Chloral hydrate, through biotransformation to dichloroacetate, inhibits maleylacetoacetate isomerase and tyrosine catabolism in humans

BACKGROUND

Chloral hydrate (CH), a sedative and metabolite of the environmental contaminant trichloroethylene, is metabolized to trichloroacetic acid, trichloroethanol, and possibly dichloroacetate (DCA). DCA is further metabolized by glutathione transferase zeta 1 (GSTZ1), which is identical to maleylacetoacetate isomerase (MAAI), the penultimate enzyme in tyrosine catabolism. DCA inhibits its own metabolism through depletion/inactivation of GSTZ1/MAAI with repeated exposure, resulting in lower plasma clearance of the drug and the accumulation of the urinary biomarker maleylacetone (MA), a metabolite of tyrosine. It is unknown if GSTZ1/MAAI may participate in the metabolism of CH or any of its metabolites and, therefore, affect tyrosine catabolism. Stable isotopes were utilized to determine the biotransformation of CH, the kinetics of its major metabolites, and the influence, if any, of GSTZ1/MAAI.

METHODS

Eight healthy volunteers (ages 21-40 years) received a dose of 1 g of CH (clinical dose) or 1.5 μg/kg (environmental) for five consecutive days. Plasma and urinary samples were analyzed by gas chromatography-mass spectrometry.

RESULTS

Plasma DCA (1.2-2.4 μg/mL), metabolized from CH, was measured on the fifth day of the 1 g/day CH dosage but was undetectable in plasma at environmentally relevant doses. Pharmacokinetic measurements from CH metabolites did not differ between slow and fast GSTZ1 haplotypes. Urinary MA levels increased from undetectable to 0.2-0.7 μg/g creatinine with repeated CH clinical dose exposure. Kinetic modeling of a clinical dose of 25 mg/kg DCA administered after 5 days of 1 g/day CH closely resembled DCA kinetics obtained in previously naïve individuals.

CONCLUSIONS

These data indicate that the amount of DCA produced from clinically relevant doses of CH, although insufficient to alter DCA kinetics, is sufficient to inhibit MAAI and tyrosine catabolism, as evidenced by the accumulation of urinary MA.

Urinary methylmalonic acid in patients with acute myocardial infarction

OBJECTIVE

To investigate urinary methylmalonic acid (uMMA) levels and their relationship with markers of myocyte necrosis and inflammation in patients with acute myocardial infarction (AMI).

SUBJECTS AND METHODS

The study participants consisted of 80 consecutive patients with AMI and 72 age- and sex-matched consecutive controls. Of the patients, 38 had ST segment elevation myocardial infarction (STEMI) and 42 had non-ST segment elevation. All patients with STEMI underwent fibrinolytic therapy. Routine laboratory tests included troponin-I, creatinine phosphokinase MB (CK-MB), high-sensitivity C-reactive protein (hs-CRP), vitamin B(12), folate, homocysteine and methylmalonic acid analyses. uMMA measurements were made by a spectrophotometric method.

RESULTS

uMMA levels were significantly higher in patients with AMI than in controls (10.1 vs. 5.2 mmol/mol creatinine, p < 0.001) and higher in patients with anterior MI compared to those with non-anterior MI (18.9 vs. 8.7 mmol/mol creatinine, p < 0.001). In addition, uMMA levels were significantly higher in patients without successful reperfusion compared to those with successful reperfusion. In patients with STEMI, a strong positive association was found between urinary MMA and plasma hs-CRP levels (r = 0.81, p < 0.001), symptom duration (r = 0.91, p < 0.001) and wall motion score (r = 0.60, p = 0.006). More importantly, a strong positive association was observed between uMMA and the size of myocardial infarction in patients without successful reperfusion (for CK-MB r = 0.81, p = 0.013; for wall motion score r = 0.82, p = 0.012).

CONCLUSION

uMMA levels were elevated in patients with AMI and, as such, may be a candidate biochemical indicator of larger infarct size and enhanced inflammation in patients with AMI.

A GC–MS/MS method for the quantitative analysis of low levels of the tyrosine metabolites maleylacetone, succinylacetone, and the tyrosine metabolism inhibitor dichloroacetate in biological fluids and tissues

We developed a sensitive method to quantitate the tyrosine metabolites maleylacetone (MA) and succinylacetone (SA) and the tyrosine metabolism inhibitor dichloroacetate (DCA) in biological specimens. Accumulation of these metabolites may be responsible for the toxicity observed when exposed to DCA. Detection limits of previous methods are 200 ng/mL (1.2 pmol/microL) (MA) and 2.6 microg/mL (16.5 pmol/microL) (SA) but the metabolites are likely present in lower levels in biological specimens. To increase sensitivity, analytes were extracted from liver, urine, plasma and cultured nerve cells before and after dosing with DCA, derivatized to their pentafluorobenzyl esters, and analyzed via GC-MS/MS.

Inhibition and recovery of rat hepatic glutathione S-transferase zeta and alteration of tyrosine metabolism following dichloroacetate exposure and withdrawal

Dichloroacetate (DCA) is an investigational drug for certain metabolic disorders, a by-product of water chlorination and a metabolite of certain industrial solvents and drugs. DCA is biotransformed to glyoxylate by glutathione S-transferase zeta (GSTz1-1), which is identical to maleylacetoacetate isomerase, an enzyme of tyrosine catabolism. Clinically relevant doses of DCA (mg/kg/day) decrease the activity and expression of GSTz1-1, which alters tyrosine metabolism and may cause hepatic and neurological toxicity. The effect of environmental DCA doses (microg/kg/day) on tyrosine metabolism and GSTz1-1 is unknown, as is the time course of recovery from perturbation following subchronic DCA administration. Male Sprague-Dawley rats (200 g) were exposed to 0 microg, 2.5 microg, 250 microg, or 50 mg DCA/kg/day in drinking water for up to 12 weeks. Recovery was followed after the 8-week exposure. GSTz specific activity and protein expression (Western immunoblotting) were decreased in a dose-dependent manner by 12 weeks of exposure. Enzyme activity and expression decreased 95% after a 1-week administration of high-dose DCA. Eight weeks after cessation of high-dose DCA, GSTz activity had returned to control levels. At the 2.5 or 250 microg/kg/day doses, enzyme activity also decreased after 8 weeks' exposure and returned to control levels 1 week after DCA was withdrawn. Urinary excretion of the tyrosine catabolite maleylacetone increased from undetectable amounts in control rats to 60 to 75 microg/kg/24 h in animals exposed to 50 mg/kg/day DCA. The liver/body weight ratio increased in the high-dose group after 8 weeks of DCA. These studies demonstrate that short-term administration of DCA inhibits rat liver GSTz across the wide concentration range to which humans are exposed.

Perturbation of maleylacetoacetic acid metabolism in rats with dichloroacetic Acid-induced glutathione transferase zeta deficiency

Glutathione transferase zeta (GSTZ1-1) catalyzes the isomerization of maleylacetoacetate (MAA) to fumarylacetoacetate, the penultimate step in the tyrosine degradation pathway. GSTZ1-1 is inactivated by dichloroacetic acid (DCA), which is used for the clinical management of congenital lactic acidosis and is a drinking-water contaminant. Metabolic changes associated with chemically induced GSTZ1-1 deficiency are poorly understood. The objective of this study was to investigate the biochemical and toxicological effects of giving 0.3-1.2 mmol DCA/kg/day for 5 days on MAA-metabolism in male Fischer rats. Urine from DCA-treated rats inhibited delta-aminolevulinic acid dehydratase (delta-ALAD) activity, which is used for the diagnosis of hereditary tyrosinemia type I. Mass spectrometric analyses of urine from rats given DCA demonstrated elevated excretion of MAA and its decarboxylation product, maleylacetone (MA); succinylacetone (SA), the reduced analogue of MA, was not detected. DCA-induced changes in MA excretion were dose-dependent and were significantly elevated after day 2 of treatment. MA excretion was reversible after discontinuation of DCA treatment and was enhanced 10-fold by the coadministration of homogentisic acid (HGA). MA was cytotoxic to hepatocytes in vitro (EC50 ~ 350 microM) but morphological changes were not observed in liver, kidney, and brain of rats given both DCA and HGA. These data indicate that DCA-induced inactivation of GSTZ1-1 leads to formation of an MAA-derived intermediate, MA, that may be a mediator and biomarker for DCA-associated toxicities.

In vivo percutaneous absorption of fragrance ingredients in rhesus monkeys and humans

The percutaneous absorption of the fragrance diethyl maleate was measured in vivo in human and monkey studies. With the application sites occluded, 54% of the applied dose of the volatile fragrance penetrated human skin in 24 hr compared with 69% absorption in the monkey skin. It was concluded that the monkey is a good model for human skin with regard to the penetration of this fragrance material since no significant difference in the absorption of diethyl maleate was observed. The percutaneous absorption of the fragrances benzyl acetate and five other benzyl derivatives (benzyl alcohol, benzyl benzoate, benzamide, benzoin and benzophenone) was determined in vivo in monkeys. Absorption through occluded skin was high for all compounds (approximately 70% of the applied dose in 24 hr) and no significant differences between the values for the different compounds were observed. No correlations were seen between skin penetration of these compounds and their octanol-water partition coefficients. Under unoccluded conditions skin penetration of the fragrances was reduced and there was great variability between compounds, presumably because of variations in the rates of evaporation from the site of application. The data suggest that humans may have significant systemic exposure to these fragrance materials.

Methylsuccinate and mesaconate in urine of patients treated with sodium benzoate

Two unusual peaks were found on gas chromatography of urine from four hyperammonemic patients treated with sodium benzoate. These peaks were identified by gas chromatography/mass spectrometric analyses as methylsuccinate and mesaconate. Of the two unusual substances, methylsuccinate was found to be a contaminant of sodium benzoate administered for the treatment of hyperammonemia. However, mesaconate was not a contaminant of sodium benzoate, though it could be detected in all urine samples from hyperammonemic patients treated with sodium benzoate. Mesaconate can be produced from methylsuccinate in vivo. Considering that mesaconate is an inhibitor of fumarase, the toxic effects of sodium benzoate may be attributable to the mesaconate. It is recommended that methylsuccinate-free sodium benzoate should be used for the treatment of hyperammonemia.

Propionyl-CoA carboxylase deficiency: case report, effect of low-protein diet and identification of 3-oxo-2-methylvaleric acid 3-hydroxy-2-methylvaleric acid, and maleic acid in urine

Vomiting, lethargy and metabolic acidosis were the main initial symptoms of metabolic disease in a 1 month old girl. Her older sister had died from a similar disease, considered to be Reye's syndrome, at an age of 15 months. The urine of the present case contained 2-methylcitric acid, 3-hydroxypropionic acid, N-propionylglycine, 2-hydroxy-3-methylbutyric acid, N-tiglylglycine, 3-hydroxyvaleric acid and glutaric acid. These metabolites are all known to be associated with propionyl-CoA accumulation. Free propionic acid was not detected in the urine. In addition, the urine contained 3-oxo-2-methylvaleric acid and 3-hydroxy-2-methylvaleric acid, probably formed by condensation of two molecules of propionyl-CoA. The identity of these metabolites was confirmed by synthesis. An elevated urinary concentration of maleic acid and fumaric acid was another constant abnormality. The activity of propionyl-CoA carboxylase in leucocytes was about 20% of the normal activity. The girl was teated with a low-protein diet since the diagnosis was made at an age of 1 month, and her psychomotor development was satisfactory at an age of 2 1/2 years. She had a few episodes of acidosis during infections.

New metabolites in isovaleric acidemia

Two metabolites, 4-hydroxyisovaleric acid and mesaconic acid, have been identified and quantified in the urine of a patient with isovaleric acidemia. These compounds do not appear to have been reported previously as being components of human metabolism. In addition, large quantities of 3-methylbutyrolactone, the lactone of 4-hydroxyisovaleric acid, were observed in the volatile profile obtained by headspace chromatography. The demonstration of 4-hydroxyisovaleric acid supports the contention that urinary methylsuccinic acid seen in patients with isovaleric acidemia has arisen by omega-oxidation of isovaleric acid. The identification of mesaconic acid may indicate that the methylsuccinic acid formed in these patients is subject to further metabolism.

Organic acids in urine from preterm infants

The organic acid excretion was studied in urine samples from 26 preterm infants on the 1st and 5th days of life and the results compared to those obtained in 5 samples from full-term neonates. Gas-chromatography-mass spectrometry with a computer system was the method used in this work. The acids tabulated were those more closely related to lactic acidosis and the Krebs cycle. Great variations were found in the excretion of these acids in preterm infants in contrast to the very homogeneous pattern obtained in full-term neonates.