Waste nitrogen excretion via amino acid acylation: benzoate and phenylacetate in lysinuric protein intolerance

Benzoate and phenylacetate improve prognosis in inherited urea cycle enzyme deficiencies by increasing waste nitrogen excretion as amino acid acylation products. We studied metabolic changes caused by these substances and their pharmacokinetics in a biochemically different urea cycle disorder, lysinuric protein intolerance (LPI), under strictly standardized induction of hyperammonemia. Five patients with LPI received an intravenous infusion of 6.6 mmol/kg L-alanine alone and separately with 2.0 mmol/kg of benzoate or phenylacetate in 90 min. Blood for ammonia, serum urea and creatinine, plasma benzoate, hippurate, phenylacetate, phenylacetylglutamine, and amino acids was obtained at 0, 120, 180, and 270 min. Urine was collected in four consecutive 6-h periods. Alanine caused hyperammonemia: maximum increase 107, 28-411 microM (geometric mean, 95% confidence interval); ammonia increments were nearly identical after alanine + benzoate (60, 17-213 microM) and alanine + phenylacetate (79, 13-467 microM) (NS). Mean plasma benzoate was 6.0 mM when extrapolated to the end of alanine + benzoate infusions; phenylacetate was 4.9 mM at the end of alanine + phenylacetate. Transient toxicity (dizziness, nausea, vomiting) occurred in four patients at the end of combined infusions, and we suggest upper therapeutic plasma concentrations of 4.5 mM for benzoate and 3.5 mM for phenylacetate. Benzoate and phenylacetate then decreased following first-order kinetics with t1/2S of 273 and 254 min, respectively. Maximal plasma hippurate (0.24, 0.14-0.40 mM) was lower than maximal phenylacetylglutamine (0.48, 0.22-1.06 mM, p = 0.008).(ABSTRACT TRUNCATED AT 250 WORDS)

[Improved high performance liquid chromatography determination of hippuric acid and methylhippuric acid isomers in urine]

A study was made on the effect of detection wavelength and separation mode of HPLC on determination of urinary hippuric acid (HA) and three isomers of methylhippuric acid (MHA). The interference of other constituents of urine in the determination was effectively decreased by detection at a short wavelength of 227.6 nm. Meta and para MHAs were separated by the addition of beta-cyclodextrine to the mobile phase. Four metabolites were successfully separated from other components of urine by the combination of ODS-silica packed-column and mobile phase (method F). The detection limits were found to be 50 and 5 mg/l for HA and MHAs, respectively. MHAs could not be detected in the non-exposed subjects. Average levels (+/- SD) of HA in non-exposed males and females were 272.2 (+/- 210.8) and 393.0 (+/- 269.8) mg/l, respectively. The urinary levels of HA in females were significantly higher than those in males.

[Renal excretion of total porphyrins and hippuric acid in rats]

The amounts of total porphyrins, hippuric acid and creatinine, excreted in urine by adult male Wistar rats, exhibited normal distributions for hippuric acid and creatinine, but a bimodal distribution for total porphyrins. This typical distribution of total porphyrins was still observed when creatinine was used as reference parameter. In biochemical and toxicological experiments in rats, the tested parameters should be therefore be investigated for homogeneity.

Direct measurement of salicylphenolic glucuronide in human urine

Indirect measurement of salicylphenolic glucuronide (SPG) has suggested that the formation of this metabolite from therapeutic doses of salicyclic acid (SA) is capacity-limited in humans. A direct high performance liquid chromatographic (HPLC) assay for SPG in human urine is described. SPG was prepared by a published method and purified by HPLC. On treatment with beta-glucuronidase, SPG yielded the expected amount of SA. Spectroscopic data, melting point, and optical rotation of the glucuronide and/or its triacetyl dimethyl ester derivative were consistent with the proposed structure. SPG was assayed using a 5-micron C18 column (temperature 55 degrees C) and fluorescence detection. A nonlinear gradient mobile phase at a flow rate of 2 ml/min was used, beginning with 100% 0.1 M pH 2.1 phosphate buffer and finishing with 84% buffer, 16% acetonitrile. Total run time was 25 min. Urine (10 microliter) was injected directly on the column, and quantitation was performed using urine standards. Within-run precision for SPG ranged from 1.2% at 150 mg/L to 2.4% at 5 mg/L. The limit of detection was less than 1 mg/L. A pilot study in two volunteers, each receiving a single 500-mg dose of sodium salicylate, was carried out to validate the usefulness of the assay.

Metabolism of nonessential 15N-labeled amino acids and the measurement of human whole-body protein synthesis rates

Eight 15N-labeled nonessential amino acids plus 15NH4Cl were administered over a 10-h period to four healthy adult males using a primed-constant dosage regimen. The amount of 15N excreted in the urine and the urinary ammonia, hippuric acid and plasma alanine 15N enrichments were measured. There was a high degree of consistency across subjects in the ordering of the nine compounds based on the fraction of 15N excreted (Kendall coefficient of concordance W = 0.83, P less than 0.01). Protein synthesis rates were calculated from the urinary ammonia plateau enrichment and the cumulative excretion of 15N. Glycine was one of the few amino acids that gave similar values by both methods.

Comparison of the effects of urinary flow on adjusted and non-adjusted excretion of heavy metals and organic substances in 'healthy' men

The effect of variation in urinary flow rate (ml urine min-1, UF) on adjusted and non-adjusted urinary excretion of metals and organic substances was examined in ten 'healthy' men. The effect of UF was found to be eliminated when urinary concentrations of lead (Pb), hippuric acid (HA), delta-aminolevulinic acid (ALA) and coproporphyrin (CP) were adjusted to urinary specific gravity and to UF. Similarly, the effect of UF on inorganic mercury (Hg) was eliminated when the concentration was adjusted to timed excretion and to UF. The effect on zinc (Zn) and copper (Cu) was eliminated when adjusted to urinary creatinine (Cn) and to UF. The difference in the effect of UF on the adjusted urinary excretion was explained by the effect of UF on timed excretion of substance, which was ranked in the following order: Pb, HA, total urinary solutes, ALA and CP; Zn; Cu; Cn; and Hg. It was concluded that 'UF-adjusted concentration' is applicable to measurement of all substances in urine as a method of minimizing UF effects, while the other three adjustment methods have only limited uses.

Quantitative analysis of urinary glycine conjugates by high performance liquid chromatography: excretion of hippuric acid and methylhippuric acids in the urine of subjects exposed to vapours of toluene and xylenes

A new method for the direct determination of hippuric acid (HA) and o-, m- and p-methylhippuric acids (MHAs) in the urine, metabolites of toluene and o-, m- and p-xylenes by high performance liquid chromatography (HPLC) is described. A stainless-steel column packed with silica gel having dinitrophenyl residue and a mixed solution of methanol/water/acetic acid (80/20/0.2) containing tetra-n-butylammonium bromide (0.2% w/v) as mobile phase was used. Concentrations of HA and MHAs were estimated from their peak height at a wave length of 225 nm. Urine can be analyzed directly without solvent extraction or pretreatment to obtain complete separation of HA and o-, m- and p-MHAs. Urine samples from male workers exposed to toluene or xylenes were analyzed for HA or MHAs. The urinary levels of HA and MHAs increased by exposure to toluene and xylenes in proportion to the environmental concentrations of the solvents, although there is a considerable variation in metabolite concentrations. The slope of regression line between toluene and HA and that between m-xylene and m-MHA were similar. The urinary concentrations of HA and MHAs corresponding to 100 ppm (TLV) of toluene was 2.35 g/g creatinine and that of m-MHA corresponding to 100 ppm (TLV) of m-xylene was 2.05 g/g creatinine. The warning levels of the urinary metabolite concentrations of a group of workers and that of an individual worker corresponding to TLV of organic solvent concentration is discussed.

Correlation of xylene exposure and methyl hippuric acid excretion in urine among paint industry workers

Different calculations of methyl hippuric acid excretion in urine were correlated to the time-weighted average (TWA) of the xylene exposure of a complete workday for 40 paint industry workers exposed to 12 different solvents. The 8-h TWA xylene exposure varied between 0 and 865 (median 69) mg/m3. The amount of methyl hippuric acid excreted in about 24 h showed only a slightly higher linear correlation to the xylene exposure than the amount of methyl hippuric acid excreted per hour during the latter part of the workshift among the 37 subjects exposed to TWA xylene air concentrations of 0-200 mg/m3. It was concluded that the methyl hippuric acid excretion rate during the latter part of the workshift can be used for crude xylene exposure categorizations.

The metabolism of aspirin in man: a population study

The metabolism of a 900 mg oral dose of aspirin has been investigated in 129 healthy volunteers. For this purpose, the 0-12 h urine was collected and analysed for the following excretion products: salicylic acid, its acyl and phenolic glucuronides, salicyluric acid, its phenolic glucuronide and gentisic acid. The total excretion of salicylate and metabolites was normally distributed within the population group studied, showing a 2.5-fold variation: a mean of 68.1% of the dose was recovered in 12 h. The excretion of salicylic acid was found to be highly variable within the study panel (1.3-31% of dose in 12 h), and was related to both urine volume and pH. Salicyluric acid was the major metabolite in the majority of the volunteers and its excretion was normally distributed amongst the study panel. The elimination of this metabolite ranged from 19.8 to 65% of the dose and was related to the total recovery of salicylate. The excretion of the two salicyl glucuronides was highly variable, ranging from 0.8 to 42% of the dose. The elimination of the glucuronides was inversely related to that of salicyluric acid. Gentisic acid and salicyluric acid phenolic glucuronide were minor metabolites of salicylate, accounting for 1 and 3% of the dose, respectively. The recovery of gentisic acid was statistically significantly greater in female subjects than in males, whilst the opposite was found for salicyluric acid and total salicylate. However, these differences were small in magnitude.

Studies on drug metabolism by use of isotopes. XXIX--Studies of the differences in biological fates of ephedrine isomers by use of a pseudo-racemic mixture

The differences in metabolic fates of the optical isomers of ephedrine were investigated by use of a pseudo-racemic mixture technique. In rats, the (-)-isomer was more easily p-hydroxylated than the (+)-isomer. A stereoselective reaction in the formation of the glucuronides of ephedrine, norephedrine and p-hydroxyephedrine was observed. The (-)-isomers were more easily subjected to glucuronide formation than the (+)-isomers. In human subjects, N-demethylation proved to be a stereoselective reaction. It is also suspected that oxidative dealkylation of norephedrine is a stereoselective reaction.

Crystalluria. Observations, interpretations, and misinterpretations

Crystalluria results from oversaturation of urine with crystallogenic substance. However, oversaturation may occur as a result of in vitro as well as in vivo events. The microscopic appearance of crystals only represents a tentative identification of their composition because variable conditions associated with their formation, growth, and dissolution may alter their appearance. Definitive identification is dependent on physical methods such as optical crystallography, x-ray diffraction, and electron microscopic analysis.

Effect of exercise and heat exposure on percutaneous absorption of methyl salicylate

The effects of exercise, heat exposure or both on the percutaneous absorption of methyl salicylate were studied in 6 healthy volunteers. Exercise was performed to 30% of VO2max, 45 min each hour for 6 h, at ambient temperatures of 22 degrees C or 40 degrees C. Systemic availability was assessed by measurement of plasma salicylate concentrations and cumulative urinary salicyluric acid excretion over an 8-h collection period. The absorption of methyl salicylate was increased to more than 3-times above control in subjects exercising in the heat. It is concluded that exercise and heat exposure, by increasing skin temperature, hydration and blood flow, enhance the percutaneous absorption of methyl salicylate.

Effect of Plasmodium berghei infection on benzoic acid metabolism in mice

The metabolism of benzoic acid was studied in Plasmodium berghei infected mice both in vitro and in vivo. Results of in vitro studies showed a considerable decrease in the ability of the infected liver to detoxify benzoic acid by hippuric acid formation. The in vivo study showed that hippuric acid formation decreases with increasing parasitemia and the emergence of benzoyl-glucuronide. This new pathway stops operating with further increase in parasitemia.

Occupational chronic exposure to organic solvents. XII. O-cresol excretion after toluene exposure

Thirty-five printing workers were investigated according to their external and internal exposure to toluene. The concentration of toluene in the air of the working place was determined using stationary air sampling and gas chromatography. To determine the levels of toluene in blood as well as the concentrations of o-cresol, hippuric acid, and phenol in urine, biological specimens were collected at the end of exposure. The parameters were determined by gas chromatography and gas chromatography/mass spectrometry. According to our results, o-cresol concentrations higher than 5.3 mg per litre of post-shift urine might indicate an external exposure higher than the present MAK-value of 200 ppm.

The validity of urinary metabolites as indicators of low exposures to toluene

Exposure to toluene was studied in a group of 14 subjects working in a printing industry, who were exposed to this solvent only. Environmental monitoring was carried out using personal samplers for the whole workshift over three consecutive days. Toluene TWA concentrations ranged from 37 to 229 mg/m3. At the end of the workshift on each day of investigation, urine samples were collected for the determination of hippuric acid and ortho-cresol. Hippuric acid was also determined for urine before the workshift and on the Saturday and Monday mornings after the end of exposure; hippuric acid was also determined in 16 controls over the same five-day period. At the end of the workshift, hippuricuria levels in exposed workers always turned out to be statistically different from pre-workshift levels and those of the controls. The end-of-workshift hippuricuria levels of exposed workers were significantly correlated with the mean daily environmental concentration (TWA): in the three days of comparative study, we found r = 0.63 (P less than 0.05) on Day 1, r = 0.90 (P less than 0.001) on Day 2, and r = 0.87 (P less than 0.001) on Day 3. Ortho-cresol turned out to be correlated with daily exposure less significantly than hippuric acid: r = 0.49 (n.s.) on Day 1; r = 0.78 (P less than 0.001) on Day 2, and r = 0.65 (P less than 0.05) on Day 3. Using all available data (41 observations), a very significant correlation (P less than 0.001) was found between the TWA and both metabolites (r = 0.80 for hippuric acid; r = 0.68 for o-cresol). The values of the two metabolites in the end-of-workshift urine samples (41 observations) also turned out to be well correlated (r = 0.70; P less than 0.001). The authors conclude that hippuric acid is a valid test for evaluating even low exposures to toluene.

Improved method for the determination of aspirin and its metabolites in biological fluids by high-performance liquid chromatography: applications to human and animal studies

An improved method has been developed for the determination of acetylsalicylic acid, salicylic acid, gentisic acid, and salicyluric acid in plasma and urine of rabbits and man. Samples are extracted with dichloromethane containing mephenytoin as an internal standard, the solvent is evaporated under reduced pressure, the residue reconstituted and analyzed by high-performance liquid chromatography. Extraction efficiencies, linearity and assay precision were determined. This method has been applied to human bioavailability studies and the data are presented.

Increased o- and p-cresol/hippuric acid ratios in the urine of four strains of rat exposed to toluene at thousands-ppm levels

Rats (Fisher, Wistar, Donryu and Sprague-Dawley strains) were exposed to 5 approximately 3500 ppm toluene for 8 h, and urine samples were analyzed for hippuric acid and cresols. While hippuric acid increased in proportion to the exposure concentration, a sharp increase in o-cresol excretion was observed at high toluene concentrations so that the o-cresol/hippuric acid ratio was elevated after 500 approximately 3500 ppm exposures. Changes in the p-cresol: hippuric acid ratio were less marked. There were strain differences in toluene metabolism. Fisher rats were highest and Sprague-Dawley rats lowest in o-cresol excretion and in the o-cresol: hippuric acid ratio, whereas Wistar rats excreted p-cresol most abundantly.

Urinary excretion of acetaminophen and its metabolites as studied by proton NMR spectroscopy

Acetaminophen and its glucuronide, sulfate, N-acetyl-L-cysteinyl, and L-cysteinyl metabolites can be rapidly detected by 1H NMR spectroscopy of intact, untreated human urine. Study of the time course of excretion of these metabolites in five clinically normal men after ingestion of the usual 1-g therapeutic dose of the drug showed that the mean 24-h excretion of the drug and these metabolites as determined by NMR was 77.3% of the dose. Respective relative proportions of the above metabolites were 49.9%, 37.6%, 3.0%, and 9.5% (L-cysteinyl plus free drug). Excretion of some other metabolites in urine, including creatinine, citrate, hippurate, and sarcosine was measured concurrently. Excretion of creatinine and sarcosine was closely correlated.

Benzyl alcohol toxicity in a neonatal intensive care unit. Incidence, symptomatology, and mortality

We unknowingly "screened" all NICU infants for elevated levels of serum benzyl alcohol (Bz-OH) over a three-month period. The fortuitous "screening" procedure resulted from the interference by Bz-OH with a routine blood CO2 assay used for all infants; validity was proved by (1) replication of the interference pattern with Bz-OH or benzoic acid; (2) confirmation of elevated benzoic acid levels in serum in two of the four screening positive infants tested but not in control infants, and (3) disappearance of the interference patterns when Bz-OH solutions were discontinued in affected infants. Screened Bz-OH-positive infants were compared to screened negative control infants, matched for weight (less than 1000 g), severity of RDS (on respirators), exposure to Bz-OH, and survival for longer than 48 hours. Intraventricular hemorrhage (IVH), metabolic acidosis appearing prior to IVH, and mortality were increased in Bz-OH-positive infants (P less than .05 in each case); hyperbilirubinemia and thrombocytopenia were not. Gasping respirations were not a major symptom. It is concluded that Bz-OH poisoning was a major cause of morbidity and mortality in NICU infants weighing less than 1000 g at birth during the three-month screening period. A retrospective review of patient records covering a 16-month period showed significant improvement in the survival rate of infants weighing less than 1000 g following the discontinuation of Bz-OH solutions.

The metabolism of cinnamic acid by healthy and phenylketonuric adults: a kinetic study

The enzyme phenylalanine ammonia lyase taken orally has been found to reduce the rise in blood phenylalanine that normally occurs following a protein meal. Therefore the enzyme has a potential use in the management of the genetic disease phenylketonuria. The enzyme mediates the conversion of phenylalanine to cinnamic acid and its possible clinical future has necessitated a more detailed study of the product of its reaction. Cinnamic acid is a compound of low toxicity which is converted in the mammalian body primarily to hippuric acid. We have examined the kinetics of this process in a healthy male and in two patients with untreated phenylketonuria. In addition we have attempted to clarify the inconsistencies in earlier published work about the status of other, minor metabolites. Following an oral load of sodium (2H6) cinnamate there is an increase in urinary hippuric acid largely due to the excretion of (2H5) hippuric acid. In the subjects studied there was no major difference in the rate of elimination although the amount of cinnamic acid converted was less in those with phenylketonuria. This may reflect reduced first-pass absorption by the liver in untreated phenylketonuria enabling increased uptake to occur in other parts of the body.

Formaldehyde generation from methenamine salts in spinal cord injury

To achieve effective suppression of bacteriuria in spinal cord injured (SCI) patients, methenamine mandelate and methenamine hippurate are commonly given with ascorbic acid. Since the effectiveness of ascorbic acid as a urinary acidifier has been challenged and as it also has been suggested that methenamine salts do not produce effective urine formaldehyde concentrations in patients with indwelling urethral catheters, we studied two groups of SCI patients to determine (1) the effect of ascorbic acid on urine pH and formaldehyde concentration when administered with methenamine salts; (2) the effect of an indwelling urethral catheter versus intermittent catheterization on formaldehyde concentration in the urine of SCI patients taking methenamine salts; and (3) the relative urine formaldehyde concentrations produced by treatment with methenamine mandelate and methenamine hippurate in SCI patients. Methenamine mandelate produced significantly higher urine formaldehyde concentrations than did methenamine hippurate, especially among patients with intermittent catheterization. Ascorbic acid produced a significant effect on urine pH but not on formaldehyde concentration.

Styrene metabolism in man: gas chromatographic separation of mandelic acid enantiomers in the urine of exposed persons

D- and L-mandelic acid are separated by gas chromatography as isopropyl ester or isopropyl ester-isopropyl urethane on capillary columns, coated with Chirasil -Val. For its determination in urine the isopropyl ester procedure gives better results because other components of the urine do not cause interference. Thus D- and L-mandelic acid in the urine of exposed workers could be detected and verified by means of GC/MS. Occupational styrene exposure near the MAK-value (100 ppm) results in a L/D-enantiomer-ratio in urine of nearly 1.5.