Comparative effect of fish oil feeding and other dietary fatty acids on plasma lipoproteins, biliary lipids, and hepatic expression of proteins involved in reverse cholesterol transport in the rat.

BACKGROUND

While elevated plasma high-density lipoprotein (HDL) levels has been associated to a reduction in cardiovascular risk, dietary fish oils rich in omega-3 polyunsaturated fatty acids (PUFAs) may protect against this disease. The protective effect of HDL is associated to its participation in the reverse cholesterol transport pathway. On the other hand, omega-3 PUFAs decrease plasma HDL levels compared to other fatty acids, which may suggest an effect on reverse cholesterol transport.

AIM

In this work, the effect of dietary fish oil on the fatty acid composition of hepatic membranes, plasma lipoprotein cholesterol profile, biliary lipids, and the expression of proteins involved in reverse cholesterol transport, was compared to other dietary oils having a different degree of fatty acid unsaturation.

METHODS

Male rats were fed a semi synthetic diet containing fish oil (omega-3), sunflower oil (omega-6), olive oil (omega-9) or coconut oil (saturated). Hepatic membrane fatty acid composition, plasma cholesterol levels, lipoprotein cholesterol profile, biliary lipids, hepatic mRNA levels for lecithin cholesterol acyltransferase, hepatic lipase, apo E, and apo A-I, and hepatic protein levels of the scavenger receptor class B type I, caveolin-1, and the ATP binding cassette transporter A1 were analyzed. Plasma apo A-I and apo E protein levels were also evaluated.

RESULTS

Compared to the other diets, omega-3 PUFAs significantly changed omega-3/omega-6 fatty acid ratio of hepatic membranes, caused a reduction of plasma total and HDL cholesterol, and selectively increased biliary cholesterol secretion. No modification in the expression levels of lecithin cholesterol acyltransferase, hepatic lipase, apo A-I and apo E mRNA was observed. Hepatic scavenger receptor class B type I, caveolin-1, and the ATP binding cassette transporter A1 protein levels were also not affected. Plasma apo A-I, but not apo E, was reduced.

CONCLUSIONS

These results show that dietary omega-3 PUFAs reduce plasma HDL cholesterol and increase biliary cholesterol without concomitant modifications in the expression of key genes and proteins involved in reverse cholesterol transport. These findings suggest that functional changes in the activity of these proteins as consequence of the incorporation of omega-3 PUFAs into hepatic membranes and plasma lipoproteins may underlie the effect of fish oil feeding on plasma and hepatic cholesterol metabolism in the rat.