Plasma Leptin Concentrations in Phenylketonuric Patients

Abstract

High levels of phenylalanine (Phe) in blood have been shown to reduce dopamine (DA) and noradrenaline (NA) production. Leptin levels rise with increasing adiposity in rodents and humans acting as a negative feedback adipostatic signal to brain centers. The aim of this study was to evaluate leptin plasma levels in phenylketonuria (PKU) patients adhering to their special diet and in those on a ‘loose diet’. Forty-nine patients with classical PKU were divided into two groups. Those in group A (n = 21) adhered very strictly to their diet (Phe: 0.15 ± 0.04 mmol/l) and those in group B (n = 28) were on a ‘loose diet’ (Phe: 0.8 ± 0.04 mmol/l). Thirty healthy children of comparable age served as controls. Both patients and controls were in pubertal stage 0 (Tanner). BMI (kg/m²) was evaluated in all the members of the groups. Their daily nutrients were calculated with a 7-day dietary protocol. Leptin was evaluated by RIA, and Phe and Tyrosine with an amino acid autoanalyser. Adrenaline (A), NA and DA were measured by an HPLC method. Plasma leptin in group B patients (28.4 ± 2.0 ng/ml) was significantly increased as compared to group A patients (16.8 ± 2.6 ng/ml) and controls (17.8 ± 3.0 ng/ml; p < 0.001). Plasma DA, A, and NA in group B was lower than in group A and controls. Additionally, leptin negatively correlated with A and DA, whereas Phe positively correlated with the hormone in all groups. Leptin, also, correlated with BMI only in group A and controls. Additionally, the hormone negatively correlated with the total energy intake only in group A (r = –0.43, p < 0.01) and in controls (r = –0.040, p < 0.01). It is suggested that the disregulation of the neuroendocrine system as well as the high Phe blood levels might play an important role in the increased leptin concentrations in PKU patients on a ‘loose diet’.