High Levels of Dietary Supplement Vitamins A, C and E are Absorbed in the Small Intestine and Protect Nutrient Transport Against Chronic Gamma Irradiation

Abstract

We examined nutrient transport in the intestines of mice exposed to chronic low-LET 137Cs gamma rays. The mice were whole-body irradiated for 3 days at dose rates of 0, 0.13 and 0.20 Gy/h, for total dose delivery of 0, 9.6 or 14.4 Gy, respectively. The mice were fed either a control diet or a diet supplemented with high levels of vitamins A, C and E. Our results showed that nutrient transport was perturbed by the chronic irradiation conditions. However, no apparent alteration of the macroscopic intestinal structures of the small intestine were observed up to day 10 after initiating irradiation. Jejunal fructose uptake measured in vitro was strongly affected by the chronic irradiation, whereas uptake of proline, carnosine and the bile acid taurocholate in the ileum was less affected. D-glucose transport did not appear to be inhibited significantly by either 9.6 or 14.4 Gy exposure. In the 14.4 Gy irradiated groups, the diet supplemented with high levels of vitamins A, C and E increased intestinal transport of fructose compared to the control diet (day 10; t test, P = 0.032), which correlated with elevated levels of vitamins A, C and E in the plasma and jejunal enterocytes. Our earlier studies with mice exposed acutely to 137Cs gamma rays demonstrated significant protection for transport of fructose, glucose, proline and carnosine. Taken together, these results suggest that high levels of vitamins A, C and E dietary supplements help preserve intestinal nutrient transport when intestines are irradiated chronically or acutely with low-LET gamma rays.

FIG. 1

Low-dose-rate gamma irradiator and caging system. Panel A: JL Shepherd Model 28A cabinet irradiator. A ¹³⁷Cs source is mounted on top of the irradiator and the beam projects downward into the cabinet. A ventilation fan is located on the lower left side. The shielded door is on the right side. Panel B: Scissors jack used to achieve reproducible placement of mouse cages within the irradiator. Three cages were stacked (not shown). Panel C: Mouse cage with tandem living quarters to accommodate two different diets. Animal diets and water bags with nipples were constrained along the back walls of the cage with stainless steel mesh. Amounts of each material were minimized to reduce absorption and scatter of the 662 keV gamma rays. Panel D: Custom-made plastic cage tops were also designed to minimize absorption and scatter of gamma rays.

FIG. 2

Design of experiments wherein mice were chronically irradiated with low-LET gamma rays and sacrificed at various times after initiation of a 3-day irradiation period at constant dose rate. Mice were fed the control or vitamin ACE diet, irradiated and sacrificed day 3, 5, 8 and 10 after initiation of chronic irradiation.

FIG. 3

Kaplan-Meier plot of animal survival as a function of time after initiating chronic irradiation of the mice. Animals were fed either the control or vitamin ACE diet according the schedule shown in Fig. 2. Absorbed doses of 0, 9.6 and 14.4 Gy were delivered over the 3-day irradiation period. Animals were censored when their intestines were harvested (day 3, 5, 8 and 10 indicated with filled circles) for analysis of the principal end point, nutrient uptake, thereby progressively reducing the number of animals at risk for assessment of survival. No animals were followed after day 10, the final harvest day for analysis of nutrient uptake.

FIG. 4

Retinoid concentrations in murine proximal jejunum (panel A), distal jejunum (panel B) and plasma (panel C), after 5 days on the vitamin ACE-enriched or control diet. Results are means 6 SE for tissue (n = 6) and for pooled plasma samples (n = 3). Marked increases in retinoid concentration were found in the intestines of mice on the vitamin ACE diet compared with control diet-fed mice.

FIG. 5

Ascorbic acid concentrations in murine proximal jejunum (panel A), distal jejunum (panel B) and plasma (panel C) after 5 days on the vitamin ACE-enriched diet or control diet. Results are means ± SE for tissue (n = 6) and for pooled plasma samples (n = 3). A greater amount of ascorbic acid was found in the intestines of mice on the vitamin ACE diet than in the control diet-fed mice.

FIG. 6

Tocopherol concentrations in murine proximal jejunum (panel A), distal jejunum (panel B) and plasma (panel C) after 5 days on the vitamin ACE-enriched diet or control diet. Results are means ± SE for tissue (n = 6) and for pooled plasma samples (n = 3). Marked increases in tocopherol concentrations were found in the intestines of mice on the vitamin ACE diet compared with control diet-fed mice.

FIG. 7

Intestinal uptake of D-glucose (panel A), 3-O-methyl-D-glucose (panel B) and D-fructose (panel C) in the proximal jejunum of mice at various days after initiation of 3-day chronic irradiation of mice with ¹³⁷Cs gamma rays. Total absorbed doses of 0, 9.6 and 14.4 Gy were administered. Mice were fed the control diet (open bars) or vitamin ACE diet (filled bars). Results are means ± SE of 6 independent experiments. Bars marked by the same letters do not differ significantly [e.g., day 8 fructose uptake for control diet 14.4 Gy (open bar annotated with “c”) is not significantly different (P > 0.05) than vitamin ACE diet 14.4 Gy (filled bar annotated with “b,c”) when compared pairwise after two-way ANOVA GLM]. Bars marked by different letters indicate significant difference [P < 0.05; e.g., control diet day 10 fructose uptake for 14.4 Gy irradiation (open bar annotated with “b”) is significantly different (P < 0.05) than 0 Gy (open bar annotated with “a”)]. A separate pairwise t test of the 14.4 Gy irradiated, vitamin ACE-fed vs. control diet-fed group was significant (denoted by “*”). Absence of letters within a given plot indicates lack of statistical difference between any bars (i.e., no effect of dose or diet). Error bars depict standard errors.

FIG. 8

Uptake of carnosine in the proximal jejunum (panel A), proline in the proximal jejunum (panel B), and taurocholate in the distal jejunum (panel C), of mice at various days after initiation of 3-day chronic irradiation of mice with ¹³⁷Cs gamma rays. Total absorbed doses of 0, 9.6 and 14.4 Gy were administered. Mice were fed the control diet (open bars) or vitamin ACE diet (filled bars). Results are means ± SE of 6 independent experiments. Bars marked by same letters do not differ significantly [e.g., day 10 carnosine uptake for control diet 14.4 Gy (open bar annotated with “a,b”) is not significantly different (P > 0.05) than vitamin ACE diet 14.4 Gy (filled bar annotated with “b”) when compared pairwise after two-way ANOVA GLM]. Bars marked by different letters indicate significant difference (P < 0.05) [e.g., day 8 TAD uptake for control diet 14.4 Gy (open bar annotated with “b”) is significantly different (P < 0.05) than control diet 0 Gy (open bar annotated with “a”)]. Absence of letters within a given plot indicates lack of statistical difference between any bars (i.e., no effect of dose or diet). Error bars depict standard errors.