Metabolism of d-glucuronolactone in mammalian systems. 2. Conversion of d-glucuronolactone into d-glucaric acid by tissue preparations

Cell-based and cell-free biocatalysis for the production of D-glucaric acid

D-Glucaric acid (GA) is a value-added chemical produced from biomass, and has potential applications as a versatile platform chemical, food additive, metal sequestering agent, and therapeutic agent. Marketed GA is currently produced chemically, but increasing demand is driving the search for eco-friendlier and more efficient production approaches. Cell-based production of GA represents an alternative strategy for GA production. A series of synthetic pathways for GA have been ported into Escherichia coli, Saccharomyces cerevisiae and Pichia pastoris, respectively, and these engineered cells show the ability to synthesize GA de novo. Optimization of the GA metabolic pathways in host cells has leapt forward, and the titer and yield have increased rapidly. Meanwhile, cell-free multi-enzyme catalysis, in which the desired pathway is constructed in vitro from enzymes and cofactors involved in GA biosynthesis, has also realized efficient GA bioconversion. This review presents an overview of studies of the development of cell-based GA production, followed by a brief discussion of potential applications of biosensors that respond to GA in these biosynthesis routes.

Hydrogen-stimulated carbon acquisition and conservation in Salmonella enterica serovar Typhimurium

Salmonella enterica serovar Typhimurium can utilize molecular hydrogen for growth and amino acid transport during anaerobic growth. Via microarray we identified H(2) gas-affected gene expression changes in Salmonella. The addition of H(2) caused altered expression of 597 genes, of which 176 genes were upregulated and 421 were downregulated. The significantly H(2)-upregulated genes include those that encode proteins involved in the transport of iron, manganese, amino acids, nucleosides, and sugars. Genes encoding isocitrate lyase (aceA) and malate synthase (aceB), both involved in the carbon conserving glyoxylate pathway, and genes encoding the enzymes of the d-glucarate and d-glycerate pathways (gudT, gudD, garR, garL, garK) are significantly upregulated by H(2). Cells grown with H(2) showed markedly increased AceA enzyme activity compared to cells without H(2). Mutant strains with deletion of either aceA or aceB had reduced H(2)-dependent growth rates. Genes encoding the glutamine-specific transporters (glnH, glnP, glnQ) were upregulated by H(2), and cells grown with H(2) showed increased [(14)C]glutamine uptake. Similarly, the mannose uptake system genes (manX, manY) were upregulated by H(2,) and cells grown with H(2) showed about 2.0-fold-increased [(14)C]d-mannose uptake compared to the cells grown without H(2). Hydrogen stimulates the expression of genes involved in nutrient and carbon acquisition and carbon-conserving pathways, linking carbon and energy metabolism to sustain H(2)-dependent growth.

Protective effects of D-glucaro-1,4-lactone against oxidative modifications in blood platelets

BACKGROUND AND AIM

Peroxynitrite (ONOO-), a highly reactive species, modulates platelet activation and function. Modifications of platelet proteins induced by ONOO- may be an important factor in the pathogenesis of platelet-related diseases. The defence mechanisms against ONOO- are therefore crucial for normal cellular function. Recently, there has been an increased interest in the screening of natural products present in the diet and herbals for possible antioxidative agents (ONOO( scavengers). D-glucaro-1,4-lactone (1,4-GL), formed from D-glucaric acid (GA), a natural compound found in fruits and vegetables, possesses detoxifying and anticancerogenic properties. However, the effect of this compound on platelet activation is unknown.

METHODS AND RESULTS

We investigated the effects of 1,4-GL on nitrative and oxidative alteration of platelet proteins and lipid peroxidation caused by two strong oxidants: ONOO- and hydroperoxide (H2O2). The action of 1,4-GL on platelet aggregation induced by adenosine diphosphate (ADP) was also studied. Exposure of platelets to ONOO- or H2O2 resulted in an increase in the level of carbonyl groups (approximately three-fold and two-fold, respectively). In the presence of 1,4-GL, a significant decrease (about 50% for the highest concentration of 1,4-GL) in carbonyl group formation was observed; however the level of nitrotyrosine residues in platelets treated with ONOO- remained unchanged.

CONCLUSIONS

We demonstrated an inhibitory effect of 1,4-GL on lipid peroxidation in platelets treated with ONOO- (0.1mM) or H2O2 (2mM). 1,4-GL inhibited platelet lipid peroxidation by about 40%. In the presence of 1,4-GL, peroxidation of plasma lipids was also reduced by about 40%. These results demonstrate that 1,4-GL possesses antioxidative properties and reduces the activation of blood platelets.

Protective effects of D-glucaro 1,4-lactone against oxidative/nitrative modifications of plasma proteins

OBJECTIVE

The protective effects of D-glucaro 1,4-lactone (1,4-GL) against oxidative/nitrative protein damage (determined by parameters such as levels of protein carbonyl groups and nitrotyrosine residues) to human plasma treated with peroxynitrite (ONOO-) or hydroperoxide (H2O2) were studied in vitro. We also investigated the effects of 1,4-GL on the level of total free thiol groups and low-molecular-weight thiols (glutathione and homocysteine) in plasma treated with ONOO- (0.1 mM).

METHODS

Levels of carbonyl groups and nitrotyrosine residues in human plasma proteins were measured by ELISA and a competition ELISA, respectively. High-performance liquid chromatography (HPLC) was used to analyze free thiols from plasma.

RESULTS

Exposure of plasma to ONOO- (0.1 mM) resulted in an increase of the level of carbonyl groups and nitrotyrosine residues in plasma proteins and in a distinct decrease in total thiols and low-molecular-weight thiols (glutathione and homocysteine) measured by high-performance liquid chromatography. In the presence of 1,4-GL (0.4-6.4 mM), a distinct decrease in carbonyl group formation and tyrosine nitration in plasma proteins and changes in plasma thiols caused by 0.1 mM of peroxynitrite were observed. Moreover, 1,4-GL inhibited plasma protein oxidation induced by H2O2 (2 mM).

CONCLUSION

The obtained results indicate that in vitro 1,4-GL has inhibitory effects on ONOO-- or hydroperoxide-mediated oxidative stress in human plasma and changes plasma redox thiol status. The mechanism of the antioxidative action of 1,4-GL present in plasma is not known yet.

Studies on the biochemical effects of the aldose reductase inhibitor 2,7-difluorospirofluorene-9,5'-imidazolidine-2',4'-dione (Al 1576, HOE 843). Detection of D-glucaric and D-glucuronic acid excretion by high resolution 1H and 13C NMR spectroscopy

The effects of two aldose reductase inhibitors on the biochemical composition of rat urine were investigated using high resolution 1H and 13C NMR spectroscopy. We report the elevated excretion of D-glucaric acid (DGA) and D-glucuronic acid (GCA) following treatment with 2,7-difluorospirofluorene-9,5'-imidazolidine-2'4'-dione (Imirestat, IM, Al 1576, HOE 843) at 50 mg/kg/day for 1 month, but not with 3-4-bromo-2-fluorobenzyl-4-oxo-3-phthalazine-1-ylacetic acid (Ponalrestat, Statil), dosed at 50 mg/kg/day for 2 weeks. Sugar aciduria was also detected following treatment with the cytochrome P450 inducer phenobarbitone (PB) at 45 mg/kg/day for 1 month, although the qualitative and quantitative pattern of excretion of sugar acids differed greatly between the IM and PB treatment groups. The levels of GCA excreted are elevated 11-fold by IM treatment from 19.0 to 210.0 mumol/24 hr, but only 2.5-fold by PB, from 9.7 to 23.9 mumol/24 hr. DGA was not detectable in control urine, although levels did increase by 30% during the study from 7.5 to 10.9 mumol/24 hr, between day 8 and day 29, with IM treatment, and by 60% from 1.7 to 4.9 mumol/24 hr following PB administration for the same time period. This predominant elevation of DGA and GCA caused by IM treatment far exceeds previous records. In contrast, PB treatment resulted in an increase in intensity of a number of partially resolved sugar resonances, but at a much lower level than resulted from IM treatment. A raised level of DGA and GCA is usually associated with hepatic P450 induction; however, we report here profound DGA and GCA uria as a result of the inhibition of the aldehyde reductase, hexonate dehydrogenase (EC 1.1.1.19, EC 1.1.1.20). This mechanism is not closely linked to P450 induction, corroborating the current view that elevated excretion of DGA is not a reliable indicator of hepatic enzyme induction. This study further demonstrates the use of high resolution NMR spectroscopy in the detection of a novel biochemical effect which may go unnoticed during routine clinical chemistry tests.

Effect of calcium glucarate on beta-glucuronidase activity and glucarate content of certain vegetables and fruits

Glucarate is normally present in tissues and body fluids and is in equilibrium with D-glucaro-1,4-lactone, a natural inhibitor of beta-glucuronidase activity. Dietary calcium glucarate, a sustained-release from of glucarate, elevates the blood level of D-glucaro-1,4-lactone which suppresses blood and tissue beta-glucuronidase activity. A single dose of CaG (4.5 mmole/kg body weight) inhibited beta-glucuronidase activity in serum and liver, lung, and intestinal microsomes by 57, 44, 37, and 39%, respectively. A chronic administration of calcium glucarate (4% in diet) also decreased beta-glucuronidase activity in intestinal and liver microsomes. Maximal inhibition of beta-glucuronidase activity in serum was observed from 12 noon to 2:00 PM. In contrast, maximum inhibition of beta-glucuronidase activity in intestinal and liver microsomes occurred during mornings, although a secondary depression in intestinal microsomes also occurred around 4 PM. A 4% calcium glucarate supplemented diet also inhibited beta-glucuronidase activity by 70% and 54%, of the bacterial flora obtained from proximal (small intestine) and distal (colon) segments of intestine, respectively. Due to the potential effect of dietary glucarate on net glucuronidation and on other metabolic pathways, glucaric acid levels in various foods were determined. The glucaric acid content varied from a low of 1.12-1.73 mg/100 g for broccoli and potatoes to a high of 4.53 mg/100 g for oranges.

Biosynthesis of D-glucaric acid in mammals: a free-radical mechanism?

In the presence of iron salts and hydrogen peroxide, D-glucuronic acid was converted into D-glucaric acid. The reaction was strongly inhibited by free-radical scavengers and is ascribed to the action of the hydroxyl radical. The formation of D-glucarate was dependent upon pH and occurred in the presence of some iron-complexing agents. The first product of oxidation was a lactone that was a strong inhibitor of beta-D-glucuronidase and assumed to be D-glucaro-1,5-lactone. Microsomal preparations in the presence of NADPH also produced D-glucarate from D-glucuronic acid, presumably due to formation of hydrogen peroxide, and the product was an inhibitor of beta-D-glucuronidase. Superoxide did not produce D-glucarate from D-glucuronate. The cytochrome P450 system is more likely than "glucuronolactone dehydrogenase" to be responsible for the production of D-glucaric acid in vivo.

Biochemical and morphological effects of long-term inhalation exposure of rats to ethylbenzene

Male Wistar rats were exposed (six hours/day, five days/week) to 0, 50, 300 or 600 p.p.m. of ethylbenzene vapour in the air, and killed after 2, 5, 9 or 16 weeks of exposure. After 600 p.p.m., liver-microsomal protein but not cytochrome P-450 concn. was slightly increased; NADPH-cytochrome c reductase was increased maximally by 30% (1.3-fold), 7-ethoxycoumarin O-deethylase (1.8-fold) and UDPG-transferase (2.3-fold). The increase in liver-cytosolic D-glucuronolactone dehydrogenase paralleled the glucuronidation activity (less than or equal to 2-fold). In the kidneys, only 7-ethoxycoumarin O-deethylase (less than or equal to 3.5-fold) and UDPG-transferase (less than or equal to 1.8-fold) showed dose-related increases. Ethylbenzene exposure did not deplete hepatic glutathione (GSH); kidney GSH was slightly increased (less than or equal to 1.3-fold) according to dose. Urine excretion of thioethers was increased with dose, and at 600 p.p.m. was eight times control levels. At 600 p.p.m. there was no increase in serum alanine aminotransferase activity, and liver cells showed slight proliferation of smooth endoplasmic reticulum, slight degranulation and splitting of rough endoplasmic reticulum and enlarged mitochondria, but no necrosis.

Separation of oestrogens in biological fluids and synthetic mixtures on Sephadex G-type gels

The separations achieved when mixtures of both free and conjugated oestrogens from a variety of sources are chromatographed on columns of Sephadex gel are reviewed. The molecular identities of oestrogen conjugates which have been separated from human urine by these methods are listed in Table 1. Tables 2 and 3 contain the key experimental details for a total of 26 separations of oestrogen mixtures, abstracted from the total of 20 papers which were published during the period 1961-82. Table 4 details corresponding experimental data for the separation of free oestriol (in human blood) achieved by methods involving a combined Sephadex gel and immunochemical procedure abstracted from a further two papers. A careful analysis of the separation data given in the tables leads to the initial conclusion that the elution profile depends on the expected chromatographic variables for gel filtration chromatography, namely, type of Sephadex gel, length of column, nature and amount of sample applied and the sensitivity of detection methods. However, the separation achieved by the Sephadex columns is also shown to be critically dependent on the column temperature and the pH and chemical composition of the eluent and wash solvents. These latter effects, together with the realization that the molecular weights of the oestrogens being separated are very similar, leads to the conclusion that the separations summarized in Tables 2 and 3 are all being achieved by an absorption process. This being the case, it is suggested that the time-consuming methods of gel filtration chromatography need not be used. Confirmation of this proposal is afforded by a discussion of a recent paper in which the rapid separation of the oestrogens from other components in the biological matrix (urine) was achieved by an adsorption procedure. It is suggested that in the future, separations of oestrogens in biological materials may be most rapidly achieved in combining this type of adsorption procedure with HPLC.

The excretion of metabolites of the D-glucuronic acid pathway in human urine. Effect of phenobarbitone administration

1. The urinary excretion of four metabolites of the D-glucuronic acid pathway, namely D-glucaric acid, free (unconjugated) D-glucuronic acid, L-gulonic acid and xylitol, has been studied in normal male volunteers and in male and female epileptic patients receiving phenobarbitone anticonvulsant therapy. 2. In normal male subjects the urinary excretion of the D-glucuronic acid metabolites, expressed per unit of creatinine, was similar in first void and total (24 h) urine samples and was fairly constant over a period of 4 weeks. 3. In male and female epileptic patients phenobarbitone treatment enhanced the urinary excretion of D-glucaric acid and xylitol and the combined excretion of D-glucaric acid, l-gulonic acid and xylitol. 4. It is suggested that the measurement of a spectrum of urinary D-glucuronic acid metabolites may provide a more reliable index for assessment of the induction of hepatic xenobiotic-metabolizing enzyme activities in man than the determination of urinary D-glucaric acid alone.

Failure of rifampin to induce the metabolism of clonidine in normal volunteers

Patients receiving rifampin and methadone often incur withdrawal symptoms related to an increased rate of metabolism of methadone induced by rifampin. In order to test the hypothesis that clonidine metabolism is similarly altered by rifampin, six normal volunteers received clonidine 0.2 mg bid for four days and clonidine concentration was assayed by a RIA procedure. Beginning on day 5, rifampin 600 mg q12h was added to the clonidine regimen. Both drugs were taken for a total of seven days. On the last day of the study, blood was again sampled for clonidine. On days 4 and 12, urine was collected for d-glucaric acid. The results demonstrate that there is no change in the elimination kinetics of clonidine before and during rifampin administration. However, there was an increase in UDGA following the rifampin dosing. It is concluded that patients receiving rifampin can also receive clonidine for treatment of narcotic withdrawal.

Investigation of accelerated metabolic function in small for gestational age infants

Small for gestational age (SGA) infants are known to develop relatively mild transient hyperbilirubinaemia, especially in comparison with premature infants. This may be interpreted as an index of accelerated maturation of particular vital functions. In the present study 12 SGA infants, 12 appropriate for gestational age (AGA) infants, and 12 premature infants had 24 h urine collections under standardized conditions on the third day of life. Urinary excretion of D-glucaric acid and creatinine, which can be increased by drugs (e.g. phenobarbital), were estimated. Haematocrit and bilirubin were determined at the age of 72h. In the 3 groups, the SGA infants had the highest mean haematocrit (SGA = 0.58, AGA = 0.5, Prem = 0.561/1) and the lowest mean bilirubin (SGA = 6.3, AGA = 8.6, Prem = 11.1 mg/dl). Despite a comparatively small urine volume (SGA = 19.6, AGA = 28.3, Prem = 37.3 ml/kg), excretion of D-glucaric acid (SGA = 0.18, AGA = 0.11, Prem = 0.06 mumol/kg) and creatinine (SGA = 101.6, AGA = 79.6, Prem = 80.2 mumol/kg) was significantly higher in the SGA infants. While the results do not provide conclusive evidence, the increased excretion of glucaric acid and creatinine associated with mild transient hyperbilirubinaemia can be considered an indicator of metabolic differences in SGA infants.

Modifications of drug metabolism by disulfiram and diethyldithiocarbamate. II. D-Glucuronic acid pathway

Hepatic enzymes connected with the formation and metabolism of free D-glucuronic acid were affected in rats after treatment with disulfiram or diethyldithiocarbamate (300 mg/kg, intragastrically, per day, 4 X). The activities of UDPglucose dehydrogenase, UDPglucuronic acid pyrophosphatase, UDPglucuronosyltransferase and L-gulonate dehydrogenase were enhanced, while those of glucose-6-phosphate dehydrogenase, beta-glucuronidase and D-glucuronolactone dehydrogenase were inhibited. These changes were more pronounced with disulfiram than diethyldithiocarbamate. Treatment with phenobarbital (80 mg/kg, i.p., per day, 4 X) enhanced UDP glucuronosyl-transferase, but brought about different effects on the other enzymes. Concurrent administration of phenobarbital with disulfiram or diethyldithiocarbamate led to potentiation or antagonism of the primary effects of each compound when given alone. The results suggest that activation of the D-glucuronic acid pathway may proceed in various ways, and that it is not necessarily followed by a simultaneous induction of the microsomal mixed-function oxygenase activity.

Uronic acid dehydrogenase from Pseudomonas syringae. Purification and properties

1. Uronic acid dehydrogenase was purified to homogeneity. After a 338-fold purification a yield of 16% was achieved with a specific activity of 81 mumol NADH formed min-1 mg protein-1. 2. The purity of the enzyme was controlled by disc electrophoresis, sodium dodecylsulfate electrophoresis and ultracentrifugation. 3. A molecular weight of 60 000 was determined by gel chromatography and by ultracentrifugation. 4. The native enzyme is composed of two subunits, their molecular weight being 30 000 as estimated by sodium dodecylsulfate electrophoresis. The subunits as such are inactive. 5. The absorption spectrum with a maximum at 278 nm shows no evidence for a prosthetic group. 6. For catalytic activity no SH groups and no metals seem to be necessary. 7. The Michaelis constants determined with the pure enzyme are for glucuronic acid Km = 0.37 mM, galacturonic acid Km = 54 muM and NAD+ (with glucuronic acid) Km = 80 muM. 8. A weak reverse reaction could be observed with glucaric acid lactones at acidic pH. 9. NADH is competitive with NAD+. The inhibitor constant is Ki = 60 muM. 10. The NAD+ binding site seems to be of lower specificity than the uronic acid binding site.

D-glucaric acid and galactaric acid catabolism by Agrobacterium tumefaciens

Cell-free extract (crude extract) of Agrobacterium tumefaciens grown on d-glucuronate or d-glucarate converts d-glucarate and galactarate to a mixture of 2-keto-3-deoxy- and 4-deoxy-5-keto-d-glucarate. These compounds are then converted by partially purified crude extract to an intermediate tentatively identified as 2,5-diketoadipate. The same enzyme preparation further decarboxylates this intermediate to alpha-ketoglutarate semialdehyde, which is subsequently oxidized in a nicotinamide adenine dinucleotide-dependent reaction to alpha-ketoglutaric acid. Since A. tumefaciens converts d-glucuronic acid to d-glucarate, a pathway from d-glucuronate to alpha-ketoglutarate in A. tumefaciens was determined.

Metabolism of D-glucuronolactone in mammalian systems. Inhibitory properties of the products of D-glucuronolactone-dehydrogenase action

1. d-Glucuronolactone was converted into d-glucaro-(1-->4)-lactone, a beta-glucuronidase inhibitor, probably via the intermediate d-glucaro-(1-->4)-(6-->3)-dilactone, by a dehydrogenase in human-liver extracts. 2. Similar experiments with mouse-liver extracts appeared to yield only d-glucaric acid or a non-inhibitory lactone. 3. A strong beta-glucuronidase inhibitor was present in mouse liver after the intraperitoneal administration of d-glucuronolactone. 4. d-Glucarodilactone decomposed spontaneously in aqueous solution to give 25% of d-glucaro-(1-->4)-lactone; the percentage conversion was unaffected by human-liver homogenates. but considerably increased by mouse-liver or pig-liver fractions.