Quantitation of phenylbutyrate metabolites by UPLC-MS/MS demonstrates inverse correlation of phenylacetate:phenylacetylglutamine ratio with plasma glutamine levels

Urea cycle disorders (UCDs) are genetic conditions characterized by nitrogen accumulation in the form of ammonia and caused by defects in the enzymes required to convert ammonia to urea for excretion. UCDs include a spectrum of enzyme deficiencies, namely n-acetylglutamate synthase deficiency (NAGS), carbamoyl phosphate synthetase I deficiency (CPS1), ornithine transcarbamylase deficiency (OTC), argininosuccinate lyase deficiency (ASL), citrullinemia type I (ASS1), and argininemia (ARG). Currently, sodium phenylbutyrate and glycerol phenylbutyrate are primary medications used to treat patients with UCDs, and long-term monitoring of these compounds is critical for preventing drug toxic levels. Therefore, a fast and simple ultra-performance liquid chromatography (UPLC-MS/MS) method was developed and validated for quantification of phenylbutyrate (PB), phenylacetate (PA), and phenylacetylglutamine (PAG) in plasma and urine. The separation of all three analytes was achieved in 2min, and the limits of detection were <0.04μg/ml. Intra-precision and inter-precision were <8.5% and 4% at two quality control concentrations, respectively. Average recoveries for all compounds ranged from 100% to 106%. With the developed assay, a strong correlation between PA and the PA/PAG ratio and an inverse correlation between PA/PAG ratio and plasma glutamine were observed in 35 patients with confirmed UCDs. Moreover, all individuals with a ratio ≥0.6 had plasma glutamine levels<1000μmol/l. Our data suggest that a PA/PAG ratio in the range of 0.6-1.5 will result in a plasma glutamine level<1000μmol/l without reaching toxic levels of PA.

Microbial metabolites are associated with a high adherence to a Mediterranean dietary pattern using a 1H-NMR-based untargeted metabolomics approach

The study of biomarkers of dietary patterns including the Mediterranean diet (MedDiet) is scarce and could improve the assessment of these patterns. Moreover, it could provide a better understanding of health benefits of dietary patterns in nutritional epidemiology. We aimed to determine a robust and accurate biomarker associated with a high adherence to a MedDiet pattern that included dietary assessment and its biological effect. In this cross-sectional study, we included 56 and 63 individuals with high (H-MDA) and low (L-MDA) MedDiet adherence categories, respectively, all from the Prevención con Dieta Mediterránea trial. A ¹H-NMR-based untargeted metabolomics approach was applied to urine samples. Multivariate statistical analyses were conducted to determine the metabolite differences between groups. A stepwise logistic regression and receiver operating characteristic curves were used to build and evaluate the prediction model for H-MDA. Thirty-four metabolites were identified as discriminant between H-MDA and L-MDA. The fingerprint associated with H-MDA included higher excretion of proline betaine and phenylacetylglutamine, among others, and decreased amounts of metabolites related to glucose metabolism. Three microbial metabolites - phenylacetylglutamine, p-cresol and 4-hydroxyphenylacetate - were included in the prediction model of H-MDA (95% specificity, 95% sensitivity and 97% area under the curve). The model composed of microbial metabolites was the biomarker that defined high adherence to a Mediterranean dietary pattern. The overall metabolite profiling identified reflects the metabolic modulation produced by H-MDA. The proposed biomarker may be a better tool for assessing and aiding nutritional epidemiology in future associations between H-MDA and the prevention or amelioration of chronic diseases.

Glycerol phenylbutyrate treatment in children with urea cycle disorders: pooled analysis of short and long-term ammonia control and outcomes

OBJECTIVE

To evaluate glycerol phenylbutyrate (GPB) in the treatment of pediatric patients with urea cycle disorders (UCDs).

STUDY DESIGN

UCD patients (n=26) ages 2months through 17years were treated with GPB and sodium phenylbutyrate (NaPBA) in two short-term, open-label crossover studies, which compared 24-hour ammonia exposure (AUC0-24) and glutamine levels during equivalent steady-state dosing of GPB and sodium phenylbutyrate (NaPBA). These 26 patients plus an additional 23 patients also received GPB in one of three 12-month, open label extension studies, which assessed long-term ammonia control, hyperammonemic (HA) crises, amino acid levels, and patient growth.

RESULTS

Mean ammonia exposure on GPB was non-inferior to NaPBA in each of the individual crossover studies. In the pooled analyses, it was significantly lower on GPB vs. NaPBA (mean [SD] AUC0-24: 627 [302] vs. 872 [516] μmol/L; p=0.008) with significantly fewer abnormal values (15% on GPB vs. 35% on NaPBA; p=0.02). Mean ammonia levels remained within the normal range during 12months of GPB dosing and, when compared with the 12months preceding enrollment, a smaller percentage of patients (24.5% vs. 42.9%) experienced fewer (17 vs. 38) HA crises. Glutamine levels tended to be lower with GPB than with NaPBA during short-term dosing (mean [SD]: 660.8 [164.4] vs. 710.0 [158.7] μmol/L; p=0.114) and mean glutamine and branched chain amino acid levels, as well as other essential amino acids, remained within the normal range during 12months of GPB dosing. Mean height and weight Z-scores were within normal range at baseline and did not change significantly during 12months of GPB treatment.

CONCLUSIONS

Dosing with GPB was associated with 24-hour ammonia exposure that was non-inferior to that during dosing with NaPBA in individual studies and significantly lower in the pooled analysis. Long-term GPB dosing was associated with normal levels of glutamine and essential amino acids, including branched chain amino acids, age-appropriate growth and fewer HA crises as compared with the 12month period preceding enrollment.

[Kinetics of nitrogenous metabolites in the kidney during chronic tetrachloromethane hepatitis]

The kinetics of ammonia, glutamine, and urea in the kidney has been studied in experiments on 203 white rats (females) at the end of chronic tetrachloromethane (CCl4) exposure (65 days) and within 14 days after cessation of CCl4. It was found that on the 65th day of CCl4 administration the arterial hyperammoniemia is formed, which lasts for 14 days after the abolition of the toxin. This is accompanied by an increased excretion of ammonia in the urine and an increase in its concentration in the blood of renal veins, which does not prevent its accumulation in renal tissue. In chronic CCl4-hepatitis model are the changes of glutamine concentration in arterial blood are developing by type of hypo- and hyperglutaminemia. CCl4 stimulates accumulation of glutamine by the kidneys at the end of exposure and at early stage of the recovery period. Toxin cessation activates processes which are stabilizing the normal concentration of glutamine in the kidney by changing glutamine incretion from kidney to renal blood flow. Long-lasting CCl4 exposure increases the concentration of urea in the arterial blood and its urinary excretion. Simultaneously urea reabsorption is activated in the kidneys, which contributes to an increase in its concentration in the blood of the renal veins.

Urinary phenylacetylglutamine as dosing biomarker for patients with urea cycle disorders

We have analyzed pharmacokinetic data for glycerol phenylbutyrate (also GT4P or HPN-100) and sodium phenylbutyrate with respect to possible dosing biomarkers in patients with urea cycle disorders (UCD).

STUDY DESIGN

These analyses are based on over 3000 urine and plasma data points from 54 adult and 11 pediatric UCD patients (ages 6-17) who participated in three clinical studies comparing ammonia control and pharmacokinetics during steady state treatment with glycerol phenylbutyrate or sodium phenylbutyrate. All patients received phenylbutyric acid equivalent doses of glycerol phenylbutyrate or sodium phenylbutyrate in a cross over fashion and underwent 24-hour blood samples and urine sampling for phenylbutyric acid, phenylacetic acid and phenylacetylglutamine.

RESULTS

Patients received phenylbutyric acid equivalent doses of glycerol phenylbutyrate ranging from 1.5 to 31.8 g/day and of sodium phenylbutyrate ranging from 1.3 to 31.7 g/day. Plasma metabolite levels varied widely, with average fluctuation indices ranging from 1979% to 5690% for phenylbutyric acid, 843% to 3931% for phenylacetic acid, and 881% to 1434% for phenylacetylglutamine. Mean percent recovery of phenylbutyric acid as urinary phenylacetylglutamine was 66.4 and 69.0 for pediatric patients and 68.7 and 71.4 for adult patients on glycerol phenylbutyrate and sodium phenylbutyrate, respectively. The correlation with dose was strongest for urinary phenylacetylglutamine excretion, either as morning spot urine (r = 0.730, p < 0.001) or as total 24-hour excretion (r = 0.791 p<0.001), followed by plasma phenylacetylglutamine AUC(24-hour), plasma phenylacetic acid AUC(24-hour) and phenylbutyric acid AUC(24-hour). Plasma phenylacetic acid levels in adult and pediatric patients did not show a consistent relationship with either urinary phenylacetylglutamine or ammonia control.

CONCLUSION

The findings are collectively consistent with substantial yet variable pre-systemic (1st pass) conversion of phenylbutyric acid to phenylacetic acid and/or phenylacetylglutamine. The variability of blood metabolite levels during the day, their weaker correlation with dose, the need for multiple blood samples to capture trough and peak, and the inconsistency between phenylacetic acid and urinary phenylacetylglutamine as a marker of waste nitrogen scavenging limit the utility of plasma levels for therapeutic monitoring. By contrast, 24-hour urinary phenylacetylglutamine and morning spot urine phenylacetylglutamine correlate strongly with dose and appear to be clinically useful non-invasive biomarkers for compliance and therapeutic monitoring.

Simultaneous LC-MS/MS determination of phenylbutyrate, phenylacetate benzoate and their corresponding metabolites phenylacetylglutamine and hippurate in blood and urine

Inborn errors of urea metabolism result in hyperammonemia. Treatment of urea cycle disorders can effectively lower plasma ammonium levels and results in survival in the majority of patients. Available medications for treating urea cycle disorders include sodium benzoate (BA), sodium phenylacetate (PAA), and sodium phenylbutyrate (PBA) and are given to provide alternate routes for disposition of waste nitrogen excretion. In this study, we develop and validate a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of benzoic acid, phenylacetic acid, phenylbutyric acid, phenylacetylglutamine, and hippuric acid in plasma and urine from children with inborn errors of urea synthesis. Plasma extracts and diluted urine samples were injected on a reverse-phase column and identified and quantified by selected reaction monitoring (SRM) in negative ion mode. Deuterated analogues served as internal standards. Analysis time was 7 min. Assay precision, accuracy, and linearity and sample stability were determined using enriched samples. Quantification limits of the method were 100 ng/ml (0.3-0.8 μmol/L) for all analytes, and recoveries were >90%. Inter- and intraday relative standard deviations were <10%. Our newly developed LC-MS/MS represents a robust, sensitive, and rapid method that allows simultaneous determination of the five compounds in plasma and urine.

Hyperaminoaciduria in mild phosphate diabetes in adults

Quantitative urinary amino acid excretion has been studied in 23 adult patients with mild phosphate diabetes (MPD), in 22 adult control patients with various renal disorders and in 15 children, 7--19 years old, with atopic disorders (normal controls). Statistically significant increases in urinary excretion of glutamine (p < 0.01), glycine (p < 0.01) and cystine (p < 0.05) were found in the MPD patients compared to the normal controls. The urinary excretion of glutamine was significantly increased while the increases in cystine and glycine excretions were non-significant when MPD patients were compared to the control patients. In addition to clinical signs and analyses of plasma and urinary phosphate, a quantitative evaluation of urinary amino acids might be a tool in the diagnosis of MPD. The significance of the increased urinary amino acid excretion in MPD is discussed.

1H NMR spectroscopy for the prediction of therapeutic outcome in patients with fulminant hepatic failure

A high-resolution (1)H NMR study of serum and urine of fulminant hepatic failure patients (n = 22) [surviving (n = 12) and non-surviving (n = 10)] is reported. Glutamine in serum and urine glutamine:creatinine ratio were higher in non-surviving patients compared with surviving patients [serum glutamine, 3.08 (1.68-7.11) vs 0.56 (0.34-0.99) mM, median and range; p = 0.0001 and urine glutamine:creatinine ratio, 1.72 (0.24-7.76) vs 0.39 (0.1-0.84), p = 0.1], and urine urea:creatinine ratio was higher in surviving patients compared with non-surviving patients [10.83 (0.2-22.6) vs 2.09 (0.96-4.0), p = 0.002]. On the other hand, no significant differences were found in the conventionally employed clinical parameters such as serum alanylaminotransferase, aspartylaminotransferase and bilirubin except prothrombin time (p = 0.02). The difference in serum glutamine and urine urea was significant in the two categories of patients and distinctly different values of serum glutamine for both the categories of patients correctly predicted the outcome. These results promise immense potential for NMR spectroscopy in rapidly deciding on the need for advanced therapeutic intervention such as artificial liver support or emergency liver transplantation in FHF.

Does acute glutamine depletion enhance the response of glutamine synthesis to fasting in muscle in adult and old rats?

BACKGROUND AND AIMS

In earlier studies, skeletal muscle glutamine synthetase (GS) activity was shown to be enhanced by fasting and glucocorticoids, and inhibited by exogenous glutamine (Gln) supplementation. The current study was designed to determine whether phenylbutyrate (PhiB), a Gln-chelating agent in humans, (1) could trap Gln and produce a decline in plasma Gln in rats, as it does in humans, and (2) if so, whether (Phi)B would further enhance the response of muscle GS activity to fasting in rats.

METHODS

Adult (6-8 months) and aged (20-21 months) rats were fasted for 5 days and received two doses of 0.5 g(Phi)Bby orogastric route at times 0 and 4 h, and were then sacrificed at 5.5 h. Plasma Gln was measured by enzymatic methods, other amino acids were quantified by amino acid analysis. GS activity was measured in soleus (SO) and tibialis anterior (TA) muscles.

RESULTS

(Phi)B treatment was associated with: (1) a 20% decline in plasma Gln concentration from 572+/-54 to 424+/-34 micromol/L (P<0.05) and from 476+/-49 to 360+/-80 micromol/L (P<0.05) in fasted adult and old rats, respectively; and (2) a preservation of GS up-regulation by fasting in TA and SO muscles in both adult and aged rats, with TA muscle GS activities of 198+/-65 vs. 203+/-68 ((Phi)B-treated vs. vehicle-treated, NS), and 244+/-81 vs. 274+/-59 (NS) nmol/h/mg protein in adult and aged rats, respectively.

CONCLUSION

These data suggest that: (1) large doses of (Phi)B deplete plasma Gln in fasted rats, regardless of age, (2) Gln depletion induced by Phi)B does not alter GS activity.

N-Acetyl Functions and Acetate Detected by Nuclear Magnetic Resonance Spectroscopy of Urine to Detect Renal Dysfunction following Aminoglycoside and/or Glycopeptide Antibiotic Therapy

BACKGROUND/AIMS

N-acetylneuraminidine (NeuNAc), N-acetylglutamine (GIcNAc) and acetate are metabolites present in normal urine. In patients treated with aminoglycosides and/or glycopeptides, elevation of these metabolites in urine suggests renal tubular injury. NeuNAc, GIcNAc and acetate are easily detected by magnetic resonance spectroscopy (MRS), in contrast to other bioanalytical methods. In the present study, these urinary metabolites were detected using MRS and compared with standard biochemical markers of renal injury in intensive care unit patients treated with aminoglycosides and/or glycopeptides.

METHODS

16 patients with clinical and biochemical signs of renal dysfunction were included in the study. Proton magnetic resonance spectra were obtained from 134 urine samples. The resonance intensity of NeuNAc, GIcNAc and acetate were reported relative to the resonance intensity of creatinine (ct). These ratios were compared with classical parameters of renal dysfunction, such as plasma creatinine and urea concentration, and 24-hour urine volume, by logistic regression and general linear models.

RESULTS

Statistical analysis showed that changes in plasma creatinine and urea concentration were reliably reflected in changes in the NeuNAc/ct ratio, and that plasma urea concentration changes also correlated with the acetate/ct ratio; however, the GIcNAc/ct ratio was not related to these measures of overall renal function.

CONCLUSIONS

NeuNAc/ct may be a useful marker of renal dysfunction in patients treated with aminoglycosides and glycopeptides; by MRS it can be both straightforward and informative to follow the renal function of patients treated with these antibiotics.

A new dimension of 1H-NMR spectroscopy in assessment of liver graft dysfunction

High-resolution 1H-NMR spectroscopy of serum and urine samples of an 11-year-old male living related orthotopic liver transplant recipient is reported. Serum glutamine increased to abnormal levels along with simultaneous abnormal excretion of urinary glutamine post-transplantation. High levels of glutamine in both blood and urine and concomitant reduced urea levels in urine were found to be evidence of impairment in urea cycle and compatible with persistently abnormal graft function. Thus glutamine levels in serum and urine, and urea in the urine as observed by 1H-NMR spectroscopy highlight their important roles in monitoring liver graft function; increased glutamine levels lead to brain damage, if untreated.

Pain intensity, illness duration, and protein catabolism in temporomandibular disorder patients with chronic muscle pain

AIMS

To investigate whether the duration of chronic pain in temporomandibular disorder (TMD) patients is associated with a net depletion of amino acids, and a distinct process from pain intensity.

METHODS

Twenty-nine patients defined by the research diagnostic criteria/TMD as having Type 1a muscle pain (TMD1A group), and 34 age- and sex-matched control subjects, were assessed for variation in urinary organic and amino acid excretion by gas chromatography-mass spectrometry.

RESULTS

The TMD1A patients' mean pain intensity, assessed on a visual analog scale (VAS), was 5.4 (95% confidence limits: 4.5 to 6.3), TMD1A illness duration was 5.0 +/- 1.2 (SD) years, number of body areas with pain/subject was 6.3 +/- 2.4 (range 0 to 10), and symptom prevalence from the Symptom Check List-90-Revised (SCL-90-R) was 25.5 +/- 11.3 symptoms/subject, which was higher than the controls (5.2 +/- 5.0 symptoms/subject, P < .001). TMD1A patient illness duration was positively correlated with symptom prevalence and body pain distribution, and all were independent of pain intensity. The TMD1A patients had: (1) and increased tyrosine:leucine ratio; and (2) reduced leucine concentrations (both P < .001), which suggests deregulated catabolism. Pain intensity was associated with: (1) changes in the multivariate urinary metabolite excretion patterns (P < .001); (2) reduced leucine concentrations (P < .001); and (3) increases in total urinary metabolites (P < .04), and in 2 unidentified molecules, UM28 (P < .001) and CFSUM1 (P < .002). TMD1A illness duration was associated with lower (1) urinary metabolite concentrations and (2) succinic acid and combined glutamine + glutamic acid levels, suggesting a progressive depletion of metabolite reserves.

CONCLUSION

In TMD1A patients, total amino acid excretion was positively correlated with pain intensity and negatively correlated with illness duration, which indicated that illness duration was associated with a different set of metabolic anomalies compared with those identified for pain intensity.

Identification of phenylbutyrylglutamine, a new metabolite of phenylbutyrate metabolism in humans

Phenylbutyrate is used in humans for treating inborn errors of ureagenesis, certain forms of cancer, cystic fibrosis and thalassemia. The known metabolism of phenylbutyrate leads to phenylacetylglutamine, which is excreted in urine. We have identified phenylbutyrylglutamine as a new metabolite of phenylbutyrate in human plasma and urine. We describe the synthesis of phenylbutyrylglutamine and its assay by gas chromatography/mass spectrometry as a tert-butyldimethylsilyl or methyl derivative, using standards of [(2)H(5)]phenylbutyrylglutamine and phenylpropionylglutamine. After administration of phenylbutyrate to normal humans, the cumulative urinary excretion of phenylacetate, phenylbutyrate, phenylacetylglutamine and phenylbutyrylglutamine amounts to about half of the dose of phenylbutyrate. Thus, additional metabolites of phenylbutyrate are yet to be identified.

An integrated (2)H and (13)C NMR study of gluconeogenesis and TCA cycle flux in humans

Hepatic glucose synthesis from glycogen, glycerol, and the tricarboxylic acid (TCA) cycle was measured in five overnight-fasted subjects by (1)H, (2)H, and (13)C NMR analysis of blood glucose, urinary acetaminophen glucuronide, and urinary phenylacetylglutamine after administration of [1,6-(13)C(2)]glucose, (2)H(2)O, and [U-(13)C(3)]propionate. This combination of tracers allows three separate elements of hepatic glucose production (GP) to be probed simultaneously in a single study: 1) endogenous GP, 2) the contribution of glycogen, phosphoenolpyruvate (PEP), and glycerol to GP, and 3) flux through PEP carboxykinase, pyruvate recycling, and the TCA cycle. Isotope-dilution measurements of [1,6-(13)C(2)] glucose by (1)H and (13)C NMR indicated that GP in 16-h-fasted humans was 10.7 +/- 0.9 micromol.kg(-1).min(-1). (2)H NMR spectra of monoacetone glucose (derived from plasma glucose) provided the relative (2)H enrichment at glucose H-2, H-5, and H-6S, which, in turn, reflects the contribution of glycogen, PEP, and glycerol to total GP (5.5 +/- 0.7, 4.8 +/- 1.0, and 0.4 +/- 0.3 micromol.kg(-1).min(-1), respectively). Interestingly, (13)C NMR isotopomer analysis of phenylacetylglutamine and acetaminophen glucuronide reported different values for PEP carboxykinase flux (68.8 +/- 9.8 vs. 37.5 +/- 7.9 micromol.kg(-1).min(-1)), PEP recycling flux (59.1 +/- 9.8 vs. 27.8 +/- 6.8 micromol.kg(-1).min(-1)), and TCA cycle flux (10.9 +/- 1.4 vs. 5.4 +/- 1.4 micromol.kg(-1).min(-1)). These differences may reflect zonation of propionate metabolism in the liver.

Identification of the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney

Glucocorticoid hormones enhance the reabsorptive capacity of filtered amino acids in rat kidney, as it was shown in previous in vivo clearance experiments. In the present study, the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney was investigated using in vivo micropuncture technique. Adult female Wistar rats were treated with dexamethasone (DEX), and fractional excretion of L-glutamine (L-Gln) and L-leucine (L-Leu) were determined and related to inulin after microinfusion into different nephron segments. DEX reduced fractional excretion of both neutral amino acids as a sign of enhanced reabsorptive capacity. The site of main DEX action on L-Leu reabsorption has been localized in the proximal straight tubule. However, in the case of L-Gln, the inhibition of gamma-glutamyltranspeptidase (gamma-GT) by administration of acivicin indicated the importance of this brush border enzyme in reduced L-Gln excretion. DEX enhanced gamma-GT activity by tubular acidification. It can be presumed a DEX-inducible transport system for neutral amino acids mainly localized in proximal straight tubules of rat kidney.

Glutamate, a window on liver intermediary metabolism

In isotopic experiments, the labeling pattern of glutamate opens a window on hepatic metabolism, particularly the citric acid cycle, gluconeogenesis and fatty acid oxidation. This is because glutamate is in isotopic equilibrium with alpha-ketoglutarate, whose labeling pattern is influenced by the following: 1) the contributions of glucose and fatty acids to acetyl-CoA, 2) the relative contributions of pyruvate carboxylase and pyruvate dehydrogenase to the entry of pyruvate carbon into the citric acid cycle, and 3) the rate of gluconeogenesis in relation to citric acid cycle activity. In humans and primates, hepatic glutamate can be sampled noninvasively via urinary phenylacetylglutamine, which is formed in liver from phenylacetate (a side product of phenylalanine catabolism) and glutamine (which equilibrates with liver glutamate and alpha-ketoglutarate). The (14)C- or (13)C-labeling pattern of the glutamate moiety of phenylacetylglutamine can be measured by sequential degradations to (14)CO(2), gas chromatography-mass spectrometry or nuclear magnetic resonance (NMR). When phenylacetylglutamine is labeled from singly labeled [(14)C]- or [(13)C]substrates, relative metabolic rates can be computed from the labeling pattern using Landau's model. In diabetic patients infused with [3-(13)C]pyruvate, the noninvasive sampling of hepatic glutamate via phenylacetylglutamine allows one to test the degree of liver insulinization via the (pyruvate carboxylase)/(pyruvate dehydrogenase) activity ratio. This ratio regulates gluconeogenesis in part. Its measurement may allow the identification of patients who might benefit from the intraperitoneal administration of insulin, or from recently developed antidiabetic drugs.

Plasma concentrations and renal clearance of orotic acid in argininosuccinic acid synthetase deficiency

Argininosuccinic acid synthetase deficiency (ASD) is a rare disorder of urea cycle metabolism, with pronounced citrullinemia and orotic aciduria being characteristic biochemical features. To further investigate the role of plasma orotic acid and its possible use for monitoring the metabolic status in ASD, we determined plasma orotic acid, amino acid, and ammonium levels in plasma samples collected over a period of 3 years from a patient who is now 8 years of age. Orotic acid plasma concentrations varied widely from less than 1 micromol/l to more than 60 micromol/l. The renal clearance of orotic acid was eightfold the glomerular filtration rate, thus supporting an active mechanism underlying the excretion of this pyrimidine. Data obtained during a metabolic crisis yielded a statistically significant linear correlation of orotic acid plasma levels with those of glutamine and ammonium, which are generally accepted for assessment of the successful treatment of this disorder. Our data revealed no advantage of plasma orotic acid concentrations over the established amino acids (glutamine and arginine) and ammonium for determining acute treatment responses. Since several effects of high levels of orotic acid have been described in mammals, further research is necessary to assess a possible contribution of orotic acid to the pathogenesis of ASD and the use of plasma orotic acid levels in the long-term monitoring of these patients.

Glutamate-containing parenteral nutrition doubles plasma glutamate: a risk factor in neurosurgical patients with blood-brain barrier damage?

OBJECTIVES

Animal studies have shown that the elevation of plasma glutamate levels increase cerebral edema formation whenever the blood-brain barrier is disturbed. Therefore, changes in plasma glutamate levels as influenced by the administration of a glutamate-containing amino acid solution were investigated in neurosurgical patients.

DESIGN

Prospective, descriptive study.

SETTING

Eight-bed neurosurgical intensive care unit in a university hospital.

PATIENTS

Twenty-three neurosurgical patients requiring parenteral nutrition.

INTERVENTIONS

Parenteral nutrition was begun 24 hrs after craniotomy. Patients receiving a glutamate-containing amino acid solution (3.75 g/L glutamate) were compared with patients infused with a glutamate-free solution.

MEASUREMENTS AND MAIN RESULTS

Arterial plasma and urine amino acids were analyzed using high-performance liquid chromatography. Administration of a glutamate-containing solution doubled plasma glutamate levels in neurosurgical patients (from 53.3 +/- 9.8 microM [preinfusion] to 98.5 +/- 18.7 microM [after 4 hrs of infusion]; p < 0.001), whereas no elevation was seen when infusing a glutamate-free solution (from 52.3 +/- 7.3 [1 hr of infusion] to 53.6 +/- 6.4 microM [4 hrs of infusion]). Upon terminating the glutamate-containing infusion, arterial plasma glutamate levels decreased immediately (from 120 +/- 13.2 microM to 81.2 +/- 19.5 microM). Glutamate as infused in excess appears to exceed a renal threshold and is eliminated renally.

CONCLUSIONS

As shown in animal models, administration of a glutamate-containing amino acid solution significantly increased plasma glutamate levels. Because such an increase in plasma glutamate levels could aggravate cerebral edema formation, glutamate-containing amino acid solutions cannot be recommended for patients with a disturbed blood-brain barrier.

Influence of epidermal growth factor (EGF) on renal transport of PAH and amino acids in amino acid loaded rats

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal transport of p-amino-hippurate (PAH), electrolytes, and amino acids was investigated. After loading with PAH (200 mg/100 g b.wt. iv.), PAH excretion in EGF treated rats (8 microg/100 g b.wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was increased by about 20 %. Continuous infusions of glutamine, arginine (both 50 mg/100 g b.wt. per hour), or alanine (90 mg/ 100 g b.wt. per hour) were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment was followed by a stimulation of renal amino acid reabsorption. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pre-treatment (0.96+/-0.10 vs. 0.62+/-0.07 ml/min x 100 g b.wt.), with a distinct increase in sodium excretion (2.98+/-0.55 vs. 4.97+/-0.71 microval/100 g b.wt. x 20 min) and with a retarded normal kidney weight gain (874+/-18 vs. 775+/-32 mg/100 g b.wt.). A simultaneous PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions.

Measurement of urinary amino acids using high-performance liquid chromatography equipped with a strong cation exchange resin pre-column

We determined the urinary amino acid concentrations by high-performance liquid chromatography (HPLC) using an eluent buffer which had been processed through a column packed with strong cation-exchange resin. With this column, ghost peaks resolved or much reduced in size and shifted to a post-arginine position. A clearer separation of peaks of urinary amino acids and ammonia was obtained. This could be due to the elimination of O-phthalaldehyde reactive substances in the eluent by the resin column. This method does not require a separate step to remove ammonia, unlike most of the methods currently used, and thus saves time.

Epidermal growth factor (EGF) increases the renal amino acid transport capacity in amino acid loaded rats

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal amino acid handling was investigated in glutamine, arginine (both 50 mg/100 g b.wt. per hour), or alanine (90 mg/100 g b.wt. per hour) loaded animals. Continuous infusions of the three amino acids were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment (8 micrograms/100 g b.wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was followed by a stimulation of renal amino acid reabsorption. The increase in the fractional excretion of the administered amino acids was significantly lower than in non-EGF-treated rats. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pretreatment (0.96 +/- 0.10 vs. 0.62 +/- 0.07 ml/min x 100 g b.wt.) and a distinct increase in sodium excretion (2.98 +/- 0.55 vs. 4.97 +/- 0.71 muval/100 g b.wt. x 20 min). After loading with p-aminohippurate (PAH; 200 mg/100 g b.wt.), PAH excretion in EGF rats was increased by about 20%, whereas urinary protein excretion was lower in EGF pretreated rats (control: 0.45 +/- 0.04 vs. EGF: 0.18 +/- 0.03 mg/100 g b.wt. x 20 min). The PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions. Furthermore, EGF pretreatment depressed normal kidney weight gain significantly (874 +/- 18 vs. 775 +/- 32 mg/100 g b.wt.). EGF can improve the renal tubular transport capacity, but, compared to well-known stimulators of renal transport like dexamethasone or triiodothyronine, its effect is only of a moderate degree.

Physiologically based pharmacokinetics and the dermal absorption of 2-butoxyethanol vapor by humans

It has generally been assumed that the skin contributes only minor amounts to the total uptake of solvent vapors, relative to the respiratory tract. Contrary to this assumption, the widely used glycol ether solvent, 2-butoxyethanol (BE), has been reported to be more effectively absorbed through the skin (75% of the total uptake) than through the lungs of humans (Johanson and Boman, 1991, Br. J. Ind. Med. 48, 788). The possibility that the finger prick blood sampling technique used in the Johanson and Boman study was confounded by locally high concentrations of BE at the site of absorption was suggested using a previously developed PBPK model (Corley et al., 1994, Toxicol. Appl. Pharmacol. 129, 61). The current study was conducted to verify the PBPK analysis and to determine whether or not the skin was the major site for absorption of BE vapor by exposing one arm from each of six human volunteers to 50 ppm 13C2-BE vapor for 2 hr. To evaluate the potential consequences of blood sampling techniques, samples were taken from both the unexposed arm (catheter; during and after exposure) and the exposed arm (finger prick; end of the exposure only) for analysis of both BE and its major metabolite, butoxyacetic acid (BAA). Butoxyacetic acid is responsible for the hemolysis observed in toxicity studies with laboratory animals. Humans, however, are significantly less sensitive to this effect. The concentration of BE in the finger prick blood samples averaged 1500 times higher than the corresponding concentration in venous blood sampled from a catheter installed in the unexposed arm at the end of the exposure. Blood BAA levels were generally within a factor of 4 of each other for the two techniques and, therefore, was considered a better indicator of systemic absorption. Urine was collected for 24 hr and analyzed for the following metabolites found in rat metabolism studies: free and conjugated BE, BAA, ethylene glycol (EG), and glycolic acid (GA), with only BAA detected in the human urine. More importantly, urinary BAA was found to be extensively conjugated ( approximately 67%) with glutamine, confirming recent reports. These results, coupled with PBPK modeling of worst-case exposure scenarios (no clothing, 100% of the body was exposed), demonstrated that no more than 15-27% (low-to-high relative temperatures and humidities), not 75%, of the total uptake of BE could be attributed to the skin of humans during simulated 8-hr exposures to the ACGIH TLV concentration of 25 ppm. Even less of the total uptake was attributed to the skin during simulations of exercise with whole-body exposures (5-9%) or by more realistic exposures of only the arms and head (1-8%). As a result, humans are unlikely to reach hemolytic concentrations of the metabolite BAA in blood following vapor exposures to BE.

Combined HPLC, NMR spectroscopy, and ion-trap mass spectrometry with application to the detection and characterization of xenobiotic and endogenous metabolites in human urine

The direct coupling of HPLC with NMR spectroscopy has been extended by splitting the HPLC eluent after conventional UV detection and sending part to a NMR spectrometer and part to an ion-trap mass spectrometer in a "triplehyphenated" HPLC-NMR-MS system. Combined UV, 1H NMR, and positive-ion electrospray MS detection was achieved in the continuous-flow mode using whole human urine from a subject dosed with acetaminophen. By means of HPLC-NMR-MS, the structural information available from the complementary spectroscopic techniques provided rapid confirmation of the identity of the acetaminophen glucuronide and sulfate metabolites, together with a number of endogenous metabolites. In particular, the HPLC-NMR-MS approach allowed the unequivocal identification of phenylacetylglutamine in human urine, an endogenous metabolite not previously observed in 1H NMR spectra of urine because of extensive overlap with resonances from other metabolites. The analytical advantages and complementarity of NMR and MS techniques in direct hyphenation with HPLC are discussed. The new technique of HPLC-NMR-MS will provide the scope for more comprehensive and fully automated analysis of biofluids and other complex mixtures than was previously available from single hyphenation of these instruments.

Increased contribution by myofibrillar protein to whole-body protein breakdown according to severity of surgical stress

A study was conducted to clarify the contribution by myofibrillar protein to whole-body protein breakdown in surgically stressed patients. Thirteen patients who underwent esophagectomy (group E) and 22 who underwent gastric or colorectal operation (group GC) were studied. Patients were all male and younger than 65 y old. Whole-body protein breakdown was determined using constant infusion of 15N-glycine. Urinary excretion of total catecholamines and 3-methylhistidine (3-MH) were measured. Amino acid composition of femoral arterial and venous blood was also analyzed. All the patients were fed exclusively by total parenteral nutrition providing 1.5 g protein and 40 kcal.kg-1.d-1 throughout the study. Whole-body protein breakdown increased significantly in group E (P < 0.01) and group GC (P < 0.05) on the 3rd postoperative day. The increase was significantly greater in group E than group GC (P < 0.01). Urinary excretion of 3-MH also increased significantly in group E (P < 0.01) and in group GC (P < 0.01) on the 3rd postoperative day. The increase was also greater in group E than group GC (P < 0.01). The ratio of urinary 3-MH excretion to whole-body breakdown protein (mumol/g), which is a indicator for the contribution of myofibrillar protein to the whole-body protein breakdown, increased significantly from 0.84 +/- 0.30 of preoperative value to 1.79 +/- 0.38 in group E (mean +/- SD; P < 0.01) and 1.42 +/- 0.18 in group GC (P < 0.05) on the 3rd postoperative day. This ratio was significantly higher in group E (P < 0.05). Furthermore, the ratio of myofibrillar to whole-body protein breakdown correlated significantly with urinary excretion of total catecholamines (r = 0.546; P < 0.01). Therefore, the contribution of myofibrillar protein to whole-body protein breakdown increased proportionately with the severity of surgical stress. On the other hand, femoral-arteriovenous differences of BCAA, Ala, Gln, Tyr, and Phe correlated significantly with the urinary excretion of 3-MH. These data suggest that skeletal muscle protein degradation is proportional to the breakdown of total myofibrillar proteins and both correlate with the severity of stress. From these data, it may be suggested that the contribution of skeletal muscle to whole-body protein catabolism is increased postoperatively, and that the increase is correlated with the severity of surgical stress.

Noninvasive probing of citric acid cycle intermediates in primate liver with phenylacetylglutamine

In human and primate liver, phenylacetate and glutamine form phenylacetylglutamine, which is excreted in urine. Probing noninvasively the labeling pattern of liver citric acid cycle intermediates with phenylacetylglutamine assumes that the labeling pattern of its glutamine moiety reflects that of liver alpha-ketoglutarate. To validate this probe, we infused monkeys with [U-13C3]lactate, [3-13C]lactate, [1, 2-13C2]acetate, [2-13C]acetate, [U-13C3]glycerol, or 2-[3-13C]ketoisocaproate and compared the labeling patterns of urinary phenylacetyl-glutamine with those of glutamate and glutamine in liver, plasma, muscle, and kidney and liver alpha-ketoglutarate. Only with [U-13C3]lactate or [3-13C]lactate does the labeling pattern of phenylacetylglutamine reflect patterns of liver alpha-ketoglutarate and glutamate. With [13C]acetate, muscle and kidney glutamate are more labeled than liver metabolites. This confirms that with [13C]acetate, the labeling pattern of liver metabolites is influenced by 13CO2 and [13C]glutamine made in peripheral tissues. Our data validate the use of phenylacetylglutamine labeled from [3-13C]lactate or [3-13C]pyruvate to probe noninvasively the pyruvate carboxylase-to-pyruvate dehydrogenase flux ratio in human subjects.

Estimates of Krebs cycle activity and contributions of gluconeogenesis to hepatic glucose production in fasting healthy subjects and IDDM patients

Normal subjects, fasted 60 h, and patients with insulin-dependent diabetes mellitus (IDDM), withdrawn from insulin and fasted overnight, were given phenylacetate orally and intravenously infused with [3-14C]lactate and 13C-bicarbonate. Rates of hepatic gluconeogenesis relative to Krebs cycle rates were estimated from the 14C distribution in glutamate from urinary phenylacetylglutamine. Assuming the 13C enrichment of breath CO2 was that of the CO2 fixed by pyruvate, the enrichment to be expected in blood glucose, if all hepatic glucose production had been by gluconeogenesis, was then estimated. That estimate was compared with the actual enrichment in blood glucose, yielding the fraction of glucose production due to gluconeogenesis. Relative rates were similar in the 60-h fasted healthy subjects and the diabetic patients. Conversion of oxaloacetate to phosphoenolpyruvate was two to eight times Krebs cycle flux and decarboxylation of pyruvate to acetyl-CoA, oxidized in the cycle, was less than one-30th the fixation by pyruvate of CO2. Thus, in estimating the contribution of a gluconeogenic substrate to glucose production by measuring the incorporation of label from the labelled substrate into glucose, dilution of label at the level of oxaloacetate is relatively small. Pyruvate cycling was as much as one-half the rate of conversion of pyruvate to oxaloacetate. Glucose and glutamate carbons were derived from oxaloacetate formed by similar pathways if not from a common pool. In the 60-h fasted subjects, over 80% of glucose production was via gluconeogenesis. In the diabetic subjects the percentages averaged about 45%.

Disposition of phenylbutyrate and its metabolites, phenylacetate and phenylacetylglutamine

Phenylacetate, an inducer of tumor cytostasis and differentiation, shows promise as a relatively nontoxic antineoplastic agent. Phenylacetate, however, has an unpleasant odor that might limit patient acceptability. Phenylbutyrate, an odorless compound that also has activity in tumor models, is known to undergo rapid conversion to phenylacetate by beta-oxidation in vivo. This phase I study examined the pharmacokinetics of phenylbutyrate and characterized the disposition of the two metabolites, phenylacetate and phenylacetylglutamine. Fourteen patients with cancer (aged 51.8 +/- 13.8 years) received a 30-minute infusion of phenylbutyrate at 3 dose levels (600, 1200, and 2000 mg/m2). Serial blood samples and 24-hour urine collections were obtained. Samples were assayed by high-performance liquid chromatography. A model to simultaneously describe the pharmacokinetics of all three compounds was developed using ADAPT II. Data were modeled as molar equivalents. The model fit the data well as shown by mean (+/- SD) coefficients of determination (r2) for phenylbutyrate, phenylacetate, and phenylacetylglutamine, which were 0.96 +/- 0.07, 0.88 +/- 0.10, and 0.92 +/- 0.06, respectively. The intrapatient coefficient of variation percentage (CV%) around the parameter estimates were small (range 7.2-33.5%). Phenylbutyrate achieved peak concentrations in the range of in vitro tumor activity (500-2000 mumol/L) and exhibited saturable elimination (Km = 34.1 +/- 18.1 micrograms/mL and Vmax = 18.1 +/- 18 mg/h/kg). Metabolism was rapid; the times to maximum concentration for phenylacetate and phenylacetylglutamine were 1 and 2 hours, respectively. The conversion of phenylbutyrate to phenylacetate was extensive (80 +/- 12.6%), but serum concentrations of phenylacetate were low owing to rapid, subsequent conversion to phenylacetylglutamine.(ABSTRACT TRUNCATED AT 250 WORDS)

13C-nuclear magnetic resonance spectroscopy studies of hepatic glucose metabolism in normal subjects and subjects with insulin-dependent diabetes mellitus

To determine the effect of insulin-dependent diabetes mellitus (IDDM) on rates and pathways of hepatic glycogen synthesis, as well as flux through hepatic pyruvate dehydrogenase, we used 13C-nuclear magnetic resonance spectroscopy to monitor the peak intensity of the C1 resonance of the glucosyl units of hepatic glycogen, in combination with acetaminophen to sample the hepatic UDP-glucose pool and phenylacetate to sample the hepatic glutamine pool, during a hyperglycemic-hyperinsulinemic clamp using [1-13C]-glucose. Five subjects with poorly controlled IDDM and six age-weight-matched control subjects were clamped at a mean plasma glucose concentration of approximately 9 mM and mean plasma insulin concentrations approximately 400 pM for 5 h. Rates of hepatic glycogen synthesis were similar in both groups (approximately 0.43 +/- 0.09 mumol/ml liver min). However, flux through the indirect pathway of glycogen synthesis (3 carbon units-->-->glycogen) was increased by approximately 50% (P < 0.05), whereas the relative contribution of pyruvate oxidation to TCA cycle flux was decreased by approximately 30% (P < 0.05) in the IDDM subjects compared to the control subjects. These studies demonstrate that patients with poorly controlled insulin-dependent diabetes mellitus have augmented hepatic gluconeogenesis and relative decreased rates of hepatic pyruvate oxidation. These abnormalities are not immediately reversed by normalizing intraportal concentrations of glucose, insulin, and glucagon and may contribute to postprandial hyperglycemia.

Appearance of intraportally infused [15N]urea in blood and urine of domestic fowl

The time course of the occurrence of intraportally infused [15N]urea in blood and urine was investigated in chickens. The infused urea appeared in ureteral urine, mostly in the form of urea, as early as 30 min after the start of infusion and the excretion further increased up to the end of 2 hr infusion. Blood urea concentration rapidly increased and reached about three times the initial level at the end of the experiment (P < 0.05 after 20 min), but no significant effects were observed on uric acid, ammonia and glutamine concentrations. Fifty-seven percent of blood urea N and 3% of blood glutamine-amide N and 1% of blood ammonia N, which were determined at the end of experiment, were derived from the infused urea N. It is concluded that urea, which is rapidly increased in blood and urine after feeding urea to chickens, is mostly derived from dietary urea.

Assay of the concentration and 13C-labeling pattern of phenylacetylglutamine by nuclear magnetic resonance

Phenylacetate, derived from phenylalanine, is converted in human and primate liver to phenylacetylglutamine. The latter, which is excreted in urine, has been used to probe noninvasively the labeling pattern of liver citric acid cycle intermediates. We present nuclear magnetic resonance assays for the urinary concentration of phenylacetylglutamine and for the 13C-labeling pattern of its glutamine moiety. The concentration of phenylacetylglutamine is calculated from the natural 13C signals of all carbons of its benzene ring and C-2 of its acetyl moiety. The limit of detection is 13 mumol of unlabeled phenylacetylglutamine. The minimum amount of phenylacetylglutamine needed to determine a 1% enrichment of one of its carbons is 26 mumol. The technique was tested by analyzing phenylacetylglutamine in the urine from monkeys infused with various 13C tracers. The labeling patterns obtained agreed with theoretical calculations and patterns reported in phenylacetylglutamine and glutamine labeled from 14C and 13C tracers, respectively.

Liquid chromatographic-mass spectrometric analysis of N-acetylamino acids in human urine

Liquid chromatography-atmospheric pressure chemical-ionization mass spectrometry (LC-APCI-MS) was used for the analysis of N-acetylamino acids that could not be determined with an amino acid analyzer. LC-APCI-MS could directly detect the protonated molecular ions of various synthetic N-acetylamino acids, distinguishing N-acetylserine from O-acetylserine and N(alpha)-acetyllysine from N(epsilon)- acetyllysine. Furthermore, N-acetylasparagine, N-acetylaspartic acid, N-acetylglutamine and N-acetylglutamic acid were identified in normal human urine. The assay data for N-acetylaspartic acid agree with a previous report using gas chromatography-mass spectrometry. These results demonstrate the usefulness of the apparatus described above for the analysis of N-acetylamino acids in biological samples.

Renal ammonia and glutamine metabolism during liver insufficiency-induced hyperammonemia in the rat

Renal glutamine uptake and subsequent urinary ammonia excretion could be an important alternative pathway of ammonia disposal from the body during liver failure (diminished urea synthesis), but this pathway has received little attention. Therefore, we investigated renal glutamine and ammonia metabolism in midly hyperammonemic, portacaval shunted rats and severely hyperammonemic rats with acute liver ischemia compared to their respective controls, to investigate whether renal ammonia disposal from the body is enhanced during hyperammonemia and to explore the limits of the pathway. Renal fluxes, urinary excretion, and renal tissue concentrations of amino acids and ammonia were measured 24 h after portacaval shunting, and 2, 4, and 6 h after liver ischemia induction and in the appropriate controls. Arterial ammonia increased to 247 +/- 22 microM after portacaval shunting compared to controls (51 +/- 8 microM) (P < 0.001) and increased to 934 +/- 54 microM during liver ischemia (P < 0.001). Arterial glutamine increased to 697 +/- 93 microM after portacaval shunting compared to controls (513 +/- 40 microM) (P < 0.01) and further increased to 3781 +/- 248 microM during liver ischemia (P < 0.001). In contrast to controls, in portacaval shunted rats the kidney net disposed ammonia from the body by diminishing renal venous ammonia release (from 267 +/- 33 to -49 +/- 59 nmol/100 g body wt per min) and enhancing urinary ammonia excretion from 113 +/- 24 to 305 +/- 52 nmol/100 g body wt per min (both P < 0.01). Renal glutamine uptake diminished in portacaval shunted rats compared to controls (-107 +/- 33 vs. -322 +/- 41 nmol/100 g body wt per min) (P < 0.01). However, during liver ischemia, net renal ammonia disposal from the body did not further increase (294 +/- 88 vs. 144 +/- 101 nmol/100 g body wt per min during portacaval shunting versus liver ischemia). Renal glutamine uptake was comparable in both hyperammonemic models. These results indicate that the rat kidney plays an important role in ammonia disposal during mild hyperammonemia. However, during severe liver insufficiency induced-hyperammonemia, ammonia disposal capacity appears to be exceeded.

Rapid determination of glutamine in biological samples by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of glutamine in biological samples is presented. Glutamine was derivatized with ortho-phthalaldehyde reagent containing 3-mercaptopropionic acid and separated by reversed phase chromatography on a C18 column containing 3-microns particles. No interference from other amino acids was observed. The assay was linear over a range from 1 to 2,000 mumol/l. Analytical recovery of plasma samples spiked with glutamine was 98.6 +/- 3.8%. Within- and between-batch imprecision were 1.5% and 2.2%, respectively. The derivatization step was fully automated. Total analysis time, including derivatization and chromatography, amounted to 6 min. The method can be used for the determination of glutamine in plasma, urine, cerebrospinal fluid and tissue homogenates.

Influence of progressive tumor growth on glutamine metabolism in skeletal muscle and kidney

OBJECTIVE

The effects of progressive malignant growth on glutamine metabolism in skeletal muscle and in kidney were investigated.

SUMMARY BACKGROUND DATA

Fast-growing tumors consume considerable quantities of glutamine and lead to a decrease in circulating glutamine concentrations.

METHODS

Experiments were performed at various stages of tumor growth in rats implanted subcutaneously with the non-metastasizing methylcholanthrene-induced (MCA) fibrosarcoma and in pair-fed non tumor-bearing controls.

RESULTS

Tumor growth stimulated a twofold increase in hindquarter (muscle) glutamine release, which was not due to an increase in blood flow, but rather to a doubling in the fractional release rate. Consequently, a progressive decrease in skeletal muscle glutamine concentrations was observed over time. Simultaneously, the activity of glutamine synthetase (GS), the principal enzyme of de novo glutamine biosynthesis, increased more than twofold. This increase in muscle GS activity was accompanied by an increase in GS mRNA but the augmentation in GS expression apparently could not match the increased rate of efflux since muscle depletion developed. In rats with large tumors and severe glutamine depletion, GS activity was not elevated. Glutamine feeding increased muscle glutamine concentrations and glutamine synthetase specific activity. Although tumor growth led to the development of mild systemic acidemia, the classic renal adaptations normally observed, i.e., elevated glutaminase activity and accelerated renal glutamine utilization, were not present in acidotic tumor-bearing rats. Instead, renal GS activity was increased in tumor-bearing animals and ammoniagenesis was enhanced, in spite of a reduction in net renal glutamine uptake.

CONCLUSIONS

These data suggest that marked alterations in muscle and renal glutamine handling occur in the host with cancer; the enhanced muscle glutamine release in conjunction with no increase in renal consumption is consistent with increased glutamine uptake in other organs, most likely the tumor itself and the liver.

Bioavailability and pharmacokinetics of fluoride from two glutamine monofluorophosphate preparations

A two-way cross-over study was conducted on 12 Caucasian male healthy volunteers aged between 25 and 38 years in order to determine the bioavailability and pharmacokinetics of fluoride after single oral administration in fasting conditions of two products (tablets and powder for oral use) of L-glutamine monofluorophosphate (G-MFP, CAS 116420-36-1). The two products contained the equivalent of 10 mg F and the equivalent of 300 mg CA as calcium gluconate and calcium citrate. The two products were found bioequivalent with regard to the release of fluoride, both on the basis of the AUC and Cmax of fluoride in plasma and of the urinary excretion of fluoride during the 48 h following the administration. The pharmacokinetics of fluoride in plasma is characterized by a short lag time (< 6 min), a rapid absorption, a peak which is reached 0.5-1.0 h after administration, followed by a biphasic elimination. The first phase with a k alpha of 1.8 h-1 is followed by a slower phase with a K beta of 0.14 h-1. Probably the terminal elimination rate is slower, about 0.05 h-1. The urinary excretion of fluoride during the 48 h after administration accounted for 40-50% of the administered dose of fluoride. The results are consistent with those found in previous studies after administration in fasting conditions of sodium fluoride or sodium monofluorophosphate alone or in combination with calcium salts.

Determination of butoxyacetic acid and N-butoxyacetyl-glutamine in urine of lacquerers exposed to 2-butoxyethanol

To determine the fraction of butoxyacetic acid (BAA) which is excreted as the amino acid conjugate N-butoxyacetylglutamine (BAA-GLN), urine samples of six lacquerers exposed to 2-butoxyethanol (BE) were collected before and after work and analysed using an HPLC-method which allows the simultaneous quantification of both BAA species. Whereas the pre-shift samples contained only little or no butoxyethanol-related material, concentrations of BAA and BAA-GLN amounted collectively to up to 7 mmol/l in the samples obtained at the end of work. The ratio BAA-GLN vs. total BAA ranged from 0.16 to 0.64 (mean value 0.48) indicating that a substantial fraction of BAA was eliminated as the amino acid conjugate. The results demonstrate that BAA-GLN is an important metabolite of BE in man. Procedures employed for the biological monitoring of exposure to BE should therefore include the quantification of BAA-GLN, otherwise exposure levels would be underestimated.

Phenylacetylglutamine may replace urea as a vehicle for waste nitrogen excretion

Phenylacetylglutamine (PAG), the amino acid acetylation product of phenylacetate (or phenylbutyrate after beta-oxidation) was evaluated as a waste nitrogen product in patients with inborn errors of urea synthesis. A boy with carbamyl phosphate synthetase deficiency receiving a low nitrogen intake excreted 80-90% of administered phenylacetate or phenylbutyrate as PAG. The amount of PAG nitrogen excreted varied from 38-44% of his dietary nitrogen, similar to the relationship between urea nitrogen and dietary nitrogen found in normal subjects receiving low dietary nitrogen. With few exceptions, neither phenylacetate nor phenylbutyrate accumulated in plasma. Treatment with relatively high dose phenylacetate or phenylbutyrate (0.5-0.6 g/kg/d) resulted in normal daytime levels of glutamine. These data suggest that PAG may replace urea as a waste nitrogen product when phenylbutyrate is administered at a dose that yields PAG nitrogen excretion equal to 40-44% of a low nitrogen intake.

Endotoxin and renal glutamine metabolism

The effect of endotoxin on renal glutamine metabolism and ammoniagenesis was investigated in vivo in the rat to gain further insight into the altered glutamine flow that characterizes critical illness. Studies were done 15 hours following a single dose of Escherichia coli lipopolysaccharide (10 mg/kg). Renal blood flow and arterial glutamine concentration were similar in control and study rats, but the kidney switched from an organ of slight glutamine uptake in controls (129 +/- 52 nmol/100 g of body weight per minute) to net release in the endotoxin-treated animals (-273 +/- 170 nmol/100 g of body weight per minute). Simultaneously, the specific activity of renal glutamine synthetase increased by almost 50% (374 +/- 40 nmol/mg of protein per hour in rats given endotoxin vs 253 +/- 12 nmol/mg of protein per hour in controls), while glutaminase was unchanged. Urinary ammonia excretion was reduced by 35% in the endotoxin-treated animals (47 +/- 6 mumol/12 h in endotoxin-treated animals vs 70 +/- 8 mumol/12 h in controls) despite a 10% fall in the arterial bicarbonate value. Endotoxin alters the net flux of glutamine across the kidney which appears to be partially regulated enzymatically. This may impair the kidneys' ability to maintain acid/base homeostasis.

Utilization of intravenously administered N-acetyl-L-glutamine in humans

L-glutamine is too unstable for inclusion in solutions for parenteral nutrition, but its acetylated analogue, N-acetyl-L-glutamine is not. The purpose of this three-part study was to investigate the utilization of intravenously (IV) administered acetylglutamine in humans. In study 1, nine healthy postabsorptive subjects were given 9.4 g acetylglutamine IV during four hours. In study 2, five healthy subjects were studied on two occasions following an overnight fast. They were given 9.4 g of acetylglutamine or an equivalent amount of glutamine as part of a total parenteral nutrition (TPN) regimen during 7.2 hours. A control group of five subjects was given the same TPN regimen, but without acetylglutamine or glutamine. The nutrient solution included glucose, amino acids, and a fat emulsion, supplying 9.4 g nitrogen and 6,300 kJ in a total volume of 1.8 L. In study 3, four patients were studied the day after major surgery. They were given the same TPN regimen as in study 2, containing 9.4 g acetylglutamine, during 7.2 hours. Plasma concentrations and urinary excretion of acetylglutamine and glutamine were measured in all three studies, and so were splanchnic and renal exchange of acetylglutamine and glutamine in study 1. In study 1, the plasma concentration of glutamine rose from 594 +/- 28 mumol/L to 728 +/- 26 mumol/L (P less than .001), whereas plasma levels of acetylglutamine exceeded 1,000 mumol/L in all subjects at the end of infusion. The eight-hour urinary excretion of acetylglutamine and glutamine corresponded to 18% of the infused amount of acetylglutamine.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Paper chromatography of urinary amino acids. A 30 year survey of dietary influences on the normal pattern, and patients' results

In the clinical laboratory, paper chromatography is still the most useful, simple, inexpensive procedure for initial identification of abnormalities of amino acid excretion. The results of its use for more than 8000 paediatric and adult renal patients is surveyed. Nonspecific generalized aminoaciduria was the most frequent abnormality found, comprising some 70% of abnormal results, with cystine-lysinuria the next most common. The identification of the abnormal excretory pattern of amino acids as distinct from the normal was complicated by the effects of the New Zealand diet. In particular, valine, citrulline, hydroxyproline and glutamic acid are found in considerable amounts as part of the normal pattern. Their dietary origin is discussed. Varying mixtures of monosaccharides and disaccharides occurred in association with a range of amino acid patterns.

A new patient with hyperornithinaemia, hyperammonaemia and homocitrullinuria treated early with low protein diet

The characteristic biochemical disturbances of the amino acid and pyrimidine metabolism are described and illustrated by the first case of the HHH syndrome reported in Norway. The disorder was treated with a low protein diet at an early age and the patient developed normally on this diet.

Effect of the blood lactate concentration on renal glutamine metabolism in dogs with chronic metabolic acidosis

It appears that glutamine and lactate are the principal substrates for the kidney in dogs with chronic metabolic acidosis. Accordingly, the purpose of this study was to determine if a higher or lower rate of renal lactate extraction would influence the rate of glutamine extraction at a constant rate of renal ATP turnover. The blood lactate concentration was 0.9 +/- 0.01 mM in 15 acidotic dogs. However, eight dogs with chronic metabolic acidosis had a spontaneous blood lactate concentration of 0.5 mM or lower. The kidneys of these dogs extracted considerably less lactate from the arterial blood (19 vs. 62 mumol/100 mL glomerular filtration rate (GFR]. Nevertheless, glutamine, alanine, citrate, and ammonium metabolism were not significantly different in these two groups of dogs. Renal ATP balance in acidotic dogs with a low blood lactate could only be achieved if a substrate other than additional glutamine were oxidized in that segment of the nephron which normally oxidized lactate; presumably a fat-derived substrate and (or) lactate derived from glucose was now the metabolic fuel at these more distal sites. When the blood lactate concentration was greater than 1.9 mM, lactate extraction rose to 219 mumol/100 mL GFR. Glutamine, alanine, citrate, and ammonium metabolism were again unchanged; in this case, ATP balance required substrate flux to products other than carbon dioxide, presumably, gluconeogenesis. It appears that renal ammoniagenesis is a proximal event and is independent of the rate of renal lactate extraction.

Sodium valproate-induced hyperammonemia in the rat: role of the kidney

The intravenous injection of sodium valproate (VPA) 200 mg/kg provoked in fasting rats a 100% increase in the arterial NH+4 concentration by the 10th min. The increase persisted at this level for at least 100 min. Simultaneous measurements of NH+4 and glutamine concentrations in the carotid artery, renal vein and suprahepatic vein showed that there were increases in the release of NH+4 and the uptake of glutamine by the kidney while the [NH+4] of suprahepatic venous blood remained stable. In binephrectomized rats injected with VPA, NH+4 levels did not change. These results suggest that the VPA-induced arterial hyperammonemia depended on the accelerated catabolism or possibly the reduced synthesis of glutamine by the kidneys. The liver of fasting rats does not seem to play a preponderant role in the VPA-induced hyperammonemia.