Differential Effects of Cod Proteins and Tuna Proteins on Serum and Liver Lipid Profiles in Rats Fed Non-Cholesterol- and Cholesterol-Containing Diets

Abstract

Fish muscles are classified into white and red muscles, and the chemical composition of the two fish muscles have many differences. Few reports have assessed the health-promoting functions of white fish muscle proteins (WFP) and red fish muscle proteins (RFP). We therefore evaluated the mechanisms underlying the alteration of lipid profiles and cholesterol metabolism following the intake of WFP prepared from cod and RFP prepared from light muscles of tuna. Male Wistar rats were divided into six dietary groups: casein (23%), WFP (23%), and RFP (23%), with or without 0.5% cholesterol and 0.1% sodium cholate. Compared to the WFP-containing diet, the RFP-containing diet supplemented with cholesterol and sodium cholate significantly increased serum and liver cholesterol contents. However, in the RFP groups, an alteration in cholesterol metabolism including an increased tendency to excrete fecal sterols and hepatic cholesterol 7α-hydroxylase was related to the reduction of hepatic cholesterol contents. This phenomenon might be related to the tendency of an increased food intake in RFP-containing diets. These results highlight the differential effects of WFP and RFP on serum and liver lipid profiles of Wistar rats fed non-cholesterol- or cholesterol-containing diets under no fasting condition.

Keywords: cholesterol; cod protein; lipid metabolism; rat; tuna protein.

Fig. 1

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of casein, WFP, and RFP. SDS-PAGE was performed using 12.5% polyacrylamide gels. M, molecular weight marker; CAS, casein; WFP, white muscle fish protein; RFP, red muscle fish protein.

Fig. 2

Time courses of degree of hydrolysis and insoluble fraction production rate in simulated gastrointestinal digestions. Data represent means±SEM (n=4). (A) Significant effects of time, protein, and time-protein interactions were identified by two-factor repeated measure analysis of variance. (B) Values in the same row not sharing a common letters (a,b) are significantly different at P<0.05 using the Tukey’s multiple comparisons test. RFP, red muscle fish protein; WFP, white muscle fish protein.