Bile salt sulfotransferase: alterations during maturation and non-inducibility during substrate ingestion

Diagnostic performance evaluation of sulfate-conjugated cholesterol metabolites as urinary biomarkers of Niemann-Pick disease type C

BACKGROUND

Niemann-Pick disease type C (NPC) is an autosomal recessive inherited disorder with progressive neuronal degeneration. Because conventional diagnostic methods are complicated and invasive, biomarker tests have drawn attention. We aimed to evaluate three urinary conjugated cholesterol metabolites as diagnostic biomarkers for NPC.

METHODS

Urine samples from 23 patients with NPC, 28 healthy controls, and 7 patients with inherited metabolic disorders were analyzed. 3β-Sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid and its glycine and taurine conjugates in urine were quantified by liquid chromatography-tandem mass spectrometry. The diagnostic performance of the three metabolites and their total concentration was evaluated.

RESULT

Creatinine-corrected concentrations of three metabolites and their total concentration were all significantly higher in NPC patients (0.0098 < P < .0448). The area under the receiver operating curve for all metabolites exceeded 0.95, the clinical specificity was 92-100%, and the clinical sensitivity was ~95%. In the urine of patients with other inherited metabolic diseases, the concentrations of the metabolites were lower than those in the urine of patients with NPC.

CONCLUSION

These conjugated cholesterol metabolites in urine can serve as useful diagnostic markers for noninvasive screening of NPC.

Age-related change of hepatic uridine diphosphate glucuronosyltransferase and sulfotransferase activities in male chickens and pigs

The hepatic activities of uridine diphosphate glucuronosyltransferase (UGT) and sulfotransferase (SULT) of male Ross 708 broiler chickens at the age of 1, 7, 14, 28, and 56 days and male Camborough-29 pigs at the age of 1 day and 2, 5, 10, and 20 weeks were investigated. Glucuronidation and sulfation of 4-nitrophenol were used to evaluate the activities. Porcine hepatic UGT and SULT activities were low at birth, peaked at around 5-10 weeks, and then declined. Both hepatic UGT and SULT activities of chickens were high at hatch and declined. Chicken hepatic UGT activity had a peak at the age of 28 days. Affinity of hepatic SULT to 4-nitrophenol is similar in chickens and pigs, but the affinity of hepatic UGT in pigs was about 10 times higher than that in chickens. 4-nitrophenol was predominantly conjugated by SULT instead of UGT in chicken livers from hatch to day 56. Conversely, hepatic UGT contributed predominantly in 4-nitrophenol conjugation than the SULT in pigs from birth to 20 weeks. Therefore, age has significant impact on hepatic activities of UGT and SULT, and the importance of UGT and SULT on conjugation is different in chickens and pigs.

Ontogeny of mammalian metabolizing enzymes in humans and animals used in toxicological studies

It is well recognized that expression of enzymes varies during development and growth. However, an in-depth review of this acquired knowledge is needed to translate the understanding of enzyme expression and activity into the prediction of change in effects (e.g. kinetics and toxicity) of xenobiotics with age. Age-related changes in metabolic capacity are critical for understanding and predicting the potential differences resulting from exposure. Such information may be especially useful in the evaluation of the risk of exposure to very low (µg/kg/day or ng/kg/day) levels of environmental chemicals. This review is to better understand the ontogeny of metabolizing enzymes in converting chemicals to either less-toxic metabolite(s) or more toxic products (e.g. reactive intermediate[s]) during stages before birth and during early development (neonate/infant/child). In this review, we evaluated the ontogeny of major "phase I" and "phase II" metabolizing enzymes in humans and commonly used experimental animals (e.g. mouse, rat, and others) in order to fill the information gap.

Developmental pharmacokinetics

The advances in developmental pharmacokinetics during the past decade reside with an enhanced understanding of the influence of growth and development on drug absorption, distribution, metabolism, and excretion (ADME). However, significant information gaps remain with respect to our ability to characterize the impact of ontogeny on the activity of important drug metabolizing enzymes, transporters, and other targets. The ultimate goal of rational drug therapy in neonates, infants, children, and adolescents resides with the ability to individualize it based on known developmental differences in drug disposition and action. The clinical challenge in achieving this is accounting for the variability in all of the contravening factors that influence pharmacokinetics and pharmacodynamics (e.g., genetic variants of ADME genes, different disease phenotypes, disease progression, and concomitant treatment). Application of novel technologies in the fields of pharmacometrics (e.g., in silico simulation of exposure-response relationships; disease progression modeling), pharmacogenomics and biomarker development (e.g., creation of pharmacodynamic surrogate endpoints suitable for pediatric use) are increasingly making integrated approaches for developmentally appropriate dose regimen selection possible.

Mechanisms of gender-specific regulation of mouse sulfotransferases (Sults)

1. Marked gender differences in the expression of sulfotransferases (Sults) are known to exist in several species including rats, mice and hamsters. However, the mechanism for this gender difference is not known. Therefore, in the present study, it was determined whether sex and/or growth hormone (GH) are responsible for the gender difference in the expression of Sults using gonadectomized (GNX), hypophysectomized (HX) and GH-releasing hormone receptor-deficient little (lit/lit) mouse models. 2. Sult1a1 and Papss2 in liver and kidney, and Sult1d1 in liver are female-predominant in mice because of suppressive effects of both androgens and male-pattern GH secretion. Sult2a1/a2 is the most markedly female-predominant Sult in mouse liver due to suppressive effects of androgens and male-pattern GH secretion, as well as stimulatory effects by estrogens and female-pattern GH secretion. Sult3a1 is female-predominant in mouse liver due to suppressive effects of androgens as well as stimulatory effects of estrogens and female-pattern GH secretion. Sult1c1 expression is male-predominant in mouse liver and kidney because of stimulatory effects of androgens in males. Sult4a1 expression is female-predominant in mouse brain due to stimulatory effects of estrogens. 3. In conclusion, gender-divergent Sults are mostly female-predominant and Sult1c1 is the only male-dominant Sult. The gender differences in expression of various mouse Sults are influenced by various mechanisms involving sex and/or GHs.

Bile Acid sulfation: a pathway of bile acid elimination and detoxification

Sulfotransferase-2A1 catalyzes the formation of bile acid-sulfates (BA-sulfates). Sulfation of BAs increases their solubility, decreases their intestinal absorption, and enhances their fecal and urinary excretion. BA-sulfates are also less toxic than their unsulfated counterparts. Therefore, sulfation is an important detoxification pathway of BAs. Major species differences in BA sulfation exist. In humans, only a small proportion of BAs in bile and serum are sulfated, whereas more than 70% of BAs in urine are sulfated, indicating their efficient elimination in urine. The formation of BA-sulfates increases during cholestatic diseases. Therefore, sulfation may play an important role in maintaining BA homeostasis under pathologic conditions. Farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor are potential nuclear receptors that may be involved in the regulation of BA sulfation. This review highlights current knowledge about the enzymes and transporters involved in the formation and elimination of BA-sulfates, the effect of sulfation on the pharmacologic and toxicologic properties of BAs, the role of BA sulfation in cholestatic diseases, and the regulation of BA sulfation.

Molecular basis of neonatal cholestasis

At present, specific evidence regarding the molecular mechanisms of neonatal cholestasis is limited. The recent explosion in the understanding of the molecular physiology of bile formation has been fueled by the discovery of several genes that are involved in familial cholestasis. The ever-growing understanding of the functional immaturity of the neonatal liver is sure to be enhanced by the study of the ontogeny of important hepatobiliary transporters as they are discovered. The understanding of the functional differences between the immature and mature liver is key to the understanding of neonatal cholestasis.

Carcinogen activation by sulfate conjugate formation

The foregoing pages presented a substantial body of data that established that sulfotransferase conjugation can transform many xenobiotics into agents that can modify cellular macromolecules. However, activation by sulfation is rarely the only metabolic pathway that is open to these compounds; other pathways can become more important in response to a variety of factors. This metabolic switching can be produced by substrate concentration, cofactor availability, kinetic factors that dictate the velocity of the various possible conjugation reactions, and, in some cases, competition between Phase-I and Phase-II metabolism. Also, it is important to realize that demonstration of activation by sulfate ester formation in vitro does not necessarily mean that a similar activation process will occur in vivo. Experience also teaches that argument by analogy can be very misleading in the case of sulfate activation. Small structural differences can upset the delicate balance between sulfate activation and the various other competing pathways. Nevertheless, sulfation is an important mechanism by which a number of chemicals are transformed to their activated forms.

Fetal and neonatal bile acid synthesis and metabolism--clinical implications

It has become apparent that with sophisticated technology we are now able to recognize defective bile acid metabolism in a wide variety of disease states. Recognition of specific aberrations, such as inborn errors in bile acid metabolism manifesting as neonatal cholestasis, offers new opportunities for therapeutic intervention. Future studies should determine the incidence of inborn errors in patients with enigmatic and unexplained liver diseases such as idiopathic neonatal hepatitis.

Cytosolic bile acid binding protein in rat liver: radioimmunoassay, molecular forms, developmental characteristics and organ distribution

Rat liver efficiently extracts bile acids from the portal blood and rapidly excretes them into bile. Little is known about the process by which bile acids traverse the liver cell from the sinusoidal to the canalicular membrane. In order to begin to define this process, we recently identified a pair of similar monomeric (33 kilodalton) cytosolic bile acid binding proteins (bile acid binders I and II, J. Biol. Chem. 1983; 258:3602-3607, Abstract). These bile acid binders have comparable binding affinities for bile acid as the YaYa and YaYc members of the family of glutathione S-transferases, the previously recognized cytoplasmic bile acid binding protein. We now report the establishment of a sensitive and specific radioimmunoassay which equally detects both bile acid binders I and II. Specificity of the antiserum was verified by the co-purification of bile acid binder immunoreactivity with the bile acid binders. Liver contained the greatest concentration of bile acid binder, where it constituted 0.33% of the total cytosolic proteins. Phenobarbital administration and lithocholate feeding had no significant effect on hepatic bile acid binder content. Examination of the ontogeny of bile acid binder revealed a rapid increase after birth to near adult levels by Day 14. In summary, we have established a sensitive radioimmunoassay for the bile acid binders. Its localization mainly in liver and its increase after birth parallel bile acid transport in the liver.

Neonatal cholestasis

The spectrum of diseases causing neonatal cholestasis presents intriguing problems for future investigation. There are many causes, and the eventual outcome of the specific entity has unique individual features, despite the wide areas of overlap. For example, extrahepatic biliary atresia may be the result of the sporadic occurrence of a virus-induced, progressive obliteration of the extrahepatic bile ducts with some degree of intrahepatic bile duct injury. This same sequence of viral infection with persisting injury may account for sporadic (nonfamilial) cases of neonatal hepatitis, as suggested by the Landing hypothesis. Conversely, the familial forms of cholestasis, either neonatal hepatitis or instances of intrahepatic cholestasis, are most likely genetic diseases that represent specific defects in the hepatic excretory process or in the bile secretory apparatus. The persistent nature of these presumed enzymatic or structural defects may explain the less favorable prognosis. Elucidation of the nature of these inborn errors of liver function may allow a better understanding of biliary physiology, and improved therapy.