Impact of dietary fat type within the context of altered cholesterol homeostasis on cholesterol and lipoprotein metabolism in the F1B hamster

Abstract

Cholesterol status and dietary fat alter several metabolic pathways reflected in lipoprotein profiles. To assess plasma lipoprotein response and mechanisms by which cholesterol and dietary fat type regulate expression of genes involved in lipoprotein metabolism, we developed an experimental model system using F1B hamsters fed diets (12 weeks) enriched in 10% (wt/wt) coconut, olive, or safflower oil with either high cholesterol (0.1%; cholesterol supplemented) or low cholesterol coupled with cholesterol-lowering drugs 10 days before killing (0.01% cholesterol, 0.15% lovastatin, 2% cholestyramine; cholesterol depleted). Irrespective of dietary fat, cholesterol depletion, relative to supplementation, resulted in lower plasma non-high-density lipoprotein (non-HDL) and HDL cholesterol, and triglyceride concentrations (all Ps < .05). In the liver, these differences were associated with higher sterol regulatory element binding protein-2, low-density lipoprotein receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and 7α-hydroxylase messenger RNA (mRNA) levels; higher scavenger receptor B1 and apolipoprotein A-I mRNA and protein levels; lower apolipoprotein E protein levels; and in intestine, modestly lower sterol transporters adenosine triphosphate-binding cassette (ABC) A1, ABCG5, and ABCG8 mRNA levels. Irrespective of cholesterol status, coconut oil, relative to olive and safflower oils, resulted in higher non-HDL cholesterol and triglyceride concentrations (both Ps < .05) and modestly higher sterol regulatory element binding protein-2 mRNA levels. These data suggest that, in F1B hamsters, differences in plasma lipoprotein profiles in response to cholesterol depletion are associated with changes in the expression of genes involved in cholesterol metabolism, whereas the effect of dietary fat type on gene expression was modest, which limits the usefulness of the experimental animal model.

Figure 1

Effect of cholesterol status and dietary fat type on fasting plasma lipid and lipoprotein cholesterol concentrations. Hamsters were fed diets enriched with coconut, olive or safflower oil and 0.1% cholesterol (cholesterol-supplemented, +C) or 0.01% cholesterol for 12-weeks plus 0.15% lovastatin and 2% cholestyramine one week prior to killing (cholesterol-depleted, −C). Data represent means ± SEM, n = 15–16 animals per group. Appropriate transformations of the data (log HDL cholesterol; square root total cholesterol, non-HDL cholesterol; inverse triglyceride) were made before statistical analysis. Bars with different letters (lowercase for cholesterol-depleted, uppercase for cholesterol-supplemented) are significantly different, P≤0.05. Asterisks indicate significant differences between cholesterol-depleted and cholesterol-supplemented hamsters within a dietary fat treatment, P≤0.05.

Figure 2

Effect of cholesterol status and dietary fat type on plasma FPLC cholesterol profiles. Hamsters were fed diets enriched with coconut, olive or safflower oil and 0.1% cholesterol (cholesterol-supplemented, +C) (A) or 0.01% cholesterol for 12-weeks plus 0.15% lovastatin and 2% cholestyramine one week prior to killing (cholesterol-depleted, −C) (B). Cholesterol concentrations were measured in odd numbered fractions using standard enzymatic reagents. Data represent the mean of 4 plasma pools of 3 hamsters per pool.

Figure 3

Hepatic and small intestinal gene expression in response to alterations in cholesterol homeostasis and dietary fat type. Real time PCR was used to measure gene expression in the liver (A and B) and small intestine (C). Values are expressed as mean ± SEM, n=14–16 animals per group. Appropriate transformations of the data (log SREBP-2, CYP7A1, MTP, apo B-100, ABCA1, HMG-CoA R [HMG-CoA reductase]; square root SR-B1, SREBP-1c, apo A-I) were made before statistical analysis. Bars with different letters (lowercase for cholesterol-depleted, −C; uppercase for cholesterol-supplemented, +C) are significantly different, P≤0.05. Asterisks indicate significant differences between +C and −C hamsters within a dietary fat treatment, P≤0.05.

Figure 4

Hepatic protein expression in response to alterations in cholesterol homeostasis and dietary fat type. LDL receptor was detected in the membrane fraction, SREBP-2 was detected in the nuclear fraction, and SRB1, ACAT-2, MTP, apo B-100, apo A-I, and apo E were detected in the cell lysate. Values are expressed as mean ± SEM, n = 14–16 animals per group. Appropriate transformations of the data (log apo A-I, apo E, LDL receptor, SREBP-1, SR-B1; square root apo B-100) were made before statistical analysis. Bars with different letters (lowercase for cholesterol-depleted, −C; uppercase for cholesterol-supplemented, +C) are significantly different, P≤0.05. Asterisks indicate significant differences between −C and +C hamsters within a dietary fat group, P≤0.05.