Investigating Sitosterolemia to Understand Lipid Physiology

Human induced pluripotent stem cell derived hepatocytes provide insights on parenteral nutrition associated cholestasis in the immature liver

Parenteral nutrition-associated cholestasis (PNAC) significantly limits the safety of intravenous parenteral nutrition (PN). Critically ill infants are highly vulnerable to PNAC-related morbidity and mortality, however the impact of hepatic immaturity on PNAC is poorly understood. We examined developmental differences between fetal/infant and adult livers, and used human induced pluripotent stem cell-derived hepatocyte-like cells (iHLC) to gain insights into the contribution of development to altered sterol metabolism and PNAC. We used RNA-sequencing and computational techniques to compare gene expression patterns in human fetal/infant livers, adult liver, and iHLC. We identified distinct gene expression profiles between the human feta/infant livers compared to adult liver, and close resemblance of iHLC to human developing livers. Compared to adult, both developing livers and iHLC had significant downregulation of xenobiotic, bile acid, and fatty acid metabolism; and lower expression of the sterol metabolizing gene ABCG8. When challenged with stigmasterol, a plant sterol found in intravenous soy lipids, lipid accumulation was significantly higher in iHLC compared to adult-derived HepG2 cells. Our findings provide insights into altered bile acid and lipid metabolizing processes in the immature human liver, and support the use of iHLC as a relevant model system of developing liver to study lipid metabolism and PNAC.

Importance of Cholesterol Side Chain in the Membrane Stability of Human Erythrocytes

Cholesterol suppresses the hemolysis and the detachment of cytoskeletal proteins from bilayer in the human erythrocyte membrane under stress conditions. However, there is little information on how cholesterol functions. So, examining the role of a short side chain of cholesterol, we used the plant sterols such as β-sitosterol and stigmasterol. Incorporation of sterols into the membrane using a sterol/methyl-β-cyclodextrin complex was confirmed by the mass spectrometry. Hemolysis of human erythrocytes under high hydrostatic pressure (200 MPa) or hypotonic conditions was suppressed by cholesterol, but not by β-sitosterol and stigmasterol. Moreover, the bilayer-cytoskeleton interaction was also strengthened by cholesterol, but not by β-sitosterol and stigmasterol. Taken together, we suggest that the short side chain of cholesterol plays an important role in the membrane stability of human erythrocytes.

Influence of gestational age and birth weight in neonatal cholesterol response to total parenteral nutrition

BACKGROUND

Premature and critically ill infants receiving total parenteral nutrition (TPN) are at risk for dyslipidemia, and altered cholesterol levels in early life may contribute to later cardiovascular risk. Data regarding plasma cholesterol response to TPN in young infants are lacking.

OBJECTIVE

To determine the changes in plasma cholesterol levels during the first week of life in infants receiving TPN and a comparison group of infants who did not receive TPN during routine care.

METHODS

In a prospective, pilot cohort study, 38 neonates (30 TPN vs. 8 No-TPN) underwent serial blood sampling during the first week of life. Gas chromatography-mass spectrometry was used to measure cholesterol in plasma and TPN administered to study participants.

RESULTS

Baseline cholesterol level was similar between groups. In contrast to infants who did not receive TPN, cholesterol levels during the first week of life were significantly higher than baseline in infants receiving TPN (maximum cholesterol response 34% vs. 103% change from baseline, No-TPN vs. TPN, respectively, P = .036). After adjusting for cumulative cholesterol received by infants receiving TPN, maximum cholesterol response remained inversely related to gestational age and birth weight (P < .05).

CONCLUSION

Plasma cholesterol significantly increases during the first week of life in neonates receiving TPN. A higher cholesterol response was induced by TPN in infants of lower gestational age and birth weight.

Kinetics of phytosterol metabolism in neonates receiving parenteral nutrition

BACKGROUND

Phytosterols in soybean oil (SO) lipids likely contribute to parenteral nutrition-associated liver disease (PNALD) in infants. No characterization of phytosterol metabolism has been done in infants receiving SO lipids.

METHODS

In a prospective cohort study, 45 neonates (36 SO lipid vs. 9 control) underwent serial blood sample measurements of sitosterol, campesterol, and stigmasterol. Mathematical modeling was used to determine pharmacokinetic parameters of phytosterol metabolism and phytosterol exposure.

RESULTS

Compared to controls, SO lipid-exposed infants had significantly higher levels of sitosterol and campesterol (P < 0.01). During SO lipid infusion, sitosterol and campesterol reached half of steady-state plasma levels within 1.5 and 0.8 d, respectively. Steady-state level was highest for sitosterol (1.68 mg/dl), followed by campesterol (0.98 mg/dl), and lowest for stigmasterol (0.01 mg/dl). Infants born < 28 wk gestational age had higher sitosterol steady-state levels (P = 0.03) and higher area under the curve for sitosterol (P = 0.03) during the first 5 d of SO lipid (AUC5) than infants born ≥ 28 wk gestational age.

CONCLUSION

Phytosterols in SO lipid accumulate rapidly in neonates. Very preterm infants receiving SO lipid have higher sitosterol exposure, and may have poorly developed mechanisms of eliminating phytosterols that may contribute to their vulnerability to PNALD.