Application of Key Events Dose Response Framework to defining the upper intake level of leucine in young men

Effect of L-Leucine Therapy on Hematopoietic Function in Elderly Myelodysplastic Syndrome Patients

Patients with myelodysplastic syndrome (MDS) often require blood transfusion and anticancer therapy; however, elderly patients are intolerant to the associated side effects of anticancer therapy. Because L-leucine can be used to treat Diamond-Blackfan anemia, which is caused by defects in ribosomal protein (RP) genes, resulting in increased in vivo hemoglobin synthesis, it is possible that some MDS patients who have aberrations in their RP genes could also be effectively treated with L-leucine. In the present study, we investigated the effects of L-leucine on hematopoietic function (reticulocyte count), red blood cell count, and hemoglobin level in MDS patients. We administered L-leucine (1.8 g, twice daily, 3 d/week) with oral vitamin B6 supplements to a final cohort of eight MDS patients for 15 (interquartile range: 11-18) weeks. We assessed the patients at 10 ± 2 weeks after therapy initiation. Only the absolute reticulocyte count was affected, improving in 6/8 (75%) patients. The median absolute reticulocyte count was 3.5 × 10⁴ (range: 2.7-6.4 × 10⁴) cells/µL, an increase of 0.5 × 10⁴ (range: 0.2-0.7 × 10⁴) cells/µL. At 10 weeks, there was only one case of an improved hemoglobin level. Non-hematological adverse events of grade 3 were observed one raised triglycerides. These data suggest that L-leucine has little effect on MDS. However, it may contribute to the recovery of hematopoietic function, futher study be desired.

Summary of workshop discussions on establishing upper limits for amino acids with specific attention to available data for the essential amino acids leucine and tryptophan

The morning of the first day of the 8th Amino Acid Assessment Workshop was organized and co-sponsored by the International Council on Amino Acid Science (ICAAS) and the International Life Sciences Institute Research Foundation and was focused on the International Life Sciences Institute Research Foundation's approach to establishing upper limits of nutrients. The remainder of d 1 and all of d 2 were focused on the safety of leucine and tryptophan, with special emphasis on determining the upper level of the safe range of intake. It was recognized that some toxicological frameworks, mainly the key-events dose response framework, might be applicable to amino acids and provide appropriate assistance to regulators in establishing upper limits for amino acids as a group of nutrients used in dietary supplements. ICAAS-funded projects for determining the upper intake limits for the essential amino acid leucine provided the main pool of leucine data discussed at the workshop. The acute clinical study suggests 500 mg/(kg · d) as a possible upper limit for leucine in healthy humans, but the safety margin needed to widen this limit to the general population has not been determined. For tryptophan, the workshop participants found less ground for consensus. Older efficacy studies suggested that tryptophan at 8-15 g/d was well tolerated, but human research was abruptly terminated in the late 1980s and no new data are available. Animal results obtained in pigs and rodents were discussed and 2 possible strategies for applying those outcomes to humans were described.