Development of tyrosine aminotransferase and para-hydroxyphenylpyruvate dioxygenase activities in fetal and neonatal human liver

Maternal and cord blood LC-HRMS metabolomics reveal alterations in energy and polyamine metabolism, and oxidative stress in very-low birth weight infants

To assess the global effect of preterm birth on fetal metabolism and maternal-fetal nutrient transfer, we used a mass spectrometric-based chemical phenotyping approach on cord blood obtained at the time of birth. We sampled umbilical venous, umbilical arterial, and maternal blood from mothers delivering very-low birth weight (VLBW, with a median gestational age and weight of 29 weeks, and 1210 g, respectively) premature or full-term (FT) neonates. In VLBW group, we observed a significant elevation in the levels and maternal-fetal gradients of butyryl-, isovaleryl-, hexanoyl- and octanoyl-carnitines, suggesting enhanced short- and medium chain fatty acid β-oxidation in human preterm feto-placental unit. The significant decrease in glutamine-glutamate in preterm arterial cord blood beside lower levels of amino acid precursors of Krebs cycle suggest increased glutamine utilization in the fast growing tissues of preterm fetus with a deregulation in placental glutamate-glutamine shuttling. Enhanced glutathione utilization is likely to account for the decrease in precursor amino acids (serine, betaine, glutamate and methionine) in arterial cord blood. An increase in both the circulating levels and maternal-fetal gradients of several polyamines in their acetylated form (diacetylspermine and acetylputrescine) suggests an enhanced polyamine metabolic cycling in extreme prematurity. Our metabolomics study allowed the identification of alterations in fetal energy, antioxidant defense, and polyamines and purines flux as a signature of premature birth.

Prenatal and postnatal expression of glutathione transferase ζ 1 in human liver and the roles of haplotype and subject age in determining activity with dichloroacetate

Glutathione transferase ζ 1 (GSTZ1), also known as maleylacetoacetate isomerase, catalyzes the penultimate step of tyrosine catabolism and metabolizes several α-halocarboxylic acids, including dichloroacetic acid (DCA), an investigational drug used for lactic acidosis and, recently, solid tumors. Age-related differences have been suggested in DCA pharmacotoxicology, but no information is available on GSTZ1 ontogeny in humans. Here, we investigated the cytosolic GSTZ1 developmental expression pattern and the influence of haplotype on GSTZ1 activity with DCA by using human livers from donors between 10 weeks gestation and 74 years. GSTZ1 expression was very low in fetal livers (<2 pmol of GSTZ1/mg cytosol). The expression began to increase after birth in an age-dependent manner until age 7 years. GSTZ1 was then sustained at stable, yet variable, levels (median, 20.0 pmol/mg cytosol; range, 4.8-47.3 pmol/mg cytosol) until age 74 years. GSTZ1 activity with DCA was strongly associated with haplotype and expression level. Samples homozygous or heterozygous for GSTZ1A exhibited ∼3-fold higher DCA dechlorinating activity than samples carrying other alleles at a given level of expression. The correlations (r²) between activity and expression were 0.90 and 0.68, respectively, for GSTZ1A carriers (n = 11) and noncarriers (n = 61). GSTZ1 is expressed in mitochondria in addition to cytosol. The GSTZ1A allele exhibited similar effects in the mitochondrial fraction by conferring a higher activity with DCA. In summary, we report a neonatal onset and an age-related increase in GSTZ1 protein expression during human liver development. Haplotype influenced GSTZ1 activity with DCA but not protein expression.

Isolation, characterization, and differentiation to hepatocyte-like cells of nonparenchymal epithelial cells from adult human liver

Activation and proliferation of human liver progenitor cells has been observed during acute and chronic liver diseases. Our goal was to investigate the presence of these putative progenitors in the liver of patients who underwent lobectomy for various reasons but did not show any hepatic insufficiency. Hepatic lesions were evaluated by histological analysis. Nonparenchymal epithelial (NPE) cells were isolated from samples of human liver resections located at a distance from the lesion that motivated the operation and were cultured and characterized. These cells exhibited a marked proliferative potential. They did not express the classic set of stem cell/progenitor markers (Oct-4, Rex-1, alpha-fetoprotein, CD90, c-kit, and CD34) and were faintly positive for albumin. When cultured at confluence in the presence of hepatocyte growth factor and either epidermal growth factor or fibroblast growth factor-4, they entered a differentiation process toward hepatocytes. Their phenotype was quantitatively compared with that of mature human hepatocytes in primary culture. Differentiated NPE cells expressed albumin; alpha1-antitrypsin; fibrinogen; hepatobiliary markers such as cytokeratins 7, 19, and 8/18; liver-enriched transcription factors; and genes characterized by either a fetal (cytochrome P4503A7 and glutathione S-transferase pi) or a mature (tyrosine aminotransferase, tryptophan 2,3-dioxygenase, glutathione S-transferase alpha, and cytochrome P4503A4) expression pattern. NPE cells could be isolated from the liver of several patients, irrespective of the absence or presence of lesions, and differentiated toward hepatocyte-like cells with an intermediate hepatobiliary and mature/immature phenotype. These cells are likely to represent a resident progenitor population of the adult human liver, even in the absence of hepatic failure. Disclosure of potential conflicts of interest is found at the end of this article.

The effect of graded intake of glycyl-L-tyrosine on phenylalanine and tyrosine metabolism in parenterally fed neonates with an estimation of tyrosine requirement

Although tyrosine is considered indispensable during the neonatal period, its poor solubility has limited its inclusion in parenteral amino acid solutions to less than 1% of total amino acids. Dipeptides of tyrosine are highly soluble, have been shown to be well used and safe in animal models and humans, and, therefore, may be used as an effective means of providing tyrosine in the parenterally fed neonate. The goal of the present study was to determine the tyrosine requirement of the parenterally fed neonate receiving graded intakes of glycyl-L-tyrosine as a source of tyrosine. Thirteen infants receiving adequate energy (340 +/- 38 kJ. kg(-1).d(-1)) and protein (2.4 +/- 0.4 g.kg(-1).d(-1)) were randomized to receive parenteral nutrition with one of five graded levels of glycyl-L-tyrosine. The mean requirement and safe level of intake were estimated using a 1-(13)C-phenylalanine tracer and linear regression cross-over analysis that identified a break point in the response of label appearance in breath CO(2) (F(13)CO(2)) and phenylalanine oxidation to graded tyrosine intake. Based on the mean estimates of whole-body phenylalanine oxidation, the tyrosine mean requirement and safe level of intake were found to be 74 mg.kg(-1). d(-1) and 94 mg.kg(-1).d(-1), respectively. This represents 3.1 and 3.9% of total amino acids, respectively, considerably higher than levels found in present commercially available pediatric amino acid solutions. These data raise concern regarding the adequacy of aromatic amino acid intake in the parenterally fed neonate.

Genotyping of a case of tyrosinaemia type I with normal level of succinylacetone in amniotic fluid

Tyrosinaemia type I is caused by a deficiency of fumarylacetoacetate hydrolase and mainly affects the liver. This disease is characterized by the presence of a high level of succinylacetone. This metabolite has been used for prenatal diagnosis from amniotic fluid samples. One case with a normal level of succinylacetone in amniotic fluid has recently been described (Grenier et al., 1996). Here, we report that this patient is a compound heterozygote for two known mutations: E364X and IVS6-1g-->t. The low level of succinylacetone cannot be explained by these mutations.

Assignment of the human tyrosine aminotransferase gene to chromosome 16

The liver enzyme tyrosine aminotransferase (TAT; EC 2.6.1.5) catalyzes the rate-limiting step in the catabolic pathway of tyrosine. Deficiency in TAT enzyme activity underlies the autosomally inherited disorder tyrosinemia II (Richner-Hanhart syndrome). Using a human TAT cDNA clone as hybridization probe, we have determined the chromosomal location of the TAT structural gene by Southern blot analysis of DNAs from a series of human X rodent somatic cell hybrids. The results assign the TAT gene to human chromosome 16.

The human tyrosine aminotransferase gene mapped to the long arm of chromosome 16 (region 16q22----q24) by somatic cell hybrid analysis and in situ hybridization

Tyrosine aminotransferase (TAT; EC 2.6.1.5) is a liver enzyme involved in amino acid metabolism and gluconeogenesis. Low levels of TAT have been implicated in several inherited disorders, particularly tyrosinemia II (Richner-Hanhart syndrome). We have determined the chromosomal location of the human TAT gene by Southern blot hybridization analysis of DNAs from 18 human X rodent hybrid cell lines, using a rat cDNA probe. The results indicate that the TAT gene maps to chromosome 16. Analysis of two hybrids containing a rearranged chromosome 16 allowed assignment of the TAT locus to 16q22----24. In situ hybridization to human metaphase chromosomes confirmed this regional assignment.

Chemical analysis of succinylacetone and 4-hydroxyphenyllactate in amniotic fluid using selective ion monitoring

A method for the measurement of the concentration of succinylacetone and 4-hydroxyphenyllactic acid in amniotic fluid was developed for the prenatal diagnosis of hereditary tyrosinemia. Succinylacetone was converted to 5-methyl-3-isoxazolepropionic acid and isolated with 4-hydroxyphenyllactic acid by liquid partition chromatography and the trimethylsilyl derivatives quantified by ammonia chemical ionization selected ion monitoring gas chromatography-mass spectrometry with 2-hydroxy-n-caproic acid as the internal standard. The concentration of 4-hydroxyphenyllactic acid in normal amniotic fluid was 1.97 +/- 0.75 (S.D.) mumol/l while succinylacetone was undetectable. A pregnancy at risk for tyrosinemia type II was monitored. The concentration of 4-hydroxyphenyllactic acid was within the normal range and a healthy child was born.

Purification and properties of human liver tyrosine aminotransferase

Tyrosine aminotransferase (EC 2.6.1.5) of human liver was purified 2200-fold by successive chromatography on DEAE-cellulose DE-52, Ultrogel AcA-34, CM-Sephadex C-50 and hydroxyapatite to a specific activity of 64 units/mg of protein. The purified enzyme had a molecular mass of 95 500. The Km-values were 1.04 X 10(-3) mol/l, 0.17 X 10(-3) mol/l and 0.69 X 10(-6) mol/l for tyrosine, 2-oxoglutarate and pyridoxal 5'-phosphate, respectively. In the final purification step the enzyme activity was divided into two major fractions and a minor third one. On isoelectric focusing, three distinct fractions of specific tyrosine aminotransferase activity were obtained. The isoelectric points of these fractions were 4.9, 5.1 and 5.3, respectively. These findings imply that the human tyrosine aminotransferase consists of three subforms. No differences in properties studied could be found between the subforms. The coenzyme, pyridoxal 5'-phosphate, could be removed by dialysis.