10-11 November 2011:8th AAAW

Thu, 2011-11-10
Washington DC, USA

The eighth in a series of Amino Acid Assessment Workshops (AAAWs) was organized in the Ritz-Carlton Hotel in Georgetown (Washington DC, USA) on November 10 and 11, 2011. Sixty-five academic, government and industry experts from 11 countries attended the meeting. The Workshop was designed to continue a dialogue among experts in amino acid nutrition, metabolism, cell and molecular biology, toxicology and regulation/policy with the objective of establishing a framework for assessing and predicting the consequences of differing levels of leucine and tryptophan intake(s) in humans under various conditions. This year’s Day 1 morning session was organized and co-sponsored with the International Life Sciences Institute Research Foundation (ILSI RF) and focused on the ILSI RF approach to establishing upper limits for nutrients. Four speakers outlined the recent approaches to estimating upper limits for impurities and nutrients.

The remaining sessions during Day 1 and Day 2 focused on the safety of leucine and tryptophan. The presentations and discussions highlighted the outcome of ICAAS-sponsored research projects on both amino acids and underlined how the available data may be used to determine the upper level of the safe range of intake. In respect to leucine, the main speakers (Drs. Paul Pencharz from the Hospital for Sick Children, Toronto, Canada and Dr. Hisanori Kato from University of Tokyo, Tokyo, Japan) attempted to draw lessons from their research in rodents and humans. The acute study by Dr. Pencharz’s group was the first to directly estimate the safe upper limit of leucine intake in humans and raised concerns that intakes greater than 550 mg•kg-1•d-1 or ~39g/d may constitute a risk to health.

The tryptophan session was mainly focused on a literature review (by Dr. Ball from Univ. Alberta, Canada and Dr. Fernstrom from Uni. Pittsburgh, USA). The speakers explained that the upper limit of tryptophan catabolism may be a possible marker for the intake above which increasing intake increases the risk of adverse effects. There do not appear to be any published data on the upper limits to tryptophan oxidation. With various health benefits in mind, people had been using tryptophan supplements at doses up to 15 grams/day (200 mg/kg/day for a 70 kg individual), with typical doses of 5-8 g/day (70-100 mg/kg/day). The duration of the efficacy studies has been from 10-28 days (occasionally longer). Of interest in the present context, side effects, where reported, have generally been mild, or absent. The final speaker, Dr. Shibata (Shiga Pref. University, Japan), however, showed in rodent experiments that a tentative NOAEL ≥ 2,000 mg/kg body weight and LOAEL ≤ 5,000 mg/kg body weight may exist and that "the urinary excretory ratio of anthranilic acid/kynurenic acid" is potentially the most appropriate surrogate breakpoint index to predict the UL for tryptophan. This study is currently being followed by a human experiment with healthy female subjects. The Proceedings of the 8th AAAW will be published during 2012 as a supplement to the ”Journal of Nutrition” and the ICAAS members hope that the proceedings will be of assistance to both academicians and regulators who will be concerned with ULs for amino acids. ICAAS is predicated on providing the scientific base which should underpin any regulatory action in this field. The results reported during this workshop make this ambition concrete and will transform future debates on ULs for amino acids.