Department of Geriatrics, Reynolds Institute on Aging, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
Department of Molecular Medicine, Lee Gil Ya Cancer and Diabetes Institute, Gachon University School of Medicine, Incheon, Republic of Korea.
J Investig Med. 2020 Jan;68(1):11-15. doi: 10.1136/jim-2019-001108. Epub 2019 Sep 24.
Whole-body protein turnover (protein synthesis, breakdown, and net balance) model enables quantification of the response to a variety of circumstances, including the response to meal feeding. In the fed state, the whole-body protein turnover model requires taking account of the contribution of absorbed tracee to the observed total appearance of tracee in the peripheral blood (exogenous appearance, Ra). There are different approaches to estimating Ra The use of an intrinsically labeled dietary protein is based on the overriding assumption that the appearance in the peripheral circulation of a tracer amino acid incorporated into a dietary protein is exactly proportional to the appearance of absorbed tracee. The bioavailability approach is based on the true ileal digestibility of the dietary protein and the irreversible loss of the tracee in the splanchnic bed via hydroxylation of the tracee (phenylalanine). Finally, Ra can be estimated as the increase above the basal rate of appearance of the tracee using traditional tracer dilution methodology. In this paper, we discuss the pros and cons of each approach and conclude that the bioavailability method is the least likely to introduce systematic errors and is therefore the preferable approach.
全身蛋白质周转率（蛋白质合成、分解和净平衡）模型能够定量评估各种情况下的反应，包括对膳食喂养的反应。在进食状态下，全身蛋白质周转率模型需要考虑吸收示踪剂对观察到的外周血中示踪剂总出现（外源性出现，Ra）的贡献。有不同的方法来估计 Ra。使用内源性标记的膳食蛋白质是基于这样一个主要假设，即掺入膳食蛋白质中的示踪氨基酸在周围循环中的出现与吸收示踪剂的出现完全成比例。生物利用度方法基于膳食蛋白质的真正回肠可消化性以及通过示踪剂（苯丙氨酸）的羟化在肠腔内不可逆损失示踪剂。最后，可以使用传统示踪剂稀释方法来估计 Ra 相对于基础示踪剂出现率的增加。本文讨论了每种方法的优缺点，并得出结论，生物利用度方法最不可能引入系统误差，因此是首选方法。
