Fig. 7.

4F increases TICE through duodenal explants and can act as a cholesterol acceptor with respect to cholesterol efflux from enterocytes. A: 800 μg d-4F (∼25–30 mg/kg)/300 μl saline or vehicle was injected into the tail veins of C57BL/6J mice (n = 5). After 30 min, the mice were euthanized and duodenal explants from the mice injected with 4F (4F-tissue) and vehicle (control) were mounted in Ussing chambers. After 30 min in vivo, the explants from 4F-injected mice had been preloaded with 4F (see Fig. 3B). The mucosal media for both groups contained fresh micelles, while all serosal media contained a fresh-mixed combination of human HDL and LDL that had been preloaded with 1 μCi/well of ³H-cholesterol. The mucosal media were sampled through 90 min, and total ³H-cholesterol effluxed into the mucosal media during that time was determined by scintillation counting. At the end of the experiment, ³H-cholesterol level in the tissues was also determined. Preloading the tissue with 4F significantly increased the amount of cholesterol label in both the mucosal media and the duodenal explants (*, ** P < 0.05). B: Primary enterocytes were stripped from the SI using EDTA and loaded with ³H-cholesterol for 30 min under constant aeration. The cells were washed and media changed, and l-4F was added to the cell suspensions. Micelles alone were also added as a positive control (n = 3/group). l-4F dose dependently increased ³H-cholesterol efflux from enterocytes (control vs. 10 μg/ml, * P = 0.001; 10 μg/ml vs. 50 μg/ml, ** P = 0.0002; control vs. micelles, *** P = 0.01). C: Duodenal explants from C57BL/6J mice were mounted in Ussing chambers. Each mouse contributed two contiguous explants, whose serosal-side media contained ³H-cholesterol loaded lipoproteins (as above). For each pair, either 50 μg/ml d-4F or vehicle was added to mucosal-side media that contained micelles. Mucosal-side 4F significantly increased cholesterol loading into the explants (** P = 0.044) as well as cholesterol efflux into mucosal media themselves (* P = 0.047) compared with the paired controls. Error is reported as SEM.