Induction of cholesteryl ester transfer protein in adipose tissue and plasma of the fructose-fed hamster

Abstract

Cholesteryl ester transfer protein (CETP) plays a pivotal role in the reverse transport of cholesterol and in the remodeling of circulating lipoproteins. While plasma and adipose tissue levels of CETP are affected by a variety of metabolic conditions, the extent of the effects of dietary factors, other than high cholesterol feeding, are not well understood. To further explore this paradigm, male Golden Syrian hamsters were fed for 4 weeks with a 60%-enriched fructose diet (F) and were compared to a matched group of animals fed with a normal chow diet (N). After feeding for 4 weeks, plasma insulin concentrations were lower in animals fed fructose than in control animals (F: 3.3 ± 0.8 vs N: 7.4 ± 1.9 ng/mL; p<0.03), but there was no significant difference in plasma glucose concentrations between the two groups (F: 138 ± 7 vs N: 148 ± 10 mg/dL; p>0.05). Fructose-fed animals showed significant increases in plasma triglyceride (F: 269 ± 22 vs N: 165 ± 22 mg/dL; p<0.01) and plasma cholesterol (F: 150 ± 10 vs N: 113 ± 6 mg/dL; p<0.02) concentrations compared with control animals. Total CETP activity and immunoreactive mass were higher in the plasma of fructose-fed animals that in that of controls (F: 1036 ± 70 vs N: 826 ± 43 pmol/h/mL, p<0.04 and F: 24.5 ± 3.1 vs N: 37.5 ± 4.3 AU, p<0.02, respectively). Adipose tissue CETP mRNA levels, assessed by the very sensitive ribonuclease protection assay, were 53% higher in fructose-fed animals than in controls (F: 14.1 ± 2.0 vs N: 9.2 ± 1.0 AU over a rRNA control; p<0.04). Adipose tissue CETP activity and immunoreactive mass also showed a statistically significant increase in the fructose-fed hamsters compared with those fed a normal diet (p<0.04). In conclusion, fructose feeding in Syrian hamsters induces a mixed dyslipidemia. These metabolic changes are accompanied by a significant increase in CETP levels, both in plasma and in adipose tissue. This phenomenon suggests that the increase in the expression of adipose tissue CETP may be caused either by the ambient hypercholesterolemia resulting from fructose feeding or by an attenuation of a possible inhibitory effect of plasma insulin concentrations on the expression of adipose tissue CETP in this feeding paradigm.