Tracing metabolic flux to assess optimal dietary protein and amino acid consumption

Wolfe Robert R.,Kim Il-Young,Park Sanghee,Ferrando Arny 생화학분자생물학회 2022 Experimental and molecular medicine Vol.54 No.-

There is a general consensus that a dietary protein intake of 0.8 g protein/kg/day will prevent symptoms of protein deficiency in young, healthy individuals. However, individuals in many physiological circumstances may benefit from higher rates of dietary protein intake. Stable isotope tracer methodology enables a variety of approaches to assessing the optimal dietary protein intake in humans. In this paper, we present an overview of a variety of tracer methods, with a discussion of necessary assumptions, as well as the clinical circumstances in which different methods may be preferable. Although we discuss the nontracer method of nitrogen balance, which has historically been used to estimate dietary protein requirements, this paper primarily focuses on tracer methods for estimating dietary protein and essential amino acid requirements under different physiological conditions. We will explain the following approaches: isotopic measurement of urea production; the arterial-venous tracer balance method; measurement of the fractional synthetic and breakdown rates of muscle protein; the indicator and the direct amino acid oxidation methods; and different approaches to measuring whole-body protein synthesis and breakdown. The advantages and limitations of each method are discussed in the context of the optimal approaches for use under different circumstances.

Quantifications of Lipid Kinetics In Vivo Using Stable Isotope Tracer Methodology

김일영,박상희,장지웅,Robert R. Wolfe 한국지질동맥경화학회 2020 지질·동맥경화학회지 Vol.9 No.1

Like other bodily materials, lipids such as plasma triacylglycerol, cholesterols, and free fatty acids are in a dynamic state of constant turnover (i.e., synthesis, breakdown, oxidation, and/or conversion to other compounds) as essential processes for achieving dynamic homeostasis in the body. However, dysregulation of lipid turnover can lead to clinical conditions such as obesity, fatty liver disease, and dyslipidemia. Assessment of “snap-shot” information on lipid metabolism (e.g., tissue contents of lipids, abundance of mRNA and protein and/or signaling molecules) are often used in clinical and research settings, and can help to understand one's health and disease status. However, such “snapshots” do not provide critical information on dynamic nature of lipid metabolism, and therefore may miss “true” origin of the dysregulation implicated in related diseases. In this regard, stable isotope tracer methodology can provide the in vivo kinetic information of lipid metabolism. Combining with “static” information, knowledge of lipid kinetics can enable the acquisition of in depth understanding of lipid metabolism in relation to various health and disease status. This in turn facilitates the development of effective therapeutic approaches (e.g., exercise, nutrition, and/or drugs). In this review we will discuss 1) the importance of obtaining kinetic information for a better understanding of lipid metabolism, 2) basic principles of stable isotope tracer methodologies that enable exploration of “lipid kinetics” in vivo, and 3) quantification of some aspects of lipid kinetics in vivo with numerical examples.

Tracing metabolic flux in vivo: motion pictures differ from snapshots

Kim Il-Young,Wolfe Robert R. 생화학분자생물학회 2022 Experimental and molecular medicine Vol.54 No.-

Since Rudolf Schoenheimer’s pioneering metabolic tracing work in the 1930s1, it is currently well appreciated that all constituents of living matter (e.g., DNAs, RNAs, proteins, lipids, and metabolites) are in a constant state of turnover at varying rates to achieve overall “dynamic” homeostasis. Furthermore, metabolic systems are highly complex, connected, and interactive, and consequently, one’s metabolic fluxes (“motion pictures”) should not be understood as individual components but as a whole system2. Unfortunately, most modern metabolic studies heavily depend on the measurements of static, snapshot information, so-called “statomics” (e.g., transcriptomics, proteomics, metabolomics, and cellular signaling cascades) of individual components of the whole system, which often fail to reflect actual metabolic status3,4. Without simultaneous considerations of metabolic flux, sole dependence on “statomics” can lead to incorrect conclusions regarding metabolic status. In this Special Feature, experts in the field of tracer methodology or fluxomics provide the basic principles and applications of the methodologies determining metabolic fluxes to various metabolic conditions. The incorporation of these state-of-the-art methodologies into metabolic research will guide researchers to a better understanding of dynamic metabolic systems with which to better dissect underlying molecular mechanisms of physiology or pathophysiology.

The Role of Dietary Essential Amino Acids in Muscle and Health

Jung Jiyeon,박상희,김창근,Wolfe Robert R.,Kim Il-Young 건강기능식품미래포럼 2022 건강기능식품미래포럼 학술지 Vol.2 No.1

Maintenance of proper skeletal muscle mass plays a critical role in health and disease. Dietary essential amino acids (EAAs), particularly when combined with resistance exercise are the most established safe and natural anabolic stimuli that lead to gains in muscle mass and function and in turn overall health. Gains in muscle mass are achieved by stimulation of muscle protein synthesis greater than muscle protein breakdown, which in turn improves muscle strength and function. It is critical that dietary EAAs should be formulated with balanced composition of 9 EAAs for an optimal anabolic response (i.e., a maximal gain in muscle mass). In this review, we will briefly cover following topics: 1) skeletal muscle and its importance in health, 2) regulation of muscle mass through protein turnover, 3) dietary EAAs as natural anabolic stimuli, 4) importance of provision of balanced mixture of EAAs, and 5) practical guidelines for dietary EAA intake to achieve optimal gains in muscle mass and improved muscle function.

In Vivo and In Vitro Quantification of Glucose Kinetics: From Bedside to Bench

김일영,박상희,김일영,김영민,장예원,최철수,서상훈,Robert R. Wolfe 대한내분비학회 2020 Endocrinology and metabolism Vol.35 No.4

Like other substrates, plasma glucose is in a dynamic state of constant turnover (i.e., rates of glucose appearance [Ra glucose] into and disappearance [Rd glucose] from the plasma) while staying within a narrow range of normal concentrations, a physiological priority. Persistent imbalance of glucose turnover leads to elevations (i.e., hyperglycemia, Ra>Rd) or falls (i.e., hypoglycemia, Ra<Rd) in the pool size, leading to clinical conditions such as diabetes. Endogenous Ra glucose is divided into hepatic glucose production via glycogenolysis and gluconeogenesis (GNG) and renal GNG. On the other hand, Rd glucose, the summed rate of glucose uptake by tissues/organs, involves various intracellular metabolic pathways including glycolysis, the tricarboxylic acid (TCA) cycle, and oxidation at varying rates depending on the metabolic status. Despite the dynamic nature of glucose metabolism, metabolic studies typically rely on measurements of static, snapshot information such as the abundance of mRNAs and proteins and (in)activation of implicated signaling networks without determining actual flux rates. In this review, we will discuss the importance of obtaining kinetic information, basic principles of stable isotope tracer methodology, calculations of in vivo glucose kinetics, and assessments of metabolic flux in experimental models in vivo and in vitro.

Understanding Muscle Protein Dynamics: Technical Considerations for Advancing Sarcopenia Research

Il-Young Kim,박상희,장지웅,Robert R. Wolfe 대한노인병학회 2020 Annals of geriatric medicine and research Vol.24 No.3

Sarcopenia, which is the loss of muscle mass and strength that occur with aging, involves imbalanced muscle protein turnover (i.e., protein breakdown exceeding synthesis), which in turn exacerbates other clinical conditions such as type 2 diabetes mellitus, obesity, osteoporosis, and cancer, thereby worsening the quality of life in older adults. This imbalance is attributed in part to the resistance of aged muscle to anabolic stimuli such as dietary protein/amino acids and resistance exercise known as anabolic resistance. Despite research efforts, no practical therapeutics have been successfully discovered possibly because of a lack of understanding of the dynamic nature of muscle protein, and the use of indirect assessments of muscle mass. Herein, we briefly discuss the regulation of protein turnover in response to the abovementioned anabolic stimuli with respect to anabolic resistance and optimal protein intake, followed by methodological considerations for advancing sarcopenia research, including assessments of muscle mass and dynamics.

척수장애인과 비장애인의 최대운동 검사 시 최대 생리적 반응 비교

신윤아 ( Yun A Shin ),이근호 ( Gun Ho Lee ),김일영 ( Il Young Kim ),( Robert R Wolfe ) 한국특수체육학회 2016 한국특수체육학회지 Vol.24 No.2

이 연구의 목적은 비장애인(AB), 척수손상 운동선수(SCIA), 척수손상 좌업생활인SCIS)을 대상으로 트레드밀과 암 에르고미터를 이용한 최대운동검사 시 생리적 최대 반응과 최고산소섭취량의 차이를 알아보는 것이다. 36명의 척수장애인(23-36세)과 동일한 연령대의 비장애인 40명이 연구에 참여하였으며, 신체 조성과 점증적 트레드밀과 암 에르고미터 검사 동안의 VEpeak, HEpeak, RERpeak , 및 V O2peak가 측정되었다. 암 에르고미터 검사 시 VEpeak는 SCIA와 AB집단이 AB 집단의 트레드밀 검사보다 높게 나타났다. 또한, 암 에르고미터 검사 시 SCIS 집단의 VEpeak는 AB집단의 암 에르고미터 검사와 트레드밀 검사 시보다 낮게 나타났다. SCIA와 AB 집단의 HEpeak는 SCIS와 AB집단의 암 에르고미터 검사 시보다 높게 나타났다. 암 에르고미터 검사 시 RERpeak는 SCIA와 AB집단의 암 에르고미터 검사와 AB집단의 트레드밀 검사보다 높게 나타났다. 암 에르고미터 검사 시 SCIS집단의 체중 당 VO2peak는 SCIA와 AB집단의 암 에르고미터 검사 시와 AB집단의 트레드밀 검사 시보다 낮게 나타났다. 또한 AB집단의 암 에르고미터 검사 시 체중 당 VO2peak는 AB집단의 트레드밀 검사 시보다 낮게 나타났다. 암 에르고미터 검사 시 SCIA집단의 상지근육량 당 VO2peak는 SCIS집단과 AB집단의 암 에르고미터 검사와 AB집단의 트레드밀 검사 시보다 높게 나타났다. 또한 암 에르고미터 검사 시 SCIS집단의 상지근육량 당 VO2peak는 AB집단보다 낮게 나타났다. 총 제지방량 당 VO2peak는 암 에르고미터 검사 시 SCIA집단이 SCIS집단과 AB집단보다, 그리고 AB집단의 트레드밀 검사보다 높게 나타났다. 특히 트레드밀 검사 시 AB집단의 총 체지방량 당 VO2peak는AB집단의 암 에르고미터 검사 시보다 낮게 나타났다. 따라서 하지의 근육량이 감소된 척수장애인들의 VO2peak는 근육량을 고려한 측정이 더 적절할 것으로 사료된다. The purpose of this study was to compare differences in physiological peak variables and peakoxygen uptake (VO2peak) during a maximal exercise test by using a treadmill and an arm ergometer inan able-bodied group (AB), a spinal cord injured athlete group (SCIA), and spinal cord injured sedentary group (SCIS). Thirty-six men with spinal cord injuries (age range, 23-36y) and 40 age-matched AB controls participated in this study. Body composition and VEpeak, HEpeak, RERpeak, and V O2peak were measured during an incremental treadmill and arm ergometer test. The VEpeak during the arm ergometer test for SCIA and AB groups was significantly higher than that in AB group during the treadmill test. In addition, the VEpeak of the SCIS group during the arm ergometer test was significantly lower than that in the AB group and during the treadmill test in the AB group. The HRpeak during the arm ergometer test in the SCIA and AB groups was significantly higher than that in the SCIS and AB groups during the arm ergometer test. RERpeak during the arm ergometer test was significantly higher than that in the SCIA and AB groups; and in the AB group during the treadmill test. For V O2peak per body weight, the SCIS group during the arm ergometer test was significantly lower than that in the SCIA and AB groups, and in the AB group during the treadmill test. Additionally, V O2peak in the AB group during the arm ergometer test was significantly lower than that in the AB group during the treadmill test. V O2peak per upper lean body mass in the SCIA group during the arm ergometer test was significantly higher than that in the SCIS and AB groups; and in the AB group during the treadmill test. Moreover, the SCIS group during the arm ergometer test had a significantly lower V O2peak than the AB group. V O2peak per total lean body mass, in the SCIA group during the arm ergometer test was significantly higher than that in the SCIS and AB groups; and in the AB group during the treadmill test. Further, the V O2peak per total lean body mass in the AB group during the treadmill test was significantly lower than that in the AB group during the arm ergometer test. Therefore, analyzing V O2peak in consideration of muscle mass may be more appropriate for persons with SCI whose lower extremity muscles are paralyzed and are therefore reduced in mass.

Tracing metabolic flux in vivo: basic model structures of tracer methodology

Kim Il-Young,Park Sanghee,Kim Yeongmin,Kim Hee Joo,Wolfe Robert R. 생화학분자생물학회 2022 Experimental and molecular medicine Vol.54 No.-

Molecules in living organisms are in a constant state of turnover at varying rates, i.e., synthesis, breakdown, oxidation, and/or conversion to different compounds. Despite the dynamic nature of biomolecules, metabolic research has focused heavily on static, snapshot information such as the abundances of mRNA, protein, and metabolites and/or (in)activation of molecular signaling, often leading to erroneous conclusions regarding metabolic status. Over the past century, stable, non-radioactive isotope tracers have been widely used to provide critical information on the dynamics of specific biomolecules (metabolites and polymers including lipids, proteins, and DNA), in studies in vitro in cells as well as in vivo in both animals and humans. In this review, we discuss (1) the historical background of the use of stable isotope tracer methodology in metabolic research; (2) the importance of obtaining kinetic information for a better understanding of metabolism; and (3) the basic principles and model structures of stable isotope tracer methodology using 13C-, 15N-, or 2H-labeled tracers.

Quality of meal protein determines anabolic response in older adults

Kim, Il-Young,Shin, Yun-A.,Schutzler, Scott E.,Azhar, Gohar,Wolfe, Robert R.,Ferrando, Arny A. Elsevier Science B.V., Amsterdam 2018 Clinical nutrition Vol.37 No.6