Ontogenesis and Modulation of Intestinal Unesterified Cholesterol Sequestration in a Mouse Model of Niemann-Pick C1 Disease

Abstract

Background: Mutations in the NPC1 gene result in sequestration of unesterified cholesterol (UC) and glycosphingolipids in most tissues leading to multi-organ disease, especially in the brain, liver, lungs, and spleen. Various data from NPC1-deficient mice suggest the small intestine (SI) is comparatively less affected, even in late stage disease.

Methods: Using the Npc1^nih mouse model, we measured SI weights and total cholesterol (TC) levels in Npc1^-/- versus Npc1^+/+ mice as a function of age, and then after prolonged ezetimibe-induced inhibition of cholesterol absorption. Next, we determined intestinal levels of UC and esterified cholesterol (EC), and cholesterol synthesis rates in Npc1^-/- and Npc1^+/+ mice, with and without the cholesterol-esterifying enzyme SOAT2, following a once-only subcutaneous injection with 2-hydroxypropyl-β-cyclodextrin (2HPβCD).

Results: By ~ 42 days of age, intestinal TC levels averaged ~ 2.1-fold more (mostly UC) in the Npc1^-/- versus Npc1^+/+ mice with no further increase thereafter. Chronic ezetimibe treatment lowered intestinal TC levels in the Npc1^-/- mice by only ~ 16%. In Npc1^-/- mice given 2HPβCD 24 h earlier, UC levels fell, EC levels increased (although less so in mice lacking SOAT2), and cholesterol synthesis was suppressed equally in the Npc1^-/-:Soat2^+/+ and Npc1^-/-:Soat2^-/- mice.

Conclusions: The low and static levels of intestinal UC sequestration in Npc1^-/- mice likely reflect the continual sloughing of cells from the mucosa. This sequestration is blunted by about the same extent following a single acute treatment with 2HPβCD as it is by a prolonged ezetimibe-induced block of cholesterol absorption.

Keywords: 2-Hydroxypropyl-β-cyclodextrin; Biliary cholesterol; Ezetimibe; Fecal sterol excretion; Lysosomal cholesterol storage disease; Small intestine.