Diphosphate Glucuronyltransferase Research Articles

Crigler–Najjar syndrome: therapeutic options and consequences of mutations in the UGT1A1 complex

Crigler–Najjar syndrome (CN), a rare inherited disorder characterized by failure of bilirubin glucuronidation, can lead to severe disability and death from kernicterus. Gilbert syndrome is a more common, benign familial unconjugated hyperbilirubinemia. The underlying problem in both conditions is impaired bilirubin conjugation and elimination due to a mutation in uridine 5’-diphosphate glucuronyltransferase. The mainstay of current management of CN is phototherapy, followed by liver transplantation. Here, we review other therapies, including hepatocyte transplantation, that have been successfully used to lessen the phenotype, although long-term engraftment of cells remains elusive. Gene therapy holds hope for the future whereby the patient’s hepatocytes are transduced with the wild-type gene. Outstanding issues include safety of the gene vector and establishing immunotolerance to both vector and the new protein. The significant advances in understanding the relevance of mutations in UGT not only in glucuronidation of bilirubin, but other drugs and substances, are also reviewed.

Correction of biotransformation of xenobiotics by α-tocopherol in combination with nicotinamide and methionine in the liver damaged by ultrasound

Six day after rat liver sonication, the content of cytochrome P-450, rate of NADPH oxidation, activity of NADPH—cytochrome P-450 reductase, and rate of aniline hydroxylation in the microsomal fraction decrease. After 12 days, the rate of ethylmorphine N-demethylation also decreases. Intragastral administration of methionine, nicotinamide, and vitamin E for 6 and 12 days activates these enzymes and uridine 5′-diphosphate glucuronyl transferase.

Determination by HPLC of the UDP-Glucuronyl Transferase Activity For 7-Hydroxycoumarin in Rabbit Tissue Samples

HPLC was used to determine the uridine diphosphate (UDP) glucuronyl transferase activity in rabbit tissues. The crude tissue samples prepared were from the liver, kidney, bladder, large intestine, lung, spleen, heart and fat. A metabolic reaction mixture was prepared that included the rabbit tissue sample, 7-hydroxycoumarin and UDP-glucuronic acid (UDPGA). The method was used to determine the level of production of 7-hydroxycoumarin-glucuronide from 7-hydroxycoumarin. Seperation of the analyte was carried out under gradient elution by reverse phase chromatography on a C18 column, with UV detection at 320 nm. It was possible to determine 7-hydroxycoumarin-glucuronide (7-OHCG) produced over time as well as the decrease in 7-hydroxycoumarin concentration as the reaction progressed. The rate of the reaction was calculated from a plot of the concentration of 7-OHCG produced versus time for each organ, and the rate calculated from the slope of the linear part of the curve. The liver showed the highest activity with a rate of production of 7-OHCG of 2.3 nmol per min per milligram of protein. The kidney showed an activity of 0.22 nmol of 7-OHCG produced per minute per milligram of protein, with the bladder and large intestine showing activities of 0.14 nmol and 7.8 pmol of 7-OHCG produced per minute per milligram of protein. The method used required minimal sample clean up and was reliable and accurate.

The effects of high dietary concentrations of sodium saccharin on in vivo metabolism of xenobiotics in rats

The effect of feeding a diet containing 7.5% sodium saccharin on the conjugation of [ 14C]phenol has been studied during neonatal development in male and female rats using a two-generation protocol. Decreased formation of phenol sulphate was observed in the F 1 saccharin-treated rats from 4 wk of age and this was compensated for by an increase in the formation of quinol glucuronide. This shift in the conjugation pattern of [ 14C]phenol, with an increase in oxidation, was not sex specific. The daily excretion of indican was significantly increased from 5 wk of age. Feeding a diet containing 7.5% sodium saccharin did not affect in vitro activities of the enzymes involved in the conjugation reactions, that is, aryl sulphotransferase and uridine-5′-diphosphate glucuronyltransferase. The incorporation of 5% cysteine into the diet of saccharin-treated rats for 1 wk prevented the change in conjugation of [ 14C]phenol observed in the saccharin-treated animals. Absorption of sodium [ 35S]sulphate from the gastro-intestinal tract was not appreciably affected by a high dietary concentration of sodium saccharin. A high dietary concentration of saccharin affected the conjugation of 3-hydroxyanthranilic acid during neonatal development, possibly as a result of sulphate depletion.

Lipid peroxidation of rat-liver microsomes. Its effect on the microsomal membrane and some membrane-bound microsomal enzymes.

Rat liver microsomes were peroxidized in vitro and chemical, physical and morphological changes in the membrane were related to the effects on certain membrane‐bound microsomal enzymes.With increasing peroxidation, microsomal phospholipids revealed decreasing concentrations of 20:4 and 22:6 fatty acids. At a high level of peroxidation, where alterations in permeability and ultrastructural changes such as breakage and deformation of microsomal vesicles were apparent, there was also a decrease in the concentration of 18:2 fatty acids.Glucose‐6‐phosphatase, cytochrome P‐450 and uridine‐5′‐diphosphate glucuronyltransferase (UDP glucuronyltransferase) (three microsomal enzymes known to be highly dependent on the integrity of the membrane for their function) responded differently to lipid peroxidation. Glucose‐6‐phosphatase showed an initial decrease in activity as well as in Km for glucose 6‐phosphate, followed by a restoration to control values at an intermediate level of lipid peroxidation. At a high level of peroxidation, both kinetic parameters were again markedly decreased. Cytochrome P‐450 concentration, on the other hand, revealed a continuous decrease with proceeding lipid peroxidation, which was only partly accounted for by a conversion to cytochrome P‐420. The loss of cytochrome P‐450 was paralleled by decreased rates of aminopyrine demethylation and 3,4‐benzpyrene hydroxylation. Glucuronyltransferase activity, finally, was activated at low, but again normalized at high, levels of lipid peroxidation.It thus seems that although electron‐microscopically observable changes in the microsomal membrane occurs only late in lipid peroxidation, chemical, physical and enzyme alterations are early phenomena during this process. The continuous loss of cytochrome P‐450 and the final decrease in glucose‐6‐phosphatase late during peroxidation probably reflect damage to membrane lipids of vital importance for the integrity and function of these enzymes whereas the activation of UDP glucuronyltransferase early during peroxidation most likely can be ascribed to increased membrane permeability.