Flavin enzymes in liver and kidney of rats from birth to weaning

The contributions of mesoderm-derived cells in liver development

The liver is an indispensable organ for metabolism and drug detoxification. The liver consists of endoderm-derived hepatobiliary lineages and various mesoderm-derived cells, and interacts with the surrounding tissues and organs through the ventral mesentery. Liver development, from hepatic specification to liver maturation, requires close interactions with mesoderm-derived cells, such as mesothelial cells, hepatic stellate cells, mesenchymal cells, liver sinusoidal endothelial cells and hematopoietic cells. These cells affect liver development through precise signaling events and even direct physical contact. Through the use of new techniques, emerging studies have recently led to a deeper understanding of liver development and its related mechanisms, especially the roles of mesodermal cells in liver development. Based on these developments, the current protocols for in vitro hepatocyte-like cell induction and liver-like tissue construction have been optimized and are of great importance for the treatment of liver diseases. Here, we review the roles of mesoderm-derived cells in the processes of liver development, hepatocyte-like cell induction and liver-like tissue construction.

Pharmacokinetics of oral D-serine in D-amino acid oxidase knockout mice

D-Amino acid oxidase (DAAO) catalyzes the oxidative deamination of D-amino acids including D-serine, a full agonist at the glycine modulatory site of the N-methyl-d-aspartate (NMDA) receptor. To evaluate the significance of DAAO-mediated metabolism in the pharmacokinetics of oral D-serine, plasma D-serine levels were measured in both wild-type mice and transgenic mice lacking DAAO. Although D-serine levels were rapidly diminished in wild-type mice (t(½) = 1.2 h), sustained drug levels over the course of 4 h (t(½) > 10 h) were observed in mice lacking DAAO. Coadministration of D-serine with 6-chlorobenzo[d]isoxazol-3-ol (CBIO), a small-molecule DAAO inhibitor, in wild-type mice resulted in the enhancement of plasma D-serine levels, although CBIO seems to have only temporary effects on the plasma D-serine levels due to glucuronidation of the key hydroxyl group. These findings highlight the predominant role of DAAO in the clearance of D-serine from the systemic circulation. Thus, a potent DAAO inhibitor with a longer half-life should be capable of maintaining high plasma D-serine levels over a sustained period of time and might have therapeutic implications for the treatment of schizophrenia.

Involvement of D-amino acid oxidase in elimination of free D-amino acids in mice

The physiological role of D-amino acid oxidase was investigated by using mutant ddY/DAO- mice lacking the enzyme. Free D-amino acid concentrations in the mutant mice were significantly higher than those of control ddY/DAO+ mice in kidney, liver, lung, heart, brain, erythrocytes, serum and urine. The results suggest that the enzyme is involved in the catabolism of free D-amino acids in the body, and that free D-amino acids are also excreted into urine.

D-amino acid oxidase in mouse liver

1. An appreciable amount of D-amino acid oxidase was found in the extract of mouse liver by enzyme-linked immunosorbent assay (ELISA). 2. The content of the enzyme in the kidney and heart extracts was also measured by the assay.

Immunoelectron microscopic localization of D-amino acid oxidase in rat kidney and liver

The intracellular localization of D-amino acid oxidase in rat kidney and liver has been investigated using the indirect immunogold postembedding technique. Different fixation and embedding conditions for optimal preservation of antigenicity and fine structure have been tested. Immunolabelling was possible only in tissues embedded in polar resins (glycol methacrylate and Lowicryl K4M). In kidney the enzyme was demonstrable only in the peroxisomes of the proximal tubule, where it was associated with the peroxisome core. The enzyme was present in all the peroxisomes of the proximal tubule and appeared to be codistributed with catalase. Control experiments and quantitative analysis confirmed the specificity of the D-amino acid oxidase immunolocalization. All the other cells in kidney failed to demonstrate any labelling. In liver, the immunolabelling was present in the matrix of the hepatocyte peroxisomes, whereas no traces of the enzyme were found in the nucleoid. The intensity of the immunolabelling in liver peroxisomes was lower than in kidney. No specific labelling was observed in cells other than hepatocytes.

Comparative and developmental studies on 4-hydroxy-2-oxoglutarate aldolase and hydroxyproline oxidase

1. In rats, liver 4-hydroxy-2-oxoglutarate aldolase and hydroxyproline oxidase activities are maximal in the suckling period. 2. Liver activities for 4-hydroxy-2-oxoglutarate aldolase, alanine-glyoxylate aminotransferase, serine-pyruvate aminotransferase and serine dehydratase, but not hydroxyproline oxidase, are increased in rats on a high-fat, carbohydrate-free diet. 3. It is suggested that 4-hydroxy-2-oxoglutarate may be a significant source of glyoxylate for glycine and hence glucose formation. 4. Mammalian liver hydroxyproline oxidase activity is higher in carnivorous species; necessary, perhaps, to metabolise a relatively large influx of hydroxyproline on a flesh diet.

Postnatal development of peroxisomal and mitochondrial enzymes in rat liver

Subcellular organellles from livers of rats three days prenatal to 50 weeks postnatal were separated on sucrose gradients. The peroxisomes had a constant density of 1.243 g/ml throughout the life of the animal. The density of the mitochondria changed from about 1.236 g/ml at birth to a constant value of 1.200 g/ml after two weeks. The peroxisomal and mitochondrial fatty acid beta-oxidation and the peroxisomal and supernatant activities of catalase and glycerol-3-phosphate dehydrogenase were measured at each age, as well as the peroxisomal core enzyme, urate oxidase, and the mitochondrial matrix enzyme, glutamate dehydrogenase. All of these activities were very low or undetectable before birth. Mitochondrial glutamate dehydrogenase and peroxisomal urate oxidase reached maximal activities per g of liver at two and five weeks of age, respectively. Fatty acid beta-oxidation in both peroxisomes and mitochondria and peroxisomal glycerol-3-phosphate dehydrogenase exhibited maximum activities per g of liver between one and two weeks of age before weaning and then decreased to steady state levels in the adult. Peroxisomal beta-oxidation accounted for at least 10% of the total beta-oxidation activity in the young rat liver, but became 30% of the total in the liver of the adult female and 20% in the adult male due to a decrease in mitochondrial beta-oxidation after two weeks of age. The greatest change in beta-oxidation was in the mitochondrial fraction rather than in the peroxisomes. At two weeks of age, four times as much beta-oxidation activity was in the mitochondria as in the peroxisomal fraction. Peroxisomal glycerol-3-phosphate dehydrogenase activity accounted for 5% to 7% of the total activity in animals younger than one week, but only 1% to 2% in animals older than one week. Up to three weeks of age, 85% to 90% of the liver catalase was recovered in the peroxisomes. The activity of peroxisomal catalase per g of rat liver remained constant after three weeks of age, but the total activity of catalase further increased 2.5- to 3-fold, and all of the increased activity was in the supernatant fraction.

The ontogeny of L-alpha-hydroxyacid oxidase isozymes in the mouse

Mouse liver hydroxyacid oxidase isozymes are present at low levels at birth and increase in activity until day 13 after which HAOX-B almost disappears and HZOS-A is reduced to approximately one half the maximum level in the adultkidney. HAOX-G appears near day 13 post partum and increases until adult levels are reached, the female having four times the activity of the male. The pregnant female has significantly lower levels of HAOX-A and HAOX-B in the liver and higher activity of HAOX-B in the kidney. Developmental changes occur in the extent of epigenetic modification of mouse liver HAOX-A during the early neonatal period.

The influence of postnatal development on drug-induced hepatic porphyria and the synthesis of cytochrome P-450. A biochemical and morphological study

The mitochondrial enzyme delta-aminolevulinate synthetase (ALAS) controls the rate-limiting step in the synthesis of porphyrins and heme. An experimental form of hepatic porphyria can be readily elicited in laboratory animals, such as the rat, by drugs and foreign chemicals which are known to enhance the de novo formation of this enzyme in the liver. The present study shows that there is a striking refractoriness to the induction of ALAS during the perinatal period in the rat. Chemicals which have potent porphyria-inducing activity in adult animals have no significant inducing effect on hepatic ALAS in neonates. The ultrastructural changes which accompany the induction of ALAS by drugs and chemicals in adult liver also fail to take place in the livers of neonates. A progressive capacity for responding to the action of chemical inducers of hepatic ALAS does, however, develop in neonatal animals so that by approximately 5-6 wk of age experimental porphyria can be elicited as effectively in them as in adults. The reasons for the refractoriness of hepatic ALAS to induction in the perinatal period are not known; but the findings of this study make it clear that ALAS belongs to that increasingly large group of liver enzymes in mammals whose appearance, increase of activity, or inducibility is developmentally determined. The occurrence of developmental changes in the indicibility of ALAS in the liver of neonates also provided an opportunity to study the relationship of this enzyme activity to the drug-mediated induction of the hepatic hemoprotein cytochrome P-450. This inducible hemoprotein serves as the terminal oxygenase in the microsomal mixed-function oxidase system in the liver. The results of this study indicate that, in contrast to the refractoriness of ALAS to induction, significant drug-induced changes of hepatic P-450 content and of hemeprecursor incorporation into this cytochrome do take place in neonates. The synthesis of P-450 thus appears to be under a regulatory control different from that of ALAS in neonates, and the relation between ALAS activity and P-450 formation is not therefore a direct one.