Features of Lipid Metabolism Disorders in Primary Biliary Cholangitis

Abstract

Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is an autoimmune liver disease that mostly affects women. A progressive disorder in the processes of bile secretion and enterohepatic bile salts circulation in patients with PBC already in its early stages, leading to an insufficient release of bile acids into the bowel and their entry into the systemic circulation. Insufficient bile acids released into the duodenum contributes to the development of malabsorption, energy malnutrition, and slowly progressive weight loss. The pathophysiological mechanisms of weight loss and its slow progression are associated with the deterioration of the fat emulsification processes and with the reduced absorption of hydrolyzed products, such as fatty acids and monoglycerides, with steatorrhea in patients with PBC, as well as in those with gut dysbiosis. Just in the early stages of the disease, this results in accelerated fatty acid β-oxidation that is aimed at compensating for progressive energy malnutrition. The entry of bile acids into the systemic circulation in PBC is accompanied by dyslipidemia. The mechanism of hyperlipidemia in patients with PBC differs from that in other conditions because along with an increase in total cholesterol (TC), there are elevated high-density lipoprotein levels and the appearance of unusual lipoprotein X (Lp-X). The appearance of Lp-X is most likely to be the body's protective reaction to inactivate the detergent effect of bile acids on the membrane structures of blood corpuscles and vascular endothelial cells. It is bile acids, rather than TC levels, that correlate with the content of Lp-X and determine its formation. Concomitant hypercholesterolemia in patients with PBC is also aimed at neutralizing the detergent effect of bile acids that have entered the systemic circulation and is most likely a compensatory reaction of the body. "Anomalous" hypercholesterolemia in PBC can serve as a model system for the search and development of new methods for the treatment of dyslipidemia since it occurs without an increase in the incidence of cardiovascular events.

Keywords: dietary lipid metabolism disorders in PBC; hypercholesterolemia; mechanism of dyslipidemia in PBC; primary biliary cholangitis (PBC).

Figure 1

Schematic diagram of the composition of lipoid-bile complexes formed in the small bowel.

Figure 2

Schematic representation of cholesterol transport in the human body in normal (left part of the picture) and with cholestasis (right part of the picture). Note: LP(s)-lipoprotein(s); LDL-C—low-density lipoproteins cholesterol; VLDL-С—very low-density lipoproteins cholesterol; HDL-C—high-density lipoproteins cholesterol; Lp-X—lipoprotein X.

Figure 3

Chemical structure of phosphatidylcholine containing palmitic and oleic fatty acids.