Implications for the Metabolic Fate of Oral Glutamine Supplementation within Plasma and Erythrocytes of Patients with Sickle Cell Disease: A Pharmacokinetics Study

A pharmacokinetic-pharmacodynamic analysis of l-glutamine for the treatment of sickle cell disease: Implications for understanding the mechanism of action and evaluating response to therapy

The mechanisms of action of l-glutamine for the treatment of sickle cell disease (SCD) are not well understood and there are no validated clinical biomarkers to assess response. We conducted a three-week, dose-ascending trial of glutamine and measured the pharmacokinetic (PK) exposure parameters, peak concentration (Cmax) and area under the curve (AUC). We used a panel of biomarkers to investigate the pharmacodynamics (PD) of glutamine and studied PK-PD relationships. There was no plasma accumulation of glutamine, glutamate, arginine or other amino acids over time, but modestly improved arginine bioavailability was observed. In standard analysis by dose levels over time, there were no measurable effects on blood counts, viscosity, ektacytometry or reactive oxygen species (ROS). In PK-PD analysis, however, higher glutamine exposure (Cmax or AUC) was associated with increased whole blood viscosity and cellular dehydration, yet also with higher haemoglobin concentration, increased haematocrit-to-viscosity ratio, decreased reticulocyte ROS, improved RBC deformability and decreased point of sickling. This novel PK-PD analysis identified biomarkers reflecting the positive and negative effects of glutamine, helping to elucidate its mechanisms of action in SCD. PK-optimized dosing to achieve glutamine exposure (AUC or Cmax) that is associated with salutary biological effects should be studied to support its therapeutic use.

A Population Pharmacokinetic Analysis of L-Glutamine Exposure in Patients with Sickle Cell Disease: Evaluation of Dose and Food Effects

BACKGROUND AND OBJECTIVE

L-Glutamine is a treatment for children and adults with sickle cell disease. A comprehensive evaluation of the pharmacokinetics of L-glutamine in sickle cell disease has not been conducted. We aimed to assess the effects of long-term dosing, multiple dose levels, and food intake on L-glutamine exposure in patients with sickle cell disease compared to normal participants.

METHODS

We conducted an open-label dose-ascending trial of L-glutamine in pediatric and adult participants with sickle cell disease (N = 8) and adult healthy volunteers (N = 4), providing a total of 400 plasma L-glutamine concentrations. Each participant received three ascending oral doses (0.1 and 0.3 g/kg twice daily and 0.6 g/kg once daily) over 3 weeks. Plasma L-glutamine concentrations were quantified using ion exchange chromatography. Both a non-compartmental pharmacokinetic analysis and a population pharmacokinetic analysis were performed.

RESULTS

L-glutamine had rapid absorption and elimination, and there was no significant change in the baseline (pre-dose) L-glutamine concentration throughout the study, indicating no drug accumulation. Pharmacokinetics was best described by a one-compartment model with first-order kinetics. The dose-normalized peak concentration decreased with dose escalation, indicating the capacity-limited non-linear pharmacokinetics of oral L-glutamine. A covariate analysis showed that baseline L-glutamine concentrations correlated negatively with glutamine clearance, whereas dose positively correlated with volume of distribution. Food intake did not significantly affect glutamine clearance, indicating that L-glutamine can be taken with or without food.

CONCLUSIONS

We report the first pharmacokinetic study of multiple-dose, long-term oral L-glutamine therapy and the first population pharmacokinetic analysis of L-glutamine for sickle cell disease. These findings may permit optimized dosing of L-glutamine for patients with sickle cell disease to maximize treatment benefits.

CLINICAL TRIAL REGISTRATION

This trial is registered at ClinicalTrials.gov (NCT04684381).

Pharmacokinetic study of single and multiple oral administration of glutamine in healthy Beagles

Glutamine is an amino acid that is mainly used for the treatment of gastrointestinal diseases in clinic, but there is a lack of such medicine in veterinary clinic, and its research in dogs has never been seen. This study aimed to investigate the pharmacokinetics of single and multiple administration of glutamine (Gln) tablets in Beagles. Twenty-four healthy Beagles were randomly selected for the pharmacokinetic study of a single dose of low (120 mg/kg), medium (240 mg/kg), and high (360 mg/kg) Gln tablets. After 7 days of washout period, six Beagles in the medium group were selected for a multiple-dose pharmacokinetic study, 240 mg/kg twice a day for 7 days. The Gln concentration in plasma was determined by a validated UPLC-MS/MS method. The results of single oral administration of different doses of Gln tablets showed that C_max, AUC_0→t, AUC_0→∝ had a certain linear relationship with the dosage. T-tests were performed for single and multiple administration of T_max, C_max, t_1/2λz, AUC_0→t, and AUC_0→∝, and the results showed no significant differences (p > 0.05). Therefore, Gln tablets were absorbed quickly by oral administration, and there was no accumulation in Beagles after 7 days of administration.