the descending and sigmoid colon. In sigmoid colon protein levels of CYP2C8 were significantly higher by ~73% than in the descending colon. In contrast, protein concentration of CYP2E1 was significantly lower by ~81% in the sigmoid colon in comparison to the descending colon.

Conclusion: The current data suggest that the expression of CYP2C, CYP2E1, and CYP3A5 varies in different parts of the colon.

Figure 1

CYP3A5, CYP2E1, CYP3A4, and CYP2C mRNA expression in human colon mucosa obtained ascending, descending, and sigmoid colon. (A) Representative agarose gel of mRNA integrity. Lane 1 and 10 = positive control, lane 2–9 = RNA extracted from colonic mucosa biopsies. (B) Representative photomicrograph of RT-PCR products of three subjects. All measurements were carried out in triplicate. Lane 1 = Histone 3.3; Lane 2 = CYP3A5; Lane 3 = CYP2E1; Lane 4 = CYP3A4; Lane 5 = CYP2C, bp = base pairs, A = ascending colon, D = descending colon, S = sigmoid colon. (C) Quantitative analysis of mRNA expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 in human ascending, descending, and sigmoid colon. Data are normalized to histone 3.3 expression. Data are means ± SEM. (n.d. = not detectable, ^aP < 0.05 compared to ascending colon)

Figure 2

CYP2E1, CYP2C8, CYP3A4, CYP3A5 protein levels in normal human colon mucosa obtained from descending and sigmoid colon. (A) Representative Western blot of CYP2E1, CYP2C8, CYP3A4, CYP3A5. (B) Representative Western blot of β-actin performed in 5 different individuals. (C) Quantitative analysis of blots. Data are means ± SEM. (^aP < 0.05 compared to descending colon)

Figure 3

Relation of CYP2E1, CYP2C8, CYP3A4, CYP3A5 protein levels and mRNA expression pattern in normal human colon mucosa obtained from sigmoid colon. Comparison of protein levels of CYP2E1, CYP2C8, CYP3A4, and CYP3A5 of subjects with detectable mRNA expression and subjects with no detectable mRNA expression of the respective CYP. Data are means ± SEM.