Abstract 628: Efficient Excretion of Xenosterols in the Absence of Abcg5/Abcg8
Hypothesis: Xenosterol excretion by the mammalian body is wholly dependent on Abcg5/Abcg8 function. Methods: To test our hypothesis, we loaded Abcg8-/- mice with dietary plant sterols until they manifested biochemical (elevated plant sterols) and pathological changes (poor body weight, macrothrombocytopenia). All dietary xenosterols were eliminated from the diet and kinetics of xenosterol loss monitored over the ensuing 16 days, monitoring plasma, bile, and stool losses, as well as whole body sterol determinations. Results: After loading Abcg8-/- mice with plant sterols, plasma sitosterol levels in both male and female mice averaged 80mg/dL. Surprisingly, there was rapid loss of xenosterols from blood as well as tissues (liver, whole body), with losses of xenosterols detected in bile and feces. By day 16, stool xenosterols were almost undetectable and reflected the dramatic loss of whole body xenosterols. Conclusions: Our data refute our hypothesis. Although loss of sterolin function leads to severe xenosterolemia in both humans and mice, at least in mice, there appears to be a pathway(s) for elimination via the biliary/intestinal route. Characterization of the transporters involved may shed further light on sterol trafficking.