Fetal bile acid metabolism during infancy: analysis of 1 beta-hydroxylated bile acids in urine, meconium and feces

Potential role of bile acids in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is one of the most common acute gastrointestinal diseases in preterm infants. Recent studies have found that NEC is not only caused by changes in the intestinal environment but also by the failure of multiple systems and organs, including the liver. The accumulation of bile acids (BAs) in the ileum and the disorder of ileal BA transporters are related to the ileum injury of NEC. Inflammatory factors such as tumor necrosis factor (TNF)-α and interleukin (IL)-18 secreted by NEC also play an important role in regulating intrahepatic BA transporters. As an important link connecting the liver and intestinal circulation, the bile acid metabolic pathway plays an important role in the regulation of intestinal microbiota, cell proliferation, and barrier protection. In this review, we focus on how bile acids explore the dynamic changes of bile acid metabolism in necrotizing enterocolitis and the potential therapeutic value of targeting the bile acid signaling pathways.

Enteral Feeding and Antibiotic Treatment Do Not Influence Increased Coefficient of Variation of Total Fecal Bile Acids in Necrotizing Enterocolitis

Introduction

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in preterm infants. In animal models, the accumulation of ileal bile acids (BAs) is a crucial component of NEC pathophysiology. Recently, we showed that the coefficient of variation of total fecal BAs (CV-TBA) was elevated in infants who develop NEC compared to matched controls. However, neither the type of enteral nutrition nor antibiotic treatments-parameters that could potentially influence BA levels-were used to match pairs. Thus, we assessed the relationships between exposure to enteral feeding types and antibiotic treatments with NEC status and CV-TBA.

Materials and methods

Serial fecal samples were collected from 79 infants born with birth weight (BW) ≤1800 gm and estimated gestational age (EGA) ≤32 weeks; eighteen of these infants developed NEC. Total fecal BA levels (TBA) were determined using a commercially available enzyme cycling kit. Relationships between CV-TBA and dichotomous variables (NEC status, demographics, early exposure variables) were assessed by independent samples t-tests. Fisher's exact tests were used to assess relationships between NEC status and categorical variables.

Results

High values for CV-TBA levels perfectly predicted NEC status among infants in this study. However, feeding type and antibiotic usage did not drive this relationship.

Conclusions

As in previous studies, high values for the CV-TBA levels in the first weeks of life perfectly predicted NEC status among infants. Importantly, feeding type and antibiotic usage-previously identified risk factors for NEC-did not drive this relationship.

Meconium-stained amniotic fluid

Green-stained amniotic fluid, often referred to as meconium-stained amniotic fluid, is present in 5% to 20% of patients in labor and is considered an obstetric hazard. The condition has been attributed to the passage of fetal colonic content (meconium), intraamniotic bleeding with the presence of heme catabolic products, or both. The frequency of green-stained amniotic fluid increases as a function of gestational age, reaching approximately 27% in post-term gestation. Green-stained amniotic fluid during labor has been associated with fetal acidemia (umbilical artery pH <7.00), neonatal respiratory distress, and seizures as well as cerebral palsy. Hypoxia is widely considered a mechanism responsible for fetal defecation and meconium-stained amniotic fluid; however, most fetuses with meconium-stained amniotic fluid do not have fetal acidemia. Intraamniotic infection/inflammation has emerged as an important factor in meconium-stained amniotic fluid in term and preterm gestations, as patients with these conditions have a higher rate of clinical chorioamnionitis and neonatal sepsis. The precise mechanisms linking intraamniotic inflammation to green-stained amniotic fluid have not been determined, but the effects of oxidative stress in heme catabolism have been implicated. Two randomized clinical trials suggest that antibiotic administration decreases the rate of clinical chorioamnionitis in patients with meconium-stained amniotic fluid. A serious complication of meconium-stained amniotic fluid is meconium aspiration syndrome. This condition develops in 5% of cases presenting with meconium-stained amniotic fluid and is a severe complication typical of term newborns. Meconium aspiration syndrome is attributed to the mechanical and chemical effects of aspirated meconium coupled with local and systemic fetal inflammation. Routine naso/oropharyngeal suctioning and tracheal intubation in cases of meconium-stained amniotic fluid have not been shown to be beneficial and are no longer recommended in obstetrical practice. A systematic review of randomized controlled trials suggested that amnioinfusion may decrease the rate of meconium aspiration syndrome. Histologic examination of the fetal membranes for meconium has been invoked in medical legal litigation to time the occurrence of fetal injury. However, inferences have been largely based on the results of in vitro experiments, and extrapolation of such findings to the clinical setting warrants caution. Fetal defecation throughout gestation appears to be a physiologic phenomenon based on ultrasound as well as in observations in animals.

Fibroblast growth factor 19 secretion and function in perinatal development

Limited work has focused on fibroblast growth factor-19 (FGF19) secretion and function in the perinatal period. FGF19 is a potent growth factor that coordinates development of the brain, eye, inner ear, and skeletal system in the embryo, but after birth, FGF19 transitions to be an endocrine regulator of the classic pathway of hepatic bile acid synthesis. FGF19 has emerged as a mediator of metabolism and bile acid synthesis in aged animals and adults in the context of liver disease and metabolic dysfunction. FGF19 has also been shown to have systemic insulin-sensitizing and skeletal muscle hypertrophic effects when induced or supplemented at supraphysiological levels in adult rodent models. These effects could be beneficial to improve growth and nutritional outcomes in preterm infants, which are metabolically resistant to the anabolic effects of enteral nutrition. Existing clinical data on FGF19 secretion and function in the perinatal period in term and preterm infants has been equivocal. Studies in pigs show that FGF19 expression and secretion are upregulated with gestational age and point to molecular and endocrine factors that may be involved. Work focused on FGF19 in pediatric diseases suggests that augmentation of FGF19 secretion by activation of gut FXR signaling is associated with benefits in diseases such as short bowel syndrome, parenteral nutrition-associated liver disease, and biliary atresia. Future work should focus on characterization of FGF19 secretion and the mechanism underpinning the transition of FGF19 function as an embryological growth factor to metabolic and bile acid regulator.

Tissue-specific mechanisms of bile acid homeostasis and activation of FXR-FGF19 signaling in preterm and term neonatal pigs

The tissue-specific molecular mechanisms involved in perinatal liver and intestinal farnesoid X receptor (FXR)-fibroblast growth factor 19 (FGF19) signaling are poorly defined. Our aim was to establish how gestational age and feeding status affect bile acid synthesis pathway, bile acid pool size, ileal response to bile acid stimulation, genes involved in bile acid-FXR-FGF19 signaling and plasma FGF19 in neonatal pigs. Term (n = 23) and preterm (n = 33) pigs were born via cesarean section at 100% and 90% gestation, respectively. Plasma FGF19, hepatic bile acid and oxysterol profiles, and FXR target gene expression were assessed in pigs at birth and after a bolus feed on day 3 of life. Pig ileal tissue explants were used to measure signaling response to bile acids. Preterm pigs had smaller, more hydrophobic bile acid pools, lower plasma FGF19, and blunted FXR-mediated ileal response to bile acid stimulation than term pigs. GATA binding protein 4 (GATA-4) expression was higher in jejunum than ileum and was higher in preterm than term pig ileum. Hepatic oxysterol analysis suggested dominance of the alternative pathway of bile acid synthesis in neonates, regardless of gestational age and persists in preterm pigs after feeding on day 3. These results highlight the tissue-specific molecular basis for the immature enterohepatic bile acid signaling via FXR-FGF19 in preterm pigs and may have implications for disturbances of bile acid homeostasis and metabolism in preterm infants.NEW & NOTEWORTHY Our results show that the lower hepatic bile acid synthesis and ileum FXR-FGF19 pathway responsiveness to bile acids contribute to low-circulating FGF19 in preterm compared with term neonatal pigs. The molecular mechanism explaining immature or low-ileum FXR-FGF19 signaling may be linked to developmental patterning effects of GATA-4.

The protective role of hydrophilic tetrahydroxylated bile acids (THBA)

Bile acids are key components of bile required for human health. In humans and mice, conditions of reduced bile flow, cholestasis, induce bile acid detoxification by producing tetrahydroxylated bile acids (THBA), more hydrophilic and less cytotoxic than the usual bile acids, which are typically di- or tri-hydroxylated. Mice deficient in the Bile Salt Export Pump (Bsep, or Abcb11), the primary bile acid transporter in liver cells, produce high levels of THBA, and avoid the severe liver damage typically seen in humans with BSEP deficiencies. THBA can suppress bile acid-induced liver damage in Mdr2-deficient mice, caused by their lack of phospholipids in bile exposing their biliary tracts to unbound bile acids. Here we review THBA-related works in both animals and humans, and discuss their potential relevance and applications as a class of functional bile acids.

Developmental Patterns of Fecal Bile Acids in Healthy Neonates and Children

Background

Normal profiles of FBAs in healthy neonates and children in Kunming city and surrounding areas in China have not been previously determined. The objective of this study was to determine a developmental pattern of fecal bile acids (FBAs) in healthy neonates and children.

Material/Methods

A cross-sectional study was performed on 238 healthy neonates and children recruited in the First Affiliated Hospital of Kunming Medical University, China from October 2015 to September 2016. Secreted primary and secondary FBAs in fresh feces were quantitated by liquid chromatography mass spectrometry (LC-MS). Amounts of FBAs in feces were compared among various age groups.

Results

Trace amounts of cholic acid and chenodiol acid of primary FBAs were detectable at day 3 after birth, with a significant increase from day 3 to day 7. The primary FBAs gradually decreased from day 25 to the age of 6 years old. In contrast, a significant amount of glycochenodeoxycholic acid was detected on day 3 but decreased to a trace amount by day 7 and onwards. Primary FBAs appeared to maintain a high level, accounting for 98% of total FBAs, with no significant changes from day 7 to day 25 after birth. They gradually decreased from 90% to 10% from age 6 months to 6 years old. While the secondary FBAs were barely detected in neonates, only accounting for 2% of total FBAs, they were gradually elevated to 90% of total FBAs from age 6 months to 6 years old.

Conclusions

The liver can effectively synthesize primary bile acids 7 days after birth, and fecal primary bile acids tend to be stable after the neonate stage. Secondary bile acids continuously increase along with the maturation of intestinal flora, which reaches a relatively stable level at around 3 years old.

Changes in conjugated urinary bile acids across age groups

Bile acid compositions are known to change dramatically after birth with aging. However, no reports have described the transition of conjugated urinary bile acids from the neonatal period to adulthood, and such findings would noninvasively offer insights into hepatic function. The aim of this study was to investigate differences in bile acid species, conjugation rates, and patterns, and to pool characteristics for age groups. We measured urinary bile acids in spot urine samples from 92 healthy individuals ranging from birth to 58 years old using liquid chromatography tandem mass spectrometry (LC/ESI-MS/MS). Sixty-six unconjugated and conjugated bile acids were systematically determined. After birth, urinary bile acids dramatically changed from fetal (i.e., Δ⁴-, Δ⁵-, and polyhydroxy-bile acids) to mature (i.e., CA and CDCA) bile acids. Peak bile acid excretion was 6-8 days after birth, steadily decreasing thereafter. A major change in bile acid conjugation pattern (taurine to glycine) also occurred at 2-4 months old. Our data provide important information regarding transitions of bile acid biosynthesis, including conjugation. The data also support the existence of physiologic cholestasis in the neonatal period and the establishment of the intestinal bacterial flora in infants.

Urinary Bile Acid Profile of Newborns Born by Cesarean Section Is Characterized by Oxidative Metabolism of Primary Bile Acids: Limited Roles of Fetal-Specific CYP3A7 in Cholate Oxidations

This work aims to investigate how the bile acid metabolism of newborns differs from that of adults along the axis of primary, secondary, and tertiary bile acids (BAs). The total unconjugated BA profiles were quantitatively determined by enzyme digestion techniques in urine of 21 newborns born by cesarean section, 29 healthy parturient women, 30 healthy males, and 28 healthy nonpregnant females. As expected, because of a lack of developed gut microbiota, newborns exhibited poor metabolism of secondary BAs. Accordingly, the tertiary BAs contributed limitedly to the urinary excretion of BAs in newborns despite their tertiary-to-secondary ratios significantly increasing. As a result, the primary BAs of newborns underwent extensive oxidative metabolism, resulting in elevated urinary levels of some fetal-specific BAs, including 3-dehydroCA, 3β,7α,12α-trihydroxy-5β-cholan-24-oic acid, 3α,12-oxo-hydroxy-5β-cholan-24-oic acid, and nine tetrahydroxy-cholan-24-oic acids (Tetra-BAs). Parturient women had significantly elevated urinary levels of tertiary BAs and fetal-specific BAs compared with female control, indicating that they may be excreted into amniotic fluid for maternal disposition. An in vitro metabolism assay in infant liver microsomes showed that four Tetra-BAs and 3-dehydroCA were hydroxylated metabolites of cholate, glycocholate, and particularly taurocholate. However, the recombinant cytochrome P450 enzyme assay found that the fetal-specific CYP3A7 did not contribute to these oxidation metabolisms as much as expected compared with CYP3A4. In conclusion, newborns show a BA metabolism pattern predominated by primary BA oxidations due to immaturity of secondary BA metabolism. Translational studies following this finding may bring new ideas and strategies for both pediatric pharmacology and diagnosis and treatment of perinatal cholestasis-associated diseases. SIGNIFICANCE STATEMENT: The prenatal BA disposition is different from adults because of a lack of gut microbiota. However, how the BA metabolism of newborns differs from that of adults along the axis of primary, secondary, and tertiary BAs remains poorly defined. This work demonstrated that the urinary BA profiles of newborns born by cesarean section are characterized by oxidative metabolism of primary BAs, in which the fetal-specific CYP3A7 plays a limited role in the downstream oxidation metabolism of cholate.

Elevated Coefficient of Variation in Total Fecal Bile Acids Precedes Diagnosis of Necrotizing Enterocolitis

Accumulation of bile acids (BAs) may mediate development of necrotizing enterocolitis (NEC). Serial fecal samples were collected from premature infants with birth weight (BW) ≤ 1800 g, estimated gestational age (EGA) ≤ 32 weeks, and <30 days old prior to initiation of enteral feeding. Nine infants that developed Bell’s Stage ≥ II NEC were matched with control infants based on BW, EGA, day of life (DOL) enteral feeding was initiated and DOL of the first sample. From each subject, five samples matched by DOL collected were analyzed for BA levels and composition. Fifteen individual BA species were measured via LC-MS/MS and total BA levels were measured using the Diazyme Total Bile Acid Assay kit. No statistically significant differences in composition were observed between control and NEC at the level of individual species (p = 0.1133) or grouped BAs (p = 0.0742). However, there was a statistically significant difference (p = 0.000012) in the mean coefficient of variation (CV) between the two groups with infants developing NEC having more than four-fold higher mean CV than controls. Importantly, these variations occurred prior to NEC diagnosis. These data suggest fluctuations in total fecal BA levels could provide the basis for the first predictive clinical test for NEC.

Bile acids and gestation

There are numerous profound maternal physiological changes that occur from conception onwards and adapt throughout gestation in order to support a healthy pregnancy. By the time of late gestation, when circulating pregnancy hormones are at their highest concentrations, maternal adaptations include relative hyperlipidemia, hypercholanemia and insulin resistance. Bile acids have now been established as key regulators of metabolism, and their role in gestational changes in metabolism is becoming apparent. Bile acid homeostasis is tightly regulated by the nuclear receptor FXR, which has been shown to have reduced activity during pregnancy. This review focuses on the gestational alterations in bile acid homeostasis that occur in normal pregnancy, which in some women can become pathological, leading to the development of intrahepatic cholestasis of pregnancy. As well as their important role in maternal metabolic health, we will review bile acid metabolism in the feto-placental unit.

Prognostic roles of tetrahydroxy bile acids in infantile intrahepatic cholestasis

Tetrahydroxy bile acids (THBAs) are hydrophilic and are present at minimal or undetectable levels in healthy human adults, but are present at high levels in bile salt export pump (abcb11)-knockout mice. The roles of THBAs in human cholestatic diseases are unclear. We aimed to investigate the presence of THBAs in patients with infantile intrahepatic cholestasis and its correlation with outcome. Urinary bile acids (BAs) were analyzed by GC-MS. Data were compared between good (n = 21) (disease-free before 1 year old) and poor prognosis groups (n = 19). Good prognosis patients had a higher urinary THBA proportion than poor prognosis patients [25.89% (3.45-76.73%) vs. 1.93% (0.05-48.90%)]. A urinary THBA proportion >7.23% predicted good prognosis with high sensitivity (95.24%), specificity (84.21%), and area under the curve (0.91) (P < 0.0001). A THBA proportion 7.23% was an independent factor for decreased transplant-free survival (hazard ratio = 7.16, confidence interval: 1.24-41.31, P = 0.028). Patients with a confirmed ABCB11 or tight junction protein 2 gene mutation (n = 7) had a minimally detectable THBA proportion (0.23-2.99% of total BAs). Three patients with an ATP8B1 mutation had an elevated THBA proportion (7.51-37.26%). In conclusion, in addition to disease entity as a major determinant of outcome, a high THBA level was associated with good outcome in the infantile intrahepatic cholestasis patients.

Maternal and fetal circulation of unusual bile acids: a pilot study

BACKGROUND

Large amounts of unusual bile acids are synthesized by the fetal liver in late gestation. These compounds are mostly transferred from fetus to mother, although some are excreted into the amniotic fluid. We investigated the role of placental transfer of bile acids in fetal bile acid metabolism, particularly with respect to the unusual bile acids (1β-hydroxylated and ketonic bile acids).

METHODS

We measured concentrations of bile acids in umbilical cord blood and urine of newborn infants, and in perinatal maternal serum and urine, using gas chromatography-mass spectrometry. Serum and urine specimens from healthy non-pregnant women were used as controls.

RESULTS

In newborn infants at delivery, cord blood and urine contained mostly primary and 1β-hydroxylated bile acids, respectively. We also detected large amounts of ketonic bile acids in their urine, and the urinary concentration of total bile acids was elevated. Main maternal bile acids at 30 and 35 weeks of gestation and at delivery were 1β-hydroxylated bile acids. After delivery, main bile acids changed from 1β-hydroxylated bile acids to primary bile acids (P < 0.03), which also predominated in healthy non-pregnant women.

CONCLUSION

Fetally synthesized unusual bile acids were transported from fetus to mother. Pregnant women appear to excrete these bile acids into the urine, lowering both fetal and maternal serum bile acid concentrations.

Measurement of transport activities of bile acids in human multidrug resistance-associated protein 3 using liquid chromatography-tandem mass spectrometry

A method has been developed for the measurement of transport activities in membrane vesicles obtained from human multidrug resistance-associated protein 3-expressing Sf9 cells for 1beta-hydroxy-, 6alpha-hydroxy- and unsaturated bile acids by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Calibration curves for the bile acids were linear over the range of 10 to 2000 pmol/mL, and the detection limit was less than 2 pmol/mL for all bile acids using selected reaction monitoring analysis. The method was applied to measurements of adenosine triphosphate-dependent transport activities of the membrane vesicles for the above-mentioned hydroxylated and unsaturated bile acids. The present study demonstrated that the human multidrug resistance-associated protein 3 vesicles accepted 1beta-, 6alpha-hydroxylated and unsaturated bile acids along with common bile acids, such as glycocholic acid and taurolithocholic acid 3-sulfate. The developed method is useful for measurements of bile acid transport activities.

Developmental pattern of urinary bile acid profile in preterm infants

BACKGROUND

Bile acid metabolism in preterm infants is yet to be fully characterized. We compared the developmental pattern of urinary bile acid profiles in ten infants born at gestational ages from 25 to 33 weeks with previous data from full-term infants from birth to about 7 months of age.

METHODS

Gas chromatography-mass spectrometry was performed on serial samples.

RESULTS

Total urinary bile acid concentrations gradually increased until 1 to 2 months of age. After this peak of excretion (30 to 60 micromol/mmol creatinine), total urinary bile acid concentrations gradually decreased to less than 20 micromol/mmol creatinine. The percentage of usual bile acids (mainly cholic acid) relative to total urinary total bile acids gradually deceased from approximately 30% at birth to less than 15% at 7 months of age. On the other hand, 1beta-hydroxylated bile acids (mainly 1beta,3alpha,7alpha,12alpha-tetrahydroxy-5beta-cholan-24-oic acid) relative to total urinary bile acids were increased gradually from 60% at birth to reach 70% to 80% at 1 month of age. The percentage of 1beta-hydroxylated bile acids relative to total urinary bile acids then remained stable at a high percentage (70% to 90%) until the age of 7 months.

CONCLUSION

Physiological cholestasis in preterm infants persists longer than in full-term infants. Moreover, as large amounts of cholic and 1beta,3alpha,7alpha,12alpha-tetrahydroxy-5beta-cholan-24-oic acids were detected in urine from preterm infants during this study, the 25-hydroxylation pathway may be particularly important for bile acid synthesis in early preterm infants.

Measurement of the transport activities of bile salt export pump using LC-MS

The high performance liquid chromatography-electrospray ionization-mass spectrometry method has been applied to the measurement of bile acid transport activities in membrane vesicles obtained from a human bile salt export pump expressing Sf9 cells. The amounts of bile acids transported using the human bile salt export pump expressing Sf9 cells were determined using liquid chromatography-electrospray ionization-mass spectrometry method and the values of the kinetic parameters were determined to be comparable with those obtained using radioisotope-labeled substrates. The developed method was highly useful for the measurements of bile acid transport activities.

Diagnostic determination system for high-risk screening for inborn errors of bile acid metabolism based on an analysis of urinary bile acids using gas chromatography-mass spectrometry: results for 10 years in Japan

BACKGROUND

Some patients with cholestasis of unknown cause may have inborn errors of bile acid metabolism (IEBAM) thus causing abnormalities of bile acid biosynthesis. Although seven types of bile acid synthetic defects have thus far been reported for this disorder, no detailed information on its incidence and so on in Japan is yet available. In order to elucidate the current status of IEBAM in Japan, in July 1996 a diagnostic determination system was established for high-risk screening for IEBAM.

METHODS

Urinary bile acids were analyzed on gas chromatography-mass spectrometry (GC-MS) and quantitative analysis was done using selected ion monitoring (SIM).

RESULTS AND CONCLUSIONS

In a total of 576 samples analyzed over the 10 year period prior to June 2005, 159 patients were found with cholestasis of unknown etiology. Of these patients, 10 (6.3%) were found to have IEBAM by this system, while 91 (61.1%) had cholestasis without a definitive diagnosis. This diagnostic determination system with GC-MS of urinary bile acids is therefore considered useful for detecting IEBAM.

Does abnormal bile acid metabolism contribute to NEC?

Bile acids (BAs) facilitate emulsification, absorption, and transport of fats and sterols in the intestine and liver and are essential for normal digestion. However, accumulation of BAs in the intestine can result in damage to the intestinal epithelium. Using the neonatal rat model of necrotizing enterocolitis (NEC), we have recently shown that BAs accumulate in both the ileal lumen and enterocytes of neonatal rats with NEC and the increased BA levels are positively correlated with disease severity. Importantly, when BAs are not allowed to accumulate, neonatal rat pups develop significantly less disease. In addition, BA transporters are altered during disease development. These data indicate that BAs play an important role in the development of experimental NEC, and suggest that the inability of neonatal rats to adequately regulate BA transporters may be a mechanism by which ileal damage occurs.

Perinatal bile acid metabolism: bile acid analysis of meconium of preterm and full-term infants

BACKGROUND

Our purpose was to evaluate the metabolism of bile acids in the fetus by analyzing the bile acid composition of meconium of preterm (less than 30 weeks' gestational age) and full-term infants and comparing the results with the bile acid composition of feces of preterm and full-term infants 6 days after delivery.

METHODS

The concentrations of individual bile acids were determined by gas chromatography-mass spectrometry after solvolysis and hydrolysis of bile acid conjugates.

RESULTS

In meconium, the main bile acids were chenodeoxycholic and hyocholic acids. The main bile acid of feces from preterm infants at 6 days of age was the same as that of meconium. We also detected large amounts of secondary bile acids, especially deoxycholic acid and ursodeoxycholic acid. The ratio of cholic acid relative to chenodeoxycholic acid in meconium of preterm and full-term infants and in feces of preterm infants was less than 1, 0.36, 0.55, and 0.55, respectively. The percentage of chenodeoxycholic acid relative to total bile acids in meconium of preterm (P < 0.05) and full-term (P < 0.01) infants was significantly higher than that in feces of 6-day-old full-term infants.

CONCLUSIONS

More than half of the main pathway, at least, for bile acid synthesis in preterm infants may be the acidic pathway until the infants reach about 7 days of age.

Hormonal regulation of renal multidrug resistance-associated proteins 3 and 4 (Mrp3 and Mrp4) in mice

Multidrug resistance-associated proteins 3 and 4 (Mrp3 and Mrp4) are expressed at much higher levels in female than male kidney. Sex steroids and sex-specific growth hormone (GH) secretion patterns often mediate gender-predominant gene expression. Thus, three models were used to investigate potential endocrine regulation of Mrp3 and Mrp4: (1) gonadectomized (GNX) mice with 17beta-estradiol (E2) or 5alpha-dihydroxytestosterone (DHT) replacement; (2) hypophysectomized (HPX) mice receiving E2, DHT, or simulated male-pattern (MP) or female-pattern (FP) GH secretion; (3) lit/lit mice, which have a spontaneous mutation in the growth-hormone releasing-hormone (GHRH) receptor, with simulated MP- or FP-GH secretion. GNX and HPX decreased Mrp3 mRNA levels compared with intact females. In both respective models E2 administration increased Mrp3 expression in GNX and HPX mice. DHT markedly repressed Mrp3 from GNX+placebo levels, however, this was not observed in the HPX model. In lit/lit mice, Mrp3 expression was lower than in wild-type controls, and MP-GH and FP-GH simulation slightly increased Mrp3 expression. Whereas GNX increased Mrp4 in males to female levels, HPX actually increased Mrp4 expression in both genders +375% and +66%, respectively. In both models DHT markedly repressed Mrp4. Furthermore, Mrp4 was higher in lit/lit than wild-type male mice, and simulation of MP-GH secretion suppressed female-predominant Mrp4 expression. In conclusion, these data indicate that E2 contributes to higher Mrp3 mRNA expression in females, yet a role for androgens in Mrp3 repression cannot be discounted. In contrast, Mrp4 mRNA is higher in females due to repression by both DHT and MP-GH secretion in males.

Perinatal bile acid metabolism: analysis of urinary unsaturated ketonic bile acids in preterm and full-term infants

AIM

To compare urinary concentrations of unsaturated ketonic bile acids in preterm and full-term infants.

METHODS

Urinary unsaturated ketonic bile acids were determined using gas chromatography-mass spectrometry.

RESULTS

Urinary concentrations of total bile acids in early preterm infants (of less than 29wk gestational age) exceeded concentrations in late preterm (between 30 and 37 wk) and full-term infants (between 38 and 41 wk; p < 0.01). The percentage of ketonic bile acids (7alpha, 12alpha-dihydroxy-3-oxo-4-cholenoic acid and 7alpha-hydroxy-3-oxo-4-cholenoic acid) among total urinary bile acids in full-term infants (20.2 +/- 14.1%) was higher than that in early preterm infants (8.94 +/- 8.1%; p < 0.05). The percentage of unsaturated bile acids (3beta-hydroxy-delta5-bile acids) among total bile acids in urine did not differ greatly between groups.

CONCLUSION

The percentage of 3-oxo-delta4 bile acids among total bile acids in urine gradually increased from early to late preterm infants, while healthy full-term infants excreted large amounts of 3-oxo-delta4 bile acids in urine at delivery.

Intractable diarrhea after liver transplantation for Byler's disease: successful treatment with bile adsorptive resin

Intractable diarrhea and prolonged growth retardation after liver transplantation for Byler's disease are serious complications limiting the ultimate outcome of liver transplantation for this disease. However, details of these complications have not been documented thoroughly. Six patients with Byler's disease developed intractable diarrhea after living donor liver transplantation. Because of high bile acid concentrations in stool, four patients were treated with bile acid adsorptive resin for bile acid diarrhea, and all showed improved bowel movements. Four of these patients who were followed up for 1 year registered a significant height gain. Also, the cause of postoperative diarrhea and growth retardation in patients with Byler's disease after liver transplantation is discussed.

Profile of urinary bile acids in infants and children: developmental pattern of excretion of unsaturated ketonic bile acids and 7beta-hydroxylated bile acids

Unusual bile acids, such as unsaturated ketonic and 7beta-hydroxylated bile acids, have been detected in urine early in life. To elucidate the normal profiles of usual and unusual urinary bile acids in the neonatal and pediatric periods, we measured the concentrations of 28 kinds in urine from normal newborns, infants, and children by gas chromatography-mass spectrometry. The mean total bile acid/Cr ratio in 7-d-old infants was significantly higher than in subjects of other age groups (birth, 2-4 mo, 5-7 mo, 11-12 mo, 2-3 y, 9-14 y, and adult) (p < 0.05). Relatively large amounts of unusual bile acids were detected during infancy, especially during the period up to 1 mo of age. At that time, 1beta,3alpha,7alpha,12alpha-tetrahydroxy-5bet a-cholan-24-oic, 7alpha, 12alpha-dihydroxy-3-oxo-5beta-chol-1-en-24-oic, and 7alpha,12alpha-dihydroxy-3-oxo-4-cholen-24-oic acids were predominant among the unusual urinary bile acids present. Moreover, the levels of 3alpha,7beta,12alpha-trihydroxy-5beta-cholan+ ++-24-oic acid increased significantly after 2-4 mo of age. These results indicate that bile acid synthesis and metabolism in the liver of developing infants are significantly different from that occurring in the liver of adults. Significant amounts of urinary isomerized 7beta-hydroxylated bile acids were detected after late infancy, probably because of changes in the intestinal bacterial flora response to a change in nutrition. We describe, for the first time, evidence of the epimerization of the 7alpha-hydroxyl group of cholic acid, which may be unique to human development.

Developmental pattern of 3-oxo-delta 4 bile acids in neonatal bile acid metabolism

AIMS

To investigate whether a fetal pathway of bile acid synthesis persists in neonates and infants.

METHODS

3-oxo-delta 4 bile acids were determined qualitatively and quantitatively in the urine, meconium, and faeces of healthy neonates and infants, using gas chromatography-mass spectrometry.

RESULTS

The mean percentage of 3-oxo-delta 4 bile acids in total bile acids in urine at birth was significantly higher than that at 3 or 7 days, and at 1 or 3 months of age. The concentration of this component in meconium was significantly higher than that in faeces at 7 days and at 1 or 3 months of age.

CONCLUSIONS

The presence of large amounts of urinary 3-oxo-delta 4 bile acids may indicate immaturity in the activity of hepatic 3-oxo-delta 4-steroid 5 beta-reductase in the first week of postnatal life. Large amounts of this component in meconium may be due to the ingestion of amniotic fluid by the fetus during pregnancy.

Determination of fetal bile acids in biological fluids from neonates by gas chromatography-negative ion chemical ionization mass spectrometry

A method has been developed for microanalysis of fetal bile acids in biological fluids from neonates by capillary gas chromatography-mass spectrometry using negative-ion chemical ionization of pentafluorobenzyl ester-dimethylethylsilyl ether derivatives of bile acids. Calibration curves for the bile acid derivatives are useful over the range 0.1-100 pg and the detection limit for bile acids was 1 fg (S/N = 5) using isobutane as a reagent gas. Recoveries of the bile acids and their glycine and taurine conjugates from bile acid-free serum and dried blood discs ranged from 92 to 101% and from 93 to 108%, respectively, of the added amounts of their standard samples. The analysis of bile acids on a dried blood disc, meconium and urine from infants, exhibited significant hydroxylation at the 1 beta-, 2 beta-, 4 beta- and 6 alpha-positions of the usual bile acids, cholic and chenodeoxycholic acids, for the urinary or fecal excretion of bile acids in the fetal and neonatal periods. The present method was applied clinically to analyze bile acids on a dried blood disc from neonatal patients with congenital biliary atresia and hyper-bile-acidemia.

Enzyme immunoassay for conjugated cholic and 1 beta-hydroxycholic acids in urine of early infancy

A direct competitive heterologous enzyme immunoassay (EIA) for conjugated cholic acid (CA) was developed using horseradish peroxidase labeled antigen having a shorter bridge length than that of the immunogen. An appropriate dose-response curve for conjugated CA was obtained in the range of 0.05-50 ng/well. Specificity of the EIA proved satisfactory in terms of cross-reactivities to 23 kinds of related bile acids. The proposed method was evaluated to be useful for the determination of conjugated CA in urine with acceptable accuracy and inter- and intra-assay precision. The results of analysis showed a reverse relationship between age and urinary excretion ratio of conjugated 1 beta-hydroxy-CA to conjugated CA in the first 9 months after birth.

Reconstitution and characterization of ATP-dependent bile acid transport in human and rat placenta

Bile acid (BA) transport across the human microvillus maternal-facing trophoblast plasma membrane (mTPM) has been recently reported to be stimulated by the presence of ATP [Marin, Bravo, El-Mir and Serrano (1993) J. Hepatol. 18, S41]. Reconstitution of BA transport activity in proteoliposomes from human mTPM is reported in this paper. Typical characteristics of BA transport in native mTPM vesicles, including a requirement for ATP hydrolysis and inhibition by other BA species, were preserved in proteoliposome preparations. BA transport into 20- and 14-day-gestation rat mTPM vesicles was also stimulated by the presence of ATP as noted in human mTPM and in the rat liver canalicular membrane. Besides this functional similarity, these ATP-dependent carriers may share structural characteristics, as demonstrated by studies using an antibody (100 Ab) raised against the 100 kDa BA carrier of the canalicular membrane from rat liver which recognized proteins in both human and rat brush-border trophoblast membranes.