ABSTRACT:UDP-glucuronosyltransferases (UGTs) are critical for the metabolism and clearance of drugs, chemicals, and hormones. The development of UGT1A1 and 1A6 was studied in 50 pediatric liver samples using bilirubin, serotonin activity assays, and Western blot as well as pharmacokinetic scaling. UGT activity developed age dependently in pediatric liver.

ABSTRACT:This article reports on the development of UDP-glucuronosyltransferase (UGT) enzyme activity in pediatric livers. The substrates 4-methylumbelliferone (4MU) and trifluoperazine (TFP) were used as probes for general glucuronidation and specific UGT1A4 activity, respectively. The activity of hepatic ␤-glucuronidase enzymes was also determined so as to investigate the balance between glucuronide clearance and systemic recirculation. UGT activity toward 4MU reached maximum levels by 20 months of age, whereas the activity of ␤-glucuronidase was highest in the neonatal liver and decreased to steady-state adult levels by 4 months. The average V max and K m values for UGT1A4 in pediatric samples were 151.9 ؎ 63.5 pmol/min/mg protein and 14.4 ؎ 9.6 M, respectively. Average V max was understandably low because of developmental dynamics, but K m was similar to values reported elsewhere.When a constant rate of enzyme development is assumed, maximum activity of UGT1A4 occurs at 1.4 years of age. When the intrinsic hepatic clearance of TFP was scaled with an allometric model, hepatic clearance of TFP by UGT1A4 did not reach maximum levels until 18.9 years of age and scaled results underestimated reported in vivo clearances in adult males. No significant differences in UGT activities or hepatic clearance were observed with gender or ethnicity. The developmental dynamics of most drug-metabolizing enzymes are unknown, and this article contains, to our knowledge, the first description of the development of a single UGT isoform in childhood. Ultimately, work such as this is important for predicting drug responses and for developing and evaluating new medications in children.

The placenta plays a vital role in pregnancy by facilitating steroid passage from maternal to fetal circulation and/or direct production of hormones. Using a murine model, we demonstrated the differences in placental steroid metabolism between pregnancies conceived naturally and with assisted reproduction technologies (ART): in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). While the ovarian steroid production was similar (estrone, 17β-estradiol) or higher (estriol) in ART pregnancies compared to mating, the levels of placental estriol were significantly lower in ART group. Placentas from ART had significantly higher activities of the steroid metabolizing enzymes UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT), which in ICSI were also coupled with decreased activity of the steroid regenerating enzymes β-glucuronidase (β-G) and Aryl sulfatase (AS). Levels of steroid metabolites androstane-3α-17β-diol glucuronide and dehydroepiandrosterone sulfate were higher in fetal compared to maternal blood in ART, but not in mating. This study demonstrates that in murine ART pregnancies, higher metabolism and clearance of steroids by the placenta may seriously affect the passage of essential hormones to the fetus. If a similar phenomenon exists in humans, this could provide a plausible explanation for obstetric and neonatal complications associated with ART, including the higher incidence of low birth weight babies.

ABSTRACT:This article reports on the development of UDP-glucuronosyltransferase 1A9 (UGT1A9) in neonatal and pediatric liver. The substrate 4-methylumbelliferone (4MU) with specific inhibition by niflumic acid was used to define specific UGT1A9 activity. Subsequently, in silico pharmacokinetic (PK) and physiology-based pharmacokinetic (PBPK) modeling was used to determine UGT1A9 maturation and hepatic clearance. Modeled maximal enzyme activity was 27.9 nmol ⅐ min ؊1 ⅐ mg protein

Abstract. Developmental inadequacy in hepatic antioxidant defenses may contribute to chemical toxicity and pediatric liver diseases. We measured a comprehensive panel of antioxidants in liver tissue from 27 normal pediatric donors. Glutathione reductase declined with age (P = 0.008, r = −0.54, Spearman) while microsomal glutathione-S-transferase increased (GST, P<0.001, r = 0.81). Males had significantly lower superoxide dismutase and vitamin E (P<0.05) and may have lower glutathione reductase (P = 0.06), while females show less cytosolic GST (P = 0.07). Hepatic antioxidants are high in neonates, decline throughout childhood, and then increase in adolescence to adult levels.