Responses of the D-glucuronic acid pathway in rat tissues to treatment with tetrachlorodibenzodioxin

1H-Nuclear magnetic resonance pattern recognition studies withN-phenylanthranilic acid in the rat: time- and dose-related metabolic effects

N-Phenylanthranilic acid (NPAA) causes renal papillary necrosis (RPN) in the rat following repeated oral dosing. Non-invasive early detection of RPN is difficult, but a number of potential biomarkers have been investigated, including phospholipid and uronic acid excretion. This study used 1H-nuclear magnetic resonance (NMR) spectroscopic analysis of urine to investigate urinary metabolic perturbations occurring in the rat following exposure to NPAA. Male Alderley Park rats received NPAA (300, 500 or 700 mg kg(-1) day(-1) orally) for 7 days, and urine was collected on days 7-8, 14-15, 21-22 and 28-29. In a separate study, urine was collected on days 1-2, 3-4, 5-6 and 7-8 from rats receiving 500 mg kg(-1) day(-1). Samples were analysed by 1H NMR spectroscopy combined with multivariate data analysis and clinical chemistry. Histopathology and clinical chemistry analysis of terminal blood samples was carried out following termination on days 4, 6, 8 and 29 (4 week time course) and days 2, 4, 6 and 8 (8 day study). Urine analysis revealed a marked, though variable, excretion of beta-hydroxybutyrate, acetoacetate and acetone (ketone bodies) seen on days 3-4, 5-6 and 7-8 of the study. It is postulated that the ketonuria might be secondary to an alteration in fatty acid metabolism due to inhibition of prostaglandin synthesis. In addition, an elevation in urinary ascorbate was observed during the first 8 days of the study. Ascorbate is considered to be a biomarker of hepatic response, probably reflecting an increased hepatic activity due to glucuronidation of NPAA.

Urinary ascorbic acid--HPLC determination and application as a noninvasive biomarker of hepatic response

A high-performance liquid chromatograph (HPLC) procedure has been developed for the determination of rat urinary ascorbic acid, a major metabolite of the hepatic glucuronic acid pathway. The presence of EDTA and HCl effectively inhibited degradation of ascorbic acid during the collection of urine specimens. The reliability of the procedure was demonstrated by its high recovery (90%), specificity (characteristic absorption maximum and discrimination from isoascorbic acid), and reproducibility (2-3% coefficient of variation). The usefulness of this assay as an indicator of hepatic response was demonstrated in preliminary experiments where increases in urinary ascorbic acid excretion were detected in male rats treated with PCB 126 (3,3',4,4',5-pentachlorobiphenyl) or PCB 105 (2,3,3',4,4'-pentachlorobiphenyl). The HPLC measurement also showed that the two PCB congeners differed markedly in their potency in stimulating urinary ascorbic acid excretion. For example, 10 micrograms/kg bw/day of PCB 126 was sufficient to cause a fourfold increase in urinary ascorbic excretion while 5000 micrograms/kg bw/day of PCB 105 was required for a sevenfold increase. In response to the administration of PCB 105 or PCB 126, urinary ascorbic acid appeared to increase to the same extent as increases in hepatic ethoxyresorufin O-deethylase (EROD) and UDP-glucuronosyltransferase (UGT) activities, and to a much higher extent than changes in liver weight and hematological and serum clinical chemical parameters. The sensitivity and specificity, the ease in obtaining timed specimens, and the noninvasive nature make this assay a useful biomarker of hepatic response in dose-finding and various acute and chronic studies.

Effects of microsomal enzyme inducers upon UDP-glucuronic acid concentration and UDP-glucuronosyltransferase activity in the rat intestine and liver

This study was conducted to evaluate UDP-glucuronosyl-transferase (UDP-GT) activity, UDP-glucuronic acid (UDP-GA) concentration, and UDP-glucose (UDPG) concentration in the rat intestine and liver following oral administration of butylated hydroxyanisole (BHA), benzo[a]pyrene (BaP), 3-methylcholanthrene (3MC), phenobarbital (PB), pregnenolone-16 alpha-carbonitrile (PCN), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), or trans-stilbene oxide (TSO). Microsomal UDP-GT activity was assayed in vitro with acetaminophen (AA), harmol (HA), and 1-naphthol (NA) as the aglycones. Intestinal HA and AA glucuronidation were enhanced by BHA, BaP, and TSO, whereas 3MC, PB, PCN, and TCDD augmented hepatic HA-glucuronide formation and BHA, PB, PCN, TCDD, and TSO significantly increased hepatic AA glucuronidation. All inducing agents except PB and PCN markedly increased both intestinal and hepatic NA glucuronidation. PB, PCN, and TCDD paradoxically decreased intestinal glucuronidation of AA and HA. A similar effect upon hepatic glucuronidation was not observed with any of the agents studied. Hepatic UDP-GA concentration was increased significantly by all inducers studied except PCN and TCDD, whereas hepatic UDPG concentration was increased only by BHA. In the intestine, significant increases in UDP-GA concentration were produced only by BHA and BaP, which also elevated intestinal UDPG. These results demonstrate that microsomal enzyme inducers evoke different effects upon intestinal and hepatic glucuronidation. These differences are manifested with regard to induced changes in UDP-GT activity as well as treatment-induced alterations in UDP-GA content. Thus, the present study further underscores the marked variance of intestinal and hepatic xenobiotic glucuronidation.

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.

Phenobarbital enhances the aldehyde dehydrogenase activity of rat hepatocytes in vitro and in vivo

Aldehyde dehydrogenase (ALDH) was measured in primary cultures of hepatocytes obtained with collagenase perfusion from livers of Long-Evans rats. After seven days in culture, basal ALDH activity, protein content and DNA content are significantly decreased. Exposure of the cultures to phenobarbital (PB, 3 mM in the media) does not prevent the decrease of DNA content, although it keeps protein at relatively higher levels. The activity of ALDH is not only preserved, but also significantly enhanced, when propionaldehyde, phenylacetaldehyde, benzaldehyde and D-glucuronolactone are used as substrates and NAD as the coenzyme. A relative increase of activity is also noted when ALDH is measured with benzaldehyde and NADP. Treatment of Long-Evans animals with PB (1 mg/ml, in drinking water for 2 weeks) leads to similar relative increases of the ALDH activity. In absolute values, however, enzyme activities found after in vivo treatment with PB are higher, compared to those obtained after in vitro exposure. These results show that ALDH activity can be greatly enhanced by PB in primary hepatocyte cultures, free from any indirect endogenous influences.

Increased urinary D-glucaric acid excretion by children living in an area polluted with tetrachlorodibenzoparadioxin (TCDD)

Extremely small doses of TCDD have been shown to induce hepatic microsomal enzymes in animals. Whether levels of environmental exposure to TCDD were sufficient to produce enzyme induction in man, has been investigated in Seveso, where in July 1976 explosion in a factory spread toxic substances, one of which was TCDD, to the surrounding area. The hepatic microsomal enzyme activity was assessed by estimating urinary d-glucaric acid (UGA) excretion in children 6-8 years old. In 31 children, urine samples were collected between August and December 1976; in 67 other children in February 1979. As a control group 60 children living in Busto Arsizio (a small industrial town near Milan) and 26 living Cannero (a non-industrialized village on Lake Maggiore) were chosen. In the first period of collection, children with chloracne (which is considered to be a characteristic manifestation of intoxication with chlorinated products), showed significantly increased levels of UGA compared with children without chloracne. In 1979, children living in the Seveso area showed a statistically significant enhancement of d-glucaric acid excretion compared to the control groups. In conclusion, this study demonstrates that many children living in the Seveso area have an increased activity of hepatic microsomal enzymes, since, although the urinary excretion of d-glucaric acid is only an indirect measure of enzyme activity, studies in man have indicated that it is both sensitive and quantitative. As far as the cause of this increase is concerned, since it is possible to exclude the influence of alcohol, contraceptives, phenobarbitone or other drugs, it is reasonable to conclude that TCDD, a potent inducer agent, could be responsible for this phenomenon.

The effect of enzyme induction on the metabolism of disopyramide in man

1 The effects of rifampicin, phenytoin, and disopyramide treatments on the metabolism of disopyramide were studied in patients and volunteers. 2 Rifampicin treatment markedly increased the metabolism of disopyramide. 3 Phenytoin had effects similar to those of rifampicin. The effect subsided in 2 weeks after stopping the treatment. 4 The metabolism of disopyramide seemed fastest in the patient group with the higher dose of disopyramide. Both in patients and volunteers a significant increase occurred in the urinary mono-N-dealkyldisopyramide/disopyramide ratio during the first week of disopyramide therapy. This change can partly be due to pharmacokinetic differences between disopyramide and its metabolite. The inducing effect of disopyramide remained uncertain.

Enhanced metabolism and diminished efficacy of disopyramide by enzyme induction?

1 Monitoring plasma levels of mono-N-dealkyldisopyramide (MND), the most important metabolite of disopyramide, has been considered unnecessary. 2 We measured plasma levels of both disopyramide and MND in 64 consecutive patients receiving long term oral therapy with disopyramide. 3 Six patients were found with high plasma levels of MND, and simultaneously low levels of disopyramide. 4 Three of these patients were taking simultaneously phenytoin. The other three had a relatively high dose of disopyramide with regard to their renal function. One patient had terminal uremia, three had less severe renal dysfunction. 5 The underlying mechanism and clinical significance of the findings are discussed.