Mjh. Geelen et al., Consumption of casein instead of soybean protein produces a transient risein the concentration of sphingomyelin in VLDL in rats, J NUTR, 129(12), 1999, pp. 2119-2122
In rats fed cholesterol-rich diets, dietary casein vs. soybean protein rais
es VLDL cholesterol concentrations. Because sphingomyelin may be an essenti
al, structural component of VLDL, we tested whether casein feeding would ra
ise VLDL-sphingomyelin. Rats were fed cholesterol-rich semipurified diets c
ontaining either soybean protein (35 g/100 g) or casein for up to 21 d. Con
sistent with previous work, casein consumption increased hepatic and VLDL c
holesterol concentrations. Dietary casein also significantly raised the amo
unt of sphingomyelin in the VLDL fraction, but this effect was transient. C
asein feeding transiently lowered LDL- and HDL-2-sphingomyelin concentratio
ns. We suggest that an increase in hepatic VLDL secretion after casein cons
umption imposed an increased demand for sphingomyelin in the liver. The act
ivity of key enzymes of sphingomyelin synthesis, i.e., serine palmitoyltran
sferase, phosphatidylcholine:ceramide phosphocholinetransferase and phospha
tidylethanolamine:ceramide phosphoethanolaminetransferase and sphingomyelin
degradation, i.e., acid sphingomyelinase, were enhanced and depressed, res
pectively, by casein consumption. Again these effects were transient. Thus,
these data indicate that the extra sphingomyelin needed after short-term c
asein feeding came about through enhanced rates of biosynthesis and reduced
rates of degradation in the liver. In addition, plasma transfer of sphingo
myelin from HDL-2 to VLDL might have contributed to the increase in VLDL sp
hingomyelin in the casein-fed rats. This study shows that dietary casein vs
. soybean protein transiently influences sphingomyelin metabolism in rats.