Predicting the phenylalanine blood concentration from urine analyses. An approach to noninvasive monitoring of patients with phenylketonuria.

The need for regular blood-drawing in the management of chronic metabolic disorders may negatively influence the compliance of patients and their parents; noninvasive analytical procedures could well alleviate this burden. Using data obtained in six adult probands with phenylketonuria, we evaluate the feasibility of noninvasive prediction of phenylalanine blood concentrations from analysis of phenylalanine and creatinine in urine. Cross-validated regression equations correct for the significant inter-individual variation of phenylalanine fractional excretion rates. With sensitive and specific enzymatic assays for phenylalanine and creatinine, the accuracy of this noninvasive procedure may also become clinically satisfactory for the purpose of self-monitoring.

A synopsis of the unconjugated acidic transamination metabolites of phenylalanine in phenylketonuria.

We present blood and urine levels of unconjugated o-hydroxyphenylacetic, phenyllactic and phenylpyruvic acids in 61 children (2 years of age and above) and juveniles with phenylketonuria on or partially off diet. The samples were obtained during 185 scheduled outpatient visits and have been analysed with gas chromatographic methods. The compiled data define reference ranges of phenylalanine transamination capacity and of renal transport of metabolites which may be of value in further studies on the pathogenesis of phenylketonuria.

Hyper-2-oxoglutaric aciduria in long-term mental handicap.

One thousand one hundred and seventy-five mentally retarded patients in an institution (733 males and 442 females) were screened for urinary excretion of 2-oxoacids using a quantitative gas chromatographic method. On follow-up, in 10 out of 31 male patients with excretion of greater than or equal to 50 mmoles 2-oxoglutaric acid per mole creatinine, a previously unrecognized bacteriuria was considered the cause of hyper-2-oxoglutaric aciduria. Of the remaining 21, nine had elevated blood citric acid, and four had borderline elevations of blood pyruvic and/or 2-oxoglutaric acid. In the 11 males with persistent hyper-2-oxoglutaric aciduria an increased incidence of seizure disorders and cerebral palsy relative to the total patient population was found. Hyper-2-oxoglutaric aciduria with concomitant abnormalities of blood metabolites is thought to represent a heterogeneous group of mild inborn errors of energy metabolism which may be compatible with survival at least into young adulthood, but not with normal development of mental and neurological functions.

Absence of a significant renal threshold for two aromatic acids in phenylketonuric children over two years of age.

There is a steady and nonlinear relationship between the levels of both phenylpyruvic acid (PPA) and o-hydroxyphenylacetic acid (oOPAA) in urine and the plasma levels of phenylalanine (phe) in children more than two years of age with phenylketonuria (PKU). If phe levels in blood rise above 0.35 mM (5.8 mg/100 ml) both aromatic acids are found regularly in urine. Typically, urinary concentrations of PPA are about 5 times higher than those of oOPAA. This report is based on the analysis of 94 samples from 51 children, on or off diet.

Quantitative analysis of beta-phenylpyruvic acid by single ion monitoring. Evaluation of isomeric internal standards.

Quantitative single ion monitoring of beta-phenylpyruvic acid at high sensitivity is possible after derivatization first with omicron-phenylenediamine and then with a silylating reagent. The resulting o-trimethyl-silyl-quinoxalinol (O-TMS-Q) has previously been shown to be highly stable during storage and on chromatography. As an internal standard the isomeric omicron-methylphenylglyoxylic (omicron-toluylformic) acid is introduced. The mass spectra of both O-TMS-Q's are characterized by abundant [M]+. at m/e 308. The concept of "class specific metabolic profiling" is discussed in relation to quantitative gas chromatography--mass spectrometry detection of aliphatic and aromatic alpha-ketoacids.

Correlations between branched-chain amino acids and branched-chain alpha-keto acids in blood in maple syrup urine disease.

In 62 blood samples from 3 patients with classical maple syrup urine disease and from one patient with a variant form, a close linear correlation was found between levels of branched chain amino acids and their corresponding alpha-keto acids. Keto acids were determined as O-trimethylsilyl quinoxalinols by gas chromatography with a nitrogen-selective detector.

O-trimethylsilylquinoxalinol derivatives of aromatic alpha-keto acids. Mass spectra and quantitative gas chromatography.

As an extension of earlier work on aliphatic alpha-keto acids, a method is described for the quantitative gas chromatographic determination of urinary aromatic alpha-keto acids. The keto acids are derivatized with o-phenylenediamine to yield the quinoxalinols. These compounds are chromatographed after trimethylsilylation. The aromatic keto acids are stabilized by sodium dithionite (4 mg/ml urine) and storage below 0 degrees. The final derivatives are stable for weeks at room temperature. Low resolution mass spectra are reported. The fragmentation mechanisms are elucidated by analysis of O-trimethylsilyl-(TMS)-quinoxalinois, O-(TMS-d9)-quinoxalinois and O-TMS-6(7)-chloroquinoxalinois.