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Lipid Metabolism in the Intestinal Tract and Its Modification by Ethanol
Published in Victor R. Preedy, Ronald R. Watson, Alcohol and the Gastrointestinal Tract, 2017
Apo B has a crucial role in the formation of lipoprotein. According to Christensen et al., apo B is synthesized in the rough ER, transferred to the smooth ER, and then added onto the lipoprotein particle.77 In a rare inherited disorder of lipoprotein metabolism, hypobetalipoproteinemia, homozygous patients have virtually no circulating apo B-containing lipoproteins (CMs, VLDL, or LDL), resulting in a deficiency of fat-soluble vitamins and eventually in spinocerebellar and retinal degeneration. Hypobetalipoproteinemia has been shown to be caused by defects in the apo B gene resulting in the total absence of apo B.78,79 While hypobetalipoproteinemia is an autosomal codomi-nant disorder, abetalipoproteinemia, whose clinical features cannot be distinguished from those of hypobetalipoproteinemia, is inherited recessively. Apo B has been demonstrated in the hepatocytes and enterocytes of individuals with abetalipoproteinemia.80-83 Recently, however, microsomal triglyceride transfer protein (MTP) was shown to be defective in patients with abetalipoproteinemia but intact in hypobetalipoproteinemia patients.84 The absence of MTP is caused by defects in the gene encoding the 97 kDa85 or 88 kDa86 subunit of MTP. MTP is a lipid-binding protein that shuttles TGs, cholesteryl esters, and phospholipids between intracellular membranes. The mechanism by which apo B and TG droplets associate to form a mature lipoprotein is not yet fully understood, but these findings strongly suggest that MTP plays a crucial role in the assembly of lipid and apo B. Patients with Anderson's disease (also referred to as chylomicron retention disease) have defects in the assembly or secretion of CMs resulting in the formation of large droplets in enterocytes.87,88 Interestingly, the synthesis of apo B-48 is not disturbed in this recessively transmitted disorder, and a normal level of TG transfer activity has been demonstrated.84 Therefore, the site of metabolic impairment in Anderson's disease is different from that of either abetalipoproteinema or hypobetalipoproteinemia.
Lessons from chylomicron retention disease: a potential new approach for the treatment of hypercholesterolemia?
Published in Expert Opinion on Orphan Drugs, 2018
During the last decades, the identification of different rare diseases inducing fat intestinal malabsorption, namely the genetic hypocholesterolemias, has led to the characterization of the physiological steps involved in the intestinal absorption of lipids. Chylomicrons are essential for intestinal absorption of lipids since they are the main carriers of dietary lipids. These triglyceride-rich lipoproteins are secreted exclusively from the enterocyte. The SAR1B gene was identified as responsible for chylomicron retention disease (CMRD), previously called Anderson’s disease (OMIM #246700) [1]. Historically, the first clinical description was in 1961 of a 7-month-old child with a persistent neonatal diarrhea [2]. Finally, in 2003, genotyping demonstrated that Anderson’s disease and CMRD were in fact the same disease [1].