Egg Yolk Feeding Induces Hyperlipidemia with a Concomitant Increase in Oxidative Stress in Liver Tissue and Erythrocyte Susceptibility to Hemolysis in Rats - Abstract
Objectives: The common belief is that egg yolk consumption is associated with hyperlipidemia, but some recent studies have reported that egg consumption may help reduce hypercholesterolemia and obesity, and is not associated with incidences of cardiovascular disease. In this study, we investigated whether feeding chicken egg yolk affects the lipid profile of rats. In addition, we measured, if, yolk supplementation affected the degree of red blood cell hemolysis and oxidative stress, which are several parameters associated with the short survival of circulating red blood cells. It is widely believed that egg yolk consumption is associated with hyperlipidemia. However, some recent studies have reported that egg consumption may help reduce hypercholesterolemia and obesity and is not associated with the occurrence of cardiovascular disease. In this study, we investigated whether feeding chicken egg yolk affects the lipid profile of rats. In addition, we measured whether yolk complementation affects the degree of red blood cell hemolysis and oxidative stress, which are several parameters associated with the short survival of circulating red blood cells. Methods: Rats were placed into three groups according to a random selection: Control group (CO), was fed with regular diet; EY1 group, was fed a diet with 20% egg yolk, and EY2 group, was fed a diet with 40% egg yolk for 10 consecutive weeks. Weight was measured every other day. Reactive oxygen species (ROS) were ascertained using fluorescent dyes 2’and 7’dichlorodihydrofluorescein diacetate (DCFDA). The concentration of lipid peroxide (LPO) was measured by determining the concentration of thiobarbituric acid-reactive substances (TBARS). Comparing RBC hemoglobin liberation estimates to the hemoglobin standard determined hemolysis. All biochemical parameters were determined using standard laboratory procedures. The rats were randomly divided into three groups: the control group (CO) was fed normal chow; Group EY1 received a 20% egg yolk diet for 10 consecutive weeks and group EY2 received a 40% egg yolk diet. Weight was measured every other day. Reactive oxygen species (ROS) were detected using the fluorescent dyes 2’- and 7’-dichlorodihydrofluorescein diacetate (DCFDA). The concentration of lipid peroxide (LPO) was measured by determining the concentration of thiobarbituric acid reactive substances (TBARS). Hemolysis was determined by comparing estimates of erythrocyte hemoglobin release to the hemoglobin standard. All biochemical parameters were determined using standard laboratory procedures. Results: Body weight, plasma total cholesterol (TC), and LDL-C levels were significantly increased in rats fed egg yolk compared to control rats, but HDL-C levels were unchanged in yolk-fed rats. In EY1 and EY2 rats, liver TC increased by 24.8% and 88.8%, respectively, and TG increased by 54.3% and 84.3%, respectively. LDL-C/HDL-C in both the plasma and liver of EY1 and EY2 rats increased significantly. Oxidative stress (OS) levels and RBC hemolytic tendencies were higher in yolk-fed rats. Body weight, plasma total cholesterol (TC), and LDL-C levels were significantly increased in egg yolk-fed rats compared to control rats, but HDL-C levels remained unchanged in egg yolk-fed rats. In EY1 and EY2 rats, liver TC increased by 24.8% and 88.8% and TG by 54.3% and 84.3%, respectively. LDL-C/HDL-C increased significantly in both plasma and liver of EY1 and EY2 rats. In rats fed egg yolk, levels of oxidative stress (OS) and hemolytic tendencies of erythrocytes were higher. Conclusion: Egg yolk feeding not only increased body weight, which is conducive to obesity, but it worsened hyperlipidemia, oxidative status, and hemolysis in rats. Augmented hemolysis may occur by enhanced incorporation of plasma cholesterol into erythrocyte membranes, leading to decreased membrane fluidity and disturbances of oxygen transport across the membrane. Egg yolk feeding not only increased body weight, which favors obesity, but also worsened hyperlipidemia, oxidative status and hemolysis in rats. Increased hemolysis can occur due to increased incorporation of plasma cholesterol into the erythrocyte membranes, leading to reduced membrane fluidity and disruption of oxygen transport
across the membrane.