ACTA ENDOCRINOLOGICA (BUC)

Phenylketonuria (PKU) is the most frequent inherited amino acid metabolic disorder, and it may also be treated by dietary means. The determination of phenylalanine (Phe) levels in the blood plasma is important not only in early diagnostic, but also in monitoring the treatment of PKU. Purpose. The aim of our work was to develop a simple, sensitive and highly accurate procedure to determine the plasma concentration of Phe. Procedure. The measurement of plasma Phe concentration involves two steps: a) separation of plasma (from the blood taken on heparin), isolation and preparation of a concentrated solution of amino acids (by ion-exchange column chromatography on Dowex-50X8 and evaporation of the eluate in vacuum at 40˚C), and b) determination of Phe concentration in the solution of amino acids by HPLC. This analysis was performed using a Dionex Ultimate 3000 instrument equipped with a Ultimate 3000 diode array detector (DAD). The values of Phe concentration in the plasma of several patients were calculated using a calibration curve made with standards of Phe (dilutions of a stock solution of 50 mg/ dL). The measurements in duplicate (plasma Phe) or a greater number of samples from the same concentration of standards of Phe showed extremely small sample to sample differences. Concentrations as low as 0.2 mg/dL could be determined. Conclusion. The whole procedure presented here is relatively simple, rather inexpensive, however very sensitive and highly accurate. Consequently, it is very adequate for confirming the diagnosis of PKU in patients with neonatal hyperphenylalaninemia, as well as for monitoring the plasma concentration of Phe in patients with PKU.

Objective. To compare two chromatographic methodologies for determination of plasma phenylalanine (Phe) and their usefulness for diagnosing hyperphenylalaninemia (HPA) and phenylketonuria (PKU). Methods. The plasma amino acids were isolated and concentrated from blood collected from infants with HPA detected by newborn screening. The plasma Phe was determined in parallel by HPLC and by image-densitometry of 2D-TLC plates. Results. Typical examples of 2D-TLC plates and HPLC chromatograms from infants with HPA and PKU are presented and evaluated. The Phe spot was visible on 2D - TLC plates at Phe concentrations higher than 300 μmol/L. The standard calibration curve traced after imagedensitometry of the Phe spot presented high dispersion of values at each concentration of Phe, high SD values, the equation of the curve having a low R-squared value (0.862). In contrast, the standard calibration curve obtained by HPLC shows linearity on the range of concentrations from 100 - 16,000 μmol/L, extremely small SD values, the equation of the curve has a very high R-squared value (0.999). Conclusions. The HPLC methodology is appropriate to confirm HPA detected by newborn or selective screening of PKU. The 2D - TLC methodology is adequate to detect patients with severe PKU.

Introduction. The determination of phenylalanine (Phe) and tyrosine (Tyr) levels in blood plasma is very important not only in early diagnostic, but also in monitoring the treatment of phenylketonuria (PKU). Purpose. We present a simple, sensitive and accurate procedure to determine simultaneously the plasma concentrations of Phe and Tyr. Procedure. The measurement involves two steps: a) separation of plasma (from blood prelevated on heparin), isolation and preparation of a concentrated solution of amino acids (by ion-exchange column chromatography on Dowex- 50X8), and b) determination of Phe and Tyr concentrations in the solution of amino acids by HPLC (using a Dionex Ultimate 3000 instrument equipped with a diode array detector). The analytical column was a Thermo Scientific Acclaim 120, C18, 5 μm Analitic (4.6 x 250 mm), coupled with an Acclaim C18 guard column. The values of Phe and Tyr concentrations in plasma of several patients were calculated using a calibration curve made with standards of Phe (1834.4 μmol/L in deionized water) and Tyr (600 μmol/L in deionized water). Concentrations as low as 24 μmol/dL of Phe and 15 μmol/dL of Tyr could be determined. Conclusion. The whole procedure presented here is relatively simple, rather inexpensive, however very sensitive and accurate. Consequently, it is very adequate for confirming the diagnosis of PKU in patients with neonatal hyperphenylalaninemia, as well as for monitoring the plasma concentrations of Phe and Tyr in patients with PKU.

Background. The modern management of phenylketonuria (PKU) consists of generalized newborn screening (NBS) for hyperphenylalaninemia (HPA), confirmation of HPA in children detected in the NBS, introduction of dietary treatment in the first weeks of life, followed by monitoring the treatment of PKU for decades to maintain phenylalaninemia within the limits that will not affect the brain. The present study aimed to evaluate the usefulness of two chromatographic methodologies for determination of plasma Phe level in the routine management of PKU: the two dimensional thin layer chromatography (2D - TLC) and the high performance liquid chromatography (HPLC) procedures, respectively. Material and Methods. Samples of blood from 23 children with HPA detected by neonatal screening or with confirmed PKU who received treatment by low-Phe diet were analyzed to estimate the plasma Phe level by the two chromatographic procedures. Results. In case of three subjects the very low concentrations of plasma Phe could not be detected by the 2D - TLC methodology, since the spot was not visible on the chromatogram. In four patients the differences between the values of plasma Phe determined by the two methodologies are not statistically significant, while in fifteen subjects the differences are highly statistically significant. This is due to the greater errors that appear in the case of 2D - TLC methodology. In the range of concentrations of plasma Phe higher than 360 μmol/L (which is the cut-off value for HPA), although in four cases there were statistically significant differences in the level of plasma Phe determined by the two methodologies, the value obtained by the 2D - TLC methodology was high enough to influence the decision of changing the diet so that HPA is kept under control. In addition, the intense spot of Phe on the 2D - TLC chromatogram may be detected even by un unexperienced laboratory specialist. Conclusion. The HPLC procedure for measurement of plasma Phe level is very suitable to be used in the routine management of PKU. The 2D - TLC procedure may be accompanied by relatively high errors; however, it detects patients with severe PKU.

Developments in the understanding of the molecular basis of water permeability of the red blood cell (RBC) have taken place rapidly since the discovery in 1985 in Cluj- Napoca, Romania, by the group of Benga of a water channel protein (WCP), later called aquaporin 1 (AQP1), in the RBC membrane. However, the physiological role of AQP1 is not yet fully understood. Investigations of RBCs from human subjects of various ages could help shed light on this important issue. We present a short review of our studies on this topic that were published in less “visible” journals and books. The diffusional water permeability (Pd) of the RBC membrane has the lowest values in the newborns. Then Pd values are increasing in children, reaching at about 7 years a value that remains rather constant in young and mature subjects. The high permeability to water of the RBC membrane can be correlated at these ages with the ability to undertake a high level of physical activity. In elderly individuals (over 65 years) a further small, but statistically significant, increase in the diffusional water permeability of RBC was observed. In this case the higher RBC water permeability can be correlated with a requirement of the RBC membrane to favour the membrane undulations and the rapid entry or exit of solutes of molecular size greater than water, in conditions when the organism is less physically active, probably has lower metabolic rates and lower mean rates of blood circulation.