Infant formula feeding increases hepatic cholesterol 7 alpha hydroxylase (CYP7A1) expression and fecal bile acid loss in neonatal piglets

Authors: MERCER, K - Arkansas Children'S Nutrition Research Center (ACNC); BHATTACHARYYA, S - Arkansas Children'S Nutrition Research Center (ACNC); DIAZ-RUBIO, M - Arkansas Children'S Nutrition Research Center (ACNC); PICCOLO, B - Arkansas Children'S Nutrition Research Center (ACNC); PACK, L - Arkansas Children'S Nutrition Research Center (ACNC); SHARMA, N - Arkansas Children'S Nutrition Research Center (ACNC); CHAUDHURY, M - Arkansas Children'S Nutrition Research Center (ACNC); CLEVES, M - Arkansas Children'S Nutrition Research Center (ACNC); CHINTAPALLI, S - Arkansas Children'S Nutrition Research Center (ACNC); SHANKAR, K - Arkansas Children'S Nutrition Research Center (ACNC); RONIS, M.J. - Louisiana State University; YERUVA, L - Arkansas Children'S Nutrition Research Center (ACNC)

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2018
Publication Date: 5/1/2018
Citation: Mercer, K.E., Bhattacharyya, S., Diaz-Rubio, M.E., Piccolo, B.D., Pack, L.M., Sharma, N., Chaudhury, M., Cleves, M.A., Chintapalli, S.V., Shankar, K., Ronis, M.J., Yeruva, L. 2018. Infant formula feeding increases hepatic cholesterol 7 alpha hydroxylase (CYP7A1) expression and fecal bile acid loss in neonatal piglets. Journal of Nutrition. 148(5):702-711. https://doi.org/10.1093/jn/nxy038.
DOI: https://doi.org/10.1093/jn/nxy038

Interpretive Summary: The intakes of specific nutrients (such as cholesterol) early in life may impact lifelong health and regulation of the body's metabolism. Typical infant formula contains very little dietary cholesterol, ~0.25 mmol/L as compared to 0.13 mmol/L in breast milk. Serum cholesterol concentrations are lower those infants receiving formula in comparison to infants receiving breast milk, yet in the formula fed infants, liver cholesterol synthesis rates are significantly elevated. The mechanisms associated with this paradox are not known. Therefore, we gave young piglets a milk-based infant formula, soy-based infant formula, or sow's milk for 21 days, and then looked to see if there were any diet-associated differences in cholesterol synthesis or breakdown pathways in the liver. In the milk formula-and soy formula-fed piglets, we observed increased expression of enzymes involved in cholesterol synthesis; paradoxically, expression of cholesterol 7-alpha hydroxylase (Cyp7a1) was also increased in the liver. This enzyme is responsible for cholesterol metabolism to bile acids, and increased expression coincided with elevated fecal bile acid concentrations, suggestive of increased synthesis. These findings suggest that low postnatal dietary cholesterol intake, as associated with formula feeding, increases cholesterol breakdown into bile acids. The primary mechanism is to reduce the potency of negative feedback mechanisms, such as the hormone FGF19-mediated receptor signaling, and Shp-mediated gene repression that keep Cyp7a1 protein expression low. The results show that in a model of neonatal nutrition, low cholesterol intake due to formula feeding can increase the body's machinery for cholesterol synthesis, possibly as an adaptive mechanism. Whether or not this can be corrected through formulas that contain more available cholesterol remains to be tested.

Technical Abstract: During the postnatal feeding period, formula-fed infants have higher cholesterol synthesis rates, and lower circulating cholesterol concentrations as compared to their breastfed counterparts. Although this disparity has been attributed to the uniformly low dietary cholesterol content of typical infant formulas, little is known of the underlying mechanisms associated with this altered cholesterol metabolism phenotype. We aim to determine the molecular etiology of diet-associated changes in early-life cholesterol metabolism using postnatal piglet feeding model. Two-day old male and female White-Dutch Landrace piglets received either sow's milk (Sow), or provided dairy (Similac Advance powder, Milk) or soy (Emfamil Prosobee Lipil powder, Soy) infant formulas until day 21. In addition to measuring serum cholesterol concentrations, hepatic and intestinal genes involved in enterohepatic circulation of cholesterol and bile acids were analyzed by real time RT-PCR and Western blot. Bile acid concentrations were measured by liquid chromatography mass spectrometry in serum, liver and feces. When compared to the Sow, Milk increased hepatic cholesterol 7 alpha hydroxylase (CYP7A1) protein expression by 3-fold, P < 0.05, with CYP7A1 protein expression 10-fold higher in Soy when compared to Milk, P<0.05. Likewise, fecal bile acid concentrations were 3-fold higher in Soy when compared to the Milk group, P<0.05. Intestinal mRNA expression of fibroblast factor 19 (Fgf19) was reduced in both formula groups, and corresponded to a 2- to 3-fold decrease in serum FGF19 in Milk and Soy when compared to Sow P<0.05. In Soy, small heterodimer protein (SHP) protein expression was reduced by 30% relative to Sow, P < 0.05. These results indicated that formula feeding leads to increased CYP7A1 protein expression and fecal bile acid loss in neonatal piglets, and this outcome is linked to reduced efficacy in inhibiting CYP7A1 expression through FGF19 and the SHP transcriptional repression mechanisms.