Pharmacokinetics of L-Glutamine (Endari) in Pediatric and Adult Sickle Cell Disease Patients: A Phase 4, Open-Label, Single-Center Study

Introduction: L-glutamine (Endari ®, Emmaus Medical, Inc.) is an amino acid approved for the treatment of sickle cell disease (SCD) by the United States Food and Drug Association (FDA) after 2 clinical trials demonstrated a reduction in painful episodes and hospitalizations. L-glutamine has many roles, including de novo synthesis of intracellular glutathione that may protect sickle erythrocytes from oxidant injury. Despite its licensure, the pharmacokinetics (PK) of multi-dose oral L-glutamine for SCD have not been studied. Methods: We conducted a dose-escalation PK trial from January to June 2021 (NCT04684381) on 3 cohorts with 4 participants each: pediatric SCD patients (0 - 18 y, cohort 1), adult SCD patients (>18 y, cohort 2), and adult healthy volunteers (>18 y, cohort 3). There were 4 weekly study visits to assess 3 ascending dose levels (Figure 1). For each visit, participants arrived in the research clinic after an overnight fast. Plasma L-glutamine and other amino acid levels were obtained before and after oral L-glutamine doses at each visit and quantified by ion exchange chromatography. On study visit 1, a dose of 0.1 g/kg of L-glutamine was administered and amino acids were measured at 30±5, 60±10, 120±15, 180±15 and 240±20 minutes after the dose. The procedure was repeated in the afternoon after a standardized meal. On study visit 2, the dose was increased to 0.3 g/kg twice daily (approximate FDA-approved dosing). On study visit 3, a single oral dose of 0.6 g/kg (once daily dosing) was given for fasting PK levels, and on study visit 4 the 0.6 g/kg dose was given with a standardized meal. After the first 3 study visits, participants continued L-glutamine at the corresponding dose level at home and completed a daily phone survey to document adherence and adverse events. Results: Baseline characteristics are summarized in Table 1. Baseline L-glutamine levels similar across the three study cohorts (Table 1). One participant from cohort 1 withdrew during study visit 1 and was replaced. Another participant from cohort 2 was withdrawn due to hospitalization for severe anemia and was replaced. One participant from cohort 3 did not complete visit 4 due to dyspepsia. Non-compartmental PK analysis (NCA) was conducted using Phoenix WinNonlin® Professional Version 8.4 (Certara, NJ, US; Figure 2). After oral administration, L-glutamine plasma levels peaked (T max) at an average (mean ± SD) of 1.2 ± 0.9 hours. Compared to doses 0.1 g/kg and 0.3 g/kg, the T max was later for 0.6 g/kg (p<0.05) indicating slower absorption at higher doses. At the lowest dose (0.1 g/kg), L-glutamine concentrations returned to baseline levels within 4 hours. However, at 0.3 or 0.6 g/kg, the plasma L-glutamine concentration remained higher than baseline at 4 hours, indicating slower elimination at higher doses. There was no significant change in the baseline plasma L-glutamine concentration levels during the study, however, indicating no evidence of drug accumulation. Peak L-glutamine concentration levels (C max) were higher at each successive dose escalation, but when the levels were normalized by dose there was a decrease in the normalized concentration with dose escalation, which implied a potential saturable absorption. Inter-patient variability in plasma L-glutamine levels was higher at 0.6 mg/kg than at lower doses. The elimination half-life (T 1/2), calculated as 0.693/elimination rate constant (λz), had an average value of 1.0 ± 0.7 hours. The most common grade 2 adverse events were dyspepsia and headache (3 instances each). There was no significant elevation in ammonia levels, and plasma concentrations of the metabolite L-glutamate was similar to L-glutamine (Figure 2). Conclusions: This is the first multi-dose PK study of L-glutamine (Endari) for SCD. Daily dosing was overall well-tolerated, with rapid absorption of 0.1 and 0.3 g/kg doses and no drug accumulation. The highest 0.6 g/kg dose was limited by palatability and featured slower and saturable absorption, so further dose escalation is likely not feasible. Ongoing analyses include possible food-drug interactions and PK-pharmacodynamic (PK-PD) studies to identify salutary effects on erythrocytes. Our findings will help inform the proper dosing of L-glutamine for patients with SCD, and potentially permit individualized PK-guided dosing to maximize treatment benefits. This was an investigator-initiated trial funded by Emmaus Medical, Inc. Figure 1 Figure 1. Disclosures Sadaf: Emmaus Medical, Inc: Research Funding. Ware: Bristol Myers Squibb: Research Funding; Addmedica: Research Funding; Hemex Health: Research Funding; Nova Laboratories: Research Funding; Novartis: Other: DSMB Chair; Editas: Other: DSMB Chair. Quinn: Emmaus Medical: Research Funding; Novo Nordisk: Consultancy; Aruvant: Research Funding; Forma Therapeutics: Consultancy. OffLabel Disclosure: Endari (L-glutamine) is FDA approved for the treatment of Sickle Cell Disease at a dose of 0.3 g/kg. However, in our pharmacokinetic study we tested doses 0.1, 0.3 and 0.6 g/kg.

Plasma glutamine status at intensive care unit admission: an independent risk factor for mortality in critical illness

Background A plasma glutamine concentration outside the normal range at Intensive Care Unit (ICU) admission has been reported to be associated with an increased mortality rate. Whereas hypoglutaminemia has been frequently reported, the number of patients with hyperglutaminemia has so far been quite few. Therefore, the association between hyperglutaminemia and mortality outcomes was studied in a prospective, observational study. Patients and methods Consecutive admissions to a mixed general ICU were eligible. Exclusion criteria were < 18 years of age, readmissions, no informed consent, or a ‘do not resuscitate’ order at admission. A blood sample was saved within one hour from admission to be analysed by high-pressure liquid chromatography for glutamine concentration. Conventional risk scoring (Simplified Acute Physiology Score and Sequential Organ Failure Assessment) at admission, and mortality outcomes were recorded for all included patients. Results Out of 269 included patients, 26 were hyperglutaminemic (≥ 930 µmol/L) at admission. The six-month mortality rate for this subgroup was 46%, compared to 18% for patients with a plasma glutamine concentration < 930 µmol/L (P = 0.002). A regression analysis showed that hyperglutaminemia was an independent mortality predictor that added prediction value to conventional admission risk scoring and age. Conclusion Hyperglutaminemia in critical illness at ICU admission was an independent mortality predictor, often but not always, associated with an acute liver condition. The mechanism behind a plasma glutamine concentration outside normal range, as well as the prognostic value of repeated measurements of plasma glutamine during ICU stay, remains to be investigated.

MRS Shows Regionally Increased Glutamate Levels among Patients with Exhaustion Syndrome Due to Occupational Stress

Despite the rapid increase of reports of exhaustion syndrome (ES) due to daily occupational stress, the mechanisms underlying ES are unknown. We used voxel-based 1H-MR spectroscopy to examine the potential role of glutamate in this condition. The levels of glutamate were found to be elevated among ES patients (n = 30, 16 females) compared with controls (n = 31, 15 females). Notably, this increase was detected only in the anterior cingulate and mesial prefrontal cortex (ACC/mPFC), and the glutamate levels were linearly correlated with the degree of perceived stress. Furthermore, there was a sex by group interaction, as the glutamate elevation was present only in female patients. Female but not male ES patients also showed an increase in N-acetyl aspartate (NAA) levels in the amygdala. No group differences were detected in glutamine concentration (also measured). These data show the key role of glutamate in stress-related neuronal signaling and the specific roles of the amygdala and ACC/mPFC. The data extend previous reports about the neurochemical basis of stress and identify a potential neural marker and mediator of ES due to occupational stress. The observation of specific sex differences provides a tentative explanation to the well-known female predominance in stress-related psychopathology.

Alterations of plasma glutamine and surgical stress in gastric cancer surgery

Background: The plasma glutamine levels are known to decrease after major surgery, which is related to a negative clinical outcome. However, the influence of surgical stress on the decrease in the plasma glutamine concentration is unclear. The aim of this study was to evaluate the change in glutamine in relation to the types of gastrectomy and approaches as well as the amount of surgical stress evaluated by serum interleukin-6(IL-6) as an objective indicator. Methods: This was a prospective observational study. The eligibility criteria were (1) gastric adenocarcinoma of the stomach confirmed by pathology and (2) patients scheduled to receive gastrectomy with lymphadenectomy for gastric cancer. Blood samples were taken at 7 AM on the day of surgery and at 12 h after surgery to measure the plasma glutamine and interleukin-6 (IL-6) levels. Results: Between May 2011 and December 2011, 81 consecutive patients were enrolled in this study. The plasma glutamine level was significantly decreased in all patients, regardless of distal or total gastrectomy and laparoscopic or open surgery. No significant differences were observed in the IL-6 level between total and distal gastrectomy patients or between patients treated via a laparoscopic or open approach. Decreases in the plasma glutamine level were positively correlated with the logarithmically transformed-plasma IL-6 (logIL6) (r =0.471, p<0.001) overall. Conclusions: Decreases in the glutamine concentration depended on the amount of surgical stress. When conducting a clinical trial to evaluate glutamine administration, personalized adjustment may be key to avoiding glutamine depletion in response to surgical stress.

Glutamine synthetase in avian muscle contributes to a positive myogenic response to ammonia compared with mammalian muscle

In mammalian models of cirrhosis, plasma ammonia concentration increases, having numerous adverse effects, including sarcopenia. The objective of this study was to identify differences between avian and mammalian myogenic response to applied ammonia and glutamine. Primary chicken breast and thigh, primary rat, and C2C12 myotubes were treated with ammonium acetate (AA, 10 mM) or glutamine (10 mM) for 24 h and compared with sodium acetate (10 mM) and untreated controls. Myostatin mRNA was significantly higher in C2C12 and rat myotubes treated with AA compared with glutamine and controls ( P < 0.01), whereas myostatin was unchanged in chicken myotubes. AA-treated C2C12 myotubes had significantly higher glutamine synthetase (GS) mRNA expression compared with controls, but GS protein expression was unchanged. In contrast, GS mRNA expression was unchanged in thigh myotubes, but GS protein expression was significantly higher in AA-treated thigh myotubes ( P < 0.05). In both breast and thigh myotubes, intracellular glutamine concentration was significantly increased in AA- and glutamine-treated myotubes compared with controls but was only increased in glutamine-treated C2C12 and rat myotubes ( P < 0.05). Glutamine concentration was significantly higher in all treatment media collected from avian myotube cultures compared with both C2C12 and rat media ( P < 0.01). Myotube diameter was significantly larger in avian myotubes after treatment with both AA and glutamine ( P < 0.05). C2C12 and rat myotubes had a significantly smaller myotube diameter after AA treatment ( P < 0.001). Altogether, these data support species differences in skeletal muscle ammonia metabolism and suggest that glutamine synthesis is a mechanism of ammonia utilization in avian muscle.

A Very Rare Etiology of Hypotonia and Seizures: Congenital Glutamine Synthetase Deficiency

Mutations in the human GLUL gene, which encodes the enzyme glutamine synthetase (GS), may cause congenital glutamine synthetase deficiency. The disease was first described in 2005 and only three patients have been reported to date. We report a fourth patient suffering from congenital GS deficiency who was found to have some distinctive clinical findings. The patient was a 30-month-old girl who was referred to us due to developmental delay and seizures which began at 5 months of age. She was seizure free for 5 months with valproic acid and vigabatrin. At presentation, she was found to have microcephaly and hypotonia. Her plasma glutamine concentration was near normal and she had mild hyperammonemia. Cranial magnetic resonance imaging (MRI) showed mild changes. Whole exome sequencing (WES) revealed a homozygous c.121C > T (p.R41C) (p.Arg41Cys) pathogenic variant of the GLUL gene. The diagnosis of this patient underlines the importance of careful evaluation of patients with borderline low glutamine levels. Treatment was begun with L-glutamine and nicotinamide and biochemical improvements have been observed at 6 months of follow-up. The outcome of this patient may provide important data about the effectiveness of glutamine and nicotinamide treatment in patients with congenital GS deficiency.

Does Glutamine Concentration Depends on the Type of the Operation?

Glutamine is the main amino acid which is substrate for gluconeogenesis in postoperative period. It is suggested that this leads to a substantial and a long-term decline in glutamine concentration. Glutamine is a source of energy for the synthesis of nucleotides, lymphocytes and cells of gastrointestinal tract. In this study, 79 patients were qualified to a coronary artery bypass surgery (Group I) or a surgery in the large intestine area (Group II). The objectives of this study were: evaluation of the impact of surgical procedures on the serum concentration of glutamine of the operated patients, assessment of gender, weight and BMI impact on glutamine concentration and analysis of the correlation between glutaminę serum concentration and laboratory parameters. The mean concentration of glutamine before surgery, the 3rd and 5th day after surgery was higher in Group I. CRP level in the 3rd and 5th postoperative day was higher in Group II. There were no significant differences betweengroups when it comes to BMI and the concentration of CRP (p &lt;0.05). Glutamine concentration depends on the severity of inflammation, the operated body cavity and the intensified catabolism which results from different pathophysiology of digestive system diseases and coronary arterial disease.