The plasma amino acid profile and its relationships to standard quantities of liver function in infants and children with extrahepatic biliary atresia and preterminal liver cirrhosis

Infants with biliary atresia exhibit an altered amino acid profile in their newborn screening

INTRODUCTION

Biliary atresia (BA) is a rare progressive neonatal cholangiopathy with unknown pathophysiology and time of onset. Newborn Screening (NBS) in Germany is routinely performed in the first days of life to identify rare congenital diseases utilizing dried blood spot (DBS) card analyses. Infants with biliary atresia (BA) are known to have altered amino acid profiles (AAP) at the time point of diagnosis, but it is unclear whether these alterations are present at the time point of NBS.

OBJECTIVES

We aimed to analyze amino acid profiles in NBS-DBS of infants with Biliary Atresia.

METHODS

Original NBS-DBS cards of 41 infants who were later on diagnosed with BA were retrospectively obtained. NBS-DBS cards from healthy newborns (n = 40) served as controls. In some BA infants (n = 14) a second DBS card was obtained at time of Kasai surgery. AAP in DBS cards were analyzed by targeted metabolomics.

RESULTS

DBS metabolomics in the NBS of at that time point seemingly healthy infants later diagnosed with BA revealed significantly higher levels of Methionine (14.6 ± 8.6 μmol/l), Histidine (23.5 ± 50.3 μmol/l), Threonine (123.9 ± 72.8 μmol/l) and Arginine (14.1 ± 11.8 μmol/l) compared to healthy controls (Met: 8.1 ± 2.6 μmol/l, His: 18.6 ± 10.1 μmol/l, Thr: 98.1 ± 34.3 μmol/l, Arg: 9.3 ± 6.6 μmol/l). Methionine, Arginine and Histidine showed a further increase at time point of Kasai procedure. No correlation between amino acid levels and clinical course was observed.

CONCLUSION

Our data demonstrate that BA patients exhibit an altered AAP within 72 h after birth, long before the infants become symptomatic. This supports the theory of a prenatal onset of the disease and, thus, the possibility of developing a sensitive and specific NBS. Methionine might be particularly relevant due to its involvement in glutathione metabolism. Further investigation of AAP in BA may help in understanding the underlying pathophysiology.

Branched-chain amino acids inhibit the TGF-beta-induced down-regulation of taurine biosynthetic enzyme cysteine dioxygenase in HepG2 cells

Taurine deficiency has been suggested to contribute to the pathogenesis and complications of advanced hepatic diseases. The molecular basis for a low level of taurine associated with hepatic failure is largely unknown. Using carbon tetrachloride (CCl₄)-induced cirrhotic rat model, we found that the activity and expression of cysteine dioxygenase (CDO), a rate-limiting enzyme in taurine synthesis, were significantly decreased in the liver of these rats. To investigate the underlying mechanisms for the suppression, we examined the effects of pathological cytokines on CDO expression in human hepatoma HepG2 cells. Among the several cytokines, transforming growth factor-β (TGF-β), one of the key mediators of fibrogenesis, suppressed Cdo1 gene transcription through the MEK/ERK pathway. Finally, we further examined potential effects of branched-chain amino acids (BCAA) on CDO expression, as it has been reported that oral BCAA supplementation increased plasma taurine level in the patients with liver cirrhosis. BCAA, especially leucine, promoted Cdo1 gene transcription, and attenuated TGF-β-mediated suppression of Cdo1 gene expression. These results indicate that the low plasma level of taurine in advanced hepatic disease is due to decreased hepatic CDO expression, which can be partly attributed to suppressive effect of TGF-β on Cdo1 gene transcription. Furthermore, our observation that BCAA promotes Cdo1 expression suggests that BCAA may be therapeutically useful to improve hepatic taurine metabolism and further suppress dysfunctions associated with low level of taurine in hepatic diseases.

Identification of the plasma metabolomics as early diagnostic markers between biliary atresia and neonatal hepatitis syndrome

Early detection is the most effective way to improve the clinical outcome of biliary atresia (BA). Emerging metabolomics provides a powerful platform for discovering novel biomarkers and biochemical pathways to improve early diagnosis. The aim of this study is to find the potential biomarkers to distinguish BA from neonatal hepatitis syndrome (NHS) by using a metabolomics method. We comprehensively analyzed the serum metabolites in a total of 124 blood samples from patients with BA or neonatal hepatitis syndrome (NHS) and from normal individuals using advanced metabolomic approaches, and found that the levels of glutarylcarnitine (C5DC) significantly increased in the BA group while the levels of threonine (Thr) significantly rose in the NHS group comparing with the other groups. The levels of glutamic acid (Glu) in the BA group were significantly elevated compared to those in the NHS group, but still lower than the hyperbilirubinemia and normal controls. The levels of propionyl carnitine (C3), isovaleryl carnitine (C5) and glutamine (Gln) were reduced in the BA group compared to those in the NHS group, but still higher than the hyperbilirubinemia and normal controls. This study demonstrates the possibility of metabolomics as non-invasive biomarkers for the early detection of BA and also provides new insight into pathophysiologic mechanisms for BA.

Mechanism of liver tyrosine aminotransferase increase in ethanol-treated mice and its effect on serum tyrosine level

Liver tyrosine aminotransferase (TAT) activity is known to increase with ethanol treatment; however, the mechanism of this increase is unclear. Upon investigation we found that TAT activity and mRNA levels started to increase 2 h after ethanol administration and continued to increase until 6 h after ethanol administration. The increase in ethanol-induced TAT activity could not be explained by calorie loading after fasting, since ethanol loading increased TAT expression, while glucose loading decreased TAT expression. In addition, liver TAT activity was not related to serum tyrosine levels. TAT activity increased when an adenosine A2 agonist, 5'-N-ethylcarboxamide adenosine, was given. Since TAT activity is increased by cAMP, and ethanol increases cAMP production via an adenosine receptor-dependent mechanism, this increase in ethanol-induced TAT activity may occur via an adenosine receptor-dependent mechanism.