Abstract
The role of selenium (Se) in modulating colon carcinogenesis induced by azoxymethane (AOM) followed by dextran sodium sulfate (DSS) was investigated in mice. Five-week old ICR mice were fed on diets containing different concentrations (0.02, 0.1 or 0.5 ppm) of Se for 24 weeks. Animals received three (0-2nd weeks) intraperitoneal injections of AOM (10 mg/kg body weight), followed by 2% DSS with drinking water for additional 1 week. There were 4 experimental groups including vehicle control group, positive control group given AOM/DSS with AIN-93G normal diet containing 0.1% Se (NSe), a low (0.02 ppm)-Se diet group (LSe) and a high (0.5 ppm)-Se diet group (HSe). Hematology was analyzed with a blood cell differential counter. Liver Se was analyzed by inductively coupled plasma-mass spectroscopy. Cell proliferation and apoptosis were determined by using proliferating cell nuclear antigen (PCNA) for proliferative activity and apoptotic index by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), respectively. HSe group showed a low incidence of colonic tumor (64.7%), compared with the NSe positive control (75%) and LSe (77.8%) groups. In contrast, HSe group exhibited lower rate of PCNA-positive cells (39.3±6.9%) than positive control (64.3±0.3%) and LSe (57.3±2.9%) groups. In addition, apoptotic index of HSe group was higher than those of positive control and LSe groups. These results indicate that Se is a chemopreventive agent for colon carcinogenesis induced by AOM+DSS in male ICR mice.
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Figure 1.
Experimental design for colon carcinogenesis in mice. AOM, azoxymethane; DSS, dextran sodium sulfate.
![lar-26-293f1.tif](/upload/SynapseXML/0169lar/thumb/lar-26-293f1.gif)
Figure 2.
Change in the body weights in mice treated with AOM/DSS and selenium (Se). The body weights of all AOM/DSS treatment groups significantly decreased compared with the body weight of vehicle control group during 2–4th weeks of treatment (P<0.05). AOM: azoxymethane, DSS: dextran sodium sulfate, NSe: normal selenium (0.1 ppm) diet, LSe: low selenium (0.02 ppm) diet, HSe: high selenium (0.5 ppm) diet.
![lar-26-293f2.tif](/upload/SynapseXML/0169lar/thumb/lar-26-293f2.gif)
Figure 3.
Hepatic selenium levels in mice following feeding of different concentrations of dietary selenium. Selenium concentration was determined using an inductively coupled plasma-mass spectroscopy. AOM: azoxymethane, DSS: dextran sodium sulfate, NSe: normal selenium (0.1 ppm) diet, LSe: low selenium (0.02 ppm) diet, HSe: high selenium (0.5 ppm) diet.
![lar-26-293f3.tif](/upload/SynapseXML/0169lar/thumb/lar-26-293f3.gif)
Figure 4.
Effect of selenium on tumor incidence and survival rate of mice treated with azoxymethane/dextran sodium sulfate (AOM/DSS). NSe: normal selenium (0.1 ppm) diet, LSe: low selenium (0.02 ppm) diet, HSe: high selenium (0.5 ppm) diet.
![lar-26-293f4.tif](/upload/SynapseXML/0169lar/thumb/lar-26-293f4.gif)
Figure 5.
Immunohistochemistry on proliferating cell nuclear antigen (PCNA) in the colon of mice treated with azoxymethane/dextran sodium sulfate (AOM/DSS) and selenium (Se). The PCNA-positive cells were greatly increased by treatment with AOM/DSS, which were markedly reduced by coadministration of a high concentration (0.5 ppm) of selenium (Se). (A) Vehicle control. (B) AOM/DSS+normal Se (0.1 ppm) diet. (C) AOM/DSS+low Se (0.02 ppm) diet. (D) AOM/DSS+ high Se (0.5 ppm) diet. ×100.
![lar-26-293f5.tif](/upload/SynapseXML/0169lar/thumb/lar-26-293f5.gif)
Figure 6.
TUNEL assay for apoptotic nuclei in distal colon sections of mice treated with azoxymethane/dextran sodium sulfate (AOM/DSS) and selenium (Se). The TUNEL-positive cells were increased by treatment with AOM/DSS, which were further enhanced by co-administration of Se in a concentration-dependent manner. (A) Vehicle control. (B) AOM/DSS+normal Se (0.1 ppm) diet. (C) AOM/DSS+low Se (0.02 ppm) diet. (D) AOM/DSS+high Se (0.5 ppm) diet. ×100.
![lar-26-293f6.tif](/upload/SynapseXML/0169lar/thumb/lar-26-293f6.gif)
Table 1.
Composition of the diets at different selenium status
Table 2.
Differential blood cell counts in ICR mice fed different selenium diets
Parameters | Vehicle | AOM/DSS | ||
---|---|---|---|---|
NSe | LSe | HSe | ||
WBC (103/µL) | 4.61±1.85 | 2.61±0.61 | 2.13±0.55 | 2.32±0.20 |
RBC (106/µL) | 8.72±0.40 | 07.11±1.66∗ | 7.72±0.23 | 7.99±0.57 |
Hemoglobin (g/dL) | 13.40±0.600 | 11.60±1.13∗ | 12.23±0.250 | 12.20±0.600 |
Hematocrit (%) | 44.05±2.800 | 38.20±4.67∗ | 40.47±1.760 | 40.97±1.440 |
MCV (fl) | 50.53±0.940 | 54.50±6.220 | 52.43±2.700 | 51.40±2.170 |
MCV (fl) MCH (pg) | 50.53±0.940 15.40±0.550 | 54.50±6.220 16.65±2.330 | 52.43±2.700 15.87±0.400 | 51.40±2.170 15.33±0.350 |
MCHC (g/dL) | 30.53±1.230 | 30.81±0.680 | 30.30±0.890 | 29.87±0.760 |
WBC: white blood cells, RBC: red blood cells, MCV: mean corpuscular volume, MCH: mean corpuscular hemoglobin, MCHC: mean corpuscular hemoglobin concentration, AOM: azoxymethane, DSS: dextran sodium sulfate, NSe: normal selenium (0.1 ppm) diet, LSe: low selenium (0.02 ppm) diet, HSe: high selenium (0.5 ppm) diet.
Table 3.
Effect of selenium on cell proliferative and apoptotic indices in AOM/DSS- induced colon carcinogenesis
Groups | Selenium (ppm) | Proliferative index (%) | Apoptotic index (%) |
---|---|---|---|
Vehicle | 0.1 | 20.33±2.91 | 1.33±0.67 |
AOM/DSS+NSe | 0.1 | ∗64.33±0.33∗ | ∗8.33±0.67∗ |
AOM/DSS+LSe | 0.02 | 57.33±2.85 | ∗4.50±0.41† |
AOM/DSS+HSe | 0.5 | ∗39.33±6.94† | 11.25±1.28†. |